Integrated Battery Charger for Electric Vehicles Based on a Dual-Inverter Drive and a Three-Phase Current Rectiﬁer

electronics

Article Integrated Battery Charger for Electric Vehicles Based on a Dual-Inverter Drive and a Three-Phase Current Rectiﬁer

Vitor Fernão Pires 1,2 , Joaquim Monteiro 1,3,*, Armando Cordeiro 1,2,3 and José Fernando Silva 1,4

1 INESC-ID, 1000-029 Lisboa, Portugal; [email protected] (V.F.P.); [email protected] (A.C.); [email protected] (J.F.S.) 2 SustainRD, EST Setubal, Polytechnic Institute of Setúbal, 2914-761 Setúbal, Portugal 3 ISEL—Polytechnic Institute of Lisboa, 1959-007 Lisboa, Portugal 4 IST—Instituto Superior Técnico, Universidade de Lisboa, 1049-001 Lisboa, Portugal * Correspondence: [email protected]; Tel.: +351-21-831-7000

Received: 30 September 2019; Accepted: 20 October 2019; Published: 22 October 2019

Abstract: This paper presents a new three-phase battery charger integrated with the propulsion system of an electric vehicle. The propulsion system consists of a dual-inverter topology connected to an induction motor via open windings. The electrical vehicles (EV) batteries are divided by two inverters. This will result in a drive with multilevel characteristics reducing the total harmonic distortion (THD) of the voltage applied to the motor. The modularity of the multilevel inverter will be maintained since two classical three-phase inverters are used. The charger will be fed by a three-phase high power factor current source rectiﬁer. The motor windings will take the role of the DC-inductor required by the rectiﬁer. In this way, an intermediate storage element between the grid and the batteries of the vehicle exist. For the control system of the battery charger, we propose the use of the instantaneous power theory and a sliding mode controller for the three-phase charger input currents. Finally, to verify the behavior and characteristics of the proposed integrated battery charger and control system, several tests are be presented.

Keywords: electric vehicles; integrated battery charger; dual-inverter drive; power factor correction (PFC); current rectiﬁer

1. Introduction The importance of electrical vehicles (EV) has been hugely increased, year after year. Certainly, their role is critical to answering the problem of the greenhouse eﬀect [1]. Indeed, in accordance with the International Energy Agency, in 2018 the global stock of electric passenger cars exceeded 5 million, which has increased 63%, taking into consideration the previous year [2]. On the other hand, several governments have passed legislation in order to encourage the transition from fuel fossil vehicles to EVs [3]. In this context, the technology solutions and research associated with these vehicles have become increasingly important. One of the fundamental areas of the EV is the charging of the EVs batteries. There are several aspects that should be considered for EV chargers connected to the grid. It should be considered whether they will be used for slow or fast charging, as well as their impact on the grid. Regarding this last issue, the charger must be designed in order to minimize the impact on the grid power quality. In this way, it should be designed to ensure that the charger is a load with high power factor. Many high power factor rectiﬁers have been proposed and studied. Their topologies have been

Electronics 2019, 8, 1199; doi:10.3390/electronics8101199 www.mdpi.com/journal/electronics Electronics 2019, 8, 1199 2 of 17 classified as Boost, Buck-Boost, and Buck, in accordance with their capability to generate an output voltage that is higher or lower than the maximum input voltage [4–13]. Usually, EV chargers are classified as off-board or on-board [14]. The off-board chargers are normally developed for high power DC fast charging. Several rectifier types have been proposed and investigated as surveyed in [15–19]. The on-board chargers are for reduced powers and are integrated into the EVs [20]. This solution gives high flexibility to the drivers since it usually allows the EV to charge through an electric power outlet. However, the integration of the charger in the EV will increase total weight, volume, and cost. Thus, to minimize this drawback, the chargers should be designed, in order to use as much as possible, the same available hardware used for the traction of the EV [14]. To implement this type of solution, it must be considered that the charging and propulsion of the EV do not occur simultaneously. Indeed, the vehicle has the electric motor stopped when the vehicle is connected to the electric grid for the charging process. So, when the EV is in charging mode, the motor(s) windings will be used as filter inductors, storage elements, or isolated transformers. Several configurations have been proposed for the integrated battery charger of EVs. These proposals have also taken into consideration the motor type. For the case of the three-phase motors, solutions using a Boost rectifier were considered, being the motor used as a filter inductor. These solutions require having access to the motor, namely to the terminals of the motors windings, or neutral point of the windings or use a contactor to reconfigure the connection of the motor windings [21–23]. An EV isolated charger for a lift truck was also proposed in [24]. Another approach was through the use of current rectifiers with Buck-Boost characteristics. An integrated charger with this type of converter and three-phase connection is presented in [25]. Due to the converter type, in charging mode, the motor is used as a coupled DC inductor. Integrated chargers have also been proposed for multiphase motors. These chargers have the advantage of avoiding the problem of torque generation in the propulsion motor that exists in systems that use three-phase motors and Boost rectifiers. So, solutions for five, six, and nine machine phases have been proposed [26–31]. However, for many EVs, the dominant motor is the three-phase and chargers for multiphase motors cannot be applied. A good possibility is the use of multilevel inverters for the drive of the three-phase AC motor. Very few works have addressed the multilevel configuration for the EVs. A charger was presented for an EV drive with two, two-level voltage source inverters (dual inverter), in [32]. However, the proposed charger was developed for connection to DC power outlets only. Another aspect is the control system for the EV chargers. Most control algorithms are intended to minimize the total harmonic distortion (THD) introduced by the rectifier in the AC power line current. Therefore, the controllers are normally associated with rectifier topologies that allow for high (almost unity) power factor operation. Many control algorithms have been proposed for the high power factor rectifiers [33]. Some of those control systems have been applied to EV chargers. One of the proposals was the use of direct power control for a unidirectional EV charger [34]. The use of model predictive control (MPC) was also used in these systems although requires complex implementation and powerful microprocessors [35,36]. An EV charger proposing a nonideal proportional and resonant (PR) controller was published in [37]. A charger nonlinear-carrier control method was proposed for a reduced-part single-stage integrated power electronics interface for automotive applications [38]. Another interesting approach was the integration of the voltage-oriented control (VOC) with pulse width modulation (PWM), but not for integrated chargers [39]. Regarding the integrated battery charger, one of the most used approaches uses a Proportional-Integral (PI) compensator associated with a PWM for the current controller [23,29]. Another approach was used for a 20 kW motor drive in which the battery charging is done by controlling the inverter dq currents, similarly to field-oriented control (FOC) [40]. For the charger based on the current rectifier, a PI compensator was proposed for the current controller [25]. However, PI compensators are highly dependent on the circuit parameters and present some lack of robustness that is typical from linear based compensators. This paper proposes a novel configuration of an integrated on-board charger for EVs that uses dual-inverter drives. For such drives, a charger is proposed to be connected to DC power outlets. Electronics 2019, 8, 1199 3 of 17

On the other hand, the proposed charger does not require adjusting the three-phase AC drive or access to the motor windings, avoiding additional terminals or reconfiguration. Note that such requirement is typical in conventional solutions. From the point of view of the charger’s impact on the grid, the proposed solution has some distinct features regarding the classic voltage source PWM rectifier, namely, their capacity to limit the inrush and DC-short-circuit currents. The proposed charger configuration is based on a three-phase high power factor current source rectifier. The motor windings are part of the charger since they will operate as a DC inductor. A fast and robust control system for the proposed EV charger will also be presented. This control is based on the sliding mode control (SMC) technique since the power electronic converters used on the EV charger are variable structure systems. On the other hand, the SMC has the capability of system order reduction and allows increasing the stability, the robustness, and the response speed, even with perturbations. To confirm the characteristics of the proposed EV charger, several tests are presented. This paper is organized as follows. Section2 describes the proposed new power converter topology for the three-phase integrated battery charger of an EV with a dual-inverter drive and the operation modes of the on-board integrated battery charger are presented. Section3 deals with the control system of the proposed battery charger based on the instantaneous power theory and sliding mode control. Simulation results are presented and analyzed in Section4, while the experimental results are shown in Section5. Section6 presents some conclusions regarding the behavior of the proposed integrated battery charger and control system.

2. Battery Charger Configuration As mentioned before, the majority of the battery EV chargers will require access to the motor. The proposed charger does not need this requirement since the output of the current-source three-phase rectifier will be directly connected to the inverters, as shown in Figure1. One of the output terminals of the three-phase rectifier will be connected to one of the inverters through a motor winding and the other output terminal will be connected to the other inverter. The proposed rectifier will present Buck-Boost characteristics, in which, the propulsion winding motor is part of the circuit and is used as a DC inductor when the system is in charging mode. Indeed, this is another advantage of the circuitElectronics since 2019, avoids 8, x FOR the PEER use REVIEW of a bulky DC inductor, needed in classic current-source rectifiers4 as of an 18 intermediate storage element.

Motor Drive iBat

SU1 SU2 SU3 i Three-phase o1 induction motor

Vbat CU Power Supply Current Source

and Input Filter Rectifier SU4 SU5 SU6

S1 S2 S3 iBat L VS1 f1 iS1 i0 SL1 SL2 SL3 io2 iA iB iC VS2 Lf2 iS2 V VS3 Lf3 iS3 bat CL

S S S SL4 SL5 SL6 Cf1 Cf2 Cf3 4 5 6

Figure 1. Power converter topology for the three-phase integrated battery charger of an electronic Figure 1. Power converter topology for the three-phase integrated battery charger of an electronic vehicle (EV) with a dual-inverter drive. vehicle (EV) with a dual-inverter drive. Some of the aspects of the charger that is important to be considered are their total weight, volume, Through the analysis of the charger circuit, it is possible to devise operation modes associated and cost. One of the key elements that contribute to these in the current-source rectiﬁers is the DC with the rectifier circuit and operation modes associated with the inverters. The definition of these operation modes should take into consideration how the windings of the propulsion motor will be used. So, since the value of the DC inductor of the rectifier influences the input line current distortion and the switching frequency, two of the motor windings will be used in a serial connection. In accordance with this choice, there will be seven operating modes associated with the rectifier. Each of these operating modes is following described: Mode 1: In this operation mode the power devices of the current source rectifier S1 and S6 are turned on (Figure 2a) and the voltage applied to the motor windings is VCf13. This mode will influence directly the currents in inductors Lf1 and Lf3, since the capacitor voltages Cf1 and Cf3 will also be dependent on the io value. Mode 2: In this operation mode the power devices of the current source rectifier S2 and S6 are turned on (Figure 2b) and the voltage applied to the motor windings is VCf23. In this mode the most influenced currents will be iLf1 and iLf3. Mode 3: In this operation mode the power devices of the current source rectifier S2 and S4 are turned on (Figure 2c) and the voltage applied to the motor windings is VCf21. This combination will essentially affect the inductor currents iLf1 and iLf2. Mode 4: In this operation mode the power devices of the current source rectifier S3 and S4 are turned on (Figure 2d) and the voltage applied to the motor windings is VCf31. This mode mostly influences the inductor currents iLf1 and iLf3. Mode 5: In this operation mode the power devices of the current source rectifier S3 and S5 are turned on (Figure 2e) and the voltage applied to the motor windings is VCf32. The phase currents iLf2 and iLf3 will be most influenced. Mode 6: In this operation mode the power devices of the current source rectifier S1 and S5 are turned on (Figure 2f) and the voltage applied to the motor windings is VCf12. The currents iLf1 and iLf2 will be most influenced. Mode 7: In this operation mode all the power devices are turned off (Figure 2g). In this mode the current source rectifier is disconnected from the motor. All the three-phase current dynamics will be influenced, namely tending to reduce, as the inductor energy is transferred to the battery.

Electronics 2019, 8, 1199 4 of 17 inductor. However, since in this proposed charger the motor windings are used as a DC inductor, the charger total weight, volume, and cost can be reduced since it is only required to include the power semiconductors of the rectifier and small input LC filter. Another aspect that must be considered is the impact of the charger on the grid. In this case, comparing the proposed solution with the classic voltage source PWM rectifier, it has some distinct features, namely, regarding their capacity to limit the inrush and DC short-circuit currents. Thus, when the charger is connected to the grid, inrush current as in the classical solution is not possible as the input rectifier is a current source device. Besides that, the grid current can be limited during a short-circuit in the DC side of the rectifier, which is not possible in the classical solution. Regarding the impact on the grid from the point of view of the harmonics and reactive power, the proposed charger is similar to classical solutions. Indeed, the TDH is similarly small and the displacement factor is practically unity. Through the analysis of the charger circuit, it is possible to devise operation modes associated with the rectifier circuit and operation modes associated with the inverters. The definition of these operation modes should take into consideration how the windings of the propulsion motor will be used. So, since the value of the DC inductor of the rectifier influences the input line current distortion and the switching frequency, two of the motor windings will be used in a serial connection. In accordance with this choice, there will be seven operating modes associated with the rectifier. Each of these operating modes is following described: Mode 1: In this operation mode the power devices of the current source rectifier S1 and S6 are turned on (Figure2a) and the voltage applied to the motor windings is V Cf13. This mode will influence directly the currents in inductors Lf1 and Lf3, since the capacitor voltages Cf1 and Cf3 will also be dependent on the io value. Mode 2: In this operation mode the power devices of the current source rectifier S2 and S6 are turned on (Figure2b) and the voltage applied to the motor windings is V Cf23. In this mode the most influenced currents will be iLf1 and iLf3. Mode 3: In this operation mode the power devices of the current source rectifier S2 and S4 are turned on (Figure2c) and the voltage applied to the motor windings is V Cf21. This combination will essentially affect the inductor currents iLf1 and iLf2. Mode 4: In this operation mode the power devices of the current source rectifier S3 and S4 are turned on (Figure2d) and the voltage applied to the motor windings is V Cf31. This mode mostly influences the inductor currents iLf1 and iLf3. Mode 5: In this operation mode the power devices of the current source rectifier S3 and S5 are turned on (Figure2e) and the voltage applied to the motor windings is V Cf32. The phase currents iLf2 and iLf3 will be most influenced. Mode 6: In this operation mode the power devices of the current source rectifier S1 and S5 are turned on (Figure2f) and the voltage applied to the motor windings is V Cf12. The currents iLf1 and iLf2 will be most influenced. Mode 7: In this operation mode all the power devices are turned off (Figure2g). In this mode the current source rectifier is disconnected from the motor. All the three-phase current dynamics will be influenced, namely tending to reduce, as the inductor energy is transferred to the battery. Electronics 2019, 8, 1199 5 of 17 Electronics 2019, 8, x FOR PEER REVIEW 5 of 18

(a) (b)

(e) (f)

Power Motor Supply Drive and Filter

(g)

FigureFigure 2. ModesModes of of the the on-board on-board integrated integrated battery battery charger: charger: ( (aa)) mode mode 1; 1; ( (bb)) mode mode 2; 2; ( (cc)) mode mode 3; 3; ( (dd)) modemode 4; ( e)) mode mode 5; 5; ( (f)) mode mode 6; ( g) mode 7.

OneOne ofof thethe critical critical aspects aspects of theof rectifierthe rectifier is the is need the for need a DC for inductor a DC toinductor work as to an intermediatework as an intermediatestorage element storage between element the gridbetween and thethebatteries grid and of the the batteries vehicle. of This the intermediate vehicle. This storage intermediate will be storageensured will through be ensured the control through of the the dual control inverters of theand dual synchronized inverters and with synchronized the rectifier. with Thus, the torectifier. ensure Thus,the success to ensure of this the procedure, success of there this procedure, will be two ther operatinge will be modes. two operating The first operatingmodes. The mode first is operating when the modeenergy is is when transferred the energy from theis transferred grid to the motorfrom the windings. grid to Inthe this motor way, windings. this operating In this mode way, will this be operatingassociated mode with will the rectifierbe associated operating with modesthe rectifier 1 to 6. operating To ensure modes that the1 to motor 6. To ensure winding that will the operate motor windingas DC inductors will operate the switches as DC inductors of the upper the switches inverter SofU1 the,SU2 upper, and SinverterU3 and theSU1,switches SU2, and ofSU3 the and lower the switchesinverter SofL5 theand lower SL6 must inverter be in S ONL5 and state SL6 (Figure must 3bea). in The ON second state operating(Figure 3a). mode The issecond associated operating with modethe transfer is associated of the energy with the from transfer the motor of the windings energy from to the the inverter motor battery.windings Thus, to the it mustinverter be ensuredbattery. Thus,that the it rectifiermust be should ensured be that disconnected the rectifier from should the inverters. be disconnected This will befrom achieved the inverters. by operating This modewill be 7. achievedRegarding by the operating switches mode of the 7. invertersRegarding in the this switches mode, allof the of them inverters must in be this switched mode, all to theof them OFF must state be(Figure switched3b). to the OFF state (Figure 3b).

Electronics 20192019,, 88,, 1199x FOR PEER REVIEW 66 of of 1718

Motor Drive

SU1 SU2 SU3

Vbat CU

SU4 SU5 SU6

SL1 SL2 SL3

Vbat CL

SL4 SL5 SL6

(a)

Motor Drive

SU1 SU2 SU3

Vbat CU

SU4 SU5 SU6

SL1 SL2 SL3

Vbat CL

SL4 SL5 SL6

(b)

Figure 3. Modes of the motor drive: ( a) mode 1; ( b) mode 2 during the charging operation.

3. Control of the Charger The proposed EV charger will be the controller in order to ensure a referencereference power and with near-unity powerpower factor. factor. In In accordance accordance with with this, this, it is proposedit is proposed a control a control system basedsystem on based the dynamic on the modeldynamic of model the rectiﬁer. of the rectifier. The model of the proposed current source rectiﬁer,rectifier, as an on-board charger, whosewhose scheme is presented inin FigureFigure1 ,1, can can be be obtained obtained considering considerin allg all semiconductors semiconductors being bein idealg ideal while while neglecting neglecting the lossesthe losses of the of inductors the inductors and capacitors. and capacitors. the operation the operation modes modes will be alsowill consideredbe also considered from the from previous the section,previous and section, the three-level and the variablesthree-levelγ1 ,variablesγ2, and γ γ3,1, in γ Equation2, and γ3, (1) in areEquation assumed (1) to are be associatedassumed to with be theassociated state of thewith power the state semiconductors. of the power Based semicond on theuctors. symmetrical Based andon the balanced symmetrical three-phase and systembalanced of three-phase system of Figure 1, and applying Kirchhoff laws to the circuit, the state-space model, in the three-phase reference frame, is given by Equation (2).

Electronics 2019, 8, 1199 7 of 17

Figure1, and applying Kirchho ﬀ laws to the circuit, the state-space model, in the three-phase reference frame, is given by Equation (2).

 ( )  1 , i f S1 is ON and S 4 is ON or S6 is ON  γ1 =  1 , i f S2 is ON and (S 3 is ON or S5 is ON)  −  0 , other combinations  ( )  1 , i f S3 is ON and S 2 is ON or S6 is ON  γ2 =  1 , i f S4 is ON and (S 1 is ON or S5 is ON) (1)  −  0 , other combinations  ( )  1 , i f S5 is ON and S 2 is ON or S4 is ON  γ3 =  1 , i f S6 is ON and (S 1 is ON or S3 is ON)  −  0 , other combinations

 R dis1 f 2 1 1 1 2 1 1 γ1  = is1 VC + VC + VC + is1 + Vs1 Vs2 Vs3 Vs1  dt − L f − 3L f f 1 3L f f 2 3L f f 3 C f 3L f − 3L f − 3L f − C f  R  dis2 f 1 2 1 1 1 2 1 γ2  = is2 + VC VC + VC + is2 + Vs1 Vs2 Vs3 Vs2  dt − L f 3L f f 1 − 3L f f 2 3L f f 3 C f 3L f − 3L f − 3L f − C f  R  dis3 f 1 1 2 1 1 1 2 γ3  = is + V + V V + is + V Vs Vs Vs  dt L f 3 3L f C f 1 3L f C f 2 3L f C f 3 C 3 3L f s1 3L f 2 3L f 3 C 3  − − f − − − f dVC (2)  f 1 = 1 γ1  VC f 1 iLo  dt C f − C f  dVC  f 2 = 1 γ2  dt C VC f 2 C iLo  f − f  dVC  f 2 1 γ3  = VC iL dt C f f 3 − C f o Applying αβ coordinates to the model of the current-source rectiﬁer presented in Equation (2), the following equations are obtained in Equation (3).

 R  dis α f 1 1  = is α VC α + Vs α  dt − L f − L f f L f  di R  s β = f 1 + 1  L is β L VC f β L Vs β  dt − f − f f dVC (3)  f α 1 γα  = is α io  dt C f − C f  dV  C f β 1 γβ  = is β io dt C f − C f For the controller design, consider the active and reactive powers to the input of the current source rectiﬁer. From the instantaneous power theory [41], the instantaneous active and reactive powers are expressed by: ( P = V i + V i Sα Sα Sβ Sβ . (4) Q = V i V i Sα Sβ − Sβ Sα From Equation (4) it is possible to obtain the required input AC currents function of the deﬁned powers. Thus, these currents will be determined in accordance with the following equation:

 PVSα+QVSβ  iSα = 2 2  VSα +VSβ  PV QV . (5)  Sβ− Sα  iSβ = 2 2 VSα +VSβ

To obtain a fast and robust controller, the sliding mode control [41–44] will be designed based on the state-space model presented in Equation (3) and Equation (5). Considering the input AC current references, isαref and isβref, proportional to the active (P) power and reactive (Q) power, respectively, sliding surfaces for the input current can be obtained, in Equations (6) and (7). d S (e , t) = (i i ) + k (i i ) (6) iα iSα Sαre f − Sα iα dt Sαre f − Sα Electronics 2019, 8, 1199 8 of 17

d S (e , t) = (i i ) + k (i i ) (7) iβ iSβ Sβre f − Sβ iβ dt Sβre f − Sβ

Where Kiα and Kiβ proportional gains are chosen in order to impose an appropriate switching frequency. Considering the sliding mode theory, the dynamics of the input current source rectiﬁer variables have a strong relative degree of 2 [42,43]. Considering the feedback tracking errors, in the previous expressions, as the state variables the control equations will be given by:

diSre f α Siα ei , t = iSre f α iS α + kiα S α − dt − (8) kiα VS α R f iS α VC = 0 L f − − f α

disre f β S e , t = i is + k iβ is β sre f β − β iβ dt − kiβ (9) Vs β R f is β VC = 0 L f − − f β In order to guarantee that sliding surfaces will be equal to zero, the following sliding mode stability conditions in Equations (10) and (11) must be veriﬁed:

• Siα(eis α , t)Siα(eis α , t) < 0, (10)

• Siβ eis β , t Siβ eis β , t < 0 . (11) For the selection of the most suitable vector, a current vector modulator associated with the previous control equations is used. In this integrated charger system, from the point of view of the output current source rectiﬁer, the motor drive will behave as a current source. In this sense and considering the several states of the current source rectiﬁer switches, in the αβ plane there are 16 vectors, 7 of them being distinct, as we can see from the space vector diagram presented in Figure4. To choose the current vector, two hysteretic comparators with the purpose to limit the switching frequency will be considered, to evaluate the output of the sliding surfaces, being 1 if they are positive or 0 if they are negative. Taking into consideration, for example, the situation in which the outputs of the two Electronicshysteretic 2019 comparators, 8, x FOR PEER are REVIEW both 1, then vector 1 should be selected. 9 of 18

iβ 2

3 1

0 iα

4 6

Figure 4. VectorsVectors available in the αβ plane.

There are some techniques [45] to devise the choice of eight vectors from the two comparators, There are some techniques [45] to devise the choice of eight vectors from the two comparators, but in this application, the choice of the vector should not be made taking only into consideration the but in this application, the choice of the vector should not be made taking only into consideration the sliding surfaces and sliding mode stability conditions, but also the maintenance of the currents in the sliding surfaces and sliding mode stability conditions, but also the maintenance of the currents in the motor windings as constant as possible. Thus, to ensure the condition of the constant motor winding motor windings as constant as possible. Thus, to ensure the condition of the constant motor winding currents, the capacitor voltages must also be considered. As an example, let us consider again the currents, the capacitor voltages must also be considered. As an example, let us consider again the situation in which the outputs of both hysteretic current comparators are 1, but the capacitor voltages V α are negative and V β are positive. In this situation, the vector near the second C f C f quadrant must be chosen. So, the vector nearest to the first quadrant (to ensure that the sling surfaces will move to zero) and to the second quadrant due to the capacitor voltages is vector 2. For the situation that the capacitor voltages V α and V β are negative then there is a conflict, since C f C f the quadrants under to be determined are the first one and the third one. The conflict is solved by choosing vector 0. On the other hand, the choice of this vector is also critical since it is the only vector that allows the transfer of the energy from the motor windings to the battery. Table 1 presents the conditions for the choice of the current vector considering the sliding surfaces and capacitor voltages.

Table 1. Choice of the current vector function of the sliding surfaces and capacitors voltages polarity.

Se(), t Se(), t VC α VC β isα is β Vector f f 0 0 4 - - 0 1 3 - - 1 0 5 - - 1 1 0 - - 0 0 4 - + 0 1 3 - + 1 0 0 - + 1 1 2 - + 0 0 5 + - 0 1 0 + - 1 0 6 + - 1 1 1 + - 0 0 0 + + 0 1 2 + + 1 0 6 + + 1 1 1 + +

Electronics 2019, 8, 1199 9 of 17 situation in which the outputs of both hysteretic current comparators are 1, but the capacitor voltages

VC f α are negative and VC f β are positive. In this situation, the vector near the second quadrant must be chosen. So, the vector nearest to the first quadrant (to ensure that the sling surfaces will move to zero) and to the second quadrant due to the capacitor voltages is vector 2. For the situation that the capacitor voltages VC f α and VC f β are negative then there is a conflict, since the quadrants under to be determined are the first one and the third one. The conflict is solved by choosing vector 0. On the other hand, the choice of this vector is also critical since it is the only vector that allows the transfer of the energy from the motor windings to the battery. Table1 presents the conditions for the choice of the current vector considering the sliding surfaces and capacitor voltages.

Table 1. Choice of the current vector function of the sliding surfaces and capacitors voltages polarity.

S(e ,t) V V S(eis α ,t) is β Vector Cf α Cf β 0 0 4 - - 0 1 3 - - 1 0 5 - - 1 1 0 - - 0 0 4 - + 0 1 3 - + 1 0 0 - + 1 1 2 - + 0 0 5 + - 0 1 0 + - 1 0 6 + - 1 1 1 + - 0 0 0 + + 0 1 2 + + 1 0 6 + + 1 1 1 + +

To control the charge of the EV batteries, there are normally two diﬀerent approaches, constant power and constant voltage [46,47]. In constant power the control is normally ensured by a current controller. Indeed, the current reference of this controller is given by the power reference. The second approach is used to regulate the voltage of the batteries. Due to that, a voltage controller must be used. However, this controller can be associated with the current controller (that also allows to limit the current of the system) in a simple cascade structure. In this way, in the inner loop there is the proposed current controller (sliding mode) and in the outer loop there is a voltage controller that gives the reference of the current controller. For the voltage controller, a PI compensator can be used.

To control the charge of the EV batteries, there are normally two different approaches, constant power and constant voltage [46,47]. In constant power the control is normally ensured by a current controller. Indeed, the current reference of this controller is given by the power reference. The second approach is used to regulate the voltage of the batteries. Due to that, a voltage controller must be used. However, this controller can be associated with the current controller (that also allows to limit the current of the system) in a simple cascade structure. In this way, in the inner loop there is the proposed current controller (sliding mode) and in the outer loop there is a voltage controller that gives the reference of the current controller. For the voltage controller, a PI compensator can be used.

4. Tests Results A detailed simulation using Simulink blocks and SimPower Systems blocks of the Matlab software, to model the proposed on-board integrated battery charger, was implemented. To test the proposed solution, the charger was connected to a grid, with 230/400 VRMS, through input filter inductors with 5 mH and capacitors with 15 μF. For the three-phase induction motor, with open windings, an equivalent leakage inductance of 10 mH was considered. These windings are used as DC inductors of the charger. For the load (batteries) a voltage source with a value of 400 V each was considered. Due to these values, the rectifier was to operate in Boost mode. The Electronics 2019, 8, 1199 10 of 17 switching frequency was not fixed since it was using a sliding mode controller. This frequency was the function of the hysteretic current comparators which used a width of 0.4 A. TheThe adoptedadopted controllercontroller waswas testedtested inin didifferentﬀerent conditions conditions allowingallowing steady-statesteady-state andand transienttransient analysis,analysis, under under di differenﬀerentt system system requirements. requirements. AA steady-state steady-state analysis analysis was was made, made, considering considering the the EV EV charging charging with with a reference a reference power power of 10 of kW 10 (ankW AC (an per AC phase per currentphase current of 14.5 Aof RMS). 14.5 A Results RMS). are Resu shownlts are in Figureshown5 ,in which Figure presents 5, which the three-phasepresents the chargerthree-phase input charger AC currents input whenAC currents the controller when the was cont testedroller in was steady-state. tested in steady-state. Based on this Based result, on itthis is possibleresult, it to is verifypossible that to the verify input that currents the input are cu sinusoidal,rrents are withsinusoidal, very low with distortion. very low distortion.

Figure 5. Results of the three-phase charger input currents. Figure 5. Results of the three-phase charger input currents. In Figure6, the results of the AC current and the grid voltage in phase 1 are presented. It can In Figure 6, the results of the AC current and the grid voltage in phase 1 are presented. It can be be seen in the figure waveforms that the current is in phase with the grid voltage of the same phase. seen in the figure waveforms that the current is in phase with the grid voltage of the same phase. This result confirms that the current source rectifier receives nearly only active power (near unity This result confirms that the current source rectifier receives nearly only active power (near unity power factor). This can also be confirmed through the obtained low total harmonic distortion (THD) of power factor). This can also be confirmed through the obtained low total harmonic distortion (THD) theElectronics current, 2019 which, 8, x FOR is PEER 3.5%. REVIEW This shows that with this topology and control system, it is possible11 of to 18 of the current, which is 3.5%. This shows that with this topology and control system, it is possible to obtain a low enough THD. obtain a low enough THD.

Figure 6. The grid voltage and current in phase 1. Figure 6. The grid voltage and current in phase 1. For the same conditions, in steady-state, Figures7 and8 present the current in motor winding A For the same conditions, in steady-state, Figures 7 and 8 present the current in motor winding A (iA) and the DC output current of the three-phase inverters (io1), respectively. The first figure shows that(iA) theand motor the DC windings output current will act asof athe DC three-phase inductor, being inverters the intermediate (io1), respectively. storage The system. first figure Regarding shows thethat other the motor current windings it is possible will act to verifyas a DC that inductor, it has a being similar the top intermediate shape, although storage it hassystem. discontinuity Regarding modes.the other Indeed, current only it is when possible the rectifierto verify is that in mode it has 7 a (all similar switches top shape, of the inverteralthough are it inhas the discontinuity OFF state) themodes. current Indeed, of the only motor when windings the rectifier will flow is in through mode 7 the (all DC switches side of of the the inverters. inverter are in the OFF state) the current of the motor windings will flow through the DC side of the inverters.

Figure 7. The motor winding current (iA).

Electronics 2019, 8, x FOR PEER REVIEW 11 of 18

Figure 6. The grid voltage and current in phase 1.

For the same conditions, in steady-state, Figures 7 and 8 present the current in motor winding A (iA) and the DC output current of the three-phase inverters (io1), respectively. The first figure shows that the motor windings will act as a DC inductor, being the intermediate storage system. Regarding the other current it is possible to verify that it has a similar top shape, although it has discontinuity modes. Indeed, only when the rectifier is in mode 7 (all switches of the inverter are in the OFF state) Electronics 2019, 8, 1199 11 of 17 the current of the motor windings will flow through the DC side of the inverters.

Electronics 2019, 8, x FOR PEER REVIEW 12 of 18

Figure 7. The motor winding current (iA). Figure 7. The motor winding current (iA).

Figure 8. The DC inverter output current (io1).

Figure 8. The DC inverter output current (io1). In order to test the performanceFigure 8. ofThe the DC EV inverter charge outputr controller, current tests(io1). in transient conditions were also Inperformed. order to test The the conditions performance for ofthe the tests EV were charger initially controller, set to tests 10 kW in transient (14.5 A RMS), conditions and weresuddenly also performed.(at 0.1In s)order changed The to conditions test to the 6 kWperformance for (8.7 the A tests RMS). of were the The initially EV resu chargelt set ofr to controller,the 10 kWthree-phase (14.5 tests A RMS), incharger transient and input suddenly conditions AC currents, (at 0.1were s) changedpresentedalso performed. to in 6 kWFigure The (8.7 9,conditions A shows RMS). that The for the resultthe controller tests of were the three-phasebased initially on setsliding charger to 10 mode kW input (14.5 control AC A RMS), currents, has a and fast presented suddenlydynamic inresponse.(at Figure 0.1 s)9 changed,In shows Figure thatto 10 6 thekW results controller (8.7 A of RMS). the based DC The onoutput resu slidinglt current of modethe ofthree-phase controlthe inverters has charger a fastare presented. dynamic input AC response. From currents, this Inwaveformpresented Figure 10 init the isFigure possible results 9, of showsto the conclude DC that output the that controller currentthis curre of basednt the is inverters proportional on sliding are presented.mode to the controlamplitude From has this ofa fastthe waveform inputdynamic AC it iscurrents.response. possible In to concludeFigure 10 thatthe results this current of the is DC proportional output current to the of amplitude the inverters of the are input presented. AC currents. From this waveform it is possible to conclude that this current is proportional to the amplitude of the input AC currents.

Figure 9. The three-phase charger input currents in transient conditions. Figure 9. The three-phase charger input currents in transient conditions.

Figure 9. The three-phase charger input currents in transient conditions.

Electronics 2019, 8, x FOR PEER REVIEW 13 of 18 Electronics 2019, 8, x FOR PEER REVIEW 13 of 18 Electronics 2019, 8, 1199 12 of 17

FigureFigure 10. 10. ResultsResults of ofthe the DC DC output output curre currentnt in in transient transient conditions conditions (io1 (i).o1 ). Figure 10. Results of the DC output current in transient conditions (io1). To verify the behavior of the EV charger in Buck operation mode, a steady-state analysis was done ToTo verify verify the the behavior behavior of ofthe the EV EV charger charger in inBuck Buck operation operation mode, mode, a steady-statea steady-state analysis analysis was was for the batteries with a value of 200 V each. It was considered again that the EV was charging with a donedone for for the the batteries batteries with with a valuea value of of200 200 V Veach. each. It wasIt was considered considered again again that that the the EV EV was was charging charging reference power of 10 kW. Figures 11 and 12 show the three-phase charger input AC currents and grid withwith a referencea reference power power of of10 10 kW. kW. Figures Figures 11 11 and and 12 12 show show the the three-phase three-phase charger charger input input AC AC currents currents voltage and AC current in phase 1. These results show a behavior similar to the one in Boost mode. It andand grid grid voltage voltage and and AC AC current current in inphase phase 1. 1.These These results results show show a behaviora behavior similar similar to tothe the one one in in is possible to conclude that the rectiﬁer can be operated in Boost or Buck mode without degradation of BoostBoost mode. mode. It Itis ispossible possible to toconclude conclude that that the the re ctifierrectifier can can be be operated operated in inBoost Boost or orBuck Buck mode mode their behavior. However, there is a slight increase in the distortion of the current to 4.1%, although still withoutwithout degradation degradation of oftheir their behavior. behavior. However, However, ther there ise isa slighta slight increase increase in inthe the distortion distortion of ofthe the tolerated as seen in the ﬁgures. currentcurrent to to4.1%, 4.1%, although although still still tolerated tolerated as asseen seen in inthe the figures. figures.

FigureFigure 11. 11. ResultsResults of of the the three-phase chargercharger input input currents currents with with the the rectiﬁer rectifier operating operating in Buck in Buck mode. Figure 11. Results of the three-phase charger input currents with the rectifier operating in Buck mode. mode.

Electronics 2019, 8, x FOR PEER REVIEW 14 of 18 Electronics 20192019,, 88,, 1199x FOR PEER REVIEW 1413 of of 1718

Figure 12. The grid voltage and current in phase 1 with the rectifier operating in Buck mode. FigureFigure 12. 12. The The grid grid voltage voltage and and current current in in phase phase 1 1 wi withth the the rectifier rectifier operating operating in in Buck Buck mode. mode. 5. Experimental Results 5.5. Experimental Experimental Results Results To support the theoretical assumptions and expectations, as well as the simulation studies, a low To support the theoretical assumptions and expectations, as well as the simulation studies, a powerTo prototype support the was theoretical used to perform assumptions additional and tests.expect Theations, charger as well was as connected the simulation to an ACstudies, power a low power prototype was used to perform additional tests. The charger was connected to an AC sourcelow power with prototype 200 Vmax and was 50 used Hz. to For perform the input addition filter, 5al mH tests. inductors The charger and capacitors was connected with 15 toµ Fan were AC power source with 200 Vmax and 50 Hz. For the input filter, 5 mH inductors and capacitors with 15 μF used.power The source battery with was200 V implementedmax and 50 Hz. using For the two input voltage filter, sources 5 mH withinductors a value and of capacitors 250 V each. with For 15 theμF were used. The battery was implemented using two voltage sources with a value of 250 V each. For hystereticwere used. current The battery comparators was implemented was used a widthusing oftwo 0.2 voltage A. An oscilloscopesources with TDS3014C a value of was 250 alsoV each. used For to the hysteretic current comparators was used a width of 0.2 A. An oscilloscope TDS3014C was also acquirethe hysteretic the waveform current signals.comparators was used a width of 0.2 A. An oscilloscope TDS3014C was also used to acquire the waveform signals. usedThe to acquire obtained the experimentalwaveform signals. results from the low power prototype of the charging process are The obtained experimental results from the low power prototype of the charging process are shownThe in obtained Figures 13experimental–16. For the results data presented from the inlow those power figures, prototype a reference of the powercharging of process 600 W was are shown in Figures 13–16. For the data presented in those figures, a reference power of 600 W was adopted,shown in which Figures gives 13–16. a current For the amplitude data presented of 2 A. From in those Figure figures, 13, it is possiblea reference to see power that the of three-phase600 W was adopted, which gives a current amplitude of 2 A. From Figure 13, it is possible to see that the chargeradopted, input which currents gives area current in accordance amplitude with of the 2 A. reference From Figure value and13, presentit is possible a shape to thatsee isthat nearly the three-phase charger input currents are in accordance with the reference value and present a shape sinusoidal.three-phase Thischarger can alsoinput be currents confirmed are throughin accordan the obtainedce with the low reference total harmonic value and distortion present (THD) a shape of that is nearly sinusoidal. This can also be confirmed through the obtained low total harmonic thethat current, is nearly which sinusoidal. is 3.9%. This The chargecan also at be unity confirmed power factor through can bethe confirmed obtained bylow Figure total 14harmonic, which distortion (THD) of the current, which is 3.9%. The charge at unity power factor can be confirmed by presentsdistortion the (THD) grid voltageof the current, and rectifier which AC is 3.9%. current The in charge phase 1.at Indeed,unity power it is possiblefactor can to be confirm confirmed that the by Figure 14, which presents the grid voltage and rectifier AC current in phase 1. Indeed, it is possible currentFigure 14, in phasewhich with presents the grid the voltage.grid voltage and rectifier AC current in phase 1. Indeed, it is possible toto confirm confirm that that the the current current in in phase phase with with the the grid grid voltage. voltage.

FigureFigure 13. 13.Result Result of of the the three-phase three-phas chargere charger input input currents currents (i (i,S1 i, iS2,and and i iS3).). Figure 13. Result of the three-phase charger input currents (iS1S1, iS2,S2, and iS3).

Electronics 2019, 8, x FOR PEER REVIEW 15 of 18

Electronics 2019, 8, 1199 14 of 17 Electronics 2019, 8, x FOR PEER REVIEW 15 of 18

Figure 14. Experimental result of the grid voltage (VS1) and current in phase 1 (iS1).

Figure 14. Experimental result of the grid voltage (VS1) and current in phase 1 (iS1). The current in the motor winding during this charging process can be seen in Figure 15. ThroughThe thiscurrent figure, in theit is motorpossible winding to confirm during that this the chargingwindings processwill act canas DC be inductorsseen in Figure since the15. currentThrough has this a figure,small ripple.it is possible The output to confirm DC current that the of windings the inverters will actcan asbe DC seen inductors in Figure since 16. theAs expected,current has this a currentsmall ripple. is similar The to output the results DC incurrent Figure of 8, theconfirming inverters that can only be whenseen in the Figure rectifier 16. is As in modeexpected, 7 (all this switches current ofis similarthe inverter to the inresults the OFF in Figure state) 8, the confirming storage energythat only in whenthat windingthe rectifier will is be in transferredmode 7 (all to switches the batteries. of the inverter in the OFF state) the storage energy in that winding will be Figure 14. Experimental result of the grid voltage (VS1) and current in phase 1 (iS1). transferred toFigure the batteries. 14. Experimental result of the grid voltage (VS1) and current in phase 1 (iS1).

The current in the motor winding during this charging process can be seen in Figure 15. Through this figure, it is possible to confirm that the windings will act as DC inductors since the current has a small ripple. The output DC current of the inverters can be seen in Figure 16. As expected, this current is similar to the results in Figure 8, confirming that only when the rectifier is in mode 7 (all switches of the inverter in the OFF state) the storage energy in that winding will be transferred to the batteries.

Figure 15. Result of the current in the winding of the motor (iA). Figure 15. Result of the current in the winding of the motor (iA). Figure 15. Result of the current in the winding of the motor (iA).

Figure 15. Result of the current in the winding of the motor (iA).

Figure 16. Result of the current ﬂowing to the batteries (io1). Figure 16. Result of the current flowing to the batteries (io1).

The current in the motorFigure winding16. Result during of the current this charging flowing processto the batteries can be (i seeno1). in Figure 15. Through this figure,Regarding it is possiblethe overall to confirmefficiency that of thethis windingscharger for will the act conditions as DC inductors of this test, since a value the current of 86% has was a smallobtained.Regarding ripple. To Thesee the the output overall percentage DC efficiency current of the of of thelosses this inverters charger associ can atedfor bethe with seen conditions this in Figure efficiency of 16this. As consideringtest, expected, a value thisofthe 86% currentseveral was ispartsobtained. similar of the toTo charger, the see results the the percentage in loss Figure breakdown8 ,of confirming the losses of the thatassoci charger onlyated whenis presentedwith the this rectifier efficiencyin Figure is in 17.considering mode From 7 (all this switchesthe figure several it of is thepossibleparts inverter of theto verifycharger, in the OFFthat the the state) loss majority breakdown the storage of the of energy lossesthe charger in are that associated is winding presented willwith in be theFigure transferred propulsion 17. From to system thethis batteries. figure (motor it is andpossible Regardinginverters). to verify theComparing that overall the majority ewithfficiency the of ofknownthe this losses chargerintegrated are associated for theEV conditionschargers, with the it of propulsionis this possible test, a systemto value see of(motorthat 86% it wasand obtained.inverters). ToComparing see the percentage with the known of the lossesintegrated associated EV chargers, with this it effiis ciencypossible considering to see that the it several parts of the charger,Figure the 16. lossResult breakdown of the current of theflowing charger to the is batteries presented (io1). in Figure 17. From this figure it is possible to verify that the majority of the losses are associated with the propulsion system (motorRegarding and inverters). the overall Comparing efficiency with of this the charger known for integrated the conditions EV chargers, of this ittest, is possiblea value of to 86% see thatwas itobtained. presents To similar see the values. percentage This of comparison the losses wasassoci madeated with considering this efficiency the chargers considering presented the several in the worksparts of [21 the,22 charger,,24,25,28 the,31 ],loss in wherebreakdown their eofffi theciency charger is 90%, is presented 87%, 89%, in 82–92%, Figure 17. 76%, From and this 83%. figure it is possible to verify that the majority of the losses are associated with the propulsion system (motor and inverters). Comparing with the known integrated EV chargers, it is possible to see that it

Electronics 2019, 8, x FOR PEER REVIEW 16 of 18

Electronics 2019, 8, 1199 15 of 17 presents similar values. This comparison was made considering the chargers presented in the works [21,22,24,25,28,31], in where their efficiency is 90%, 87%, 89%, 82–92%, 76%, and 83%.

Figure 17. BreakdownBreakdown of the charger under study. 6. Conclusions 6. Conclusions A new integrated propulsion motor drive and battery charger for EVs to be connected to a A new integrated propulsion motor drive and battery charger for EVs to be connected to a three-phase system are proposed in this work. The motor drive is based on a dual inverter that three-phase system are proposed in this work. The motor drive is based on a dual inverter that provides a multilevel operation with the use of classical two-level three-phase voltage source inverters. provides a multilevel operation with the use of classical two-level three-phase voltage source The proposed rectifier presents Buck-Boost characteristics and allows operation at unity power factor. inverters. The proposed rectifier presents Buck-Boost characteristics and allows operation at unity Another important advantage under the point of view of the design is that the proposed configuration power factor. Another important advantage under the point of view of the design is that the was developed in order to avoid having access to the motor terminals. This was achieved through the proposed configuration was developed in order to avoid having access to the motor terminals. This direct connections of the rectifier output terminals to each of the inverters. Besides that, the windings was achieved through the direct connections of the rectifier output terminals to each of the inverters. of the motor were also integrated into the rectifier topology since they will behave as DC inductors. Besides that, the windings of the motor were also integrated into the rectifier topology since they Associated with the proposed charger, a controller was presented to ensure high power factor of the will behave as DC inductors. Associated with the proposed charger, a controller was presented to rectifier. For this controller the instantaneous power theory was used and proposed a sliding mode ensure high power factor of the rectifier. For this controller the instantaneous power theory was controller for the three-phase charger input currents. The characteristics and behavior of the proposed used and proposed a sliding mode controller for the three-phase charger input currents. The charger and control system were verified through simulation and experimental tests. characteristics and behavior of the proposed charger and control system were verified through Authorsimulation Contributions: and experimentalV.F.P. conceived tests. the theory; V.F.P. and J.M. designed, implemented and performed the theoretical experiments; A.C. implemented and performed the experimental tests; V.F.P., J.M. and J.F.S.; analyzed theAuthor data Contributions: and wrote the paper. V.F.P. conceived the theory; V.F.P. and J.M. designed, implemented and performed the theoretical experiments; A.C. implemented and performed the experimental tests; V.F.P., J.M. and J.F.S.; Funding: This work was supported by national funds through FCT—Fundação para a Ciência e a Tecnologia, underanalyzed project the data UID /andCEC wrote/50021 the/2019 paper. ConflictsFunding: ofThis Interest: work wasThe supported authors declare by national no conflict funds of throug interest.h FCT – Fundação para a Ciência e a Tecnologia, under project UID/CEC/50021/2019

ReferencesConflicts of Interest: The authors declare no conflict of interest. 1. Vilchez, J.; Julea, A.; Peduzzi, E.; Pisoni, E.; Krause, J.; Siskos, P.; Thiel, C. Modelling the impacts of EU References countries’ electric car deployment plans on atmospheric emissions and concentrations. Eur. Transp. Res. Rev. 1. 2019Vilchez,, 11, J.; 1–17. Julea, [CrossRef A.; Peduzzi,] E.; Pisoni, E.; Krause, J.; Siskos, P.; Thiel, C. Modelling the impacts of EU 2. Rietmann,countries’ electric N.; Lieven, car deployment T. A Comparison plans ofon Policyatmospheric Measures emissions Promoting and Electricconcentrations. Vehicles Eur. in 20 Transp. Countries. Res. InRev.The 2019 Governance, 11, 1–17. of Smart Transportation Systems; Finger, M., Audouin, M., Eds.; The Urban Book Series; 2. Springer:Rietmann, Cham, N.; Lieven, Switzerland, T. A Comparison 2019. of Policy Measures Promoting Electric Vehicles in 20 Countries. In 3. InternationalThe Governance Energy of Smart Agency. TransportationGlobal EV Systems Outlook; 2019Finger,; International M., Audouin, Energy M., Agency:Eds.; The Paris, Urban France, Book 2019. Series; 4. Kolar,Springer: J.; Friedli,Cham, T.Switzerland, The Essence 2019. of Three-Phase PFC Rectifier Systems—Part I. IEEE Trans. Power Electron. 3. 2013International, 28, 176–198. Energy [CrossRef Agency.] Global EV Outlook 2019; International Energy Agency: Paris, France, 2019. 5.4. Qiu,Kolar, M.; J.; Wang,Friedli, P.; T. Bi, The H.; Essence Wang, Z.of ActiveThree-Phase Power PFC Decoupling Rectifier DesignSystems—Part of a Single-Phase I. IEEE Trans. AC-DC Power Converter. Electron. Electronics2013, 28, 176–198.2019, 8, 841. [CrossRef] 6.5. Huber,Qiu, M.; L.;Wang, Kumar, P.; Bi, M.; H.; Jovanović,M. Wang, Z. Active Performance Power Decoupling Comparison Design of of Three-Step a Single-Phase and AC-DC Six-Step Converter. PWM in Average-Current-ControlledElectronics 2019, 8, 841. Three-Phase Six-Switch Boost PFC Rectifier. IEEE Trans. Power Electron. 2016, 6. 31Huber,, 7264–7272. L.; Kumar, M.; Jovanović, M. The Essence of Three-Phase PFC Rectifier Systems—Part I. IEEE Trans. Power Electron. 2016, 31, 7264–7272.

Electronics 2019, 8, 1199 16 of 17

7. Pires, V.F.; Silva, J.F. Single-Stage Three-Phase Buck-Boost Type AC-DC Converter with High Power Factor. IEEE Trans. Power Electron. 2001, 16, 784–793. [CrossRef] 8. Gangavarapu, S.; Rathore, A. Three-Phase Buck-Boost Derived PFC Converter for More Electric Aircrafts. IEEE Trans. Power Electron. 2019, 34, 6264–6275. [CrossRef] 9. Hafezinasab, H.; Eberle, W.; Gautam, D.; Botting, C. Universal Input AC Three-Phase Power Factor Correction with Adaptive Intermediate Bus Voltage to Optimize Efficiency. IEEE Trans. Ind. Appl. 2019, 55, 1698–1707. [CrossRef] 10. Pires, V.F.; Silva, J.F. Three-Phase Single-Stage Four-Switch PFC Buck-Boost Type Rectifier. IEEE Trans. Ind. Electron. 2005, 52, 444–453. [CrossRef] 11. Xu, J.; Zhu, M.; Yao, S. Distortion Elimination for Buck PFC Converter with Power Factor Improvement. J. Power Electron. 2015, 15, 10–17. [CrossRef] 12. Ohnuma, Y.; Itoh, J.I. A Novel Single-Phase Buck PFC AC-DC Converter with Power Decoupling Capability Using an Active Buffer. IEEE Trans. Ind. Appl. 2014, 50, 1905–1914. [CrossRef] 13. Pires, V.F.; Silva, J.F. Single-Stage Double-Buck Topologies with High Power Factor. J. Power Electron. 2011, 11, 655–661. [CrossRef] 14. Yilmazand, M.; Krein, P.T. Review of battery charger topologies, charging power levels, and infrastructure for plug-in electric and hybrid vehicles. IEEE Trans. Power Electron. 2013, 28, 2151–2169. [CrossRef] 15. Kim, D.H.; Kim, M.S.; Hussain Nengroo, S.; Kim, C.H.; Kim, H.J. LLC Resonant Converter for LEV (Light Electric Vehicle) Fast Chargers. Electronics 2019, 8, 362. [CrossRef] 16. Lee, J.-H.; Moon, J.-S.; Lee, Y.-S.; Kim, Y.-R.; Won, C.-Y. Fast charging technique for EV battery charger using three-phase AC-DC boost converter. In Proceedings of the IECON 2011-37th Annual Conference of the IEEE Industrial Electronics Society, Melbourne, VIC, Australia, 7–10 November 2011; pp. 4577–4582. 17. Hartmann, M.; Friedli, T.; Kolar, J.W. Three-phase unity power factor mains interfaces of high power EV battery charging systems. In Proceedings of the Power Electronics for Charging Electric Vehicles ECPE Workshop, Valencia, Spain, 21–22 March 2011; pp. 1–66. 18. Khaligh, A.; Dusmez, S. Comprehensive topological analysis of conductive and inductive charging solutions for plug-in electric vehicles. IEEE Trans. Veh. Technol. 2012, 61, 3475–3489. [CrossRef] 19. Dusmez, S.; Cook, A.; Khaligh, A. Comprehensive analysis of high quality power converters for level 3 off-board chargers. In Proceedings of the 2011 IEEE Vehicle Power and Propulsion Conference, Chicago, IL, USA, 6–9 September 2011; pp. 1–10. 20. Williamson, S.S.; Rathore, A.K.; Musavi, F. Industrial Electronics for Electric Transportation: Current State-of-the-Art and Future Challenges. IEEE Trans. Ind. Electron. 2015, 62, 3021–3032. [CrossRef] 21. Lacressonniere, F.; Cassoret, B. Converter used as a battery charger and a motor speed controller in an industrial truck. In Proceedings of the 2005 European Conference on Power Electronics and Applications, Dresden, Germany, 11–14 September 2005; pp. 1–7. 22. Pellegrino, G.; Armando, E.; Guglielmi, P. An integral battery charger with power factor correction for electric scooter. IEEE Trans. Power Electron. 2010, 25, 751–759. [CrossRef] 23. Bolte, S.; Speerschneider, A.; Fröhleke, N.; Böcker, J. A comparison of on-board chargers for electric vehicles with variable DC-link voltage. In Proceedings of the 2015 IEEE International Conference on Smart Energy Grid Engineering, Oshawa, ON, Canada, 17–19 August 2015; pp. 1–5. 24. Haghbin, S.; Lundmark, S.; Alakula, M.; Carlson, O. An isolated high-power integrated charger in electrified vehicle applications. IEEE Trans. Veh. Technol. 2011, 60, 4115–4126. [CrossRef] 25. Shi, C.; Tang, Y.; Khaligh, A. A Three-Phase Integrated Onboard Charger for Plug-In Electric Vehicles. IEEE Trans. Power Electron. 2018, 33, 4716–4725. [CrossRef] 26. Subotic, I.; Bodo, N.; Levi, E.; Dumnic, B.; Milicevic, D.; Katic, V. Overview of fast on-board integrated battery chargers for electric vehicles based on multiphase machines and power electronics. IET Electr. Power Appl. 2016, 10, 217–229. [CrossRef] 27. Subotic, I.; Bodo, N.; Levi, E. An EV Drive-Train with Integrated Fast Charging Capability. IEEE Trans. Power Electron. 2016, 31, 1461–1471. [CrossRef] 28. Diab, M.; Elserougi, A.; Abdel-Khalik, A.; Massoud, A.; Ahmed, S. A Nine-Switch-Converter-Based Integrated Motor Drive and Battery Charger System for EVs Using Symmetrical Six-Phase Machines. IEEE Trans. Ind. Electron. 2016, 63, 5326–5335. [CrossRef] Electronics 2019, 8, 1199 17 of 17

29. Subotic, I.; Bodo, N.; Levi, E.; Jones, M.; Levi, V. Integration of Six-Phase EV Drivetrains into Battery Charging Process with Direct Grid Connection. IEEE Trans. Energy Convers. 2017, 32, 1012–1022. [CrossRef] 30. Chinmaya, K.; Singh, G. Integrated onboard single-stage battery charger for PEVs incorporating asymmetrical six-phase induction machine. IET Electr. Syst. Transp. 2019, 9, 8–15. [CrossRef] 31. Bodo, N.; Levi, E.; Subotic, I.; Espina, J.; Empringham, L.; Johnson, C.M. Eﬃciency Evaluation of Fully Integrated On-Board EV Battery Chargers with Nine-Phase Machines. IEEE Trans. Energy Convers. 2017, 32, 257–266. [CrossRef] 32. Shi, R.; Semsar, S.; Lehn, P. Constant Current Fast Charging of Electric Vehicles via a DC Grid Using a Dual-Inverter Drive. IEEE Trans. Ind. Electron. 2017, 64, 6940–6949. [CrossRef] 33. Singh, B.; Singh, B.N.; Chandra, A.; Al-Haddad, K.; Pandey, A.; Kothari, D.P. A review of three-phase improved power quality AC-DC converters. IEEE Trans. Ind. Electron. 2004, 51, 641–660. [CrossRef] 34. Fasugba, M.A.; Krein, P.T. Gaining vehicle-to-grid beneﬁts with unidirectional electric and plug-in hybrid vehicle chargers. In Proceedings of the 2011 IEEE Vehicle Power and Propulsion Conference, Chicago, IL, USA, 6–9 September 2011; pp. 1–6. 35. Tan, A.S.; Ishak, D.; Mohd-Mokhtar, R.; Lee, S.; Idris, R.N. Predictive control of plug-in electric vehicle chargers with photovoltaic integration. J. Mod. Power Syst. Clean Energy 2018, 6, 1264–1276. [CrossRef] 36. Pedrosa, D.; Gomes, R.; Monteiro, V.; Fernandes, J.C.A.; Monteiro, J.; Afonso, J.L. Model Predictive Control of an On-Board Fast Battery Charger for Electric Mobility Applications. In CONTROLO 2016. Lecture Notes in Electrical Engineering; Garrido, P., Soares, F., Moreira, A., Eds.; Springer: Cham, Switzerland, 2017; Volume 402. 37. Kisacikoglu, M.C.; Kesler, M.; Tolbert, L.M. Single-phase on-board bidirectional PEV charger for V2G reactive power operation. IEEE Trans. Smart Grid 2015, 6, 767–775. [CrossRef] 38. Dusmez, S.; Khaligh, A. A charge-nonlinear-carrier-controlled reduced-part single-stage integrated power electronics interface for automotive applications. IEEE Trans. Veh. Technol. 2014, 63, 1091–1103. [CrossRef] 39. Al-Ogaili, A.; Aris, I.; Verayiah, R.; Ramasamy, A.; Marsadek, M.; Rahmat, N.; Hoon, Y.; Aljanad, A.; Al-Masri, A. A Three-Level Universal Electric Vehicle Charger Based on Voltage-Oriented Control and Pulse-Width Modulation. Energies 2019, 12, 2375. [CrossRef] 40. Haghbin, S.; Khan, K.; Zhao, S.; Alaküla, M.; Lundmark, S.; Carlson, O. An integrated 20 kw motor drive and isolated battery charger for plug-in vehicles. IEEE Trans. Power Electron. 2013, 28, 4013–4029. [CrossRef] 41. Akagi, H.; Kanazawa, Y.; Nabae, A. Instantaneous Reactive Power Compensator Comprising Switching Devices Without Energy Storage Components. IEEE Trans. Ind. Appl. 1984, 20, 625–630. [CrossRef] 42. Gao, W.; Hung, J. Variable structure control of nonlinear systems: A new approach. IEEE Trans. Ind. Electron. 1993, 40, 45–55. 43. Silva, F.; Pinto, S. Linear and Nonlinear Control of Switching Power Converters. In Power Electronics Handbook; Rashid, M.H., Ed.; Elsevier Inc.: London, UK, 2018; pp. 1141–1220. 44. Gao, W.; Hung, J. Variable structure control: A survey. IEEE Trans. Ind. Electron. 1993, 40, 2–22. 45. Martins, J.F.A.; Pires, A.J.; Silva, J.F. A novel and simple current controller for three-phase PWM power inverters. IEEE Trans. Ind. Electron. 1998, 45, 802–805. [CrossRef] 46. Inthamoussou, F.A.; Pegueroles-Queralt, J.; Bianchi, F.D. Control of a Supercapacitor Energy Storage System for Microgrid Applications. IEEE Trans. Energy Convers. 2013, 28, 690–697. [CrossRef] 47. Pires, V.; Foito, D.; Cordeiro, A. A DC–DC Converter with Quadratic Gain and Bidirectional Capability for Batteries/Supercapacitors. IEEE Trans. Ind. Appl. 2018, 54, 274–285. [CrossRef]

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