Power-Balanced Modified TPWM Strategy for Three-Phase Cascaded H-bridge Inverters

For realizing the power balance between cascaded H-bridge cells and enhancing the utilization ratio of DC voltage, a power-balanced modified trapezoidal pulse width modulation (PB-MTPWM) strategy is proposed for three-phase cascaded H-bridge inverters in this paper. The proposed PB-MTPWM strategy can be summarized as following two points. Firstly, the utilization ratio of DC voltage can be enhanced by using quasi-trapezoidal wave as modulation wave. The quasi-trapezoidal wave is obtained by truncating a sinusoidal wave. Secondly, the power balance is realized by adjusting arrangement methods of triangular waves. The principles of sinusoidal ratio selection and the methods of triangular wave reconstruction are elaborated through simulation analyses and theoretical derivations, which indicates that the optimum sinusoidal ratio is 0.58 and that the required times of power balance are 3Tc. When compared with traditional sinusoidal and trapezoidal PWM strategies, the higher utilization ratio of DC voltage, the lower total harmonic distortion of line voltage, and the shorter required times can be obtained by using the proposed PB-MTPWM strategy. The feasibility and correctness of PB-MTPWM strategy are validated through extensive experimental studies.