Abstract: A high voltage converter system including a high voltage power line at a first voltage level, a step-down device connected to a second voltage level lower than the first voltage level, and a high voltage switch module including a plurality of voltage limited controllable switch elements including components to limit the voltage across each the voltage limiting controllable switch element to a predetermined voltage when each the voltage limiting controllable switch element is in an open state and to a zero voltage when each the voltage limiting controllable switch element is in a closed state. The voltage limiting controllable switch elements are typically connected in series between the power line and the step-down device. The high voltage down-converter system also includes a control system to selectively set the open state and the closed state of each the voltage limiting controllable switch elements to control the current through the step-down device.

Abstract: An apparatus to sense an SCR short circuit failure and prevent overheating of solid-state power supply equipment, such as a welder, during an occurrence of the short circuit failure is provided. The apparatus includes a detector circuit capable of sensing a short circuit of an SCR in the power supply equipment. The detector circuit senses each voltage of a poly-phase input and generates a fault signal upon substantially simultaneous detection of a zero-cross voltage condition for each phase of the poly-phase input. A control circuit is configured to receive the fault signal of the detector circuit and generate an output to prevent fault current flow through to power supply equipment.

Abstract: A method and system for compensating for line imbalances in line commutated converters. The controller includes a phase-locked loop (PLL) synchronizing tool which receives the line to line voltage signals and generates firing angle and frequency signals used for synchronizing the two input signals. The PLL controller, in addition to the firing angle and frequency signals, also generates signals representative of filtered values of amplitudes for each of the line to line voltage signals. A voltage imbalance compensation processor associated with the bridge firing controller receives the filtered amplitude signals and also a signal representative of the firing sector of the bridge. The voltage imbalance compensation processor generates, based upon the sector signal and the received filtered amplitude signals a amplitude signal used by a current regulator which is compensated for line imbalances present in the line voltage.

Abstract: The present invention provides for an apparatus and corresponding method for controlling inrush current in an AC-DC power converter by controlling the state of a plurality of silicon-controlled rectifiers (SCRs) when AC power is lost. The present invention provides full control of inrush current even during cold startup, warm startup, and power line disturbance conditions. The present invention controls inrush current without the need for an extra series dissapative device and its consequent additional losses. The preferred embodiment includes use of the present invention for AC-DC converters having active power factor correction. An alternative embodiment is for use in non-power factor corrected applications.

Abstract: In a power conversion device according to the present invention, an AC power source voltage signal Vac which is the instantaneous value of AC power source 1 detected by a power source voltage detection circuit comprising a transformer 5, rectifier 6 and A/D converter 7 is averaged by an averaging circuit 9 and an average AC power source voltage signal Vave is output. This average AC power source voltage signal Vave and AC power source voltage signal Vac are compared in comparator 8 and, if their deviation is more than a prescribed value, a power source voltage drop detection signal PSF_S is output. Spurious detection of power source voltage drop resulting from the effect of power source fluctuations can thereby be prevented.

Abstract: A method and system for determining zero current level occurrences in a reversible power converter without requiring additional component complexity and costs. A digital controller selectively determines the line to line voltage for the most recently fired thyristor pair. The selected line to line voltage is identified as the bridge reconstruction voltage and is compared against the actual bridge output voltage for the conducting bridge. The difference between the two voltage signals is identified as the bridge error voltage and the sign of its magnitude is indicative of a load current zero level occurrence. A zero current level occurrence happens whenever the bridge error voltage drops below zero. This indication is positive and substantially instantaneous and safely enables the reversal of power flow without the risk of line faults due to cross-bridge short circuits.

Abstract: A converter of a high A.C. voltage into a low D.C. voltage, including a one-way switch between a first terminal of application of the A.C. voltage and a first positive output terminal, and circuitry for controlling the output voltage to a desired value, the one-way switch being controlled in linear mode.

Abstract: The present invention is a fault tolerant apparatus for regulating the flow of electricity. The apparatus comprises a light radiating circuit which includes a first light source for radiating a first light signal, a second light source for radiating a second light signal and a first light sensor for receiving at least one of the first and second light signals and for generating a first light sensor output signal in response to the first and second light signals. The radiating circuit further includes a control circuit for actuating the first light source to radiate the first light signal when the control circuit receives a control input signal and for actuating the second light source to radiate the second light signal when the control circuit fails to receive the first light sensor output signal from the first light sensor within a predetermined time after the control circuit has received the control input signal.

Abstract: A plant for transmission of high voltage direct current is coupled to an alternating current network (3) with a fundamental frequency (.function.), and has a control equipment (CEQ) and a direct current link (5). A device (76) for damping an oscillation in a current (ID) in the direct current link at a frequency equal to the fundamental frequency has means (81) for generating reference signals (SSIN, SCOS ) oscillating with an influenceable reference frequency (.function..sub.R), and means (821, 822,-831, 832, 84, 85, 86) for forming an actuating signal (SAS), oscillating with the reference frequency (.function..sub.R), and with a phase position equal to the sum of an adjustable phase angle displacement (.sigma.) and of a phase position (.phi.) of the oscillation in the current in the direct current link in relation to a voltage (UC) of the alternating current network. The device further has means (107) for forming a control signal (.alpha.

Abstract: A method and apparatus for protecting a high-performance power converter. The high-performance power converter comprises a mains power converter, which converts an alternating voltage from a mains power supply into a direct voltage and supplies the direct voltage to an intermediate direct voltage circuit. The intermediate direct voltage circuit is equipped with an intermediate circuit capacitor, and includes a second power converter which converts the direct voltage from the intermediate direct voltage circuit into an alternating voltage, whereby each of the mains power converter and the second power converter is set up as a bridge circuit and each contains a number of IGBTs (Insulated Gate Bipolar Transistors) arranged in pairs in bridge arms.

Abstract: A device for supervising different positions of a valve of a high voltage converter station located on a high voltage potential level comprises members arranged on a high voltage potential level and adapted to detect function parameters of the valve on a high voltage potential level and send values detected thereby to first control units for controlling the semiconductor components of the valve. The first control units have devices for processing the detected values and the first control units are adapted to utilize light conductors running back therefrom to a valve control unit for sending data resulting from the processing to an arrangement for supervising the valve located on a low potential level.

Abstract: An integrated power factor converter utilizes a silicon controlled rectifier (SCR) bridge which limits the inrush current by controlling the conduction angle of the SCR's. The same SCR bridge shuts down the output in case of short circuit and recovers automatically at a predetermined duty cycle rate. In case the input voltage exceeds approximately 275 VAC, the SCR bridge regulates the output voltage to below 400 VDC. The input inrush current is reduced by phasing up the input voltage in a controlled manner. The use of SCR's in the input bridge produces no additional losses, since the rectifier function is required regardless of which topology is used. The integrated power factor converter interfaces universal voltage mains to DC/DC converters while reducing input harmonics.

Abstract: An active power line compensation circuit for providing a power distribution network with a series compensation system that utilizes a transformer-coupled three-phase voltage-source inverter. A solid-state thyristor shorting ("crowbar") switch is provided on a third winding of a coupling series transformer. The transformer couples the ac output of a three-phase voltage-source inverter (VSI) to the power distribution network. The crowbar switch circuitry utilizes three diode-thyristor pairs, where each pair is connected to one phase leg of the VSI. The thyristors of the crowbar switch are each controlled by an fault output signal from an overcurrent or overvoltage sensor, that is coupled to a tertiary winding of the transformer. The fault signal closes the thyristors and thereby shunts overcurrent that would otherwise flow through the VSI. When the fault signal ceases, the thyristors automatically switch open when a null current is present in the normal three-phase line current.

Abstract: A power supply includes a diode bridge rectifier. The diode bridge rectifier output provides direct current to a primary capacitor. A current-limiting resistor is connected in series with the rectifier output and the primary capacitor. The current-limiting resistor acts to limit inrush current to the primary capacitor when the power supply is turned on. A triac is coupled in parallel with the current-limiting resistor. When charged, the primary capacitor provides a primary signal and primary current to a switched load, which includes a first winding of a transformer and a load switching device. The transformer also has a second winding connected in series with the triac's gate terminal. When the primary signal reaches a satisfactory level, the load switching device switches the load, causing current transients in the first winding. The first winding current transients, in turn, induce current in the second winding and in the triac gate terminal.

Abstract: A plant for transmitting electric power between a direct voltage network and an alternating voltage network through a power station. A converter of a station has two current valves connected in series, each having one turn-on and turn-off type breaker and a diode connected anti-parallel therewith. Circuits are provided to detect the direction and the intensity of the current through the converter, as well as the current valve through which it flows to actuate the control apparatus on the basis of the detected current level and the identity of the valve carrying the current. The control apparatus operates to commutate current through the valve which is not carrying current when a detected current level in the current carrying valve exceeds a first predetermined level.

Abstract: A three-level NPC converter includes at least one phase leg including four series coupled electrical switches having a first pair junction between the first two switches and a second pair junction between the second two switches. First and second inner switch snubber capacitors are coupled in series at a neutral junction. First and second inner switch snubber diodes are respectively coupled to the first and second pair junctions and respectively coupled at first and second inner diode-capacitor junctions to the first and second inner switch snubber capacitors. First and second inner switch snubber resistors are respectively coupled between the first and second inner diode-capacitor junctions and respective portions of a DC bus. In one embodiment, the NPC converter further includes first and second outer switch snubber diodes coupled between respective first and second inner diode-capacitor junctions and respective portions of the DC bus.

Abstract: A parallel array of a plurality of controlled rectifier bridges for converting multi-phase AC current to DC. Each bridge includes a plurality of rectifier segments. One segment for each polarity of each phase of current. A sensor monitors the current and temperature at each rectifier. The sensor outputs for corresponding segments among the bridges are compared and the timing of the conduction of the rectifiers are controlled to maintain the current and temperatures among the corresponding segments in balance.

Abstract: A power converter comprises a pulse generator capable of outputting two different levels of gate power. A thyristor (LTT) is turned on by the first gate power output from the pulse generator, and the second gate power is supplied to the thyristor (LTT) during the transient period from the time the thyristor valve current is cut off to the time the withstand voltage of the thyristor (LTT) recovers to the rated value. The second gate power is set at a low level by which the thyristor (LTT) will not be turned on when the second gate power with the normal level of voltage is applied to the thyristor.

Abstract: A two-wire power supply switch connected in series with a load between two poles of an alternating current mains electrical power supply conventionally includes a main triac between two terminals of the switch which is turned on by the conduction of an optotriac with a time-delay relative to the zero crossing of the voltage between the switch terminals determined by the breakdown voltage of a series of Zener diodes. The switch includes a power supply unit with a rectifier bridge connected to one terminal directly and connected to the other terminal via a capacitor. An auxiliary triac shunting the capacitor is turned on by the optotriac on each zero crossing of the voltage between the switch terminals. This optimizes conditions when the switch is open and when the switch is closed separately.

Abstract: A power converter protective apparatus for protecting an AC-DC converter against an excess fault current by preventing the fault current of a power system from flowing into the AC-DC converter. The protective apparatus comprises a series transformer, whose primary winding is connected in series with a power system and whose secondary winding is connected to a voltage-type AC-DC converter, first current bypass means of a normally open-type connected in parallel with the primary winding, a current transformer for detecting a fault current in the power system, and a control unit for outputting a bypass control signal to the first current bypass means when the current transformer detects the fault current, whereby when the fault in the power system is detected, a fault current flowing through the primary winding is bypassed by the first current bypass means.

Abstract: A common turn-off circuit for a thyristor power converter is specified. The common turn-off circuit is particularly suitable for AC converters such as, for example, railway grid couplings. The turn-off thyristors are directly connected to the secondary transformer windings. Additionally provided is a special freewheeling path via which the energy stored, in particular, in the transformer inductors or other relevant inductors can be drawn away. What is advantageous is the fact that all of the thyristors of the power converter can be turned off reliably and without any special precautions, since the common turn-off circuit is automatically ready for turning off. Overvoltages are avoided, moreover, by the special freewheeling path.

Abstract: A semiconductor switching circuit using semiconductor devices includes steep front wave thyristors which are connected in parallel and inverse with each other in their forward directions. An inductor is connected in series between a power source and the semiconductor switching circuit. The semiconductor switching circuit has an instant disconnection time of 100 to 1000 microseconds.

Abstract: A converter circuit arrangement is specified in which actively controllable current and voltage rise limiting means are provided in parallel with a semiconductor switch. These means also take over the function of a reverse-connected parallel diode and essentially comprise a bipolar transistor which is driven by a control circuit.

Abstract: A control and protection system for an AC-DC conversion system for exchanging an electric power between two AC power systems. The AC-DC conversion system is composed of two power converters and two circuit breakers connected to the two AC power systems. Each of the power converters is composed of a plurality of switching devices controlled by a gate signal and converts AC power into DC power or DC power into AC power. The control and protection system is composed of two control and protection units. Each of the control and protection units includes a protection unit for detecting a fault of the power converter to generate a first protection order signal when the fault is detected, and a phase control unit for continuously generating firing pulses to the switching devices of the power converter.

Abstract: The invention relates to a method for supervising the functioning of a plurality of valve units, a system for performing the method, a control unit and a control assembly for cooperation with the control unit. Each valve unit in the system comprises a semiconductor element (THY1-THYN) and a control unit for controlling the semiconductor element. The control unit comprises a trigger order input for receiving a trigger order (FP), an indication output for emitting a first indication signal (TP) and a trigger signal output (100) for emitting a trigger signal to the semiconductor element. The method comprises the steps: detecting a positive forward voltage (U.sub.T) across the semiconductor valve, generating a first indication signal (IP) when the forward voltage (U.sub.T) exceeds a first threshold value (U.sub.1), generating a trigger signal upon detected receival of the triggering order signal (FP), and the step: generating a second indication signal (SSTP) when the forward voltage (U.sub.

Abstract: An uninterruptible power supply, with passing neutral, comprises a twin step-up chopper whose input is connected to a battery and to a rectifier circuit connected to the mains power system. The twin step-up chopper comprises a positive step-up chopper supplying a first output voltage between a positive DC output and neutral, and a negative step-up chopper supplying a second output voltage between a negative DC output and neutral. The control circuit of the twin step-up chopper comprises means for regulating imbalance between the output voltages of the positive and negative step-up choppers, suitable both for operation on the mains power system and for operation on the battery.

Abstract: Apparatus and related method for deriving, from voltage across a power switch, power for a gate drive which opens and closes the power switch in response to a control signal includes a first voltage converter connected in parallel with the power switch and a series combination also connected in parallel with the power switch. The first voltage converter converts a high input voltage which appears across the power switch when the power switch is open to a low output voltage. The series combination includes a second voltage converter for receiving the low output voltage from the first voltage converter, converting it, and providing the converted voltage to the gate drive. The series combination also includes a high-voltage switch, connected in series with the second voltage converter, for opening and closing when the power switch is opened and closed by the gate drive in response to the control signal.

Abstract: A "figure 8" shaped saturable reactor including a central leg, two lateral legs, an upper bar connecting the upper ends of each leg, a lower bar connecting the lower ends of each leg, and a coil wrapped around the central leg, the cross-sectional area of the central leg at its narrowest point being less than the cross-sectional areas of the two lateral legs combined so that the central leg saturates prior to the lateral legs saturating.

Abstract: A current source gate drive circuit for simultaneous firing of a set of series or parallel thyristors is described. The circuit includes two current loops, each of which serves as a current transformer primary. Electrically insulating tubes enclose the current loops. Current transformer cores, around which are wound a certain number of secondary turns, surround the current loops, thus magnetically coupling the primary current of the current transformer to the secondary turns. Thyristor gate driver circuits are electrically coupled to the current transformer cores. Each of the thyristor gate driver circuits receives and rectifies ac current signals from the current loops and forms a current pulse train firing signal. Each thyristor gate driver circuit has a corresponding thyristor that is fired by the current pulse train firing signal. The thyristors operate at a high voltage, but are electrically isolated from the current loops by the insulating tubes.

Abstract: A control circuit for an H-bridge circuit comprises a single capacitor, a charge/discharge circuit for charging/discharging the capacitor in response to a control command signal, a voltage detector circuit for detecting a voltage appearing across the capacitor and a hold circuit for holding the control command signal in response to of a predetermined voltage detected by the voltage detection circuit. Charge and discharge of the capacitor is controlled in dependence on changes in the control command signal to thereby prevent occurrence of a through-current flow in the H-bridge circuit while allowing the bridge circuit to be changed over to the operation state indicated by the control command signal after lapse of charge/discharge period. The control circuit for the H-bridge circuit can be implemented in a miniaturized size with high reliability of operation while decreasing the number of elements attached externally even in the case where the control circuit is implemented in the form of an integrated circuit.

Abstract: An object of the present invention is to provide a thyristor valve arrester capable of measuring leakage currents of arrester elements in a simple construction and a DC power transmission thyristor valve having it used therein.A multiple of laminated arrester sets are arranged in parallel with a multiple of thyristor valves. Each arrester set is made of a plurality of arrester units arranged in parallel. Each adjoining arrester sets has through an insulator an inter-stage connecting conductor therebetween at a position corresponding to the respective thyristor valve terminals. An end of each arrester set and the respective inter-stage connecting conductors have a leakage current ammeter and a surge counter connected therebetween in electrical parallel. Each inter-stage connecting conductor and the respective thyristor valve stage are connected together by a thyristor valve connecting conductor.

Abstract: An improved temperature control system for a power conversion circuit having two or more power converters operating in parallel and providing output power to a single load. The temperature control system maintains the temperature of each of these power converters at approximately the average temperature of the power converters. A detector coupled to each power converter detects the temperature of the power converter and generates a measurement signal that is a function thereof. A reference signal is generated that is a function of each measurement signal. A control circuit responsive to the measurement signal of each power converter adjusts the output power of that respective converter as a function of the difference between that converter's measurement signal and the reference signal such that the temperature of each power converter approximates the average of temperature of the power converters.

Abstract: A protection system for a thyristor valve composed of a plurality of thyristors connected in series. The protection system includes a forward voltage detection circuit for generating a forward voltage signal, a first reverse voltage detection circuit for detecting that a reverse voltage in excess of a first reverse voltage level is applied to the thyristor to generate a first reverse voltage signal, and a second reverse voltage detection circuit for detecting that a reverse voltage in excess of a second reverse voltage level larger than the first reverse voltage level is applied to the thyristor to generate a second reverse voltage signal.

Abstract: A high-power modulator includes a plurality of means for limiting voltage and a plurality of controllable switches. Each of the switches is connected in parallel with a different one of the voltage limiting means to form a plurality of parallel pairs. Each of the parallel pairs is connected to each other in a series combination. A first parallel pair in the series combination can be connected to a main power source, and a last parallel pair in the series combination can be connected to a load. Each of the switches is switchable from an off or open position to an on or closed position.

Abstract: A method and a device for recognizing defects in a triggering system of a controlled series compensator. An intervention is made in the closed-loop control of the controlled series compensator on the basis of an impedance differential (.DELTA.Z) determined from a setpoint impedance (Z.sub.S1, Z.sub.S2) and from an effective impedance (Z.sub.i) calculated from system variables (i.sub.L,u.sub.C), and in dependence upon the voltage level of a measured conduction current (i.sub.L). When the conduction currents (i.sub.L) are smaller than a limiting value (i.sub.LG), the firing is blocked in the branches, and when the conduction currents (i.sub.L) are greater than a limiting value (i.sub.LG), a firing-angle signal (S.sub..alpha.S) is generated, through which means the valve (Th1, Th2) can be protectively fired. Thus, one is able to recognize defects in the triggering system of the controlled series compensator by applying system variables (i.sub.L,u.sub.

Abstract: The power conversion system of this invention comprises line-commutated power converting means in which a line-commutated power conversion circuit that performs line-commutated commutation and a coupling diode are coupled to form a DC circuit and for converting DC power into AC power or AC power into DC power. Further, the system comprises self-commutated power converting means, in which a self-commutated power conversion circuit is coupled to the coupling diode in order to form a DC circuit and for reducing reactive power, or the reactive power and harmonics generated by the line-commutated converting means. Accordingly, their respective strengths can be made use of and their mutual weaknesses can complement each other.

Abstract: A fault current surge bypassing and transitional impedance compensation system for preventing subsynchronous currents on electrical power lines, with parallel lines being protected from the clearing of transient faults. Capacitor banks serve as only a partial solution to the disturbances with transient faults during conventional recovery modes of operation. The fault current bypassing and impedance compensation system, coupled in series to each transmission line, clears a transmission line fault current and dynamically balances the inductor impedance on the transmission line after the fault mode clears when a return is made to the normal mode of operation. A circuit based solid-state switching power converter or "voltage-sourced inverter" with self-commutating GTO semiconductor switches is used, having all GTOs switched-on and maintained in this condition for the fault current to pass.

Abstract: These and other objects are achieved by an improved active power line conditioner in accordance with the invention. The active power line conditioner includes series inverter coupled to an energy input source, and a parallel inverter coupled to a non-linear load. The non-linear load is powered by a load current which includes fundamental components and harmonic components. An energy storage element is electrically connected between the series inverter and the parallel inverter. A fault condition shorting circuit is supplied in accordance with the invention. The fault condition shorting circuit is coupled to a secondary transformer winding within the series inverter. The fault condition shorting circuit includes a diode bridge which conveys diode bridge current only in the presence of an overvoltage or overcurrent condition. A threshold device is connected to the diode bridge and conducts threshold device current in response to the diode bridge current.

Abstract: A bidirectional protection component comprises two reverse connected thyristors, each of which is in anti-parallel with a diode, the gates of the two thyristors being interconnected and floating. This component, which can be monolithic comprises two vertical thyristors having the same orientation and two vertical diodes having the same orientation, opposite that of the thyristors. Semiconductor regions (P3, N2, P1) constituting the thyristors are common except for their cathode regions (N11, N12). The component comprises three metallizations: a rear surface metallization (M1) connecting the common anodes of the thyristors with the cathodes of the diodes, a first front surface metallization (A1) connecting the cathode (N11) of a thyristor to the anode (P21) of a diode, and a second front surface metallization (A2) connecting the cathode (N12) of the other thyristor to the anode (P22) of the other diode.

Abstract: A semiconductor power conversion system comprising a multiphase bridge circuit which includes semiconductor devices having a controllable firing function and a reverse blocking characteristic, a gate control circuit which gives firing commands to the semiconductor devices, a short circuiting switch in which switching devices having a controllable firing function and a reverse blocking characteristic are connected in parallel with a DC output side of the multiphase bridge circuit, and a protection control device for performing a control for protecting the multiphase bridge circuit.

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: A method and circuit for detecting rapid increase in line voltages applied to variable speed drives utilizing a phase controlled converter. A three phase alternating current line voltage is applied to a full wave bridge rectifier to generate a direct current signal. A buffer amplifier having a high input impedance is coupled to the output of the rectifier and a diode is utilized to ensure that only positive voltage transients are detected. Positive voltage transients output through the buffer amplifier rapidly charge a capacitor through the low output impedance of the buffer amplifier and that charge is permitted to bleed off slowly through an associated resistor. The rate of change of the capacitor charge level is compared to a preset voltage level and increases beyond that preset level are utilized to trigger an inhibit signal which momentarily resets the delay angle of the switching devices within the phase controlled converter.

Abstract: A power converting apparatus comprises self-commutated converter, fault current restricting device, fault detector, and cutoff circuit. Self-commutated converter converts AC power supplied from an AC power system into DC power and supplying the DC power to a common DC circuit, and for converting DC power supplied from the DC circuit into AC power and supplying the AC power to the AC power system. The fault current restricting device is inserted between the self-commutated converted and the DC circuit, and includes a diode provided to permit a DC circuit current to flow from the self-commutated coverter to the DC circuit, and a series circuit having a reactor and a DC power supply and connected in parallel to the diode. The fault detector detects a fault current generated when self-commutated converter is short-circuited. When the fault detector detects a short circuit occurring in self-commutated converter, the cutoff circuit cuts off power supply to that self-commutated converter.

Abstract: In a control apparatus for controlling the firing timing of each of thyristor valves constituting a thryistor bridge by use of at least two series of control systems, a bypass-pair control circuit for thyristor bridge includes a circuit for detecting the conduction states of the thyristor valves, and a circuit for determining a conductive valve at the time of bypass-pair operation in accordance with a result of detection of the conduction state of each thyristor valve.

Abstract: A method and apparatus for protecting thyristors in a power converter from overvoltages. Voltage detectors determine if the forward voltage of each thyristor has increased in the converter. If such an overvoltage occurs during a predetermined period after the conduction of the thyristor, forced triggering of all the thyristors prevent damage to the thyristors.

Abstract: There is disclosed a method for detecting thyristor conduction using voltage sensing means (400) rather than prior art current sensing means (112). Circuitry for protecting back-to-back thyristor bridges (300) is also disclosed having two levels of protection. One level comprises circuitry (540) for detecting firing commands to the bridges. When such commands to one bridge are detected, the circuitry is operative to prevent the transmission of firing commands to the other bridge. The other level of protection comprises circuitry (400) for detecting conduction by any thyristor in the bridges (300). When conduction by a thyristor in one bridge is detected, the bridge conduction detection circuitry is operative to prevent the transmission of firing commands to the other bridge.

Abstract: An improved electric power conversion system comprising a multi-phase bridge circuit composed of semiconductors such as thyristors and an associated firing circuit. It is so constructed that: if the AC input current Iac flowing in the bridge circuit is equal to or larger in value that the DC output current Idc flowing out of the bridge circuit, it will be decided than an inner defect or fault is caused, and possible expansion of inner defect will be prevented by disabling the firing circuit to extinguish the thyristors in the bridge circuit, and if the AC input current Iac is smaller than the DC output current Idc in value, the bridge is permitted to continue the operation of power conversion, thus eliminating unnecessary interruption which otherwise would be caused by exterior disturbances. Also, an improved electric power conversion system may be equipped with a device to prevent an adverse effect from being caused by abnormal rise of thyristors' temperature.

Abstract: An adaptable current regulating system provides a regulated current in accordance with both the actual characteristics of a system under control and the actual measured period of an AC supply. The system constantly monitors its status, and provides a master controller with the status of the system, and is programmed to provide control in accordance with information received from the master controller.

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: A gate signal generator comprises U- and X-phase set circuits for discriminating, after the conduction period of every cycle, whether OFF time intervals of U- and X-phase thyristors are greater or smaller than a predetermined value, a reset circuit for detecting that both the U- and X-phase circuits do not provide outputs, a flip-flop set in response to an output from the U- or X-phase set circuit and reset in response to an output from the reset circuit, AND gates for calculating AND products of an output from the flip-flop and U- and X-phase forward voltage signals and for outputting the signals at a start of the forward voltage application after setting the flip-flop, and OR gates for calculating OR sums of outputs from the AND gates and outputs from the normal gate circuits. Gate signals are applied to the thyristors in response to the outputs from the OR gates.