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A novel control strategy for voltage balancing of flying capacitor multilevel converters controlled with phase shifted SPWM is presented. Based on the polarity of the phase current, a relatively small square wave is added to the nominal modulation signals (typically sinusoidal) controlling the converter switches and in this way the flying capacitor voltages can be directly regulated. A simple algorithm is developed to explore an optimal solution for multiple capacitor voltage regulation. The impact of the proposed control strategy on the flying capacitor voltage variation and converter output voltage is analysed. The effectiveness of the control strategy is validated by simulation results of a five-level converter.
Date of Publication: 8 May 2004