Control Schemes for Equalization of Capacitor Voltages in a Neutral Clamped Shunt Compensator

Voltage imbalance in capacitors is a well-known problem in compensator topologies that use two or more capacitors. This imbalance may exist even if the load does not contain any dc component, due to practical factors. However, when the load contains a dc part, the voltage imbalance problem becomes critical. In this paper, a two-quadrant chopper is used to regulate the capacitor voltages in a two-capacitor compensator structure. Two different control strategies for the two-quadrant chopper to equalize the voltage of the capacitors are proposed. The strategies are validated through detailed simulation studies. Experiments were carried out to validate the hysteresis control of the chopper.