An Improved Pulse Density Modulator in Inductive Power Transfer System

Inductive power transfer (IPT) has been widely applied in various applications such as electric vehicles and consumer electronics. In this article, a voltage controller base on an improved pulse density modulator (IPDM) for H-bridge active rectifier in IPT is proposed. To reduce the power loss caused by the pulse sequence of the traditional pulse density modulation (PDM) controller, a general optimization method of the pulse sequence is given and proved in detail. More importantly, an analytical model, which illustrates the relation between interharmonics and power losses of the system, has been derived. Compared with traditional PDM, the stress on switching devices is reduced under various load resistance, and the overall system efficiency can be improved. The experiment results based on a 1-kW laboratory prototype demonstrate the proposed IPDM design method. Under different load conditions, ranging from 22.6-102 omega, the overall system efficiency could reach up to 96%. Compared with phase-shift modulation and PDM, the efficiency is at most improved by 3.508%.