Energy-based modulation error control for high-power drives with output LC-filters and synchronous optimal pulse width modulation

In order to reduce the switching frequencies of power semiconductors, synchronous optimal pulse width modulation provides an appropriate solution. The switching angles result from complex offline calculations, assuming steady-state operation. Medium voltage drives when applied to the retrofit of existing fixed speed induction motors often include an output LC-filter which introduces a resonant circuit. Therefore, only in steady-state operations the combination of a high-power drive with a LC-filter and optimized pulse width modulation delivers satisfactory behavior. Changes in operating conditions cause weakly damped electrical oscillations, which can be described as dynamic modulation errors. In this paper, a novel energy-based control method is proposed, in order to damp the LC-filter excitation without increasing the switching frequency. The introduced control technique has been verified by simulations of a 2.4 kV induction motor drive.