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 with placing a high priority on the application 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 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 objective of this project.

Main results
We chose a pole-mount STATCOM*1 (Table 1) for distribution systems as an object for practical development of SiC device applied equipment. STATCOM is indispensable when introducing large amount of PV
generation into the distribution system, and the application of SiC devices brings a substantial advantage inachieving high efﬁciency and space saving. Development has been implemented under the cooperative researchwith Toshiba Corporation.
In 2009 FY, technical feasibility of a pole-mount STATCOM has been demonstrated through a conceptual design study and the applicability of SiC-JFET*2 devices commercially available has been veriﬁed.
1. Optimal circuit conﬁguration for a pole-mount STATCOM
A transformerless conﬁguration is required to achieve compactness and light weight. We ﬁrst chose several alternatives for the circuit conﬁguration. Through a comparison of the required number of semiconductor
devices, total volume of elements, efﬁciency and simplicity of manufacturing, we ﬁnally selected the Y-connection Modular Multilevel Converter (MMC)*3 (Fig. 1) as the optimal circuit conﬁguration for a pole-mount
STATCOM [R09010].
2. Structural design of a pole-mount STATCOM
The practicability of installation on a distribution pole has been examined through a structural design of aSTATCOM with the Y-connection MMC topology based on the electrical design results such as ﬁlter parametersand efﬁciency (Fig. 2). External dimensions and weight can be estimated as W0.8m×D0.5m×H1.5m and 500kg(ac ﬁlter 300kg, inverter 200kg) respectively.
3. Evaluation of applicability of SiC-JFET device
The applicability of a newly commercialized SiC-JFET device*4 was veriﬁed by obtaining the following
experimental results on its characteristics. 1) characteristic on-resistance is low as 2.8 mΩcm2, 2) turn-on loss andturn-off loss decrease to 1/6 and 1/8 respectively compared to the same rating Si-IGBT, 3) stable inverter operation can be achieved in an all SiC conﬁguration combined with an SiC Schottky barrier diode.
These results on the characteristics of the SiC-JFET device prove that the device is applicable to a demonstration equipment of a pole-mount STATCOM.
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Environmental and Energy Utilization Technology
Table 1

Design speciﬁcation of a pole-mountSTATCOM
As this equipment is embedded into a distribution network, the design speciﬁcation is decided considering thereduction of harmonics and audible noise as well.

SiC Cell Cell Cell

Rated capacity

100 kVA

SiC Cell Cell Cell

Rated voltage

6600 V

Harmonics

Total current
distortion factor< 2.5%SiC Cell Cell Cell

DC voltage deviation< 5%

Equivalent switchingfrequency

20 kHzEach cell consists of SiC
switching devices and
SiC diodes.

Fig. 1 STATCOM conﬁguration with the Y-connection MMC topology
As a result of performance comparison between circuit conﬁgurations available, we decided the Y-connection MMC is
optimal for a compact STATCOM.

0.8m

AC filter
T shaped L-C-L filtercombined with aninterconnection reactor
Inverter unit

1.5m

Inverter unit consisting of 9SiC cells

0.25m

0.5m0.5m(a) STATCOM mounted ona distribution pole(b) Inner structure(c) SiC cellFig. 2 Illustration of a 6.6kV-100kVA pole-mount STATCOM
The practicability of a pole-mount STATCOM was demonstrated through the structural design.

*1: STATCOM (STATic synchronous COMpensator): Reactive power compensation equipment using Voltage Source
Converter*2: Among SiC switching devices, SiC-JFET and SiC-MOSFET are now under intensive development. At present, SiCJFET is the most promising device close to commercialization.
*3: An inverter conﬁgured with the series connection of multiple cells or modules (Fig. 1).
*4: Normally off type device. Rated voltage: 1200V, rated current: 30A.

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