A Simplified Calculating Method of Busbar Inductance and Its Application for Stray Resonance Analysis in Inverter DC Link

Abstract

Sinusoidal PWM control method is widely applied to power electronic converters. Its carrier frequency of recent converter product gradually becomes higher in order to decrease current harmonics as much as possible. However, in DC filter circuit of large capacity converters, the capacitance of an unit capacitor is relatively large, and busbars are relatively long. Therefore, its resonant frequency is lower than that of small capacity ones. Consequently, there is concern that the carrier frequency will become close to the resonant frequency which will cause some troubles. On the other hand, it is often necessary to decrease the inductance of the loop circuit which is composed of a switching device and its by-pass circuit, in order to suppress switching surge voltage.
In both cases described above, it is important to be sure of the exact value of busbar inductance for reliable designing. In this paper, a simplified calculating method of busbar inductance is proposed. This method is based on the partial inductance theory. Especially, the characteristics of a pair of busbars are described, and its utilization is proposed. Finally, the application for stray resonance analysis in DC filter circuit of three level inverter is described in comparison with experimental data. From these results, it is confirmed that the proposed method is suitable to estimate busbar inductance quickly and also exactly.