Research On Double-sided LCC Compensation Method For IPT System

The double-sided LCC compensation network is widely used in wireless power transfer(WPT)due to its constant current and voltage output characteristics and high working efficiency.However,many passive compensation components and two working modes bring the problem of complicated parameter design and large size of the system,which make it unable to be used in small volume system.In addition,the error in actual parameter and theoretical parameters of the compensation component in application,resulting in the system unable to achieve soft switching.Therefore,this paper studies the compensation method about symmetric and asymmetric double-sided LCC compensation network in the inductive WTP,and derives a optimized method of parameter,which that can realize soft switching in both working modes.The T-circuit equivalent model and the couple circuit model about the WPT are analyzed.This two model have their own advantages in different applications.: Tthe T-circuit type equivalent model is suitable for solving the input and output characteristics of the compensation network,but,the couple circuit model for solvingsolving the internal voltage and current of the compensation network.Moreover,the high-order compensation network can be regarded as composed of several low-order compensation networks,hence,the transmission characteristics of the complex high-order compensation network can be obtained by the low-order network.To solve the complex parameter design problem,the equivalent impedance of the system should be purely resistive in the two operating modes for reducing the reactive power transmission,the inverter simultaneously works in the state of zero phase angle.By analyzing the different modes of the equivalent circuit and calculating the T transmission parameter matrix of the double-sided LCC compensation network is calculated,the relationship between the system operating frequency and the coupling coefficient under different operating modes is obtained,and then the symmetrical parameter design method is obtained.For the large size problem,the asymmetrical parameter design method is studied based on the symmetrical parameter design method,which can reduce the size of the coupling coil at the receiving end of the system.Moreover,the gallium nitride-based device is applied to the WPT to improve the operating frequency of the system,which can obviously reduce the weight and volume of the system.In the two working modes of constant current and voltage,the equivalent input impedance of the system should be weak inductive,so that the switch tube can realize soft switching in both modes.By analyzing the influence of each compensation element in the double-sided LCC compensation network on the system impedance under different operating modes,a parameter optimization method to enable the system to achieve soft switching in both modes is presented.The correctness of the two proposed double-sided LCC compensation methods is verified by MATLAB/Simulink and PLECS simulation software respectively.The both methods can switch the constant current and constant voltage working mode by changing the frequency,and achieve load-independent compensation.A gallium nitride based experimental prototype with an operating frequency of 349 k Hz in constant current mode and 418 k Hz in constant voltage mode was built to verify the proposed method.The experimental results are consistent with the simulation results.The system with the highest efficiency 92.3% all achieves soft switching when working in two modes.