Motor control device and motor control method

Abstract

Provided are a motor control device and a motor control method that can reduce the influence of errors on estimated values due to sensor errors during magnet temperature estimation. A motor control device 100 is provided with: a d-axis harmonic current superimposition unit 121 that superimposes a harmonic current on a d-axis current; a first d-axis inductance computation unit 40 that, when a d-axis harmonic current produced by superimposition of the harmonic current is within a first prescribed range, computes an estimated value Ld_est1 for a first d-axis inductance on the basis of the d-axis harmonic current; a second d-axis inductance computation unit 41 that, when the d-axis harmonic current is within a second prescribed range having an upper-limit value smaller than a lower-limit value of the first prescribed range, computes an estimated value Ld_est2 for a second d-axis inductance on the basis of the d-axis harmonic current; and a magnet temperature computation unit 42 that, on the basis of the estimated value Ld_est1 for the first d-axis inductance and the estimated value Ld_est2 for the second d-axis inductance, computes a magnet temperature estimated value emt of a motor 20.

Description

Motor control device and motor control method

[0001] The present invention relates to a motor control device and a motor control method.

[0002] Patent Document 1 discloses a driving device for a permanent magnet synchronous motor that includes a superposition unit that superimposes a voltage or current of a frequency different from the frequency of the fundamental wave on the d-axis, and that estimates the magnet temperature from the superimposed voltage or current and the current or voltage obtained by the superposition.

[0003] Furthermore, Patent Document 2 discloses a means for determining an equivalent inductance value of the d-axis and an estimation method for calculating an estimated value of the magnetic flux amount of a permanent magnet based on the equivalent inductance value.

[0004] JP 2015-133891 A Japanese Patent No. 6158115 A

[0005] Patent Document 1 discloses a driving device for a permanent magnet synchronous motor that includes a superposition unit that superimposes a voltage or current of a frequency different from the frequency of the fundamental wave on the d-axis, and that estimates the magnet temperature from the superimposed voltage or current and the current or voltage obtained by the superposition.

[0006] Patent Document 2 discloses a determination means that includes a d-axis inductance equivalent value determination means, an estimation method that calculates an estimated value of the magnetic flux amount of a permanent magnet based on the inductance equivalent value, a high-frequency voltage application means that applies a high-frequency voltage to the d-axis, and a high-frequency current amplitude detection means that detects the amplitude of the high-frequency current flowing on the d-axis in accordance with the voltage applied by the high-frequency voltage application means, and that determines the inductance equivalent value based on the high-frequency voltage and high-frequency current amplitude.

[0007] However, in the technology described in Patent Document 1, if an error exists in the voltage sensor or current sensor, an error occurs in the superimposed voltage or current and the current or voltage obtained by the superposition, and as a result, an error also occurs in the estimated magnet temperature value.

[0008] Similarly, in the technology described in Patent Document 2, if there is an error in the voltage sensor or current sensor, an error occurs in the high-frequency voltage and high-frequency current amplitude, and as a result, an error occurs in the inductance equivalent value.

[0009] To estimate the magnet temperature or the inductance equivalent value with high accuracy, it is necessary to reduce the influence of sensor errors on the estimated value.

[0010] However, the techniques described in Patent Documents 1 and 2 do not describe a method for reducing the effect of sensor errors on the estimated value, and therefore, it is believed that there is room for improvement in the techniques described in Patent Documents 1 and 2.

[0011] An object of the present invention is to provide a motor control device and a motor control method that can reduce the influence of errors on the estimated value due to voltage sensor errors and current sensor errors when estimating magnet temperature.

[0012] In order to achieve the above object, the present invention is configured as follows.

[0013] A motor control device that drives a motor using an inverter includes a d-axis harmonic current superimposing unit that superimposes a harmonic current on a d-axis current, a first d-axis inductance calculation unit that calculates an estimated value of a first d-axis inductance based on the d-axis harmonic current when the d-axis harmonic current on which the harmonic current is superimposed is within a first predetermined range, a second d-axis inductance calculation unit that calculates an estimated value of a second d-axis inductance based on the d-axis harmonic current when the d-axis harmonic current is within a second predetermined range having an upper limit value that is smaller than a lower limit value of the first predetermined range, and a magnet temperature calculation unit that calculates an estimated value of a magnet temperature of the motor based on the estimated value of the first d-axis inductance and the estimated value of the second d-axis inductance.

[0014] Furthermore, in a motor control method for driving a motor with an inverter, a harmonic current is superimposed on a d-axis current, and when the d-axis harmonic current on which the harmonic current is superimposed is within a first predetermined range, an estimated value of a first d-axis inductance is calculated based on the d-axis harmonic current, and when the d-axis harmonic current is within a second predetermined range having an upper limit value that is smaller than a lower limit value of the first predetermined range, an estimated value of a second d-axis inductance is calculated based on the d-axis harmonic current, and an estimated value of a magnet temperature of the motor is calculated based on the estimated value of the first d-axis inductance and the estimated value of the second d-axis inductance.

[0015] According to the present invention, it is possible to provide a motor control device and a motor control method that can reduce the influence of sensor errors on estimated values ​​when estimating magnet temperature.

[0016] Problems, configurations, and effects other than those described above will become apparent from the following description of the embodiments.

[0017] 1 is a schematic configuration diagram showing a motor control device of Example 1. FIG. 1 is a schematic diagram showing the structure of a PM motor. FIG. 2 is a diagram showing the relationship between a rotor position and the phase of each winding of a stator. FIG. 3 is a block diagram of a power conversion circuit and a current detection unit. FIG. 4 is a diagram showing the relationship between a PWM carrier signal and a voltage command value. FIG. 5 is a diagram showing an example configuration of a voltage command value calculation unit. FIG. 6 is a control block diagram of an example configuration of a d-axis harmonic current superimposition unit of a magnet temperature calculation unit of Example 1. FIG. 7 is a diagram showing an example waveform of a d-axis harmonic current command value Idh*. FIG. 8 is a diagram showing another example waveform of the d-axis harmonic current command value Idh*. FIG. 9 is a diagram showing yet another example waveform of the d-axis harmonic current command value Idh*. FIG. 10 is a control block diagram of another example configuration of a d-axis harmonic current superimposition unit of a magnet temperature calculation unit of Example 1. FIG. 11 is a diagram showing an example relationship between magnet temperature and a d-axis inductance estimate value. FIG. 12 is a control block diagram of an example configuration of a magnet temperature calculation unit. FIG. 13 is a diagram showing an example relationship between magnet temperature and a ratio between a first d-axis inductance and a second d-axis inductance. 1 is a diagram showing an example of a table of magnet temperature estimated values ​​using a first d-axis inductance estimated value and a second d-axis inductance estimated value as parameters. FIG. 2 is a diagram showing a magnet temperature estimation error from a first d-axis inductance estimated value with respect to a voltage sensor error and a current sensor error. FIG. 3 is a diagram showing a magnet temperature estimation error from a ratio of a first d-axis inductance to a second d-axis inductance with respect to a voltage sensor error and a current sensor error. FIG. 4 is a diagram showing an example of a characteristic of a magnet temperature change rate of a d-axis inductance estimated value for Example 2. FIG. 5 is a diagram showing an example of setting a first predetermined range average value and a second predetermined range average value. FIG. 6 is a diagram showing another example of setting the first predetermined range average value and the second predetermined range average value.

[0018] In an embodiment of the present invention, for example, during harmonic current superposition operation for the purpose of estimating the magnet temperature or magnet flux of an electric motor, a first d-axis inductance is calculated when the harmonic current is in a first predetermined range, and a second d-axis inductance is calculated when the harmonic current is in a second predetermined range, and a magnet temperature estimate is calculated based on the first d-axis inductance and the second d-axis inductance.By taking advantage of the fact that the sensor error effects of the first d-axis inductance and the second d-axis inductance are the same, a magnet temperature estimate is calculated with reduced sensor error effects.

[0019] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings, in which like reference numerals denote like elements and the same description will not be repeated.

[0020] The various components of the present invention do not necessarily have to be independent entities, and it is acceptable for multiple components to be formed as a single member, for one component to be formed from multiple members, for one component to be part of another component, or for part of one component to overlap with part of another component, etc.

[0021] (First Embodiment) <Schematic Configuration of Motor Control Device 100> Fig. 1 is a schematic configuration diagram of motor control device 100. In Fig. 1, motor control device 100 includes a control unit 10, an electric motor (PM motor) 20, an inverter 30, a current detection means 50, an angle sensor 60 such as a resolver or an encoder, a DC voltage source 120, and a voltage sensor 70. Although not shown, a mechanism that mechanically or magnetically transmits mechanical output is connected to PM motor 20, and motor control device 100 controls the rotation speed or torque of PM motor 20 to a desired value.

[0022] Although the present invention does not limit the operating principle of the electric motor 20, the following description will be given using an example in which a permanent magnet synchronous motor (PMSM) having a permanent magnet in the rotor is used as the electric motor 20. Various types of electric motors are applicable as the electric motor 20, and the subject of this disclosure is an electric motor having the characteristic that the magnetic flux of the permanent magnet changes depending on the temperature of the rotor.

[0023] Inverter 30 is connected to DC voltage source 120 such as a battery, has a bridge circuit made up of switching elements, and outputs a voltage by switching the switching elements in response to an input drive signal. Assuming that the switching operation of the switching elements is ideally performed without delay, the voltage output from inverter 30 is a pulsed voltage. The voltage of DC voltage source 120 is detected by voltage sensor 70.

[0024] Using the well-known concept of pulse width modulation, the pulsed voltage can be considered an AC voltage. In pulse width modulation, the cycle at which the switching element is turned on and off, i.e., the switching frequency, is generally set sufficiently high relative to the frequency of the equivalent AC voltage (which corresponds to the rotational frequency of the single-phase motor in this case). However, it is also possible to consider the fundamental component of the pulsed voltage. For example, when the switching frequency is close to the rotational frequency of the PM motor, such as approximately 1 to 3 times, the fundamental component of the pulsed voltage can be considered to be applied to the PM motor 20. Therefore, in this specification, the following description will be given assuming that the output voltage of the inverter 30 has an AC waveform.

[0025] Instead of a DC voltage source, an AC power source may be converted into DC power by rectification, etc. Alternatively, a DC / DC converter may be used that controls a DC voltage source to a different voltage.

[0026] The control unit 10 includes, as an example configuration, a current command value calculation unit 11, a voltage command value calculation unit 12, a PWM signal generation unit 14, a coordinate conversion unit 13, an angular velocity calculation unit 15, a first d-axis inductance calculation unit 40, a second d-axis inductance calculation unit 41, and a magnet temperature calculation unit 42. The voltage command value calculation unit 12 includes a d-axis harmonic current superimposition unit 121 that superimposes a harmonic current on the d-axis current, and a current control unit 122.

[0027] The coordinate conversion unit 13 receives as input a current detection value Iw, which is information about the current flowing through the electric motor (PM motor) 20 and is obtained by the current detection unit 50, and a motor electrical angle detection value θed, which is obtained by the Iu angle sensor 60. The coordinate conversion unit 13 converts the three-phase UVW axes into dq axes, the definitions of which will be described later, and outputs a d-axis current detection value and a q-axis current detection value.

[0028] The angular velocity calculation unit 15 receives the motor electrical angle detection value θed and outputs the electrical angular velocity ωe. The voltage command value calculation unit 12 receives the rotation speed command value or the torque command value and generates a d-axis voltage command value vd* and a q-axis voltage command value vq* based on the d-axis current command value id* and the q-axis current command value iq* output by the current command value calculation unit 11, the d-axis current detection value idc and the q-axis current detection value iqc output by the coordinate conversion unit 13, and the electrical angular velocity ωe output by the angular velocity calculation unit.

[0029] The voltage of DC voltage source 120 is detected as a voltage detection value Edc by voltage sensor 70, and PWM signal generation unit 14 outputs a PWM signal that controls the on / off of switching elements that make up inverter 30 based on the detected voltage value, d-axis voltage command value vd*, and q-axis voltage command value vq*. In Fig. 1, the rotation speed command value and torque command value are shown in control unit 10, but there is no problem if they are obtained from, for example, a higher-level control system or another control system not shown.

[0030] Furthermore, the first d-axis inductance calculation unit 40 and the second d-axis inductance calculation unit 41 receive the d-axis voltage command value vd*, the d-axis current detection value idc, the q-axis current detection value iqc, and the electrical angular velocity ωe as input, but there is no problem if they are configured to use only some of the values ​​instead of inputting all of the values.

[0031] <Structural Example of PM Motor 20> Fig. 2 is a diagram showing a schematic diagram of the structure of the PM motor 20. In Fig. 2, the PM motor 20 is composed of a stator 21 and a rotor 22. The stator 21 has a plurality of stator poles 28, each of which has a winding (coil) 25 wound around a stator core (stator iron core) 26. The rotor 22 has a permanent magnet 27.

[0032] 2 shows an example in which the number of magnetic poles (also called the number of slots) of the stator is six and the number of magnetic poles of the rotor 22 is two. The number of magnetic poles of the stator 21 and the rotor 22 can be selected freely, and it does not matter if the numbers of magnetic poles of the stator and the rotor 22 are not equal. Furthermore, the connection of the multiple windings 25 does not matter whether they are connected in parallel or in series. In this specification, the windings 25 of opposing stator poles 28 are connected in series to form one phase, and the PM motor 20 will be described as being configured with three-phase windings 25.

[0033] When a current flows through the windings 25, the stator magnetic poles 28 generate magnetic poles in the manner of electromagnets, and the polarity (north pole, south pole) can be changed depending on the direction of the current through the windings 25. In this specification, the rotation angle (rotation angle position) of the rotor 22 when the stator magnetic poles 28 become south poles when a positive direct current flows through the windings 25 and the north pole of the permanent magnet 27 of the rotor 22 is attracted is defined as zero degrees.

[0034] Hereinafter, the rotational angular position of the rotor 22 will be referred to as rotor position θd. If there are multiple windings 25, one of them will be defined as the reference position. In this specification, the winding 25 on the right side of FIG. 2 (the winding closest to the U-phase) will be described as the reference position. In this specification, the counterclockwise rotation direction of the rotor 22 is defined as positive rotation.

[0035] The processing within the motor control device 100 utilizes information about the rotor position θd of the rotor 22 of the PM motor 20, and the following description will be given assuming that the position information is detected by a resolver, encoder, or the like as the angle sensor 60. Naturally, it is also possible to use a configuration in which the position information is obtained by position sensorless control using a position estimation means that outputs an estimated rotational angle position of the PM motor 20 from the current flowing through the PM motor 20 and the voltage applied to the PM motor 20.

[0036] <Explanation of Coordinate Axes> Here, the definitions of the coordinate axes will be explained. FIG. 3 is an explanatory diagram of the coordinate axes, showing the relationship between the rotor position θd and the phases of each winding 25 of the stator 21. The three-phase windings, UV and W, are arranged with an electrical angle difference of 120 degrees. The d-axis is defined as the direction of the main magnetic flux of the permanent magnet 27 provided in the rotor 22, and the d-q axis is defined as the q-axis that is electrically 90 degrees (electrical angle 90 degrees) ahead of the d-axis in the direction of rotation. The d-q axes are a rotating coordinate system. The d-axis can also be defined as the rotational angle position at which the magnetic flux of the permanent magnet 27 that links with the reference winding 25 is maximized.

[0037] <Inverter 30> Next, the configurations of the inverter 30 and the current detection unit 50 will be described with reference to the block diagram of the power conversion circuit and the current detection unit 50 shown in FIG.

[0038] As shown in FIG. 4, the inverter 30 is connected to a DC voltage source 120 and includes an inverter module 131 and a gate driver circuit 132. Here, the output of the DC voltage source 120 is a DC voltage Edc. The inverter module 131 includes switching elements 32a to 32f (e.g., semiconductor switching elements such as IGBTs and MOS-FETs) and freewheeling diodes connected in parallel to the switching elements 32a to 32f. The switching elements 32a to 32f are collectively referred to as "switching elements 32" (the same applies hereinafter). A shunt resistor 135 is connected in series to the DC voltage source 120. This resistor protects the switching elements 32 from excessive current.

[0039] Two sets of these switching elements 32 are connected in series to form upper and lower arms for each phase. In the example shown in FIG. 4 , the upper and lower arms for the U phase are formed by switching elements 32a and 32b, the V phase by switching elements 32c and 32d, and the W phase by switching elements 32e and 32f. The junctions of the upper and lower arms for each phase are connected to the motor 20. The gate driver circuit 132 receives a pulse-shaped drive signal (details of which will be described later) output by the PWM signal generator 14 shown in FIG. 1 and outputs drive signals 34a to 34f based on the pulse-shaped drive signal. The drive signals 34a to 34f can be generated using known techniques. For example, as shown in FIG. 5 , the drive signals can be generated based on the magnitude relationship between a triangular wave carrier signal and a voltage command value for each phase. In the inverter module 131, the switching of each switching element 32 is controlled based on the drive signals 34a to 34f.

[0040] Depending on the switching state of the upper and lower arms, the voltage of each phase of the inverter 30 becomes either a DC voltage Edc or zero voltage. In the inverter 30, switching is performed at a frequency that is sufficiently higher than the frequency of the AC voltage appearing at the motor 20, so the output voltage of each phase of the inverter 30 can be freely adjusted by changing the switching ratio (switching duty) of the upper and lower arms. In other words, a three-phase AC voltage of any frequency can be applied to the electric motor 20, thereby enabling variable speed drive and torque control of the electric motor 20.

[0041] <Current detection unit 50> The current detection unit 50 detects the current flowing in the U-phase and W-phase of the three-phase AC current flowing from the inverter 30 to the electric motor (PM motor) 20, and outputs the results as AC current detection values ​​Iu and Iw. Of course, it is possible to detect the AC current of all phases, but according to Kirchhoff's first law, if two of the three phases can be detected, the current of the remaining phase can be calculated from the detected two phases. A current detection means 50 such as a CT (current transformer) can be provided on the lower arm of the inverter module 131.

[0042] The current detection unit 50 may employ, for example, a phase shunt current method in which a shunt resistor is added to the lower arm of the inverter module 131 instead of a CT, and the current of each phase flowing through the inverter 30 is detected from the current flowing through the shunt resistor. Instead of or in addition to the current detection unit 50, a single shunt current detection method may be employed in which the current on the AC side of the inverter 30 is detected from the DC current flowing through a shunt resistor 135 added to the DC side of the inverter 30. The single shunt current detection method utilizes the fact that the current flowing through the shunt resistor 135 changes over time depending on the conduction state of the switching elements 32a to 32f that make up the inverter 30.

[0043] <Method of Driving PM Motor 20> When driving a motor having permanent magnets 27 in rotor 22, maximum torque can be obtained with minimum current by generating magnetic flux from winding 25 at a position 90 electrical degrees ahead in the direction of rotation of the magnetic flux from permanent magnet 27. Driving in this manner not only makes it possible to reduce the size and weight of the motor, but also has the effect of enabling the inverter 30 to be made smaller.

[0044] The aforementioned d-axis and q-axis can be thought of as the magnet flux axis and the winding flux axis, respectively, and it is particularly important to appropriately control the current on the q-axis. Separating the current flowing through the motor into a field component and a torque component on the rotating coordinate axes and controlling the voltage phase and magnitude to control the motor's rotational speed or torque is generally called vector control. The PM motor 20 is driven by control on the d- and q-axes, but known coordinate transformation techniques can be used to convert from the three-phase UVW axes to the d- and q-axes.

[0045] An example of the configuration of the voltage command value calculation unit 12 is shown in 12a of Fig. 6. The voltage command value calculation unit 12a in Fig. 6 receives the d-axis current command value Id* and the q-axis current command value Iq* calculated by the current command value calculation unit 11 and the motor electrical angular velocity ωe as input, and performs vector calculations as shown in equations (1) and (2) to obtain a d-axis voltage command value Vd* and a q-axis voltage command value Vq*.

[0046] Vd* = R x Id** - ωe x Lq x Iqf** (1) Vq* = R x Iq** + ωe x Ld x Idf** + ωe x Φd0 (2) In equations (1) and (2), R is the winding resistance per phase of the PM motor 20, Ld is the d-axis inductance, Lq is the q-axis inductance, and Φd0 is the magnet magnetic flux. Φd0 is also called the induced voltage constant.

[0047] To ensure that the d-axis and q-axis currents flow as commanded, the configuration of Fig. 6 uses a d-axis current control unit 114a and a q-axis current control unit 114b. In the circuit configuration of Fig. 6, reference numerals 91d to 91f denote subtractors that calculate the difference between the current command values ​​(Id* and Iq*) and their detected values ​​(Idc and Idc), reference numerals 92c to 92k denote proportional circuits that add a predetermined gain to the difference, reference numerals 94c and 94d denote integrators, and reference numerals 90b to 90d denote adders that add the proportional and integral components to calculate the proportional-integral value. The outputs from these adders are the d-axis and q-axis current command values ​​(Id** and Iq**).

[0048] Id** and Iq** are multiplied by the winding resistance value R per phase of the PM motor 20 in multipliers 92g and 92i to obtain the first terms on the right-hand sides of equations (1) and (2).

[0049] The d-axis and q-axis current command values ​​(Idf** and Iqf**) in the second terms on the right-hand sides of equations (1) and (2) are values ​​obtained by filtering the q-axis and d-axis current command values ​​(Iq** and Id**) using filter circuits 98a and 98b in FIG. 6. Multipliers 92h and 92j multiply Idf** and Iqf** by the q-axis inductance Lq and the d-axis inductance Ld, respectively, and also by the motor electrical angular velocity ωe to obtain the second terms on the right-hand sides of equations (1) and (2). Furthermore, multiplier 92k multiplies the motor electrical angular velocity ωe by the magnet magnetic flux Φd0 to obtain the third term on the right-hand side of equation (2).

[0050] A subtractor 91f subtracts the output of the multiplier 92h from the output of the multiplier 92g to obtain a d-axis voltage command value Vd* of the equation (1). An adder 90d obtains the sum of the outputs of the multipliers 92i, 92j, and 92k to obtain a q-axis voltage command value Vq* of the equation (2).

[0051] 6 is characterized in that a d current control section 114a and a q current control section 114b are connected in series to the voltage calculation in a voltage command value calculation section 12a, and that there are first-order lag filters (low-pass filters) 98a and 98b having a cutoff frequency equivalent to the electrical time constant of the motor 20. These establish an inverse model of the motor 20, which has the effect of realizing ideal vector control even when the calculation cycle of the control section 10 is restricted.

[0052] The d-axis harmonic current superimposing unit 121 in the voltage command value calculation unit 12 will be described later.

[0053] <Challenges in Improving Torque Precision> The motor control device 100 controls the rotation speed or torque of the PM motor 20 to a desired value, but when driving the PM motor 20, if the temperature of the magnet changes, the magnetic flux changes in response to the temperature, and therefore there is a problem that torque precision will deteriorate unless some kind of response is taken.

[0054] If the magnet temperature can be measured, it is possible to improve torque accuracy by adjusting the current command value based on the temperature. However, directly connecting a temperature sensor to the magnet inside the rotor is difficult due to issues with durability and productivity. Therefore, estimating the magnet temperature is an effective solution.

[0055] A particularly useful method when the motor is stopped or rotating at low speed is to apply a harmonic voltage to the motor and superimpose a harmonic current, estimate the inductance from the harmonic voltage and superimposed harmonic current, and then estimate the magnet temperature from the relationship between magnet temperature and inductance. However, errors in the inverter's voltage sensor will cause errors in the applied harmonic voltage. Similarly, errors in the inverter's current sensor will cause errors in the measured harmonic current. Therefore, if there are errors in the voltage sensor or current sensor, errors will occur in the estimated inductance. Because the change in inductance relative to magnet temperature is small, errors in the estimated inductance will result in a large error in the magnet temperature estimation.

[0056] Therefore, there is a strong need to reduce the influence of voltage sensor errors and current sensor errors in magnet temperature estimation.

[0057] <Objective of First Embodiment> The objective of the first embodiment is to calculate a magnet temperature estimate with reduced influence of sensor errors by calculating a first d-axis inductance when the harmonic current is in a first predetermined range and a second d-axis inductance when the harmonic current is in a second predetermined range during harmonic current superposition operation for the purpose of estimating magnet temperature or magnet flux, and by calculating a magnet temperature estimate based on the first d-axis inductance and the second d-axis inductance, the influence of voltage sensor and current sensor errors appearing on the first d-axis inductance and the second d-axis inductance becomes the same.

[0058] 7 shows the configuration 12a of a voltage command value calculation unit including a d-axis harmonic current superimposing unit 121a. A d-axis harmonic current command value generation unit 123 generates a d-axis harmonic current command value Idh*, and the sum of the d-axis current command value id* and the d-axis harmonic current command value Idh* is input to a current control unit 122. The current control unit 122 controls the d-axis current detection value idc so that it is always equal to the sum of the d-axis current command value id* and the d-axis harmonic current command value Idh*.

[0059] The d-axis harmonic current command value generator 123 performs a superimposing operation to change the d-axis harmonic current command value Idh* so that it passes through a first predetermined range at least once and a second predetermined range at least once. A first d-axis inductance calculator 40 and a second d-axis inductance calculator 41 (described later) calculate d-axis inductance estimates based on the d-axis current values ​​in the first and second predetermined ranges, respectively. Therefore, as long as the d-axis current passes through the first and second predetermined ranges, the waveform pattern of the d-axis harmonic current command value Idh* may have any shape.

[0060] 8A is a diagram showing an example of the waveform of the d-axis harmonic current command value Idh*. In FIG. 8A, the 1-2 predetermined value is greater than the upper limit of the first predetermined range, and the 1-1 predetermined value is less than the lower limit of the first predetermined range. Also, the 2-2 predetermined value is greater than the upper limit of the second predetermined range, and the 2-1 predetermined value is less than the lower limit of the second predetermined range.

[0061] In this example, the d-axis harmonic current command value generator 123 repeats the superimposition operation of the first predetermined range N times (N: an integer equal to or greater than 1), changing the current from a 1-1 predetermined value, which is equal to or less than the lower limit of the first predetermined range, to a 1-2 predetermined value, which is equal to or greater than the upper limit of the first predetermined range, and then changing it back to the 1-1 predetermined value. Then, the superimposition operation of the second predetermined range is repeated M times (M: an integer equal to or greater than 1), changing the current to a 2-1 predetermined value, which is equal to or less than the lower limit of the second predetermined range, changing it from the 2-1 predetermined value to a 2-2 predetermined value, which is equal to or greater than the upper limit of the second predetermined range, and then changing it back to the 2-1 predetermined value. The example shown in FIG. 8A shows an example waveform when N=3 and M=3.

[0062] A superposition pause period may be provided between the N repetitions of the superposition operation in the first predetermined range and the M repetitions of the superposition operation in the second predetermined range, during which the superposition operation is not performed consecutively and the d-axis harmonic current command value Idh* is kept constant.Furthermore, a superposition pause period may be provided between the superposition operation in the first predetermined range and the superposition operation in the second predetermined range, during which the d-axis harmonic current command value Idh* is kept constant.

[0063] Furthermore, after the overlapping operation in the first predetermined range and the overlapping operation in the second predetermined range are completed, the overlapping operation in the first predetermined range and the overlapping operation in the second predetermined range may be repeatedly performed.

[0064] 8B shows another example of the waveform of the d-axis harmonic current command value Idh*, where the number of repetitions N of the superimposition operation in the first predetermined range is 1, the number of repetitions M of the superimposition operation in the second predetermined range is 1, and after the superimposition operations in the first predetermined range and the second predetermined range are completed, the superimposition operations in the first predetermined range and the second predetermined range are repeatedly performed.

[0065] 8C is a diagram showing yet another example waveform of the d-axis harmonic current command value Idh*, in which the upper and lower limit values ​​of the first predetermined range are positive current values, and the upper and lower limit values ​​of the second predetermined range are negative current values.

[0066] Fig. 8D is a diagram showing yet another example waveform of the d-axis harmonic current command value Idh*, in which the first-1 predetermined value and the second-2 predetermined value are set to 0. In other words, the upper and lower limit values ​​of the first predetermined range are positive current values, and the upper and lower limit values ​​of the second predetermined range are negative current values. Even if the first predetermined range and the second predetermined range have a positive / negative relationship as shown in Fig. 8D, the same effect as the example shown in Fig. 8A can be obtained.

[0067] The configuration of the voltage command value calculation unit 12a shown in Fig. 7 is an example of a configuration in which a harmonic current command value is added to a current command value. In contrast, the configuration of a voltage command value calculation unit 12b, which adds a harmonic voltage command value to a voltage command value, is shown in Fig. 9.

[0068] In FIG. 9 , the d-axis harmonic voltage command value generating unit 124 outputs a positive voltage when increasing the d-axis current and outputs a negative voltage when decreasing the d-axis current, thereby superimposing a d-axis current similar to the examples shown in FIGS. 8A, 8B, 8C, and 8D.

[0069] The configuration 12b of the voltage command value calculation unit is not affected by the delay in the response of the current detection value to the current command value by the current control unit 122. The configuration 12a, which adds the harmonic current command value to the current command value, requires a waiting time until the current detection value follows the current command value when harmonic superposition starts and ends. In contrast, the configuration 12b makes it possible to shorten the time required to start and end the harmonic superposition operation.

[0070] The larger the first and second predetermined ranges are, the larger the harmonic current amplitude becomes, and therefore the first d-axis inductance estimated value and the second d-axis inductance estimated value described below can be calculated with high accuracy while minimizing the influence of disturbances such as noise. The larger the harmonic current amplitude, the greater the noise and vibration generated during harmonic current superposition operation. Since the noise and vibration are unpleasant to people in the vicinity and may cause failure of the motor control device and its peripheral devices, the first and second predetermined ranges are determined taking into consideration the relationship between the calculation accuracy of the first d-axis inductance estimated value and the second d-axis inductance estimated value and the generated noise and vibration.

[0071] The smaller the difference between the 1-1 predetermined value and the lower limit of the first predetermined range, the greater the proportion of the first predetermined range relative to the difference between the 1-2 predetermined value and the 1-1 predetermined value, which is the overall harmonic current amplitude when calculating the first d-axis inductance. By reducing the difference between the 1-1 predetermined value and the lower limit of the first predetermined range, noise and vibrations generated during harmonic current superposition operation can be suppressed. On the other hand, increasing the difference between the 1-1 predetermined value and the lower limit of the first predetermined range can ease the required accuracy of the measurement timing of the current sensor 50. The difference between the 1-1 predetermined value and the lower limit of the first predetermined range is determined taking into account the noise and vibrations generated during harmonic current superposition operation and the required accuracy of the measurement timing of the current sensor 50. Similarly, the differences between the 1-2 predetermined value and the upper limit of the first predetermined range, the difference between the 2-1 predetermined value and the lower limit of the second predetermined range, and the difference between the 2-2 predetermined value and the upper limit of the second predetermined range are also determined taking into account the noise and vibrations generated during harmonic current superposition operation and the required accuracy of the measurement timing of the current sensor 50.

[0072] The period from when the d-axis harmonic current changes from the 1-1 predetermined value to the 1-2 predetermined value and then returns to the 1-1 predetermined value is the harmonic current period during calculation of the first d-axis inductance. The smaller the harmonic current period, the larger the d-axis voltage amplitude when the harmonic current is superimposed, and the first d-axis inductance estimate value (described below) can be calculated with high accuracy while minimizing the influence of disturbances such as noise. However, due to the switching frequency of the inverter 30 and the measurement period of the current sensor 50, there is a lower limit to the harmonic current period at which superposition and current measurement are possible. The harmonic current period is determined taking into account the calculation accuracy of the first d-axis inductance estimate value, the switching frequency of the inverter 30, and the measurement period of the current sensor 50. Similarly, the period from when the d-axis harmonic current changes from the 2-1 predetermined value to the 2-2 predetermined value and then when it returns to the 2-1 predetermined value is the harmonic current period when the second d-axis inductance is calculated, and is determined taking into consideration the calculation accuracy of the second d-axis inductance estimate value, the switching frequency of the inverter 30, and the measurement period of the current sensor 50.

[0073] <Operation of the first d-axis inductance calculation unit 40 and the second d-axis inductance calculation unit 41> The relationship between the d-axis voltage command value vd*, the motor resistance value R, the d-axis current value detection value idc, the q-axis current value detection value iqc, the d-axis inductance Ld, the q-axis inductance Lq, and the electrical angular velocity ωe can be expressed by the following equation (3).

[0074] Vd*=R×idc+Ld×didc / dt−ωe×Lq×iqc (3) The d-axis inductance estimated value Ld_est is calculated by the following equation (4) based on equation (3).

[0075] Ld_est = (Vd* - R × idc + ωe × Lq × iqc) / (didc / dt) (4) Here, the slope (didc / dt) of the detected d-axis current is calculated from the slope of the detected d-axis current Idc as it changes within a predetermined current range. The first d-axis inductance calculator 40 determines the predetermined current range for calculating the slope (didc / dt) of the detected d-axis current Idc as the first predetermined range, and the second d-axis inductance calculator 41 determines the second predetermined range. Furthermore, the q-axis inductance Lq is stored as a design value, an actual measurement value, or a value calculated by electromagnetic field simulation, and is used during inductance estimation.

[0076] When the PM motor 20 is running at a low speed or is stopped and the electrical angular velocity ωe is approximately zero, or when the motor torque is approximately zero and the detected q-axis current value iqc is approximately zero, equation (4) can be simplified to the following equation (5).

[0077] Ld_est = (Vd* - R × idc) / (didc / dt) (5) Therefore, when the PM motor 20 is at a low speed or stopped and the electrical angular velocity ωe is approximately zero, or when the motor torque is approximately zero and the q-axis current detection value iqc is approximately zero, the first d-axis inductance calculation unit 40 and the second d-axis inductance calculation unit 41 do not receive the q-axis current detection value iqc or the electrical angular velocity ωe as input, and there is no need to store ωeLq, and it is possible to calculate the d-axis inductance estimate value from the d-axis voltage command value vd* and the d-axis current detection value idc.

[0078] The first d-axis inductance calculator 40 calculates the first d-axis inductance estimate Ld_est1 from the d-axis voltage command value vd*, the d-axis current detection value idc, the q-axis current detection value iqc, and the electrical angular velocity ωe during a period when the d-axis harmonic current calculator 121 is performing the superposition operation and the d-axis current is within a first predetermined range. The first d-axis inductance calculator 40 calculates the first d-axis inductance estimate Ld_est1 from the slope of the change from the lower limit value of the first predetermined range to the upper limit value of the first predetermined range, or from the upper limit value of the first predetermined range to the lower limit value of the first predetermined range. In this case, the slope of a partial section between the lower limit value of the first predetermined range and the upper limit value of the first predetermined range may be used instead of the slope of the entire range between the lower limit value of the first predetermined range and the upper limit value of the first predetermined range.

[0079] When the d-axis current detection value i dc is within the first predetermined range, the d-axis voltage command value vd* is Vd1*, the d-axis current detection value is Id1, and the gradient didc / dt of the d-axis current detection value is G1, then the first d-axis inductance estimate value Ld_est1 is given by the following equation (6) using equation (5).

[0080] Ld_est1=(Vd1*-R×Id1) / G1 (6) The second d-axis inductance calculation unit 41 calculates the estimated value Ld_est2 of the second d-axis inductance from the d-axis voltage command value vd*, the d-axis current detection value idc, the q-axis current detection value iqc, and the electrical angular velocity ωe during the period when the d-axis harmonic current superposition unit 121 is performing the superposition operation and the d-axis current is within a second predetermined range.

[0081] The second d-axis inductance calculator 41 calculates the second d-axis inductance from the slope of the change from the lower limit of the second predetermined range to the upper limit of the second predetermined range, or from the upper limit of the second predetermined range to the lower limit of the second predetermined range. Here, the slope of a partial section between the lower limit of the second predetermined range and the upper limit of the second predetermined range may be used, rather than the slope of the entire range between the lower limit of the second predetermined range and the upper limit of the second predetermined range. When the d-axis current detected value i dc is within the second predetermined range, the d-axis voltage command value is Vd2*, the d-axis current detected value is Id2, and the slope didc / dt of the d-axis current detected value is G2. Based on equation (5), the second d-axis inductance estimate Ld_est2 is expressed by the following equation (7).

[0082] Ld_est2=(Vd2*-R×Id2) / G2 (7) When an error exists in voltage sensor 70 and the detected voltage value is Kv times larger than the true voltage value of DC voltage source 120, the d-axis voltage applied to PM motor 20 becomes 1 / Kv times the d-axis voltage command value. Compared to when there is no error, the d-axis voltage becomes 1 / Kv times larger, and therefore the slopes G1 and G2 of the detected d-axis current values ​​also become 1 / Kv times larger.

[0083] Furthermore, if there is an error in the current sensor 50 and the measured value is Kc times larger than the true value, the detected d-axis current will be Kc times the d-axis current flowing through the PM motor 20. Compared to when there is no error, the detected d-axis current value idc is Kc times larger, and therefore the slopes G1 and G2 of the detected d-axis current value idc are also Kc times larger. Therefore, the slopes G1 and G2 are Kc / Kv due to the voltage sensor error and the current sensor error.

[0084] When a voltage sensor error and a current sensor error exist, if the first d-axis inductance estimated value is Ld_est1′ and the second d-axis inductance estimated value is Ld_est2′, the following equations (8-1) and (8-2) are obtained from equations (6) and (7).

[0085] Ld_est1' = Vd1 * / (Kc / Kv × G1) = Kv / Kc × Ld_est1 (8-1) Ld_est2' = Vd2 * / (Kc / Kv × G2) = Kv / Kc × Ld_est2 (8-2) Here, the resistance voltage drop R × Id is ignored because it is minute. From equations (8-1) and (8-2), when a voltage sensor error and a current sensor error exist, both the first d-axis inductance estimated value and the second d-axis inductance estimated value will be Kv / Kc times the value when there are no errors.

[0086] <Operation of magnet temperature calculation unit 42> The magnet temperature calculation unit 42 calculates the magnet temperature estimate from the ratio between the first d-axis inductance estimate and the second d-axis inductance estimate. As the magnet temperature rises, the magnet magnetic flux decreases, and the magnetic flux density inside the motor decreases. This alleviates magnetic saturation inside the motor, and the d-axis inductance increases. By using this relationship, the magnet temperature is estimated from the d-axis inductance estimate.

[0087] An example of the relationship between the d-axis inductance estimate value and the magnet temperature is shown in Fig. 10. In order to focus on the tendency of the d-axis inductance estimate value to change with temperature, in Fig. 10, the first d-axis inductance estimate value and the second d-axis inductance estimate value at the reference temperature are normalized to 1.

[0088] The change in the estimated d-axis inductance value with respect to the magnet temperature is affected by the magnetic flux density inside the motor, and therefore differs depending on the current range when calculating the estimated d-axis inductance value. Figure 10 shows an example in which the temperature change rate of the first estimated d-axis inductance value is greater than that of the second estimated d-axis inductance value.

[0089] It is possible to estimate the magnet temperature using only the estimated d-axis inductance value calculated in one current range. However, if there is a voltage sensor error and a current sensor error, the estimated d-axis inductance value will be multiplied by Kv / Kc, resulting in an error in the estimated magnet temperature value.

[0090] In contrast, by using the first d-axis inductance estimated value and the second d-axis inductance estimated value, the influence of voltage sensor error and current sensor error on the magnet temperature estimated value can be reduced. With only one d-axis inductance estimated value, it is not possible to distinguish whether a change in the d-axis inductance estimated value is due to a change in magnet temperature or a sensor error. By using the first d-axis inductance estimated value and the second d-axis inductance estimated value, which have different temperature change rates, it is possible to distinguish whether a change in the d-axis inductance estimated value is due to a change in magnet temperature or a sensor error.

[0091] 11 shows a configuration example of the magnet temperature calculation unit 42. This is a configuration example that uses the ratio between the first d-axis inductance estimate value and the second d-axis inductance estimate value. A divider 421 calculates the first / second d-axis inductance ratio, which is the ratio between the first d-axis inductance estimate value and the second d-axis inductance estimate value.

[0092] An example of the relationship between the ratio of the first d-axis inductance to the second d-axis inductance and the magnet temperature is shown in Fig. 12. The rate of change of the ratio of the first d-axis inductance to the second d-axis inductance with respect to the magnet temperature is, by approximation, the difference between the rates of change of the estimated first d-axis inductance and the estimated second d-axis inductance with respect to the magnet temperature.

[0093] Therefore, if the rates of change of the first d-axis inductance estimate and the second d-axis inductance estimate with respect to magnet temperature are different, the first / second d-axis inductance ratio will change according to the magnet temperature, and it will be possible to estimate the magnet temperature from the first / second d-axis inductance ratio.

[0094] The inductance ratio magnet temperature conversion unit 422 calculates a magnet temperature estimation value using the ratio between the first d-axis inductance and the second d-axis inductance as input. The inductance ratio magnet temperature conversion unit 422 can be configured to measure or calculate by electromagnetic field simulation the magnet temperature versus the ratio between the first d-axis inductance and the second d-axis inductance, store the calculated value, and create a table of magnet temperature estimation values ​​using the ratio between the first d-axis inductance and the second d-axis inductance as a parameter for use during estimation. Alternatively, the relationship between the magnet temperature versus the ratio between the first d-axis inductance and the second d-axis inductance may be expressed as a mathematical formula, which is used during estimation.

[0095] When there is a voltage sensor error and a current sensor error, the ratio between the first d-axis inductance and the second d-axis inductance is given by the following equation (9).

[0096] Ld_est1' / Ld_est2' = Kv / Kc × Ld_est1 / (Kv / Kc × Ld_est2) = Ld_est1 / Ld_est2 (9) From equation (9), the ratio Ld_est1' / Ld_est2' between the first d-axis inductance and the second d-axis inductance when there is a voltage sensor error and a current sensor error is the same as the ratio Ld_est1 / Ld_est2 between the first d-axis inductance and the second d-axis inductance when there is no sensor error.

[0097] This reduces the influence of voltage sensor error and voltage sensor error that appears in the magnet temperature estimate.

[0098] Another example of the configuration of the magnet temperature calculation unit 42 is to calculate and store the relationship between the magnet temperature and the first d-axis inductance estimate value or the second d-axis inductance estimate value by measurement or electromagnetic field simulation, and to create a table of magnet temperature estimate values ​​using the first d-axis inductance estimate value and the second d-axis inductance estimate value as parameters for use during estimation. Alternatively, the relationship between the magnet temperature and the first d-axis inductance estimate value and the second d-axis inductance estimate value may be expressed as a mathematical formula and used during estimation.

[0099] FIG. 13 shows an example of a magnet temperature estimate table using the first d-axis inductance estimate and the second d-axis inductance estimate as parameters. The magnet temperature estimate (unit: °C) corresponding to the input parameters, the first d-axis inductance estimate and the second d-axis inductance estimate, are represented by contour lines. One method for creating the table involves varying the magnet temperature, voltage sensor error, and current sensor error within the ranges expected by the motor control device, calculating the first d-axis inductance estimate and the second d-axis inductance estimate through measurement or circuit / electromagnetic field simulation, and saving the results as a table. The minimum and maximum values ​​of the change in the first d-axis inductance estimate when the magnet temperature, voltage sensor error, and current sensor error change correspond to Ld1_min and Ld1_max in FIG. 13. Similarly, the minimum and maximum values ​​of the change in the second d-axis inductance estimate correspond to Ld2_min and Ld2_max in Figure A1. During estimation, even if there is a voltage sensor error or a current sensor error, the table stores the relationship between the magnet temperature and the first d-axis inductance estimated value and the second d-axis inductance estimated value after changes due to the voltage sensor error and the current sensor error, so the influence of the voltage sensor error and the current sensor error appearing in the magnet temperature estimated value can be reduced. In the first embodiment, it is sufficient that the magnet temperature estimated value can be calculated from the first d-axis inductance estimated value and the second d-axis inductance estimated value, and the calculation method is not important.

[0100] <Effects of Example 1> Fig. 14A shows the magnet temperature estimation error relative to the voltage sensor error and the current sensor error when the magnet temperature is estimated from the first d-axis inductance estimate value and when the magnet temperature is estimated from the first / second d-axis inductance ratio. Fig. 14B also shows the magnet temperature estimation error relative to the voltage sensor error and the current sensor error when the magnet temperature is estimated from the ratio between the first d-axis inductance estimate value and the second d-axis inductance estimate value. The magnet temperature estimation error (unit: °C) relative to the voltage sensor error and the current sensor error is shown by contour lines.

[0101] 14A, a large estimated temperature error occurs due to the voltage sensor error and the current sensor error. A voltage sensor error of +5% and a current sensor error of -5% results in an estimated temperature error of +50°C.

[0102] When estimating the magnet temperature from the ratio between the first d-axis inductance estimate and the second d-axis inductance estimate shown in Figure 14B, the estimated temperature error is within ±4°C compared to the voltage sensor error of ±5% and the current sensor error, making it possible to significantly reduce the impact of sensor errors.

[0103] In other words, according to the first embodiment of the present invention, it is possible to provide a motor control device and a motor control method that can reduce the influence of errors on the estimated value due to voltage sensor errors and current sensor errors when estimating the magnet temperature.

[0104] (Embodiment 2) Next, embodiment 2 will be described. The configuration of embodiment 2 can be the same as embodiment 1 except for the following points. Embodiment 2 relates to the d-axis harmonic current superimposing unit 121 and the magnet temperature calculation unit 42.

[0105] Since the ratio between the first d-axis inductance and the second d-axis inductance varies for each calculation due to the influence of noise, in order to reduce the estimated temperature variation, it is desirable that the rate of change of the ratio between the first d-axis inductance and the second d-axis inductance with respect to the magnet temperature of the PM motor 20 is large.

[0106] For this reason, it is necessary to increase the difference in the rate of change of the first d-axis inductance estimated value and the second d-axis inductance estimated value relative to the magnet temperature.

[0107] Figure 15 shows an example of the relationship between the rate of change of the estimated d-axis inductance per 10°C of magnet temperature and the average value of the specified d-axis current range when the estimated d-axis inductance is calculated. The average value of the specified d-axis current range is the average of the upper limit value and the lower limit value of the specified d-axis current range. The rate of change of the estimated d-axis inductance with temperature varies depending on the average value of the specified d-axis current range when the estimated d-axis inductance is calculated. Although characteristics differ depending on the motor structure, Figure 15 shows an example of a motor that exhibits small characteristics in the negative d-axis current range and large characteristics in the positive d-axis current range.

[0108] FIG. 16A shows an example of setting the first and second predetermined range average values. The first predetermined range average value is the average of the two values: the upper limit value of the first predetermined range and the lower limit value of the first predetermined range. The second predetermined range average value is the average of the two values: the upper limit value of the second predetermined range and the lower limit value of the second predetermined range. The rate of change of the ratio of the first d-axis inductance to the second d-axis inductance with respect to magnet temperature is preferably 1% or more per 10°C change in magnet temperature. This value is equal in magnitude to the rate of change of the magnetic flux of a neodymium magnet with temperature, which is approximately -1% per 10°C. One method for estimating magnet temperature during motor rotation uses the temperature change of magnet flux. To maintain the same level of estimated temperature variation due to noise, the temperature change rate of the physical property values ​​used to estimate magnet temperature must also be similar.

[0109] 16A is the rate of change of the ratio of the first d-axis inductance to the second d-axis inductance with respect to the magnet temperature, the first and second predetermined ranges are determined so that this is 1% or more per 10° C. In other words, the first and second predetermined ranges are set so that the difference between the rate of change of the first d-axis inductance estimated value Ld_est1 with respect to the magnet temperature or rotor temperature of the motor 20 and the rate of change of the second d-axis inductance estimated value Ld_est2 with respect to the magnet temperature or rotor temperature is 1% or more per 10° C.

[0110] Another example of setting the first and second predetermined range average values ​​is shown in Figure 16B. Figure 16B shows a case where the first predetermined range average value is positive and the second predetermined range average value is negative. In the setting example shown in Figure 16B, if the temperature change rate difference is set to 1% or more per 10°C, as in Figure 16A, the absolute values ​​of the first and second predetermined range average values ​​can be made smaller than in the case of Figure 16A.

[0111] Note that the temperature range of the magnet temperature or rotor temperature when calculating the rate of change of the estimated values ​​of the first d-axis inductance and the second d-axis inductance and the difference between each rate of change are not limited to 1% per 10°C as described above; the predetermined difference value for a predetermined temperature range may be, for example, 2% per 20°C or 3% per 30°C. If the predetermined temperature range is A x 10°C (A: real number greater than 0), the predetermined difference value may be A x 1%. In these examples, when the predetermined temperature is converted to 10°C, the predetermined difference value becomes 1%.

[0112] Therefore, according to the second embodiment, the same effect as that of the first embodiment can be obtained, and compared to the first embodiment, the amplitude of the superimposed harmonic current can be further reduced, which makes it possible to reduce the power consumption during superimposition and the vibration noise generated by the superimposed harmonic current.

[0113] The present invention is not limited to the above-described embodiment, and includes various modifications. For example, the above-described embodiment has been described in detail to clearly explain the present invention, and the present invention is not necessarily limited to an embodiment having all of the described configurations.

[0114] Furthermore, the above-described configurations, functions, processing units, processing procedures, etc. may be partly or entirely realized in hardware, for example, by designing them as integrated circuits, etc. Furthermore, the above-described configurations, functions, etc. may be realized in software, by a processor interpreting and executing a program that realizes each function.

[0115] Furthermore, the signal lines and information lines shown are those considered necessary for explanation, and do not necessarily represent all control lines and information lines. Furthermore, the above-mentioned configurations, functions, processing units, processing procedures, etc. do not necessarily need to be located in the same physical location; for example, some may be located on a network or in the cloud via communication, etc.

[0116] Also, while the motor has been described as having an inner rotor structure with the rotor placed inside the stator, it can of course also have an outer rotor structure. It also does not matter whether it is a radial gap motor or an axial gap motor. In addition to PMSM, a synchronous motor or SRM with a magnet can also be used.

[0117] DESCRIPTION OF SYMBOLS 10...Control unit, 11...Current command value calculation unit, 12...Voltage command value calculation unit, 13...Coordinate conversion unit, 14...PWM signal generation unit, 15...Angular velocity calculation unit, 16...Torque command value limiting unit, 17...d-axis voltage command value limiting unit, 18...q-axis current command value limiting unit, 20...Electric motor (PM motor), 27...Permanent magnet, 30...Inverter, 40...First d-axis inductance calculation unit, 41...Second d-axis inductance calculation unit, 42...Magnet temperature calculation unit, 50...Current detection unit, 70...Voltage sensor, 100...Motor control device, 114a...d-axis current control unit, 114b...q-axis current control unit, 121...d-axis harmonic current superposition unit, 122...Current control unit, 123...d-axis harmonic current command value generation unit, 124...d-axis harmonic voltage command value generation unit

Claims

1. A motor control device that drives a motor using an inverter, comprising: a d-axis harmonic current superimposition unit that superimposes harmonic current on a d-axis current; a first d-axis inductance calculation unit that calculates an estimated value of a first d-axis inductance based on the d-axis harmonic current when the d-axis harmonic current on which the harmonic current is superimposed is within a first predetermined range; a second d-axis inductance calculation unit that calculates an estimated value of a second d-axis inductance based on the d-axis harmonic current when the d-axis harmonic current is within a second predetermined range; and a magnet temperature calculation unit that calculates an estimated value of a magnet temperature of the motor based on the estimated value of the first d-axis inductance and the estimated value of the second d-axis inductance.

2. A motor control device according to claim 1, wherein the first d-axis inductance calculation unit and the second d-axis inductance calculation unit set the first predetermined range and the second predetermined range so that the difference between the rate of change of the estimated value of the first d-axis inductance over a predetermined temperature range of the magnet temperature or rotor temperature of the motor and the rate of change of the estimated value of the second d-axis inductance over a predetermined temperature range of the magnet temperature or rotor temperature is equal to or greater than a predetermined value.

3. A motor control device according to claim 1 or 2, wherein the d-axis harmonic current superimposing unit repeats a superimposing operation N times (N is an integer of 1 or more) of changing the d-axis harmonic current from a 1-1 predetermined value that is equal to or less than the lower limit of the first predetermined range to a 1-2 predetermined value that is equal to or greater than the upper limit of the first predetermined range, and then changing it back to the 1-1 predetermined value; and thereafter repeats a superimposing operation M times (M is an integer of 1 or more) of changing the d-axis harmonic current from a 2-1 predetermined value that is equal to or less than the lower limit of the second predetermined range to a 2-2 predetermined value that is equal to or greater than the upper limit of the second predetermined range, and then changing it back to the 2-1 predetermined value.

4. A motor control device according to claim 1 or claim 2, characterized in that the magnet temperature calculation unit calculates the magnet temperature estimate based on the ratio between the estimated value of the first d-axis inductance and the estimated value of the second d-axis inductance.

5. A motor control device according to claim 3, wherein the upper and lower limit values ​​of the first predetermined range are positive current values, and the upper and lower limit values ​​of the second predetermined range are negative current values.

6. A motor control device according to claim 3, wherein the first-1 predetermined value and the second-2 predetermined value are both zero.

7. A motor control device as claimed in claim 1, characterized in that the first predetermined range and the second predetermined range are determined based on the relationship between the calculation accuracy of the estimated value of the first d-axis inductance and the estimated value of the second d-axis inductance and the generated sound and vibration.

8. A motor control method for driving a motor using an inverter, comprising: superimposing a harmonic current on a d-axis current; calculating an estimated value of a first d-axis inductance based on the d-axis harmonic current when the d-axis harmonic current on which the harmonic current is superimposed is within a first predetermined range; calculating an estimated value of a second d-axis inductance based on the d-axis harmonic current when the d-axis harmonic current is within a second predetermined range; and calculating an estimated value of a magnet temperature of the motor based on the estimated value of the first d-axis inductance and the estimated value of the second d-axis inductance.

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