Abstract: A method of synthesizing load invariant dc drive system comprising positive armature current feedback of exactly specified nature and value of its transfer function. The system transfer function independent of load is realized while stability and dynamics of the system are controlled by additional voltage loop.

Abstract: A control for a clothes dryer with an induction drive motor and an electric resistance heater element. A single sense winding is threaded through sensors monitoring drive motor current and heater current, generating an output voltage each time the alternating motor or heater current passes through a zero-crossing. The control monitors the ON/OFF condition of the heater and samples the lagging phase angle of the motor current, to provide an improved means of detecting when the clothes load is dry by measuring variation in motor torque due to minute differences in the way that the clothes load is tumbling from one drum revolution to the next revolution, ignoring cyclical, repetitive variation due to uneven drum rotational friction. The control provides a clothes cooldown period with controlled moisture regain as per the user dryness selection.

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

Abstract: An electric floor cleaner is of the type arranged to drive a three-phase motor, whose rated voltage is substantially equal to a voltage obtained by voltage doubling and rectifying a single-phase commercial power line and then by converting a voltage doubled d.c. voltage into three-phase a.c. by an inverter. The voltage and frequency of the three-phase a.c. output from the inverter are controlled for a predetermined period of time after a power switch is put into a turned on state from a turned off state. It is therefore possible to reduce the starting current to a small value enabling the use of a larger rated output motor than a motor in a conventional system within an allowable current limit of a commercial power line.

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 AC-excited generator/motor apparatus comprising; an AC-excited generator/motor having an armature mounting thereon; an armature winding connected to an AC power system and a rotor mounting thereon; and an exciting winding excited by an AC current. An exciting device for supplying a controlled AC exciting current to the exciting winding comprises; a device for calculating a real slip frequency based on a difference between the phase of an armature voltage appearing on the armature winding and the rotational phase of the rotor; and a device for controlling the exciting current supplied to the exciting winding from the exciting means in response to a deviation of the real slip frequency from a predetermined allowable range of slip frequencies so as to restore the real slip frequency within the allowable range of slip frequencies.

Abstract: The present invention relates to method and apparatus for asyncyhronous motor's speed regulation using strobe control, which may be carried out graded or nongraded speed regulation in conventional monospeed squirrel cage motor with simplicity, reliability, cheapness and high efficiency. It provides a notable electricity-saving result with good economical efficiency, especially in asynchronous motors speed regulation of ventillator and water pump driving. The said speed regulation method is using switch 5,6 sequentially to transmit a positive half-wave voltage and a negative half-wave voltage between the input terminals of strating and working windings of asynchronous motor 1, and then, will be repeated above said cycle continuously.

Abstract: The present invention is an apparatus for the control of a three-phase a.c. motor, especially a squirrel-cage motor. The apparatus includes inverse-parallel connected solid-state components (D,T) in each phase. At least one of the components is controllable. In the apparatus, the control circuit of at least one controllable solid-state component (T), e.g. thyristor, in each phase is connected via resistors (R.sub.2) to the control circuits in the other two phases.

Abstract: A motor control circuit for operating a permanent split capacitor motor from an ac source. The motor control circuit causes the motor to accelerate and decelerate according to a velocity profile. A driver circuit connects the motor to the ac source. The driver circuit receives a pulse signal at a predetermined time point after a zero crossing of the ac source and connects the ac line current to the motor at the predetermined time point, then the driver circuit disconnects the ac source from the motor at the next zero crossing of the ac source. A ramp wave signal is generated, each ramp thereof beginning at a zero crossing of the ac source and a dc voltage representative of the speed of the motor is also generated. A velocity profile having a predetermined period is provided on an output of a velocity profile generator. A first comparator circuit has a first input for receiving the dc voltage and a second input for receiving the velocity profile. An error signal is provided on an output thereof.

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: A three-phase electric motor is coupled to each phase line of an electric source by pairs of SCR's coupled in inverse parallel relationship. One of the SCR's in each pair is triggered by a signal from a conventional motor control circuit which regulates the phase angle at which the SCR turns on. The other SCR in each pair is an optically triggered device which is activated by light emitted from an LED in one of the legs of a three-phase rectifier bridge in the control circuit power supply. When the LED within a leg of the power supply is forward biased so as to conduct current, it emits light which triggers a correspondingly biased opto-SCR to supply current to the motor. A separate transistor is connected in parallel across each of the LED's to provide a current shunt path when the motor is to be turned off so that the LED does not emit light and trigger the SCR.

Abstract: A three-phase A-C speed controller for small integral and fractional horsepower motors includes a phase locked loop comprised principally of a phase comparator and voltage controlled oscillator to generate phase delayed trigger signals for energizing the windings of a three-phase A-C motor. A pair of shift registers are cascaded with a flip-flop to generate the 60.degree. phase delay between phases as is necessary in a three-phase system.

Abstract: An apparatus and method for automatic leveling of elevator cars by controlled DC plugging of AC induction motors. The invention utilizes, in a novel circuit and control arrangement, the external neutral connection of a Y-wound motor design to inject controlled direct current into the neutral to dynamically control the braking to a stop. The elevator car is thus more safely and accurately leveled at the desired floor than has heretofore been known in the art. A novel speed control method is also disclosed which compares and sums positive and negative DC signals and which switches to the motor braking mode at a desired time.

Abstract: An electric motor having a rotor, a stator and a plurality of windings on the stator is provided with power, via a plurality of rectifiers, from an a.c. polyphase source. The rectifier means are coupled between individual ones of the plurality of windings and respective individual ones of the a.c. polyphase source. The rectifier means may be full-wave or half-wave rectifiers. The rectifiers may be diodes, SCR's, TRIACS or the like. The windings are wound on the stator with substantially equal angular distribution. The winding may have a concentric and/or overlapping relationship. High and low (half) speed operation may be affected, using a plurality of switches.

Abstract: The present invention relates to a method for controlling an ac motor supplied by an inverter having several switches. In order that the torque can be adjusted to be as desired as rapidly as possible both with maximum voltage and in the vicinity thereof, one proceeds in accordance with the invention in such a way that a value (.DELTA..gamma.) representing the difference between the reference value and actual value of the angle between the stator flux and rotor flux of the motor is determined on the basis of a value representing the requirement for torque change of the motor, e.g. by means of the difference (.DELTA.T) between the reference valve (T*) and actual valve (T) of the torque, and a quantity representing the magnetic state of the motor, the next switching moment of the switches of the inverter, i.e. the so called limit between flux sectors (.DELTA..phi.), is shifted with a first quantity (k.sub.1 .DELTA..gamma.) proportional to the determined differential value to change the angle (.gamma.

Abstract: In order to feed to the converter on the load side of an intermediate-link frequency converter a frequency control signal (fI(S)*) which is formed by means of an angle controller (RW) from the difference of an angle reference value (wi(F)*) and a corresponding actual value (wI(F)), an actual value of the phase current is required which, for stable operation, must not contain heavy harmonics in stable operation nor must not be damped excessively dynamically by smoothing. Therefore, the measured actual angle value (wI(S)) is fed as the reference value of a servo controller (RS), to the output of which the integral (wI(S)*) of the frequency control quantity is added and the output of which is fed back to the input of the servo controller (RS).

Abstract: A blower motor control for an air conditioner is carried out so that when a detected actual rotation speed has come into an allowable deviation range to a target rotation speed at the time of controlling the motor so as to approach its rotation speed to the target rotation speed, the output for adjusting the rotation speed is not changed. As a result, a stable rotation speed can be obtained as long as the load on the motor does not fluctuate. Furthermore, after the output has been fixed, the allowable deviation range is expanded to prevent the output from changing even if slight load fluctuation is caused. This allows stable controls.

Abstract: A system for controlling a polyphase electric motor, particularly at low speeds, using a load commutated inverter includes the generation of half sine wave signals within a range of desired frequencies which are subsequently converted to single phase alternating current power for application to selected windings of the motor. In a single channel polyphase embodiment, motor starting is achieved using zero current commutation and normal phase control. A two channel embodiment results in what amounts to two phase operation of the motor.

Abstract: A current source inverter for a load commutated induction motor drive is controlled in relation to the direct and quadrature components of the current vector as assigned in response to stator voltage, speed reference and actual speed. Control is on the inverter and the converter in relation to both components.

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: A variable speed 3-phase a-c motor is connected to a 3-phase source of alternating voltage via a plurality of controllable solid state electric valves which are so arranged and controlled that motor speed can be reduced by skipping selected cycles of the source voltage. For half speed operation 12 valves are arranged to interconnect the source and motor phases, and over two consecutive periods of the source voltage six separate, uniformly spaced "firing windows" are selected during which the conducting states of different pairs of these valves are initiated in a predetermined pattern that results, in each phase of the motor, in a double-pulse current waveform having one-half the fundamental frequency of the source voltage.

Abstract: A self-excited induction motor variable speed drive using a known self-excitation method in which a capacitor is connected in parallel with the motor. Power is supplied by a supply convertor, a D.C. link and a motor convertor, the latter running at the motor frequency. The motor convertor includes a current bypass switching circuit comprising a capacitor bank connected to the motor terminals and to a neutral point between a pair of thyristors connected across the D.C. link.

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: A method for reducing the instantaneous voltage ripple of an electrical drive which is fed by a current intermediary circuit frequency converter with phase sequence quenching. During pulsed operation of asynchronous rotating machinery, driven by a current intermediary circuit frequency converter with phase sequence quenching, an interfering instantaneous voltage ripple occurs due to the inverter minimum time required for the completion of a complete commutation. The operating capacity of the inverter is not imparied, even if the switch-on time of individual thyristors falls below the minimum time. Depending on the degree of incomplete commutation occurring in the process, a difference is made beween one of a "first kind" and one of the "second kind" and, in the case of the second kind, the duration of the actual switch-on pulses for maintaining a linear relationship between the current time area and the nominal pulse duration is advantageously adapted through a correction function.

Abstract: A speed control system for an a.c. electric motor (1) comprises a microcomputer (6) having an interrupt signal input (INT/TO) to which is coupled the outputs of a detector (10) for detecting zero-crossings of the a.c. supply voltage and a tachogenerator (11) driven by the motor. The microcomputer supplies firing pulses to a triac (2), connected in series with the motor, in response to an overflow of a clocked counter (CT). This counter is suitably preloaded at each zero-crossing. The counter is read each time a tachogenerator pulse occurs and the time which this reading indicates has elapsed since the immediately preceding zero-crossing is stored. A record is also kept in a register (ZCSLTA) of how many zero-crossings occur between each tachogenerator pulse and the next and from this, and the stored times relating to the relevant pulses, the period of the tachogenerator pulses and hence the actual speed of the motor is calculated.

Abstract: In a microcomputer-based multi-function thyristor-controlled AC induction motor drive, the microcomputer effectuates the several control functions of the motor drive during respective time intervals corresponding to the sequence of firing of the thyristors, and upon each new time interval, depending upon the required delay angle, firing is effected as a function of a residual angle in terms of a multiple of said time intervals, and the firing sequence is shifted by an amount of time intervals in relation to the integer number of such time intervals within such delay angle. As a result, firing of the thyristor is performed by the microcomputer without impeding control function determination and with improved response to change in the delay angle.

Abstract: A variable frequency AC induction motor servo control system wherein slip is momentarily increased in response to error signal transients. In a preferred embodiment, a phase shift is introduced in the energizing stator current as the servo velocity error signal increases over at least the lower portion of the error signal range, the maximum phase shift being between 45.degree. and 90.degree..

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.

Abstract: A three-phase induction motor control apparatus resorting to a slip frequency control type vector control system having three-phase sine wave generating device, first operation device, second operation device, and vector operation device; whereby a current command value and a frequency command value are determined in accordance with a difference between a set velocity and a real velocity to determined a control current value. The three-phase sine wave generating device generates a three-phase sine wave having a frequency according to the frequency command value. The first operation device multiplies one of outputs, which are outputted from the three-phase sine wave generating device and mutually have a phase difference of 120.degree., and a preset value to determine one current component value.

Abstract: A method for operating a DC motor controller according to a first gain when the armature current of the DC motor is discontinuous, according to a second gain when the armature current is continuous, and according to a third gain when the armature current is in transition from the discontinuous to continuous conduction. The gains have proportional and integral terms and the integral term in the discontinuous and transition regions varies inversely to a current reference in the controller.

Abstract: A UFC is controlled with polar coordinates, a phase checked loop combining with an angular demand to establish a predetermined and tuned sequence of switch combinations between the converters of the UFC, to generate between the output phase-loads the desired voltage vector.

Abstract: To a controller utilizing thyristors have been added delayed resetting circuits connected to timing circuits for enabling delayed firing, and also circuits for inverting polarity of error signal in order to accommodate regenerative and reverse-plug braking. Other additional circuits include circuits for controlling a ramp generator for developing different segments of a ramp required for different modes of operation of a motor. Sequence switching circuits in the circuits controlling operation of the motor determine that full acceleration or deceleration of a selected mode is completed before a newly selected mode is started.

Abstract: A method and apparatus for controlling a permanent magnet synchronous motor (M), wherein an inverter (4) is controlled in response to PWM signals (PA-PF) obtained by comparing a reference carrier wave (VA) with signals representing differences between armature winding current command signals (RTC, STC, TTC) of the respective phases and detected armature currents (IR, IS, IT).The degree of saturation of the difference signals defined in association with a peak value of the reference carrier wave (VA) is detected. The phases of the current command signals (RTC, STC, TTC) are changed from those which provide an orthogonal relation between a resultant armature current and a main flux of a magnetic field.

Abstract: When a synchronous motor (6) using a permanent magnetic field is controlled by the control of an inverter (4) receiving a pulse width modulation signal, wherein the reactive component of an armature winding current is defined as I.sub.b, the inductance of the armature winding as L, the counter electromotive force constant of the synchronous motor as K.sub.1, and the constant introduced from the pole number of the synchronous motor as K.sub.2, the value of the reactive component I.sub.b of the armature winding current is limited so that the multiplied product of K.sub.2, L, and I.sub.b does not exceed the value of K.sub.1.

Abstract: The invention discloses a speed variator for an AC motor included preferably in a food processing apparatus. The variator comprises a controllable switching member, such as a triac, and an RC circuit for regulating the motor speed to a predetermined speed. A current compensating circuit is provided, connected across the terminals of capacitors in the regulating circuit and to a terminal of the variator for compensating a current increase to maintain the predetermined motor speed regardless of the fluctuations of the load torque on the motor during motor operation.

Abstract: A method for supplying the excitation to a four quadrant drive DC electric motor having a forward and reverse controllable bridge rectifier power regulators for controlling the direction of motor rotation. The motor control system is capable of operating in a continuous and discontinuous current mode of operation and includes an electronic control circuit for calculating a firing angle from desired and measured system parameters.The electronic control system includes a reversing controller for developing a current command for generating firing pulses to fire selected switching elements in the power regulators for controlling the magnitude and polarity of the excitation, and a current sensor for sensing motor current. The method provides a smooth, continuous transitioning between the forward and reverse bridge in response to a sensed requirement for reversing excitation to the motor.

Abstract: A control system for an AC motor to be driven by an inverter, wherein a control lead angle .beta. of the AC motor drive current is controlled based on the detection of an actual overlapped angle, a set overlapped angle, a detected motor speed, a detected magnitude of the acceleration-deceleration rate of motor speed, a detected amount of current from a power source and/or a detected magnitude of the change rate in the current from the power source.

Abstract: A method of controlling an AC motor which exhibits a constant torque characteristic at a rotational speed N below a base speed Nb and a constant output characteristic at a rotational speed N above the base speed Nb, comprising the steps of finding a base speed N.sub.L after limiting the output power of the AC motor, N.sub.L being derived from the base speed Nb and the ratio .eta. between maximum output power Pmax.sub.1 and maximum output power Pmax.sub.2 before and after the output power of the AC is limited, respectively, rendering the slip frequency of the AC motor constant until the rotational speed N of the AC motor reaches the base speed N.sub.L, varying the slip frequency in inverse proportion to the rotational speed N for N between N.sub.L and Nb (N.sub.L <N.ltoreq.Nb), and varying the slip frequency in proportion to the rotational speed N for N above Nb (Nb<N), whereby the output power of the AC motor is rendered constant at a rotational speed N above N.sub.L.

Abstract: A single microcomputer controls the firing time determination for two independent current regulators for two six pulse AC/DC converters which are part of a twelve pulse parallel controlled current inverter (CCI) AC motor drive. A very short high priority interrupt occurs when a motor channel source converter thyristor fires. This interrupt calls a longer, low priority current regulator interrupt informing it that a master channel source converter thyristor has just been fired. The current regulator causes a count to be loaded into a master fire counter and also loads a firing mask into a hardware latch or buffer. When the master fire counter times out the next thyristor pair of the master channel source converter is fired directly out of hardware. Similarly, there is a separate slave channel fire counter loaded after the current regulator is called by a short high priority interrupt when a thyristor in the slave channel source converter fires.

Abstract: A controlled current inverter (CCI) induction motor drive is controlled by controlling motor current and the angle between motor flux and motor current. The angle between motor flux and current is derived directly via a microcomputer phase-locked loop synchronized to the integrated motor voltage. The delay between the application of a firing signal to a thyristor and the initiation of line current is determined and compensated for to achieve the desired angle between motor flux and motor current.

Abstract: Method and apparatus for controlling DC traction motors on opposite sides of a vehicle, particularly a mining machine, by means of an SCR converter. The motors are accelerated while controlling the firing angles of the SCR's such that the current and voltage supplied to the motors increase along ramps until desired normal operating values of voltage and current are reached with the voltage across the series-connected motors being of a substantially greater value than the value it would be if the motors were connected in parallel. In contrast to prior art systems, the traction motors are maintained in a series-connected configuration during normal, essentially steady-state operation; while the voltage across the motors is maintained at said substantially higher value. When one of two drive wheels connected to the traction motors is slipping, the motors are connected in parallel to increase torque with a corresponding decrease and increase in voltage and current, respectively.

Abstract: A variable speed 3-phase a-c motor is connected via a plurality of controllable bidirectional switches to a 3-phase source of alternating voltage having a variable fundamental frequency (f) and an rms magnitude (v) that varies with f, and the switches are suitably arranged and controlled so that motor speed can be reduced by skipping selected cycles of the source voltage. When operating at a fraction of full speed, the magnitude-to-frequency ratio of motor voltage is maintained substantially the same as at full speed by varying the "firing angle" at which the switches start conducting current so as to minimize any deviation of the rms magnitude of the motor voltage from the product of v times said fraction.

Abstract: A control system for driving a variable speed AC motor employing a fixed frequency AC power source, combines pulses representative of a desired slip frequency with pulses of a frequency proportional to the speed of the motor. The combined pulses are employed with a speed command signal to set a threshold which determines the fraction of each cycle of the AC primary power which is fed to the motor. In addition, the speed and slip pulses are employed to direct the AC power to specific ones of the windings of the motor to thereby create a rotating magnetic field in the induction motor. An array of silicon-controlled rectifiers does the actual gating and an SCR protect circuit ensures that transfer of control from one SCR to another is inhibited until all current creases to flow in an SCR being extinguished. A forced commutation circuit forces the extinction of all current remaining in the last conducting SCR feeding a motor winding at the transfer time from that motor winding to the next.

Abstract: A variable-voltage variable-frequency elevator control apparatus is disclosed in which a circuit for the consumption of regenerated power produced during regenerative braking is provided on the DC side of the apparatus rather than on the AC side. During regenerative braking with an emergency generating unit in operation, regenerated power is consumed by the consumption circuit on the DC side of the circuit and is prevented from being returned to the emergency generating unit. This prevents the production of voltage notches commonly produced during regenerative braking by thyristor commutation in conventional circuits. Because no voltage notches are produced, a reduction in the size of the emergency generating unit can be achieved. In addition, since it consumes DC power rather than 3-phase AC power, the consumption circuit requires fewer elements than in conventional control apparatuses.

Abstract: The present invention generates a motor slip frequency value and two current magnitude values representing quadrature components of the motor stator current to be generated. Closed-loop control of the motor operation is provided by feeding back a signal representative of the motor shaft speed or position calculate the torque required from the motor. The feedback signal is separated into high and low frequency components. Additional circuitry changes the value in response to detected variations in the high frequency components of the feedback signal. The addition of this circuitry causes the motor control circuit to no longer represent the inverse of the motor transfer function network.

Abstract: A current control apparatus includes an instructor for providing a DC amplitude instruction and an AC phase instruction, and a cycloconverter for supplying an induction motor with AC load currents. These load currents are detected by sensors. The sensed signals from the sensors are applied to a detector. The detector generates a DC phase error signal and a DC amplitude signal according to the load currents and the phase instruction. The amplitude instruction, amplitude signal and phase error signal are applied to a comparator circuit. The comparator circuit generates a first voltage instruction and a second voltage instruction. These first and second voltage instructions are applied to a control circuit. The control circuit supplies the cycloconverter with voltage instructions. The comparator circuit, control circuit, cycloconverter, sensors and detector constitute a closed DC feedback control loop which utilizes a vector control method.

Abstract: A motor control system in which an actual torque indication is derived from the motor and compared with a reference, or demand, torque. From the difference signal is derived a stator M.M.F. in magnitude and position relative to a reference frame locked to the rotor. Orthogonal components of this stator M.M.F. are derived and transformed to stator phase winding drive signals.

Abstract: Method and system of controlling an inverter are disclosed. A reference rotary magnetic flux as a desired magnetic flux of an AC motor is so determined as to make a uniform rotary motion, an actual magnetic flux of the AC motor is detected, voltage vectors are selected such that a deviation between this reference rotary magnetic flux and the magnetic flux of the AC motor may be a value held within a tolerance, and switching elements of the inverter are on-off controlled so that the voltage vectors thus selected can be obtained.

Abstract: An apparatus for determining the common frequency w of two independently variable a-c quantities is described. In a rotating-field machine, the flux, for instance, is described by two electrical a-c quantities which together determine the magnitude and direction of the field. The two a-c quantities are variable independently of each other and the instantaneous direction of the field is given by an angle.alpha. according to the relation a.sub.1 /a.sub.2 =cotan.alpha., where a.sub.1 and a.sub.2 are the two a-c quantities. In order to determine the frequency of rotation w=d.alpha./dt of the field from these quantities, the quantities a.sub.1 and a.sub.2 are each fed to smoothing stages and thence to a computing circuit, wherein the quotient (d.sub.1 .multidot.a.sub.2 -d.sub.2 .multidot.a.sub.1)/(d.sub.1 .multidot.a.sub.1 +d.sub.2 .multidot.a.sub.2) proportional to the frequency is formed from a.sub.1 and a.sub.2 and the smoothed quantities d.sub.1 and d.sub.2.

Abstract: A control circuit for a DC inverter for an induction motor comprises:circuitry to produce a control waveform characterized by a sequence of pulse groups wherein the durations of the pulse groups increase with time, and wherein the widths of the pulses within each group increase with time, the circuitry supplying the waveform to the inverter.The circuits typically includes:(i) a first oscillator having a sawtooth output,(ii) a ramp generator having a voltage output which changes with time,(iii) a first comparator operatively connected with and responsive to the first oscillator and ramp generator outputs to produce an output characterized by a duty cycle which increases with time, and(iv) a second oscillator responsive to the comparator output to produce an output having a frequency which increases with time.