The study of novel PDM-based Induction heating frequency tracking control

Adjustment for conventional pulse density modulation (PDM) control of induction heating power supply in output power with level and recovering from natural attenuation to the output power state needs to re-lock the operating frequency, this paper presents an improved frequency tracking control strategy. Output load current is applied to fast frequency tracking, thus the phase-locked loop (PLL) have enough time to lock, and when the load current down to a very small value, that is, into the natural attenuation state, the operation of sample and hold (S/H) circuit in the modified phase-locked loop (MPLL) ensure the power inverter operates in the vicinity of the resonant frequency and the inverter circuit always works at zero current (ZCS) and zero voltage switching state (ZVS).