Improved dynamic operation for direct flux control of active front ends with low switching frequency

A three-fold pulse pattern for direct flux control of high-power multilevel active front ends (AFE) with low switching frequency useful for reducing the harmonic content within the converter terminal voltage is introduced. It is shown that compared to a square-wave pulse pattern the increased switching frequency cannot serve to improve the dynamic response of the AFE. Within the framework of direct flux control a general method to increase the dynamic behavior of the AFE for a positive power change is then presented and experimental results obtained from implementation on a 200-kW double three-level IGBT converter test bench are shown and discussed.