Abstract: This disclosure describes circuits and techniques for identifying potential problems with control signals for power switches. More specifically, this disclosure describes the use of registers, e.g., volatile or non-volatile storage elements, configured to count the rising and/or falling edges of pulse modulation (PM) signals within driver circuits or other control circuits. By counting the edges of PM signals within driver circuits, signaling problems can be identified based on mismatch between different counters. The techniques may be used by a driver circuit to detect circuit problems, or readout of the registers can be done after device failure, in order to help identify whether signaling problems may have caused the device failure.

Abstract: A control module comprises software instructions for execution by an electronic data processor. An inductance estimator is configured to estimate direct inductance and quadrature inductance associated with the electric machine based on a first set of equations that assume constant rotor resistance and constant magnetic flux. A torque estimator is configured to estimate an observed torque associated with a rotor of the electric machine based a commanded direct-axis voltage and a commanded quadrature-axis voltage, where the observed torque is proportional to the observed power consumption of the electric machine. A pulse-width-modulation (PWM) module is configured to provide pulse-width modulated signals to the electric machine based on the commanded direct-axis voltage and a commanded quadrature-axis voltage. A back-electromotive force adjustment is derived from an estimated, observed torque and a commanded torque.

Abstract: Method and system for protecting induction motors from stalled start conditions provide a motor overload protection device that includes a stalled start detector capable of differentiating long start from stalled start conditions. This helps the motor overload protection device identify a stalled start condition right away and trip immediately rather than allowing the motor to continue drawing locked rotor current for the duration of the startup interval. Such a motor overload protection device may be used with any suitable multiphase induction motors, including two-phase motors, three phase motors, and the like. And because only the motor phase currents are used to detect the stalled start condition, the motor overload protection device disclosed herein does not require voltage phase shift information and/or motor speed measurements, thereby simplifying overall management of the motor.

Abstract: A method is provided for controlling a gaseous component concentration of a gaseous mixture, which is recirculated by a ventilator in an oven, which is supplied with power at a predetermined mains frequency and voltage, the ventilator being driven by an asynchronous electric motor of known synchronism speed, the mixture being subjected to a known pressure. The method includes: detecting the temperature of the mixture in the cooking chamber, varying the motor's power supply voltage in order to maintain the motor's rotation speed at a predetermined value, measuring the difference between the mains voltage that supplies the motor and the motor's power supply voltage at the predetermined speed, using the voltage difference, the temperature and the known pressure to determine the component concentration in the mixture, comparing the component concentration which is found with a desired concentration value and, adjusting the component concentration in the cooking chamber.

Abstract: A lower limit value setting unit (52) variably sets a lower limit value (Vth) of a target voltage (Vh*) in a range of a voltage that is higher than the maximum value of voltages (Vb1, Vb2) of power storage devices and is not affected by a dead time provided for converters, based on temperatures (Tb1, Tb2) and required electric powers (Pb1*, Pb2*). A maximum value selection unit (53) sets the maximum value among the voltages (Vb1, Vb2) of the power storage devices and required voltages (Vm1*, Vm2*) of motor-generators, as the target voltage. A target voltage limiting unit (54) compares the target voltage with the lower limit value (Vth), and if the target voltage is lower than the lower limit value (Vth), the target voltage limiting unit (54) sets the lower limit value (Vth) as the target voltage (Vh*).

Abstract: The present invention relates generally to systems and methods for detecting ground faults (i.e., line-to-ground faults) in motor drive systems. In particular, the embodiments described herein include a common mode choke of a motor drive system having additional (i.e., secondary) turns wound around a core of the common mode choke. These secondary turns are in addition to and separate from a plurality of sets of primary turns wound around the core of the common mode choke, each set of primary turns corresponding to a phase of AC power to which the common mode choke is directly coupled. The secondary turns terminate in series with a burden resistor. Ground faults may be detected by monitoring the voltage across the burden resistor.

Abstract: A power conversion apparatus includes: a line breaker that is connected in series to a direct-current power supply; a first capacitor that is connected in parallel to the direct-current power supply through the line breaker; a discharge circuit that includes a resistor and a first switching circuit connected in series and is connected in parallel to the first capacitor; a power converter for driving a synchronous machine; a second capacitor that is connected in parallel to a direct-current side of the power converter; a second switching circuit that is connected in series between the first capacitor and the second capacitor; and a control circuit for controlling the discharge circuit. The control circuit controls the discharge circuit on the basis of the voltage of the first capacitor and the voltage of the second capacitor.

Abstract: A feedback system for controlling a servo motor comprising at least one rotary angle sensor and at least one rotary speed sensor, wherein the rotary angle sensor supplies a measured rotary angle value to a computer, wherein the rotary speed sensor supplies a measured rotary speed value to the computer, the actual rotary speed values are the measured rotary angle values interpolated according to the integrated measured rotary speed values, and wherein at high rotary speeds, the actual rotary speed values are the calibrated measured rotary angle values, differentiated with respect to time, and at low rotary speeds, the actual rotary speed values are the measured rotary speed values.

Abstract: For the present invention, under various running speeds statuses, the voltage supplied to the DC brushless motor is relatively increased or decreased on the basis of the internal setting of the motor drive control device according to the increased or decreased rotational output speed, so as to prevent the shortcoming of too much variation of the input impedance caused by the inductive reactance of the winding accordingly changed when the speed of the DC brushless motor is changed, specifically, to prevent the shortcoming of unable producing required torque resulting from the increased inductive reactance caused by increasing the rotational speed which makes the current value become too low when input by the original working voltage.

Abstract: An active reactive induction motor is provided. The motor comprises two sets of three-phase windings. One set of windings carries the active power and is called the power windings. The second set of windings carries the reactive power and is called the flux windings. The power windings carrying the active power provides more power to the induction motor than the flux windings carrying the reactive power. A driver circuit for driving the active reactive induction motor and the corresponding modes of operation is also provided.

Abstract: Power electronics equipment includes air-cored insulating transformers inserted between a control circuit grounded to a vehicle body and an upper arm biased at a high voltage, and air-cored insulating transformers between the control circuit grounded to the vehicle body and the lower arm biased at a high voltage. Each of the air-cored insulating transformers includes a primary winding and a secondary facing to each other. The power electronics equipment facilitates improving resistance against hazardous environments, suppressing the deterioration by aging, reducing the adverse effects of noise caused by external magnetic flux, and transmitting and receiving signals while insulating the low and high voltage sides electrically from each other.

Abstract: A brushless motor circuit is for driving a brushless direct current (BLDC) motor. The motor includes a rotor and exciting coils for respective phases in a three-phase winding in a star configuration. A neutral point in the star configuration is configured to switch to one of a ground voltage, a supply voltage, and an open circuit voltage to provide more combinations. The combinations provide extra steps in one revolution for a better resolution with enhanced efficiency.

Abstract: A system and method for controlling a permanent magnet motor are disclosed. Briefly described, one embodiment receives a torque command and a flux command; receives information corresponding to a direct current (DC) bus voltage and a motor speed; computationally determines feedforward direct-axis current information and feedforward quadrature-axis current information from a plurality of parameters associated with the permanent magnet motor; determines a current signal (idq*) based upon at least the requested torque command, the flux command, the DC bus voltage, the motor speed, the feedforward direct-axis current information, and the feedforward quadrature-axis current information; and controls a power inverter that converts DC power into alternating current (AC) power that is supplied to the permanent magnet motor, such that the permanent magnet motor is operated in accordance with the determined idq*.

Abstract: Disclosed is an apparatus, controlling the number of rotations per minute of a brushless DC motor, the apparatus comprising: a brushless DC motor that rotates at a constant speed when a rotation current is applied, and stops rotating when a stop current is applied; a pulse applying unit that outputs input pulses according to a pulse apply frequency, which is predetermined or inputted by a user; a rotation detecting unit that detects the number of rotation pulses, and outputs a predetermined output signal per rotation of the brushless DC motor; and a current controlling unit that applies the rotation current to the brushless DC motor in correspondence with the input pulse, and the stop current to the brushless DC motor in correspondence with the output signal.

Abstract: In accordance with certain embodiments, the present technique provides a reduced current field-oriented-control scheme. For example, the present technique provides a method of controlling an induction device in which a predetermined reduction factor is employed to reduce the flux-current vector of a field-oriented-control scheme. By reducing this vector, less current and less power are drawn by the induction device, in turn reducing resistive heating and stator core losses, for instance.

Abstract: A power supply apparatus driving and controlling motor generators (MG1, MG2) includes a battery (10) generating an input voltage (Vb), a converter (110) converting the input voltage into a motor operating voltage (Vm) according to a voltage command value (Vmr), a smoothing capacitor (120) holding the motor operating voltage, inverters (131, 132) receiving the motor operating voltage and driving and controlling the motor generators (MG1, MG2) according to a torque command value (Tref), and a control unit (15) generating the voltage command value and the torque command value.

Abstract: A control device for a plurality of rotating electrical machines has a single current control device with an inverter, gate driver, and a motor controller, which supplies a control current to each rotating electrical machine allowing rotation control in response to the rotational phase of the rotor. In this control device, the current control device determines the control current of each rotating electrical machine based on the target torques and rotational angular velocities of all rotating electrical machines, and supplies a composite current obtained by combining the determined control currents for each rotating electrical machine to all rotating electrical machine. In this control device for a plurality of rotating electrical machines, the required voltage does not exceed the voltage of the power source and the peak value of the composite current does not exceed the permitted range of the inverter.

Abstract: A switched reluctance drive is supplied from a voltage source which varies from the voltage at which the control laws for the drive were determined. The control system compensates for this by modifying both the speed and torque values used to determine the correct firing angles for the demanded load. The system works over a very wide range of voltage variation and is independent of the shape of the torque/speed curve of the drive.

Abstract: A method of monitoring the operation of a brushless motor is disclosed. The method comprises the steps of monitoring the current flowing into or out of the windings of the motor using a current measurement circuit to produce an output signal indicative of the current; measuring the output of the current measurement circuit when the instantaneous current flow through the current measurement circuit is known to be substantially zero; and producing a modified output signal which is compensated for any differences between the actual measured output signal value and an ideal output signal value. The method enables any drift in the output signal to be compensated “on-line” whilst the is running.

Abstract: An available input of to a motor controller is used to measure the motor power supply voltage. Typically, a scaled down version of the voltage is sensed. The microprocessor is used to calculate the motor control current, in that case, is then calculated from the scaled down version. A scale factor that depends upon the sensitivity of the motor current to the motor supply voltage is calculated by the microprocessor. Driving parameters in the controller are then adjusted to account for the scale factor. In a preferred embodiment, the driving parameters are PWM parameters, and the microprocessor multiplies the measured power supply voltage to obtain a scale factor that can then be multiplied by the nominal PWM values to obtain the new PWM values.

Abstract: The present invention relates to a control of an AC motor, and in particular to a control device for an AC motor which can prevent an overvoltage from being applied to the motor, and minimize voltage consumption of a reactor itself during the starting and accelerating operation of the motor, by restricting a sharp increase of a motor line voltage resulting from a high-speed switching of an inverter during a high-speed operation of the motor, and a voltage reflection phenomenon of input terminals of the motor generated due to non-matching of a characteristic impedance between a power line and the motor, by inserting the reactor having a bar shaped core between the inverter and the motor.

Abstract: A speed control apparatus for varying the speed of an AC motor while maintaining the torque and power constant over a range of angular speeds The AC motor is driven by a D.C. source. A universal conmutator capable of providing two symmetrical non-contending signals with a frequency that can be selectively varied. A microprocessor unit for monitoring the frequency of the signals and control proportionally varying the duty cycle of the signals calculates the necessary duty cycle to maintain the torque constant over a range of angular speeds.

Abstract: A controller for a starter/generator used with an aircraft engine, includes means for monitoring field return current in a generator field winding; means for monitoring generator voltage; and microprocessor control means for adjusting generator field current as a function of the field current and voltage and field return current. The field return current and output voltage monitoring functions allow for open field, field integrity, over voltage, field weakening and torque limiting functions to be realized in an integrated programmable system configuration.

Abstract: A synchronous motor control system which can freely regulate n-phase electric currents in a synchronous motor to control the characteristics of the synchronous motor. The synchronous motor control system can enhance the output torque per unit weight of a synchronous motor (40) simultaneously with reducing torque ripples. The waveform of three phase alternating currents is freely corrected over a range of +30 degrees from a specified electrical angle, at which a target phase current drawing a sine-wave curve reaches its peak value. It is assumed that this range of .+-.30 degrees corresponds to a range of 0 degree to 60 degrees. By way of example, the waveform is controlled to the peak value of the phase current in a range of 0 degree to 28 degrees. The correction of the phase current is carried out for the target phase which produces the primary magnetic flux of a revolving magnetic field.

Abstract: A circuit and method for controlling the speed of a universal motor driven by an AC source is disclosed. The method includes the steps of measuring a value of a temporal property of a current through the motor and determining a speed of rotation of the universal motor using the temporal property. The method for controlling the speed of the universal motor further includes comparing the determined speed of rotation with a desired speed of rotation and adjusting the current through the motor so that the speed of the motor approaches the desired speed of rotation.

Abstract: A commutation control strategy for eliminating torque ripple and noise from a brushless motor which has a plurality of motor phases connected in a bridge, each phase having a top switching device provided between a phase winding and a positive voltage supply and a bottom switching device provided between the phase winding and a less positive voltage supply in which following commutations of the motor, when the current flowing in a first phase is decaying towards zero and the current in a second phase is rising from zero, the switching devices are operative between a state in which the current flowing in the first phase is caused to decay at a first rate, and another state in which the current flowing in the first phase is caused to decay at a second rate which is lower than the first rate so that the rate of decay of the current in the first phase substantially matches the rate of rise of the current in the second phase.

Abstract: An electric current compensation circuit for use with a multiple-phase burshless motor to reduce ripples in the output torque is disclosed. It contains a plurality of electric current compensation loops each for a respective phase winding and each of the electric compensation loops contains: (a) a first input for receiving a line current from the driver; (b) a second input for receiving the compensation current from the motor sensor; (c) a forward rectifying circuit for forwardly rectifying the line current and the compensation current; (d) a reverse rectifying circuit for reversely rectifying the line current and the compensation current; and (e) a summation circuit for summing the forwardly rectified compensation current and the reversely rectified compensation current and outputting a synthetic current to a phase winding of the motor.

Abstract: The invention concerns an improved system for windshield wipers in vehicles. An induction motor is used, in which speed is accurately controlled by controlling frequency of power supplied to the motor. The induction motor may be of the consequent-pole type, which ordinarily does not produce sufficient torque. Addition of (a) auxiliary tooth slotting and (b) skew has raised the torque produced to acceptable levels.The invention includes a control system, which senses excess load on the motor, which occurs as the windshield dries, and reduces motor speed, subject to a minimum, in response.

Abstract: A disk drive including firmware for overcoming stiction and breaking free the heads of a disk drive which may adhere to the disk surface when the disk is at rest. Upon start-up of the disk drive, if stiction at the head/disk interface occurs, the voltage to the spindle motor and/or actuator motor may be rapidly fluctuated so as to cause a pulsing of the spindle motor and/or actuator motor. Pulsing both the spindle motor and actuator motor creates forces in a plurality of radial directions to allow the head(s) to break free from the disk(s) in the direction of least resistance. Moreover, as the resonant frequency of the spindle motor varies depending on the number of heads that are stuck, the firmware pulses over a range of frequencies including the various resonant frequencies of the spindle motor corresponding to various numbers of heads stuck.

Abstract: Pre-defined driving profiles for the distinct phase-windings of an electronically controlled brushless motor are continuously reconstructed for each switching phase and forced in the form of a drive current or voltage on the respective windings, in synchronism with a signal indicative of the rotor position, from just a first complete sequence and at least a first sample of the successive sequence of a number of sequences, each of N samples, equal to the number of switching phases of the motor, in which is divided a complete digitized pre-defined profile. The digital samples are stored in a nonvolatile memory and that are scanned at a continuously regulated clock frequency and with varying order and direction of scanning for reconstructing the instantaneous driving profiles for all the windings.

Abstract: In a motor drive circuit, the collector-emitter paths of two npn-type transistors are connected in series between a power line and ground, and the junction between the two transistors is connected to a motor coil. A control circuit feeds a control current to the base of the transistor connected to the power line so that this transistor supplies a drive current to the motor coil. A current mirror circuit is provided which is constituted of two pnp-type transistors whose emitters are connected to the power line, and the base and collector of the input-side transistor is connected to the control circuit through a diode. The base of another pnp-type transistor is connected to the cathode of the diode, and the emitter of this transistor is connected to the collector of the output-side transistor of the current mirror circuit and to the base of the transistor connected to the power line.

Abstract: The drive system (210) comprises an electronically commutated motor (220) having three windings (225, 226 and 227). The motor (220) is energized by an energizing circuit (270). The energizing means (270) is controlled by three Hall elements (241, 242 and 243) which supply sensor signals (H.sub.1, H.sub.2 and H.sub.3). The motor comprises a permanent-magnetic part whose position is measured by means of the Hall elements. The drive system (210) comprises a status generator (280) which generates status signals (Q.sub.1, Q.sub.2, Q.sub.3 and Q.sub.4) which are dependent upon the ratio between the actual values of the sensor signals (H.sub.1, H.sub.2 and H.sub.3). The drive system (210) further comprises a multiplexer (290) and an inverter (295) which are controlled by the status signals (Q.sub.1, and Q.sub.2, respectively) in order to generate a position signal (P). A corrected position signal (P') is applied to a comparator (260) to generate an error signal (E).

Abstract: An electric machine control system includes a torque smoothing device including a torque monitoring device connected to the electric machine and supplying torque signals. A smoothing processor receives the torque signals and receives at least one torque reference signal and produces torque smoothing signals. A smoothing generator receives the smoothing signals and supplies smoothing electric power to the machine to make its torque conform to the torque reference.

Abstract: A pulse width modulated (PWM) motor drive with back EMF monitoring of the floating phase of a polyphase motor is arranged so that zero crossings of the back EMF can be read without interference by PWM switching. A measure is taken of an interval between two zero crossings and, in the next interval, the PWM switching is stopped near to and before the next expected zero crossing, based on the time of the last prior interval. A period counter counts up during the first interval and another counter, loaded with the previous count reached by the period counter, counts down at the same rate during the second interval until a certain number is reached, near to but before zero, to generate a signal that results in stopping PWM switching until after the next zero crossing is detected.

Abstract: An alternating current induction motor having a multitapped RUN winding and including a controller which automatically determines an instant tap selection in response to changes in applied a.c. electric power voltage level appearing immediately at the motor terminals. A measure of instant level of the motor terminal voltage is utilized to automatically reselect the RUN winding tap selection in order to maintain a near constant level of magnetic excitation in the stator field irrespective of immediate changes or variations in the available motor terminal voltage. Electric lawn mowers, power tool motors and other heavily loaded motors which may normally be operated at the end of various lengths of especially long and lossy extension cords or the like may advantageously utilize my control technique to maintain operation with an about normal and constant level of power, independent from usual performance degrading voltage drop losses commonly encountered in the extension cord.

Abstract: A system and method that may be implemented in a power inverter or controller, for example, that uses the speed of a rotor to control the torque output of a motor of an electric vehicle. A rotor encoder coupled to the rotor of the motor provides encoder signals that indicate the speed of the rotor and thus the speed of the vehicle. Alternatively, wheel speed sensors may be employed in lieu of the encoder to provide sensed signals that are processed to produce traction control of the vehicle. By monitoring the rate of change of the signals from the encoder or sensor, the controller determines if the drive wheels are spinning due to loss of traction. If this condition is detected, the controller reduces torque until traction has been regained.

Abstract: An electric motor monitoring circuit apparatus for an electric motor has a three phase electric motor having an electric motor starter circuit. An insulation monitoring circuit is coupled to the electric motor and monitors insulation leakage of the electric motor and inhibits activation of the electric motor starter circuit when an insulation leakage exceeds a preselected threshold. A three phase monitor circuit is coupled to the electric motor for monitoring phase sequence in voltage amplitude for the electric motor.

Abstract: A control system (100) for a five-phase brushless DC motor (102) including a stator having five windings and a rotor (116) mounted for rotation relative to the windings (114). The windings (114) are adapted to be electronically commutated in response to the rotary position of the rotor (116). The control system (100) includes a sensing circuit (106) to sense the rotary position of the rotor (116) using an optical or magnetic sensor or the back electromotive force voltages in the windings (114). Electronic switches (112) control the flow of current through the windings (114) in response to control signals generated by a control circuit (110) in response to the rotary position of the rotor (116). The control circuit (110) includes start-up logic to start the motor (102).

Abstract: An induction motor control system for electric vehicles having a DC power supply, an inverter, and an induction motor, includes a current control mechanism having a flux controller. The flux controller reduces the stator flux to improve the torque output of a motor at the limit of the voltage supply from the inverter. The reduction in flux is adjustable as the actual limit of voltage available to power the motor varies. A flux reference .lambda..sub.so generated according to efficiency control requirements can be adjusted by a flux weakening quantity generated by the controller in the constant power range of operation. The DC bus voltage, the rotor speed and stator flux reference values are input to the flux controller so that the motor can be operated to achieve improved torque output approaching the theoretical maximum torque output or to maximize efficiency as needed.

Abstract: A quiet motor speed controller is disclosed which varies an amplitude of an AC voltage signal provided from an AC source to drive an AC motor. The controller includes a first impedance in series connection between the source and the motor. A second impedance is electrically connectable with the first impedance in accordance with settings of a switch such that the total impedance interposed between the source and the load is varied by switching. The first and second impedances are substantially defined by first and second capacitive values, preferably including resistive elements to limit current flow at charging and discharging.

Abstract: An asynchronous motor is supplied with power from an AC line voltage via a variable speed drive including a rectifier bridge connected to the AC line voltage, a DC voltage intermediate circuit including a capacitor and an inverter including switches and connected to the phase windings of the motor. A system for controlling the power supply to the motor includes a device for controlled resumption of motor speed after supply of power to the motor is interrupted.

Abstract: An asynchronous motor is supplied with power from an AC line voltage via a variable speed drive including a rectifier bridge connected to the AC line voltage, a DC voltage intermediate circuit including a capacitor, and an inverter including switches controlled by a control circuit and connected to the phase windings of the motor. A cascade regulation structure includes a frequency regulator, a current limiter and a current regulator driving the control circuit. The frequency regulator input is connected to a ramp generator supplying the motor start speed and the frequency regulator output is connected to the current limiter. The output of the current limiter is connected to the current regulator. The cascade regulation structure is associated with the intermediate circuit to limit the DC voltage at the capacitor by means of the current limiter.

Abstract: A motor drive control apparatus having an electrical power amplifier for supplying an electrical power to a motor, and a current control loop and speed control loop for controlling the drive of the motor, which includes a current feedforward component calculation section for creating voltage commands to be imposed on respective phases from current commands for the respective phases for the motor and the impedance model of the motor for carrying out a feedforward control by using the voltage commands to be imposed on the respective phases.

Abstract: A polyphase alternating current motor has in addition to a main winding that can be connected to a voltage source, a auxiliary winding arranged in the stator, such that at least one condenser is connected to both windings per phase. A decrease in condenser size while at the same time improving the degree of effectiveness is possible by virtue of the fact that the main and auxiliary windings are arranged in such a way as to yield an increase and phase leading of the voltage adjacent to the condenser. The condensers are connected to the windings in such a way that only capacitative leakage current flows in the auxiliary winding and the geometrical total of active and leakage current flow in the main current.

Abstract: An improved motor controller is intended for use with an induction motor and has a control loop which includes an auxiliary winding, a capacitor and a saturable reactor. The auxiliary winding is electro-magnetically coupled to the stator winding in a manner such that the capacitive reactance of the control loop is effectively in parallel with the magnetizing reactance and the rotor leakage reactance of the motor. The control loop is devoid of any direct electrical connection to the motor.By varying the magnitude of current in its D-C control winding, the inductance of the reactor is adjusted so that the capacitive reactance of the control loop, as electro-magnetically reflected into the motor, is generally in resonance with the parallel combination of the magnetizing reactance and the rotor leakage reactance.

Abstract: An electrical control means useful in systems wherein a motor, such as a blower motor for an air handling unit, must be run at different speed levels and wherein low voltage power must simultaneously be supplied to another part of the system such as a condenser unit. The invention combines auto-transformer and transformer technologies into a single motor control unit. Wiring to the auto-transformer portion of the unit is arranged in such manner that it may be readily field changed to accommodate the various line voltage and frequency levels encountered worldwide. Thus, a signle standardized unit allows accurate motor speed control and simultaneous low voltage power supply without motor overheating or instability under various line voltage and frequency conditions encountered throughout the world.

Abstract: Disclosed is a voltage regulation-unbalanced voltage compensation control connected intermediate the supply and load of the polyphase system, the control including separately adjustable variable impedance elements provided by saturable core reactors for independently varying the voltage drops between the supply and load terminals for each phase. The independent adjustment of the variable impedance elements is effected by a feedback control network varying the magnitude of current supplied to the DC control winding of each saturable core reactor in response to the existing load voltages across the load terminals.

Abstract: A motor control circuit comprises first, second and third saturable reactors connected between three supply lines and the three phases of a motor. The reactors can be excited to energize the motor to give a high torque output in a forward direction. Two further reactors ("reverse" reactors) are connected between the second and third supply lines and the third and second motors phases.In the "forward" condition, the "reverse" reactors are unexcited and have line voltage across them. To drive the motor in the reverse direction at a lower torque level, the first reactor and the "reverse" reactors are excited at a lower level and the second and third reactors are unexcited. However, the latter two reactors are made to operate at a point above the magnetization curve knee point by passing current through them up to their full-load current, and they are thereby "stretched" across a voltage only slightly (say 13%) above the phase voltage. Hence, only the fourth and fifth reactors have to withstand full line voltage.