Motor drive device, motor drive method, and computer-readable medium

Abstract

To provide a motor drive device and a method and a computer-readable medium capable of limiting a command torque at an appropriate limit rate to thermally protect an inverter circuit with certainty.SOLUTION: A motor drive device that controls a motor on the basis of a command torque and has a case, and a capacitor and a power module housed in the case, comprises: a temperature detection unit that detects a capacitor temperature, a power module temperature, and an in-case temperature, respectively; a limit rate decision unit that decides a torque limit rate for limiting the command torque on the basis of the command torque, and the capacitor temperature, the power module temperature, and the in-case temperature detected by the temperature detection unit; and a torque control unit that calculates a torque upper limit value on the basis of the torque limit rate decided by the limit rate decision unit and controls the motor by using a smaller one of the command torque and the torque upper limit value as a target torque.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a motor drive device, a motor drive method, and a computer-readable medium storing a program for executing the motor drive method, and more particularly to a motor drive device and a motor drive method for driving a motor of an electric vehicle or the like by an inverter circuit according to a command torque from a vehicle controller.

Background Art

[0002] Conventionally, in an inverter circuit used in a motor drive device, since switching elements such as thyristors and IGBTs constituting a power module are likely to be thermally damaged, usually, a limitation rate is provided for the current command value of a motor ECU (Electronic Control Unit) according to the temperature of the inverter circuit. Specifically, for example, on a limitation rate reduction curve with the temperature of the inverter circuit on the horizontal axis and the limitation rate of the current command value on the vertical axis, the limitation rate is gradually changed from 100% to 0% until the temperature of the switching element rises from a certain reference temperature to another reference temperature.

[0003] However, when the two reference temperatures are fixed values, it is difficult to calculate an accurate limitation rate, and there is a problem that overprotection or underprotection may occur. In order to address such a problem, for example, in Patent Document 1, it is proposed to adjust the reference temperature of a limitation rate reduction curve with the current of the inverter circuit as a variable together with the temperature of the switching element. According to this aspect, even if there is variation in the detected temperature of the switching element, the variation can be corrected, and the occurrence of overprotection or underprotection can be prevented. Also, conventionally, there is a technique for controlling a motor based on a command torque from a VCU.

[0004] In this case, to prevent damage to the inverter, motor, etc. due to overcurrent, overvoltage, temperature rise, etc., it is common practice to refer to a correspondence table between motor rotation speed and torque, calculate the upper torque limit from the rotation speed, and limit the commanded torque based on this upper torque limit. However, if torque is limited only by a fixed value set according to the motor speed, it becomes difficult to handle situations where it is necessary to maintain low rotation speed and high torque, such as on uphill or downhill slopes. To address these problems, for example, Patent Document 2 proposes calculating a command torque limiting factor based on at least one of the following temperatures: motor temperature, switching element temperature, and the temperature of the substrate on which the switching element is mounted, and then controlling the motor based on the limited command torque.

[0005] According to this embodiment, appropriate torque limiting can be achieved even when it is difficult to limit the commanded torque using a table, such as when there are continuous uphill or downhill slopes. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Patent No. 3430907 [Patent Document 2] Japanese Patent Publication No. 2019-193445 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] Conventionally, when determining the limiting factor of commanded torque according to temperature, it was common to consider the temperature of the motor, the switching element, or the circuit board on which the switching element is mounted. However, if a power module containing switching elements is housed in a case along with a capacitor that smooths the current flowing through the switching elements, the temperature rise of other heat-generating elements in the inverter circuit, in addition to the switching elements, will affect the thermal protection of the motor drive unit. Furthermore, the magnitude of the commanded torque also affects the thermal protection of the motor drive system. For example, the larger the commanded torque, the higher the risk of overheating in the inverter circuit, so thermal protection measures become more stringent. [Means for solving the problem]

[0008] The present invention has been made to solve the above problems, and its objective is to provide a motor drive device, a motor drive method, and a computer-readable medium storing a program that consequently executes the motor drive method, which can limit the commanded torque with an appropriate limiting factor and reliably thermally protect the inverter circuit to prevent failure. To solve the above problems, the motor drive device according to claim 1 of the present invention is a motor drive device that controls a motor based on an external command torque, and comprises a case, a capacitor and a power module housed in the case, and is characterized by comprising: a temperature detection unit that detects the capacitor temperature of the capacitor, the power module temperature of the power module and the case temperature, respectively; a limiting rate determination unit that determines a torque limiting rate to limit the command torque based on the command torque and the capacitor temperature, power module temperature and case temperature detected by the temperature detection unit; and a torque control unit that calculates a torque upper limit value based on the torque limiting rate determined by the limiting rate determination unit and controls the motor with the smaller of the command torque and the torque upper limit value as the target torque.

[0009] According to the motor drive device described above, in addition to the temperatures of the capacitor and power module, the temperature inside the case is detected, and the torque limiting rate for limiting the commanded torque is determined based on the capacitor temperature, power module temperature, and case temperature. Therefore, compared to conventional methods, thermal protection can be performed while comprehensively considering the temperature rise inside the module due to the temperature rise of each heat-generating element, and failures can be reliably prevented.

[0010] Furthermore, since the torque limiting factor is determined based on the magnitude of the commanded torque, it is possible to obtain the effect of strengthening protection when the commanded torque is large.

[0011] Furthermore, the motor drive device according to claim 2 of the present invention is characterized in that the limiting rate determination unit determines a first limiting rate based on the higher of the case temperature and the capacitor temperature when the higher of the two temperatures exceeds a predetermined first temperature threshold, determines a second limiting rate based on the power module temperature when the power module temperature exceeds a predetermined second temperature threshold, and sets the smaller of the first limiting rate and the second limiting rate as the torque limiting rate.

[0012] According to the motor drive device described above, by comprehensively considering the temperature of each heat-generating element, it is possible to select a relatively small, i.e., strict limiting factor to limit the commanded torque, thereby obtaining a more appropriate limiting factor and more reliably preventing the occurrence of failures.

[0013] Furthermore, the motor drive device according to claim 3 of the present invention is characterized in that, when the command torque exceeds a predetermined torque threshold, the limiting rate determination unit determines the first limiting rate using a third temperature threshold that is lower than the first temperature threshold, instead of the first temperature threshold.

[0014] According to the motor drive system described above, even when the commanded torque is large, it can be appropriately limited even if the case temperature and capacitor temperature are low, thereby increasing the thermal protection effect and further preventing the occurrence of failures.

[0015] Further, in the motor drive device according to claim 4 of the present invention, the first limit rate and the second limit rate gradually decrease from 100% to 0% along a first curve having the temperature on the horizontal axis and the limit rate on the vertical axis as the temperature increases.

[0016] According to the above motor drive device, the limit rate can be reduced at high temperatures to obtain a thermal protection effect.

[0017] Also, by increasing the limit rate at low temperatures, overprotection can be avoided.

[0018] Further, in the motor drive device according to claim 5 of the present invention, after the torque control unit controls the motor with the target torque, the first limit rate and the second limit rate gradually return to 100% along a second curve that is 5°C lower than the first curve as the temperature decreases.

[0019] According to the above motor drive device, instead of immediately restoring the limit rate when the temperature drops, the restoration starts gradually after the temperature has stably dropped by 5°C. Therefore, the thermal protection effect can be stabilized for a certain period of time to more reliably prevent the occurrence of failures.

[0020] Further, the motor drive device according to claim 6 of the present invention further includes a control board on which a control unit for controlling the power module is mounted. The control unit includes the temperature detection unit, the limit rate determination unit, and the torque control unit. The control board, the capacitor, and the power module are sequentially stacked in the thickness direction of the motor drive device and arranged in the case. The temperature detection unit includes a first temperature detection element mounted on the capacitor for detecting the capacitor temperature, a second temperature detection element mounted on the power module for detecting the power module temperature, and a third temperature detection element mounted on the control board for detecting the temperature inside the case.

[0021] According to the above motor drive device, the temperature rise in the module due to the temperature rise of each heating element can be comprehensively detected with a simple configuration, and thermal protection can be performed more reliably. Further, the motor drive method according to claim 7 of the present invention is a motor drive method used in a motor drive device that controls a motor based on an externally commanded torque, and includes a case, a capacitor and a power module housed in the case, and the motor drive method includes a temperature detection step of detecting a capacitor temperature of the capacitor, a power module temperature of the power module, and a temperature inside the case of the case, respectively; a limit rate determination step of determining a torque limit rate for limiting the commanded torque based on the commanded torque and the capacitor temperature, the power module temperature, and the temperature inside the case detected in the temperature detection step; and a torque control step of calculating a torque upper limit value based on the torque limit rate determined in the limit rate determination step and controlling the motor with the smaller torque of the commanded torque and the torque upper limit value as a target torque.

[0022] According to the above motor drive method, in addition to the temperatures of the capacitor and the power module, the temperature inside the case is detected, and a torque limit rate for limiting the commanded torque is determined based on the capacitor temperature, the power module temperature, and the temperature inside the case. Therefore, compared with the prior art, thermal protection can be performed in consideration of the temperature rise in the module due to the temperature rise of each heating element comprehensively, and the occurrence of failures can be surely prevented.

[0023] Further, since the torque limit rate is determined based on the magnitude of the commanded torque, an effect of strengthening protection can be obtained when the commanded torque is large.

[0024] Furthermore, the motor driving method according to claim 8 of the present invention is characterized in that, in the limiting rate determination step, when the higher of the case temperature and the capacitor temperature exceeds a predetermined first temperature threshold, a first limiting rate is determined based on the higher temperature, when the power module temperature exceeds a predetermined second temperature threshold, a second limiting rate is determined based on the power module temperature, and the smaller of the first limiting rate and the second limiting rate is set as the torque limiting rate.

[0025] According to the motor drive method described above, by comprehensively considering the temperature of each heat-generating element, it is possible to select a relatively small, i.e., strict limiting factor to limit the commanded torque, thereby obtaining a more appropriate limiting factor and more reliably preventing the occurrence of failures.

[0026] Furthermore, the motor driving method according to claim 9 of the present invention is characterized in that, in the limiting rate determination step, when the command torque exceeds a predetermined torque threshold, the first limiting rate is determined by a third temperature threshold that is lower than the first temperature threshold, instead of the first temperature threshold.

[0027] According to the motor drive method described above, when the commanded torque is large, it can be limited in a timely manner even if the case temperature and capacitor temperature are low, thereby increasing the thermal protection effect and further preventing the occurrence of failures.

[0028] Furthermore, the motor driving method according to claim 10 of the present invention is characterized in that the first limiting ratio and the second limiting ratio gradually decrease from 100% to 0% along a first curve with temperature on the horizontal axis and the limiting ratio on the vertical axis as the temperature increases. According to the above motor drive method, thermal protection can be achieved by reducing the limiting factor at high temperatures.

[0029] Furthermore, increasing the restriction rate at low temperatures can help avoid overprotection.

[0030] Furthermore, the motor driving method according to claim 11 of the present invention is characterized in that, after controlling the motor with the target torque by the torque control step, the first limiting ratio and the second limiting ratio gradually return to 100% along a second curve that is 5°C lower than the first curve as the temperature decreases.

[0031] According to the motor drive method described above, instead of restoring the limiting factor immediately after the temperature drops, the recovery gradually begins after a stable 5°C decrease. This allows the thermal protection effect to be stabilized for a certain period of time, making it possible to more reliably prevent failures.

[0032] Furthermore, the computer-readable medium according to the twelfth aspect of the present invention stores a program for executing the motor drive method described in any of the seventh to eleventh aspects of the present invention.

[0033] According to the above-mentioned computer-readable medium, the program for the motor drive method of the present invention can be easily executed using a control unit such as a CPU. [Effects of the Invention]

[0034] According to the motor drive device, motor drive method, and computer-readable recording medium storing a program for executing the motor drive method according to the present invention, the command torque can be limited by an appropriate limiting factor, and the inverter circuit can be reliably thermally protected to prevent failures. [Brief explanation of the drawing]

[0035] Figure 1 is a schematic diagram showing the configuration of a motor drive device according to the present invention.

[0036] Figure 2 is a block diagram showing the configuration of a motor control system including a motor drive device according to the present invention.

[0037] Figure 3(a) is a graph showing an example of the relationship between the first limiting factor and temperature when the commanded torque does not exceed the torque threshold.

[0038] Figure 3(b) is a graph showing an example of the relationship between the first limiting factor and temperature when the commanded torque exceeds the torque threshold.

[0039] Figure 4 is a graph showing an example of the relationship between the second limiting factor and temperature.

[0040] Figure 5 is a graph showing an example of when the limit rate returns to normal.

[0041] Figure 6 is a flowchart showing the motor drive method according to the present invention.

[0042] Figure 7 is a flowchart showing the specific details of the limit rate determination step in Figure 6. [Modes for carrying out the invention]

[0043] Next, the configuration of the motor drive device according to this embodiment will be described with reference to Figures 1 and 2.

[0044] Figure 1 is a schematic diagram showing the configuration of the motor drive device 100 according to this embodiment, and Figure 2 is a block diagram showing the configuration of the motor control system including the motor drive device 100.

[0045] As shown in Figure 1, the motor drive unit 100 includes a case 4, and inside the case 4, the power module 1, capacitor 2, and control board 3 are sequentially stacked in the thickness direction (vertical direction in the figure).

[0046] Note that Figure 1 is merely a schematic representation of the stacked arrangement, and the actual positional relationships are not limited to this.

[0047] Power module 1 is a modular semiconductor composed of switching elements such as IGBTs (Insulated Gate Bipolar Transistors) that constitute an inverter circuit, and FWD (Freewheeling Diode) chips, which are bridged together in a specific circuit.

[0048] During the operation of the inverter circuit 40, the performance of the IGBT is susceptible to temperature, and generally, it undergoes thermal saturation in about 3 seconds due to the peak current.

[0049] Capacitor 2 smooths the current flowing through switching elements such as IGBTs in power module 1.

[0050] During circuit operation, the performance of a capacitor is also susceptible to temperature changes, and it generally reaches thermal saturation in about 60 minutes depending on the rated current.

[0051] The control board 3 is for controlling the operation of the power module 1.

[0052] The control board 3 is equipped with a control unit, such as a CPU (Central Processing Unit), and its peripheral circuits, which control the power module 1.

[0053] Furthermore, as shown in Figure 1, in this embodiment, the first temperature detection element 10a, the second temperature detection element 10b, and the third temperature detection element 10c are mounted on the capacitor 2, the power module 1, and the control board 3, respectively.

[0054] A first temperature detection element 10a and a second temperature detection element 10b are housed inside the capacitor 2 and power module 1, respectively.

[0055] A third temperature sensing element 10c is mounted on the surface of the control board 3.

[0056] Figure 1 schematically shows only the positional relationship of the temperature sensing elements, but the positional relationship of the temperature sensing elements is not limited to this.

[0057] Here, the first temperature detection element 10a detects the temperature of the capacitor 2, i.e., the capacitor temperature.

[0058] The second temperature detection element 10b detects the temperature of the power module 1, i.e., the power module temperature.

[0059] Furthermore, since the control board 3 is located inside the case 4 along with the capacitor 2 and the power module 1, the third temperature detection element 10c attached to the control board 3 can detect the temperature inside the case 4, i.e., the internal case temperature.

[0060] These temperature detection elements 10a, 10b, and 10c together constitute the temperature detection unit 10, which will be described later.

[0061] As shown in Figure 2, the motor drive unit 100 is connected, for example, to an upstream VCU (Vehicle control unit) 200 and a downstream motor 300, respectively, and controls the motor 300 based on the command torque from the VCU 200 (external).

[0062] The motor drive unit 100 includes a temperature detection unit 10, a limiting ratio determination unit 20, and a torque control unit 30.

[0063] The temperature detection unit 10 uses, for example, a first temperature detection element 10a, a second temperature detection element 10b, and a third temperature detection element 10c to detect the capacitor temperature of the capacitor 2, the power module temperature of the power module 1, and the internal temperature of the case 4.

[0064] Examples of temperature detection elements include thermistors, thermocouples, or temperature sensors.

[0065] The limiting ratio determination unit 20 acquires the capacitor temperature, power module temperature, and case temperature from the temperature detection unit 10, and also acquires the command torque from the VCU 200. Based on the acquired capacitor temperature, power module temperature, case temperature, and command torque, it determines a torque limiting ratio to limit the command torque.

[0066] The specific method for determining the torque limit rate will be described in detail later.

[0067] The torque control unit 30 obtains the determined torque limiting ratio from the limiting ratio determination unit 20, obtains the command torque from the VCU 200, calculates the torque upper limit value based on the obtained torque limiting ratio, and controls the motor 300 using the smaller of the command torque and the torque upper limit value as the target torque.

[0068] Specifically, the torque control unit 30 may, for example, calculate the upper torque limit value by multiplying the torque limiting rate from the limiting rate determination unit 20 by the torque limiting value, and set the smaller of the calculated upper torque limit value and the commanded torque as the target torque.

[0069] The torque limit value is, for example, a torque value determined according to the rotational speed based on a table stored in advance by the torque control unit 30, where the motor rotational speed is on the horizontal axis and torque is on the vertical axis.

[0070] Thus, since the upper torque limit is calculated by multiplying the torque limit by the torque limiting factor, a small torque limiting factor does not necessarily mean that the limit is weak.

[0071] In this embodiment, the limiting ratio determination unit 20 and the torque control unit 30 are included, for example, in the control unit on the control board 3 as described above.

[0072] Furthermore, the motor drive unit 100 is further equipped with an inverter circuit 40.

[0073] As described above, this inverter circuit 40 is composed of switching elements such as IGBTs and elements such as FWDs.

[0074] Figure 2 schematically shows only a configuration in which the inverter circuit 40 is directly controlled by the torque control unit 30. However, in reality, various conversion circuits may be placed between the torque control unit 30 and the inverter circuit 40 to convert the target torque into a current command, then into a voltage command, and output a three-phase PWM signal based on the duty cycle of the voltage command as a drive signal to the inverter circuit 40. By switching and controlling switching elements such as IGBTs in the inverter circuit 40, the inverter circuit 40 may apply voltage to the motor 300 and control the motor 300.

[0075] The detailed structure and operating method of the above-mentioned conversion circuit can be found by referring to various structures and methods in the prior art, and will not be explained here.

[0076] According to the above configuration of the motor drive device 100 of this embodiment, in addition to the temperatures of the capacitor 2 and the power module 1, the temperature inside the case 4 is detected by a third temperature detection element 10c mounted on the control board 3, and the torque limiting rate for limiting the commanded torque is determined based on the capacitor temperature, the power module temperature and the temperature inside the case. Therefore, compared to conventional methods, thermal protection can be performed while comprehensively considering the temperature rise inside the module due to the temperature rise of each heat-generating element, and the occurrence of failures can be reliably prevented.

[0077] Furthermore, since the torque limiting factor is determined by considering various temperatures as well as the magnitude of the commanded torque, it is possible to obtain an effect that further enhances protection when the commanded torque is large.

[0078] Next, with reference to Figures 3 to 5, a specific method by which the limiting rate determination unit 20 determines the torque limiting rate will be described.

[0079] Figure 3(a) is a graph showing an example of the relationship between the first limiting factor and temperature when the commanded torque does not exceed the torque threshold, Figure 3(b) is a graph showing an example of the relationship between the first limiting factor and temperature when the commanded torque exceeds the torque threshold, Figure 4 is a graph showing an example of the relationship between the second limiting factor and temperature, and Figure 5 is a graph showing an example when the limiting factor returns to normal.

[0080] The limiting factor determination unit 20 first compares the internal case temperature and the capacitor temperature from the temperature detection unit 10 and selects the higher temperature.

[0081] Next, the limiting ratio determination unit 20 determines whether the command torque from the VCU 200 exceeds a predetermined torque threshold.

[0082] The torque threshold should preferably be a value that does not affect continuous operation.

[0083] For example, the torque threshold is set so as not to have any impact on performance, such as torque reduction.

[0084] As shown in Figure 3(a), if the command torque does not exceed the torque threshold, the limiting rate determination unit 20 determines whether the higher of the temperature detected by the first temperature detection element 10a and the temperature detected by the third temperature detection element 10c exceeds a predetermined first temperature threshold.

[0085] The first temperature threshold is preferably set to the maximum temperature at which the film capacitor can operate without failure.

[0086] The limit rate determination unit 20 then determines the first limit rate based on the higher of the above temperatures.

[0087] Specifically, if the higher of the above temperatures has not reached the first temperature threshold, the first limiting factor is maintained at 100%, as shown to the left of the dashed line in Figure 3(a).

[0088] If the higher of the above temperatures exceeds the first temperature threshold, the first limiting factor is gradually reduced from 100% along a descent curve with temperature on the horizontal axis and the limiting factor on the vertical axis, as shown to the right of the dashed line in Figure 3(a), as the temperature rises.

[0089] As shown in the figure, when the temperature rises above the first temperature threshold, for example to 10°C, the first limiting factor decreases to 0%.

[0090] On the other hand, as shown in Figure 3(b), if the command torque exceeds the torque threshold, the limiting factor determination unit 20 determines whether the higher temperature exceeds a predetermined third temperature threshold.

[0091] This third temperature threshold is lower than the first temperature threshold.

[0092] The limit rate determination unit 20 then determines the first limit rate based on the higher of the above temperatures.

[0093] Specifically, if the higher of the above temperatures has not reached the third temperature threshold, the first limiting factor is maintained at 100%, as shown to the left of the dashed line in Figure 3(b).

[0094] If the higher of the above temperatures exceeds the third temperature threshold, the first limiting factor is gradually reduced from 100% along a descent curve with temperature on the horizontal axis and the limiting factor on the vertical axis, as shown to the right of the dashed line in Figure 3(b), as the temperature rises.

[0095] As shown in the figure, when the temperature rises above the third threshold, the first limiting factor decreases to 0%.

[0096] Subsequently, as shown in Figure 4, the limiting rate determination unit 20 determines whether the power module temperature from the second temperature detection element 10b exceeds a predetermined second temperature threshold.

[0097] The second temperature threshold is preferably set to the maximum temperature at which the power module can operate without failure.

[0098] Specifically, when the power module temperature has not reached the second temperature threshold, the second limiting factor is maintained at 100%, as shown to the left of the dashed line in Figure 4.

[0099] Torque limiting is initiated when the power module temperature reaches the second temperature threshold; that is, as shown to the right of the dashed line in Figure 4, the second limiting rate is gradually reduced from 100% along a decreasing curve with temperature on the horizontal axis and the limiting rate on the vertical axis.

[0100] As shown in the figure, when the power module temperature rises to, for example, 10°C above the second temperature threshold, the second limiting factor decreases to 0% due to the limit of the inverter circuit 40 (i.e., the conversion capability of the inverter circuit), and the torque is limited to 0 Nm.

[0101] The limiting ratio determination unit 20 then outputs the smaller of the determined first limiting ratio and second limiting ratio to the torque control unit 30 as the torque limiting ratio.

[0102] According to the limiting rate determination unit 20 described above, the command torque can be limited by selecting a relatively small, i.e., strict limiting rate after comprehensively considering the temperature of each heating element, thereby obtaining a more appropriate limiting rate and more reliably preventing the occurrence of failures.

[0103] Furthermore, the limiting rate determination unit 20 can appropriately limit the command torque even when the case temperature or capacitor temperature is low, when the command torque is large. This increases the thermal protection effect and further prevents the occurrence of failures.

[0104] Furthermore, the limiting factor determination unit 20 can reduce the limiting factor at high temperatures, thereby providing thermal protection.

[0105] Furthermore, increasing the restriction rate at low temperatures can help avoid overprotection.

[0106] Furthermore, the temperature detection unit 10 continues to detect the capacitor temperature, power module temperature, and case temperature even after the torque control unit 30 controls the motor 300 with the target torque obtained based on the torque limiting ratio from the limiting ratio determination unit 20.

[0107] When the temperature detected by the temperature detection unit 10 begins to decrease, the torque limiting unit 20 gradually returns the torque limiting ratio to 100% in the direction of the arrow in Figure 5 as the temperature decreases.

[0108] Specifically, as shown in Figure 5, when the temperature rises above the first temperature threshold, the first limiting rate gradually decreases from 100% along the first curve A, and when the temperature reaches, for example, 10°C higher than the first temperature threshold, the first limiting rate is set to 0%.

[0109] On the other hand, if a temperature drop occurs after torque limiting begins, the limiting rate determination unit 20 gradually returns the first limiting rate to 100% along a second curve B that is 5°C lower than the first curve A.

[0110] For example, as the temperature begins to decrease, the first limiting factor is kept at 0%, and the first limiting factor is gradually restored until the temperature drops to, for example, 5°C above the first temperature threshold.

[0111] When the temperature drops below the first temperature threshold, for example to 5°C, the first limiting factor returns to 100%.

[0112] Furthermore, for example, if the higher of the temperature detected by the first temperature detection element 10a and the temperature detected by the third temperature detection element 10c is 2°C higher than the first temperature threshold, the limiting factor is determined based on the first curve A.

[0113] Subsequently, when the temperature drops to 3°C below the first temperature threshold, the limiting factor is gradually restored based on the second curve B.

[0114] Here, both the first curve A and the second curve B represent derating curves.

[0115] The above explanation described the case in which the torque limiting ratio is restored using the first limiting ratio as an example, but the present invention is not limited thereto.

[0116] In the case of restoring the torque limit rate as described above, the same applies to the second limit rate.

[0117] With the above configuration, instead of restoring the limiting factor immediately after a temperature drop, the recovery gradually begins after a stable 5°C decrease. This allows the thermal protection effect to be stabilized for a certain period of time, more reliably preventing failures.

[0118] Next, the motor drive method of this embodiment will be described with reference to Figures 6 and 7.

[0119] Figure 6 is a flowchart showing the motor drive method according to this embodiment, and Figure 7 is a flowchart showing the specific details of the limiting factor determination step in Figure 6.

[0120] Furthermore, the motor drive device 100 according to the present invention repeatedly performs each of the steps shown in Figure 6 throughout the entire operation.

[0121] First, the temperature detection step begins. As shown in Figure 6, first, the capacitor temperature of the capacitor 2 is detected by the first temperature detection element 10a in the temperature detection unit 10 (step S1), the power module temperature of the power module 1 is detected by the second temperature detection element 10b (step S2), and the internal temperature of the case 4 is detected by the third temperature detection element 10c (step S3).

[0122] Next, the limiting ratio determination unit 20 acquires the capacitor temperature, power module temperature, and case temperature from each of the first temperature detection elements 10a to the third temperature detection elements 10c, and also acquires the command torque from the VCU 200. Based on this command torque and the capacitor temperature, power module temperature, and case temperature, it determines a torque limiting ratio to limit the command torque (step S4).

[0123] The specific method for this step S4 will be described in detail later.

[0124] Next, the torque control step is initiated. The torque control unit 30 then obtains the determined torque limiting ratio from the limiting ratio determination unit 20 and calculates the torque upper limit value based on this torque limiting ratio (step S5).

[0125] The specific method for calculating the torque upper limit is as described above, and will not be explained here.

[0126] Subsequently, the torque control unit 30 obtains the command torque from the VCU 200 and determines whether the command torque is greater than the upper torque limit (step S6).

[0127] If the commanded torque is determined to be greater than the torque upper limit (Step S6: Yes), the target torque is set as the torque upper limit (Step S7). On the other hand, if the commanded torque is determined to be less than or equal to the torque upper limit (Step S6: No), the target torque is set as the commanded torque (Step S8).

[0128] Finally, after the torque control unit 30 controls the motor 300 to the target torque, the temperature detection unit 10 determines whether the capacitor temperature, power module temperature, or case temperature has decreased (step S9).

[0129] If it is determined that the temperature has not decreased (Step S9: NO), the process returns to Step S4, and the torque limiting factor is determined based on the current capacitor temperature, power module temperature, case temperature, and commanded torque.

[0130] On the other hand, if it is determined that the temperature is decreasing (Step S9: YES), the torque limiting ratio is gradually returned to 100% along a second curve B (derating curve) which is 5°C lower than the first curve A (derating curve) used to determine the torque limiting ratio, with temperature on the horizontal axis and the limiting ratio on the vertical axis (Step S10), and the current loop is terminated.

[0131] Next, we will explain the details of step S4 in Figure 6.

[0132] As shown in Figure 7, when the limiting factor determination step is started, the limiting factor determination unit 20 first determines whether the temperature inside the case is greater than the capacitor temperature (step S401).

[0133] If the case temperature is determined to be higher than the capacitor temperature (step S401: Yes), the limiting factor determination unit 20 determines a first limiting factor based on the case temperature, which is the higher temperature, and then determines whether the command torque is below the torque threshold (step S402).

[0134] If the commanded torque is determined to be greater than the torque threshold (step S402: NO), the limiting factor determination unit 20 continues to determine whether the temperature inside the case is greater than the first temperature threshold (step S403).

[0135] If it is determined that the temperature inside the case is below the first temperature threshold (step S403: NO), the first limiting factor is fixed at 100% (step S404).

[0136] On the other hand, if it is determined that the temperature inside the case is greater than the first temperature threshold (step S403: Yes), the first limiting factor is determined based on the temperature inside the case by gradually decreasing the first limiting factor from 100% to 0% along a decrease curve with temperature on the horizontal axis and the limiting factor on the vertical axis as the temperature inside the case rises (step S405).

[0137] On the other hand, if it is determined in step S402 that the command torque is below the torque threshold (step S402: Yes), the limiting rate determination unit 20 determines the first limiting rate using a third temperature threshold that is lower than the first temperature threshold, instead of the first temperature threshold.

[0138] Specifically, the limit rate determination unit 20 continues to determine whether the temperature inside the case is greater than the third temperature threshold (step S406).

[0139] If it is determined that the temperature inside the case is below the third temperature threshold (step S406: NO), the first limiting factor is fixed at 100% (step S407).

[0140] On the other hand, if it is determined that the temperature inside the case is greater than the third temperature threshold (step S406: Yes), the first limiting factor is determined based on the temperature inside the case by gradually decreasing the first limiting factor from 100% to 0% along a decrease curve with temperature on the horizontal axis and the limiting factor on the vertical axis as the temperature inside the case rises (step S408).

[0141] Furthermore, if it is determined in step S401 that the temperature inside the case is below the capacitor temperature (step S401: NO), steps S409 to S415 are executed.

[0142] Steps S409 to S415 are basically the same as steps S402 to S408 described above, except that the first limiting factor is determined using the capacitor temperature, so the explanation is omitted here.

[0143] After determining the first limiting factor, the limiting factor determination unit 20 determines whether the power module temperature is greater than the second temperature threshold (step S416).

[0144] If it is determined that the power module temperature is below the second temperature threshold (step S416: NO), the second limiting factor is fixed at 100% (step S418).

[0145] On the other hand, if the power module temperature is determined to be greater than the second temperature threshold (step S416: Yes), the second limiting factor is determined based on the power module temperature by gradually decreasing the second limiting factor from 100% to 0% along a descent curve with temperature on the horizontal axis and the limiting factor on the vertical axis as the power module temperature rises (step S417).

[0146] Then, the limit rate determination unit 20 determines whether the first limit rate is less than or equal to the second limit rate (step S419).

[0147] If it is determined that the first limiting ratio is less than or equal to the second limiting ratio (step S419: YES), the torque limiting ratio is set to the first limiting ratio (step S420), and the limiting ratio determination process is terminated.

[0148] On the other hand, if it is determined that the first limiting ratio is greater than the second limiting ratio (step S421: NO), the torque limiting ratio is set to the second limiting ratio (step S421), and the limiting ratio determination process is terminated.

[0149] The above describes the case in which the motor drive method of the present invention is implemented in hardware, but the present invention is not limited thereto.

[0150] The motor drive method of the present invention may be implemented using software, or it may be implemented using a combination of software and hardware.

[0151] Furthermore, a program for executing the motor drive method of the present invention may be stored in various computer-readable media and loaded and executed on a CPU or the like as needed.

[0152] Computer-readable media are not particularly limited and can include, for example, HDDs, CD-ROMs, CD-Rs, MOs, MDs, DVDs and other optical discs, IC cards, flexible disks, mask ROMs, EPROMs, EEPROMs, flash ROMs and other semiconductor memories.

[0153] In the above, "small restriction rate" refers to a situation where the restriction is strict, and "large restriction rate" refers to a situation where the restriction is lenient.

[0154] For example, if the limiting rate determined by the limiting rate determination unit 20 is 80%, the torque upper limit will be the torque limit value multiplied by 80%. If the limiting rate is 30%, the torque upper limit will be the torque limit value multiplied by 30%, and the latter will be a smaller value.

[0155] Furthermore, the embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive.

[0156] The scope of the present invention is indicated by the claims rather than by the embodiments described above, and all modifications and variations within the meaning and scope equivalent to the claims are intended to be included. [Industrial applicability]

[0157] As described above, the motor drive device, motor drive method, and computer-readable medium storing a program for executing the motor drive method according to the present invention are useful for controlling the torque of a motor using an inverter. [Explanation of Symbols]

[0158] 1 Power Module 2 Capacitors 3. Control board 4 cases 10 Temperature detection unit 10a First temperature detection element 10b Second temperature detection elements 10c Third temperature sensing element 20 Limit Rate Determination Unit 30 Torque control unit 40 Inverter Circuit 100 Motor drive unit 200 VCU 300 motor

Claims

1. A motor drive device housed in a case that controls the motor based on an externally commanded torque, A power module is provided, which is housed in the aforementioned case and contains switching elements that constitute an inverter circuit for driving the motor. A capacitor housed within the aforementioned case and smoothing the current flowing through the switching element, A temperature detection unit that detects the capacitor temperature of the capacitor, the power module temperature of the power module, and the internal temperature of the case, respectively. A limiting ratio determination unit that determines a torque limiting ratio for limiting the command torque based on the command torque and the capacitor temperature, power module temperature, and case internal temperature detected by the temperature detection unit, A torque control unit calculates a torque upper limit value based on the torque limiting ratio determined by the limiting ratio determination unit, and controls the motor using the smaller of the command torque and the torque upper limit value as the target torque. Includes, The aforementioned limit rate determination unit, When the higher of the case temperature and the capacitor temperature exceeds a predetermined first temperature threshold, a first limiting factor is determined based on the higher temperature; when the power module temperature exceeds a predetermined second temperature threshold, a second limiting factor is determined based on the power module temperature; and the smaller of the first limiting factor and the second limiting factor is set as the torque limiting factor. The first limiting factor and the second limiting factor gradually decrease from 100% to 0% along a first curve in a Cartesian coordinate system with temperature and limiting factor as coordinate axes, as the temperature increases. The first and second limiting ratios gradually return to 100% along a second curve, which is obtained by shifting the first curve by -5°C along the temperature-corresponding coordinate axis as the temperature decreases, after the torque control unit has controlled the motor with the target torque. Motor drive device.

2. The motor drive device according to Claim 1, wherein the limiting rate determination unit determines the first limiting rate with a third temperature threshold lower than the first temperature threshold when the command torque exceeds a predetermined torque threshold.

3. The control board further includes a control unit on which a control unit for controlling the power module is located, The control unit includes the temperature detection unit, the limiting rate determination unit, and the torque control unit, The temperature detection unit includes a first temperature detection element for detecting the temperature of the capacitor, a second temperature detection element for detecting the temperature of the power module, and a third temperature detection element attached to the control board for detecting the temperature inside the case. The control board, the capacitor, and the power module are stacked in order and arranged inside the case. A motor drive device according to claim 1 or 2.

4. A motor drive device comprising a power module containing a switching element that constitutes an inverter circuit for driving a motor, which is housed in a case, and a capacitor that smooths the current flowing through the switching element, and a motor drive device housed in the case that controls the motor based on an external command torque, wherein the motor drive device controls the motor based on an external command torque, A temperature detection step that detects the capacitor temperature of the capacitor, the power module temperature of the power module, and the internal temperature of the case, respectively. A limiting ratio determination step in which a torque limiting ratio is determined to limit the commanded torque based on the commanded torque and the capacitor temperature, power module temperature, and case temperature detected in the temperature detection step, A torque control step which involves calculating a torque upper limit value based on the torque limiting ratio determined in the limiting ratio determination step, and controlling the motor with the smaller of the commanded torque and the torque upper limit value as the target torque. Includes, The aforementioned limit rate determination step is: When the higher of the case temperature and the capacitor temperature exceeds a predetermined first temperature threshold, a first limiting factor is determined based on the higher temperature; when the power module temperature exceeds a predetermined second temperature threshold, a second limiting factor is determined based on the power module temperature; and the smaller of the first limiting factor and the second limiting factor is set as the torque limiting factor. The first limiting factor and the second limiting factor gradually decrease from 100% to 0% along a first curve in a Cartesian coordinate system with temperature and limiting factor as coordinate axes, as the temperature increases. The first and second limiting ratios gradually return to 100% after the motor has been controlled with the target torque in the torque control step, along a second curve obtained by shifting the first curve by -5°C along the coordinate axis corresponding to temperature as the temperature decreases. Motor drive method.

5. The motor drive method according to claim 4, wherein in the limiting rate determination step, when the command torque exceeds a predetermined torque threshold, the first limiting rate is determined by a third temperature threshold that is lower than the first temperature threshold instead of the first temperature threshold.

6. A computer-readable medium on which a program for causing a computer to execute the motor drive method according to any one of claims 4 and 5 is recorded.

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