Temperature estimation device

Abstract

To estimate a temperature of a permanent magnet with high accuracy.SOLUTION: A control circuit as a temperature estimation device for estimating a magnet temperature Tm, and the magnet temperature Tm is a temperature of a permanent magnet provided by a rotor provided to a motor. The motor comprises: a stator core; and a plurality of stator coils wound to the stator core. The control circuit as a temperature estimation device executes a processing of steps S15 to S17 of estimating the magnet temperature Tm on the basis of a coil temperature as a temperature of each stator coil and an integration current obtained by integrating an actual value of a coil current flowing in each stator coil for an integration period.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a temperature estimation device. [Background technology]

[0002] Conventionally, a temperature estimation device that estimates the temperature of a permanent magnet provided in a rotor is known (for example, Patent Document 1). The temperature estimation device described in Patent Document 1 is provided in a motor. The motor includes a rotor having a permanent magnet, a stator core, and a stator coil wound around the stator core. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-016226 Summary of the Invention [Problem to be solved by the invention]

[0004] Incidentally, the temperature of the permanent magnet affects rotor characteristics such as the conditions under which irreversible demagnetization occurs and the magnitude of the rotor torque. For this reason, there has been a demand for accurate measurement of the temperature of the permanent magnet in order to accurately control the motor and suppress deterioration of the permanent magnet. However, it is difficult to directly install a temperature sensor on the rotating rotor. For this reason, it is preferable to accurately estimate the temperature of the permanent magnet from various parameters that can be measured by the motor. [Means for solving the problem]

[0005] A temperature estimation device that solves the above problem is a temperature estimation device that estimates a magnet temperature, wherein the magnet temperature is the temperature of a permanent magnet provided in a rotor provided in a motor, the motor includes a stator core and a plurality of stator coils wound around the stator core, and the temperature estimation device estimates the magnet temperature based on a coil temperature, which is the temperature of the stator coils, and an integrated current, which is obtained by integrating the effective value of the coil current flowing through each of the stator coils over an integration period.

[0006] According to this, the integrated current corresponds to the copper loss of the stator coil. When estimating the magnet temperature, the magnet temperature Tm can be estimated with high accuracy by taking into account the contribution of the copper loss of the stator coil to the magnet temperature.

[0007] The temperature estimation device may estimate the magnet temperature based on an average current that is an average value of an effective value of the coil current in an averaging period. According to this, the average current corresponds to the steady state that the motor reaches, so by taking the average current into account when estimating the magnet temperature, it is possible to accurately estimate the magnet temperature even in the steady state.

[0008] The temperature estimation device may estimate the magnet temperature based on a rotation speed of the rotor. According to this, the rotor speed is correlated with the windage loss and heat dissipation of the rotor, so by incorporating the effect of the rotor speed, the magnet temperature can be estimated with higher accuracy.

[0009] The temperature estimation device may estimate the magnet temperature based on a d-axis current and a q-axis current flowing through the stator coil. According to this, the d-axis current and the q-axis current are correlated with the magnitude of iron loss in the permanent magnet. Therefore, when estimating the magnet temperature, the heat generated by the permanent magnet due to the rotating magnetic field generated by the stator coil can be taken into consideration. Therefore, the magnet temperature can be estimated with higher accuracy.

[0010] The temperature estimation device may include an iron loss calculation unit that calculates iron loss of the permanent magnet based on the d-axis current and the q-axis current, and estimates the magnet temperature based on the iron loss calculated by the iron loss calculation unit.

[0011] According to this, by calculating the iron loss in advance from the d-axis current and the q-axis current, the calculation load on the temperature estimation device in estimating the magnet temperature can be reduced, and therefore the magnet temperature can be estimated faster. Effect of the Invention

[0012] According to the present invention, the temperature of a permanent magnet can be estimated with high accuracy. [Brief description of the drawings]

[0013] [Figure 1] FIG. 2 is a diagram showing an outline of the overall configuration including a motor. [Diagram 2] FIG. 4 is a diagram showing an example of a motor control process. [Diagram 3] FIG. 11 is a diagram showing an example of a temperature estimation process. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] <Configuration> An embodiment of a temperature estimation device will be described below. The temperature estimation device of this embodiment is applied to a motor provided in a vehicle.

[0015] 1, the vehicle Ve includes an electricity storage device 100, a start switch 110, and a drive device 10. The vehicle Ve is driven by electric power, and is, for example, an electric vehicle or a hybrid vehicle.

[0016] The power storage device 100 is a power source that outputs DC power and is, for example, a secondary battery. The secondary battery is, for example, a lithium ion battery or a lead storage battery. The power storage device 100 serves as a power source for driving the vehicle Ve.

[0017] The start switch 110 is a switch for switching between a running state and a stopped state of the vehicle Ve. The start switch 110 is operated, for example, by a passenger in the vehicle Ve. The running state is a state in which the vehicle Ve can run. The stopped state is a state in which the vehicle Ve cannot run. The start switch 110 is also called an ignition switch or a system start switch. The running state is also called ignition on, and the stopped state is also called ignition off.

[0018] The drive device 10 drives a vehicle Ve. The drive device 10 includes a rotating shaft Ax, a power transmission mechanism G1, a motor 20, a rotation speed measurement unit 24, a coil temperature measurement unit 25, an inverter circuit 30, a current measurement unit 40, and a control circuit 50.

[0019] The rotating shaft Ax transmits power to an axle (not shown) to drive the vehicle Ve. The power transmission mechanism G1 connects the rotation shaft Ax and the axle. The specific embodiment of the power transmission mechanism G1 is arbitrary, but is, for example, a gear box having gears and gear oil. The power transmission mechanism G1 may be provided with a temperature sensor that measures the temperature of the gear box.

[0020] The motor 20 converts the electric power of the power storage device 100 into motive power. The motor 20 includes a rotor 21, a stator core 22, and a plurality of stator coils . The rotor 21 is configured to be rotatable integrally with the rotation axis Ax. The rotor 21 includes a permanent magnet 21a.

[0021] The permanent magnet 21a is, for example, a ferrite magnet. Any ferromagnetic material may be used as the permanent magnet 21a. For example, the permanent magnet 21a may be a hard magnetic material such as a rare earth magnet such as a neodymium magnet or an alnico magnet, or a soft magnetic material such as soft ferrite. The permanent magnet 21a may undergo irreversible demagnetization after passing through a predetermined state. The predetermined state is represented by the temperature Tm of the permanent magnet 21a or an external magnetic field applied to the permanent magnet 21a. The predetermined state depends on the material of the permanent magnet 21a. For example, in the case of a ferrite magnet, the external magnetic field in which irreversible demagnetization occurs becomes lower as the temperature Tm of the permanent magnet 21a becomes lower. In the case of a neodymium magnet, the external magnetic field in which irreversible demagnetization occurs becomes lower as the temperature Tm of the permanent magnet 21a becomes higher. Hereinafter, for convenience of explanation, the temperature Tm of the permanent magnet 21a is referred to as the "magnet temperature Tm". The spontaneous magnetization of the permanent magnet 21a is different before and after irreversible demagnetization even under the same temperature and the same external magnetic field. Therefore, in order to suppress deterioration of the motor 20, it is preferable to suppress the occurrence of irreversible demagnetization of the permanent magnets 21a.

[0022] The stator core 22 is disposed around the rotor 21. Specifically, the stator core 22 is disposed facing the rotor 21. An air gap is provided between the stator core 22 and the rotor 21.

[0023] The stator coils 23 are each wound around the stator core 22. The stator coils 23 are three-phase coils. Each stator coil 23 is, for example, Y-connected. The rotor 21 rotates when each stator coil 23 is energized in a predetermined pattern. That is, the motor 20 of this embodiment is a three-phase motor. Note that the connection mode of the stator coils 23 is not limited to Y-connection and may be any other mode, for example, delta connection.

[0024] Three-phase coil currents Iu, Iv, and Iw flow through the three-phase stator coil 23. As a result, an external magnetic field is applied to the permanent magnet 21a in the stator coil 23. The magnitude and direction of the external magnetic field are determined by the magnitude and phase of the coil currents Iu, Iv, and Iw. The external magnetic field may induce irreversible demagnetization of the permanent magnet 21a.

[0025] When the coil currents Iu, Iv, and Iw flow through the stator coil 23, heat is generated in the permanent magnet 21a due to the iron loss Pi of the permanent magnet 21a, etc. This causes the temperature Tm of the permanent magnet 21a to rise. The magnet temperature Tm rises due to the iron loss Pi of the permanent magnet 21a and falls due to heat dissipation from the permanent magnet 21a to the surroundings. The iron loss Pi includes the hysteresis loss and eddy current loss of the permanent magnet 21a.

[0026] A temperature difference ΔT may occur between the magnet temperature Tm and the coil temperature Tcoil due to thermal resistance between the stator coil 23 and the rotor 21. Therefore, the magnet temperature Tm can be expressed as Tm=Tcoil+ΔT using the coil temperature Tcoil and the temperature difference ΔT. One factor that may cause thermal resistance is the air gap provided between the rotor 21 and the stator coil 23, for example.

[0027] The rotation speed measurement unit 24 is a sensor that measures the rotation speed N1 per unit time of the rotor 21. The specific embodiment of the rotation speed measurement unit 24 is arbitrary, and may be an electromagnetic resolver or an optical sensor. In the following, for convenience of explanation, the rotation speed per unit time will be simply referred to as the "rotation speed".

[0028] The coil temperature measuring unit 25 measures the temperature of each stator coil 23. The coil temperature measuring unit 25 may be any type, such as a thermistor, a thermocouple, or a radiation thermometer. In the following description, for convenience of explanation, a representative value of the temperature of each stator coil 23 is referred to as the coil temperature Tcoil. The coil temperature Tcoil is, for example, the average value, median value, or maximum value of the temperature of each stator coil 23. The coil temperature Tcoil rises due to the contribution of copper loss Pc generated in the stator coil 23, and falls due to the contribution of heat dissipation to the surroundings, etc.

[0029] The inverter circuit 30 converts the DC power from the power storage device 100 into three-phase AC power. The inverter circuit 30 outputs the three-phase AC power to the motor 20. As a result, three-phase coil currents Iu, Iv, and Iw flow through the stator coil 23. The inverter circuit 30 may output three-phase AC power by, for example, PWM (Pulse Width Modulation) controlling the switching elements provided in the inverter circuit 30 with an appropriate phase relationship and smoothing the output. Note that the specific form of the inverter circuit 30 is arbitrary, and may be a current type or a voltage type. In addition, the control method is not limited to PWM control, and may be PFM (Pulse Frequency Modulation) control.

[0030] The current measuring unit 40 is a sensor that measures three-phase coil currents Iu, Iv, and Iw. The specific form of the current measuring unit 40 is arbitrary, and may be, for example, a shunt resistor or a Hall element.

[0031] The control circuit 50 includes a processor and a storage unit. The processor may be, for example, a central processing unit (CPU), a graphics processing unit (GPU), or a digital signal processor (DSP). The storage unit includes a random access memory (RAM) and a read only memory (ROM). The storage unit stores program code or instructions configured to cause the processor to execute a process. The storage unit, i.e., the computer-readable medium, includes any available medium accessible by a general-purpose or special-purpose computer. The control circuit 50 may be configured by a hardware circuit such as an application specific integrated circuit (ASIC) or a field programmable gate array (FPGA). The control circuit 50, which is a processing circuit, may include one or more processors operating according to a computer program, one or more hardware circuits such as an ASIC or an FPGA, or a combination thereof.

[0032] The control circuit 50 can obtain the detection results of the measurement units 24, 25, and 40. The control circuit 50 performs a motor control process to control the rotation speed N1 of the rotor 21. In the motor control process, the control circuit 50 calculates a d-axis current Idr and a q-axis current Iqr that make the rotation speed N1 become the target rotation speed N1t based on a target rotation speed N1t input from an ECU (Electronic Control Unit) (not shown). The d-axis current Idr and the q-axis current Iqr are command values ​​for outputting coil currents Iu, Iv, and Iw, respectively. The d-axis current Idr and the q-axis current Iqr correspond to the coil currents Iu, Iv, and Iw in a two-phase rotating coordinate system (dq coordinate system) based on the rotor 21. The d-axis current Idr contributes to the excitation of the permanent magnet 21a, and the q-axis current Iqr contributes to the generation of torque of the rotor 21. The control circuit 50 outputs three-phase coil currents Iu, Iv, and Iw to the motor 20 based on the d-axis current Idr and the q-axis current Iqr. Therefore, it can be said that the d-axis current Idr and the q-axis current Iqr are currents flowing through the stator coil 23. When the coil temperature Tcoil exceeds a predetermined temperature, for example, the withstand temperature of the stator coil 23, the control circuit 50 controls the inverter circuit 30 to reduce the coil currents Iu, Iv, and Iw. This makes it possible to suppress the copper loss Pc of the stator coil 23 and reduce the amount of heat generated by the stator coil 23.

[0033] The control circuit 50 starts the motor control process when it receives a start signal that starts the supply of power to the motor 20. Also, it ends the motor control process when it receives a stop signal that stops the supply of power to the motor 20. The start signal is, for example, a signal that switches the vehicle Ve from a stopped state to a running state by operating the start switch 110. The stop signal is, for example, a signal that switches the vehicle Ve from a running state to a stopped state by operating the start switch 110. Note that the start signal and the stop signal are not limited to this, and any form can be adopted. For example, when the start signal and the stop signal are provided in a relay switch between the power storage device 100 and the inverter circuit 30, they may be commands to turn the relay switch to an ON state and an OFF state. In these cases, it can be said that the motor control process is performed when the vehicle Ve is in a running state.

[0034] <Motor control processing> Next, the motor control process will be described in detail. 2, in step S1, the control circuit 50 executes a temperature estimation process to estimate the magnet temperature Tm. The temperature estimation process will be described in detail later.

[0035] Next, the control circuit 50 proceeds to step S2 and determines the limit current value Ix based on the magnet temperature Tm estimated in step S1. The limit current value Ix is smaller than the coil currents Iu, Iv, and Iw at which irreversible demagnetization of the permanent magnet 21a occurs when the magnet temperature is Tm. In this embodiment, the limit current value Ix corresponds to the maximum value of the d-axis current Idr. Note that the limit current value Ix is not limited to this and can be set arbitrarily. For example, the limit current value Ix may correspond to the magnitude of a current vector represented by the d-axis current Idr and the q-axis current Iqr.

[0036] Next, the control circuit 50 proceeds to step S3, and acquires a target rotation speed N1t from, for example, an ECU (not shown). The target rotation speed N1t is a target value of the rotation speed N1. The target rotation speed N1t is calculated based on, for example, the accelerator opening and running speed of the vehicle Ve, and the input voltage from the power storage device 100 to the inverter circuit 30.

[0037] Next, the control circuit 50 proceeds to step S4 and calculates the d-axis current Idr and the q-axis current Iqr based on the target rotation speed N1t. The control circuit 50 can control the rotation speed N1 by calculating the d-axis current Idr and the q-axis current Iqr that make the rotation speed N1 the target rotation speed N1t. Note that any calculation method may be used, but for example, the control circuit 50 can calculate the d-axis current Idr and the q-axis current Iqr based on the target rotation speed N1t by referring to a map of the d-axis current Idr and the q-axis current Iqr for the target rotation speed N1t that is stored in advance.

[0038] Next, the control circuit 50 proceeds to step S5 and determines whether the d-axis current Idr is equal to or less than the limit current value Ix. If the result of the determination in step S5 is negative, the control circuit 50 proceeds to step S6. On the other hand, if the result of the determination in step S5 is positive, the control circuit 50 skips step S6 and proceeds to step S7.

[0039] In step S6, the control circuit 50 changes the d-axis current Idr to the limited current value Ix, and proceeds to step S7. Note that in step S6, the control circuit 50 may change the d-axis current Idr to less than the limited current value Ix. That is, in step S6, the control circuit 50 may change the d-axis current Idr to less than the limited current value Ix. The control circuit 50 limits the d-axis current Idr to less than the limited current value Ix by executing steps S5 and S6. At this time, the control circuit 50 may change the q-axis current Iqr to correspond to the changed d-axis current Idr.

[0040] Next, the control circuit 50 proceeds to step S7, and outputs the coil currents Iu, Iv, and Iw to the motor 20 by controlling the switching elements of the inverter circuit 30 based on the d-axis current Idr and the q-axis current Iqr. Any method can be used to determine the coil currents Iu, Iv, and Iw. For example, the inverter circuit 30 may be controlled so that the output coil currents Iu, Iv, and Iw are the target values ​​obtained by performing two-phase to three-phase conversion on the d-axis current Idr and the q-axis current Iqr. The rotor 21 rotates according to the coil currents Iu, Iv, and Iw. Therefore, it can be said that the control circuit 50 controls the number of revolutions N1 by controlling the coil currents Iu, Iv, and Iw based on the d-axis current Idr and the q-axis current Iqr.

[0041] When the d-axis current Idr is changed to the limit current value Ix by the process of step S6, the control circuit 50 outputs the coil currents Iu, Iv, and Iw to the motor 20 based on the changed d-axis current Idr and q-axis current Iqr in step S7. At this time, the control circuit 50 allows the rotor 21 to rotate in a state where the rotation speed N1 is less than the target rotation speed N1t. Therefore, it can be said that the control circuit 50 limits the rotation speed N1 based on the limit current value Ix.

[0042] Next, the control circuit 50 proceeds to step S8 and determines whether the vehicle Ve is in a stopped state. If the determination result of step S8 is negative, that is, if the vehicle Ve is in a running state, the control circuit 50 returns to step S1 and continues the motor control process. On the other hand, if the determination result of step S8 is positive, the control circuit 50 proceeds to step S9 and stores the time when the vehicle Ve became in a stopped state. After that, the control circuit 50 ends the motor control process.

[0043] <Temperature estimation process> Next, the temperature estimation process will be described in detail. In the following description, the time when the vehicle Ve is in a stopped state before the temperature estimation process is started is called a stop time t1, the time when the vehicle Ve is in a started state before the temperature estimation process is started is called a start time t2, and the time when the process of step S11 described later is performed is called an estimated time t3. The estimated time t3 can also be said to be the start time of the temperature estimation process. During the stop period Δt1 from the stop time t1 to the start time t2, the vehicle Ve is in a stopped state, and during the integration period Δt2 from the start time t2 to the estimated time t3, the vehicle Ve is in a started state. Note that the stop time t1 may be the time stored in the process of step S9.

[0044] As shown in FIG. 3, in step S11, the control circuit 50 acquires estimated parameters. The estimated parameters are parameters used to estimate the magnet temperature Tm. In this embodiment, the estimated parameters include the rotation speed N1, the coil temperature Tcoil, the coil currents Iu, Iv, Iw, the d-axis current Idr, the q-axis current Iqr, the stop period Δt1, and the integration period Δt2. The stop period Δt1 and the integration period Δt2 may be calculated from the times t1, t2, and t3. The control circuit 50 may acquire the estimated parameters from the measurement units 24, 25, and 40 or the memory unit of the control circuit 50.

[0045] Next, the control circuit 50 proceeds to step S12 and calculates the offset temperature Toffset based on the coil temperature Tcoil and the stop period Δt1. The offset temperature Toffset is an estimate of the magnet temperature Tm at the start time t2. The offset temperature Toffset can also be said to be the initial temperature of the magnet temperature Tm.

[0046] During the stop period Δt1, the contribution of iron loss Pi to magnet temperature Tm decreases, and the contribution of heat dissipation increases. As a result, magnet temperature Tm gradually decreases, and an equilibrium state is reached where magnet temperature Tm and coil temperature Tcoil match. Matching does not only mean that the two values ​​match perfectly, but also includes being within a specified range. The specified range takes into account, for example, measurement errors and fluctuations.

[0047] The offset temperature Toffset may be calculated by any method. For example, the control circuit 50 may calculate the offset temperature Toffset by referring to a correspondence table of the offset temperature Toffset with respect to the coil temperature Tcoil and the stop period Δt1. The correspondence table may be determined in advance by testing, thermal fluid analysis, or the like. The process of step S12 may be executed only in the first temperature estimation process performed after the start time t2. In other words, the process of step S12 may be omitted in the temperature estimation process performed after the first temperature estimation process.

[0048] Next, the control circuit 50 proceeds to step S13, and calculates the iron loss Pi based on the d-axis current Idr and the q-axis current Iqr. The calculation method of the iron loss Pi is arbitrary, and for example, it may be calculated from a correspondence table that can be calculated by electromagnetic field analysis, or it may be calculated using the finite element method or the like from a physical model that represents the motor 20. In this embodiment, the control circuit 50 that executes step S13 corresponds to the iron loss calculation unit.

[0049] Next, the control circuit 50 proceeds to step S14, and calculates an integrated current Iint and an average current Iave based on the coil currents Iu, Iv, and Iw. The integrated current Iint is a value obtained by integrating the effective values ​​Ieff of the coil currents Iu, Iv, and Iw over an integration period Δt2. Hereinafter, for convenience of explanation, the effective values ​​Ieff of the coil currents Iu, Iv, and Iw are treated as being equal to each other, and are simply referred to as the "effective value Ieff." The stator coil 23 has a resistance component. Therefore, when the coil currents Iu, Iv, and Iw flow through the stator coil 23, the stator coil 23 consumes power in proportion to the effective value Ieff. Therefore, the integrated current Iint obtained by integrating the effective value Ieff over the integration period Δt2 corresponds to the copper loss Pc that occurs during the integration period Δt2.

[0050] The average current Iave is the average value of the effective value Ieff in the averaging period Δt3. The average current Iave is obtained, for example, by dividing the integrated current Iint by the averaging period Δt3. When the averaging period Δt3 is 0, the average current Iave is 0. The averaging period Δt3 in this embodiment coincides with the integration period Δt2. That is, the average current Iave is the average value of the effective value Ieff in the integration period Δt2. In this case, the averaging period Δt3 becomes 0 when the estimated time t3 coincides with the start-up time t2.

[0051] Next, the control circuit 50 proceeds to step S15, and calculates the contribution to the temperature difference ΔT from each of the rotation speed N1, the iron loss Pi, and the integrated current Iint. The contribution of the iron loss Pi to the temperature difference ΔT is represented by a first function f1. The contribution of the rotation speed N1 to the temperature difference ΔT is represented by a second function f2. The contribution of the integrated current Iint to the temperature difference ΔT is represented by a third function f3. Each of the functions f1 to f3 is represented by, for example, a polynomial of the respective arguments. In particular, by making each of the functions f1 to f3 a linear function of the respective arguments, the calculation load of the control circuit 50 can be reduced. In this embodiment, the constant coefficient of each of the functions f1 to f3 is 0.

[0052] The first function f1 represents the effect of heat generation of the permanent magnet 21a due to iron loss Pi on the magnet temperature Tm. The second function f2 represents the effect of heat generation of the permanent magnet 21a due to windage loss and cooling of the permanent magnet 21a due to heat transfer on the magnet temperature Tm. The first function f1 and the second function f2 may be determined in advance through experiments or the like, or may be obtained through numerical analysis such as thermal fluid analysis. The third function f3 represents the effect of heat generated by copper loss Pc of the stator coil 23 on the magnet temperature Tm.

[0053] The heat transferred from the stator coil 23 to the permanent magnet 21a is correlated with the integrated current Iint. As described above, the integrated current Iint is associated with the copper loss Pc. The copper loss Pc is a factor that increases the coil temperature Tcoil. Here, if only the copper loss Pc over the integration period Δt2 is considered, the increase in the coil temperature Tcoil continues to increase over time. However, as the temperature of the coil temperature Tcoil increases, the amount of heat dissipated from the stator coil 23 to the surroundings increases. Therefore, the time rate of change of the coil temperature Tcoil becomes smaller and eventually reaches a steady state. Therefore, a discrepancy occurs between the time change of the coil temperature Tcoil measured by the coil temperature measurement unit 25 and the time change of the coil temperature Tcoil caused by the copper loss Pc. Such a discrepancy indicates the magnitude of heat dissipation from the stator coil 23. A part of the heat dissipated from the stator coil 23 is transferred to the permanent magnet 21a by heat exchange through the air, for example. This causes the magnet temperature Tm to change. Therefore, by using the integrated current Iint when calculating the temperature difference ΔT, it is possible to take into account the effect of the copper loss Pc of the stator coil 23 on the magnet temperature Tm. Note that the coefficient (e.g., heat transfer coefficient) indicating the heat exchange between the stator coil 23 and the permanent magnet 21a may be determined in advance by thermal fluid analysis, experiments, or the like in a system including the motor 20.

[0054] Next, the control circuit 50 proceeds to step S16 and calculates the temperature difference ΔT based on each contribution calculated in step S15. In this embodiment, the temperature difference ΔT at the start time t2 is Toffset-Tcoil. At this time, the argument of each of the functions f1 to f3 is 0. Therefore, the temperature difference ΔT can be expressed by the relational expression ΔT=Toffset-Tcoil+f1(Pi)+f2(N1)+f3(Iint). In the above relational expression, the symbols in parentheses indicate the arguments of each function.

[0055] Next, the control circuit 50 proceeds to step S17 and estimates the magnet temperature Tm based on the coil temperature Tcoil and the temperature difference ΔT. In detail, the control circuit 50 estimates the magnet temperature Tm by substituting the coil temperature Tcoil acquired in step S11 and the temperature difference ΔT calculated in step S16 into Tm=Tcoil+ΔT. The magnet temperature Tm calculated in this manner is used in the motor control process described above. In this embodiment, the control circuit 50 that executes the process of step S17 corresponds to the temperature estimation device.

[0056] Next, the control circuit 50 proceeds to step S18 to calculate the steady-state magnet temperature Tms. The steady-state magnet temperature Tms is the magnet temperature Tm in the steady state corresponding to the average current Iave. The average current Iave corresponds to the copper loss Pc of the stator coil 23 per unit time. The copper loss Pc of the stator coil 23 per unit time and the heat dissipation amount of the stator coil 23 are balanced. In the steady state, the coil temperature Tcoil and the magnet temperature Tm each have a value corresponding to the steady state. Using such a correlation between the average current Iave and the steady state of the motor 20, the coil temperature Tcoil and the magnet temperature Tm in the steady state corresponding to the average current Iave are calculated. The specific calculation method of the steady magnet temperature Tms is arbitrary, but a map determined in advance by an experiment or the like may be referenced, or the steady magnet temperature Tms may be calculated from a function of the average current Iave.

[0057] Next, the control circuit 50 proceeds to step S19 and determines whether the magnet temperature Tm is equal to or lower than the estimated magnet temperature Tms. If the determination result in step S19 is negative, the control circuit 50 proceeds to step S20, changes the magnet temperature Tm to the steady-state magnet temperature Tms, and ends the temperature estimation process. On the other hand, if the determination result in step S19 is positive, the control circuit 50 skips step S20 and ends the temperature estimation process. This eliminates the absurdity that the magnet temperature Tm estimated in step S18 is greater than the steady-state magnet temperature Tms corresponding to the average current Iave. Therefore, it can be said that the control circuit 50 estimates the magnet temperature Tm based on the average current Iave.

[0058] The control circuit 50 performs the processes of steps S2 to S9 using the magnet temperature Tm estimated in this way. When the integration period Δt2 becomes greater than the estimation period Δt3, the control circuit 50 may omit the above temperature estimation process and perform the motor control process. The estimation period Δt3 is arbitrary, but is, for example, the period until the magnet temperature Tm reaches a steady state. This makes it possible to accurately estimate the magnet temperature Tm during the period when the temperature change in the magnet temperature Tm is large immediately after the vehicle Ve is in the start-up state, and also reduces the burden of the motor control process. Omission of such processes is particularly useful when the lower the magnet temperature Tm, the more likely irreversible demagnetization occurs, for example, when the permanent magnet 21a is a ferrite magnet.

[0059] <Actions and Effects> The operation and effects of this embodiment will be described below. (1) The control circuit 50, acting as a temperature estimation device, executes the processes of steps S15 to S17 to estimate the magnet temperature Tm based on the coil temperature Tcoil, which is the temperature of the stator coil 23, and the integrated current Iint, which is the effective value Ieff of the coil currents Iu, Iv, Iw flowing through each stator coil 23, integrated over an integration period Δt2.

[0060] According to this, the integrated current Iint obtained by integrating the effective value Ieff over the integration period Δt2 corresponds to the copper loss Pc generated during the integration period Δt2. The copper loss Pc is a factor that increases the coil temperature Tcoil. Here, if only the copper loss Pc over the integration period Δt2 is considered, the increase in the coil temperature Tcoil continues to increase over time. However, as the coil temperature Tcoil increases, the amount of heat dissipated from the stator coil 23 to the surroundings increases. Therefore, the time rate of change of the coil temperature Tcoil becomes smaller and eventually reaches a steady state. Therefore, a discrepancy occurs between the time change of the coil temperature Tcoil measured by the coil temperature measurement unit 25 and the time change of the coil temperature Tcoil caused by the copper loss Pc.

[0061] Such a deviation indicates the amount of heat dissipated by the stator coil 23. A part of the heat dissipated from the stator coil 23 is transferred to the permanent magnet 21a, for example, via the air. This causes the magnet temperature Tm to change. Therefore, by using the integrated current Iint when calculating the temperature difference ΔT, it is possible to take into account the effect of the copper loss Pc of the stator coil 23 on the magnet temperature Tm. Therefore, the magnet temperature Tm can be estimated with high accuracy.

[0062] (2) The control circuit 50 executes steps S19 and S20 to estimate the magnet temperature Tm based on the average current Iave, which is the average value of the effective values ​​Ieff of the coil currents Iu, Iv, Iw during the averaging period Δt3.

[0063] According to this, when the magnet temperature Tm reaches the steady-state magnet temperature Tms in the steady state, it is possible to prevent the estimated magnet temperature Tm from becoming greater than the steady-state magnet temperature Tms corresponding to the average current Iave. Therefore, it is possible to prevent the deviation between the estimated magnet temperature Tm and the actual magnet temperature Tm. Therefore, it is possible to accurately estimate the magnet temperature Tm even in the steady state.

[0064] (3) The control circuit 50 executes the processes of steps S15 to S17 for estimating the magnet temperature Tm based on the rotation speed N1 of the rotor 21. According to this, by taking into account the influence of windage loss and air cooling, it is possible to estimate the magnet temperature Tm in accordance with the driving state of the motor 20.

[0065] (4) The control circuit 50 executes the processes of steps S13, S15, and S17 for estimating the magnet temperature Tm based on the d-axis current Idr and the q-axis current Iqr flowing through the stator coil 23. According to this, the heat generated by the iron loss Pi can be taken into account and the magnet temperature Tm can be estimated with higher accuracy.

[0066] (5) The control circuit 50 executes the process of step S13 to calculate the iron loss Pi of the permanent magnet 21a based on the d-axis current Idr and the q-axis current Iqr. Then, the control circuit 50 executes the processes of steps S15, S16, and S17 to estimate the magnet temperature Tm based on the iron loss Pi calculated in step S13.

[0067] According to this, by converting the d-axis current Idr and the q-axis current Iqr into the iron loss Pi, the calculation load is reduced compared to the case where the magnet temperature Tm is directly estimated, and therefore the magnet temperature Tm can be estimated faster.

[0068] <Modification> The embodiment can be modified as follows: The embodiment and the following modified examples can be combined with each other to the extent that there is no technical contradiction.

[0069] The motor control process and the temperature estimation process in the embodiment are merely examples, and are not limited to these. In addition, the control circuit 50 that executes each process does not have to be configured as a single device, and may be configured by multiple devices that cooperate with each other.

[0070] The expression of the temperature difference ΔT is not limited to that in the embodiment. For example, it may include a contribution including two or more of the arguments Pi, N1, and Iint. In the temperature estimation process, the control circuit 50 may use the temperature of the power transmission mechanism G1 to estimate the magnet temperature Tm. The power transmission mechanism G1 is connected to the rotor 21 (specifically, the permanent magnet 21a) via the rotating shaft Ax. Therefore, a part of the heat of the permanent magnet 21a is transferred to the power transmission mechanism G1 via the rotating shaft Ax. For example, a correction term f5 indicating the heat transfer to the power transmission mechanism G1 may be applied to the temperature difference ΔT. The correction term f5 may be a function of the temperature of the power transmission mechanism G1 determined by an experiment or the like.

[0071] The d-axis current Idr and q-axis current Iqr used to estimate the magnet temperature Tm do not have to be command values ​​used to output the coil currents Iu, Iv, and Iw. For example, the d-axis current Idr and q-axis current Iqr used to estimate the magnet temperature Tm may be output values ​​obtained by performing a 3-phase to 2-phase conversion on the output coil currents Iu, Iv, and Iw. This improves the accuracy of calculating the iron loss Pi, making it possible to estimate the magnet temperature Tm with greater accuracy.

[0072] The averaging period Δt3 does not have to be the same as the integration period Δt2. For example, the averaging period Δt3 may be a period going back a certain period from the estimated time t3. The predetermined period can be set arbitrarily. In other words, the average current Iave may be a so-called moving average, not an overall average over the entire integration period Δt2 of the effective value Ieff. This reduces the load of the calculation process of the average current Iave, and speeds up the temperature estimation process.

[0073] The control circuit 50 does not need to execute the process of step S13 in which the iron loss Pi is calculated based on the d-axis current Idr and the q-axis current Iqr. In this case, the temperature difference ΔT may be calculated directly from the d-axis current Idr and the q-axis current Iqr instead of the first function f1. In this case, for example, a function f4 that expresses the contribution of the d-axis current Idr and the q-axis current Iqr to the temperature difference ΔT may be used. The function f4 may be obtained by an experiment or the like, or may be obtained by a numerical analysis or the like.

[0074] In step S17, the control circuit 50 does not have to estimate the magnet temperature Tm based on the rotation speed N1. For example, the control circuit 50 does not have to take the second function f2 into consideration when calculating the temperature difference ΔT in step S16.

[0075] The control circuit 50 does not have to estimate the magnet temperature Tm based on the d-axis current Idr and the q-axis current Iqr in step S17. For example, the control circuit 50 does not have to take into account the function f1 or the function f4 in calculating the temperature difference ΔT in step S16.

[0076] The control circuit 50 does not need to execute the processes of steps S19 and S20 for estimating the magnet temperature Tm based on the average current Iave. The integrated current Iint only needs to be taken into account in the calculation of the magnet temperature Tm. Even in this case, the magnet temperature Tm before the steady state is reached can be accurately estimated.

[0077] The stator core 22 does not have to be disposed around the rotor 21. For example, the rotor 21 may be disposed around the stator core 22. In other words, the motor 20 is not limited to a so-called inner rotor type, and may be an outer rotor type.

[0078] The motor 20 is not limited to being used for driving the vehicle Ve. For example, the motor 20 may be used for a compressor, a blower, or the like. [Explanation of symbols]

[0079] 20...motor, 21...rotor, 21a...permanent magnet, 22...stator core, 23...stator coil, 50...control circuit, Iave...average current, Idr...d-axis current, Ieff...effective value, Iint...integrated current, Iqr...q-axis current, Iu, Iv, Iw...coil current, N1...rotation speed, Pi...iron loss, Tcoil...coil temperature, Tm...magnet temperature, Δt2...integration period, Δt3...average period.

Claims

1. A temperature estimation device for estimating a magnet temperature, comprising: the magnet temperature is the temperature of a permanent magnet provided in a rotor of a motor, The motor includes a stator core and a plurality of stator coils wound around the stator core. The temperature estimation device estimates the magnet temperature by adding up the coil temperature, which is the temperature of the stator coil, and a temperature difference calculated based on an integrated current obtained by integrating the effective value of the coil current flowing through each stator coil over an integration period.

2. The temperature estimation device according to claim 1 , wherein the temperature estimation device estimates the magnet temperature based on an average current that is an average value of an effective value of the coil current in an averaging period.

3. The temperature estimation device according to claim 1 , wherein the temperature estimation device estimates the magnet temperature based on a rotation speed of the rotor.

4. 4. The temperature estimation device according to claim 1, wherein the temperature estimation device estimates the magnet temperature based on a d-axis current and a q-axis current flowing through the stator coil.

5. the temperature estimation device includes an iron loss calculation unit that calculates an iron loss of the permanent magnet based on the d-axis current and the q-axis current, The temperature estimation device according to claim 4 , wherein the magnet temperature is estimated based on the iron loss calculated by the iron loss calculation unit.

Images