General Electric Company

Electric Power Research Institute Incorporated

Loren H Walker

John H Cutler

Paul M Espelage

John D D'Atre

Georges R Lezan

Herbert W Weiss

David L Lippitt

James W Sember

William P Kornrumpf

Armand P Ferro

Fred Henry Boettner

John P Walden

Leland C Tupper

Robert Louis Steigerwald

Einar Vaughn Larsen

John Norton Park

John D Harnden, Jr

Thomas E Anderson

Russell E Tompkins

Ole N Ibsen

Murray A Eitzmann

William D Brackman, Jr

Willard B Jarvinen

Marvin W Smith

Russel G Shiflett

William G Wright, Deceased

Roy A Carter

A metal oxide varistor in series with a semiconductor switch forms a protection circuit that reduces the steady-state voltage across the metal oxide varistor during normal operation, During an overvoltage transient condition, the semiconductor switch is gated on and the metal oxide varistor is placed in the voltage clamping mode.

Switched MOV device

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

A power conversion scheme for transferring power between a DC current source and an AC voltage source employs a polyphase bridge and a thyristor to short circuit the DC current source to interrupt AC current. Comutation of the thyristor is achieved by scheduling firing switch devices of the bridge as a function of phase voltages of the AC voltage source.

Power conversion scheme employing shorting means to control current

A power conversion scheme employing a group of parallel connected, individually controlled converter circuits each providing output currents employs a scheme of distributed notches in the output currents to facilitate connection between common DC current and AC voltage sources. By the parallel connection of a pair of groups, time phase displaced group to group, additional power capability and harmonic reduction is achieved.

Power conversion scheme employing paralleled units

A power switching system for controlling the conductivity of a plurality of thyristors of the gate turn-off type (GTOs) which are connected in parallel between two power sources by gradually introducing a time compensation to force the times of turn-off of each of the thyristors toward matched values by determining the turn-off time during each conduction cycle and thereafter advancing or retarding the turn-off signal for the following conduction cycle to correct for the difference in turn-off times. A difference signal is generated between time of turn-off of an average current of the thyristors and the time of turn-off of an individual current in one of the thyristors from which a time advance or delay signal is added to the thyristor turn-off signal in response to the current flowing in a capacitor type integrator. This allows the turn-off times to reach a perfect match during periods in which the current is the same for several cycles.

Method and apparatus for matching turn-off times of parallel connected

An electrical power converter including both DC and AC power terminals which are respectively connected to a DC current source and an AC voltage source, the latter comprising the grid of an AC power utility. A capacitor is coupled to the AC terminals along with a load. A control and gating circuit is coupled to the converter for supplying control signals for the thyristors of a converter bridge included in the polyphase converter. When disconnected from the utility grid, a relatively fast acting control loop is coupled to the control and gating circuit and is responsive to the current flowing in the capacitor and an AC reference voltage to accommodate the current source characteristics of the converter for maintaining an output voltage of substantially constant amplitude across the AC terminals. A second and relatively slower acting control loop is also coupled to the control and gating circuit via the fast acting control loop and is responsive to the AC voltage across the capacitor and the load for providing regulation of the voltage across the AC terminals during steady state operation.

Control system for a current source converter supplying an AC bus

Apparatus controls a power converter 34 to interchange power between first and second electric sources, 30 and 32. Typically the first source 30 is a standard utility bus and the second source 32 is a storage battery. A controller generates control signals in response to the utility bus voltage, to a command specifying the required power interchange and to a feedback signal indicative of the actual power being interchanged. These signals control the power converter 34 to produce the required power interchange.

Method and apparatus for controlling a power converter

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 method of developing a signal representative of the instantaneous frequency of an alternating current signal encompasses first determining the apparent frequency of the signal at the ends of sampling periods (e.g., half cycles). From successively derived apparent frequencies the rate of change in frequency is calculated. The actual frequency signal is then generated as a function of the apparent frequency and the rate of change. In a specific implementation, the method is employed to develop a signal representative of the rotational speed of a motor.

Frequency measurement system

A system for controlling the operation of an alternating current induction motor having windings supplied by electrical power from the polyphase alternating current source includes a load commutated inverter circuit which is connected between the power source and the induction motor for furnishing electrical power to the motor. Controllers responsive to a command signal and a feedback signal indicative of motor operating parameters control the operation of said load commutated inverter circuit. There is further provided a fixed capacitor circuit connected between the windings of the motor for supplying reactive volt amperes (VARs) to said load commutated inverter circuit and said motor. Finally, there is provided a variable VAR generator connected between the motor windings for supplying VARs to said load commutated inverter circuit and said motor in response to the output of a third feedback control path which is also responsive to a command signal and prescribed operating parameter(s) of said load and/or said commutated inverter.

Flux control for induction motor drive using load commutated inverter

An alternating current motor drive in which the motor is furnished with electrical excitation from an alternating current source through a controllable power converter also includes first and second capacitor circuits connected to the common point between the converter and the motor. The first capacitor circuit is connected to the common point through an isolating inductor circuit. The second capacitor circuit is connected to the common point via the parallel combination of an inductor circuit and a resistor circuit. A further embodiment includes a variable VAR generator connected to the junction of the second capacitor circuit and the parallel combination of the inductor and resistor circuits.

Alternating current motor drive having current filter

Improved control of a var generator of the static type using thyristors wherein control is accomplished by generating a capacitance command representing the value of an equivalent capacitor, as opposed to a current command or a var command. The gating times or angles of the thyristors are determined by the capacitance command acting through an intermediate control which may be an open-loop feed-forward control or a closed loop feedback control operating in response to the difference between the capacitance command and a capacitance feedback, or a combination of both these types of control. The effect of the capacitance control is to provide an improved response of the var generator for changes in source voltage or frequency. The capacitance control also provides an improved linearity of control.

Capacitance control for a static var generator

A system for controlling the operation of an alternating current induction motor having windings supplied by electrical power from the polyphase alternating current source includes a load commutated inverter circuit which is connected between the power source and the induction motor for furnishing electrical power to the motor. Controllers responsive to a command signal and a feedback signal indicative of motor operating parameters control the operation of said load commutated inverter circuit. There is further provided a fixed capacitor circuit connected between the windings of the motor for supplying reactive volt ampheres (VARs) to said load commutated inverter circuit and said motor. Finally, there is provided a variable VAR generator connected between the motor windings for supplying VARs to said load commutated inverter circuit and said motor in response to the output of a third feedback control path which is also responsive to a command signal and prescribed operating parameter(s) of said load and/or said commutated inverter.

Growing community of inventors

Salem, VA, United States of America

Loren H Walker