Suzuo Saito

Evaluation of parallel and series connection of silicon carbide Schottky barrier diode (SiC-SBD)

Silicon carbide Schottky barrier diodes (SiC-SBD) have recently come onto the market, and have attracted a great deal of public attention. Generally, high current and high voltage power devices are achieved by making the device area large and the breakdown voltage high. However, if these parameters are limited (for example, yield rate, cost, etc), high current and high voltage power modules are realized by connecting power devices in parallel and in series. The problems of parallel connection are current sharing and resonance among parallel devices, and the problem of the series connection is voltage sharing. As described in this paper, even when the characteristics of eight chips connected in parallel vary, if the impedances of the parallel circuit are equal and small, and the thermal resistances from junction to ambient are equal, neither current sharing nor resonance became fatal problems. Even when the characteristics of two modules connected in series varies, by installing balance resistors and balance capacitors, voltage sharing can be equalized. Furthermore, replacing reverse parallel diode of IGBT from PN junction diode (Si-PND) to SiC-SBD greatly decreases the inverter loss. This tendency is remarkable at high carrier frequencies and high rated voltages.

New Application of Current-Type Inverter

It is important to take commutation and torque ripple into consideration when applying a current-type inverter to a large- capacity induction motor (pump, blower, etc.) for reducing power consumption. To solve the problems, a new multiple connected current -type inverter which has quasi-sinusoidal output current wave- form has been developed. With a view to attaining exact speed control and quick response, an induction motor vector control technique fed by a current-type inverter has been developed. Examples of these application techniques in multiple connected and vector control current -type inverters are described.