Abstract
Offsets between the primary and secondary coils of loosely coupled transformers (LCT) are attributable to the efficiency decline of the wireless power transfer (WPT) system. To improve the misalignment tolerance of efficiency in WPT system, this paper presents a LCT system with a movable intermediate coil and adjustable system frequency, which can promote the efficiency of the WPT system under misalignment condition. First, the influences of the position and compensation parameter of intermediate coil on the system efficiency during migration are summarized. The optimal compensation parameter and optimal position selection method of intermediate coil are proposed. Then, the influence of frequency on system efficiency is studied, and the detailed control strategy of intermediate coil’s position and system frequency is proposed. A 3-kW prototype WPT with the proposed three-coil LCT is manufactured and experimental validations are also performed. The results show that the efficiency declines of three-coil LCT with the proposed control strategy is 1.8% when the lateral offsets reach 300mm, namely 43% of the outer diameter of coil.
Highlights
Owing to the rapid growth of the electric vehicle (EV) industry, obvious momentum in research of energy storage system charging was witnessed in the last few years [1]
EQUIVALENT CIRCUIT MODELING OF TWO-COIL loosely coupled transformers (LCT) The equivalent circuit model of the two-coil LCT with series-series (SS) compensation is shown in Fig.1, where Up is the high-frequency supply; Lp and Ls are the selfinductances of the primary and secondary coils, respectively; Rp and Rs are the resistances of the coils, respectively; Cp and Cs are the compensation capacitance of the coils; respectively, Mps is the mutual inductance between the primary and secondary coils, and Req is the equivalent resistance of the load
EQUIVALENT CIRCUIT MODELING OF THREE-COIL LCT The equivalent circuit model of the three-coil LCT is shown in Fig.2, where Li is the self-inductance of intermediate coil, Ci and Ri stand for the compensation capacitance and resistance of the intermediate coil, respectively
Summary
Owing to the rapid growth of the electric vehicle (EV) industry, obvious momentum in research of energy storage system charging was witnessed in the last few years [1]. As for the optimal design of LCT, a double D-shaped (DD) coil and a DD-quadrature (DDQ) coil with additional orthogonal coil were proposed on the primary side [9] and the EV side [10], respectively, for improving the misalignment tolerance of WPT’s efficiency. The above measures can improve the misalignment tolerance of efficiency to some extent, but they adopted a more complex structure, compensating topology, and even complex control strategy. In [27], a WPT system with an intermediate coil is analyzed, and an optimal design method is proposed for high system efficiency. To improve the misalignment tolerance of the WPT’s efficiency with a simple structure or simple control strategy, a novel LCT with intermediate coil and control strategy of intermediate coil’s position and system frequency is proposed. The effect to promote misalignment tolerance of the proposed control strategy in this paper is verified on a 3-kW LCT
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