High-Voltage Stations for Electric Vehicle Fast-Charging: Trends, Standards, Charging Modes and Comparison of Unity Power-Factor Rectifiers

Emission of greenhouse gases and scarcity of fossil fuels have put the focus of the scientific community, industry and society on the electric vehicle (EV). In order to reduce CO2 emissions, cutting-edge policies and regulations are being imposed worldwide, where the use of EVs is being encouraged. In the best of scenarios reaching 245 million EVs by 2030 is expected. Extensive use of EV-s requires the installation of a wide grid of charging stations and it is very important to stablish the best charging power topology in terms of efficiency and impact in the grid. This paper presents a review of the most relevant issues in EV charging station power topologies. This review includes the impact of the battery technology, currently existing standards and proposals for power converters in the charging stations. In this review process, some disadvantages of current chargers have been identified, such as poor efficiency and power factor. To solve these limitations, five unidirectional three-phase rectifier topologies have been proposed for fast EV charging stations that enhance the current situation of chargers. Simulation results show that all the proposed topologies improve the power factor issue without penalizing efficiency. The topologies with the best overall performance are the Vienna 6-switch and the Vienna T-type rectifier. These two converters achieve high efficiency and power factor, and they allow a better distribution of losses among semiconductors, which significantly increase the life-cycle of the semiconductor devices and the reliability of the converter.

road vehicles will be around 2 billion in 2050 [5]. In this context, the electrification of the transport sector in general, and that of road vehicles in particular, becomes essential to overcome the environmental problems mentioned above. This challenge demands improvements in all the power chain of the electric vehicle (batteries, power converters, semiconductors, charging stations. . . ), providing innovative solutions that facilitate end-customer access to the electric vehicle (EV) [6], [7]. With this objective, several initiatives and campaigns are being promoted worldwide: Electric Vehicles Initiative (EVI) [8], EV30@30 campaign [9], EV100 [10], Global EV Pilot City program [2], Drive to Zero campaign [2], GEF-7 global program [11], etc.  Regarding EV sales, the IEA [2] estimates that the global stock of EVs can reach 140 million by 2030 with stated policy scenarios (STEPS), and if ambitious sustainable development scenarios (SDS) are implemented, it would reach 245 million units (see Fig. 1). In this sense, the IEA forecasts a surge in the global electricity demand of EVs, in both stated policies scenarios and sustainable development scenarios (Fig. 1-STEPS and Fig. 1-SDS) [2]. As it can be seen in Fig. 2, an increase around 550 TWh is expected from 2019 to 2030 according to STEPS. Conversely, in the SDS scenario reaching 1000 TWh is expected, which is equivalent to an 11 fold increase compared to 2019. While EVs today represent a small fraction of total electricity consumption (globally less than 0.5 %), this will change in the future. According [2], in 2030 EVs could represent between 1-4 % of global electricity consumption in the STEPS scenario and between 2-6 % in the SDS [2].
In such a context, the EV takes on a lot of relevance for the grid. The grid will have to be dimensioned so that these demands will not become a source of problems for the electrical supply system. Many aspects need to be considered: change of peak and valley hours in the demand curve, re-evaluation of rating of the power grid and others. During the past few years there has been a focus on increasing grid power quality. Today the greatest part of the harmonic distortion in the electric grid is caused by the input stage of power electronic converters. International standards, such as IEEE 519 and EN 61000, set the limits to power qualityrelated parameters (harmonic currents and voltages). Moreover, the power factor (PF) is one of the key performance parameters for a grid without distortion, where power factor (PF) 1 is necessary for that purpose [13].  [12]).
Regarding the electrification of the vehicles, there are several alternatives (see Fig. 3) to internal combustion engines (ICE) [14]- [20]: battery electric vehicles (BEV), plug-in hybrid electric vehicle (PHEV), hybrid electric vehicles (HEV), fuel cell electric vehicles (FCEV), and fuel cell hybrid electric vehicles (FCHEV). Nowadays, there is a trend among manufacturers towards BEV and PHEV and it seems that it will be maintained in the near future [14], [21]. Table 1 shows some examples of commercialized electric vehicles (BEV) and plug-in hybrids (PHEV).
The majority of light EVs are equipped with battery packs with nominal voltage range between 300 V and 420 V, while for heavy EVs this voltage can reach up to 800 V [22]. However, according to some studies [23]- [27], a change in trend is expected in the battery voltage of light EVs, and an increase in the DC bus to 800 V systems 1 is expected. With this change, a substantial reduction in the conductive wire weight could be achieved, since half the current will be handled for the same power [23]. Increasing the voltage of the battery pack would also reduce quadratic conduction losses (P = I 2 R). Therefore, with this change in the battery voltage, the efficiency of the EV will be improved. Battery voltage has a great impact in the selection of the charging station power converter topology. Section II presents the most extended types of batteries and their expected evolution for 2030. In section III, the standards applicable to each of the stages of the recharging system are reviewed. In addition, the charging modes that support current EVs and the types of existing charging stations are reviewed, and also a study of DC fast-charge stations from different manufacturers is carried out. In Section IV, a classification of valid power converter topologies for the fast-charging application is shown from a general perspective. Finally, in Section V, a comparison is made between the most suitable topologies selected with the criteria of high efficiency, unity power factor, and high power rating for fast-charging.

II. BATTERIES: CURRENT STATUS AND FUTURE PROSPECTS
Batteries play a crucial role in making EVs competitive against ICEs [28], [29]. The batteries, apart from supplying energy to EVs, can also act as energy storage systems (ESS) for the grid. Charging the batteries in the hours of less energy demand (off-peak hours) and then providing that energy in the periods with higher demand [30]- [32] enables to make the energy demand curve flatter, with the benefits that this entails [33]- [37]. According to the International Renewable Energy Agency (IRENA), using ESSs would reduce energy installation costs between 50 % and 66 % (see Fig. 4) [38].
As far as battery technologies are concerned, there are no one-size-fits-all solutions in the ESS, and the decision to opt for one storage technology over another depends on several parameters, such as power density, lifetime, efficiency and operation temperature [39], [40]. In this context, some of the best known materials for battery systems are lead-acid [41]- [43], nickel-cadmium [44], [45] and lithium-ion [46]- [48]. Lead-acid batteries are one of the most mature and inexpensive battery technologies [38], [41], [49] but they are not as suitable as lithium-ion for EV application, since VOLUME 9, 2021  their energy density is low [42]. Even so, they are still widely used for the stabilization of the grid [43]. Nickel-cadmium batteries serve special markets where energy must be stored in extreme weather conditions, as they work well where temperatures are very low (down to −40 o C) [44]. The biggest drawback to using them in the application of the EV is its high price and low power density [44]. In this context, lithiumion batteries have entered the industrial market (see Table 1), drawing on the extensive experience gained in developing batteries for electric and hybrid vehicles. The choice of lithium-ion for EVs is justified by high energy density, lowcharge operation capability [47], [48] and long lifetime which could reach the full EV operating life [40]). This technology is versatile, highly scalable and can be adapted to almost any power requirement [40], [46].
According with the Association of European Automotive and Industrial Battery Manufacturers (EUROBAT), Table 2 shows how lead-acid, nickel-cadmium and lithiumion batteries will be improved by 2030 [40]. These three types of batteries tend to improve their efficiencies (here lithiumion batteries achieve 95 % efficiency, 5 % and 10 % higher than lead-acid and nickel-cadmium respectively), power densities (lithium-ion batteries are expected to reach 1100 Wh/l, more than 7 times greater than its most direct rival, lead-acid), recycling capabilities (lithium-ion is expected to improve the most, until almost reaching lead-acid batteries recycling capacity of 90 %) and lifetime (here lithium-ion reaches >10.000 life cycles, twice that of its competitors) [40]. EV manufacturers are currently selecting lithium-ion batteries and it seems that in the near future this trend will not change, since none of the other battery materials reach the levels of power density required in EVs. In addition, according to the international organization Bloomberg-NEF [50], [51], the price trend of batteries is downward   (see Fig. 5), which will make lithium-ion technology much more competitive.

III. ELECTRIC VEHICLE: STANDARDS, CHARGING MODES AND CHARGING STATIONS
Electric vehicle charging points [1], [2], [8], [9] are spreading around the world due to the growing demand of EVs. This has led to the regulation of charging stations. In this context, there are several standards defined by organizations for EV charging established worldwide [52]- [55]: IEC, SAE, IEEE, GB/T, CHAdeMO, among others. Figure 6 shows the electric stages of an EV: (I) the charging stage, (II) the battery stage (where there is a 7 battery system, which is charged through the stage (I)) and finally, (III) the power train (composed by the power converter 8 and the electric motor 9 which is responsible for transmitting the power to the wheels). Regarding (I) the charging stage, there are standards related to 1 the grid power-connection, 1 the grid central management system communications, 4 the EV charging cable power and communication capability, 5 the vehicle connectors, 5 the battery management system (it can be an on-board charger, if not, 6 can act as off-board charger). Table 3 summarizes the standards( Fig. 6 -1 to 6) classified by regions. The EV charging modes are included in the IEC 62196 (international standard for the set of electrical connectors and charging modes), IEC 61851 (international standard for conductive electric vehicle systems) and SAE J1772 (general physical, electrical, communication protocol and performance requirements) standards, used in Europe and in USA, respectively. These regulations are being updated as technology matures, adapting to increasing power ratings for lower charging times. 2 Regarding the EV charging modes (see Table 4), some of best known battery charging modes are described in the IEC 61851, IEC 62196 and SAE J1772 standards. The charger power ranges from 4 kW (IEC 61851-1:2020, mode 1) to 600 kW (IEC 61851-23:2014, mode 4), which shows that these regulations contemplate a wide range of chargers. Special attention should be paid to the fastest chargers (120-600 kW) since they would decrease the anxiety of EV owners caused by the lack of large autonomy-range and the non-possibility of fast-charging [24], [57]- [63]. In this sense, many manufacturers are working in EV fast-charging system development. Some of them are shown in Table 5. According to the data provided by these manufacturers the power converters have an efficiency of 94-95 %.
Another important aspect that characterizes the charging station is the power factor (1. A suitable electric vehicle charger is one that demands unity power factor, PF = 1.  The distortion factor, (DistF), measures the effect of the total harmonic distortion (THD), and the displacement factor, (DispF), also known as cos( ), measures the effect of the phase displacement of the current first harmonic and the grid voltage. Figure 7 shows the different parameters affecting power factor. Assuming that cos( ) is equal to 1 in the converters in Table 5, from (1), the PF values provided by the manufacturers, between 0,96 and 0,99, would mean the THD i is between 29 % and 14 %.
There is a need to improve harmonic distortion in the charging stations (THD i ). In this sense, a niche for improvement is the power converter of the battery chargers, where several topologies can provide power factor close to unity (PF 1). Section IV analyses alternatives of power converter topologies that can achieve these targets.

IV. UNIDIRECTIONAL THREE-PHASE RECTIFIERS FOR FAST EV CHARGING STATIONS
In the actual stage of development of technology users who normally require fast-charging do not act as power suppliers to the grid, and therefore the charger does not have to be bidirectional. In the short and medium term there is no ESS capability in the grid. Thus, fast-charging stations demand unidirectional rectifiers for users who need a quick emergency charge, those who do not have electric chargers at their homes, 3 and customers who are on long routes [65]- [67]. In this context, the converters (see Fig. 8) that meet the requirements of the energy demand of this type of customer can be divided in three main groups [68], [69]: (1) passive, (2) hybrid and (3) active rectifiers: 1) Passive rectifiers: these are low complexity rectifiers that are divided into two groups: single diode bridges and multi-pulse rectifiers. These type of topologies  allow easy implementation, but at the same time lack of controllability results in low quality input current and output voltages [68], [70], [71], which makes ageing of batteries worse [72]- [74]. 2) Many of the unidirectional three-phase rectifiers that appear in the literature are located in the subset of hybrids rectifiers. They are divided into three groups: those based on reactance, those obtained by combining diodes and DC/DC converters and, finally, the topologies that allow injection of the third harmonic [68]. In general, the hybrid converters are made up of passive (capacitors and inductors) and active semiconductor devices, the latter being found in reduced quantities, increasing the degree of controllability compared to passive rectifiers. However, the quality of the output voltages given by the hybrid topologies is still not suitable for the EV charging application [68]. 3) Active rectifiers are known for their high degree of controllability, synthesizing better input currents (THD i < 5%) and output voltages, and potentially they could achieve excellent efficiencies (up to 99%) [75]- [81]. These converters use higher amounts of active components compared to passive and hybrid rectifiers. Active rectifiers can be divided in two subgroups: direct and phase-modular systems. These topologies are used extensively in industry; however their use is rarely seen implemented for the EV charging application. This is due to the fact that currently (as Table 1 shows) most EVs use battery systems around 300-400 V. However, there is a change in trend towards 800 V battery systems [23]- [27]. In this context, this work focuses on boost-type unidirectional three-phase rectifier topologies, adapted to the trend towards 800 V battery systems [23]- [27]. These topologies are the most suitable for EV charging stations and they are selected for comparison in this work. The scientific literature proposes several active threephase rectifiers, which can be classified into (Fig. 8): Grid-connected rectifiers [82]- [96], Power Factor Corrector (PFC) [97]- [107] and Vienna rectifiers [108]- [118]. There is a large number of proposed converters, however, in order to reduce the number of studied converters, a parallel analysis of those topologies used by manufacturers has been made. Table 6 shows that most manufacturers use the following topologies: NPC, Vienna 6-switch rectifier, Vienna T-type and the three-phase two-level converter (3θ − 2L).
As a result of the previous review the most suitable topologies for fast charging of high voltage batteries have been identified (see Fig. 9): VOLUME 9, 2021 (a) Conventional three-phase two-level rectifier (3θ − 2L) [119] is characterized by its simplicity and controllability ( Fig. 9(a)). This topology is well positioned in the market. For this reason, it has been used as benchmark in this work. The semiconductor devices must block the voltage of the entire DC bus and the switching takes place between the two devices in each phase (one leg). Modulation and proper control techniques allow the voltage and current to be maintained in phase [83], [84]. However, two-level converters cannot synthesize the same waveforms quality as three-level topologies [120], [121]. (b) Neutral Point Clamped converter (NPC) [122] is a topology that can provide three voltage levels and is made up of twelve switches and six diodes ( Fig. 9(b)). The devices must block half of the voltage of the entire DC bus [117]. This allows lower voltage rating semiconductors with lower conduction voltage drop. This topology also applies double effective frequency in the output, reducing the size of the output capacitors. High levels of efficiency (around 97 %) have been achieved with these converters [123]- [130]. These topologies have some drawbacks such as fluctuations on the output DC bus and mismatches in the distribution of losses between power devices [131], [132]. However, using suitable modulation techniques or additional control circuits, this problems can be minimized [133]. (c) Vienna 6-switch rectifier [68] is an adaptation of the original NPC topology in which non-current switches are turned-off during the rectifying operation. This topology is a three voltage level rectifier, it has six switches and twelve diodes ( Fig. 9(c)) and can achieve very high efficiency (98%) [75], [76]. The semiconductor devices must block half of the voltage of the DC bus and high frequency switching takes place between one diode and the switch [117]. This topology greatly facilitates the process of precharging their output capacitors due to the path of the diodes [68]. However, one of the main drawbacks of this topology is the high number of devices. (d) The Vienna 3-switch rectifier [134] (Fig. 9(d)), like the previous topology, is also classified among three-level voltage rectifiers. It is built by three switches and eighteen diodes. It reduces the number of controlled switches at the cost of increasing the number of simultaneously on devices to three units. The devices must block half the voltage of the entire DC bus and it can achieve a high efficiency (97-98 %) [77], [78]. The number of semiconductors can be considered its biggest disadvantage compared to other rectifiers. Among the analysed topologies, this is the one with the least number of active switches. (e) The Vienna T-type rectifier [135], together with the Vienna 6-switch rectifier, is the most extended Vienna-type topology in the scientific literature. This topology is also a three voltage level rectifier. It is built by six diodes, making a three-phase diode rectifier and six switches forming three bidirectional switches (Fig. 9(e)). The devices must block all the DC bus voltage and the switching occurs between the diode and two series connected switches, one on diode-mode and the other in MOSFETmode [117]. This topology can reach an efficiency can be achieved using advanced modulations like interleaving technique [79]. The drawback of this topology is that in the fast commutation-cell three devices have to switch at the same time: a diode, and two MOSFETs. Furthermore, the MOSFETs carry current in both half cycles, therefore the losses are highly concentrated in these devices. (f)-(g) The Y-switch ( Fig. 9(f)) and -switch rectifiers ( Fig. 9(g)) are alternatives of the T-type topology with variations of the composition of the T-type structures between phases. Since it is a two-level rectifier (the output bus is not split in two and connected to the midpoint), it is not possible to obtain the benefits of three-level rectifiers [120], [121]. For this reason, these two topologies are not considered as suitable for the EV charging application.

V. COMPARISON OF SELECTED THREE-PHASE BOOST-TYPE RECTIFIERS FOR FAST EV CHARGING STATIONS
This section compares the topologies of interest for fastcharging of the EVs reviewed in the previous section through simulations performed with the PSIM simulation tool. For that purpose, a Forward Oriented Control (FOC) and Pulse Width Modulation (PWM) have been used. When analysing the results, several figures of merit have been taken into account, such as the number of devices and blocking voltage, efficiency, quality of input currents (PF 1, THD i < 5%, and cos( ) = 1), quality of output voltage (low voltage ripple ( V out ) and capacitor currents (i Crms )) and, finally, a good distribution of semiconductor losses (which is very important regarding the lifetime of the converter [136]).
The proposed simulation scheme (Fig. 10) consists of a three-phase input source 1, input inductors 1, boosttype three-phase rectifier topology under test 4 (3θ − 2L, NPC, Vienna 6-switch, Vienna 3-switch and Vienna T-type), output capacitors 4 and resistive load simulating battery current-demand 5. The test setup is described in Table 7, where the parameter values of the simulation models are detailed. 4,5 Simulation results are summarized in Table 8. 3θ − 2L topology presents the lowest component count with only six semiconductors, but voltage rating of each one of them is the entire bus voltage,V BUS . The Vienna 3-switch is the topology with the highest component count (21). Regarding efficiency, the 3θ − 2L, the Vienna 6-switch and the Vienna T-type present the highest efficiency with values greater 4 The SKKD8112 diodes can only be used in Vienna 6-switch (Fig. 9(c)) and Vienna 3-switch ( Fig. 9(d)) topologies, since the input diodes (D 1 , D 1 , D 2 , D 2 , D 3 , D 3 ) in these topologies do not switch current at high frequency. With the implementation of these diodes at the input, conduction losses are greatly improved due to their low resistance. 5 Silicon Carbide (SiC) MOSFET semiconductors has been used to carry out the simulations, since they have better switching performance compared to the Silicon (Si) devices [51]. In this sense, increasing the switching frequency is a suitable technique to reduce the size of the reactive components, thus improving the power density of the converters.  than 96 %. The input current and output voltage waveforms in all the converters (THD i < 5%, V BUS < 4.81 V and i Crms ∈ (42.7 A, 47.1 A) are of high quality, and any of these topologies is valid to achieve the figures of merit required by fast-chargers. Even so, comparing the input current and normalized frequency response (FFT) (Fig. 11), it can be observed that compared to three-level topologies, the 3θ − 2L has worse input current quality, as it has the highest  high-frequency current ripple (4 A) and the highest levels of distortion (THD i = 4, 04 %). The latter confirms the negative aspect of the two-level voltage converters [120], [121]. Fig. 13(a) shows that distribution of losses is very different for each of the topologies. The first thing that stands out is that the Vienna 6-switch and the Vienna T-type topologies have Distribution of losses among semiconductors is a very relevant aspect for the reliability of the converter. One of the most extended model for the estimation of lifetime of semiconductors is the Arrhenius and Coffin-Manson combination [136] of laws of degradation (2), where A, and α are device dependent constants, R gas is the gas constant (8.314 J /mol.K ), Tm j = T jmin + (T jmax − T jmin )/2 is the mean cycle temperature expressed in Kelvin, and the internal energy Q is 7.8×10 4 Jmol −l . Tj is the variation of the junction temperature. The constants α = −5, and, A=640 are obtained from curve fitting in the LESIT study. Fig. 13(b) shows the temperature change for each vehicle charge using the same semiconductor device in the five topologies. As shown in Fig. 13(b), the differences in temperature that occur in the diodes are practically negligible. The biggest differences occur in the MOSFETs. In this sense the 3θ − 2L, the NPC and the Vienna 3-switch topologies have respectively 163,7 o C, 140,8 o C and 145,1 o C junction temperature (T j ) excursion, which makes these topologies very sensitive regarding lifetime compared to the Vienna 6-switch and Vienna T-type topologies that have respectively 92,5 o C and 122,6 o C. Regarding the loss distribution, topologies with best thermal behaviour are the Vienna 6-switch and the Vienna T-type, with a maximum temperature deviation between devices of 27,2 o C and 39,2 o C, respectively.
In order to analyse how much this increase in temperature affects lifetime, LESIT study curves have been chosen (see Fig. 13(c)) to show an approximation of how a few degrees of temperature can vary the lifetime of a device. In this analysis, referring to a 50 kW charging system, it can be seen that the MOSFETs of the Vienna 6-switch can last 1.64 E +06 cycles. Conversely, for the Vienna T-type this number is reduced to 6.18 E + 04. The number of cycles would be much lower in the other three topologies.
According to the defined comparison criteria, the Vienna 6-switch and the Vienna T-type are the best alternative, due to their high efficiency, good quality of input currents and output voltages, and for their better distribution of losses between semiconductors. Because of the similar performance of both topologies (Vienna 6-switch and Vienna T-type), an additional aspect has been considered to make a more accurate comparison, the scalability in switching frequency of the rectifiers. This aspect is relevant since there is a trend towards power converters with higher power densities. In this sense, one of the ways to achieve this is by reducing inductances and capacities by increasing the switching frequency. The Vienna 6-switch high-frequency commutation-cell consists of a single MOSFET and a diode (Fig. 14(a)). On the other side, Vienna T-type ( Fig. 14(b)) has to commutate two MOSFETs in series that work as a bidirectional switch. In this sense, series connection on the T-type topology results in an increase in resistive and parasitic components such as inductances, which will cause greater power losses and overshoots in voltage and current. Additionally, this effect can be increased if discrete devices are used instead of modules, since they have higher values of parasitic inductances because of their packaging [137]- [139]. Due to the structure of the Vienna 6-switch, the commutation-cell area is reduced VOLUME 9, 2021 with the use of a snubber capacitor very near commutationcell. The result of using these cells have been demonstrated in several works [140]- [142], where commutation cells of about 6 nH are implemented. Moreover, the effectiveness of using snubber capacitors has been also demonstrated in other works [143], [144], reducing switching losses produced by parasitic overshoots on voltage.
The general review and subsequent comparative of electric vehicle charging topologies has concluded with five valid topologies for the EV charging application. Therefore, taking into account the analysis carried out, the most appropriate converters for the application of electric vehicle charging are the Vienna 6-switch and the Vienna T-type, especially for their efficiency, input power quality and stability of the output voltage, all with a suitable distribution of the losses between devices.

VI. CONCLUSION
There is a growing turned towards implementation of policies to reduce the GHG emissions, where the EVs have crucial relevance. Battery systems have a special relevance in EV and that is why short-term improvements have been analysed. In this context, lithium batteries currently are the prevailing technology, and according to the literature they will continue to be so, since these batteries improve the energy density the most (which is expected to double to 1000 Wh/l), increase the number of charging cycles (which will triple the current batteries lifetime), and reduce the price of battery systems (which is expected to be below $ 61/kWh, compared to current prices of $ 156/kWh). Regarding operating voltages, nowadays, most of the EV propulsion systems works at 300-420 V, but the trend is to increase these voltage levels to 800 V. With this trend-change, a reduction on the system current is achieved, making it possible to reduce the wire gauge, thus reducing the weight. It has also been seen that fast-charging users normally only demand power from the grid. In this context, single phase rectifiers require very high currents and would not be able to provide sufficient power levels for fast-charging. Therefore, it is necessary to use threephase converters, with which the problem of power and high current at the input of the fast-charging rectifiers is solved.
Five suitable topologies (3θ − 2L, the NPC, the Vienna 6-switch, the Vienna 3-switch and the Vienna T-type) have been analysed that improve the current situation of the fastcharging stations of the EVs. Although with some shortcomings, all the presented topologies meet the criteria established in this work, where specially the Vienna 6-switch and the Vienna T-type have an advantage over the other due to their performance, particularly in efficiency, quality of the input currents and output voltages, and in the distribution of losses. Using LESIT study results, it has been shown that small increases in operating temperature can greatly reduce the lifetime of semiconductors and it is important to use designs in which the power losses are distributed between devices.
Finally, it is shown that increasing the switching frequency is feasible in order to reduce passive components, such as coils and capacitors, thus improving the power density of the converters. In this context, it is pointed out that using the Vienna 6-switch rectifier has advantages with respect to scalability in switching frequency, since it has a better commutation-cell if compared to Vienna T-type, the closest rival in the comparison.