review on power converters for electric vehicles

Review on Power Converters for Electric

Vehicles 1Kondreddy Sreekanth Reddy, Research Scholar, IEEE Member

Centre for Research in Power Electronics

Presidency University, Bengaluru, Karnataka, India

2Dr. Sreenivasappa B. V, Associate Professor, IEEE Member

Centre for Research in Power Electronics

Presidency University, Bengaluru, Karnataka, India

Abstract

The utmost protuberant concern in the Electric Vehicles (EVs) primarily is the process by which the charging of the

batteries should be done and secondly the growing appeal of power required due to the quick demand of electric power

necessitated by EVs, Hybrid Electric Vehicles (HEVs) and Plug-in Hybrid Electric Vehicles (PHEVs). There has been a

detailed, critical evaluation of converters that are being used for the charging modules of electric vehicles. This paper has

enlisted seventeen power converters that are being used within the charging modules of electric vehicles in terms of their

features, performance parameters, advantages, disadvantages, circuit complexities and cost. Further it has been illustrated

that owing to the simplicity of structure and operational mode, electric vehicles are much more efficient than HEV and

PEV. Amongst these seventeen converters, the use of four converters namely Half Bridge LLC (HBLLC), Full Bridge LLC

resonant converter (FBLLC), EF2 converter and Full Bridge (FB) converters are gaining popularity. This is due to the fact

that these converters have an increased factor of efficiency and improved performance. Therefore a fair conclusion states

that the use of FB LLC resonant converter best suited for the charging modules of electric vehicle applications.

Keywords— Electric vehicle, Bridge converter, Bidirectional converter, Resonant Converter.

I. INTRODUCTION

Electric vehicles are being slowly infused in the transportation world owing to its significant positive impact on the

environment. However, the numbers of EVs are quite less even though a lot of them are being manufactured [50].

Most EVs use incumbent form of Lithium ion batteries [13]. Although with electric vehicles and plug in along with

hybrid vehicles are best suited in terms of fuel consumption, these have not been adopted widely. The primary reasons

for not adopting these vehicles are that they affect the power factor of the grid that they are connected, battery life, cost

and charger complications. Another problem with PHEV in relation to standard fuel station is the lack of proper and

appropriate charging infrastructure and lack of policy supporting, storage options for the energy required to power

these vehicles [26]. Considering Hybrid vehicles as opposed to normal EV’s, use of lithium ion batteries that are

faster than the ones used in EV’s and are therefore less efficient[59]. Apart from the state of the batteries, plug in

electric vehicles along with Hybrid vehicles have many other disadvantages when compared to EVs. For instance, the

efficiency of fuel consumption of HEV is quite low as compared to an EV [44]. The power converters commonly used

for powering these vehicles are “bi directional AC to DC converters and DC-to-DC converters” of the same origin.

“Full bridge resonant converters” are also being widely used these days to power up few of these electric vehicles.

Hybrid vehicles are being powered with hybrid storage systems for their energy that is in turn increasing the cost of

these vehicles [65]. Most HEVs have rendered normal covered based charger systems to be inefficient and therefore

battery chargers that are based on dual active bridges are being used [68]. In the case of HEVs, the economy of fuel

is distributed by 11% in urban cycles, while 6% in highway cycles [30]. Considering PEVs, the availability of charging

portals are scarce and since the technology is new, charging portals are scarce. Further, PEV do not use standard

topology as bi directional converters, the converters are generally unidirectional bridge rectifiers. Therefore, the

conclusion based on the evidence gathered is that EV’s are more efficient in nature than any HEV or PHEV [18],

because of zero emission, high efficiency, less sound, harmless, smooth action and independency of petroleum fuels.

The key advantage of EV being during the process of braking, in this case, the electric motor functions similar to a

generator and thereby the battery is recharged as the kinetic energy is being totally converted to potential energy [12].

This research has evaluated on various converter topologies that are used within the charging unit of an electric vehicle.

This paper enables the researcher to learn about the various mechanisms that are present within the converters that

operates the charging module. Further, in spite of research being conducted on wireless power transfer system

followed by fast charging, this research has provided valuable insight on the power converter topology that is ideal.

Journal of Xi'an University of Architecture & Technology

Volume XII, Issue VIII, 2020

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Apart from the advancement in technology, charge supply from the power source and its related sustainability is

another cause for concern. Therefore, in this research, the power converter topology deemed ideal would also aid in

the factor of sustainability.

General configuration of an EV charging system:

The EV battery chargers are usually designed based on the basic DC of the AC power converters that must be highly

powerful and effective. Usually, DC-DC converters are Buck / Boost or switch-mode converters, with AC DC

converters based on unregulated or regulated rectifiers. Normally DC-AC converters are based on single-phase H-

bridge inverters or three-legged inverters for a three-phase network.

Figure 1: General topology of EV charging panel [60]

Figure 1 shows the general EV charging unit configuration. The power converters used in figure 1 for each form, a

comprehensive discussions of different converters will be given (numbered from number 1 to number 6). The onboard

charger (level 1, 2) or off board charger may be used to charge EV batteries (level 3). As an on-board charger or

isolated outboard charger, EV battery charger can be built into a Car. The power flow may be unidirectional or

bidirectional between the EV batteries and the grid. Thanks to the simplicity and durability of their topologies and

function, the unidirectional power flow is implemented in all recent commercial on-board chargers [60]. It is possible

to control bidirectional chargers to pump the EV battery power into the grid. An EV battery can be considered as an

efficient distributed source with multiple operating modes with the bidirectional functionality. As shown in Fig. 1, AC

-DC converters and DC-DC converters are included in all on / off board loaders. Nevertheless, in each category of

chargers the topologies and the power rating of the converters vary completely.

II. POWER CONVERTERS

2.1 AC-DC Bi-directional converter

AC-DC bidirectional converters is common for electric vehicles since they provide efficient sinusoidal grid current to

these vehicles [29]. This equipment use power factor correctors, and are therefore efficient in nature. Pareto Front

analysis, that effectively assigns resources, is used in case of these converters to analyse the current output provided

to the motors [21].



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Figure 2: On board Bi-directional Converter block representation [18]

These converters commonly use Gallium nitride or Silicon carbide because of their wide range of band gap. However,

newer models as indicated in Figure 2, these converters use Super junction devices [4]. Lyapunov based function

utilising the modified predictive method for modelling is being prepared to modify the factor of efficiency of the AC-

DC converters [63]. Lyapunov functions are used to indicate the stability or the state of equilibrium. However, the

current efficiency in terms of converting the energy stored within a battery into electric current is greatly reduced.

These techniques for controlling a converter is based on either control that is voltage oriented or flux oriented [68].

Figure 3: Bi-directional AC-DC converter [2]

The flow of power in this converter occurs from the voltage bus of DC to voltage end of AC. Both EV’s and HEV’s

use bidirectional converters that are DC-DC, indicated in Figure 3. EVS and HEVs have multiple sources of energy

namely super capacitors along with batteries [2]. Therefore, these converters act as regulators that control the flow of

power from these multiple sources [37]. The critical aspect of these converters are dependent on limitation of core

materials and therefore core losses followed by the change in flux [68].

Figure 4: Block structure of energy managing source [42]

The block structure in Figure 4 depicts the bidirectional class E converter attached to the circuit that takes in the

voltage from the source and then optimises it according to the needs of the traction motor. This function ensures that

the motor is fed with a contain source of high frequency loss less power. [Refer to Appendix 1]

2.2 Full Bridge Converter (FB Converter)

A FB converter has an efficient energy storage scheme compared to “bi-directional DC-DC converter”, further it is

also a source of uninterrupted supply of power. This converter has three operational stages, namely the inverter

(conversion from DC to AC), followed by a high frequency transformer (HFT) (step up the AC voltage) and followed

by a rectifier (conversion of the AC back to DC) as shown in Figure 5. Using the negative component of the hysteresis

loop cuts the core concentration as the current flows in the opposite direction during alternating half-cycles, turning

the core flux from negative to positive. The PWM signal's service cycle can be increased or decreased promptly so

that even with increasing input origin voltage, the output voltage is kept constant. Nonetheless, to secure

semiconductor switches, the task ratio must be kept above 50%.Hence, identical control signals are used in two legs,

which alternate with half period duration. As an HFT is used, a high step-up voltage is possible. Moreover, it provides



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galvanic isolation between the input side and the load side. At 30 kW load, the efficiency of the converter is

approximately 91.5% [45].

Figure 5: Configuration of Full Bridge Converter [18]

Considering a light electric vehicle, the lithium ion battery could be used for fast charging the electric vehicle through

the implementation of a FB converter. The primary reason for choosing this converter is that there is a low value of

loss due to switching and an increased value of efficiency. The output can be further improved by using the ZVS

technique and the PWM (Phase Shifted Pulse Width Modulation) command. Since this is a current fed topology, the

suppression of EMI filters is necessary to comply with IEEE standards-519[51]. Although this converter has

moderately high efficiency, due to the high electrical pressure in the switching circuit, the impact of HFT leakage

inductance is crucial. In order to solve the problem of peak voltage in the switching circuit, a clamping circuit is

needed.Since electric vehicles are gradually taking up wireless topologies for their charging unit, resonant topologies

are being used more and more. This is because there is precise impedance provided by these resonant topologies that

match the Rx aligning with the Tx couple. The Tx and Rx coils are aligned arbitrarily within the circuit [24].

2.3 Multi-port converter

Multi-port Multi cell converters, commonly known as MPMC converters are used in electric vehicles as it can provide

a constant non-fluctuating power density.

Figure 6: Topology of MPMC converter [41]

Owing to the lack of space for mounting the charging module on the vehicles, a high level of integration is required

[34]. These MPMC converters are used two independent ports and therefore provide high integration to the distribution

network as shown in Figure 6. Multiple sub converters are used as indicated in the topology, each of the sub converter



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processes the same share of the power distributed on all the converters. These converters provide a myriad of features

namely; it has the capability to handle huge output currents within the low voltage bus [41]. Apart from that, the High

voltage bus port has the capability to ensure bidirectional flow of power. As indicated in the Figure 6, during the

charging stage, the HV DC-DC converter is operational in an isolated state while the “DC-DC step down converter”

remains idle. Thus after the charging phase when the driving phase is resumed, the step down converter feeds power

to the low voltage bus [41]. The step down converter transfers power from the bus of high voltage to the low voltage

bus without affecting the converter of high voltage.

Figure 7: Waveform of MPMC converter [41]

The three rectangular waveforms are generated in Figure 7 by the three full bridge converters. The corresponding

winding is directly supplied with these respective waveforms. The transfer of power between multiple ports can be

done through adjusting the respective duty cycles, in this case Da, Db, Dc. Apart from the three duty cycles; three

phase shifts also need to be adjusted within the respective rectangular waveforms. The topology has a significant

drawback, as the high impedance that is generated from the series inductance [44]. The impedance obtained from the

leakage inductors are quite low compared to the series inductance and are therefore neglected. However, the series

inductance impedance lowers the efficiency of these converters.

2.4 Unidirectional Converter

The primary advantage that enforces the selection of unidirectional converters as opposed to bidirectional converters

for electric vehicles over bidirectional converters is the latter provides inadequate conversion ratios.

Figure 8: Unidirectional converter topology A. Interleaved B. Multilevel [16]

Unidirectional quadratic converters provide high voltage gains in either step up or step down operations [56]. The

control technique for a unidirectional converter banks on simplicity since only one semiconductor needs to be



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controlled during the phase of “step up or step down”. A unidirectional converter can also be modified through

replacing the diodes within the circuit with switches.

The operation of a unidirectional converter is generally in a buck mode and the energy available from the source is

transferred to the storage device [16]. Therefore, considering the energy transfer, the voltage obtained from output is

modified by a single transistor through switching the duty cycles. During the buck mode of operation, S1 is the switch

that is kept active and therefore it controls the power transfer from the high voltage to low voltage side. In this phase,

the switch S2 is kept off [16]. Similarly, in the boost mode, S2 is kept on and it controls the power transfer while S1

is kept off as depicted in the second figure in Figure 8. Passive filter is used in a unidirectional buck converter to

receive sinusoidal input current waveform, but it renders the circuit voluminous, and with a diode bridge rectifier, the

power factor will be small and harmonic current will be pumped into the source, making the system unsafe. In this

topology, current wave shaping technique is proposed [49] to achieve unit power factor, dc voltage regulated. The

single phase unidirectional high power input voltage and output voltages are shown in Figure 9. The input voltage is

boosted to 400V by 230 V. In this case, although the ripple content is comparatively low while the power factor has

a high rating, the switching losses are not up to the expected standard. The voltage gain is also not up to the standard

and this causes a decrease in efficiency.

Figure 9: Input output waveforms from a unidirectional buck converter [49]

The output voltage characteristics of the circuit with a coupled inductor are used as shown in Figure 10. At step down

phase, the terminal voltage of 230V is stepped down to 169 V [49]. However, ZVS full bridge converters provide a

better voltage gain when compared to the unidirectional converters [55].

Figure 10: Waveforms with coupled inductor [49]



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2.5 ZVS Converter

The topology of the ZVS converter indicates that the full bridge converter is considered the primary circuit of the

transformer like the resonant and FB LLC converter [78]. The power devices such as MOSFET or IGBT are denoted

through M1 to M4. D1 to D6 are considered the parasitic diodes of the respective power converter devices as shown

in Figure 11. Apart from the diodes and the power devices, a parasitic capacitor along with a resonant inductor is also

used within the topology.

Figure 11: ZVS converter topology [78]

When compared to an isolated bidirectional converter, the voltage supplied to a ZVS converter is the voltage obtained

from the DC bus [30]. The maximum voltage obtained from the switch was equal to the circuit of the half bridge

converter and this operation happened while keeping the power level static.

Figure 12: Efficiency curve obtained from ZVS converter [78]

Zero volt switching is not achieved by alternating lagging current and therefore the generated output has a rating

higher than 40A. Therefore, in current with an alternating lagging nature, the efficiency of these converters is estimated

to be around 90 % depicted in Figure 12 [44]. However, with an input rating of 160 V with an output situation being

around 50A efficiency is estimated to be around 92.5%. Therefore, it is evident that ZVS converters produce a less

amount of output voltage, in comparison to full bridge resonant converter [78]. The latter has an efficacy rating of

95.05 to 95.5% which can be further boosted to 97.5 %.



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2.6 Zeta Converter:

Zeta converter is a non-inverted buck-boost converter for the fourth order. Zeta converter as shown in Figure 13. One

is a switch (S1), a diode (D1), two inductors (L1 and L2), two condensers (C1 and C2) and a load (R). The zeta

converter will operate two modes; on and off modes. The on-mode happens when S1 is switched on and D1 is turned

off, while the off-mode occurs when S1 and D1 are turned off. It operates as a standard buck-

boost, but with an uninverted polarity of output voltage. Zeta converter has many advantages, simple design, small

settling time, low switching pressure and high-frequency transformers can be connected to it.

Figure 13: Topology of a Zeta converter [39]

2.7 Z-Source Converter

The topology of a Z-Source converter is achieved through the implementation of LC networks within traditional

converters using half bridges. The Z-Source converter can produce both asymmetric and symmetric voltages with

varying amplitude that is produced during the negative along with the positive half cycles [13]. The duty cycle needs

to be varied to obtain the optimum value of duty cycles thereby achieving the characteristics of a traditional half bridge

converter. However, the added benefit of this converter over traditional half bridge converters is that at output it can

produce zero voltage. Thus, it is clear from the topology in Figure 14, four capacitors are used in parallel with two

voltage sources and two switches.

Figure 14: Topology of a traditional Z-source converter [7]



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(a) (b)

Figure 15: Current and Voltage Waveform of switch (a) During turn on (b) During turn off [7]

In an operating mode switches S1 and S2 are turned off, therefore, the sum of D1 and D2 is less than equal to 1 in this

stage [48]. “Thus, during this operation the circuit would not be able to operate under ST state as depicted in Figure

15. There are three states, first when S1 and Dn are turned on while S2 and Dp are turned off [7]. This step is followed

by turning on S2 and Dp while turning off S1 and Dn.”

2.8 EF2 Converter

Electric vehicles are being fitted with wireless power sources and therefore EF2 inverters are used. The EF2 inverters

are mostly multi resonant and modified voltage fed, the modification is in the section of an inductor [35]. The

traditional EF2 inverters use a choke inductor with an infinite input; however, a modified EF2 inverter uses resonant

inductor [35]. These resonant inductors and the EF2 converter works within a frequency range of 85 to 100 kHz. Zero

voltage switching is maintained by the converter during the period of load changing [62]. The primary advantage of

these converters is that it contains all the inherent positive aspect of the E class converters. The efficiency of class E

converter can be improved by adding a resonant circuit either in series or in parallel with load network, due to which

the voltage and current stress can also be reduced. The way a resonant network is connected to the charging network

is called an EFn converter which is depicted in Figure 16. The ‘n’ subscript refers to an integer number greater than or

equal to 2 and is the ratio of the resonant frequency of the added resonant network to the inverter switching frequency.

Figure 16: EF2 Converter [35]

However, the primary issue faced by these converters is that it faces efficiency issues with the feature of load

independence [62]. The load independence issue becomes a cause for concern when the distance that exists between

the coils is subject to a rapid change within the charging system [5]. The EF2 converters use the feature of soft



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switching thereby eradicating the possibility of switching loss. However, the load-changing feature decreases the total

efficiency of these converters by 5 % to 6 % [29].At perfect condition of alignments; the converters produce a net

efficiency of 90 %.

2.9 FBLLC Converter

Full bridge LLC converters are used for application that requires a wide margin of frequency input as opposed to HB

LLC converters, and therefore these are used in Electric vehicles [24]. The FB LLC converters are used for the wireless

charging modules since these are small and can operate for a wide frequency range [80]. Further, there is an increased

reduction in switching losses.

Figure 17: Topology of a FBLLC resonant converter [24]

The primary topology of these converters as shown in Figure 17 consists of diodes that act as secondary rectifiers

along with primary switches. The voltage gain is not dependent on the quality factor of the respective outcome [18].

The magnetizing inductor being used within the topology alongside the diodes has little to no impact on the gain in

the voltage as shown in Figure 18.

Figure 18: Waveforms obtained from FB LLC converters [51]

The D within the waveforms indicates the duty ratio and in this scenario it is 0.05. The duty cycle estimated for

switches Q3 and Q4 is 50 % while that in Q5 and Q6 is 100% [51]. When the voltage input is varied between any

ranges extending from Vmin to Vmax, then the duty cycle changes for Q3 to Q6. For Q3 and Q4 it lies between the

range of 0 to 50%, while for Q4 and Q6 it lies within 50 % to 100 % [14]. Multiple inductor ratios can be obtained by

plotting the phase angle against duty cycle; these curves provide the inductor ratios.



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2.10 HBLLC Converter

In power supply designs and their applications greater efficiency, higher power density and higher element density

have become popular. Resonant energy converters–particularly those with LLC half-bridges–have been renewed due

to this trend and to their ability to achieve both higher change-over frequencies and lower switching losses. But there

are many obstacles to designing these converters, including the fact that the LLC resonant half-bridge transformer

conducts energy conversion with frequency modulation, instead of pulse-width modulation, which requires a different

design approach. An LLC half bridge resonant converter explains a standard isolated converter [24]; how it operates,

how it models the circuit, and what is known as the voltage-gain mechanism between the input and the output voltages.

shown in Figure 19.The HB LLC converters are used to make fast charger by fitting it with super capacitors and Li

ion batteries [29]. A fast charger with an 800 Wh Li ion battery along with a super capacitor of 50 Wh using a HB

LLC converter has an increased efficiency of 96.4% [10]. However, the major drawback of HB LLC converters is that

it increases the weighting of the charging unit.

Figure 19: Half bridge LLC resonant converter for a fast charging system [32]

Figure 20 displays a typical waveform of the LLC resonant converter. Between the two successive switching

transitions, a slight delay is added. Together with the resonant current iLr, the magnetizing current iLm starts to increase.

Figure 20: Resonant converter operational waveform [32]

If the LLC converter is operating at resonant frequency, as shown in Figure 20, ID01 is set to zero after Q1 is switched

off [32]. A traditional charging unit weighs less than 100 kg, but the HB LLC powered charging unit weighs 110 to

115 kg [18]. Therefore, it is evident that the total weight of the charging panel increases by 10 % to 15 %.The algorithm

that controls the converter has two sub algorithms [29], namely the CC and the CV mode are shown in Figure 21. The

CC or the controlling current mode algorithm for the current input while the CV or the controlling voltage model alters

the voltage output is used for this converter.



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Figure 21: Charging overlay of the CC and the CV mode [24]

2.11 Bi-directional Multi input Power Converters.

The power converter topologies used in Hybrid Energy Storage System HEES can be categorized in two main sets,

namely, isolated and non-isolated. A transformer is a galvanic insulation between sources and output is given in

isolated HEES systems topologies. In terms of design and function, non-isolated power converters are much simpler

than isolated power converters [3]. One of the easiest way to build a non-isolated HESS is through two-way DC-DC

Converter to connect some sources directly to dc bus as shown in Figure 22.Taking into consideration the non-isolated

DC-DC converters into account, these converters are that it allows active sharing and thereby controls the energy

storage systems power [28]. The non-isolated hybrid energy storage systems are connected to a few of the sources

directly and thus link the other components to the dc bus video converters [3]. These non-isolated DC-DC converters

possess the characteristics of ideal storage, since it contains long life cycles along with high density of power.

Figure 22: Topology of non-isolated DC-DC converter [3]

If the input frequency supplied is 20 kHz and there are two input sources connected to the converters then the

waveforms during the charging mode in Figure 23.a. and the efficiency of the proposed converter is above 93 percent

in both modes under the entire power range as shown in Figure 23.b.

(a) (b) Figure 23: (a) Waveform achieved in the charging mode (b) Efficiency [3]



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2.12 Buck Boost converter

A buck boost power converter for an electric vehicle is implemented through a SiC based MOSFET shown in Figure

24, this converter exhibits a 22 kW/L gravimetric density of power. It uses both the topologies of buck and boost

separately, in series. This power density is volumetrically obtained for the vehicle power train and the gravimetric

power density is found to be 20 kW/g. The architecture of the composite converter is composed of a buck boost bridge

that is partially powered. Apart from the buck boost converter, a bridge model of a dual active bridge is also used. The

experience has resulted in few observations namely a 60% reduction in average CAFE losses [6]. The power density

has risen astronomically by a margin of 280%. The magnetic volume losses as seen for a traditional Si based IGBT

converter has reduced by 76%. However, these gains and reduction in losses are not just based on the designing of the

circuit, but there has been significant optimisation of a circuit.

Figure 24: Topology of the buck boost converter [25]

The optimisation was mainly done based on a comprehensive loss model including the optimisation of magnetic losses

as well as the switching losses of traditional Sic IGBT converter. The optimisation method was based on FEM method.

The average efficiency that was projected from using his converter in an electric vehicle as calculated to be 97.5%.

2.13 Boost Converter

Boost converters used for electric vehicles are implemented through using four interleaved DC-DC boost converters

placed parallel to each other as shown in Figure 25. The duty cycle displays the gate signals of the switching device

at d = 0.25 where the duty cycle is denoted by d [6]. The gate signals in this case are phase shifted and this phase shift

is represented by a fraction of the switching fraction and the number of phases along with the number of parallel

switches in each phase.

Figure 25: Topology of the interleaved boost converter [6]

“Both the frequencies of the output voltage and the input current are n times increased than the original frequency of

switching.” This topology is helpful when the loading conditions of an electric vehicle are varied greatly. Further, the

efficiency is greatly increased when there is a steep load step variation. The overshoot of the input current is calculated

to be a little over 5% and therefore it increases the efficiency of the overall circuit performance. The settling time is



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however increased by 25% and therefore this is a major drawback of this topology [6]. Nevertheless, the dynamic

responses of the converters are quite high.

2.14 Buck converter

A buck converter is sometimes used for electric vehicles, it possess a topology of multiple outputs. Compared to

unidirectional characteristics of a DC-DC converter, a bi directional converter of the same orientation has significantly

less losses related to its power. These converters employ three power switches and generally two low pass filters. The

switches are indicated as S1, S2 and S3 in Figure 26, while the filters are represented through L1-C1 and L2-C2 [1].

Figure 26: Buck converter topology of single input multiple output [1]

There are eight methods of operating this particular buck converter since there are three switches and two respective

states for each switch. The table below represents the topological states of the converter.

Table 1: Topological states of the converter [1]

This buck converter is designed in such a manner that it operated in a conduction mode that is continuous in its flow.

The output voltage of the converter controls the Voltages Vr1 and Vr2. using pulse width modulation on both the

generators, the output generated is of the order of logic 1. Apart from the general structure, a PI controller is also used;

the proportional integral controller is used to control the voltage output [12]. Thus by controlling the output voltage

obtained from the converter, the requisite amount of voltage is supplied to the vehicle.

2.15 Charge Pump Converter

Electric vehicles generally have a need of ratio of voltage conversion to be quite high and therefore need bi directional

flow of current from the converters. Therefore, a cascaded unregulated level converter is fitted with a two phase

interleaved buck boost charge pump converter to achieve a high ratio of voltage. The control circuit of the converter

is simple in nature and in the discharge state; it acts as a two-stage voltage doubler. This voltage doubler is beneficial

as it acts as an apt circuit to achieve a high conversion ratio of the step up voltage.

Figure 27: Cascaded topology of a charge pump converter [26]

The primary significance of the charge pump converter is that there is no need for any transformers or inductors since

this converter is capacitor based as depicted in figure 25. However there are certain drawbacks related to this topology,

they are namely; the complexity associated with the topology along with the high cost of building the circuit, the

topology is shown in Figure 27. The power level associated with the circuit is quite low and the pulsating current



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present in the input side is quite high [73]. Therefore, techniques of switch capacitors are used to get a suitable ratio

of voltage conversion and the conversion efficiency is greatly increased. The need of more power switches as well as

capacitors.

2.16 Luo Converter

A DC-DC Luo converter contains two inductors and two capacitors along with two inductors and a load resistance

and is quite similar to a bidirectional DC-DC converter. In Figure 28, the capacitors are denoted through C1 and C2

while the inductors are denoted by L1 and L2 [20]. The load resistance is denoted by R. However, it is to be noted that

the harmonics of a Luo converter is quite less when compared to a buck converter. A power switch is placed in series

with a freewheeling diode. There are two modes switch on and switch off.

Figure 28: Cascaded topology of a Luo converter [33]

When the switch is in an ON state, then the inductor L1 is charged with the help of the supply voltage and

simultaneously inductor L2 absorbs energy from C1. The capacitor C2 acts as the load during the ON state [33]. When

considering the OFF state, the current, which is drawn from the source, becomes zero and therefore the current voltage

curve is varied. The freewheeling diode acts as a charger for the capacitor. This topology is useful for obtaining a

stable output that has almost little to no ripple present.

2.17 Bi-directional DC-DC converter

A “bidirectional DC-DC converter” is placed between the inverter and the energy source of an electric vehicle. The

main purpose that this converter serves is that it serves is that it is used for conditioning various levels of voltage and

thereby provide a stable form of voltage from the DC bus [33]. Further, these “Bi-directional DC-DC converters”

allow operations that are based on vehicle to grid power transfers, therefore charging decks can use this converter.

DC-DC converters can be formed in two ways, firstly with the inductor in the middle of two bridges and it is named

CBB-IIM (cascaded buck boost inductor) as shown in Figure 29 (a). Secondly as shown in Figure 29 (b), there is a

buck boost capacitor that is placed in between the bridges and is in cascaded nature.

(a)

(b)

Figure 29: (a) IIM converter topology (b) CIM (Cascaded inductor) converter topology [20]



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Stability analysis of both these circuits was done by varying the input voltages between 100 V to 400 V; however the

loads were kept constant for altering voltage levels. Upon varying the load resistance from 1 ohm to 50 ohm, and

maintaining a constant output voltage rating of 300 V, the output power obtained varied in the range of 90 to 1.8 kW

[20]. Considering the mechanism of switching for these converters, both require a single switch to conduct buck or

boost operations. The second switch is to be kept at an ON state throughout the process for proper conduction of

current. Comparing the switching rates of the converters, components such as weight along with size and cost depend

on the election of switches. There are freewheeling diodes present within all these converters along with four switches

that support the configuration of “single input and single output”. Figure 30 contain the waveforms of the converters

in buck and boost mode, it is evident from the waveforms that the input voltage is greater than Vcm in boost mode.

Further, in buck mode, the Vcm is greater than the output voltages Vout1 and Vout 2. This is expressed though the

voltage in the switches and their respective inductors.

Figure 30: Waveform of the converters [20]

Another primary factor that results in DC-DC converters being chosen for EV is that the ability to apply interleaving

techniques on them. The technique of interleaving is applied in order to reduce stress of switching along with the

current and voltage rating of the switches within the topology [76]. Interleaving is also used for increasing the effective

frequency of switching; this property also allows the reduction of output voltage along with ripples in the current.

Since electric vehicles require multiple input sources along with multiple auxiliary outputs. The compressor belt that

was previously mechanical is replaced with an electrical unit to reduce emissions and thereby improve mileage [80].

For the DC-DC converters, in V2G mode of operation, the ultra-capacitor bank along with the battery pack act as the

multiple source of input. The external dc load is applied across the fourth capacitor and the output voltage. The

efficiency for these converters is 94.5% when the load is varied to 5.5kW.

III. COMPARISON

Therefore, comparing all the statistics from the table for these converters, it can be seen that the Buck, boost along

with the Buck boost converters are the cheapest form of converters. However, there are certain drawbacks when it

comes to these converters, firstly, buck and boost converters use MOSFETs along with IGBTs, therefore this increases

the cost of the converter leaving the efficiency at a mere value of 90 % [71]. Therefore, the additional cost not

justifying the low level of efficiency. Further, converters such as ZVS along with the resonant converters provide

phase shifting capabilities along with increased efficiency count, therefore these converters re not ideal for the electric

vehicles of today [73]. Further, these buck and boost converters do not allow the scope to implement fast charging or

wireless transfer of power. The price range provided within Table 2 indicates the price listing of the various converter

components. The price is indicated as a summation of various components such as MOSFTS, IGBT, diodes, inductors

and resistors.

The “Bi-directional AC-DC converter” works in grid to vehicle charging mode, therefore it takes up power from grids

and thereby transfers it to the electric vehicle. Further, it also conditions the input voltage along with the output current.

However, its major drawback when compared to the resonant converters is that it uses super junction devices and

therefore the efficiency is reduced. Further, these converters are designed based on Lyapunov function and therefore

the complexity is quite high. Apart from that the efficiency rating, ranges from 88 % to 92 %, which is quite

less compared to the resonant and buck boost converters [21]. Observing the table, out is observed that only the buck

boost converter can achieve an efficiency rating of 97.5 % [63]. Although this is the highest rated efficiency comparing

all the converters, it is only achieved through modifications. Further, buck boost converters use MOSFETS that are

SiC based and therefore, the overall cost of the converter increases and the modifications necessary to increase

efficiency and also increase the cost.



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Table 2: Comparison of the converters

Converters Constructional

features

Application List of

components Cost (￡) Design parameter

equations

Efficiency Advantages Drawbacks

Bi-directional

AC-DC converter

The filters are

used alongside the rectifier

circuit [2] [29]

Charging

module, V2G and G2V, conditions

output current

and input voltage [63] [68]

Emi filter,

output filter

420 to 460 𝑉𝑑𝑐 = 𝑉𝑑 − 𝑉𝑐

=4

𝜋∗ 𝑉 ∗ sin (𝜑 ∗

𝐷𝐶

2)

∗ 𝑒𝑗∗(𝜋2−𝜑∗𝐴𝐷−𝜑∗𝐷𝐶2)

K=𝐿𝑚1+𝐿𝑚2

𝐿𝑟

K = inductance ratio

88 % to 92

%

A rectifier

circuit is used that

increases the

efficiency.

Super

junction devices

reduce

efficiency, Lyapunov

based

functions make the

structure

complicated

Bi-directional DC-DC

converter

Cascaded topology of the

inductors and

capacitors are available [26]

[46]

Charging module, V2G and

G2V [12]

Four switches, two capacitors

400 to 450 𝑉ℎ =

1

1 − 𝐷𝑉𝑙

𝐿𝑚𝑖𝑛=𝐷∗(1−𝐷)2𝑅𝐻

2𝑓

92% to 94.5 %

Four switches

enable the

utilisation of a cascade

topology that

controls output

voltages

Absence of soft

switching

means that switching

losses are

present

Buck

converter

The filters within

the circuit are

represented through L1 C1

and L2 C2 [70]

Charging module

[65]

Three switches,

IGBT,

MOSFETS

300 to 450 𝐿=𝑉𝑜𝑢𝑡∗(𝑉𝑖𝑛−𝑉𝑜𝑢𝑡)

𝛥𝐼𝑙∗𝑓𝑠∗𝑉𝑖𝑛

𝑉01 = 𝐷𝑉𝑆

𝑉02 = (1 − 𝐷)𝑉𝑆

90 % to 93

%

It uses IGBT

and

MOSFETS that increase

the

efficiency

IGBT,

MOSFETS

increase the cost of these

converters

Boost

converter

Eight IGBT are

placed parallel to each other and

the voltage

source [71]

Charging

module, Employed when

high DC voltage

gain is required (> 4%).

Six IGBT,

four resistors, four inductors

300 to 450 𝐿

=(𝑉𝑜𝑢𝑡 − 𝑉𝑖𝑛 + 𝑉𝐷) ∗ (1 − 𝐷)

𝑚𝑖𝑛(𝑖𝑙𝑜𝑎𝑑)𝑓

L = inductance

90 % to

92.5 %

The output

voltage is increased

based on the

input source

IGBT,

MOSFETS increase the

cost of these

converters

Buck Boost converter

The topology of buck and boost

are placed

parallel to each other[6] [72]

Charging module Two bridges, SiC based

MOSFET

320 to 450 𝐿

=𝑉𝑜𝑢𝑡

𝑓𝑠𝑤 × 4 × 𝑁 × ∆𝐼𝑚𝑎𝑥

𝐶

=𝐼𝑜𝑢𝑡

𝑓𝑠𝑤 × 4 × 𝑁 × ∆𝑉𝑜𝑢𝑡

These specification values are for interleaved 4-

Phase DC-DC boost

converter.

𝐷 = 1 − 𝑉𝑖𝑛

𝑉𝑜𝑢𝑡

94 % to 97.5 %

Uses both the buck and the

boost

topologies to gain a high

efficiency

rating

SiC based MOSFETS

are

expensive and 97 %

efficiency is

only achieved

through

modificatio

ns

Charge pump

converter

The charged state

and the discharged state

are cascaded to

one another

Voltage doubler

two stage, output voltage control

Three

capacitors, two switches, one

diode

630 to 737 η=𝑉𝑜𝑢𝑡

𝐾∗𝑉𝑖𝑛

η = efficiency

88 % to 93

%

A voltage

doubler is used to boost

the output

voltage

Complex

topology and quite

expensive

construction

Full bridge

LLC resonant converter

“A DC chopper

along with a resonant tank and

a rectifier and

ZVS is achieved Four switches,

four diodes, two inductors,

one capacitor

600 to 660 𝐾 =

𝑉𝑜𝑎𝑐(𝑆)

𝑉𝑖𝑛𝑎𝑐(𝑆)

K= resonant tank gain

90 % to

93.3 %

Uses a

chopper circuit in

series with a

Quality

factor is independent

of voltage



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load is connected

to a transformer” [22] [28]

resonant tank

that amplifies the

waveforms

gain,

magnetizing inductor has

no impact

on voltage gain

Half bridge LLC resonant

converter

A ac dc rectifier is placed in series

to a FB LLC

rectifier [4] [1]

ZVS is achieved Four switches, four diodes,

two inductors,

one capacitor, AC DC

rectifier

500 to 650 𝑉𝑔𝑒

√2

π∗ 𝑉𝑑𝑐

𝐿𝑟 = 𝑄𝑅𝑎𝑐

2𝜋𝑓𝑜

𝐶𝑟 = 1

2𝜋𝑄𝑓𝑜𝑅𝑎𝑐

92 % to 94.6 %

It mainly acts as a rectifier

Increases the weight

of charging

panel by 10 % to 15 %

Bi-directional

Multiport DC-

DC converter

The switch is in

isolation from the

circuit [3] [28]

Charging

module, V2G

Two capacitor,

two inductors

600 to 650 𝐿 ≥

Vin ∗ D

2 ∗ f(SW) ∗ Il

90 % The switch

being

isolated does not

contribute to

the switching losses

Not suitable

for wireless

power transfer or

fast

charging

Full bridge converter

The construction is very

simple.[18]

Charging module, V2G and

G2V, accepts a

wide range of frequency,

ZVS and ZVC is

derived, Fast charging,

wireless power transfer.[45]

DC chopper, LLC resonant

tank, rectifier,

transformer

480 to 570 𝑉𝑟𝑖𝑝𝑝𝑙𝑒 =

𝑉𝑚𝑎𝑥 − 𝑉𝑚𝑖𝑛

𝑉𝑎𝑣𝑔

𝑉𝑎𝑣𝑔= Average value of

maximum and minimum

voltage

94 % to 96 %

Has the capability to

support V2G

and G2Vtechnolo

gies. Can be

used in eh fast charger

module of EVs

High cost compared to

other

traditional converters,

huge gap

between constant

current and voltage

modes

EF2 converter The choke

inductor and the

resonant inductor are placed in

parallel [2] [16]

Charging

module, Fast

charging, wireless power

transfer

Choke

inductor,

resonant inductor

650 to 730 𝐼𝑚

𝐼𝑜

= 𝑝 ∗ (𝑘 + 1)

90 % Supports

WPT and fast

charging

Load

independenc

e hinders efficiency,

high gap

between coils

Luo Converter Construction of circuit is

simple.[33]

Charging module, Motor

drive control

Two inductors, Two

capacitors,

Diode, Switch

550 to 590 𝐷 =

𝑇𝑜𝑛

𝑇

𝑉𝑜 = 𝐷𝑉𝑖𝑛

1 − 𝐷

𝐿1 = 𝐷 𝑇 𝑉𝑖𝑛

∇I. 𝐿1

𝐶1 = (1 − 𝐷). 𝐼1. 𝑇

∇𝑉𝐶1

L2 = 𝐼𝐿1(1−𝐷)

𝐷

89 % 92% The output ripple and

parasitic

effects are very less.

The equivalent

resistance

Zeta converter An inductor is

placed parallel to a diode and

capacitor in series

[39]

Duty cycle can be

varied [74]

Two

capacitors, one inductor

610 to 660 𝐷 =

𝑉𝑜𝑢𝑡

𝑉𝑜𝑢𝑡 + 𝑉𝑖𝑛

D = Duty cycle

𝐿1 = 𝐷 . 𝑉𝑚𝑝𝑝

f. ∇I. 𝐿1

𝐿2 = (1 − 𝐷) 𝑉𝑜𝑢𝑡

f. ∇I. 𝐿2

𝐶1 = . 𝐼1. 𝑇

∇𝑉𝐶1

85 % The duty

cycle is controllable

and parallel

circuit reduces loss

Low

efficiency compared to

other

converters



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Taking into account charge pump converters along with “Full bridge resonant LLC converter” and “Half bridge

resonant LLC converter”, it can be seen that half bridge converter is most effective. The primary reason for considering

HB LLC converters to be the most suitable amongst the three is because of the efficiency rating that ranges from 92

% to 94.6 % [68]. Charge pump converters are one of the most obsolete and unused converters for electric vehicles

since its efficiency is quite less compared to the cost. Charge pump converters have an average price of ￡700 and its

average efficiency lies within 88 % to 93 %. Further, the constructions of charge pump converters are higher than the

rest. The FB LLC along with the HB LLC both use four switches and four diodes along with two inductors. However

the HB LLC uses an AC-DC rectifier and therefore its efficiency rating is slightly higher. A maximum efficiency

rating of 94.6 % can be achieved for HB LLC converters and therefore these converters are widely used in electric

vehicles. Further, both the HB and the FB LLC converters use soft switching thereby eliminating any form of

switching losses from the circuit. Thereafter ZVS or “Zero Volt Switching” is also achieved through both these

topologies and this contributes to the increased efficiency. Therefore, it is evident that FB LLC and HB LLC converters

are more efficient and less costly compared to charge pump converters. HB LLC converters are the most suited

amongst these three since it can reach an efficiency criteria of 94.6 % and apart from that, it costs less than a FB LLC

converter. Analysis of various studies reveals that, it is quite common to use AC-DC converter since the power factor

correctors paired with the Pareto front analysis is used to endure the efficiency of the current output. Nevertheless,

there has been a wider adoption of AC converter since the super capacitors and batteries together form a backup charge

system [23] [63]. These super capacitors or batteries provide a reserve power system that is used in case of an

Z source

converter

Two capacitors

are placed in series with a

diode[7] [39] [31]

Variation of duty

cycle

Four

capacitors, four inductors

620 to 690 C = (1−𝐷𝑆𝑇)

2

4 𝑅𝐿𝑓𝑠𝐷𝑆𝑇(1−2𝐷𝑆𝑇)𝑋𝑐%

𝐿 = 𝑅𝐿𝐷𝑆𝑇(1 − 2𝐷𝑆𝑇)

𝑓𝑠𝑋𝐿

𝑉𝑐

𝑉𝑜

=𝑇1

𝑇1 − 𝑇0

85 % to 92

%

Stable

converter and provides

static output

voltage

Modificatio

ns need to be made to

reach 92 %

efficiency level

ZVS full

bridge

converter

The switches are

placed parallel to

the diode circuit [78]

Variation of duty

cycle, zero

voltage output is achieved [30]

MOSFET,

IGBT

570 to 620 𝑉𝑐

𝑉𝑜

=𝑁𝑠

𝑁𝑝

∗ 𝑝ℎ − 𝐼0

∗ (𝑁𝑠

𝑁𝑝

∗𝑁𝑠

𝑁𝑝

) ∗𝐿𝑘

𝑉𝑖𝑛∗ 𝑓

𝐿𝑚 ≤𝑉𝑖𝑛 𝐷 𝑇𝑠

2 (−𝑛1𝐼0 +2𝐶𝑑𝑠𝑉𝑖𝑛

𝑇𝑑𝑒𝑎𝑑)

90 % Duty cycle

can be varied

while controlling

zero volt

switching

Cannot

operate for a

wide range of

frequency,

low efficiency

rating

Multi-port converter

A single phase rectifier is

connected to an

isolated converter and it is very

complex because

of multiple sources and

converters. [41]

High integration of services, two

ports.[34]

Two ports, sub converters

600 to 670 𝐿 =

𝑉𝑜𝑢𝑡 × 𝑉𝑖𝑛

𝑤 × 𝑃𝑜

× 𝜑12

𝑉1𝑖1 + 𝑉2𝑖2

= 𝑉1𝑖1 + [ 1

𝑔× 𝑖 × 1

× (−𝑔 𝑣 1)] = 0 P= electric power K= gain

92 % to 94.5 %

Two input ports are

used,

boosting input current

and

efficiency

The impedance

from series

inductance lowers

efficiency

Unidirectional

converter

Two switches are

connected to an

inductor and

diode

each.[16][49]

Energy transfer,

modification of

output

waveforms.[55]

Two

semiconductors

six diodes

530 to 660 𝐿1

=𝑉1 ∗ D

I ∗ (𝐿1) ∗ (𝑃𝑝) ∗ f(SW)

75 % to 90

%

Single

direction

flow of

current

reduces loss

within the circuit

High

voltage gain

often

restricts

efficiency,

using an ultra-

capacitor

involves additional

costs



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interrupted supply of power. The main topology of AC-DC converter resides on the fact that ac electrical power is

sent over a long distance and is thereby stepped down to DC power. This step down results in losses since ac current

is converted to DC current, hence the name step down [21][63]. However, this concept is used in transmission lines,

in case of electric vehicles is where the ac power is provided into plug in outlets where PEVs are connected and it acts

as a source of power. The power source of an EV that is the batteries power is changed to either AC or DC.

Figure 31: Types of DC-DC converters

The DC-DC converters can be broadly classified into three types, namely, the linear mode followed by the hard

switching and the soft switching mode shown in Figure 31. The linear model is simple and is therefore favoured for

its simplicity of use. However, the linear mode DC-DC converter is only used in case of smaller devices. When

considering switching of resonant DC-DC converters, it can be established using a wide range of frequencies and can

incorporate a break of the switching pulse. Since Lithium, ion batteries are used in electric vehicles in the modern day,

and these batteries use the fast charging function that is only supported through principles of constant voltage along

with current [36]. Resonant full bridge DC-DC converters are used to provide a proper phase shift of the constant

current and the voltage, although the control gap of these two modes is quite high. Further, resonant converters can

also be used for isolation of high frequencies that in turn increases the overall efficiency of the system. Although this

feature might seem beneficial, some intrinsic properties lead to loss within the circuit [19].

This property is the wide span of frequency that is used by the converter; this feature can lead to the loss of soft

switching function. Therefore, there is a dire need of pulse width modulation for these converters to control this wide

frequency range. Although the techniques of pulse width modulation and the additional components are quite

expensive and the resonant DC-DC converter is expensive in itself, the output of the converters display an increased

quantum of efficiency in terms of power conversion and power output.

Often, “full bridge resonant converters” are compared to the “isolated DC-DC converters” since both belong to the

same family of DC-DC converters. However, for isolated converters, the efficiency rating is quite low compared to

resonant converters. Resonant converters have the capability to reach an efficiency level of 96 % without any

additional modifications [45]. Further, isolated converters do not possess the grid to vehicle transfer of power, and it

also does not possess the capability to control ZVS current or voltage [17]. Therefore the Full bridge rectifier is the

most suited topology for electric vehicle charging. FB resonant converters also allow a wide input frequency and

therefore frequency can be varied, as per the requirement. Further an additional benefit of FB resonant converters is

that it can implement fast charging technique while implementing wireless transfer of power [22]. However there are

certain drawbacks to this topology, firstly, there is a huge gap between the constant voltages along with the constant

current mode. These converters are slightly highly priced because of their construction mechanism.

Considering the EF2, Z source converters along with the ZVS converters and the Zeta converters, the Z source

converters can reach an efficiency level of 92%. EF2 converter uses a choke inductor along with a resonant inductor

and therefore this makes the circuit additionally expensive compared to the others. The price of EF2 converters can

range from ￡650 to ￡730. Further, the heat produced in the winding of the choke coil decreases the efficiency. The

inductor is also exposed to two kinds of losses, firstly the copper loss of the coil that is expressed by𝐼 2. 𝑅, followed

by the iron losses. The iron losses of an inductor can be broadly classified into two losses, namely the hysteresis loss



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and the Eddy current loss. This reduces the efficiency level of the EF2 converter and thus, it has an efficiency rating

of 90 %. However, a major advantage of using EF2 converter is that it can be used for transferring power through a

wireless ode and it is also used within the fast charging module. Albeit it has a low efficiency rating, these advantages

make a commonly chosen converter when designing the charging module of an electric vehicle.

The Zeta converter is simple based on its construction; it is constructed using a simple inductor placed parallel to a

diode and a capacitor. Zeta converters can be used to achieve variation of duty cycle and therefore it is opted for the

charging module. However, the use of two capacitors increases the dielectric losses emitted from the capacitor and

therefore the efficiency is largely decreased. Further, it is expensive compared to other traditional power converters

and its efficiency reaches a maximum limit of 85 %. The major drawback of Zeta converter is that 85 % of efficiency

is significantly less than the other converters. Therefore it is not as widely used as the other converters. The Z source

converter along with the ZVS converter can use the technique of “pulse width modulation”. In both these converts

there is a diode circuit use in parallel to two capacitors in case of Z source converter and in parallel to switches for

ZVS converter. There are modifications made within the diode circuit in order to increase the efficiency and therefore

Z source inverters can reach a maximum efficiency of 92 %.

Comparing specifications of ZVS converter with Z source converter, ZVS converter has an added benefit since it can

use “pulse width modulation” and it can also vary the duty cycle. Further, output of a zero voltage rating along with

“zero volt current” is also achieved through ZVS inverter. Nevertheless, Z source inverters are more common that

ZVS converters since they have an added extra efficiency. Normally for Z source converters, the efficiency lies within

the range of 85 to 92 %, but it can reach 92 % and provide a constant output of 92 % for a full duty cycle. ZVS

converters have a maximum efficiency rating of 90 % and it does not increase beyond that.

Lastly the multiport converter and the unidirectional converters are being evaluated. Multiport converters are

significantly useful when considering the metrics of efficiency, as it can reach a maximum efficiency of 94.5 %.

However, since two ports are used, its overall construction cost increases and thus cheaper alternatives such as “full

bridge resonant converters” are used. The multiport converters usage requires the implementation of a high voltage

bus and therefore it allows current to flow in two directions. Considering unidirectional converters, its only advantage

is that it provides conversion ratios that are adequate for electric vehicles charging module. Apart from the conversion

ratios, another major advantage is the simplicity of operation of these unidirectional converters. During the operation

phase of unidirectional current flow, only one semiconductor needs to be controlled to obtain maximum efficiency.

Nevertheless, the overall efficiency of these converters is quite low as the range is from 75 % to 90 % and is therefore

not used anymore within the changing panels. Thus by comparing the converters within this study, it is quite evident

that “full bridge resonant converters” are the best fit for charging modules of electric vehicles.

IV. CONCLUSION

A review on power converters for electric vehicle is presented in this paper. It has been found that, out of the seventeen

converters discussed and evaluated within this study, FB converter, HBLLC converter along with “full bridge resonant

converter” and EF2 converter support fast charging and WPT. However, if one converter would be chosen as the ideal

fit for modern day electric vehicles it would be the “full bridge resonant converter or FB resonant converter or FBLLC

converter”. There are many reasons why this converters is placed above all else. Firstly, comparing to its class of

resonant converters, FB resonant converter is better that HBLLC and FB converter in terms of efficiency, and cost.

Although all three of these resonant converters provide “zero volt switching”, only FB resonant converters allow both

V2G and G2V transmission. V2G technology is a sought after technology as it enables the energy that is stored within

an electric vehicles to be transferred to the grid. This solves the issues of power shortages in the grid and therefore is

being implemented in the charging modules. Although there are certain drawbacks of FB resonant converters, namely,

it has a slightly higher cost compared to other converters and there is a huge gap between constant voltage and current.

Thus gap between constant current and voltage can be mitigated by controlling the polarisation index along with

regulation of primary side. The secondary side regulation could also be achieved through the use of an opto isolator.

Apart from this technique, constant voltage mode and constant current mode can be utilized simultaneously. Lastly,

the only converter that has a higher efficiency rating than FB resonant converter is buck boost converter. However,

buck boost converter does not possess the capability to support WPT or fast charging. Therefore, considering all the

factors of construction along with cost, operation and efficiency rating, FB resonant converter is the most suited

converter for the charging module of an electric vehicle applications.



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Page No: 102

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[2] Akter, M.P., Mekhilef, S., Tan, N.M.L. and Akagi, H., “Modified model predictive control of a bidirectional AC–DC converter based on Lyapunov function for energy storage systems” IEEE Trans. on Ind., Electron., 63(2), pp.704-715. 2015.

[3] Akar, F., Tavlasoglu, Y., Ugur, E., Vural, B. and Aksoy, I., “A bidirectional non isolated multi-input DC–DC converter for hybrid energy storage systems in electric vehicles”, IEEE Trans. on Vehicular Technology, 65(10), pp.7944-7955. 2015.

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Appendices

Appendix 1: Bidirectional class E converter of an EV

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