Project Subjects
Low-loss Compact Inverter Applied Equipment
Background and Objective
Innovation in power electronics technology can play an important role in realizing a low-carbon society through promoting energy saving, electrification of energy usage, and the introduction of renewable energy
sources. As a core of the innovation, the development of electric equipment and apparatus which utilize SiC
semiconductor devices (SiC devices) can achieve high efficiency, small size and high control performance. For
the wide practical use of such high performance equipment, it is important to initiate practical development of
SiC devices while placing a high priority on applications where the largest benefit can be gained through their use.
In this project, aiming at the practical use of electric equipment with SiC devices, we intend to develop an
SiC device applied equipment after selecting an appropriate application. To establish the simulation and control
technologies of power electronics circuit with SiC devices is another important objective of this project.
Main results
1. Development of an SiC Device Applied Transformerless STATCOM for 6.6kV Distribution Systems
We developed a prototype of a 6.6kV transformer-less STATCOM1) incorporating an all SiC converter
and verified its performance (Fig. 1). Specifically, in terms of efficiency improvement and miniaturization,
Y-connection Modular Multilevel Converter2) topology (Fig. 2) was applied to the prototype as an optimal circuit
configuration for the SiC device applied STATCOM. At the beginning of the development, over current and
over voltage capability of 1.2kV SiC-JFET3) devices which were applied to the prototype were verified. Then the
circuit design was optimized in terms of loss reduction. Experimental verification proves the effects of the design
optimization and clarifies the stable operation performance of controls developed for the STATCOM operation.
Moreover, we have designed a power circuit, a control and protection circuit, and a three-dimensional
configuration to store a pole-mount container based on a thermo-fluid analysis (Fig. 3) for the practical equipment. Fundamental design technologies for the practical use of the SiC device applied STATCOM were established through these detailed design processes.
The development has been implemented under cooperative research with Toshiba Corporation.
2. Development of Control Schemes for SiC Device Applied Converters
In order to accelerate the practical use of the SiC device applied STATCOM for distribution systems in
several years, a control scheme was developed for a hybrid configuration of 1.2kV SiC device which is close to
commercialization and high blocking voltage Si-IGBT. Conventional hybrid converters require DC sources in
each cell to maintain the DC voltages because the converters consist of several cells with different voltage ratings.
The proposed control scheme eliminates the DC sources by enabling energy transfer between cells without output
voltage distortion, and realizes highly practical system which achieves the reduction of converter size and cost
[R10014]. Moreover, a new control scheme was developed for Y-connection multilevel converters2) to compensate unbalanced three-phase voltages which has increasing demand in the STATCOM application to distribution
systems [R10022].
Other reports
[R10027] [R10039]
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Environment and Energy Utilization Technology
SiC-JFET
1200mm
SiC-JFET
A single-phase inverter module
単相インバータモジュール
500mm
AC filters
600mm
交流フィルタ
Fig. 1　Prototype
of of
the
allallSiC
Fig 1 Prototype
the
SiCSTATCOM
STATCOM(rated
(ratedat
at 2.2kV,
2.2kV, 33.5kVA)
33.5kVA)
Circuit design and control system design technologies were established through manufacturing and testing an all SiC
Circuit design and control system design technologies were established through manufacturing and testing an all SiC
converter prototype applying 1.2kV SiC-JFET devices.
converter prototype applying 1.2kV SiC-JFET devices.
6.6kV
6.6 kV
distribution
system
配電系統
AC filter
フィルタ
Module (cell)
モジュール
（セル）
SiC
Si
L-C-L
filter
L-C-Ltype
typeharmonic
harmonic
filter
All
consist
of identical
SiC
All SiC
SiC converters
converters
consist
of identical
modules,
and hybrid
converters
of SiC
SiC modules,
and
hybridconsist
converters
module
module
havingand
different
voltage
consistand
of SiSiC
module
Si module
rating.
having different voltage rating.
SiC
Si
SiC Schottky
barrier diode
SBD
Si
SiC
Si
SiC
SiC
SiC
SiC
SiC
SiCJFET
JFET
FIN
Heatsink
CAPACITOR
CAPACITOR
Fig. 2　Configuration of the Y-connection mulFig.
3　Thermo-fluid
analysisofofthe
theinverter
inverter
module
Fig.
3 Thermo-fluid analysis
module
Fig. 2 Configuration of the Y-connection
tilevel converter1), 2)
The
thermo-fluid
analysis
verified
that
highest
temperature
The thermo-fluid analysis verified that highest
multilevel converter 1), 2)
All SiC converter and hybrid converter have the identi(119℃) in the module is within the acceptable level (125℃).
temperature (119℃) in the module is within the
All SiC
converter and
hybrid converter have the
cal circuit
configuration
(topology).
acceptable level (125℃).
identical circuit configuration (topology).
1) STATCOM (STATic synchronous COMpensator）: Reactive power compensation equipment using Voltage Source
1) STATCOM (STATic synchronous COMpensator）: Reactive power compensation equipment using Voltage
Converter
Source
Converter
2) Multilevel
converters
consist of series connected several single phase inverter modules (cells). Modular multilevel
2) Multilevel converters consist of series connected several single phase inverter modules (cells). Modular
converter is the converter consisting of modules having the identical voltage rating among them. There are Y-connecmultilevel converter is the converter consisting of modules having the identical voltage rating among
tion type
andThere
Δ-connection
type converters.
them.
are Y-connection
type and Δ-connection type converters.
SiC
switching
devices,
SiC-JFET
and SiC-MOSFET
are now are
under
intensive
At present, SiC3) Among
3) Among SiC switching devices,
SiC-JFET
and SiC-MOSFET
now
under development.
intensive development.
At
JFET present,
is the most
promising
device
close
to commercialization.
SiC-JFET
is the
most
promising
device close to commercialization.
4) A
consisting
of SiC of
devices
and Si devices
called aishybrid
this article.
configuration
4) converter
A converter
consisting
SiC devices
and Si isdevices
calledconverter
a hybridinconverter
in Its
this
article. Its is
configuration
is awhich
multilevel
converter,
which
of several
with using
different
rated
voltagesand
using
a multilevel
converter,
consists
of several
cellsconsists
with different
ratedcells
voltages
1.2kV
SiC-JFETs
high
1.2kV
SiC-JFETs
and high blocking voltage Si-IGBTs.
blocking
voltage
Si-IGBTs.
2
63