Analytical computation of the RMS current stress on the DC-link capacitor in DC-link PWM converter systems powering N-phase rotating field machines in PWM and square wave mode

摘要

This paper describes an easy to handle analytical method for the computation of the rms current stress on the DC-link capacitor of PWM converters. Both the PWM and the square wave mode (SWM) operation powering rotating field machines e.g. induction- or synchronous machines are considered. The rms current stress on the DC-link capacitor mainly affects its working temperature. Therefore it is a significant factor for the estimation of its duty cycle. On the one hand the value of the DC-link capacitor current is determined by the amplitude and the phase angle of the inverter output phase current, deriving from the actual load. On the other hand it is influenced by the modulation depth and the phase number of the arrangement as well. The results achieved with the simple analytical model match very well with results of complex simulation models. The equivalent computing time compared to common simulation tools at reasonable time steps is reduced by more than a factor of thousand.