JP5345433B2 - Steering control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a steering control device capable of suppressing heat generation of an inverter while at least suppressing reduction of output of the inverter. <P>SOLUTION: A carrier frequency in PWM control of the inverter 13b is controlled according to an inverter temperature Ti by a conveying wave production part 28. When the inverter temperature Ti exceeds a predetermined carrier frequency reduction setting temperature, the conveying wave production part 28 reducing switching loss in the inverter 13b to suppress heat generation of the inverter 13b by setting the carrier frequency lower than the case where the inverter temperature Ti is not more than the predetermined carrier frequency reduction setting temperature. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a steering control device that drives and controls an electric motor for applying a steering force to a steering mechanism that steers a steered wheel of a vehicle by PWM control of an inverter.

  When the electric motor is driven by PWM control of the inverter, current flows through the inverter, and the inverter generates heat. Therefore, for example, in the technique described in Patent Document 1, when the temperature of the motor drive circuit that supplies power to the electric motor exceeds a predetermined set temperature, the output of the motor drive circuit is limited to limit the output of the motor drive circuit. To protect against overheating.

JP 2006-341795 A

  However, in the technique described in Patent Document 1, since the output of the motor drive circuit is limited in order to suppress the heat generation of the motor drive circuit, this significantly reduces the output of the electric motor. There was a problem.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a steering control device that can suppress heat generation of the inverter while at least suppressing a decrease in the output of the inverter.

  According to the first aspect of the present invention, when the inverter temperature rises and exceeds a predetermined carrier frequency reduction set temperature, the carrier frequency in PWM control is set higher than when the inverter temperature is equal to or lower than the carrier frequency reduction set temperature. It is characterized by a low setting.

According to the first aspect of the present invention, when the inverter temperature rises to exceed a predetermined carrier frequency reduction set temperature and the manual steering torque exceeds a predetermined value , the inverter temperature is equal to or lower than the carrier frequency reduction set temperature. It is characterized in that the carrier frequency in PWM control is set lower than when it is present.

  Therefore, according to the present invention, since the switching loss in the inverter is reduced by reducing the carrier frequency, it is possible to suppress heat generation of the inverter while at least suppressing a decrease in the output of the inverter. .

BRIEF DESCRIPTION OF THE DRAWINGS The figure which shows the outline of the electric power steering apparatus with which the steering control apparatus concerning this invention was applied as 1st Embodiment of this invention. The figure which shows the detail of the control unit in FIG. The figure which shows the detail of the inverter in FIG. The figure which shows the carrier frequency map in the carrier wave generation part shown in FIG. The figure (a) is a figure which shows the change of inverter temperature accompanying the electricity supply to an inverter, The figure (b) is a figure which shows the change of the electric current which an inverter can output. The figure which shows the change of the inverter temperature accompanying the electricity supply to an inverter. The figure which shows a carrier frequency map as the 1st modification of 1st Embodiment. The figure which shows the relationship between a carrier frequency and the frequency of the carrier wave in another electronic device. The figure which shows a carrier frequency map as the 2nd modification of 1st Embodiment. The figure which shows a carrier frequency map as the 3rd modification of 1st Embodiment. The block diagram which shows the detail of a control unit as the 4th modification of 1st Embodiment. The figure which shows the carrier frequency map in the carrier wave generation part shown in FIG. The block diagram which shows the detail of a control unit as the 5th modification of 1st Embodiment. The figure which shows the carrier frequency map in the carrier generation part shown in FIG. The block diagram which shows the detail of a control unit as the 2nd Embodiment of this invention. The figure which shows the carrier frequency map in the carrier wave generation part shown in FIG. Explanatory drawing of the average steering torque Ta in the 1st modification of 2nd Embodiment. The block diagram which shows the detail of a control unit as the 2nd modification of 2nd Embodiment. Explanatory drawing of the steering frequency S in the 2nd modification shown in FIG. The figure which shows the carrier frequency map in the carrier wave generation part shown in FIG. The figure which shows the detail of a control unit as the 3rd modification of 2nd Embodiment. The figure which shows the carrier frequency map in the carrier wave generation part shown in FIG. The block diagram which shows the detail of a control unit as a 4th modification of 2nd Embodiment. The figure which shows the carrier frequency map in the carrier wave generation part shown in FIG. The block diagram which shows the detail of a control unit as the 5th modification of 2nd Embodiment. The block diagram which shows the detail of a control unit as the 3rd Embodiment of this invention. The figure which shows the carrier frequency map in the carrier wave generation part shown in FIG. Explanatory drawing of 2nd setting target electric current Iq2 in 3rd Embodiment.

  FIG. 1 is a diagram showing an outline of an electric power steering apparatus to which a steering control apparatus according to the present invention is applied as a first embodiment of the present invention.

  The electric power steering apparatus shown in FIG. 1 is a so-called column assist type that transmits the assist torque generated by the electric motor 1 driven with three-phase AC power to the steering shaft 3 via the speed reducer 2. A steering wheel 4 that rotates integrally with the steering shaft 3 is provided at one end of the steering shaft 3, and a pinion shaft 5 is connected to the other end of the steering shaft 3 via a universal joint 6.

  The pinion shaft 5 and the rack bar 7 constitute a so-called rack and pinion type steering gear 8. That is, when the steering wheel 4 is rotated together with the pinion shaft 5, the rotational motion of the pinion shaft 5 is converted into the linear motion of the rack bar 7, and the tie rods connected to the rack bar 7 and the left and right ends of the rack bar 7, respectively. The left and right steered wheels 11, 11 which are front wheels of the vehicle are steered via a link mechanism 10 as a steering mechanism composed of 9, 9. In FIG. 1, 7a and 7a are dust boots. The left and right ends of the rack bar 7 and the left and right tie rods 9 and 9 are connected to each other by universal joints (not shown) provided in the dust boots 7a. Yes.

  A manual steering torque T for rotating the steering wheel 4 by the driver is detected by a torque sensor 12 provided on the steering shaft 3, and in addition to the output of the torque sensor 12, a resolver 1 a attached to the electric motor 1. The control unit 13 drives the electric motor 1 based on the output. As a result, the electric motor 1 generates an assist torque that assists the manual steering torque, and the assist torque is transmitted and applied as a steering force to the link mechanism 10 via the steering shaft 3 and the steering gear 8.

  FIG. 2 is a diagram showing details of the control unit 13. As shown in FIG. 2, the control unit 13 includes a main control unit 13a that generates PWM control signals PWMu, PWMv, and PWMw for driving the electric motor 1 based on outputs of the torque sensor 12 and the resolver 1a, and a PWM. And an inverter 13b for supplying electric power from the battery 14 to the electric motor 1 by a switching operation based on the control signals PWMu, PWMv, and PWMw. The battery 14 is connected to the inverter 13b via the cable 14a.

  As shown in FIG. 3, inverter 13b has U-phase arm 15u, V-phase arm 15v, and W-phase arm 15w. Each arm 15u, 15v, 15w is formed by connecting high-side FETs 16u, 16v, 16w, which are switching elements, and low-side FETs 17u, 17v, 17w in series, and among these arms 15u, 15v, 15w, the high-side FET 16u, The ends on the 16v, 16w side are connected to the battery 14, while the ends on the low side FETs 17u, 17v, 17w side of the arms 15u, 15v, 15w are grounded. Further, the intermediate points between the high-side FETs 16u, 16v, 16w and the low-side FETs 17u, 17v, 17w among the arms 15u, 15v, 15w are connected to the coils of the respective phases of the electric motor 1. As is well known, the inverter 13b supplies three-phase AC power to the electric motor 1 by the switching operation of each FET.

  Next, a specific configuration of the main control unit 13a will be described with reference to FIG. As shown in FIG. 2, the main control unit 13 a controls the electric motor 1 by vector control using a rotating coordinate system including a q axis that is the rotation direction of the electric motor 1 and a d axis that is orthogonal to the q axis. It is supposed to be.

  Specifically, the assist torque calculation unit 18 of the main control unit 13 a calculates the target assist torque TA based on the manual steering torque T detected by the torque sensor 12, and the target assist torque TA is supplied to the target current calculation unit 19. Output.

The target current calculation unit 19 uses, in addition to the target assist torque TA, the d-axis and q-axis target currents Id ^* and Iq based on the rotation speed ω of the electric motor 1, that is, the rotation speed ω of the rotor not shown in the electric motor 1. ^* Is calculated, and the target currents Id ^* and Iq ^* are output to the d-axis and q-axis first calculation units 23d and 23q which are current deviation calculation units. The rotational speed ω is calculated based on the output of the resolver 1a, and the rotational position calculation unit 21 calculates the rotational position θ of a rotor (not shown) in the electric motor 1 based on the output of the resolver 1a. The rotational speed calculation unit 22 calculates the rotational speed ω by differentiating the rotational position θ.

Here, as is well known, the q-axis target current Iq ^* is a q-axis component current in vector control using a rotating coordinate system, and controls the magnitude of torque generated by the electric motor 15. The d-axis target current Id ^* is a d-axis component current in vector control using a rotating coordinate system, and is used to weaken the field of the electric motor 15.

Then, the d-axis first calculation unit 23d calculates the d-axis current deviation ΔId by subtracting the d-axis actual current Id flowing through the electric motor 1 from the d-axis target current Id ^* , and the d-axis current deviation ΔId is calculated. The current deviation ΔId is output to the d-axis PI control unit 20d which is an operation amount calculation unit. On the other hand, the q-axis first computing unit 23q calculates the q-axis current deviation ΔIq by subtracting the q-axis actual current Iq from the q-axis target current Iq ^*, and calculates the q-axis current deviation ΔIq. This is output to the q-axis PI control unit 20q which is an operation amount calculation unit.

  Here, the d-axis and q-axis actual currents Id and Iq are converted from the three-phase excitation currents Iu, Iv, and Iw supplied to the electric motor 1 into a rotating coordinate system by the three-phase to two-phase conversion unit 25. It is a thing. Specifically, among the three-phase excitation currents Iu, Iv, and Iw, the U-phase and V-phase excitation currents Iu and Iv are detected by the actual current sensors 25u and 25v, while the W-phase excitation current Iw is detected by the U-phase and V-phase. Based on the excitation currents Iu and Iv of the phase, the three-phase to two-phase converter 25 calculates.

Both PI control units 20d and 20q calculate the d-axis and q-axis target supply voltages Vd ^* and Vq ^* by so-called PI control (proportional integral control). Specifically, the d-axis PI control unit 20d includes a proportional term obtained by multiplying the d-axis current deviation ΔId by a proportional gain Kp, and an integral term obtained by multiplying an integral value of the d-axis current deviation ΔId by an integral gain Ki. The d-axis target supply voltage Vd ^* is calculated by proportional-integral calculation added by the d-axis second calculation unit 24d. On the other hand, the q-axis PI control unit 20q calculates a proportional term obtained by multiplying the q-axis current deviation ΔIq by the proportional gain Kp, and an integral term obtained by multiplying the integral value of the q-axis current deviation ΔIq by the integral gain Ki. The target supply voltage Vq ^* for the q-axis is calculated by proportional-integral calculation added by the second calculation unit 24q for the axis.

Then, the target supply voltage d-axis and q-axis Vd ^*, Vq ^*, in order to prevent mutual interference between the d-axis current and the q-axis current, the correction target supply voltage Vd ^** by mutual interference voltage compensation unit 26, Vq ^It is corrected to ^** and output to the PWM control unit 27. Specifically, the mutual interference voltage compensator 26 calculates the d-axis and q-axis compensation voltages based on the d-axis and q-axis actual currents Id and Iq and the rotational speed ω of the electric motor 1, and compensates for them. By adding the voltages to the d-axis and q-axis target supply voltages Vd ^* and Vq ^* , respectively, the d-axis and q-axis corrected target supply voltages Vd ^** and Vq ^** are obtained, respectively.

The PWM control unit 27 converts the d-axis and q-axis corrected target supply voltages Vd ^** and Vq ^** into a three-phase target supply voltage, which is generated by the three-phase target supply voltage and a carrier wave generation unit 28 described later. By comparing with the triangular carrier signal C which is the carrier wave, three-phase PWM control signals PWMu, PWMv and PWMw having a pulse shape are generated and output to the inverter 13b. Then, each FET of the inverter 13b performs switching operation according to the PWM control signals PWMu, PWMv, and PWMw, so that electric power is supplied to the electric motor 1, and the electric motor 1 generates assist torque corresponding to the target assist torque TA. become.

Here, when electric power is supplied from the inverter 13b to the electric motor 1, the inverter 13b generates heat due to the current flowing through the inverter 13b. Therefore, in order to protect the inverter 13b from overheating, overheating as an output suppression control unit is performed. A protection controller 29 is provided in the main controller 13a. This overheat protection control unit 29 is connected to a temperature sensor 30 that is a temperature detection unit disposed in the vicinity of the inverter 13b, and the inverter temperature Ti that is the output of the temperature sensor 30 has exceeded a predetermined output suppression set temperature Ti1. In this case, the assist torque limit command signal T _lim is output to the assist torque calculator 18. In the present embodiment, the temperature sensor 30 is installed in the vicinity of the inverter 13b. However, in the inverter 13b, more specifically, in the vicinity of each FET serving as a main heat source of the inverter 13b, the temperature sensor 30 is provided. May be installed.

Then, when the assist torque limit command signal T _lim is input, the assist torque calculation unit 18 limits the target assist torque TA by a predetermined upper limit value or corrects the target assist torque TA by multiplying it by a limit gain smaller than 1. As a result, the output of the inverter 13b is limited to suppress the heat generation of the inverter 13b.

  On the other hand, the carrier generation unit 28 sets the carrier frequency of the carrier signal C from the carrier frequency map shown in FIG. 4 based on the inverter temperature Ti input from the temperature sensor 29. In other words, the carrier generation unit 28 sets the carrier frequency of each PWM control signal PWMu, PWMv, PWMw according to the inverter temperature Ti.

  That is, as is well known, when the inverter 13b is driven by PWM control signals PWMu, PWMv, and PWMw having a predetermined carrier frequency, the inverter 13b performs a switching operation at a frequency corresponding to the carrier frequency, and the switching operation causes a so-called switching loss. Will occur. In order to reduce the switching loss, it is effective to set the carrier frequency low to reduce the frequency of the switching operation in the inverter 13b. However, if the carrier frequency is reduced to the audible frequency, the inverter 13b The switching sound based on the switching operation is easily perceived by the passenger as noise. Thus, since the quietness and the low loss in the inverter 13b are in a trade-off relationship, in this embodiment, whether quietness is important or low loss is determined based on the inverter temperature Ti, The carrier frequency is changed accordingly.

  The carrier frequency map shown in FIG. 4 will be described more specifically. The inverter temperature Ti is equal to or lower than a predetermined carrier frequency reduction setting temperature Ti2 set lower than the output suppression setting temperature Ti1, and the carrier frequency reduction setting is set. When the predetermined carrier frequency rise set temperature Ti3 set to a temperature lower than the temperature Ti2 is exceeded, the carrier frequency is set to the medium set frequency fcm which is a non-audible frequency higher than the audible frequency. Become. Note that the temperature range corresponding to the medium set frequency fcm is a temperature range corresponding to the steady running of the vehicle, and the medium set frequency fcm corresponding to the medium temperature region A1 is set at the highest frequency as the carrier frequency. become.

  Further, when the inverter temperature Ti rises from the temperature corresponding to the medium set frequency fcm and exceeds the carrier frequency reduction set temperature Ti2, in the temperature range from the carrier frequency reduction set temperature Ti2 to the output suppression set temperature Ti1, As the inverter temperature Ti rises, the carrier frequency is continuously reduced. When the inverter temperature Ti reaches the output suppression set temperature Ti1, the low set frequency fcl that is an audible frequency is set as the carrier frequency, and the carrier frequency is maintained at the low set frequency in the temperature range equal to or higher than the output suppression set temperature Ti1. Will be. As a matter of course, when the inverter temperature Ti that has once increased decreases to become the carrier frequency reduction set temperature Ti2 or less, the carrier frequency is set to the medium set frequency fcm again.

  On the other hand, when the inverter temperature Ti is lower than a predetermined maximum carrier frequency setting temperature Ti4 set lower than the carrier frequency increase setting temperature Ti3, for example, when the vehicle is cold started, the carrier frequency is The high set frequency fch is set. When the inverter temperature Ti rises from this state and reaches the maximum carrier frequency set temperature Ti4, the inverter temperature Ti rises in the temperature range from the maximum carrier frequency set temperature Ti4 to the carrier frequency rise set temperature Ti3. The carrier frequency is gradually decreased gradually. When inverter temperature Ti reaches carrier frequency increase set temperature Ti3, medium set frequency fcm is set as the carrier frequency.

  More specifically, each set frequency is set such that the high set frequency fch is set to 25 kHz, the medium set frequency fcm is set to 20 kHz, and the low set frequency fcl is set to 10 kHz considering the balance between noise and switching loss in the inverter 13b. It is preferable.

  5 and 6 are diagrams comparing the present embodiment with a comparative example in which the carrier frequency is set to the medium set frequency fcm regardless of the inverter temperature Ti, and FIG. 5A shows the inverter. FIG. 5B is a diagram showing the relationship between the energizing time 13b and the inverter temperature Ti, and FIG. 5B is a diagram showing the relationship between the energizing time of the inverter 13b and the amount of current that can be output by the inverter 13b. In FIGS. 5A and 5B, only the time range in which the inverter temperature Ti is in the vicinity of the output suppression set temperature Ti1 is illustrated. FIG. 6 is a diagram showing the relationship between the energization time of the inverter 13b and the inverter temperature Ti, and shows only the time range in which the inverter temperature Ti is near the maximum carrier frequency setting temperature Ti4.

  Here, changes in the inverter temperature Ti accompanying energization of the inverter 13b in the present embodiment will be described in comparison with a comparative example with reference to FIGS. First, as shown in FIG. 5A, in the present embodiment, when the inverter temperature Ti exceeds the carrier frequency reduction set temperature Ti2, the carrier generation unit 28 sets the carrier frequency lower than the medium set frequency fcm. As a result, the increase in the inverter temperature Ti becomes slower than in the comparative example, that is, the increase amount of the inverter temperature Ti per unit time is reduced. This is because when the carrier frequency is reduced, the switching loss of the inverter 13b is reduced and the heat generation amount of the inverter 13b is reduced. That is, as shown in FIG. 5 (b) in addition to FIG. 5 (a), in the comparative example, the inverter temperature Ti reaches the output suppression set temperature Ti1 earlier than in the present embodiment. The current that can be output is limited relatively early. In other words, in the present embodiment, when the inverter temperature Ti exceeds the carrier frequency reduction set temperature Ti2, since the heat generation of the inverter 13b is suppressed as described above, the inverter temperature Ti reaches the output suppression start temperature Ti1. Is longer than that of the comparative example, and the time during which a large current can be output from the inverter 13b is longer than that of the comparative example.

  On the other hand, as shown in FIG. 6, when the inverter temperature Ti is equal to or lower than the carrier frequency rise set temperature Ti3, for example, during cold start, in the present embodiment, the carrier frequency is set higher than the medium set frequency fcm. As compared with the comparative example, the temperature rise of the inverter 13b is faster. This is because by setting the carrier frequency high, the switching loss in the inverter 13b increases and the amount of heat generated in the inverter 13b increases. That is, in the present embodiment, for example, by setting the carrier frequency high when the inverter 13b is at a low temperature such as during cold start, not only the inverter 13b but also the entire control unit 13 including the inverter 13b and the control unit The responsiveness is improved by raising the temperature of the electric motor 1 in the vicinity of the motor 1 at an early stage.

  Therefore, according to the present embodiment, the noise of the inverter 13b can be reduced by setting the carrier frequency to a non-audible frequency during steady running that does not require suppression of heat generation in the inverter 13b, while the temperature of the inverter 13b rises. By reducing the carrier frequency to reduce the switching loss in the inverter 13b, further heat generation of the inverter 13b can be suppressed without causing a decrease in the output of the inverter 13b.

  Further, by suppressing the heat generation of the inverter 13b, the volume of the heat sink to be set in the control unit 13 can be reduced, which is advantageous not only in reducing the size and weight of the control unit 13. There is a merit that is advantageous in terms of cost.

  In addition, when the inverter temperature Ti exceeds the output suppression set temperature Ti1, the carrier frequency is reduced to a temperature lower than the output suppression set temperature Ti1 while ensuring sufficient safety by suppressing the output of the inverter 13b. Since the set temperature Ti2 is set and the carrier frequency is reduced before the inverter temperature Ti reaches the output suppression set temperature Ti1, the inverter 13b can output a large current for a long time. Thereby, there is an advantage that the frequency at which the output of the inverter 13b is limited by the overheat protection control unit 29 can be reduced.

  In addition, when the output of the inverter 13b is limited by the overheat protection control unit 29, since the heat generation of the inverter 13b is suppressed by the reduction of the carrier frequency, the output limitation of the inverter 13b by the overheat protection control unit 29 is relaxed. There is a merit that becomes possible.

  Further, since the carrier frequency is continuously changed according to the change of the inverter temperature Ti, there is an advantage that the deterioration of the steering feeling due to the sudden change of the carrier frequency can be prevented.

  In the first embodiment, an example in which the present invention is applied to an electric power steering apparatus has been described. However, the present invention can also be applied to a hydraulic power steering apparatus in which a hydraulic pump is driven by an electric motor. Needless to say.

  Here, in the first embodiment described above, the carrier frequency is continuously changed in accordance with the change in the inverter temperature Ti, but in particular, between the middle set frequency fcm and the low set frequency fcl. 7 includes a center frequency of a carrier wave in another electronic device represented by a radio, for example, or an order multiple of the center frequency, as a first modification of the first embodiment. As shown in FIG. 2, the carrier frequency may be changed stepwise to avoid interference between the carrier signal C for PWM control and the carrier wave in the electronic device. That is, in this modification, in the temperature range where the inverter temperature Ti exceeds the carrier frequency reduction set temperature Ti2 and is equal to or lower than the output suppression set temperature Ti1, the carrier frequency in other electronic devices and the order times the center frequency are In order to avoid this, the carrier frequency is changed step by step. FIG. 7 shows only the temperature range near the output suppression set temperature Ti1 in the carrier frequency map, and the other parts are the same as those in the first embodiment described above. Also, the frequencies f1 and f2 shown in FIG. 7 indicate the center frequency of the carrier wave in another electronic device as described above, or the order multiple of the center frequency.

  That is, in the first modification, as shown in FIG. 8 in addition to FIG. 7, when the inverter temperature Ti exceeds the carrier frequency reduction set temperature Ti2, the center frequency f1 of the carrier in other electronic devices is avoided to avoid the center frequency f1. The carrier frequency is set to a frequency fc1 lower than the frequency f1. Therefore, according to the first modified example, in addition to the substantially same effect as that of the first embodiment described above, there is an advantage that it is possible to prevent noise from being mixed into the carrier wave in other electronic devices.

  Further, when emphasizing the suppression of heat generation in the inverter 13b, as shown in FIG. 9 as a second modification of the first embodiment, when the inverter temperature Ti exceeds the carrier frequency reduction set temperature Ti2, The carrier frequency may be suddenly changed from the medium setting frequency fcm to the low setting frequency fcl. FIG. 9 shows only the temperature range near the output suppression set temperature Ti1 in the carrier frequency map, and other parts are the same as those in the first embodiment described above.

  That is, in the second modification, when the inverter temperature Ti1 rises, the carrier frequency is set to the low set frequency fcl earlier than the first embodiment described above, and thus the first implementation described above. In addition to substantially the same effect as this embodiment, there is a merit that heat generation in the inverter 13b can be more effectively suppressed.

  On the other hand, when the quietness is particularly important, as shown in FIG. 10 as a third modification of the first embodiment, when the inverter temperature Ti exceeds the output suppression set temperature Ti1, the medium set frequency fcm The carrier frequency may be suddenly changed from low to the low set frequency fcl. In FIG. 10, only the temperature range in the vicinity of the output suppression set temperature Ti1 is shown in the carrier frequency map, and other parts are the same as those in the first embodiment.

  That is, in this third modification, when the inverter temperature Ti1 rises, the carrier frequency is maintained at an inaudible frequency until the inverter temperature Ti reaches the output suppression set temperature Ti1, and noise that is a switching sound of the inverter 13b is reduced. Since the passenger cannot be heard, there is a merit that the quietness can be further improved in addition to the substantially same effect as the first embodiment.

  In addition, as shown in FIG. 11 as a fourth modification of the first embodiment, a vehicle speed sensor 32 that detects the traveling speed v of the vehicle is provided, and the carrier wave generation unit 31 that is a carrier frequency control unit is connected to the inverter temperature Ti. In addition, the carrier frequency may be set in consideration of the traveling speed v of the vehicle. The other parts in the fourth modification are the same as those in the first embodiment described above.

  Specifically, as shown in FIG. 12, the carrier wave generation unit 31 sets the carrier frequency to a low set frequency when the inverter temperature Ti exceeds the output suppression set temperature Ti1 and the vehicle running speed v exceeds a predetermined set running speed v1. On the other hand, when the vehicle traveling speed v is equal to or lower than the set traveling speed v1, the carrier frequency is set to the medium set frequency fcm even if the inverter temperature Ti exceeds the output suppression set temperature Ti1. It is supposed to keep on. Note that FIG. 12 shows only the temperature range near the output suppression set temperature Ti1 in the carrier frequency map, and the other parts are the same as those in the first embodiment described above.

  That is, in this fourth modification, when the traveling speed v is low, the road noise is small and the noise of the inverter 13b easily reaches the passenger's ear. In such a case, the carrier frequency is set to the medium setting frequency fcm. On the other hand, the quietness is improved by setting the carrier frequency to the low setting frequency fcl when the traveling speed v is high and the road noise is large, so that the noise of the inverter 13b is mixed with the road noise. Therefore, according to the fourth modified example, substantially the same effect as that of the first embodiment described above can be obtained, and the noise of the inverter 13b is not easily detected by the occupant. There is a merit that can prevent discomfort in the body.

  Furthermore, as shown in FIG. 13 as a fifth modification of the first embodiment, a rotational speed sensor 34 for detecting the rotational speed ωe of the engine is provided, and a carrier generation unit 33 as a carrier frequency control unit is connected to an inverter temperature Ti. The carrier frequency may be set in consideration of the rotational speed ωe in addition to the traveling speed v. Other parts are the same as those in the fourth modification of the first embodiment described above.

  Specifically, as shown in FIG. 14, the carrier wave generation unit 33 has an inverter temperature Ti that exceeds the output suppression set temperature Ti1, the vehicle travel speed v exceeds the set travel speed v1, and the engine rotational speed ωe is The carrier frequency is set to the low set frequency fcl when the predetermined set speed ωe1 is exceeded, while the vehicle running speed v is equal to or lower than the set running speed v1, or the engine speed ωe is set to the set speed. If it is equal to or less than ωe1, the carrier frequency is maintained at the medium set frequency fcm even if the inverter temperature Ti exceeds the output suppression set temperature Ti1.

  In other words, in the fifth modification, when both the traveling speed v and the engine rotational speed ωe are high, the vehicle road noise and the engine operating noise become louder. By setting to fcl, the noise of the inverter 13b is mixed with road noise and engine operating sound. Therefore, in the fifth modification, the noise of the inverter 13b becomes difficult to be detected by the occupant, and there is an advantage that it is possible to more effectively prevent the passenger from feeling uncomfortable due to the noise of the inverter 13b.

  In the second embodiment shown in FIG. 15, the steering angle sensor 36 that detects the steering angle θs that is the rotational position of the steering wheel 4 and the steering speed ωs that is the rotational speed of the steering wheel 4 are based on the steering angle θs. A steering speed calculation unit 37 serving as a steering speed detection unit for calculating, and a carrier frequency generation unit 35 serving as a carrier frequency control unit is configured to generate a carrier frequency based on a steering speed ωs that is a state quantity related to the heat generation amount of the inverter 13b. Is set.

  Further, the carrier wave generation unit 35 is also connected to the torque sensor 12, and the carrier wave generation unit 35 sets the carrier frequency in consideration of the manual steering torque T in addition to the steering speed ωs. That is, when the steering speed ωs is high and the manual steering torque T is large, the amount of heat generated by the inverter 13b becomes large in order to cause the electric motor 1 to generate a high output. In addition, the carrier frequency is reduced to suppress the heat generation of the inverter 13b. Other parts are the same as those in the first embodiment described above.

  Specifically, as shown in FIG. 16, the carrier wave generating unit 35, when the steering speed ωs exceeds a predetermined first set steering speed ωs1, when the manual steering torque T exceeds a predetermined first set torque T1. The carrier frequency is set to the medium setting frequency fcm when the manual steering torque T is equal to or lower than the second setting torque T2 set lower than the first setting torque T1, while the carrier frequency is set to the low setting frequency fcl. When the manual steering torque T exceeds the second set torque T2 and is equal to or less than the first set torque T1, the carrier frequency is gradually decreased as the manual steering torque T increases.

  On the other hand, when the steering speed ωs is equal to or lower than the first set steering speed ωs1, the carrier wave generator 35 sets the carrier frequency to the medium set frequency fcm regardless of the manual steering torque ωs. The first set steering speed ωs1 and the set torques T1 and T2 may be appropriately set in consideration of the relationship between the steering speed ωs and the manual steering torque T and the amount of heat generated by the inverter 13b.

  Therefore, according to the second embodiment, substantially the same effect as that of the first embodiment described above can be obtained, and the carrier frequency can be set when the inverter 13b is in a traveling state where high output is required. Since the switching loss of the inverter 13b is reduced, the temperature rise of the inverter 13b can be more effectively suppressed.

  In the second embodiment, the carrier frequency is set according to the steering speed ωs and the steering torque T. As shown in FIG. 17 as a first modification of the second embodiment. In addition, the absolute value | T | of the steering torque is measured for a predetermined sampling time Ts, and the average of the absolute value | T | of the steering torque at the sampling time Ts is calculated as the average steering torque Ta. The carrier frequency may be set based on Ta. In this modification, the horizontal axis of the carrier frequency map shown in FIG. 16 may be read as the average steering torque Ta. Therefore, also in the first modified example, substantially the same effect as that of the second embodiment described above can be obtained.

  Further, as in the second modification of the second embodiment shown in FIG. 18, a steering frequency calculation unit 39 that calculates the steering frequency S that is the frequency of the steering operation by the driver based on the steering torque T is provided. The carrier wave generation unit 38 as the carrier frequency control unit may set the carrier frequency in accordance with the steering frequency S instead of the steering torque T in the second embodiment described above. The other parts in the second modification are the same as those in the second embodiment described above.

  Specifically, as shown in FIG. 19, the steering frequency calculation unit 39 counts the number of times that the absolute value | T | of the manual steering torque exceeds the torque threshold value Tl during a predetermined sampling time Ts, and steers that number. The frequency S is assumed. For example, the steering frequency S is 5 in the example shown in FIG.

  Further, the carrier wave generation unit 38 sets the carrier frequency according to the carrier frequency map shown in FIG. Specifically, when the steering speed ωs exceeds the first setting steering speed ωs1, the carrier frequency is set to the low setting frequency fcl when the steering frequency S exceeds the predetermined first setting steering frequency S1. When the steering frequency S is equal to or lower than the second set steering frequency S2 set lower than the first set steering frequency S1, the carrier frequency is set to the medium set frequency fcm, and the manual steering torque T is set to the second set torque. When the torque exceeds T2 and is equal to or less than the first set torque T1, the carrier frequency is gradually decreased as the manual steering torque T increases.

  On the other hand, when the steering speed ωs is equal to or lower than the first set steering speed ωs1, the carrier wave generation unit 38 sets the carrier frequency to the medium setting frequency fcm regardless of the steering frequency S. Both the set steering frequencies S1 and S2 may be appropriately set in consideration of the relationship between the steering frequency S and the amount of heat generated in the inverter 13b.

  That is, when the steering frequency S is high, a high output of the electric motor 1 is required frequently, and thus the amount of heat generated by the inverter 13b increases. Therefore, in this second modification, in such a case, the carrier frequency is reduced to reduce the switching loss, thereby suppressing the temperature rise of the inverter 13b. Therefore, according to the second modified example, substantially the same effect as that of the second embodiment described above can be obtained, and the inverter 13b can reduce the carrier frequency and reduce the carrier frequency when the inverter 13b generates a large amount of heat. Since the switching loss in 13b is reduced, the temperature rise of the inverter 13b can be more effectively suppressed.

  Further, as in the third modification of the second embodiment shown in FIG. 21, a vehicle speed sensor 32 that detects the vehicle running speed v is connected to the carrier wave generation unit 40 that is a carrier frequency number control unit, and the carrier wave generation is performed. The unit 40 may set the carrier frequency according to the traveling speed v instead of the steering torque T in the second embodiment described above. The other parts in the third modification are the same as those in the second embodiment described above.

  Specifically, as shown in FIG. 22, when the traveling speed v exceeds a predetermined first set traveling speed v2, the carrier wave generation unit 35 determines that the steering speed ωs exceeds a predetermined first set steering speed ωs1. The carrier frequency is set to the low set frequency fcl while the carrier speed is set to the medium set frequency fcm when the steering speed ωs is equal to or lower than the predetermined second set steering speed ωs2 set lower than the first set steering speed ωs1. And further. When the steering speed ωs exceeds the second set steering speed ωs2 and is equal to or lower than the first set steering speed ωs1, the carrier frequency is gradually decreased as the steering speed ωs increases.

  When the travel speed v is equal to or lower than the second set travel speed v3 set lower than the first set travel speed v2, the carrier wave generator 35 sets the carrier frequency to the medium set frequency fcm regardless of the steering speed ωs. It will be.

  Further, when the travel speed v exceeds the second set travel speed v3, the travel speed v is equal to or lower than the first set travel speed v2, and the steering speed ωs exceeds the second set steering speed ωs2, the carrier wave generation unit 35 Will gradually decrease the carrier frequency as the vehicle running speed v increases.

  That is, in the third modification, as in the fourth modification of the first embodiment described above, the carrier frequency is reduced by reducing the carrier frequency when the traveling speed v is high and the road noise is large. The increasing noise of the inverter 13b is mixed with road noise. Therefore, according to the third modified example, in addition to the substantially same effect as the second embodiment described above, there is an advantage that it is possible to prevent the passenger from feeling uncomfortable due to the noise of the inverter 13b.

  In the fourth modification of the second embodiment shown in FIG. 23, the carrier wave generation unit 41 as the carrier frequency control unit replaces the steering torque T in the second embodiment described above, and the ABS controller 42 as the brake control unit. The carrier frequency is set according to the operation state of the carrier, and the carrier wave generation unit 41 is used by a vehicle communication system in which information indicating the operation state of the ABS controller 42 is represented by, for example, a CAN communication system. To be offered. As is well known, the ABS controller 42 controls the braking force of the vehicle according to the traveling state of the vehicle in order to prevent the wheels of the vehicle from locking during braking. Other parts are the same as those in the second embodiment described above.

  Specifically, as shown in FIG. 24, when the ABS controller 42 is in the brake control operation, the carrier wave generation unit 41 sets the carrier frequency low when the steering speed ωs exceeds the first set steering speed ωs1. While the frequency fcl is set, the carrier frequency is set to the medium setting frequency fcm when the steering speed ωs is equal to or lower than the second setting steering speed ωs2, and the steering speed ωs exceeds the second setting steering speed ωs2, and When the steering speed ωs1 or less is set, the carrier frequency is gradually decreased gradually as the steering speed ωs increases.

  On the other hand, the carrier wave generation unit 41 sets the carrier frequency to the medium setting frequency fcm regardless of the steering speed ωs during the non-brake control operation in which the ABS controller 42 does not perform the brake control.

  That is, in the fourth modification, whether or not the inverter 13b requires a high output is determined based on the operating state of the ABS controller 42, and the carrier frequency is set according to this, so that There is an advantage that substantially the same effect as the second embodiment can be obtained.

  Further, since the running state of the vehicle is unstable during the brake control operation of the ABS controller 42, the output of the electric motor 1 is reduced by reducing the carrier frequency and reducing the switching loss of the inverter 13b in this case. There is a merit that it is possible to sufficiently secure and improve the controllability of the vehicle.

  In the fourth modification, the carrier frequency is set according to the operating state of the ABS controller 42. However, instead of the operating state of the ABS controller 42, the carrier frequency is set according to the operating state of the VDC controller. May be set. Note that the VDC (Vehicle Dynamics Control) is also called VSC (Vehicle Stability Control), and controls the braking force of each wheel of the vehicle in order to suppress a side slip of the vehicle and maintain a stable running posture. The vehicle behavior is controlled by adjusting the brake control. In this case, the carrier frequency may be set using the carrier frequency map shown in FIG.

  In the fifth modified example of the second embodiment shown in FIG. 25, the carrier wave generating unit 43 serving as the carrier frequency control unit replaces the operating state of the ABS controller 42 in the fourth modified example of the second embodiment described above. The carrier frequency is set based on the operating state of the automatic steering controller 44 as the automatic steering control unit, and the other parts are the same as in the fourth modification of the second embodiment described above. It is.

  Specifically, the automatic steering controller 44 outputs an automatic steering command signal to the assist torque calculation unit 18 based on information on the vehicle and the surrounding environment of the vehicle, thereby automatically changing the steering angle of the steered wheels 11. It comes to perform control. Typically, as this automatic steering control, so-called lane keeping control for preventing the vehicle from deviating from the traveling lane, so-called parking assist control for assisting parking of the vehicle, and so-called vehicle behavior control for controlling the running posture of the vehicle. Is mentioned.

  The automatic steering command signal from the automatic steering controller 44 is provided to the assist torque calculation unit 18 and the carrier wave generation unit 43, respectively, by a vehicle communication system represented by a CAN communication system, for example. . In setting the carrier frequency in the carrier wave generating unit 43, it is preferable to replace the “brake control” in the carrier frequency map shown in FIG. 24 with “automatic steering control”.

  Therefore, in the fifth modification, the carrier frequency is reduced during the automatic steering control operation of the automatic steering controller 44 that requires a high output from the electric motor 1, and therefore the second embodiment described above. As a result, there is an advantage that the temperature rise of the inverter 13b can be more effectively suppressed.

In the third embodiment shown in FIG. 26, the carrier generation unit 45, which is a carrier frequency control unit, sets the carrier frequency based on the q-axis target current Iq ^* , which is a state quantity related to the heat generation amount of the inverter 13b. The other parts are the same as those of the first embodiment described above.

Specifically, as shown in FIG. 27, the carrier wave generation unit 45 increases the q-axis target current Iq ^* from a value corresponding to the medium set frequency fcm, and exceeds a predetermined second set target current Iq2. , The carrier frequency is gradually decreased as the q-axis target current Iq ^* increases in the range up to a predetermined first set target current Iq1 set higher than the second set target current Iq2. . When the q-axis target current Iq ^* reaches the first set target current Iq1, the carrier wave generation unit 45 sets the carrier frequency to the low set frequency fcl. As a matter of course, when the q-axis target current Iq ^* once increased decreases to become the second set target current Iq2 or less, the carrier frequency is set again to the medium set frequency fcm.

Here, the second set target current Iq2 for starting the reduction of the carrier frequency may be appropriately set in consideration of the relationship between the q-axis target current Iq ^* and the temperature rise amount of the inverter 13b. Specifically, as shown in FIG. 28, the q-axis target current Iq ^{* at} which the temperature rise amount of the inverter 13b starts to increase rapidly may be set as the second set target current Iq2.

That is, in the present embodiment, when the q-axis target current Iq ^* increases, the output of the inverter 13b increases and the amount of heat generated by the inverter 13b increases. In such a case, the carrier frequency is reduced. The temperature rise of the inverter 13b is suppressed. Therefore, the present embodiment can provide substantially the same effects as those of the first embodiment described above.

  Here, the technical idea grasped from each of the embodiments described above and not described in the scope of the claims will be described below together with the effects thereof.

  (1) The carrier frequency control unit increases the carrier frequency when the inverter temperature falls below the carrier frequency reduction set temperature when compared with when the inverter temperature exceeds the carrier frequency reduction set temperature. The steering control device according to claim 1, wherein the steering control device is set.

  In this configuration, when it is not necessary to suppress heat generation in the inverter, there is an advantage that the noise of the inverter can be suppressed by setting the carrier frequency high.

  (2) The carrier frequency control unit is configured to continuously change the carrier frequency according to the inverter temperature when the inverter temperature exceeds the carrier frequency reduction set temperature. The steering control device according to claim 1.

  In this configuration, by continuously changing the carrier frequency, it is possible to prevent the driver from feeling uncomfortable due to a sudden change in the carrier frequency, so that there is an advantage that the steering feeling is improved.

  (3) A vehicle speed sensor for detecting a traveling speed of the vehicle is further provided, wherein the carrier frequency control unit has the inverter temperature exceeding the carrier frequency reduction set temperature, and the traveling speed exceeds a predetermined set traveling speed. 2. The steering control device according to claim 1, wherein a carrier frequency is set lower than when the inverter temperature is equal to or lower than the carrier frequency reduction set temperature.

  In this configuration, the road noise increases when the traveling speed is high. In this case, by reducing the carrier frequency, the inverter noise that increases due to the reduction of the carrier frequency is mixed with the road noise, and the inverter noise is reduced. Noise can be made inconspicuous.

  (4) The apparatus further includes a rotation speed sensor that detects a rotation speed of a prime mover that rotationally drives driving wheels of the vehicle, wherein the carrier frequency control unit is configured such that the inverter temperature exceeds the carrier frequency reduction set temperature and the traveling When the speed exceeds the set traveling speed and the rotational speed exceeds a predetermined set rotational speed, the carrier frequency is set lower than when the inverter temperature is equal to or lower than the carrier frequency reduction set temperature. The steering control device according to (3), characterized in that:

  In this configuration, when the rotational speed is high, the noise generated by the prime mover increases. Therefore, by reducing the carrier frequency in this case, the noise of the inverter that increases due to the reduction of the carrier frequency is changed to the road noise. In addition, the noise generated by the prime mover can be confused to make the inverter noise less noticeable.

  (5) The carrier frequency control unit is characterized in that the carrier frequency is set so as not to coincide with the center frequency of the carrier wave and the order multiple of the center frequency in other electronic devices mounted on the vehicle. The steering control device according to claim 1.

  With this configuration, noise mixed in the carrier wave of the other electronic device can be reduced at least.

  (6) When the inverter temperature is equal to or lower than the carrier frequency increase set temperature set lower than the carrier frequency decrease set temperature, the inverter temperature exceeds the carrier frequency increase set temperature. The steering control device according to claim 1, wherein the carrier frequency is set higher than the time.

  In this configuration, the carrier frequency is set high when the inverter is at a low temperature, and the temperature of the inverter is positively increased. For example, at a cold start, the inverter can be operated stably. The temperature can be raised quickly.

  (7) The vehicle controller further includes a brake control unit that controls the braking force of the vehicle according to the traveling state of the vehicle, and the carrier frequency control unit is configured to perform the above operation when the steering speed exceeds the set steering speed. The steering control device according to claim 3, wherein a carrier frequency is set in accordance with an operation state of the brake control unit.

  In this configuration, whether or not high output is required for the inverter is determined according to the operating state of the brake control unit in addition to the steering torque, and the carrier frequency is set accordingly, thereby the inverter Can be effectively suppressed.

  (8) A torque sensor that detects manual steering torque for rotating the steering wheel is further provided, and the carrier frequency control unit is configured to detect the manual steering torque when the steering speed exceeds the set steering speed. 4. The steering control device according to claim 3, wherein a carrier frequency is set according to the frequency.

  In this configuration, whether or not high output is required for the inverter is determined according to the manual steering torque in addition to the steering torque, and the carrier frequency is set accordingly, thereby increasing the temperature of the inverter. Can be effectively suppressed.

  (9) A steering frequency calculation unit that calculates a steering frequency that is a frequency of a steering operation by the driver based on the manual steering torque is further provided, and the carrier frequency control unit is configured such that the steering speed is equal to the set steering speed. When the steering frequency exceeds a predetermined set steering frequency, the carrier frequency is set lower than when the steering speed is equal to or lower than the set steering speed ( The steering control device according to 8).

  In this configuration, when the steering frequency is high, the amount of heat generated by the inverter increases. In such a case, the carrier frequency is reduced to suppress the heat generation of the inverter, thereby increasing the temperature of the inverter more effectively. Can be suppressed.

  (10) When the steering speed is equal to or lower than the set steering speed, or when the steering frequency is equal to or lower than the set steering frequency, the carrier frequency control unit exceeds the set steering speed, and The steering control device according to (9), wherein the carrier frequency is set higher than when the steering frequency exceeds a predetermined set steering frequency.

  In this configuration, the noise of the inverter can be suppressed by setting the carrier frequency high when suppression of heat generation in the inverter is unnecessary.

  (11) The vehicle frequency sensor further includes a vehicle speed sensor that detects a travel speed of the vehicle, wherein the carrier frequency control unit exceeds the predetermined set steering speed and the travel speed exceeds the predetermined set travel speed. 4. The steering control device according to claim 3, wherein the carrier frequency is set lower than when the steering speed is equal to or lower than the set steering speed.

  In this configuration, the road noise increases when the traveling speed is high. In this case, by reducing the carrier frequency, the inverter noise that increases due to the reduction of the carrier frequency is mixed with the road noise, and the inverter noise is reduced. Noise can be made inconspicuous.

  (12) The carrier frequency control unit continuously increases the carrier frequency according to a change in the traveling speed when the steering speed exceeds the set steering speed and the traveling speed exceeds the set traveling speed. The steering control device as set forth in (11), wherein the steering control device is configured to change continuously.

  In this configuration, by continuously changing the carrier frequency, it is possible to prevent the driver from feeling uncomfortable due to a sudden change in the carrier frequency, so that there is an advantage that the steering feeling is improved.

  (13) A torque sensor that detects a manual steering torque that rotates the steering wheel, and a steering frequency calculation unit that calculates a steering frequency that is a frequency of a steering operation by a driver based on the manual steering torque. The carrier frequency control unit, when the steering speed is less than the set steering speed when the steering speed exceeds the set steering speed and the steering frequency exceeds a predetermined set steering frequency. The steering control device according to claim 3, wherein the carrier frequency is set lower than the steering frequency.

  In this configuration, when the steering frequency is high, the amount of heat generated by the inverter increases. In such a case, the carrier frequency is reduced to suppress the heat generation of the inverter, thereby increasing the temperature of the inverter more effectively. Can be suppressed.

  (14) The carrier frequency control unit is configured to continuously change the carrier frequency according to a change in the target current when the target current exceeds the set target current. The steering control device according to claim 5.

  In this configuration, by continuously changing the carrier frequency, it is possible to prevent the driver from feeling uncomfortable due to a sudden change in the carrier frequency, so that there is an advantage that the steering feeling is improved.

  (15) The carrier frequency control unit sets the carrier frequency higher than when the target current exceeds the set target current when the target current decreases and becomes equal to or less than the set target current. The steering control device according to claim 5.

  With this configuration, there is an advantage that noise of the inverter can be suppressed by setting the carrier frequency high when suppression of heat generation in the inverter is unnecessary.

DESCRIPTION OF SYMBOLS 1 ... Electric motor 4 ... Steering wheel 10 ... Link mechanism (steering mechanism)
DESCRIPTION OF SYMBOLS 11 ... Steering wheel 12 ... Torque sensor 13b ... Inverter 19 ... Target electric current calculation part 20d, 20q ... PI control part (operation amount calculation part)
27: PWM control unit 28 ... Carrier wave generation unit (carrier frequency control unit)
29. Overheat protection control unit (output suppression control unit)
30 ... Temperature sensor (Temperature detector)
31 ... Carrier wave generation unit (carrier frequency control unit)
32 ... Vehicle speed sensor 33 ... Carrier wave generation unit (carrier frequency control unit)
34 ... rotational speed sensor 35 ... carrier wave generation unit (carrier frequency control unit)
37: Steering speed calculation unit (steering speed detection unit)
38 ... Carrier wave generation unit (carrier frequency control unit)
39: Steering frequency calculation unit 40 ... Carrier wave generation unit (carrier frequency control unit)
41 ... Carrier wave generation unit (carrier frequency control unit)
42 ... ABS controller (brake control part)
43 ... Carrier wave generation unit (carrier frequency control unit)
44 ... Automatic steering controller (automatic steering controller)
45 ... Carrier wave generation unit (carrier frequency control unit)

Claims (1)

In a steering control device that drives and controls an electric motor for applying a steering force to a steering mechanism that steers a steered wheel of a vehicle according to a rotation operation of a steering wheel ,
A torque sensor for detecting manual steering torque for rotating the steering wheel;
An operation amount calculator for calculating an operation amount of the electric motor;
A PWM control unit that generates a PWM control signal based on the operation amount;
An inverter for supplying power to the electric motor with a switching operation based on the PWM control signal;
A temperature detector that detects or estimates the temperature of the inverter as the inverter temperature;
A carrier frequency control unit for controlling the carrier frequency of the PWM control signal based on the inverter temperature;
An output suppression control unit that limits the output of the inverter when the temperature of the inverter exceeds a predetermined output suppression set temperature;
With
The carrier frequency control unit, when the inverter temperature rises and exceeds a predetermined carrier frequency reduction set temperature set lower than the output suppression set temperature , and when the manual steering torque exceeds a predetermined value , A steering control device, wherein a carrier frequency is set lower than when the inverter temperature is equal to or lower than a carrier frequency reduction set temperature.

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