Development of PWM Inverter Employing GTO

Application techniques of a gate turn-off thyristor (GTO) to a pulse-width modulation (PWM) inverter are presented. The switching characteristics of a GTO greatly depend on those peripheral circuits, so that it is very important to establish the application techniques to design the gate circuit and the main circuit of the GTO. For the gate circuit, the relations of the GTO's turn-off characteristics to impedance elements of an off-gate circuit and to the circuit system are described. For an on-gate circuit, a new narrow-pulse method is developed which can keep the conduction of the GTO in spite of the performance state of an inverter depending on the power factor of a load. Using this new on-gate circuit, the power dissipation of the gate circuit is reduced to one-fourth compared with a commonly used wide-pulse method. The transmitting section of a control signal is evaluated for disturbance of a PWM inverter, caused by switching operations. It is concluded that the gate circuit which is provided with separate power supplies used to turn the device on and off would be most advantageous. For the main circuit, the effects of the snubber capacitor's capacitance and wiring inductance on GTO turn-off characteristics are considered. Also discussed is a protection method for the GTO at the occurrence of a short-circuit fault, which utilizes its self-extinguishing capability. Some practical examples of the PWM inverter employing the GTO for driving induction motors (IM) are presented. These inverters have been made smaller in volume or much higher in performance.