Abstract: In one embodiment, a system includes: an enclosure; a plurality of first converters adapted within the enclosure to receive grid power at a distribution grid voltage and convert the distribution grid voltage to at least one second voltage; at least one high frequency transformer adapted within the enclosure and coupled to the plurality of first converters to receive the at least one second voltage; a plurality of second converters adapted within the enclosure and coupled to an output of the at least one high frequency transformer to receive the at least one second voltage and convert the at least one second voltage to a third voltage; and a dielectric fluid adapted within the enclosure to provide dielectric isolation.

Abstract: An example HVAC system includes a furnace including a gas valve, a circulator motor to circulate air through the HVAC system, and a current sensor configured to detect a current supplied to the circulator motor. The system also includes a controller configured to disable the gas valve when a detected current supplied to the circulator motor is outside of a specified operating current range. A detected current to the circulator motor outside of the specified operating current range is indicative of a malfunction of the circulator motor. Example methods of operating a gas valve in an HVAC system are also disclosed.

Abstract: A multi-pulse transformer with multiple taps provides a constant magnitude voltage output to a variable speed chiller's compressor motor over a range of input voltages. The 3-phase transformer includes primary windings and a plurality of secondary windings. The secondary windings are electromagnetically coupled with the associated primary winding. The primary windings include taps for receiving multiple input AC voltages and the secondary windings have a single output terminal for supplying a predetermined output voltage which, after rectification produces a DC multi-pulse waveform for powering a DC link of a variable speed drive. Alternatively the 3-phase transformer includes multiple taps on the secondary windings. Each of the primary windings has a terminal for receiving an input AC voltage. The taps of the secondary windings provide an output voltage that is converted to a multi-pulse waveform for powering a DC link of a variable speed drive.

Abstract: An alternating current chopper circuit with low noise is disclosed. The circuit includes a switching circuit, a first freewheel circuit, and a second freewheel circuit. The switching circuit has a control switching unit, which turns on and or off accordingly to a control signal. The first freewheel circuit and the second freewheel circuit are for providing a current-conducting path to the motor, when the control switching unit is turned off.

Abstract: A drive controller arranged to provide electrical power from a power supply to a machine or load over a long AC power cable of the order of kilometers. The drive controller is arranged with circuits and/or control processes to provide AC current at a constant ratio of voltage and frequency to said machine or load. The drive controller maintains voltage and frequency at the machine terminals despite fluctuations in voltage and/or frequency that would ordinarily be caused by the load. This is done by estimating the voltage and current at the machine terminals and adapting the drive controller output accordingly to actively vary the converter output dependent on the load of the machine or other load. In other aspects of the invention a method and a computer program for carrying out the method are described.

Abstract: An alternating current-to-direct current (AC-to-DC) power supply has a first stage providing a first DC voltage and a second stage providing a second DC voltage. The AC-to-DC power supply has a first efficiency at the first stage and a second efficiency at the second stage that is less than the first efficiency. The second DC voltage is also less than the first DC voltage. A blower is electrically connected to the first stage of the AC-to-DC power supply to receive the first DC voltage from the AC-to-DC power supply to power the blower. Electrical connection of the blower to the first stage of the AC-to-DC power supply instead of to the second stage of the AC-to-DC power supply wastes less power and is more efficient.

Abstract: A system and method for determining the stator winding resistance of AC motors is provided. The system includes an AC motor drive having an input connectable to an AC source and an output connectable to an input terminal of an AC motor, a pulse width modulation (PWM) converter having switches therein to control current flow and terminal voltages in the AC motor, and a control system connected to the PWM converter. The control system generates a command signal to cause the PWM converter to control an output of the AC motor drive corresponding to an input to the AC motor, selectively generates a modified command signal to cause the PWM converter to inject a DC signal into the output of the AC motor drive, and determines a stator winding resistance of the AC motor based on the DC signal of at least one of the voltage and current.

Abstract: An electrical submersible pumping (ESP) system can include a pump located in a wellbore, a motor attached to the pump, a power source located at the surface, a cable electrically coupling the power source and the motor, and a current sensor. The ESP system can also include a controller communicating with the current sensor to calculate a voltage drop associated with the cable responsive to an impedance of the cable. The controller can also control a power source output voltage responsive to the calculated voltage drop. For example, the controller can adjust the power source output voltage to minimize a cable current while maintaining a minimum motor voltage. The controller can also control a motor shaft speed by changing a power source output voltage frequency to compensate for changing slip and adjust the power source output voltage to minimize the cable current while maintaining a minimum motor voltage.

Abstract: In a method for field-oriented operation to zero speed of an encoder-less asynchronous machine, wherein the associated field-oriented regulation device has a monitor with a machine model and rotation-speed adaptation, a model flux and a model current are calculated from a calculated actuating voltage and an adapted rotation speed, from which, in conjunction with a determined machine current, a complex difference is calculated. Also calculated is a model slip rotation speed as a function of the model flux and the model current, which is then scaled. The adapted rotation speed is then superimposed, and the sum is used as the rotation speed actual value which supplied to a rotation-speed regulator. An asynchronous machine without an encoder can therefore be operated to zero speed on a field-oriented basis.

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: An object of the present invention is to provide a power converter in which the open-phase can be detected in a broader frequency region even if a predetermined relation is kept between the output voltage and the frequency. In order to achieve the above objects, a power converter including: an inverter unit having phase unit inverters provided with a plurality of multiple connected single-phase cell inverters for every phase; an inverter controller for controlling the inverter unit so that a predetermined relation is kept between an output voltage and a frequency; and a plurality of transformers for detecting output voltages of the plurality of phase unit inverters, in which the inverter controller is provided with a fault detection unit for detecting whether a phase-to-phase voltage deviation calculated by the output voltage is within range of an allowable voltage deviation calculated as a function of the frequency is provided.

Abstract: A variable frequency drive system for controlling the frequency of a high-voltage power source supplied to a first electric motor includes a transformer section that includes a motorized loadbreak switch system, control power transformers, a controller programmed with control logic to ensure that the motorized loadbreak switch system opens contacts between the high-voltage power source and the variable frequency drive system once the power source is removed, and a tank containing a dielectric fluid, wherein the tank also contains, within the dielectric fluid, a manual isolation switch to supply or remove power to the transformer section, an impedance for use in soft-starting the variable frequency drive system, a primary winding, and a plurality of phase-shifted secondary windings.

Abstract: A method for providing electrical energy to an actuator is disclosed. In at least one embodiment, the method includes having a first voltage (UBUS) from a data bus; ii) converting the electric current to a current having a second voltage that is higher than the first voltage; iii) storing electrical energy of the second electric current; and discharging the stored electrical energy to an actuator. A device is also disclosed for providing electrical energy to an actuator.

Abstract: Apparatus for controlling the voltage supplied to a load, comprising: a multi-phase transformer having a primary and a secondary winding for each phase, each secondary being connected in series between an input line and an output directed to the load; and the primary is configurable by switches such that the phase of the voltage of the secondary is different from the line to which it is connected by a phase different from 0 and 180 degrees.

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: Fan relay boards are provided that include terminals configured to receive line power of approximately 115 volts, 208 volts, 230 volts, and 277 volts. The boards are configured to convert the line power to an approximately 24 volt output that is applied to a distribution circuit to select a high, medium, or low fan speed using relays. The boards may be coupled to a control device that designates the fan speed selected by the relays. The boards also may provide an approximately 24 volt power supply to external devices such as electric heaters, valves, and switches.

Abstract: A control device for electric power steering apparatus, in which when torque ripples at the time of the rotation of a motor is reduced by simple arithmetic, smooth and safe assist limitation is performed without deteriorating steering feeling, is provided. For this reason, in the control device for electric power steering apparatus adopting a vector control system for applying an assist force of a motor to a steering system, a phase delay according to an angular velocity is obtained, a corrected electric angle is calculated by adding the phase delay to an electric angle, and generation of a current command value in the vector control is compensated based on the corrected electric angle.

Abstract: A three-phase direct-current motor is controlled by cyclically repeating three first switching states. In each of the three first switching states, one of the three phases of the direct-current motor is periodically switched over between a first and a second input voltage, whereas the two other phases are continuously connected to the first input voltage.

Abstract: An apparatus for driving a motor of a dishwasher includes an AC power source, a rectification circuit for converting an AC power from the AC power source to a DC power, an inverter circuit for converting the DC power from the rectification circuit to an AC power, a motor driven by the inverter circuit to drive a wash pump and/or a drain pump, a current detector for detecting an output current of the inverter circuit, and a controller for performing a PWM (pulse width modulation) control of the inverter circuit based on an output signal of the current detector to thereby control the motor to rotate at a set rotation speed. A phase difference between an output voltage and the output current of the inverter circuit or a reactive current is controlled to have a predetermined value.

Abstract: An inverter device capable of smoothly driving an alternating current synchronous motor of large capacity and high-speed rotation is provided. The inverter device includes a power rectification main circuit for converting alternating current power into direct current power and a PWM control inverse transformation main circuit. A transformer raises output terminal of the alternating current power of the inverse transformation main circuit to drive an alternating current synchronous motor. The alternating current motor is started bypassing the transformer and limiting output voltage of the inverse transformation main circuit to a low value through PWM control of the inverse transformation main circuit.

Abstract: A circuit device is provided for driving an AC electric load, of the type inserted between a terminal of an AC power supply line and a terminal of the electric load to be driven and including a generator of PWM signals to be transferred to the load. This circuit is an AC/AC converter adapted to power supply the load from any level of the power supply line sinusoid and comprising first and second voltage driven switches, the first switch to power supply the load and the second switch to enable loop-back of the current. The switches always operate in a complementary manner, i.e., when the first switch is on, the other is off, and vice versa.

Abstract: A controller for a vector control of an induction motor, which is capable of easily determining a rotor resistance for use in calculation of a slip frequency. A temperature sensor is provided for detecting a temperature of a stator. Information on relation between the rotor temperature and the rotor resistance predetermined based on measurement is stored in a table. In driving the induction motor, the rotor resistance for the stator temperature detected by the temperature sensor is read from the table. A torque command I2 is divided by a magnetic flux command ?2 and the obtained quotient is multiplied by the read value of the rotor resistance to obtain the slip frequency ?s, so that the vector control is performed based on the obtained slip frequency ?s. The value of the rotor resistance is easily determined by simply referring the table without complicated calculation.

Abstract: A method and apparatus for regulating a harmonic current component of an inverter fed motor drive system comprises measuring a phase current of the motor, substantially eliminating the fundamental component of the phase current, demodulating the phase current having the fundamental component substantially eliminated to produce a first current signal and providing the first current signal to a PWM control input of an inverter drive of the inverter fed motor drive system to affect the inverter output voltage by driving a first harmonic current of the motor substantially to zero thereby to achieve harmonic current control. More accurate, estimated motor voltages can also be provided by the system.

Abstract: A control system for an electric vehicle, such as a golf car, that includes a plurality of power MOSFETs. The vehicle includes a shunt wound motor including an armature coil and a field coil. One of the MOSFETs is connected in parallel across the armature coil and another MOSFET is connected in series with the armature coil. The MOSFET across the armature coil includes a freewheel diode. When the motor is operating below its base speed, i.e., when the back EMF is below the power supply voltage, a current flow can be induced by momentarily turning on the series MOSFET, shorting the armature coil. Because of the residual inductance in the motor, a current flow in the counter clockwise direction is initiated at which point the series MOSFET is turned off. Consequently, a large voltage spike across the motor occurs which results in current flow back into the battery pack. By quickly turning the series MOSFET on and off the current flow can be maintained, and the regenerative braking can occur even at slow speeds.

Abstract: A stepping motor driver having current sensors that detect winding current values, an angle detection device that detects a rotational angle of a rotor, a first coordinate transformation device that transforms winding current values in a rotational coordinate system, an angle calculation device that calculates a command angle value. A third coordinate transformation device transforms the command current values in the rotational coordinate system according to the difference between the command angle value and the rotor angle value, a current control device that generates current control signals in the rotational coordinate system based on the differences between the command current values in the rotational coordinate system and the winding current values in the rotational coordinate system.

Abstract: A method and apparatus for controlling flux in an induction motor. During initial start of an induction motor drive the motor flux has to be charged up. The method provides time optimal flux forcing under limited inverter ampere capability. Command stator flux and current are generated and coordinated through a motor flux model. Charging of the motor flux and flux current are accelerated up to nominal operating values in coordinated manner.

Abstract: A system (10) for controlling the torque of an induction motor (12) utilizes a flux observer (14). The flux observer (14) receives stator current inputs (16, 18) and a rotor speed estimate (80) and then outputs a rotor flux estimate (20) that provides increased motor control stability at all speeds.

Abstract: A control system for an electric vehicle, such as a golf car, that includes a plurality of power MOSFETs. The vehicle includes a shunt wound motor including an armature coil and a field coil. One of the MOSFETs is connected in parallel across the armature coil and another MOSFET is connected in series with the armature coil. The MOSFET across the armature coil includes a freewheel diode. When the motor is operating below its base speed, i.e., when the back EMF is below the power supply voltage, a current flow can be induced by momentarily turning on the series MOSFET, shorting the armature coil. Because of the residual inductance in the motor, a current flow in the counter clockwise direction is initiated at which point the series MOSFET is turned off. Consequently, a large voltage spike across the motor occurs which results in current flow back into the battery pack. By quickly turning the series MOSFET on and off the current flow can be maintained, and the regenerative braking can occur even at slow speeds.

Abstract: A control device for an alternating current motor includes: a target current generating unit which generates a current order value, based on a torque order, as a d-axis target current and a q-axis target current on dq coordinates; a current detection device which detects an alternating current supplied to each phase of a polyphase alternating current motor; a coordinate transforming unit which transforms the alternating current detected by the current detection device into a d-axis current and a q-axis current on the dq coordinates; and a vector control unit which carries out a current feedback control so that the d-axis current follows up the d-axis target current and the q-axis current follows up the q-axis target current.

Abstract: An induction motor system operable in a wet environment comprises an induction motor and an apparatus for controlling the speed of the motor. The motor is adapted to be coupled to an AC source for supplying an AC signal. The motor includes a rotor having rotor laminations. The reflected rotor resistance over reflected rotor reactance ratio of the motor is adjusted to be greater than one. The controlling apparatus includes a switching device, user controls, controller means and isolation means. The switching device is connected in series with the motor and is operative in either a high impedance state wherein significant current flow through the motor is prevented or a low impedance state wherein current flow through the motor is substantially undisturbed. The user controls provide motor speed input signals.

Abstract: A noise attenuation circuit is disclosed for use in a motor drive system. The motor drive system includes a pulse width modulated inverter providing three phase power output on three phase conductors for driving a motor. The noise attenuation circuit includes a common mode transformer including a common mode choke having a core, with first, second and third choke windings on the core, each connected in series with one of the three phase conductors, and a fourth winding on the core. A three phase iron core transformer creates a neutral point representing common mode voltage. The iron core transformer has three primary windings connected in a wye configuration. A capacitor circuit is connected between the iron core transformer and the three phase conductors to prevent saturation of the iron core transformer during pulsed DC operating conditions. The fourth winding is connected between the neutral point and the DC bus and develops a common mode voltage that is equal and opposite to that existing in the system.

Abstract: A drive system for providing ac drive power to an induction machine with asymmetrical rotor resistance and for sensorless rotor tracking of the induction machine includes: a signal injector for determining a stator command signal in a reference frame which is aligned with either an estimated rotor reference frame; a signal determiner for determining a feedback stator signal of the induction machine in a stator reference frame; and a rotor position and velocity tracker for using the feedback stator signal to estimate a rotor velocity and position by transforming the feedback stator signal into an orthogonal axis feedback stator signal in the estimated rotor reference frame, isolating a component of the orthogonal axis feedback stator signal which is in-phase with the injected stator command signals, filtering the isolated component to isolate an error term, and generating a position estimate by driving the isolated error term towards zero.

Abstract: An improved downhole pumping system that employs a variable speed PWM inverter and a non-gap transformer to drive an induction motor over a range of different speeds, without saturating the transformer. The variable speed PWM inverter provides a rectangular PWM signal that may be varied according to inputs from a controller to adjust the speed of the motor. The PWM inverter is electrically connected to the transformer, and the transformer is electrically attached to the motor via cables, which may be lengthy in downhole applications. The motor may be started by ramping flux producing current to a first preset value at a low frequency, then ramping torque producing current to a second preset value. If a flux measurement indicates the motor has stalled, the second preset value is increased, and the routine is restarted. Otherwise, if no stall has occurred, the motor's speed is ramped to the desired value.

Abstract: An improved downhole pumping system that employs a variable speed PWM inverter and a non-gap transformer to drive an induction motor over a range of different speeds, without saturating the transformer. The variable speed PWM inverter provides a rectangular PWM signal that may be varied according to inputs from a controller to adjust the speed of the motor. The PWM inverter is electrically connected to the transformer, and the transformer is electrically attached to the motor via cables, which may be lengthy in downhole applications. The motor may be started by ramping flux producing current to a first preset value at a low frequency, then ramping torque producing current to a second preset value. If a flux measurement indicates the motor has stalled, the second preset value is increased, and the routine is restarted. Otherwise, if no stall has occurred, the motor's speed is ramped to the desired value.

Abstract: A variable speed controller for an induction motor that estimates the primary angular frequency and the speed without causing any error in the drive region where the induced voltage is low. The primary angular frequency and speed estimating device includes: a changeover signal generator that generates a changeover signal indicative of a first mode of operation when the induced voltage is greater than the changeover threshold, and a second mode of operation when the induced voltage is less than the changeover threshold; a differentiator, filter, etc.

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: 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: 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: A brushless resolver having a stator and a rotor, and a resolver part axially displaced to one another and a transformer part and having associated windings is provided. An additional short-circuited winding arranged parallel with the transformer rotor winding with few turns on the iron core thereof is also provided. A lowpass filter is thereby formed, which compensates the unwanted frequency-dependent phase displacement between the input voltage and the output voltages for the respective frequency.

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 apparatus for controlling the supply of power to a variable-speed induction motor converts an AC power source voltage to a motor supply voltage at a designated frequency, with the amplitude of the motor supply voltage being controlled in accordance with the motor load such that the degree of slip conforms to a predetermined optimum slip charactistic, whereby high efficiency and stability are maintained over a wide range of load values. The motor supply voltage amplitude is detected to provide an indication of the motor load, an optimum value of an operating parameter of the motor which varies in accordance with degree of slip is derived based on the designated frequency and the detected voltage amplitude, using a predetermined function corresponding to that frequency, and the motor supply voltage amplitude is controlled such as to reduce an amount of difference between the optimum value of the operating parameter and a detected value of that parameter.

Abstract: The DC link current from one leg of a DC link of an inverter is provided to a primary winding of an AC current transformer, and a voltage across the secondary winding of the current transformer is integrated for providing an envelope indicative of the DC link current.

Abstract: An energy-saving system for feeding an electric induction motor serving as a load, and which is operated from a 3-phase voltage power line, and in conjunction with feeding conductors for the motor includes a power-delivery sub-system operating in a magnetically linear region and coupled to the 3-phase voltage power line for providing variable feeding voltages to the induction motor, a sensing device coupled to the induction motor for generating a signal indicative of the derivatives of active power consumed by the induction motor with respect to the voltage of at least one phase provided to the induction motor, and a control apparatus coupled to the sensing device and to the power-delivery sub-system for regulating at least one of the feeding voltages, so that the derivative of the active power with respect to the voltage of that at least one phase is always substantially zero; thus for a given mechanical power output the power consumption of the induction motor is optimized, while concurrently losses in the

Abstract: A control system for electrically powering from an external alternating-current power source a direct-current underwater hand-operated tool or light activated by a switch. The control system includes a relay for connecting and disconnecting the external AC power source to and from the system, a transformer connected to the relay for transforming the AC power to a desired lower voltage level, a converter connected to the transformer for converting the transformed AC to DC power, cables for supplying the DC power to the tool, and a control circuit for sensing the voltage level of the transformed AC power and in response to the sensed voltage level increasing beyond a predetermined safe level, causing the relay to disconnect the external AC power source from the system. The control includes a Zener diode for sensing the voltage level of the transformer AC power, and a transistor and an SCR for controlling the operation of the relay.

Abstract: In order to minimize the current consumption of an alternating-current motor of the induction or the synchronous type (or possibly a plurality of such motors connected in parallel) driving a variable load, a sensor coupled to a supply line of the motor detects the occurrence of a significant change in its operating current and determines the sense of that change. A controller responsive to signals from the sensor then reduces the supply voltage by an incremental or decremental step and, if the sensor detects a resulting decrease in amperage, continues with one or more similar steps until the current levels off. If the initial voltage modification causes the current to rise, the controller progressively changes the supply voltage in the opposite sense until the amperage reaches a minimum.

Abstract: A permanent split capacitor single phase electric motor achieves balanced operation at more than one operating point by adjusting the voltage supplied to the main and auxiliary windings and adjusting the capacitance in the auxiliary winding circuit. An intermediate voltage tap on an autotransformer supplies voltage to the main winding for low speed operation while a capacitive voltage divider is used to adjust the voltage supplied to the auxiliary winding for low speed operation.

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.