Surge analysis of induction heating power supply with PLL

Surges are undesirable with respect to both the reliability and the efficie ncy of power devices. In this paper, the surge mechanism of an induction he ating power supply is studied. First, a modified phase locked loop (PLL) co ntroller is proposed such that the changing resonant frequency of the heate d load can be tracked correctly and the zero voltage switching (ZVS) can be reliably maintained simultaneously. Then, a very simple and practical surg e model is proposed. Surge analyzes for both ZVS and non-ZVS modes are made in sequence. It is found that the extra energy built up in the line induct ance during the reverse recovery process of the diodes plays a very importa nt role in generating huge voltages. Finally, some simulation and measured results are provided to verify the validity of the proposed surge model.