Modeling of Series Resonant Inverter for Induction Heating Application

Induction heating is preferred over other heating methods because of efficiency, rapid heating, cleanliness and safety. Series Resonant Inverter (SRI) is a simple and cost-effective topology when it comes to induction heating. Several hybrid control schemes have been proposed in literature for optimal control of resonant inverters for which modeling becomes imperative. Compared to PWM converters, the method of averaging fails in resonant converters/inverters. A simple and straight forward modeling method for series resonant inverter is proposed in this work. The proposed model captures the small signal and large signal dynamics of the inverter. The analytical expression for small signal control to output power is derived. With the proposed model, one can control the state variable, namely the quadrature component of resonant current so as to improve the performance characteristics of the inverter. The small signal inverter transfer functions are derived facilitating hybrid control.