Design of LCC impedance matching circuit for wireless power transfer system under rectifier load

In wireless power transfer system, impedance matching circuits are usually used to match the impedance between actual load and the optimal load, to achieve the maximum transfer efficiency (coil to coil efficiency). It is easily to design impedance matching circuit parameters for linear load. However, the load is always the rectifier one in many applications. The equivalent impedance of rectifier load is complex impedance, which is affected not only by itself, but also by pre-stage circuit, such as impedance matching circuit parameters. It is hard to calculate the equivalent impedance of rectifier load directly to design the impedance matching circuit parameters. This paper investigates the LCC impedance matching design method for secondary side under rectifier load. Firstly, the transfer efficiency characteristic under rectifier load is studied, and the equivalent impedance is analyzed according to transfer efficiency. Then the impedance calculation method of secondary side under rectifier load is derived via formula derivation and Fourier series theory, and the LCC circuit parameters design method is proposed. Lastly, a wireless charging system for electric vehicle is established to verify the method that can transfer 3.3 kW power over 20 cm distance with 92.7% system efficiency (end to end efficiency).