具有LC串联补偿拓扑结构的无线充电系统的约束效率优化

Constrained Efficiency Optimization for the Wireless Charging System with LC-Series Compensating Topology

开发基于感应功率传输的无线充电系统是一个很有前途的研究领域。本研究的目的在于,在给定谐振频率和给定发射线圈和接收线圈之间距离的情况下,优化具有LC串联补偿拓扑结构的无线充电系统的约束效率。这些约束反映了线圈的尺寸限制、输入电压限制下所需的传输功率,以及部件上的过电压。为了达到目标,制定了优化标准。已经为频域中优化标准的每个组件建立了对无线充电系统谐振电路参数的依赖性。由于这些依赖关系看起来非常复杂,在给定的情况下利用参数之间的联系,并采用最小二乘法的切比雪夫多项式近似,它们在优化任务中被简化为一个变量。因此,理论上已经获得了指示优化标准满足的谐振电路参数。利用为电动卡车ET-20132专门制造的无线充电系统对所提出的约束效率优化方法进行了实验验证。实验和理论的比较表明,它们在谐振频率上具有良好的收敛性,由数学模型中的假设引起的谐振频率偏差是可接受的。经实验证明,无线充电系统的效率为91%。

The intensive development of electric vehicles contributes to advancing battery charging systems.One of the promising areas is wireless charging systems based on inductive power transfer.However,parameter optimization of the resonant circuit’s inductances and capacitances can affect the wireless charging system’s efficiency.This paper aims to optimize the constraint efficiency of wireless charging systems with LC-series compensating topology at a given resonant frequency and a given distance between transmitting and receiving coils.The constraints reflect dimensional restrictions on coils,ensuring transferred power is within an input voltage limit and limiting excess voltages on components.A mathematical model is used that assumes load as active resistance,no loss besides the ohm one,and the idealized inverter,rectifier,and power supply.The optimization criteria include four components:(1)the efficiency functionξ1 to be maximized;(2)the constraint functionξ2 determining the amount of transferred power to be lower limited;(3)and(4)the constraint functionsξ3 andξ4 determining the excess voltage on the primary and secondary capacitors that to be upper limited.The dependencies are established using a frequency domain to describe each component of the optimization criteria on the resonant circuit parameters of the wireless charging systems.Due to complexity,some resonant circuit parameters are treated as constants in the given circumstance and discarded.Next,the dependencies between the rest of the parameters are obtained using Chebyshev polynomial approximation through the least-squares method,reducing the parameters to the coil inductance L.Moreover,the dependenciesξ1(L)~ξ4(L)are compared with their boundary conditions.Thus,the resonant circuit parameters that fulfill optimization criteria are theoretically obtained.The presented constrained efficiency optimization is validated using the specially-made wireless charging system for the electric truck ET−20132.Addressing various sources of loss,including those caused by the skin effect,transistors in the high-frequency inverter,diodes in the high-voltage bridge rectifier,and control schemes,is considered.Comparison of experiments and theoretical analysis shows good convergence at the resonant frequency 91.3 kHz,with acceptable deviations beyond the frequency range(approximately below 88 kHz and beyond 96 kHz).The wireless charging system normally operates within the frequency range of 91.3 kHz to 92.5 kHz,where the experimental load current closely aligns with the model,indicating that all the required power is transferred.Minimal average deviations between experiments and theoretical analysis are voltages on the primary and secondary side capacitors.The experimental results generally exceed model predictions.The efficiency can reach 91%.