Power Electronics Lab Manual

The circuit is a typical class C parallel inverter. Assume TN to be ON and TP to be turned OFF .The bottom of the commutating capacitor is charged to twice the supply voltage and remains at this value until Tp is turned on. When Tp is turned on, the current flows through lower primary ,Tp and commutating inductance L. Since voltage across c cannot raise instantaneously, the common SCR cathode point raises approximately to 2Vdc and reverse biases TN. Thus TN turns off and C discharges through L, the supply circuit and recharges in the reverse direction. The auto transformer action makes C to charge making now its upper point to reach +2Vdc Volts ready to commutate Tp, when TN is again turned on, and the cycle repeats. The major purpose of the commutating inductance L is to limit the commutating capacitor charging current during switching. Freewheeling diodes Dp and DN assists the inverter in handling various range of loads and the value of C may be reduced since the capacitor now does not have to carry the reactive current. To dampen the feedback diode currents within the half period, feedback diodes are connected to the tapings of the transformer at 25V tapings.