A simplified method of calculating busbar inductance and its application for stray resonance analysis in an inverter dc link

Abstract

Sinusoidal PWM control is widely applied to power electronic converters. The carrier frequency of recent converter products is gradually being raised in order to decrease current harmonics as much as possible. However, in the dc filter circuits of large capacity converters, the capacitance of a unit capacitor is relatively large, and the busbars are relatively long. Therefore, the resonant frequency is lower than those of small capacity converters. Consequently, there is a concern that the carrier frequency will become close to the resonant frequency, which will cause trouble. On the other hand, it is often necessary to decrease the inductance of the loop circuit consisting of a switching device and its by-pass circuit, in order to suppress the switching surge voltage. In both cases described above, it is important to be sure of the exact busbar inductance for reliable design. In this paper, a simplified method of calculating busbar inductance is proposed. This method is based on the partial inductance theory. In particular, the characteristics of a pair of busbars, and the use of the method are described. Finally, an application to stray resonance analysis in the dc filter circuit of a three level inverter is described in comparison with experimental data. From these results, we confirmed that the proposed method is usable to estimate busbar inductance quickly and accurately. © 1999 Scripta Technica, Electr Eng Jpn, 126(3): 49–63, 1999