Analysis of a Forced Commutation Circuit for Design of a Class or Thyristor Inverters

The literature contains a variety of inverter circuits with forced commutation. In general, the auxiliary circuit for switching off the load current carrying thyristors is composed of a number of energy storage components and semiconductor switches which are affected by losses. These circuits demonstrate specific advantages under certain conditions. The analysis of a forced commutated inverter with a series LC-resonant circuit is presented in this article. The peak capacitor voltage depends on the quality of the resonant circuit and the ratio of the peak capacitor current vs. the maximum load current. This can cause high stresses on all the components of the inverter circuit. The set of equations for the circuit is established and used for the computation of results. The peaks of stored energy and the losses in the commutation circuit are calculated and given in a normalized form. Design parameters in normalized form are derived therefrom and presented in this article.