Motor control device

Abstract

The objective is to provide a motor control device that can operate continuously. [Solution] The motor control device according to this embodiment comprises a plurality of switching elements that generate a plurality of phase alternating currents supplied to the motor, a control unit that controls the operation of the motor by controlling the switching elements, and a calculation unit that calculates a current threshold for the current supplied to the motor based on the temperature of the refrigerant that cools the switching elements and the input voltage. When the rotational speed of the motor is less than or equal to a predetermined rotational speed, the control unit controls the rotational speed of the motor based on a comparison between the cumulative value of the difference in the value of the current supplied to the motor at each predetermined period that exceeds the current threshold and the current threshold.

Description

Technical Field

[0001] Embodiments according to the present invention relate to a motor control device.

Background Art

[0002] In some cases, a three-phase alternating current synchronous motor is controlled by an inverter using a PWM (Pulse Width Modulation) control method. The inverter has, for example, a power module including a plurality of switching elements (power elements). When the motor stops or rotates at an extremely low speed, the loss and heat generation of the switching elements increase. When an overheat error of the switching element is detected, the gate of the switching element turns off and the motor stops.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Patent Document 6

Patent Document 7

Patent Document 8

Patent Document 9

Summary of the Invention

Problems to be Solved by the Invention

[0004] The objective is to provide a motor control device that can operate continuously. [Means for solving the problem]

[0005] The motor control device according to this embodiment comprises a plurality of switching elements that generate a multi-phase alternating current supplied to the motor, a control unit that controls the operation of the motor by controlling the switching elements, and a calculation unit that calculates a current threshold for the current supplied to the motor based on the temperature of the refrigerant that cools the switching elements and the input voltage. The control unit controls the rotation speed of the motor when the motor rotation speed is below a predetermined rotation speed, based on a comparison between the cumulative value of the difference in the value of the current supplied to the motor at each predetermined period that exceeds the current threshold and the current threshold. [Brief explanation of the drawing]

[0006] [Figure 1] This is a block diagram showing an example of the configuration of a motor control device according to the first embodiment. [Figure 2] This graph shows an example of the time until the restriction is applied according to the first embodiment. [Figure 3] This is a block diagram showing an example of the configuration of a motor control device according to the second embodiment. [Modes for carrying out the invention]

[0007] Embodiments of the present invention will be described below with reference to the drawings. These embodiments are not limiting to the present invention. The drawings are schematic or conceptual, and the proportions of each part may not necessarily be the same as those of actual objects. In the specification and drawings, elements similar to those described above with respect to previously shown drawings are denoted by the same reference numerals, and detailed explanations are omitted as appropriate.

[0008] (First Embodiment) Figure 1 is a block diagram showing an example of the configuration of the motor control device 100 according to the first embodiment. In the following description, the motor control device 100 will be explained assuming its use in a vehicle such as an EV (Electric Vehicle). However, the motor control device 100 may also be used in industrial machinery, etc.

[0009] The motor control device 100 receives a direct current (DC) power supply voltage from the power supply 200. Hereafter, the power supply voltage of the power supply 200 will also be called the input voltage. The power supply 200 is, for example, a battery such as an on-board battery. However, the power supply 200 may also be an AC power supply that provides alternating current (AC) power supply voltage.

[0010] The motor control device 100 comprises a motor 10, a position sensor 20, a current sensor 30, and an inverter 40.

[0011] Motor 10 is connected to a drive mechanism (not shown) and operates the drive mechanism. Motor 10 is, for example, a three-phase AC motor. Motor 10 is, for example, a motor for an EV (Electric Vehicle).

[0012] The position sensor 20 detects the position (angle) of the motor 10. The position sensor 20 transmits position feedback of the detected position to the inverter 40. The position sensor 20 may also transmit speed feedback to the inverter 40. The speed feedback is obtained by differentiating the position feedback. The position sensor 20 is, for example, an encoder or a resolver.

[0013] The current sensor 30 detects the current values ​​of U, V, and W supplied to the motor 10. That is, the current sensor 30 detects the current value of each phase current among the multi-phase AC currents generated by the inverter 40. The current sensor 30 transmits the detected current values ​​as current feedback to the inverter 40.

[0014] The inverter 40 receives a speed command from a controller (not shown) such as an ECU (Electronic Control Unit). The inverter 40 generates a three-phase alternating current based on the speed command and supplies the three-phase alternating current to the motor 10.

[0015] The inverter 40 includes an inverter section 41, a cooling section 42, and a speed current control section 43.

[0016] The inverter section 41 has a plurality of switching elements. The switching elements are, for example, transistors. The inverter section 41 receives, for example, a PWM (Pulse Width Modulation) signal and generates a multi-phase alternating current supplied to the motor 10. The inverter section 41 has six switching elements including, for example, two on the + side and two on the - side of the U phase, two on the + side and two on the - side of the V phase, and two on the + side and two on the - side of the W phase.

[0017] The inverter section 41 further has a plurality of overheat detection circuits provided for each switching element or an overheat detection function. This overheat detection circuit or overheat detection function exists for preventing thermal damage of the switching elements and is used, for example, for determining an overheat error. When it is determined that there is an overheat error, in order to protect the switching elements from overheating, the gates of the switching elements are turned off and the motor 10 stops operating.

[0018] The cooling section 42 cools a plurality of switching elements with a refrigerant. The cooling section 42 is, for example, a heat sink. Hereinafter, the cooling section 42 will be described as a water-cooled type using cooling water as the refrigerant. However, the cooling section 42 may be an air-cooled type.

[0019] The cooling section 42 has a thermometer 421. The thermometer 421 detects the temperature of a refrigerant such as cooling water. The detection result of the thermometer 421 is transmitted to the speed current control section 43.

[0020] The speed current control section 43 includes a control section 431 and a calculation section 432.

[0021] The control unit 431 generates a PWM signal to the inverter unit 41 based on speed commands, position feedback or speed feedback, and current feedback, etc. The control unit 431 controls the operation of the motor 10 by controlling the current supplied to the motor 10 by controlling the inverter unit 41.

[0022] Here, the motor control device 100 is provided with a protection function against the overheating error described above. For example, if the rotational speed of the motor 10 decreases, the losses of the switching element may increase several times. In this case, the overheating detection circuit or overheating detection function of the IC that drives the switching element may activate, causing the switching element to turn off as an overheating error protection, and the motor 10 to stop.

[0023] However, for example, it may be preferable for a vehicle to continue operating, even at a low speed, rather than coming to a complete stop. Therefore, the speed current control unit 43 continues the operation of the motor 10 at the maximum output within the range in which the overheat detection circuit or overheat detection function of the IC driving the switching element does not function, even if the motor 10 stops or moves at an extremely low speed and the losses of the switching element increase.

[0024] The calculation unit 432 calculates the current threshold for the current supplied to the motor 10 based on the cooling water temperature (detection result of the thermometer 421) and the input voltage. The calculation unit 432 may also calculate the current threshold for the current supplied to the motor 10 based on the cooling water temperature (detection result of the thermometer 421), the input voltage, and the amount of loss increase in the motor stopped state. The "motor stopped state" is a state in which the rotational speed of the motor 10 is less than or equal to the stop detection rotational speed (predetermined rotational speed), and the loss of the switching element increases. The "amount of loss increase" is the amount of loss increase of the switching element. The calculation unit 432 calculates the current threshold by, for example, comparing the detection result of the thermometer 421 and the input voltage with a map or calculation formula for calculating the current threshold. That is, the calculation unit 432 calculates the current threshold by applying a pre-created relationship (map or calculation formula) between the cooling water temperature, the input voltage, and the current threshold to the current (while the motor 10 is operating) cooling water temperature and input voltage. The resulting relationship may also include the increase in losses when the motor is stopped. The current cooling water temperature is the result detected by thermometer 421. The current input voltage may be input as a set value for each connected power supply 200, for example, or it may be the result of detecting the output voltage from power supply 200.

[0025] The map or calculation formula may include, for example, the upper limit of the current that can be supplied to the motor 10 when the motor is stopped, given a certain cooling water temperature and a certain input voltage. The map or calculation formula may be pre-created and stored in a memory unit (not shown). The memory unit may be located inside the speed-current control unit 43 or outside the speed-current control unit 43.

[0026] More specifically, the calculation unit 432 calculates the current threshold so that it fluctuates over time. This means the calculation unit 432 constantly calculates the current threshold. As a result, the current threshold can be adjusted to an optimal value based on the cooling water temperature and input voltage.

[0027] A preliminary test is performed to create a map or calculation formula. First, for example, the temperature of the switching element is detected while changing the current supplied to the motor 10 at a certain cooling water temperature. Then, after changing the cooling water temperature to another temperature, the process of detecting the temperature of the switching element while changing the current supplied to the motor 10 is repeated. Since the multiplier of the loss in the switching element when the motor 10 stops or moves at an extremely low speed is known from the characteristics of the switching element, the temperature of the switching element when the motor 10 stops or moves at an extremely low speed can be calculated. After that, the obtained data is graphed and approximations such as linear approximation are performed. This gives a formula for calculating the current threshold. The formula for calculating the current threshold is expressed by, for example, Equation 1. Current threshold = Current threshold reference value - Input voltage × Voltage correction coefficient - Coolant temperature × Water temperature correction coefficient (Formula 1) The current threshold reference value, voltage correction coefficient, and water temperature correction coefficient are calculated from the actual measurement results.

[0028] The control unit 431 determines whether the rotational speed of the motor 10 is less than or equal to the stop detection rotational speed (predetermined rotational speed). Based on this, the control unit 431 determines whether the motor 10 is stopped or moving at an extremely low speed. The rotational speed of the motor 10 may be determined by speed feedback or by speed calculated from position feedback. The stop detection rotational speed (predetermined rotational speed) is, for example, 100 revolutions per minute.

[0029] The control unit 431 limits the current supplied to the motor 10 based on the amount by which the value of the current supplied to the motor 10 exceeds a current threshold when the rotational speed of the motor 10 is below a predetermined rotational speed. This limitation suppresses the rotational speed of the motor 10, preventing it from producing the specified output, but it allows the motor 10 to continue operating within a safe range. As a result, for example, the vehicle can continue to operate without stopping on slopes, etc. The value of the current supplied to the motor 10 is, for example, the measurement result of the current sensor 30.

[0030] More specifically, when the rotational speed of the motor 10 is below a predetermined rotational speed, the control unit 431 controls the rotational speed of the motor 10 based on a comparison between the cumulative value of the difference in the value of the current supplied to the motor 10 at predetermined cycles that exceeds the current threshold and the current threshold. Furthermore, if the cumulative value exceeds the current threshold, the control unit 431 reduces the output of the motor 10 by lowering the current supplied to the motor 10 to below the current threshold. As a result, the motor 10 cannot output the required torque, and the rotational speed will not be as commanded. Details regarding the limiting and continuous operation of the rotational speed of the motor 10 will be explained later.

[0031] The calculation unit 432 may be included in the control unit 431. Furthermore, the control unit 431 and the calculation unit 432 constituting the speed-current control unit 43 may be implemented by a single CPU (Central Processing Unit), or they may be implemented by separate CPUs.

[0032] Next, we will explain the limitations on the rotational speed and continuous operation of the motor 10.

[0033] First, the calculation unit 432 constantly calculates the current threshold based on the input voltage and the cooling water temperature.

[0034] Next, the calculation unit 432 accumulates the difference between the absolute value of the current supplied to the motor 10 and the calculated current threshold. If the absolute value of the current supplied to the motor 10 is lower than the current threshold, the calculation unit 432 resets the accumulated value to zero. If the rotational speed of the motor 10 is equal to or greater than a predetermined rotational speed, the calculation unit 432 resets the accumulated value to zero. Note that the rotational speed threshold for resetting the accumulated value to zero is not limited to a predetermined rotational speed and may be changed.

[0035] More specifically, the calculation unit 432 calculates the difference by multiplying it by the gain of the time constant matched to the switching element. 16 Multiply the result by a factor of 2 and add the result to the sum. 16The multiplication is explained below. To protect against the thermal time constant of the switching element, the calculation unit 432 performs integration at high speed. The integration period (predetermined period) is a period corresponding to the thermal time constant of the switching element, for example, 50 μsec. Because integration is performed at high speed, the amount of integration in one step is small, and it is necessary to secure a 16-bit fractional part to improve accuracy. Note that when the control unit 431 later compares the integrated value with the current threshold, 2 16 Taking into account that it has been doubled, the cumulative value is 2 16 It is divided by .

[0036] Next, the control unit 431, 16 The integrated value after division is compared with the current threshold. If the integrated value exceeds the current threshold, the control unit 431 sets the current limit value to a level slightly below the current threshold (for example, 90%).

[0037] The control unit 431 gradually changes (decreases) the current supplied to the motor 10 so that the current supplied to the motor 10 reaches a current limit value. That is, a filter is used that takes, for example, a predetermined time until the current value supplied to the motor 10 reaches the target current limit value. This suppresses shocks to the drive mechanism caused by sudden changes in current. More specifically, the control unit 431 changes the current supplied to the motor 10 in a curve (exponential) that satisfies both the drive mechanism and overheat protection.

[0038] Next, I will explain the time until the restriction is applied.

[0039] Figure 2 is a graph showing an example of the time until the limit is imposed according to the first embodiment. The vertical axis represents the alarm occurrence time t. The horizontal axis represents the current value Ia. The current value Ia is the detection result of the current sensor 30.

[0040] The alarm activation time is the time it takes for the current supplied to the motor 10 to reach the current limit value. The alarm activation time decreases as the overload percentage increases.

[0041] The alarm generation time t (sec) is expressed by Equation 2, using a constant k (e.g., 50 msec) according to the specifications of each switching element, a current threshold L, and the current value Ia. t = k / ((Ia / L) - 1) (Equation 2) This allows the alarm activation time to be adjusted to an optimal time depending on the current value Ia.

[0042] In the example shown in Figure 2, if a current twice the current threshold L (overload rate of 200%) continues to flow through the motor 10, the alarm will be triggered at 50 msec.

[0043] As described above, according to the first embodiment, the calculation unit 432 calculates a current threshold for the current supplied to the motor 10 based on the temperature of the refrigerant that cools the switching element and the input voltage. When the rotational speed of the motor 10 is below a predetermined rotational speed, the control unit 431 controls the rotational speed of the motor 10 based on a comparison between the cumulative value of the difference in the current supplied to the motor 10 at each predetermined cycle that exceeds the current threshold and the current threshold. As a result, even if the motor 10 stops or becomes extremely slow and the losses of the switching element increase, the overheat detection circuit of the inverter unit 41 does not function and stop the motor 10, allowing the motor 10 to continue operating at a minimum output.

[0044] Furthermore, as described above, an overheating error may be detected by the overheating detection circuit or function of the IC that drives the six switching elements. Due to the overheating error, the gates of the switching elements turn off, causing the motor to stop.

[0045] In contrast, in the first embodiment, if the motor 10 stops or becomes extremely slow and losses increase, the motor 10 (drive mechanism) can continue to operate at a minimum output (torque (current) and motor rotation speed) without stopping the motor 10 before an overheating error is determined.

[0046] (Second Embodiment) Figure 3 is a block diagram showing an example of the configuration of the motor control device 100 according to the second embodiment. The second embodiment differs from the first embodiment in that a manufacturing unit 433 is provided.

[0047] The speed current control unit 43 further includes a manufacturing unit 433.

[0048] If the inverter unit 41 is changed, the calculation unit 432 determines whether a map or calculation formula corresponding to the changed inverter unit 41 is stored in the memory unit. If a map or calculation formula corresponding to the changed inverter unit 41 is stored in the memory unit, the calculation unit 432 calculates the current threshold based on the map or calculation formula stored in the memory unit. On the other hand, if a map or calculation formula corresponding to the changed inverter unit 41 is not stored in the memory unit, the calculation unit 432, in initial setting mode, causes the creation unit 433 to create (generate) a map or calculation formula.

[0049] The creation unit 433 performs preliminary tests by controlling the inverter unit 41, thermometer 421, and cooling unit 42, etc., and creates a relationship (map or calculation formula) between the cooling water temperature, input voltage, and current threshold, as well as the thermal time constant of the switching element. The created relationship may also include the amount of loss increase when the motor is stopped. This allows the map or calculation formula to be created automatically.

[0050] The calculation unit 432 calculates the current threshold by applying the map or calculation formula created by the creation unit 433 to the current cooling water temperature and input voltage.

[0051] The creation unit 433 may be included in the control unit 431 or the calculation unit 432. Furthermore, the control unit 431, the calculation unit 432, and the creation unit 433 that constitute the speed current control unit 43 may be implemented by a single CPU (Central Processing Unit), or they may each be implemented by separate CPUs.

[0052] As in the second embodiment, a manufacturing unit 433 may be provided. The motor control device 100 according to the second embodiment can obtain the same effects as the first embodiment.

[0053] At least a portion of the data processing method in the motor control device 100 according to this embodiment may be implemented in hardware or in software. If implemented in software, a program that implements at least a portion of the functions of the data processing method may be stored on a recording medium such as a flexible disk or CD-ROM, loaded into a computer, and executed. The recording medium is not limited to removable ones such as magnetic disks or optical disks, but may also be a fixed recording medium such as a hard disk drive or memory. Furthermore, the program that implements at least a portion of the functions of the data processing method may be distributed via a communication line such as the Internet (including wireless communication). In addition, the program may be encrypted, modulated, or compressed, and then distributed via a wired or wireless line such as the Internet, or stored on a recording medium.

[0054] While several embodiments of the present invention have been described, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These embodiments can be carried out in a variety of other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims and their equivalents. [Explanation of symbols]

[0055] 100 Motor control device, 200 Power supply, 10 Motor, 20 Position sensor, 30 Current sensor, 40 Inverter, 41 Inverter unit, 42 Cooling unit, 421 Thermometer, 43 Speed / current control unit, 431 Control unit, 432 Calculation unit, 433 Creation unit

Claims

1. Multiple switching elements that generate multi-phase alternating current supplied to the motor, A control unit controls the operation of the motor by controlling the switching element, A calculation unit that calculates a current threshold for the current supplied to the motor based on the temperature of the refrigerant used to cool the switching element and the input voltage, Equipped with, The control unit controls the rotation speed of the motor when the rotation speed of the motor is below a predetermined rotation speed, based on a comparison between the cumulative value of the difference in the value of the current supplied to the motor at each predetermined period exceeding the current threshold and the current threshold.

2. The motor control device according to claim 1, wherein the control unit reduces the output of the motor by lowering the current supplied to the motor to below the current threshold when the accumulated value exceeds the current threshold.

3. The motor control device according to claim 2, wherein the control unit gradually reduces the current supplied to the motor.

4. The motor control device according to claim 2, wherein the control unit sets the value of the current supplied to the motor to 90% of the current threshold.

5. The motor control device according to claim 1, wherein the calculation unit calculates the current threshold so that it fluctuates over time.

6. The motor control device according to claim 1, wherein the predetermined period is a period corresponding to the thermal time constant of the switching element.

7. The motor control device according to claim 1, wherein the control unit resets the integrated value when the value of the current supplied to the motor is lower than the current threshold.

8. The motor control device according to claim 1, wherein the control unit resets the accumulated value when the rotational speed of the motor is equal to or greater than the predetermined rotational speed.

9. The calculation unit multiplies the integrated value by a gain corresponding to the thermal time constant. １６ Multiply by the double, The control unit is 2 １６ A motor control device according to claim 1, which compares the integrated value obtained by dividing by the current threshold with the current threshold.

10. The motor control device according to claim 1, wherein the calculation unit calculates the current threshold by applying a pre-established relationship between the temperature of the refrigerant, the input voltage, and the current threshold to the current temperature of the refrigerant and the input voltage.

11. A cooling unit that cools the switching element with the refrigerant, A thermometer for detecting the temperature of the refrigerant, A creation unit that controls a plurality of switching elements, a cooling unit, and a thermometer to create a relationship between the temperature of the refrigerant, the input voltage, and the current threshold, Furthermore, The motor control device according to claim 1, wherein the calculation unit calculates the current threshold by applying the relationship created by the creation unit to the current temperature of the refrigerant and the input voltage.

12. The motor is a three-phase AC motor. The motor control device according to claim 1, comprising six of the switching elements.

13. The motor control device according to claim 1, wherein the refrigerant is cooling water.

14. The motor control device according to claim 1, wherein the input voltage is the power supply voltage.

15. The motor and, A position sensor for detecting the position of the motor, A current sensor detects the value of the current supplied to the motor. The motor control device according to claim 1, further comprising:

Images