Conducted Emission Analysis of a Near-Field Wireless Power Transfer System

In modern inductive power transfer (IPT) systems, especially if devoted to electric vehicle (EV) charging, the alignment between the transmitter and receiver coils still represents one of the most relevant issues. Besides a well-known drop in the efficiency and transferred power, operating in a misalignment condition also affects the conducted emissions towards the grid, that increase as the coupling between the transmitter and receiver weakens. This paper investigates the conducted emissions of an IPT system for different alignment conditions. The system is supplied by a full-bridge inverter and feeds an equivalent load of 5 Ω through a full-bridge diode rectifier. The inductive coupling is realized with two identical square coils, that resonate with lumped capacitors connected in series at the resonant frequency of 147 kHz. A simple model has been used for the prediction of the differential-mode conducted emissions and the results have been compared with experiments. The measurements have been performed with the general setup for conducted emissions described in IEC standards and the disturbance voltages have been processed to assess the highest emission level which defines the worst case scenario for electromagnetic compatibility.