Model-based voltage calculation for inverters with small DC-Link capacitance

Abstract

Employing only a small capacitance in the DC-link of an adjustable speed drive (ASD) enables the replacement of electrolytic capacitors with film capacitors. Unfortunately, in combination with a diode bridge rectifier the DC-link voltage exhibits a significant six-pulse ripple. By measuring the DC-link voltage and providing the load side control with its value as widely done, this ripple can be compensated. In the following, a method is presented calculating the varying DC-link voltage by referring exclusively to the transfer function of the rectifier. This way, the DC-link voltage sensor can be omitted. Additionally, a partially damped mains filter is implemented to reduce line current oscillations. Experimental results verify the suitability of both the filter design and the model-based control.