An IPT System with Constant Current and Constant Voltage Output Features for EV Charging

Inductive power transfer (IPT) system for electric vehicle battery charging has many advantages over the traditional plug-in system. EV battery can be regarded as a wide range load according to the charging profile. The charging process requires constant current (CC) stage and constant voltage (CV) stage. The charging profile for IPT system is influenced by inductively coupled transformer, compensation structure and operating frequency. This paper proposes an IPT topology which naturally obtains CC and CV output functions simultaneously without increasing the complexity of control system. The system switches between the two charging modes in succession along with the change of load condition. It operates under the CC mode when the load resistance is small, which corresponds to the beginning of battery charging state. With the increase of load resistance, it switches to CV mode at a load turning point after which the battery is under the state of cutoff voltage. As the system is completely compensated, zero phase angle input is achieved during the entire charging process, which realizes soft switching for the entire load range. A fixed frequency control method is used to adjust the output accurately. The experimental IPT system is established to verify the theoretical analysis.