Abstract: A coordination control device of a power output apparatus includes a coordination control unit. The coordination control unit calculates an intermediate value between the maximum value and minimum value among voltage controls for a first motor generator, and voltage control from an AC voltage control generation unit to generate an AC voltage across neutral points of first and second motor generators, and outputs a value that is each phase voltage control for the first and second motor generators minus the calculated intermediate value to a signal generation unit as the final voltage control for the first and second motor generators.

Abstract: The motor control device includes a current detecting portion for detecting a phase current that flows in an armature winding of a stator of a three-phase motor based on current that flows between an inverter for driving the motor and a DC power supply. The motor control device performs a position sensorless vector control for the motor based on a control current that is obtained by a three-phase to two-phase conversion of the phase current based on an estimated rotor position of the motor. The motor control device farther includes a superposing portion for superposing a superposed voltage having a predetermined frequency on a drive voltage for driving the motor and an estimating portion for deriving the estimated rotor position based on the superposed current that is extracted from the control current and flows in the motor in accordance with the superposed voltage. A voltage vector locus of the superposed voltage from the superposing portion presents an ellipse.

Abstract: A desired current is caused to flow through a coil by controlling switching of switching elements by a PWM controller. For a voltage sensor, a value of Vo??V, which is a difference between a midpoint voltage Vo of the switching elements and a predetermined threshold voltage ?V, and a value of Vo?(Vc??V), which is a difference between the midpoint voltage Vo and a value obtained by subtracting the threshold voltage ?V from a voltage Vc of an upper line, are determined. Then, the determined results obtained from the voltage sensor are input to the PWM controller through flip-flops and a dead time compensator to compensate for dead time, such as, for example, for a command for PWM control signal generation.

Abstract: In a motor driving control device, a high-frequency alternating voltage or rotation voltage (having a frequency of ?h) is applied to a motor so that magnetic saturation occurs in the motor, thereby extracting, from a ?-axis current, a high-frequency second-harmonic component (a frequency component of 2×?h) that is obtained by attenuating at least a direct-current component of the ?-axis current. The polarity checker detects the polarity of the magnetic pole of the rotor based on the difference, caused by magnetic saturation, between the positive and negative amplitudes of the high-frequency second-harmonic component.

Abstract: A feed motor lock detection device detects a back-electromotive voltage in a feed motor M and checks whether the feed motor M is in a driven state or in a non-driven state based on the level of the back-electromotive voltage.

Abstract: Apparatus and methods for phase current detection used for driving a motor by supplying outputs from a pulse width modulation (PWM) converter to the motor. One method presented provides detecting a DC link current and a vector pattern, determining whether a voltage vector lengths exceeds a predetermined value, and adjusting the voltage vector by adding a positive or reversed voltage based upon the above determination and an integrated error value.

Abstract: Provided is a vector control apparatus for an induction motor which is capable of obtaining stable rotation in a short period of time for adjustment even at the time of low-speed operation by increasing the SN ratio of an output voltage to suppress the arithmetic error in the primary angular frequency arithmetic value based on a magnetic flux command value calculated from a circuit constant and an actual measurement of the induction motor even in the case where the rotation velocity of the induction motor is lower.

Abstract: Apparatus and methods for phase current detection used for driving a motor by supplying outputs from a pulse width modulation (PWM) converter to the motor. One method presented provides detecting a DC link current and a vector pattern, determining whether a voltage vector lengths exceeds a predetermined value, and adjusting the voltage vector by adding a positive or reversed voltage based upon the above determination and an integrated error value.

Abstract: An apparatus for controlling an operation of a reciprocating motor compressor includes a current integrator for integrating an alternating current applied to a motor of the compressor during each one cycle thereof; and a controller for differently controlling a firing angle of a triac during the positive phase and the firing angle of the triac during the negative phase of the AC voltage applied to the motor based on the integrated value of the current. A loss in the motor can be reduced by avoiding presence of a DC component in the current applied to the motor of the compressor.

Abstract: In an elevator control apparatus, a power supply voltage monitoring circuit monitors a power supply voltage supplied to a processing portion. A voltage monitoring soundness checking function circuit outputs a monitoring input voltage forcible change signal for forcibly changing a power supply voltage input to the power supply voltage monitoring circuit in response to a control signal from the processing portion. A voltage abnormality detection signal from the power supply voltage monitoring circuit is input to the voltage monitoring soundness checking function circuit. The processing portion checks the soundness of the power supply voltage monitoring circuit by reading data held by the voltage monitoring soundness checking function circuit.

Abstract: A technique is provided for controlling operation of motors of different sized or ratings. Components used to apply and interrupt current to the motors may be shared in control devices for the different motors. The components may include contactors or circuit interrupters, and instantaneous trip devices. The components may be sized for the higher rated motors, and be oversized for the lower rated motors. Control circuitry permits the devices to be controlled in accordance with the characteristics of the particular motor to which the devices are applied, providing accurate circuit interruption while reducing the number of different components and component packages in a product family for the various motors.

Abstract: A method is provided for operating a converter circuit, in particular a pulse-width modulated frequency converter circuit having a DC voltage intermediate circuit, which controls two or more winding sections of a polyphase dynamo-electrical machine, in particular a three-phase asynchronous motor for a laundry appliance. The method determines one or more parameters of the dynamo-electrical machine, before a rotating field is produced in the dynamo-electrical machine by the converter circuit. The parameters can be used to deduce a variant of the dynamo-electrical machine, and to select open-loop and closed-loop control parameters which are associated with the variant. Likewise, the method allows possible machine faults to be determined by using the parameters.

Abstract: In a method for measuring motor speed and position by detecting the back-EMF generated during pole-pair interactions, fluctuations of a three-phase motor power supply that may affect back-EMF detection are reduced. One phase of the power supply is tristated for a certain interval preceding and during back-EMF detection. For a shorter interval during back-EMF detection, the voltage drop across the motor is reduced from the full power supply voltage. This preferably is accomplished either by pulling a first of the other two power supply phases low, while pulling a second of the other two power supply phases up to a regulated voltage below the power supply voltage, or by pulling the second of the other two phases up to the power supply voltage and pulling the first of the other two phases down to a regulated voltage above ground.

Abstract: A simple and accurate dead time dispersion measurement method and a voltage source inverter control method that can prevent the occurrence of an unstable phenomenon are provided. The control method controls a voltage source inverter of a PWM system, which includes a power semiconductor device controlling a level of a voltage, a frequency and a phase. According to the control method, before operation, voltage error information for each polarity of respective phase currents of the inverter is stored. And during the operation, the voltage error information is read to compensate for a voltage instruction value or a pulse width of a PWM instruction signal, so that a voltage error can be corrected.

Abstract: An induction motor controller that may include three phase paths leading from a power input to a power output, a solid-state switching device interposed between the power input and the power output on each of the three phase paths, a voltage sensor coupled to two of the phase paths between the solid-state switching device and the power output, a current sensor on one of the phase paths, a processor communicatively coupled to the voltage sensor, the current sensor, and the solid state switching device; and a memory coupled to the processor. The processor may be configured to calculate a motor parameter based on a signal from the voltage sensor and a signal from the current sensor and store the calculated motor parameter in memory.

Abstract: A motor driving apparatus includes: a current instruction calculator, for calculating a current instruction value based on a deviation between a speed instruction value and an estimated speed value; a current controller, for controlling an output current based on the current instruction value; a frequency instruction calculator, for calculating a frequency instruction value based on an output voltage instruction value or an output voltage detection value, wherein, when an induction motor is to be activated, the current instruction value and the frequency instruction value are calculated directly using the speed instruction value, and an output current and an output frequency are controlled in accordance with the current instruction value and the frequency instruction value.

Abstract: A method of and apparatus for controlling an electric machine. The method can include using a controller to detect whether power is present at a first node of the controller, detect whether power is present at a second node of the controller, generate at least one signal based at least in part on the detection, and energize the electric machine using a detected power when the at least one signal indicates power is present at at least one of the first node, the second node, and a combination of the first node and the second node.

Abstract: A motor control apparatus capable of expanding a voltage output and a modulating wave signal generating method for a PWM inverter apparatus of the motor control apparatus, which is controlled by a pulse width modulating signal obtained by comparing a modulating wave signal of a voltage instruction with a carrier wave are provided. An upper limit value calculation unit 105 and a modulation wave limiter unit 4 are provided, and an upper limit value 14 of a modulating wave, which is equal to or smaller than the maximum value of the carrier wave and equal to or larger than the minimum value of the carrier wave is produced in the upper limit value calculation unit 105 and modulating wave instructions 13 for a plurality of phases are corrected by the modulating wave control unit 4 by using the upper limit value 14 of the modulating wave.

Abstract: In an electric car control apparatus for driving an induction motor, detection accuracy of a DC voltage is improved. A DC power supply device is provided which has a maximum potential terminal A, an intermediate potential terminal B, a minimum potential terminal C, an upstream side capacitor 6 between the maximum potential terminal A and the intermediate potential terminal B, and a downstream side capacitor 7 between the intermediate potential terminal B and the minimum potential terminal C. Also, an overvoltage suppression part is provided which includes a resistor 8 and a thyristor 9 between the maximum potential terminal A and the minimum potential terminal C.

Abstract: A method of protecting a frequency converter against overvoltage by controlling an AC motor during braking or during light load and a frequency converter, wherein the frequency converter is a voltage-controlled PWM frequency converter operating in single quadrant (1Q) and comprising at least one uncontrolled rectifier bridge (10) to be connected to a AC supply line (UL1, UL2, UL3), a direct-voltage intermediate circuit and at least one controlled inverter bridge (11) for feeding an AC motor (12) with an alternating voltage (Uu, Uv, Uw) of varying magnitude and frequency, in which method: the angle (??) between the output voltage vector (Us) and current vector (Is), i.e. the power factor, is measured, the angle (??) between the output voltage vector (Us) and current vector (Is), i.e. the power factor, is controlled on the basis of the measurement, and the angle (??) between the output voltage vector (Us) and current vector (Is), i.e.

Abstract: A motor driving apparatus for driving a motor includes a single-phase rectifier circuit having an input connected to a single-phase AC power supply, an inverter circuit that is connected to the single-phase rectifier circuit and applies a current and a voltage to the motor, and an inverter control unit for controlling the inverter circuit. The inverter control unit controls the current applied to the motor, i.e., the output of the inverter circuit, so that the inverter input voltage becomes equal to the absolute value of the voltage of the single-phase AC power supply.

Abstract: A solid state soft start controller system has a power supply, an electric motor, a thyristor electrically interconnected between the power supply and the electric motor so as to selectively allow current to pass from the power supply to the phases of the electric motor, a laser diode optically connected to the thyristor, and a controller connected to the laser diode for triggering the laser diode. Separate thyristors are connected to each phase of the polyphase electric motor. Separate laser diodes and associated light pipes connect the laser diode to the separate thyristors.

Abstract: The invention relates to a method of, and system for, linear speed control for an electric motor, in which a digital to analog converter means is used for converting an 8-bit digital signal to an analog voltage for setting voltage across a motor, a digital state machine means is used for converting the duty cycle of an input signal for output to the digital to analog converter means, and a closed loop feedback loop means is used for monitoring and setting the voltage across the motor. An over-current sense circuit can be used for monitoring the current across the electric motor. An over/under voltage sense circuit can be used for monitoring voltage of the electric motor. The resulting 8-bit digital control signal is converted to an analog voltage for the electric motor. Such methods and systems find particular use in automotive applications.

Abstract: The invention relates to a circuit arrangement for self-commuting control of a brushless, permanently excited direct current motor. Said circuit arrangement determines the commutation interval by evaluating the induction signal of a signal phase. A capacitive interference suppression component is arranged between the signal phase and an adjacent motor phase in the commutation cycle in order to suppress interferences of the induction signal. The capacitive interference suppression component is dimensioned in such a way that interfering influences of the power-switch element upon the induction signal are compensated for. This makes it possible to more accurately determine the momentary rotating position of the rotor and, hence, a differentiated control or adjustment of performance-influencing manipulated variables during operation. This has positive effects upon the efficiency, the power/weight ration and energy consumption of the motor and enables stable operation.

Abstract: A position-sensorless motor control device has a superposer that superposes, on the drive current with which the motor is driven, a superposed current having a different frequency than the drive current, a superposed component extractor that extracts, from the motor current fed to the motor, the ?-axis and ?-axis components of the superposed current, and a controller that controls the motor so that the direct-current component of the arithmetic product of the extracted ?-axis and ?-axis components of the superposed current converges to zero.

Abstract: A motor system includes a BLDC (brushless direct current) motor; an inverter driving the BLDC motor; a current detector detecting a direct current of the inverter; an induced voltage detector detecting an induced voltage of the BLDC motor; and a controller controlling at least one of an output voltage and an output frequency of the inverter based on the direct current detected by the current detector and the induced voltage detected by the induced voltage detector.

Abstract: A circuit for protecting against controller failure wherein the controller provides control signals for controlling a DC to AC inverter fed by a DC bus and driving a permanent magnet motor, the circuit comprising a first circuit for monitoring the DC bus voltage and, in the event the DC bus voltage exceeds a first threshold due to a counter EMF generated by the motor, for producing a signal to the controller to provide a switch state to the inverter whereby the counter EMF is dissipated substantially in a motor circuit resistance of the permanent magnet motor as a result of a short circuit condition provided by the switch state of the inverter, thereby preventing the DC bus voltage of the inverter from exceeding the first threshold and causing the permanent magnet motor speed to be reduced.

Abstract: A circuit for controlling a brushless permanent magnet motor is provided. The circuit comprises windings, each of the windings having a first end connected at a common node and each of the windings having a second end connectable directly to supply voltages by switches, the second end connected to an upper supply voltage or connected to a lower supply voltage or disconnected from the supply voltages; blocking circuitry connectable with the second ends, the blocking circuitry producing a blocked voltage; a comparator receiving the blocked voltage on one input and a reference voltage on another input, the comparator result indicating polarity of a back emf voltage in the associated winding; and a latch providing control signals for the circuit, an input of the latch enabled by an enable signal, an output of the latch comprising a back emf voltage detection signal. The blocking circuitry and the comparator are duplicated for each of the windings.

Abstract: In a method for measuring motor speed and position by detecting the back-EMF generated during pole-pair interactions, fluctuations of a three-phase motor power supply that may affect back-EMF detection are reduced. One phase of the power supply is tristated for a certain interval preceding and during back-EMF detection. For a shorter interval during back-EMF detection, the voltage drop across the motor is reduced from the full power supply voltage. This preferably is accomplished either by pulling a first of the other two power supply phases low, while pulling a second of the other two power supply phases up to a regulated voltage below the power supply voltage, or by pulling the second of the other two phases up to the power supply voltage and pulling the first of the other two phases down to a regulated voltage above ground.

Abstract: A pump assembly for pumping a liquid and a method of controlling the pump assembly. The pump assembly includes a motor coupled to a pump, and an electronic switch assembly electrically connected to the motor to control the current through the motor. The electronic switch assembly includes an electronic switch, a generator that provides a substantially periodic pulsing signal, a circuit control configured to provide a second signal, and decision logic connected to the generator, the circuit control, and the electronic switch. The decision logic receives the periodic pulsing and second signals and generates a control signal that selectively controls the electronic switch based on the periodic pulsing and second signals.

Abstract: A vector-control system and method of a “sensorless” type for electric drives with a.c. motors is based upon generation of an oscillating magnetic field and upon measurement of the deviation, with respect to said oscillating field, of the flux generated thereby on account of anisotropy, whether natural or induced, of the magnetic structure of the machine.

Abstract: The invention provides techniques for reducing or altering the magnetic noise of an AC rotary electric machine. A magnetic noise reducing harmonic current of order n, whose frequency is n times the frequency of the fundamental frequency component of a polyphase AC current fed to an armature of a polyphase AC rotary electric machine, is superimposed on the polyphase AC current, thereby reducing or altering a harmonic component having a frequency (n?1) times the frequency of the fundamental frequency component and occurring due to a radial magnetic excitation force acting radially on an iron core of the AC rotary electric machine.

Abstract: A controller for a variable frequency drive monitors electrical power from a variable frequency drive motor while a brake is maintaining a load driven or moved by the motor without requiring additional feedback components of a closed loop configuration. If excess electrical power is being generated by the motor, an undesirable condition in the brake is indicated. Support or maintenance of the load is assumed by the motor in that event. Appropriate alarms or indicators are also activated.

Abstract: In accordance with certain embodiments, the present technique provides a reduced current field-oriented-control scheme. For example, the present technique provides a method of controlling an induction device in which a predetermined reduction factor is employed to reduce the flux-current vector of a field-oriented-control scheme. By reducing this vector, less current and less power are drawn by the induction device, in turn reducing resistive heating and stator core losses, for instance.

Abstract: A controller for an electric machine. The controller includes a first voltage input that directly provides a first voltage to the electric machine, a second voltage input configured to receive a second voltage, and an inverter coupled to the second voltage input. The inverter is configured to be activated by the second voltage, to frequency-regulate the second voltage to generate a frequency-regulated voltage, and to provide the frequency-regulated voltage to the electric machine.

Abstract: A robot (1) is provided which includes a situated behaviors layer (SBL) (58). This SBL (58) is formed in the form of a tree structure in which a plurality of schemata (behavior modules) is connected hierarchically in such a matter that the schemata are highly independent of each other for each of them to behave uniquely. A patent schema can define a pattern in which child schemata are connected, such as an OR type pattern in which the child schemata are caused to behave uniquely, AND type pattern in which the plurality of child schemata are caused to behave simultaneously or a SEQUENCE type pattern indicating a sequence in which the plurality of child schemata should behave, thereby permitting to select a behavior pattern of the robot (1). Also, a new child schema can additionally be included in the SBL (58) without having to rewrite the schemata connection in the tree structure, whereby a new behavior or function can be added to the robot (1).

Abstract: To a neutral point of a motor is connected a positive electrode of an auxiliary battery and an auxiliary load. Voltage on a power supply line to the auxiliary load, a neutral point voltage, is detected, and disconnection of the auxiliary battery is determined when an increase of ripples in the neutral point voltage is detected. When a voltmeter cannot be used, control of the neutral point voltage is continued by measuring current of the auxiliary battery and performing control such that the current value becomes 0. A resolver is further provided on the motor for detecting the rotor angle with high accuracy. A control circuit generates, in accordance with an output of the resolver, a voltage control signal for each phase current having the same amplitude as the carrier amplitude during startup, and compares the voltage control signal to carrier to obtain a gate signal having the same frequency as the carrier frequency.

Abstract: A method of conditioning a signal being communicated between a system to be controlled and a controller may include monitoring an actual output signal and conditioning the actual output signal. The method also includes determining the difference between the actual output signal and the condition signal and causing the actual output signal to be filtered based on the relationship between the difference between the actual output signal and the conditioned signal.

Abstract: While the motor drive amplifier is not operating, electromagnetic switch contacts are held closed for a predetermined period of time, three-phase power is rectified by a rectifier circuit and a smoothing capacitor is charged. Then, the smoothing capacitor is discharged through a discharging resistor and, when a predetermined voltage is reached, a contact is closed, with the result that a closed circuit is formed by the smoothing capacitor, a detection resistor, a motor coil, motor insulation resistance, and ground. A voltage generating across the detection resistor due to leakage current is detected and compared with a reference value. If the detected voltage exceeds the reference value, an insulation degradation signal is delivered.

Abstract: A control apparatus for a brushless DC motor that rotatably drives the brushless DC motor including a rotor having a permanent magnet, and a stator having stator windings of a plurality of phases that generate a rotating magnetic field for rotating the rotor, by a current passage switching device constituted by a plurality of switching elements and performing successive commutation of current to the stator windings. The control apparatus includes: an angular error calculation device for calculating a sine value and a cosine value of an angular difference between an estimated rotation angle with respect to the rotation angle of the rotor and an actual rotation angle, based on a line voltage that is a difference between phase voltages of the plurality of phases on an input side of the stator winding and phase currents of the plurality of phases; and an observer for calculating the rotation angle of the rotor based on the sine value and the cosine value of the angular difference.

Abstract: In a control apparatus for a rotating machine, an integration unit integrates a primary angular frequency based on an angular velocity command and computes phase, a power converting unit applies three-phase voltages to the rotating machine according to three-phase voltage commands, a current detecting unit detects three-phase currents flowing through to the rotating machine, a coordinate converting unit converts the currents detected by the current detecting unit into currents on rotating two-axis coordinates based on the phase output by the integration unit and converts voltage commands on the rotating two-axis coordinates into the three-phase voltage commands, and a voltage command computing unit computes the voltage commands based on the absolute value of deviations of the primary angular frequency and the current components along each of the rotating two-axis coordinates.

Abstract: A control system for controlling the work output delivered to a floor surface by a work tool associated with a floor maintenance machine, such as a burnisher, is provided. In one embodiment, a voltage regulator regulates the voltage provided to the motor assembly that drives the work tool. A current sensor monitors the motor current drawn by the motor assembly and provides a signal representative thereof to a controller. The controller also receives as an input a work selector signal representative of a desired level of work output. Based on the work selector signal and the sensed motor current, the controller provides a control signal to an actuator. In response to the control signal, the actuator raises or lowers the work tool relative to the floor as need to control the work output delivered to the floor.

Abstract: A three-phase spindle motor has three terminals each driven with pulse width modulated signals. Rotation of the motor is controlled by iteratively measuring an electrical period of the motor, determining a rotational position of the motor, and synchronizing the sinusoidal pulse width modulation of the spindle motor with the measured electrical period. The electrical period of the motor is measured by detecting zero crossings in the a back electromotive force induced at a first terminal of the motor and determining the time between successive zero crossings. The rotation position of the motor is determined based upon the last measured electrical period and a location of last detected zero crossing. The zero crossings are detected by selecting a time window during which the back electromotive force signal is sensed for zero crossings. The time window is selected as a function of the last measured electrical period and the rotational position of the motor.

Abstract: A method of controlling the torque of a multiphase induction motor includes the step of energizing the stator windings of the motor from a power converter using thyristors, inserted between a multiphase main supply and the windings producing a stator current set point expressed by its amplitude and its phase, predicting phase coincidences between the stator current and the set point, and commanding the power converteer so that the windings receive current waves substantially when such coincidences occur.

Abstract: An inverter includes an upper ECU, a communication microcomputer receiving an instruction from the upper ECU, a motor control microcomputer receiving an instruction from the communication microcomputer, a gate driving circuit controlled by the motor control microcomputer, and a switching element driven by the gate driving circuit for converting a direct current of a high-voltage battery into an alternating current to drive a motor. The communications between the upper ECU and the communication microcomputer is performed according to a CAN protocol. The communications between the communication microcomputer and the motor control microcomputer is performed according to a low-speed serial communication protocol.

Abstract: A system is provided for sensing a motor current from a three phase inverter. A first resistor is coupled between a first transistor of the inverter and a supply voltage, and a second resistor is coupled between a second transistor of the inverter and ground. Circuitry coupled to the first and second resistors generates an upper and lower current. When the first transistor is active, the upper current is proportional to the sum of a reference voltage and a voltage across the first resistor, and the lower current is proportional to the reference voltage. When the second transistor is active, the upper current is proportional to the reference voltage, and the lower current is proportional to the sum of the reference voltage and a voltage across the second resistor. Based on the difference of the lower and upper currents, the circuitry provides an output current proportional to the motor current.

Abstract: The invention relates to a device and a method for estimating the speed of a slip ring asynchronous machine. The asynchronous machine includes a stator having a stator winding, arranged to be fed with three-phase voltage and current in order to generate a varying magnetic flux, and a rotor having a rotor winding in which the magnetic flux is arranged to induce a voltage to create an electromagnetic torque. The device includes a measuring member arranged to measure the value of the voltage in the rotor winding during at least one time period and a calculating unit, which is arranged, using the above measured voltage, to calculate a value of the rotor speed.

Abstract: A switch assembly including a switch (e.g., an electronic switch) and a controller connected to the switch to control the switch. The switch assembly can also include a power supply connectable to a power source and connected to the controller. The power supply is configured to receive power from the power source and controllably power the controller. The switch assembly can also include a generator and decision logic. The switch assembly can be used in an electric machine (e.g., a motor).

Abstract: While a rotor 4 of a permanent-magnet rotary machine 1 is rotating and an armature current thereof is substantially zero, a motor controller 2 performs a dq vector control process to control the permanent-magnet rotary machine 1 in a dq coordinate system which has a d-axis representing the direction of a magnetic field of the rotor 4 and a q-axis representing a direction perpendicular to the d-axis, and determines a magnetic pole position correcting quantity ?ofs to correct a magnetic pole position ?act detected by a magnetic pole position detector 8 so that a d-axis voltage command value Vdc determined by the dq vector control process will be substantially zero. The motor controller 2 controls the phases of armature voltages Vuc, Vvc, Vwc with magnetic pole positions corrected by the magnetic pole position correcting quantity ?ofs.

Abstract: The motor driver having a plurality of output circuits each having two switching elements connected in series includes: a phase switch circuit for putting a switching element on one side of one output circuit among the plurality of output circuits in the ON state during a time period corresponding to a predetermined electrical angle, and performing switching operation for switching elements on the other side of plural output circuits among the remaining output circuits; and a conduction period control section. The conduction period control section generates a signal for controlling the switching operation. Specifically, when the number of times of switching operation performed during the time period corresponding to the predetermined electrical angle is equal to or less than a predetermined value, a switching element corresponding to a phase, for which the magnitude of the current should be decreased, is turned OFF in the time period corresponding to the next predetermined electrical angle.