Adaptive Phase Control Method for Load Variation of Resonant Converter with Piezoelectric Transformer

this paper proposes a new method eliminating external effect from (load, temperature) variation on a Piezoelectric Transformer (PT) converter by utilizing the phase-locked loop (PLL) modulation technique. The PLL control scheme involves detecting phase difference between injected sinusoidal signal and demodulated terminal voltage of PT. Generally, frequency control method decreases the efficiency of PT in wide input range. And, duty cycle control method has a problem of insufficient operating range for the load variation. In other to overcome these problems, this paper introduces a two loop control (PWM and PLL) with PT which provides wide ZVS condition nearly independent of the load variation, and excellent line regulation for the universal input voltage and load range. The performance of the proposed control method is verified by experimental result with 40 [W] DC/DC converter hardware prototypes.