A comparison of the carrier-based PWM techniques for voltage balance of flying capacitor in the flying capacitor multilevel inverter

This paper presents the analysis and comparison of carrier-based PWM techniques for the flying capacitor multilevel inverter (FCMI). The FCMI has the natural problem with voltage unbalance of flying capacitors. This problem generates distortion of output voltage and load current. It also causes serious breakdown of switching device. The FCMI has various PWM techniques for voltage control of flying capacitor to ensure the balance of flying capacitor voltage. Among them, this paper is focused on three carrier-based PWM techniques, which are the phase-shifted (PS) PWM technique, the modified carrier-redistribution (MCR) PWM technique and the saw-tooth-rotation (STR) PWM technique. They are analyzed and compared precisely in flying-capacitor 3-level inverter with respect to voltage balance of flying-capacitors and harmonic contents of output waveform. The experimental results describe performances and characteristics of them.