Capacitor Clamped Series Resonant Inverter with an Auxiliary Switched Cell for an Induction Heating System

Abstract

This dissertation discusses the design analysis and the modeling of a capacitor clamped resonant inverter topology for induction heating cookers to improve the power capability of the previous resonant inverter under a soft-switching operation and to observe the dynamic characteristics of the inverter system. Commonly resonant and quasi-resonant type inverter topologies including full-bridge, half-bridge, series resonant, and parallel resonant configurations are used in IH home applications due to their high performances within certain power levels. However, a new type of capacitor clamped series resonant inverter using an auxiliary switching cell is introduced with its high power density characteristics. Besides, there are many modulation techniques used in induction heating system namely, pulse frequency, pulse density, pulse width, phase shift and so on. Among these modulation techniques, pulse width modulation is generally used for every type of inverter topology because of its advantages and better performance. For an unperturbed operation, the PWM technique with asymmetric gating signals is used in the proposed inverter topology. The describing function is used to model the series resonant type inverter circuit because the model parameters of the resonant circuit are altered continuously. The steady state operation of the inverter is taken into account to find the small signal model and the transfer function of output power to duty factor. Also, the full-load and the maximum duty-factor characteristics are considered. The first harmonic approximation is taken into account as the basic condition of describing function technique. After approximation, the equations are linearized with operating points and perturbation, and the control to output transfer function is obtained. To verify the analysis practically, a small scale prototype of the capacitor clamped inverter circuit has been implemented in the laboratory. The analytical results and the experimental results are matched incredibly. In addition, the power capability of the inverter to maintain the zero-voltage turn-on under certain operating condition is assured. A comparative study is made between the half-bridge and the newly proposed inverter topologies. Following the comparison, the conclusion has been written that the proposed inverter topology provides higher output power than that of a two switched half-bridge type inverter topology. This benefit makes the circuit superior and more useful in the induction heating home applications.