Improved efficiency determination for a PLL-controlled series resonant inverter for induction metal surface hardening

In this paper, an improved efficiency evaluation approach is proposed and described for a controlled Series Resonant Inverter for induction surface metal hardening using phase locked loop technique. This efficiency is assessed at the induction coil side, through the heat power being transferred to the work-piece, by monitoring the temperature evolution at the metal surface during the hardening process. In addition, its impact is examined by measurement of the hardness of the work-piece made out of 1038h (AISI/SAE). Further, an efficient digital control technique was designed, implemented and integrated into the induction heating system in the range of 1kW power range, at an operating frequency of 6.4 to 7.1 kHz. Its features are flexibility, low cost hardware, and higher response time. Also, the experimental results are presented to show the validity of the simulation model, and to evaluate the system performances.