Capacitor Voltage Balancing of Four-Level ANPC and π-type Converters Based on Simplified Virtual-VectorPWM

Multilevel $\pi$ -type and ANPC converters without flying capacitors and clamping diodes are emerging candidates for industrial applications due to their simple structure, less number of devices, and better harmonic performance. However, the voltage balancing difficulty is the key issue of these topologies similar to diode-clamped topology under conventional PWM methods. The unbalance of capacitors voltages may affect the system integrity and stability, and may degrade harmonic performance. To sort out this issue, a simplified virtual vector PWM method to balance the dc-link capacitors voltage of four-level three-phase $\pi$ -type and ANPC converters is presented in this paper. Simulation results show how easily and efficiently the proposed method can control the voltage of the capacitors for different modulation index values under balanced and unbalanced loads.