Active damping of LC-filters for high power drives using synchronous optimal pulsewidth modulation

To meet the increasing demand on very low switching frequencies of power semiconductors in order to reduce switching losses, synchronous optimal pulsewidth modulation (SO-PWM) techniques provide an appropriate solution. They result from offline calculations, assuming steady state operation of the drive system. These drives are often used with an LC output filter, which represents a resonant circuit. Therefore, only in steady state operations does the combination of an LC-filter with offline optimized pulse patterns deliver satisfactory behavior of the drive system. Changes in operating conditions cause weakly damped oscillations in the filter, followed by high overcurrents in the motor, which can be described as dynamic modulation errors. In this paper, a novel control method is proposed in order to keep the benefits of SO-PWM in dynamic operations when applied to drives with LC-filters. The method actively damps the LC-filter resonance and compensates the dynamic modulation errors without increasing the switching frequency. The effectiveness and dynamic capability of the introduced control technique are presented by simulation results of a 2.4 kV induction motor drive.