Abstract: Device for controlling electric motors of the asynchronous motor type operated by means of three-phase alternating current. For producing the operating current of the motor (5) a voltage-controlled oscillator (2) is foreseen and a generator (4, 6) controlled by the same and conditionally fed from a direct current source (1). The control device (3, 7, 8) is arranged to receive the pulse which arises upon operation of the motor (5) in its feed conductors (10-12) for alternating current and is thereby arranged to detect changes in the pulse shape of the operating voltage which occur due to electromotive forces induced from the motor windings when these are passed by the induced field of the rotor. These changes vary with the size of the slip. On the basis of the level of said deviations, a proportional voltage is induced which is transferred to the oscillator for its frequency control.

Abstract: A vector control unit that has an inverter connected with an induction motor which is not only electrically driven but is also being operated in a regenerative condition. The vector control unit comprises a detection circuit for detecting that the induction motor is being operated at a low speed and for detecting that signs of a rotor electrical angular velocity command and a slip angular velocity command differ from each other, and a control circuit for performing control such that the slip angular velocity command is not included in the angular velocity command when the induction motor is being operated at low speed and the signs of the rotor electrical angular velocity command and the slip angular velocity command differ from each other.

Abstract: A controller for a motor for raising and lowering a lift car in a lift well is disclosed which comprises transistor bridge circuits (10) for providing power to said motor (m), a first processor having a multiplexer (54) for passing one of a plurality of signals containing data relating to the state of said transistor bridge circuits (10) to an analogue to digital converter (38) for converting analogue signals to digital signals and providing said digital signals to a main processor (70), a polar conversion circuit (78) for receiving said signals from said transistor bridge circuits (10) and for converting the signals into signals having a magnitude and a phase component, an overcurrent sensor (85) for sensing whether the current supplied by the transistor bridge circuits (10) is too high, said overcurrent and sensor circuit being coupled to a pulse modulator circuit (87) for controlling the pulse width of the signal applied to the transistors in said transistor bridge circuits, and a second processing circuit

Abstract: A control device for an asynchronous motor (2), notably intended for the drive system of an electric vehicle, comprises electric supply source (10) able to produce an AC supply voltage whose frequency (FAL) and amplitude (UAL) may be adjusted independently of one another. For a given frequency of the supply voltage, the amplitude of the voltage is able to vary between a minimum value and a maximum value, the difference between the frequency of rotation of the turning magnetic field in the vicinity of the rotor and the frequency of rotation of the rotor being maintained substantially constant as long as the amplitude of the supply voltage is less than the maximum value. Once the maximum value has been reached, the torque on the shaft of motor (2) is increased by increasing the slip.

Abstract: A power converter apparatus includes a control mechanism for sampling input signals at a sampling frequency and generating an alternating current control voltage in response and for generating a two-axis voltage command. A phase correcting mechanism operating at a second frequency higher than the sampling frequency is provided for correcting the phase of the control voltage at the second frequency. A coordinate converting mechanism converts the voltage command into a multi-phase voltage command in response to the phase of the voltage after the phase correction by the phase correcting mechanism.

Abstract: In a speed control arrangement for an induction motor or an a.c. permanent magnet motor in which any one of a number of power frequencies may be selected for application to the motor, there is provided circuitry to control the rate of change of frequency from one selected power frequency to another to control the acceleration or deceleration of the motor.

Abstract: In order to carry out commercial synchronous exchange for disconnecting an induction motor from its driving power supply and connecting it to a variable frequency power supply, or commercial synchronous switching for disconnecting the induction motor from the variable frequency power supply and connecting it to a commercial power supply, without any accompanying adverse shock, an induction-motor vector control technique is utilized. A phase-locked loop (PLL) is formed to detect the difference in phase between the output voltage from the variable frequency power supply or the magnetic flux phase of the induction motor on the one hand, and the phase of the power supply voltage on the other, so that the difference in phase thus detected can be maintained at a predetermined value.

Abstract: In an AC drive, a method for stator flux oriented control of a waveform generator providing switching signals to an inverter supplying pulse width modulated current to a three-phase, variable frequency induction motor is provided. The method includes generating a quadrature axis stator voltage signal, a direct axis stator voltage signal, and a stator frequency signal to which switching signals from the waveform generator to the inverter are responsive.

Abstract: A system for increasing the power delivered to a brushless dc or induction motor from a sinusoidal motor drive by maximizing the dynamic range available to the motor winding excitation signals. According to one embodiment of the invention, sinusoidal excitation currents are applied to all but one of the primary windings of a brushless dc or induction motor. A variable voltage drive is applied to the one remaining winding. The voltage drive maximizes the dynamic range available to the sinusoidal excitation currents by selecting the voltage applied to that one remaining winding to be the difference between one half the dc source voltage and the instantaneous average of the highest and lowest of the motor terminal voltages.

Abstract: A hoist having an alternating current induction motor for rotating the drum of the hoist and an adjustable frequency power supply connected to the motor has a first control connected to the adjustable frequency power supply for directing the power supply to provide power to the motor at a first voltage level at the initiation of a raising operation. A second control is also connected to the adjustable frequency power supply for directing the power supply to provide power to the motor at the initiation of a lowering operation at a second voltage level which is lower than the first voltage level. The voltage level supplied to the hoist at the initiation of a raising operation may comprise a voltage level which is increased by a raising o first voltage boost value above the voltage level that would be applied without the first voltage boost value. At the initiation of a raising operation, the first voltage level may include a first voltage boost value.

Abstract: A current transformer (4) detects the output currents of a voltage-type inverter (INV), and comparators (6) check whether the outputs from the current transformer exceed a predetermined limit value. The detected output currents are fed to a vector analyzer (8) to determine the location of the output current vector. A zone determining circuit (9) determines the location of the current vector in the zones. An output pattern generating circuit (10) responds to the output from the zone determining circuit (9) and provides a switching pattern corresponding to the voltage vector nearest to a vector having the direction opposite to that of the output current vector. A selector (2), being controlled by the comparator (6), selects a switching pattern from the output pattern generating circuit and provides it to the inverter (INV), when the comparator (6) detects that the magnitude of the current vector exceeds the predetermined limit value.

Abstract: As a method for energizing a three-phase stepping motor of Y-connection, driving current values are set to be values resembling sine wave input approximation, thus making it possible to effect driving at small vibration. Energizing of the three-phase stepping motor is performed by a two-three phase driving scheme which calls for alternately effecting a two-phase excitation of the coils in the motor and a three-phase excitation of the coils in the motor. The driving current flowing through each of the coils approximates a sine wave having normalized values defined by .+-. 1, .+-. 0.87, .+-. 0.5 and 0.

Abstract: Methods and apparatus are provided wherein air gap flux magnitude and relative position are determined from stator voltage harmonic components and stator current in operating alternating current machines having a stator, a rotor and an air gap therebetween. Such determinations have various uses, such as for efficiency control. Various new and improved efficiency controllers are provided which utilize these measurements.

Abstract: A motor control circuit and a motor drive system using the same, in which a first transistor between the collector-emitter of which a first current in response to a drive signal for driving a motor is flown and a second transistor the base of which is connected to the base of the first transistor and between the collector-emitter of which a second current in response to the first current is flown are included, and the second current or a current dependent upon the second current is outputted to the coil of the motor as a motor drive current and the second transistor is turned to the saturation condition when the voltage at the coil rises more than a predetermined value, comprising a detection circuit of the saturation condition which is connected to the base of the second transistor and generates a detection signal in response to a voltage variation of the base of the second transistor when the second transistor operates under the saturation condition; and a feed-back circuit which decreases the second curren

Abstract: An object of the invention is to provide a control device of an induction motor where an inverter circuit can be protected from overcurrent by stable current limitation operation not only at steady operation but also at rapid acceleration/deceleration or at regenerative braking. A current component calculation circuit calculates a first current component from primary current detected by a current detector and output frequency. A correction frequency calculation circuit calculates a frequency correction value using a current limit value and the first current component according to prescribed function calculation. A subtractor subtracts the frequency correction value from a primary frequency command value. A voltage component calculation circuit calculates a primary voltage component command value according to the subtracted output.

Abstract: A motor control apparatus composed of a first pulse multiplier circuit for multiplying command pulses by a first factor, encoder circuit for detecting a position of a motor-driven object, a second pulse multiplier circuit for multiplying a detection pulse from the encoder circuit by a second factor, a deviation counter circuit for detecting a difference between output pulses of the first and second multipliers, a divider circuit for dividing an output signal of the deviation counter by the second factor, and driving source driven by the control apparatus in accordance with an output of the divider.

Abstract: A controller for a motor for raising and lowering a lift car in a lift well is disclosed which comprises transistor bridge circuits (10) for providing power to said motor (m), a first processor having a multiplexer (54) for passing one of a plurality of signals containing data relating to the state of said transistor bridge circuits (10) to an analog to digital converter (58) for converting analog signals to digital signals and providing said digital signals to a main processor (70), a polar conversion circuit (78) for receiving said signals from said transistor bridge circuits (10) and for converting the signals into signals having a magnitude and a phase component, an overcurrent sensor (85) for sensing whether the current supplied by the transistor bridge circuits (10) is too high, said overcurrent and sensor circuit being coupled to a pulse modulator circuit (87) for controlling the pulse width of the signal applied to the transistors in said transistor bridge circuits, and a second processing circuit com

Abstract: The invention is carried out by providing an adjustable frequency power supply connected to an alternating current induction motor which is rotated at speeds in excess of 60 hertz. A plurality of sequential frequency ranges are selected which, together, comprise a total frequency range from a maximum frequency range in excess of 60 hertz to 60 hertz which is applied to the motor. For each frequency range, a maximum breakdown torque of the motor is determined. When it is desired to decrease the speed of the motor, it is decelerated sequentially through each frequency range at a different deceleration rate for each range such that the maximum breakdown torque of the motor within each frequency range is not exceeded. Each different deceleration rate for each frequency range is determined by selecting the minimum period of time, for each frequency range, during which the motor may be decelerated without exceeding the maximum breakdown torque of the motor within that frequency range.

Abstract: The invention relates to a method of determining the estimate of the stator flux of an electric machine, comprising the determination of a stator flux estimate (.PHI..sub.sest) of the electric machine as a time integral of the difference between the voltage (u.sub.s) supplied to the stator and the product of the stator current (i.sub.s) and the stator resistance estimate (R.sub.sest), whereby the stator resistance estimate (R.sub.sest) of the electric machine is determined by correcting the initial value or another earlier value of the stator resistance on the basis of the stator current component (i.sub.d.sup.s, i.sub.d.sup..delta., i.sub.d.sup.r) parallel to the stator flux estimate (.PHI..sub.sest), the air gap flux estimate (.PHI..sub..delta.est) or the rotor flux estimate (.PHI..sub.rest). To be able to follow changes in the stator resistance of the electric machine in different operational conditions of the machine, said current component (i.sub.d.sup.s, i.sub.d.sup..delta., i.sub.d.sup.

Abstract: An induction motor vector control apparatus employing a rotating Cartesian coordinate system (d,q) having a d-axis held in coincidence with a secondary flux of the induction motor. Another rotating Cartesian coordinate system (.gamma., .delta.) having a .gamma.-axis held in coincidence with the induction motor primary current to detects a .delta.-axis induction motor primary voltage change caused by a change in the induction motor secondary resistance. The .delta.-axis primary voltage change contains no component related to a primary resistance change and it is used to compensate the secondary resistance for its change.

Abstract: A velocity control apparatus in which velocity of a servomotor (12) is controlled by PWM-control of an inverter is so adapted that the gain (K') of an amplifier section (11) in a current loop is held constant by detecting the power supply voltage of the inverter.

Abstract: A brushless motor comprises a rotor having multipolar magnets magnetized, a stator coil having a plurality of phases of winding, a rotor position detecting circuit to detect a specified position of the rotor and to output a signal having levels which alternately change in accordance with revolution of the rotor, and a phase changing circuit to output driving signals to the stator coil in accordance with the output of the rotor position detecting circuit, a stop time signal generating circuit to output a drive-stop signal for stopping the actuation of the stator coil for a predetermined time from the time when a level of the output signal of the rotor position detecting circuit is changed, a temperature detecting element to detect the temperature of an object to be cooled, an instruction value generating circuit to output to the stop time signal generating circuit an instruction signal in response to the output of the temperature detecting circuit so as to change the specified time, and an overheat detecting c

Abstract: In a motor control apparatus and a motor controlling method, when a connector is disconnected while an operation signal is ON, an excitation current component signal becomes zero and does not reach a predetermined value even after a predetermined period of time. In this case, a current component signal discriminating circuit discriminates that an amplitude of the excitation current component signal is equal to or less than the predetermined value, a timer issues an alarm signal because the predetermined period has passed from input of the operation signal, and a stop circuit stops operation of an inverter upon reception of the alarm signal, so that the inverter is prevented from breakdown.

Abstract: A polyphase machine fed by a pulse-controlled a.c. converter in which the current is controlled between rectangular and sine-shaped waveforms in each half cycle according to the required torque. Independently of the current control, the active number of phase windings is reduced as a function of the rotational speed of the machine.

Abstract: A slip frequency type vector control apparatus for an induction machine which is provided with first and second feedback circuits for correcting respective magnetization current command and torque current command supplied feed-forwardly so as to eliminate the influence of a change in temperature of the induction machine secondary resistance and realize a correct vector control.

Abstract: The drive arrangement suitable especially for a hoist mechanism comprises a pole-changing two-speed three-phase motor which is united into one construction unit with a friction brake which can be released by an electromagnet. The two three-phase field windings dimensioned for different pole numbers are connected in star circuit arrangement and have star points conducted out at the motor terminal box of the three-phase motor. The electromagnet of the friction brake is connected through a rectifier circuit arrangement to the star points and when the three-phase motor is switched on is energized by the differential voltage then occurring between the two star points for the release of the friction brake.

Abstract: A device and associated method to control the electromechanical energy conversion process of a variable speed drive utilizing a doubly fed machine, which provides the mechanical energy as demanded by some mechanical load. Alternatively, a device and associated method is provided for a synchronous motor. The terminals of either the stator or rotor winding of the doubly fed machine are directly connected to a polyphase AC power grid of a certain grid frequency. The device establishes through electronic control a stable operation of the drive at a desired power factor at the terminals of these windings, irrespective of varying load conditions. This capability is provided without the need for computing or sensing this desired power factor and the subsequent feedback of its deviation from the desired value through a properly designed regulator.

Abstract: A control system for an AC motor driven cyclic load, such as a beam pumping unit, includes a flywheel, transducer, tachometer, outside set point source, controller, and variable frequency power supply. The flywheel is rotatably connected between the motor and the cyclic load for receiving and storing rotational kinetic energy from the motor and the load during portions of a cycle of the cyclic load when there is excess energy and returning the stored rotational kinetic energy to drive the cyclic load during portions of a cycle when there is an energy demand by the cyclic load. The transducer generates a transducer signal which is a function of the cycle speed. The tachometer means generates a tachometer signal which is a function of the speed of rotation of the motor's rotor. The outside set point source generates an outside set point signal representative of a desired set point cycle speed of the cyclic load.

Abstract: A method and apparatus for vector control of an induction motor. A slip frequency is calculated based on a desired motor torque, a desired motor flux and a motor secondary time constant. An actual value for induction motor angular velocity is estimated as a function of primary current and voltage applied to drive the induction motor. The calculated slip frequency is added to the estimated angular velocity to calculate an angular frequency. The calculated angular frequency is used along with the desired motor torque and the desired motor flux to vary the primary current and voltage so as to drive the induction motor with no .beta.-axis secondary flux.

Abstract: A control apparatus for controlling a PWM inverter, the PWM inverter receiving AC power and generating an AC output having a controlled frequency to be supplied to an AC motor, comprises a circuit for generating, on the basis of a given running command, a PWM signal controlling the inverter with a given sampling period, and a circuit for controlling the PWM signal generating circuit, whereby the AC motor generates an electromagnetic tone preselected so as to correspond to desired information when the AC motor is driven by output of the inverter controlled by the PWM signal. The above described desired information may be information representing the running state of the motor or selected music.

Abstract: A circuit and method to improve power efficiency of AC induction motors is described for adopting an AC PWM chopper method in power input controls. For a period of several seconds after initially supplying power source voltage, the starting voltage is bypassed by a relay switch to prevent malfunctioning of devices.A PWM waveform is provided by a microcomputer and it is combined with a zero crossing signal of the power source voltage. The combined signal is controlled and buffered by photo couplers, by which power source voltage is controlled with transistors of a power controller unit.A current flow through the motor is detected and store into memory of the microcomputer. In a next sequence, another PWM waveform is provided to again detect other current flow through the motor and its detected value is compared with the previous value store in the memory. These sequences are repeated to search for a minimum current value according to variation of loading on the motor.

Abstract: An inverter driving method for has an arrangement polyphase induction motor, for altering a plurality of winding connections of the motor and a storage arrangement for a plurality of motor control constant groups preset corresponding to the respective winding connections so as to perform optimal vector control. When the classification of the winding connection is selected, one set of motor control constant groups corresponding to the winding connection is read out of the storage arrangement and applied to a control unit of the induction motor as control constants.

Abstract: In an induction motor controller, for the amount equivalent to the secondary interlinkage flux computed by use of a component of lag of first order based on the search coil voltage or the primary voltage of the induction motor, an error with respect to the actual secondary interlinkage flux is increased in a low-speed range. However, since an estimated amount equivalent to the secondary interlinkage flux computed based on the estimated amount of the secondary interlinkage flux is also attended with the same error with respect to the secondary interlinkage flux, when the former is substracted from the latter, there only remains a term concerning the speed estimation error, which enables an estimation of the speed to be conducted also in the low-speed range.

Abstract: In speed control apparatus and method for a motor operable to drive a load whose magnitude varies over a predetermined period which use a unit for controlling voltage or current supplied to the motor such that the speed of the motor can coincide with a command speed, n pieces of data indicative of voltages or currents supplied to the motor and corresponding to n divisions of the predetermined period are independently stored in a read/write storage, at least one of the n pieces of data is corrected at the rate of each of the n divisions in accordance with a difference between the command speed and the speed of the motor, and the voltage or current supplied to the motor is controlled in accordance with at least the one of the n pieces of data, so that pulsation and noise occurring especially under low revolutions can be minimized.

Abstract: An inverter including a manual torque boost mechanism for outputting a constant voltage/frequency pattern by manually setting a constant voltage corresponding to a constant frequency regardless of the magnitude of a current value of a drive power supplied to a rotation drive apparatus such as a motor and an auto boost mechanism operative based on the constant voltage/frequency pattern set by the manual torque boost mechanism for automatically correcting the voltage/frequency pattern according to the magnitude of the input current of the rotation drive apparatus and is capable of compensating for the torque decrease of the input current by use of the manual and auto torque boost mechanisms especially when the input current of the rotation drive apparatus is in the low-frequency range.

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 direct drive motor system for controlling driving of the joints of a multi-jointed robot, comprising a motor portion, a rotation detecting portion, a position control portion, a speed control portion, a driving circuit and a tuning portion, wherein the motor portion is of an inductor type, the rotation detection portion uses an optical rotary encoder or magnetic resolver, and the position control portion is arranged to control in a feedback manner the rotational position of the motor with a tertiary servo system with software. The system's driving circuit has a feedback control loop for the current of the motor coil, and a detection circuit for the current includes a small signal isolator. The tuning portion tunes the servo systems of the speed control portion and the position control portion. As a result, the system simultaneously satisfies various requirements of such a direct drive motor.

Abstract: A method and an arrangement for controlling an asynchronous motor fed via a frequency converter. The control is accomplished with a model implemented in a microcomputer which is provided with data derived from the characteristics of the motor set forth on the rating-plate of the asynchronous motor along with data derived directly from the operating characteristics.

Abstract: A turbine helper drive apparatus includes a turbine for driving a load, a motor coupled to the turbine, and a power converter for controlling an output from the motor based on a predetermined power reference. The power converter controls the motor so that the motor performs either a motoring operation, wherein the motor drives the load together with the turbine, or a regenerating operation, wherein the motor serves as a load for the turbine to generate an electric power.

Abstract: A vector control system for an induction motor driven by a power converter which generates three phase ac currents containing harmonics.

Abstract: An apparatus for controlling a three-phase inverter supplying the a.c. motor of an elevator, the inverter having a power stage implemented with semiconductor switches, and the apparatus comprising an electronic control unit for producing a velocity reference value and a tachometer generator for producing an actual velocity value, voltage measuring elements for measuring a.c. voltages at the inverter output, and pulse width modulators and drivers for controlling the semiconductor switches in the inverter's power stage with control signals derived from the pulse width modulators. With the apparatus of the invention, fast control of the control voltage is achieved. Moreover, simpler voltage measuring elements may be used instead of current measuring elements.

Abstract: A method of forming the amplitude of the reference voltage of a three-phase inverter supplying a squirrel cage motor requires no current measuring elements. In this method, the amplitude is formed by finding in predetermined constant flux curves which represent the squirrel cage motor in question, and in which the motor rotor current frequency appears as parameter, a curve from which is obtained the amplitude of the motor stator voltage, i.e. of the inverter reference voltage, corresponding to the frequency of the motor's stator voltage, i.e. of the inverter reference voltage, so that the magnetic flux in the stator will be constant.

Abstract: A control system for an induction motor includes a power presumption circuit for presuming an electric energy F.sub.o, which is associated with a reactive power generated in the induction motor, on the basis of the numerical constants including the secondary winding resistance, the actual primary current and the actual rotation speed or angle of the induction motor. The electric energy F.sub.o is used to compensate for the change of the numerical constants of the induction motor, which is caused by the change in temperature.

Abstract: A control system for an M-phase a.c. machine which measures the currents in at least (M-N) phases, where N=2 if M is even and N=1 if M is uneven, measures the instantaneous values of the voltages in (M-N) phases and obtains control signals for alteration of the input voltage and/or current to the motor to maintain the motor in an efficient running condition.

Abstract: A reduced-order, discrete-time rotor flux estimator for use in a field-oriented induction motor control system utilizing rotor speed as an input.

Abstract: A reversible variable-speed two-phase motor is disclosed. The motor comprises two sets of stator coils of equal impedance displaced in space by 90 degrees and transistor inverters to provide exciting current to the stator coils. The current supplied to one of the sets of stator coils is 90 degrees out of phase with the current supplied to the other set of stator coils, and the direction of the current in each set of stator coils reverses every 180 degrees so that a smoothly rotating magnetic field is produced. The motor can be operated as an induction motor or as a synchronous motor or as a direct current brake.

Abstract: A control system for controlling a PWM inverter so that the inverter drives an induction motor at a variable voltage and a variable frequency while keeping constant a ratio of the output voltage of the inverter to the output frequency thereof, is disclosed which includes current component detecting means for detecting an effective current corresponding to a load, from the input current of the induction motor, frequency setting means for setting the output frequency of the PWM inverter, flux setting means for setting the amount of magnetic flux generated in the induction motor, correcting-frequency calculating means for calculating a frequency correcting quantity proportional to the effective current, and correcting-flux calculating means for calculating a flux correcting quantity proportional to the effective current.

Abstract: In a servo-system of a conventional numerical control (NC) device, a delay in response or deformation is always observed on an output side with respect to an inputted speed command or position command and an actual output response behaves differently from a command value. Such delay or deformation of the output response constitutes a significant problem particularly in case of controlling one object simultaneously by a plurality of servo-system, which results in a remarkable defect in a controlling performance. According to this invention, when a transfer function of a servo-system of the type comprising a control system and a control object is designated by W, a device or a signal conversion system with an inverse function 1/W of the transfer function W is located a a pre-compensation system in advance of the control system thereby to input a speed or position to be controlled into the pre-compensation system.

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 control apparatus and method are provided for a load energized by an inverter coupled with a DC power source. The lag current angle between the current and the load voltage is utilized to determine when the output current is positive and when the output current is negative. The conduction times of the respective upper and lower gate turn off thyristors of each pole of the inverter are controlled in relation to the established current angle, with a provided modification of those conduction times being phased out in response to the desired output voltage for said load.