Sliding mode PLL-PDM controller for induction heating system

Abstract

In this study, a sliding mode controlled phase locked loop (SMC-PLL) was developed for induction heating (IH) applications with a resonant inverter. PLL applications are widely used in induction heating applications to achieve zero voltage switching and zero current switching. In many PLL applications, the frequency tracking is too slow and unreliable. Therefore, a sliding mode controller was developed to provide robust and fast PLL. Furthermore, a pulse density modulation (PDM) control strategy was developed to work at the resonant frequency for all power levels. The PDM power control is a good solution for the design of high-frequency inverters because of a great reduction of switching losses and electromagnetic noise. The PDM pattern for the desired output power is determined according to the set temperature value of the work piece. The proposed system was simulated in PSIM and a 250-W laboratory prototype was implemented with operating frequency of 35-42 kHz.