2015 Tenth International Conference on Ecological Vehicles and Renewable Energies (EVER)

Automotive Battery Charging ApplicationsGeorgios E. Sfakianakis, Student Member, IEEE, Jordi Everts, Member, IEEE,

and Elena A. Lomonova, Senior Member, IEEE

Electromechanics and Power Electronics (EPE) groupDepartment of Electrical Engineering

Eindhoven University of Technology (TU/e)Eindhoven, The Netherlands

g.e.sfakianakis@tue.nl

Abstract—This paper is divided into three main parts.In the first part, i.e. Section II, a general outline of thesystem level aspects regarding battery chargers (powerconverters) for plug-in electric vehicles (PEVs) is given.Thereby, the different charging modes of the converters,the corresponding power levels, and the infrastructural fa-cilities are discussed. Moreover, Vehicle-to-Grid (V2G) op-eration by means of grid-forming, grid-feeding, and grid-supporting converter functionality is briefly explained, andthe input power quality and electromagnetic compatibilityrequirements are summarized. In the second part, i.e.Section III, the mutually coupled indices that determinethe overall performance of the system, such as powerlosses (efficiency), volume (power density), weight (specificpower), failure rate (reliability), and costs (relative cost),are outlined. In this context, the role that wide band-gappower semiconductors (e.g. SiC, GaN) can play in orderto further improve the system performance is highlighted.In the third part, i.e. Section IV, a concise overview ofthe possible topological implementations for the mentionedpower converters is provided. The focus is on conductive,isolated AC–DC converter topologies with high AC inputpower quality in terms of power factor correction (PFC)and harmonic distortion, and with bidirectional power flowcapability in order to facilitate V2G operation.

Index Terms—Bidirectional Isolated AC–DC Converters,Battery Chargers, Conductive Charging, Plug-in ElectricVehicles

I. INTRODUCTION

The number of plug-in hybrid electric vehicles(PHEVs) and battery electric vehicles (PBEVs), hereafter

Fig. 1. Typical PBEV electric power system architecture [3]. ThePBEV turns into a PHEV in case an internal combustion enginepresent (gray colored part).

generally denoted as plug-in electric vehicles (PEVs),has constantly been increasing during the past years[1]. Due to their superior fuel economy and perfor-mance compared to internal combustion engine vehicles(ICEVs), they can effectively contribute to a lower envi-ronmental impact of the ever-increasing use of personalvehicles [2].

978-1-4673-6785-1/15/$31.00 ©2015 European Union

Overview of the Requirements and Implementationsof Bidirectional Isolated AC–DC Converters for

Figure 1 shows a typical electric power system archi-tecture of a pure-electric PBEV, comprising an electricmachine (EM) which draws energy from a high voltage(HV) battery during propulsion, and recharges the batteryduring regenerative braking. For the case at hand, boththe EM and the HV battery are connected to a HVDC bus1 via a bidirectional, non-isolated AC–DC andDC–DC power electronic converter respectively. Alsoconnected to the HV DC bus via power convertersare the high power loads, such as the air conditioningand the power streering, and a low voltage (LV, typ-ically 14 VDC) DC bus for providing energy to thelow power loads (e.g. lightning, instrumentation, pumps,etc.). When adding an internal combustion engine (ICE)and electric generator to the power system, connectingthem to the HV DC bus via an AC–DC rectifier as shownby the gray colored part in Figure 1, the PBEV turns intoa series PHEV.

For all types of PEVs, the HV battery can be externallyrecharged by plugging into the low voltage utility gridusing different types of conductive or inductive batterychargers. The charger shown in Figure 1 is an on-board, conductive, single-phase AC–DC converter whichcan either be directly connected to the HV battery orto the HV DC bus (case at hand). At first, i.e. inSection II of this paper, an overview of all standardizedbattery charger options is given by means of the socalled ‘charging modes’, the corresponding power levels,and the infrastructural facilities. PEV battery chargerscan also be distinguished by their capability to manageunidirectional or bidirectional power flow. The class ofbidirectional converters is becoming more attractive asbesides charging of the HV battery, they can also transferenergy from the battery to the grid in order to provideVehicle-to-Grid (V2G) services. The features of grid-forming, grid-feeding, and grid-supporting V2G opera-tion are discussed in Section II as well. Lastly, the ACinput power quality and electromagnetic compatibilityrequirements for battery chargers are summarized.

In the design of power electronic converters, especiallyin automotive applications, there is a historical trendtoward lower losses, volume, weight, failure rate, andcosts [2]. These indices that determine the overall per-formance of the system, as well as their mutual coupling,are outlined in Section III. In this context, the role thatwide band-gap power semiconductors (e.g. SiC, GaN)can play in order to further improve the system perfor-

1Voltage levels of 200 VDC to 400 VDC, and even up to 650 VDC

for the HV DC bus are rather common [2].

mance is also highlighted, along with the importanceof thermal management. Since multiple objectives needto be considered for the design of a power electronicconverter, the necessity of multi-objective optimization(MOO) of converter systems is described too.

In Section IV of this paper, a concise overview ofthe possible topological implementations for conduc-tive AC–DC converters is given. The topologies areclassified into two families: single-stage and two-stagearchitectures. The focus is on single-phase and three-phase converters with high AC input power quality interms of power factor correction (PFC) and harmonicdistortion, and with bidirectional power flow capabilityin order to facilitate V2G operation. Only topologieswith galvanic isolation are considered since they are seenas a favorable option in conductive chargers2 [5].

II. BATTERY CHARGERS: SYSTEM LEVEL ASPECTS

A. Charging Modes

Battery chargers for PEVs can be subdivided into twomain categories: conductive and inductive chargers [5].As far as it concerns the conductive chargers, power istransfered through metal-to-metal contact between theconnector on the charging port of the vehicle and theAC power lines, or a dedicated electric vehicle supplyequipment (EVSE) that is interfaced with the AC utilitygrid. Thereby the required AC–DC power conversioncan either take place within the PEV utilizing an on-board charger, or within the EVSE involving an off-board charger. For the latter, DC power is fed to thevehicle through a cable. This method is also known as‘DC charging’, enabling higher charging current/powerand thus smaller charging times. The international stan-dard IEC 61851-1 [4] was created by the InternationalElectrotechnical Commission (IEC) in order to providea framework that applies to on-board and off-board con-ductive charging equipment for PEVs, inter alia definingrequirements regarding the cable connection betweenthe PEV and the charging point, the types of plugsand sockets, and the corresponding safety measures andcommunication features [6], [7]. Most relevant for thisoverview are the different charging modes, which mainlyrelate to the current and power levels of the chargers:

• Mode 1 charging (on-board); Figure 2(a): slowcharging whereby energy is sourced from the AC

2Besides increased safety, galvanic isolation provides more con-venience to fulfill the requirements given in the standards [4]. Forexample, in non-isolated chargers, the presence of common-modecurrents, noise, and so on, requires a considerable effort to preventunwanted earth fault protection trip [5].

(a) Mode 1 and mode 2 charging

(b) Mode 3 charging

(c) Mode 4 (DC) charging

(d) Inductive charging

Fig. 2. Charging infrastructure for conductive (a)-(c) and inductive(d) charging. Note that the DC output of the battery chargers mightalso be directly connected to the terminals of the HV battery.

grid utilizing a typical single-phase or three-phasehousehold-type socket. The charging current is lim-ited to 16 AAC, while the AC voltage may not ex-ceed 250 VAC for a single-phase, and 480 VAC fora three-phase supply outlet. The IEC-recommendedAC voltage is 230/400 VAC, resulting in a maxi-mum charging power of 3.7 kW (single-phase) and11 kW (three-phase) [6], [7].

• Mode 2 charging (on-board); Figure 2(a): slowcharging from a household-type socket with an in-cable protection device. The voltage ratings are thesame as for mode 1, but the maximum current is32 AAC. Thus, the achievable charging power is7.4 kW (single-phase) and 22 kW (three-phase) [6],[7].

• Mode 3 charging (on-board); Figure 2(b): slowor fast charging using dedicated EVSE, involvinga PEV socket outlet with control, protection func-tion, and other additional safety features installed.Charging currents up to 63 AAC are allowed. Themaximum power level is thus 14.5 kW (single-phase) and 43.5 kW (three-phase). Very high ACcharging currents up to 250 AAC are also describedby the standard [4], [6], [7].

• Mode 4 charging (off-board); Figure 2(c): fastDC-current charging, with charging currents up to400 ADC that are provided by an off-board chargerwhich is located within the EVSE.

For inductive chargers, the power is transfered viaa magnetic coupling (wireless, see Figure 2(d)) [8].This technology offers galvanic isolation, connector ro-bustness, power compatibility, durability, and a userfriendly interface. However, these advantages come ata cost of a low conversion efficiency and the needfor new, costly charging infrastructure [5]. A separateinternational standard, SAE-J2954, is currently beingprepared by the Society of Automotive Engineers (SAE),concerning the alignment of the vehicle as well as theinfrastructure needed. Inductive battery chargers are notfurther discussed.

B. Vehicle-to-Grid (V2G) Operation

Conventional unidirectional battery chargers can onlyabsorb power from the utility grid in order to chargethe batteries. Recently, the concept of Vehicle-to-Grid(V2G) operation has gained an increasing interest as anopportunity to improve the efficiency and reliability ofthe grid by providing grid support services. Thereby,energy stored in the batteries of the total fleet of PEVsthat are parked and connected to the grid can be injectedinto the grid, enabling for example the implementationof peak shaving, voltage control, and the integration ofmore renewable energy sources. Evidently this requiresbidirectional power electronic converters. The role thatthese grid-connected converters can play in providingancillary services depends on how they are designed andoperated [9], [10]:

• Grid-forming converters (see Figure 3(a)) are rep-resented as an ideal voltage source with low outputimpedance [9]. They are controlled to generate avoltage with given amplitude and frequency. Anexample of a grid-forming converter is a standbyuninterruptible power supply (UPS), where in caseof grid failure the UPS converter forms the grid.

(a) (b)

(c)

(d)

Fig. 3. Simplified representation of grid-connected power converters[9]. (a) Grid-forming, (b) grid-feeding, (c) grid-supporting (current-source-based), and (d) grid-supporting (voltage-source-based).

• Grid-Feeding converters (see Figure 3(b)) are rep-resented as an ideal current source with high parallelimpedance [9]. They are controlled to deliver acertain amount of active and reactive power toan energized grid. Grid-forming converters cannotoperate in island mode.

• Grid-Supporting converters (see Figures 3(c) and3(d)) are represented as either a current source withparallel impedance (Figure 3(c)) or a voltage sourcewith a link impedance (Figure 3(d)) [9]. Their activeand reactive power are controlled to contribute tothe regulation of the grid voltage and frequency.The current source implementation does need anenergized grid to operate while the voltage sourceimplementation does not.

C. Standards of Operation

1) AC Input Power Quality: The quality of the ACinput power can be quantified using both the power factorand the amount of harmonic current injection into thegrid. For single-phase and three-phase converters ratedless than 16 AAC per phase, which include mode 1 charg-ers, IEC has created an international standard knownas IEC 61000-3-2 [11]. Thereby, electrical devices are

TABLE ILIMITS FOR CLASS A EQUIPMENT [11]

Harmonic order n Maximum permissibleharmonic current (A)

Odd harmonics3 2.305 1.147 0.779 0.4011 0.3313 0.21

15 6 n 6 39 2.25/n

Even harmonics2 1.084 0.436 0.30

8 6 n 6 40 1.84/n

divided into 4 classes according to their power and appli-cation. Battery chargers are classified in Class A, wherethe low-frequency harmonics of the mains current shouldnot exceed the values listed in Table I. For convertersrated greater than 16 AAC per phase (which includemode 2, 3, and 4 chargers) and that are intended to beconnected to public low-voltage AC distribution systems,the IEC 61000-3-4 standard [12] applies, defining limitsto the low-frequency harmonics of the mains current ina similar way as IEC 61000-3-2. Additionally, the IEEEhas created a guide [13] which is applicable to single-phase converters rated less than 600 VAC and 40 AAC. Itis suggested that the maximum total harmonic distortion(THD) of the current should be less than 15%, and thatthe 3rd current harmonic should be less than 10% of thefundamental current component, while the power factorshould not be less than 0.95. For lower power devices,the maximum allowed values are doubled to 30% for theTHD of the current and to 20% of the fundamental forthe 3rd current harmonic.

2) Electromagnetic Compatibility (EMC): The highlevels of switched currents and voltages can be seenas the main characteristics of a power converter [14].As a result of this characteristic, power converters gen-erate electromagnetic fields/emission which are guidedthrough conductors (conducted emission; 150 kHz -30 MHz) or air (radiated emission; 30 MHz - 1 GHz),and which potentially lead to electromagnetic interfer-ence (EMI). Therefore, the IEC has created the Interna-tional Special Committee on Radio Interference–CISPR,defining standards in order to ensure electromagnticcompatibility (EMC) of converter systems that are to becommercialized. The CISPR 11 [15] and CISPR 22 [16]

Fig. 4. Quasi-peak limits for conducted emissions at the main portsof Class A and Class B equipment according to CISPR 11 and 22.

have been created for Class A (residential) and Class B(light industrial) equipment. Common for both CISPR 11and CISPR 22 are the quasi-peak limits for conductedemissions which are shown in Figure 4 for both Class Aand B equipment.

Although efforts have been put on the study of theimpact of modulation schemes and soft-switching tech-niques on conducted emissions, filtering circuits thateffectively limit the propagation of electrical noise cannot be avoided [14]. In [17], for example, a designprocedures has been proposed for the optimal designof these filter circuits. Thereby, the switching frequencyshould be selected carefully in order to minimize theimpact on the power density and efficiency, and to max-imize the dynamic response [18]. Radiated emissions,on the other hand, are typically reduced and controlledby development of good layout techniques and shielding[14].

III. CONVERTER PERFORMANCE

A. Performance Indices

The main quantities that determine the performanceof a power electronic converter are the power losses,the volume, the weight, the failure rate, and the systemcosts [19]. In order to assess and compare differentconverters, and in order to define a plan of action for thefurther development of converter systems, these mutuallycoupled factors can be expressed by relative quantitiesthat are termed ‘performance indices’, being respectivelythe efficiency, power density, specific power, reliability,and relative costs. Their continuous enlargement is oneof the main design objectives for future (on-board) PEVbattery chargers. This is illustrated in Figure 5, while asummary of the performance indices is presented below.

1) Power Losses (Efficiency): Due to environmentalreasons and in connection with rising energy prices,

Fig. 5. A spider graph illustrating the State of the Art (SoA) andfuture expected performance indices of a power electronic convertersystem.

the efficiency of converter systems is gaining moreimportance. The efficiency of a converter is defined as:

η = 100 · Po

Pi[%] , (1)

where Po is the output power and Pi the input power.Efficiency is directly related to power losses, wherethree main sources of them can be distinguished: powersemiconductors, passive components and auxiliary com-ponents. The power semiconductor part of the lossescan be split in two parts, the switching and the con-duction losses. Regarding switching losses, a trade-off isintroduced since by increasing the switching frequency,in order to reduce the size of passive components, theswitching losses are increased. However, by means ofsoft-switching techniques such as zero voltage switching(ZVS) or zero current switching (ZCS), the switching ofthe semiconductors with quasi-zero switching losses isachieved. Furthermore, passive components (inductors,capacitors) used for filtering and energy transfer, con-sume quite a lot of energy which can reach almost 20%of the total losses [18]. Auxiliary losses consist of lossesrelated to the power supply of the cooling system, thedigital control, and the power semiconductor drivers. Itshould be noted that an increased efficiency also resultsin reduced cooling requirements and thus a lower weight,volume, and again cost.

2) Volume (Power Density) and Weight (SpecificPower): Power density expresses how compact a systemis, while specific power can define the nominal powerof a converter in respect of weight. Power density ρ andspecific power γ are defined as the nominal output powerPo,nom of the converter divided by its volume V and its

Fig. 6. A typical reliability curve (also known as Bathtub curve),indicating the failure rate of a device during different time intervalsof its lifetime.

weight W , respectively:

ρ =Po,nom

V[kW/liter, kVA/liter] , (2)

γ =Po,nom

W[kW/kg, kVA/kg] . (3)

A low converter weight and volume enable simple han-dling, installation, and maintenance of the system [2]. Incase no thermal limitations apply, this can be achieved byincreasing the switching frequency, resulting in smallerpassive components like transformers, capacitors andinductors, and thus again in lower weight and cost [2].Note that a reduced weight also results in a driving rangeexpansion of the vehicles. However, as mentioned above,an increased switching frequency comes at the cost ofhigher power losses.

3) Failure Rate (Reliability): The reliability is theability of a system or component to perform its requiredfunctions under stated conditions for a specified periodof time [20]. A quantitative measure to determine thereliability is the failure rate λ, i.e. the availability ofan item after an elapsed time. A typical failure ratecurve is illustrated in Figure 6, which is know as thebathtub curve. Three main periods can be distinguished:the burn-in, the useful life, and the wear-out period.The useful life of a battery charger, as part of a PEV,should be close to the lifetime of the vehicle. Thiswill further increase the penetration of PEVs into themarket. However, in order to increase the reliabilityof the system, typically more components are required[20], which might result in decreased performance ofother attributes (e.g. power density, specific power, cost),requiring a trade-off analysis.

4) System Cost (Relative Cost): By providing cheapersolutions for battery chargers and propulsion systems,the integration of PEVs into vehicle market can beaccelerated. A quantitative measure to define the overall

system cost is the ‘relative cost’ performance index:

σ =Po,nom

C[kW/$, kVA/$, kW/e, kVA/e] ,

(4)

which expresses the nominal power divided by the totalcost of the system. Furthermore, an important figureis the time needed for a technology to be available inthe market, known as ‘time to market’. For example,despite the fact that first attempts of realization of SiliconCarbide (SiC) power semiconductors were reported inthe 1990s [21], the first commercially available SiC JFETswitch was only recently introduced in the market [22].

B. The Role of Wide Band-Gap Devices

Wide band-gap semiconductors such as Gallium Ni-tride (GaN) and Silicon Carbide (SiC) are to play a keyrole in the advancement of power electronic switchingdevices and thus converters [23]–[25]. The advantages ofwide band-gap materials compared to Silicon, whereofthe performance is close to its physical limits [23],are their high-voltage blocking capability, low on-stateresistance, high switching speed, and high-temperatureoperation. The latter is due to the small intrinsic carrierdensities. Experiments with GaN and SiC transistorshave proved a stable operation at 300 ◦C and 450 ◦Crespectively, while silicon transistors achieve stable oper-ation at temperatures up to 150 ◦C [26], [27]. Moreover,switching frequencies of a few hundred kilohertz in hard-switching operation are feasible [28], [29], while for Sidevices this is only possible by employing soft-switchingstrategies. In [30] efficiencies exceeding 99.5% havebeen reported, utilizing SiC JFET devices in an inverterapplication. This could be achieved due to the lowvoltage drop across the devices (i.e. small on-resistance),resulting in low conduction losses, and due to the shortswitching time, leading to low switching losses. Toconclude, wide band-gap devices form an new era inpower electronics, which might be the enabler of ultra-high performance power converters systems.

C. The Role of Multi-Objective Optimization (MOO)

In the design of power electronic systems, the trendis to minimize the volume and maximize the availablepower. Moreover, general requirements are also appliedfor cost minimization and lifetime increase, while envi-ronmental issues highlight efficiency maximization as amajor concern. As a result, multiple objectives should beconsidered, which are the minimization of the volume,the weight, the losses, the cost as well as the failurerate. As mentioned before, these objectives are translated

into measurable ’Performance Indices’ and based onthem, quantitative assessments are possible. Thereforethe process of optimization of a system requires totake into account more objectives and a mathematicalprocedure (MOO) is required to assure the best possibleexploitation of the available degrees of freedom andtechnologies [19].

The mathematical MOO procedure maps a multi-dimensional Design Space (Decision Space) into amulti-dimensional Performance Space (Objective Space),which is defined by the different Performance indices pi,as illustrated in Figure 7.

Fig. 7. Qualitative representation of the Design Space (left) andPerformance Space (right), illustrating a random mapping of a designdecision (x,k) to the corresponding performance. The boundary of thePerformance Space is defined by the pareto front which representsthe best possible performance of the power electronics system.

IV. AC–DC CONVERTER TOPOLOGIES

In this section a concise overview of the possible topo-logical implementations for conductive battery chargerswhich can be used for mode 1, mode 2, mode 3, andmode 4 charging (acc. to Section II-A) is presented.The focus is on single-phase and three-phase AC–DCconverters with high AC input power quality in terms ofpower factor correction (PFC) and harmonic distortion,and with bidirectional power flow capability in order tofacilitate V2G operation (see Section II-B). As explainedin the introduction (see Section I), only topologies withgalvanic isolation are considered. Assuming that eachconverter is made up of a set of building blocks asshown in Figure 8, the topologies are classified into twofamilies: single-stage and dual-stage architectures.

A. Dual-Stage AC–DC Converter Topologies

As shown in Figure 8(a), dual-stage bidirectional andisolated AC–DC converters are most commonly realizedusing a power factor correction (PFC) converter followedby an isolated DC–DC converter, being both bidirec-tional. The PFC performs the rectification of the ACline voltage into a DC voltage that might be boostedto a higher level. The PFC also must assure the quality

(a)

(b)

Fig. 8. General representation of (a) dual-stage AC–DC convertertopologies and (b) single-stage AC–DC converter topologies.

of the AC input power in terms of power factor andharmonic distortion. In addition, an AC filter is present atthe AC side in order to filter the high-frequency harmoniccomponents of the AC input current. The DC output sideof the PFC converter is connected to a DC-link storageelement which can be an inductor (current DC-link) ora capacitor (voltage DC-link). The later is used moreoften and therefore considered only in this paper. Thesmoothed DC-link voltage (or current) is further inputtedto the isolated DC–DC converter, providing power tothe DC facility (e.g. the HV DC bus or the HV batteryof the car). Dual-stage converters have the advantagethat the PFC stage and the isolated DC–DC conversionstage are decoupled via the DC energy storage element.Consequently, both systems can be optimized withinnarrow specifications.

1) PFC Converter Topologies: The most widespreadway to implement bidirectional PFC front-ends is touse pulse-width-modulated bridge circuits that interfacethe DC-link storage capacitor (voltage DC-link) withthe mains [31]–[33]. Thereby, one or more bulky lineinductors are typically present. Figures 9(a) and 9(b)respectively show a single-phase half-bridge and full-bridge PFC, while Figure 9(c) shows a three-phase full-bridge variant. The line inductors are useful to suppressthe current harmonics injected into the grid by the PWMvoltage that is impressed at the AC terminals of the PFCconverter. However, an additional AC filter section isgenerally required to comply with the standards.

In [33] and [34], an extensive review of the single-phase, boost-type PFC front-end converters, such as theones shown in Figures 9(a) and 9(b), is presented, alongwith some other variants such as multi-level (e.g. neutral

(a) (b) (c)

Fig. 9. Bidirectional PFC AC–DC converter topologies based on conventional bridge circuits. (a) Single-phase half-bridge converter, (b)single-phase full-bridge converter, and (c) three-phase full-bridge converter.

Fig. 10. Single-phase, bidirectional, multi-cell, totem-pole PFC AC–DC converter.

point clamped (NPC) or T-type), buck-type, and buck-boost-type architectures. Furthermore, a bidirectionalmulti-cell totem-pole PFC converter (acc. to Figure 10)is described in [35], [36], employing a triangular currentmode (TCM) soft-switching modulation scheme over thecomplete mains period.

In [37], a comparative evaluation of the two-levelthree-phase, boost-type PFC front-end converter shownin Figure 9(c) and the three-level NPC variant of thisconverter is presented. Reference [38] presents a compar-ative evaluation of three-phase, buck-type, bidirectionalPFC converters based on conventional unidirectional rec-tifier topologies that are modified using an inverting link-circuit. Besides the unidirectional six-switch PFC systemand the anti-parallel six-switch converter, also topologiesbased on the 3rd harmonic injection concept such as thebidirectional SWISS converter [39] are investigated.

2) Isolated DC–DC Converter Topologies: Numerousdifferent types of isolated DC–DC converter topologiesare proposed in literature, such inter alia the soft-switching dual active bridge (DAB) topologies and theresonant topologies, whether or not combined with activeauxiliary snubber circuits and/or a second non-isolatedDC–DC conversion stage. Extensive overviews, topologysurveys, and comparative evaluations are presented in[40]–[44]. Figure 11 shows the full-bridge full-bridgeDAB implementation which, amongst other variants, isconsidered as the most suitable candidate for the real-

Fig. 11. Isolated, bidirectional, full-bridge full-bridge DAB DC–DCconverter.

ization of high-efficiency, high-power density, isolatedDC–DC conversions [42].

B. Single-Stage AC–DC Converter Topologies

Besides the traditional dual-stage approach, bidirec-tional and isolated AC–DC converters with PFC canalso be realized using a single power conversion stage.These single-stage AC–DC converters are identified bythe absence of an intermediate DC-link storage elementand can be referred to as matrix-type converters. Due tothe effective omission of a complete power conversionstage and DC-link energy storage element they have thepotential to benefit the system performance with regardto efficiency, volume (power density), number of com-ponents (reliability), weight, and costs [2]. For single-phase converters this comes at the cost of an increasedfiltering effort on the DC side in order to reduce the low-frequency output ripple due to the power variation at thedouble line frequency. This deficiency vanishes for three-phase architectures which only require storage at theswitching frequency in case of symmetrical sinusoidalcurrent consumption. Another deficiency of the single-stage converters is that all converter functionalities suchas the PFC, the galvanic isolation, the suppression ofthe line frequency harmonics, and the output voltageregulation are performed by a single conversion stagethat consequently needs to be designed and optimizedwithin wide specifications.

Fig. 12. Single-stage, single-phase, bidirectional, isolated, soft-switched AC–DC converter based on the full-bridge full-bridge DAB.

Fig. 13. Single-stage, single-phase, bidirectional, isolated, soft-switched AC–DC converter, using a cycloconverter on the AC side,a voltage-source converter on the DC side, and a medium frequencytransformer in between.

Different types of single-stage, single-phase, bidi-rectional, and isolated AC–DC converters have beenproposed in literature, such as the true bridgeless PFCconverter [45] and different variants of the single-stageDAB AC–DC converter topologies [46]–[52], which usematrix-type ‘low-frequency AC to high-frequency AC’modules at the AC side. A very promising variant isthe single-stage full-bridge full-bridge DAB AC–DCconverter presented in [51]–[53] and shown in Figure 12.It is shown in [53] that this converter can be controlledunder soft-switching conditions within its complete op-erating range. In [54], [55] another single-stage, soft-switched AC–DC converter topology is proposed. Thistopology is shown in Figure 13, using a cycloconverteron the AC side, a voltage-source converter on the DCside, and a medium frequency transformer in between.

Single-stage, three-phase, bidirectional, and isolatedAC–DC converters comprise the three-phase DAB [56],and the three-phase soft-switched converter that con-sists of a cycloconverter and a voltage-source converter[57] (acc. to Figure 14). Another approach based on astackable multi-port converter is presented in [58] andshown in Figure 15, combining three separate single-phase matrix-type ‘low-frequency AC to high-frequencyAC’ modules using a single transformer structure. As can

Fig. 14. Single-stage, three-phase, bidirectional, isolated, soft-switched AC–DC converter, using a cycloconverter on the AC side,a voltage-source converter on the DC side, and a medium frequencytransformer in between.

Fig. 15. Single-stage, three-phase, bidirectional, isolated, soft-switched AC–DC converter based on separate single-phase matrix-type ‘low-frequency AC to high-frequency AC’ modules using asingle transformer structure.

be seen from Figure 15, this converter has a close simi-larity with the single-stage, single-phase DAB convertertopology depicted in Figure 12. Besides the advantageof modularity, low voltage semiconductor devices canbe used which feature a low on-state resistance and fastswitching behavior. Additionally, the converter can becontrolled with a modulation scheme that facilitates soft-switching operation.

V. CONCLUSION

In this paper the requirements and the implementationsof bidirectional isolated AC–DC converters for automo-tive battery charging applications have been overviewedand different aspects have been discussed into three

main parts. In the first part, a general outline of thesystem level aspects regarding battery chargers for PEVsis given. Furthermore, Vehicle-to-Grid (V2G) operationis briefly explained while the input power quality andelectromagnetic compatibility requirements are outlined.In the second part, the mutually coupled indices thatdetermine the overall performance of the system, suchas power losses (efficiency), volume (power density),weight (specific power), failure rate (reliability), andcosts (relative cost), are summarized. The role that wideband-gap power semiconductors (e.g. SiC, GaN) canplay in order to further improve the system performanceis highlighted, as well as the role of Multi-Objective Op-timization (MOO). In the last part, a brief overview of thepossible topological implementations for the mentionedpower converters is provided. The focus is on conductive,isolated AC–DC converter topologies with high AC inputpower quality in terms of power factor correction (PFC)and harmonic distortion, and with bidirectional powerflow capability in order to facilitate V2G operation.

ACKNOWLEDGMENTS

This paper is part of the ADvanced Electric PowertrainTechnology (ADEPT) project which is an EU fundedMarie Curie ITN project, grant number 607361. WithinADEPT a virtual and hardware tool are created to assistthe design and analysis of future electric propulsions.Especially within the context of the paradigm shift fromfuel powered combustion engines to alternative energysources (e.g. fuel cells, solar cells, and batteries) invehicles like motorbikes, cars, trucks, boats, planes. Thedesign of these high performance, low cost and cleanpropulsion systems has stipulated an international coop-eration of multiple disciplines such as physics, math-ematics, electrical engineering, mechanical engineeringand specialisms like control engineering and safety. Bycooperation of these disciplines in a structured way, theADEPT program provides a virtual research lab com-munity from labs of European universities and industries[59].

REFERENCES

[1] C. C. Chan, “The State of the Art of Electric, Hybrid, and FuelCell Vehicles,” Proceedings of the IEEE, vol. 95, no. 4, pp.704–718, April 2007.

[2] J. Everts, “Modeling and Optimization of Bidirectional DualActive Bridge AC–DC Converter Topologies,” Ph.D. disserta-tion, University of Leuven (KU Leuven), Leuven, Belgium,2014.

[3] A. Emadi, K. Rajashekara, S. S. Williamson, and S. M. Lukic,“Topological Overview of Hybrid Electric and Fuel Cell Ve-hicular Power System Architectures and Configurations,” IEEETransactions on Vehicular Technology, vol. 54, no. 3, pp. 763–770, May 2005.

[4] IEC 61851-1, “Electric Vehicle Conductive Charging System –Part 1: General Requirements.” IEC, International Electrotech-nical Commission, Geneva, Switzerland, 2001.

[5] S. Haghbin, S. Lundmark, M. Alakula, and O. Carlson, “Grid-Connected Integrated Battery Chargers in Vehicle Applications:Review and New Solution,” IEEE Transactions on IndustrialElectronics, vol. 60, no. 2, pp. 459–473, Feb. 2013.

[6] S. Luyten, N. Leemput, F. Geth, J. Van Roy, J. Buscher, andJ. Driesen, “Standardization of Conductive AC Charging Infras-tructure for Electric Vehicles,” in 22nd International Conferenceon Electricity Distribution (CIRED 2013), June 2013, Paper0476.

[7] A. Mathoy (BRUSA Elektronic). (2008) Definition andImplementation of a Global EV Charging Infrastructure (Lastaccessed: 23/07/2013). [Online]. Available: http://www.park-charge.ch/documents/EV-infrastructure%20project.pdf

[8] M. G. Egan, D. L. O’Sullivan, J. G. Hayes, M. J. Willers, andC. P. Henze, “Power-Factor-Corrected Single-Stage InductiveCharger for Electric Vehicle Batteries,” IEEE Transactions onIndustrial Electronics, vol. 54, no. 2, pp. 1217–1226, April2007.

[9] J. Rocabert, A. Luna, F. Blaabjerg, and P. Rodriguez, “Controlof Power Converters in AC Microgrids,” IEEE Transactions onPower Electronics, vol. 27, no. 11, pp. 4734–4749, Nov. 2012.

[10] Li, Y W and Kao, C.-N., “An Accurate Power Control Strategyfor Power-Electronics-Interfaced Distributed Generation UnitsOperating in a Low-Voltage Multibus Microgrid,” IEEE Trans-actions on Power Electronics, vol. 24, no. 12, pp. 2977–2988,Dec. 2009.

[11] IEC 61000-3-2, “Electromagnetic Compatibility (EMC) – Part3-2: Limits for Harmonic Current Emissions (Equipment InputCurrent 6 16 A per Phase).” IEC, International Electrotech-nical Commission, Geneva, Switzerland, 1995.

[12] IEC 61000-3-4, “Electromagnetic compatibility (EMC) – Part3-4: Limitation of Emission of Harmonic Currents in Low-Voltage Power Supply Systems for Equipment with RatedCurrent Greater than 16 A.” IEC, International ElectrotechnicalCommission, Geneva, Switzerland, 1998.

[13] “IEEE Draft Guide for Applying Harmonic Limits on PowerSystems,” IEEE P519.1/D12, pp. 1–124, July 2012.

[14] M. L. Heldwein, “EMC Filtering of Three-Phase PWM Con-verters,” Ph.D. dissertation, Swiss Federal Institute of Technol-ogy (ETH Zurich), Power Electronic Systems (PES) Laboratory,Zurich, Switzerland, 2008.

[15] C.I.S.P.R., “Specification for Industrial, Scientific and Medical(ISM) Radio-Frequency Equipment - Electromagnetic Distur-bance Characteristics - Limits and Methods of Measurement– Publication 11.” IEC, International Special Committee onRadio Interference, Geneva, Switzerland, 2004.

[16] ——, “Limits and Methods of Measurement of Radio Distur-bance Characteristics of Information Technology Equipment–Publication 22.” IEC, International Special Committee onRadio Interference, Geneva, Switzerland, 1993.

[17] T. Nussbaumer, M. L. Heldwein, and J. W. Kolar, “DifferentialMode Input Filter Design for a Three-Phase Buck-Type PWMRectifier Based on Modeling of the EMC Test Receiver,” IEEETransactions on Industrial Electronics, vol. 53, no. 5, pp. 1649–1661, Oct. 2006.

[18] J. W. Kolar, F. Krismer, Y. Lobsiger, J. Muhlethaler, T. Nuss-baumer, and J. Minibock, “Extreme Efficiency Power Elec-tronics,” in 7th International Conference on Integrated PowerElectronics Systems (CIPS 2012), March 2012, pp. 1–22.

[19] J. W. Kolar, J. Biela, S. Waffler, T. Friedli, and U. Badstueb-ner, “Performance Trends and Limitations of Power ElectronicSystems,” in 6th International Conference on Integrated PowerElectronics Systems (CIPS 2010), March 2010, pp. 1–20.

[20] Y. Song and B. Wang, “Survey on Reliability of PowerElectronic Systems,” IEEE Transactions on Power Electronics,vol. 28, no. 1, pp. 591–604, Jan. 2013.

[21] G. Kelner, M. S. Shur, S. Binari, K. J. Sleger, and H. S.Kong, “High-Transconductance β–SiC Buried-Gate JFETs,”IEEE Transactions on Electron Devices, vol. 36, no. 6, pp.1045–1049, June 1989.

[22] J. Rabkowski, D. Peftitsis, and H. P. Nee, “Silicon CarbidePower Transistors: A New Era in Power Electronics is Initiated,”IEEE Industrial Electronics Magazine, vol. 6, no. 2, pp. 17–26,June 2012.

[23] J. Everts, J. Das, J. Van den Keybus, M. Germain, andJ. Driesen, “GaN-Based Power Transistors for Future PowerElectronic Converters,” in Proceedings of the IEEE BeneluxYoung Researchers Symposium on Smart Sustainable PowerDelivery (YRS 2010), March 2010.

[24] J. Rabkowski, D. Peftitsis, and H. P. Nee, “Silicon CarbidePower Transistors: A New Era in Power Electronics is Initiated,”IEEE Industrial Electronics Magazine, vol. 6, no. 2, pp. 17–26,June 2012.

[25] J. Millan and P. Godignon, “Wide Band Gap Power Semi-conductor Devices,” in IEEE Spanish Conference on ElectronDevices (CDE 2013), Feb. 2013, pp. 293–296.

[26] L. F. Eastman and U. K. Mishra, “The Toughest Transistor Yet[GaN Transistors],” IEEE Spectrum, vol. 39, no. 5, pp. 28–33,May 2002.

[27] P. G. Neudeck, R. S. Okojie, and L.-Y. Chen, “High-Temperature Electronics - a Role for Wide Bandgap Semicon-ductors?” Proceedings of the IEEE, vol. 90, no. 6, pp. 1065–1076, June 2002.

[28] J. S. Glaser, J. J. Nasadoski, P. A. Losee, A. S. Kashyap,K. S. Matocha, J. L. Garrett, and L. D. Stevanovic, “DirectComparison of Silicon and Silicon Carbide Power Transistorsin High-Frequency Hard-Switched Applications,” in IEEE 26thAnnual Applied Power Electronics Conference and Exposition(APEC 2011), March 2011, pp. 1049–1056.

[29] J. Biela, M. Schweizer, S. Waffler, and J. W. Kolar, “SiC versusSi – Evaluation of Potentials for Performance Improvementof Inverter and DC–DC Converter Systems by SiC PowerSemiconductors,” IEEE Transactions on Industrial Electronics,vol. 58, no. 7, pp. 2872–2882, July 2011.

[30] J. Rabkowski, D. Peftitsis, and H. P. Nee, “Design Steps Towarda 40-kVA SiC JFET Inverter With Natural-Convection Coolingand an Efficiency Exceeding 99.5%,” IEEE Transactions onIndustry Applications, vol. 49, no. 4, pp. 1589–1598, July 2013.

[31] M. Bertoluzzo, N. Zabihi, and G. Buja, “Overview on BatteryChargers for Plug-In Electric Vehicles,” in IEEE 15th Inter-national Power Electronics and Motion Control Conference(EPE/PEMC 2012), Sept. 2012, pp. LS4d.1–1 – LS4d.1–7.

[32] M. Yilmaz and P. T. Krein, “Review of Battery Charger Topolo-gies, Charging Power Levels, and Infrastructure for Plug-InElectric and Hybrid Vehicles,” IEEE Transactions on PowerElectronics, vol. 28, no. 5, pp. 2151–2169, May 2013.

[33] B. Singh, B. N. Singh, A. Chandra, K. Al-Haddad, A. Pandey,and D. P. Kothari, “A Review of Single-Phase Improved Power

Quality AC-DC Converters,” IEEE Transactions on IndustrialElectronics, vol. 50, no. 5, pp. 962–981, Oct. 2003.

[34] J. P. M. Figueiredo, F. L. Tofoli, and B. L. A. Silva, “A Reviewof Single-Phase PFC Topologies Based on the Boost Converter,”in IEEE/IAS 9th International Conference on Industry Applica-tions (INDUSCON 2010), Nov. 2010, pp. 1–6.

[35] C. Marxgut, J. Biela, and J. W. Kolar, “Interleaved TriangularCurrent Mode (TCM) Resonant Transition, Single Phase PFCRectifier with High Efficiency and High Power Density,” inInternational Power Electronics Conference (IPEC 2010), June2010, pp. 1725–1732.

[36] C. Marxgut, F. Krismer, D. Bortis, and J. W. Kolar, “UltraflatInterleaved Triangular Current Mode (TCM) Single-Phase PFCRectifier,” IEEE Transactions on Power Electronics, vol. 29,no. 2, pp. 873–882, Feb. 2014.

[37] J. Moia, J. Lago, A. J. Perin, and M. L. Heldwein, “Compar-ison of Three-Phase PWM Rectifiers to Interface AC Gridsand Bipolar DC Active Distribution Networks,” in IEEE 3rdInternational Symposium on Power Electronics for DistributedGeneration Systems (PEDG 2012), June 2012, pp. 221–228.

[38] M. F. Vancu, T. Soeiro, J. Muhlethaler, J. W. Kolar, andD. Aggeler, “Comparative Evaluation of Bidirectional Buck-Type PFC Converter Systems for Interfacing Residential DCDistribution Systems to the Smart Grid,” in IEEE 38th AnnualConference on Industrial Electronics Society (IECON 2012),Oct. 2012, pp. 5153–5160.

[39] T. B. Soeiro, T. Friedli, and J. W. Kolar, “SWISS Rectifier– A Novel Three-Phase Buck-Type PFC Topology for ElectricVehicle Battery Charging,” in IEEE 27th Annual Applied PowerElectronics Conference and Exposition (APEC 2012), Feb.2012, pp. 2617–2624.

[40] R. L. Steigerwald, “A Comparison of Half-Bridge ResonantConverter Topologies,” IEEE Transactions on Power Electron-ics, vol. 3, no. 2, pp. 174–182, April 1988.

[41] R. L. Steigerwald, R. W. De Doncker, and M. H. Kheraluwala,“A Comparison of High-Power DC–DC Soft-Switched Con-verter Topologies,” IEEE Transactions on Industry Applications,vol. 32, no. 5, pp. 1139–1145, Sept.-Oct. 1996.

[42] F. Krismer, J. Biela, and J. W. Kolar, “A Comparative Evalu-ation of Isolated Bi-directional DC/DC Converters with WideInput and Output Voltage Range,” in 40th Industry ApplicationsConference Annual Meeting (IAS 2005).

[43] A. Mehdipour and S. Farhangi, “Comparison of Three IsolatedBi-Directional DC/DC Converter Topologies for a BackupPhotovoltaic Application,” in 2nd International Conference onElectric Power and Energy Conversion Systems (EPECS 2011),Nov. 2011, pp. 1–5.

[44] N. M. L. Tan, T. Abe, and H. Akagi, “Topology and Applicationof Bidirectional Isolated DC–DC Converters,” in IEEE 8thInternational Conference on Power Electronics and ECCE Asia(ICPE 2011 - ECCE Asia), May 2011, pp. 1039–1046.

[45] S. Cuk, “True Bridgeless PFC Converter Achieves Over 98%Efficiency, 0.999 Power Factor,” Power Electronics TechnologyMagazine, Part 1: pp. 10–18, July 2010; Part 2: pp. 34–40, Aug.2010; Part 3: pp. 22–31, Oct. 2010.

[46] K. Vangen, T. Melaa, S. Bergsmark, and R. Nilsen, “EfficientHigh-Frequency Soft-Switched Power Converter with SignalProcessor Control,” in IEEE 13th International Telecommuni-cations Energy Conference (INTELEC 1991), Nov. 1991, pp.631–639.

[47] M. H. Kheraluwala and R. W. De Doncker, “Single Phase UnityPower Factor Control for Dual Active Bridge Converter,” in

IEEE Industry Applications Society Annual Meeting, vol. 2, Oct.1993, pp. 909–916.

[48] J. Everts, J. Van den Keybus, and J. Driesen, “SwitchingControl Strategy to Extend the ZVS Operating Range of a DualActive Bridge AC/DC Converter,” in IEEE Energy ConversionCongress and Exposition (ECCE 2011), Sept. 2011, pp. 4107–4114.

[49] J. Everts, J. Van den Keybus, F. Krismer, J. Driesen, and J. W.Kolar, “Switching Control Strategy for Full ZVS Soft-SwitchingOperation of a Dual Active Bridge AC/DC Converter,” inIEEE 27th Annual Applied Power Electronics Conference andExposition (APEC 2012), Feb. 2012, pp. 1048–1055.

[50] F. Jauch and J. Biela, “Single-Phase Single-Stage BidirectionalIsolated ZVS AC-DC Converter with PFC,” in 15th Inter-national Power Electronics and Motion Control Conference(EPE/PEMC 2012), Sept. 2012, pp. LS5d.1–1–LS5d.1–8.

[51] J. Everts, F. Krismer, J. Van den Keybus, J. Driesen, and J. W.Kolar, “Charge-Based ZVS Soft Switching Analysis of a Single-Stage Dual Active Bridge AC-DC Converter,” in IEEE EnergyConversion Congress and Exposition (ECCE 2013), Sept. 2013,pp. 4820–4829.

[52] N. D. Weise, K. Basu, G. Castelino, and N. Mohan, “ASingle-Stage Dual Active Bridge Based Soft Switched AC–DCConverter with Open-Loop Power Factor Correction and OtherAdvanced Features,” IEEE Transactions on Power Electronics,vol. 29, no. 8, pp. 4007–4016, Aug. 2014.

[53] J. Everts, F. Krismer, J. Van den Keybus, J. Driesen, and J. W.Kolar, “Optimal ZVS Modulation of Single-Phase Single-StageBidirectional DAB AC–DC Converters,” IEEE Transactions onPower Electronics, vol. 29, no. 8, pp. 3954–3970, Aug. 2014.

[54] S. Norrga, “A Soft-Switched Bi-Directional Isolated AC/DCConverter for AC-Fed Railway Propulsion Applications,” inInternational Conference on Power Electronics, Machines andDrives (PEMD 2002), June 2002, pp. 433–438.

[55] ——, “Experimental Study of a Soft-Switched Isolated Bidi-rectional AC-DC Converter Without Auxiliary Circuit,” IEEETransactions on Power Electronics, vol. 21, no. 6, pp. 1580–1587, Nov. 2006.

[56] N. D. Weise, K. Basu, and N. Mohan, “Advanced ModulationStrategy for a Three-Phase AC–DC Dual Active Bridge forV2G,” in IEEE Vehicle Power and Propulsion Conference(VPPC 2011), Sept. 2011, pp. 1–6.

[57] S. Norrga, S. Meier, and S. Ostlund, “A Three-Phase Soft-Switched Isolated AC–DC Converter Without Auxiliary Cir-cuit,” IEEE Transactions on Industry Applications, vol. 44,no. 3, pp. 836–844, May 2008.

[58] F. Jauch and J. Biela, “Modelling and ZVS Control of anIsolated Three-Phase Bidirectional AC-DC Converter,” in IEEE15th European Conference on Power Electronics and Applica-tions (EPE 2013), Sept. 2013, pp. 1–11.

[59] A. Stefanskyi, A. Dziechciarz, F. Chauvicourt, G. E.Sfakianakis, K. Ramakrishnan, K. Niyomsatian, M. Curti,N. Djukic, P. Romanazzi, S. Ayat, S. Wiedemann, W. Peng,and S. Stipetic, “Researchers within the EU funded Marie CurieITN project ADEPT, grant number 607361,” , 2013-2017.