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Constant voltage (CV) charging and efficiency improvement are the most basic and main targets to be achieved in inductive power transfer (IPT) systems. However, efficiency may be jeopardized as battery charging progresses, especially under a light-load condition, which accounts for most of the charging time. Traditional maximum-efficiency tracking (MET) control provides an effective solution to the above issues. However, MET control not only brings the difficulties of complicated control and increased cost/volume, but also increases the additional power losses because of the introduction of additional converters or hard-switching in dual-shift phase control. To address the above difficulty, a light-load efficiency improvement (LLEI) technique is presented in this study. Under a heavy-load condition, both the inverter and rectifier operate in conventional full-bridge mode with satisfactory efficiency. Under a light-load condition, both the rectifier and inverter are reconfigured as a voltage-doubler rectifier and half-bridge inverter, respectively, to achieve two targets: one is to keep the charging voltage roughly unchanged, and the other is to force the equivalent load resistance (ELR) approach to the optimal point to improve system power transfer efficiency. A demonstrative experimental prototype with a charging voltage of 60 V is constructed and tested to validate the LLEI method proposed in this study. The experimental results show that the proposal can ensure stable CV charging and significantly improve the system efficiency under a light-load condition over the whole charging process.
Zhou et al. (Wed,) studied this question.