General Electric Company

John H Cutler

Loren H Walker

John D D'Atre

Paul M Espelage

Fred Henry Boettner

Willard B Jarvinen

Loyal N Stallard

Each of the three phase power source voltages coupled to a three phase (3.0.) thyristor power converter are respectively half-wave rectified to provide both positive and negative voltages. Signals representing the largest positive rectified voltage and the smallest positive rectified voltage are developed as are signals representing the largest negative rectified voltage and the smallest negative rectified voltage. Using signals from both the positive and negative rectified voltages, at least one comparison is made to determine a difference which, when in excess of a predetermined limit, effects a logic signal to provide an indication that an asymmetrical fault exists either phase to neutral or phase to phase across the power converter and the power lines connecting the converter to a polyphase alternating current (AC) source. Following a suitable delay, protective action is initiated, which action comprises either phasing back of gating to the converter thyristors and/or tripping of a circuit breaker or contactor which operates to interrupt the supply of AC power to the converter.

Method and apparatus for the protection of a thyristor power conversion

A scheme for determining the stator resistance of an alternating current motor includes the determination of the actual flux of the motor through the sensing of motor voltage and motor current. The motor current is also utilized to develop a signal representing the anticipated motor flux which will result from that current. These two flux signals are combined to develop a flux error signal, the polarity of which is determined by whether the motor is in the motoring or regenerative mode of operation, which in turn is integrated to give the signal representing the motor stator resistance. Additionally, when the motor changes mode of operation, there is provided a step function which assures a motor stator resistance value being used which insures control stability.

Method and apparatus for determining the resistance of an AC motor stator

A system, for use with a controlled current inverter to prevent malfunction of inverter action resulting from an insufficient capacitor voltage to effect commutation of an inverter bridge controlled rectifier, provides that the capacitor voltage is sensed and, if it is of insufficient value to effect rectifier commutation, the application of gating signals to the next to be rendered conductive controlled rectifier is inhibited. In order to achieve initial inverter operation, the inverter current is also sensed and the inhibit function is rendered ineffective until such time as the current reaches a predetermined value.

Commutation failure correction scheme for a controlled current inverter

A twelve-pulse control current inverter system having two six-pulse powered channels connected to a source of variable dc current is selectively operable to control either a three-phase motor or a double three-phase motor. Signals representing the phase currents of each of the two channels are combined with direct and quadrature motor flux signals, the latter signals being shifted in phase in the case of the double three-phase motor, to produce torque signals representing the motor torque produced by each of the two powered channels. These two torque signals are then combined to provide a total torque signal which, in turn, is utilized in the development of an angle signal for the control of the two current inverters.

Twelve-pulse operation of a controlled current inverter motor drive

A controlled current inverter system forms the basis of an AC motor drive system for furnishing a motor load 22 with a variable frequency, variable magnitude AC current from a thyristor controlled DC to AC inverter 16 which is supplied current from a thyristor controlled AC to DC converter 10 by way of a DC link including an inductor 14. The frequency of the inverter is controlled by means of a control circuit including a voltage controlled oscillator 18. In the event that the converter 10 operates in such manner as to place a short circuit across the DC link 14 during a regenerative mode of operation of the motor 22, apparatus 36 is shown and described and a method is disclosed for providing a momentary advance gating of the inverter 16 which causes the motor 22 to shift from the existing regenerative mode toward a motoring mode and thereby quench any build-up of excessive converter-inverter circulating currents.

Protective method and apparatus for a controlled current inverter and

A detection system for detecting unintentional impedances between the power conductors and a first node of either a power conversion circuit or a load, the first node typically being an earth ground. The circuit has power level lines utilizing a wye-connected line filter network which has equal impedance values for each leg of the line filter and which defines a first node at the common connection thereof. A different impedance network is also connected in wye-fashion to the power level lines and defines a second node at the common connection thereof. Each impedance leg of the impedance network is also equal in impedance value whereby the second node normally has the same potential as the first node. The potential difference between the first and second nodes is frequency compensated to produce a system output signal indicative of a predetermined value of current in unintentional impedance between any of the power conductors and the first node.

Unintentional impedance detection system

A controlled current inverter system forms the basis of an AC motor drive system for furnishing the motor load 18 with a variable frequency, variable magnitude AC current from an inverter 14 which is supplied from a variable DC current source such as a converter 12 by way of a DC link including an inductor 17. Motor speed and torque are controlled through the control of motor current I.sub.M and angle .theta., which is the angle formed between vectors designating motor current and flux through first and second control signal channels 39 and 59 coupled to the DC source 12 and the inverter 14, respectively. A control function of this angle, defined in terms of both method and apparatus, is implemented by means 61 and 63 which limits this angle to predetermined values for relatively low levels of motor current, for example, values of current corresponding to the current required for maintaining a minimum amount of motor flux. Thus, if actual motor current becomes lower than the anticipated motor current, the angle .theta. will be limited in a manner which maintains a minimum motor flux.

Controlled current inverter with angle command limit

Apparatus and method for high slip operation of an AC electric motor at substantially zero rotation and substantially zero torque in an AC electric motor drive system is disclosed. The electric motor produces a rotation in response to an outgoing signal, such as a drive current, of variable magnitude and frequency supplied by the drive system. An idle control signal is furnished when the drive system is in a substantially zero rotation and substantially zero torque state, where the frequency of the current is approximately zero. The idle control signal causes substantially simultaneously an adjustment of the magnitude of the current to a predetermined magnitude level and a rapid raising of the frequency of the current to a higher frequency value to produce per-unit slip s=(n.sub.1 -n)/n.sub.b greater than 0.1, where n.sub.1 is the synchronous rotation of the stator field of the motor, n is the rotation of the rotor of the motor, and n.sub.b is the synchronous speed of the stator field at motor rated rpm. The adjustment in the magnitude and the rapid increase in the frequency of the current causes the motor to produce substantially zero rotation and substantially zero torque because the motor is operating in the high slip region of its torque-rotation curve. The apparatus and method of the present invention allows the motor to accelerate rapidly on command from the substantially zero rotation and substantially zero torque high slip mode.

Apparatus and method for high slip operation of an AC electric motor at

A fixed gating sequence apparatus and method for an inverter is disclosed. In one aspect of the invention, an outgoing signal of variable frequency is generated by the inverter in response to gating signals provided by an inverter control. The gating signals effectively are provided by a shift register of an inverter control to the gates of the conduction controlled rectifying devices in the inverter in response to a clocking signal. The clocking signal is provided to the clock input of the shift register at a normal system rate when an idle condition (idle control signal) is not present and at a predetermined cycling rate from when the idle condition occurs until a desired fixed gating pattern effectively is provided by the shift register to the inverter. The shift register remains at the stage providing the desired fixed gating pattern until the idle condition no longer is present, whereupon the normal clocking signals are again provided to the shift register. In another aspect, the gating signals, which effectively are normally supplied to the conduction controlled rectifying devices of the inverter, are blocked or inhibited from when the idle condition occurs until the desired fixed gating pattern is provided by the shift register of the control stage of the inverter. Thus, in this aspect, the inverter does not produce a moderate frequency burst of outgoing signal when the shift register cycles through and stops at the desired fixed gating pattern.

Fixed gating sequence apparatus and method for an inverter

A controlled current inverter motor control system including a controlled source of direct current for supplying a variable frequency inverter by way of a direct current link circuit which includes, within the link circuit, a selectively insertable dynamic braking resistive element. Upon a call for a dynamic braking mode of operation, the source of direct current is short circuited and the normal operational or running control of the motor is discontinued. Special circuitry is provided which then forces a special frequency control of the inverter to thus control the angle between the motor flux and motor current to a prescribed value proportional to the extant value of a motor operating parameter (motor current or motor flux) prior to the insertion of the dynamic braking resistive element into the link circuit.

Method and apparatus for dynamic braking in a motor control system

A substantially zero rotation and substantially zero torque detector and method for an AC electric motor drive system includes an AC electric motor producing a rotation in response to an outgoing signal, e.g., drive current, of variable magnitude and frequency. An actual rotation signal is generated and is proportional to the rotation of the AC electric motor or to the frequency of the outgoing signal. A rotation reference signal proportional to a desired level of rotation is established. A rotation difference signal representative of any difference between the rotation reference signal and the actual rotational signal is generated. A torque command signal is provided as a function of the rotation difference signal and is used to produce a frequency control signal and a current control signal. Alternatively, the torque command signal is generated proportional to a desired level of torque when the drive system utilizes a desired torque level as opposed to a desired rotation level. The outgoing signal, for example, the drive current, is supplied to the motor at a frequency controlled in response to the frequency control signal and at a magnitude varied in accordance with the current control signal. In the case of a drive system utilizing a desired level of rotation, the substantially zero rotation and substantially zero torque detector and method furnishes an idle control signal when the torque command signal and at least two of the rotation reference signal, the actual rotation signal, and the rotation difference signal are less than respective predetermined values. Alternatively, in the case of a drive system utilizing a desired level of torque, the substantially zero rotation and substantially zero torque detector and method furnishes an idle control signal when the actual rotation signal and the torque reference signal are less than respective predetermined values. In either case, the idle control signal is effective to control an operation parameter or function of the drive system and indicates when the drive system is in the substantially zero rotation and substantially zero torque mode.

Zero rotation and zero torque detector and method for an AC electric

Disclosed is an AC motor drive system having a variable frequency, variable magnitude AC current supplied from a controlled inverter coupled to a variable DC current source in the form of a converter by way of a DC link including an inductor. The AC motor load is controlled so as to have dual modes of operation in order to optimize torque at any speed which can be produced within the voltage and current limitations of the variable frequency power source. The first mode comprises a constant slip or constant angle mode for operating speeds up to the corner point speed which is defined as the speed at which the motor voltage at full torque matches the maximum voltage the variable frequency inverter coupled thereto can provide. Thereafter, the system enters the second mode by automatically shifting to a constant horsepower variable slip or changing angle mode for operating speeds beyond the corner point speed.

Dual mode AC motor drive system

An apparatus and method for providing signals indicative of the magnitude and angular position of the DC motor flux of an AC induction motor is disclosed. The AC induction motor provides controllable rotation and torque in accordance with a drive current of variable magnitude and frequency. A first signal is provided proportional to the rate of change of the flux of the motor. A second signal is supplied proportional to the magnitude of the drive current. A flux signal is generated proportional to the integral of the first signal when the frequency of the output signal is above a preselected value and which is proportional to the second signal when the frequency of the output signal is below the preselected value. A representative value for the preselected frequency value is 3 Hertz in a 60 Hertz drive system. The flux signal is effective to control the generation of the drive current. An embodiment of the present invention is shown for the case where the motor is stopped at a predetermined position in accordance with a predetermined conduction state of the inverting supplying the drive current. Additional embodiments are shown for the general cases where the motor can be stopped at any position and where two flux axes or three flux axes are sensed. The present invention is particularly applicable for use in an AC induction motor drive system.

Apparatus and method for providing a signal proportional to flux in an

Disclosed is a three phase AC motor drive system wherein a variable frequency variable magnitude AC current is fed to an AC motor load from a thyristor controlled DC to AC inverter which is supplied from a thyristor controlled AC to DC converter by way of a DC link including an inductor. The DC load current is commanded to rise at a rate limited by the difference between the output voltage of the converter and the input voltage to the inverter which voltage appears across the inductor. As a result of the inherent commutation transport lag encountered for commands in the negative direction, an error signal clamp is placed in a feedback signal path controlling the AC to DC converter for limiting the command for changes in the positive direction thereby providing a system response in the positive direction which is more nearly like the response in the negative direction.

AC Motor drive system having clamped command error signal

An inverter system including a controlled direct current (d.c.) power source for providing a variable d.c. voltage to a variable output frequency inverter circuit by way of a suitable d.c. link, includes suitable circuitry for detecting a commutation fault or shoot-through condition within the inverter circuit and for taking appropriate remedial action to correct such condition. The shoot-through condition is determined as a function of the d.c. input current to the inverter circuit, the output alternating current (a.c.) of the inverter circuit and the extant condition of the load. In the particular embodiment of the invention illustrated, the load is an a.c. motor and the load condition sensed is whether the motor is in the running or idle mode of operation.

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Roanoke, VA, United States of America

John H Cutler