Experimental Validation of 40 kW EV Charger Based on Vienna Rectifier and Series-Resonant Dual Active Bridge ^†

Abstract

This work presents the experimental validation of a 40 kW electric vehicle (EV) charger. The proposed system comprises two 20 kW modules connected in parallel at the input and output. Each module has two stages—as a grid converter Vienna Rectifier (VR) was chosen, and as an isolated DC/DC stage, two Series-Resonant Dual-Active-Bridges (SRDABs) in input-series-output-parallel (ISOP) configurations were applied. The AC/DC and DC/DC stages were enclosed in 2U rack standard housing. A bipolar DC-link with ±400 V DC voltage was employed to connect both stages of the charger module while the charger’s output is dedicated to serving 800 V batteries. VRs operated at 66 kHz switching frequency and the SRDABs operated at 100 kHz. The converters used in the charger structure were based on silicon carbide (SiC) power devices. The description and parameters of the built hardware prototypes of both—AC/DC and DC/DC—converters are provided. Moreover, the experimental validation of each stage and the whole charging system, including oscilloscope waveforms and power analyzer measurements at nominal power, are included. Such a configuration enables energy conversion with high efficiency without a negative impact on the grid and high-quality grid waveforms.

1. Introduction

The consequences of global warming [1], mainly caused by human activity, force us to take decisive action to counteract them. One of the leading international contracts regarding this issue is the Paris Agreement [2]. According to the regulations adopted in this document, the vital actions that should be taken are focused on achieving climate neutrality by 2030. Therefore, CO₂ emissions and fuel consumption have to decrease in the coming years drastically. In the European Union alone, carbon dioxide emission must be reduced by almost 40% before 2030 compared to 2021, wherein the trend to downscale the CO₂ issue has been observed since the start of the 21st century [3]. Furthermore, in recent years, it has been shown that the supplies of fossil fuels could be drastically disturbed at any moment by circumstances including global epidemics or war, whose effects are still felt today.

Consequently, there are plenty of economic, environmental, legal, and other motivations to go from obtaining electrical energy from fossil fuels to green energy produced from renewable resources. However, this will transform the electrical grid from a centralized to a more distributed system [4]. Another vital aspect of electrical grid transition would be medium and high voltage DC systems instead of today’s AC solutions [5].

Another sector that needs significant alteration is transportation, which is responsible for over 25% of global CO₂ emissions [6]. Nowadays, cars with internal combustion engines (ICE) account for over 90% of the global car market [7]. To reduce CO₂ emissions in the transportation sector, cars with ICE must be replaced by cars driven by electrical engines, which is happening [7]. Electric vehicles (EVs) are growing popular and are more often seen on the roads. Nonetheless, some concerns must be addressed to replace ICE cars with EVs fully. The current main issue with EVs is their energy storage [8]. Firstly, battery packs are still expensive, and their cost is a significant part of the total car price. Secondly, the parameters of batteries deteriorate with aging. Last but not least, the range of state-of-the-art EVs is lower than its conventional counterparts. The most extended range of EVs given by manufacturers is slightly above 600 km, while ICE vehicles can easily drive over 1000 km without refueling. Moreover, the range of EV producers declares it is usually shorter on the actual road.

As seen above, while the battery parameters and technology of its manufacturing do not fully allow the fuel tank to be replaced by a battery pack, in terms of driving convenience on long journeys, the development of battery chargers is essential. In particular, fast off-board chargers are gaining much research interest as potentially ensuring full battery “refueling” during an ordinary stop on the road [9].

Off-board EV chargers are mainly built with two stages—AC/DC and DC/DC. Depending on the requirements of the individual system, the AC/DC converter could act only as a rectifier (unidirectional power flow) or could be a rectifier and inverter in one topology (bidirectional power flow) [9]. However, the second solution will be needed only if vehicle-to-grid (V2G) operation is used, which is unlikely in the case of fast off-board chargers. On the other hand, the grid converter should have a power factor correction (PFC) function implemented. In that way, the sinusoidal currents could be drawn from the grid—the negative impact on the grid is minimized. Such a solution reduces the total harmonic distortion (THD) factor of charger input currents and reactive input power. Moreover, the emitted electromagnetic interference (EMI) is also decreased. In some solutions, the bipolar DC-link (with three ports) is utilized [9]. This configuration enables more options in the DC/DC conversion stage, such as the application of lower power DC/DC converters, which could be connected in series at the input, a wider choice of DC/DC topologies, or convenient connection of other systems as energy storage or energy from renewable sources.

The second DC/DC stage is directly responsible for interfacing the EV battery storage and DC-link. As in the AC/DC stage case, the DC/DC converter could ensure unidirectional or bidirectional power flow. However, the second option is preferred. For safety reasons, DC/DC converter must provide isolation between the output and the rest of the charging system. In the case of charger failure, the battery pack in the car should not be damaged, and what is more critical, the hazardous potential cannot shock the person using the charger. The most popular topology at that stage is Dual-Active-Bridge (DAB) in several variants [9], a well-established structure that guarantees isolation and bidirectional power flow simultaneously.

To provide ultra-fast charging of EVs, the chargers of the highest power levels employ extra DC energy storage, which is connected in parallel to DC-link between AC/DC and DC/DC stages [10,11]. The current from additional energy storage reaches high values, resulting in rapid battery charging at the expense of accelerated battery aging.

In up-to-date EV chargers, silicon carbide (SiC) power semiconductors are becoming standard solutions rather than something special. It is caused by the superior performance of SiC devices compared to Si technology. Moreover, the availability of SiC power semiconductors is increasing while the prices of such devices are continuously falling. In that way, high switching frequencies, high energy conversion efficiency, and high power density could be achieved at a reasonable price and with a high degree of reliability.

In the literature, some realization concepts for such a charging system are presented [12,13,14,15]. A medium voltage (1500 V) bipolar DC-link was proposed in [12]. This solution reduced conduction losses with higher voltage in the system. The multilevel ANPC topology was proposed to avoid using high-blocking voltage devices. Moreover, the ANPC leg was a base for the submodule used in each converter of the charging system. A three-phase ANPC converter was proposed from the grid side, while a DC/DC stage, Series-Resonant DAB is applied. The system also included battery storage for the highest charging power when needed. Nevertheless, the charger still required complete experimental evaluation to confirm its properties. Two AC/DC/DC solutions for off-board battery chargers were examined experimentally in [13]. The first approach was based on Si components, and the second on SiC devices. In addition, several topologies in each stage of the charger were compared. The experimental tests were carried out up to the 50 kW power range, reaching a peak efficiency of over 97%. The presented study confirmed the superior performance of SiC-based converters over standard Si technology. Nevertheless, the switching frequency was maximally 12 kHz, resulting in significant passive components and low power density. More complex EV charging system converters solutions were shown in [14,15]. The five-level ANPC bidirectional converter connected with Dual-Active-Half-Bridge (DAHB) was proposed for grid-to-vehicle (G2V) and V2G operation modes. Experimental results confirmed the grid current’s excellent quality and high energy conversion efficiency. Nevertheless, the proposed setup was tested only for a 1-phase AC grid and needed further validation with 3-phase input. In [15], instead of a 1-phase, the 3-phase DAB was examined and optimized according to several criteria. Insightful optimization allows for reaching as high as almost 98.7% peak energy conversion efficiency. However, the AC/DC stage is still required to build the complete EV charging system. Moreover, the last two concepts are complex and novel and require further research.

After a literature review and according to the abovementioned considerations, the authors proposed a concept of a 40 kW EV charger—see Figure 1. The mentioned system consists of two modules—each rated at 20 kW nominal power. The modules are connected in parallel at the input and the output. A single module has a two-stage configuration. As a converter from the grid side (marked as L1, L2, L3), Vienna Rectifier (VR) has been chosen [16,17,18,19,20,21,22,23]—see Figure 2a. Vienna topology enables PFC operation with high-quality grid waveforms and low emitted EMI. This topology provides unidirectional power flow. However, as noticed above, such a feature is not required in the off-board chargers, mainly used to quickly “refuel” a car’s battery storage. From the grid side, an LC filter is also added. At the input of the AC/DC stage, fuses and contactors are employed to ensure the safe operation of the charger. The output of the VR forms the bipolar DC-link with 2 × 400 V DC voltages (V₁, V₂) connected in series. The output ports of VR are marked: “+”, “0“, and “−” and are supported by high-capacitance DC-link capacitors (Figure 2a).

Simultaneously, V₁ and V₂ voltages are the DC/DC stage inputs. The second stage of the charger module consists of two 10 kW Series-Resonant Dual-Active-Bridge (SRDAB) converters [24,25,26], which are in the input-series-output-parallel (ISOP) configuration—see Figure 1. Each of the SRDABs contains a transformer in its structure, providing the required galvanic isolation of the EV charger DC/DC stage. Such a solution enables bidirectional power flow, which could be beneficial in the case of system extension with energy storage. Moreover, to achieve high energy conversion efficiency, the Series-Resonant circuit (L_r, C_r—see Figure 2b) was applied on the primary side of the transformer. Therefore, the resonant current in the transformer is sinusoidal instead of trapezoidal, as in non-resonant DAB. This improves magnetic elements’ operating conditions and, more importantly, enables the soft-switching of power semiconductors [27,28]. The outputs of both 10 kW SRDABs are connected in parallel, forming an 800 V output consistent with the common battery standard. At the output of the DC/DC stage, an LC filter was applied to improve the output waveforms.

This work is an expanded version of the paper [29]. In the mentioned work, the authors proposed, designed, built, and validated experimentally a 20 kW module for the off-board EV charger. Nevertheless, the experimental evaluation of the whole charging system at 40 kW was still missing. This paper delivers experimental results from tests of a complete charging system at nominal power. Moreover, the new results of each stage of the EV charger module, including oscilloscope waveforms and power analyzer measurements, are included. Additionally, the description of the control system of the whole charger, which was previously missing, is present in the current version of the article.

The paper is organized as follows: after the introduction, a detailed description of the EV charging system is included. Section 2 is divided into three subsections: the first two are focused on the hardware prototypes and parameters of each stage of the charging system, and the last one delivers the description of the control system of the whole charger. Then, the experimental results of the built EV charger prototype are presented in Section 3. The oscilloscope waveforms and power analyzer measurements at nominal power (20 kW) of either the AC/DC and DC/DC stage of a single charger module are included. Subsequently, the results recorded for the complete, single module of the charger are presented. Finally, the collected results of the whole charging system operating at 40 kW are shown. The article is concluded in Section 4.

2. Description of the EV Charging System

The EV charging system consists of two power conversion stages realized using an AC/DC rectifier and an isolated DC/DC converter. The first one has been proposed as a Vienna Rectifier power electronics structure dedicated to operation with 20 kVA nominal power, while the isolation stage has been realized with two 10 kW Series-Resonant Dual-Active-Bridges. The electrical configuration of the VR and SRDABs has been presented in Figure 2a,b, respectively. Supplied from a three-phase electrical system (400 V/50 Hz), Vienna Rectifier converts energy to 2 × 400 V DC output terminals connected to each of two SRDABs, as a series connection of each input. Output terminals (800 V) have been connected on the isolated side in parallel. This chapter presents the general parameters of each power electronics stage.

2.1. The 20 kVA Vienna Rectifier

Topology on the input stage, Vienna Rectifier, has been presented in Figure 2a. It consists typical three-phase diode rectifier built with six diodes: D_1a,b,c D_4a,b,c, and three legs built with six transistors in the configuration of two series-connected SiC MOSFETs (sources are connection points): T_2a–T_3a; T_2b–T_3b and T_2c–T_3c. All semiconductors have been cooled using three heatsinks (one per leg consisting of two diodes and two transistors) type LAM5. In addition to the capacitance-voltage divider built with DC-link capacitors (C) and active working of transistors, the rectifier delivers two-level DC voltage at the output (between “+”, “0”, and “−” terminals). Using silicon carbide technology allows setting switching frequency equal to 66 kHz, which contributed to reducing input filter parameters, built finally with 220 µH inductors and 2 µF capacitors. The parameters of the LC filter were selected using tests and simulation studies, taking into account the following constraints:

• The maximum current ripples are less than 10% of the rated current.
• The maximum reactive power does not exceed 1% of the rated power.
• The filter resonant frequency was designed in the medium-frequency band, which is ten times higher than the fundamental harmonic and lower than half of the switching frequency.

Regarding electromagnetic compatibility standards, the EMI filter has also been designed and applied to the grid supply side of the rectifier. The basic parameters of described laboratory model have been presented in

Table 1. Basic parameters of 20 kVA Vienna Rectifier.

Symbol	Parameter	Value	Unit
L1, L2, L3	Phase voltages	230	V
V1, V2	Output voltages	400	V
Sn	Rated power	20	kVA
fs	Switching frequency	66	kHz
T2a, T2b, T2c, T3a, T3b, T3c,	SiC MOSFETs	C3M0030090K	-
D1a, D1b, D1c, D4a, D4b, D4c,	Diodes	STPSC20H12	-
LA, LB, LC	Input filter inductors	220	µH
CA, CB, CC	Input filter capacitors	2	µF
C	DC-link capacitors	180	µF

.

A 20 kVA Vienna Rectifier prototype has been presented in Figure 3. All presented components have been mounted on PCBs, while construction has been designed for 2U Rack Mount System.

2.2. The 10 kW Series-Resonant Dual-Active-Bridge

The isolation stage of the EV charging system has been built with Series-Resonant Dual-Active-Bridges, which topology is presented in Figure 2b. Each SRDAB consists of two full bridges: M1 and M2, and a series-connected resonant circuit built with a transformer (T_r) with turns ratio n = n₁/n₂ = 1/2, inductor L_r, and capacitor C_r connected on the primary side. M1 and M2 contain four SiC MOSFET transistors: T₁ ÷ T₄ for the primary and T_1S ÷ T_4S for the secondary side of the converter. The cooling system dedicated to semiconductor power loss dissipation contains one LAM5 heatsink for each bridge transistor. The basic parameters of the described laboratory model have been presented in

Table 2. Basic parameters of 10 kW SRDAB.

Symbol	Parameter	Value	Unit
V1 or V2	Input voltage	400	V
VBAT	Output voltage	800	V
Pn	Rated power	10	kW
fs	Switching frequency	100	kHz
T1 ÷ T4	SiC MOSFETs	MSC035SMA070B4	-
T1S ÷ T4S	SiC MOSFETs	NVH4L040N120SC1	-
n = n1/n2	Transformer ratio	1/2	-
Lr	Resonant inductor	8	µH
Cr	Resonant capacitor	1.188	µF
C	DC-link capacitors	180	µF
LF	Output filter inductor	33	µH
CF	Output filter capacitor	1.2	µF

.

A prototype of 2 × 10 kW SRDABs has been presented in Figure 4. All presented components have been mounted on PCBs, while construction has been designed for 2U Rack Mount System, similar to Vienna Rectifier.

2.3. Control System of the Vienna Rectifier

The operation of the converter strongly depends on implemented control method. One of the most common control strategies based on current regulation is Voltage Oriented Control (VOC) [30], presented in Figure 5. The VOC consists of two inner active I_d and reactive I_q current control loops implemented in a rotating dq reference frame and one outer DC link voltage (U_DCsum) control loop. In order to improve power quality and operation performance, the primary form of VOC was extended by Higher Harmonics Compensation (HHC) [31] module and improved phase locked loop.

The typical synchronization method based on Synchronous Reference Frame Phase Locked Loop (SRF-PLL) [32] has been extended by the Dual Second Order Generalized Integrator (DSOGI) [33] module to reduce sensitivity for the disturbances appearing in the grid voltage and increase the accuracy of the estimated angle and frequency of the fundamental harmonic. In this module, the grid voltage’s positive U_Pxpos and negative U_Pxneg sequence components are estimated. The extraction and separation process of these components is realized by Second Order Generalized Integrator (SOGI) [34], presented in Figure 6. Each SOGI module generates two output signals: one (U’_Px) is the first harmonic of the input signal U_Px, and the other (qU’_Px) is its quadrature equivalent. Applying SOGI for both α and β components of the grid voltage allows for extracting positive U_Pxpos and negative U_Pxneg components of the grid voltage (U_P). The further synchronization process is performed based on the positive voltage (U_Pαpos, U_Pβpos) component only. The block scheme of the extended synchronization module is presented in Figure 6.

The higher harmonics compensation algorithm operates based on extracting particular harmonics from measured grid current I_P. The extracted signals V_hx are gained and finally added to the signals V_cα, V_cβ of the main control loop. The most significant and frequently occurring harmonics in the grid voltage are: 5-th, 7-th, 11-th, and 13-th. Therefore only these harmonics are compensated. Generalized Integrators (GI) [33] blocks were used to separate and control particular harmonics. GI is a resonant structure that performs the function of the integrator for sinusoidal signals. This structure is also a fundamental block of the control system known as Proportional Resonant (PR) controllers. The HHC block with the GI structures, applied to I_Pα and I_Pβ components of the grid currents, is presented in Figure 7. The DC link is split into two banks of capacitors with three output terminals and separated loads. Keeping the voltages (U_DC1, U_DC2) of both capacitor banks equal is essential for the proper operation of the converter. Therefore the DC link voltage balancing is performed on two levels. The first one, implemented on the control algorithm level, relies on calculating the voltage difference U_DCdiff between the upper and lower capacitors and use as a common mode signal for duty calculation in the modulator block. Another DC-link voltage balancing method is implemented on the master control level and is based on sending individual reference current signal I_ref for each DC-DC submodule. The master controller sends a global reference current signal to each Vienna Rectifier control unit. Next, the VR controller, based on measured DC link voltages V₁ and V₂, calculates the imbalances and individual reference currents I_ref and sends them through the CAN interface to the DC-DC submodules. The low-level balancing method is performed with the switching frequency (66 kHz), while the high-level balancing is performed a thousand times slower, i.e., 66 Hz.

2.4. Control System of the Series-Resonant Dual-Active-Bridge Converter

In each SRDAB submodule, the output current I_OUT is adjusted through the PI controller, which modifies the phase shift between the PWM signals of the bridges M1 and M2. The reference current I_ref is taken from the primary controller through the CAN communication interface. To achieve smooth current regulation, the phase shift module with the increased resolution is used to reach the time step accuracy on the order of 150 ps. The block scheme is presented in Figure 8. The input U_IN and output U_OUT voltages are also measured; however, they are used only for protection purposes and to determine U_IN/U_OUT ratio. The converter is designed to ensure soft switching and low power losses in certain conditions. The optimal working condition is when the U_IN/U_OUT ratio is 0.5; however, in order to increase the operating range, changes of +/−50% are allowed.

3. Experiments with the Complete System

Presented parts of the EV charging system have been tested under various configurations. Firstly, correct operation, power losses, and efficiency measurements have been initially checked for the standalone operation of each—VR and two SRDABs. Following, the operation of a single charger module (VR + 2×SRDAB) at nominal power of 20 kW has been validated. This stage included power quality and efficiency measurements together with the start-up procedure of the module. Finally, the EV charging system has been tested under nominal parameters (40 kW).

3.1. Standalone Operation of 20 kVA Vienna Rectifier

In standalone operation mode VR was supplied from a 3 × 400 V grid and loaded by two series-connected resistors. As expected Vienna Rectifier gives a stable DC output voltage (2 × 400 V DC). Moreover, the PFC function enables sinusoidal grid current waveforms. As shown in Figure 9, the recorded results for one grid phase show that proper steady-state operation of input and output waveforms has been achieved. The visible sinusoidal shapes of voltage and current at the input seem to have excellent quality, which can also be seen in parameters measured by the power analyzer, especially the THD level (Figure 10). Furthermore, the screen from the Yokogawa power analyzer presents parameters of three-phase voltages and currents, as well as load voltage and the current. Results obtained by the power measurements at the input and output of the rectifier show around 330 watts of power losses, which gives almost a 98.4% efficiency level. It proves that silicon carbide semiconductors combined with high switching frequency and selected rectifier topology gave promising results in suitable electric parameters such as efficiency and THD levels.

3.2. Standalone Operation of Two 10 kW Series-Resonant DABs

In the second step, the standalone operation of two 10 kW Series-Resonant DABs has been verified. For these tests, two 400 V/10 kW DC supplies have been connected to the inputs and resistive load to the output of converters, where 800 V voltage was expected. The cooperation of two SRDAB converters using the described in the previous section control strategy resulted in a phase shift between corresponding waveforms of each 10 kW converter. Proper steady-state operation with nominal power of 10 kW of each DAB has been checked, as illustrated in Figure 11.

Furthermore, power loss and efficiency measurements have been made. Results presented in Figure 12 show power conversion with nearly 430 watts of power loss, which result in 97.9% of efficiency.

3.3. Operation of the Single Module of the Charger at 20 kW Nominal Power

After initial tests of each charger stage in standalone operation, the EV charging module was investigated using a test bench, as presented in Figure 13. In addition to the EV charging module (VR and two SRDABs in ISOP configuration), the setup contains a digital oscilloscope and power analyzer. As a load, the power resistor was applied, and to keep the voltage constant, the Magna XR800 power supply was connected in parallel, supporting stable 800 V DC voltage at the output. The whole system is controlled by the overall control system interfaced with the CAN standard.

Figure 14 shows the start-up process of the system. Initially, the control unit checks the grid voltage level (C1) before the system is switched on. The system is ready to operate when the grid voltage reaches a nominal value. At time t₁, the DC link capacitor pre-charging process is initiated. After charging the capacitors to the appropriate voltage (C5, C6), the main circuit of the converter is switched on (t₂). Note that the small reactive current (C2) starts to flow through the input filter. At time t₃, the start signal is set to the VR, and the transistors start switching. The control algorithm adjusts the DC link voltage to the reference value. After time t₄, the voltages (C5 and C6) on the capacitors in the DC circuit are in a steady state, and then the start-up sequence of the DC/DC converters is carried out. During this time, the input and output voltage levels are measured and verified, the capacitor pre-charging process is initialized, the synchronization of converters is performed, and then the DC/DC converters start operation. After time t₅, the DC/DC converter control system regulates the phase shift between the H bridges, adjusting the current to the referenced value and causing the battery charge.

Figure 15 presents the system input and output waveforms in a steady state at a nominal power of 20 kW and 800 V output recorded with a digital oscilloscope. It can be seen that the grid current (C2) is sinusoidal and in phase with grid voltage (C1); thus, the power factor is close to unity. The voltages on the DC-link capacitors (C5 and C6) of the Vienna Rectifier are distributed evenly and without an excessive ripple. The load current (C4) is also stable and flat without distortion. However, slight disturbances in the output voltage of DC/DC converters are visible, caused by using an inductive filter at the output.

According to the scheme in Figure 13, the system was also observed using a Yokogawa WT5000 precision power analyzer. In Figure 16, a set of measurements of three-phase voltages and currents, as well as load voltage and the current, are presented, confirming high power quality. The active power P in all three phases is almost equal to the apparent power S, which means that the power factor is close to unity. Moreover, the measured Total Harmonic Distortion (THD) factors are on the level of 1.4 to 1.6% for phase voltages and currents, which is much below the standards.

In addition, laboratory measurements show an efficiency of 95.93% at a slightly higher power than the nominal value (22 kW), as presented in Figure 17. Thus, the power loss dissipated in three power converters and two power conversion stages is slightly above 900 W value. However, the maximum measured efficiency was over 97% achieved for about half of the nominal power level with less than 350 W dissipated. Taking into account the size of the system and operation at rather a high switching frequency in all conversion stages, these values can be recognized as very promising.

3.4. Operation of the Entire Charger at 40 kW Nominal Power

Finally, the complete system of 40 kW EV system composed of two presented 20 kW modules—see Figure 18—has been verified experimentally. The scheme of the laboratory setup for these tests is presented in Figure 19. This time the battery at the charger’s output was emulated with two 30 kW supplies EA-PSBE from Elektro-Automatik applied together with parallel load resistors. Again, to measure such output and bidirectional power LEM Norma D6000 power analyzer was employed.

The results of conducted tests are presented in Figure 20 and Figure 21, where waveforms during steady-state operation for slightly above nominal power of 40 kW are shown. The input phase current and output voltages of the Vienna Rectifier are presented in Figure 20, confirming the proper operation of the converter at the nominal load. It can be seen that the measured current is sinusoidal with low harmonics distortion, while the DC link voltages are balanced and stable, providing good operation conditions for SRDAB converters. Unfortunately, the available range of the current sensors in the applied power analyzer was below the maximum grid current during the 40 kW operation. Thus, the total grid current was not measured, and there are no power quality measurements for this test. However, the very good performance of each module at 20 kW and the waveform of the grid current in Figure 20 may lead to the conclusion that the complete system shows the same good power quality. Due to the same reason, the total efficiency was not measured—only the output power is presented in Figure 21. Again, there is a very solid base for the statement that the efficiency of the whole 40 kW system is comparable to the efficiency of each 20 kW submodule.

4. Conclusions

As demand for fast off-board EV chargers is growing and will even increase in the following years, the 40 kW EV charger was proposed, built, and validated experimentally to overcome this issue. The system is modular—it consists of two 20 kW modules, each operating in parallel at the input and output. The charger is supplied from a 3 × 400 V grid and, at the output, could handle with 800 V battery. Each module has a two-stage structure—from the grid side Vienna Rectifiers (VRs) were used, and from the battery side, Series-Resonant Dual-Active-Bridges (SRDABs) were applied. All converters of the system are based on silicon carbide power semiconductors. AC/DC and DC/DC stages are enclosed in 2U rack housings. After describing the hardware prototypes, their parameters, and the control system, VR and SRDAB were validated experimentally in standalone operation. The grid converter achieved about 98.4% efficiency at nominal conditions, while the DC/DC stage operated with almost 97.9% energy conversion efficiency. The proper operation of the EV charger single module was also confirmed, and for the rated module power equal to 20 kW, the energy conversion efficiency exceeded 96%, with peak efficiency over 97%. Moreover, the charging system has no negative impact on the grid with sinusoidal current waveforms at the input—the measured THD was equal to 1.6% in the worst case. Finally, the tests of the EV charger at 40 kW demonstrated the proposed charging system’s noteworthy properties and correct operation. The recorded waveforms showed appropriate performance at the charger’s input and output. The presented EV charger could be successfully utilized in off-board charger applications. Additionally, due to the employment of bipolar DC-link in the structure, the system could be conveniently extended with energy storage to ensure fast or ultra-fast charging of EV battery packs.

Further works will be focused on the expansion of possibilities of the modular system by the addition of battery storage. Moreover, works towards improvements in the management of individual converters and power management algorithms are planned. The application of energy storage predisposes the system to be used at points with the increased demand for fast charging such as highway car parks, shopping centers, or sports facilities, even despite limited grid connection power.