Motor control device

Abstract

To provide a motor control device capable of suppressing noise and vibration of a motor while estimating magnet temperature.SOLUTION: A motor control device 100 drives a motor (electric motor 20) by an inverter 30. A processor (control unit 10) of the motor control device 100 superimposes a d-axis harmonic current on a d-axis current (d-axis harmonic current superimposing unit 121), calculates a d-axis inductance estimation value based on the d-axis harmonic current (d-axis inductance estimating unit 40), and calculates a magnet temperature estimation value based on the d-axis inductance estimation value (magnet temperature estimating unit 41). The processor repeats superimposition operations in which the d-axis harmonic current is changed from a first predetermined value to a second predetermined value and then is changed back to the first predetermined value again N times (N is an integer equal to or greater than 2). In the processor, a maintenance period (superimposition stop period) indicating a period in which the d-axis harmonic current is maintained at the first predetermined value after at least each of the (N-1) th superimposition operations is provided.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a motor control device. [Background technology]

[0002] Patent Document 1 discloses a driving device for a permanent magnet synchronous motor that includes a superimposing unit that superimposes a voltage or current of a frequency different from the fundamental wave frequency 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. Patent Document 2 discloses a d-axis inductance equivalent value determining means, and an estimation method that calculates an estimate of the magnetic flux amount of a permanent magnet based on the inductance equivalent value. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2015-133891 A [Patent Document 2] Patent No. 6158115 Summary of the Invention [Problem to be solved by the invention]

[0004] Patent Document 1 discloses a drive 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 a 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.

[0005] Patent Document 2 discloses a determination means that includes a d-axis inductance equivalent value determination means, an estimation method for calculating an estimated value of the magnetic flux amount of a permanent magnet based on the inductance equivalent value, high-frequency voltage application means for applying a high-frequency voltage to the d-axis, and high-frequency current amplitude detection means for detecting 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.

[0006] The current with a frequency different from that of the fundamental wave that flows due to superposition in Patent Document 1 and the high-frequency current in Patent Document 2 generate sound and vibration at the superposition frequency, which is unpleasant for people around the motor control device, so there is a need to reduce the sound and vibration. However, Patent Documents 1 and 2 do not mention a method for reducing the sound and vibration that occurs when the current is superimposed. Therefore, it is believed that there is room for improvement.

[0007] An object of the present invention is to provide a motor control device that can suppress noise and vibration of the motor when estimating the magnet temperature. [Means for solving the problem]

[0008] In order to achieve the above-mentioned object, the present invention provides a motor control device that drives a motor using an inverter, and includes a processor that superimposes a d-axis harmonic current on a d-axis current, calculates a d-axis inductance estimate based on the d-axis harmonic current, and calculates a magnet temperature estimate based on the d-axis inductance estimate, wherein the processor repeats a superimposition operation N times (N: an integer of 2 or more) of changing the d-axis harmonic current from a first predetermined value to a second predetermined value and then changing it again to the first predetermined value, and provides a holding period indicating a period during which the d-axis harmonic current is kept at the first predetermined value after each of at least (N-1) superimposition operations. Effect of the Invention

[0009] According to the present invention, it is possible to suppress the noise and vibration of the motor when estimating the magnet temperature. Problems, configurations and effects other than those described above will become apparent from the following description of the embodiments. [Brief description of the drawings]

[0010] [Figure 1] 1 is a schematic diagram illustrating a motor control device according to a first embodiment of the present invention; [Diagram 2] FIG. 1 is a schematic diagram showing the structure of a PM motor. [Diagram 3] FIG. 2 is an explanatory diagram of coordinate axes. [Figure 4] FIG. 2 is a block diagram of a power conversion circuit and a current detection unit. [Diagram 5] 6 is a diagram illustrating a relationship between a PWM carrier signal and a voltage command value. [Figure 6] FIG. 2 is a diagram illustrating an example of a configuration of a voltage command value calculation unit. [Figure 7] FIG. 4 is a control block diagram of a configuration example of a d-axis harmonic current superimposing unit of the magnet temperature estimator in the first embodiment. [Figure 8A] 8 is a waveform example of a d-axis harmonic current command value in FIG. 7. [Figure 8B] 8 is another example of a waveform of the d-axis harmonic current command value in FIG. 7 . [Figure 9] FIG. 11 is a control block diagram of another configuration example of the d-axis harmonic current superimposing unit of the magnet temperature estimator in the first embodiment. [Figure 10] 10 is a waveform example of a d-axis current detection value and a d-axis harmonic voltage command value in FIG. 9 . [Figure 11] 13 is an example of the relationship between magnet temperature and an estimated d-axis inductance value. [Figure 12] 13 is an example of a frequency analysis result when a d-axis harmonic current is superimposed. [Figure 13] 13 is an example of a waveform of a detected d-axis current value in the configuration of the second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] The present disclosure relates to a motor control device, a magnet temperature estimator, and a drive device using them. In an embodiment of the present disclosure, for example, during a harmonic current superimposition operation for the purpose of estimating a magnet temperature or a magnet magnetic flux, after a superimposition stop period in which the harmonic current is kept at a predetermined value, a repetitive operation is performed in which the superimposition operation is repeated a predetermined number of times, and the superimposition stop period is changed for each repetitive operation, thereby reducing the peak value of the harmonic current spectrum by spectrum spreading, and reducing the sound and vibration of the generated superimposition frequency.

[0012] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Like elements are designated by like reference numerals, and the same description will not be repeated.

[0013] The various components of the present disclosure do not necessarily have to be independent entities, and it is permitted that multiple components are formed as a single member, that one component is formed from multiple members, that one component is a part of another component, that part of one component overlaps with part of another component, etc.

[0014] [Example 1] <Outline of the motor control device> 1 is a schematic diagram of a motor control device 100. The motor control device 100 includes a control unit 10 (processor), an electric motor (PM motor) 20, an inverter 30, a current detection unit 50, and an angle sensor 60 such as a resolver or an encoder. Although not shown, a mechanism for mechanically or magnetically transmitting mechanical output is connected to the electric motor 20, and the motor control device 100 controls the rotation speed or torque of the electric motor 20 to a desired value.

[0015] Although the embodiment of the present invention does not limit the operating principle of the electric motor 20, the following description will be given by taking an example in which the electric motor 20 is a permanent magnet synchronous motor (PMSM) having a permanent magnet in the rotor. Various types of electric motors are applicable as the electric motor 20, and the subject of this disclosure is an electric motor having a characteristic in which the magnetic flux of the permanent magnet changes depending on the temperature of the rotor.

[0016] Inverter 30 has a DC voltage source 120 (FIG. 4) such as a battery and 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 will be a pulsed voltage.

[0017] Using the well-known concept of pulse width modulation, the pulsed voltage can be regarded as an AC voltage. In pulse width modulation, the cycle at which the switching element is turned on and off, that is, the switching frequency, is generally set sufficiently high relative to the frequency of the equivalent AC voltage (corresponding to the rotation frequency of a single-phase motor in this case).

[0018] However, it is also possible to consider the fundamental wave component of the pulsed voltage. For example, when the switching frequency is close to, for example, about 1 to 3 times the rotation frequency of the PM motor, it can be considered that the fundamental wave component of the pulsed voltage is applied to the 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.

[0019] Note that instead of a DC voltage source, an AC power source may be converted to DC power by rectification, etc. Alternatively, a DC / DC converter may be used that controls a DC voltage source to a different voltage.

[0020] 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 d-axis inductance estimation unit 40, and a magnet temperature estimation unit 41. The voltage command value calculation unit 12 includes a d-axis harmonic current superposition unit 121. The coordinate conversion unit 13 receives as input a current detection value, which is information about a current flowing through the PM motor obtained by a current detection unit 50, and a motor electrical angle detection value obtained by an angle sensor 60, and converts from the three-phase UVW axes to 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.

[0021] Angular velocity calculation unit 15 receives the motor electrical angle detection value as input and outputs the electrical angular velocity. A voltage command value calculation unit 12 generates a d-axis voltage command value and a q-axis voltage command value based on the d-axis current command value and the q-axis current detection value and the electrical angular velocity output by current command value calculation unit 11 receiving the rotation speed command value or the torque command value as input. PWM signal generation unit 14 outputs a PWM signal that controls the on / off of the switching elements constituting inverter 30 based on the d-axis voltage command value and the q-axis voltage command value. In FIG. 1, the rotation speed command value and the torque command value are shown in control unit 10, but they may be obtained from, for example, a higher-level control system or another control system not shown.

[0022] In addition, the d-axis inductance estimator 40 receives the d-axis voltage command value, the d-axis current detection value, the q-axis current detection value, and the electrical angular velocity as input, and the magnet temperature estimator 41 receives the d-axis inductance estimated value as input, but there is no problem with a configuration in which only some of the values ​​are used instead of all of the values ​​being input.

[0023] <Example of electric motor structure> 2 is a diagram showing a schematic structure of an electric motor (PM motor) 20. The electric motor 20 is composed of a stator 21 and a rotor 22. The stator 21 has a plurality of stator poles 28 each having a winding (coil) 25 wound around a stator core (stator iron core) 26. The rotor 22 has a permanent magnet 27.

[0024] 2 shows an example in which the number of magnetic poles of the stator (also called the number of slots) 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 freely selected, and it does not matter if the numbers of magnetic poles of the stator and the rotor are not equal. Furthermore, it does not matter whether the multiple windings 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 electric motor 20 is described as being configured with three-phase windings.

[0025] When a current flows through the winding 25, the stator magnetic pole 28 generates magnetic poles in the manner of an electromagnet, and the polarity (N pole, S pole) can be changed depending on the direction of the current through the winding 25. In this specification, the rotation angle (rotation angle position) of the rotor 22 when the stator magnetic pole 28 becomes a S pole when a positive DC current flows through the winding 25 and attracts the N pole of the permanent magnet 27 of the rotor 22 is defined as zero degrees. Hereinafter, the rotation angle position of the rotor is expressed as the rotor position θd. When there are multiple windings 25, one of them is defined as the reference position. In this specification, the winding 25 on the right side of FIG. 2 (the winding closest to the description of the U phase) is described as the reference position. In this embodiment, the counterclockwise rotation direction of the rotor 22 is defined as positive rotation.

[0026] The processing in the motor control device 100 utilizes information on the rotor position θd of the rotor 22 of the electric motor 20, and the position information will be described as being detected by a resolver, an encoder, or the like as the angle sensor 60. Naturally, it may be configured to obtain the position information by position sensorless control using a position estimation means that outputs an estimated rotational angle position of the electric motor 20 from the current flowing through the electric motor 20 and the voltage applied to the electric motor 20.

[0027] <Explanation of coordinate axes> Here, the definition of the coordinate axes will be explained. Fig. 3 is a diagram showing the relationship between the rotor position θd and the phase of each winding 25 of the stator 21. The three-phase windings U, V, and W are arranged with a difference of 120 degrees in electrical angle. The d-axis is defined as the main magnetic flux direction of the permanent magnet provided in the rotor 22, and the dq-axis is defined as being composed of the q-axis that is electrically 90 degrees (electrical angle 90 degrees) ahead of the d-axis in the rotational direction. The dq-axis is a rotating coordinate system. The definition of the d-axis can be rephrased as the rotation angle position at which the magnetic flux of the permanent magnet 27 that links with the reference winding 25 is maximum.

[0028] <Inverter> Next, the configurations of the inverter 30 and the current detection unit 50 will be described with reference to the block diagram shown in FIG.

[0029] As shown in Fig. 4, inverter 30 has inverter module 131, DC voltage source 120, and gate driver circuit 132. Here, the output of DC voltage source 120 is DC voltage Edc. Inverter module 131 has switching elements 32a-32f (for example, semiconductor switching elements such as IGBT and MOS-FET) and a free wheel diode connected in parallel thereto. Switching elements 32a-32f are collectively referred to as "switching elements 32" (hereinafter the same). A shunt resistor 135 is connected in series to DC voltage source 120. This serves to protect switching elements 32 so that excessive current does not flow.

[0030] These switching elements 32 configure upper and lower arms of each phase by connecting two sets of switching elements 32 in series. In the example of Fig. 4, the upper and lower arms of the U phase are configured 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 connection point of the upper and lower arms of each phase is connected to the electric motor 20. The gate driver circuit 132 receives a pulse-shaped drive signal (described in detail later) output by the PWM signal generating unit 14 shown in Fig. 1, and outputs drive signals 34a to 34f based on the signal.

[0031] A known technique can be used to generate the drive signals, but for example, as shown in Fig. 5, the drive signals can be generated based on the magnitude relationship between the triangular wave carrier signal and the voltage command values ​​of the respective phases. In the inverter module 131, the switching of each switching element 32 is controlled based on these drive signals 34a to 34f.

[0032] Depending on the switching state of the upper and lower arms, the voltage of each phase of the inverter 30 becomes either the DC voltage Edc or zero voltage. In the inverter 30, since switching is performed at a frequency sufficiently higher than the frequency of the AC voltage appearing in the motor 20, 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. That is, a three-phase AC voltage of an arbitrary frequency can be applied to the motor 20, thereby enabling variable speed drive and torque control of the motor 20.

[0033] <Current detection unit 50> The current detection unit 50 detects the currents flowing in the U-phase and W-phase among the three-phase AC currents flowing from the inverter 30 to the motor 20, and outputs the results as AC current detection values Iu and Iw. Of course, it is also possible to detect the AC currents of all phases, but according to Kirchhoff's first law, if two of the three phases can be detected, the other one phase can be calculated from the two detected phases. A current detection unit 50 such as a CT (current transformer) can be provided on the lower arm of the inverter module 131.

[0034] As the current detection unit 50, for example, instead of a CT, a phase shunt current detection method can be adopted in which a shunt resistor is added to the lower arm of the inverter module 131, and the current flowing in the shunt resistor is used to detect the current of each phase flowing into the inverter 30. Instead of or in addition to the current detection unit 50, a single shunt current detection method can be adopted in which the current on the AC side of the inverter 30 is detected from the DC current flowing in the 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 in the shunt resistor 135 changes over time depending on the energization state of the switching element 32 constituting the inverter 30.

[0035] <Driving method of PM motor> 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 of the magnetic flux from permanent magnets 27 in the direction of rotation. Driving in this way not only makes it possible to reduce the size and weight of the motor, but also has the effect of making inverter 30 smaller.

[0036] The aforementioned d-axis and q-axis can also be said to be the magnet flux axis and the q-axis the winding flux axis, 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 axis, and controlling the phase and magnitude of the voltage to control the motor's rotation speed or torque, is generally called vector control. Note that while control is performed on the dq axes as a driving method for PM motors, known coordinate transformation techniques can be used to convert from the three-phase UVW axes to the dq axes.

[0037] 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 and q-axis current command values ​​(Id* and Iq*) calculated by the current command value calculation unit 11 and the motor electrical angular velocity ωe as input, and performs vector calculation as in equations (1) and (2) to obtain a d-axis voltage command value Vd* and a q-axis voltage command value Vq*.

[0038]

number

[0039]

number

[0040] In equations (1) and (2), R is the winding resistance value per phase of the 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.

[0041] In order to make the dq-axis currents flow as commanded, the configuration of d-axis current controller 114a and q-axis current controller 114b is used in Fig. 6. In the circuit configuration of Fig. 6, 91 is a subtractor that calculates the difference between the current command values ​​(Id* and Iq*) and their detected values ​​(Idc and Iqc), 92 is a proportional circuit that adds a predetermined gain to the difference, 94 is an integrator, and 90 is an adder that adds the proportional and integral components to calculate the proportional integral value. The output from this is the d-axis and q-axis current command values ​​(Id** and Iq**).

[0042] Id** and Iq** are multiplied by the winding resistance value R per phase of the motor 20 in multipliers 92g and 92i to obtain the first terms on the right-hand sides of equations (1) and (2).

[0043] The d-axis and q-axis current command values ​​(Idf** and Iqf**) in the second term on the right-hand side of equations (1) and (2) are values ​​obtained by filtering the q-axis and d-axis current command values ​​(Iq** and Id**) using filter circuit 98 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 multiply them by the motor electrical angular velocity ωe to obtain the second term on the right-hand side of equations (1) and (2). Furthermore, multiplier 92k multiplies the motor electrical angular velocity ωe by the d-axis inductance Ld to obtain the third term on the right-hand side of equation (2).

[0044] A subtractor 91f subtracts the output of a multiplier 92h from the output of a multiplier 92g to obtain a d-axis voltage command value Vd* of the equation (1). An adder 90d obtains the sum of the output of a multiplier 92i, the output of a multiplier 92j, and the output of a multiplier 92k to obtain a q-axis voltage command value Vq* of the equation (2).

[0045] The circuit configuration example in Fig. 6 is characterized in that current controllers 114a and 114b are connected in series to the voltage calculation in voltage command value calculation unit 12a, and first-order lag filters (low-pass filters) 98a and 98b having a cutoff frequency equivalent to the electrical time constant of the motor are provided. These establish an inverse model of the motor, which has the effect of realizing ideal vector control even when the calculation period of control unit 10 is restricted.

[0046] The d-axis harmonic current superimposing section in the voltage command value calculation section 12 will be described later.

[0047] <Challenges for improving torque precision> The motor control device 100 controls the rotation speed or torque of the electric motor 20 to a desired value, but when driving a PM motor, if the temperature of the magnet changes, the magnetic flux changes depending on the temperature, so there is a problem that torque accuracy will deteriorate unless some kind of measure is taken.

[0048] If the magnet temperature can be measured, it is possible to improve torque accuracy by adjusting the current command value according to the temperature. However, it is difficult to directly connect a temperature sensor to the magnet inside the rotor due to issues with durability and productivity. Therefore, estimating the magnet temperature is an effective solution.

[0049] As a method that is particularly useful when the motor is stopped or rotating at a low speed, there is a method of superimposing a harmonic current on the motor current, estimating the inductance from the harmonic current, and estimating the magnet temperature from the relationship between the magnet temperature and the inductance. However, since the harmonic current generates sound and vibration at the superimposed frequency and is felt uncomfortable by people around the motor control device, it is necessary to reduce the sound and vibration. In a motor control device for driving an electric vehicle such as an electric car, since the passengers and the motor control device are in close proximity, there is a high need to reduce the sound and vibration generated by the motor control device. Also, when estimating the initial temperature of the magnet temperature at power-on, it is necessary to execute it in conjunction with various diagnostic functions of the motor control device, so it is necessary to shorten the magnet temperature estimation time. Especially in an electric car, there is a high need to shorten the magnet temperature estimation time in order to reduce the waiting time until the start of the driver's operation.

[0050] <Object of this embodiment> The object of this embodiment is to perform a repetitive operation of repeatedly performing a superimposed operation after a superimposed stop period of maintaining the harmonic current at a predetermined value a predetermined number of times during a harmonic current superimposed operation for the purpose of estimating the magnet temperature or magnet magnetic flux, and by changing the superimposed stop period for each of the repetitive operations, reducing the peak value of the harmonic current spectrum due to spectral diffusion and reducing the generated sound and vibration at the superimposed frequency.

[0051] <Concept of the embodiment of the present invention> To achieve the above object, the d-axis harmonic current superimposing section performs a superimposing operation of changing the harmonic current from a first predetermined value to a second predetermined value and then changing back to the first predetermined value again, and after a superimposed stop period of maintaining the harmonic current at the first predetermined value, performs a repetitive operation of repeatedly performing the superimposed operation a predetermined number of times, and changes the superimposed stop period for each of the repetitive operations.

[0052] <Configuration and operation of the d-axis harmonic current superimposing section> FIG. 7 shows a configuration 12a of a voltage command value calculation section including a d-axis harmonic current superimposing section 121a. A d-axis harmonic current command value generation section 123 generates a d-axis harmonic current command value, and the sum of the d-axis current command value and the d-axis harmonic current command value is input to a current controller 122.

[0053] Fig. 8A shows the waveform of the d-axis harmonic current command value. The d-axis harmonic current command value generator 123 performs a superimposition operation to change the d-axis harmonic current command value from the first predetermined value to the second predetermined value and then back to the first predetermined value, and performs a repetitive operation to repeat the superimposition operation a predetermined number of times after a superimposition stop period in which the d-axis harmonic current command value is maintained at the first predetermined value, and the superimposition stop period is changed for each repetitive operation. The current controller controls the d-axis current detection value to always be equal to the sum of the d-axis current command value and the d-axis harmonic current command value, so that the d-axis current detection value has a waveform approximately equal to the d-axis harmonic current command value in Fig. 8A.

[0054] The d-axis harmonic current command value generating unit 123 determines (outputs, calculates, derives, etc.) the superimposition stop period by using, for example, a random number. The random number is generated by using, for example, a random number generator, a function that generates random numbers in a standard library, or a random number table. Preferably, the d-axis harmonic current command value generating unit 123 adjusts the average value of the superimposition stop period. Note that it is also possible not to provide a superimposition stop period only once. In this case, it is also possible to set one of the different superimposition stop periods to 0.

[0055] The configuration 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 to this, Fig. 9 shows a configuration 12b of a voltage command value calculation unit in which a harmonic voltage command value is added to a voltage command value. A d-axis harmonic voltage command value generation unit 124 generates a d-axis harmonic voltage command value, and calculates a d-axis voltage command value (second d-axis voltage command value) from the sum of the output of the current controller 122 (first d-axis voltage command value) and the d-axis harmonic voltage command value.

[0056] Fig. 10 shows waveforms of the d-axis current detection value and the d-axis harmonic voltage command value in Configuration 12b of the voltage command value calculation unit. The d-axis harmonic voltage command value generation unit 124 performs a superimposition operation in which the d-axis harmonic voltage command value is set to a positive voltage value so that the d-axis current detection value changes from a first predetermined value to a second predetermined value, and is set to a negative voltage value so that the d-axis current detection value changes from the second predetermined value to the first predetermined value. After a superimposition stop period in which the d-axis harmonic voltage command value is set to a constant value so that the d-axis current detection value becomes the first predetermined value, a repetition operation is performed in which the superimposition operation is repeated a predetermined number of times, and the superimposition stop period is changed for each repetition operation.

[0057] Configuration 12b is not affected by the follow-up delay of the current detection value with respect to the current command value by the current controller 122. In Configuration 12a in which the harmonic current command value is added to the current command value, a standby time is required until the current detection value follows the current command value at the start and end of harmonic superimposition. On the other hand, in Configuration 12b, it is possible to shorten the time required for the start and end of the harmonic superimposition operation.

[0058] <Operation of d-axis Inductance Estimation Unit> The d-axis inductance estimation unit 40 calculates a d-axis inductance estimated value from the d-axis voltage command value, the d-axis current detection value, the q-axis current detection value, and the electrical angular velocity during the period in which the d-axis harmonic current superimposition unit 121 performs the superimposition operation.

[0059] The relationship between the d-axis voltage command value Vd*, the motor resistance value R, the d-axis current value detection value Id, the q-axis current value detection value Iq, the d-axis inductance Ld, the q-axis inductance Lq, and the electrical angular velocity ωe can be expressed by the following equation (3).

[0060]

Equation

[0061] The d-axis inductance estimated value Ld_est is calculated by the following equation based on equation (3).

[0062]

Equation

[0063] Here, the gradient dId / dt of the d-axis current detection value is calculated from the gradient when the d-axis current detection value changes from the first predetermined value to the second predetermined value, or from the second predetermined value to the first predetermined value. In this case, the gradient of a part of the range between the first predetermined value and the second predetermined value may be used instead of the gradient of the entire range between the first predetermined value and the second predetermined value. Lq is stored as a design value, an actual measurement value, or a value calculated by an electromagnetic field simulation, and is used when estimating the inductance.

[0064] When the motor is running at a low speed or stopped and ωe is approximately zero, and when the motor torque is approximately zero and Iq is approximately zero, equation (4) can be simplified to the following equation (5).

[0065]

number

[0066] Therefore, when the motor is at a low speed or stopped and ωe is approximately zero, and when the motor torque is approximately zero and Iq is approximately zero, d-axis inductance estimator 40 does not receive the q-axis current detection value or the electrical angular velocity as input, and does not need to store Lq, and is able to calculate the d-axis inductance estimate from the d-axis voltage command value and the d-axis current detection value.

[0067] <Operation of magnet temperature estimation unit> The magnet temperature estimation unit 41 calculates the magnet temperature estimate from the d-axis inductance estimate. When 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.

[0068] An example of the relationship of the d-axis inductance estimate value to the magnet temperature is shown in Figure 11. One configuration example of the magnet temperature estimator 41 is one in which the magnet temperature relative to the d-axis inductance estimate value is measured or calculated by electromagnetic field simulation and stored, and a table of magnet temperature estimate values ​​with the d-axis inductance estimate value as a parameter is created and used during estimation. Alternatively, the relationship of the magnet temperature to the d-axis inductance estimate value may be expressed as a formula and used during estimation. In this embodiment, the calculation method is not important as long as the magnet temperature estimate value can be calculated from the d-axis inductance estimate value.

[0069] <Effects of this embodiment> FIG. 12 shows the frequency analysis results when the difference between the first and second predetermined values ​​is set to 100A and a d-axis harmonic current with an amplitude of 100A is superimposed. The superimposition operation period is set to Ti [s], and three cases are shown in the figure: no superimposition stop period, a constant superimposition stop period of 4Ti, and a superimposition stop period that is changed for each repetitive operation and has an average value of 4Ti. When there is no superimposition stop period, a large current spectrum peak of 40A or more appears at the superimposition frequency of 1 / Ti [Hz]. When the superimposition stop period is constant, the peak of the current spectrum is reduced and moves to a lower frequency. When the superimposition stop period is changed for each repetitive operation, the peak value of the current spectrum is further reduced by spectrum spreading.

[0070] 8A, the d-axis harmonic current command value generating unit 123 determines (calculates using a formula or derives using a table, etc.) the superposition stop period so that the average value of the different superposition stop periods becomes 4Ti when the superposition frequency is 1 / Ti [Hz]. Note that the superposition operation period Ti is the period from the first predetermined value to the second predetermined value until the d-axis harmonic current command value returns to the first predetermined value again.

[0071] There is a known technique for changing the carrier frequency in the PWM signal generating unit 14 for each carrier cycle in order to reduce the noise and vibration of the motor drive device. When changing the carrier frequency, the range of change in the carrier frequency is limited in order to control the current normally, and the amount of reduction in harmonic current peaks by spectrum spreading is limited. In contrast, since the time constant of the magnet temperature change is long, about several seconds, and frequent temperature estimation is not necessary, the superposition stop period in this embodiment can be made sufficiently long compared to the superposition operation period. The range of change in the superposition stop period can be made large, the effect of spectrum spreading is large, and it is possible to significantly reduce harmonic current peaks.

[0072] The main features of the first embodiment can be summarized as follows.

[0073] As shown in FIG. 1, the motor control device 100 drives a motor (electric motor 20) by an inverter 30. The processor (control unit 10) of the motor control device 100 superimposes a d-axis harmonic current on a d-axis current (d-axis harmonic current superimposition unit 121), calculates a d-axis inductance estimate based on the d-axis harmonic current (d-axis inductance estimation unit 40), and calculates a magnet temperature estimate based on the d-axis inductance estimate (magnet temperature estimation unit 41). As shown in FIG. 8A, the processor repeats a superimposition operation N times (N: an integer of 2 or more) in which the d-axis harmonic current is changed from a first predetermined value to a second predetermined value and then changed back to the first predetermined value. After each of the superimposition operations at least (N-1) times, the processor provides a holding period (superimposition stop period) indicating a period during which the d-axis harmonic current is kept at the first predetermined value. Note that the second predetermined value is greater than the first predetermined value.

[0074] By providing a hold period (superimposition stop period), the current spectrum shifts to the lower frequency side and the peak value decreases, as shown in Figure 12. As a result, the noise and vibration of the motor during magnet temperature estimation can be suppressed.

[0075] The processor (control unit 10) generates a d-axis harmonic current command value (d-axis harmonic current command value generating unit 123) and adds the d-axis harmonic current command value to the d-axis current command value, as shown in Fig. 7. Alternatively, the processor (control unit 10) generates a d-axis harmonic voltage command value (d-axis harmonic voltage command value generating unit 124) and adds the d-axis harmonic voltage command value to the d-axis voltage command value, as shown in Fig. 9. This makes it possible to superimpose the d-axis harmonic current on the d-axis current.

[0076] The processor (control unit 10) changes the hold period (superimposition stop period) for each superimposition operation. As shown in Fig. 12, the peak value of the current spectrum is further reduced by the spectrum spreading.

[0077] Preferably, the respective hold periods (superimposition stop periods) are different from each other, which causes the current spectrum to spread over a wide range and further reduces the peak value of the current spectrum.

[0078] For example, the processor (control unit 10) determines the holding period (superimposition stop period) using a random number, which makes it possible to easily generate holding periods (superimposition stop periods) that are different from one another.

[0079] During the superimposition operation, the processor (control unit 10) calculates the d-axis inductance estimate based on the gradient of the d-axis harmonic current (≒ d-axis current detection value) and the d-axis voltage command value (for example, equation (4) or (5)). This makes it possible to easily calculate the d-axis inductance estimate.

[0080] As shown in Fig. 8B, in the superimposition operation, the processor (controller 10) may change the d-axis harmonic current to a second predetermined value, then to a third predetermined value, and then to the first predetermined value again. Note that the third predetermined value is smaller than the first predetermined value. By lengthening the period of the superimposition operation, for example, there is more time in the period for detecting the gradient of the d-axis harmonic current (the d-axis current detection value).

[0081] [Example 2] The configuration of this embodiment can be the same as that of the first embodiment, except for the following points. This embodiment relates to the d-axis harmonic current superimposing unit 121.

[0082] 13 shows the waveform of the d-axis current detection value in this embodiment. It differs from embodiment 1 in that the first predetermined value is set to 0. The d-axis harmonic current superimposition unit 121 is the same as embodiment 1 in that it has a configuration 121a that adds a harmonic current command value to a current command value and a configuration 121b of a voltage command value calculation unit that adds a harmonic voltage command value to a voltage command value, but the first predetermined value is set to 0. This operation makes the d-axis current in the superimposition stop period 0, making it possible to reduce power consumption. It is particularly preferable to set the superimposition stop period longer than the superimposition operation period because the amount of power consumption reduction is large.

[0083] The main features of the second embodiment can be summarized as follows.

[0084] 13, the first predetermined value is 0. This makes it possible to reduce power consumption.

[0085] The present invention is not limited to the above-mentioned embodiment, and includes various modified examples. For example, the above-mentioned embodiment has been described in detail to explain the present invention in an easily understandable manner, and the present invention is not necessarily limited to the embodiment having all of the described configurations.

[0086] In addition, the above-mentioned configurations, functions, processing units, processing procedures, etc. may be realized in part or in whole by hardware, for example, by designing them as integrated circuits, etc. In addition, the above-mentioned configurations and functions, etc. may be realized in software, by a processor interpreting and executing a program that realizes each function.

[0087] In addition, the signal lines and information lines are those considered necessary for the explanation, and do not necessarily show all control lines and information lines. In addition, the above configurations, functions, processing units, processing procedures, etc. do not necessarily need to be in the same physical location, and for example, some of them may be on a network or in the cloud via communication, etc.

[0088] Also, the motor has been explained as having an inner rotor structure with the rotor placed inside the stator, but of course an outer rotor structure is also acceptable. It can also be a radial gap motor or an axial gap motor. In addition to PMSM, a synchronous motor or SRM with magnets can also be used.

[0089] The embodiment of the present invention may have the following aspects.

[0090] (A1). A motor control device that drives a motor using an inverter, comprising: a d-axis harmonic current superimposition unit that superimposes a d-axis harmonic current on a d-axis current; a d-axis inductance estimation unit that estimates a d-axis inductance based on the d-axis harmonic current; and a magnet temperature calculation unit that calculates an estimated magnet temperature value based on the estimated d-axis inductance, wherein the d-axis harmonic current superimposition unit performs a superimposition operation to change the d-axis harmonic current back to the first predetermined value after it has changed from a first predetermined value to a second predetermined value, and performs a repetitive operation to repeat the superimposition operation a predetermined number of times after a superimposition stop period in which the d-axis harmonic current is kept at the first predetermined value, or without the superimposition stop period.

[0091] (A2) The motor control device described in (A1), wherein the d-axis harmonic current superimposition unit includes a d-axis harmonic current command value generation unit that generates a d-axis harmonic current command value and adds the d-axis harmonic current command value to the d-axis current command value, or includes a d-axis harmonic voltage command value generation unit that generates a d-axis harmonic voltage command value and adds the d-axis harmonic voltage command value to the d-axis voltage command value.

[0092] (A3) The motor control device according to (A2), wherein the d-axis harmonic current superimposition unit changes the superimposition stop period for each of the repeated operations.

[0093] (A4) The motor control device described in (A3), wherein the d-axis inductance estimation unit calculates the d-axis inductance estimation value based on the gradient of the d-axis harmonic current and the d-axis voltage command value during the superposition operation of the d-axis harmonic current superposition unit.

[0094] (A5) The motor control device according to any one of (A1) to (A4), wherein the first predetermined value is 0.

[0095] According to (A1)-(A5), after a superposition stop period during which the harmonic current is kept at a predetermined value, the superposition operation is repeated a predetermined number of times, and the superposition stop period is changed for each repetition, whereby the peak value of the harmonic current spectrum is reduced by spectrum spreading, and the generated noise and vibration of the superposition frequency can be reduced. [Explanation of symbols]

[0096] 10...Control section 11...Current command value calculation section 12...Voltage command value calculation unit 13... Coordinate conversion section 14...PWM signal generation section 15...Angular velocity calculation section 16...Torque command value limiting section 17...d-axis voltage command value limiter 18...q-axis current command value limiter 20...Electric motor (PM motor) 27...Permanent magnet 30…Inverter 40...d-axis inductance estimation section 41...Magnet temperature estimation section 121...d-axis harmonic current superposition section 122...Current controller 123...d-axis harmonic current command value generator 124...d-axis harmonic voltage command value generator

Claims

1. A motor control device that drives a motor by an inverter, A processor that superimposes a d-axis harmonic current on a d-axis current, calculates a d-axis inductance estimate based on the d-axis harmonic current, and calculates a magnet temperature estimate based on the d-axis inductance estimate, The processor, a superimposing operation of changing the d-axis harmonic current from a first predetermined value to a second predetermined value and then changing it back to the first predetermined value is repeated N times (N: an integer equal to or greater than 2); After each of the superimposing operations at least (N-1) times, a hold period is provided which indicates a period during which the d-axis harmonic current is maintained at the first predetermined value. A motor control device comprising:

2. 2. The motor control device according to claim 1, The processor, generating a d-axis harmonic current command value and adding the d-axis harmonic current command value to the d-axis current command value; or A d-axis harmonic voltage command value is generated, and the d-axis harmonic voltage command value is added to the d-axis voltage command value. A motor control device comprising:

3. 2. The motor control device according to claim 1, The processor, The holding period is changed for each superimposition operation. A motor control device comprising:

4. 2. The motor control device according to claim 1, The processor, During the superimposing operation, the d-axis inductance estimate value is calculated based on the gradient of the d-axis harmonic current and the d-axis voltage command value. A motor control device comprising:

5. 2. The motor control device according to claim 1, The first predetermined value is 0. A motor control device comprising:

6. 4. The motor control device according to claim 3, Each of the retention periods is different from each other. A motor control device comprising:

7. 7. The motor control device according to claim 6, The processor, The retention period is determined using a random number. A motor control device comprising:

8. 2. The motor control device according to claim 1, The processor, In the superimposing operation, the d-axis harmonic current is changed to the second predetermined value, then changed to a third predetermined value, and then changed again to the first predetermined value. A motor control device comprising:

9. 2. The motor control device according to claim 1, The second predetermined value is greater than the first predetermined value. A motor control device comprising:

10. 9. The motor control device according to claim 8, The third predetermined value is smaller than the first predetermined value. A motor control device comprising:

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