Autonomous Battery Swapping System and Methodologies of Electric Vehicles

energies

Review Autonomous Battery Swapping System and Methodologies of Electric Vehicles

Feyijimi Adegbohun *, Annette von Jouanne and Kwang Y. Lee Department of Electrical and Computer Engineering, Baylor University, Waco, TX 76798, USA; [email protected] (A.v.J.); [email protected] (K.Y.L.) * Correspondence: [email protected]; Tel.: +1-304-809-4122

Received: 18 January 2019; Accepted: 12 February 2019; Published: 19 February 2019

Abstract: The transportation industry contributes a significant amount of carbon emissions and pollutants to the environment globally. The adoption of electric vehicles (EVs) has a significant potential to not only reduce carbon emissions, but also to provide needed energy storage to contribute to the adoption of distributed renewable generation. This paper focuses on a design model and methodology for increasing EV adoption through automated swapping of battery packs at battery sharing stations (BShS) as a part of a battery sharing network (BShN), which would become integral to the smart grid. Current battery swapping methodologies are reviewed and a new practical approach is proposed considering both the technical and socio-economic impacts. The proposed BShS/BShN provides novel solutions to some of the most preeminent challenges that EV adoption faces today such as range anxiety, grid reliability, and cost. Challenges and advancements specific to this solution are also discussed.

Keywords: battery swapping station (BSS); battery sharing station (BShS); battery sharing network (BShN); battery energy storage system (BESS); battery energy control module (BECM) electric vehicle (EV); zero emission vehicle (ZEV); direct current fast charging (DCFC); universal battery pack (UBP); state of health (SOH); state of charge (SOC)

1. Introduction Electric vehicles (EVs) have been deemed as being the future of mobility both by auto industry experts as well as major original equipment manufacturers (OEMs) globally. General Motors (GM) announced that it will release more than twenty new models by 2023; Daimler AG (Mercedes Benz parent company) announced that all of the models available will be electrified by 2022; Ford Motor Co. announced 40 electrified models by 2022; several other automakers have committed to an all-electric future [1]. In addition to the original equipment manufacturers’ (OEMs’) commitments to an all-electric future, government agencies across the world have also set various zero emission mandates. The California Air Resource Board (CARB), Zero Emission Vehicle (ZEV) regulation has a mandate to reduce emissions level by 40% in 2030 in comparison to the level in 1990, and 80% by 2050 through regulations and ZEV credits for automakers that produce a significant number of electrified vehicles. China’s New Energy Vehicle (NEV) mandate is similar in implementation to CARB’s policies, requiring 2.5% of vehicles sold to be ZEVs by 2018 and 8% by 2025. Norway and the Netherlands have also committed to 100% EVs by 2025 and 2030, respectively. According to [1], the EV market share is expected to grow from roughly 1% today to about 30% in Europe and around 15% in the U.S. by 2025, totaling 130 million by 2030 globally. This exponential increase in EV adoption within a short period of time poses significant technical challenges; specifically, grid reliability issues as the current state/capacity of generation and power distribution grid is not designed to support the load profile of this number of EVs [2–4]. Another

Energies 2019, 12, 667; doi:10.3390/en12040667 www.mdpi.com/journal/energies Energies 2019, 12, 667 2 of 14 concept that poses a significant technical challenge and could also critically affect the reliability and stability of the power grid is fast DC charging of EVs. Fast charging of EVs at 50 kW and up can lead to unsustainable load spikes on the distribution grid, especially at the peak-load periods. Therefore, fast charging will require that local energy storage/generation be present at the charging stations to meet these demands, mitigate the negative impact on the grid, and reduce operational costs during the peak-load of the grid [5]. Studies have also shown that the degradation of existing Li-ion battery cells at DC fast charging (DCFC) is much faster than slower AC charging of less than 10 kW [6]. For EVs to be adopted at scale, the charging infrastructure and integration with the power grid must also evolve rapidly. It is therefore imperative that these technical issues be studied and that new methods of replenishing the energy in EVs and extending the range of EVs be developed. Today, an EV of 110 km range requires 2–3 h to charge the battery from 0% to 100% state of charge (SOC) using AC charging, or 30 min to 1 h for DCFC. While fast charging shows a great deal of promise, it still poses critical technical challenges and current technologies do not offer the convenience that traditional vehicles offer in terms of replenishment of energy within 5–10 min. An optimized battery swapping station (BSS) has been presented in [7]; however, this method is based on the assumption that consumers are willing to lease their battery as opposed to owning the battery. Several automakers and start-ups including Tesla Motors [8] and Better Place [9] have introduced a BSS similar to this model; however, consumer acceptance of not owning the battery and their original battery being tampered with during a swap has plagued the success of this model. This paper proposes a battery sharing station (BShS) and a battery sharing network (BShN) as a novel solution to mitigate the impact of the EVs’ scale and improve the reliability/stability of the grid. The BShS proposed in this paper is based on some of the concepts and methods that Tesla and Better Place have implemented in their BSS, but it is focused on solving the issues of consumer acceptance, standardization of battery architecture and mitigation of grid impact by EV battery charging. The BShN topology proposed is comprised of several subsystems and components such as the connected battery energy storage system (BESS) or battery, connected battery charger, renewable energy source (RES), power electronic converters, control systems, power distribution grid, and the participating EVs. The term connected in this case, refers to the internet of things (IoT) as well as grid coupling, enabling the BESS and BShN to interact and become an aggregator providing different services to the smart grid as a whole [10]. The structural design of the BSS model is detailed in the patent in [11], and the architecture of battery placement in the vehicle is also detailed in [11]. A RES integrated with the BSS is reviewed in [12], and the interaction and power exchange between different components of the BShN and the power grid is also detailed in [12]. An optimal configuration of a BSS in terms of the number of chargers and battery packs is discussed in [13]. Converters and charger topologies for enabling grid-to-vehicle (G2V) and vehicle-to-grid (V2G) power exchanges are discussed in detail in [14]. This paper serves as a survey paper highlighting the current state-of-the-art battery swapping technologies and implementations available today. In addition, this paper presents a newly revamped model of battery swapping methodologies that resolves some of the issues that current battery swapping technologies face, highlighting technical challenges that face this newly proposed model and technological advancements in the near future. Section Section2 presents current battery swapping technologies, using the Tesla BSS as a main point of reference. The mechanical design of the swapping station system and vehicle architecture is described. Following this, the electrical design of the vehicle system, BESS, BSS, and charging system are described in detail. Section3 introduces a novel BShS and BShN model. The mechanical, electrical, and economic advantages over the current state-of-the-art battery swapping technology are also highlighted. Finally, the research opportunities and technical hurdles related to this novel model are presented, highlighting the important differences, the benefits, and the technological advancements needed to commercialize this proposed model. Table1 is a list of acronyms and abbreviations with definitions of technical terminology used in this paper. Energies 2019, 12, 667 3 of 14

Energies 2019, 12, x 3 of 14 Table 1. Acronyms and abbreviations. Table 1. Acronyms and abbreviations. Acronym/Abbreviation Description Acronym/Abbreviation Description BSSBSS Battery Battery Swapping Swapping Station Station BShSBShS Battery Battery Sharing Sharing Station Station BShNBShN Battery Battery Sharing Sharing Network Network BESSBESS Battery Battery Energy Energy Storage Storage System System BECMBECM Battery Battery Energy Energy Control Control Module Module EVEV Electric Electric Vehicle Vehicle UCUC Ultracapacitor Ultracapacitor DCFCDCFC Direct Direct Current Current Fast Fast Charging Charging ZEVZEV Zero Zero Emission Emission Vehicle Vehicle SOHSOH State State of of Health Health (Battery (Battery Life Life Cycle) Cycle) SOCSOC State State of of Charge Charge (Battery (Battery Capacity) Capacity) CARBCARB California California Air Air Resource Resource Board Board NEVNEV New New Energy Energy Vehicle Vehicle RESRES Renewable Renewable Energy Energy Source Source G2VG2V Grid-to-Vehicle Grid-to-Vehicle V2GV2G Vehicle-to-Grid Vehicle-to-Grid UBPUBP Universal Universal Battery Battery Pack Pack IoTIoT Internet Internet of ofThings Things C-rateC-rate Charge Charge and and Discharge Discharge Rate Rate

2. Overview2. Overview of Current of Current Battery Battery Swapping Swapping StationStation Technology In thisIn section,this section, a general a general overview overview of of the the mainmain components components of of a BSS a BSS is illustrated, is illustrated, with with the Tesla the Tesla BSS as a case study. The BSS consists of mechanical and structural components as well as electrical BSS as a case study. The BSS consists of mechanical and structural components as well as electrical components. Figure 1 is a conceptual description of the BSS. components. Figure1 is a conceptual description of the BSS.

Figure 1. Conceptual design of a battery swapping station (BSS). Figure 1. Conceptual design of a battery swapping station (BSS). 2.1. Structural Design of a BSS The2.1. Structural Tesla BSS Design shown of in a FigureBSS 2 includes a vehicle platform, a vehicle lift, battery lifts, vehicle alignment The Tesla BSS shown in Figure 2 includes a vehicle platform, a vehicle lift, battery lifts, vehicle equipmentEnergies 2019, rollers, 12, x electrical connection alignments, battery conveyor shuttles, and battery storage racks4 of and 14 rails.alignment Figure2 shows equipment an EV rollers, that has electrical arrived connection at a BSS and alignments, is ready tobattery be engaged conveyor in shuttles, a swap. and battery storage racks and rails. Figure 2 shows an EV that has arrived at a BSS and is ready to be engaged in a swap.

Figure 2. Diagram of an electric vehicle (EV) at a BSS ready to engage in a battery swap [15]. Figure 2. Diagram of an electric vehicle (EV) at a BSS ready to engage in a battery swap [15].

2.2. Mechanical Operation of BSS A compatible EV with a battery architecture designed for the BSS is needed in order to participate in battery swapping. In addition, prior to arriving at the BSS, the EV must schedule the battery swap ahead of time to confirm that a battery pack will be available for swap. When the EV arrives at the BSS, it climbs up a slight ramp as shown in Figure 2 and this constitutes the beginning of the swap. Figure 3 is the flow of operation of the battery swap [15]. The vehicle is positioned correctly in the X direction and the vehicle power is turned off for safety. Next, the vehicle is raised with the vehicle lift as shown in Figure 4, where the lift boards, in this case, engage the jack pads on the vehicle to provide support. Once the vehicle is lifted, horizontal doors underneath the vehicle are opened to allow access to the battery that sits underneath the vehicle. Next, the battery lift is raised until it touches the underside of the battery pack in order to support it for removal. Once the lift is correctly placed underneath the battery securely, the fastener removal can begin. Next, a battery conveyor shuttle is brought underneath the battery lift as shown in Figure 5. The used battery, now on the battery lift, is lowered onto the battery conveyor shuttle; the used/depleted battery is replaced by a fresh one from the battery rack shown in Figure 6. The fresh battery is then raised up underneath the vehicle. The battery is again positioned and secured by the battery lifts, the fasteners are engaged and doors closed. Now, the vehicle is ready to be lowered and powered back on to get back on the road with a fully replenished battery pack.

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Energies 2019, 12, 667 4 of 14 Figure 2. Diagram of an electric vehicle (EV) at a BSS ready to engage in a battery swap [15].

2.2.2.2. MechanicalMechanical Operation Operation of of BSS BSS AA compatible compatible EV EV with with a battery a battery architecture architecture designed designed for the BSSfor the is needed BSS is in needed order to in participate order to inparticipate battery swapping. in battery In swapping. addition, priorIn addition, to arriving prior at to the arriving BSS, the at EV the must BSS, schedule the EV must the battery schedule swap the aheadbattery of swap time toahead conﬁrm of time that to a confirm battery packthat a will battery be available pack will for be swap. available When for the swap. EV arrivesWhen the at the EV BSS,arrives it climbs at the upBSS, a slightit climbs ramp up asa slight shown ramp in Figure as shown2 and in this Figure constitutes 2 and this the constitutes beginning the of thebeginning swap. Figureof the3 swap. is the Figure ﬂow of 3 operation is the flow of of the operation battery swapof the [ 15battery]. swap [15]. TheThe vehicle vehicle is is positioned positioned correctly correctly in thein the X direction X direction and theand vehicle the vehicle power power is turned is turned off for safety.off for Next,safety. the Next, vehicle the vehicle is raised is withraised the with vehicle the vehicle lift as shownlift as shown in Figure in Figure4, where 4, where the lift the boards, lift boards, in this in case,this case, engage engage the jack the jack pads pads onthe on the vehicle vehicle to provideto provide support. support. Once Once the the vehicle vehicle is is lifted, lifted, horizontal horizontal doorsdoors underneathunderneath thethe vehiclevehicle areare openedopened toto allowallow accessaccess toto thethe batterybattery thatthat sitssits underneathunderneath thethe vehicle.vehicle. Next,Next, thethe batterybattery liftlift isis raisedraised untiluntil itit touchestouches thethe undersideunderside ofof thethe batterybattery packpack inin orderorder to to supportsupport it it for for removal. removal. OnceOnce thethe liftlift isis correctly correctly placed placed underneathunderneath thethe batterybattery securely,securely, the the fastener fastener removalremoval can can begin. begin. Next, Next, a a battery battery conveyor conveyor shuttle shuttle is is brought brought underneath underneath the the battery battery lift lift as as shown shown inin Figure Figure5 .5. The The used used battery, battery, now now on on the the battery battery lift, lift, is is lowered lowered onto onto the the battery battery conveyor conveyor shuttle; shuttle; thethe used/depleted used/depleted battery battery is is replaced replaced by by a fresh a fresh one on frome from the batterythe battery rack rack shown shown in Figure in Figure6. The fresh6. The batteryfresh battery is then is raised then upraised underneath up underneath the vehicle. the ve Thehicle. battery The battery is again is positioned again positioned and secured and secured by the batteryby the lifts,battery the fastenerslifts, the arefasteners engaged are and engaged doors an closed.d doors Now, closed. the vehicle Now, isthe ready vehicle to be is lowered ready to and be poweredlowered backand powered on to get back on to the get road back with on ath fullye road replenished with a fully battery replenished pack. battery pack.

Figure 3. Battery swapping procedure ﬂow chart [15].

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Energies 2019, 12, x 5 of 14 Figure 3. Battery swapping procedure flow chart [15]. Figure 3. Battery swapping procedure flow chart [15]. Energies 2019, 12, x 5 of 14

Energies 2019, 12, 667 5 of 14 Figure 3. Battery swapping procedure flow chart [15].

Figure 4. EV raised with the vehicle lift in preparation for a swap [15]. Figure 4. EV raised with the vehicle lift in preparation for a swap [15].

FigureFigure 4.4. EVEV raisedraised withwith thethe vehiclevehicle liftlift inin preparationpreparation forfor aa swapswap [[15].15].

Figure 5. Battery lift lowering the depleted battery from the EV [15]. Figure 5. Battery lift lowering the depleted battery from the EV [15]. Figure 5. Battery lift lowering the depleted battery from the EV [15].

Figure 5. Battery lift lowering the depleted battery from the EV [15].

Figure 6. Fully charged battery packs on a rack ready for battery swaps [15]. Figure 6. Fully charged battery packs on a rack ready for battery swaps [15]. 2.3. Electrical DesignFigure of6. BSSFully charged battery packs on a rack ready for battery swaps [15]. 2.3. Electrical Design of BSS In today’s implementation, the BSS is heavily dependent on the distribution grid and represents 2.3. Electrical Design of BSS new high power consumption loads for the distribution system operators. The electrical components Figure 6. Fully charged battery packs on a rack ready for battery swaps [15]. of the BSS are mainly composed of a distribution transformer, AC/DC chargers, battery packs, and a battery energy control module (BECM). Figure7 is a block diagram of the electrical relationship 2.3. Electrical Design of BSS between the components of the BSS.

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Energies 2019, 12, x 6 of 14 In today's implementation, the BSS is heavily dependent on the distribution grid and represents new high power consumption loads for the distribution system operators. The electrical components In today's implementation, the BSS is heavily dependent on the distribution grid and represents of the BSS are mainly composed of a distribution transformer, AC/DC chargers, battery packs, and a new high power consumption loads for the distribution system operators. The electrical components battery energy control module (BECM). Figure 7 is a block diagram of the electrical relationship of the BSS are mainly composed of a distribution transformer, AC/DC chargers, battery packs, and a between the components of the BSS. Energiesbattery2019 energy, 12, 667 control module (BECM). Figure 7 is a block diagram of the electrical relationship6 of 14 between the components of the BSS. Battery Packs Distribution AC Transformer grid Battery Packs Distribution AC Transformer grid Bidirectional AC/DC Charger Bidirectional AC/DC Charger

Figure 7. Block diagram of BSS electrical design. Figure 7. Block diagram of BSS electrical design. Figure 7. Block diagram of BSS electrical design. The distribution grid provides the AC power at the distribution voltage level, and because of The distribution grid provides the AC power at the distribution voltage level, and because of the high power demand of the BSS, this voltage level will be between 33 kV and 11 kV. Charging the highThe powerdistribution demand grid of provides the BSS, the this AC voltage power level at the will distribution be between voltage 33 kV level, and 11 and kV. because Charging of power levels for EV battery packs range from Level 1 charging at 120 V/15 A single-phase; Level 2 powerthe high levels power for demand EV battery of the packs BSS, range this fromvoltage Level level 1 chargingwill be between at 120 V/15 33 kV A and single-phase; 11 kV. Charging Level 2 Charging at 240 V (up to 80 A, 19.2 kW); and Level 3 Charging at 50 kW and up [15]. Depending on Chargingpower levels at 240 for VEV (up battery to 80 A,packs 19.2 range kW); andfrom Level Level 3 1 Charging charging at at 50 120 kW V/15 and A up single-phase; [15]. Depending Level on 2 the size of the BSS and the voltage level available at the distribution grid, different charging modes theCharging size of at the 240 BSS V and(up theto 80 voltage A, 19.2 level kW); available and Level at the 3 Charging distribution at 50 grid, kW different and up charging[15]. Depending modes canon can be implemented. bethe implemented. size of the BSS and the voltage level available at the distribution grid, different charging modes Charging profiles determine the rating of the AC/DC charger. In our case study, a unidirectional can beCharging implemented. proﬁles determine the rating of the AC/DC charger. In our case study, a unidirectional AC/DC charger is implemented which is connected to the AC transformer and converts the AC power AC/DCCharging charger profiles is implemented determine the which rating is connectedof the AC/D toC thecharger. AC transformerIn our case study, and converts a unidirectional the AC to DC power to charge the batteries directly. Figure 8 is a single switch unidirectional boost converter powerAC/DC to charger DC power is implemented to charge the which batteries is connected directly. toFigure the AC8 transformeris a single switch and converts unidirectional the AC power boost with passive filtering for the BSS AC/DC charger topology. The number of unidirectional buck converterto DC power with to passivecharge the ﬁltering batteries for thedirectly. BSS AC/DC Figure 8 chargeris a single topology. switch unidirectional The number of boost unidirectional converter converters, control strategies, and component selections are discussed in detail in [16]. buckwith converters,passive filtering control for strategies, the BSS andAC/DC component charger selections topology. are The discussed number in of detail unidirectional in [16]. buck converters, control strategies, and component selections are discussed in detail in [16].

La1 La2  Idc La1 La2   Ia Va Lb1 Lb2 Idc  a Ia d Va Lb1 Lb2 b C Load  a Vdc Ib c Vb Lc1 Lc2 b Cd Load  Vdc Ib c Vb Lc1 Lc2  Ic Vc  Ic Vc

Ca Cb Cc

Ca Cb Cc Figure 8. Unidirectional boost converter charger for BSS. (Adapted from [16]). Figure 8. Unidirectional boost converter charger for BSS. (Adapted from [16]). 2.4. Battery Energy Management and Thermal Design of BSS Figure 8. Unidirectional boost converter charger for BSS. (Adapted from [16]). 2.4. Battery Energy Management and Thermal Design of BSS Battery temperature is a primary factor in regards to performance and life cycle of an EV battery2.4.Battery Battery [17 ].temperatureEnergy Li-ion Management batteries is a primary should and Thermal factor ideally in Design operateregards of BSS to between performance 25 ◦C and life 40 ◦cycleC for of optimal an EV battery life and [17]. Li-ion batteries should ideally operate between 25 °C and 40 °C for optimal life and performance. performance.Battery temperature Using air as is a a heat primary transfer factor medium in regards is a cheapto performance and simple and method life cycle for of battery an EV cooling;battery Using air as a heat transfer medium is a cheap and simple method for battery cooling; however, it is however,[17]. Li-ion it batteries is very inefficient should ideally in comparison operate between to liquid cooling.25 °C and Some 40 °C of for the optimal limiting life factors and performance. of air cooling very inefficient in comparison to liquid cooling. Some of the limiting factors of air cooling in EVs are inUsing EVs air are as limited a heat transfer flow rate medium of cooling is a air,cheap noise, and inhomogeneous simple method for temperature battery cooling; distribution however, within it is limited flow rate of cooling air, noise, inhomogeneous temperature distribution within batteries, batteries,very inefficient dependence in comparison on vehicle to liquid cabin cooling. air temperature, Some of the and limiting safety concerns factors of due air cooling to the emission in EVs are of dependence on vehicle cabin air temperature, and safety concerns due to the emission of toxic gases toxiclimited gases flow from rate the of batterycooling packs air, noise, [17]. inhomogeneous temperature distribution within batteries, from the battery packs [17]. dependenceLiquid thermalon vehicle management cabin air temperature, is a much more and efficient safety concerns method of due cooling to the Li-ion emission batteries; of toxic however, gases Liquid thermal management is a much more efficient method of cooling Li-ion batteries; itfrom is more the battery costly andpacks complex [17]. to implement. In liquid cooling, a cooling plate can be placed on the however, it is more costly and complex to implement. In liquid cooling, a cooling plate can be placed surfaceLiquid of the thermal battery management and a liquid coolingis a much or heating more ef refrigerantficient method can be of passed cooling through Li-ion tubes batteries; onto on the surface of the battery and a liquid cooling or heating refrigerant can be passed through tubes thehowever, plate toit is draw more heat costly from and the complex battery to cells. implement. Figure9 isIn a liquid photo cooling, of an EV a batterycooling forplate the can Chevy be placed Bolt, whichon the usessurface this of method the battery of cooling and a forliquid thermal cooling management or heating ofrefrigerant the battery. can be passed through tubes

Energies 2019, 12, x 7 of 14 onto the plate to draw heat from the battery cells. Figure 9 is a photo of an EV battery for the Chevy Energies 2019, 12, 667 7 of 14 Bolt, which uses this method of cooling for thermal management of the battery.

Figure 9. Chevy Bolt battery with cooling metal plates on the surface of battery cells. Figure 9. Chevy Bolt battery with cooling metal plates on the surface of battery cells. In the BSS, some of the constraints of air-cooling in the EV are not present, as the batteries can be In the BSS, some of the constraints of air-cooling in the EV are not present, as the batteries can stored in an area where the temperature of the room or storage facility is not a concern. Since the BSS be stored in an area where the temperature of the room or storage facility is not a concern. Since the is also designed to be fully automated, some of the safety concerns with air-cooling in EVs are also not BSS is also designed to be fully automated, some of the safety concerns with air-cooling in EVs are present in the BSS. The battery storage chamber is also heavily insulated to increase the efficiency of also not present in the BSS. The battery storage chamber is also heavily insulated to increase the air-cooling and achieve a more uniform temperature distribution across the cells. efficiency of air-cooling and achieve a more uniform temperature distribution across the cells. In the BSS, a combination of air and liquid cooling can be implemented to maximize efficiency In the BSS, a combination of air and liquid cooling can be implemented to maximize efficiency and cost. The BECM is critical in the BSS as it is constantly responsible for monitoring the charging and cost. The BECM is critical in the BSS as it is constantly responsible for monitoring the charging power of battery cells, voltage across each cell, as well as the temperature of each cell. The BECM is power of battery cells, voltage across each cell, as well as the temperature of each cell. The BECM is also responsible for balancing the voltage and charging across all of the cells of each battery pack in also responsible for balancing the voltage and charging across all of the cells of each battery pack in the BSS and maintain the safe temperature range of battery cells. the BSS and maintain the safe temperature range of battery cells. 2.5. Battery Swapping System Challenges and Opportunities 2.5. Battery Swapping System Challenges and Opportunities A major hindrance to the adoption of EVs is the high cost of ownership, which is directly linked to theA costmajor of hindrance the onboard to the battery. adoption In modern of EVs is EVs the today,high cost the of cost ownership, of the battery which isis 25directly−50% linked of the toentire the cost cost of of the the onboard vehicle [battery.1]. BSS haveIn modern a unique EVsopportunity today, the cost to relieveof the battery some ofis 25 the−50% pain of points the entire that costEV adoption of the vehicle faces. In[1]. an BSS ideal have BSS a system, unique aopportun third partyity willto relieve have the some ownership of the pain of the points battery that and EV is adoptionresponsible faces. for replacingIn an ideal the BSS depleted system, batteries a third ofpa itsrty partnerswill have or the customers ownership with of fully the battery charged and ones, is responsibleas well as monitoring for replacing the healththe depleted of the batteriesbatteries andof its decommissioning/repurposing partners or customers with fully the charged batteries ones, once asthe well life as is nomonitoring longer suitable the health for theof the e-mobility batteries use and case. decommissioning/repurposing This leasing/pay-as-you-go the model batteries could once be particularlythe life is no attractive longer suitable for fleet for use the cases e-mobility such as ride-sharinguse case. This and leasing/pay-as-you-go package delivery services model (who could drive be particularlya significant attractive number of for miles fleet daily use andcases cannot such affordas ride-sharing a lot of downtime). and package In additiondelivery toservices significantly (who drivereduced a significant waiting times number compared of miles to DCFC, daily BSS and can cann provideot afford two additionala lot of downtime). benefits to theIn addition power grid to significantlyin terms of reliability. reduced Thewaiting behavior times of compared EV owners to inDC termsFC, BSS of charging can provide is stochastic two additional and unpredictable, benefits to whichthe power could grid lead in toterms unsustainable of reliability. penetration The behavior of the of grid EV asowners EV adoption in terms increases of charging in scale. is stochastic BSS can andallow unpredictable, for controlled/scheduled which could charging lead to ofunsustainable depleted batteries, penetration postponing of the charging grid as ofEV batteries adoption to increasesoff-peakhours in scale. thereby BSS can acting allow as for a large controlled/scheduled flexible load from charging the grid’s of perspective. depleted batteries, BSS can postponing also act as chargingenergy storage of batteries aggregators to off-peak with enough hours storagethereby capacity acting toas participatea large flexible in electrical load from energy the markets, grid’s providingperspective. services BSS can to the also system act as such energy as voltage storage support, aggregators regulation with reserves, enough and storage energy capacity arbitrage. to participateHowever, in electrical the roadblocks energy thatmarkets, surround providing BSS still services remain: to Standardizationthe system such ofas EVvoltage battery support, packs; regulationconsumer acceptancereserves, and of BSSenergy model; arbitrage. reliable estimation of battery state-of-health. Another important However, the roadblocks that surround BSS still remain: Standardization of EV battery packs; factor to consider is the distribution and cost of BSS and charging infrastructure. Standardization consumer acceptance of BSS model; reliable estimation of battery state-of-health. Another important of EV battery packs, while necessary, appears to be very unlikely; this is largely due to the fact that factor to consider is the distribution and cost of BSS and charging infrastructure. Standardization of the competitive edge for EV OEMs are closely aligned with their underlying proprietary battery EV battery packs, while necessary, appears to be very unlikely; this is largely due to the fact that the technology. The battery pack is also a core piece of the car’s strength, stability, and safety at design competitive edge for EV OEMs are closely aligned with their underlying proprietary battery time, making it increasingly difficult for OEM’s to share a similar battery architecture across the board. technology. The battery pack is also a core piece of the car’s strength, stability, and safety at design Individual OEMs, however, can share battery architectures across several models as is seen in the time, making it increasingly difficult for OEM’s to share a similar battery architecture across the battery architecture design of the Tesla Model S and Model X [8]. A similar battery architecture across board. Individual OEMs, however, can share battery architectures across several models as is seen in models and brands of individual OEMs will foster the feasibility of BSS models similar to OEM specific the battery architecture design of the Tesla Model S and Model X [8]. A similar battery architecture service dealerships.

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The concerns of consumers with regards to the BSS model are related to both the consumer anxiety of not owning the battery at the time of purchase of the EV as in the business of Better Place [9] or the EV owner receiving a battery which he/she has no guarantee of the current state of health and degradation of the swapped battery as in the case of the Tesla BSS [9]. The warranty issues surrounding the replaced battery pack caused a low participation by EV owners for Tesla’s BSS pilot launch at the Harris Ranch facility in California [9]. Accurate SOC and SOH estimation of the Li-ion battery to ensure its safe operation and its capabilities in BSS applications is critical. Accurate estimation of Li-ion battery SOH and cycle life are typically empirical in nature, requiring induced aging tests conducted under several conditions of Li-ion batteries specific to the battery chemistry. As EVs have evolved, several approaches have been proposed in the literature to predict the SOC and SOH of the EV battery both onboard as well as offline [18–22]. An accurate offline SOC and SOH estimation plays a significant role in the technical feasibility of BSS models as batteries are constantly moved around; the importance of the online estimation of battery health and capacity is highlighted in the next section. Another important modeling challenge is the optimized distribution and sizing of BSS across the EV network. Modeling of BSS penetration and interaction with the grid both as a flexible load and as an energy storage market participant or aggregator is also of utmost importance. In [23], a modified differential evolution algorithm is adopted to solve the problem of geo-distribution and scale of BSS for optimal cost–benefit and safe operation. The proposed method is also verified on the IEEE 15-bus and 43-bus radial distribution system. A proposed model aimed at scheduling battery charging with respect to the availability of battery chargers, and hourly demand for battery swapping is presented in [24]. The participation of the BSS in the electricity market plays an important role in the economic viability of the BSS; a BSS model based on the short-term battery management is presented in [25] and includes the mathematical formulation of the problem as well as the market strategy.

3. Advanced Battery Sharing Station and Battery Sharing Network Current state-of-the-art implementations of battery swapping stations have been discussed, with the Tesla BSS that was launched in 2014 as a case study. However, this current implementation possesses several technical and economic challenges. Such challenges are the nonstandard battery interface across EV manufacturers and consumer acceptance of not owning their battery or their original battery being tampered with and replaced with a lower performance battery during a swap. Another critical challenge is the heavy dependency of the BSS on the distribution grid, and the high power demand of the BSS, which could have a negative impact on the grid during peak loading periods. In this section, a new design of the EV battery architecture is proposed to achieve a common standardized modular battery interface across EV manufacturers. In addition, a RES and a bidirectional AC/DC charging interface is introduced, which allows the BSS to become a service utility that supports the grid in terms of distributed generation and storage. Finally, in the next section, some technological advancements and research opportunities are presented, which could stem from this proposed BSS model.

3.1. Battery Architecture Structural Re-Design Traditional EVs contain a large BESS as the source of power for the vehicle propulsion system. The battery pack is typically 50−100 kWh in capacity, costing thousands of dollars and has an adverse effect on the weight of the vehicle. However, studies have shown that the typical daily drive cycle for the average consumer is approximately 40 miles (64 km) for 95% of their drive cycles, corresponding to about 15 kWh capacity requirement for daily driving. A connected universal battery pack (UBP), referred to in this paper as a boost pack, is proposed as an alternative to the traditional battery pack. It has a highly reduced weight and can charge more quickly than conventional packs, it also has the capability of being able to be combined with additional boost packs when a longer range is necessary. In addition, the battery packs are also connected through IoT to constantly manage the battery state of health (SOH), state of charge (SOC), and broadcast its various data points with the BShS and the BShN. Energies 2019, 12, 667 9 of 14

Energies 2019, 12, x 9 of 14 Energies 2019, 12, x 9 of 14 Figure 10 is a diagram of the new battery placement architecture proposed inside of an EV. As seen in InIn addition,addition, thethe batterybattery packspacks areare alsoalso connectedconnected ththroughrough IoTIoT toto constantlyconstantly managemanage thethe batterybattery statestate the description,ofof healthhealth the (SOH),(SOH), OEM statestate has ofof charge thecharge option (SOC),(SOC) to, andand design broadcbroadcast aast custom itsits variousvarious battery datadata pointspoints pack with thatwith thethe is permanently BShSBShS andand thethe part of the vehicle,BShN.BShN. enough FigureFigure to 1010 coverisis aa diagramdiagram the daily ofof thethe driving newnew batterybattery needs placplacementement of the architecturearchitecture EV owners, proposedproposed provided insideinside that ofof anan they EV.EV. AsAs are able to seenseen inin thethe description,description, thethe OEMOEM hashas thethe optionoption toto designdesign aa customcustom batterybattery packpack thatthat isis permanentlypermanently charge atpart home of the daily. vehicle, This enough greatly to cover reduces the daily the loaddriving demand needs of thatthe EV the owners, EV owner provided puts that on they the are grid as the battery canpart be of charged the vehicle, over enough a long to cover stretch the daily of time driving at night needs whenof the EV load owners, is minimal provided and that thethey electricity are is ableable toto chargecharge atat homehome daily.daily. ThisThis greatlygreatly redureducesces thethe loadload demanddemand thatthat thethe EVEV ownerowner putsputs onon thethe cheaper. Thegridgrid UBPasas thethe slot batterybattery in the cancan vehiclebebe chargedcharged is designedoverover aa longlong to strestretch providetch ofof timetime the atatEV nightnight owner whenwhen ﬂexibility loadload isis minimalminimal to participate andand thethe in the BShN. Theelectricityelectricity UBP and isis cheaper.cheaper. slot are TheThe standard UBPUBP slotslot and inin thethe capable vehiclevehicle ofisis designeddesigned providing toto provideprovide a range thethe of EVEV 100 ownerowner miles flexibilityflexibility (161 km) toto or more and availableparticipateparticipate on demand inin thethe BShN.BShN. at a TheThe BShS UBPUBP discussed andand slotslot areare standa next.standardrd Figure andand capablecapable 11 is of aof descriptionprovidingproviding aa rangerange of the ofof 100100 connected milesmiles UBP. (161 km) or more and available on demand at a BShS discussed next. Figure 11 is a description of the The UBP is(161 modular km) or more and and consists available of on high demand voltage at a BShS (HV) discussed connectors, next. Figure low voltage 11 is a description (LV) connectors, of the tube connectedconnected UBP.UBP. TheThe UBPUBP isis modularmodular andand consistsconsists ofof highhigh voltagevoltage (HV)(HV) connectors,connectors, lowlow voltagevoltage (LV)(LV) connectors for thermal management, and an embedded device for autonomous onboard diagnostics of connectors,connectors, tube tube connectors connectors for for thermal thermal manage managementment,, andand an an embedded embedded device device for for autonomous autonomous the batteryonboardonboard pack. diagnosticsdiagnostics ofof thethe batterybattery pack.pack.

Figure 10. EV with modular pack and slot for the universal battery pack (UBP). Figure 10.FigureEV 10. with EV with modular modular pack pack and and slotslot for for the the universal universal battery battery pack (UBP). pack (UBP).

Smart Device Smart Device LV Connectors LV Connectors HV Connectors HV Connectors

Sealed Coolant SealedInlet/Outlet Coolant Inlet/Outlet

FigureFigure 11. Universal11. Universal battery battery p packack (UBP) (UBP) design. design. Figure 11. Universal battery pack (UBP) design. The speciﬁcationsThe specifications of the UBP of the proposed UBP proposed is detailed is detailed below. below. Its controls Its controls and electrical and electrical and and mechanical The specifications of the UBP proposed is detailed below. Its controls and electrical and mechanical connections are designed with the intent of providing propulsion power to the vehicle as connectionsmechanical are designed connections with are the designed intent with of providing the intent of propulsion providing propulsion power to power the vehicle to the vehicle as well as as being well as being able to be connected to the grid through the BShN. The base UBP and EV design able to bewell connected as being able to the to be grid connected through to thethe grid BShN. through The the base BShN. UBP The and base EV UBP design and EV speciﬁcations design are specifications are as follows: as follows:specifications are as follows: Universal Battery Specs UniversalUniversal Battery Battery Specs Specs

Capacity = 30 kWh (110 MJ) Battery Mass = 480 lb (220 kg) Charge time = 4.5 h at 220 V

EV with Universal Battery Specs

Energy Cost = 218 Wh/mi (252 Wh/mi for Chevy Bolt), Energy Cost = 137 MPGe Energies 2019, 12, 667 10 of 14

Car Weight = 3083 lb (1396 kg) Volume = 142.5 L Energy Usage = 0.2 kWh/m Range = 137 miles (220 km) Cost = $145/kWh, $4350 Power Rating = 150 hp (111 kW) 0–60 m/h = 9 s

3.2. Battery Sharing Station and Battery Sharing Network The BSS discussed in the first section of this paper is modified to include an RES. A PV system is integrated with the BSS. In addition, a bidirectional AC/DC converter topology discussed in [15] is implemented allowing the battery packs in the BSS to provide V2G services to the smart grid. Figure 12 is a block diagram description of the system structure of the proposed BShS. The BShS is also a part of a network of BShS, referred to as a BShN, linked together through the IoT and telecommunication interfaces, communicating to optimize the cost of charging, reduce the waiting time for battery swaps by forecasting battery swaps and share the UBPs amongst each other through participating EVs and EV customers. EV owners can participate in the BShN and transport battery packs from the BShS where they are located to the BShS where they are needed for incentives such as free battery swaps or payment. The UBPs are transported from BShS to BShS through the embedded UBP slot on optimized routes convenient for EV owners. This reduces, or completely eliminates, the need for dedicated vehicles for transportation of EV battery packs from station to station. Figure 13 is a conceptual illustration of the BShN. The BShN consists of several functional subsystems; the communication between these systems is handled by the BShN Management System. This system coordinates the bidirectional flow of power between the BShS and the smart grid which is designed for distributed generation and bidirectional power flow. It also coordinates the optimized routing of boost packs in the BShN through the EVs that participate in the network. In addition, the BShN management system controls the scheduling of battery swaps as well as forecasting of future swaps and grid loading. The BShN management system in this proposed scheme becomes a grid utility, providing services to the grid, such as peak shaving and load balancing, and serves as a reserve for the grid during contingency situations. The proposed BShN consists of several technical hurdles that need to be addressed in order to become commercially available. Some of these technical hurdles are presented as researchEnergies opportunities 2019, 12, x in the following section. 11 of 14

Distribution Grid

Battery Sharing Station Bidirectional AC/DC Charger PV Array Generation

DC/DC Converter Battery Packs

Figure 12.FigureBattery 12. Battery sharing sharing station station (BShS) (BShS) withwith a loca locall renewable renewable energy energy source source (RES) connected (RES) connected bidirectionallybidirectionally to the grid.to the grid.

BSHN Management System

EV Customers with Universal BSHS with RES Generation Battery Pack architecture BSHS with RES Generation

Smart Grid

Figure 13. Battery sharing network (BShN) communication Interface between components and the smart grid.

4. Research Opportunities

4.1. Structural Design of Modular Battery EV A structural design for EVs that is compatible with a UBP needs to be further investigated. The positioning of the battery slot for ease of access during a swap is critical to determining how fast and convenient a swap/boost will take place. Consumers are more likely to switch to EVs if replenishment

Energies 2019, 12, x 11 of 14

Distribution Grid

Battery Sharing Station Bidirectional AC/DC Charger PV Array Generation

DC/DC Converter Battery Packs

Figure 12. Battery sharing station (BShS) with a local renewable energy source (RES) connected Energies 2019, 12, 667 11 of 14 bidirectionally to the grid.

BSHN Management System

EV Customers with Universal BSHS with RES Generation Battery Pack architecture BSHS with RES Generation

Smart Grid

Figure 13. Battery sharing network (BShN) communication Interface between components and the Figure 13. Battery sharing network (BShN) communication Interface between components and the smart grid. smart grid. 4. Research Opportunities 4. Research Opportunities 4.1. Structural Design of Modular Battery EV 4.1. Structural Design of Modular Battery EV A structural design for EVs that is compatible with a UBP needs to be further investigated. The positioningA structural ofdesign the battery for EVs slot that for is easecompatible of access with during a UBP a needs swap isto criticalbe further to determininginvestigated. howThe fastpositioning and convenient of the battery a swap/boost slot for ease will of takeaccess place. during Consumers a swap is critical are more to determining likely to switch how to fast EVs and if replenishmentconvenient a swap/boost of energy iswill under take 5–10place. min. Consumers Furthermore, are more electrical likely connectorsto switch to andEVs cablesif replenishment capable of withstanding thousands of swaps safely without signiﬁcant wear need to be developed.

4.2. Thermal Management of Batteries during Normal Mode and Boost Mode Thermal management systems of EVs today are typically liquid based and tightly coupled with the EV battery. In order for modular battery packs to be hot-swapped from an EV, the thermal management design is critical. Currently, before a swap is done, all of the thermal ﬂuid in the battery pack must be drained completely to avoid spillage. Furthermore, when a new boost pack is added, it must integrate seamlessly with the existing thermal management architecture of the EV. Similarly, when the battery pack is taken off of an EV and placed at a BShS, it must be integrated seamlessly with the BShS thermal management system. A cost-effective and somewhat standardized method of thermal management such as ambient air-cooling or other forms of gases must be researched in order for the UBP to become practical.

4.3. Electrical Design of Power Electronic Converters and Control A major beneﬁt of the modular battery pack design for the EV is the reduction in the weight which increases the overall efﬁciency of the EV. However, with the addition of boost packs, additional circuitry must be added to the vehicle in order to balance the power between both battery packs during boost mode. This additional circuitry adds additional cost in terms of weight to the vehicle that is not needed during normal operating modes; therefore, it is necessary to investigate and come up with Energies 2019, 12, x 12 of 14 of energy is under 5–10 minutes. Furthermore, electrical connectors and cables capable of withstanding thousands of swaps safely without significant wear need to be developed.

4.2. Thermal Management of Batteries during Normal Mode and Boost Mode Thermal management systems of EVs today are typically liquid based and tightly coupled with the EV battery. In order for modular battery packs to be hot-swapped from an EV, the thermal management design is critical. Currently, before a swap is done, all of the thermal fluid in the battery pack must be drained completely to avoid spillage. Furthermore, when a new boost pack is added, it must integrate seamlessly with the existing thermal management architecture of the EV. Similarly, when the battery pack is taken off of an EV and placed at a BShS, it must be integrated seamlessly with the BShS thermal management system. A cost-effective and somewhat standardized method of thermal management such as ambient air-cooling or other forms of gases must be researched in order for the UBP to become practical.

4.3. Electrical Design of Power Electronic Converters and Control A major benefit of the modular battery pack design for the EV is the reduction in the weight which increases the overall efficiency of the EV. However, with the addition of boost packs, additional circuitry must be added to the vehicle in order to balance the power between both battery packsEnergies during2019, 12 ,boost 667 mode. This additional circuitry adds additional cost in terms of weight to12 ofthe 14 vehicle that is not needed during normal operating modes; therefore, it is necessary to investigate and come up with multidirectional, high power density, low-cost power electronic converter schemes multidirectional, high power density, low-cost power electronic converter schemes that accommodate that accommodate for different modes of operation of the EV. for different modes of operation of the EV.

4.4.4.4. Electrical Electrical Power Power Management Management of of EV EV to to Include Include Ultracapacitor Ultracapacitor during during Heavy Heavy Loads Loads AA reduced reduced capacity capacity in in EVs EVs to to accommodate accommodate for for th thee boost boost pack pack in in the the EV EV also also implies implies reduced reduced maximummaximum power. power. This This is is so sometimesmetimes undesirable undesirable during during acceleration acceleration from from a a dead dead stop stop or or at at higher higher drivingdriving speeds. speeds. Therefore, Therefore, a a high high power power density, density, low-energy low-energy density density source source such such as as a a supercapacitor supercapacitor oror ultracapacitor ultracapacitor needs needs to to be be integrated integrated with with th thee main main battery battery to to provide provide additional additional power power to to the the wheelswheels during during short short heavy heavy load load demand demand periods. periods. Figure Figure 1414 fromfrom [17] [17] is is a a circuit circuit diagram diagram illustrating illustrating thethe addition addition of of a a supercapacitor supercapacitor with with a a battery battery fo forr additional additional power power during during heavy heavy load. load. During During the the lowerlower or or normal normal loading loading periods, periods, the the main main battery battery quickly quickly recharges recharges the the ultra-capacitor. ultra-capacitor. A A practical practical implementationimplementation ofof suchsuch a a scheme scheme is ais needed a needed topic to ofpic research of research for the for advancement the advancement of smaller of modularsmaller modularbattery packs battery with packs high wi performance.th high performance.

 

Battery UC Power Converter Load

 

Figure 14. EV battery with ultracapacitor combined to provide power during high load demands. Figure 14. EV battery with ultracapacitor combined to provide power during high load demands. (Adapted from [17]). (Adapted from [17]). 4.5. Further Topics 4.5. Further Topics Aside from the topics discussed above, other topics where research is needed in the area of battery swappingAside asfrom a practical the topics solution discussed to EV above, adoption other include topics the where following: research is needed in the area of battery swapping as a practical solution to EV adoption include the following: • Smart charging of EV batteries at BShS  Smart charging of EV batteries at BShS • Standardized IoT/telecommunication schemes for BShN components and interaction with the grid

• Automated scheduling and billing system for BShN • Forecasting of battery swaps and storage availability from the BShS • Optimization of routes for battery delivery in the BShN • Cost–beneﬁt analysis of the BShN model over traditional BShS and DCFC.

5. Conclusions In this paper, a method of battery swapping technology with the Tesla battery swapping station as a case study was reviewed. Technical challenges that are prevalent in implementing this technology commercially were also identiﬁed. A novel methodology for advanced battery swaps and a battery sharing network topology was introduced. Finally, research opportunities and technological advancements were also identiﬁed that will enable this novel method to become commercially viable.

Author Contributions: Conceptualization, F.A.; methodology, F.A. and A.v.J.; validation, F.A., K.Y.L. and A.v.J.; data curation, F.A.; writing—original draft preparation, F.A.; writing—review and editing, F.A., A.v.J. and K.Y.L. Funding: This research received no external funding. Conﬂicts of Interest: The authors declare no conﬂict of interest. Energies 2019, 12, 667 13 of 14

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