Abstract: The invention provides a control unit for at least one electric motor, wherein the control unit performs open-loop or closed-loop control of the motor speed of the electric motor in such a way that in the case of control values in specific ranges which are typical of a fault when the setpoint value is being predefined, such a fault being, for example, a line break, a voltage failure or a short circuit, the control unit drives the motor with a predefined setpoint value which differs from the current control value.

Abstract: A control system for an electric motor is arranged to determine the position of the motor from at least one electrical parameter by means of a position determining algorithm. It is further arranged to monitor at least one algorithm parameter defined by the algorithm and if the monitored parameter meets a predetermined fault condition to generate a fault indication.

Abstract: A power converter for converting power supplied to a rotating electric machine that includes windings of N-phase (N?2), includes an inverter section, a voltage detecting portion, one or more resistors, and an abnormality detecting portion. The voltage detecting portion detects a voltage applied to each winding of M-phase, where 1?M<N. Each resistor is coupled between a corresponding winding of (N?M)-phase whose voltage is not detected and a high-potential side or a low-potential side of the power source. The abnormality detecting portion detects abnormality based on the voltage detected by the voltage detecting portion. At least one of the resistors is coupled between the corresponding winding and the high-potential side of the power source.

Abstract: When an output pattern (LLL or HHH) due to a signal with a prescribed logic level corresponding to a ground short or instantaneous interruption of an output signal line of Hall ICs 17 is supplied via the output signal lines, and if output patterns based on detection signals supplied before and after the output pattern are found to be different by comparing them, a decision is made that there is a possibility that a shift of a rotor 11 from a target position and counterrotation of the rotor 11 involved with it can occur.

Abstract: A power management module for a winch system comprises an overload and low voltage interrupt module within a housing. The overload interrupt determines operating current for the winch system and provides an interrupt signal when the current is greater than a threshold. The low voltage interrupt determines voltage of a power source and provides an interrupt signal when the voltage is less than a threshold. A method of operating the power management module comprises determining operating current of the winch system with an overload interrupt module and voltage of a vehicle power source with a low voltage interrupt module. The overload and low voltage interrupt modules are located within a housing. The overload interrupt provides an interrupt signal when the operating current is greater than a threshold. The low voltage interrupt provides an interrupt signal when the voltage is less than a threshold.

Abstract: To make it possible to avoid an unstable state with a simple configuration even one of the phases of the motor fails. A motor drive system in accordance with the present invention includes a motor to which a plurality of phase coils of five phases or more are connected in a star connection, an inverter connected to one end of each of the phase coils, the inverter being configured to convert a DC power into an AC power and supply the AC power to each phase of the motor, a power relay disposed at another end of each of the phase coils, the power relay being configured so as to be able to cut off a supply power to at least one phase coil among the plurality of phase coils of the motor by using a plurality of contact points interposed between the star-connected coils, and a control unit that generates a control signal for the inverter and thereby controls driving of the motor.

Abstract: The present invention relates to a method for operating a brushless electric motor whose windings are driven by an inverter with the aid of six switches, having an identification unit being provided in order to identify defective switches, a unit for voltage measurement at the outputs of the inverter, and a microcontroller for controlling the switches. Particularly in safety-relevant applications, it is important to quickly determine what characteristic the defective switch has, for example in order to continue to operate the electric motor in an emergency mode, or to switch it off immediately. The defect (F1, F2, F3) is traced and the nature of the defect (F1, F2, F3) in a switch determined by using a different voltage (PWM1, PWM2) to drive those windings (V, W) which are not associated with the defective switch, while a voltage measurement is carried out on the winding (U) associated with the defective switch.

Abstract: Brushless DC motor (4) is driven based on a first or second waveform signal output from operation switching unit (11), which switches output so that a first waveform signal by first waveform generation unit (6) is output when the speed of rotor (4a) is determined to be lower than a predetermined speed, and a second waveform signal by second waveform generation unit (10) is output when the speed of rotor (4a) is determined to be higher than the predetermined speed. Thus, there is provided a motor driving device in which drive is stable even at high speed/under high load, and a driving range is extended.

Abstract: In a normal operating mode, a motor controller provides motor drive current to windings of a motor based on sensor signals to drive the windings in a normal commutation sequence, and monitors for occurrence of a motor stall condition. Upon detecting the motor stall condition in a given commutation state, then in a first driving step, the windings are momentarily driven according to an advanced commutation state, and during the first driving step, a reverse transition of the sensor signals to a state corresponding to a preceding commutation state is detected.

Abstract: A system comprises host logic and a programmable motor drive coupled to the host logic and configured to drive a motor. The programmable motor drive comprises a plurality of H-bridge circuits and the programmable motor drive is programmable to cause any two or more H-bridge circuits to be operated in parallel.

Abstract: A detection and control device is provided for detecting a motor fault of an electric motor with star point topology, with an evaluation unit, a control unit, and a return unit. The return unit is configured for returning a star point potential of the electric motor to the evaluation unit, the evaluation unit is configured for evaluating the star point potential and the control unit is designed for passivating a motor fault on the basis of the evaluation. The function of the return unit and of the evaluation unit may also be assumed by control lines and by the control unit.

Abstract: A power drive control device is provided, in which, even if drive of a synchronous motor becomes impossible due to abnormalities of a control circuit for controlling the synchronous motor, it is possible to perform the drive control of the synchronous motor concerned easily with a simple configuration as emergency action. Failure of one of a first controller and a second controller is recovered by configuration of the other. Here, the first controller performs rotational drive control and regenerative control of a synchronous motor, based on a current signal of a fixed winding of the synchronous motor and a sense output from a rotation angle sensor of the synchronous motor, and the second controller performs power generation control of a synchronous generator based on a current signal of a fixed winding of the synchronous generator and a sense output from a rotation angle sensor of the synchronous generator.

Abstract: A method and a device for monitoring the startup of an electric drive, which has a polyphase machine, a pulse-controlled inverter and a control unit. The control unit is provided to compare rotational speed values that are successive in time to one another during the startup of the drive, and when recognizing a non-increase in the rotational speed of the rotor shaft, to detect a mixup of phase lines or pulse-controlled inverter lines.

Abstract: A fan control circuit for controlling a fan to dissipate heat from an electrical device includes a comparator and an electrical switch. The comparator has a comparator input terminal, a comparator reference terminal, and a comparator output terminal. The comparator input terminal is connected to a power source via a first resistor and is also connected to the electrical device to receive a working current draw of the electrical device. The comparator reference terminal is receiving a reference voltage. The comparator output terminal is capable of outputting a comparison result between a voltage received by the input terminal and the reference voltage. The electrical switch has a control terminal, a first terminal, and a second terminal. The control terminal is connected to the comparator output terminal of the comparator to receive the comparison result. The first terminal is connected to the power source via a resistor. The second terminal is grounded and connected to the terminal via a fan.

Abstract: Stall detection apparatus for an electric motor controller has an input for receiving a drive error flag indicating if the controller is unable to achieve the required motor velocity and an input for receiving a signal in order to measure, directly or indirectly, the actual motor velocity. The actual motor velocity is determined in order to indicate whether the motor is stationary and, only if so, a stall signal is outputted in order to indicate that said motor has stalled.

Abstract: The present invention relates to a drive apparatus and drive method for switching an energization mode when a voltage of a non-energized phase of a brushless motor crosses a threshold. In threshold learning, first, the brushless motor is stopped at an initial position. The brushless motor is then rotated by performing phase energization based on the energization mode from the stopped state. The voltage of the non-energized phase at an angular position of switching the energization mode is detected from a maximum value or a minimum value of the voltage of the non-energized phase during the rotation, and the threshold is learned based on the detected voltage. Alternatively, the brushless motor is positioned at the angular position of switching the energization mode by maintaining one energization mode, and then the energization mode is switched to the next energization mode.

Abstract: A fan starting method including following steps is provided. A fan module including a control unit and a fan is provided, wherein the control unit and the fan are electrically connected with each other. An electric power is supplied to the fan module, wherein the electric power drives the fan to rotate at a full speed. Whether the fan rotates is determined by the control unit within a predetermined time. If the fan rotates, the fan is controlled to rotate at a predetermined load speed after the predetermined time. If the fan does not rotate, an alarm signal or an off signal is issued by the control unit.

Abstract: A blower motor assembly having a variable speed motor that is suitable for direct, drop-in replacement in a residential HVAC (heating, ventilation, and air conditioning) system that employs a PSC motor. The blower motor assembly includes at least a neutral input and two hot AC line connections, one for connection to the heating power source and the other to the cooling power source. A sensing circuit senses which of the inputs is energized by sensing either voltage or current on the inputs. The sensing circuit delivers a corresponding signal to a motor controller to control the speed of the variable speed motor. The blower motor assembly may also be equipped with additional hot AC inputs, more than one neutral line, and several sensing circuits for sensing current or voltage in the hot inputs and/or the neutral lines for controlling various aspects of the variable speed motor.

Abstract: The present invention provides a pumping system (60) comprising: a pumping mechanism (64); a motor (51) for driving the pumping mechanism; a drive control (50) for controlling the motor; and means (52) for monitoring at least one state within the system; wherein, to improve the performance of the system, the drive control causes the system to operate for transient periods in an overload condition which can result in said monitored state exceeding a predetermined operational limit, and when operating in said overload condition said drive control controls the power to the motor dependent on the level of said monitored state thereby avoiding said state from exceeding said operational limit.

Abstract: A controller controls switching of IGBT devices of an inverter according to the desired output of the permanent magnet motor. The controller includes: a magnet temperature detection device that detects the magnet temperature of the permanent magnet motor based on the output of a temperature sensor; a setting device that sets a threshold value of the magnet temperature corresponding to the desired output of the permanent magnet motor, based on a predetermined relation between the output from the permanent magnet motor and a critical temperature, up to which demagnetization in the permanent magnet motor is not caused; and a carrier frequency control device that, when the magnet temperature detected by the magnet temperature detection device exceeds the threshold value, changes the carrier frequency, at which the IGBT devices are switched, such that a ripple current superimposed on a motor current that flows through the permanent magnet motor is reduced.

Abstract: A method for ascertaining the rotor temperature of a permanent-magnet synchronous machine (10), in which a first estimate (TR1) for the rotor temperature is ascertained as a function of a remanent flux density of permanent magnets contained in a rotor of the synchronous machine (10). A second estimate (TR2) for the rotor temperature is ascertained via a Kalman filter containing a thermal model of the synchronous machine (10), the first estimate (TR1) for the rotor temperature being supplied at least intermittently to the Kalman filter.

Abstract: An electronically commutated one-phase motor (20) has a stator having at least one winding strand (30, 32) and a permanent-magnet rotor (22). The rotor, as it rotates, induces a voltage (uind) in the at least one winding strand (30, 32). The motor has an electronic calculation device (26), preferably a microcontroller ?C, which is configured to execute, during operation, the steps of a) sensing the value of the instantaneous operating voltage (Ub); (b) using the operating voltage value (Ub) and optionally further parameters, adjusting a time duration (TON) of a switch-on current pulse (i30) for the motor, in order to apply a consistent amount of electrical energy to the windings during start-up attempts, thereby maximizing the probability of successful start-up, regardless of possible fluctuations in motor operating voltage and related operating parameters. The switch-on current pulse duration (TON) can be adjusted longer or shorter, as a function of operating experience.

Abstract: A multiphase alternating current permanent magnet synchronous electric motor is coupled to an actuator. A sensorless electric motor drive control system controls operation of the electric motor. An initial phase angle and a rotational speed of a rotor of the electric motor are estimated. Operation of the sensorless electric motor drive control system and the electric motor are monitored using the estimated initial phase angle and the estimated rotational speed of the rotor of the electric motor. A fault in one of the sensorless electric motor drive control system and the electric motor is detected based upon the monitored operation.

Abstract: A voltage application unit applies voltage to windings of a motor without passing though an inverter unit. A first detection unit detects a short circuit failure in switching elements of the inverter unit based on a terminal voltage between each of the switching elements and a corresponding winding and a power voltage of a power supply. Before rotation of the motor, when no short circuit failure is detected and when a switching unit switches at least one of the high and low potential-side switching elements of the inverter unit on and subsequently switches all the switching elements off, a second failure detection unit determines whether the switching unit is incapable of rendering the switching element non-conductive based on the terminal voltage and the power voltage.

Abstract: A microcomputer compares a low voltage LV and a middle voltage MV to a predetermined voltage Vth set at a value in the vicinity of the grounded voltage (0 V) on the basis of detected phase voltages Vu, Vv and Vw, and thus, detects a break in a power supply line.

Abstract: Provided is an electric pump device that can continue to supply hydraulic pressure to hydraulically actuated equipment and that is also of reduced size. An electric pump device is provided with an oil pump that supplies oil to a stepless transmission device, a brushless motor that drives the oil pump, and a control device that controls the brushless motor. The control device is provided with a power supply part that supplies drive power to the brushless motor, and an out-of-synch determination part that determines whether or not the brushless motor is out of synch. The control device is provided with a drive control part that controls the power supply part so that supply of power to the brushless motor is stopped, and then controls the power supply part so that the brushless motor is started, when the out-of-synch determination part determines that the brushless motor is out of synch.

Abstract: A motor driving apparatus has a loss-of-synchronism monitoring circuit that monitors the rotation of a rotary machine such as a brushless DC motor to detect a sign of transition to a state of loss of synchronism. When the sign is detected, an energization control circuit temporarily stops driving of the rotary machine to bring it into a free running state, and thereafter carries out control so as to resume driving of the rotary machine. Further, the motor driving apparatus has an inverter and a drive control circuit that controls switching operation of the inverter based on rotation of the rotary machine.

Abstract: A motor drive device has a drive unit for driving a motor based on an ON/OFF operation of a switching element by a PWM (Pulse Width Modulation) signal. The motor drive device uses a PWM control method and performs abnormal determination based on an application voltage value and an actual measurement voltage value of the motor. The motor drive device does not make a false determination of determining as abnormal when it is normal, when determining the presence of abnormality based on the application voltage value and the actual measurement voltage value of the motor.

Abstract: A failure identification part identifies a switching element pair having off-failure, in which a FET of the switching element pair in a first inverter part is disabled to turn on. A failure-time control part controls other switching element pairs and of the first inverter part based on failure-time phase current command values calculated as a function of a rotation position and a q-axis current command value. The failure-time control part controls a second inverter part normally. A motor is persistently driven with the minimum reduction in motor torque, even when the FET fails.

Abstract: An apparatus and a method for detecting a lock error in a sensorless motor are disclosed, where the apparatus includes a multiplexer, a negative booster, a comparator and a timer. The multiplexer can receive a coil voltage from the sensorless motor. The negative booster can receive a neutralizing voltage from the sensorless motor and drop the neutralizing voltage. The comparator can compare the coil voltage with the dropped neutralizing voltage for outputting a zero-crossing signal. The timer can count time duration during the zero-crossing signal maintained at the a logic level and determine the lock error in the sensorless motor when the time duration exceeds a predetermined period.

Abstract: Various methods of detecting a found rotor, a lost rotor, a locked rotor and a caught rotor after a power disruption using flux estimates are disclosed. Also disclosed are permanent magnet motor controllers and assemblies suitable for performing one or more of these methods.

Abstract: Method and system for motor oscillatory state detection. According to various embodiments, the present invention presents a method for determining whether a motor is in an oscillatory state. The method includes powering up a motor for a period of time and then monitoring the movement of the motor during a period after the power if turned off. Based on the movement of the motor and/or impeller during a time period after the power is turned off, whether the motor is in an oscillatory state is determined. The method also includes initiating a process for handle error if the motor is in the oscillation state.

Abstract: A control circuit for a motor includes a voltage regulator having a thermal shutdown apparatus that turns off the voltage regulator while retaining power to a micro-controller preventing an automatic restart of the motor absent a recycling of power when the temperature of the control circuit rises above a pre-determined threshold level, wherein the voltage regulator is used to provide power to a plurality of insulated gate bipolar transistors controlling a plurality of stator windings of the motor. Thus the voltage regulator prevents the control circuit and the various components on the control circuit from being damaged from overheating. An embodiment of the control circuit is adapted to generate an error code in response to the shutdown of the voltage regulator and to monitor the operation of the motor to ensure that the motor has been turned off and then on before turning on the power supply to a plurality of phase windings.

Abstract: A motor control device that includes a first speed estimator estimating the rotation speed of the rotor of a permanent-magnet synchronous motor and that controls the motor so that a first estimated rotation speed estimated by the first speed estimator follows the specified speed value further includes a second speed estimator that estimates the rotation speed of the rotor by an estimation method different from that used by the first speed estimator. The motor control device detects synchronization failure based on a comparison between a second estimated rotation speed estimated by the second speed estimator and the first estimated rotation speed or the specified speed value.

Abstract: Disclosed is a drive circuit for generating the drive current used to energize the windings of a motor. The drive circuit includes a data processing unit that produces two outputs used to control an H-bridge and generation of the drive current. One output, a commutation signal, controls the timing of generation of drive current. The drive current in turn is determined based on the other output, a speed signal. The speed signal waveform includes blanking portions to avoid occurrences of shoot through in the H-bridge.

Abstract: The Brushless Multiphase Self-Commutation Controller or BMSCC is an adjustable speed drive for reliable, contact-less and stable self-commutation control of electric apparatus, including electric motors and generators. BMSCC transforms multiphase electrical excitation from one frequency to variable frequency that is automatically synchronized to the movement of the electric apparatus without traditional estimation methods of commutation and frequency synthesis using derivatives of electronic, electro-mechanical, and field-oriented-control. Instead, BMSCC comprises an analog electromagnetic computer with synchronous modulation techniques to first establish magnetic energy and then dynamically share packets of magnetic energy between phase windings of a multiphase, position dependent flux, high frequency transformer by direct AC-to-AC conversion without an intermediate DC conversion stage.

Abstract: In an electric power steering system, an ECU 11 that controls the operation of the system includes three independent microcomputers 18u, 18v, 18w that perform phase current feedback control with respect to the corresponding phases, so that sinusoidal current is applied to each phase of the motor 12 as a non-connected motor. Also, each of the microcomputers 18u, 18v, 18w monitors a deviation of an actual current value from a phase current command value, with respect to each of two phases other than the corresponding phase, and determines that an abnormality occurs in the phase in question when the deviation exceeds a predetermined threshold value. When two of the microcomputers 18u, 18v, 18w determine that the abnormality occurs in the remaining one phase, the ECU 11 confirms the determination that the phase in question is in an abnormal condition.

Abstract: An electronically commutated electric motor (110) has a permanent-magnet rotor (28), a stator having a stator winding arrangement (40), a motor control module (20) implemented as an IC and having a control logic unit (27), and an external power stage (50), separate from the IC, for influencing the current flow in the stator winding arrangement (40). The motor control module (20) has an internal power stage (29) having at least one open collector output (21, 23). The control logic unit (27) is configured to process a rotor position signal (24?, 24?) and to generate therefrom control signals (27?) for the internal power stage (29), which control signals (27?) serve to apply control to the internal power stage (29). Using an external power stage (50) reduces vulnerability to motor overheating and provides design flexibility.

Abstract: A protection circuit is configured to change control modes in a drive control process of a drive circuit for a motor when overvoltage is applied to a power source line while the motor is driven. With overvoltage applied, the control process is changed to a control mode to perform forced commutation control. When a predetermined time period passes after the voltage of the power source line returns to a predetermined level, the control process is changed to a sensorless control mode using a position detection circuit. This configuration can provide a motor drive apparatus capable of performing an overvoltage protection operation appropriately even when the sensorless control mode is adopted.

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 protecting device of a fan system includes at least one first switch element and at least one control unit. The first switch element receives a first input signal. The control unit is electrically connected with the first switch element, receives the first input signal, and controls the first switch element to turn on or turn off according to the first input signal. The control unit stops outputting the first input signal when the first switch element turns on. The control unit outputs the first input signal when the first switch element turns off, so that a fan of the fan system can be driven by the first input signal.

Abstract: A drive system for a permanently excited synchronous machine includes a drive converter, and a control device, wherein terminals of the synchronous machine are connected to corresponding outputs of the drive converter by connecting lines. Controllable asymmetrically blocking semiconductor switches are arranged in each of the connecting lines, with each switch having a thyristor connected in parallel with a reverse-biased diode, with anodes of the thyristors and cathodes of the diodes connected together to corresponding terminals of the synchronous machine. A control device has an input receiving a fault signal and an output connected to control inputs of the drive converter. The control device further includes control outputs connected to control inputs of the semiconductor switches. An easily controlled protective circuit for the drive converter of the drive system is obtained.

Abstract: A cooling system is provided with a motor drive device, a fan motor, and a Hall element. The motor drive device includes a lock protection circuit and a lock controller. When a control signal instructing rotation of the fan motor that is to be driven instructs stoppage of the motor for a predetermined time-period or longer, the lock controller has the lock protection circuit inactive. At an occasion when the control signal has continued to instruct stoppage of the fan motor for a first time-period or longer, a standby controller starts time measurement, and after a further predetermined second time-period has elapsed, makes at least a part of the motor drive device transition to a standby mode.

Abstract: A technique can recover from motor stalls caused by misalignment of motor position sensors such as Hall-effect sensors. In a normal operating mode, a motor controller provides motor drive current to the motor windings based on the sensor signals according to a normal commutation sequence, and monitors for occurrence of a motor stall condition. Upon detecting the motor stall condition, the motor controller first momentarily drives the windings according to one of an advanced commutation state and a delayed commutation state each adjacent to the given commutation state in the normal commutation sequence, and determines whether the motor stall condition persists. If the stall condition persists, then the motor controller next momentarily drives the windings according to the other of the advanced commutation state and the delayed commutation state.

Abstract: A winding switching apparatus for switching windings of an AC three-phase motor is provided. In each winding switching section of the winding switching apparatus, a positive-side charging resistor, a negative-side charging resistor, and a capacitor are connected in series between a positive-side DC bus and a negative-side DC bus of an inverter; the positive side of the capacitor is connected to the cathodes of respective diodes of a diode unit; and switching between high-speed windings and low-speed windings is carried out, with a capacitor potential being the same as an inverter DC bus voltage. A state detector and a comparator are also provided for each winding switching section to detect erroneous wiring and component abnormalities.

Abstract: A fan system comprising a first switch, a second switch, a coil, and a drive device. The drive device comprises a third switch and a fourth switch. The third switch, the fourth switch, the first switch, the second switch and the coil form a bridge connection.

Abstract: A protection scheme to protect pulse width modulated drives is described. The scheme is implantable in both hardware and software and combinations thereof. The semiconductor devices of the drive are protected from transient signals such as power line spikes and loss of line. The present scheme uses an adaptive technique to determine the normal or steady state distortion (transients and harmonics) value in an unfiltered power signal. The present distortion value is compared to the normal distortion. If the present distortion exceeds the steady state value by a given amount, then the drive is placed in freewheel mode to protect the semiconductor devices in the drive.

Abstract: A motor speed controller detects out-of-control reverse rotation of a motor even when the pulse signal obtained from the motor and synchronized with the rotation is of only one kind. A target instruction signal is generated on the basis of a target rotational speed ?T of the motor. A compensation instruction signal is generated on the basis of an error signal Ve that corresponds to a difference between the actual rotational speed ? and ?T. A composite signal is generated by combining above two instruction signals. A state in which the control direction of the composite signal with respect to ? is the reverse of the direction of ?T, and the strength of the composite signal exceeds a designated threshold continues for a designated period, is judged as a state of out-of-control reverse rotation, and restoration to the normal state is performed.

Abstract: A torque command (Tht) used in the calculation of a voltage command (Vht) of a voltage-up converter is generated by adding an upper limit value (Tc_max) of damping control that can be set by a motor drive device with a target drive torque (Tbt). Accordingly, the torque command (Tht) exhibits a waveform absent of variation, differing from a torque command (Tcmd) that is generated by adding damping torque generated based on revolution count variation component with the target drive torque (Tbt). Therefore, the voltage command (Vht) calculated based on the torque command (Tht) exhibits a waveform absent of variation. Accordingly, increase in current passing through the voltage-up converter caused by variation in the voltage command (Vht) can be suppressed. As a result, power loss at the voltage-up converter is reduced and operation of the motor at high efficiency can be realized. Further, the voltage-up converter can be protected from element fracture.

Abstract: When a fan drive current has become excessive, a fan drive device intercepts that current, waits for just a fixed time period T1, and thereafter flows that current for a second time. The fan power supply current flowed to the fan drive device is detected by a shunt resistor R. The value of the fan power supply current detected by the shunt resistor R is inputted to a controller, and the cause of any abnormality of the fan is decided upon by this controller, based upon the magnitude of the above described fan power supply current and the time period over which it has continued.