Motor control device

Abstract

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 superimposition unit 121), calculates a d-axis inductance estimation value on the basis of the d-axis harmonic current (d-axis inductance estimation unit 40), and calculates a magnet temperature estimation value on the basis of the d-axis inductance estimation value (magnet temperature estimation unit 41). The processor repeats N times (N: an integer of 2 or more) a superimposing operation of changing the d-axis harmonic current from a first predetermined value to a second predetermined value and then changing the d-axis harmonic current to the first predetermined value. The processor is provided with a holding period (superimposition stop period) indicating a period in which the d-axis harmonic current is maintained at the first predetermined value after at least (N-1) times of the superimposition operations. Thus, the sound and vibration of the motor during magnet temperature estimation can be suppressed.

Description

Motor control device

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

[0002] Patent Document 1 discloses a drive 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 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 also discloses a d-axis inductance equivalent value determining means and an estimation method that calculates an estimate of the magnetic flux amount of the permanent magnet based on the inductance equivalent value.

[0003] JP 2015-133891 A Patent No. 6158115 A

[0004] 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.

[0005] 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.

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

[0008] In order to achieve the above 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 superimposing 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, and provides a holding period indicating a period during which the d-axis harmonic current is maintained at the first predetermined value after each of at least (N-1) superimposing operations.

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

[0010] 8 is a schematic diagram showing an example of a motor control device according to a first embodiment. FIG. 9 is a schematic diagram showing the structure of a PM motor. FIG. 10 is an explanatory diagram of coordinate axes. FIG. 11 is a block diagram of a power conversion circuit and a current detection unit. FIG. 12 is a diagram showing the relationship between a PWM carrier signal and a voltage command value. FIG. 13 is an example of a configuration diagram of a voltage command value calculation unit. FIG. 14 is a control block diagram of an example configuration of a d-axis harmonic current superimposition unit of a magnet temperature estimator according to a first embodiment. FIG. 15 is a waveform example of the d-axis harmonic current command value in FIG. 7. FIG. 16 is another waveform example of the d-axis harmonic current command value in FIG. 7. FIG. 17 is a control block diagram of another example configuration of the d-axis harmonic current superimposition unit of the magnet temperature estimator according to a first embodiment. FIG. 18 is a waveform example of the d-axis current detection value and the d-axis harmonic voltage command value in FIG. 10. FIG. 11 is a relationship example between the magnet temperature and the d-axis inductance estimation value. FIG. 12 is an example of a frequency analysis result when a d-axis harmonic current is superimposed. FIG. 13 is an example waveform of the d-axis current detection value in the configuration of a second embodiment.

[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 harmonic current superposition operation for the purpose of estimating magnet temperature or magnet magnetic flux, after a superposition stop period in which the harmonic current is maintained at a predetermined value, the superposition operation is repeated a predetermined number of times, and by changing the superposition stop period for each repetition, the peak value of the harmonic current spectrum is reduced by spectrum spreading, and the generated superposition frequency noise and vibration are reduced.

[0012] 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.

[0013] The various components of the present disclosure 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 a part of another component, or for part of one component to overlap with part of another component, etc.

[0014] [Example 1] <Schematic Configuration of Motor Control Device> Figure 1 is a schematic configuration 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 that mechanically or magnetically transmits mechanical output is connected to the electric motor 20, and the rotation speed or torque of the electric motor 20 is controlled to a desired value by the motor control device 100.

[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 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.

[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, i.e., the switching frequency, is generally set sufficiently high relative to the frequency of the equivalent AC voltage (which corresponds 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 is possible to consider the fundamental wave component of the pulsed voltage as being applied to the electric 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] 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.

[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 the 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. The coordinate conversion unit 13 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] An angular velocity calculation unit 15 receives a motor electrical angle detection value as input and outputs an electrical angular velocity. A rotation speed command value or a torque command value is received as input, and 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 q-axis current command value output by a current command value calculation unit 11, the d-axis current detection value, the q-axis current detection value, and the electrical angular velocity. A PWM signal generation unit 14 outputs a PWM signal that controls the on / off of switching elements constituting the inverter 30 based on the d-axis voltage command value and the q-axis voltage command value. While the rotation speed command value and the torque command value are shown in the control unit 10 in FIG. 1 , they may be obtained from, for example, a higher-level control system or another control system (not shown).

[0022] Furthermore, the d-axis inductance estimation unit 40 receives as input the d-axis voltage command value, the d-axis current detection value, the q-axis current detection value, and the electrical angular velocity, and the magnet temperature estimation unit 41 receives as input the d-axis inductance estimation value, 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] <Structural example of electric motor> Figure 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 of which has 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 (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 rotor 22 can be freely selected, and it does not matter if the numbers of magnetic poles of the stator and 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 will be described as having three-phase windings.

[0025] 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 (rotational angular position) of the rotor 22 when a positive DC current flows through the windings 25 and the stator magnetic poles 28 become south poles, attracting the north poles of the permanent magnets 27 of the rotor 22, is defined as zero degrees. Hereinafter, the rotational angular position of the rotor will be referred to as rotor position θd. If 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 U-phase) will be described as the reference position. In this embodiment, the counterclockwise rotation of the rotor 22 is defined as positive rotation.

[0026] The processing within the motor control device 100 utilizes information about 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, encoder, or the like as the angle sensor 60. Naturally, the position information may be obtained 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> The definition of the coordinate axes will now be explained. FIG. 3 is a diagram 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 provided in the rotor 22, and the d-q axis is defined as the q-axis, which is electrically advanced 90 degrees (electrical angle 90 degrees) in the direction of rotation from the d-axis. 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 linking with the reference winding 25 is maximized.

[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, the inverter 30 includes an inverter module 131, a DC voltage source 120, and a gate driver circuit 132. Here, the output of the DC voltage source 120 is assumed to be 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 flow.

[0030] Two sets of these switching elements 32 are connected in series to form upper and lower arms of each phase. In the example of Fig. 4, the upper and lower arms of 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 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 pulsed drive signal (details of which will be described later) output by the PWM signal generating unit 14 shown in Fig. 1, and outputs drive signals 34a to 34f based on this signal.

[0031] Although the drive signals can be generated using known techniques, for example, the drive signals can be generated from the magnitude relationship between the triangular wave carrier signal and the voltage command values ​​of each phase, as shown in Fig. 5. 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 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 electric 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 driving and torque control of the electric motor 20.

[0033] <Current Detector 50> The current detector 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 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. The current detector 50, such as a CT (current transformer), can be provided on the lower arm of the inverter module 131.

[0034] 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 32 that constitute the inverter 30.

[0035] <PM Motor Driving Method> 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.

[0036] The aforementioned d-axis and q-axis can also be described 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 axis and controlling the voltage phase and magnitude to control the motor's rotational speed or torque is generally called vector control. While PM motors are driven by control on the d- and q-axes, known coordinate transformation techniques can be used to convert from the three-phase UVW axes to the d- and q-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 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*.

[0038]

[0039]

[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] To ensure that the d-axis and q-axis currents flow as commanded, the configuration of Fig. 6 uses a d-axis current controller 114a and a q-axis current controller 114b. In this circuit configuration of Fig. 6, reference numeral 91 denotes a subtractor that calculates the difference between the current command values ​​(Id* and Iq*) and their detected values ​​(Idc and Iqc), 92 denotes a proportional circuit that adds a predetermined gain to the difference, 94 denotes an integrator, and 90 denotes an adder that adds the proportional and integral components to calculate a proportional-integral value. The outputs are 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 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 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 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 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 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).

[0045] 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 that 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 in 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 in response to the temperature, and therefore there is a problem that torque precision will deteriorate unless some kind of response is taken.

[0048] 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.

[0049] A particularly useful technique for estimating magnet temperature when a motor is stopped or rotating at low speed is to superimpose harmonic currents on the motor current, estimate inductance from the harmonic currents, and then estimate magnet temperature from the relationship between magnet temperature and inductance. However, harmonic currents generate noise and vibrations at the superimposed frequencies, which can be unpleasant for people around the motor control device, so noise and vibration must be reduced. In motor control devices for driving electric vehicles, such as electric cars, the occupants are located close to the motor control device, so there is a high need to reduce the noise and vibration generated by the motor control device. Furthermore, when estimating the initial magnet temperature at power-on, this must be performed in conjunction with various diagnostic functions of the motor control device, so the magnet temperature estimation time must be shortened. In particular, in electric vehicles, there is a high need to shorten the magnet temperature estimation time in order to reduce the waiting time until the occupants begin driving.

[0050] <Purpose of this embodiment> The purpose of this embodiment is to perform a repetitive operation during harmonic current superposition operation for the purpose of estimating magnet temperature or magnet magnetic flux, in which the harmonic current is kept at a predetermined value after a superposition stop period, and to repeat the superposition operation a predetermined number of times, by changing the superposition stop period for each repetitive operation, thereby reducing the peak value of the harmonic current spectrum through spectrum spreading and reducing the generated sound and vibration of the superposition frequency.

[0051] <Concept of an embodiment of the present invention> In order to achieve the above object, the d-axis harmonic current superimposing unit performs a superimposing operation to change the harmonic current from a first predetermined value to a second predetermined value and then back to the first predetermined value, and after a superimposing stop period in which the harmonic current is maintained at the first predetermined value, performs a repetitive operation to repeat the superimposing operation a predetermined number of times, and changes the superimposing stop period for each repetitive operation.

[0052] 7 shows a 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, 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] 8A shows the waveform of the d-axis harmonic current command value. The d-axis harmonic current command value generator 123 performs a superposition operation in which the d-axis harmonic current command value changes from a first predetermined value to a second predetermined value and then back to the first predetermined value. After a superposition stop period in which the d-axis harmonic current command value is maintained at the first predetermined value, the d-axis harmonic current command value generator 123 performs a repetitive operation in which the superposition operation is repeated a predetermined number of times, and the superposition stop period is changed for each repetition. The current controller controls the d-axis current detection value so that it is always 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 shown in FIG. 8A.

[0054] The d-axis harmonic current command value generation unit 123 determines (outputs, calculates, derives, etc.) the superposition stop period using, for example, a random number. The random number is generated 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 generation unit 123 adjusts the average value of the superposition stop period. Note that it is also possible not to set a single superposition stop period. In this case, it is also possible to set one of the different superposition 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] 10 shows the waveforms of the d-axis current detection value and the d-axis harmonic voltage command value in the configuration 12b of the voltage command value calculation unit. The d-axis harmonic voltage command value generation unit 124 performs a superposition 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 a negative voltage value so that the d-axis current detection value changes from the second predetermined value to the first predetermined value, and after a superposition 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, performs a repetitive operation in which the superposition operation is repeated a predetermined number of times, and the superposition stop period is changed for each repetition.

[0057] Configuration 12b is not affected by the delay in the response of the current detection value to the current command value by current controller 122. Configuration 12a, which adds a 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, configuration 12b makes it possible to shorten the time required to start and end harmonic superposition operation.

[0058] <Operation of d-axis inductance estimation unit> The d-axis inductance estimation unit 40 calculates a d-axis inductance estimate 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 when the d-axis harmonic current superposition unit 121 is performing the superposition operation.

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

[0060]

[0061] The d-axis inductance estimate Ld_est is calculated using the following equation based on equation (3):

[0062]

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

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

[0065]

[0066] Therefore, when the motor is running at a low speed or is stopped and ωe is approximately zero, or when the motor torque is approximately zero and Iq is approximately zero, the 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 an estimated magnet temperature value from an estimated d-axis inductance value. 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 estimated d-axis inductance value.

[0068] An example of the relationship between the d-axis inductance estimate value and the magnet temperature is shown in Figure 11. One configuration example of the magnet temperature estimator 41 is to measure the magnet temperature against the d-axis inductance estimate value or calculate and store it by electromagnetic field simulation, and create a table of magnet temperature estimates using the d-axis inductance estimate value as a parameter to use during estimation. Alternatively, the relationship between the d-axis inductance estimate value and the magnet temperature may be expressed as a mathematical 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] 12 shows the results of frequency analysis when the difference between the first and second predetermined values ​​is set to 100 A and a d-axis harmonic current with an amplitude of 100 A is superimposed. The superimposition operation period is set to Ti [s], and the figure shows three cases: no superimposition stop period, a constant superimposition stop period of 4 Ti, and a superimposition stop period that is changed for each repetitive operation and has an average value of 4 Ti. When there is no superimposition stop period, a large current spectrum peak of 40 A or more appears at the superimposition frequency, 1 / Ti [Hz]. When the superimposition stop period is constant, the current spectrum peak is reduced and shifted 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 due to spectral spreading.

[0070] 8A, when the superposition frequency is 1 / Ti [Hz], the d-axis harmonic current command value generator 123 determines the superposition stop period (calculated using an equation or derived from a table) so that the average value of the different superposition stop periods is 4Ti. 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 reducing noise and vibration in a motor drive device by changing the carrier frequency in the PWM signal generation unit 14 every carrier cycle. When changing the carrier frequency, the range of change in the carrier frequency is limited in order to properly control the current, and the amount of reduction in harmonic current peaks achieved by spread spectrum is limited. In contrast, since the time constant of magnet temperature change is long, on the order of several seconds, and frequent temperature estimation is not necessary, the superposition stop period in this embodiment can be made sufficiently longer than the superposition operation period. The range of change in the superposition stop period can be made larger, the effect of spread spectrum is significant, and significant reduction in harmonic current peaks is possible.

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

[0073] As shown in FIG. 1 , a motor control device 100 drives a motor (electric motor 20) using an inverter 30. The processor (controller 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 estimator 40), and calculates a magnet temperature estimate based on the d-axis inductance estimate (magnet temperature estimator 41). As shown in FIG. 8A , the processor repeats the superimposition operation N times (N: an integer greater than or equal to 2) to change the d-axis harmonic current from a first predetermined value to a second predetermined value and then back to the first predetermined value. After each of at least (N-1) superimposition operations, the processor sets a holding period (superimposition stop period) during which the d-axis harmonic current is maintained 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, it is possible to suppress the noise and vibration of the motor when estimating the magnet temperature.

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

[0076] The processor (controller 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 be spread over a wide range and further reduces the peak value of the current spectrum.

[0078] For example, the processor (controller 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] 8B , during 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 extending the period of the superimposition operation, for example, there is more time available for detecting the gradient of the d-axis harmonic current (the detected d-axis current value).

[0081] [Embodiment 2] The configuration of this embodiment can be the same as that of embodiment 1, 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 the first embodiment in that the first predetermined value is set to 0. The d-axis harmonic current superimposing unit 121, like the first embodiment, 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 zero during the superimposition stop period, making it possible to reduce power consumption. Setting the superimposition stop period longer than the superimposition operation period is particularly preferable 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-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.

[0086] 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.

[0087] 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.

[0088] 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.

[0089] The embodiment of the present invention may be configured as follows.

[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 that changes the d-axis harmonic current from a first predetermined value to a second predetermined value again to the first predetermined value, and performs a repetitive operation that repeats the superimposition operation a predetermined number of times after a superimposition stop period in which the d-axis harmonic current is maintained at the first predetermined value, or without the superimposition stop period.

[0091] (A2) The motor control device according to (A1), wherein the d-axis harmonic current superimposing unit includes a d-axis harmonic current command value generating 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 generating 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 superimposing unit changes the superimposition stop period for each of the repeated operations.

[0093] (A4) The motor control device according to (A3), wherein the d-axis inductance estimation unit calculates the d-axis inductance estimation value based on a 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 in 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 repeat operation. This reduces the peak value of the harmonic current spectrum through spectrum spreading, thereby reducing the noise and vibration of the superposition frequency that is generated.

[0096] 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...d-axis inductance estimating unit 41...Magnet temperature estimating unit 121...d-axis harmonic current superimposing unit 122...Current controller 123...d-axis harmonic current command value generating unit 124...d-axis harmonic voltage command value generating unit

Claims

1. A motor control device that drives a motor using an inverter, comprising 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 back 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.

2. A motor control device according to claim 1, wherein the processor generates a d-axis harmonic current command value and adds the d-axis harmonic current command value to a d-axis current command value, or generates a d-axis harmonic voltage command value and adds the d-axis harmonic voltage command value to a d-axis voltage command value.

3. A motor control device according to claim 1, characterized in that the processor changes the hold period for each superimposition operation.

4. A motor control device according to claim 1, wherein the processor calculates the d-axis inductance estimate value based on the gradient of the d-axis harmonic current and the d-axis voltage command value during the superposition operation.

5. A motor control device according to claim 1, characterized in that the first predetermined value is zero.

6. A motor control device according to claim 3, characterized in that the respective holding periods are different from each other.

7. A motor control device according to claim 6, wherein the processor determines the retention period using a random number.

8. A motor control device as claimed in claim 1, characterized in that, in the superposition operation, the processor changes the d-axis harmonic current to the second predetermined value, then to a third predetermined value, and then to the first predetermined value again.

9. A motor control device according to claim 1, characterized in that the second predetermined value is greater than the first predetermined value.

10. A motor control device according to claim 8, wherein the third predetermined value is smaller than the first predetermined value.

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