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.

中文翻译：

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一种改进的基于谐波的ICPT系统脉冲密度调制策略

为了提高电感耦合电力传输系统中高频逆变器 (HFI) 的效率，经常使用脉冲密度调制 (PDM)。但是，HFI 的输出电流波动很大，尤其是在轻载时。它影响系统的稳定运行和零电压切换的实现。在本文中，提出了一种改进的脉冲密度调制 (IPDM) 以减少电流波动。它采用谐波脉冲代替基波脉冲和零态，均匀分布开关序列，减少电流波动。同时，通过瞬态分析的方法得到谐波的最佳移相角，进一步减小输出电流波动。经理论分析，IPDM电流波动小于PDM，轻载时效率更高，而PDM重载时效率更高。因此，应用混合调制策略，IPDM 和 PDM 分别用于轻载和重载。实验结果表明，HFI输出电流纹波系数降低了15%～62%，轻载时效率提高。