Abstract: In a thyristor with turn-off facility (AT) and overvoltage protection, the voltage limitation is achieved by a parallel-connected controllable resistor, in particular in the form of a J-FET (JF) which is driven by an overvoltage sensor (OS).The separation of sensor function and bypass function produce advantages for a simple and compact construction.

Abstract: A voltage supply for an electric filter is disclosed. The supply comprises a high-voltage rectifier, a pulsed voltage circuit including a resonant circuit and a parallel circuit of a thyristor and a diode which controls resonance in the resonant circuit. The thyristor is fired to trigger the resonant circuit and generate an oscillation which is delivered to the filter as a pulsed voltage. In order to prevent damage to the thyristor, it is fired whenever the duration of the current flowing through the diode is shorter than the thyristor recovery time.

Abstract: The circuit contains a separate firing and extinguishing circuit, each having a respective capacitive charge store for generating the firing and the extinguishing current pulses for a GTO thyristor. A fast switching element which can be directly activated via a push-pull stage is provided which, when activated, discharges a respective charge store via the gate-cathode path of the GTO thyristor. As a result, the GTO thyristor can be operated at a high cycle frequency of up to at least 12,000 Hz and can be used in audio frequency transmitters for ripple control systems.

Abstract: For maintaining the current-blocking switching state of a thyristor that can be turned off, a low-resistance shunt is added between the gate and cathode terminal of the thyristor in the event of a fault, i.e., in case of a failure of the blocking negative gate- cathode voltage. The shunt preferably is a self-conducting field-effect transistor which is kept in the cut-off state, at least with the thyristor turned off by the negative thyristor gate-cathode voltage itself or indirectly by a supply voltage causing this voltage. The drain-source path of the transistor is connected in series with a diode having a low forward voltage in order to prevent undesirable inverse operation of the transistor.

Abstract: There is disclosed a protecting apparatus for a secondary excitation type variable speed AC generator/motor having a primary winding connected to an electric power system and a secondary winding each phase of which is AC excited by an independent power converter unit. The protecting apparatus is arranged to detect an electrical event which includes at least one of an overvoltage and overcurrent appearing at each phase of the secondary winding of the AC generator/motor, to decide whether the detected electrical event meets a predetermined condition and to close, when the electrical event detected in respect to any of phases of the secondary winding is decided as meeting the predetermined condition, a switch circuit connected in the corresponding phase of the secondary winding.

Abstract: A triggering method for a thyristor switch which has at least two thyristors wired in series and a thyristor wired in antiparallel to each of these thyristors. The thyristor switch is triggered or cut off as a function of a specifiable on-off signal. At least a single triggering of a thyristor to be switched-on takes place at the earliest if a positive anode-cathode voltage is applied to it which exceeds a specifiable switch-on voltage limiting value. The method comprises generating a trigger standby signal if the on-off signal is in the switch-on condition and, with a specifiable minimum number of thyristors to be triggered wired in series, their anode-cathode voltage is greater than the specifiable switch-on voltage limiting value. At least a single triggering of each thyristor to be switched on takes place by means of a short-duration trigger pulse only during the duration of the trigger standby signal.

Abstract: A protection circuit is provided which digitally detects the presence/absence of individual forward voltages across all thyristors at a level low enough compared to the allowable voltage, judges a partial turn-off in accordance with the number of detection signals indicative of the presence/absence, and determines simultaneous firing protection of all the thyristors in accordance with the result of the judgement.

Abstract: A variable speed motor control system includes a power control circuit and a forced commutation control circuit for controlling the torque and rotational speed respectively of an induction motor. The power control circuit and the forced commutation control circuit are independently controlled by signals from a speed control circuit. An overcurrent sensor monitors the motor current and, if excessive current is detected, a speed and power monitor limits the response of the power control circuit and forced commutation control circuit to the speed command. The forced commutation control circuit and power drive circuit contain silicon-controlled rectifiers both for controlling the amount of power fed to the induction motor as well as for controlling the switching of power between combinations of motor windings.

Abstract: A fault detector apparatus for a power converter in which a plurality of GTOs, functioning at a predetermined potential, are used. The apparatus includes a first fault-detecting circuit, coupled to the gate-cathode path of one of the GTOs, for generating a first fault signal when this GTO malfunctions, a second fault-detecting circuit, coupled to the gate-cathode path of another one of the GTOs, for generating a second fault signal when this GTO malfunctions, a photocoupler for transmitting a DC-isolated optical signal corresponding to the first fault signal, and one optical fiber system for transmitting a DC-isolated output signal, corresponding to the logical sum of the optical signal transmitted by the photocoupler and the second fault signal, to external circuits set at a potential different from the potential at which the GTOs are arranged. The fault-detecting circuits are provided in the same number as the GTOs. The fault-detecting circuits are coupled by the optical signals.

Abstract: A fault current protection arrangement for a power converter circuit utilizes gate turn-off thyristors as electronic switching devices. A gate turn-off thyristor is connected between relatively positive and negative voltage buses with a circuit interruption device connected in electrical series arrangement with a cathode terminal of the thyristor. A gate driver circuit is connected for providing control signals to the gate terminal of the thyristor for controlling its on and off states during normal operation. Upon detection of the fault current condition, the gate driver circuit is inhibited and the interruption device open-circuits the cathode terminal of the thyristor to divert current in the thyristor into the gate terminal. The resulting anode-to-gate current results in rapid turn-off of the thyristor.

Abstract: An inverter controller for controlling an inverter having a plurality of electric valves each formed by connecting a switching element and a diode in anti-parallel with each other. On the basis of an output current command value, an ON/OFF signal is supplied to a switching element which needs to operate, and the supply of an ON signal to a switching element which need not operate is inhibited. Thus, it becomes unnecessary to provide dead time which has heretofore been needed.

Abstract: A circuit for detecting current flow in a triac, wherein the circuit operates with only one operating voltage with one pole of this operating voltage being connected to a current terminal of the triac and simultaneously being the voltage reference point for the triac. The triac gate voltage fluctuating around the voltage reference point is used to detect the triac current flow, the gate voltage of the triac is transformed, if necessary, into the voltage range of the operating voltage of the detector circuit, and digital information is generated as a function of the gate voltage to indicate whether a load current is flowing in the triac or not.

Abstract: A voltage converter provided for use in power electronics, particularly as an inverter for generating alternating voltages for vehicle motors. Electric energy is supplied to the converter via direct-voltage connections (2, 3). The desired alternating voltage can be tapped off at an alternating-voltage connection (1). The alternating-voltage connection (1) is connected via at least one of series connected gate turn-off thyristors (Th1, Th2) and via at least one current limiting reactor (L1), which is connected in series with the gate turn-off thyristors to respective of the positive and negative direct-voltage connection (2, 3). Each gate turn-off thyristor is provided with a turn-off relief circuit (5). In parallel with the current limiting reactor, a reactor free-wheeling diode (D1) is connected in series with a reactor free-wheeling resistor (R1) in a free-wheeling branch.

Abstract: For suppressing an abnormal rise in the anode-cathode voltage of a gate turnoff thyristor (GTO), a main snubber circuit and a number of sub snubber circuits are disposed across the anode and cathode of the GTO, and selected ones of the sub snubber circuits are selectively activated by a control circuit in accordance with the magnitude of a main current flowing through the GTO in order to minimize the power loss of the entire snubber circuit. The main snubber circuit includes a capacitor of comparatively small capacity corresponding to a comparatively small and steady main current. The control circuit includes a current detector detecting the main current. For a small steady load, only the main snubber circuit is operated, but at higher loads the control circuit selectively activates an increasing number of the sub snubber circuits.

Abstract: A device for failure detection in series-connected semiconductor rectifiers (1) comprises transformers (2) whose number is equal to that of the rectifiers (1) and which comprise input windings (3), supply windings (6), and additional parallel-connected windings (9), RC-circuits whose number is equal to that of the rectifiers (1), having resistors (4) and capacitors (5), and also a pulse generator (7), and a measuring element (8).The input winding (3) of each transformer (2) has one lead-out thereof connected to a cathode of the respective rectifier (1), and another lead-out to the capacitor (5) of the respective RC-circuit. The resistors (4) of each RC-circuit are connected to the anodes of each rectifier (1). The supply windings (6) of the transformers (2) are connected to one another in series and connected by one terminal to the first lead-out of the pulse generator (7).

Abstract: An improved priming and sweep-out circuit in which losses are obviated or minimized by transferring energy resulting from such processes back to the power supply, and wherein a single common storage inductance is used in a secondary winding circuit of a saturable-core inductor transformer, the primary of which is series-connected in the SCR-switching energy storage and discharge pulse generating circuit, to serve both in the priming and sweep-out functions, and wherein reset circuit inductance does not participate in the energy transfer or storage functions.

Abstract: For recognizing the blocked state of a thyristor which can be switched off (GTO thyristor), especially also if it is alloyed through or the driver addressing the thyristor is defective, a state signal indicating the actual advent of the blocked state is generated after the occurrence of a turn-off signal, if the derivative in time of the gate current has exceeded a positive upper limit, which indicates that the thyristor has been turned off successfully. The maxima of the derivative in time of the gate current are almost independent of the actual anode-cathode current to be extinguished. The derivitive in time of the gate current is advantageously determined via a coupling inductance. Preferably, the method and apparatus are used with a mutual adaptive turn-on interlock of GTO thyristors in converter equipment and can be urged to release protective measures in time if permanent conduction (short circuiting) of a thyristor occurs.

Abstract: In order to protect converter equipment which includes GTO switching-off thyristors and having d-c inputs and a protective inductance connected in series therewith against short circuit currents, a short circuit path for d-c current flowing from a d-c supply source on the one hand, and on the other hand, an energy storage device, is inserted into the d-c circuit, closed via an auxiliary thyristor, of the converter equipment in such a manner that through the change of the state of storage of the energy storage device, a countervoltage is impressed on the d-c terminals, which leads to the forcible commutation of the switching-off thyristors. The energy storage device advantageously comprises an auxiliary winding of a limiting choke serving as a protective inductance.

Abstract: An electrostatic precipitator is fed high voltage pulses by a pulse generating circuit including a high voltage transformer and a first thyristor switch connected in series with a primary winding of the transformer. Magnetic saturation of the core of the high voltage transformer is prevented by recurrently short circuiting the primary winding of the transformer by means of a second thyristor switch connected in parallel to the primary winding. The second thyristor switch is closed for a period of time extending from a first instant following a high voltage pulse crest to a second instant at or before the start of a pulse generating cycle subsequent to the pulse crest.

Abstract: Transistors or GTO's of an inverter are switched ON/OFF with a delay circuit which has a capacitor first charged at a forcing rate, then, held at an intermediary level, and which is first discharged at a forcing rate, then held at an intermediary level, thereby to provide underlap, minimum ON and OFF time control and noise filtering with a high precision.

Abstract: A reverse-conducting GTO thyristor comprises a gate turn-off thyristor and a diode which are formed on a single semiconductor substrate so as to have a common layer and be connected electrically in an inverse-parallel connection. A power converter is composed of a plurality of pairs of these reverse-conducting GTO thyristors connected in series, each pair of thyristors being controlled so that they are turned on and off in opposite phases. An OFF gate pulse for one of each pair of thyristors continues from a time on or after the generation of an ON gate pulse for the other thyristor to the time when a recovery current flowing through the diode portion of the first thyristor is extinguished. The thus-extended OFF gate pulse functions to prevent any displacement current flowing through the GTO portion of the first thyristor during the recovery time for the diode portion thereof.

Abstract: An apparatus for controlling a thyristor converter includes a plurality of voltage detectors provided for individual series-connected thyristors respectively for detecting the presence or absence of voltage applied to the thyristors, and elements for generating a thyristor triggering pulse signal representative of the logical sum of the voltage presence-absence signals from the voltage detectors and a triggering command signal commanding the desired triggering phase and on-period of the thyristor converter. The apparatus comprises a plurality of differentiation circuits differentiating the output signals of the plural voltage detectors respectively, and a signal synthesis circuit synthesizing the output signals of the differentiation circuits to generate an output signal indicative of the voltage presence or absence. By virtue of the above construction, the thyristor converter can continuously operate without being shut down even when any one of the thyristor voltage detection signals is disabled.

Abstract: The invention is a method and a circuit for the emergency firing of individual thyristors in a thyristor valve that have a protection circuit for providing an emergency gate control signal for firing the thyristor when the voltage applied thereto equals or exceeds a predetermined initial emergency voltage triggering level. In operation a thyristor is initially fired using the emergency gate control signal produced by the protection circuit when the voltage applied thereto equals or exceeds the emergency voltage triggering level. The emergency voltage triggering level is then reduced. The subsequent firing of the thyristor by the protection circuit occurs when the applied voltage equals or exceeds the reduced emergency voltage triggering level. This allows both economy of operating conditions and protection of the individual thyristor and its associated snubber circuit during prolonged emergency firing conditions.

Abstract: In a power converter switching system, the instantaneous blocking ability of semiconductor switching elements is determined by monitoring the reverse blocking ability of a control junction in each switching device. A gate firing circuit applies negative turn-off drive to the control junction. The control junction impedance is monitored and switch recovery is indicated by a change in the magnitude of the impedance. A switch recovery logic signal is then generated and used to initiate the firing of the next successive switch element. When switches are combined in multipulse groups, the recovery signals may be logically combined to provide proper switching coordination, emergency protection and diagnostic information.

Abstract: Each of the three phase power source voltages coupled to a three phase (3.0.) thyristor power converter are respectively half-wave rectified to provide both positive and negative voltages. Signals representing the largest positive rectified voltage and the smallest positive rectified voltage are developed as are signals representing the largest negative rectified voltage and the smallest negative rectified voltage. Using signals from both the positive and negative rectified voltages, at least one comparison is made to determine a difference which, when in excess of a predetermined limit, effects a logic signal to provide an indication that an asymmetrical fault exists either phase to neutral or phase to phase across the power converter and the power lines connecting the converter to a polyphase alternating current (AC) source.

Abstract: A power supply for providing a selectable predetermined regulated output voltage. A switching regulator circuit provides the conversion of an input voltage to a DC output voltage and a control circuit, which senses the output voltage, controls the conversion of the switching regulator circuit. In the present invention, an amplifier, having selectable gain values, is interposed in the feedback loop, i.e., between the output terminal of the power supply and the control circuit. Thus a predetermined portion of the output voltage is fed back to the control circuit, thereby selectively determining the output voltage without necessitating changes to the switching regulator circuit or the control circuit.

Abstract: An equalizer circuit for switches connected in series between a voltage source (21) and a load (16), each switch (4, 11) being connected in parallel with a respective equalizing capacitor (2, 9) via a respective diode (7, 8). The circuit further includes a transformer (20) having a plurality of windings (6, 13) connected in series with respective diodes (5, 12), with each switch having a respective winding-diode series connection connected in parallel therewith. In this manner, electrical energy initially stored in the capacitors is transferred to be stored in magnetic form by the windings when the switches are closed and is re-used when the switches are opened to accelerate charging of the less charged capacitors until all the capacitors reach the voltage of the most charged capacitor.

Abstract: A device comprising a series circuit consisting of a plurality of thyristors connected in series, and a reverse-blocking semiconductor element such as a diode connected in an antiparallel relationship to the series circuit. The device further includes means for detecting whether a sufficient turn-off time is secured for each of the thyristors anterior or posterior to a reference moment at the zero point of a current flowing in the diode, and means for turning on the entirety of the thyristors when the sufficient turn-off time is not secured. Since none of the thyristors is turned off in the state where the turn-off time is insufficient, it becomes possible with certainty to achieve exact prevention of a fault that one or more thyristors, turned off earlier than others are led to breakdown by an overvoltage.

Abstract: A thyristor apparatus employing light-triggered thyristors comprises forward voltage detecting circuits (15) and a thyristor number detecting circuit (17). The forward voltage detecting circuits (15) detect forward voltages applied to light-triggered thyristors (13) to provide detected signals. The thyristor number detecting circuit (17) is responsive to the detected signals to cause light-triggered thyristors in a thyristor arm (U) to be turned on simultaneously in the case where the number of the light-triggered thyristors being supplied with forward voltages is one or more but not more than a predetermined number. Accordingly, if and when an overvoltage is applied to the thyristor arm (U), overvoltage suppressing elements (14) are prevented from being damaged even if partial commutation failure occurs in the light-triggered thyristors.

Abstract: An overcurrent detector for an inverter is provided, which detector includes a filter capacitor and snubber circuits, and comprises: a first circuit which detects a current flowing through the DC main circuit of the inverter and provides a first signal in proportion to the magnitude of this current; a second circuit which generates a second signal corresponding to the magnitude of snubber currents flowing through said snubber circuits; and a third circuit which generates a third signal corresponding to the difference between the first signal and the second signal. The third signal is an output signal of the overcurrent detector, a protection circuit of the inverter being made operative by this third signal.

Abstract: A thyristor converter control system comprising a voltage detector for detecting the thyristor voltage and a detector output suppressing circuit provided at the output of the voltage detector. The detector output suppressing circuit operates to detect an erroneous output of the voltage detector that it provides a voltage-presence signal while it must provide a voltage-absence signal, and cuts off the output of the voltage detector upon detecting the erroneous output from the voltage detector.

Abstract: The DC to AC power inverter is of the class B, C, D or E type and includes a battery, at least one power SCR and associated capacitor circuitry, at least one input winding on a main transformer core and at least one output secondary winding on the transformer core. Such inverter requires a quiescent current to establish operating current for capacitor commutation charge and includes a feedback loading circuit for feeding current generated by the quiescent current back to the battery. The inverter also includes a self-detecting load demand circuit coupled to a line from said output winding for cyclically energizing the inverter, for sensing a minimum AC load and for holding said inverter in an energized state until less than a minimum AC load is sensed during an energizing cycle.

Abstract: A system, for use with a controlled current inverter to prevent malfunction of inverter action resulting from an insufficient capacitor voltage to effect commutation of an inverter bridge controlled rectifier, provides that the capacitor voltage is sensed and, if it is of insufficient value to effect rectifier commutation, the application of gating signals to the next to be rendered conductive controlled rectifier is inhibited. In order to achieve initial inverter operation, the inverter current is also sensed and the inhibit function is rendered ineffective until such time as the current reaches a predetermined value.

Abstract: A snubber circuit coupled across each thyristor to be gated in a chain of thyristors determines the critical output of a NOR LATCH whenever one snubber circuit could not be charged and discharged under normal gating conditions because of a short failure.

Abstract: The current in each phase of a multiple phase chopper is sensed and compared to a reference overcurrent value. Any chopper phase reaching overcurrent and any chopper phase on for a longer period of time are turned off immediately. The conduction periods of chopper phases that have been on for a shorter period of time than the overcurrent phase are similarly shortened to maintain balanced phase conduction and minimize the ripple content of the source current. The phase relationship among the various chopper phases is adjusted in response to an overcurrent turn-off to allow the commutation network associated with such phase to be adequately charged before the generation of a current turn-on for another phase.

Abstract: A power converter which converts alternating current (AC) utility power or direct current (DC) power to any DC output voltage by use of at least one switch and a resonant circuit resulting in power conversion by means of sinusoidal waveshapes. The resonant circuit defines the frequency of operation of the commutation circuit such that the frequency changes only a moderate amount with loads ranging anywhere from an open circuit to a short circuit, thereby providing reliable commutation and circuit operation under all load conditions.

Abstract: A vehicle propulsion motor control apparatus includes a motor current regulating chopper apparatus and a free wheeling diode in the motor circuit. It is desired that the chopper apparatus not be commutated OFF when the free wheeling diode is conducting motor current to prevent damage to the free wheeling diode. A current detector is provided to prevent commutation of the chopper apparatus in response to sensing a current flow through the free wheeling diode.

Abstract: In a thyristor valve having a plurality of series-connected thyristors, each thyristor has an individual recovery protection device arranged in its entirety at the potential of the thyristor. For each thyristor, the protection device comprises a voltage-sensing member whch indicates the point of time when the thyristor takes up reverse blocking voltage. A time-determining member defines a certain time interval, counting from said point of time. Control members are arranged to deliver a control pulse for firing the thyristor if the off-state voltage of the thyristor during the time interval exceeds a predetermined value.

Abstract: A multiple phase SCR chopper controller for establishing a normal phase relationship among the various SCR phases and for modifying the normal phase relationship for input signals for which the SCR commutation networks cannot be sufficiently charged. These input signals correspond to conduction period overlap, and the modified phase relationship avoids chopper commutation failure under such conditions.

Abstract: An overcurrent protection system adaptable for use with power controllers the single or multi-phase ac, or dc types includes a load current sensing element in combination with an overcurrent sensing/inverse time delay circuit, a power switch and a crowbar circuit. The system also includes a drive circuit, a drive circuit input current sensor, a trip signal detector and a logic circuit. The overcurrent protection system, according to the present invention, uses the drive circuit to power the overcurrent sensing/inverse time delay circuit, to drive the power switch, and to provide a coupling path for an overcurrent fault signal across electrical isolation interface(s) thereof to the logic circuit. Thus, the need for a separate isolated power supply for powering the overcurrent sensing/inverse time delay circuit and the need for separate optical and/or electromagnetic isolation interfaces for coupling of the overcurrent fault signal are eliminated.

Abstract: Disclosed is a DC motor drive circuit adapted to prevent thyristor commutation failure when a thyristor-controlled three-phase full-wave reversible bridge undergoes a transition in operating mode from a power inversion mode to a power rectification mode.

Abstract: A fault detector for detecting shoot-through conditions in series connected solid state rectifiers (326, 329) of a power inverter (314) is disclosed. A capacitor (311) discharges when a shoot-through occurs and the discharge current is detected by a current transformer (315). An SCR (317) is gated on by the detector to short circuit the DC bus (327, 328) and prevent damage to the solid state rectifiers (326, 329).

Abstract: The secondary voltage of a wound-rotor induction motor is rectified by a multi-phase full-wave rectifier circuit of Gratz connection. An inverter connected to the full-wave rectifier circuit through a DC intermediate circuit regulates the amount of AC voltage fed back to the AC power source thereby controlling the speed of the induction motor. A smoothing reactor is disposed in one of the DC buses of the DC intermediate circuit, with its inverter-side terminal being connected to at least two of the AC-side terminal of the full-wave rectifier circuit through series circuits of a resistor and thyristors. A DC gate signal is applied to the thyristors in the series circuits upon detection of interruption of AC power supply, and application of the DC gate signal is ceased in a predetermined period of time after recovery of the AC power supply voltage. The system of simple structure can thus prevent commutation failure of the inverter even when the supply of the AC power supply voltage is interrupted momentarily.

Abstract: An overcurrent protection circuit of an inverter supplied with power through a switching regulator which has the basic features of the circuit constructed in such a manner that, when the input current of the inverter exceeds a set point, the circuit forcefully energizes conduction circuits of two systems including PUT or UJT through a pulse generation circuit (turn-on circuit) connected to the switching regulator and instantaneously shuts off the overcurrent of the inverter and a driving signal of the switching regulator.

Abstract: A circuit for commutating a thyristor (21) by shunting its current for a minimum interval, thereby removing sustaining voltage to said thyristor, then subsequently restoring voltage to said thyristor at a predetermined rate, utilizes a series combination of a commutation electronic switch (22) and an isolated dc voltage supply (23) connected in parallel with the thyristor. The voltage supply is arranged with a polarity that permits the current flowing through the thyristor in one direction to be bypassed through the series combination while the commutation switch is turned on and to reverse bias the thyristor when the commutation switch is fully on. A dv/dt control circuit (24) limits the rate of rise of voltage across the commutation switch (22) as it is turned off in response to a command input signal.

Abstract: A method and apparatus for controlling a resonant power module comprising a resonant power circuit which is coupled to a load. First and second switching elements are coupled to the resonant circuit for alternately supplying a flow of current. Trigger generator means are provided for supplying trigger signals to alternately enable the first and second switching elements. A control means is coupled to the trigger generator for operating the power module in a first mode in which the resonant circuit current is controlled by varying the repetition rate of the trigger signals. The control means operates the power module in a second mode by maintaining the trigger signal repetition rate at a fixed limit and controlling the resonant circuit current by varying the on/off duty cycle of the power module.

Abstract: A frequency inverter using thyristor(s), wherein a gate circuit produces both positive triggering signals and negative reverse-bias signals by utilizing outputs of the timer in order not to fail turnings of the thyristor, and the timing of both signals are automatically controlled to by synchronized with oscillation of the resonance circuit connected to the anode and the cathode of the thyristor, so as to respond to a change of load condition, so that always suitable triggering signals and reverse-bias signals are applied to the gate of the thyristor.

Abstract: A snubber circuit is connected between the anode and cathode of a gate turn-off (GTO) thyristor. To the GTO thyristor a saturable reactor is connected in series. A gate off signal is supplied to the gate of the GTO thyristor and to the saturable reactor as backward current to reset the saturable reactor.

Abstract: A power converter having improved efficiency and useful, for example, in the propulsion system of an electric vehicle. The power converter includes a dual chopper having an output level variable over a rather wide range for controlling the speed of the vehicle from stop to cruising. A commutating inverter is transformer coupled to the chopper for commutating thyristors in the chopper. Efficiency is considerably enhanced by programming the amount of energy in the commutating inverter in accordance with the power being delivered by the chopper so as to minimize power losses and thereby increase the range of the vehicle.

Abstract: A thyristor overvoltage protection circuit wherein an avalanche diode conducts to divert overvoltage energy from a thyristor to avoid self-ignition of the thyristor when the overvoltage reaches a particular level. A simulator circuit monitors the thermal loading on the conducting diode and activates an ignition pulse device if the thermal loading exceeds the safe operational range of the diode. The activated ignition pulse device ignites the thyristor so that the thyristor may divert the overvoltage energy and thereby discharge the diode.