Abstract: In association with a polyphase hybrid 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 or at least reducing the probability of the occurrence of a commutation fault. This is achieved by first producing a timing signal which is representative of the time intervals during which a voltage exists across a load being supplied by the bridge and by then combining the timing signal with a basic reference signal representing a minimum time period during which this voltage should exist to guard against a commutation failure of the controlled rectifiers. When a prescribed relationship exists between the timing signal and the basic reference signal, the normal control means is overridden and the firing angle of the controlled rectifiers is advanced to a point which will guarantee commutation.

Abstract: A new and improved control subassembly for HVDC power converters and method of its use during transient faults affecting the A. C. system employed in the HVDC power transmission system to assure the presence of adequate firing and commutating voltages across the respective HVDC thyristor valves during selected intervals of the alternating current periods of the respective phases. The HVDC power converters used in the system include gating circuits for gating-on respective ones of the thyristor valves during selected intervals of the alternating current periods of the respective phases. The gating circuits include equidistant-spaced gate firing pulse generating circuits for supplying equidistant-spaced gating-on firing pulses to the gate drives for the respective HVDC thyristor valves of the HVDC bridge power converter during normal operation of the converter in the presence of symetrically-shaped A. C. system voltage waveforms.

Abstract: In order to monitor the conduction cutoff phase angles of a plurality of controllable rectifiers arranged in two groups in a rectifier bridge, a signal proportional to the angle for each rectifier is stored in a respective sample and hold member after each occurrence of a positive blocking voltage at that rectifier, and the minimum of the currently stored signals is observed.

Abstract: A digital firing control circuit is disclosed for controlling the generation of firing pulses for the eight controlled rectifiers (thyristors) in a bridge power converter in five distinct operating modes as well as effecting a smooth continuous transition between modes. The circuit compares and combines a plurality of locally generated time related waveforms according to a predetermined control algorithm in response to an applied analog command voltage to control the d.c. output voltage as well as providing certain protection functions such as end stops or inversion limits. The locally generated time related waveforms comprise sets of square voltage signals generated in accordance with selected cross-overs of the line voltages of the a.c. sources as well as the cross-overs of six firing reference ramp voltage signals separated from each other by 60.degree. and extending 240 electrical degrees.

Abstract: A three-phase rectifier utilizes three feedback controlled ferroresonant regulators to convert a three-phase signal into a regulated DC voltage. A monitoring circuit is included which responds to a signal loss at any input phase to actuate an alarm signal.

Abstract: A method of controlling the thyristors of an a.c. to d.c. bridge converter, having neutral connected thyristors, at relatively low power levels by gating each phase leg thyristor conductive for a predetermined minimum period within the electrical separation between adjacent line to neutral phase voltages and immediately gating the respective neutral leg thyristor conductive for the remainder of the period such that there are no intervals in the cycle when both neutral leg thyristors are in conduction. In a three phase bridge converter system, this requires at least 60 electrical degrees minimum conduction for each phase leg thyristor followed by a 60.degree. conduction of the neutral leg thyristors. In any event, the sum of the phase leg conduction and the neutral leg conductions is always equal to 120.degree. in a three phase system.

Abstract: A power conversion unit for supplying electrical power to a load from a polyphase a.c. source includes a controlled rectifier bridge connected between the source and the load. Control of the rectifiers is provided through the generation of a firing wave signal for each phase of the source which wave signals are phase displaced with respect to the phase-to-phase source voltages by a prescribed amount. Reference signals proportional to the desired output of the bridge and steering signals defining prescribed relationships between the firing wave signals are combined with the wave signals to generate signals utilized to control the conduction of the bridge rectifiers.

Abstract: A system, for supplying electrical power from a source to a load, of the type employing phase controlled rectifiers for controlling the power from a polyphase source to the load includes circuitry to detect the existence of a rectifier which is conducting at an improper time and to provide appropriate corrective action to terminate such improper conduction.

Abstract: A three phase AC to DC voltage converter includes separate single phase AC to DC converters for each phase of a three phase source with the DC voltage output of the three converters paralleled and controlled to provide necessary regulation. Each of the single phase AC to DC converters includes a full-wave bridge rectifier feeding a substantially resistive load including an inverter and a second single phase full-wave bridge rectifier. To the extent that each inverter and second single phase full-wave bridge rectifier approximate a resistive load, the source current harmonics are reduced. Additionally, the triplen harmonics produced in the three phase source lines by each of the three AC to DC converters are cancelled by the triplen harmonics produced in the three phase source lines by the remaining two AC to DC converters.

Abstract: The phase control arrangement of a valve converter according to the invention comprises a control signal former having one input connected to the valve converter and another input connected to a reference signal unit. The output pulse from the control signal former is fed, concurrently with the output signal of a sawtooth oscillator, to a zero element having its output connected, via a phase limiter, to the input of the control pulse generator. Control pulses are distributed among the converter valves by means of a pulse distributor. The sawtooth oscillator has two inputs of which one is connected to the input of the pulse distributor and the other is connected to the output of the control signal former. The arrangement provides for correspondence of performance parameters of the converter to the preset values and maximum response speed in transient conditions.

Abstract: In a high current power supply controlled by thyristors mounted in antiparallel in the primary of the power transformers, saturation of the transformers is prevented by a detection circuit responsive to an unbalance in such bilateral switch and protective action is automatically triggered. Display is provided to identify the defective bilateral switch.

Abstract: A three phase electric arc welding power supply using SCR rectifiers for output control which has improved output characteristics, fault protection and current and voltage controls. The main power transformer includes two secondaries connected in a double wye with the neutral points supplying power to one of the output terminals a pair of independent inductances are in series, one with each set of secondaries. Increased phaseback of the SCR's may be effected without the use of additional inductance in the output circuit. The fault protection circuit has a time-current trip curve closely approximating the time-current overload curve of the SCR's whereby the minimum size SCR's for a given maximum current output is obtained. The control circuit is fast responding and gives either: constant voltage output; or variable voltage, constant current output with both line voltage compensation and with increase of current when the arc is shorted and the arc voltage drops below a predetermined amount.

Abstract: A control unit for the thyristors of a cycloconverter is disclosed. The thyristors are supplied by a three phase network and the control unit is also responsive to such network. In particular, in the control unit a measuring voltage is derived from a phase voltage, and phase-shift means and smoothing means are provided to shift the phase of the measuring voltage so that its zero crossing is in the vicinity of the zero crossing of a phase voltage. The phase-shifted measuring voltage is then fed to a sawtooth integrator which generates a sawtooth voltage in dependence on the zero crossing of the applied phase-shifted measuring voltage. The sawtooth voltage is then used to generate firing commands for the thyristors.

Abstract: An over-voltage interrupt circuit is provided which senses the local output of the phase controlled regulator. A reference is generated which is utilized in a comparator as the over-voltage threshold. When the sensed regulator output is above this threshold setting an override signal is produced which overrides the condition of the on/off control. The comparator is arranged to have a lower reset threshold value than the setting threshold so that the on/off control is again switched in response to the sensed voltage dropping below the reset threshold level. If the over-voltage condition persists, the comparator continues to set and reset and, accordingly, the on/off control is continually switched off and on giving a limited average voltage output from the regulator. The on/off control operates through a walk-in circuit which controls the voltge during turn on and off to prevent over and undershoot voltage problems.

Abstract: A direct current power supply for manual arc welding having a steeply drooping, adjustable characteristic, comprising a polyphase transformer and a polyphase rectifier system including triggered rectifier means and a control system therefor providing both welding current and welding voltage feed-back. The welding current feed-back is substantially fixed. The welding voltage feed-back is adjustable for adjustment of the slope of the characteristic.