Abstract: A power supply for a gate drive voltage supply system for a power inverter is coupled to receive a variable DC voltage and operable to produce a regulated DC output voltage to each of a plurality of distributed electronic switching devices. The system includes a plurality of linear voltage regulators with each respective one of the regulators having a power input terminal coupled to a common DC link. Each of the regulators is separately connected to a ground reference at a ground reference power terminal of a corresponding one of the switching devices so as to eliminate ground loops and voltage drops over a common ground bus.

Abstract: In an electrical propulsion system on board a moving traction vehicle (such as a rapid transit rail car) having current collectors in contact with an energized third rail, controllable switch means is used to connect the system to the current collectors. From time to time the current collectors traverse gaps between adjacent sections of the third rail, in which event regenerative braking operation of the system will be prevented unless the next third rail section is energized by a wayside source of voltage. The switch means comprises the parallel combination of a diode that conducts current when the system is operating in a motoring mode and a reversely-poled thyristor that conducts regenerative braking current once a firing signal is applied thereto.

Abstract: For responding to a shorted gate in a gate turnoff thyristor the gate electrode of which is connected by means of a controllable switch to a control voltage terminal having a negative potential with respect to the cathode potential of the thyristor, the controllable switch being arranged to conduct negative gate current in response to a thyristor turnoff command, voltage comparing means is coupled to the controllable switch for detecting when the switch is conducting negative gate current of relatively high magnitude, timing means is active for a predetermined interval following the start of said thyristor turnoff command, and logic means is operative to cause the switch to stop conducting negative gate current if the voltage comparing means detects high gate current at the end of such interval.

Abstract: Flashover protection is provided for a locomotive propulsion system including a plurality of d-c traction motors each having a commutator subject to flashovers, a traction alternator having armature and field windings and a rotor driven by a prime mover, a controllable source of excitation current connected to the alternator field, and means including an electric power rectifier for connecting the alternator to the motor commutators. It comprises means for producing a fault signal whenever a flashover occurs in any motor, a solid-state controllable electric valve connected between the excitation current source and the alternator field and having alternative conducting and non-conducting states, and means for changing the valve from conducting to non-conducting states in response to a fault signal being produced, whereupon the magnitude of excitation current in the alternator field is rapidly reduced toward zero and the alternator's output current is correspondingly decreased whenever a flashover occurs.

Abstract: Flashover protection is provided for a locomotive propulsion system including a plurality of d-c traction motors each having a commutator subject to flashovers, a traction alternator having armature and field windings and a rotor driven by a prime mover, a controllable source of excitation current connected to the alternator field, and means including an electric power rectifier for connecting the alternator to the motor commutators. It comprises means for producing a fault signal whenever a flashover occurs in any motor, a solid-state controllable electric valve connected between the excitation current source and the alternator field and having alternative conducting and non-conducting states, and means for changing the valve from conducting to non-conducting states in response to a fault signal being produced, whereupon the magnitude of excitation current in the alternator field is rapidly reduced toward zero and the alternator's output current is correspondingly decreased whenever a flashover occurs.

Abstract: A variable speed 3-phase a-c motor is connected to a 3-phase source of alternating voltage via a plurality of controllable solid state electric valves which are so arranged and controlled that motor speed can be reduced by skipping selected cycles of the source voltage. For half speed operation 12 valves are arranged to interconnect the source and motor phases, and over two consecutive periods of the source voltage six separate, uniformly spaced "firing windows" are selected during which the conducting states of different pairs of these valves are initiated in a predetermined pattern that results, in each phase of the motor, in a double-pulse current waveform having one-half the fundamental frequency of the source voltage.

Abstract: A variable speed 3-phase a-c motor is connected via a plurality of controllable bidirectional switches to a 3-phase source of alternating voltage having a variable fundamental frequency (f) and an rms magnitude (v) that varies with f, and the switches are suitably arranged and controlled so that motor speed can be reduced by skipping selected cycles of the source voltage. When operating at a fraction of full speed, the magnitude-to-frequency ratio of motor voltage is maintained substantially the same as at full speed by varying the "firing angle" at which the switches start conducting current so as to minimize any deviation of the rms magnitude of the motor voltage from the product of v times said fraction.

Abstract: A hybrid phase-controlled rectifying bridge includes both controlled and uncontrolled electric valves referred to as thyristors and diodes, respectively. Each of a pair of thyristors is periodically fired at an "angle" that can be advanced or retarded as desired, whereupon load current commutates to the thyristor from the corresponding diode. Subsequently the thyristor is turned off at a desired extinction angle by the action of cyclically operative forced commutation means. To avoid reverse recovery overvoltages across a diode when the desired extinction angle is only slightly larger than the firing angle, means is provided for temporarily preventing any turnoff action during the diode-to-thyristor commutation interval and for an additional interval that gives the diode sufficient time to fully recover its reverse blocking capability.

Abstract: A phase-controlled ac-to-dc rectifying circuit includes a pair of alternately conducting main controllable electric valves and cyclically operative forced commutation means for turning off the main valves. The forced commutation means comprises a pair of auxiliary controlled rectifiers respectively connected, in circuit with a commutating capacitor, across the main valves, and the auxiliary rectifiers are alternately turned on in response to periodic trigger signals that are normally produced by associated control means. Protective means is provided for inhibiting the trigger signals when the magnitude of voltage across the commutating capacitor is lower than a critical level which depends on the magnitude of the current being conducted by the main valves, thereby avoiding a risk of commutation failure due to low capacitor voltage.