A Simplified Virtual Vector PWM Algorithm to Balance the Capacitor Voltages of Four-Level Diode-Clamped Converter

The voltage balancing problem of dc-link capacitors in multilevel diode-clamped converters limits their applications in industry under some operational conditions. Virtual vector PWM (VVPWM) can attain the capacitor voltage balancing under all operational conditions but it increases the complexity and computation burden by increasing the number of triangular regions for higher levels as compared to conventional space vector PWM (CSVPWM). In order to solve the dc-link voltage balancing problem in four-level diode-clamped converter, a simplified virtual vector PWM (SVVPWM) algorithm is proposed in this paper. The pair of new virtual vectors is defined in such a way that the space vector diagram of four level converter is transformed into three level space vector diagram that lessens the complexity and computation burden by decreasing the number of triangular regions. The balancing of capacitor voltages can be achieved by using proposed SVVPWM algorithm for the whole range of modulation index load power factor. Steady state and dynamic performance of the SVVPWM algorithm is verified through the simulations and experiments.