JP2009113676A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric power steering device capable of accurately detecting a motor driving current while suppressing variation of steering performance caused by temperature variation of a switching element of a motor drive circuit. <P>SOLUTION: A current instruction value is calculated based on at least steering torque T, and an electric motor 12 is driven/controlled based on the current instruction value and the motor current detection values Iu-Iw. The motor current detection values Iu-Iw are calculated based on a FET part voltage descending value Vdeff of the motor drive circuit 24 and ON-resistance Ron of FET calculated with reference to ON-resistance temperature characteristic memorized in a memory device based on the FET temperature Tj. At this time, the device is provided with ON-resistance temperature characteristic correction function for correcting the ON-resistance temperature characteristic. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an electric power steering apparatus that applies a steering assist force to reduce a steering burden on a driver to a steering mechanism, and more particularly to an electric power steering apparatus that detects a motor drive current with high accuracy.

As a conventional electric power steering device, a device that detects a drain-source voltage of a switching element (FET) of a motor drive circuit and detects a motor current from this voltage is known (for example, see Patent Document 1). . Here, an overheat protection function is realized by utilizing the characteristic that the on-resistance of the switching element becomes higher as the temperature rises and by reducing the actual current when the temperature is high.
JP-A-5-338542

However, in the conventional device described in the above-mentioned patent document, since the control that lowers the motor current works as the temperature of the switching element increases, the basic performance required for the electric power steering device by the temperature change of the switching element is achieved. A certain steering performance may change greatly, and there is a possibility that merchantability may be impaired.
Therefore, an object of the present invention is to provide an electric power steering device that can detect a motor current with high accuracy while suppressing a change in steering performance due to a temperature change of a switching element of a motor drive circuit.

In order to solve the above-described problem, an electric power steering apparatus according to claim 1 calculates a current command value based on steering torque detection means for detecting steering torque and at least steering torque detected by the steering torque detection means. An electric motor that is driven through a drive circuit constituted by a semiconductor element and applies a steering assist force to the steering system; and a drive current detector that detects a motor drive current of the electric motor; An electric power steering apparatus comprising: motor control means for driving and controlling the electric motor based on a deviation between the current command value and the motor drive current;
The drive current detection means includes a potential difference detection means for detecting a potential difference of the semiconductor element, a temperature detection means for detecting a temperature of the semiconductor element, and a temperature characteristic setting means for setting a temperature characteristic of an on-resistance of the semiconductor element; On-resistance calculation means for calculating the on-resistance of the semiconductor element based on the temperature detected by the temperature detection means and the temperature characteristic set by the temperature characteristic setting means; and the potential difference of the semiconductor element detected by the potential difference detection means And current calculation means for calculating the motor drive current based on the on-resistance calculated by the on-resistance calculation means.

According to a second aspect of the present invention, there is provided the electric power steering apparatus according to the first aspect of the invention, wherein the temperature characteristic setting means is configured to apply the predetermined current to the semiconductor element at at least two different temperatures. The on-resistance of the semiconductor element is calculated on the basis of the potential difference, and the on-resistance temperature characteristic is set based on the calculated on-resistance.
The electric power steering apparatus according to a third aspect of the present invention is the electric power steering apparatus according to the second aspect, wherein the temperature characteristic setting means is configured to apply the predetermined current to the semiconductor element at at least two different temperatures. The on-resistance of the semiconductor element is calculated based on the potential difference, and an offset amount with respect to the basic characteristic of the preset on-resistance temperature characteristic is calculated based on the calculated on-resistance, and the basic characteristic is calculated by the offset amount. It is characterized in that the on-resistance temperature characteristic is set by correction.

According to a fourth aspect of the present invention, there is provided the electric power steering apparatus according to any one of the first to third aspects, wherein the temperature detecting means is incorporated in a thermistor provided in the vicinity of the semiconductor element or in the semiconductor element. The temperature of the semiconductor element is estimated based on the temperature detection value obtained by the thermistor.
Furthermore, in the electric power steering apparatus according to claim 5, in the invention according to any one of claims 1 to 4, the potential difference detection unit detects a potential difference of a semiconductor element arranged in a lower stage of the drive circuit. It is characterized by being configured.

  According to the electric power steering apparatus of the present invention, the on-resistance of the semiconductor element is calculated according to the temperature of the semiconductor element, and the motor drive current is detected based on the on-resistance and the potential difference between the semiconductor elements. The current can be properly detected regardless of the temperature change of the element, and good steering performance can be obtained. Further, by providing a temperature characteristic correction function for the on-resistance of the semiconductor element, a more accurate current detection function can be realized.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is an overall configuration diagram showing an embodiment of an electric power steering apparatus according to the present invention.
In the figure, reference numeral 1 denotes a steering wheel, and a steering force applied to the steering wheel 1 from a driver is transmitted to a steering shaft 2 having an input shaft 2a and an output shaft 2b. The steering shaft 2 has one end of the input shaft 2a connected to the steering wheel 1 and the other end connected to one end of the output shaft 2b via a torque sensor 3 as steering torque detecting means.

  The steering force transmitted to the output shaft 2 b is transmitted to the lower shaft 5 via the universal joint 4 and further transmitted to the pinion shaft 7 via the universal joint 6. The steering force transmitted to the pinion shaft 7 is transmitted to the tie rod 9 via the steering gear 8 and steers steered wheels (not shown). Here, the steering gear 8 is configured in a rack and pinion type having a pinion 8a connected to the pinion shaft 7 and a rack 8b meshing with the pinion 8a, and the rotational motion transmitted to the pinion 8a is linearly moved by the rack 8b. It has been converted to movement.

A steering assist mechanism 10 for transmitting a steering assist force to the output shaft 2b is connected to the output shaft 2b of the steering shaft 2. The steering assist mechanism 10 includes a reduction gear 11 coupled to the output shaft 2b, and an electric motor 12 coupled to the reduction gear 11 and generating a steering assist force with respect to the steering system.
The torque sensor 3 detects a steering torque applied to the steering wheel 1 and transmitted to the input shaft 2a, and a torsional angle displacement of a torsion bar (not shown) in which the steering torque is interposed between the input shaft 2a and the output shaft 2b. The torsional angular displacement is detected by, for example, a potentiometer. The torque detection value T output from the torque sensor 3 is input to the controller 15.

The controller 15 operates by being supplied with power from a vehicle-mounted battery 17 (for example, the rated voltage is 12V). The negative electrode of the battery 17 is grounded, and the positive electrode thereof is connected to the controller 15 via an ignition switch 18 that starts the engine, and is also connected to the controller 15 without passing through the ignition switch 18.
Further, the electric motor 12 of the present embodiment is, for example, a three-phase brushless motor. As shown in FIG. 2, one end of the U-phase coil Lu, the V-phase coil Lv, and the W-phase coil Lw are connected to each other so The other ends of the coils Lu, Lv, and Lw are connected to the controller 15, and motor drive currents Iu, Iv, and Iw are individually supplied.

As shown in FIG. 2, the controller 15 receives the steering torque T detected by the torque sensor 3 and the vehicle speed detection value V detected by the vehicle speed sensor 16 as vehicle speed detection means.
Further, the controller 15 receives motor drive currents Iu, Iv and Iw supplied to the phase coils Lu, Lv and Lw of the electric motor 12 detected by the current detection circuit 22. A specific configuration of the current detection circuit 22 will be described later.

  The controller 15 outputs a motor voltage command value Vu, Vv, and Vw for generating the steering assist force according to the steering torque T and the vehicle speed detection value V by the electric motor 12, for example. A pulse width modulation (PWM) based on a motor drive circuit 24 composed of a field effect transistor (FET) for driving the electric motor 12 and phase voltage command values Vu, Vv and Vw output from the control arithmetic unit 23. And an FET gate drive circuit 25 that executes control processing and controls the gate current of the field effect transistor of the motor drive circuit 24.

  The motor drive circuit 24 includes a series circuit in which two field effect transistors Qua and Qub are connected in series, and a series circuit of two field effect transistors Qva and Qvb connected in parallel with the series circuit, and a field effect transistor. It consists of a series circuit of Qwa and Qwb. Then, the connection points of the field effect transistors Qua and Qub, the connection points of the field effect transistors Qva and Qvb, and the connection points of the field effect transistors Qwa and Qwb of the motor drive circuit 24 are connected to the respective excitation coils Lu of the electric motor 12 in a star connection. , Lv and Lw.

  In the vicinity of the field effect transistors Qub, Qvb, and Qwb arranged at the lower stage of the motor drive circuit 24, temperature sensors 26u to 26w configured by thermistors and the like are provided and detected by these temperature sensors 26u to 26w. The temperatures Tcu to Tcw are input to the current detection circuit 22. The field effect transistors Qub, Qvb, Qwb are provided with differential amplifier circuits 27u-27w for detecting the voltage drop values, respectively, and the FET section voltages detected by the differential amplifier circuits 27u-27w are provided. The drop values Vdiffu to Vdiffw are also input to the current detection circuit 22.

  The controller 15 also has a power relay circuit 30a for opening and closing a power supply line from the battery 17 to the motor drive circuit 24, and a motor relay circuit for opening and closing a power supply line from the motor drive circuit 24 to the electric motor 12. 30b and 30c. These relay circuits 30 a to 30 c are driven and controlled by a fail safe processor 31.

The control arithmetic unit 23 calculates a torque command value corresponding to the input torque detection value T and the vehicle speed detection value V, calculates a three-phase current command value based on the calculated torque command value, and this three-phase current. The voltage command values Vu, Vv, and Vw are calculated so that the deviation between the command value and the motor currents Iu to Iw detected by the current detection circuit 22 is zero, and feedback control is executed.
The FET gate drive circuit 25 receives the voltage command values Vu, Vv, and Vw as inputs and calculates a PWM gate signal to the motor drive circuit 24. The motor drive circuit 24 is PWM-controlled by the gate signal. Thereby, each phase current Iu, Iv, Iw is controlled to become the current command value.

Next, the configuration of the current detection circuit 22 will be described in detail.
The current detection circuit 22 detects the motor current Iu based on the FET section voltage drop value Vdiffu of the field effect transistor Qub and the on-resistance Ronu of the field effect transistor Qub, and also detects the FET section voltage drop value Vdiffv of the field effect transistor Qvb. And the on-resistance Ronv of the field effect transistor Qvb is detected, and the motor current Iw is determined based on the FET voltage drop value Vdiffw of the field-effect transistor Qwb and the on-resistance Ronw of the field-effect transistor Qwb. It comes to detect.

FIG. 3 is a flowchart showing a current detection processing procedure executed by the current detection circuit 22. Note that this current detection processing is executed for each phase, and in order to simplify the description, the description will be made by omitting the symbols (u, v, w) indicating the types of phases. First, in step S1, the temperature Tc detected by the temperature sensor 26 is acquired, and the process proceeds to step S2.
In step S2, the FET temperature Tj of the field effect transistor is estimated based on the temperature Tc acquired in step S1, and the process proceeds to step S3.

  In step S3, the on-resistance Ron of the field effect transistor is calculated with reference to the on-resistance calculation map shown in FIG. 4 based on the FET temperature Tj estimated in step S2. Here, it is assumed that the on-resistance calculation map is stored in a storage device or the like in advance. The horizontal axis represents the FET temperature Tj, the vertical axis represents the on-resistance Ron, and the higher the FET temperature Tj, the larger the on-resistance Ron is calculated. Is set to

Note that this on-resistance calculation map is stored individually for each FET.
The on-resistance temperature characteristic may be a non-linear characteristic as shown by a solid line in FIG. 4 or a linear approximate expression (Ron = a × Tj + b: a and b are constants) as shown by a broken line.
Next, the process proceeds to step S4, the FET section voltage drop value Vdef output from the differential amplifier circuit 27 is acquired, and the process proceeds to step S5.

In step S5, based on the on-resistance Ron calculated in step S3 and the FET section voltage drop value Vdef acquired in step S4, a motor current value I is calculated based on the following equation, and then a current calculation process is performed. Exit.
I = Vdef / Ron (1)
As described above, in this embodiment, the on-resistance Ron corresponding to the FET temperature Tj is calculated, and the motor drive current I is calculated by dividing the FET voltage drop value Vdef by the on-resistance Ron. Accordingly, it is possible to obtain an appropriate motor current value by correcting the fluctuation of the current due to the temperature change.

Next, an on-resistance temperature characteristic correction process for correcting the on-resistance calculation map will be described.
FIG. 5 is a flowchart showing the on-resistance temperature characteristic correction processing procedure executed by the current detection circuit 22. First, in step S21, the motor drive circuit 24 is left in the ambient temperature Ta = A ° C. (for example, 25 ° C.), and the process proceeds to step S22, and after a predetermined current Ia is applied to the field effect transistor for a short time. Control goes to step S23.

In step S23, the FET section voltage drop value Vdiff output from the differential amplifier circuit 27 is acquired, and the process proceeds to step S24. The FET section voltage drop value acquired here is the FET section voltage drop value when the energizing current Ia is energized at the ambient temperature Ta = A.
In step S24, the on-resistance Ron_ @ Ta = A is calculated based on the energization current Ia and the FET section voltage drop value Vdef acquired in step S23. FIG. 6A is a diagram showing the relationship between the energization current value at the ambient temperature Ta = A and the FET voltage drop value, and the on-resistance Ron_ @ Ta = A has a slope of FIG. Equivalent to.

Next, in step S25, the motor drive circuit 24 is left in the ambient temperature Ta = B ° C. (for example, 75 ° C.), the process proceeds to step S26, and a predetermined current Ia is applied to the field effect transistor for a short time. To step S27.
In step S27, the FET section voltage drop value Vdiff output from the differential amplifier circuit 27 is acquired, and the process proceeds to step S28. The FET section voltage drop value acquired here is the FET section voltage drop value when the energizing current Ia is energized at the ambient temperature Ta = B.

In step S28, the on-resistance Ron_ @ Ta = B is calculated based on the energization current Ia and the FET section voltage drop value Vdiff acquired in step S27. FIG. 6B is a diagram showing the relationship between the energization current value and the FET voltage drop value at the ambient temperature Ta = B, and the on-resistance Ron_ @ Ta = B has a slope of FIG. 6B. Equivalent to.
Then, the process proceeds to step S29, and the on-resistance Ron_ @ Ta = A calculated in step S24 and the on-resistance Ron_ @ Ta = B calculated in step S28, as shown in FIG. After the temperature characteristic is corrected and stored in the storage device, the on-resistance correction process is terminated.

In FIG. 7, a characteristic line indicated by a broken line is a basic characteristic of an on-resistance temperature characteristic stored in advance, and a characteristic line indicated by a solid line is an on-resistance temperature characteristic after correction.
First, an offset amount with respect to the basic characteristic is calculated based on the on-resistance Ron_ @ Ta = A and the on-resistance Ron_ @ Ta = B. For example, the difference between the on-resistance at A ° C. in the basic characteristics and the on-resistance Ron_ @ Ta = A calculated in step S24, the on-resistance at B ° C. in the basic characteristics and the on-resistance Ron_ calculated in step S28. The average value of the difference value from @ Ta = B is calculated as the offset amount. Then, by offsetting the basic characteristic by the offset amount, the corrected on-resistance temperature characteristic shown by the solid line can be obtained.

When the on-resistance temperature characteristic is a linear approximate expression (Ron = a × Tj + b), an approximate expression after direct correction based on the on-resistance Ron_ @ Ta = A and the on-resistance Ron_ @ Ta = B. May be calculated (the constants a and b are calculated).
In FIG. 2, the current detection circuit 22, the temperature sensor 26, and the differential amplifier circuit 27 correspond to drive current detection means, the control arithmetic unit 23 corresponds to current command value calculation means, and the FET gate drive circuit 25 corresponds to motor control means. The temperature sensor 26 corresponds to the temperature detection means, and the differential amplifier circuit 27 corresponds to the potential difference detection means. In the process of FIG. 3, step S3 corresponds to the on-resistance calculating means, and step S5 corresponds to the current calculating means. Further, the process of FIG. 5 corresponds to the temperature characteristic setting means.

Next, operations and effects in the present embodiment will be described.
If the vehicle is now stopped and the driver is not operating the steering wheel 1, the steering torque T detected by the torque sensor 3 is “0” and the vehicle speed V detected by the vehicle speed sensor 16. Since “0” is also “0”, the torque command value calculated by the control calculation device 23 is also “0”. Further, since the FET voltage drop values Vdiffu to Vdiffw output from the differential amplifier circuits 27u to 27w are “0”, and the motor drive currents Iu to Iw detected by the current detection circuit 22 are also “0”. The motor voltage command values Vu to Vw calculated by the control calculation device 23 are also “0”, and as a result, the electric motor 12 continues to be stopped.

When the steering wheel 1 is turned to the right (or left) while the electric motor 12 is stopped, the torque sensor 3 detects the steering torque T corresponding to the steering direction, and the steering torque T is supplied to the controller 15. . Then, a torque command value corresponding to the steering torque T is calculated by the control arithmetic device 23, and the electric motor 12 is driven according to this torque command value.
At this time, if the temperature of the field effect transistors Qub to Qwb of the motor drive circuit 24 is relatively low, the current detection circuit 22 refers to the on-resistance calculation map in step S3 of the current detection process of FIG. The resistance Ron is calculated to a relatively small value. Then, based on the on-resistance Ron and the FET section voltage drop value Vdiff acquired in step S4, motor drive currents Iu to Iw are calculated in step S5.

  The motor drive currents Iu to Iw calculated in this way are input to the control arithmetic unit 23, where the deviation between the motor drive currents Iu to Iw and the three-phase current command value is “0”. Voltage command values Vu, Vv and Vw are calculated as follows. The electric motor 12 is driven and controlled by turning on / off the field effect transistors Qua to Qwb of the motor drive circuit 24 by PWM signals based on these. As a result, a steering assist force corresponding to the steering torque applied to the steering wheel 1 is generated by the electric motor 12, and this is transmitted to the output shaft 2b via the reduction gear 11, so that the driver performs light steering. Can do.

On the other hand, when the temperature of the field effect transistors Qub to Qwb of the motor drive circuit 24 is relatively high, the current detection circuit 22 calculates the on-resistance Ron to a relatively large value in step S3 of FIG. Then, motor drive currents Iu to Iw are calculated based on the on-resistance Ron and the FET section voltage drop value Vdiff.
Thus, in the present embodiment, the motor drive current is calculated using the on-resistance Ron calculated in consideration of the temperature characteristics and the FET voltage drop value Vdiff.

By the way, if the on-resistance Ron is not corrected according to the FET temperature Tj as described above, the control works in the direction of decreasing the motor current at a high temperature, which is a basic performance required for the electric power steering device. There is a risk that the steering performance will change greatly and the merchantability will be impaired.
On the other hand, in this embodiment, since the on-resistance Ron is corrected according to the FET temperature Tj, current detection can be performed with high accuracy regardless of the temperature change of the field effect transistor, and good steering performance is ensured. can do.

In addition, since the on-resistance temperature characteristic is corrected for each individual field effect transistor, current detection can be performed with higher accuracy.
For example, when the actual on-resistance temperature characteristic is offset downward with respect to the basic characteristic as shown in FIG. 7, the on-resistance Ron calculated in step S3 in FIG. It can be prevented that the motor current value is calculated to be smaller than the actual current value due to being calculated to be larger than Ron. As a result, it is possible to prevent erroneous control in the direction of increasing the motor current.

  Thus, in the above embodiment, the on-resistance of the semiconductor element is calculated according to the temperature of the semiconductor element, and the motor drive current is detected based on the on-resistance and the potential difference between the semiconductor elements. Current detection can be performed properly regardless of changes, and good steering performance can be obtained. As a result, the steering assist control can be performed without causing the driver to feel uncomfortable. Further, by providing a temperature characteristic correction function for the on-resistance of the semiconductor element, a more accurate current detection function can be realized.

In addition, since the motor drive current is detected based on the potential difference of the semiconductor element, the number of parts can be reduced compared to current detection using a general shunt resistor or current detection using a non-contact type current sensor. It is possible to reduce mounting density and cost.
Further, when calculating the on-resistance of the field-effect transistor, the on-resistance temperature characteristics and arithmetic expressions stored in advance in the storage device are used, so that the on-resistance can be corrected relatively easily.

  In addition, since the on-resistance temperature characteristic is corrected by the on-resistance value calculated based on the potential difference generated when a specific current is passed at at least two different temperatures, the on-resistance temperature of each field effect transistor is corrected. Even when the characteristics vary or when the on-resistance temperature characteristics change due to changes over time, the temperature characteristics can be corrected appropriately, and more accurate current detection can be realized.

Further, an offset amount for correcting the on-resistance temperature characteristic is calculated based on an on-resistance value calculated based on a potential difference generated when a specific current is passed at at least two different temperatures. Therefore, even if the temperature characteristic is non-linear, it can be corrected appropriately.
Further, since the current detection means is provided in the lower stage of the motor drive circuit, the drive current value of the electric motor can be detected relatively easily.

In the above embodiment, the case where the on-resistance Ron is calculated in step S3 of FIG. 3 with reference to the on-resistance calculation map shown in FIG. 4 is described. However, the on-resistance temperature characteristic stored in the storage device or the like is described. The on-resistance Ron can also be calculated by calculation using an approximate expression (Ron = a × Tj + b).
In the above embodiment, the case where the on-resistance temperature characteristic is corrected based on the on-resistance (Ron_ @ Ta = A, Ron_ @ Ta = B) calculated at two different temperatures has been described. On-resistance temperature characteristics can also be corrected based on the on-resistance calculated at different temperatures above the point.

Furthermore, although the case where the thermistor arrange | positioned in the vicinity of the field effect transistor was applied as a temperature detection means was demonstrated in the said embodiment, the thermistor incorporated in the field effect transistor can also be applied.
Moreover, in the said embodiment, although the case where a brushless motor was applied as an electric motor was demonstrated, a brush motor system is also applicable.

1 is a schematic configuration diagram of an electric power steering apparatus according to an embodiment of the present invention. It is a block diagram which shows the structure of a controller. It is a flowchart which shows an electric current detection processing procedure. It is an on-resistance calculation map. It is a flowchart which shows an on-resistance temperature characteristic correction process sequence. It is a figure explaining the correction method of on-resistance temperature characteristic. It is a figure explaining an ON resistance temperature characteristic correction function.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Steering wheel, 2 ... Steering shaft, 3 ... Torque sensor, 10 ... Steering assist mechanism, 11 ... Reduction gear, 12 ... Electric motor, 15 ... Controller, 16 ... Vehicle speed sensor, 17 ... Battery, 18 ... Ignition switch, 22 DESCRIPTION OF SYMBOLS ... Current detection circuit, 23 ... Control arithmetic unit, 24 ... Motor drive circuit, 25 ... FET gate drive circuit, 26 ... Temperature sensor, 27 ... Differential amplifier circuit

Claims (5)

Driving through a steering torque detecting means for detecting a steering torque, a current command value calculating means for calculating a current command value based on at least the steering torque detected by the steering torque detecting means, and a drive circuit composed of semiconductor elements An electric motor for applying a steering assist force to the steering system; drive current detection means for detecting a motor drive current of the electric motor; and the electric motor based on a deviation between the current command value and the motor drive current. An electric power steering device comprising motor control means for driving control,
The drive current detection means includes a potential difference detection means for detecting a potential difference of the semiconductor element, a temperature detection means for detecting a temperature of the semiconductor element, and a temperature characteristic setting means for setting a temperature characteristic of an on-resistance of the semiconductor element; On-resistance calculation means for calculating the on-resistance of the semiconductor element based on the temperature detected by the temperature detection means and the temperature characteristic set by the temperature characteristic setting means; and the potential difference of the semiconductor element detected by the potential difference detection means And an electric power steering device comprising: current calculation means for calculating the motor drive current based on the on-resistance calculated by the on-resistance calculation means.   The temperature characteristic setting means calculates an on-resistance of the semiconductor element based on a potential difference of the semiconductor element when a predetermined current is passed through the semiconductor element at at least two different temperatures, and calculates each on-resistance 2. The electric power steering apparatus according to claim 1, wherein an on-resistance temperature characteristic is set based on   The temperature characteristic setting means calculates an on-resistance of the semiconductor element based on a potential difference of the semiconductor element when a predetermined current is passed through the semiconductor element at at least two different temperatures, and calculates each on-resistance 3. The on-resistance temperature characteristic is set by calculating an offset amount with respect to a basic characteristic of the on-resistance temperature characteristic set in advance based on the basic characteristic, and correcting the basic characteristic by the offset amount. Electric power steering device.   The temperature detection means estimates the temperature of the semiconductor element based on a temperature detection value by a thermistor provided in the vicinity of the semiconductor element or a thermistor built in the semiconductor element. 4. The electric power steering apparatus according to claim 1.   5. The electric power steering apparatus according to claim 1, wherein the potential difference detection unit is configured to detect a potential difference between semiconductor elements arranged in a lower stage of the drive circuit. 6. .

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