Enhanced Pulse-Density-Modulated Power Control for High Frequency Induction Heating Inverters

This paper presents a 100 kW, 100 kHz IGBT series resonant inverter for induction heating applications that uses an improved power control scheme based on the standard pulse density modulation (PDM). This standard power control is a good solution for the design of high frequency inverters because the output power factor is near to unity in a wide range of output power, resulting in a great reduction of switching losses and electromagnetic noise. However, the output current can be in discontinuous mode especially for resonant loads of low quality factor or for low output power or low load operation. This output current fluctuation produces a high output current ripple that can lead to an increase of power losses and loss of accuracy of the response of the frequency tracking control. The proposed control strategy, called enhanced pulse density modulation (EPDM), provides twice less output current ripple, thus resulting in an improved inverter behaviour in terms of frequency tracking accuracy and energy efficiency. Experimental tests have been made in order to compare the EPDM strategy with standard power control schemes.