Abstract: In a motor control apparatus arranged to drive a motor by rectifying a.c. voltage and smoothing a rectified voltage by a capacitor, a voltage across the capacitor is detected to see if the voltage is below a reference voltage or not by a first comparator (24), and if so, an output voltage (V) is produced. This output voltage (V) is used to change another reference voltage of another comparator (21) used for detecting if current to the motor (5) or a motor drive circuit (4) is greater than the reference. When the current is larger than the reference, the comparator (21) produces a low level output causing a control circuit (23) to control the drive circuit (4) to reduce the current to motor (5).

Abstract: The drive system of an induction motor wherein the exciting current command value I.sub.o of the induction motor (14) is held constant and the rotational speed thereof is caused to quickly respond to a command speed by the vector control circuit the induction motor (104) has exceeded a predetermined speed, an exciting current amplitude-controlling circuit (51) increases the exciting current command value in accordance with the rotational speed. The level of the driving supply voltage of the induction motor is sensed by a supply voltage output circuit (52), whereupon the exciting current amplitude-controlling circuit (51) is controlled so that the predetermined speed serving as a threshold value for changing the exciting current command value may be increased in accordance with the sensed level.

Abstract: A power converter for driving an AC motor includes a main circuit and a control circuit such that: the main circuit includes a forward conversion circuit that forwardly converts AC power from an input AC power source into DC power, and an inverter circuit that inversely converts the thus forwardly converted and smoothed DC power into AC power of a specified voltage and frequency; the control circuit includes a calculation device that calculates a torque current component of the AC motor, a detection device that detects occurrence of an instantaneous interruption in the AC power source, a command device that commands a frequency to be fed into the AC motor, a control device that receives a signal relative to an output signal of the command device so as to control a terminal voltage of the AC motor, and a compensation device that adjusts the output signal of the command device so that the output signal of the calculation device is caused to be substantialloy zero in response to the output signal of the detectio

Abstract: In an induction motor drive a signal representative of the torque T as derived by sensing only the stator armature current I, and the slip frequency f.sub.2 and by calculating instantaneously T=I.sub.1.sup.2 F, where F is a function of f.sub.2 /R.sub.2, where R.sub.2 is the rotor resistance of the motor. The value of R.sub.2 is adjusted to match temperature by generally two alternative methods: (1) measuring the stator temperature, relying on the change of resistance R.sub.1, known experimentally, and applying an equivalent change for the rotor resistance R.sub.2 ; (2) by running the motor at rated speed and determining experimentally R.sub.2 /f.sub.2 as a function of F.

Abstract: A drive circuit for a three-phase induction motor comprises an inverter bridge consisting of six bridge switches, and a logic speed controller which controls switching of the inverter bridge in dependence on the motor current as sensed by a total current sense resistor. The speed controller is arranged to switch the bridge switches so as to supply alternating current to each phase of the motor at a fundamental frequency which may be varied in accordacne with the required motor speed. However, additionally, at least during low speed operation, the speed controller switches at least three of the bridge switches at high frequency during each cycle of the fundamental frequency switching. In this case the switching points are not predetermined but rather occur when the current as sensed by the resistor reaches a preset limit for switch turn-off and when the current falls to a specified point for turn-on. Such a circuit can be realized simply and enables the motor to be driven at a range of speeds.

Abstract: An air conditioner having a heat exchange cycle which includes at least a compressor motor that is driven by an inverting apparatus at a variable speed, an indoor heat exchanger and an outdoor heat exchanger is provided.

Abstract: In a controller for an AC elevator in which the frequency of AC power applied to a driving induction motor is varied by a frequency converter, the output frequency of the frequency converter when the elevator is running at its rated speed is at least as high as the frequency of the AC supply, and the AC supply is applied directly onto the induction motor without any frequency conversion during low-speed running, so that the elevator can be run slowly without using the frequency converter.

Abstract: A control circuit is connected between a three-phase power supply and a motor and ensures the correct application of phase signals to the motor, regardless of the way in which the control circuit is connected to the power supply. A first output signal of the supply is connected directly to an input of the motor via the circuit. Supply of power to the other two inputs is controlled by four switches, two of which receive signals from the second supply output and have their outputs connected to respective motor inputs, and the other two of which receive signals from the third supply output and have their outputs connected to respective motor inputs. The switches are controlled such that two switches are on, and the other two switches are off if the third output signal is positive with respect to the first output signal when the second signal passes through zero with respect to the first signal in a positive sense.

Abstract: A system consisting of a motor that drives a load, an analog signal generator that outputs an analog signal which increases as the motor is accelerated, a speed commander that determines a motor speed and commands the motor to operate at the determined speed, and an energizing circuit that receives signal representing difference between the output from the speed commander and the output from the analog signal generator and that energizes the motor so as to operate at the speed in accordance with the signal for the difference is provided with a pulse generator that outputs a pulse corresponding to the current motor speed and with a control circuit that controls the signal for the difference in such way that when the motor is operated at a low speed at which the interval of pulses output from the pulse generator becomes long the signals for the difference issued during a pulse interval sequentially increase.

Abstract: A load-commutated inverter for operating a synchronous motor having two sets of 3-phase windings. The difference of phase angles between the two sets of the 3-phase windings is 30 degrees. The load-commutated inverter is provided with two sets of inverters and a control circuit. Each of the inverters, is formed of thyristors. The inverters are coupled respectively to the 3-phase windings of the motor. The commutation of each of the thyristors is controlled in accordance with a given advanced control angle. The control circuit is coupled to the inverters and is responsive to a commutation overlapping angle of currents (e.g., IU1, IV1 in FIG. 4A) supplied from the inverters to the 3-phase windings of the motor. The control circuit adjusts the given advanced control angle so as to retain a relation:u+.gamma.*.ltoreq.30 degreeswherein u denotes the commutation overlapping angle and .gamma.* corresponds to the reverse-biasing time applied to each of the thyristors.

Abstract: The output frequency of a variable frequency power source for driving a motor which drives a rotary body such as a fan in a variable-speed control mode is fixed, when abnormality in a control signal supplied to the variable frequency power source from outside to determine the output frequency of the variable frequency power source is detected, at the output frequency of the variable frequency power source immediately before the detection of abnormality in the control signal, and thereby the abnormal variation of the revolving rate of the motor resulting from the abnormality in the control signal is avoided.

Abstract: The present invention relates to a device for driving an induction motor comprising:a variable converter which converts an alternating current into a direct current;an inverter device which converts a D-C output of said variable converter into an alternating current;an induction motor driven by said inverter device;a speed detector which detects the speed of said induction motor; anda speed controller which amplifies a reference speed signal input to the inverter device and which provides as an output signal therefrom the difference between the reference speed signal and the speed of the induction motor;wherein the output of said speed controller is changed depending upon the running speed of the induction motor.

Abstract: The operation of an interior permanent magnet synchronous motor is extended to the constant horsepower regime by causing the stator current vector to follow the voltage-limit ellipse in the counter-clockwise direction. The error between commanded stator current and actual stator current is determined to signal a saturation of the inverter and the commanded stator current is modified to reduce the error.

Abstract: In order to maintain the flux in an asynchronous machine supplied by an intermediate-link converter in the event of a network disturbance, the converter is initially blocked at the beginning of the network disturbance. After the intermediate-link current has decayed, the timing of the free-running converter on the machine side and the ignition of two series-connected controlled rectifiers of the converter on the network side are effected. The flux still present in the machine induces in the stator circuit closed in this manner a machine current which is controlled by a supplemental current controller in an operation slightly on the generator side, whereby, at the expense of the kinetic energy of the synchronized machine, a current through the circuit is generated which is required for covering the dielectric losses and for maintaining the desired flux.

Abstract: A variable-frequency, variable-voltage (VVVF) converter is interposed in the line between an AC source and an asynchronous escalator motor. Current to the motor is sensed to determine load in conjunction with a passenger detector and load simulating electronic system and the frequency and voltage of the converter are automatically adjusted in response thereto to control escalator speed. The system includes a converter to supply the asynchronous drive motor of the escalator with variable frequency and an appropriate control circuit for manual or automatic operation of the escalator at different speeds, which is equivalent to different motor frequencies.

Abstract: The inverter device for performing a.c.-d.c.-a.c. conversion has a power discrimination circuit for discriminating whether a power source is of a single phase or three phases. As a result of discrimination, a suitable overload protecting circuit provided in the device is selected or a reference level for overcurrent is changed to thereby protect structural elements such as a converter, a smoothing capacitor etc. from breakage caused by overcurrent.

Abstract: A speed control apparatus for an elevator is so constructed that an operating period of time is limited on the basis of a predetermined current command value or an output from a detector for detecting current to be supplied to an induction motor, thereby to render a load time factor of the induction motor a predetermined value or less and to maintain at or below a permissible value a temperature rise value based on a quantity of heat generated by a winding of the induction motor.Thus, the induction motor is prevented from burning even when the induction motor is operated at low speed in, for example, a manual operation mode for installation, maintenance and inspection, or the like.

Abstract: In this context, a frequency converter generates a multiphase alternating current of variable frequency which current feeds an alternating-current machine via alternating-current lines into which for each alternating current phase line one commutating choke is integrated for limiting the change of current with respect to time di/dt. Since the efficiency of a synchronous motor is best when fed with a sinusoidal alternating current, a frequency-variable filter is provided as a bypass circuit to the synchronous motor which makes the alternating current sinusoidal within a predeterminable frequency range. The frequency of the alternating current is measured with a frequency meter and monitored for exceeding a limit in a frequency limit detector. The filter can be tuned step-by-step by means of switching signals to different frequencies by changing the inductance or capacitance of series-tuned circuits step-by-step. Undesirable harmonic frequencies can thus be attenuated with-in a relatively large frequency range.

Abstract: An AC motor drive includes a power converter which supplies current to a DC bus from three-phase power lines. An inverter drives the motor from power delivered to the DC bus and it regenerates power to the DC bus when the motor is decelerated. The power converter in turn regenerates the power to the power lines by controlling line current such that it is substantially in-phase with the applied line voltages. Current overload protection is provided for the transistor switches employed in the power converter bridge circuit.

Abstract: When an inverter is disconnected from a rotating motor due to power failure or motor accident, it is necessary to connect the inverter power again to the motor rotating by the inertia force in order to keep the motor rotating. To achieve the above reconnection, the inverter is controlled in accordance with the open-loop control method, without use of any motor speed detecting means, thus improving control response speed. In reconnection, the inverter is started at a frequency higher than the rotating motor speed and at a voltage lower than the rated value; only the frequency is decreased gradually but increased gradually again when the detected motor driving current reaches zero or the motor regenerated current starts flowing; and the voltage is raised when the detected motor regenerated current reaches its maximum value.

Abstract: A pulse-width-modulated motor drive includes means for the derivation of a signal representative of the torque by sensing the DC-link current directly, or indirectly, and by dividing the sensed signal by the modulation index of the motor drive to obtain proportionality through the duty-cycle long range succession.

Abstract: Programmed digital equipment is utilized to generate three-phase pulse width modulated waveforms that are used in controlling an induction motor. A microprocessor is programmed to initialize conditions in the system, to perform a main task including the storage of converted analog signal, the checking of limits of motor motion and information fed back from the motor concernings its position, and the ramping of frequencies to change the position of the motor. A memory is provided for the programming which memory also contains tables that correspond to 90.degree. of each desired wave form. A single 90.degree. segment of each wave form is needed to generate all parts of each of the three phases. An analog to digital converter is utilized to convert analog information concerning gain, set point, dead band and feedback signal into digital signals which are stored and processed by the microprocessor.

Abstract: An AC motor such as an induction motor or a synchronous motor is driven by a PWM inverter circuit. Power switching elements of the inverter circuit are ignited by PWM pulses resulting from comparison of a carrier wave signal with a sine wave modulation signal at a frequency proportional to a frequency setting signal so as to control the inverter circuit. A current polarity detector detects positive and negative components of a DC current flowing in the input side of the inverter circuit. The frequency setting signal is so corrected as to be decreased when only the positive current component flows in excess of one period of the carrier wave signal or increased when only the negative current component flows in excess of the one period.

Abstract: Disclosed is an induction motor drive apparatus which produces three-phase current commands using a speed error (ER) between a speed command and an actual speed (n) for driving an induction motor (10) on the basis of the current commands. The induction motor drive apparatus receives the speed error (ER) and the actual speed (n) as input signals and generates, through digital processing, a first phase sinusoidal signal and a second phase sinusoidal signal shifted by 2.pi./3 from the first phase sinusoidal signal. The first and second sinusoidal signals are used for generating a phase current (i.sub.w) in a first and second phase currents (i.sub.u, i.sub.v) which are in turn used to generate a third phase current (i.sub.w) such that the first, second and third phase current commands will have a sum equal to zero.

Abstract: A method and a device for controlling a brushless alternating current motor (23) driven by an inverter (31-36) connected to a direct current supply (24,25). The direct current supplied to the inverter is sensed. The signal is passed through a peak detector (41) to a regulator (45), which decreases its frequency controlling output signal if the peak value input signal exceeds a predetermined value. A control signal corresponding to the torque demand of the motor is also produced. This signal controls the voltage supplied to the motor. Negative pulses at the turning off of the inverter switches are also sensed and used for controlling the degree of magnetization of the motor.

Abstract: A method and circuit for regulating an alternate or three-phase current motor, a pulse inverter with a capacitive direct current intermediate circuit is used through which the motor is supplied with a substantially constant voltage by means of electronic switches and corresponding antiparallel recovery diodes. For this purpose, the reactive motor current is measured for utilization in the feedback control system. To this end, the feedback current from the motor inductance to the capacitor of the intermediate circuit is measured and the value obtained is used to form a control signal for regulating the reactive current.

Abstract: A variable speed drive for an AC motor has features to reduce the speed of the motor if excess temperature is encountered in the variable speed drive system. The system has a rectifier that converts AC supply voltage into DC voltage on the positive and negative rails. Frequency switches switch the DC voltage to power conductors in a sequence and at a rate to determine the selected frequency. The frequency switches are controlled by a DC demand voltage. A temperature sensor provides an electrical response corresponding to the temperature in the system. The temperature response is compared to a reference voltage, and if it exceeds the reference voltage, the comparator provides an output that draws down the demand voltage by a value corresponding to the difference. Lowering the demand voltage lowers the speed of the motor to allow the system to cool under reduced load conditions.

Abstract: The invention relates to a stabilizing circuit for an inverse rectifier motor control which includes a D.C. voltage supply having a D.C. voltage regulator followed by a smoothing intermediate circuit. A frequency control circuit converts the supply voltage from the intermediate circuit to a frequency control voltage. Following the frequency control circuit is a generator for converting the frequency control voltage to control signals for the inverse rectifier motor control.

Abstract: The current in the windings of a polyphase motor are individually sensed, and individual signals that indicate that current are provided. Using these signals, the difference between positive and negative current flow through the motor is determined, and if that difference exceeds a first level, for a preset duration of time, the motor is permitted to operate for a limited time. But, if it exceeds a second level, for a preset duration of time, the motor is slowed down in a programmed manner. Total current flow through the motor is determined from these signals as well, and if it exceeds a maximum for a preset duration of time, the motor is stopped in a programmed manner.

Abstract: The invention relates to a digital control device for an inverse rectifier having controllable switching elements for driving an A.C. motor operable at a variable frequency. The device has a pulse generator for producing timing pulses at a multiple of the frequency of the inverse rectifier frequency and a location counter 26 controlled by the timing pulses. A control store in the form of a ROM has at least two storage zones occupied by different controlling tables of which the data characterizes the periodically changing signal pattern for the ignition and extinction signals of the controlled switching elements of the inverse rectifier. A table selecting apparatus which, depending on setting and operating parameters, delivers a preparatory selecting signal for the desired control table and, after a change in this selecting signal, appropriately switches the storage zone over.

Abstract: Apparatus and method for protecting a squirrel cage induction motor against excessive temperatures which can occur in the rotor, provides a thermal model of the rotor. The thermal model has three regions A, B and C representing the starting portion of the rotor conductor, and the rotor core. The rotor is frequency sensitive and currents of higher frequency induced in the conductors tend to be in region A, and currents of lower frequency tend to be in region B. Equipment connected to the stator winding determines values for the positive and negative sequence components of the supply for the fundamental frequency and preferably also for the second and third harmonics present, and provides signals representing these values. Heat calculation circuitry receives the values for all the positive and negative sequence components and a signal representing speed, determines the currents that would be induced in regions A, B and C, and derives equivalent currents which would produce the same heat.

Abstract: A microcomputer-based motor control system provides overload protection by incrementing a register whenever a full power condition exists and decrementing the register when less than a full power condition exists. When the register reaches a predetermined value, this indicates an overload condition.

Abstract: In recent years the induction motor speed has come to be controlled by changing the frequency and voltage of the commercial power supply by means of an invertor. The frequency of the commercial power supply, however, differs from country to country and even in the same country differs from region to region. If the motor controller designed for a supply frequency of f.sub.L is operated connected to the supply having a frequency f.sub.H higher than f.sub.L, an overvoltage will result. Conversely, if the motor controller designed for a supply frequency of f.sub.H is connected to the supply with a frequency f.sub.L lower than f.sub.H, then a sufficient torque cannot be obtained. To eliminate the above drawback, the present invention detects the input frequency of the motor controller and selects or calculates control constants in accordance with the detected value so as to enable stable operation even when the input frequency changes.

Abstract: In a speed control system of a three phase induction motor, a resolver is connected to the rotor of the motor for producing a phase modulated signal Esin (.omega.t+.theta.) containing the rotational angle .theta.. This signal is converted into a speed signal K.sub.2 E(d.theta./dt) which is compared with a speed instruction signal to produce an error signal. The error signal is multiplied with the phase modulated signal and the product is rectified with three synchronous rectifier units respectively controlled by three reference signals having phase differences of 0, 2.pi./3 and 4.pi./3 for producing three phase voltages applied to the stator winding of the induction motor. The control system enables to control the speed while maintaining the slip frequency at a constant value.

Abstract: In servo-controlling a servomotor by a rotational velocity feedback loop and current feedback loop, a compensatory rotational velocity signal is produced to render the current feedback loop independent of the actual rotational velocity of the servomotor. To this end, the actual rotational velocity of the servomotor is amplified by a predetermined multiplication factor, and the resulting amplified signal is applied to a pulse width modulation signal obtained on the basis of a current difference between the actual current of the servomotor and a commanded current, which is based on a commanded velocity. The modulation signal resulting from the application of the amplified signal is applied to a current drive circuit of the servomotor.

Abstract: 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.

Abstract: A variable speed a-c drive motor is controlled by a current feedback pulse width modulation scheme which effectively isolates the controlled motor current from variations in the input d-c voltage. An additional control loop is provided to superimpose a control signal on the amplitude command input circuit of the pulse width modulation control scheme. The additional loop responds to line current and particularly line current resonance between the input d-c filter and the line inductance. Instantaneous line current is then maintained at the minimum required to support instantaneous power flow to the a-c motor so that resonance current is suppressed.

Abstract: A regenerative drive control is connectable to an AC power source and includes a negative converter bridge (10) having an input (12, 14, 16) connectable to the AC power source and an output connectable to a DC bus, including a positive bus (18) and a negative bus (20), a load (24) having inductance and resistance and operable to generate regenerative current and direct regenerative current through the negative converter bridge to the AC power source. The negative converter bridge includes a plurality of SCR's (41, 42, 43, 44, 45, 46) arranged in a plurality of series connected pairs with each series connected pair forming a leg of the converter bridge which extends between the positive and negative buses. A gating circuit (80) is provided for sequentially gating the SCR's to establish a controllable DC output on the DC bus. Sensing means (110) for generating an inhibit signal indicative of a fault is provided.

Abstract: An apparatus for driving an A.C. motor includes a circuit for computing the sum of polyphase A.C. signals used to drive a pulse-width modulation circuit for controlling an inverter, and for limiting the amplitude of a current command when said sum is other than zero. When an imbalance occurs in the polyphase A.C. signals, the current command amplitude is immediately limited in accordance with the state of the imbalance to prevent saturation of a current amplifier that is operable to produce the polyphase A.C. signals by amplifying the outputs of an arithmetic circuit. These outputs are difference currents obtained by computing the difference between polyphase command currents and corresponding ones of detected polyphase currents actually applied to the A.C. motor. Preventing saturation of the current amplifier assures that the polyphase currents actually applied to the A.C. motor will be held in a balanced state at all times.

Abstract: An AC motor control method and apparatus therefor, for controlling an AC motor 11 by holding the excitation current I.sub.0 of the AC motor 11 constant and varying primary current I.sub.1 in accordance with a speed deviation .DELTA.n. Stored previously in a memory device 18 are a torque T-slip frequency .omega..sub.s characteristic, a slip frequency .omega..sub.s -primary current vector I.sub.1 characteristic, and a slip frequency .omega..sub.s and phase .phi..sub.1 characteristic which take secondary leakage reactance into account. Slip frequency .omega..sub.s, primary current vector I.sub.1 and phase .phi..sub.1 are read out of the memory device in accordance with the torque command T obtained from the speed deviation .DELTA.n, whereby three-phase current commands i.sub.u, i.sub.v, i.sub.w are produced. Accordingly, torque irregularity is suppressed and an excellent response obtained.

Abstract: A voltage or current balancing control for supplying a balanced three-phase alternating current supply to an electrical three-phase load. Three controllable full wave semiconductor gates respectively feed one phase of a three-phase alternating current supply to the electrical load. The semiconductor gates are adapted to controllably adjust the voltage or current of a phase of the supply in accordance with a gate control signal to be applied thereto. A comparator circuit is connected to receive the three-phase alternating current supply and is adapted to compare either the voltage or current characteristics, or both (power) of each phase to determine an unbalanced condition therebetween which is analyzed by an analog or digital computer, which accordingly supplies gate control signals to the semiconductor gates respectively to independently control them in accordance with the unbalanced condition to adjust the voltage and/or current of all three phases of the supply to an equal or balanced condition.

Abstract: 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.

Abstract: A method and apparatus for controlling an induction motor, in which an AC power source is connected to the induction motor through a switch and a frequency converter, and the motor speed is controlled by controlling the output frequency and output voltage of the frequency converter. In the starting operation, the induction motor in a free-running state is supplied with an initial voltage in a given frequency which is expected to make the absolute value of the motor current minimum or near minimum, and then the supply voltage is increased gradually from the initial voltage with its frequency being retained at the given voltage. When the output frequency of the frequency converter reaches a predetermined value, the output frequency and voltage thereof are increased gradually with the ratio therebetween being maintained at a given value.

Abstract: A microcomputer for use with an induction motor drive system processes machine drive system currents, voltages and speed to compute real time machine efficiency. From real time machine efficiency determinations, the microcomputer determines the optimum combination of machine slip frequency and machine air gap flux. The magnitude and frequency of machine stator current are regulated, responsive to the difference in magnitude between optimum machine air gap flux and actual machine air gap flux, and the difference in magnitude between optimum slip frequency and actual slip frequency, respectively, to assure machine steady state operation at maximum efficiency irrespective of machine load conditions.

Abstract: 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.

Abstract: Method and apparatus for matching the power output of a high slip motor to the demand requirement of a pumpjack unit. The stators of the high slip motor are automatically connected in various different configurations to provide the optimum torque as required by the pumpjack unit due to the downhole pumping condtions. A novel control circuitry is connected between the motor starter and the motor stators. The control measures the power drawn by the stators and selects the most optimum configuration thereof for the load required by the pumpjack. This selection operates the motor in the lowest possible torque mode, which is considered the best electrical and mechanical operation of the pumpjack apparatus.

Abstract: Flux saturation in a current-excited induction motor is detected by sensing an accompanying increase in the level of the third harmonic in the waveform of the voltage across the stator windings. The level of the third harmonic relative to a fixed reference represents flux error. Nulling the flux error with a servo loop facilitates torque control by maintaining constant flux.

Abstract: Electric motor starter circuits for operating motors which cannot be restarted under load, but which maintain sufficient momentum during merely momentary interruptions of AC power to continue normal operation upon power restoration. Conventional motor starter circuits drop the motor off line, even in the event of momentary interruptions. The starters disclosed herein prevent unintended and unnecessary equipment down time as a result of AC motor starters dropping out during mere momentary power interruptions through the provision of a delayed drop out circuit including a DC voltage storage capacitor connected to the coil of the motor starter relay subsequent to the initiation of normal AC energization. In one embodiment, actual motor rotation is sensed to determine when to allow the motor starter relay to drop out.

Abstract: A motor starter, which may be microprocessor-controlled, is taught wherein a signal conditioning means is provided for receiving from the motor windings parallel inputs and motor bearings which are related to the motor winding and bearing temperatures and for operating on these parallel input signals in such a manner as to provide a single serial output signal for use by a control means to cause the motor control starting sequence or the normal motor run condition to be interrupted, for example, if any one of the temperatures is above a predetermined level.

Abstract: A current limiter for a load commutated inverter-synchronous motor drive including a source side AC to DC converter (12) and a load side DC to AC converter (14) coupled via a DC link circuit including an inductor (16) wherein a torque reference signal (TORQUE REF) generated for controlling both the converters is limited in response to the peak value .psi..sub.MAX of the pseudo flux waveform (.psi..sub.ab, .psi..sub.bc, .psi..sub.ca) which is derived from the integral (.intg.) of the motor terminal voltage (v.sub.ab, v.sub.bc, v.sub.ca) in order to limit the motor stator current I.sub.s to a value corresponding to the region of peak output torque T.sub.MAX obtainable for the motor field current I.sub.f applied. Control of both the source side converter (12) and the load side converter (14) by the torque reference signal operates to control the magnitude of the current I.sub.L in a DC link circuit which corresponds to the motor stator current I.sub.