Based on energy injection and free resonant mode, an approach to optimize the startup frequency setting of the voltage-fed inductive power transfer (IPT) system is proposed to mitigate the effects of uncertain system parameters and load conditions. Differential equations of the primary resonant network on the free resonant mode is firstly established, then the free resonant frequency with different parameters and load conditions is calculated and verified with the soft-switching frequency of system based on stroboscopic mapping modeling method and fixed points theory. By controlling the micro-energy injection of system and free resonance, the frequency of free resonant mode is detected, and is regarded as the fixed frequency of startup process. Hence, the proposed strategy solves the uncertainty of the startup frequency and system re-setting to fit with changed system parameters and load conditions. This method also initiates immediate protection when the system operates under zero loads. In sum, our experimental results verify the theoretical implication, effectiveness, and merits of the proposed approach.
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