Synchronous Optimal PWM With Continuous Switching-to-Fundamental Frequency Ratio

In high-power applications, the synchronous optimal pulse width modulation (SOPWM) serves as a vital modulation method that achieves an excellent tradeoff between the switching losses and the current harmonic. However, the optimized pulse patterns of SOPWM are constrained due to the discrete pulse numbers, which leads to the underutilization of the allowable maximum switching frequency. Therefore, the corresponding current harmonic could not be reduced as low as possible. In response to this issue, the SOPWM with a continuous switching-to-fundamental frequency ratio is proposed in this article. First, the deduction of the traditional pulse patterns is introduced based on the symmetry of the voltage pulse waveform. Then, the principle of the proposed strategy is illustrated in detail, and an overall comparison with traditional SOPWM is given theoretically. With the proposed strategy, a considerable reduction of the current THD is achieved over almost the whole high-speed range, and the losses and efficiency of the system are analyzed by the finite element method (FEM). Finally, theoretical results are verified by simulation and experimental tests.