An Extended Pulse-Density-Modulated Series-Resonant Inverter for Induction Heating Applications

This paper presents an extended series-resonant inverter (SRI) with the output current control based on the pulse-density-modulation (PDM) control technique. The use of the extended SRI with a PDM technique is proposed to reduce the amplitude fluctuation of the SRI output current. The extended SRI topology is a combined topology of full-bridge and half-bridge inverters. The operation principle of the extended SRI with the PDM technique is shown. The effectiveness of using the extended SRI topology is also demonstrated compared to a conventional full-bridge SRI topology with PDM. The evaluation of effectiveness is determined in two ways: the difference between the values of the minimum amplitude current and reducing relative values of the peak-to-peak current amplitude fluctuation. Theoretical analysis shows that it is possible to achieve the effectiveness in increasing the minimum current amplitude up to 19.8% at the quality factor of 5 and reduce peak-to-peak current amplitude fluctuations at least twice. The extended pulse-density-modulated SRI is theoretically discussed and also verified with an experimental setup. Some of the experimental results are shown.