A novel fuzzy logic DC bus voltage balancing controller for a D-SSSC cascaded H-bridge converter

In this paper a new method to balance the DC bus voltage of cascaded H-bridge converters is proposed. This balancing algorithm needs the DC capacitor voltages and the converter branch current which are commonly used in all multilevel cascaded H-bridge topologies. The balancing method applies at the innerest level of control system regardless of the main control method and PWM strategy. The voltage balancing procedure swaps the output voltage of each H-bridge cell in order to stabilize the DC bus voltages and provide the required output voltage. A fuzzy logic control method is used to apply the swapping in order to keep the switching frequency almost constant. The simulation results for different kinds of PWM strategy show the ability of this method to balance the DC bus voltages.