“Swiss Rectifier a Novel 3-Phase PFC Concept for High Power EV ...

“Swiss Rectifier a Novel 3-Phase PFC Concept for High Power EV Battery Charging Systems”
ABSTRACT
This paper introduces a new three-phase buck-type unity power factor converter appropriate for high power
Electrical Vehicle (EV) battery charging mains interfaces. The characteristics of the novel converter, named the
“SWISS Rectifier”, including the principle of operation, modulation strategy, suitable control structure, and
dimensioning formulas, are described in detail in this paper. Additionally, this rectifier solution is compared to a
conventional buck-type PFC rectifier, by using a comprehensive evaluation method, where the total required
semiconductor chip area and the total volume and weight of the passive components are assessed. Finally, the
feasibility of the SWISS Rectifier for EV battery charging applications is demonstrated by means of measurements
taken from a hardware demonstrator.
I. INTRODUCTION
Charging of Electrical Vehicle (EV) batteries inherently requires conversion of energy from the AC mains into DCquantities.
Several charging voltage and power levels have been defined by different standardization organizations
(IEC 61851, IEC62196, SAE J1772) [1]. Single-phase
Power Factor Corrector (PFC) mains interfaces are
commonly employed for low charging power levels
(e.g. P < 5 kW), whereas for higher charging power levels
3-phase PFC mains interfaces have to be applied. Possible
Power Electronics (PE) configurations for charging of EVs
are given in Figure 1. The EV charger, typically
implemented as two-stage systems, i.e. comprising a PFC
rectifier input stage followed by a DC/DC converter can be
either integrated into the car (on-board) or accommodated
in specially designed EV charging stations (off-board).
Figure 1: Overview of basic power electronics
converter topologies for EV charging systems.
In the particular case of fast charging stations (off-board),
the PE system should be able to guarantee voltage
adaptation to cope with the different specifications of
several types of vehicles. Typically, for AC mains
operating at 400V or 480V (line-to-line rms), EV chargers
with DC-bus voltage in the range of 250V-450V are
commonly used. Buck-type 3-phase PFC rectifiers are
Figure 2: Basic configuration of the SWISS Rectifier.

appropriate for high power EV chargers, as a direct connection to
the DC-bus could be used. If isolation of the PFC output from the
DC-bus is desired due to safety considerations, this could be
facilitated by an isolated DC/DC converter connected in series,
which could additionally be used for voltage level adaptation [2].
Compared to boost-type topologies, buck-type ones provide a
wider output voltage control range, while maintaining PFC
capability at the input, and allowing for dynamic current limitation
[3]. In addition, 3-phase boost rectifiers produce an output voltage
too high to directly feed the DC-bus (typically 700V-800V),
requiring a step-down DC/DC converter at their output.
This paper introduces a new 3-phase buck-type PFC rectifier
topology, named as “SWISS Rectifier” [4] [5] (cf. Figure 2),
appropriate for high power EV battery charging systems (coloured
AC/DC converter blocks in Figure 1). Other suitable applications
include power supplies for telecommunication systems, future
more electric aircraft, variable speed AC drives and high power
lighting systems. The characteristics of the new topology, which
constitutes a new 3-phase active third harmonic injection rectifier
and a suitable control stage, are presented in Section II.
Additionally, the methods for calculating losses of all the
Figure 3: The four conduction states of the
SWISS Rectifier for u a >u b >u c .
components, semiconductors and passives, are given. In Section III, the SWISS Rectifier is systematically compared
with the 6-switch buck-type rectifier, which is a conventional buck-type PFC rectifier approach. Finally, in Section
IV, measurements taken from constructed hardware prototypes are used to confirm the theoretical considerations.
II. SWISS RECTIFIER: A NEW 3-PHASE AC/DC BUCK-TYPE CONVERTER
Figure 2 shows the basic circuit configuration of the SWISS Rectifier, which was derived from a 3-phase boost-type
active third harmonic injection rectifier proposed by [6]. With this new buck-type topology and a relatively low
complexity control stage, not only controlled output voltage can be achieved, but also unity power factor operation.
Four different conduction states can be defined by T + and T - within a pulse period, where the active current
injection occurs always into only one mains phase as illustrated in Figure 3 for the interval ωt ϵ [0,π/3] (u a >u b >u c ).
The proper selection of the switching states of T + and T - allows control over the current ripples across the inductor L

and the injection current, i y . Accordingly, the converter can
be strategically modulated in order to minimize the current
ripple of i y or of the output current I DC . Sinusoidal mains
currents (i a =Gu a , i b =Gu b and i c =Gu c ) can be achieved if the
duty cycles of T + , k 1 , and T - , k 2 , are defined as follows:
k
u
max( u , u , u )
a b c
1 pn 2 2 2
ua ub uc
and
k
u
min( u , u , u )
a b c
2 pn 2 2 2
ua ub uc
Figure 4: Circuit operation for interval u a >u b >u c .
For instance, within the interval u a >u b >u c , k 1 and k 2 are
driven by:
u u u Gu u i i
k
pn a pn a pn a a
1
u 2 2 2 2 2 2
a
ub uc G u P
a
ub uc
o
IDC
and
k
u u u Gu u i i
. The
pn c pn c pn c c
2
u 2 2 2 2 2 2
a
ub uc Gua u P
b
uc
o
IDC
circuit equivalent of the possible conduction states (cf. Figure 3) is shown in Figure 4, where the converter current
formation is given by i 1k I 1k I i . This mathematical expression combined with the modulation
y 1 DC 2 DC b
definition k 1 =i a /I DC and k 2 =-i c /I DC , leads to i a +i b +i c =0, confirming the resistive mains behavior.
A suitable feedback PWM control structure, EMI filtering, and the main converter dimensioning formulas, which
include the average and rms current values of the power semiconductors, are given in Figure 5. In the proposed
control, by setting the PWM modulator for T + and T - to operate with in-phase carriers, the current ripple across i y
will be reduced while the output current I DC ripple will be maximized. For interleaved operation of these carriers, the
opposite will occur. The simulation results describing the principle of operation of the SWISS Rectifier are shown in
Figure 6. The converter specification given in Table I is considered in the simulation where operation with in-phase
or interleaved PWM carriers, and load steps (from 5 kW to 10 kW), are presented. As can be observed, the results
demonstrate that the line currents, i a,b,c , can effectively follow the sinusoidal input voltages, u a,b,c , even in case of
Figure 5: SWISS Rectifier: PWM control structure, EMI filtering and current stress across the semiconductors.

Table. I- SWISS rectifier specifications.
Input voltage, u a,b,c : 230Vrms
Input frequency, f in : 50Hz
Switching frequency, f S : 72kHz
Output power, P 0 : 10kW
Output capacitor, C 0 : 400µF
Inductor, L:
300µH
load steps, attesting the feasibility of the
proposed rectifier and PWM control. More
details for this system, including the EMI
emissions modelling and filter design, as well
as the control analysis, will be given in the
final paper.
III. COMPARATIVE EVALUATION
In order to evaluate and compare the SWISS
Rectifier with a standard buck-type AC/DC
converter, i.e. the 6-switch buck-type PFC
rectifier (cf. Figure 7), several normalized
performance indices are defined. Based on
these performance metrics a comparative
Figure 6: Simulation results for SWISS rectifier operating with inphase
or interleaved PWM carriers and load steps (5kW to 10kW).
evaluation of the proposed systems is
performed graphically, as illustrated in
Figure 8. An advantageous system would preferably cover the smallest area in the selected graphical representation.
According to the results, the SWISS Rectifier is the topology of choice for a buck-type PFC of an EV charger.
Figure 7: Power circuit structure of a conventional 6-switch
buck-type PFC rectifier and dimensioning formulas.
Figure 8: Comparative evaluation of 3-phase PFC
buck rectifier topologies for EV charging systems.

In the final paper, a more comprehensive evaluation method for PFC rectifier systems will be introduced, where the
total required semiconductor chip area and the total volume and weight of the passive components will be assessed.
This approach not only provides a distinct Figure-of-Merit for comparison, but also enables the semiconductor costs,
efficiency, and power density of the different topologies to be determined.
IV. EXPERIMENTAL RESULTS
In this section, the feasibility of the SWISS Rectifier and the 6-switch buck-type PFC rectifier for EV battery
charging systems is demonstrated by measurements taken from constructed hardware prototypes. In this Digest only
results of the experimental tests carried out for the latter rectifier are shown. However, in the final version of this
paper, the prototype and experimental results for the SWISS Rectifier will also be presented.
In Figure 9(a), an ultra-efficient (≈99%) 6-switch buck-type rectifier prototype is shown. The power density of this
system is 2.2 kW/dm 3 . Figure 9(b) presents the measured sinusoidal input currents for 4.5 kW operation. The results
obtained with the prototype confirm the operation and advantages of this system for EV applications.
i a i b i c
(a)
(b)
Figure 9: (a) 6-switch buck-type rectifier prototype and (b) experimental results.
5A/Div
2ms/Div
V. CONCLUSIONS and FINAL PAPER
This paper proposes a novel 3-phase unity power factor AC/DC converter appropriate not only for high power EV
battery charging systems, but also power supplies for telecommunication systems, future more electric aircraft,
variable speed AC drivers and high power lighting systems. The converter concept, named as “SWISS Rectifier”, is
comprehensively compared with a conventional 6-switch buck-type PFC rectifier. According to the results, the
SWISS Rectifier is the topology of choice for a buck-type PFC mains interface of an EV battery charger.
In the final version of this paper, the requirements for mains interface converters in EV battery charging applications
will be described in detail. More information for the SWISS Rectifier, including the EMI emissions modelling and
filter design, as well as the control analysis, will be given. In addition, a detailed analysis of component losses for 10
kW systems employing Si and SiC semiconductor devices will be shown. Finally, the prototype and experimental
results for a 10 kW SWISS Rectifier will be presented.

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