Operating electrical high speed drives with pulse patterns of specific harmonic content

Operating inverter-fed electrical drives with optimized pulse patterns allows to take influence on certain harmonics in the generated output voltage. The typical optimization process is as follows: A symmetrical pulse pattern shape is at first optimized offline to receive the required switching angles eliminating certain harmonics. These are then stored in look-up tables and downloaded to a microcontroller. This optimization procedure is rather time-consuming and also inflexible if the pulsed output voltage should contain a specific harmonic content that varies between different operation points. In this paper a new approach to calculate the switching angles using Walsh functions will be presented. The established algorithm could for example be used to reduce the harmonic distortion of the phase currents in steady state iteratively over several controller cycles by varying the amplitudes of the low frequency harmonics. Simulation results evaluate the proposed method by modifying the harmonic content during operation.