Mechanism Analysis of Output Fluctuation in a Three-Phase Dynamic Wireless Charging System

In a dynamic wireless charging (DWC) system, the mutual inductance between the transmitter and receiver coils may vary with the position of the receiver, resulting in a fluctuation of the output voltage. Although a three-phase DWC system can reduce output fluctuation by traveling wave magnetic field, the existing three-phase systems still cannot achieve a uniform output voltage. In order to further improve the output stability, this article analyzes the cause of output voltage fluctuation. The magnetic field generated by the three-phase transmitter coils is decomposed into the fundamental and the harmonic traveling wave magnetic fields for analysis in this article. And a new calculation method of induced voltage is proposed from the perspective of dynamic electromotive force. Then, the voltages induced by the fundamental and the harmonic magnetic fields in the receiver coil are compared, revealing that the fifth and above harmonic magnetic fields are the ultimate cause of the output fluctuation. Subsequently, two fundamental methods to reduce the output fluctuation are proposed, and the effect of the output fluctuation on the efficiency is analyzed. Finally, a prototype was built to verify the correctness of the theoretical analysis and the feasibility of the proposed output fluctuation reduction methods.