Generalized DC-link voltage balancing control method for multilevel inverters

This paper presents a general dc-link voltage balancing control method for multilevel inverters based on a generalized space vector pulse width modulation (SVPWM) scheme, with no requirements for additional auxiliary-power circuits. The SVPWM scheme generates all the available switching states and switching sequences based on two simple mappings, and calculates the duty cycles simply as for a two-level SVPWM, thus independent of the level of the inverter. The optimal switching sequence and optimal duty cycles for dc-link voltage balancing control are provided in the paper. Because all the measured signals are instantaneous values, the dc-link voltage balancing control method in the paper is suitable for any load without any assumption on the output current waveforms. The dc-link voltage balancing control in the paper is effective even when the capacitances of the dc-link capacitors of the multilevel inverter are not strictly equal or the voltage of the dc source of the multilevel inverter is fluctuating. Simulation results for a five-level inverter are given.