Battery Life Enhancement in a Hybrid Electrical Energy Storage System Using a Multi-Source Inverter

Article Battery Life Enhancement in a Hybrid Electrical Energy Storage System Using a Multi-Source Inverter

Yogesh Mahadik * and K. Vadirajacharya

Department of Electrical Engineering, Dr. Babasaheb Ambedkar Technological University, Lonere 402104, Maharashtra, India; [email protected] * Correspondence: [email protected]

Received: 13 February 2019; Accepted: 1 April 2019; Published: 12 April 2019

Featured Application: This research work can used in designing energy management systems (EMS) for pure electric vehicles, which will enhance driving range, lower the energy storage system cost, and result in higher efficiency and improved lifetime of storage batteries.

Abstract: This paper introduces a new topology using a multi-source inverter with the intention of reducing the battery current and weight, while enhancing the battery life and increasing the driving range for plug-in electric vehicles, with the combination of a battery and an ultracapacitor (UC) as storage devices. The proposed topology interconnects the UC and battery directly to the three-phase load with a single-stage conversion using an inverter. The battery life is considerably reduced due to excess (peak) current drawn by the load, and these peak load current requirements are met by connecting the ultracapacitor to the battery, controlled through an inverter. Here, the battery is used to cater to the needs of constant profile energy demands, and the UC is used to meet the dynamic peak load profile. This system is highly efficient and cost-effective when compared to a contemporary system with a single power source. Through a comparative analysis, the cost-effectiveness of the proposed energy management system (EMS) is explained in this paper. Energy and power exchange are implemented with an open-loop control strategy using the PSIM simulation environment, and the system is developed with a hardware prototype using different modes of inverter control, which reduces the average battery current to 27% compared to the conventional case. The driving range of electric vehicles is extended using active power exchange between load and the sources. The dynamics of the ultracapacitor gives a quick response, with battery current shared by the ultracapacitor. As a result, the battery current is reduced, thereby enhancing the driving cycle. With the prototype, the results of the proposed topology are validated.

Keywords: energy management system (EMS); power management; inverter; ultracapacitor (UC); battery; optimum sizing of EMS

1. Introduction As everyone is aware, fuel sources are dwindling day by day and demand is increasing at a rapid pace, resulting in an exponential rise in prices. In today’s scenario, due to the increase in cost and pollution, there is an urgent requirement for attractive and reliable solutions to replace conventional vehicles, which can cater to the needs of society as a whole. Keeping this in mind, the manufacturing of electric vehicles is taking rapid strides. Basically, there are three types of electric vehicles: battery electric vehicles, hybrid electric vehicles, and plug-in hybrid electric vehicles. Out of these, battery electric vehicles are totally powered by electrical energy. On the other hand, hybrid electric vehicles operate on multiple sources, such as an internal combustion engine (ICE), fuel cell, or renewable energy source [1–5].

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Unlike hybrid electric vehicles, plug-in electric vehicles can be recharged externally using either a domestic supply or charging stations. Also, the main advantage of plug-in hybrid electric vehicles is that the smart grid concept can be applied, which means that the battery in the electric vehicle works as a sink or source with an electric grid [6,7]. Several distinguished authors [8–12] shed light on the research design by considering different objectives with respect to electric vehicles, as outlined below. Remaining useful life (RUL) is affected due to the peak loading conditions of the battery storage system, which also results in a severe degradation of system level performance and affects safety concerns. Li et al. [8] suggested a hybrid RUL prediction model using the long short-term memory (LSTM) and Elman neural networks, which could simultaneously capture the battery capacity degradation characteristics with increased cycle number in the long term and represent the capacity recovery at certain cycles in the short term. Zhang et al. [9] focused on a comprehensive analysis of the thermal safety issues of lithium ion batteries, in terms of thermal behavior, thermal runaway modeling, and safety management strategies for battery packs, considering the heat production mechanisms and thermal characteristics of batteries. In addition to the different engineering approaches to material refinement, certain additives from thermal, electrical, and mechanical designs were required for thermal runaway prevention. Li et al. [10] emphasized the analysis of accurate battery state-of-health (SOH) monitoring, which is crucial to guarantee the safe and reliable operation of electric vehicles. In this paper, an incremental capacity analysis (ICA) for battery SOH estimation was elaborated. This method used gray relational analysis in combination with the entropy weight method. The health indices were then extracted from the partial incremental capacity curves for gray relational analysis, and the entropy weight method was used to evaluate the significance of each health index. The battery SOH was assessed by calculating the gray relational degree between the reference and comparative sequences. Based on the experimental analysis of the two batteries with the same specifications, the results were validated using a combination of the incremental capacity analysis method (ICA) with gray relational analysis (GRA). The GRA method was used to quantitatively calculate the difference between the reference and comparative sequences. On the other hand, in the study by Wang et al. [11], the SOH model was further established on the basis of Gaussian process regression (GPR), in which the optimal hyper parameters were calculated through the conjugate gradient method and the multi-island genetic algorithm (MIGA). The effects of different kernel functions were also analyzed. The multi-island genetic algorithm was validated to find a SOH estimation scheme and was verified through the accelerated battery life test. Zhang et al. [12] stressed the optimization of a hybrid energy storage system (HESS) sizing the considering coordinated operation of a battery and ultracapacitor using SOH, weight, and cost as objectives. From the above references, it is evident that hybridization enhances remaining useful life, prevents thermal runaway, maintains state of health, and optimizes weight, leading to a reduction in EMS size. The cumulative effect of all these parameters is the enhancement of overall battery life and the driving cycle of electric vehicles, which eventually makes the system cost-effective. This paper gives deep insight into the effects of different modes of hybridization on the above objectives with the help of a simulation and hardware analysis. In electrical vehicles, the battery is the main source of energy. Batteries used in electrical vehicles have certain drawbacks, such as a lower life cycle, a high charging time, a lower rate of charge–discharge, and lesser power density. The high discharge rate of batteries affects the energy-delivering capacity. The battery temperature increases due to the internal resistance of the battery. In energy storage systems, the battery is one of the most important elements. Thus, the safe operation of the battery is challenged at peak load. In battery-based energy storage systems, the balancing of the cell is a major concern, whereby frequent charging and discharging adversely affect the battery life [4]. The above problems were approached using the combined operation of an ultracapacitor (UC) and battery, where different methods were used to enhance the battery life via the combined battery–UC WorldWorld Electric Electric Vehicle Vehicle Journal Journal20192019, 10, 10, 17, x FOR PEER REVIEW 3 3 of of 26 27

battery–UC topology. The UC ensured proper utilization of energy and also controlled thermal topology. The UC ensured proper utilization of energy and also controlled thermal management and management and peak power demand, thus leading to an increase in the efficiency of the vehicle as peak power demand, thus leading to an increase in the efficiency of the vehicle as a whole [13–15]. a whole [13–15]. The Ragone plot gives an idea about the comparative study of the power and energy density The Ragone plot gives an idea about the comparative study of the power and energy density performance of various energy devices. From this plot, it is evident that the batteries have a relatively performance of various energy devices. From this plot, it is evident that the batteries have a high energy density but lower power density. On the contrary, the UC has a much lower energy density relatively high energy density but lower power density. On the contrary, the UC has a much lower and a sufficiently higher power density. In addition, the life cycle of the UC is much higher than that energy density and a sufficiently higher power density. In addition, the life cycle of the UC is much of batteries. Furthermore, UCs have a better low-temperature performance than batteries. Figure1 higher than that of batteries. Furthermore, UCs have a better low-temperature performance than shows the Ragone plot. Hence, the combination of an Li-ion battery and a UC was used to get better batteries. Figure 1 shows the Ragone plot. Hence, the combination of an Li-ion battery and a UC was results.used to From get better the Ragone results. chart, From we the can Ragone conclude chart, that we the can power conclude density that of the UC power is high density (6800 Wof /UCkg); is therefore,high (6800 the W/kg); UC fulfills therefore, the peak the load UC demand.fulfills the On peak the otherload demand. hand, the On energy the other density hand, of a batterythe energy is highdensity (up toof 100 a tobattery 265Wh is/kg); high therefore, (up to the100 combination to 265Wh/kg); offers therefore, better performance the combination as compared offers to better the useperformance of either alone as compared [4–7,13]. to the use of either alone [4–7,13].

FigureFigure 1. 1.Ragone Ragone plot. plot.

TableTable11 represents represents a a comparison comparison of of various various energyenergy storagestorage elements. According According to to the the table, table, the thebattery battery is ismore more suited suited to to provide provide High High Specific Speciﬁc Energy (HSE),(HSE), whereaswhereas thethe ultracapacitor ultracapacitor is is more more suitedsuited to to provide provide High High Speciﬁc Specific Power Power (HSP). (HSP). Hence Hence a combination a combination of ultracapacitor of ultracapacitor and battery and battery gives excellentgives excellent performance. performance.

TableTable 1. 1.Comparison Comparison of of energy energy storage storage elements. elements.

Sr.Sr. No. No. Storage Storage ElementElement Specific Speciﬁc EnergyEnergy Density Density (Wh (Wh/Kg)/Kg) EnergyEnergy Density Density (Wh (Wh/Ltr)/Ltr) PowerPower Density Density (W/kg) (W/kg) CycleCycle/Life/Life 11 Lead Lead Acid BatteryBattery 4040 8080 100100 10001000 22 Ni-MH 8080 200200 100 to100 250 to 250 20002000 33 High-energy High-energy Li-IonLi-Ion 7777 250250 750 to750 1500 to 1500 20002000 4 Ultra-capacitor 4.5 6.4 2000 500,000 4 Ultra-capacitor 4.5 6.4 2000 500,000

1.1.1.1. Comparative Comparative Analysis Analysis of of Energy Energy management management system system (Cost, (Cost, Weight) Weight) AsAs a casea case study, study, a comparative a comparative analysis analysis that clarifies that clarifies the eff ectivenessthe effectiveness of the hybridization of the hybridization of sources of issources carried out.is carried An energy out. management An energy systemmanagement is designed system based is ondesigned the peak based power on requirements the peak ofpower an electricrequirements vehicle. of A conventionalan electric vehicle. energy A management conventional system energy consists management of batteries system that consists deliver bothof batteries peak powerthat deliver and energy both peak to the powe vehicle.r and The energy Ragone to the chart vehicle. gives The an idea Ragone of the chart power gives and an energyidea of densitiesthe power ofand various energy energy densities and power of various sources. energy Some and researchers power sources. [14] carried Some out researchers a comparative [14] carried analysis out by a usingcomparative a battery analysis alone, an by ultracapacitor using a battery alone alone, and combiningan ultracapacitor the two alone sources, and i.e., combining the battery the and two ultracapacitor.sources, i.e., the On thebattery basis and of di ultracapacitor.fferent driving On cycles, the peakbasis power of different requirements driving are cycles, considered peak power 20% inrequirements the entire driving are considered cycle. Consider 20% in a vehiclethe entire as havingdriving 150cycle. kW Consider as the maximum a vehicle power as having requirement, 150 kW as fromthe maximum which 30 kW power is the requirement, peak power from requirement which 30 kW and is 120 the kW peak is thepower average requirement power requirement.and 120 kW is the average power requirement. Conventional battery-based energy management systems are World Electric Vehicle Journal2019, 10, x FOR PEER REVIEW 4 of 27 World Electric Vehicle Journal 2019, 10, 17 4 of 26 designed for 150 kW, so the system becomes bulky (100 kg). As per the datasheet and the Ragone chart, an ultracapacitor provides peak power demand 6800W/kg, but the energy rating is 4.1 Wh/kg, soConventional this system (22.05 battery-based kg) cannot energy fulfill management the continuous systems energy are demands designed of for a vehicle. 150 kW, As so a the solution, system batteriesbecomes can bulky be used (100 kg).with Asan perultracapacitor the datasheet (hyb andrid theEMS) Ragone having chart, a high an po ultracapacitorwer-delivering provides capability peak (6800power W/kg) demand and 6800W energy/kg, delivering but the energy capability rating of is 4. 4.11 Wh/kg. Wh/kg, soThis this effectively system (22.05 minimizes kg) cannot the fulfillaverage the W/kgcontinuous of the system energy by demands reducing of cost, a vehicle. weight As with a solution, enhancing batteries life (due can to be reduction used with in an peak ultracapacitor currents), and(hybrid performance EMS) having of vehicle a high power-deliveringdue to fast dynamics capability of ultracapacitor (6800 W/kg) [14]. and energyUsing the delivering marketcapability costs of batteriesof 4.1 Wh and/kg. ultra-capacitors, This effectively minimizesa comparative the averageanalysis W is/ kgcarried of the out system as follows by reducing in Table cost, 2 and weight Table with 3. enhancing life (due to reduction in peak currents), and performance of vehicle due to fast dynamics of ultracapacitor [14]. UsingTable the market2. Specifications costs of of batteries the battery and and ultra-capacitors, ultracapacitor. a comparative analysis is carried out as follows in Tables2 and3. Specifications Battery (EME LIR18650) Ultracapacitor (Maxwell BCAP0650) Rated Capacity Table 2. Specifications - of the battery and ultracapacitor. 650F Rated Voltage 3.7 Volt 2.70V MassSpecifications Typical Battery 46(EME g LIR18650) Ultracapacitor 160 (Maxwell g BCAP0650) SpecificRated CapacityPower 1500 W/kg - 6800 650 W/kg F SpecificRated Energy Voltage 265 Wh/kg 3.7 Volt 4.1 Wh/kg 2.70 V Mass Typical 46 g 160 g Life 5–10 years 10 to 15 years Specific Power 1500 W/kg 6800 W/kg SpecificCost Energy$224/kW 265 Wh/ kg $500/kW 4.1 Wh/kg Life 5–10 years 10 to 15 years CostTable 3. Comparative $224 /analysiskW for energy management $500 system./kW

EMS Using EMS using Battery and Ultracapacitor (Hybrid EMS Using Battery Table 3. ComparativeUltracapacitor analysis for energy management system.EMS) Weight (Kg) Cost ($) Weight (Kg) Cost ($) Wt (Kg) Cost ($) EMS using Battery and Ultracapacitor (Hybrid EMS Using Battery EMS Using Ultracapacitor UC pack - - 150×1000/6800 150×500 30×1000/6800 EMS) 30×500 Battery 150×1000/1500Weight (Kg) 150×224 Cost ($) - Weight (Kg) - Cost ($) 120×1000/1500 Wt (Kg) Cost 120×224 ($) Pack UC pack - - 150 1000/6800 150 500 30 1000/6800 30 500 × × × × Battery Pack 150 1000/1500 150 224 - -UC=4.41 kg 120 + Battery1000/1500 =80 kg 1500+26880 120 224 = Total 100× 33,600 × 22.05 75,000 × × UC = 4.41 kg + Battery = Total 100 33,600 22.05 75,000 =84.41 kg 1500 + 2688028,380= 28,380 80 kg = 84.41 kg Hybrid EMS weight and cost decreased by 15.59% and 15.53%, respectively. Penetration of the ultra-capacitorHybrid EMS leads weight to a savings and cost in decreasedterms of maintenance by 15.59% and and 15.53%, EMS replacement respectively. costs. Penetration of the ultra-capacitor leads to a savings in terms of maintenance and EMS replacement costs. 1.2. Overview of developed strategies in HESS (Hybrid Energy Storage System) 1.2. Overview of developed strategies in HESS (Hybrid Energy Storage System) In conventional methods the rechargeable battery or UC combination is used. Batteries were chargedIn conventionalthrough a plug-in methods charging the rechargeable system while battery the vehicle or UC was combination idle; there is is used. a requirement Batteries were for largecharged DC/DC through converters. a plug-in However, charging these system converters while the are vehicle expensive was idle;and theremake isthe a requirementsystem bulky. for Also, large theDC use/DC of converters. these converters However, adversely these converters affects the are efficiency expensive of andthe electric make the vehicle system [15 bulky.–16]. Also, the use of theseFigure converters 2 shows adverselya DC/DC aconverter,ﬀects the ewhichﬃciency aims of theto use electric a basic vehicle combined [15,16]. rechargeable battery and UCFigure to obtain2 shows constant a DC /DC voltage converter, and power which output aims to and use autilizes basic combined UC power rechargeable to meet peak battery current and demand.UC to obtain constant voltage and power output and utilizes UC power to meet peak current demand.

FigureFigure 2. 2. PassivePassive parallel parallel design. design. WorldWorld Electric Electric Vehicle Vehicle Journal JournalJournal20192019, ,,10 10, ,,x x 17 FOR FOR PEER PEER REVIEW REVIEW 5 5 5 of of of 27 2627

1.2.1.1.2.1. Passive Passive Parallel Parallel Design Design 1.2.1. Passive Parallel Design InIn thisthis design,design, thethe combinationcombination ofof aa batterybattery andand ultracapacitorultracapacitor isis directlydirectly connectedconnected toto thethe loadload withoutwithoutIn thisusing using design, a a power power the electronic combinationelectronic converter; converter; of a battery hence, hence, and this this ultracapacitor design design is is cheap cheap is directlyand and compact compact connected as as compared compared to the load to to otherwithoutother designs designs using because because a power of of electronic the the absence absence converter; of of a a DC/DC DC/DC hence, co co thisnverternverter design [10,15]. [10,15]. is cheap As As the the and charging charging compact and and as compareddischarging discharging to dynamicsotherdynamics designs ofof UCUC because isis fastfast of comparedcompared the absence toto of aa a battery,battery, DC/DC UC converterUC getsgets dischargesdischarges [10,15]. As inin the loadload charging beforebefore and batterybattery discharging andand itit frequentlydynamicsfrequently of takestakes UC is aa currentfastcurrent compared toto maintainmaintain to a battery, thethe terminalterminal UC gets voltage;voltage; discharges thus,thus, in theloadthe batterybattery before batterysufferedsuffered and fromfrom it frequently frequentfrequent charges.takescharges. a current to maintain the terminal voltage; thus, the battery suﬀered from frequent charges.

1.2.2.1.2.2. UC/Battery UC/Battery UC/Battery Design Design ThisThis design design is is more more complex complexcomplex than thanthan a aa passive passive parallel parallel one. one. In In the the figure Figurefigure 33 below,below, thethe batterybattery isis connectedconnected directly directly to to a a DC DCDC link linklink and andand the thethe UC UCUC is isis connected connectedconnected to toto the thethe DC DCDC link linklink via viavia a aa DC/DC DCDC/DC/DC converter. converter.

FigureFigure 3. 3. UC/battery UC/batteryUC/battery design. design.

ThisThis design design is is advantageous advantageous inin thethe sensesense thatthat therethere isis nono variationvariation inin thethe DCDC linklink voltagevoltage [11];[11]; [11]; thethe majormajor drawback drawbackdrawback is isis that thatthat it requiresitit requiresrequires a large aa largelarge converter converterconverter to handle toto handlehandle the power thethe ofpowerpower UC. Hence, ofof UC.UC. it Hence, adverselyHence, itit adverselyaadverselyﬀects the affects costaffects and thethe size costcost of theandand ESS sizesize (Energy ofof thethe Storage ESSESS (Energy(Energy System). StorageStorage Partial System).System). active control PartialPartial is active possibleactive controlcontrol due to isis a possiblebidirectionalpossible due due to DCto a a /bidirectional DCbidirectional converter. DC/DC DC/DC converter. converter.

1.2.3.1.2.3. Battery/UC Battery/UC Battery/UC Design Design ThisThis design design is is configured conﬁguredconfigured by by simply simply switchingt switchingtheswitchingthehe positionspositions ofof thethe UC UC and and battery battery in in the the above above design.design. HereHere Here (Figure(Figure 4)44)) the thethe batterybattery is isis connected connectedconnected to toto the thethe DC DCDC link linklink via viavia a aa DC/DC DCDC/DC/DC bidirectionalbidirectional converter,converter, converter, whereaswhereas the the UC UC is is connected connected directly directly to toto the thethe DC DCDC link. link.link. Here, Here, the the main main objective objective of of using using the the converter converter isis to to supply supply a a specific speciﬁcspecific constant constant powerpower fromfrom thethe battebatte batteryryry to to thethe loadload by by controlling controlling thethe the sourcesource source current.current. current. OnOn the the other other hand, hand, the the converter converter is is much much smaller smaller than than that that used used in in UC/battery UCUC/battery/battery design design and and the the main main advantageadvantage of of this this design design is is the the wide wide power power range range of ofof UC UCUC [11]. [[11].11].

FigureFigure 4. 4. Battery/UC Battery/UCBattery/UC design. design. World Electric Vehicle Journal 2019, 10, 17 6 of 26 World Electric Vehicle Journal2019, 10, x FOR PEER REVIEW 6 of 27

InIn order order to to understand understand the the operation operation using using Battery Battery/UC/UC design, design, there there are are four four operating operating modes modes asas follows: follows: World Electric Vehicle Journal2019, 10, x FOR PEER REVIEW 6 of 27 Mode-1:Mode-1: Slow Slow Constant constant Speed speed InIn order this this mode, tomode, understand the the converter converter the operation power power is usingis always always Battery/UC greater greater than thandesign, the the demandthere demand are power,four power, operating hence hence only modesonly the the asbatterybattery follows: provides provides power power to to the the three-phase three-phase motor motor through through a a DC DC/DC/DC converter, converter, i.e., i.e., boost boost operation, operation, asas shown shown in in Figure Figure5. 5. Mode-1: Slow constant speed In this mode, the converter power is always greater than the demand power, hence only the battery provides power to the three-phase motor through a DC/DC converter, i.e., boost operation, as shown in Figure 5.

FigureFigure 5. 5.Slow Slow constant-speed constant-speed operation. operation. Mode-2: Fast Constant Speed Mode-2: Fast constant speed In this mode (Figure6), the demand power is greater than the converter power; therefore, the control switch is forward biasedFigure and 5. theSlow battery constant-speed supplies operation. power directly to the motor. In this mode, a DC/DC converter is not used. In constant-speed mode, the UC voltage is higher than the battery Mode-2:voltage and Fast hence constant in this speed mode UC does not absorb or provide power to the three-phase motor [16].

Figure 6. Fast constant-speed operation.

In this mode (Figure 6), the demand power is greater than the converter power; therefore, the control switch is forward biased and the battery supplies power directly to the motor. In this mode, a DC/DC converter is not used.Figure In constant-speed 6. FastFast constant-speed constant-speed mode, operation. the UC voltage is higher than the battery voltage and hence in this mode UC does not absorb or provide power to the three-phase motor [16]. Mode-3:In this Acceleration mode (Figure 6), the demand power is greater than the converter power; therefore, the controlMode-3:At switch the Acceleration inception is forward of accelerationbiased and the (Figure battery7), suppl the UCies voltagepower directly is greater to the than motor. the battery In this voltagemode, a DC/DCand the converter demand power is not isused. greater In thanconstant-speed the converter mode, power. the Therefore,UC voltage both is higher UC and than battery the battery via the voltageconverter. and As hence the ratein this of mode acceleration UC does remains not absorb constant, or provide the UC power voltage to the drops three-phase to the same motor level [16]. as the battery voltage; consequently, the battery and UC directly combine through a control switch and Mode-3:provide powerAcceleration to the three-phase motor [15,16]. World Electric Vehicle Journal 2019, 10, 17 7 of 26 World Electric Vehicle Journal2019, 10, x FOR PEER REVIEW 7 of 27 World Electric Vehicle Journal2019, 10, x FOR PEER REVIEW 7 of 27

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Figure 7. Acceleration mode. FigureFigure 7. 7. AccelerationAcceleration mode. mode. Mode-4: DecelerationAt the inception of acceleration (Figure 7), the UC voltage is greater than the battery voltage At the inception of acceleration (Figure 7), the UC voltage is greater than the battery voltage and the demand power is greater than the converter power. Therefore, both UC and battery via the and the demand power is greater thanFigure the converte7. Accelerationr power. mode. Therefore, both UC and battery via the (Vconverter.UC is the As terminal the rate of voltage acceleration of the remains ultracapacitor constant, and the VUCUC_target voltageis drops the maximum to the same charging level as the voltage converter. As the rate of acceleration remains constant, the UC voltage drops to the same level as the of thebattery capacitor.) voltage; consequently, the battery and UC directly combine through a control switch and batteryAt voltage;the inception consequently, of acceleration the battery (Figure and 7), UC the directly UC voltage combine is greater through than a thecontrol battery switch voltage and Thisprovide mode power (Figure to the8 three-phase) is also called motor regenerative [15,16]. braking because in this mode the UC starts to andprovide the demandpower to power the three-phase is greater motorthan the [15,16]. converte r power. Therefore, both UC and battery via the charge,converter. and the As DC the/DC rate converter of acceleration is in boostremains operation constant, (orthe thereUC voltage is no operation).drops to the same Converter level as operation the Mode-4: Deceleration is totallybatteryMode-4: dependent voltage; Deceleration consequently, upon the target the UCbattery voltage and (VUCUC__target directly ).combine through a control switch and provide power to the three-phase motor [15,16].

Mode-4: Deceleration

Figure 8. Regenerative braking when VUC< VUC__target. FigureFigure 8. Regenerative 8. Regenerative braking braking when when VVUCUC<< VUC__targetVUC__target. . (VUC is the terminal voltage of the ultracapacitor and VUC_target is the maximum charging voltage (VUC is the terminal voltage of the ultracapacitor and VUC_target is the maximum charging voltage Inof the continuous capacitor.) decelerating mode (Figure9) the DC /DC converter goes into buck operation, thereby transferringof the capacitor.) the energy from theFigure UC 8. to Regenerative the battery braking [16]. Duringwhen VUC regenerative< VUC__target. braking, the ultracapacitor recovers energy from the motor in a negligible time on the order of 0.2–3 s. The DC/DC converter (VUC is the terminal voltage of the ultracapacitor and VUC_target is the maximum charging voltage transfersof the this capacitor.) energy recovered by UC with a controlled rate of charging of the battery.

Figure 9. Regenerative braking when VUC> VUC_target. Figure 9. Regenerative braking when VUC> VUC_target. This mode (Figure 8) is also called regenerative braking because in this mode the UC starts to This mode (Figure 8) is also called regenerative braking because in this mode the UC starts to charge, and the DC/DC converter is in boost operation (or there is no operation). Converter charge, and the DC/DCFigure converterFigure 9. Regenerative 9. Regenerative is in boost braking braking operation when when VV(orUCUC >there >VUC_targetVUC_target is. no .operation). Converter operation is totally dependent upon the target UC voltage (VUC__target). operation is totally dependent upon the target UC voltage (VUC__target). 1.2.4. MultipleThis mode DC/ DC(Figure Converter 8) is also Design called regenerative braking because in this mode the UC starts to charge, and the DC/DC converter is in boost operation (or there is no operation). Converter The battery and UC are connected through separate converters (Figure 10); one is current-controlled operation is totally dependent upon the target UC voltage (VUC__target). and connected at the output side of the battery, whereas the other is voltage-controlled and connected World Electric Vehicle Journal2019, 10, x FOR PEER REVIEW 8 of 27

In continuous decelerating mode (Figure 9) the DC/DC converter goes into buck operation, thereby transferring the energy from the UC to the battery [16]. During regenerative braking, the ultracapacitor recovers energy from the motor in a negligible time on the order of 0.2–3s. The DC/DC converter transfers this energy recovered by UC with a controlled rate of charging of the battery. World Electric Vehicle Journal 2019, 10, 17 8 of 26 World1.2.4. Electric Multiple Vehicle Journal DC/DC2019, 10 Converter, x FOR PEER Design REVIEW 8 of 27 at the UCIn side. continuous The outputs decelerating of both mode these (Figure converters 9) the are DC/DC the same converter as the DCgoes link into [ 16buck,17 ].operation, In this design, it is possiblethereby transferring to maintain the a voltageenergy from level the below UC theto th DCe battery link voltage. [16]. During The mainregenerative advantage braking, of this the design is thatultracapacitor the UC is utilized recovers to energy the best from possible the motor extent. in a negligible On the othertime on hand, the or theder drawback of 0.2–3s. The of thisDC/DC design is converter transfers this energy recovered by UC with a controlled rate of charging of the battery. that it requires two full bridge converters, thus resulting in an increase in the overall size and cost of ESS1.2.4. [18,19 Multiple]. DC/DC Converter Design

Figure 10. Multiple DC/DC converter design.

The battery and UC are connected through separate converters (Figure 10); one is current-controlled and connected at the output side of the battery, whereas the other is voltage-controlled and connected at the UC side. The outputs of both these converters are the same as the DC link [16,17]. In this design, it is possible to maintain a voltage level below the DC link voltage. The main advantage of this design is that the UC is utilized to the best possible extent. On the other hand, the drawbackFigureFigure 10. 10.of Multiplethis design DC/DC DC /isDC converterth converterat it requires design. design. two full bridge converters, thus resulting in an increase in the overall size and cost of ESS [18,19]. 1.2.5. UCThe/Battery battery with and Inverter UC are Design connected through separate converters (Figure 10); one is current-controlled1.2.5. UC/Battery and with connected Inverter Designat the output side of the battery, whereas the other is voltage-controlledBasic topologies areand implemented connected at the using UC multisourceside. The outputs connected of both to these load converters through a are DC the/DC same converter. Basic topologies are implemented using multisource connected to load through a DC/DC In theas proposedthe DC link topology, [16,17]. In an this inverter-fed design, it ACis possible link is usedto maintain to connect a voltage the battery level below and thethe ultracapacitorDC link converter. In the proposed topology, an inverter-fed AC link is used to connect the battery and the via thevoltage. space The vector main pulse advantage width of modulationthis design is techniquethat the UC (Figure is utilized 11). to The the designbest possible reduces extent. the On size and ultracapacitor via the space vector pulse width modulation technique (Figure 11). The design weightthe ofother the hand, system. the drawback of this design is that it requires two full bridge converters, thus reduces the size and weight of the system. resulting in an increase in the overall size and cost of ESS [18,19].

1.2.5. UC/Battery with Inverter Design Basic topologies are implemented using multisource connected to load through a DC/DC converter. In the proposed topology, an inverter-fed AC link is used to connect the battery and the ultracapacitor via the space vector pulse width modulation technique (Figure 11). The design reduces the size and weight of the system.

FigureFigure 11. UC 11./battery UC/battery with with inverter inverter design. design.

HardwareHardware for the for UC the/battery UC/battery design design simulated simulate andd and implemented implemented to to validate validate thethe design.design.

2. Materials2. Materials and Methods and Methods To understand the charging and discharging behavior of the ultracapacitor, a simulation is To understand the charging and discharging behavior of the ultracapacitor,a simulation is carried carried out in the MATLAB environment as follows. out in the MATLAB environmentFigure as follows. 11. UC/battery with inverter design.

2.1. BasicHardware Simulation for Work the UC/battery design simulated and implemented to validate the design.

2.To Materials validate and the Methods dynamic response of the ultracapacitor, the simulation is carried out in a MATLAB environment wherein the battery is directly connected to the DC link and the ultracapacitors connected to the DCTo link understand via a DC /theDC charging converter. and To discharging understand behavior the basic of analogythe ultracapacitor, of hybridization, a simulation a simulation is carried out in the MATLAB environment as follows. for design 1.2 (a DC/DC converter based on UC/battery design) was chosen. In this design the resistive load is increased gradually over time [15]. A 12 V battery voltage (VB) with 50 Ah is selected with a 12 V,20 Farad ultracapacitor. Three resistive loads with time delays are connected for loading purposes and low charge protection is provided with World Electric Vehicle Journal2019, 10, x FOR PEER REVIEW 9 of 27

2.1. Basic Simulation Work To validate the dynamic response of the ultracapacitor, the simulation is carried out in a MATLAB environment wherein the battery is directly connected to the DC link and the ultracapacitors connected to the DC link via a DC/DC converter. To understand the basic analogy of hybridization, a simulation for design 1.2 (a DC/DC converter based on UC/battery design) was Worldchosen. Electric VehicleIn this Journal design2019 the, 10 resistive, 17 load is increased gradually over time [15]. 9 of 26 A 12 V battery voltage (VB) with 50 Ah is selected with a 12 V, 20 Farad ultracapacitor. Three resistive loads with time delays are connected for loading purposes and low charge protection is controlprovided switches. with Thecontrol results switches. (Figure The 12) areresults obtained (Figur frome 12) theare Simscopeobtained toolfrom in the MATLAB Simscope along tool within Simulink.MATLAB The along total with simulation Simulink. time The is total 1000 simulation s. time is 1000 s. TheThe resistive resistive load load comes comes into into the the circuit circuit at at time timesteps steps ofof 300300 s,s, 400400 s, and 700 s. s. During During the the dynamicdynamic change change of of the the load, load, the the peak peak load load is is shared shared byby thethe ultracapacitor (12 (12 Farad) Farad) and and the the battery. battery. TheThe simulation simulation results results reveal reveal that that the the battery battery discharging discharging startsstarts atat 320 s with a a small small reduction reduction in in the the batterybattery terminal terminal voltage voltage (V (VB)B due) due to to the the internal internal resistance resistance ofof battery;battery; the current current obtained obtained is is 2 2A. A.

World Electric VehicleFigure Journal2019 12., 10Simulink, x FOR PEER model REVIEW of energy management system. 10 of 27 Figure 12. Simulink model of energy management system.

Figure 13.FigureBattery 13. Battery charge, charge, current, current, powerpower and and ultra-ca ultra-capacitorpacitor current, current, voltage characteristics. voltage characteristics.

The dynamic change in load demand is shared by UC, (Figure 13), thereby maintaining the DC link voltage. In the basic simulation, it is observed that at the peak power requirements of the load, the ultracapacitor provides the power requirements dynamically (at t = 300 s).

2.2. Proposed Work Energy storage system of plug-in EV as an active power source [18–20]: A hybridized source (battery + ultracapacitor) is used to fulfill the dynamic requirements of the motor. The dynamic power demands can be fulfilled using a combination of a battery and an ultracapacitor in an energy storage system of electric vehicle (EV). Real power (P) and reactive power (Q) can be injected or absorbed from the load. When this vehicle is used as a plug-in vehicle, this phenomenon of power control enhances the smartness of the grid. During EV working, power from an energy storage system is injected into the electrical propulsion system (here a three-phase voltage source inverter-fed motor is used). Driving conditions associated with torque reflect on the motor current. The driving cycle is simulated by using load as induction motor drive. Energy sharing between the battery and ultracapacitor is observed using the PSIM software environment. World Electric Vehicle Journal 2019, 10, 17 10 of 26

2.2. Proposed Work Energy storage system of plug-in EV as an active power source [18–20]: A hybridized source (battery + ultracapacitor) is used to fulfill the dynamic requirements of the motor. The dynamic power demands can be fulfilled using a combination of a battery and an ultracapacitor in an energy storage system of electric vehicle (EV). Real power (P) and reactive power (Q) can be injected or absorbed from the load. When this vehicle is used as a plug-in vehicle, this phenomenon of power control enhances the smartness of the grid. During EV working, power from an energy storage system is injected into the electrical propulsion system (here a three-phase voltage source inverter-fed motor is used). Driving conditions associated with torque reflect on the motor current. The driving cycle is simulated by using load as induction motor drive. Energy sharing between the battery and ultracapacitor is observed using the PSIM software environment. The circuit consists of two separate inverters connected to the battery and ultracapacitor. SVPWM (Space Vector Pulse Width Modulation) is used to control the various circuit parameters. AHESS uses World Electric Vehicle Journal2019, 10, x FOR PEER REVIEW 11 of 27 a multi-source inverter to connect the battery and ultracapacitor directly to the three-phase smart grid when the vehicleThe iscircuit idle, consists and the of sametwo separate system inverter connectss connected to the load to the during battery prolusion and ultracapacitor. without adding a DC/DC converter.SVPWM (Space Elimination Vector Pulse of Width the DC Modulation)/DC converter is used enhancesto control the the various compactness. circuit parameters. The battery life AHESS uses a multi-source inverter to connect the battery and ultracapacitor directly to the depends on the peak power demand of the load. This peak power requirement is in turn fulfilled by three-phase smart grid when the vehicle is idle, and the same system connects to the load during connectingprolusion the ultracapacitor without adding along a DC/DC with converter. a battery. Elimination Herethe of the specific DC/DCenergy converter demand enhances andthe the peak power demandcompactness. for HEV The arebattery provided life depends by the on batterythe peak andpower the demand ultracapacitor, of the load. respectively.This peak power In addition, the benefitsrequirement of this new is in batteryturn fulfilled/ultracapacitor by connecting topology the ultracapacitor are a reduction along with in a thebattery. size Here and the hence in the specific energy demand and the peak power demand for HEV are provided by the battery and the overall cost of the energy storage system, along with improved life, endurance, and efficiency of ultracapacitor, respectively. In addition, the benefits of this new battery/ultracapacitor topology are the system.a reduction The HESS in the system size and was hence studied in the in overall depth cost and of analyzed the energy usingstorage a system, PSIM environment-basedalong with simulation,improved the results life, endurance, of which and are efficiency discussed of the below. system. The HESS system was studied in depth and analyzed using a PSIM environment-based simulation, the results of which are discussed below. 3. Simulation Results and Discussion 3. Simulation Results and Discussion The simulationThe simulation consisted consisted of an of inverter-fed an inverter-fed AC AC load load (induction (induction motor) (Figure (Figure 14), 14 wherein), wherein a a novel inverter isnovel connected inverter tois connected an AC link. to an The AC batterylink. The (voltagebattery (voltage= 24 volts)= 24 volts) source source feeds feeds inverter-1,inverter-1, whereas the ultracapacitorwhereas the (300 ultracapacitor Farad, 24 volts)(300 Farad, feeds 24 inverter-2. volts) feeds The inverter-2. simulation The simulation depicts thedepicts characteristics the of power sharingcharacteristics between of power the battery sharing andbetween ultracapacitor. the battery and ultracapacitor.

Figure 14.FigureSimulation 14. Simulation of aof hybrid a hybrid inverter inverter with with load load (induction (induction motor) motor) [18,19]. [18,19].

The main feature of this simulation is the use of a space vector analogy using a PSIM Script file. Using script control block, control signals are obtained. Current and torque feedbacks are taken from the sensors. The two DC sources are designed using an ideal battery and ultracapacitor source. A multisource inverter is designed with IGBTs. The load is designed by a three-phase induction motor. As the induction motor itself is the balanced load, the phase current of one phase is sensed by the current sensor; the shaft speed is also sensed. The simulation time selected is 2 s. This simulation shows P‒Q control in load (induction motor). Considering inductive load, the power factor of the motor is lagging. The simulation results indicate the active and reactive power requirements of the load. • Active power (P) with positive magnitude is the power flowing from the DC bus to the load. • Reactive power (Q) in Var with positive magnitude is reactive power being supplied to the load. • Bidirectional power flow in any combination is possible, where negative magnitudes inject active and reactive power from the DC bus to the load. World Electric Vehicle Journal 2019, 10, 17 11 of 26

The main feature of this simulation is the use of a space vector analogy using a PSIM Script ﬁle. Using script control block, control signals are obtained. Current and torque feedbacks are taken from the sensors. The two DC sources are designed using an ideal battery and ultracapacitor source. A multisource inverter is designed with IGBTs. The load is designed by a three-phase induction motor. As the induction motor itself is the balanced load, the phase current of one phase is sensed by the current sensor; the shaft speed is also sensed. The simulation time selected is 2 s. This simulation shows P-Q control in load (induction motor). Considering inductive load, the power factor of the motor is lagging. The simulation results indicate the active and reactive power requirements of the load.

Active power (P) with positive magnitude is the power ﬂowing from the DC bus to the load. • Reactive power (Q) in Var with positive magnitude is reactive power being supplied to the load. • Bidirectional power ﬂow in any combination is possible, where negative magnitudes inject active • Worldand Electric reactive Vehicle Journal power2019 from, 10, thex FOR DC PEER bus REVIEW to the load. 12 of 27 3.1. PSIM Simulation Results 3.1. PSIM Simulation Results Simulation is carried out for the following modes. Simulation is carried out for the following modes. There are three operating modes corresponding to the switching states [21–26]: There are three operating modes corresponding to the switching states [21–26]:

• Mode-1Mode-1 (Battery(Battery andand Motor Motor or or RL RL load): load):In In this this mode, mode, V VBBdrives drivesthe themotor motor/RL/RLload loadand andV VUU isis • notnot used.used. • Mode-2Mode-2 (Battery,(Battery, Ultracapacitor Ultracapacitor and and Motor Motor or or RL RL load): load):In In this this mode, mode, V VBdrives drives thethe loadload (for(for • B motormotor oror grid)grid) byby chargingcharging thethe ultracapacitor ultracapacitor (V(VUU).). The eeffectiveﬀective outputoutput voltagevoltage isis equalequal toto (V(VBB-V-VUU). • Mode-3Mode-3 (Ultracapacitor(Ultracapacitor andand MotorMotor// RL RL load):load): Here,Here, VVB isis notnot used;used; thethe ultracapacitorultracapacitor alonealone (V (VU)) • B U drivesdrives thethe motor.motor.

SimulationSimulation resultsresults forfor allall modesmodes areare discussed discussed below: below:

3.1.1.3.1.1. Mode-1Mode-1 (Battery(Battery && MotorMotor oror RLRL Load)Load) InIn mode-1mode-1 (Figure (Figure 15 ),15), the the motor motor operates operates on 24 on V 24 battery V battery input viainput an inverter.via an inverter. The basic The inverter basic modeinverter is observedmode is observed through simulationthrough simulation results with results a simulation with a simulation time of 1 s.time of 1 s.

Inverter-1 Output Voltage

Inverter-1 Output Current

Figure 15. For mode-1 inverter 1 output (fed by battery). Figure 15. For mode-1 inverter 1 output (fed by battery).

Active Power

Reactive Power

Figure 16. For mode-1: active and reactive power consumed. World Electric Vehicle Journal2019, 10, x FOR PEER REVIEW 12 of 27

3.1. PSIM Simulation Results Simulation is carried out for the following modes. There are three operating modes corresponding to the switching states [21–26]:

• Mode-1 (Battery and Motor or RL load): In this mode, VB drives the motor/RL load and VU is not used. • Mode-2 (Battery, Ultracapacitor and Motor or RL load): In this mode, VB drives the load (for motor or grid) by charging the ultracapacitor (VU). The effective output voltage is equal to (VB-VU). • Mode-3 (Ultracapacitor and Motor/ RL load): Here, VB is not used; the ultracapacitor alone (VU) drives the motor. Simulation results for all modes are discussed below:

3.1.1. Mode-1 (Battery & Motor or RL Load) In mode-1 (Figure 15), the motor operates on 24 V battery input via an inverter. The basic inverter mode is observed through simulation results with a simulation time of 1 s.

Inverter-1 Output Voltage

Inverter-1 Output Current World Electric Vehicle Journal 2019, 10, 17 12 of 26

As the above results show that the magnitude of power is in the positive direction, active and reactive power are injectedFigure towards 15. For the mode-1 motor (Figureinverter 161 output). (fed by battery).

Active Power

Reactive Power

Figure 16. For mode-1: active and reactive power consumed. Figure 16. For mode-1: active and reactive power consumed. Mode-2 is the mixed mode, where the motor is driven by the battery and ultracapacitor via an inverter.

3.1.2. Mode-2 (Battery, Ultracapacitor & Motor or RL Load) Simulation is carried out for1s. At t = 0.3 s, the load reference is increased. As the dynamics of ultracapacitor are fast, the ultracapacitor shares the peak power demand, which reduces the current stress during peak power requirements. From the waveform (Figures 17 and 18), it is evident that the ultracapacitor gets discharged in load at 0.3 s. Current stress on the battery is shared by the ultracapacitor.

Figure 17. Inverter-1 voltage and current output.

World Electric Vehicle Journal 2019, 10, 17 13 of 26

Figure 18. Ultracapacitor terminal voltage.

Reference currents in Figure 19 generated from the abc reference frame are converted to a dq reference frame transformation, which decides the power sharing. The ultracapacitor and battery both provideWorld Electric power Vehicle to Journal the load2019,(induction 10, x FOR PEER motor REVIEW/grid) during the simulation period. 14 of 27

Active power

Reactive Power

Figure 19. Active and reactive power (reference vs. calculated). Figure 19. Active and reactive power (reference vs. calculated). 3.1.3. Mode-3 (Ultracapacitor and Motor/RL Load) InReference mode-3, currents fast dynamics in figure of the19 generated ultracapacitor from is the observed. abc reference We can frame use theare ultracapacitorconverted to a as dq a sourcereference with frame respect transformation, to motor connection which decides [21]. Sharing the power of power sharing. during The operation ultracapacitor is observed and battery with theseboth provide characteristics power (Figureto the load 20). (induction At 0.3 s the motor/grid) load reference during is increased, the simulation which period. initializes the power sharing of ultracapacitor and the battery. 3.1.3.As Mode-3 per the (Ultracapacitor simulation results, and (FiguresMotor/RL 21 Load) and 22 ), it is observed that mode-2 reduces the stress on the batteryIn mode-3, with simultaneousfast dynamics use of ofthe an ultracapacitor ultracapacitor. is Validation observed. is We carried can use out withthe ultracapacitor a small prototype as a usingsource a with combination respect to of motor the battery connection and ultracapacitor [21]. Sharing controlledof power during with a noveloperation hybrid-type is observed inverter. with Inthese the characteristics next section the (Figure design, 20). operation, At 0.3 s experimentation,the load reference and is increased, results are which elaborated initializes upon. the power sharing of ultracapacitor and the battery.

Current

Voltage

Figure 20. Inverter output voltage and current. World Electric Vehicle Journal2019, 10, x FOR PEER REVIEW 14 of 27

Active power

Reactive Power

Figure 19. Active and reactive power (reference vs. calculated).

Reference currents in figure 19 generated from the abc reference frame are converted to a dq reference frame transformation, which decides the power sharing. The ultracapacitor and battery both provide power to the load (induction motor/grid) during the simulation period.

3.1.3. Mode-3 (Ultracapacitor and Motor/RL Load) In mode-3, fast dynamics of the ultracapacitor is observed. We can use the ultracapacitor as a source with respect to motor connection [21]. Sharing of power during operation is observed with Worldthese Electric characteristics Vehicle Journal (Figure2019, 10, 20). 17 At 0.3 s the load reference is increased, which initializes the 14power of 26 sharing of ultracapacitor and the battery.

Current

Voltage

World Electric Vehicle Journal2019, 10, x FOR PEER REVIEW 15 of 27

World Electric Vehicle Journal2019, 10, x FOR PEER REVIEW 15 of 27 Figure 20. Inverter output voltage and current. Figure 20. Inverter output voltage and current.

Active Power Active Power

Reactive Power Reactive Power

Figure 21. Active and reactive power (reference vs. calculated). Figure 21. Active and reactive power (reference vs. calculated). Figure 21. Active and reactive power (reference vs. calculated).

Power injection by ultracapacitorPower observedinjection byfrom ultracapacitorvoltage drop observed(at 0.3 from s) voltage drop (at 0.3 s)

Figure 22. Ultracapacitor voltage. Figure 22. Ultracapacitor voltage. Figure 22. Ultracapacitor voltage. As per the simulation results, (Figure 21 and 22), it is observed that mode-2 reduces the stress on the battery with simultaneous use of an ultracapacitor. Validation is carried out with a small As per the simulation results, (Figure 21 and 22), it is observed that mode-2 reduces the stress prototype using a combination of the battery and ultracapacitor controlled with a novel hybrid-type on the battery with simultaneous use of an ultracapacitor. Validation is carried out with a small inverter. In the next section the design, operation, experimentation, and results are elaborated upon. prototype using a combination of the battery and ultracapacitor controlled with a novel hybrid-type inverter. In the next section the design, operation, experimentation, and results are elaborated upon. 4. Hardware Implementation 4. HardwareThe main Implementation purpose of this topology (Figure 23) is to cascade several DC sources to the three-phase AC motor. In this case, two DC sources, namely the battery (VB) and ultra-capacitor (VU), The main purpose of this topology (Figure 23) is to cascade several DC sources to the are connected. The main advantage of this topology is that it does not add any additional stages three-phase AC motor. In this case, two DC sources, namely the battery (VB) and ultra-capacitor (VU), between the motor and the sources, which results in an improved response of electric vehicle by are connected. The main advantage of this topology is that it does not add any additional stages enhancing energy and power demand fulfilment. In the proposed control strategy, the source between the motor and the sources, which results in an improved response of electric vehicle by current is controlled according to the torque requirements of the driving cycle. In a closed-loop enhancing energy and power demand fulfilment. In the proposed control strategy, the source system three switching modes are selected according to the power requirements of the grid or the current is controlled according to the torque requirements of the driving cycle. In a closed-loop acceleration, cruising, and braking of an electric vehicle [13]. Here the modes are selected with system three switching modes are selected according to the power requirements of the grid or the open-loop control and to observe the characteristics during the sharing of sources. acceleration, cruising, and braking of an electric vehicle [13]. Here the modes are selected with open-loop control and to observe the characteristics during the sharing of sources. World Electric Vehicle Journal 2019, 10, 17 15 of 26

4. Hardware Implementation The main purpose of this topology (Figure 23) is to cascade several DC sources to the three-phase AC motor. In this case, two DC sources, namely the battery (VB) and ultra-capacitor (VU), are connected. The main advantage of this topology is that it does not add any additional stages between the motor and the sources, which results in an improved response of electric vehicle by enhancing energy and power demand fulﬁlment. In the proposed control strategy, the source current is controlled according to the torque requirements of the driving cycle. In a closed-loop system three switching modes are selected according to the power requirements of the grid or the acceleration, cruising, and braking of an electric vehicle [13]. Here the modes are selected with open-loop control and to observe the

Worldcharacteristics Electric Vehicle during Journal2019 the, 10 sharing, x FOR ofPEER sources. REVIEW 16 of 27

FigureFigure 23. 23. PowerPower circuit circuit [13,14]. [13,14].

ThereThere are are three three operating operating modes modes corr correspondingesponding to to the the switching switching states: states:

• Mode-1: The switches SU1, SU2, SU3, and SL1, SL2, SL3 enable the discharging of the battery (VB) to Mode-1:Mode-1: TheThe switches switches S SU1U1, ,SSU2U2, S,SU3U3, and, and SL1 S,L1 S,SL2,L2 S,SL3 L3enableenable the the discharging discharging of of the the battery battery (V (VB)B )to to • supply the motor (RL load); an ultra-capacitor (VU)is not used. (The ultra-capacitor is charged supplysupply the the motor motor (RL (RL load); load); an an ultra-capacitor ultra-capacitor (V (VUU)is)is not not used. used. (The (The ultra-capacitor ultra-capacitor is is charged charged through the battery using switches SU21, SU22, SU23 along with switches SU1, SU2, SU3 in closed-loop throughthrough the the battery battery using switchesswitches SSU21U21,,S SU22, SSU23U23 alongalong with with switches switches S SU1U1, ,SSU2,U2, SSU3U3 inin closed-loop closed-loop controlcontrol by by sensing sensing the the load load current current and and terminal terminal voltage voltage of of the the ultra-capacitor; ultra-capacitor; see see Figure Figure 24). 24 ).

SU11 S SU1 SU2 SU3 SU11 SU21 SU1 SU2 SU3 Battery + 3 PHASE + SU12 SU22 INDUCTION - MOTOR - S S MOTOR SU13 SU23 SL1 SL2 SL3 Ultracapacitor

Figure 24. Operation of circuit under mode-1. Figure 24. Operation of circuit under mode-1.

Mode-2: The switches SU1,SU2, SU3 and SU11,SU12, SU13 enable the battery (VB) to supply the • U1 U2, U3 U11 U12, U13 B • • Mode-2: The switches SU1, SU2, SU3 and SU11, SU12, SU13 enable the battery (VB) to supply the motor Mode-2:motor (RL The load) switches with dischargingS , S S and ultracapacitor S , S S (V Uenable) (Figure the 25 battery). (V ) to supply the motor U (RL load) with discharging ultracapacitor (VU) (Figure 25).

SU11 S SU1 SU2 SU3 SU11 SU21 SU1 SU2 SU3 Battery + 3 PHASE + SU12 SU22 INDUCTION - MOTOR - S S MOTOR SU13 SU23 SL1 SL2 SL3 Ultracapacitor

Figure 25. Operation of circuit under mode-2.

1O 2O 3O The phase voltages (V1O, V2O, V3O) are functions of the state of the switches and input voltages: V1O= ESU1VB + EU11VU − Zai1 V1O= ESU1VB + EU11VU − Zai1

2O SU2 B U12 U b 2 V2O= ESU2VB + EU12VU − Zbi2

3O SU3 B U13 U c 3 V3O= ESU3VB + EU13VU − Zci3 World Electric Vehicle Journal2019, 10, x FOR PEER REVIEW 16 of 27

Figure 23. Power circuit [13,14].

There are three operating modes corresponding to the switching states:

• Mode-1: The switches SU1, SU2, SU3, and SL1, SL2, SL3 enable the discharging of the battery (VB) to supply the motor (RL load); an ultra-capacitor (VU)is not used. (The ultra-capacitor is charged through the battery using switches SU21, SU22, SU23 along with switches SU1, SU2, SU3 in closed-loop control by sensing the load current and terminal voltage of the ultra-capacitor; see Figure 24).

SU11 SU21 SU1 SU2 SU3 Battery 3 PHASE + SU12 SU22 INDUCTION - MOTOR SU13 SU23 SL1 SL2 SL3 Ultracapacitor

Figure 24. Operation of circuit under mode-1.

• Mode-2: The switches SU1, SU2, SU3 and SU11, SU12, SU13 enable the battery (VB) to supply the motor World Electric Vehicle Journal 2019, 10, 17 16 of 26 (RL load) with discharging ultracapacitor (VU) (Figure 25).

SU11 SU21 SU1 SU2 SU3 Battery 3 PHASE + SU12 SU22 INDUCTION - MOTOR SU13 SU23 SL1 SL2 SL3 Ultracapacitor

Figure 25. Operation of circuit under mode-2. Figure 25. Operation of circuit under mode-2.

TheThe phase phase voltages voltages (V (V1O1O, V,V2O2O, V,V3O)3O are) are functions functions of ofthe the state state of ofthe the switches switches and and input input voltages: voltages: V1O= ESU1VB + EU11VU − Zai1 V = E V + E V Zai 1O SU1 B U11 U − 1 V2O= ESU2VB + EU12VU − Zbi2 V2O = ESU2VB + EU12VU Zbi2 V3O= ESU3VB + EU13V−U − Zci3 V = E V + E V Zci 3O SU3 B U13 U − 3 where Z = impedance of load and World Electric Vehicle Journal2019, 10, x FOR PEER REVIEW 17 of 27 E and E = switching functions Where Z = impedance of load SU1,and 2, 3 U11, 12, 13

ESU1, 2,Similarly 3 and EU11, input 12, 13 = currents switching [IB ,IfunctionsU] can be expressed as:

Similarly input currents [IB, IU] can be expressed as: IB = ESU1.i1 + ESU2.i2 + ESU3.i3 IB = ESU1.i1 + ESU2.i2 + ESU3.i3 IU = EU11.i1 + EU12.i2 + EU13.i3. IU = EU11.i1 + EU12.i2 + EU13.i3. Mode-3: The battery (VB)is not used and switches SL1,SL2,SL3, and SU11,SU12, SU13 enable the •• Mode-3:ultracapacitor The battery (VU) to (V supplyB)is not the used motor and (RL switches load) (Figure SL1, S L226, ).SL3, and SU11, SU12, SU13 enable the ultracapacitor (VU) to supply the motor (RL load) (Figure 26).

SU11 SU21 SU1 SU2 SU3 Battery 3 PHASE + SU12 SU22 INDUCTION - MOTOR SU13 SU23 SL1 SL2 SL3 Ultracapacitor

Figure 26. Operation of circuit under mode-3. Figure 26. Operation of circuit under mode-3. The hardware consists of the Buﬀer IC (74HC244) to control modes with an adjustment of the duty The hardware consists of the Buffer IC (74HC244) to control modes with an adjustment of the cycle using the enable signal. EN1 is used to control upper switches SU1,SU2,SU3. EN2 controls SL1, duty cycle using the enable signal. EN1 is used to control upper switches SU1, SU2, SU3. EN2 controls SL2,SL3, whereas EN1* and EN2* are used to control SU11,SU12,SU13, and SU21,SU22,SU23, respectively. SAL1, lowSL2, stateSL3, whereas (digital EN1* zero) ofand latch EN2* allows are used input to at control latch output SU11, SU12 (Figure, SU13, 27and). TheSU21, simulation SU22, SU23, respectively. is carried out Ausing low state the Proteus (digital Design zero) of Suite latch environment allows input [27 at– 29latch]. output (Figure 27). The simulation is carried out using the Proteus Design Suite environment [27–29].

Figure 27. Mode control using the buffer.

MOSFET switches are controlled through latch, explained as table 4.

World Electric Vehicle Journal2019, 10, x FOR PEER REVIEW 17 of 27

Where Z = impedance of load and

ESU1, 2, 3 and EU11, 12, 13 = switching functions

Similarly input currents [IB, IU] can be expressed as:

IB = ESU1.i1 + ESU2.i2 + ESU3.i3

IU = EU11.i1 + EU12.i2 + EU13.i3.

• Mode-3: The battery (VB)is not used and switches SL1, SL2, SL3, and SU11, SU12, SU13 enable the ultracapacitor (VU) to supply the motor (RL load) (Figure 26).

SU11 SU21 SU1 SU2 SU3 Battery 3 PHASE + SU12 SU22 INDUCTION - MOTOR SU13 SU23 SL1 SL2 SL3 Ultracapacitor

Figure 26. Operation of circuit under mode-3.

The hardware consists of the Buffer IC (74HC244) to control modes with an adjustment of the duty cycle using the enable signal. EN1 is used to control upper switches SU1, SU2, SU3. EN2 controls SL1, SL2, SL3, whereas EN1* and EN2* are used to control SU11, SU12, SU13, and SU21, SU22, SU23, respectively. World ElectricA low Vehicle state Journal(digital2019 zero), 10, of 17 latch allows input at latch output (Figure 27). The simulation is carried17 of 26 out using the Proteus Design Suite environment [27–29].

FigureFigure 27. 27.Mode Mode control control using using the the bu buffer.ﬀer.

WorldMOSFET ElectricMOSFET Vehicle switches Journal switches2019 are, controlled10are, x controlled FOR PEER through REVIEWthrough latch, latch, explained explained asas Tabletable 4.4. 18 of 27

TableTable 4. 4.Latch Latch andand switchswitch enable St Statesates for for modes-1,2, modes-1,2, and and 3. 3.

EN1 (SU1, SU2, EN2 (SL1, SL2, EN1 * (SU11, SU12, EN2 * (SU21, SU22, ControlControl State State EN1 (SU1,SU2,SU3) EN2 (SL1,SL2,SL3) EN1 * (SU11,SU12,SU13) EN2 * (SU21,SU22,SU23) SU3) SL3) SU13) SU23) UC (Charging)UC (Charging) ONON OFFOFF OFF OFF ON ON Battery (Discharging) ON ON OFF OFF Battery (Discharging) ON ON OFF OFF Battery (Discharging) + Battery (Discharging) + UC ON ON ON OFF UC (Discharging) ON ON ON OFF (Discharging)

SwitchSwitch control control through through the the SVPWM SVPWM (Space (Space Vector Vector Pulse Pulse Width Width Modulation) Modulation) technique technique is shown is inshown Figure in28 Figure. 28.

FigureFigure 28. 28.Space Space Vector Vector PulsePulse WidthWidth ModulationModulation (SVPWM) (SVPWM) control control signal signal generation generation in inprotease. protease.

The operation of the circuit is explained with a flowchart (Figure 29) as follows.

1 START 2

ENABLE EN1 AND EN2 CONFIGURE I/O PORT PINS OF OPERATION ONLY CONTROLLER SELECT TIME DURATION OF MODE-1 , MODE-2 & MODE-3 TO START 3PHASE BE APPLIED PWM SIGNAL BLINK LED ( TO CHECK CONTROLLER RUNNING) START PWM STOP 4 DISPLAY “WELCOME” MSG AND NAME OF PROJECT ON LCD SET MODE-1 TIME DURATION IN PERIOD 4 REGISTER FOR EN1& EN2 TO BE ENABLE 3 SELECT MODE USING SWITCH

ENABLE EN1 AND EN2* SET MODE-2 TIME OPERATION ONLY DURATION IN PERIOD REGISTER FOR EN1 & MODE-1/ EN1* &EN2TO BE ENABLE START 3 PHASE MODE-2/ PWM SIGNAL MODE-3

SET MODE-3 TIME DURATION IN PERIOD STOP? REGISTER FOR EN1 & MODE-1/ EN1* TO BE ENABLE MODE-2/ MODE-3 4 STOP 4 STOP

2 3 1 Figure 29. Process chart. World Electric Vehicle Journal2019, 10, x FOR PEER REVIEW 18 of 27

Table 4. Latch and switch enable States for modes-1,2, and 3.

EN1 (SU1, SU2, EN2 (SL1, SL2, EN1 * (SU11, SU12, EN2 * (SU21, SU22, Control State SU3) SL3) SU13) SU23) UC (Charging) ON OFF OFF ON Battery (Discharging) ON ON OFF OFF Battery (Discharging) + UC ON ON ON OFF (Discharging)

Switch control through the SVPWM (Space Vector Pulse Width Modulation) technique is shown in Figure 28.

World Electric Vehicle Journal 2019, 10, 17 18 of 26 Figure 28. Space Vector Pulse Width Modulation (SVPWM) control signal generation in protease.

TheThe operation operation of of the the circuit circuit is is explained explained with with a a flowchart ﬂowchart (Figure (Figure 29)29) as as follows.

1 START 2

ENABLE EN1 AND EN2* SET MODE-2 TIME OPERATION ONLY DURATION IN PERIOD REGISTER FOR EN1 & MODE-1/ EN1* &EN2TO BE ENABLE START 3 PHASE MODE-2/ PWM SIGNAL MODE-3

SET MODE-3 TIME DURATION IN PERIOD STOP? REGISTER FOR EN1 & MODE-1/ EN1* TO BE ENABLE MODE-2/ MODE-3 4 STOP 4 STOP

2 3 1 FigureFigure 29. 29. ProcessProcess chart. chart.

World InElectric hardware Vehicle Journal implementation,2019, 10, x FOR the PEER battery REVIEW and ultracapacitor drive the load (Motor/Grid/RL 19 Load); of 27 we observe the power and energy sharing during dynamic loading situations. The observations are carriedIn outhardware for diﬀ erentimplementation, combinations the of battery three modes and ultracapacitor (i.e., mode-1: Batterydrive the only load as a (Motor/Grid/RL source; mode-2: BothLoad); sources we observe acting simultaneously, the power and handling energy the sharing dynamic during power dynamic requirement loading situation; situations. and mode-3: The Ultracapacitorobservations are as carried a source). out for different combinations of three modes (i.e., mode-1: Battery only as a source;Hardware mode-2: is Both implemented sources usingacting six simultaneo IGBTs, whichusly, constitutehandling thethe three-phase dynamic power inverter, requirement supplying batterysituation; power and tomode-3: the AC Ultracapacitor link and an ultracapacitor as a source). bank connected to AC link through six IGBTs. Thus, a totalHardware 12 IGBTs areis usedimplemented in the implementation. using six IGBTs, which constitute the three-phase inverter, supplyingHardware battery was power implemented to the AC (Figure link and 30) basedan ultracapacitor on three modes, bank as connected stated previously. to AC link Using through express six PCBIGBTs. software, Thus, a thetotal PCB 12 IGBTs was designed. are used in the implementation.

Figure 30. Hardware implementation.

Hardware was implemented (Figure 30) based on three modes, as stated previously. Using express PCB software, the PCB was designed.

Figure 31. PCB (Printed Circuit Board) layout. World Electric Vehicle Journal2019, 10, x FOR PEER REVIEW 19 of 27

In hardware implementation, the battery and ultracapacitor drive the load (Motor/Grid/RL Load); we observe the power and energy sharing during dynamic loading situations. The observations are carried out for different combinations of three modes (i.e., mode-1: Battery only as a source; mode-2: Both sources acting simultaneously, handling the dynamic power requirement situation; and mode-3: Ultracapacitor as a source). Hardware is implemented using six IGBTs, which constitute the three-phase inverter, supplying battery power to the AC link and an ultracapacitor bank connected to AC link through six IGBTs. Thus, a total 12 IGBTs are used in the implementation.

World Electric Vehicle Journal 2019, 10, 17 19 of 26

A single-side PCB was etchedFigure and prepared30. Hardware with implementation. ﬁxing components (Figure 31). The microchip processor 18F4520 was used with a control strategy based on the lookup table, with signal generation Hardware was implemented (Figure 30) based on three modes, as stated previously. Using using the SVPWM analogy. Digital control signals were developed within six sectors using dqo vectors express PCB software, the PCB was designed. (Figure 32 and Table5).

World Electric Vehicle Journal2019, 10, x FOR PEER REVIEW 20 of 27

A single-side PCB was etched and prepared with fixing components (Figure 31). The microchip processor 18F4520 was used with a control strategy based on the lookup table, with signal generation using the SVPWM analogy. Digital control signals were developed within six sectors using dqo vectors (Figure 32 and Table 5).

Table 5. Space Vector Pulse Width Modulation (SVPWM) signal generation

Position A’ A B’ B C’ C Hex Code 1 0 1 1 0 1 0 XX68 2 0 1 0 1 1 0 XX58 3 1 0 0 1 1 0 XX98

4 1 0 0 1 0 1 XX94 5 1 0 1 0 0 1 XXa4 6 0 1 1 0 0 1 XX64

Figure 31. PCB (Printed Circuit Board) layout. Figure 31. PCB (Printed Circuit Board) layout. 3 2

010 110

4 1 011 100

5 6 001 101 Figure 32. SVPWM analogy.

Table 5. Space Vector PulseFigure Width Modulation32. SVPWM (SVPWM)analogy. signal generation.

To reduce thePosition computation A’ time A of the B’ controller B C’, a lookup C Hextable Code with 864 states is included; thus, we obtained a two-level1 inverter 0 1 output. 1 Bu 0ffer (74HC244) 1 0 is used XX68 to select the modes. 2 0 1 0 1 1 0 XX58 5. Results 3 1 0 0 1 1 0 XX98 4 1 0 0 1 0 1 XX94 In this section, 5experimental 1 results 0 1with 0different 0 combinations 1 XXa4 of the three modes are discussed in detail. 6 0 1 1 0 0 1 XX64 Case-1: In this case, the battery acts as a source and provides power to the resistive load (mode-1).To reduce Here, the computation inverter voltage time ofand the current controller, for acase-1, lookup for table SVPWM-based with 864 states outputs, is included; are obtained thus, we obtainedfrom the inverter. a two-level inverter output. Buﬀer (74HC244) is used to select the modes. World Electric Vehicle Journal 2019, 10, 17 20 of 26

5. Results In this section, experimental results with diﬀerent combinations of the three modes are discussed in detail. Case-1: In this case, the battery acts as a source and provides power to the resistive load (mode-1). Here, inverter voltage and current for case-1, for SVPWM-based outputs, are obtained from the inverter. TheWorld input Electric voltage Vehicle Journal obtained2019, 10, from x FOR thePEER battery REVIEW to inverter is 24 V DC. The output obtained 21 of 27 with line to line voltage is 12 volts with a current of 1.2 A (Figure 33) (readings measured across 1 ohm resistor connected in line with RL load). The waveform below (Figure 34) shows the phase displacement between diﬀerent phase voltages of the inverter. World Electric Vehicle Journal2019, 10, x FOR PEER REVIEW 21 of 27

Figure 33. Line voltage and current at inverter output.

The input voltage obtained from the battery to inverter is 24 V DC. The output obtained with line to line voltage is 12 volts with a current of 1.2 A (Figure 33) (readings measured across 1 ohm resistor connected in line with RL load). The waveform below (Figure 34) shows the phase Figure 33. Line voltage and current at inverter output. displacement betweenFigure different 33. phLinease voltagevoltages and of the current inverter. at inverter output. The input voltage obtained from the battery to inverter is 24 V DC. The output obtained with line to line voltage is 12 volts with a current of 1.2 A (Figure 33) (readings measured across 1 ohm resistor connected in line with RL load). The waveform below (Figure 34) shows the phase displacement between different phase voltages of the inverter.

FigureFigure 34. 34.Phase Phasevoltages voltages at at inverter inverter output. output.

Figure 34. Phase voltages at inverter output. World Electric Vehicle Journal 2019, 10, 17 21 of 26

World Electric Vehicle Journal2019, 10, x FOR PEER REVIEW 22 of 27 The output with input for case-1 (Figure 35), where the battery supplies power to the load, is as follows. ReadingsThe output of with battery input current for case-1 are (Figure noted 35), by awhere variation the battery in the supplies three phase power load to the with load, continuous is as follows. Readings of battery current are noted by a variation in the three phase load with continuous intermittent switching of 10 s. intermittent switching of 10 s.

FigureFigure 35.35. Battery current. current.

In thisIn case,this case, the totalthe total energy energy requirement requirement is fulfilledis fulfilled by by the the battery battery alone. alone. The The current currentdrawn drawn from from the battery in this case is 4 A for 5 s and 2 A for next 5 s interval, which gives an average battery the battery in this case is 4 A for 5 s and 2 A for next 5 s interval, which gives an average battery current current of 3 A. of 3 A. Case-2: By using latch enable signals, the mode can be changed. This is the proposed mode Case-2(Figure: 36) By where using findings latch enable and conclusions signals, theare analyzed mode can and be interpreted changed. by This applying is the a combination proposed mode (Figureof different36) where sources findings simultaneously and conclusions (mode-2, are mode-3). analyzed and interpreted by applying a combination of different sourcesBy adjusting simultaneously the duty cycle (mode-2, of source mode-3). utilization, the prototype is tested for different Bycombinations adjusting theof sources. duty cycle The duty of source cycle utilization,adjustment provision the prototype is incorporated is tested forin the diff hardwareerent combinations using of sources.a potentiometer. The duty The cycle duty adjustment cycle is set provision for three di isfferent incorporated combinations in the and hardware the average using current a potentiometer. of the The dutybattery cycle is calculated is set for threefor a constant different load. combinations A battery alone and theand average the battery current ultra-capacitor of the battery combination is calculated for aare constant used for load. 0.5 ms A batterythroughout alone the and cycle. the The battery battery ultra-capacitor current for mode-2 combination is 1.60 A; for are mode-3, used for it 0.5is ms 0.04 A. The average battery current obtained for 1 ms with the two modes concerned was found to throughout the cycle. The battery current for mode-2 is 1.60 A; for mode-3, it is 0.04 A. The average be 0.82 A. battery current obtained for 1 ms with the two modes concerned was found to be 0.82 A. Case-3: In this case (Figure 37) the load is fulfilled through individual ultracapacitor, battery and ultracapacitor together, and individual battery for 0.5ms each. For mode-3, the battery current is 0.04 A, for mode-2 it is 1.6 A and for mode-1 it is 2.8 A. The average battery current is 1.48 A. Case-4 This case involves the load being fulfilled through a battery and ultracapacitor together (mode-2), and individual battery (mode-1), for 0.5 ms each. World Electric Vehicle Journal2019, 10, x FOR PEER REVIEW 23 of 27

World Electric Vehicle Journal 2019, 10, 17 22 of 26 World Electric Vehicle Journal2019, 10, x FOR PEER REVIEW 23 of 27

Figure 36. Battery and ultra-capacitor currentsmode-2 and mode-3 with t1 = 0.5 ms t2 = 0.5 ms.

Case-3: In this case (Figure 37) the load is fulfilled through individual ultracapacitor, battery

and ultracapacitor together, and individual battery for 0.5ms each. For mode-3, the battery current is Figure 36. Battery and ultra-capacitor currentsmode-2 and mode-3 with t1 = 0.5 ms t2 = 0.5 ms. 0.04 A,Figure for mode-2 36. Battery it is and1.6 A ultra-capacitor and for mode-1 currentsmode-2 it is 2.8 A. The and average mode-3 battery with t1 =current0.5 ms is t2 1.48= 0.5 A. ms.

Case-3: In this case (Figure 37) the load is fulfilled through individual ultracapacitor, battery and ultracapacitor together, and individual battery for 0.5ms each. For mode-3, the battery current is 0.04 A, for mode-2 it is 1.6 A and for mode-1 it is 2.8 A. The average battery current is 1.48 A.

Figure 37. Battery and ultracapacitor currents, mode-3, mode-2, and mode-1 with t1 = 0.5 ms, t2 = 0.5 Figure 37. Battery and ultracapacitor currents, mode-3, mode-2, and mode-1 with t1 = 0.5 ms, t2 = ms, t3=0.5 ms. 0.5 ms, t3 = 0.5 ms.

The above waveforms (Figure 38) depict the load shared by the battery alone, i.e., mode-1 (2.4A), Figure 37. Battery and ultracapacitor currents, mode-3, mode-2, and mode-1 with t1 = 0.5 ms, t2 = 0.5 and the load shared when the battery and ultra-capacitor, i.e., mode-2, are used together (1.2 A). ms, t3=0.5 ms. The average battery current obtained with these modes (mode-2 and mode-3) is 1.8 A. World Electric Vehicle Journal2019, 10, x FOR PEER REVIEW 24 of 27

WorldCase-4 Electric Vehicle This Journalcase involves2019, 10, 17 the load being fulfilled through a battery and ultracapacitor together23 of 26 (mode-2), and individual battery (mode-1), for 0.5 ms each.

Figure 38. Battery and ultra-capacitor currents, mode-2, mode-1with t1 = 0.5 ms, t2 = 0.5 ms. Figure 38. Battery and ultra-capacitor currents, mode-2, mode-1with t1 = 0.5 ms, t2 = 0.5 ms.

AsThe an above ultracapacitor waveforms is used (Figure to supply 38) depict power the demands load shared of short by duration, the battery mode-3 alone, cannot i.e., bemode-1 used independently(2.4A), and the toload meet shared long-term when energythe battery requirements. and ultra-capacitor, i.e., mode-2, are used together (1.2 A). TheHere average (Table battery6), we usecurrent the obtained conventional with modethese modes (battery (mode-2 supplying and energy)mode-3) oris 1.8 a mixed A. mode, whereinAs an the ultracapacitor ultracapacitor is alone used andto supply the battery powe andr demands ultra-capacitor of short togetherduration, can mode-3 be preferred cannot be to minimizeused independently the average to batterymeet long-term current. Thisenergy enhances requirements. the operating cycle/driving cycle of an electric vehicle (or any load). Mixed mode (case-2) gives an average current of 0.82 A in comparison to the individual battery mode, whichTable gives 6. Current an average comparison battery fo currentr different of cases. 3 A, which clearly shows average battery current 27.33% (0.82 A 100 Case-1/3 A)(Mode-1) compared Case-2 to (Mode-2&3) other modes Case-3 of (Mode-1,2 control & (case-1), 3) Case-4 thereby (Mode-1&2) leading × to a muchAverage improved Battery Current range of driving cycles.3 A 0.82 A 1.48 Amp 1.8 Amp Ultracapacitor Current (Discharging) 0 A 2 A 2 A 1.6 A

Table 6. Current comparison for different cases. Here (Table 6), we use the conventional mode (battery supplying energy) or a mixed mode, wherein the ultracapacitor alone andCase-1 the batteryCase-2 and ultra-capacitorCase-3 together Case-4can be preferred to minimize the average battery current.(Mode-1) This enhances(Mode-2&3) the operating(Mode-1,2 cycle/driving & 3) (Mode-1&2) cycle of an electric vehicle (orAverage any load). Battery Mixed Current mode (case-2) 3 A gives 0.82 an Aaverage current 1.48 Amp of 0.82 A 1.8in comparison Amp to the Ultracapacitor Current individual battery mode, which gives0 A an average 2 A battery current 2 A of 3 A, which 1.6 A clearly shows (Discharging) average battery current 27.33% (0.82 A × 100/3 A) compared to other modes of control (case-1), thereby leading to a much improved range of driving cycles. The experimental work was carried out using a small prototype of an energyenergy managementmanagement system consistingconsisting ofof a a battery, battery, ultra-capacitors, ultra-capacitors, a control a control board, board, a power a power supply, supply, and a digitaland a storagedigital oscilloscopestorage oscilloscope with a di withfferential a differential probe. probe. The hardware (Figure 39) was tested for different cases via mode-1, mode-2, and mode-3. World Electric Vehicle Journal 2019, 10, 17 24 of 26 World Electric Vehicle Journal2019, 10, x FOR PEER REVIEW 25 of 27

Figure 39. Experimental setup.

6. ConclusionsThe hardware (Figure 39) was tested for different cases via mode-1, mode-2, and mode-3. In this paper, a suitable multi-source inverter topology for HESS was proposed. The main 6. Conclusions advantage of this topology is that it does not add any additional stages between the grid/motor and battery.In this This paper, novel multisourcea suitable multi-source connection results inverter in improved topology powerfor HESS demand was fulfillmentproposed. ofThe the main load, therebyadvantage improving of this topology the efficiency is that of it electric does not vehicles. add any Also, additional with a multi-source stages between inverter, the grid/motor smooth current and sharingbattery. andThis lower novel average multisource currents connection are achieved. results On in the improved other hand, power the batterydemand can fulfillment directly driveof the a motorload, thereby without improving any boost the operation, efficiency as of is doneelectric with vehicles. a DC/ DCAlso, converter, with a multi-source thereby reducing inverter, the smooth overall costcurrent of the sharing converter and andlower also average increasing currents the EMS are achiev efficiency.ed. On Active the other power hand, and energythe battery sharing can betweendirectly multipledrive a motor sources without is possible any boost during operation, dynamic as load is do demandsne with a obtained DC/DC converter, using a SVPWM-based thereby reducing control the strategy,overall cost which of improvesthe converter the stability and also of theincreasing load as anthe induction EMS efficiency. motor. Finally, Active the power performance and energy of a multisourcesharing between inverter multiple topology sources is studied is possible with a scaled-downduring dynamic prototype. load demands From experimentation, obtained using it isa observedSVPWM-based that with control multisource strategy, topology, which improves a higher drivingthe stability range of is the achieved load as with an ainduction reduction motor. in the averageFinally, currentthe performance of 27% compared of a multisource to that drawn inverter from a batterytopology during is studied conventional with a modes scaled-down of EMS controlprototype. with From greater experimentation, thermal stability, it ais reductionobserved inthat overall with size,multisource and an enhancement topology, a higher of the lifedriving time ofrange anenergy is achieved storage with system. a reduction in the average current of 27% compared to that drawn from a battery during conventional modes of EMS control with greater thermal stability, a reduction in Authoroverall Contributions:size, and an enhancementY.M. wrote the of originalthe life time draft; of presented an energy the storage methodology, system. simulation, and hardware environment with technical data and practical information to make this study applicable for industry; and investigated the results from a technical point of view. K.V. reviewed and edited the manuscript and also providedAuthor Contributions: supervision. Y.M. wrote the original draft; presented the methodology, simulation, and hardware environment with technical data and practical information to make this study applicable for industry; and Funding: This research received no external funding. investigated the results from a technical point of view. K.V. reviewed and edited the manuscript and also Acknowledgments:provided supervision.We acknowledge Sutar Amol make for the support to our research group. Conflicts of Interest: The authors declare no conflict of interest. Funding: This research received no external funding.

ReferencesAcknowledgments: We acknowledge Sutar Amol make for the support to our research group.

1.ConflictsPereirinha, of Interest: P.G.; The Trov authorsão, J.P. declare Multiple no Energyconflict Sourcesof interest. Hybridization: The Future of Electric Vehicles? Chapter 8. In New Generation of Electric Vehicles; IntechOpen: London, UK, 2012; pp. 237–262. [CrossRef] References World Electric Vehicle Journal 2019, 10, 17 25 of 26

2. Burke, A.F. Batteries and Ultracapacitors for Electric, Hybrid, and Fuel Cell Vehicles. Proc. IEEE 2007, 95, 806–820. [CrossRef] 3. Sauer, D.U.; Kleimaier, M.; Glaunsinger, W. Relevance of energy storage in future distribution networks with high penetration of renewable energy sources. In Proceedings of the CIRED 2009 20th International Conference and Exhibition on Electricity Distribution, Prague, Czech Republic, 8–11 June 2009; pp. 1–4. 4. Akatsu, K.; Watanabe, N.; Fujitsuna, M.; Doki, S.; Fujimoto, H. Recent Related Technologies for EV/HEV Applications in Japan. In Proceedings of the IEEE ECCE Asia Downunder, Melbourne, Australia, 3–6 June 2013; pp. 141–146. 5. Lukic, S.M.; Cao, J.; Bansal, R.C.; Rodriguez, F.; Emadi, A. Energy Storage Systems for Automotive Applications. IEEE Trans. Ind. Electron. 2008, 55, 2258–2267. [CrossRef] 6. Somayajula, D.; Crow, M.L. An Integrated Active Power Filter–Ultracapacitor Design to Provide Intermittency Smoothing and Reactive Power Support to the Distribution Grid. IEEE Trans. Sustain. Energy 2014, 5, 1116–1125. [CrossRef] 7. Manfredi, S.; Paganm, M.; Raimo, R. Ultracapacitor-based Distributed Energy Resources to support time-varying smart-grid power ﬂows. In Proceedings of the International Symposium on Power Electronics, Electrical Drives, Automation and Motion, Sorrento, Italy, 20–22 June 2012; pp. 1148–1153. 8. Li, X.; Zhang, L.; Wang, Z.; Dong, P. Remaining useful life prediction for lithium-ion batteries based on a hybrid model combining the long short-term memory and Elman neural networks. J. Energy Storage 2019, 21, 510–518. [CrossRef] 9. Zhang, J.; Zhang, L.; Sun, F.; Wang, Z. An Overview on Thermal Safety Issues of Lithium-ion Batteries for Electric Vehicle Application. IEEE Access 2018, 6, 23848–23863. [CrossRef] 10. Li, X.; Wang, Z.; Zhang, L.; Zou, C.; Dorrell, D.D. State-of-health estimation for Li-ion batteries by combing the incremental capacity analysis method with grey relational analysis. J. Power Sources 2019, 410–411, 106–114. [CrossRef] 11. Wang, Z.; Ma, J.; Zhang, L. State-of-health estimation for lithium-ion batteries based on the multi-island genetic algorithm and the gaussian process regression. IEEE Access 2017, 5, 21286–21295. [CrossRef] 12. Zhang, L.; Hu, X.; Wang, Z.; Sun, F.; Deng, J.; Dorrell, D. Multi-objective optimal sizing of hybrid energy storage system for electric vehicles. IEEE Trans. Veh. Technol. 2018, 67, 1027–1035. [CrossRef] 13. Aharon, I.; Kuperman, A. Topological Overview of Powertrains for Battery-Powered Vehicles with Range Extenders. IEEE Trans. Power Electron. 2011, 26, 868–876. [CrossRef] 14. Schupbach, R.M.; Balda, J.C.; Zolot, M.; Kramer, B. Design methodology of a combined battery-ultracapacitor energy storage unit for vehicle power management. In Proceedings of the IEEE 34th Annual Conference on Power Electronics Specialist (PESC 03), Acapulco, Mexico, 15–19 June 2003. 15. Emadi, A.; Rajashekara, K.; Williamson, S.S.; Lukic, S.M. Topological Overview of Hybrid Electric and Fuel Cell Vehicular Power System Architectures and Conﬁgurations. IEEE Trans. Veh. Technol. 2005, 54, 763–770. [CrossRef] 16. Cao, J.; Emadi, A. A new battery/ultracapacitor hybrid energy storage system for electric, hybrid, and plug-in hybrid electric vehicles. IEEE Trans. Power Electron. 2012, 27, 122–132. 17. Lukic, S.M.; Wirasingha, S.G.; Rodriguez, F.; Jian, C.; Emadi, A. Power management of an ultracapacitor/ battery hybrid energy storage system in an HEV. In Proceedings of the 2006 IEEE Vehicle Power and Propulsion Conference, Windsor, UK, 6–8 September 2006; pp. 1–6. 18. Dorn-Gomba, L.; Magne, P.; Danen, B.; Emadi, A. On the concept of the multi-source inverter for hybrid electric vehicle powertrains. IEEE Trans. Power Electron. 2018, 33, 7376–7386. [CrossRef] 19. Dorn-Gomba, L.; Emadi, A. A novel Hybrid Energy Storage System Using the Multi Source Invereter. In Proceedings of the 2018 IEEE Applied Power Electronics Conference and Exposition (APEC), San Antonio, TX, USA, 4–8 March 2018. 20. Soltani, M.; Ronsmans, J.; Kakihara, S.; Jaguemont, J.; Van den Bossche, P.; Van Mierlo, J.; Omar, N. Hybrid Battery/Lithium-Ion Capacitor Energy Storage System for a Pure Electric Bus for an Urban Transportation Application. Appl. Sci. 2018, 8, 1176. [CrossRef] 21. Xiangjun, L.; Liangfei, X.; Jianfeng, H.; Jianqiu, L.; Minggao, O. Regenerative braking control strategy for fuel cell hybrid vehicles using fuzzy logic. In Proceedings of the International Conference on Electrical Machines and Systems, Wuhan, China, 17–20 October 2008; pp. 2712–2716. World Electric Vehicle Journal 2019, 10, 17 26 of 26

22. Wu, X.; Wang, T. Optimization of Battery Capacity Decay for Semi-Active Hybrid Energy Storage System Equipped on Electric City Bus. Energies 2017, 10, 792. [CrossRef] 23. Xiangjun, L.; Liangfei, X.; Jianfeng, H.; Jianqiu, L.; Minggao, O. Control algorithm of fuel cell/battery hybrid vehicular power system. In Proceedings of the IEEE Vehicle Power and Propulsion Conference, Harbin, Hei Longjiang, China, 3–5 September 2008; pp. 1–6. 24. Jiya, I.N.; Gurusinghe, N.; Gouws, R. Combination of LiCs and EDLCs with Batteries: A New Paradigm of Hybrid Energy Storage for Application in EVs. World Electr. Veh. J. 2018, 9, 47. [CrossRef] 25. Miñambres-Marcos, V.M.; Guerrero-Martínez, M.Á.; Barrero-González, F.; Milanés-Montero, M.I. A Grid Connected Photovoltaic Inverter with Battery-Supercapacitor Hybrid Energy Storage. Sensors 2017, 17, 1856. [CrossRef][PubMed] 26. Liu, J.; Jin, T.; Liu, L.; Chen, Y.; Yuan, K. Multi-Objective Optimization of a Hybrid ESS Based on Optimal Energy Management Strategy for LHDs. Sustainability 2017, 9, 1874. [CrossRef] 27. Jiuyu, D.; Minggao, O.; Wang, H. Battery electric vehicle parameters design targeting to cost-beneﬁt objective. In Proceedings of the IEEE Vehicle Power and Propulsion Conference, Seoul, Korea, 9–12 October 2012; pp. 1160–1164. 28. Trovão, J.P.; Jorge, H.M.; Pereirinha, P.G. Design Methodology of Energy Storage Systems for a Small Electric Vehicle. In Proceedings of the EVS24, Stavanger, Norway, 13–16 May 2009. 29. Trovao, J.P.F.; Santos, V.D.N.; Antunes, C.H.; Pereirinha, P.G.; Jorge, H.M. A real-time energy management architecture for multisource electric vehicles. IEEE Trans. Ind. Electron. 2015, 62, 3223–3233. [CrossRef]

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