The stroboscopic method of analysis of transient phenomena in a parallel capacitor compensated medium frequency inverter during starting and sudden load disturbances

The purpose of the paper is to analyse the transients that occur in a parallel capacitor inverter for medium frequency induction heating during starting in `open loop´, due to change-over from open-loop to closed-loop frequency control and subsequent sudden changes in parameters. A simple analytical method called the `stroboscopic´ method has been used to study the voltage and current transients arising out of the conditions mentioned above. The essence of the method is that it deals with the transient behaviour of the amplitudes of the voltages and currents (i.e., envelopes) rather than with their instantaneous values. The fact that the envelopes vary slowly as compared to the instantaneous values results in great reduction in computational effort in evaluating the transient behaviour. The results of the analysis are useful in finding out the maximum voltages and currents which the devices have to withstand and also to check whether the device turn-off time is adequate during transients