Abstract: An SCR firing circuit allows the firing point to be changed. The firing circuit includes a ROM which has an output for each gate of each SCR. The ROM is programmed to fire the SCRs in a desired sequence. The ROM is driven by a counter, which counts pulses from an oscillator, the frequency of which is variable. The difference between the zero cross of the waveform and the ROM output is compared and averaged. The comparator output is summed with a variable DC demand voltage. The sum is applied to an integrator, which provides an integrated output to the oscillator to change the frequency of the oscillator if the firing point is changed.

Abstract: Power delivered to a load by a three-phase supply is controlled by six thyristors which are controlled by a control signal generator comprising a programmed microcomputer (2), a zero-crossover detector (3), a clock pulse generator (6) and a counter (7) so that the thyristor conduction angles are determined by a digital signal applied to an input (17) of the microcomputer. In order to obtain a fast response to changes in the supply frequency and to take into account any unbalance between the supply phases, the microcomputer repeatedly measures the actual length of each nominally 60.degree. portion of a complete period of the supply by starting the counter at a predetermined point within each portion, the counter subsequently being stopped by the output of the detector when the next zero-crossover occurs and then being read by the microcomputer.

Abstract: A control apparatus for a thyristor converter which supplies electric power to a load generating a changeable electromotive force, wherein, in response to a load current being changed from an intermittent load current mode to a continuous load current mode, an actual main circuit constant of the load is calculated on the basis of a pregiven main circuit constant of said load, a predetermined minimum value of a DC average motor current at which a compensation control angle is zero, a DC average load current and a set control angle at a time when the load current just changed from the intermittent load current mode to the continuous load current mode.The compensation control angle is obtained on the basis of the calculated actual main circuit constant and the DC average load current.The calculated compensation control angle is added to the set control angle to thereby apply the added angle to the thyristor converter as a firing control angle.

Abstract: A phase control device for a power converter with a plurality of controlled rectifier elements, including a phase detector for detecting a phase of an AC voltage of the power converter to produce a phase signal. A processing circuit for receiving an electrical quantity appearing at an AC side or a DC side of the power converter as a feedback signal and for comparing the feedback signal with a reference signal to produce a phase control signal so that the feedback signal becomes equal to the reference signal, and a firing pulse determination circuit for comparing the phase signal with the phase control signal to produce a plurality of firing pulses, which are adapted to be connected to selected of the controlled rectifier elements to fire the controlled rectifier elements. The processing circuit includes a monitoring circuit which judges whether or not the phase control device has failed based on the phase signal, the phase control signal and a specific firing pulse from the firing pulse determination circuit.

Abstract: A phase detecting apparatus comprises a first PLL and a second PLL having a response time shorter than the response time of the first PLL. An AC voltage signal produced by the first PLL which is in phase with the detected AC voltage except until the expiration of the response time of the first PLL after an abrupt change in the phase of the detected AC voltage is normally applied to the second PLL. Until expiration of the response time of the first PLL after rising of the detected AC voltage to a certain level, the detected AC voltage is applied, in place of the AC voltage signal produced by the first PLL, to the second PLL. The second PLL provides a digital signal indicative of the phase of the detected AC voltage.

Abstract: A multi-loop control system for convertors of the kind used in h.v.d.c. transmission and industrial applications. The invention consists in a control circuit which effects transfer between two or more control loops, e.g. a constant-current loop and a constant .alpha. loop, in a smooth and precise manner, without extra smoothing lags, even in the presence of ripple in the controlled quantities.

Abstract: This invention relates to an apparatus for controlling a D.C. power transmission system having a line-commutated converter which is connected between a first A.C. system and D.C. power transmission lines and which performs power conversion between A.C. power and D.C. power, and a forced-commutated converter which is connected between the D.C. power transmission lines and having a second A.C. system and which performs power conversion between A.C. power and D.C. power. In order to control transmission power in the two-terminal D.C. power transmission system wherein the two A.C. systems are associated by direct current, a control apparatus for a D.C. power transmission system according to this invention includes a voltage detector which detects a D.C. voltage of the D.C.

Abstract: Ramp generating circuits, for synchronizing SCR firing control signals to the phase-varying signals derived from a three-phase AC power source, each have a compensating circuit connected across an operational amplifier and a capacitor to control the peak value of the ramp signal generated at the output of the operational amplifier. The compensating circuit maintains the peak value of the ramp signal close to its calculated value despite variations in the actual value of the capacitor from its nominal or rated value and despite changes in power line frequency between 50 hertz and 60 hertz. The compensating circuit includes a T-section passive network, a voltage-following amplifier and several feedback resistors connected from the output of the operational amplifier to its inverting (-) input. This compensating circuit increases or decreases charging current to the capacitor according to the type of compensation that is necessary.

Abstract: A control circuit for a power converter which converts between polyphase periodic power and unidirectional power is disclosed. The control circuit includes first means for sensing a parameter of the periodic power and a ramp generator coupled to the first means for generating a ramp signal having a frequency equal to the frequency of the periodic power. A second means senses a parameter representative of a condition at the output of the power converter and a comparator combines the outputs from the ramp generator and the second means to generate a pulse train having a frequency equal to the frequency of the periodic power but shifted in time relative thereto, with the shift being dependent upon the output parameter. A phase-locked loop, of PLL, multiplies the frequency of the pulse train and additionally develops a signal which is coupled to the ramp generator to maintain the amplitude of the output therefrom at a constant level irrespective of changes in frequency of the periodic power.

Abstract: A method of adaptively controlling the time of rendering the individual controlled devices of a controllable power conversion bridge includes the sensing of the instant in time at which the current from the bridge to a load becomes discontinuous. From the time of this sensing, the time period to a predetermined time such as a normally calculated time of rendering the controlled devices conductive is derived. This time period is then multiplied by a multiplier and the resultant product is combined with the predetermined time to provide an actual time of rendering the controlled devices conductive.

Abstract: The power delivered from a three-phase A-C power source and through a network of SCR's (connected, for example, to form a full wave rectifier bridge or to provide an A-C switch) to a load circuit is adjusted by controlling the conduction angles of the SCR's. The control is achieved by developing, from only one of the three alternating phase voltages provided by the A-C power supply, a reference square wave signal of the same frequency and whose amplitude excursions are precisely synchronized or keyed to the zero voltage crossings of the selected phase voltage, even though that phase voltage may include undesired harmonics, noise, transients or other distortion components.

Abstract: A high response motor controller is disclosed which operates directly from a multi-phase AC power line without a DC link. The controller directly converts power from a fixed frequency multi-phase input to a D.C. or variable frequency output current. The output frequency is not limited by the AC power line frequency and the switching frequency is independent of the AC power line frequency. Controlled switching devices are connected between the multi-phase power input line and the power output line. Analog input signals are compared with signals representative of actual motor currents to produce current error signals. These current error signals control the conduction state of the controlled switching output transistors by a two state modulation process.

Abstract: A method and apparatus for use in conjunction with a power conversion system employing a plurality of switching elements for controlling the electrical power supplied to a load from a source includes the sensing of the instantaneous voltage furnished to the load and providing a signal representing the time derivative of the sensed voltage. The derivative signal thus developed is compared with predetermined reference values to develop output signals which are logically combined to provide a final signal representative of the instant in time at which one of the switching elements is commutated (turned off).

Abstract: A microprocessor-based static converter control circuit includes a free-running counter which is synchronized with the powerline phase and frequency using a zero-crossing detector circuit. Firing angle commands are received and converted to a corresponding firing count. The microprocessor outputs a firing code for the thyristor firing pulse circuit when the count of the free running counter reaches the firing count.

Abstract: An electrical power system has a variable speed multi-phase alternator. A multi-phase full wave rectifier with controlled rectifier elements converts the electrical power to DC. The DC voltage is regulated by a control circuit which determines the angle of conduction of the rectifier elements. If the alternator frequency is excessive, the controlled rectifier elements are not reliably commutated. The control circuit compares the alternator frequency with a reference. When the frequency is above a selected value, rectifier operation is modified either for half wave rectification or for full wave rectification of less than all of the phases from the alternator. Additional switching time is provided, improving reliability.

Abstract: A gate pulse phase shifter is designed so as to generate pulses at intervals of 60.degree. regardless of distortions in the AC power supply voltage, and so that, for linearity in control, the phase reference signal and the DC output voltage of AC-DC converters connected to the device are proportionally related.

Abstract: A timing generator for use with multi-phase controlled rectifier systems is disclosed in which a ramp signal is produced in phase synchronization with the power source and compared with the value of a command signal. The command signal is indicative of the desired SCR ignition angle. A sequencing circuit, having a finite number of output states is cyclically stepped from one state to the next by a comparator. The sequencing circuit couples a source of SCR-gating pulses to the appropriate SCR in accordance with its state and with a predetermined pattern of SCR ignitions which characterize the multi-phase source.One aspect of the invention provides the multiplexing of the comparator output whereby the command signal is offset by 60.degree. (electrical) after each comparator transition to set up conditions for the next transition.A further aspect of the invention provides for the generation of an alternate ramp, 180.degree.

Abstract: A circuit arrangement for the compensation of voltage variations of the electrical AC polyphase power line for an AC-DC converter (3).The invention comprises a first circuit (5) for determining the voltage variations at the input of each trigger rectifier (Th.sub.1, Th.sub.2, Th.sub.3) of a converter (3) and a compensating circuit (6) for compensating the firing angle of each trigger rectifier. The compensating circuit (6) is connected to an output (7) of the first circuit (5) for determining the variations in the input voltage of each rectifier. Outputs of the compensating circuit (6) are connected to control inputs of the pulse generator (4) for controlling the firing angle of each rectifier so as to adjust the period of the firing pulses of each trigger rectifier (Th.sub.1, Th.sub.2, Th.sub.3). The invention is particularly applicable to electrical DC power supplys for data processing systems.

Abstract: A three-phase regenerative rectifier provides power flow from ac to dc using a three-phase rectifier bridge. The reversal of the input ac voltage at the input frequency commutates current in the rectifier devices. A power transistor or field-effect transistor is coupled in inverse parallel with each rectifier device to provide a path for current from the dc output of the rectifier back to the ac supply during regeneration. The rectifier devices can be phase controlled thyristors or diodes. Control means sense the three-phase voltage and switch the transistors in phase with the ac supply. Commutation of the transistors is provided by their self-contained turn-off capabilities.

Abstract: Magnetizing current supplies are disclosed for supplying current for magnetizing parts in a magnetic particle inspection system, including SCR's connected in circuit with a three-phase voltage step-down transformer to accurately control the duration and magnitude of magnetizing current. In one type of supply, six SCR's are connected between magnetizing apparatus and terminals of three center tapped secondary windings of a three-phase voltage step-down transformer, the SCR's being operable to rectify current and also being connected to a phase control circuit which controls firing times of all SCR's to control the magnitude of the magnetizing current.

Abstract: A digital phase-shifting circuit employed for a thyristor converter, which operates on a polyphase power supply. In the digital phase-shifting circuit which is simply constructed as a whole, a counter portion consists of an N-bit binary counter and a divide-by-six ring counter, and a comparator portion consists of a common comparator which compares data bits and simply constructed two-bit comparators that are provided for each of the phases.

Abstract: The proposed method consists in that a narrow control pulse is applied to the thyristors of the arrangement at the beginning of the conduction interval of the arrangement. The positive voltage across the monitored thyristors is measured and a monitor signal is formed at the point in time when the voltage reaches a preset level. Using the received monitor signals, one can count the number of the thyristors whose positive voltage exceeds a preset level. At the point in time when the number of the monitor signals reaches a preset value, additional narrow control pulses are applied to the thyristors.The proposed control system comprises devices for measuring the positive voltage across the monitored thyristors and an adder connected to the devices. The adder and a reference signal source are coupled to a comparison circuit which, like a sync pulse source, is connected to an AND gate. The AND gate and the sync pulse source are connected to an OR gate which couples an amplifier-former connected to the arrangement.

Abstract: A rectifier controller for controlling bridge connected silicon control rectifiers (SCRs) (1 to 6) of a three-phase rectifier which is used to supply a direct current (DC) voltage to an inverter (314) used for injecting pulse coded audio frequency signals on a power line. The controller supplies gate control signals to the SCRs (1 to 6) of the rectifier bridge in accordance with the envelope of the three-phase supply voltages and provides for protection of the inverter (314) when shoot-through conditions occur in the inverter (314) and provides for output DC voltage adjustment by controlling the firing time of the rectifier bridge SCRs.

Abstract: An elevator system including an elevator car and a drive machine having a DC drive motor, a dual converter, and a phase controller for providing gate drive signals for the dual converter. A reference signal relates to the desired motor armature current is developed in response to the operation of the elevator system. The reference signal indicates when the current source should be switched from one converter bank to the other converter bank. The switching is accomplished by a method which includes retarding the firing angle of the gate drive signals applied to the operative converter, until current is extinguished, applying the gate drive signals to the other converter bank, and advancing the firing angle towards rectification to initiate current flow in the on-coming converter. The rate at which the firing angle is advanced towards rectification is a function of the control signal.

Abstract: An apparatus for preventing malfunctions in a phase control mechanism of the type in which the firing angle of thyristors in a thyristor bridge is controlled to regulate the rotational speed of a DC motor comprising the load of the thyristor bridge. Thyristor firing pulses are produced each time a rising analog speed command signal generated in response to the phases of a N-phase power supply intersects N-number of sawtooth signals. Immediately after the generation of each firing pulse, the thyristors are not supplied with firing pulses for a time interval at least equivalent to the thyristor commutation overlap time.

Abstract: The effect of commutation notches 35 appearing in the nominally sinusoidal alternating current (AC) line-to-line voltage, for example, v.sub.ab used to synchronize the firing of thyristors in three phase, phase-locked power converters 12 and 14 is essentially eliminated by reconstructing the corrupted line-to-line voltage by summing the integral of the corrupted line-to-line voltage .PSI..sub.ab with a signal proportional to the product of the delta load current, for example, i.sub.ab and the commutation inductance L.sub.c. The composite waveform .PSI..sub.ab +i.sub.ab .times.L.sub.c) resulting from the summation has well defined zero crossings 41 from which synchronizing pulses are generated for synchronizing the phase-locked thyristor firing circuit 18 implemented by either software or hardware techniques. Additionally, the reconstructed waveform is used to control commutation, particularly in the control of a load side converter i.e. inverter 14 which is utilized in an AC motor drive system.

Abstract: A power supply circuit (20) having an inductive load (12), three power lines (A,B,C) for conducting current of a 3-phase AC source, an SCR network (24) of six SCRs (1-6) for coupling the current of the source between the power lines (A,B,C) and the load (12), a phase sensor (30) for generating a reference signal in response to one reference phase voltage (AB) of the source, and a trigger circuit (35) for triggering "on" the SCRs (1-6) at predetermined phase angles relative to the voltage (AB). The power supply circuit (20) overcomes constraints such as load inductance which limit the rate of current build-up or decay through the load (12) by gating "on" the SCRs (1-6) at the predetermined phase angles to maximize such current build-up or decay.

Abstract: A method and apparatus for monitoring current data in a thyristor-controlled direct current drive, the drive system comprising two thyristor bridges converting alternating current into direct current for the drive motor and a current measuring unit. With the aid of a current controller the drive system is caused to operate in one of two different modes of operation, so that as the system approaches zero current condition, the normal mode of operation changes to an oscillating mode, the direct current circuit being monitored with the aid of a delayed current indicator datum in the zero current situation as well.

Abstract: An electric power source device for electrolytical production or coloring of alumilite, wherein pulses are generated at a predetermined phase of A.C. source, the pulses are frequency-divided by a non-contact circuit and, depending on the results of the frequency division, analogue switches respectively comprising a non-contact circuit are driven to actuate rectifier units for rectifying the A.C. source. Outputs of alternately reversed polarities with distinctly sharp rising and falling are provided.

Abstract: A-C energy, from an a-c power system, is converted by a phase-controlled SCR rectifier bridge, which is followed by a series-connected filter choke and a shunt-connected filter capacitor, to d-c power for delivery via a d-c bus to a load, such as an inverter and an a-c induction motor driven by the inverter. When there is a decrease in load demand, for example when the motor speed is to be reduced, fast speed control is obtained by regenerating power back into the a-c power system from the load. Power flow through the d-c power supply is reversed by means of a switching network, interposed between the filter choke and capacitor, having a pair of reverse SCR's for cross-coupling the positive and negative lines of the d-c bus. When the reverse SCR's are fired into conduction, the connections between the filter capacitor and the bridge's output terminals are effectively reversed, thereby facilitating power flow from the load to the a-c power system.

Abstract: In a thyristor-controlled converter system the non-canonical harmonics are minimized by active filtering through control of the firing angle of the thyristors in accordance with the undesired harmonic component.

Abstract: Control signals for phase-delay rectifiers, which require a variable firing angle that ranges from 0.degree. to 180.degree., are derived from line-to-line 3-phase signals (.phi.A, .phi.B, .phi.C) and both positive and negative firing angle control signals (+.alpha. and -.alpha.) which are generated by comparing (at 20) current command and actual current (sensed at 16). Line-to-line phases are transformed (32) into line-to-neutral phases and integrated (at 34) to produce 90.degree. phase delayed signals (A.phi., B.phi., and C.phi.) that are inverted (at 26a, b, c) to produce three cosine signals (C, A and B RAMP) such that for each its maximum occurs at the intersection of positive half cycles of the other two phases which are inputs to other inverters. At the same time, both positive and negative (inverted) phase sync signals are generated for each phase by comparing (at 27a, b, c) each with the next and producing a squarewave when it is greater.

Abstract: A timing generator for use with multi-phase controlled rectifier systems is disclosed in which a ramp signal is produced in phase synchronization with the power source and compared with the value of a command signal. The command signal is indicative of the desired SCR ignition angle. A sequencing circuit, having a finite number of output states is cyclically stepped from one state to the next by the comparator. The sequence circuit couples a source of SCR-gating pulses to the appropriate SCR in accordance with its state and with a predetermined pattern of SCR ignitions which characterize the multi-phase source.One aspect of the invention concerns the multiplexing of the comparator output whereby the command signal is offset by 60.degree. (electrical) after each comparator transition to set up conditions for the next transition.A further aspect of the invention concerns the generation of an alternate ramp, 180.degree.

Abstract: A trigger system and method for use in a line commutated power converter as used in either a rectification or an inversion mode of operation and more particularly a trigger system and method for a static converter for accurately controlling the firing angles for controlled rectifiers for converting between multiphase a-c power and d-c power by use of digital signal having magnitudes which are varied for varying firing angles for providing a converted output having a regulated voltage and/or current.

Abstract: An AC resonant charger for a capacitive load, such as a PFN, is provided with a variable repetition rate unrelated to the frequency of a multi-phase AC power source by using a control unit to select and couple the phase of the power source to the resonant charger in order to charge the capacitive load with a phase that is the next to begin a half cycle. For optimum range in repetition rate and increased charging voltage, the resonant charger includes a step-up transformer and full-wave rectifier. The next phase selected may then be of either polarity, but is always selected to be of a polarity opposite the polarity of the last phase selected so that the transformer core does not saturate. Thyristors are used to select and couple the correct phase just after its zero crossover in response to a sharp pulse generated by a zero-crossover detector. The thyristor that is turned on then automatically turns off after a full half cycle of its associated phase input.

Abstract: In a gate control circuit for a thyristor converter, in which thyristor valves each having a plurality of series thyristors are connected to form a bridge, a detector for detecting a forward voltage applied across one of the thyristors and a circuit for supplying a gate signal to the gate of that thyristor valve are provided. The gate control circuit further comprises a circuit for supplying, when a bypass pair operation of the thyristor converter is switched over to a deblock operation, a signal to the gate of a continually conductive thyristor valve according to a control signal to a thyristor valve to be operated in deblock with the continually conductive thyristor valve and also a gate signal to the continually conductive thyristor valve.

Abstract: A method and an apparatus for converting a three phase input into a constant voltage to a load, which voltage is substantially free of harmonics and ripples includes dividing the voltage to the load into two component voltages, with one component voltage comprising at least 80% of the total. The one component voltage is maintained constant and load independent. The voltage to the load is compared to a first reference voltage to obtain the difference therebetween and the value of the other component voltage is adjusted to minimize the difference. The two component voltages are added to form the voltage to the load.

Abstract: A solid state control circuit is connected to the output of an engine or motor driven alternator to provide a direct current output primarily for welding purposes. The control circuit includes gate controlled thyristors (SCRs) which are gated on at precise times within each cycle in order to provide an output having desired characteristics, such as constant current or constant voltage. Synchronizing windings associated with the alternator provide signals used to control the time of gating for the SCRs. Circuit means are included to insure that the control signals will be unaffected by any disturbances generated within the synchronizing signals due to the operation of the SCRs, and one such means includes an amplifier having a feedback circuit providing a hysteresis greater than any voltage change in the synchronizing signal caused by the operation of the SCRs.

Abstract: A circuit for use in a multiphase regulated supply to provide regulation of the ripple current contained in the filtered d.c. output signal of the supply. The supply regulates its output voltage and/or current by controlling the conduction time of the switching elements contained in the rectifier portion of the supply. The switching element conduction time is controlled by controlling the generation of firing pulses to the switching elements as a function of an error control signal which is equal to a first error signal. This signal is equal to the amount by which the actual value of said voltage and/or current deviates from a reference value of said parameter. When the ripple regulation circuit is included in the supply, a second error signal is generated which represents the deviation of the d.c. value of the ripple from a predetermined reference.

Abstract: Ignition control signals for a multipulse controlled rectifier are combined in a sequence which is fed through a first time delay stage to a phase control circuit having a voltage-controlled oscillator which generates a phase-locked, gated, highly accurate square-wave oscillation as a trigger pulse series. The ignition control signals and the trigger pulse series of the voltage-controlled oscillator are conjunctively coupled in and gates are then amplified to form firing (ignition) pulses. A second time delay stage is provided for safety, in the event of dynamic control processes, and follows the first time delay stage. The output signals of the second time delay stage are linked to the ignition control signals in additional and gates and are subsequently amplified.

Abstract: Converter apparatus including gate drive control of the stored energy type. Control logic arms the next controlled rectifier device to be gated a predetermined period of time following the gating of the immediately preceding controlled rectifier device in the gating sequence.

Abstract: In a method and apparatus for controlling an output current of a controlled rectifier connected to an AC power supply, by firing angle control of the controlled rectifier in accordance with the result of comparison of a value corresponding to the rectifier output current with a predetermined reference value, an average value of a detected rectifier output current over a period having a length equal to an integer multiple of the average period of the firing angle control is calculated, and a signal for firing the controlled rectifier is produced at an angle determined in accordance with comparison of the calculated average value with the reference value.

Abstract: A constant current welding power supply having a single transformer with a primary winding connected to a three phase input source of line voltage and two secondary windings each having a bridge rectifier for providing an open circuit starting voltage separate from the arc working voltage. Each bridge rectifier is fired by separate firing means controlled by a logic control means. One bridge rectifier is energized with an advancing firing angle proportional to a ramp output signal enabled through the control means in response to a predetermined drop in output voltage. The other bridge rectifier is energized in synchronism with the line voltage for a predetermined period of time following the predetermined drop in output voltage.

Abstract: Converter apparatus including a power converter having controlled rectifier devices connected, and gated in a predetermined sequence, to interchange electrical power between a source of alternating potential and a direct current load circuit, a phase controller for controlling the conduction angle of the controlled rectifier devices, and circuitry for maintaining synchronous operation between the phase controller and the power converter. The circuitry for maintaining synchronous operation constrains the conduction angle between predetermined end stops by logically combining first and second logic signals developed for each controlled rectifier device from the source of alternating potential, with a logic signal associated with the immediately preceding controlled rectifier device in the gating sequence.

Abstract: The firing phase of the power converter which can change power to be supplied to a load is determined by the firing angle instruction produced from the current control circuit in accordance with the magnitude of the current difference between the current target value and the current actual value flowing through the load. The nonlinear compensating circuit produces a correction angle instruction predetermined in accordance with the magnitude of the current actual value in the current intermittent region in which the load current becomes intermittent. In the current intermittent region, the sum of the firing angle instruction from the current control circuit and the correction angle instruction is used to determine the firing phase of the power converter and thereby to compensate for nonlinear response. The nonlinear compensation in the current intermittent region is made only in the transient state when the difference between the current target value and the current actual value exceeds a preset value.

Abstract: Several static frequency changers and control units for controlling the voltage supply of D.C. motors are combined in one equipment, functions common to all frequency changers being contained in a central unit.

Abstract: A method of digital control of m-phase thyristor-pulse converters, in which the duration of the conductive state of the thyristors of each phase of an m-phase thyristor-pulse converter is changed by sending time-shifted and time-constant pulse trains successively from each control channel to the thyristors of respective phases with simultaneous shift of the onset of operation of the thyristors of each phase by (1/m) period of switching the thyristors. Successive connection of each control channel to a respective phase is effected upon achieving the maximum value of the control zone of each control channel. The apparatus for carrying out the proposed method includes a master oscillator connected to a clock counter whose outputs are connected to the inputs of a decoder for decoding the time-constant pulse trains and to the logic inputs of "m" decoders for decoding the time-shifted pulse trains.

Abstract: In a power converter system wherein each thyristor of a three-phase full-wave bridge circuit having thyristors connected in all of bridge arms is fired for its controlling to thereby control the dc output voltage, when the dc output voltage is low, the firing angle of a group of thyristors on the negative side is fixed to a large value and the firing angle of a group of thyristors on the positive side is rendered variable within a small range so that a period may occur through which two thyristors connected in series in the full-wave bridge circuit are fired simultaneously. When the dc output voltage is high, the firing angles of groups of thyristors on both the positive and negative sides are made equal to each other and varied simultaneously. The system improves power factor and form factor over the entire controlling range of the dc output voltage.

Abstract: A power supply unit for a plasma plant, in particular for a plasma spraying plant, comprises an isolating transformer for connection to three-phase mains, a current control array and a rectifier array. The rectifier array comprises silicon wafer thyristors in a three-phase bridge configuration, which thyristors are electronically controlled through a current control loop, and an exterior voltage control loop is provided for additional electronic control of the silicon wafer thyristors.In the output from the thyristor array, a filter with a transient voltage suppressor may be provided as high-frequency protection and with di/dt limitation.

Abstract: In association with a polyphase rectifying bridge having controlled rectifiers there is employed, in addition to the normal means for controlling the firing time of the controlled rectifiers, additional circuitry for preventing the occurrence of a commutation fault. This is achieved by first producing a timing signal representative of the time intervals during which a commutation between successively fired controlled rectifiers of the bridge actually exist. This timing signal, after being properly shaped is combined with a basic reference signal representative of a predetermined value to which the rectifiers may be phased back in their firing angle without resulting in a commutation failure. Stated in another way, the width of the existing commutation period serves to set a minimum to which the next commutation period must conform.