A new simplified model of the dynamics of the current-fed parallel resonant inverter

In this paper, the transient analysis of a current-fed parallel inverter, widely used in industrial applications (such as for the heating and melting of metals), is performed. A high-inductance smoothing inductor is usually connected in the input of the inverter and its load may be represented by a parallel resonant circuit characterized by high quality factor Q. To simplify the dynamic analysis of such an inverter, approximating it by a second-order switchless continuous dynamic link (i.e., RLC circuit) is suggested. The comparative analysis of the inverter and approximating circuit, whose parameters are properly chosen, shows the permissibility of such an approximation. It also shows how to assure desired aperiodic dynamic behavior. Then, by analyzing the approximating circuit, the expressions for inverter parameters are found. With these expressions, the values of a smoothing inductor, a compensating capacitance and a voltage factor, in order to ensure the aperiodic behavior of the inverter, can be calculated. The results of the proposed analysis were checked on laboratory and industrial prototypes of the above inverter. The theoretical and experimental results are in good agreement.