Reconsidering Regulator Capacitor Selection for Wireless Charging System with a Receiver-Side Buck

To control the charging process, a cascaded buck converter is usually employed between the front wireless charging system (FWCS) and battery. A regulator capacitor is placed after rectification to filter out the high frequency voltage and acts as a passive power buffer for the cascaded buck. In this paper, instability problem caused by improper selection of the regulator capacitance is newly reported. First, output impedance of the FWCS and input impedance of the cascaded buck are derived to establish the analytical model. Then, the Middlebrook criterion is adopted to judge the cascaded stability. It is found that improper capacitance design is prone to instability. Finally, experimental results verify the analysis. This unstable phenomenon aggravates the receiver current stress in the resonant tank.