Abstract

The inherent problem of dc-link capacitor voltage imbalance in multilevel diode-clamped converters limits their development and industrial applications. By using conventional space vector PWM (CSVPWM), for higher voltage levels (>3), the balancing of capacitors voltages cannot be attained under some operational conditions. Virtual vector PWM (VVPWM) assures the balancing of capacitor voltages for all operational conditions with the expense of computation burden by rapid increase in triangular regions for higher levels as compared to CSVPWM. To overcome this problem, this paper presents a simplified virtual vector PWM (SVVPWM) algorithm for four-level diode-clamped converter. 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 reduces the computation burden by decreasing the number of triangular regions. The proposed modulation algorithm guarantees the balancing of middle capacitor voltage in each carrier cycle and the balancing of bottom and top capacitor voltages in a fundamental cycle. The simulation results validate the proposed algorithm under the full range of load power factor and modulation index.

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