Inexpensive High-Performance STM32-based Software PLL for Series-Resonant Inverters in Induction Heating Equipment

This paper presents an inexpensive and high-performance STM32-based software phase-locked loop (PLL) for series-resonant inverters in induction heating equipment. The proposed PLL system provides high accuracy of the phase synchronization between the output voltage and the output current of the high-frequency converters. In the paper, the structure of a digital control system based on an STM32 microcontroller with the software PLL is presented. System parameters and current/power control techniques can also be easily changed by changing only the software. A 2.5kW prototype of a transistor converter with the digital control system based on STM32 with the software PLL was implemented and the experimental results confirmed the high accuracy of the PLL setting the phase synchronization.