Optimized Pulse Density Modulation Control for the Secondary Side Controlled WPT System With Active Rectifier to Reduce Output Voltage Ripple

The pulse density modulation (PDM) technology enjoys the advantage of low switching loss and is extensively utilized in wireless power transfer systems. Nevertheless, the traditional approach features a lengthy conduction time, giving rise to a significant output voltage ripple and severe current fluctuations. This article presents an optimized PDM method for the secondary controlled wireless power transfer system with active rectifier. An optimal sequence generator is devised for the optimal distribution of output current pulses, thereby suppressing the output voltage ripple to a considerable extent. By selecting the switching modes of the rectifier, the periodic operation of the switch is accomplished without raising the frequency, and the difficulty of control implementation is mitigated. The switching rules are formulated based on the current polarity to enable soft-switching. Experimental results show that the voltage ripple ratio of the proposed method is 4.5%, representing a decrease of at least 6.6% compared with other methods. Meanwhile, the proposed method reduces the switching losses and the additional losses caused by the output voltage ripple. Compared with other methods, the system efficiency increases by 1.65%.