Reset circuit for auto-sequential commutated inverter

Abstract

An improved auto-sequential commutated controlled current inverter for driving a multi-phase load from a source of controlled magnitude direct current is disclosed. The auto-sequential commutated inverter comprises a plurality of parallel connected branch sub-circuits with each branch sub-circuit comprising at least one gate controlled power thyristor device connected in series circuit relationship with a respective power diode. The branch sub-circuits thus comprised are connected between a respective phase input to the multi-phase load and a common direct current power supply terminal for connection to the source of controlled magnitude direct current. A respective commutating capacitor is interconnected between the junctures of the power thyristor and power diode of each respective branch sub-circuit and the power thyristor and power diode of the next adjacent branch sub-circuit. An improved reset circuit is connected to the auto-sequential commutated inverter thus constructed for improving the frequency response characteristics of the inverter, thereby, allowing it to operate at higher frequencies with minimum size power components. The improved reset circuit comprises a common impedance for assisting in the discharge of energy stored in the commutating capacitors. The common impedance has one terminal connected to the common direct current power supply terminal and the remaining terminal connected in common to corresponding terminals of a plurality of coupling diodes. There is one coupling diode for each phase of a multi-phase load being supplied with each coupling diode having one terminal connected in common with the corresponding terminals of the remaining coupling diodes to the said one terminal of the common impedance. The remaining terminals of the respective coupling diodes are connected respectively to the juncture of the power thyristor and power diode of a respective branch sub-circuit. The common impedance preferably comprises a common inductive reactance having resistance for dissipating energy stored in the common inductive reactance and further preferably comprises a discrete inductor having an inductive reactance which series resonates with the equivalent capacitance of the commutating capacitors at a higher frequency than the desired operating frequency of the inverter. The dissipating resistance may be in the form of a discrete resistor connected either in series or in parallel with the discrete inductor. Other embodiments of the reset circuit are described.