Circulating Current Suppression and Current Sharing Strategy for Parallel IPT System Based on d-q Synchronous Rotating Frame

A modular-parallel IPT system with multi-inverters is proposed to enhance power capacity and expansibility for primary power equipment. In order to balance the actual output power of each inverter, a control strategy is designed to minimize circulating-current and equalize output current. In the process of circulating current suppression, current could be decoupled into the following two parts through a d-q synchronous rotating frame: virtual active and reactive current. Then, the above two virtual current components can be adjusted by PWM and PPM. A close-loop control method based on master-slave scheme is proposed to improve the scalability for a practical IPT system, and an impedance matching and its ZCS method is proposed to avoid detuning caused by a change of the number of modules. Finally, an IPT experiment platform with 3-parallel modules is established to verify availability of the proposed control methods. As shown in the experiment, circulating current of the prototype can be reduced from 2.6 A to 0.3 A, and the difference of output power of each module is less than 1 % when deviation of the input DC voltage, the delay of driving signals, and the resonant inductance is 10%, respectively. The overall efficiency of the modular IPT system is up to 92.5% at 3.3 kW.