Abstract: Provided is an apparatus and method for improving generation efficiency of a distributed generation facility, and more specifically, to an apparatus and method for improving generation efficiency of a distributed generation facility configured to improve generation efficiency by boosting a voltage within an allowable voltage range according to a linkage capacity when the generated power of the distributed generation facility is linked and supplied to a power transmission and distribution side.

Abstract: Provided is a method of controlling a sensorless motor for an air compressor. The method controls early driving of a sensorless motor for an air compressor, overcomes related-art problems, and improves control response. A position of a rotor of the motor, finally estimated by a sensorless control logic at a point in time at which the motor is determined to be in the stopped state, is determined to be an alignment target position. An alignment start position is determined from the alignment target position in accordance with a predetermined alignment offset angle. The position of the rotor of the motor is controlled to change from the determined alignment start position to the alignment target position.

Abstract: A device may include a sensor, a sampling unit, and an interpolator. The sensor may be configured to sense motion and output a sensed signal. The sampling unit may be configured to sample the sensed signal with a sensor clocking signal to generate a plurality of sampled values. The interpolator may be coupled to the sampling unit and may be configured to receive the plurality of sampled values, the sensor clocking signal, and a reference clocking signal external to the device. The interpolator may be configured to interpolate the plurality of sampled values based on the reference clocking signal and further based on the sensor clocking signal to generate a plurality of output values.

Abstract: The present disclosure provides an apparatus with a prime mover coupled to a generator that is directly electrically coupled to an electric motor. A propeller or fan may be coupled to and driven by the electric motor. A bi-directional power converter may be coupled to the generator and further coupled to an energy storage device. The energy storage device may be selectively coupled to the electric motor. Methods of using the apparatus are also provided.

Abstract: A drive apparatus includes a magnet rotor having a plurality of magnetic poles that are magnetized, a stator having a magnetic pole portion that opposes each pole of the magnet rotor, a coil configured to excite the magnetic pole portion, a position detector configured to detect a position of the magnet rotor, a first driver configured to switch an electrification state of the coil in accordance with a preset time interval, a second driver configured to switch an electrification state of the coil in accordance with an output of the position detector, and a controller configured to select the first driver when the output of the position detector is less than a first threshold, and to select the second driver when the output of the position detector is equal to or larger than the first threshold.

Abstract: A system and method for exciting an electrical machine with instantaneous non-sinusoidal current waveforms is disclosed. The system includes an inverter that controls current flow and terminal voltages in an electrical machine. The controller is further programmed to receive feedback on an air gap magnetic field in the electrical machine generated by an initial sinusoidal current demand, generate a non-sinusoidal current demand based on received air gap magnetic field feedback, and input the non-sinusoidal current demand to the inverter, thereby causing the inverter to output a non-sinusoidal current.

Abstract: A hybrid drive device includes a first motor; an operative mechanism that drivingly connects the first motor to an engine of a vehicle; a second motor that is drivingly connected to a drive wheel; an engine rotation speed sensor that detects a rotation speed of the engine; a magnetic pole position sensor that detects a magnetic pole position of the second motor; a current sensor that detects a current flowing to the first motor; a sensorless motor control device that estimates a magnetic pole position of the first motor based on the current detected by the current sensor, and drivingly controls the first motor; and a second motor control device that drivingly controls the second motor based on the magnetic pole position detected by the magnetic pole position sensor.

Abstract: A circuit arrangement for automatic, load-dependent control of at least one winding current of a respective motor winding of a self-timed bipolar stepper motor, includes a first power driver circuit for a first motor winding and a second power driver circuit for a second motor winding. The circuit arrangement includes a first XOR gate and a second XOR gate, and a first resistor connected so as to couple the first XOR gate to an anode of a first diode. A cathode of the first diode is coupled to the comparator input of the first power driver circuit via a second resistor. A third resistor is connected so as to couple the second XOR gate to an anode of a second diode. A cathode of the second diode is coupled to the current-controlling comparator input of the second power driver circuit via a fourth resistor.

Abstract: A method of constant airflow control includes various controls to accomplish a substantially constant airflow rate over a significant change of the static pressure in a ventilation duct. One control is a constant I·RPM control, which is primarily used in a low static pressure range. Another control is a constant RPM control, which is primarily used in a high static pressure range. These controls requires neither a static pressure sensor nor an airflow rate sensor to accomplish substantially constant airflow rate while static pressure changes.

Abstract: In various embodiments, a phase current sampling apparatus (300, 600, FIGS. 3, 6), an electric motor drive system (100, FIG. 1), and a motor vehicle (1200, FIG. 12) include switching circuitry adapted to receive first and second phase current waveforms. The switching circuitry provides the first phase current waveform during at least two offset sampling instants, and provides the second phase current waveform during a reference sampling instant. An analog-to-digital converter is adapted to sample the first phase current waveform at the offset sampling instants, and to sample the second phase current waveform at the reference sampling instant. An embodiment of a method for regulating phase current waveforms includes an analog-to-digital converter generating samples of a first phase current waveform at sampling instants that occur before and after a reference sampling instant, and generating a sample of a second phase current waveform at the reference sampling instant.

Abstract: A signal transmission apparatus of a DC brushless motor for a ceiling fan is provided. The signal transmission apparatus comprises a transmitting line. The transmitting line is configured to transmit processed output signals of a plurality of electromagnetic sensors, in which usage of transmission lines is reduced. The output signals of the electromagnetic sensors represent the operation of the magnetic poles of the DC brushless motor.

Abstract: A robot control device that controls operation of a robot having an actuator includes a casing, an actuator driver, a drive-control board, a main control board, a main power supply board, a vent passage, a cooling fan, and a holding member. The actuator driver is accommodated in the casing and drives the actuator. The drive-control board is accommodated in the casing and controls operation of the actuator driver. The main control board is accommodated in the casing and controls operation of the drive-control board. The main power supply board is accommodated in the casing and supplies a power to the drive-control board and the main control board. The vent passage is defined by at least the drive-control board, the main control board, and the main power supply board and has an end open to the exterior of the casing. The cooling fan is arranged at an end of the vent passage and causes the air to flow through the vent passage. The holding member is provided in the vent passage and holds the actuator driver.

Abstract: The present invention relates to electrically magnetized synchronous machine comprising an electrically magnetized rotor, and electrically supplied sator windings, whereby it further comprises non-linear means, optionally controllable, such as rectifying means in a series with three sator phase windings, whereby a rotor field winding is arranged to be fed from said non-linear means.

Abstract: A synchronous machine control apparatus which can produce a torque level as close as possible to a desired torque command level while considering limitations on an output current of a power conversion unit.

Abstract: Solving Means: A field coil current and a stator current are controlled by a controller. The stator current is controlled under vector control and is controlled so that the phase keeps an efficient motor zone. In a case of rated power generation, when the motor speed is low, the phase current and field coil current are increased to reserve the generated power. And, as the speed is increased, the phase current is decreased to reduce the copper loss, while in place of decreasing the phase current, the field coil current is kept high to reserve the generated power. Thereafter, as the speed is increased more, the field coil current is decreased to reduce the iron loss, while in place of decreasing the field coil current, the phase current is increased to reserve the generated power.

Abstract: A method for the control of a wound rotor synchronous motor comprises measuring a plurality of electromagnetic entities indicative of the operation of the motor, generating voltage on a stator of the motor to obtain a stator current, further generating a further voltage on the rotor to obtain a rotor current, before the generating and the further generating, the entities being processed to calculate references for the stator current and for the rotor current, the references corresponding to the generation by the motor of the maximum torque obtainable per ampere of stator current supplied.

Abstract: The control system for controlling a permanent magnet synchronous motor includes: a position detection member, an angular speed calculator, a speed controller, a current command generator, a three phase/d-q coordinate converter, a current controller, a d-q/three phase coordinate converter, and an inverter. The speed controller generates a torque command based on a difference between an angular speed command value and the calculated angular speed. The current command generator generates a q-axis current command and a d-axis current command corresponding to the torque command and the angular speed. The three phase/d-q coordinate converter generates a q-axis current feedback signal and a d-axis current feedback signal. The current controller generates a q-axis voltage command and a d-axis voltage command. The d-q/three phase coordinate converter converts the q-axis current command and the d-axis current command into three phase voltage commands.

Abstract: A motor control system for a wound field synchronous dynamoelectric machine used as an electrical starter and a generator for aeronautical engines that uses its integral auxiliary permanent magnet generator as an angular position sensor in its starting mode.

Abstract: A method for referencing a polyphase stepper motor by monitoring the current step response in at least one driven phase is presented. The coil current step response is compared to past step responses in order to determine when an increase in or maximum load is present. A combination of step to step variance, step response variance from mean current magnitude, and average current magnitude variance, as well as other measures can be combined to create an algorithm output. The output is compared to a pre-determined threshold and if the value is greater than the threshold, the motor is commanded to halt its position, which remains magnetically synchronous. This position is then used as a reference point to zero, or to home the motor.

Abstract: In the control of a synchronous motor having a permanent magnet, an alternating current power supply voltage that is input to a power amplifier or a direct current link voltage of which input voltage is rectified is measured. A reactive current (a d-axis current) or a current control phase advance is changed, according to this power supply voltage. With this arrangement, reactive current control or current phase control can be carried out directly according to a change in the input power supply voltage. A motor control device includes a voltage measuring unit that measures a voltage supplied to a driving amplifier, and a current control unit that controls a current passed to a synchronous motor based on the measured voltage. The voltage measuring unit measures a voltage supplied to the amplifier. The current control unit controls a current that is passed to the synchronous motor, according to the measured voltage.

Abstract: A sensorless motor drive apparatus and a method for protecting and controlling the same. The sensorless motor drive apparatus includes a unit for determining the presence or absence of a position estimation error of a rotor contained in a motor using a current value applied to the motor and a position estimation angle of the rotor. Therefore, the sensorless motor drive apparatus determines the presence or absence of the position estimation error of the rotor without using a sensor, so that it reduces production costs, prevents the motor from generating a faulty operation, and prevents a compressor including the motor from being damaged.

Abstract: An apparatus is provided for controlling a synchronous motor. The apparatus comprises a first calculator calculating a voltage characteristic showing a characteristic of voltages to be applied to armature coils of a stator and a producer producing a command signal to provide the armature coils with the phase currents on the basis of the voltage characteristic. The apparatus still comprises a current detector detecting a signal depending on an amplitude of at least one of the phase currents, a second calculator calculating a rate of changes in a current amount indicating amplitudes of the phase currents, by using the signal from the current detector, and a feed-back member feed-backing the rate of changes in the current amount into the calculation of the voltage characteristic.

Abstract: A stepping motor control apparatus in accordance with the present invention comprises: a current detection unit that detects phase currents flowing into a stepping motor; an equivalent model-of-motor arithmetic unit that includes a coefficient multiplication block which performs multiplication using a coefficient ka?=Ts/? as a multiplier, a coefficient multiplication block which performs multiplication using a coefficient kb?=?/(Ts+?) as a multiplier, and a coefficient multiplication block which performs multiplication using a coefficient kg?=I0/E0 as a multiplier, and that calculates an estimated angle of excitation; a current control unit that controls an exciting current on the basis of the estimated angle of excitation, an angle command, and the phase currents detected by the current detection unit; and a variable voltage inverter that applies phase voltages to phase windings included in the stepping motor according to outputs of the current control unit.

Abstract: A stepping motor driver according to the present invention includes a torque component current calculating means for calculating a torque component current from phase currents and a rotor rotation angle, an absolute value converting means for obtaining an absolute value of the torque component current, a high speed-response judging means adapted for outputting a first control signal when a speed deviation between a command speed and a rotor speed is not more than a reference level, and outputting a second control signal when the speed deviation exceeds the reference level, and a current command outputting means adapted for outputting a current command according to the absolute value of the torque component current when the first control signal is outputted, and outputting a maximum current command value as the current command when the second control signal is outputted.

Abstract: An apparatus is described which reduces a time delay and a resultant phase shift in a gyroscope motor drive signal. The motor drive signal originates from a numerically controlled oscillator whose output is sampled at a predetermined rate. The apparatus includes a first element which upsamples the oscillator output signal samples and a band pass filter configured to receive an output from the first element and remove spectral components from the output of the first element. The apparatus further includes a third element which generates a tuning parameter, ??o, for tuning of the band pass filter and a scaling multiplier configured to normalize an output of the filter.

Abstract: The object of the invention is to inhibit the axial displacement caused by the insufficiency of a control response angular frequency of a frequency arithmetic unit of a synchronous motor and realize high-precision torque control also in acceleration/deceleration. To achieve the object, the axial displacement of the synchronous motor caused by the insufficiency of the control response angular frequency of the frequency arithmetic unit is estimated in consideration of the control response angular frequency and input ??c3 (=??c1+??c2) including an estimated value ??c2 in addition to an axial displacement operated value ??c1 to the frequency arithmetic unit is acquired. Hereby, even if the frequency arithmetic unit has an insufficient control response angular frequency, the quantity of axial displacement which will be caused by the insufficiency is estimated as a second axial displacement signal ??c2, is added and input.

Abstract: A motor control apparatus includes a phase current detecting section for detecting phase currents to a motor, a current phase/current peak value calculating section for calculating a current phase based on the phase currents, a voltage phase setting section for adding a predetermined phase difference to the current phase and setting the resultant sum as a voltage phase, a phase voltage setting section for setting phase voltages to the motor based on the voltage phase and the command voltage. Basically, the motor is operated by maintaining the voltage at constant and always monitoring the current/voltage phases so as to maintain a constant phase difference, without the motor axis position being predicted.

Abstract: The stepping motor driver comprises an inverter for feeding stepped currents to windings of a stepping motor, a position detector for obtaining a detected angle of a rotor of the stepping motor and a current controller for controlling the inverter. In a d-q rotational coordinate system in which the d-axis is in the direction of the magnetic flux of the rotor and the q-axis is in the direction perpendicular to the d-axis, an excitation angle for a winding is determined from a d-axis component and a q-axis component of a command current to the winding, a lead angle control signal is computed from the excitation angle, and a phase of an applied voltage to the stepping motor is controlled using the lead angle control signal.

Abstract: A device for monitoring a measuring system of an electric drive is described, including a measuring system (12) for detecting at least one measured quantity of an electric drive (10), at least one controller (78) which receives at least the measured quantity detected by the measuring system (12) and generates at least one manipulated variable for controlling the drive (10), where at least one signal acquisition (34, 73, 79, 89, 91, 93) is provided for detecting errors in the measuring system (12).

Abstract: A method of maximizing the power or torque output of a synchronous motor with reluctance effect is disclosed. Bases on torque and voltage set points, in the regulation of the synchronous motor, an optimal torque- and field producing current is generated. The method can further generate an optimal voltage which can maximize the power output of a synchronous motor since changes of inductances generated by the current itself can be accounted for.

Abstract: In an actuator having an integrated drive circuit, a switching current flowing in a coil within the actuator is included in a position sensor signal of the actuator. According to the present invention, by arranging a detection circuit which performs sampling in synchronization with noise, a rotational position which does not include higher harmonic waves can be detected even if the switching noise in a motor coil current in the actuator itself is generated. Consequently, elimination of the influence of the noise allows posture and position control with less vibration to be realized.

Abstract: A motor control apparatus includes an inverter for applying voltage to a synchronous motor and a control apparatus 4 for calculating a voltage instruction value to be applied by a PWM signal. There are provided a current difference sensing unit of the synchronous motor, a current difference calculation unit for calculating a current change attributed to the voltage applied, and a position sensing unit for estimating a counter electromotive force direction according to the current change sensed by the current change sensing unit and the current change calculated by the current difference calculation unit. The magnetic pole position of the rotor of the synchronous motor is estimated according to the counter electromotive force direction estimated by the position sensing unit and the voltage applied to the synchronous motor is controlled according to the estimated magnetic pole position.

Abstract: A sensorless detector 25 uses a rotor angle finally detected by a sensor interpolation detector 24 as an estimated value (&thgr;{circumflex over ( )}) of the rotor angle of a motor 3 in a first control cycle upon changing from a rotor angle detecting process carried out by the sensor interpolation detector 24. In subsequent control cycles, the sensorless detector 25 uses estimated values (&thgr;{circumflex over ( )}, &ohgr;{circumflex over ( )}) of the rotor angle and a rotor angular velocity in a preceding control cycle as calculation parameters, updates the calculation parameters with an observer which sequentially updates the calculation parameters depending on a phase difference (&thgr;−&thgr;{circumflex over ( )}) calculated in the preceding control cycle in order to eliminate the phase difference, for thereby calculating the estimated value (&thgr;{circumflex over ( )}) of the rotor angle of the motor 3 in the present control cycle.

Abstract: A sensorless detector 25 uses a rotor angle finally detected by a sensor interpolation detector 24 as an estimated value (&thgr;ˆ ) of the rotor angle of a motor 3 in a first control cycle upon changing from a rotor angle detecting process carried out by the sensor interpolation detector 24. In subsequent control cycles, the sensorless detector 25 uses estimated values (&thgr;ˆ , &ohgr;ˆ ) of the rotor angle and a rotor angular velocity in a preceding control cycle as calculation parameters, updates the calculation parameters with an observer which sequentially updates the calculation parameters depending on a phase difference (&thgr;−&thgr;ˆ ) calculated in the preceding control cycle in order to eliminate the phase difference, for thereby calculating the estimated value (&thgr;ˆ ) of the rotor angle of the motor 3 in the present control cycle.

Abstract: An excitation controller includes a reactive current detector for detecting a reactive current output from a synchronous machine connected, by way of a tap-changer-equipped transformer including a tap changer for changing taps of the transformer under load conditions, to a transmission system, a tap controller for setting a tap ratio of the tap-changer-equipped transformer according to an output terminal voltage of the synchronous machine, and a voltage setter for setting a reference voltage for an output voltage of the synchronous machine based on a second reference voltage of the tap-changer-equipped transformer at a side connected to the transmission system, the tap ratio set by the tap controller, and the reactive current detected by the reactive current detector. The excitation controller further includes a control unit for controlling an excitation system for exciting the synchronous machine according to the first reference voltage set by the voltage setter.

Abstract: A control device for controlling current to a motor includes a current sensor connected to a power module for generating an electric signal corresponding to magnitude of the current to the motor, and a processor connected to first and second current detecting circuits, which are connected to the current sensor and the power module. The first current detecting circuit determines whether the current to the motor is larger than a first predetermined value, and generates a first flag signal provided to the power module. The second current detecting circuit determines whether the current to the motor is larger than a second predetermined value, which is larger than the first predetermined value, and generates a second flag signal provided to the power module. The power module inhibits connection between the motor and a power supply unit upon receiving either one of the first and second flag signals.

Abstract: A step-motor-driving device includes (a) a step-motor having driving-windings in plurality of phases, (b) an exciter for supplying power to excite driving-windings, (c) a position detector for detecting a position of a mover of the motor and outputs a position-detecting-signal, and (d) an excitation-timing-controller for receiving a driving-instruction-signal and a position-detecting-signal, and outputs an exciting signal to the exciter responsive to an input of one of the driving-instruction-signal and the position-detecting-signal.

Abstract: A device and method for driving a concentrated winding synchronous motor which, upon supply of a given electric current to a stator coil of the motor, generates an increased torque. Periodical corrections are executed to the waveform of the current to be supplied to the coils of each phase of the stator and corrections are executed to decrease the alternating current supplied to the coil of any tooth at which a portion of a magnetic field generated, with respect to the pole of the closest rotor, is in a direction reverse to a rotation of the rotor.

Abstract: A method for the starting and steady-state supply of a permanent-magnet synchronous motor, particularly for driving a centrifugal hydraulic pump. The method comprises three successive steps: a first learning step, a second starting step, and a third steady-state step. During the first step, the rotor is turned through two angles of 180 mechanical degrees in the same direction, storing the parameters of the rotor and particularly determining the initial current and the mechanical zero point of the rotor. During the second step, by generating with a power supply (inverter) a practically sinusoidal current waveform, the rotor is started with a higher current than the stating current and with a low frequency which gradually increases, waiting for the rotor at its transit through 80, 100, 260 and 280 mechanical degrees. Once the intended steady-state speed has been reached, a practically sinusoidal current is applied and the rotor is waited for at transit through the zero points.

Abstract: A drive control apparatus for an electric synchronous machine is composed of armature current control means and transient operation detection means. When the synchronous machine is intended to increase power in a transient operation, the current control means supplies the armature winding with compensation current to cancel counter-electromotive force formed when field current is supplied to the field winding through a mutual inductance of the field winding and the armature winding.

Abstract: The present invention provides a controller with a function of detecting status to be losing synchronism for a stepping motor driven by constant-current system. A current controller 404 applies the driving-current to a stepping motor 401 in accordance with the command derived from a control unit 407. The applied current is observed by a current measuring unit 403, and stored in a current observing unit 409 in response to the sampling signals generated from a sampling signal generating unit 408. After an excitation has completed, the observing waveform is compared with a predetermined reference waveform in the control unit, and it is determined that a loss of synchronism occurs in the stepping motor when these do not agree within a predetermined tolerance.

Abstract: A converter for synchronous motor starting rectifies the input voltage from a polyphase input power source to develop a starting current having a substantial DC component. The starting current is then sequentially applied to each of the phase windings in the synchronous motor, with the sequential rate of application occurring at a continuously increasing frequency. The angular velocity of the motor synchronously increases with the increasing frequency of the sequential rate of application of the starting current to the phase windings. By application of the starting current at an increasing frequency, the synchronous motor operates in a forced commutation mode. The starting current is removed when the angular velocity of the motor is synchronous with the constant frequency of the polyphase input power source. When the starting current is removed, and the motor is synchronous with the input power, the input power may then be applied directly to the motor in a natural commutation mode.

Abstract: A controller of a synchronous motor for stably controlling the synchronous motor from a low speed to a high speed. The controller includes a multi-phase synchronous motor, a multi-phase square wave oscillator circuit, a magnetic pole position detection unit for detecting a position of the magnetic pole of a rotor of the multi-phase synchronous motor, and a unit for calculating a detection period of the magnetic pole position of the rotor by the magnetic pole position detection unit. The controller further includes a unit for dividing multi-phase square waves for each phase generated from the multi-phase square wave oscillator circuit into a plurality of pulses for each period to produce the divided square pulses. The controller also includes an excitation current control unit for controlling the divided square pulses for each phase in accordance with the detection period to supply the pulses to stator coils of the motor.

Abstract: The problem of providing aircraft engine starting is solved with an engine start control apparatus operating a generator (12) as a synchronous motor. The motor (12) receives power from a main inverter (46) and an excitation inverter (48) through an exciter (14) operating as a rotary transformer. These inverters (46, 48) are controlled by a control unit (22) which provides for constant power characteristics in the field weakening range. The control unit (22) includes a pulse width modulation (PWM) generator (100) which is responsive to a voltage command (102) and a commutation command (104) to develop switching signals (88) for controlling the switches (S1-S6) in the main inverter (46). The voltage command (102) is used to vary the duty cycle of the PWM signals. The commutation angle command (104) is used to control the timing of the PWM signals. The voltage command (102) and the commutation angle command (104) are controlled using closed loop current control.

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

Abstract: A rotation control circuit for a Hall motor of reduced-size and suppressed irregular rotation and having a controller that stores in a memory circuit data indicative of an irregular magnetization of a rotor magnet derived from a change of the magnetic field of the rotor magnet detected by a Hall element as an irregular rotation informationsignal, in which the irregular rotation information signal is input to a speed servo loop of the Hall motor, whereby the change of magnetic field of the rotor magnet is used as an FG signal to form a speed servo circuit.

Abstract: A variable speed controller for an alternating current induction motor reestablishes the start time for firing pulses and clock pulses in a circuit having a uniform frequency generator generating firing and clock pulses. Feedback from the stator terminals sets an oscillator with a sawtooth type ramp output. Subsequent feedback from the stator terminals are compared with the output of the oscillator in a comparator that establishes a time or phase shift in the generated output having the same frequency, for resetting the firing pulses so that the frequency of current to the stator winding is a function of the relationship between the stator and rotor positions, and of the current amplitude in the stator windings. Adjustment of the circuit parameters reduces the difference between the rotor and stator positions and optimizes stator current to maintain flux balance.

Abstract: An AC motor having AC windings with an internal electromotive force is driven by an electric valve feeding apparatus having electric valves commutated by the internal electromotive force of the AC windings. The commutation of the electric valve is carried out under the condition of U>.pi./m where m designates the number of commutation times per AC cycle of the electric valve feeding apparatus and U designates a commutation overlapping angle of the electric angle to feed the current to the AC windings whereby the motor is driven by the electric valve feeding apparatus.

Abstract: Apparatus for controlling the starting of a three-phase, salient pole, synchronous motor employs a signal representing slip frequency obtained from a power sensor connected to the motor supply. It requires no connection to the field coil or to other motor component. Since the signal can be obtained from a power sensor, the starting can be controlled from a location remote from the motor, for example at the motor control switchgear. A detector determines when the signal has decreased in frequency to a point representing a rotor speed where field excitation should be applied and it provides an output control signal. This control signal causes field excitation to be applied. In its broadest sense the apparatus may be used to indicate slip frequency remotely.