Efficiency Optimization of Double-sided LCC Matching Network for Electric Vehicle Inductive Power Transfer System




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This thesis presents an efficiency optimization of double-sided inductor-capacitor-capacitor (LCC) matching network for inductive power transfer (IPT) systems. Compensation factors of the primary and secondary LCC circuit are defined and optimized, both analytically and numerically. Through this investigation, the secondary compensation factor, krx, highly influences the copper loss of the wireless coupler, while the primary compensation factor, ktx, affects the switching loss and conduction loss of the input inverter. With a proper selection of these compensation factors, it is possible to achieve a high and sustained efficiency over a wide range of load and misalignment. For the analysis-based optimization, the matching networks are assumed to be lossless in order to simplify the process of the analytical derivation. The established formulae presented in this thesis is compact and convenient to use. In order to take into account the conduction loss of the input inverter and rectifier, and the losses on components of matching networks, a Genetic Algorithm (GA) - based optimization is implemented. The primary and secondary compensation factor are the variables needed to be solved by the GA optimization. The fitness function is the total loss of the circuit, and the GA optimization will search for a pair of variables, ktx and krx, to minimize the fitness function, while satisfies a constraint, which is the output power. It will be shown later that the results of the GA optimization agree excellently with the ones from the analysis-based optimization. Therefore, both methods presented can be utilized in practice, providing a convenient tool for designers who deals with the LCC-LCC matching network in IPT applications. In addition, a sensitivity analysis study is presented in this thesis in order to investigate the impact of components’ tolerance on the winding-to-winding efficiency and input power factor. In order to demonstrate the feasibility and validity of the proposed method, a scaled-down prototype of an IPT system has been implemented with the operating frequency of 85kHz, transfer gap of 170mm and misalignment of up to 100mm. Experimental results show a good agreement with the theoretical analysis. The peak efficiency of the proposed system is 91.6% under the perfect alignment or at the coupling coefficient of 0.172. The efficiency still remains at 86.37% even under 100mm misalignment with the coupling coefficient of 0.123. The optimization method presented in this thesis is for the double-sided LCC topology, however, the author believes the optimization methodology can be applied for other topologies of matching networks in IPT systems.



Engineering, Electronics and Electrical