New power converter of high-voltage/large-capacity; switching frequency = 2kHz

A new power converter of high voltage and large capacity has been developed.
The major improvements of the power converter are:
1) The switching frequency of the power converter is considerably increased (4 times).
2) As the result of the increase of the switching frequency, a power converter facility using the power converters is significantly reduced ((about 1/5).
This type of the power converter will find its application in near-future electric power fields, including smart grid, mega-solar, wind power generation, and high speed railways.
The technologies and products in those fields are developed and market-deployed currently and in near future in the world. In this respect, the power converter technology developed this time is significant.
Co-developed by AIST, TOSHIBA, TMEIC, Tokyo Metolopolitan University, and Ibaraki National College of Technology
1) The switching frequency of the power converter is considerably increased. The switching frequency achieved this time is 4 times that of the conventional power converter. The power elements used are SiC diode and Si-IEGT. Specifically, large area SiC-PiN diodes of 4 mm square and Si-IEGTs were combined into a high speed switching module. Si-IEGT was supplied from TOSHIBA. The large area SiC-PiN diode is of 6 kV class and has excellent features of low loss and high speed operation. The SiC-PiN diode was developed on the basis of the SiC-element area-increasing technology, developed and accumulated by AIST. A cooling device for cooling the switch modules and a high-speed gate drive circuit were also developed (Figure 3). The switching frequency of the switching module formed was 2kHz. This figure is four times of the conventional device.
The conventional power converter is based on Si diode and Si-IEGT. The switching characteristic of the Si diode inherently limits the switching frequency of the Si-IEGT to 500 Hz.
A prototype of a power converter was constructed which used high speed switching modules and was based on the single-phase three-level power conversion, and the power capacity of which was ± 5 kV – 300 kVA (Fig. 5)
The performances of the prototype were demonstrated. The figure representative of its switching frequency was confirmed.
2) A power converter facility using the power converters newly developed is significantly reduced. The considerable increase of the switching frequency of the power converter allows a designer to employ the 3-level power conversion system for the power conversion (Fig. 4). Where this power conversion system is used, there is no need of using the insulating transformer. Further, the considerable increase of the switching frequency improves the wave shape of the output power of the power converter. The improved wave shape remarkably reduces the capacity of the filter for filtering out the distorted wave components. The size of the power converter facility was about 1/5 of the conventional one.
In the conventional high-voltage/large-power power converter, the serial multiplexing system has been used for power conversion. This power conversion system essentially needs the insulating transformer. The transformer occupies about the half of the entire space of the power converter facility. The filter occupies about 1/4 of the entire space.
When the output powers of the 3-level power converter and the switching element are compared with each other, the former is substantially double of the latter in terms of switching frequency.
Written based on AIST’s news release, issued on August 4, 2009
[Copyright by FuelCell japan: http://www.fcpat-japan.com/]
Note: For figures used, refer to Aist's news release written in Japanese.
If any, ask AIST or feel free to contact us at infonenryo@gmail.com

Keywords: power converter, high voltage, high capacity, switching frequency, power converter facility, SiC-PiN diode, Si-IEGT, 3-level power converter