Direct power control of a multilevel inverter based active power filter

This paper proposed a cascaded H-bridge multilevel inverter based direct connected active power filter for medium/high voltage application without using the bulky transformer or passive filter. Due to the limited switching frequency (typically below 1 kHz) of high-power solid-state devices (GTO/IGCT), multiple synchronous/stationary reference frame current controller are reviewed and derived. To improve the dynamic performance, a hybrid frame structure based current controller is presented. Furthermore, a direct power controller is then proposed based on the understanding between the instantaneous reactive power (IRP) and synchronous reference frame (SRF) theory, ft has clear physical meaning and can be considered as a simplified version of the hybrid frame current controller. Simulations on a 4160 V/1.2 MVA system and experimental results on a 208 V/6 KVA laboratory prototype are presented to validate the proposed active power filter design.