A soft switching class D current source inverter for induction heating with ferromagnetic load

A class D current source resonant inverter (CSRI) for induction heating power supplies for ferromagnetic load is proposed in this paper. The converter operates in zero-current switching mode. The switching devices are connected through the common ground and need only a single dc power supply for the gate driver circuitry. A small input inductor (500 μH) is used for shaping the line current with the aim of unity power factor operation on the line input. The operating frequency of the CSRI is automatically adjusted to maintain a small constant leading phase angle under load parameter variation. The maximum output power transferred to the load for this prototype is 1.26 kW. It can heat a 30-mm diameter and 150-mm long steel work-piece from room temperature to approximately 680°C within 10 minutes.