General Electric Company

General Electric Corporation Gmbh

Georges R Lezan

Loren H Walker

Fred W Kelley, Jr

Marvin W Smith

A scheme for maintaining current balance within a plurality of semiconductor devices, particularly thyristors and gate turn-off thyristors, which plurality is connected between two electrical power sources which devices are configured to be simultaneously conductive to share the current between the two sources, employs the scheme for maintaining the current within the several devices of the plurality equal. The scheme provides for the generation of individual current signals which represent the individual current magnitudes within the several devices. Further generated is an average current signal representing the average current within the plurality. A difference signal is generated with respect to each of the individual current signals which represents the difference between the average and the individual current signal. The difference signal is then employed to vary the time of application of the next control signal to the associated one of the devices to thereby minimize current imbalance within the plurality.

Method and apparatus for achieving current balance in parallel connected

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.

Method and apparatus for determining the control electrode to cathode

A scheme for determining the operational state of a control turn-off semiconductor, of the type having an anode, a cathode and control electrode to which signals are applied to control the conductive state of the semiconductor, utilizes the extant voltage at the control electrode to determine the actual conductive state of the semiconductor. A first signal representing the desired operational state of the semiconductor and a second signal representing the actual operation of the state of the semiconductor and appropriately combined in one embodiment to generate an indication of the operational state of the control turn-off semiconductor. A further embodiment, employed in a series connection of two such control turn-off semiconductors beteen dc buses, uses the second signals in a cross-coupled arrangement between the two semiconductors to inhibit the application of control signals to a first semiconductor if the second semiconductor is conductive. In a still further embodiment, the cross-coupled system just described is further combined with an anode sensing system to provide an improved, more positive system of preventing the dc short by providing the anode system sensing output system as a further input to the combination of the cross-coupled second signal and signal representing desired conduction. In an additional modification a latch function serves, in the cross-coupled embodiments, to render the cross-coupling inhibiting ineffective, once a semiconductor has been rendered conductive, for the commanded period of conduction.

Apparatus and method for failure testing of a control turn-off

A pulse shaping and amplifying circuit receives direct current electrical power from a source and serves to supply a pulse of electrical energy to a load. First and second switches (e.g., transistor switches) are interconnected such that only one is conductive at any one time. The first switch, when conductive serves to connect a capacitor which forms part of an oscillatory circuit, further including an inductor in the form of a transformer primary winding, to the source to place an electrical charge on that capacitor in a first direction. When the second switch is rendered conductive (and the first opened) the load is connected in circuit with the oscillatory circuit and the capacitor discharges to deliver a pulse of electrical power to the load with any excess power being utilized to charge the capacitor in the second direction. A flyback current path including a transformer secondary winding, closely coupled to the primary winding, and a diode is connected in parallel with the capacitor such that the capacitor again changes direction of charge to thus be charged in the direction for supplying the next pulse to the load. If desired, a second capacitor may be connected in parallel with the oscillatory circuit to improve the rise time of the pulse supplied to the load.

Pulse shaping and amplifying circuit

An overvoltage protection circuit for a circuit array including one or more semiconductor devices such as thyristors derives its energization solely from the voltage across the array. A unidirectional current is developed to respond to that voltage and this current is utilized to develop an electrical charge of not more than a predetermined magnitude. The unidirectional current is also utilized to develop a signal which is proportional to the voltage across the array. When this signal reaches a predetermined level, indicative of an overvoltage condition of the array, a switching current is rendered operative to cause the stored charge to be applied to the gating electrodes of the array semiconductor devices to thereby render each such device conductive.

Overvoltage protection circuit

A voltage regulating or control system employing a triac for controlling the power supplied to a load from an alternating current (a.c.) voltage source uses an oscillator as a phase controller to initiate a first switching pulse in each half-cycle of the voltage source. A feedback loop responsive to the first pulse in each half-cycle acts to increase the output frequency of the oscillator to thereby provide pulse train firing of the triac. An additional circuit acts to define a 'window' which serves to establish a period within each half-cycle of the a.c. source during which the delivery of switching of pulses is prohibited.

Voltage regulating system

A semiconductor valve type converter for supplying single phase load current at power frequency from an N phase polyphase power system without unbalance of polyphase current or voltage comprises a transformer having KN secondary phase voltages displaced by 180/KN electrical degress (where K is an integer) and a bridge type thyristor network for connecting each secondary phase voltage source alternately to positive and negative network buses. The network buses are connected through a centertapped reactor with the single phase load connected between the reactor tap and the secondary phase voltage sources. A commutating circuit effectively connected across the last thyristor to fire during each positive and negative half cycle of single phase output voltage may be provided if necessary to effect the network reversal of single phase current at each half cycle of power frequency.

Phase converter

In an alternating current electric power system subject to rapid load voltage regulation as a result of variations in reactive load current, reactive load current compensation is provided by fixed capacitors and inductors in parallel with the load, the inductors being in series with static switches which are phase controlled to continuously maintain the net reactive compensating current substantially equal and opposite to the reactive component of load current. Compensation control determines firing time of the static switches in accordance with the magnitude of reactive load current and regulating means additionally controls firing time to maintain line current and voltage at a selected line location substantially in phase coincidence.

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Roanoke, VA, United States of America

Georges R Lezan