JPH0970195A - Motor controller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To cope with the abrupt heat generation of a motor by predicting the abrupt heat generation of a plurality of switching elements from the number of revolutions of the motor and operating a protective control means during the predicted period or normal control means during the other period. SOLUTION: An EV-ECU 16 generates pulse width modulating signals for controlling the turning-on/off switching of the switching elements Q1-Q6 of an inverter 12 in accordance with a decided control target and supplies the signals to the corresponding elements Q1-Q6. The EV-ECU 16 then predicts the abrupt heat generation of the elements Q1-Q6 or a plurality of windings U, V, and W from the number of revolutions of a motor 10 and performs an inverter protective process during the predicted period. The ECU 17 performs normal control during the other period. Therefore, the abrupt heat generation of the motor 10 which occurs when the rotation of the motor 10 is locked can be coped with without waiting for the output of a temperature sensor.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a motor control device having a function of protecting a winding of a motor or a corresponding switching element from damage due to heat.

[0002]

2. Description of the Related Art When an AC motor is driven by a DC power supply, a power converter, such as an inverter, which converts the power supply output into AC is required. In a power conversion device such as an inverter, power conversion is performed by switching at high frequency and high power. Such switching normally causes a switching element (for example, a high-power transistor such as an IGBT) to generate heat. Therefore, when controlling the power conversion device, it is necessary to take measures or protection against overheating of the switching element. . For example, Japanese Patent Laid-Open No. 7-6738
In No. 9, a temperature sensor such as a thermistor is provided on the radiator of the inverter, and the motor operation is stopped when the temperature sensor detects an overheated state of the inverter.

[0003]

However, when a permanent magnet excitation type synchronous motor (PM motor) or the like is driven by a power converter such as an inverter, if the rotation of the motor is locked by an external force, Current concentrates on only one phase of the multi-phase winding provided in the motor, and as a result, among the multiple switching elements provided in the power converter, the switching element corresponding to this phase suddenly increases. Fever. When such rapid heat generation occurs, the switching element may be destroyed by heat before the overheated state is detected by the temperature sensor.

The present invention has been made to solve the above problems, and predicts heat generation based on the number of rotations of a motor, so that sudden rotation occurs when the rotation of the motor is locked. The purpose is to be able to deal with such fever. Another object of the present invention is to achieve the above-mentioned object while preventing torque shortage and torque shock by switching the control mode of the switching element. It is a further object of the present invention to allow the user to hear and identify the fever situation. The present invention is
It is an object of the present invention to realize a device suitable for controlling the drive system of an electric vehicle and the drive control of a PM motor.

[0005]

In order to achieve such an object, the first structure of the present invention is such that each winding is provided so that a target current is supplied to a plurality of windings provided in a motor. Normal control means for controlling a plurality of switching elements provided corresponding to the wires, and protection control means for controlling the plurality of switching elements so that heat generation in the plurality of switching elements or the plurality of windings is suppressed. When,
In a control device including: a heat generation predicting unit that predicts steep heat generation in the plurality of switching elements or the plurality of windings based on the rotation speed of the motor; and a protection control unit during a period in which the steep heat generation is predicted. , And the control mode switching means for operating the normal control means respectively during the other periods. In this configuration, control for protecting the switching element and the winding from damage due to heat is executed based on the result of prediction based on the motor rotation speed, that is, without waiting for the output of the temperature sensor. Therefore, it is possible to cope with abrupt heat generation that occurs when the rotation of the motor is locked, and thus it is possible to realize a device suitable for controlling the drive system of the electric vehicle and the drive control of the PM motor.

According to a second aspect of the present invention, in a control device that executes a predetermined protection operation in order to protect a switching element corresponding to each winding of the motor from being destroyed by heat, a rotation speed for detecting the rotation speed of the motor. Switching loss is reduced while the detection means and the heat generation prediction means that determines whether or not the rotation of the motor is locked by an external force based on the detected value of the rotation speed and the determination that the rotation is locked are established. As described above, a protection control unit that temporarily reduces the switching frequencies of the plurality of switching elements is provided. In this configuration, depending on the result of the determination regarding the motor rotation speed, that is, without waiting for the output of the temperature sensor,
Control is performed to protect the switching elements from thermal damage. Therefore, it is possible to cope with abrupt heat generation that occurs when the rotation of the motor is locked, and thus it is possible to realize a device suitable for controlling the drive system of the electric vehicle and the drive control of the PM motor. Further, even if the switching frequency is changed, the maximum output torque of the motor does not change, so that neither torque shortage nor torque shock occurs. in addition,
Since the frequency of the electromagnetic resonance sound of the motor changes due to the change in the switching frequency, the user can hear and identify the heat generation state.

According to a third aspect of the present invention, in a control device for executing a predetermined protection operation in order to protect a motor having a plurality of windings or a switching element corresponding to each winding from being destroyed by heat, a motor rotation is performed. A rotation speed detecting means for detecting the number, and a heat generation predicting means for judging whether or not the rotation of the motor is locked by an external force based on the detected value of the rotation speed,
Protection control means forcibly and alternatingly switching the switching element and the winding where the current is concentrated so that the switching element or the winding that generates heat changes alternately while the determination that the lock is established is established. It is characterized by including. Also in this configuration, control for protecting the windings and the switching elements from damage due to heat is executed based on the result of the determination regarding the motor rotation speed, that is, without waiting for the output of the temperature sensor. Therefore, it is possible to cope with abrupt heat generation that occurs when the rotation of the motor is locked, and thus it is possible to realize a device suitable for controlling the drive system of the electric vehicle and the drive control of the PM motor.

According to a fourth aspect of the present invention, in the control device according to the third aspect, the switching in which the current is concentrated is suppressed so that the torque associated with the switching is suppressed while the determination that the lock is established is established. It is characterized by comprising current increasing / decreasing means for increasing / decreasing the current in synchronism with the alternating change of the element and the winding. In this configuration, the same action as the third configuration occurs. In addition, as a result of reducing torque shock,
A suitable device is realized by controlling the drive system of the electric vehicle and the drive control of the PM motor.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a system configuration of an electric vehicle suitable for implementing the present invention. In this system, a three-phase AC PM motor is used as the motor 10 for running the vehicle. The drive current of the motor 10 is supplied from the battery 14 via the inverter 12. The inverter 12 has switching elements Q1 to Q6 that are provided corresponding to the U-, V-, and W-phase windings of the motor 10 and are three-phase bridge-connected to each other in order to convert the discharge output of the battery 14 into a three-phase AC. are doing. As the switching elements Q1 to Q6, for example, high power transistors such as IGBT can be used. The inverter 12 also has a capacitor C for smoothing the output voltage of the battery 14 and a discharge resistance R of the capacitor C.

The operation of the inverter 12, particularly the switching operation of the switching elements Q1 to Q6, is performed by the EV-ECU 1
Controlled by 6. As shown in FIG. 2, the EV-ECU 16 turns on the relay unit 20 according to the operation of the ignition switch, for example, and connects the battery 14 and the inverter 12 (100). EV-ECU16
Inputs an accelerator signal indicating the amount of depression of the accelerator pedal by the pilot, a brake signal indicating the amount of depression of the brake pedal by the pilot, a shift position signal indicating the shift position input by the pilot (102), and inputs them to these. Based on the torque command value for the motor 10, that is, the motor 10
The value of the torque to be output from is calculated (104).
At that time, the EV-ECU 16 limits the torque command value according to the temperatures of the inverter 12 and the motor 10 detected by a temperature sensor such as a thermistor. EV-ECU16
Converts the torque command value thus obtained into a current command value (106). The current command value referred to here is the exciting current Id for generating an exciting magnetic flux in the motor 10 and the motor 10
A combination of torque currents Iq (Id, Iq) that determines the torque to be output from the motor, or the absolute value I of the motor current Iq.
= (Id ² + Iq ² ) ^1/2 and its deviation angle θ = tan ⁻¹ (I
d / Iq) (I, θ).

The EV-ECU 16 receives feedback of the detected values of the phase currents Iu, Iv, Iw of the motor 10 from the inverter 12 (108), and a rotor position sensor 18 such as a resolver attached to the motor 10. Then, the number of rotations of the motor 10 (that is, position change of the rotor of the motor 10) is input (110). The EV-ECU 16 converts the detected values of the phase currents Iu, Iv, and Iw into the form of (Id, Iq) or (I, θ), and then the command value (Id, Iq) obtained in step 106 or In addition to the current control error (deviation) obtained as a result of comparison with (I, θ), the motor 10
The control target of each phase current Iu, Iv, Iw or the control target of each phase voltage Vu, Vv, Vw is determined by using the rotation speed of (112). The EV-ECU 16 proceeds to step 112.
Switching elements Q1 to Q1 according to the control target determined in
A pulse width modulation (PWM) signal for controlling ON / OFF switching of Q6 is generated and supplied to the corresponding switching elements Q1 to Q6 (114). afterwards,
The operation of the EV-ECU 16 returns to step 100.

The control procedure of FIG. 2 is characterized in that step 116 relating to motor lock determination / inverter protection processing is executed prior to step 112. In step 116, it is determined that the motor 10 is locked by an external force when the rotation speed of the motor 10 is reduced (motor lock determination), and when it is determined that the motor 10 is locked, the switching elements Q1 to Q6 of the inverter 12 are protected. Processing (inverter protection processing) is executed.

As shown in FIG. 3, in the first embodiment of the present invention, the inverter protection processing is realized by lowering the carrier frequency of the PWM signal, that is, the switching frequency of the switching elements Q1 to Q6. . Reducing the carrier frequency of the PWM signal, that is, the switching frequency of the switching elements Q1 to Q6 leads to the reduction of the switching loss of the switching elements Q1 to Q6, and thus the switching elements Q1 to Q6.
This will reduce the heat generation of Q6.

In this embodiment, the EV-ECU 16 is
First, the carrier frequency of the PWM signal is set to a frequency (for example, 10 kHz) at which the efficiency of the motor 10 and the inverter 12 = (axis output of the motor 10) / (input from the battery 14 to the inverter 12) is good (200). E
Next, the V-ECU 16 goes through step 202, and determines the necessity of protection (204) and the motor lock determination (206).
To execute. The protection necessity judgment here is a judgment as to whether or not the switching elements Q1 to Q6 are thermally destroyed even if the current carrier frequency is maintained. That is, as shown in FIG. 4 as "inverter allowable time line",
The larger the current flowing through the U, V, and W phase windings of the motor 10, the shorter the maximum time (time to thermal destruction) during which the corresponding switching element can be energized. Also,
When the current value is below the value indicated by A in the figure, thermal destruction does not occur. In step 204, the EV-ECU 16
It is determined whether or not the current command (specifically, its absolute value I) obtained in step 106 is A or more. If it is not A or more, the switching elements Q1 to Q6 are thermally destroyed even if the current carrier frequency is maintained. It is determined not to. The motor lock determination here is a determination as to whether or not the detected value of the rotation speed of the motor 10 is a predetermined value (for example, 60 rpm) or less, and the EV-ECU 16 determines the detected value of the rotation speed of the motor 10. Is less than or equal to a predetermined value, it is determined that the rotation of the motor 10 is locked by an external force. When it is determined that "the switching elements Q1 to Q6 are not thermally destroyed even with the current carrier frequency" (204) and "motor 10
If it is determined that the rotation of "is not locked by external force" (206), the EV-ECU 16 determines that the polygonal line "motor lock determination time line" in the region on the left side of the curve "inverter allowable time line" in FIG. ", And the initial value of the remaining allowable time is set in accordance with the current command obtained in step 106 (208). Then, EV-ECU1
The operation of 6 returns to step 202. In step 202, it is determined whether the current carrier frequency of the PWM signal is 10 kHz or 1.25 kHz. If the process returns from step 208 to step 202, the PW
Since the current carrier frequency of the M signal is 10 kHz, the operation of the EV-ECU 16 proceeds to step 204.

When it is judged that "the switching elements Q1 to Q6 may be thermally destroyed if the current carrier frequency is kept as it is" (204) and "the rotation of the motor 10 is locked by an external force" ( 206)
The EV-ECU 16 determines the elapsed time from the time when the previous step 208 or 210 was executed to the present, the remaining allowable time initial value set when the previous step 208 was executed, or the remaining allowable time calculated when the previous step 210 was executed. By subtracting from the time, the remaining allowable time at the present time, that is, a time indicating how much time has elapsed after which thermal destruction occurs in the switching elements Q1 to Q6 (or whether the possibility is significantly increased) is calculated. Yes (210). E
The V-ECU 16 lowers the carrier frequency of the PWM signal to a lower frequency (for example, 1.25 kHz) until the remaining allowable time becomes less than 0 (212) (214) and accordingly various control gains (for example, current command). (2) While switching the proportional gain, integral gain, etc.
16), execute the control shown in FIG. Step 21
After executing 6, the operation of the EV-ECU 16 returns to step 202. When the process returns from step 216 to step 202, the current carrier frequency of the PWM signal is 1.25k.
Since the frequency is in Hz, the EV-ECU 16 operates in step 2
The routine proceeds from 02 to step 218.

In step 218, the EV-ECU 16
Executes the protection necessity judgment similar to step 204. When it is determined in step 218 that "the switching elements Q1 to Q6 are not thermally destroyed even if the carrier frequency is returned to the original frequency (that is, the current command I <A)", the EV-ECU
16 returns the carrier frequency to the original frequency of 10 kHz (2
22), in response thereto, the various control gains are returned to the original values (224), the initial value of the remaining allowable time is set similarly to step 208 (226), and the process proceeds to step 202. When it is determined in step 218 that “the switching elements Q1 to Q6 may be thermally destroyed when the carrier frequency is returned to the original frequency (that is, the current command I ≧ A)”, the EV-ECU 16 determines the same motor as in step 206. A lock determination is performed (220). However, in order to prevent a complicated change (hunting) in the control mode, the determination threshold value is set to 200 rpm instead of 60 rpm. When it is determined in step 220 that "the rotation of the motor 10 is not locked by an external force", the EV-ECU
16 executes the operation of shifting to step 222 and
If it is determined that “0 rotation is locked by an external force”, the process returns to step 202.

As described above, according to the present embodiment, the possibility of heat generation is predicted based on the number of rotations of the motor 10, and the control for reducing the carrier frequency of the PWM signal = the switching frequency of the switching elements Q1 to Q6 is executed. Therefore, the switching element Q
The windings of 1 to Q6 and the motor 10 are not destroyed by heat. Therefore, for example, even when the accelerator is stepped on while the side brake is on when the vehicle starts on a slope, or when the accelerator is stepped on while the wheels are hitting the car stop, the switching elements Q1 to Q6 and the like are not hindered. . Also,
Use a device with a large current capacity to prevent thermal destruction,
Since there is no need to say, switching elements Q1 to Q6
Can be made smaller and cheaper. Furthermore, since only the carrier frequency of the PWM signal is lowered and the current of the motor 10 is not reduced, the change in the maximum output torque of the motor 10 and the change in torque and torque shock do not occur. Further, since hysteresis is added in steps 206 and 220, it is possible to switch from 1.
Frequent switching of control modes to 25 kHz switching and vice versa does not occur. In addition, 1.25kH
At the time of z switching, the electromagnetic resonance sound of the motor 10 is in the audible range, so that the operator or the like can hear the overloaded state of the motor 10. The switching of the carrier frequency of the PWM signal can be realized by software or hardware. Further, the above-mentioned various parameters (threshold value of the number of rotations, etc.) can be appropriately changed.

Further, as shown in FIG. 5, in the second embodiment of the present invention, when the rotation of the motor 10 is locked by the outside, the phase shift of the current flowing through each phase winding of the motor 10 is Periodically, the phases are alternately and sequentially switched to the phase shifted by 120 ° in electrical angle. By this switching, U phase →
As a result of switching of the phase in which the current is concentrated in the order of V phase → W phase or U phase → W phase → V phase, a certain phase of the winding of the motor 10 or one of the switching elements Q1 to Q6 of the inverter 12 is specified. The current will not be concentrated only on the switching elements, and the thermal destruction of the inverter 12 can be prevented.

In this embodiment, step 200 in the first embodiment is not executed. Further, step 202A in place of step 202 in the first embodiment, step 214A in place of steps 214 and 216, and step 222A in place of steps 222 and 224 are executed, respectively. In step 214A, the electrical angle is 1
Excitation current Id of the motor 10 so that the phases are shifted by 20 °
The peak of is switched forcibly. At that time, FIG.
As shown in, the motor current I is temporarily reduced. As a result, torque shock caused by phase switching is prevented. In step 222A, the control shown in step 214A is switched to the normal control, that is, the current control synchronized with the rotor position obtained by the rotor position sensor 18 is performed. Step 202A is a determination as to whether the control relating to step 214A is being executed. Therefore, in this embodiment, similarly to the above-described first embodiment, the switching element Q1
It is possible to prevent thermal destruction such as Q6. Also, for example, when the accelerator is stepped on while the side brakes are turned on when starting on a slope, a shock may occur if only 120 ° phase switching is performed, but such a problem occurs because the current control shown in FIG. 6 is completed. Does not occur.

In the above description, each embodiment of the present invention has been described by taking an electric vehicle as an example, but the present invention can be applied to a system other than an electric vehicle. Also,
Although a three-phase AC PM motor is taken as an example of the motor 10, the number of phases of the motor 10 is not limited at all. In addition, the present invention can be combined with the configuration utilizing the temperature sensor disclosed in JP-A-7-67389.

[0022]

As described above, according to the first configuration of the present invention, the steep heat generation in the winding of the motor or the corresponding switching element is predicted based on the rotation speed of the motor, and the steep heat generation is predicted. Since the switching element is controlled so that the heat generation in the switching element or winding is suppressed while the motor is rotating, the output of the temperature sensor does not have to wait for the sudden heat generated when the rotation of the motor is locked. Therefore, a device suitable for controlling the drive system of an electric vehicle and the drive control of a PM motor can be realized.

According to the second aspect of the present invention, whether or not the rotation of the motor is locked by the external force is determined based on the detected value of the motor rotation speed, and the determination is made while the lock is established. Since the switching frequency is temporarily reduced to reduce the switching loss, the sudden heat generated when the rotation of the motor is locked, etc.
This makes it possible to deal with the situation without waiting for the output of the temperature sensor, and thus realizes a device suitable for controlling the drive system of an electric vehicle and the drive control of a PM motor. Further, even if the switching frequency is changed, the maximum output torque of the motor does not change, so that neither torque shortage nor torque shock occurs. In addition, since the frequency of the electromagnetic resonance sound of the motor changes due to the change of the switching frequency, the user can hear and identify the heat generation state.

According to the third aspect of the present invention, whether or not the rotation of the motor is locked by the external force is determined based on the detected value of the motor rotation speed, and heat is generated while the determination of the lock is established. Since the switching elements and windings in which current concentrates are forcibly and alternately switched so that the switching elements and windings that are operated change alternately, the sudden heat generation that occurs when the rotation of the motor is locked, etc. On the other hand, it becomes possible to cope with the situation without waiting for the output of the temperature sensor, and eventually a device suitable for controlling the drive system of the electric vehicle and the drive control of the PM motor is realized.

According to the fourth configuration of the present invention, in addition to the third configuration, while the determination of being locked is established, it is synchronized with the alternating change of the switching element and the winding where the current is concentrated. Since the current is increased / decreased, the same effect as that of the third configuration is obtained, and the torque shock is reduced. As a result, a device more suitable for the control of the drive system of the electric vehicle and the drive control of the PM motor is realized. It

[0026]

[Addendum] The present invention can also be understood as the following configuration.

In the control method according to the fifth aspect of the present invention, the steep heat generation in the plurality of windings provided in the motor or the plurality of switching elements provided corresponding to each winding is used as the number of rotations of the motor. Based on the step of controlling the plurality of switching elements so that a target drive current is supplied to the plurality of windings during a period in which the steep heat generation is not predicted, Controlling the plurality of switching elements so that heat generation in the plurality of switching elements or the plurality of windings is suppressed for a predicted period. According to this configuration, the same operational effect as the first configuration can be obtained.

The control method according to the sixth aspect of the present invention comprises a step of detecting the number of revolutions of a motor having a plurality of windings, and a detection value of the number of revolutions indicating whether or not the rotation of the motor is locked by an external force. The switching frequency of the plurality of switching elements is reduced so that the switching loss in the plurality of switching elements provided corresponding to each winding is reduced while the step of determining based on And temporarily reducing. According to this structure, the same effect as the second structure can be obtained.

The control method according to the seventh aspect of the present invention comprises a step of detecting the rotational speed of a motor having a plurality of windings and a detection value of the rotational speed as to whether or not the rotation of the motor is locked by an external force. During the step of making a decision based on the above, and while the decision of being locked is established, the winding and the switching element where the current is concentrated are forced so that the winding that generates heat and the corresponding switching element change alternately. And alternatingly switching. According to this configuration, the same operational effect as the third configuration can be obtained.

In the control method according to the eighth structure of the present invention, the winding method in which the current is concentrated so that the torque due to the switching is suppressed while the lock is determined in the seventh structure. It has a step of increasing or decreasing the current in synchronism with an alternating change of the line and the switching element. According to this structure, the same effect as the fourth structure can be obtained.

In a ninth configuration of the present invention, in the second to fourth or sixth to eighth configurations, a target current for the plurality of windings is obtained while the lock is not determined. Is controlled so that the plurality of switching elements are supplied. According to this configuration, in addition to the operational effects of the second to fourth or sixth to eighth structures, the operational effects of the first structure can be obtained.

In a tenth structure of the present invention, in the ninth structure, when the detected value is lower than the first predetermined value, it is determined that the lock has occurred, and the second predetermined value larger than the first predetermined value is exceeded. In this case, it is determined that the lock is released. According to this configuration, the same operational effect as the ninth configuration can be obtained. Further, since the hysteresis characteristic is introduced into the lock determination based on the detected value of the rotation speed, hunting of the control mode (frequent change of the control mode) does not occur, and more stable operation is realized.

The eleventh configuration of the present invention is the ninth or tenth aspect.
In the above configuration, when the current or the control target value thereof falls below a third predetermined value, the target current is supplied to the plurality of windings regardless of whether the current is locked or not. It is characterized by controlling the switching element. According to this configuration, the same operational effect as the ninth configuration can be obtained. Furthermore, when the above current is a small current such that heat generation of the winding or the switching element does not cause a problem, the control mode does not switch to a mode related to protection,
More stable operation is realized.

[Brief description of drawings]

FIG. 1 is a block diagram showing a system configuration of an electric vehicle suitable for carrying out the present invention.

FIG. 2 is a flowchart showing the overall flow of the operation of the EV-ECU.

FIG. 3 is an EV-ECU according to the first embodiment of the invention.
3 is a flowchart showing the flow of the main part operation of FIG.

FIG. 4 is a characteristic diagram showing the content of an initial value of an allowable remaining time in the first embodiment.

FIG. 5 is an EV-ECU in the second embodiment of the invention.
3 is a flowchart showing the flow of the main part operation of FIG.

FIG. 6 is a timing chart showing details of motor current control at the time of phase step switching in the second embodiment.

[Explanation of reference numerals] 10 motors, 12 inverters, 14 batteries, 1
6 EV-ECU, 18 rotor position sensor.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI Technical indication location H02M 7/48 9181-5H H02M 7/48 MH02P 3/18 H02P 3/18 A

Claims (4)

[Claims] 1. A normal control means for controlling a plurality of switching elements provided corresponding to each winding so that a target current is supplied to a plurality of windings provided on a motor, and And a protection control means for controlling the plurality of switching elements so that heat generation in the plurality of switching elements or the plurality of windings is suppressed, a steep heat generation in the plurality of switching elements or the plurality of windings. And a control mode switching means for operating the protection control means during the period when the steep heat generation is predicted, and the normal control means during other periods, respectively. A control device comprising. 2. A control device for executing a predetermined protection operation to protect a switching element corresponding to each winding of a motor from being destroyed by heat, the rotation speed detecting means for detecting a rotation speed of the motor, and the motor by an external force. Heat generation predicting means for determining whether or not the rotation is locked based on the detected value of the rotation speed, and the switching loss of the plurality of switching elements so as to reduce the switching loss while the determination that the rotation is locked is established. A control device comprising: a protection control unit that temporarily reduces the switching frequency. 3. A controller for executing a predetermined protection operation to protect a motor having a plurality of windings or a switching element corresponding to each winding from thermal damage, and a rotation speed detection for detecting a rotation speed of the motor. Means, heat generation predicting means for determining whether or not the rotation of the motor is locked by an external force based on the detected value of the number of rotations, and a switching element or winding that generates heat while the lock is determined. A control device, comprising: a switching element in which a current concentrates so as to change in an alternating manner and a protection control means for forcibly and alternatingly switching the winding. 4. The control device according to claim 3, wherein while the determination that the lock is established is established, an alternating change of the switching element and the winding in which the current is concentrated so that the torque accompanying the switching is suppressed. A control device comprising a current increasing / decreasing means for increasing / decreasing the current in synchronization with the current.