A new McMurray-type inverter with asymmetric SCR´s

The standard, simple McMurray inverter is improved in three steps. The first step, adding recharging and energy feedback pulses, keeps the inverter operating satisfactorily at low loads and also limits overcharging of the commutation capacitor. The second step involves replacing the standard LC ringing circuit (for commutation) by a long line which has to be approximated by concentrated elements. This changes the sinusoidal commutation current pulse to a rectangular shape and eliminates wasted time due to the rise of the sine wave in the standard circuit. The system therefore needs only 70% of the commutation time required for the standard system, so that about 1.4 times higher pulse frequencies can be realized. The third step, using newly developed asymmetric silicon-controlled rectifiers (ASCRs), is made possible by the structure of the improved inverter, where diodes are used in antiparallel to the main thyristors. The ASCRs require about 1/3 of the turn-off time of conventional thyristors. Altogether, inverter output frequencies of up to 1.4×3=4.2 times the frequencies achievable with conventional means were obtained