Abstract: A power control apparatus for controlling power supplied to an electric motor rotating a rotor employed in a centrifuge is provided. The power control apparatus includes first and second inverters and a smoothing capacitor disposed between the first and second inverters. In a motor power mode, the first inverter charges the smoothing capacitor with power supplied by an AC power supply, while the second inverter charges, in a motor braking mode, the smoothing capacitor with power regenerated by the motor during a braking operation for returning the regenerated power back to the AC power supply through the first inverter. An reactor is arranged between the AC power supply and the first inverter for reducing harmonic components contained in the current supplied from or back to the AC power supply.

Abstract: A control unit for a motor and a control method for it, which are adapted for conducting control at a high speed so that efficiency of the motor by inverter operation of an induction motor is maximum at all times. This unit comprises means (3) for detecting effective power delivered to a motor (14), calculation means (1, 2, 4, 5, 6, 7, 8 16, S.sub.1, S.sub.2, S.sub.3) for calculating, from the detected effective power and frequency (f) of an A.C. voltage delivered to motor (14), supply voltage (V.sub.1) to motor (14) where efficiency of motor (14) becomes maximum, and means (9, 10, 11, 12) for delivering the calculated supply voltage (V.sub.1) to motor (14).

Abstract: A system for increasing the efficiency of single and multi-phase induction motors. The system is comprised of a microcontroller which combines a time when the AC line current reaches zero amps with a time when AC line voltage to the AC motor reaches zero volts and with a digital measurement provided by an A/D converter to determine a servo error. The servo error determines whether the A/C motor needs more or less power. The microprocessor provides a control signal to a switching means to supply the minimum power required based on the servo error.

Abstract: An input power control apparatus for use with an AC induction motor adjusts a firing angle to allow the motor to run at near a rated speed of the motor and then to find a minimum power point at some voltage level in a variation of the applied voltage.

Abstract: A Power Factor Corrector system for use with AC induction motors which detects information from the motor voltage and motor current and decreases the power input to the motor proportional to the detected phase displacement between the current and voltage resulting in reduced electrical power input to the motor as the mechanical load is decreased.

Abstract: A control system for a permanent magnet synchronous motor includes a position estimator means having for cross correlating the back EMF of the unenergized winding with a reference waveform to determine the estimated position of the rotor for determining rotor angle position error; an error compensator, responsive to the rotor angle position error, for determining the angular speed of the field; an angle generator, responsive to the angular speed of the field, for generating the field angle position; and a waveform generator, responsive to the rotor angle position, for generating a periodic signal corresponding to each winding and designating a segment of that signal for driving that winding to adjust the field speed to the rotor speed.

Abstract: A method for determining the real power of an electrical drive, preferably an electrical fitting drive, includes subtracting an ohmic or resistive power loss in a stator of the drive from a measured real power. It is intended that an ohmic or resistive power loss in a connecting line of the drive also be subtracted. A device for determining the real power of an electrical drive includes line pairs each connecting two connecting lines remotely from the drive, to a DC voltage source. A known ohmic or non-reactive resistor is inserted into one of the lines in each case. Each of the lines is connected on the side of the ohmic or non-reactive resistor facing toward the drive, through a voltmeter, to the other line. The voltmeters are connected to an evaluation unit.

Abstract: A power control apparatus for controlling power supplied to an electric motor rotating a rotor employed in a centrifuge is provided. The power control apparatus includes first and second inverters and a smoothing capacitor disposed between the first and second inverters. In a motor power mode, the first inverter charges the smoothing capacitor with power supplied by an AC power supply, while the second inverter charges, in a motor braking mode, the smoothing capacitor with power regenerated by the motor during a braking operation for returning the regenerated power back to the AC power supply through the first inverter. An reactor is arranged between the AC power supply and the first inverter for reducing harmonic components contained in the current supplied from or back to the AC power supply.

Abstract: A pump control and protection system comprised of an analog module and a digital module. The analog module includes a synchronous phase detector, a pressure transducer and an over voltage/under voltage circuit. The synchronous phase detector determines the phase angle between a current signal supplied to a water pump and a voltage signal supplied to the pump. The output of the phase detector is directed to a programmable array logic device in the digital module and used to activate a solid state relay that controls the power supplied to the pump. The water pressure in the system is displayed on a digital display.

Abstract: A shredder motor circuit with power factor correction is provided. A permanent split capacitor motor under full load will run at peak efficiency with a high power factor. However, at no-load or at partial load the power factor will drop significantly, resulting in wasted energy and a possible overheating of the motor. This condition is inventively corrected by the present invention by lowering the voltage to the motor when the motor is partially loaded. The purpose of this shredder motor circuit with power factor correction is to vary the voltage to the motor instantaneously as the load changes due to increased amounts of paper placed in the shredder and thereby supplying the right amount of power required to result in higher efficiency and a cooler operating motor.

Abstract: A method and apparatus to be used with a motor controller for determining the speed of the motor rotor using current zero crossing times of the stator winding currents. An error signal set, consisting of phase angle errors between consecutive zero crossings over a sampling period, is generated and analyzed in a region of interest in either the time or frequency domain, producing a signal frequency, the signal frequency being the frequency of the motor rotor.

Abstract: A method for determining at least one operating parameter to determine the operating condition of a polyphase electric motor system comprises sensing the instantaneous current signal and the instantaneous voltage signal as a function of time for more than one electrical phase of the motor. The sensed current signals and the sensed voltage signals are both amplitude demodulated and phase demodulated to provide amplitude demodulated current and voltage signals as a function of time and phase demodulated current and voltage signals as a function of time. The resulting amplitude and phase demodulated signals are used to determine one or more of the following electrical parameters as a function of time: total real power, real power per phase, total reactive power, reactive power per phase, total apparent power, apparent power per phase, overall power factor, power factor per phase, electrical impedance per phase, and electrical balance.

Abstract: An induction motor is operated at a high electrical efficiency level by employing a line current peak detector in conjunction with an electronic phase angle controller and a microprocessor system controller. If the line current peaks remain substantially constant the phase angle controller increases a phase gap in the applied line voltage to a width incrementally greater than a full-load value, at which point the line current peak value increases substantially. The increase in line current peak value is sensed by the line current peak detector and a signal is transmitted to the microprocessor system controller which in turn automatically adjusts the control input to the phase angle controller in order to incrementally decrease the existing phase gap in the output of the phase angle controller. Varying mechanical loads are therefore automatically accommodated while keeping the motor running efficiently.

Abstract: A unity power factor power supply for an electric motor. A switch-mode circuit is employed which, in a first mode, transfers power from AC main to a constant voltage DC bus. In a second mode, power generated on the DC bus is fed back to the main power supply. The circuit of the invention automatically maintains the DC bus voltage constant and sets an adequate operation mode by processing the DC bus voltage signal. In both operation modes, the unity power factor and sinusoidal waveform of the AC main side are maintained.

Abstract: An induction motor control apparatus, for converting an AC power supply voltage to a motor supply voltage for an induction motor, includes a feedback control loop for controlling the level of the motor supply voltage such that the induction motor operates close to a predetermined value of power factor, and also includes circuits for deriving a signal which varies in accordance with the motor admittance (or impedance), and for differentiating that signal to obtain a parameter variation signal which indicates an amount and direction of any sudden change in the motor load torque. The parameter variation signal is applied to the control loop such as to immediately increase or decrease the motor supply voltage, as required, when any sudden change in load occurs, thereby ensuring rapid control response together with stability of control.

Abstract: Power factor control of a pulse width modulated inverter supplied permanent magnet motor is achieved by using Park Vectors for automatically adjusting a pulse width modulating signal for approximately unity power factor, thereby avoiding the heretofore required manual adjustment during operation of the motor for power factor changes in accordance with changes in EMF and motor resistance.

Abstract: A power control circuit for induction motors wherein a servo loop is used to control power input by controlling the minimal power consumption of motor operation. The minimum power consumption is measured by sensing current or power and operating the servo loop at or near a minimally sensed power consumption level. The negative derivative of power consumption vs voltage curve, dP/dV, is sensed and a minimal value is used in a servo loop's error summing point wherein compensating slightly drives the power consumption point past the minimal power consumption point to regulate minimal power consumption by a smooth, minimal cycle. Maximum energy savings is thus attained with a smooth, stepless regulating method placing no mechanical stress on the motor-and-load combination. An indicator of power savings and normal operation is inherent in this type of control system which provides for a device for both indicating the level of savings and alerting of system faults.

Abstract: In the open-loop control of A.C. power controllers through the phase-angle control of semiconductor valves (4), the chronological sequence of the firing signals (Z) for the semiconductor valves (4) is determined by reference signals (X). When the reference signals (X) fail for one or more periods, this chronological sequence is disturbed and damage to the load (2) to be controlled can result. Therefore, according to the invention, a method is provided whereby a safety firing signal (ZS) is always derived from the preceding firing signals (Z) when the expected reference signal (X) fails. In addition, a device for implementing the method is specified.

Abstract: A power factor control system for an A.C. induction motor determines the difference in phase between the voltage applied to the motor and the current drawn by the motor. Based upon this difference in phase, an integrator generates an error signal. The error signal is compared with a ramp wave to derive a pulse signal which controls the voltage applied to the motor, which in turn controls the amount of current supplied to the motor, in order to reduce the power consumed by the motor. The integrator includes a dual-path feedback filter having a polarized capacitor in each path. A power supply is used to quickly provide the full operating bias voltages required by several of the components contained in the control system.

Abstract: A power factor control system for an A.C. induction motor determines the difference in phase between the voltage applied to the motor and the current drawn by the motor. Based upon this difference in phase, an integrator generates an error signal. The error signal is compared with a ramp wave to derive a pulse signal which controls the voltage applied to the motor, which in turn controls the amount of current supplied to the motor, in order to reduce the power consumed by the motor. The integrator includes a dual-path feedback filter having a polarized capacitor in each path. A power supply is used to quickly provide the full operating bias voltages required by several of the components contained in the control system.

Abstract: An energy-saving induction motor control apparatus maintains the operation of a motor at an optimum power factor irrespective of changes in motor load, by generating a power factor compensation value which is varied in accordance with the motor supply voltage. The motor supply voltage is controlled such as to reduce any difference between the optimum power factor value and a measured power factor value, thereby ensuring that stable operation with minimum energy consumption are achieved over a wide range of motor load values.

Abstract: A variable speed drive system for an induction motor is disclosed which utilizes power factor correction capacitors to allow an induction motor to be driven by a line-commutated inverter using variable phase angle triggering of the thyristers in the inverter to compensate for frequency-induced changes in the operating point of the system.

Abstract: A drive system for an automatic washer or dryer having a rotatable drum about a horizontal axis. An induction motor drives the drum and is connected to and disconnected from a source of alternating voltage by a microprocessor to control the speed of the motor. The microprocessor senses the zero crossing of the alternating voltage and the zero crossing of alternating current flowing in the motor to determine the time to connect the motor to the alternating voltage. The microprocessor analyzes successive readings of the motor's back emf to detect undesirable load distributions and effect redistribution.

Abstract: An electric induction motor is coupled to a source of alternating current by a thyristor switch. A control circuit triggers the thyristor switch to create conductive and non-conductive states during each cycle of the alternating current. A circuit senses the voltage across the thyristor switch during a non-conductive state. From that sensed voltage and known characteristics of the motor being controlled, the control circuit derives a measurement of the current flowing through the motor in the conductive state of the thyristor switch. One of two different derivation techniques is used depending upon the length of the non-conductive state. The control circuit includes a means for calibrating the derivation of the current measurement for a specific motor.

Abstract: An onboard power generation system for use on board a vehicle, such as a passenger car, includes a brushless doubly-fed generator. The generator has a rotor with rotor conductors and a stator with stator windings, the stator windings comprising first and second polyphase stator systems. The generator rotor is mechanically coupled to and driven by the vehicle engine with a driving force to produce an AC power output from the first polyphase stator system. The generation system has a rectifier which receives and rectifies the generator first polyphase stator system AC power output into DC power for delivery to a DC bus of the generator power system. A sensor senses a parameter of the AC power output received by the rectifier and produces a sensor signal in response thereto. A converter receives the sensor signal, and in response thereto, converts power received from an excitation power source into excitation power for the generator second polyphase stator system.

Abstract: An energy efficient electric motor is provided with a supplementary run winding arrangement which operates in conjunction with the motor's main run winding to produce a combined magnetic field with sufficient strength to operate the motor under full load. Less than full load operation obtains increased efficiency through a reduction of power flow to the supplementary run winding arrangement, which brings about a significant reduction in stator core structure (eddy current) losses and winding (resistance) losses. A controller may predetermine the normal amount of magnetic field strength necessary during each portion of the motor's usual operating cycle and variously modulate the instant level of power coupled with the supplementary run winding arrangment.

Abstract: A drive system for an automatic washer or dryer having a rotatable drum about a horizontal axis. An induction motor drives the drum and is connected to and disconnected from a source of alternating voltage by a microprocessor to control the speed of the motor. The microprocessor senses the zero crossing of the alternating voltage and the zero crossing of alternating current flowing in the motor to determine the time to connect the motor to the alternating voltage. The microprocessor analyzes successive readings of the motor's back emf to detect undesirable load distributions and effect redistribution.

Abstract: The invention relates to a motor output changeover control apparatus used for the spindle motor of machine tools. Conventionally, since a constant output over a wide range is realized by gears, a spindle motor is constituted by a single winding. The amount of heat produced by the winding is great, and a speed-change mechanism employing the gears is large in size.With the motor output changeover control apparatus of the invention, output characteristics over a wide range from high to low speeds is stabilized by changing over the connection of the power lines of an AC motor.

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

Abstract: An improved induction motor control system utilizes an inverter supplying a variable frequency AC voltage to drive the induction motor, and volt/frequency (V/F) control section controlling the inverter to produce a suitable voltage and frequency in a predetermined relationship therebetween. A power factor detecting section is included to detect a power factor phase angle between the motor current and the inverter output voltage as indicative of an amount of load imposed on the motor. The detected power factor phase angle is compared with a predetermined phase angle which is a frequency dependent angle indicative of a standard load at a given frequency, in order to provide a control output in response to which the V/F control section alters the inverter output voltage out of the predetermined relationship with the frequency for improving motor efficiency. Thus, the detected load (i.e.

Abstract: A three-phase motor is operated by a controller having sets of thyristors which trigger electricity from each phase of a supply to the motor. The controller measures the interval .phi. between the voltage and the current when one phase of the motor makes a zero crossing and measures the interval .gamma. when the thyristors are non-conductive during a half-cycle of the voltage for one phase. A control angle .theta. is calculated according to the equation .theta.=.phi.+K.gamma., where K is a positive number. The control angle .theta. is compared to a reference value to derive an error value. The times at which the thyristors are triggered is controlled in response to the error value. To start the motor, the reference value is gradually decreased to trigger the thyristors progressively earlier during each half cycle of the supply voltage. To stop the motor, the reference value is gradually increased to trigger the thyristors progressively later during each half cycle of the supply voltage.

Abstract: A DC braking system for an inverter-driven induction motor, (e.g., three-phase). When a braking command occurs, the normal gating sequence of the inverter stops. Mode 1 of the braking procedure starts. In Mode 1, two semiconductor phase switches of the group connected with one of the DC buses and the semiconductor switch of the third phase that is connected with the other DC bus are latched in a conducting state. The motor essentially receives DC current, which increases until it actuates a current limit device, clearing the latch. Then all six switches are turned off. That drives the motor current through the back-biased parallel diodes. The negative DC bus voltage is available to suppress motor current despite large motor speed voltages. The apparatus repeats the Mode 1 procedure for a predetermined time interval, after which Mode 2 of the braking procedure starts. In Mode 2, just as in Mode 1, two switches of one bus and one switch of another bus conduct until an overcurrent limit is reached.

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: An electronic motor starter for use with a single-phase induction motor in which the hysterisis width can be adjusted in the range of 75 volts by providing for the control of a positive feedback characteristic of NAND gates and a strength of input signal. The motor starter according to the present invention utilizes an induced voltage across the starting winding of a motor to start the motor and maintains a steady operation thereof.

Abstract: A driver system for an ultrasonic probe using a tunable inductor in series with the piezoelectric crystal excitation transducer in the probe. The bias current through this flux moduation coil is controlled by the system such that the inductance of the tunable inductor cancels out the capacitive reactance of the load impedance presented by the probe when the probe is being driven by a driving signal which matches the mechanical resonance frequency of the probe. The resulting overall load impedance is substantially purely resistive. The system also adjusts the frequency of the driving signal to track changing mechanical resonance conditions for the probe at different power levels. This method of operation insures substantially maximum power transfer efficiency and substantially linear power control over a range of power dissipation levels.

Abstract: An improved induction motor control system. Single-phase and three-phase AC induction motors are controlled in accordance with the equation y=m=x+b, where y is the phase angle, m is the slop, x is the firing delay and b is the offset. Subsequently, the firing delay is increased by predetermined amounts, the behavior of the phase angle is evaluated for several cycles, and the motor is controlled based on the results of the evaluation, thereby minimizing energy consumption.

Abstract: This invention relates to a control system for an induction motor which has power factor control means for altering the power factor of the input current of a converter composed of self-arc extinguishing elements, such as transistors, to vary the d.c. output voltage of the converter to perform a pulse-amplitude modulation control in a variable voltage, variable frequency controller for controlling the rotating speed of the induction motor by the converter of a sinusoidal wave input to reduce noise generated by the operation of the motor.

Abstract: A high frequency link power converter apparatus includes a power source, a circulating current type AC-AC converter having an output terminal connected to the power source, a high frequency phase-advancing capacitor connected to an input terminal of the AC-AC converter, a phase controller for controlling a firing phase of the AC-AC converter, an external oscillator for supplying phase reference signals to the phase controller, a first circuit for controlling a crest value of voltages applied to the phase-advancing capacitor, a second circuit for detecting a phase difference between the reference signals and the voltages applied to the phase-advancing capacitor, and a third circuit for controlling the phase difference, so that the magnitude of the phase difference becomes substantially zero.

Abstract: An automatic power factor control apparatus for an inductive load such as an AC induction motor includes a circuit for producing a signal varying in accordance with the load power factor, which is applied to control the duty cycle with which switching elements are alternately set in the conducting and non-conducting states by high frequency switching operation. A level of voltage applied to the control winding of a saturable reactor connected in series with the load is controlled by the switching elements, and the saturable reactor thereby continuously controls the input voltage and load current of the inductive load in accordance with the power factor.

Abstract: Timing the firing of thyristors in a motor controller is done by using a microprocessor for timing relative to the event of current reaching zero, and by using hardware that generates firing signals in response to the voltage crossing zero. A motor controller has: thyristors for connecting the motor to a source of AC electrical energy; motor voltage zero crossing circuitry and motor current zero crossing circuitry for measuring a LAG TIME indicative of the time interval between the event of voltage applied; to the motor crossing zero and current flow to the motor reaching zero; a microprocessor generating a desired OFF TIME indicative of a desired time interval between the event of current flow to the motor reaching zero and firing of the thyristors; phase angle controller circuitry for firing the thyristors at a firing time after the event that the voltage applied to the motor crosses zero, the firing time being computed by adding the LAG TIME and the OFF TIME.

Abstract: A motor having a capacitor in series with its coil permits the motor to operate at a higher voltage or range of voltages over its design voltage. A method determines the correct value of a capacitor to change the design voltage of a motor to a different operating voltage. A receptacle can be used to receive capacitors of different values to vary the operating voltage of a motor. The receptacle is provided with a capacitor holding device which is marked with the operating voltage set by the capacitor. A timer clock has a motor of a design voltage which can be changed to a plurality of operating voltages. The timer clock can have the receptacle accessible from the exterior with a cover having the operating voltage marked thereon.

Abstract: An electric power converter, in which a plurality of converters convert a first electric power having a first frequency into a second electric power having a second frequency, and the second electric power is supplied to a load such as an electric motor, and in which a correction controller changes a reference voltage to generate reference voltage signals to be supplied to the converters in order to shift firing phase angles of the converters, thereby preventing a generation of higher harmonics of integer orders of the first electric power.

Abstract: The present invention is a load sensor for use in an automatic portal operator such as an industrial gate operator. An induction motor is employed to move the gate. The power factor of the AC electric power supplied to the induction motor is monitored. A safety operation is triggered when the power factor indicates the motor load is greater than a predetermined amount, as when an obstruction is encountered by the gate.

Abstract: A load state detecting apparatus of an induction motor having two coils, the apparatus having a drive voltage supplying unit for supplying a drive voltage to the coils in the induction motor, a phase difference detecting unit for detecting a phase difference between the drive voltage supplied across the coils of the induction motor and a current flowing through one of the coils upon application of the drive voltage and for generating a phase difference signal, and a load state detecting unit for comparing the phase difference signal generated by the phase difference detecting unit with a predetermined reference value and generating a signal depending on a load state of the induction motor.

Abstract: An electric motor is coupled to the power lines by thyristors. The motor is braked by triggering the thyristors at the proper times to produce a electro-magnetic field within the motor which opposes the residual magnetic field of the rotor. The proper time to trigger the thyristors is determined by comparing the polarity of the voltage across the power lines to the back emf voltage from the motor. The thyristors are triggered when these two voltages have opposite polarities. The braking circuit also regulates the duty cycle of the thyristors to control the magnitude of the current applied to brake the motor.

Abstract: An indication that a motor has reached full speed operation is produced by generating an up to speed signal based upon measurement of the phase angle between the voltage applied to the motor and electric current flowing to the motor. A motor up to speed detector has; means for connecting an electric motor to an electric power source; means for measuring the time interval between the event of voltage applied to the motor crossing zero and the event of current flow to the motor reaching zero to obtain a measured value of current lag; and, means for comparing successive measured values of the current lag at predetermined time intervals after electric power is applied to the motor as the motor is started, and for generating a signal indicative that the motor has reached an up to speed condition in the event that successive measured values of the current lag increase.

Abstract: Electric power consumed by an a.c. induction motor is measured and sensed changes in power factor are used to modulate the combined magnetic flux produced in the motor field by two sets of RUN windings. A main RUN winding set, which normally couples fully with the a.c. power, is engineered to have sufficient ampere-turns to produce just enough magnetic flux to operate the motor with a light load and maintain a moderately high power factor. Motor driven load increases are determined by sensing a corresponding increase in the power factor of the main RUN winding set, whereupon power flow to a secondary RUN winding is proportionately increased. Considerable energy savings occurs when the motor drives a fluctuating load due to reduced magnetic field excitation under all but full load conditions, with the result that energy ordinarily wasted by eddy currents, copper losses, and poor power factor operation is considerably lessened. Other possible losses due to harmonic distortion of the a.c.

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: Many induction motor controllers employ a reference angle relative to the supply voltage which is a target for the phase lag of current behind voltage but the choice of the optimum reference angle for energy saving varies from motor to motor. In the present invention firing signals for thyristors connected between a supply and a motor to be controlled are generated by firing circuits under the control of a microprocessor 18. The firing angle for the thyristors is continuously adjusted according to the phase lag as indicated by supply voltage zero crossings and current sensing circuits, load on the motor, and a signal indicating the tendency of the motor to stall obtained from the back e.m.f. of the motor. Using the said signal can be regarded as equivalent to adjusting the reference angle for the optimum value mentioned above. A procedure for starting a motor and setting the initial value of the reference angle is also described.

Abstract: An AC motor drive apparatus of this invention is constituted by an AC power source, a first circulating current type cycloconverter having an output terminal coupled to the AC power source, a phase-advanced capacitor coupled to an input terminal of the first cycloconverter, a second circulating current type cycloconverter having an input terminal coupled to the phase-advanced capacitor, and an AC motor coupled to an output terminal of the second cycloconverter. The first cycloconverter controls a current supplied from the AC power source to be a sine wave in the same phase as that of the power source voltage, so that a voltage crest value of the phase-advanced capacitor becomes substantially constant. The second cycloconverter supplies a sine wave current of a variable frequency to the AC motor.