Abstract: A method is described for controlling synchronous motor torque, utilizing a three-phase switch connected in a circuit to the input of a polyphase synchronous motor, and a switch control circuit. The switch control circuit senses the AC voltages input to the synchronous motor and produces signals that open and close the three-phase switch in phase with the input motor voltage, producing positive motor torque during normal operation. If input AC power is lost, the switch control circuit acts to prevent a reverse flow of high current from the motor from entering the power source bus. When input power, after a short time, returns, the switch control circuit acts to close the three-phase switch in such a manner as to permit only real power applied to the synchronous motor and thus positive torque that accelerates the motor speed and quickly restores the motor to synchronism with the input power source.

Abstract: A polyphase AC motor drive system comprises an electric power inverter and control means which enables operation in, and allows smooth transition between, a current controlled PWM mode and a quasi-square wave mode of operation. At low motor speeds, the system operates in PWM mode. At higher speeds, above the corner point speed of the motor, the system operates in a quasi-square wave mode. Smooth transitions between modes of operation are controlled by a microcomputer which counts the number of current chops made by a switching device in a preselected phase leg of the inverter over a time interval that varies with the desired fundamental period of the motor current. As speed increases and approaches the corner point, the number of chops decreases below a first predetermined number, and the system transitions from PWM to quasi-square wave mode. As speed decreases, the number of chops increases above a second predetermined number (larger than the first), and the system transitions back to PWM mode.

Abstract: A drive arrangement is described, comprising a multi-phase synchronous motor whose phase windings are energized with energizing currents whose strengths are periodic functions (f1, f2, f3) of a rotor-position or translator-position measurement value (p) which is determined by means of an incremental detection system. The drive arrangement has means for adjusting the initial position-measurement value (p) before the motor is energized with the periodic energizing currents. For determining the initial value, the phase windings are energized in different consecutive time intervals (T) with measurement alternating currents (im1, im2, im3) whose amplitudes are equal to K times the function values (f1, (ROPOS), f2(ROPOS), f3(ROPOS)) of the periodic functions (f1, f2, f3) associated with different auxiliary values (ROPOS). The frequency and amplitudes are selected in such a way that the rotor or translator performs a vibration whose vibration amplitude corresponds to only a few electrical degrees.

Abstract: A reduced voltage starter for gradually starting a polyphase motor having an acceleration control circuit for gradually applying power to the motor and detector circuits for detecting various fault conditions for terminating power to the motor. A shorted solid state switch detector senses when one of the semiconductor switches applying power to the motor is shorted to terminate the application of power from the remaining phases. A phase angle control circuit insures a uniform application of power to the motor. A phase rotation detection circuit detects when the three phases are in other than their correct sequence and terminates power in the event of such detection. An underload detection circuit senses when the current drops beneath a preselected reference after the motor has reached its full speed and terminates power in response to such detection. A line-to-line-to-line-to-neutral convertor produces signals representative of the line-to-neutral voltages which are necessary for other circuit functions.

Abstract: The present invention is directed to a method and apparatus for connecting a static inverter to a free-running motor, wherein the inverter is supplied with D.C. power by a regulator-controlled rectifier. An oscillator connected to both the rectifier regulator and the inverter governs the frequency of the three-phase inverter output, while voltage feedback from the inverter output to the rectifier regulator is employed to establish a proper volts/hertz output characteristic in the inverter output waveform. During the connection process, a synchronizing circuit causes the oscillator to generate a high pulse rate signal which raises the inverter output frequency to a level above that associated with the rotational speed of the free-running motor. Simultaneously, the D.C. output of the rectifier is clamped by the current regulator to current-limit the inverter output. The inverter is subsequently connected to the free-running motor and the inverter output frequency is allowed to decrease gradually.

Abstract: A method of controlling current in an AC motor to inhibit small torques on an unloaded motor output shaft and to improve buildup of steady-state operating flux in a rotor includes supplying current to the stator windings through a plurality of semiconductor switches, operating the semiconductor switches to supply a plurality of gradually increasing currents to the stator windings over a time interval corresponding to approximately one rotor time constant to bring flux in the rotor up to approximately 10% of a steady-state operating flux in the rotor, operating the semiconductor switches to supply a current that is the maximum current rated for pulsed operation of the semiconductor switches for a time interval over which a product of current and time is sufficient to produce steady-state operating flux in the rotor, and then reducing the stator current to a level for maintaining steady-state operating flux in the rotor. A microelectronic apparatus for carrying out the method is also disclosed.

Abstract: A hermetic box contains a motor and a self reset type protector which interrupts the supply of electric power to the motor when an abnormally heated condition takes place in the hermetic box and automatically supplies again the electric power when the abnormally heated condition ceases. The motor is energized by an inverter having AC output terminals connected to the motor outside of the hermetic box. A current detector which detects that no current is flowing into the motor is provided on the output side of the inverter outside for a hermetic box.

Abstract: When induction motors are lightly loaded their power factors and efficiency are poor but in the present invention power factor is controlled regardless of load. An induction motor is connected by way of a triac to a supply. The voltage across the triac is monitored by a comparator for voltage steps which correspond to current turn-off and a signal is developed at the output of an amplifier which represents error from required phase lag. A further comparator and a trigger pulse generator trigger the triac in accordance with the error. An override circuit overrides the control system during starting. A number of further induction motors may be connected in parallel with the motor. Additional circuits deal with problems arising when a three-phase induction motor is connected by three wires only.

Abstract: A reluctance motor comprises a stator (S) provided with coils (W1, W2), and a rotor (R). The rotor R has pairs of positions of stable equilibrium and pairs of positions of unstable equilibrium. The reluctance motor is started by first bringing the rotor into a first position of stable equilibrium (.theta.=-.theta.ms) by means of a first energizing current and subsequently rotating it towards a second (.theta.=0) of stable equilibrium by means of a second energizing current.

Abstract: A control apparatus for an induction motor comprises a variable voltage, variable frequency inverter feeding the motor, which is controlled by the PWM control. A secondary current component and an exciting current component of the motor are obtained by the calculation on the basis of a motor current and an actual slip frequency of the motor. From the thus obtained secondary current component, an actual torque produced by the motor is calculated. A frequency reference for the PWM control is obtained by the comparison result of the actual torque and a torque reference. A modulation factor reference for the PWM control is obtained by the comparison of the exciting current component and an exciting current reference. According to this control apparatus, the torque of the induction motor can be controlled to follow the torque reference with a high accuracy.

Abstract: A low cost, low part content single phase AC induction motor control starting circuit is provided which is speed sensitive, load sensitive and AC line voltage fluctuation insensitive. A dual comparator chip (20, 22) senses and compares relative magnitudes of AC line and auxiliary winding voltages (48, 40) to de-energize the auxiliary winding (2) at cut-out speed, and automatically re-energize the auxiliary winding at cut-in speed to accelerate or restart the motor from an overload or stall condition. Hysteresis circuitry (20, 50, 52, 57, 80) provides a lower cut-in speed than cut-out speed. Simplified power supply and voltage detection circuitry is also disclosed.

Abstract: A substantial reduction in required startup current is obtained in a drive arrangement with a three phase motor in that the stator winding of the motor comprises more than two winding legs per phase, all the winding legs of one phase being arranged in identical slots. During running up to speed of the motor, the more than two winding legs of each phase are wired symmetrically and are connected to the network in such a way that the magnetic fields produced by at least two winding legs per phase cancel each other out and only the remaining winding legs produce a rotating field.

Abstract: A method for providing a smooth transition to powered operation in a motor control system in which a variable voltage inverter regulates power to the motor on a volts per Hertz basis. The method is particularly applicable to systems for energizing and rapidly gaining control of a motor driving a load in which the motor armature is turning at the time that power is supplied from the variable voltage converter. The method is implemented by sweeping the frequency of the excitation applied to an alternating current motor while holding the magnitude of the excitation at a level sufficient to prevent over current excitation of the motor.

Abstract: A circuit is provided for controlling energization of the start winding of an alternating current motor whose shaft is divided into a number of angular segments equal to the number of poles of the motor. A shaft pulse is generated each time one of the angular segments rotates past a predetermined point. A line pulse is generated for each half cycle of line voltage. The shaft pulses are multiplied by the denominator of a selected trip-out ratio while the line pulses are multiplied by the numerator of the trip-out ratio. The multiplied shaft and line pulses are provided to an up/down counter which counts the shaft pulses down and the line pulses up. During the counter overflow condition, the circuit connects the start winding to the line voltage source. During the counter underflow condition, the circuit disconnects the start winding from the line voltage source.

Abstract: In the field-oriented control of an asynchronous machine, the flux angle of which is calculated by a flux computer from the current and the voltage as the integral of the EMF, the correct flux vector must be available already at the start-up of the machine. For this purpose, one axis (M.phi.1) of a model coordinate system as well as the components (iO*, iM*=0), referred to the model coordinate system, of a vector parallel to this axis is determined at an input device (E1, E2) by a constant, given starting angle (.phi.MO*). This vector is transformed by means of the field angle (.phi.s) calculated by the flux computer for forming the converter control variables into the stator coordinate system while the machine is excited but standing still. The angle deviation (.phi.MO*-.phi.s) of the calculated field angle from the starting angle is used by a controller (CR) for correcting the calculated field angle.

Abstract: A motor starting circuit in which a triac connected in series with the starting winding of the motor is gated into conduction for only a preselected time period following motor start-up. A switching circuit, in parallel with the serially connected triac and starting winding, includes an SCR which provides a low resistance signal path to the gate of the triac at such time that the SCR is in a conducting state. The SCR is gated by a resistance network and the time period is established by an RC circuit which gates a switch at the end of the selected time period to short out the portion of the resistance net work to which the gate of the SCR is connected so as to turn off the SCR and leave a high resistance path through the switching circuit to the gate of the triac.

Abstract: In a load commutated inverter (LCI) motor drive, the motor is started from a rotor rest position by modulating the rotor winding with a field current at a constant rate to induce stator voltages which are detected in terms of signs, so as to identify the rotor rest position. The induced stator voltages are used to select an initial pair of thyristors of the inverter to be turned on in the firing sequence for the chosen direction of rotation under normal operation of the drive.

Abstract: The present invention provides a method for starting motors by harmonics for synchronous motors, wound-rotor and cage-rotor asynchronous motors started thereby. During the starting period, according to the present invention, the connection of the stator winding is changed so as to create some very strong harmonic fields. The harmonic fields are associated with the rotor windings and are used to improve the starting performance of the motor. The three motors all have large starting torque, small starting current and can be started by direct-on-line. The wound-rotor asynchronous motor has no brushes or, slip rings on the rotor and there is no electric contact thereby increasing the reliablity of starting and running. The running efficiency is superior to the cage-rotor asynchronous motor.

Abstract: A self-extinguishing element such as a gate turn-off thyristor (GTO) is used for each arm of the inverter. A capacitive load is connected to the output terminal of the inverter. In a region where the output frequency of the inverter is low, the self-extinguishing element is forcibly commutated. In a high-frequency region, where the output frequency of the inverter is higher than that in the low-frequency region, the capacitive load causes the self-extinguishing element to be load-commutated.

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 rotating motor by the inertia force in order to keep the motor rotating. To achieve the above reconnection, the inverter is controlled in accordance with 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; when a predetermined time has elapsed after the starting voltage was applied to the motor, only the frequency is decreased; when inverter driving current drops below a predetermined value, the frequency is held and only the voltage is increased until the voltage-to-frequency ratio reaches a predetermined value.

Abstract: A variable frequency adjustable speed motor drive allows restart of a spinning induction motor by initially increasing the frequency of the associated inverter while keeping the DC voltage source thereof low, then by decreasing the frequency of the inverter while monitoring the effective motor impedance V.sub.DC /I.sub.DC or V.sub.AC /I.sub.AC until the latter jumps at an initial level indicating matching of the frequency with the motor spinning speed. Thereafter, the DC voltage is restored in magnitude and the inverter is increased in frequency to match the desired motor speed.

Abstract: A reference current lag for a motor controller is selected so that the reference current lag approximates the motor current lag when the motor is fully loaded. A motor controller has a plurality of thyristors for controlling electric current flow to the motor. A firing circuit fires the thyristors at a selected firing angle. A current lag, as a phase angle between a power line voltage applied to the motor and electric current flow to the motor, is measured. The selected firing angle is adjusted so that the measured current lag is substantially equal to a reference current lag. A temporary value of the reference current lag is selected. The motor current is monitored, and in the event that the motor current becomes between an upper predetermined motor current and a lower predetermined motor current, the reference current lag is given a final value.

Abstract: When actuating again an induction motor rotating inertially by applying power to the induction motor from an inverter capable of changing both of its output frequency and output voltage, the power is once supplied to the induction motor to increase the residual voltage if the residual voltage of the induction motor is not sufficient, and the frequency of an initial impressed voltage that is in agreement with the rotating speed of the induction motor is determined.

Abstract: A shaded pole induction motor includes a plurality of series-connected running windings and a plurality of series-connected shaded pole coils (windings). A normally closed, centrifugal-force-responsive switch is provided in series with the shaded pole coils to effect an interruption in current therethrough when the motor reaches a predetermined speed. As a replacement to the normally closed switch, a switch constituted by a relay winding and normally open relay contacts may be provided, the contacts being in series with the shaded pole coils, these normally open contacts being closed in response to high initial starting current in the running windings flowing through a relay winding and being opened again when the motor gets up to a predetermined speed; less current flows in the relay winding and in the running windings under this condition. A heat-responsive circuit breaker may be placed in series with the normally open contacts or centrifugal-force responsive switch.

Abstract: In a single phase AC motor having a main winding (1) and an auxiliary winding (2) both connectable to an AC power source (4), and having a start switch (24, 49) for automatically connecting and disconnecting the auxiliary winding to and from the AC source (4) in starting and running modes, respectively, and having a user operated reversing switch (7-12) for reversing the voltage polarity applied from the AC source (4) to one of the windings relative to the other winding, circuitry is provided for detecting the polarity reversal by sensing when one of the main and auxiliary winding voltages shifts from a leading to a lagging position relative to the other winding voltage, whereupon the circuit automatically instantly reconnects the auxiliary winding (2) to the AC source (4) to immediately apply reverse torque.

Abstract: A digital controller for synchronous motors prevents excessive heating of squirrel cage windings during motor starting. It reduces motor excitation if the actual accrued excitation time exceeds the maximum allowable excitation time of the controlled motor. It provides for adjustment of allowable time responsive to changes in excitation voltage. The thermal characteristic of the controlled motor is automatically derived from merely a few manually entered set point values.

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 stator winding of a single-phase brushless DC motor with symmetrical rotor and stator air gap geometry is comprised of two serially connected relatively displaced sections energized with a source of direct current in accordance with the rotary position of the motor rotor. In the run mode, the full winding is energized; in the start mode, one of the sections is momentarily short-circuited if the initial winding energization fails to produce sufficient torque for starting.

Abstract: A control circuit (10) is provided for automatically re-applying starting torque to a single phase AC induction motor by reconnecting the auxiliary or starting winding (2) to the AC power source (3) if the motor has not accelerated to a given cut-out speed, or otherwise begins to stall. Multiple reconnections of the auxiliary winding (2) are automatically provided as needed, without external intervention, to provide multiple bumping action. The auxiliary winding (2) is connected to the AC source (3) during initial energization of the motor, and is disconnected after a given starting interval. Induced voltage in the auxiliary winding (2) is sensed and compared against a reference voltage (17) for reconnecting the auxiliary winding (2) when the sensed auxiliary winding voltage drops below a given value relative to the reference voltage. The disconnecting, sensing and reconnecting functions are accomplished with a minimum number of components.

Abstract: An induction motor starting method comprises the steps of supplying a predetermined low-frequency current to the primary winding of an induction motor through a first cycloconverter having its input side connected to a commercial-frequency power source and its output side connected to the primary winding, supplying a voltage of a frequency from zero up to a first frequency through a second cycloconverter having its first input side connected to the commercial-frequency power source and its output side connected to the secondary winding, controlling the first cycloconverter to increase the frequency of the low frequency voltage supplied to the primary winding to the first frequency when the rotation speed of the induction motor reaches substantially a first rotation speed, and disconnecting the output side of the first cycloconverter with the primary winding to connect the output side of the first cycloconverter to the second input side of the second cycloconverter and connect the primary winding to the commer

Abstract: A digital controller for synchronous motors prevents excessive heating of squirrel cage windings during motor starting. It reduces motor excitation if the actual accrued excitation time exceeds the maximum allowable excitation time of the controlled motor. It provides for adjustment of allowable time responsive to changes in excitation voltage. The thermal characteristic of the controlled motor is automatically derived from merely a few manually entered set point values.

Abstract: A standard, unmodified induction motor starts with reduced input current, energy consumption and mechanical stress and is further protected from AC power source "phase loss", excessively low or high voltage or a locked-rotor condition during start-up or any subsequent moment while running when its stator winding is energized from a sine wave source through a signal-responsive wave modifier operative to control the portion of each cycle of the sine wave which is coupled from said source to the stator winding.

Abstract: Gradual starting of an electric motor is provided by increasing the voltage applied to the motor. A reduced voltage starter controls the application of a voltage derived from a line voltage to a motor by using a voltage ramp acceleration control circuit comprising, means for generating a ramp voltage having a predetermined rate of rise, means for controlling the voltage applied to the motor in response to the ramp voltage, means for sensing that the motor is running at substantially full speed, and means responsive to the means for sensing that the motor is running at substantially full speed for increasing the predetermined rate of rise of the ramp voltage, whereby under conditions where the motor is running at substantially full speed before the voltage applied to the motor reaches the line voltage, then the voltage applied to the motor will rise at the increased predetermined rate of rise of the ramp voltage.

Abstract: In order to minimize the initial in-rush produced on first energisation of a polyphase induction motor (10), careful control is exercised over the firing of controlled switching means (11) connected in series with each of the supply phases (A, B, C) or motor windings. This control includes effecting an initial selective firing of the switching means (11) such as to cause current to flow between two only (B,C) of the supply phases, the firing being timed to occur such that the voltage between these two phases (B,C) is decreasing in value at the moment of firing. Thereafter, the switching means (11) are sequentially fired in a manner resulting in the progressive increase in the angle of conduction of each switching means (11).

Abstract: A voltage to be applied to the primary winding of a drive motor is automatically and time-functionally adjusted in relation to the rated voltage of the drive motor in order to provide sufficiently large torque for beating during the starting period of the loom running and transit to normal running of the loom is carried out at a preselected moment other than the moment of beating motion. Change in voltage is effected through either switching in mode of connection for the primary winding or transforming the power source voltage which is maintained constant.

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

Abstract: Motor power-factor controllers (12) act, in the presence of varying motor loads, to maintain the phase lag angle (.phi..sub.M) between motor voltage and current at a preset demand or reference phase-lag value (.phi..sub.R) by regulating the firing angle of gate-controlled switching devices (11) connected in series with the motor supply (A, B, C). The optimum reference phase-lag value (.phi..sub.R) depends on the motor characteristics and will be as small as possible while providing for a stable, unambiguous control characteristic. A reference-setting unit (14) is provided for automatically setting an appropriate reference phase lag (.phi..sub.R). This unit (14) monitors the motor phase lag (.phi..sub.M) during start up and sets the reference phase lag (.phi..sub.R) to a value corresponding to the minimum monitored phase lag plus a predetermined amount (for example 8.degree.). The unit (14) can be arranged to seek to improve on the set reference (.phi..sub.

Abstract: A method of starting an AC motor from any initial speed using open loop control is provided. Sufficient current is provided to the motor so that motor flux can be developed. The frequency provided to the AC motor is varied and the stator frequency at which the motor peak flux occurs is determined. A transition to a control responsive to an external command at approximately the stator frequency at which the peak flux occurred is made.

Abstract: A self-starting single phase induction motor wherein the required quasi-second phase for starting is provided by controlling the phase of the voltage applied to one stator winding (91) of the motor relative to the phase of the voltage applied to another stator winding (87) of the motor by means of an electronic switching arrangement (93) and an associated control circuit (95).

Abstract: A control circuit for a three phase induction motor includes a voltage controller having a silicon controlled rectifier in each of a first, second and third supply line connected to the motor. The control circuit further includes a first, second and third phase control means for controlling the firing angles of the respective silicon controlled rectifiers, a circuit for providing a positive ramp signal, and a circuit for providing a constant level signal. A starter circuit includes a "run" push button and a "brake" push button. The depressing of the "run" push button connects a three phase power supply to the supply lines of the voltage controller and causes the positive ramp signal to be applied to the first, second and third control means to control the firing angles of the silicon controlled rectifiers to provide a soft start for the motor.

Abstract: This method of starting a variable-speed induction motor utilizes a speed control of the induction motor by varying the output frequency from a cycloconverter. The method comprises applying an output from the cycloconverter to the secondary winding of the induction motor while the primary winding of the induction motor is short-circuited during the start-up of the motor, applying a voltage lower than the line voltage to the primary winding when the induction motor is operating within an intermediate speed range, and applying the line voltage within a speed region near the rated speed. This method enables speed control over a wide range, and provides a sufficiently large start-up torque for the induction motor.

Abstract: An induction motor operating system having a pulse width modulation operating system and a time domain signal generating system.The induction motor is operated from the time domain system to provide extremely large motor starting forces compared to the nominal motor force. Opposite ends of each of first, second and third motor windings are connected across a D.C. power supply and individual power supply. Waveforms are supplied to said respective motor windings during a predetermined brief interval. The first waveform, supplied to a first winding, is configured such that current initially flows through the first winding to establish a first magnetic field in the motor. The second and third waveforms are configured so that current is supplied to the second and third windings after establishment of the first magnetic field to establish second and third magnetic fields reacting with the first magnetic field to create a motive force acting on the moving element of the motor.

Abstract: A three-phase motor control system (FIG. 1) having a current control regulator (CCR) that includes adjustable current ramp time or adjustable current level during starting and acceleration and incorporates a load voltage-current displacement regulator (VCFB) that automatically becomes effective when the motor approaches synchronous speed, thereby to reduce the power input to the motor to what is needed to run the load, thus saving energy. Additionally, a second quadrant detector (SQD) senses overhauling load conditions and operates a gate (NG) to lock out the load voltage-current displacement feedback signal thereby allowing the reference signal to place the motor across the line until the motor operation returns to the motoring quadrant. The system further includes means (24 in FIG. 2h) affording integral control and means (30 in FIG.

Abstract: A reluctance motor comprises a rotor (22) of soft magnetic material with two diametrically opposed poles (23,24) of equal size. The motor further includes a stator which in a corresponding way is provided with two poles (12,13). The stator poles (12,13) have windings (14,15) which can be activated separately. Further the stator poles are so designed that the radial line of symmetry (26) of one stator pole (13) forms an angle to the radial line of symmetry (25) of the other stator pole (12). Means are provided which on start drive the two windings alternately and in continuous operation drive them simultaneously.

Abstract: A microprocessor controlled motor starter is utilized in which the sign values of two phases of voltage are sampled and stored prior to actual motor startup to determine if a phase reversal, a phase imbalance, or a phase loss exists. If any of the preceding conditions exist, the motor start operation is aborted. This generally requires sampling the signs of the appropriate voltages three times during each voltage cycle at approximately equal intervals of 120.degree., give or take 10.degree. or so, and then forming a matrix of voltage signs versus sampling intervals. By comparing diagonal measurements of the sign values in the matrix for three diagonals in a direction of advancing time, phase loss or imbalance can be determined. The determining factor is that each diagonal must contain two values which should be equal, that is, both should be digital ones or both should be digital zeros. If such is the case for the three diagonal measurements, then no phase imbalance or loss exists.

Abstract: A microprocessor control motor starter is utilized in which the microprocessor measures the status of AC input signals which are coupled thereto by way of an isolating electro-optical device. The electro-optical device provides a square wave output signal. Thirty-six samples are made to determine if the output signal is at a digital "1" level or a digital "0" level. If more than 18 digital "1's" are found, that is an indication that the device has failed and a trip operation is initiated by the microprocessor. If less than 18 but greater than some arbitrarily chosen small number such as 6 is found, that is an indication that the switch empowering the optoelectrical device is in a closed but valid disposition. If a number less than 6 is found, that is an indication that the switch is in the open disposition. If the device is failed, the microprocessor will trip the motor.

Abstract: A microprocessor control motor starter is utilized in which a capacitor-backed random access memory is utilized to store certain critical data about the status of a motor so that if the power supply voltage temporarily drops below a certain value the critical information will not be lost. The microprocessor which controls the motor attempts to reinitialize itself as in the case long term power outage. A subroutine is provided which determines whether the motor can immediately be placed in the state it was in before the power outage occurred, or whether an automatic restart may take place, or whether the motor must be operator restarted manually.

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 control for an A.C. motor operates to feed a high average value of voltage to the motor during a starting period of predetermined duration and to then automatically switch the voltage supplied the motor to a lower average voltage of substantially fixed value. This lower value of average voltage is determined without feedback to the control circuit. The control may be designed for use with single phase or multiple phase motors and for motors of various different power ratings.