New SVPWM control scheme for three-phase diode clamping multilevel inverter with balanced DC voltages

This paper presents a new SVPWM control scheme for three-phase diode clamping multilevel inverters. First, it is proved that if the switch states are selected in a given mapping relation, the voltages of DC capacitors will be symmetrical. Voltage offsets of each two symmetrical capacitors fluctuate at the three-time frequency of AC currents. This rule can be applied to N-level (N>2) inverters and simplify the approach to solve unbalanced capacitor voltages. Then based on it, a new control strategy is presented to maintain the balanced voltages on the four DC capacitors of a diode clamping five-level inverter. Finally an experiment drive system is implemented on a TMS320F240 DSP in the Lab. The validity of the proposed method is demonstrated by simulation and experimental results.