Effects of T-Type/Π-Type Resonant Networks on Harmonics of Inverter Currents in WPT Systems

For wireless power transfer (WPT) systems, T-type/Π-type compensation networks have the advantage of converting the voltage source input to a constant-current output. However, the higher order harmonics in the output current can reduce the power factor of the inverter as well as shift the zero-crossing point of the inverter current, which increases the switching losses of the inverter. This problem is especially prominent under light load conditions. The existing solution is to add extra series power filters. There is still a lack of solutions that utilize the harmonic suppression capability of the T-type/Π-type topology, even less the comparison of the harmonic suppression capability of various types of compensation. In this paper, the higher order harmonic suppression capability for the inverter current of different T-type/Π-type compensation networks are systematically analyzed. An evaluation method based on the ratio of harmonic and fundamental of current is proposed, and the mapping of the third harmonic content of the inverter current in different compensation networks is obtained by using the ratio of the input and output fundamental currents of the topology as the independent parameter. On this basis, selection guides of T-type/Π-type compensation networks in WPT systems are given. The related experiments verify the correctness of the analytical results.