Evaluation of Control Methods for Isolated Threephase AC-DC converter
using Modular Multilevel Converter Topology
Toshiki Nakanishi

Jun-ichi Itoh

Dept. of Electrical, Electronics and Information Engineering
Nagaoka University of Technology
Nagaoka Niigata, Japannakanishi@stn.nagoakaut.ac.jp

Dept. of Electrical, Electronics and Information Engineering
Nagaoka University of Technology
Nagaoka Niigata, Japan
itoh@vos.nagaokaut.ac.jp

Abstract— This paper discusses a novel isolated three-phase
AC-DC converter using Modular Multi-level Converter (MMC)
topology for a medium voltage application. The MMC at a
primary stage of an isolated AC-DC converter can directly
convert a three-phase AC into a high-frequency AC voltage of 1
kHz. In this paper, the features of the proposed circuit are
discussed according to the voltage ratings of the switching
devices. Moreover, the total harmonic distortion (THD) of the
input current, the output voltage, the number of cells and thecapacitance of the DC capacitor are evaluated on each switching
devices in the proposed system. Finally, the proposed system
performance with SiC MOSFET of 3.3 kV is demonstrated by thesimulation. As a result, the proposed converter achieves the low
THD of the input current waveform which is approximately
2.64%.

level converters because of the cascade connection of each cellwhich is constructed from switching devices and a DC
capacitor. (ii) The MMC can reduce the harmonic distortions in
the output voltage due to use of many voltage levels which issimilarly to the multi-level converters. Therefore, the MMC
topology can be applied in high capacity power applications;such as Static synchronous Compensator (STATCOM) andmedium adjustable speed drive systems [6-9].
However, the high power converters which use MMC resultthat the volume of the converters becomes larger due to thehuge transformer which is operated with line-frequency
between the grid and the converter for safety purpose. In orderto reduce the size of the transformer, a high frequency
operation of converter is effective. Furthermore, a small andsimple transformer can be used by applying a high frequency
link of single-phase. However, three-phase to single-phase ACAC direct power converters using MMC which convert
commercial frequency AC voltage into high frequency voltage
have not been so many reported [10].

Kywords—Modular Multi-level converter; Capacitor Voltage
Control; Direct Power Conversion; H-bridge Cell; Isolated Threephase AC-DC converter;I.

INTRODUCTION

This paper proposes a novel isolated three-phase AC-DC
converter using MMC and the control strategy. Three-phase to
single-phase MMC topology is used at primary stage in theisolated AC-DC converter. The proposed system can directly
convert an input three-phase voltage into a high frequency
single-phase voltage of 2.6 kV and 1 kHz. Furthermore, thevolume of the proposed system can become small due to highfrequency transformer. In addition, the input current and theDC capacitor voltage of the cells can be controlled
independently. This paper organized as follows; first, thecircuit topology of the MMC is explained. Second, each of thecontrol strategy which controls the input current, the cell
capacitor voltage and the output voltage of the MMC, aredescribed. Finally, the comparative evaluations of the systemdesign based on the rated voltage of switching devices are
considered. In particular, the numbers of cells and switching
devices, the electrostatic energy of the DC capacitors, the THDof the input current and the efficiency considering the loss at
switching devices are evaluated when high rated voltage
devices: 2.5-kV IGBT, 3.3-kV IGBT and 3.3-kV SiCMOSFET are applied to the proposed system.

Recently, the multi-level converter topologies have been
discussed actively in the medium voltage application such as
3.3 kV or 6.6 kV [1-4]. However, the conventional high power
converters have some disadvantages: (i) the malfunctions or
failures of other power conversion due to harmonics
disturbance, and (ii) the cost is high due to high voltage rating
devices and passive components. On the other hand, the multilevel converters are able to decrease the harmonic distortionsand volumes of the input or output filters. Moreover, thevoltage stress of a switching device can be reduced. Therefore,switching devices, which are high speed switching and the low
rated voltage can be used in the multi-level converters.
However, the circuit configuration of the multi-level converter
becomes complicated because the number of the circuitcomponents increase proportional to the power capacity. Thus,
it is difficult to increase the power capacity for theconventional multi-level converter topologies.
In order to solve this problem, Modular Multi-level
Converter (MMC) has been proposed as one of the multi-level
converter topologies [5]. The advantages of the MMC are
follows; (i) the circuit configuration is simpler than other multi-

978-1-4799-0482-2/13/$31.00 ©2013 IEEE

52

II.

voltage control block uses two controls, namely an averagecontrol and a balance control [5].

MAIN CIRCUIT CONFIGURATION

Fig.1(a) shows the circuit configuration of the isolated
three-phase AC-DC converter using MMC topology. E Eachleg consists of two interconnection reactors Lb and H-bridge
cells. Then, each of the leg is connected to a load in parallel.
Due to the cascade connection of cells, the proposed converter
can achieve a multi-level voltage waveform and also can
reduce the rated voltage of each cell. Thus, increasing thenumbers of the cascaded cells are benefits because theharmonic distortions can be reduced, and low voltage rating
switching devices can be applied.

A. Average Voltage Control
The average voltage control corrects the error between the
average value of the capacitors voltage in each arm group andthe voltage command that is generated from a PI control. The
average value of the capacitors voltage vc_ave is given by (1).

vc _ ave =Furthermore, the proposed system can directly convert an
input three-phase voltage into a high frequency single-phasevoltage. Therefore, a high frequency transformer can beapplied. Moreover, the volume of the proposed system canbecome small due to the high frequency transformer. In
addition, it is able to be isolated between an input side and an
output side by the high frequency transformer.

(1)

where n is the number of cells at each leg and vcrm, vcsm andvcsm are each capacitor voltage in the each arm. The number ofcells is set n/2 to calculate the average value of the capacitors
voltage in each arm group because each arm group is
independently controlled.
B. Balance Voltage Control
The average voltage control is used to keep the voltage of
all capacitor voltage. However, an unbalance voltage which
occurs among the capacitors cannot be suppressed by theaverage voltage control only because the average control
corrects only the error between the average value of thecapacitors voltage in each group in subjects to the voltage
command. Therefore, the balance voltage control is used tocorrect the error between each of the capacitors voltage and thevoltage command.

The proposed system can control each arm group separately.
In this paper, the arm group on the upper side is defined agroup A, the arm group on the downside is defined a group B.
Fig.1(b) shows a configuration of the H-bridge cell. Eachcell consists of four switching devices and a DC capacitor. The
output voltage of each cell is controlled by pulse widthmodulation (PWM). Furthermore, it is necessary to keep thecapacitor voltage constantly in order to operate the main
circuit.
III.

1 n/2
∑ (vcrm + vcsm + vctm )3 m =1(

CONTROL STRATEGY)

vce _ km = K C vc * −vc _ km ik

Fig. 3 shows the control block of the proposed converter.
The proposed control is applied to each arm group A and B as
shown in Fig. 1. The proposed control block diagram isseparated into two blocks, the capacitor voltage control blockand the input current control block. Moreover, the capacitork = r, s, t

m = 1,2 ,...n / 2(2)where vcrm, vcsm and vcsm are each capacitor voltage in the eacharm, KC is the gain of the balance voltage control, k is the index
of each phase, m is the index of the cell step.

(a) Main circuit configuration.
(b) H-bridge cell.
Fig. 1. Circuit diagrams of the proposed circuit for AC-DC isolated converter with MMC topology.

53

Fig. 2. Control block diagrams of the proposed circuit for the arm group A.

Moreover, the error between the capacitor voltage
command vc* and each capacitor voltage contains non-linear
factor. Therefore, the high response angular frequency has tobe set. In the proposed control method, it is possible to achieve
the voltage balance by multiply the error by each arm current ik
at the low response angular frequency. Moreover, it is notnecessary to erase the error exactly because the balance control
is the auxiliary control for the average voltage control.
Therefore, the balance control can be constructed by only aproportional control.

Finally, the output voltage of the cell is given by (3). Notethat the sign of the MMC output voltage command vmmc* has tobe changed because the direction of cell output voltage isdifferent in the group A and the group B.

(

)

(

)

1
2v Ak + vmmc * −vce _ Akm
n1
vBkm = 2vBk − vmmc * −vce _ Bkm
nv Akm =

C. Input Current Control
The input current separately flows to the upper side armand the downside arm in each phase. Therefore, the input
current can be determined by controlling the current whichflow in buffer reactors. In addition, the input current control
does not need the link operation between the group A and thegroup B. Furthermore, the control systems are able to separate
between the group A and the group B.

k = r , s ,t

m = 1,2 ,...n / 2 (3)E. Capacitor Voltage Command
The MMC output voltage command vmmc* that uses toobtain the high frequency output voltage is added to the output
block of the input current control. The change of voltage value
in each cell depends on the number of cells at each leg since
the cells are connected to the load in series. In addition, eachcapacitor voltage also depends on the input and output voltage.
The capacitor voltage command vc*is given by (4).

The input current control is implemented by PI controllers,
and the compensators for the cross terms of id and iq which areprovided from the transformation of rotating frame. The input
current control is separated into the active current control (id)and the reactive current control (iq). The reactive current iq* is
set to zero to control the input power factor to 1 and to reduce
the absolute value of the input current.

⎞1⎛ 2
vc * ≥ ⎜ 2 E + Vmmc ⎟
⎟
⎜
n⎝ 3
⎠

(4)

where E is an effective value of the input line to line voltage,
Vmmc is a maximum value of the MMC output voltage
command and n is the number of cells at each leg. From (4),the output voltage of each cell becomes smaller as thenumbers of cells increase. Therefore, the capacitor voltage
command can be lower.

Therefore, the same input current command is given to eachcell because cascaded cells control the common arm current.
D. MMC Output Voltage Control
The same command of the MMC output voltage control isgiven to each cell in order to convert a three-phase input
voltage to a high frequency voltage. The output voltage of acell is required vmmc*/n when the command of the MMC output
voltage control is vmmc* and the number of cells in a leg is.

IV.

EVALUATION OF THE PROPOSED SYSTEM

A. Evaluation Condition
In the proposed system, from (4), the capacitor voltage isdepends on the input current control and the MMC output
voltage control. Therefore, the rated voltage of the switching54

device is depends on the capacitor voltage of the cell. In cases
where the high rated voltage devices are applied, it is possible
to reduce the number of the circuit components in the proposedsystem. On other hand, in cases where the low rated voltage
devices are applied and the number of cells increases, it ispossible to suppress the harmonic distortion of the input current
due to the high speed switching and many voltage levels withusing the low voltage rating devices. Thus, the design factors:
the number of cells, the capacitor voltage and the THD of the
input current are different. Therefore, the comparing of thecircuit performance based on the rated voltage of switching
devices is required. In comparison of the circuit performance,some IGBTs with the high rated voltage and SiC with the rated
voltage 3.3 kV are employed.

Table 1. Device Parameters and switching frequency.

2.5-kV IGBT
CM400DY-50H

3.3-kV IGBT
CM800E2C-66H

6.5-kV IGBTFZ400R65KE3

The conditions in order to compare the circuit performance
are as follow.

Device Parameters
VCE=2.5kV, Ic=400A,
Eon = 500 mJ @ Ic = 400 A,
VCE = 1.25kV, RGon = 7.5 Ω, VGE = ±15 V
Eoff = 400 mJ @ Ic = 400 A,
VCE = 1.25kV, RGoff = 7.5 Ω, VGE = ±15 V
VCE=3.3kV, Ic=800A,
Eon = 1200 mJ @ Ic = 800 A,
VCE = 1.65kV, RGon = 2.5Ω, VGE = ±15 V
Eoff = 1000mJ @ Ic = 800 A,
VCE = 1.65kV, RGoff = 2.5 Ω, VGE = ±15 V
VCE=6.5kV, Ic=400 A,
Eon = 3450 mJ @ Ic = 400 A,
VCE = 3.6kV, RGon = 1.9 Ω, VGE = ±15 V
Eoff = 2250 mJ @ Ic = 400 A,
VCE = 3.6kV, RGoff = 13 Ω, VGE = ±15 V

fs
9 kHz

3 kHz

1 kHz

Table 2. Comparison for numbers ofcells and switching devices depending on the rated voltage of theswitching device.

a) The rated voltages of IGBT are 2.5 kV, 3.3 kV and6.5 kV.
b) The capacitor voltage is set 20% more than the value
which is calculated by (4). Moreover, the rated voltage is set
30% more than the capacitor voltage.
c) The ripple of the capacitor voltage is within 2%
against the average value of the capacitor voltage.
d) The output power is set 400 kW and the output
voltage is set 450 V.
e) MMC output voltage command vmmc* is set 2.6 kV, 1
kHz.
f) Buffer reactor Lb is 1 mH (the percent
impeadance %Z = 0.62 in all system.).
g) Each cell has only one DC capacitor.

Rated
Voltage
2.5 kV
3.3 kV
6.5 kV

Numbers of Cells
@leg
10
8
4

Numbers of
Switching devices
120
96
48

However, the switching speed of 6.5-kV IGBT is lower than
2.5-kV IGBT and 3.3-kV IGBT. Furthermore, the large valueof DC capacitor has to be applied since the response angularfrequency of the average control ωAVR becomes low. In addition,
the large inductance of buffer reactors are also applied since
the response angular frequency of the input current control
ωACR becomes low. In proposed system, MMC outputs a highfrequency voltage. However, the voltage drop becomes large
since a voltage-dividing occur between the high frequency
transformer and buffer reactors. In the worst case, it is difficult
to transmit a high frequency power to secondary side oftransformer when buffer reactors are large. Therefore, it isnecessary to reduce the inductance of buffer reactors totransmit the high frequency power.

B. Comparative Evaluation of the proposed system
The numbers of cells, switching devices and DC capacitors
are found by (4) and condition b).
Table 4 shows the comparison result for the number of cells
and switching devices depending on the rated voltage of theswitching device.

To conclude, high rated voltage devices with a low
switching speed are unfitted for the proposed circuit.

In cases where IGBTs with the rated voltage of 2.5 kV are
applied, 10 cells are required per leg. Moreover, 120 IGBTs are
required. On other hand, 2.5-kV IGBT is able to be set the highresponse angular frequency due to a high speed switching.
Therefore, it is possible to reduce the value of buffer reactors
and DC capacitors.

C. Evaluation of the proposed system by appling SiC devices
SiC devices have some advantages: the high rated voltage,
the low loss, the high switching speed. Therefore, many
applications of SiC devices are considered. Especially, it isexpected to apply SiC devices to a high voltage and high power
conversion system depending on the high device performance.
Recently, SiC-MOSFET with the rated voltage of 10 kV has
been developed [11]. However, dv/dt at winding wires of thehigh frequency transformer becomes greatly large and theinsulation degradation among winding wires may occur when
the proposed system is operated by the high rated voltage
devices. From considering of the previous chapter, it isdesirable to set the switching frequency of 9 kHz to operate thehigh frequency transformer in 1 kHz. Therefore, it is necessary
to consider the operation of the proposed system in the case of
applying 3.3-kV SiC-MOSFET [12] to the proposed system.

On other hand, in cases where IGBTs with the rated voltageof 3.3 kV are applied, 8 cells per leg and 96 IGBTs are
required. The number of cells and switching devices can be
reduced compared with that of 2.5-kV IGBT. However, theswitching frequency is limited because the switching speed islower than that of 2.5-kV IGBT. Therefore, it is necessary toincrease the value of DC capacitors since the response angularfrequency of the control system is low.
In cases where IGBTs with the rated voltage of 6.5 kV are
applied, 4 cells per leg and 48 IGBTs are required. The numberof cells and switching devices can be significantly reduced
compared with that of 2.5-kV IGBT and 3.3-kV IGBT.

55

Ec =

1
2
CVc × N
2

Total Capacitance Engegy [kJ]

Fig. 3 shows the comparison result of total energy which
all capacitor charges. The total electrostatic energy EC is givenby (5)(5)

where C is a capacitance of each capacitor, N is the number ofcapacitors in MMC and VC is the average value of the capacitor
voltage. VC is equal to the capacitor voltage command vc* when
all capacitor voltage is kept constant by the average control andthe balance control.
From the comparison result, the total electrostatic energy is
the largest when 3.3-kV IGBTs are applied. In the case of
applying 3.3-kV IGBTs, the large capacitance has to be set
since the response angular frequency of the average control
ωAVR becomes low.

Fig. 3. Comparison of total electrostatic energy in DC capacitors
according to the switching device.
Output power

In the case of applying 2.5-kV IGBTs to the proposedsystem, the total electrostatic energy is lower than that of 3.3kV IGBTs since the capacitance C and the capacitor voltage VC
become lower than that of 3.3-kV IGBTs. However, the ripple
voltage against the average value of the capacitor voltage
becomes large. Therefore, the capacitance cannot be reduced
greatly compared with that of 3.3-kV IGBTs.

Input voltage frequency

In the case of applying 3.3-kV SiC-MOSFETs to the
proposed system, the total electrostatic energy is the lowest
since the number of cells and the ripple voltage against the
average value of the capacitor voltage can be reduced.
Furthermore, applying the 3.3-kV SiC-MOSFETs to the system
can achieve the downsizing of the proposed system since thenumber of circuit components can be reduced and the heat loss
at switching devices is suppressed.
V.

Table 3 Simulation parameters
400 kW
Input voltage rms
50 Hz

Output voltage

6.6 kV
450 V

Number of cell per leg n

8

DC capacitor C

2 mF

Load R

0.5 Ω

Output capacitor Cr

3 mF

Turn ration pri.: sec.

3.6 : 1

Carrier frequency

9 kHz

Interconnection reactor Lin

4.5 mH (%Z = 1.38)

Buffer reactor Lb

1 mH (%Z = 0.62)

Leakage inductance at primary of the transformer

36 μH

Leakage inductance at primary of the transformer

10 μH

components: 100 Hz and 1 kHz. Then, the ripple of 1 kHz issmaller than that of 100 Hz. Furthermore, the ripple of 100 Hz
comprises a majority of the capacitor voltage ripple. However,
the maximum ripple of each capacitor voltage is obtained by
2.0 %. Thus, it is confirmed that the voltage ripple does notaffect the circuit operation in the proposed system.

OPRERATION EVALUATION BY SIMULATION

A. Fundamental Operation
Table 3 shows the simulation parameters. The switchingfrequency of SiC-MOSFET is set to 9 kHz. Note that the ideal
elements are used in the switching device. In addition, theoutput voltage command is a square-wave of 2.6 kV, 1 kHz.

Fig. 7 shows the output voltage waveforms of MMC, it canbe confirmed that the high frequency AC voltage which is 1
kHz is obtained. However, the error between the output
voltage of the MMC and the command occur. This is thereason that the voltage drops in each buffer reactor. Moreover,
the output voltage waveform is dropped when the voltage
polarity changes. This is the reason that the high frequency
current flows in all diode of the rectifier circuit due to theaction of the leakage inductance of the high frequency
transformer. The voltage is depended on the voltage drop of
the leakage inductance.

Fig. 4 shows the input phase voltage and current
waveforms. From Fig. 5, it is confirmed that the unity power
factor can be obtained in the input stage. Moreover, the total
harmonic distortion (THD) of the input current isapproximately 2.64 %. The input current waveform includes a
few of pulse-beat. However, the pulse-beat does not affect the
THD of the input current since the frequency of the pulse-beatis very high order compared with the fundamental frequency.

B. Comparison with respect to THD of Input Current
Fig. 8 shows the comparison result with respect to THD of
the input current. From Fig. 8, The THD is the lowest in cases
where IGBTs with the rated voltage of 2.5 kV. In the system
which is applied of 2.5-kV IGBTs, the number of cells is thehighest. Furthermore, the harmonic distortion is suppressedsince the input voltage becomes multi-level waveform due tomulti-cells. On the other hand, the system which is applied
SiC-MOSFETs can improve the THD of the input current
compared with the system which is applied 3.3-kV IGBTs
since it is possible to set the response angular frequency theFig. 5 shows the output voltage waveform. From the result,the output voltage is constantly controlled at approximately
450 V. Thus, the power conversion from three-phase AC
waveforms into a DC waveform can be confirmed.
Fig. 6 shows the voltage waveforms of the cell capacitor
which are connected to the r-phase. The cell capacitor voltages
are controlled accordingly to the capacitor voltage commandvc* by the average control and the balance control. In thecapacitor voltage, the ripples include two frequency

56

input current control ωACR to high due to the high switching
speed.
C. Comparison Evaluation of Efficiency
Fig. 9 shows the Efficiency comparison of the proposedsystem considering the loss at switching devices.
Fig. 10 shows comparison result of the switching loss andthe conduction loss.
In the case of applying 2.5-kV IGBTs to the proposedsystem, the loss at which occur at the switching device is thelarger than other one. This is because the system which isapplied 2.5-kV IGBTs has the largest number of switching
device and the switching frequency is high. Therefore, theefficiency of the system which is applied 2.5-kV IGBTs is thelower than other one.

Fig. 4. Waveforms of the input phase voltage and current.
500

Output voltage vo [V]

480
460

In the case of applying 3.3-kV IGBTs to the proposedsystem, the loss at switching devices is smaller than the system
which is applied 2.5-kV IGBTs. From the table 1, both theturn-on loss and the turn-off loss are larger than that of 2.5 kVIGBTs. However, the total loss of 3.3 kV IGBTs is lower than
the total loss of 2.5-kV IGBTs because the switching frequency
is lower than that of 2.5-kV IGBTs. Therefore, it is expected
for the system which is applied 3.3 kV IGBTs to achieve thehigh efficiency of 92.9%.

440
420

20[msec]

400

Fig. 5. Waveform of the output voltage
at.the diode bridge rectifier

In the case of applying 3.3-kV SiC-MOSFETs to the
proposed system, the loss at switching devices is the lowest
because both the turn-on loss and the turn-off loss are lower
than the loss of both IGBTs. Furthermore, the efficiency is thehighest.
In conclusion, applying the 3.3-kV IGBTs or 3.3-kV SiCMOSFETs is suitable for the proposed system in order toachieve the high efficiency. Moreover, SiC-MOSFET is themost suitable because SiC-MOSFET has the high performance
which can reduce the harmonic distortion of the input current,
can achieve the high efficiency and the downsizing of thesystem. On the other hand, 3.3-kV IGBTs also has good
performance for the efficiency. Furthermore, it is necessary toconsider in more detail in order to achieve reduction of theharmonic distortion of the input current and the downsizing of
the system.
V.

Fig. 6. Waveform of the capacitor voltage.

CONCLUSION

In this paper, a novel isolated three-phase AC-DC converter
using MMC and the control strategy were proposed for a
medium voltage application. Three-phase to single-phase
MMC topology was used at primary stage in the isolated ACDC converter. The proposed system could directly convert an
input three-phase voltage into a high frequency single-phasevoltage. Therefore, the proposed system could reduce thevolume of the isolated transformer since the single-phase highfrequency transformer could be applied to the high frequency
link.

Fig. 7. Waveform of the MMC output voltage.

MMC topology was constructed some cells and buffer
reactors. The cell was constructed 4 switching devices and DC
capacitor. The voltage of the DC capacitor was kept constantly
in order to operate MMC. The proposed control system could

Fig. 8. Comparison of the input current THD
according to the switching devices.

57

control not only the voltage of all DC capacitor but also the
input current and the high frequency output voltage of MMC.
Total Efficiency [%]The comparison evaluations of the proposed system which
is applied each high rated voltage: a 2.5-kV IGBT, a 3.3-kV
IGBT and a 3.3-kV SiC-MOSFET were demonstrated by asimulation. As a result, in the case of applying 3.3-kV SiCMOSFETs to the proposed system, the total electrostatic
energy in DC capacitors is the lowest compared with other highrated voltage IGBTs. Furthermore, the system which is applied
3.3-kV SiC-MOSFETs could achieve the downsizing of the
proposed system when considering the common value ofenergy density in all capacitor. Moreover, the system which isapplying 3.3-kV SiC-MOSFETs could achieve the low THD
input current waveform which is approximately 2.36 % and the
maximum ripple factor of each capacitor voltage isapproximately 2.0 %. Finally, from Efficiency Comparison
result of the proposed system, it was confirmed that theefficiency can be achieved by over 90% by using 3.3 kV
IGBTs and 3.3-kV SiC-MOSFET. Furthermore, applying the
3.3-kV IGBTs or 3.3-kV SiC-MOSFETs is suitable for the
proposed system in order to achieve the high efficiency. It isnecessary for the system which is applying 3.3-kV IGBTs toconsider in more detail in order to achieve reduction of theharmonic distortion of the input current and the downsizing of
the system.

Fig. 9. Efficiency Comparison of the proposed system
considering the loss at switching devices.

200
Switching loss

160

Conduction loss

120

In future works, the control gain will be optimized. Besides,
the effectiveness of the proposed system will be verified by theexperimental of the prototype and the optimized design will beconsidered.

80
40

REFERECES
[1]

[2]

[3]

[4]

[5]
[6]

[7]

[8]

[9]

0

P. K. Steimer and M. Winkelnkemper, “Transformerless Multi-Level
Converter based Medium Voltage Drives”, ECCE2011 pp. 3435 -3441，(2011)R.l Crosier, S. Wang and M. Jamshidi, “A 4800-V Grid-ConnectedElectric Vehicle Charging Station that Provides STACOM-APF
Functions with A Bi-directional, Multi-level,Cascaded Converter”,
APEC2012, pp. 1508-1515R. Nicole, “Title of paper with only firstword capitalized,” J. Name Stand. Abbrev., in press.
H. M. Pirouz and M. T. Bina, “New Transformerless STATCOM
Topology for Compensating Unbalanced Medium-Voltage Loads”,
Power Electronics and Applications, 2009. EPE '09. 13th European
Conference, (2009)
H. Li, Thomas L. Baldwin, C. A. Luongo, and D. Zhang , “A Multilevel
Power Conditioning System for Superconductive Magnetic Energy
Storage”, IEEE Trans. On Applied Superconductivity, Vol. 15, No. 2,
pp. 1943-1946 (2005)
M. Glinka and R. Marquardt, “A new ac/ac multilevel converter family”,
IEEE Trans. Industrial Electronics, vol. 52, No. 3, pp. 662–669, (2005)
M. Hagiwara and H. Akagi, “Control and Experiment of PulsewidthModulated Modular Multilevel Converters”, IEEE Trans. on PowerElectronics, Vol. 24, No. 7, pp. 1737-1746 (2009)
M. Hagiwara, R. Maeda and H. Akagi, “Negative-Sequence ReactivePower Control by a PWM STATCOM Based on a Modular Multilevel
Cascade Converter (MMCC-SDBC)”, IEEE Trans. on Industry
Applications, Vol. 48, No. 2, pp .720-729 (2012)
Fang Z. Peng, Wei Qian, and Dong Cao, “Recent Advances inMultilevel Converter/Inverter Topologies and Applications”, IPEC
2010, pp. 492-501 (2010)
S. Kenzelmann, A. Rufer, M. Vasiladiotis, D. Dujic, F. Canals and Y. R.
de Novaes, “A Versatile DC-DC Converter for Energy Collection and2.5 kV IGBT
(10 cells, 9 kHz)

3.3 kV IGBT
(8 cells,3 kHz)

3.3 kV SiC MOSFET(8 cells, 9 kHz)

Fig. 10. Comparison of the switching loss and the conduction loss.

Distribution using the Modular Multilevel Converter”, PowerElectronics and Applications (EPE 2011), Proceedings of the 2011-14th
European Conference, (2011)[10] M. Vasiladiotis, S Kenzelmann, N. Cherix and A. Rufer, “Power and DC
Link Voltage Control Considerations for Indirect AC/AC Modular
Multilevel Converters”, Power Electronics and Applications (EPE2011), Proceedings of the 2011-14th European Conference, (2011)[11] M. K. Das, C. Capell, D. E. Grider, R. Raju, M. Schutten, J. Nasadoski,
S. Leslie, J. Ostop, A. Hefner ; “10 kV, 120 A SiC Half H-Bridge PowerMOSFET Modules Suitable for High Frequency, Medium Voltage
Applications”, IEEE, ECCE, pp.2689-2692 (2011)[12] R. Lai, L. Wang, J. Sabate, A, Elasser and L. Stevanovic, “High-Voltage
High-Frequency Inverter using 3.3 kV SiC MOSFETs”, PowerElectronics and Motion Control Conference (EPE/PEMC), 2012,
DS2b.6-1 - DS2b.6-5 (2012)58