Abstract: The invention provides a motor with a low speed start function and a soft start function. The motor includes a first pulse generation circuit generating a first pulse signal of which a first duty ratio of one of logic levels is increased as a drive voltage corresponding the target rotation speed of the motor is increased, a second pulse generation circuit generating a second pulse signal of which a second duty ratio of one of logic levels is different from the first duty ratio, and a drive control circuit supplying a drive current to a motor coil at the second duty ratio in order to start the rotation of the motor that is stopping and supplying a drive current to the motor coil at the first duty ratio after a predetermined time passes from the start of the rotation of the motor in response to a rotation signal corresponding to the rotation of the motor.

Abstract: A fan is electrically connected with an alternating current power source. The fan includes an impeller, a motor and a controlling device. The controlling device includes a commutating unit, a magnetic detecting unit, a first switching unit, a second switching unit, a third switching unit and a controlling unit. The alternating current power source is electrically connected with the first switching unit, the second switching unit and the commutating unit, respectively. The commutating unit is electrically connected with the magnetic detecting unit and the controlling unit, respectively. The controlling unit is electrically connected with the third switching unit and the first switching unit, respectively. The third switching unit is electrically connected with the second switching unit. The first switching unit and the second switching unit are electrically connected with the motor, respectively. A controlling device of the fan is also disclosed.

Abstract: In a motor control circuit which controls energization of a coil on the basis of a detection result of a rotor position, control is performed so that continuous rotation of the rotor by inertia is suppressed, rotation is stopped quickly, and reverse rotation of the rotor is prevented. When an external control signal CTL is changed from L to H, the normal rotation control is switched to reverse rotation control, and a reverse brake state is effected. When motor rotation speed is monitored and reduced to a set rotation speed, a brake control signal SPSB is changed from L to H, and a short brake state is effected. However, the motor continues to be rotated by its own inertia, and a position detection signal HALL is changed. Thus, reverse brake control is temporarily performed (only during a time period corresponding to a pulse width TRB). The short pulse reverse brake control is intermittently performed until the motor is completely stopped.

Abstract: A drive control device of motor capable of starting up even a motor of such a type that the polarity of induced voltage does not switch every 180° of electrical angle or the polarity, positive or negative, does not occur with accuracy without causing a reverse rotation is provided. In a start-up control of motor, the following operation is performed: a current is passed through any coils in two phases, and the polarity of voltage induced in the non-conducting phase is detected. A conducting phase at start-up is determined based on the detected polarity of induced voltage. The average value of induced voltages in non-conducting phase detected with respect to the coils in respective phases is determined. The average value and the detected induced voltages are compared with each other, and relative polarities are determined from the magnitude relation with the average value to determine a conducting phase at start-up.

Abstract: In one aspect, a control circuit to control a speed of a motor includes a control logic circuit connected to a multifunction port. The control logic circuit is configured to receive a control signal provided at the multifunction port and to provide response signals based on the control signal to place the motor in at least two of a sleep mode, a brake mode and a pulse-width modulation (PWM) mode. The motor control circuit also includes an H-bridge circuit configured to control the motor based on the response signals.

Abstract: An apparatus for controlling a BLDC motor includes a frequency controller configured to increase frequency of a drive signal that is applied to the motor to reach a first target speed at a relatively low speed region. The apparatus also includes a sensorless controller configured to observe location of a rotor of the motor at the low speed region, and provide a control signal to the motor by comparing a command speed with an estimated speed based on detection of a voltage and/or a current of the motor at a relatively high speed region. Further, the apparatus includes a control unit configured to select one of the frequency controller and the sensorless controller based on the speed of the motor.

Abstract: An AC generator is connected to an engine and generates AC power, which is then converted into DC power by an AC/DC converter. A DC/AC converter converts the DC power output from the AC/DC converter into AC power for driving an AC motor. When a cruising-speed determining unit determines that the speed of a movable body has reached a cruising speed, a control unit connects the AC generator to the AC motor through a bypass unit, changes over at least one of the number of poles of the AC generator and the number of poles of the AC motor, and sets frequencies of the AC generator and the AC motor to values corresponding to the cruising speed.

Abstract: A phase current estimation device of a motor includes: an inverter which uses a pulse width modulation signal to sequentially commutate an electric flow to a motor of a three-phase alternating current; a pulse width modulation signal generation unit generating the pulse width modulation signal from a carrier signal; a control unit performing a startup control and a self control of the motor using the inverter; a direct current sensor detecting a direct current of the inverter; and a phase current estimation unit estimating a phase current based on the direct current detected by the direct current sensor.

Abstract: An apparatus for use with a flight control actuator and method for assembling the same is provided. The apparatus includes a motor drive system and a control unit. The motor drive system includes a capacitor-based energy storage configured to store and provide energy within or proximate to the actuator. The control unit is coupled to the motor drive system and is configured to facilitate managing power within or proximate to the actuator.

Abstract: A brushless motor control device according to the present invention drives a brushless motor including a stator having coils of three phases U, V, and W and a neutral line, and a sub coil provided in any one phase of the phases U, V, and W, for detecting a voltage induced in the coil of the one phase, and the brushless motor control device carries out a conduction control function, for the respective phase coils of the brushless motor, that performs a 120° conduction when a rotation speed of the brushless motor is lower than or equal to a predetermined rotation speed, and that performs a 180° conduction when the rotation speed is higher than or equal to the predetermined rotation speed, and the brushless motor control device includes a motor control unit that controls the brushless motor based on information of the rotor stop position when activating the brushless motor, controls the brushless motor based on the first rotor position information when in the 120° conduction, and controls the brushless motor bas

Abstract: The system (ECS) comprises a rectifier circuit (RC) to supply a direct current voltage (VB) as output; a driver circuit (DC) which is connected to a rectifier circuit (RC) and includes a plurality of controlled switches (SW1-SW4) which can permit passage of a current in the stator winding (W) selectively in one direction and in the opposite direction; a sensor (PS) which can supply a signal (H) which is indicative of the angular position of the rotor (R); and a control circuit (CC) which is designed to receive a signal (RS) which is indicative of the speed of rotation required (?ref) for the motor (M), and is connected to the position sensor (PS).

Abstract: A method of operating a direct current motor fan assembly is provided in which a motor controller operates to apply full power to kick-start a motor to overcome static forces. As soon as a sensor determines that the motor has begun to rotate, the motor controller changes the motor drive level from full power to a predetermined lower level to maintain a desired rotational speed.

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 sensorless method for starting a three-phase brushless direct-current motor includes generating a start-up control signal, a start mode selection signal, and a control signal commutation period; switching to a start mode according to the start mode selection signal; implementing a position aligning procedure according to the start-up control signal and the control signal commutation period; detecting a zero crossing point of back electromotive forces during each control signal commutation period; outputting a sensorless mode selection signal while detecting the zero crossing points of the back electromotive forces during consecutive control signal commutation periods; switching to a sensorless mode according to the sensorless mode selection signal; and detecting a zero crossing point of back electromotive forces in the sensorless mode to determine a starting result of the three-phase brushless direct-current motor.

Abstract: A method for determining accuracy of an actual position of a plurality of independent motors in a printing press is provided. The method includes commanding each of the plurality of motors in the printing press via a controller to move a desired initial position, comparing an actual position of each motor to the desired initial position of each motor, determining if the actual position of each motor is within a predetermined tolerance of the desired initial position, and resetting any motor outside the predetermined tolerance to be within the predetermined tolerance. A printing press is also provided. The printing press includes a plurality of printing press components and a plurality of motors. Each motor drives at least one of the printing press components and each of the motors has a desired initial position. The printing press also includes a position detector for determining an actual position of the motor with respect to the desired initial position of the motor.

Abstract: For starting a three-phase four-pole sensorless brushless motor including a stator having three-phase coils and a four-pole magnet rotor provided in correspondence with the stator, it is arranged to energize any two-phase coils of the three-phase coils in a predetermined energizing sequence; monitor magnetic flux generated in the other one-phase coil; and switch the two-phase coils according to a specific case where the monitored magnetic flux changes to a positive or negative side and in mid-course further changes to an opposite side. For instance, when the specific case is a case where the magnetic flux monitored by first energization changes to the negative side and in mid-course further changes to the positive side, the first energization is immediately stopped and switched to fourth energization by skipping two energizations in the predetermined energizing sequence.

Abstract: An apparatus for controlling an electric motor is provided. A plurality of switches is provided for controlling a direction of current through motor coils of the electric motor. A brushless motor control circuit is connected to each of the plurality of switches. Responsive to a request to adjust one of an angular velocity and an angular acceleration of the electric motor, the plurality of switches are activated to place the motor coils in a predetermined configuration to maximize torque or reduce a total back electromotive force (BEMF) from the motor coils.

Abstract: The present invention relates to a method for bringing a brushless motor, such as a multiphase brushless motor, operatively connected to for example a compressor into an optimal angular starting position in an energy saving manner, the method comprising the steps of applying a first drive voltage to a first phase winding of the motor and measuring a current flowing in another phase winding of said motor, said current being generated in response to the first drive voltage applied to the first phase winding. The method further comprises the step of switching the applied first drive voltage off when said current reaches a steady-state condition. By applying the method of the present invention a significant amount of power can be saved. The present invention further relates to a system for carrying out the present invention.

Abstract: An H-bridge circuit is connected to a coil of the vibration motor that is to be driven. A comparator receives Hall signals indicating position information of a rotor of the vibration motor, and converts to an FG signal. A pulse width modulator generates a pulse-modulated pulse signal specifying energization time of the coil of the vibration motor. The pulse width modulator, in a first mode, after commencing start-up of the vibration motor, sets a duty ratio of the pulse signal to 100%, and after that, switches the duty ratio to a predetermined value in accordance with rotational frequency of the motor. In a second mode, the duty ratio of the pulse signal continues to be set to 100%. In a third mode, frequency and the duty ratio of the pulse signal are set based on a control signal of a pulse form inputted from outside. The control signal is used also in switching mode.

Abstract: A method and system is provided for starting a motor which is useful, among other things, is useful for motors under unknown or variable load/inertia conditions. If a first attempt to start the motor using a first frequency ramp-up rate fails, a subsequent start attempt may be performed at a decreased frequency ramp-up rate. Iteration may be performed until starting of the motor is successfully achieved.

Abstract: A low cost switching system for an electrical motor, which is speed sensitive, direction of rotation insensitive, load insensitive and voltage fluctuation insensitive. The switch contains a power supply, a control circuit, a zero cross detector circuit, a triggering circuit and an electronic switch to provide the switching action. A time delay hysteresis inducement circuit is provided in the switching system to energized and deenergized the capacitor at a predetermined synchronous speed of the motor. The switching system first checks the speed of the motor before reenergizing the start capacitor, which increases the life of the motor. The switching system operates in high temperature range and regardless the value of the capacitor used.

Abstract: Provided is an AC motor driving apparatus and an AC motor control method capable of utilizing the conventional PWM system as-is even in an ultra-compact AC motor having an extremely few turns of exciting coil and preventing occurring of vibration and noise. The AC motor driving apparatus has an inverter converting a DC voltage to an AC voltage and supplying the AC voltage to an AC motor; a PWM device controlling a magnitude and a frequency of an output voltage of the inverter and means for changing a time constant of the AC motor in accordance with a carrier frequency of the PWM device. Between the PWM device and the AC motor, there is provided a condenser and/or a coil for adjusting the time constant, and the capacity thereof is adjusted in accordance with the carrier frequency of the PWM device.

Abstract: Various systems and methods for controlling DC motors are disclosed herein. For example, one method provides for controlling a polyphase, brushless DC motor. The method includes providing a DC motor that has a plurality of phases. Such a DC motor operates by inducing a current in the plurality of phases in accordance with a plurality of commutation states. In the example, six commutation states are discussed, but fewer than or more than six commutation states may exist. The method further includes initializing a count, inducing a current in the plurality of phases in accordance with a first commutation state, and incrementing the count until the current achieves a threshold in the first commutation state. Then, a current is induced in the plurality of phases in accordance with a second commutation state, and the count is decremented until the current achieves the threshold in the second commutation state.

Abstract: A motor control is provided with both open loop and closed loop controllers. The open loop and closed loop controllers provide commutation signals back to gate drives for an inverter, wherein the commutation signals utilize sinusoidal signals in open loop control, and utilize six step commutation in closed loop control.

Abstract: A motor control unit or a semiconductor integrated circuit device for an air conditioner is provided.

Abstract: An apparatus for estimating rotor position for brushless motors capable of accurately estimating rotor position is provided. The apparatus may be used as a start-up system for brushless motors. The apparatus performs accurate estimation even though power source voltage fluctuates, and is able to provide compact configuration. The apparatus supplies voltage to the coils respectively. In each supplying period, the apparatus counts voltage supply period of time until current value reaches to a current threshold value. Since a coil indicative of rotor stop position is prone to be magnetically saturated. The apparatus estimates the rotor stop position based on the voltage supply periods. Then, the apparatus starts a switching sequence based on the rotor stop position.

Abstract: An apparatus for estimating rotor position for brushless motors capable of accurately estimating rotor position even though power source voltage fluctuates is provided. First, the power source voltage is detected, and voltage is supplied only for a certain period of time and a current response is detected. The current detection value is multiplied by the ratio of a reference voltage to the power source voltage detected to correct the current detection value. Specifically, the peak current detection value is corrected upwardly or downwardly in each direction. A voltage supplying direction in which the current detection value is maximized is searched for to estimate the rotor position and a brushless motor is started.

Abstract: Disclosed is an electric motor that includes a stator with a plurality of main poles, each of which includes a coil, and a rotor rotatable about an axis and having a magnet with magnetic poles in which N and S poles are alternating. The motor further includes a first sensor group of a plurality of magnetic sensors fixed relative to the stator, and a second sensor group of a plurality of magnetic sensors fixed relative to the stator. When operating the motor, the first sensor group can be selected so as to rotate the rotor in a first direction. The second sensor group can be selected so as to rotate the rotor in a second direction opposite to the first direction.

Abstract: A motor controller capable of suppressing a large speed change generated at the time of changeover from a synchronous operation mode to a position feedback operation mode and implementing even acceleration characteristics regardless of the load torque by estimating a torque of a permanent magnet motor in the synchronous operation mode for driving the permanent magnet motor and setting an initial value of a current command value in a position sensor-less operation mode on the basis of information of the torque estimated value.

Abstract: An electronically commutated motor (ECM 20) has a rotor (28) and a stator, associated with which is a winding arrangement (26) to which electrical current (i1) is applied to drive the motor (20), a computer (36), and a PWM generator (84) associated therewith. The motor (20) is designed for operation in a parameter range that encompasses at least one variable parameter, e.g. operating voltage or ambient temperature, that can have different values. The computer (36) is configured to operate by carrying out these steps: After the motor (20) is switched on and before normal startup begins, during an initial time phase (T1), current (i1) delivered to the stator winding arrangement (26) is switched off and on using a pulse duty factor (pwm) derived from said variable parameter, in order to produce startup of the motor (20); subsequent to phase (T1), when the rotor (28) is rotating, normal startup is performed.

Abstract: A control controls starting of an AC rotary machine by calculating a resistance drop component, corresponding to a resistance drop of the AC rotary machine, based on a detection current, and adjusts angular frequency of an AC output voltage based on subtracting the resistance drop component from a voltage command, and, simultaneously, adjusting amplitude of the AC output voltage so that amplitude of an AC phase current may change in conformity with a predetermined function.

Abstract: Electronic motor regulation for a pump with a multi-phase permanent-magnet synchronous motor (PMSM). The system is enabled to detect and estimate a rotor phase position and rotary speed. Foam or air operation is detected by way of fluctuations in the estimated rotary speed.

Abstract: A driving device for three-phase alternating current synchronous motors controls state of charge of a capacitor, and a three-phase alternating current synchronous motor is started prior to the operation of the synchronous motor. Prior to control by a normal operation control unit, the state of charge of the capacitor is controlled by an initial state control unit and a synchronization control unit. Passage of large current through the capacitor immediately after the start of the execution of control by the normal operation control unit is suppressed. As a result, the operating state of the three-phase alternating current synchronous motor does not become unstable and the execution of control by the normal operation control unit can be started with the output voltage of the capacitor stable.

Abstract: A starting and generating multiplying control system and a method for using the system. The system comprises a motor drive controller, a motor and a magneto-electric change-over switch. The motor comprises a starting winding and a motor assistant winding. Both outputs of the starting winding and the motor assistant winding are connected with the motor drive controller through the magneto-electric change-over switch respectively. When the magneto-electric change-over switch turns on the starting winding and the motor drive controller, the start winding makes the motor started. After exceeding the rated speed, the magneto electric change-over switch turns on the motor assistant winding and the motor drive controller, the motor assistant winding generates motor assistant. And an electromotion mixed dynamic vehicle uses the above system and method.

Abstract: A drive system of a permanent magnet motor is constituted of a mode switching trigger generator which monitors a state of a permanent magnet motor and issues a mode switching trigger, a conduction mode determining unit which receives the mode switching trigger and switches the mode of the permanent magnet motor, and a PWM generator which outputs a PWM signal to an inverter in accordance with the output of the conduction mode determining unit. The mode switching trigger is generated on condition that the speed electromotive force of the permanent magnet motor exceeds a constant or variable threshold value.

Abstract: The method for initially starting the motor improves the reliability to the start of the motor. In particular, even though the external load is at more than a predetermined level, a rotor located at an arbitrary angle can be aligned to an accurate initial position. Moreover, it can prevent the damage of the motor or the damage of the electronic device where the motor is installed. In order to initially align the rotor of the motor, a position on a stationary coordinate system, to which an alignment current of a rotation magnetic field is applied, is varied.

Abstract: The disclosed invention achieves a significant reduction in the noise and vibration of a brushless motor from a startup up to the number of steady revolutions. To drive the brushless motor from stop up to the number of steady revolutions, when the arithmetic sequencer detects a rise of a clock signal CARYCLK, current control arithmetic is executed. On detecting a fall of the clock signal, the arithmetic sequence determines whether a division control signal DIVCNT has changed. If this signal has changed, soft switch arithmetic is executed. When the division control signal has not changed or after the completion of soft switching arithmetic, the arithmetic sequencer determines whether a rise of a mask signal MASK has occurred during one cycle of the PWM carrier signal CARYCLK. If a rise of the mask signal has not occurred, the operation returns to the first step. If a rise of the mask signal has occurred, PLL control arithmetic is executed, then the operation returns to the first step.

Abstract: A method and structure receives a desired rotational speed and/or step frequency for an electric motor. If the desired rotational speed is above a predetermined limit, the method performs closed-loop mode control of coil current of the electric motor by varying the average voltage supplied to the electric stepper motor according to observed feedback current from the current feedback loop connected to the electric stepper motor. To the contrary, if the desired rotational speed is not above the predetermined limit, the method performs open-loop mode control of coil current of the electric stepper motor by setting the average voltage supplied to the electric stepper motor according to values computed from the step frequency, irrespective of the observed feedback current from the current feedback loop.

Abstract: A control system controls a multiphase rotating machine by a 120° energization process and a PWM process. In the 120° energization process, respective ones of switching elements of a high side arm and switching elements of a low side arm of a power conversion circuit are turned on. In the PWM process, the switching elements of the power conversion circuit turn on/off so that two phases that are connected to the switching elements that are in the on-state are alternately rendered conductive to the high potential side input terminal and the low potential side input terminal of the power conversion circuit.

Abstract: A motor control apparatus has a start control section. When the motor control apparatus receives a motor start command from a host control unit when a motor is in a stop state or a low-speed rotating state where a sensorless control cannot be applied, the control section starts the motor that rotates a vehicle fan by a forced commutation which supplies a pseudo sinusoidal drive signal caused by a complementary PWM control. Thereafter, the motor control apparatus switches over to a sensorless control using a rectangular wave drive signal at an energization angle of lower than 180°.

Abstract: A motor drive circuit includes: a pulse generation circuit configured to generate a pulse signal whose duty ratio of one logic level is increased as a drive voltage is increased in accordance with a target rotation speed of a motor; and a drive control circuit that configured to drive the motor with the drive voltage using a duty ratio higher than the duty ratio of the pulse signal when the motor starts rotating from the stopped state, and configured to drive the motor with the drive voltage during a period when the pulse signal is at the one logic level after the motor starts rotating, based on a rotation signal corresponding to the rotation of the motor.

Abstract: A monitoring device for an electric motor has in input a signal representing zero crossings of the back-electromotive force of the motor and comprises a monitor that detects the signal in first periods of time arranged around instants of time in which the zero crossings are expected. The device comprises a setting circuit that sets second periods of time that are less than the first periods of time and each second period of time is centered on the instant of time in which the zero crossing is expected. The monitor comprises a detector that tests whether each actual zero crossing occurs inside the second period of time and a controller that modifies by a quantity the subsequent period of electric revolution time between two consecutive expected instants of zero crossing if said actual zero crossing occurs outside the second period of time.

Abstract: A motor control is provided with both open loop and closed loop controllers. The open loop and closed loop controllers provide commutation signals back to gate drives for an inverter, wherein the commutation signals utilize sinusoidal signals in open loop control, and utilize six step commutation in closed loop control.

Abstract: A circuit that includes a controller and at least one control I/O pin. When the controller is placed into an initial state, the controller initializes the circuit into an initial operation mode. Depending on whether or not signal(s) satisfying predetermined criteria are applied to at least one of the control I/O pins, the controller will cause the circuit to enter one of two or more post-initial operation modes. Accordingly, by initializing the controller, and by controlling a signal on the control I/O pin(s), the operating mode of the circuit may be controlled. In one embodiment, a given control pin might be configurable to be both analog and digital, depending on the circuit's operation mode.

Abstract: An electrical machine having a stator and a rotor. The stator includes a core and a plurality of windings disposed on the core in a multiple-phase arrangement. The rotor is disposed adjacent to the stator to interact with the stator. A method of operating the motor includes applying a pulsed voltage differential to first and second terminals of the windings resulting in movement of the rotor; monitoring the back electromotive force (BEMF) of the windings to sense rotor movement; after the applying and monitoring steps, monitoring the BEMF of the windings to determine whether the rotor is rotating in a desired direction, and electrically commutating the motor when the rotor is rotating in the desired direction and zero or more other conditions exist.

Abstract: In a storage device, a BEMF control is not performed on a motor and the motor is stopped if the motor is in a BEMF-control possible state. Once the motor has completely stopped, a start-up control is performed on the motor.

Abstract: A compressor having a sensorless motor and a driving method thereof. The compressor includes a sensorless motor having a rotation shaft connected to a rotator, a piston for performing a compression stroke and an intake stroke between a top dead center and a bottom dead center thereof, and a crank connecting the rotation shaft to the piston. The method includes forcibly aligning the rotator such that the rotator is positioned at a start position in the intake stroke of the piston, and accelerating rotation of the forcibly aligned rotator.

Abstract: A motor drive unit capable of detecting the position of a stationary rotor of any type of sensorless motor, determining a proper startup logic for the rotor, and starting up the motor in a stable condition. To do this, multiple stator coils of the sensorless motor are supplied with rotor-position detecting drive voltages that are adapted to vary the middle point voltage of the multiple stator coils but do not rotate the motor. The middle point voltage of the stator coils is compared with a detection reference voltage. When the result of the comparison matches one of predetermined detection logic patterns, a proper startup logic is generated in accordance with the position of the rotor specified by the matching detection logic pattern to start up the motor. Otherwise, the detection reference voltage is changed in level, and a new rotor-position detecting signal is generated to repeat the procedure for detecting the rotor position.

Abstract: In a brushless motor driving apparatus, a drive circuit arranged to rotate a magnet rotor by sequentially switching energization of coils of phases, detect a position of the magnet rotor based on back electromotive force voltage generated in each phase coil, and control the energization of each phase coil based on the detected position. The drive circuit is configured to energize each phase under duty control and, before the back electromotive force control, perform initial setting twice sequentially for sweeping energization duty with respect to each phase coil to set the magnet rotor in a predetermined initial position.

Abstract: A drive control device of motor capable of starting up even a motor of such a type that the polarity of induced voltage does not switch every 180° of electrical angle or the polarity, positive or negative, does not occur with accuracy without causing a reverse rotation is provided. In a start-up control of motor, the following operation is performed: a current is passed through any coils in two phases, and the polarity of voltage induced in the non-conducting phase is detected. A conducting phase at start-up is determined based on the detected polarity of induced voltage. The average value of induced voltages in non-conducting phase detected with respect to the coils in respective phases is determined. The average value and the detected induced voltages are compared with each other, and relative polarities are determined from the magnitude relation with the average value to determine a conducting phase at start-up.