Total Harmonic Distortion and Output Current Optimization Method of Inductive Power Transfer System for Power Loss Reduction

Inductive power transfer (IPT) system is widely used in material handling. A typical structure of the system takes an H-bridge inverter with an inductor-capacitor-inductor (LCL) resonant filter to realize a constant track current supplying changeless energy to the second side. However, the output voltage total harmonic distortion (THD) of the inverter increases, which causes the increase of output current circulation, when using voltage width control method to eliminate source voltage fluctuating. Therefore, a two-stage converter is proposed to optimize the output current circulation. The two-stage IPT system is composed of a boost converter cascaded with an H-bridge resonant inverter. The boost converter is employed to provide a higher and stable DC bus voltage. The H-bridge resonant inverter operates in a fixed width with a constant switching frequency. With the proposed topology, the THD of the high frequency voltage maintains the minimum value to realize minimum output current circulation in the LCL filter. The soft switching is realized to reduce the losses. Furthermore, expressions of coil and track model are presented by combining the theoretical analysis and finite element analysis (FEA). The experimental results show that over 76.6% efficiency is demonstrated in conditions of an 800 W load at the 14% source voltage fluctuation and the maximum efficiency was 78.6 %. The range of efficiency variation was 2% compared to a full-bridge system with voltage pluse-width control of which was 4.6%.