General Electric Company

David L Lippitt

Paul M Espelage

Loren H Walker

Leland C Tupper

Allen Michael Ritter

John D D'Atre

Herbert W Weiss

Jordan Brantley Casteel

James M Nowak

B Paul Chausse

A method for supplying the excitation to a four quadrant drive DC electric motor having a forward and reverse controllable bridge rectifier power regulators for controlling the direction of motor rotation. The motor control system is capable of operating in a continuous and discontinuous current mode of operation and includes an electronic control circuit for calculating a firing angle from desired and measured system parameters.

Programmable deadband current regulator

A power conditioner having a source and load converter each using a phase-locked loop to control their respective converter firings achieves synchronization with a supply mains by determining the phase error between supply mains and motor voltages by obtaining the instantaneous difference between the output signals of the source and load phase locked loops. This phase error is passed through a simple gain and summed with a speed regulator setpoint, which now becomes an inverter frequency regulator with the nominal setpoint being the supply mains frequency. The voltage amplitude error between the supply mains and the motor is obtained by comparing the absolute value of the source voltage with the properly scaled absolute value of the integrated motor voltage and this error signal is input to the flux regulator in a synchronous or induction motor controller in place of the normal input when not synchronizing.

Control for bumpless transfer of an AC motor between a solid-state

A controlled current inverter (CCI) induction motor drive is controlled by controlling motor current and the angle between motor flux and motor current. The angle between motor flux and current is derived directly via a microcomputer phase-locked loop synchronized to the integrated motor voltage. The delay between the application of a firing signal to a thyristor and the initiation of line current is determined and compensated for to achieve the desired angle between motor flux and motor current.

Phase-locked loop control of an induction motor drive

The non-linear control characteristic of a force commutated current source inverter operating as a var generator is linearized to provide a similar dynamic response in both leading and lagging modes of operation by two inter-related control schemes. The first control scheme comprises a linear closed loop feedback which controls a thyristor firing circuit in response to a difference or error signal between a var command signal and an actual var feedback signal while the second control comprises a feed-forward non-linear network having a signal transfer function which models the non-linear control characteristic of the var generator and is operative to control the thyristor firing circuit in response to the summation of scaled values of the var command signal and the actual var feedback signal and wherein the scaled values provide a combined gain which is equal to unity.

Control for a force commutated current source var generator

A fault protective system for a load commutated inverter motor drive including an AC to DC source side converter coupled from an AC source to a DC to AC load side converter via a DC link circuit and wherein the load side converter supplies AC power of varying magnitude and frequency to the synchronous motor load. A pair of microcomputers interlinked by a common digital memory respectively control the inverters and interface with hardware type sensor means for detecting the occurrence of a plurality of different types of faults. Additionally, a number of stored instructional sets or programs are respectively included in both microcomputers to detect by software means another plurality of faults. The detection of a fault on either side of the link circuit is communicated to the respective computer which subsequently communicates with the other microcomputer to effect a coordinated protective action in response to thyristor cell failures, circuit failures, and abnormal operating conditions. Cell failure faluts include those instances where a thyristor cell actually fails due to an open or short circuit as well as those cases where a cell fails to commutate properly due to firing strategy problems. Cirucit failures include open and short circuits both in the supply line and the motor leads, while abnormal operating conditions involve such things as low line voltage or excessive motor voltage.

Coordinated load commutated inverter protection system

A load commutated inverter synchronous motor drive system wherein a thyristor firing control of the inverter is determined by the amplitude of pesudo flux waveforms which are derived from the integral of the line voltages coupling the inverter to the motor being driven. A firing strategy is provided based on the premise that optimum thyristor firing in a load commutated inverter operating at a leading power factor occurs at a point just below the peak of the forthcoming pseudo flux waveform which point comprises an amount of volt-seconds necessary to effect current commutation plus a nominal safety margin. The determination and control is implemented, preferably, in a software phase lock loop but can, when desirable, be implemented in hardware.

Flux feedback firing control for a load commutated inverter

The load side converter or inverter in a load commutated inverter motor drive, including a source side AC to DC converter coupled to a DC to AC converter via a DC link circuit, is adapted to have at least three and preferably four modes of operation for bringing an AC motor load, and more particularly a synchronous motor, up to speed. In the preferred embodiment, the first mode constitutes an idle mode wherein the converter thyristors are maintained in a non-conducting state until commanded for normal operation. The second mode constitutes an initial start-up mode which assumes no knowledge of initial rotor position of the motor and simply utilizes a fixed low frequency firing signal to sequentially gate the thyristors using forced commutation to commutate the off-going thyristor. Thirdly, a second type of forced commutation mode is next entered into where the inverter frequency is synchronized to the rotor of the motor by sensing pseudo-flux waveforms until 5% to 10% of rated motor speed is achieved whereupon a fourth mode is entered into which comprises a self-commutation mode utilizing a phase lock loop operation using pseudo-flux wave zero crossings as synchronizing signals. In the three mode embodiment, the third mode is eliminated and the second mode modified to vary the load side converter frequency on a time basis until reaching some preset value (e.g., five (5) to fifteen (15) percent of motor rated frequency) at which time transition is made to the self-commutation mode.

Transitioning between multiple modes of inverter control in a load

A control system for powering an AC load such as a polyphase synchronous motor having at least two sets of three phase (3.phi.) windings. Each three phase winding set is powered by an independently operable six pulse load commutated inverter drive including a source side converter and a load side converter coupled together by means of a DC link and wherein the source side converter and the load side converter are operated in accordance with respective current and load angle regulators which respond to torque command signals generated by speed regulators. The two motor drives operate concurrently in separate control channels which are substantially independent of one another with the exception that in one embodiment, which is the preferred embodiment, the speed regulator and the motor terminal overvoltage regulator are cross-coupled to effect a balanced torque command and motor terminal voltage from each channel while still providing for continued motor operation by one of the motor drive channels in the event that the other becomes inoperative for any reason. In a second embodiment, one of two redundant speed regulators is adapted to provide a common torque command to both channels with the other speed regulator taking over in the event of the failure of said one speed regulator.

Twelve pulse load commutated inverter drive system

A speed regulator and control system for controlling a motor from a polyphase AC source includes a data processor and a regulator and rectifier control interfacing the data processor with a controllable rectifier driving the motor is disclosed. The regulator and rectifier control, under control of the data processor, selectively transfers system parameters to the data processor, receives a calculated value proportional to firing angle from the data processor and supplies firing pulses to the rectifier to selectively connect each phase of the AC source to the motor as calculated by the data processor.

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Scotia, NY, United States of America

David L Lippitt