An Improved Pulse Density Modulation Strategy Based on Harmonics for ICPT System

To improve the efficiency of high frequency inverter (HFI) in inductively coupled power transfer system, pulse density modulation (PDM) is often used. However, the output current of the HFI fluctuates seriously, especially at light load. It affects the stable operation of the system and the implementation of zero voltage switching. In this article, an improved pulse density modulation (IPDM) is proposed to reduce current fluctuation. It applies harmonics pulse to replace the fundamental pulse and zero state, and evenly distributes the switching sequence to reduce current fluctuation. Simultaneously, the best phase-shift angle of harmonics is obtained by using the transient analysis method to further reduce the output current fluctuation. The IPDM current fluctuation is less than PDM and the efficiency become higher at light load by the theoretical analysis, while PDM is better at heavy load. So, a hybrid modulation strategy is applied that IPDM and PDM are used for light and heavy load, respectively. The experimental results show that the HFI output current ripple coefficient is reduced by 15% to 62% and the efficiency is improved at light load.