A new modulation strategy and power balance method of unsymmetrical CHB inverter

Abstract

Abstract There exist the problems of the low utilization rate of DC voltage, power imbalance and current backflow in the modulation process of traditional unsymmetrical cascaded units. In view of these, a pulse width modulation strategy with an improved trapezoidal wave as the modulation wave and its corresponding power balance method are proposed. First, through double Fourier analysis of the output line voltage, an appropriate sine coefficient δ is obtained. Second, the waveform of the modulation wave is determined according to δ. Third, through the simple logic operation of the initial driving signals of the switch transistors, the required switch driving signals are obtained, and the power balance of each unit with the same voltage level is realized. In order to verify the effectiveness of the strategy and the method, a simulation and experiment platform are built, and a large number of simulations and experiments are carried out. The results show that compared with the traditional sinusoidal modulation method, the utilization rate of DC voltage obtained by the method can be improved by 22.28% and compared with the trapezoidal wave modulation method, the waveform distortion coefficient of the output voltage can be significantly reduced, and the utilization rate of DC voltage can be further improved. Meanwhile, the power balance can be achieved within one voltage cycle and the phenomenon of current backflow is eliminated.

Keywords

• Mathematical analysis
• Power electronics, supply and supervisory circuits
• Control of electric power systems
• Mathematical analysis
• Power convertors and power supplies to apparatus