The prototyped power inverter with an output of 300kVA
The SiC diodes are formed on a 2-inch wafer.
The switching module and the gate drive circuit
The multiple series connection method (left) and the three-level conversion method (right)
Japanese researchers prototyped a power inverter with an output of 300kVA based on silicon carbide (SiC) diodes.
The inverter was jointly developed by the National Institute of Advanced Industrial Science and Technology (AIST), Toshiba Corp, Toshiba Mitsubishi-Electric Industrial Systems Corp (TMEIC), Tokyo Metropolitan University and Ibaraki National College of Technology. It is expected to be used for large power conversion equipment in the fields of power generation, industries, railway transportation and so forth.
The inverter can drastically reduce the overall size of power conversion equipment including an output filter. The size can be reduced to about one fifth that of existing equipment because SiC diodes enabled to enhance the switching frequency to 2kHz. With Si diodes, the switching frequency of existing inverters is about 500Hz.
This time, the researchers used a pin SiC diode with a withstand voltage of 6kV and a device area of 4 x 4mm. The switching device is a Si-IEGT (injection enhanced gate transistor), which is also used for existing inverters.
When the switching frequency increases, it becomes possible to employ a circuit method for small inverters. So far, the multiple series connection method using an insulating transformer has been employed for inverters because of the low switching frequency. But, this time, it became possible to use the three-level conversion method, which eliminates the need for an insulating transformer, enabling to downsize power conversion equipment.
Furthermore, the three-level conversion method uses a circuit architecture that doubles the equivalent switching frequency. In other words, the equivalent switching frequency of the new inverter is 4kHz, enabling to employ small inductors and capacitors for the output filter and make the filter small.
AIST manufactured the SiC diode and developed a loss simulation technology to measure device loss. Toshiba supplied the Si-IEGT and manufactured the switching module. TMEIC was in charge of the basic design and test of the inverter. Tokyo Metropolitan University was responsible for the inverter control and the design of the refrigeration unit. Ibaraki National College of Technology designed the gate drive circuit of the Si-IEGT.
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