A novel control strategy for hybrid multilevel inverters

Abstract

Hybrid multilevel inverter can use less power cells to generate more output voltage levels. Under the general control strategy, it is very complex to be applied and hard to make full use of different semiconductors. A novel control strategy which combines the fast switching ability of IGBT or MOSFET and the high voltage blocking capability of GTO or IGCT is presented in this paper to resolve this problem. A hybrid converter which is composed of two sub-converters (converter1 and converter2) is proposed. Converter1 and converter2 operate with different frequency and different voltage. The function of converter1 is to minimize the peak value of the difference between the supposed output sine voltage and the output voltage of converter1 that is to make sure that converter1 can operate with the lowest dc bus voltage, and converter2's function is to enhance the quality of output voltage. Converter1 operates with high voltage and low frequency, and converter2 operates with low voltage and high frequency. Therefore the control strategy is very simple and can make full use of different kind of semiconductors. The simulation results prove the practicability and validity of the control strategy.