Power conversion device

Abstract

To solve a problem which has arisen such as a large processing load required for estimating the temperature of a switching element and the delay in temperature estimation in a locked state.SOLUTION: A power conversion device in which a state determination unit determines that a motor is in a locked state when the rotation speed of the motor is equal to or less than a first threshold, and determines that the motor is in a low rotation state among rotation states when the rotation speed is equal to or less than a second threshold greater than the first threshold and exceeds the first threshold, and an element temperature estimation unit that estimates the element temperature of the switching element on the basis of the current value flowing through the switching element provided between the power supply and the motor performs estimation only in the low rotation state among rotation states, and when the motor transitions from the low rotation state to a locked state, the element temperature estimated in the low rotation state is set as the initial value of the element temperature in the locked state.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The technology disclosed in this specification relates to a power conversion device that adjusts the power supply from a power source to a motor. [Background technology]

[0002] Patent Document 1 discloses an inverter device for driving a motor that includes an inverter circuit having a plurality of switching elements and a control circuit that controls the inverter circuit. According to Patent Document 1, the control circuit changes the temperature estimation logic of the switching elements from normal estimation logic to locked state estimation logic when the rotation speed of the motor is equal to or lower than a preset rotation speed threshold and the torque of the motor is equal to or higher than a preset torque threshold. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2022-183064 Summary of the Invention [Problem to be solved by the invention]

[0004] The heavy processing load on the processor caused by continuing to estimate the element temperature of the switching element at a predetermined sampling frequency while the motor is rotating has been a problem. Furthermore, when an external force causes a sudden decrease in motor rotation speed and the motor transitions to a locked state, the actual temperature of the switching element rises sharply. However, if element temperature estimation is started after the motor transitions to a locked state, a delay occurs in the temperature estimation, resulting in a large discrepancy between the actual temperature and the estimated temperature. This specification provides technology that contributes to solving these problems. [Means for solving the problem]

[0005] This specification discloses a power conversion device that adjusts the power supply from a power source to a motor. The power conversion device includes a switching element provided between the power source and the motor, a state determination unit that determines whether the motor is in a rotating state or a locked state based on the rotation speed of the motor, and an element temperature estimation unit that estimates the element temperature of the switching element based on the value of a current flowing through the switching element. The state determination unit determines that the motor is in the locked state when the rotation speed is equal to or less than a predetermined first threshold, and determines that the motor is in a low rotation state among the rotating states when the rotation speed is equal to or less than a predetermined second threshold that is greater than the first threshold and exceeds the first threshold. The element temperature estimator performs the estimation only in the low rotation state among the rotating states, and when the motor transitions from the low rotation state to the locked state, the element temperature estimated in the low rotation state is set as the initial value of the element temperature in the locked state.

[0006] According to the above configuration, the element temperature estimator performs the estimation only in the low rotation state among the rotation states. This reduces the processing load on the processor in the rotation state. Furthermore, when the rotation state transitions from the low rotation state to the locked state, the element temperature estimator sets the element temperature estimated in the low rotation state as the initial value of the element temperature in the locked state. This allows the element temperature to be obtained without delay in response to a sudden temperature rise in the locked state, thereby reducing the discrepancy between the actual temperature and the estimated temperature. [Brief explanation of the drawings]

[0007]

Figure 1

Figure 2

Figure 3

Figure 4

Best Mode for Carrying Out the Invention

[0008] With reference to the drawings, this embodiment will be described. Each drawing is merely an example, and this embodiment is not limited to the illustrated content. Also, since each drawing is an example, the illustrated shape may not be accurate or a part may be omitted.

[0009] FIG. 1 simply shows the configuration of the power conversion device 10 of this embodiment. The power conversion device 10 generally includes an inverter circuit 20 and a control circuit 30 that controls the inverter circuit 20. The power conversion device 10 can adjust the power supplied from the power source 21 to the motor 40. The power source 21 is a DC power source, and the inverter circuit 20 converts the DC supplied from the power source 21 into AC and supplies it to the motor 40. The power conversion device 10 can be adopted, for example, in an electric vehicle that runs on the motor 40, a hybrid vehicle, a fuel cell vehicle, etc.

[0010] The basic configuration of the inverter circuit 20 will be briefly described. According to the example of FIG. 1, the inverter circuit 20 includes a plurality of switching elements 22a, 22b, 22c, 22d, 22e, 22f provided between the power source 21 and the motor 40, and constitutes a so-called three-phase (U-phase, V-phase, W-phase) inverter circuit. Hereinafter, without distinguishing the switching elements 22a to 22f, each one will be simply described as the switching element 22. The circuit configuration of the power conversion device 10 is not particularly limited. The power conversion device 10 only needs to have at least one switching element 22 for controlling the power supply to the motor 40.

[0011] Among the switching elements 22a to 22f, the first switching element 22a and the second switching element 22b are connected in series and constitute one leg (i.e., a pair of upper and lower arms) of the three-phase inverter circuit. The first switching element 22a is arranged on the upper arm, and the second switching element 22b is arranged on the lower arm. Similarly, among the switching elements 22a to 22f, the third switching element 22c and the fourth switching element 22d are connected in series and constitute another leg of the three-phase inverter circuit. The third switching element 22c is arranged on the upper arm, and the fourth switching element 22d is arranged on the lower arm.

[0012] Similarly, among the switching elements 22a to 22f, the fifth switching element 22e and the sixth switching element 22f are connected in series and constitute another leg of the three-phase inverter circuit. The fifth switching element 22e is arranged on the upper arm, and the sixth switching element 22f is arranged on the lower arm. The switching element 22 is not particularly limited, and for example, it may be a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) or an IGBT (Insulated Gate Bipolar Transistor). Also, a freewheeling diode may be connected in anti-parallel to each of the switching elements 22.

[0013] The connection points of the switching elements 22 of the upper and lower arms of each phase are respectively connected to the corresponding phase coils of the motor 40. In the power conversion device 10, under the control of the control circuit 30, these switching elements 22a to 22f are selectively and intermittently turned on and off, so that three-phase AC power is supplied to the motor 40. The control circuit 30 has a plurality of drive ICs and processors for driving each of the switching elements 22a to 22f. The control circuit 30 may be regarded as one of the ECUs (Electronic Control Unit).

[0014] The control circuit 30 receives feedback of a signal indicating the rotational speed of the motor 40 from the motor 40. Since the rotational speed is the number of rotations per unit time, it may also be referred to as the rotational speed. Further, the control circuit 30 receives a command regarding the target torque of the motor 40 from a higher-level controller (not shown), and outputs drive signals to the switching elements 22a to 22f individually based on the command and the feedback rotational speed. The drive signal is not particularly limited, but is, for example, a pulse width modulation (PWM) signal.

[0015] FIG. 2 shows a control circuit 30 that executes element temperature estimation of the switching element 22 in the rotational state of the motor 40. The control circuit 30 includes a state determination unit 31 that determines whether the motor 40 is in a rotational state or a locked state based on the rotational speed of the motor 40, and an element temperature estimation unit 32 that estimates the element temperature of the switching element 22 based on the current value flowing through the switching element 22. The element temperature estimation unit 32 can estimate the element temperature for each of the switching elements 22a to 22f. Of course, the state determination unit 31 and the element temperature estimation unit 32 are only a part of the functions of the control circuit 30.

[0016] The element temperature estimation unit 32 inputs the current value flowing through each switching element 22 from the inverter circuit 20 through a circuit for current detection (not shown). Further, parameters such as the DC voltage value of the power supply 21, the carrier frequency, and the water temperature information are input to the element temperature estimation unit 32. The carrier frequency is a frequency for determining the switching frequency of the switching element 22, and is determined, for example, by a functional unit (not shown) that controls PWM control and is included in the control circuit 30. The water temperature information is information indicating the water temperature of the cooling water for cooling the switching element 22. A cooler (not shown) is installed adjacent to the module of the inverter circuit 20, and the water temperature of the cooling water flowing through the cooler is input to the element temperature estimation unit 32 as the water temperature information.

[0017] When the rotational speed of the motor 40 is equal to or lower than a predetermined first threshold value, the state determination unit 31 determines that the motor 40 is in a locked state. Further, when the rotational speed of the motor 40 is greater than the first threshold value and equal to or lower than a predetermined second threshold value, the state determination unit 31 determines that the motor 40 is in a low rotation state among the rotation states.

[0018] The element temperature estimation unit 32 recognizes the state of the motor 40 with reference to the determination by the state determination unit 31. The element temperature estimation unit 32 estimates the element temperature only in the low rotation state among the rotation states of the motor 40. When estimating the element temperature in the low rotation state of the motor 40, the element temperature estimation unit 32 acquires the effective value of the current flowing through the switching element 22 at a predetermined sampling period and uses it for the estimation.

[0019] As the estimation of the element temperature based on the current value, various methods and logics including those proposed so far can be adopted. The element temperature estimation unit 32 obtains the element temperature as an estimation result, for example, by inputting the current value into a function, a table, or the like that is optimized for calculating the element temperature according to the input and is generated in advance by experiments or simulations.

[0020] The element temperature estimation unit 32 may estimate the element temperature based on at least one of the voltage value, the carrier frequency, and the water temperature information input as described above in addition to the current value. The current value, the voltage value, the carrier frequency, and the water temperature information can be said to be parameters having a correlation with the heat generation of the switching element 22. The element temperature estimation unit 32 may obtain the element temperature as an estimation result by, for example, inputting these parameters into the above-described function.

[0021] FIG. 3 shows the control circuit 30 that performs element temperature estimation of the switching element 22 when the motor 40 is in a locked state. Explanations of FIG. 3 that are common to those of FIG. 2 will be omitted. When estimating the element temperature when the motor 40 is in a locked state, the element temperature estimator 32 acquires the instantaneous value of the current flowing through the switching element 22 at a predetermined sampling period and uses this value for estimation. Furthermore, when the motor 40 transitions from a low rotation state to a locked state, the element temperature estimator 32 sets the element temperature estimated in the low rotation state, i.e., the element temperature estimated immediately before the transition to the locked state (the immediately preceding estimated value), as the initial value of the element temperature in the locked state. Therefore, the element temperature estimator 32 has already obtained an estimate of the element temperature the moment the motor 40 enters a locked state.

[0022] FIG. 4 illustrates a graph showing the transition of the estimated element temperature in this embodiment. In FIG. 4, the element temperature estimated by the element temperature estimator 32 is indicated by a solid line, and the actual element temperature is indicated by a dashed line. As shown in FIG. 4, the element temperature of the switching element 22 temporarily drops and then rapidly rises when the motor 40 transitions from a rotating state to a locked state. Furthermore, if the element temperature estimator 32 determines that the estimated element temperature has reached the heat-resistant temperature Tmax of the switching element 22, the control circuit 30 reduces the output from the inverter circuit 20 to the motor 40 to protect the switching element 22 from overheating. In this case, the control circuit 30 can reduce the power consumption of the switching element 22 in various ways, such as by reducing the carrier frequency, the current flowing through the switching element 22, or the duty ratio of the PWM signal. The heat-resistant temperature Tmax is a type of threshold value that the control circuit 30 recognizes in advance. Although not shown in FIG. 2, the control circuit 30 compares the estimated element temperature with the heat-resistant temperature Tmax not only in the locked state but also in a low-speed rotation state.

[0023] According to this embodiment, the power conversion device 10 that adjusts the power supply from the power source 21 to the motor 40 includes a switching element 22 provided between the power source 21 and the motor 40, a state determination unit 31 that determines whether the motor 40 is in a rotating state or a locked state based on the rotation speed of the motor 40, and an element temperature estimation unit 32 that estimates the element temperature of the switching element 22 based on the current value flowing through the switching element 22. The state determination unit 31 determines that the motor 40 is in a locked state when the rotation speed is equal to or lower than a predetermined first threshold value, and determines that the motor 40 is in a low rotation state among the rotating states when the rotation speed is higher than the first threshold value and equal to or lower than a predetermined second threshold value. The element temperature estimation unit 32 performs the estimation only in the low rotation state among the rotating states, and when the motor 40 transitions from the low rotation state to the locked state, sets the element temperature obtained by the estimation performed in the low rotation state as the initial value of the element temperature in the locked state.

[0024] According to the above configuration, the element temperature estimation unit 32 estimates the element temperature only in the low rotation state among the rotating states. Therefore, the processing load on the processor included in the control circuit 30 in the rotating state can be reduced. Further, when the element temperature estimation unit 32 transitions from the low rotation state to the locked state, it sets the immediately previous estimated value estimated in the low rotation state as the initial value of the element temperature in the locked state. Therefore, the element temperature can be obtained without delay in response to a rapid temperature rise in the locked state, and the deviation between the actual temperature and the estimated temperature can be reduced. When the element temperature estimation unit 32 estimates the next latest element temperature based on parameters such as the current value with reference to the element temperature estimated once in the locked state, since it obtains the immediately previous estimated value, that is, the reference element temperature, at the time of transitioning to the locked state, it can estimate the element temperature with high accuracy without delay.

[0025] Also, according to the present embodiment, the element temperature estimation unit 32 may perform the estimation based on the effective value of the current in the low rotation state. According to this configuration, the element temperature estimation unit 32 acquires the effective value of the current flowing through the switching element 22 at a predetermined sampling period in the low rotation state of the motor 40 and uses it for the estimation, so that the accuracy of the element temperature estimation can be improved.

[0026] Also, according to the present embodiment, the element temperature estimation unit 32 may perform the estimation based on the instantaneous value of the current in the locked state. According to this configuration, the element temperature estimation unit 32 acquires the instantaneous value of the current flowing through the switching element 22 at a predetermined sampling period in the locked state of the motor 40 and uses it for the estimation, so that the accuracy of the element temperature estimation can be improved in response to a rapid current change.

[0027] Also, according to the present embodiment, the element temperature estimation unit 32 may perform the estimation based on at least one of the voltage applied to the switching element 22, the carrier frequency that determines the switching frequency of the switching element 22, and the water temperature of the cooling water for cooling the switching element 22, in addition to the current value. According to this configuration, the accuracy of the element temperature estimation can be improved by the estimation using various parameters including the current value.

Explanation of Reference Numerals

[0028] 10: Power conversion device, 20: Inverter circuit, 21: Power supply, 22: Switching element, 30: Control circuit, 31: State determination unit, 32: Element temperature estimation unit, 40: Motor

Claims

1. A power conversion device that regulates power supply from a power source to a motor, comprising: a switching element provided between the power source and the motor; a state determination unit that determines whether the motor is in a rotating state or a locked state based on the rotational speed of the motor; an element temperature estimation unit that estimates the element temperature of the switching element based on the current value flowing through the switching element; and the state determination unit determines that the motor is in the locked state when the rotational speed is equal to or less than a predetermined first threshold value, and determines that the motor is in a low rotation state among the rotating states when the rotational speed is greater than the first threshold value and equal to or less than a predetermined second threshold value that is greater than the first threshold value; the element temperature estimation unit performs the estimation only in the low rotation state among the rotating states, and when the motor transitions from the low rotation state to the locked state, sets the element temperature obtained by the estimation performed in the low rotation state as the initial value of the element temperature in the locked state. A power conversion device.

2. The power conversion device according to claim 1, wherein the element temperature estimation unit performs the estimation based on the effective value of the current in the low rotation state.

3. The power conversion device according to claim 1 or claim 2, wherein the element temperature estimation unit performs the estimation based on the instantaneous value of the current in the locked state.

4. The power conversion device according to claim 1, wherein the element temperature estimation unit performs the estimation based on at least one of the voltage applied to the switching element, the carrier frequency that determines the switching frequency of the switching element, and the water temperature of the cooling water for cooling the switching element, in addition to the current value.

Images