Abstract: A traction motor drive protection circuit which provides the inverter protection capability of a conventional commutation arrangement, but which limits or eliminates fault currents that stress the internal elements of the alternator and traction machines. A series protection thyristor is connected between a commutation thyristor and the inverter circuit to block motor fault currents, and RC elements are connected in series with the commutation thyristor to limit alternator fault currents. Normal inverter gating is continued in the presence of a fault, to circulate the stored inductive energy and discharge the filter capacitor, providing a "ride-through" operation which is substantially transparent to the traction motor. The RC elements in the commutation circuit not only limit the alternator faul current, and hence the stress on the eommutation thyristor, but also commutate the commutation thyristor to provide automatic reset capability.

Abstract: A DC power supply circuit arrangement for supplying DC power from a power source through a common conductor to a load, comprises a plurality of switches connected between the power source and the common conductor and/or between the common conductor and the load, each of the switches having one terminal connected to the power or the load and the other terminal connected to the common conductor, an energy absorber having two terminals, a first diode connected between the one terminal of each of the plurality of switches and one of the two terminals of the energy absorber in a polarity so as to allow a current to flow from the one terminal of the switch to the one terminal of the energy absorber, a second diode connected between the one terminal of each of the plurality of switches and the other terminal of the energy absorber in a polarity so as to allow a current to flow from the other terminal of the energy absorber to the one terminal of the switch, and a circuit connecting the other terminal of the energy a

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 inverter circuit which converts d.c. from a d.c. source to single or multiple phase a.c.. Two semiconductor switching elements for each phase are connected in series between two poles of a d.c. source. A signal generator provides a pulse width modulated signal for operating the switching elements. Blocking elements are provided between the signal generator and the switching elements. A control circuit senses current flow at the a.c. output and selectively enables the blocking elements in accordance with the direction of the current flow to prevent short circuiting between the switching elements.

Abstract: An electrically isolated high speed optical switching arrangement for use as a computer over-voltage sensing circuit utilizing first and second optoisolator devices, the first having an input, a first signal from the output of a bus sensing circuitry which provides two complementary outputs, with the output voltage of the optoisolator controlling power-down circuitry for the computer in response to an over-voltage condition. A second control optoisolator has its output in parallel with a resistor in the base to emitter path of the first optoisolator. The complementary signal of the bus-sensing circuitry provides the input to the second optoisolator. During normal power conditions, the first optoisolator is conductive and the second is non-conductive.

Abstract: A snubber circuit for use with a power seimconductor switching device of a power converting circuit. The snubber circuit includes a snubber capacitor, coupled across the switching device for charging with current bypassing the switching device when the switching device is turned off. The snubber circuit also includes a transformer having a primary winding coupled in series with the snubber capacitor to conduct the flow of current discharged by the snubber capacitor when the switching device is turned on. The snubber circuit further includes an inductor, coupled in series with a secondary winding of the transformer, for regulating the flow of discharged current from the capacitor. The snubber circuit is coupled to return the energy discharged from the snubber capacitor to a power source to which the power converting circuit is coupled.

Abstract: An improvement of control for prevention of a short circuit between controllable elements used as switching elements in a pulse-width modulation type inverter apparatus which outputs a variable amplitude or variable frequency a.c. voltage. The pulse-width modulation type inverter apparatus is of a type wherein, a selecting means selects an output from a processing means within a period during which the result of detection by a current detector falls within a region of substantially zero level and also selects only a signal corresponding to each switching element which effectively acts on the generation of the output current, out of signals generated by a PWM signal generating means during a period other than the above-described period, thereby to output the same as a drive signal for the switching element.

Abstract: A power supply module for control electronics of a DC motor, the module comprising a power cell of the stepdown type controlled as a function of peak current, the current flowing in both directions, and the module including a bridge stage likewise capable of passing current in both directions and including a reactive element constituted by one of the windings of the DC motor. The invention is particularly suitable for space applications.

Abstract: In an electric power converter comprising at least one pair of serially-connected, alternately conducting controllable electric valves spanning a pair of d-c conductors, the conducting state of each valve is detected by comparing the actual magnitude of valve current with a predetermined low threshold level and by comparing the difference between the juncture potential of the two valves and a reference potential of one of the d-c conductors with the potential diffence between both d-c conductors. If both comparisons indicate the valve is in a conducting state and if this state is indicted concurrently for both valves, logic means is operative to indicate that a "shoot through" fault has occurred. In this abnormal event, whatever turn on and turn off signals for the two valves were extant at the time such operation of the logic means commenced will be prevented from changing while both valves are conducting.

Abstract: In a method and device, extinction blocking signals for gate-turn-off power semiconductors, particularly GTO thyristors, are formed in static converters in order to suppress unacceptable extinction attempts and to protect the power semiconductors against destruction. An extinction blocking signal is emitted when the sum of the actual load current of one phase of the converter and the product of the derivation with respect to time of the load current and the maximum storage time of one power semiconductor is greater than the maximum periodically interruptible anode current of one power semiconductor. Furthermore, an extinction blocking signal is emitted when the derivation of a branch current of the converter with respect to time exceeds a threshold value proportional to the voltage supplied to the converter and a short-circuit of the converter is therefore present.

Abstract: A method is provided for balancing a current distribution to a plurality of switching device of full-bridge inverter composed of N modules. Each of the N modules includes series connected first and second switching devices. The N modules are arranged in a row. First and second supply feeder bars for connection to a dc power source are provided along one side of the row of N modules, and first and second load feeder bars are provided on the opposite side of the row of N modules for connection to a load. Each of the N modules is selectively connected to one of the first and second load feeder bars and to one of the first and second supply feeder bars such that a current flow direction of each module is the same as the a current flow direction of one adjacent module and is opposite a current flow direction of the other adjacent module.

Abstract: An induction motor torque/flux control system the motor flux is forced down while accelerating and force up while decelerating to maintain a required flux level at all speeds. This is achieved through vector control by generating a direct current component in relation to the flux demand while imposing limits thereto corresponding to the maximum desirable resultant current vector, and by generating a quadrature current component which is held between limits defined by the sum of the squares of the two current components. The three-phase currents of the motor generated by vector control transformation are used to control a voltage-source inverter in a bang-bang fashion. The conventional bang-bang technique is improved by typing up one pole while controlling in the bang-bang mode the two other poles. To this effect the motor back emf is detected when the poles are simultaneously tied to one of the DC link terminals, and the tied-up pole is selected by the emf so detected.

Abstract: A method of operating a three-step inverter that supplies a polyphase machine whose electric output variables are formed by scanning two zero-shifted setpoint signal sets with triangular modulation signal, in a space vector representation using double modulation. A first or second interval value is formed between the maximum or minimum value of phase signal waveforms of the setpoint signal sets and an upper or lower scanning limit. The first and second interval values are added or subtracted from the phase signal waveforms of the first and second setpoint signal sets, to thereby increase the linear control range of the inverter and reduce the harmonic spectrum in the inverter output signals.

Abstract: A method for transverse-current-free operation of a push-pull circuit configuration having two output transistor arrays of complementary types with output circuits interconnected in series, and a trigger circuit triggering the output transistor arrays with two push-pull signals being derived from one input signal and having mutually associated edges consecutively following one another with temporal separation, and detecting output currents of the output transistor arrays. The method includes releasing the particular triggering push-pull signal for an output transistor array without delay whenever the output current of the complementary output transistor arrays drops below a predetermined positive minimum value. An apparatus for performing the method includes comparators associated with the output transistor arrays for detecting the predetermined minimum output currents. The comparators each have an output cross-coupled directly to the first input of a respective logical linkage element.

Abstract: In a device for controlling and regulating the current through an electric consumer with a bridge circuit, the consumer being located in one of its diagonals, four current control members of the logic level power MOSFET type are provided, a pair of voltage regulating circuits for the gate voltage supply and a pair of current control circuits for the gate voltage control being connected respectively, two of to the four current control members. Each of the voltage regulating circuits is assembled of a diode having its anode connected to a d.c. power source and to the collector of a N-P-N transistor and, via a resistor, to the base of the transistor and to the cathode of a Zener diode whose anode is connected to a terminal of the consumer. The emitter of the transistor is connected to the gate of the assigned current control member.

Abstract: A configuration for starting an inverter includes a capacitor which is provided for overvoltage protection in a half-controlled 3-phase bridge, with a discharging resistor used for charging an intermediate-circuit capacitor through a switch and a diode, in such a manner that an isolating transformer at the output of an inverter is premagnetized so that the inverter reliably turns on during the starting process.

Abstract: A DC to DC series-parallel resonant converter (10) having a plurality of switches (Q1-Q4) which are switched alternatively between on and off states to cause electrical current to flow alternatively in first and second directions through a series-resonant circuit (60) Including a variable frequency ramp generator (28) having a reset input (R) for casuing an output ramp signal produced at an output to drop to zero in response to each reset signal; a comparator (30) having an input coupled to the output of the ramp signal generator, a second input for controlling the output DC voltage of the series-parallel resonant circuit and an output which changes level each time the ramp signal reaches the magnitude of the second input; a bistable circuit (32) having first and second outputs (Q, Q) for respectively outputting first and second signals, the output signals changing in response to a change in the output signal of the comparator coupled to the input; a pulse generator (26), coupled to the series-parallel resona

Abstract: A power converter comprising: a three phase bridge circuit, each phase of which is composed of series-connected positive and negative arms, each of which arms includes series-connected GTOs; free-wheel diodes coupled in reverse parallel with every GTO; phase snubber circuits provided for every phase, each of which includes series-connected diodes coupled across the series-connected arms through a first capacitor, a junction of the diodes being coupled to a junction of the series-connected arms through a second capacitor and a junction of the first capacitor and the series-connected diodes being coupled to a negative dc terminal through a resistor; and individual snubber circuits provided in the respective GTOs, each of which includes a series connection of a diode and a third capacitor as well as a resistor connected in parallel with the diode; in which the first capacitor has capacitance much larger than the second capacitor, which in turn has capacitance much larger than the third capacitor.

Abstract: A novel inverter circuit having symmetrical gate turnoff thyristors (GTO) includes reactive circuit elements for recovering stored energy. The circuit is characterized by a center tapped transformer configured without tightly coupled anti-parallel diodes, thereby allowing for the presentation of reverse voltages to each GTO.

Abstract: A method and apparatus for commutating a load-independent current between the valve arms of a static converter device. Each valve arm has a valve device with blocking capability in the reverse direction, and a valve damping circuit. The valve device of a current-assuming valve arm is actuated at the time of commutation, and the valve device of the current-delivering valve arm reaches a zero current level upon commutation. In order to prevent a dangerous overvoltage via the inductance of the valve damping circuit, actuation of the valve device in the current-assuming valve arm is delayed until the valve device in the current-delivering valve arm substantially attains a zero current level after being turned off. During this delay, the current can commutate to the valve damping circuit of the current-delivering valve arm and generate a positive voltage there, thus expediently avoiding a reverse current and its dangerous consequences.

Abstract: A detecting apparatus for abnormality in an inverter circuit comprising an inverter circuit for converting electric power in a DC circuit into that in an AC circuit and vice versa based on a command signal for commutation, a detecting circuit for commutation in a main circuit, the detecting circuit being composed of a current detecting circuit provided between a voltage dividing point of the DC circuit and the inverter circuit and provided with its one end connected to the voltage dividing point and a differentiating circuit connected between the other end of the current detecting circuit and the AC terminal of the inverter circuit, and, a logic circuit for judgement of abnormality in commutation, the logic circuit comparing a detected signal of the detecting circuit for commutation in the main circuit with a command signal for commutation for commanding its commutation for the inverter circuit, and, at the same time, detecting inconsistency in logics of the detecting signal and command signal for commutation

Abstract: An autocontrol circuit for a resonance current or voltage undulator comprising a power supply, a parallel or series resonant circuit connected to the supply, and circuit elements (K.sub.1 to K.sub.4) for reversing the polarity of the resonant circuit's connection to the power supply. The power supply comprises a DC voltage generator and an inductive or capacitive element (2). The autocontrol circuit comprises circuit elements for detecting the voltages or currents of both the DC voltage generator and the output of the power supply. Differences between these two measured quantities are related to the load variations of the resonant circuit. The autocontrol circuit also comprises a comparator (11) for determining these differences, and circuit elements to use the comparator's output to produce signals which control switches (K.sub.1 to K.sub.4) which determine the polarity of the resonant circuit's connection to the power supply.

Abstract: Converter inverters, such as are used in the operation of alternating current machines, have turn-off reverse-conducting GTO thyristors in the bridge arms. Parallel to each GTO thyristor there is provided a series circuit composed of a turn-off load-shedding capacitor with a turn-off load-shedding diode. The common junction points of the respective turn-off load-shedding capacitors and diodes are connected in series to a choke via at least one capacitor load-shedding diode. The inductance of the choke is 2 to 3 times as large as the inductance of the circuit. The reverse-conducting GTO thyristors are directly connected in series, without the series connection of a choke. There thus arises a damping circuit of the GTO thyristor, which is very simple and, at the same time, feed back ring-around energy.

Abstract: A three-level inverter, in which the upper and lower half of each phase relieves the semiconductor switching elements from excessive values of the rate of rise of the recurring positive forward blocking voltage. This is done with a circuit arrangement in each half has a wiring diode, a switching off relief capacitor, a further wiring diode, a storage capacitor and a discharging resistor serving as the d-c load. Additional energy feedback devices feed back, into the supplying d-c voltage source, energy which is produced in the switching-off process and is temporarily stored in the circuitry.

Abstract: A circuit for sensing the magnitude and sense of a current flowing through the load of an H-bridge stage driving the load in a switching mode by means of a clocked, square-wave driving signal and the inverted signal thereof applied, respectively, to two pairs of analog switches arranged in a bridge configuration and functionally switching the load between a supply node and a virtual ground node is made by utilizing a single sensing resistance connected between the virtual ground node and the real ground node of the circuit, the signal across the resistance and the inverted signal thereof are fed to two inputs of an analog multiplex whose output signal is fed to the input of a comparator in order to obtain at the output of the latter a signal with an amplitude proportional to the intensity of the current and a polarity determined by the polarity of a reference voltage which is applied to another input of the comparator.

Abstract: The invention relates to a parallel oscillatory circuit frequency converter comprising: a rectifier (1); an inverse rectifier (4) having thyristors disposed in a bridge circuit; a parallel oscillatory circuit (5) having an inductance (L) and a series connection of two capacitors (C, C.sub.K) whereby one capacitor (C) is connected to the load points of the bridge circuit; and a gate-controlled turn-off time control device (6) for the alternate firing (switching) of the thyristors a, b forming the particular diagonally adjacent bridge branches with a cycle frequency adapted to maintain a minimum turn-off time, a safety firing circuit (24, 25) controlled by a detector circuit (11-23) to detect incorrect switching delivering firing pulses without delay to all the thyristors at least until all the thyristors are current-carrying.

Abstract: An overcurrent protection system for AC motor control systems which provides a separate overcurrent shut down mechanism for each phase of the AC power used in an AC motor. These separate phase shutdown mechanisms provide protection for minor overcurrent conditions without shutting down the entire motor control system. The overcurrent protection system also provides a mechanical feedback apparatus for totally shutting down the motor control system only in a severe overcurrent condition.

Abstract: A DC/DC power converter 10 which avoids shoot-through current by employing an energy storage fly-back inductor 27 having two separate primary windings 28 and 29, one for current in each direction. The fly-back inductor 27 is located inside the switching bridge. In addition, a transformer 30 having two separate windings 42 and 44 is also employed. Thus, shoot-through is avoided and an extra switch for pulse width modulation is not required. In addition, the device does not apply a greater voltage than the line voltage to the switches and "holes" in the output current are not created so that less noise is generated by the device.

Abstract: Low-loss external wiring, for the switching-off relief of the semiconductor switching elements in a stage of a three-level inverter provides a switching-off relief capacitor which is connected to the stage output. Wiring capacitors are coupled to each of the upper and lower ends of the stage. The inverter also includes a diode network. Additional d-c consumers which are preferably either ohmic resistors or energy recovery devices take up energy which is interim-stored in the wiring capacitors.

Abstract: In a snubber circuit, two transformers for regenerating snubber energy are commonly provided for more than two switching elements in each of the arms of an inverter. The number of snubber energy regenerating transformers can be limited to only two, regardless of the number of switching elements. The circuit can be simple and compact, without decreasing the efficiency of regeneration of snubber energy.

Abstract: In an inverter supplied with power from a DC power supply whose voltage rises at a light load operation, if an overcurrent failure occurs at a light load operation at the inverter output side as seen from the DC power supply, a surge voltage higher than a voltage withstanding of the switching elements of the inverter is generated across the elements, the surge voltage being higher by the amount corresponding to a rise in the DC power supply voltage. Therefore, there arises a possibility of breaking the switching elements. This inconvenience can be solved by lowering the overcurrent detection level by the amount corresponding to a rise in the DC voltage, when a light load operation as seen from the DC power supply side is performed.

Abstract: A high voltage power supply circuit for a high frequency medical X-ray generator comprises a high voltage transformer having a primary and a secondary and an inverter circuit responsive to predetermined control input signals for producing corresponding inverter output signals. A responant circuit is coupled with the inverter circuit and is resonsive to the inverter output signals for producing corresponding voltage pulses for energizing the primary of the high voltage transformer. The resonant circuit includes a capacitive component and an inductive component, the latter being provided by the primary of the high voltage transformer coupled in series circuit with the inverter circuit and with the capacitive component. A KVP regulator circuit provides the control input signals for the inverter circuit in the form of a series of KV firing pulses.

Abstract: A transient protection circuit for an inverter has a rectifier capable of supplying direct current from an alternating current power source, where protection is provided against a voltage transient in the AC power source. A DC bus is fed by the rectifier. A bus capacitor is connected across the DC bus. Solid state switches are connected to the DC bus for supplying alternating current to a load. The DC bus voltage is sensed. In response to a transient rise in the DC bus voltage, a resistor is connected across the bus capacitor to provide a discharge path, the solid state switches are disconnected from the DC bus, and after the transient dies away from the DC bus, the solid state switches are reconnected to the bus and the discharge resistor is disconnected from across the bus capacitor.

Abstract: A frequency converter is provided for the power supply of an asychronous motor, comprising:a rectifier bridge (11) connected to a multiphase network and to an intermediate DC circuit (12);an inverter (13) comprising three pairs of static switches (T1-T6) connected in a Graetz bridge; characterized by;a means (21) for reading the current associated with the intermediate circuit (12) and elaborating an image signal of the reverse circuit and delivering an image signal of the current in this circuit;a stabilization control circuit (22) connected to said means (21) and delivering a reverse current excess signal (ST) when the signal (I.sub.d) exceeds an adjustable threshold; anda means (25) for reducing the output voltages of the inverter, and adapted for modifying the modulated pulses, this means being controlled by the output signal (ST) of the stabilization control circuit (22).

Abstract: A polyphase inverter includes a plurality of unit inverters connected to a single power source to form an a.c. output with the unit inverters being polyphase, thus to take out the resultant output. In this polyphase inverter, a series circuit including a capacitor and a fuse, and a reactor for protection coordination of the fuse are connected between the d.c. power source and each unit inverter. The resonance frequency of a resonance circuit constituted by the capacitor and the reactor is selected so that it is substantially equal to the product of the number of unit inverters, the number of pulses of the unit inverter, and the output fundamental frequency.

Abstract: An energy converter of the type utilizing a series-resonant bridge circuit (1) containing at least two thyristors (6A, 7A, 6B, 7B) with diodes (8A, 9A, 8B, 9B) antiparallel connected thereto, a high-frequency output transformer (12), and an energy buffer (2). A control circuit (3) is incorporated for generating trigger pulses for the appropriate thyristors in response to the energy of the buffer (2). The energy converter further comprises a switching circuit (24) connected in at least one of the supply lines of the supply source to the series-resonant circuit for ensuring that the diode, antiparallel connected to the last-conducting thyristor, starts to draw current immediately after this thyristor is blocked. The control circuit (3) furthermore generates signals indicative of the presence of current flowing through the diodes, which signals control the supply of the trigger pulses to the thyristors.

Abstract: An apparatus and method relative to the operating of a control turn-off semiconductor device provide for determining the actual control electrode to cathode voltage upon the application of a turn-off control signal by adjusting the apparent value of that voltage by a value representing the voltage drop due to inductance in lead lines. The thusly adjusted value is employed to develop an output signal which indicates that the device has been turned off. In a further embodiment, the output signal may also be employed to reduce the value of the control signal from a first, relatively high value to a second, relatively low value.

Abstract: A control for an inverter operable for converting direct voltage and current to alternating voltage and current. The inverter includes a plurality of electrical valves each operable to conduct current in a single direction upon the application of a positive voltage in the forward direction and the receipt of a trigger pulse. The control provides successive trigger pulses for commutating the current between successive valves at predetermined electrical firing angles and includes a voltage-time area calculating circuit for calculating the maximum permissible firing angle which will permit successful commutation. An inverter commutation failure prevention circuit is coupled to the alternating current network for detecting abnormal voltage conditions and for producing a control signal functionally related to any deviation in the alternating voltage from the expected voltage condition. The control is responsive to the control signal for reducing the electrical angles of the trigger pulses provided to the valves.

Abstract: A switched mode power supply has two separate, alternately conductive switching paths, each including two switching elements. Smoothing capacitors are connected in series across the series connection of one switching element in each of the switching paths and to the supply lines via further capacitors. In a further embodiment, a primary winding of a transformer is connected in series with the load and a capacitive network incorporating a secondary winding of the transformer is provided in conjunction with one of the switching elements in each path. Current draw from a rectified supply input is controlled at least once in each cycle by current flowing in the secondary due to the current in the primary.

Abstract: A power switching circuit for switching power repetitively to a load at a relatively low frequency employs a power switching device which is driven across an isolating transformer interface. The drive signals are high frequency pulse signals which are modulated with the low frequency switching information, the modulations being detected in the secondary circuit of the transformer. Such an arrangement affords isolated driving with fast switching edges and requires only a small transformer. Power for the detection circuit is derived by rectification of the high frequency signals induced in the transformer secondary.

Abstract: A welding system with an electronic control includes four switching elements coupled together to form a bridge. An inductor with a center tap is located between two legs of the bridge. A load, including an output electrode and the metal parts being welded, is coupled between the center tap of the inductor and the other two branches of the bridge. Two of the switching elements are turned on and off at a relatively high rate to control the power to the load. The other two are turned on and off at a relatively low rate to control the duty cycle and polarity of the load voltage and current.

Abstract: In the ion nitriding power supply disclosed herein, power to the discharge chamber is normally current-regulated by a pulse-width modulated current switching device effectively in series with a switching inverter which energizes the chamber, instantaneous current variations being smoothed by a series inductance which, together with the chamber, is shunted by a freewheeling diode. Incipient arcing is quickly extinguished by semiconductor switching devices incorporated in the inverter which, when energized simultaneously, shunt the chamber, instantaneous current limiting being provided by the series inductance. The shunt switching devices are triggered when the voltage across the discharge drops below a level indicative of the formation of an arc.

Abstract: A circuit supplied with direct voltage serves for generation of voltages and/or currents of differing curve shape and differing frequency and/or differing polarity. A load L with ohmic, inductive, capacitive or complex resistance behavior is switched in series with a choke D. Furthermore, at least two controlled semiconductor switches T.sub.1 and T.sub.2 are provided, which are each, respectively in series, as far as the load L and the choke D are connected, but which, however, lie in current paths 1 and 2 which are connected at different potentials of the supply voltage. In operational use, the one switch T.sub.2 is held open while the other switch T.sub.1 is opened and closed in alternating sequence, and after termination of an adjustable and controllable time period, the switch T.sub.1, which has been hitherto operated in alternating sequence, is now kept open, while the switch T.sub.

Abstract: A reactive power processing circuit for a current source GTO invertor in which a reactive current generated from a load of the GTO invertor is rectified by means of a fly wheel circuit and is sent to a capacitor so as to store a commutation surge voltage generated whenever a commutation of the invertor occurs, an excessive charge voltage across the capacitor is regenerated to a direct current output side of a power rectifier, and a pair of GTO (Gate Turn Off Thyristors) thyristors are connected between the capacitor and the direct current output side of the power rectifier in their forward directions so as to carry out a discharge operation for the excessive charge voltage across the capacitor. Consequently, with the number of circuit elements remarkably reduced, the reactive power processing at times of a high-frequency operation and acceleration/deceleration (variable speed) operation of the invertor can be achieved.

Abstract: The field windings of large generators of hydroelectric power stations which are continuously connected to a three-phase system and are designed to produce large capacitive powers, are fed from a "positive" main static converter, designed for 8 kA, via a field circuit. An anti-parallel "negative" auxiliary static converter designed for 600 A maintains a link current (i.sub.Z) of 200 A in a direct-current link with a link choke. To prevent overcurrents, which can be harmful for the link choke and the auxiliary static converter, in the direct-current link due to disturbances such as, for example, a short-circuit in the three-phase system or connection or disconnection of capacitor banks, a free-wheeling residual current is initiated in the direct-current link when the link current (i.sub.Z) exceeds a predeterminable first current limit value (i.sub.G1), corresponding to 120% of the nominal link current, during a minimum period of time of 0.5 ms.

Abstract: An inverter comprises a pair of reactors connected in series between a positive arm element and a negative arm element, snubbers each connected in parallel to respective arm elements, and a feedback circuit for transferring electrical energy stored in the snubbers back to the d.c. power source. The feedback circuit includes a self turn-off switching device which is controlled to become conductive during a certain period in correspondence to the on-off operation of the arm elements so that energy stored in the snubbers is fed back to the d.c. power source through a current transformer and a rectifying circuit during the on-state of the device.

Abstract: The invention concerns a converter (2) provided with GTO thyristors the frequency and characteristic shape of its output voltage (U.sub.A) being constrained by a load (3). The frequency of the converter (2) is matched to the constrained output voltage (U.sub.A) with the aid of a regulating circuit (4). Non-simultaneously switched GTO thyristors are switched on and off in a predetermined timed relation to each other (FIG. 3).

Abstract: Center-tapped DC power to a self-oscillating full-bridge inverter-type fluorescent lamp ballast is obtained from a regular power line by way of a voltage doubler. The DC power is supplied to the inverter through an inductor means having two separate windings on a common magnetic core--with one winding being positioned in each leg of the DC power supply. The full-bridge inverter, which comprises four switching transistors connected in usual full-bridge fashion, comprises a center-tapped parallel-tuned L-C circuit connected across its AC output, thereby providing a center-tapped sinusoidal voltage to its load, which consists of a fluorescent lamp connected in series with a current-limiting capacitor. Due to the effect of the inductor means, the current provided to the bridge is substantially constant during a complete period of the inverter's oscillation.

Abstract: A crowbar circuit is provided in an inverter for diverting overcurrents from the inverter switches. The crowbar circuit includes a crowbar switch and a crowbar winding which is magnetically coupled with the inverter snubber reactors. The size and the coupling of the crowbar winding are chosen so as to reduce or make negative the di/dt of the snubber reactors when the crowbar switch is turned on.

Abstract: This invention concerns a procedure to operate a turn-off thyristor which can be set to a current-conducting state or a current-blocking state as a function of a switch-on command or a switch-off command. To permit particularly reliable and optimal operation of the turn-off thyristor, the voltage between its gate terminal, G, and its cathode terminal, K, is detected and when it drops below a negative threshold current value U.sub.GKS, a status signal, Z, is generated which indicates the current-blocking state of the turn-off thyristor. A further embodiment detects the gate current of the turn-off thyristor and after the appearance of the switch-off command, the status signal is generated as the polarity changes in accordance with the time derivative of the gate current.