Abstract: A current component, in which a phase angle is different by a predetermined reference angle from a magnetic flux occurring in an inductive load, is brought to a q-axis current. The q-axis current is computed on the basis of phase current. A phase angle of the magnetic flux is detected. A q-axis-current control phase and a reference potential phase are determined on the basis of the result of pulse-width-modulation computation and the phase angle. The q-axis-current control phase is controlled in a pulse-width-modulation manner. A potential of the remaining reference potential phase if fixed to a reference potential. Thus, interference among the phases is prevented to reduce current ripple.

Abstract: A motor control method is disclosed in which a drive motor is connected to an adjustable frequency power supply in which the frequency of the power supplied to the motor can be selectively varied. While the motor is running at a constant speed as determined by the frequency of the power supplied to the motor, the value of the current being supplied to the motor by the power supply is sensed and an actual current signal representative of said actual current value is produced. A reference current signal which is representative of a selected maximum current value and thereby a maximum load at which the motor speed may be increased is also provided. The actual current signal is compared with the reference current signal and if the former is less than or equal to the latter, an output signal is provided. In response to the output signal resulting from the comparison, the value of the actual frequency of the power supplied to the motor is increased to a preselected value so that the motor speed also increases.

Abstract: An electrically powered suspension for a vehicle including a roadwheel and tire assembly, an electrically powered suspension unit having one end attached to the roadwheel and tire assembly and the other end attached to the chassis of the vehicle, with the suspension unit including an electric motor for positioning the roadwheel with respect to the chassis, and a controller for operating the electric motor so as to control the vertical movement of the wheel and tire assembly with respect to the vehicle's chassis. The electric motor may include either a linear or rotating electric motor, acting either alone or in parallel with a static load carrying device such as a fluid or coil spring.

Abstract: In a computer-based motor drive, a microcomputer is responsive to a plurality of input signals drived from the motor AC lines whenever contacts, or pushbuttons, commanding specific control operations to be performed, are closed. In such case, opto-couplers convert such AC voltage into a square pulse train which conveys a succession of digital high and low levels. A reference signal is derived, through an opto-coupler form the AC line, which in its high and low logic form is delayed in relation to the input signal trains. By sampling the input signal upon the occurrence fo a falling edge of the reference signal, then at least after the delay existing between the signals, the validity of the input signal is tested by comparing the two successive samples, thereby insuring a true command addressed to the microcomputer.

Abstract: A control circuit for maintaining power output of a motor, irrespective of amplitude changes in line voltage. The output of an amplifier is indicative of the line voltage. A ramp generator generates a ramp voltage which is consistent and repetitive, irrespective of changes in the line voltage. A comparison is made between the ramp voltage and the amplifier output, causing a triac to fire when the two are equal. The equalization point is a point at which sufficient power can be derived from the remainder of the line voltage to assure consistent and repetitive operation.

Abstract: The present invention relates to a motor control apparatus having a discharge circuit 7 for reducing a voltage which is regenerated from motor 5 to the driving circuit 4 in the braking of an AC servomotor or the like, a protection circuit 8 for protecting the discharge circuit 7, and a voltage-drop detection circuit 20 for making the driving circuit stop after an activation of the protection circuit 8. The motor control apparatus contains a detection circuit 16, which detects a voltage of the smoothing capacitor 3 which is connected to the input terminal of the driving circuit 4 via the protection circuit 8 which is connected in series to the discharge circuit 7, and a voltage-drop detection circuit 20 which stops the driving circuit 4 after activation of the protection circuit 8.

Abstract: The problem of excess size and weight resulting from the use of current sensors in a VSCF start system is solved by a motor control system which utilizes a current estimator to develop a current feedback value. The current estimator is coupled to a rotor position detector and an input power detector to develop a signal representing the estimated current drawn by the motor.

Abstract: An induction motor torque/flux control system the motor flux is forced down while accelerating and force up while decelerating to maintain a required flux level at all speeds. This is achieved through vector control by generating a direct current component in relation to the flux demand while imposing limits thereto corresponding to the maximum desirable resultant current vector, and by generating a quadrature current component which is held between limits defined by the sum of the squares of the two current components. The three-phase currents of the motor generated by vector control transformation are used to control a voltage-source inverter in a bang-bang fashion. The conventional bang-bang technique is improved by typing up one pole while controlling in the bang-bang mode the two other poles. To this effect the motor back emf is detected when the poles are simultaneously tied to one of the DC link terminals, and the tied-up pole is selected by the emf so detected.

Abstract: A frequency control method is incorporated in a motor drive to prevent overcurrent trips when an induction motor is subjected to impact loads or reconnection under load. The drive includes a current regulator loop to control stator current and a voltage regulator loop to control the command to the current regulator. Motor voltage is sensed and a voltage error is developed. This voltage error is processed through a proportional-integral control loop which controls an operating frequency signal to the current regulator. The drive responds during current limit conditions to reduce operating frequency and speed until the current limit conditions subside. The motor can then be re-accelerated up to the desired operating speed.

Abstract: A motor control for controlling current in an induction motor. A microcomputer generates three inputs to control an inverter circuit that energizes the three phase windings of the motor. A speed control modulates the three inputs to adjust motor speed and voltage. A current sensing circuit also modulates the three inputs to reduce motor current using a technique that over rides the speed control. By monitoring the current sensing circuit the microcomputer adjusts the speed control to force motor current to a level near a set threshold value.

Abstract: An apparatus for starting and controlling a motor. The apparatus includes means for monitoring the load current values in each phase of a motor. These means can include an apparatus such as a current transformer. The apparatus utilizes a circuit for modeling a motor and estimating the temperatures of the motor's windings and housing. THe circuit preferably is defined by a programmed microprocessor. The estimated temperatures are based on the load current values and time. These estimated temperatures are then compared to allowable limits and, based on the comparison, the motor is either stopped or allowed to run.

Abstract: A method and apparatus for controlling the operation of an oil well pumping unit in which the prime mover is a polyphase AC electric motor. The system comprises means for generating a plurality of signals representative of motor fault parameters including a motor winding overtemperature fault, undervoltage fault, and a phase imbalance fault. Upon occurence of a fault, a contactor in the motor supply leads is open to shut down the motor. After such shutdown because of undervoltage or phase imbalance faults the fault parameters are continuously scanned and once the fault has been cleared the motor is restarted. Where motor shutdown occurs because of an over temperature fault, the motor is maintained in a latched off shut down condition until an operator implemented reset occurs. An accessible counting memory is provided having separate registers for each of the fault conditions.

Abstract: A method and circuit for application in a PMW inverter for controlling power to an AC motor in which a hysteresis modulator is employed as a current limiter to override sine-triangle modulation in a PWM generator circuit. When the magnitude of motor current reaches a hysteresis band upper limit, the hysteresis modulator generates a large limit current to a summing input on a current regulator which feeds the PWM generator to override and mask out the normal sine-triangle modulated signal. When the magnitude of motor current decreases to a hysteresis band lower limit, the limit current is terminated, and the sine-triangle modulation is resumed.

Abstract: An apparatus for controlling an adjustable-speed alternating current motor coupled to drive an elevator cage. The apparatus includes a converter connected to a source of AC power for converting the AC power into DC power, an inverter connected through relatively positive and negative conductors to the converter for inverting the DC power into DC output power having adjustable frequency, voltage magnitude, and current magnitude to drive the motor, and a control circuit for controlling an inverter to drive the motor at an adjustable speed. When a power failure occurs, the control circuit prevents flow of power through the converter to the power source and reduces the current magnitude of the inverter output power to a predetermined minimum limit enough to maintain a synchronous relationship between the inverter and the motor.

Abstract: A compressor drive system that includes a thermostat producing a signal indicating the measured air temperature, a modulation control circuit connected to the thermostat to produce a motor drive signal from the temperature signal and which is output to a motor drive switching bridge circuit. The motor drive switching bridge circuit is connected to a rectifier that converts single phase alternating current to direct current. The switching bridge uses the motor drive signal from the modulation control circuit and the rectifier output to produce multiphase power including a speed control signal imposed on the power for regulating speed. A motor connected to drive a compressor is included. The motor is powered by the motor drive switching bridge circuit multiphase power output. The speed of the motor is controlled as a function of the temperature signal.

Abstract: An inductio motor torque/flux control system the motor flux is forced down while accelerating and force up while decelerating to maintain a required flux level at all speeds. This is achieved through vectory control by generating a direct current component in relation to the flux demand while imposing limits thereto corresponding to the maximum desirable resultant current vector, and by generating a quadrature current component which is held between limits defined by the sum of the squres of the two current components. The three-phase currents of the motor generated by vector control transformation are used to control a voltage-source inverter in a bang-bang fashion. The conventional bang-bang technique is improved by tying up one pole while controlling in the bang-bang mode the two other poles. To this effect the motor back emf is detected when the poles are simultaneously tied to one of the DC link terminals, and the tied-up pole is selected by the emf so detected.

Abstract: An overcurrent protection system for AC motor control systems which provides a separate overcurrent shut down mechanism for each phase of the AC power used in an AC motor. These separate phase shutdown mechanisms provide protection for minor overcurrent conditions without shutting down the entire motor control system. The overcurrent protection system also provides a mechanical feedback apparatus for totally shutting down the motor control system only in a severe overcurrent condition.

Abstract: An apparatus for controlling an adjustable-speed electric motor. The actual motor speed is sensed and compared with a commanded motor speed. A speed error signal, which depends on the difference between the actual and desired values of motor speed, is derived and applied to a proportional-plus-integral control circuit which converts it into a first torque command signal. The speed command signal is converted into a second torque command signal proportional to the rate of change of the speed command signal. The second torque command signal is added to the first torque command signal to provide a torque command signal. A control circuit responds to the torque command signal by controlling the operation of the motor in accordance with the torque command signal.

Abstract: A control circuit for a forced-air heating system comprises a silicon diode that is positionable in thermally-conductive relationship with the interior space of a furnace plenum. A current source supplies current to the silicon diode, and the potential drop across the silicon diode is sensed. The operating speed of the blower is controlled in response to the voltage drop across the silicon diode in a manner such that when the temperature in the plenum is below a first level, the blower is not driven; when the temperature reaches the first level, the blower is driven at a first speed; and when the temperature reaches a second level, which is higher than the first level, the blower is driven at a second speed, which is higher than the first speed.

Abstract: An AC Motor Speed Controller used to control the Speed, Torque and Horsepower of an AC motor. It allows the speed of the motor to be adjusted to the desired level and is calibrated to develop the desired torque, either automatically through load feedback or through a predetermined or preset level. It also allows for excessive torque to be developed under starting and acceleration conditions while providing for controlled deceleration with proportional braking of the inertia load.

Abstract: A frequency converter is provided for the power supply of an asychronous motor, comprising:a rectifier bridge (11) connected to a multiphase network and to an intermediate DC circuit (12);an inverter (13) comprising three pairs of static switches (T1-T6) connected in a Graetz bridge; characterized by;a means (21) for reading the current associated with the intermediate circuit (12) and elaborating an image signal of the reverse circuit and delivering an image signal of the current in this circuit;a stabilization control circuit (22) connected to said means (21) and delivering a reverse current excess signal (ST) when the signal (I.sub.d) exceeds an adjustable threshold; anda means (25) for reducing the output voltages of the inverter, and adapted for modifying the modulated pulses, this means being controlled by the output signal (ST) of the stabilization control circuit (22).

Abstract: An induction motor control method includes producing a primary current as a current command which takes all constants of an induction motor (d) into consideration. An output torque is obtained which is linear with respect to a torque command (Tm), a voltage at a DC link portion is detected, and an excitation flux command is varied by this DC voltage (V). This enables constant-output control to be performed irrespective of fluctuations in power supply voltage. Further, a power-factor adjusting circuit (q) is provided for adjusting the phase between voltage on the AC power supply side and current at the time of regenerative braking, so that reactive power is reduced.

Abstract: A rotary anode type X-ray apparatus includes an arithmetic unit for calculating the optimum number of revolutions of the anode, on the basis of the previously measured and stored temperature-characteristic data of the X-ray tube, at least one of the tube voltages applied to the X-ray tube, the X-ray radiation time, and the tube current. According to frequency of revolution data derived from the arithmetic unit, the motor controller drives the motor to rotate the rotary anode at an appropriate number of revolutions. This number is determined by the X-ray tube drive conditions, including the tube current.

Abstract: The acceleration/deceleration control apparatus using slip speed detects an angular frequency .omega.r corresponding to an execution speed of an induction motor and derives an angular frequency .omega.s corresponding to a slip speed corresponding to a slip speed in response to a torque of the said motor, from a vector controller of the said motor.On the other hand, an allowable value .omega.s' of said angular frequency corresponding to the said .omega.r is prepared beforehand, and is compared with said angular frequency .omega.s.According to the result of this comparison, the IM rotation is controlled. So even if the induction motor is used as servo motor, no shock of the torque will flow through the motor and the motor itself will not be stalled.

Abstract: There is disclosed a protecting apparatus for a secondary excitation type variable speed AC generator/motor having a primary winding connected to an electric power system and a secondary winding each phase of which is AC excited by an independent power converter unit. The protecting apparatus is arranged to detect an electrical event which includes at least one of an overvoltage and overcurrent appearing at each phase of the secondary winding of the AC generator/motor, to decide whether the detected electrical event meets a predetermined condition and to close, when the electrical event detected in respect to any of phases of the secondary winding is decided as meeting the predetermined condition, a switch circuit connected in the corresponding phase of the secondary winding.

Abstract: Disclosed is a control apparatus for a brush-less motor, which can prevent commutation failure of an inverter for driving the motor. The control apparatus, according to the invention detects a counter EMF of the motor, and the detected counter EMF is applied to a PLL circuit. In the course of normal operation of the motor, an output of the PLL circuit is used for controlling the advanced control angle of a motor drive inverter. Any abnormality in the condition of the motor, such as that arising from an abrupt change in load of the motor, causes a sudden and substantial variation in the magnitude and phase of the counter EMF. Since the internal condition of the PLL circuit changes in response to this counter EMF variation, a signal generated by the PLL circuit is therefore used to detect the counter EMF variation.

Abstract: A circuit is described for controlling the speed of an A.C. motor driving a cooling fan in response to the temperature at a point being cooled in which a temperature responsive impedance is used to control the current in an impedance of the output circuit of an amplifier that is connected in series or parallel with the windings of the motor.

Abstract: A three-phase induction motor control method according to the present invention subjects a three-phase induction motor to vector control by an output from an inverter which is supplied with a direct current obtained by conversion from an AC input. The method includes sensing a DC-converted voltage at a DC link section, varying a flux command in dependence upon the sensed DC voltage, and controlling the motor to obtain a constant output irrespective of a fluctuation in power supply voltage.

Abstract: An electronic control for a motor drives the motor with pulses of current, and protects the motor from extreme values of line voltage and motor current. A current sensor, connected in series with a conductor which supplies current to the motor windings, develops a monitoring signal that is sensed for the purpose of shutting down the motor when the monitoring signal indicates that the motor current is excessive. A power supply in the control isolates the control from the AC line voltage, provides regulated DC voltages to power various portions of the control, and provides an unregulated DC sense voltage which indicates when the AC line voltage is too high or too low so that the motor can be shut down.

Abstract: A variable speed motor control system includes a power control circuit and a forced commutation control circuit for controlling the torque and rotational speed respectively of an induction motor. The power control circuit and the forced commutation control circuit are independently controlled by signals from a speed control circuit. An overcurrent sensor monitors the motor current and, if excessive current is detected, a speed and power monitor limits the response of the power control circuit and forced commutation control circuit to the speed command. The forced commutation control circuit and power drive circuit contain silicon-controlled rectifiers both for controlling the amount of power fed to the induction motor as well as for controlling the switching of power between combinations of motor windings.

Abstract: An induction generator/motor system has an induction machine connected at its secondary side to a cyclo-converter. An induced voltage develops when the cyclo-converter pauses during a transient phenomenon occurring in the system. When the induced voltage exceeds a predetermined voltage range which covers the maximum output voltage derivable from the cyclo-converter, the polarity of thyristor converters of the cyclo-converter is switched such that the induced voltage is applied to a thyristor converter to be rendered conductive next in forward relationship therewith, thereby preventing occurrence of an overvoltage.

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 method and apparatus for detecting rotor faults in an induction motor. A flux sensor generates a flux signal corresponding to the magnetic flux at a predefined flux detection point external to the motor. A current sensor generates a current signal proportional to the current drawn by said motor. A time series of data points is stored, representing the values of the flux signal and the current signal over a period of time. The time series are transformed by FFT into a set of flux spectra and into a set of current spectra. Then the line frequency of the motor's power supply is determined by finding the maximum of the current spectra. Similarly, the slip frequency of the motor is determined by finding the maximum of the flux spectra in a predefined spectral range (e.g., below 2 Hz). The analysis of the rotor is then performed by comparing the amplitude of the current spectra, at a set of rotor fault harmonic frequencies, with specified fault threshold criteria.

Abstract: A motor protection relay is taught which determines effective and RMS values of current on a cycle-by-cycle basis by measuring three-phase currents at 10.degree. intervals in a line cycle and then determining the positive and negative sequence components thereof by storing the accumulated information in a memory. In order to increase the dynamic range of the sensing apparatus, only the negative half wave of each current is sensed and the positive half wave is reconstructed by finding the 180.degree. phase shifted equivalent thereof in the negative half wave.

Abstract: An induction motor torque control system is provided for resolving an excitation current command and a secondary current command into an excitation flux vector component and electromotive force-direction (torque direction) vector component, respectively, based on a torque command for the motor and an excitation flux command, decided for the motor, in such a manner that a linear output torque is obtained in response to these commands. A primary current command for the motor is obtained by combining these vector values.

Abstract: A control apparatus for an escalator wherein a low speed operation is performed in the absence of passengers at the escalator, and a high speed operation is performed in the presence of passengers at the escalator the alternating current of a three-phase A-C power source is converted by frequency conversion means into a three-phase alternating current of low frequency, with which an induction motor is energized to perform the low speed operation, so that the induction motor is rotated near a synchronous speed corresponding to the low frequency, to realize the low speed operation of high efficiency.Moreover, when passengers have been detected, the frequency of the alternating current from the conversion means is gradually raised, and the conversion means is thereafter switched to the three-phase A-C power source upon detecting the synchronism of this alternating current with the alternating current of the three-phase A-C power source, so that smooth switching free from shocks becomes possible.

Abstract: Disclosed in a variable speed pumping-up electrical power system comprising a variable speed generator/motor, a frequency converter connected between the generator/motor and an a.c. power system, a controller controlling an effective power input to the generator/motor by controlling the frequency converter on the basis of the difference between an actual effective power input from the a.c. power system and an externally-applied effective power command, and a correction circuit correcting the effective power command on the basis of the difference between the frequency of the a.c. power system and a frequency setting.

Abstract: In an induction motor drive controlled by SCR devices connected in the AC power supply phase lines of the motor, a plurality of channels establish, on a common input to a digital gate pulse generator of the SCR's, various signals occurring in the course of the motor drive operation. These signals relate to motor operating modes, such as soft start tripping, current limit. A central large scale integrated (LSI) chip responds digitally to such common input so as to establish the required firing angle at any instant and for any situation.

Abstract: To determine the flux in the air gap of an electrical machine having distributed stator windings, the voltages across two coils of a phase belt in certain phases of the stator are measured and the voltage across one coil in each phase belt is subtracted from the voltage in the other coil. The voltage differences are integrated to provide a measure of the air gap flux. Measurement of the entire air gap flux about the machine can be obtained utilizing two coils in a phase belt per phase of the machine. The instantaneous electromagnetic torque in the machine can be calculated directly as a function of the calculated air gap flux and of the currents in the stator windings. Such flux and torque measurements are obtained utilizing electrical connections to the existing coils of the machine, without the need to modify the machine by adding further windings or sensors. The flux and torque signals so obtained may be utilized in motor controllers, and are particularly useful for control of AC induction motors.

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 converter produces signals representative of the line-to-neutral voltages which are necessary for other circuit functions.

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 apparatus for an A.C. elevator having a variable voltage and variable frequency inverter for driving an induction motor coupled to a cage of the elevator, a control device for controlling the inverter in accordance with a deviation between a speed signal detected from the induction motor and a speed command signal having a preset value, and an abnormality detection device for interrupting feed of the A.C. power to the induction motor upon detecting that a slip frequency command corresponding to the deviation is greater than a predetermined set value and continues exceeding the predetermined set value in excess of a predetermined period of time.

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: Battery powered variable speed motor drives typically control the speed of the motor in accordance with a speed command. If the battery discharges to a point where the speed command is greater than that speed which can be supported by the battery voltage, the current drawn from the battery by the motor increases, thereby accelerating discharge of same. This problem is obviated by a control for an AC motor drive according to the present invention which includes means for deriving a signal from the output of the battery representing the maximum motor speed which the battery voltage can support, means for summing the maximum motor speed signal with the speed command signal to derive an error signal and means for summing the error signal with the speed command signal when the commanded speed is greater than that speed which can be supported by the battery voltage to reduce the speed command to the inverter and thereby maintain a predetermined voltage to frequency relationship in the inverter output.

Abstract: A variable frequency power unit controlling system for controlling a variable frequency power unit to supply an electric current of a frequency corresponding to a desired revolving rate of an electric motor. A control signal designating the revolving rate of the electric motor is integrated by an integrating circuit and the output frequency of the variable frequency power unit is held at a predetermined value regardless of the control signal, when the change rate of the output signal of the integrating circuit deviates from a predetermined range of change rate.

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

Abstract: 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: An induction motor is powered from a DC source through a DC to AC inverter. The inverter frequency and the AC output voltage of the inverter are controlled as a function of motor current to minimize motor starting current and to accommodate a range of DC supply voltages.

Abstract: A current source inverter operates in a full current regenerative mode without the use of a tachometer, rather a constant volts-per-hertz loop is used in a motor feedback loop to generate a torque signal determining the current reference in a DC link current control loop, and the DC link voltage is sensed to derive a signal in magnitude and sign to allow maximizing current control under torque limits established on the basis of such sensed DC link voltage.

Abstract: When actuating again in 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.