An optimized frequency and phase shift control strategy for constant current charging and zero voltage switching operation in series-series compensated wireless power transmission

In this paper, a three loop control strategy (TLCS) based on decoupled zero voltage switching angle (ZVSA) loop is proposed for a series-series (SS) compensated wireless power transmission (WPT) system. To realize constant current charging for EVs and ZVS operation of primary inverter, variable frequency and phase shift control strategy (VF-PSC) is adopted. However, the control variables that are frequency and duty cycle, are highly coupled. Therefore, by decoupling the ZVSA loop, the ZVSA is only a function of operation frequency and irrelevant with duty cycle. And the ZVSA can be controlled as a positive phase angle for realizing ZVS completely. Simultaneously, an inner primary resonant current loop is adopted to enhance the systematic dynamic response and limit the primary resonant current to protect the system. Based on the received output current signals, an outer output current loop is applied to obtain a stable charging current. To make full use of the characteristic of SS compensated WPT system, an optimal operation frequency range in a certain load and coupling coefficient is analyzed in detail, which can guide us to select the appropriate ZVSA. Finally, a 500W WPTS is fabricated to verify the correctness of theoretical analysis and the effectiveness of the proposed control strategy.