motor control device

Abstract

The purpose of this invention is to improve the accuracy of magnet temperature estimation by correcting the current dependence of magnetic flux variation caused by temperature changes when estimating magnet temperature. The control unit (10) of the electric motor of this invention includes a magnet temperature estimation unit (40), which takes into account the q-axis voltage command value calculated based on any one of the motor speed command value and torque command value, the electrical angular velocity, the d-axis current detection value calculated based on the current detection value, and the q-axis current detection value, and estimates the temperature of the permanent magnet. The magnet temperature estimation unit (40) includes: a d-axis flux variation calculation unit (41), which inputs the q-axis voltage command value, electrical angular velocity, d-axis current detection value and q-axis current detection value, and calculates the d-axis flux variation; a d-axis flux variation correction unit (42), which calculates the corrected d-axis flux variation; a magnet flux reference value calculation unit (43), which calculates the magnet flux reference value; and a magnet temperature calculation unit (44), which calculates the magnet temperature estimation value of the permanent magnet based on the corrected d-axis flux variation and the magnet flux reference value.

Description

Technical Field

[0001] This invention relates to an electric motor control device. Background Technology

[0002] As a technique for estimating the magnet temperature of an electric motor, techniques described in, for example, Patent Document 1 and Patent Document 2 have been proposed.

[0003] Patent document 1 discloses a drive device for a permanent magnet synchronous motor, which estimates the change in magnet flux at different times based on a voltage command value and outputs an estimated value of magnet temperature change equivalent to the change in magnet flux.

[0004] In addition, Patent Document 2 discloses a method for estimating the temperature of a motor magnet, which changes the target current value, calculates the magnet flux based on the d-axis flux linkage number, and estimates the magnet temperature based on the calculated magnet flux.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent Application Publication No. 2021-2949

[0008] Patent Document 2: Japanese Patent Application Publication No. 2021-16226 Summary of the Invention

[0009] The technical problem that the invention aims to solve

[0010] The purpose of the technology described in Patent Document 1 is to eliminate the influence of constant errors between individuals caused by manufacturing differences in motors, and to accurately estimate magnet flux or magnet temperature. Furthermore, Patent Document 1 discloses a drive device for a permanent magnet synchronous motor that includes a method for calculating d-axis flux error based on the difference between the q-axis voltage command value and a reference q-axis voltage calculated based on constants used in control, and for calculating the d-axis flux error at a reference temperature. Calculate the d-axis flux error when the magnet temperature changes from the reference temperature. according to and The difference is used to calculate the change in magnetic flux of the magnet, and an estimated value of the change in magnet temperature corresponding to the change in magnetic flux is output.

[0011] In Patent Document 1, when a certain d-axis current and q-axis current are reached, the following will be determined: and The variation in d-axis flux calculated from the difference is directly used as the variation in magnet flux. Since the variation in d-axis flux and magnet flux caused by magnet temperature change has different current dependence depending on the d-axis current and q-axis current, the estimated value of the variation in magnet flux will be incorrect when the d-axis current and q-axis current are not zero. The estimated value of magnet temperature will also be incorrect, so there is room for improvement.

[0012] Patent Document 2 discloses a method for estimating the magnet temperature of an electric motor. This method involves determining the d-axis flux before and after changing the target current, calculating the magnet flux based on each d-axis flux, and estimating the magnet temperature based on the calculated magnet flux. In Patent Document 2, when estimating the magnet temperature based on the magnet flux, a table showing the correspondence between parameters such as magnet flux, d-axis current, and q-axis current and the magnet temperature is used. Furthermore, the current dependence of the flux variation caused by temperature changes is considered when estimating the magnet temperature. However, because a table with three parameter inputs is used, there is room for improvement in terms of the increased amount of table data, the longer measurement time required to create the table, and the greater processing load for table reference.

[0013] The purpose of this invention is to provide an electric motor control device that improves the accuracy of magnet temperature estimation by correcting the current dependence of magnetic flux variation caused by temperature changes when estimating magnet temperature.

[0014] Technical means for solving technical problems

[0015] To achieve the above objectives, the motor control device of the present invention includes a control unit for controlling a motor having a permanent magnet. The control unit includes a magnet temperature estimation unit, which inputs: a q-axis voltage value calculated based on either a speed command value or a torque command value of the motor, or a voltage detection value of the motor; an electrical angular velocity calculated based on the electrical angle of the motor; and a d-axis current value and a q-axis current value calculated based on the voltage detection value or the current detection value of the motor, or based on the command value. The magnet temperature estimation unit estimates the temperature of the permanent magnet. The magnet temperature estimation unit includes a d-axis magnetic flux variation calculation unit. The d-axis flux variation calculation unit takes the q-axis voltage value, the electrical angular velocity, the d-axis current value, and the q-axis current value as input, and calculates the difference between the d-axis flux and the d-axis flux reference value, i.e., the d-axis flux variation; the d-axis flux variation correction unit calculates the corrected d-axis flux variation based on the d-axis current value and the q-axis current value; the magnet flux reference value calculation unit calculates the magnet flux reference value based on the q-axis current value; and the magnet temperature calculation unit calculates the estimated magnet temperature of the permanent magnet based on the corrected d-axis flux variation and the magnet flux reference value.

[0016] Invention Effects

[0017] According to the present invention, when estimating the magnet temperature, the accuracy of magnet temperature estimation can be improved by correcting the current dependence of the magnetic flux variation caused by temperature change.

[0018] The problems, structures, and effects beyond those described above become clearer through the following description of the implementation methods. Attached Figure Description

[0019] Figure 1 This is a simplified structural diagram of the motor control device 100 according to Embodiment 1 of the present invention.

[0020] Figure 2 This is a schematic diagram showing the structure of the PM motor 20.

[0021] Figure 3 This is a diagram showing the relationship between the rotor position θd and the phases of each winding 25 of the stator 21.

[0022] Figure 4 This is a block diagram showing the structure of the inverter 30 and the current detection unit 50.

[0023] Figure 5 It is a diagram representing the AC voltage command value and the triangular wave carrier signal used to generate the drive signal.

[0024] Figure 6 This is a diagram showing an example of the structure of the voltage command value calculation unit 12.

[0025] Figure 7 This is a graph showing the relationship between the d-axis flux and the d-axis current under a certain q-axis current.

[0026] Figure 8 This is a control block diagram of the magnet temperature estimation unit 40.

[0027] Figure 9 It is a block diagram including a voltage sensor 70 that measures the output voltage of the inverter 30.

[0028] Figure 10 This is the control block diagram of the d-axis flux variation calculation unit 41.

[0029] Figure 11 This is a diagram illustrating an example of the relationship between the d-axis flux reference value Ψd_std stored as a table or mathematical formula in the d-axis flux reference value calculation unit 412 and the corresponding d-axis current value Id and q-axis current value Iq.

[0030] Figure 12 This is a diagram illustrating an example of the relationship between the q-axis current value Iq and the magnet flux reference value Ψd0_std.

[0031] Figure 13 This is the control block diagram of the d-axis flux variation correction unit 42.

[0032] Figure 14 This is a diagram illustrating an example of the relationship between the correction coefficient K stored as a table or mathematical formula in the correction coefficient calculation unit 421 and the corresponding d-axis current value Id and q-axis current value Iq.

[0033] Figure 15 This is the control block diagram of the magnet temperature calculation unit 44.

[0034] Figure 16 This is a diagram illustrating an example of the relationship between the estimated magnet temperature Tm_est, stored as a table or mathematical formula in the magnet temperature conversion unit 441, and the corresponding magnetic flux change ratio KΨ.

[0035] Figure 17 This is a control block diagram showing an example of the structure of a magnet temperature estimation unit when the d-axis flux variation correction unit is not included and the magnet flux reference value is set to a constant.

[0036] Figure 18 This is a diagram showing an example of the magnet temperature estimation error of the magnet temperature estimation unit when the d-axis flux variation correction unit is not included and the magnet flux reference value is set to a constant.

[0037] Figure 19 This is a control block diagram showing a structural example of a magnet temperature estimation unit without the d-axis flux variation correction unit.

[0038] Figure 20 This is a diagram showing an example of the magnet temperature estimation error of the magnet temperature estimation section without the d-axis flux variation correction section.

[0039] Figure 21 This is a diagram showing an example of the magnet temperature estimation error in the magnet temperature estimation section.

[0040] Figure 22 This is a control block diagram illustrating a variation of Embodiment 1.

[0041] Figure 23 This is a block diagram showing the structure of the control unit 10a according to Embodiment 2 of the present invention.

[0042] Figure 24 This is a diagram showing a structural example of the torque command value limiting unit 16, the d-axis current command value limiting unit 17, and the q-axis current command value limiting unit 18.

[0043] Figure 25 This is a block diagram showing the structure of the control unit 10b according to Embodiment 3 of the present invention. Detailed Implementation

[0044] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The same reference numerals will be assigned to the same structural elements, and the same descriptions will not be repeated.

[0045] The various structural elements of the present invention do not necessarily have to exist independently. Instead, it is permissible for multiple structural elements to be composed of a single component, for a single structural element to be composed of multiple components, for a certain structural element to be part of another structural element, or for a part of one structural element to be a duplicate of a part of another structural element.

[0046] [Example 1]

[0047] <Brief Structure of Electric Motor Control Device>

[0048] Figure 1 This is a simplified structural diagram of the motor control device 100 according to Embodiment 1 of the present invention. The motor control device 100 includes a control unit 10, a PM motor 20, an inverter 30, a current detection unit 50, and an angle sensor 60 such as a rotary transformer or encoder. Although not shown, a mechanism for mechanically or magnetically transmitting mechanical output is connected to the PM motor 20, and the motor control device 100 controls the speed or torque of the PM motor 20 to a desired value.

[0049] In the following description, an example of an electric motor using a PM motor 20, i.e., a permanent magnet synchronous motor (PMSM), will be used as an example, but the present invention is not limited thereto. The present invention can be applied to any electric motor having the characteristic that the magnetic flux of the permanent magnet changes with the rotor temperature.

[0050] Inverter 30 has a DC voltage source 120 such as a battery (see reference). Figure 4 The inverter 30 consists of a bridge circuit composed of switching elements, which switches the switching elements to output voltage according to the input drive signal. Assuming that the switching action of the switching elements is instantaneous and ideal, the voltage output from the inverter 30 is a pulsed voltage. Using the well-known concept of pulse width modulation, the pulsed voltage can be considered as an AC voltage.

[0051] Furthermore, in pulse width modulation, the switching frequency, i.e., the period during which the switching elements are turned on / off, is typically set high enough relative to the frequency of the equivalent AC voltage (here equivalent to the rotational frequency of a single-phase motor). However, the fundamental component of the pulsed voltage can also be considered. For example, when the switching frequency is approximately 1 to 3 times the rotational frequency of the PM motor, it can be assumed that the fundamental component of the pulsed voltage is applied to the PM motor 20. Therefore, in this specification, it is assumed that the output voltage of the inverter 30 is an AC waveform, as explained below.

[0052] Alternatively, a structure can be used to convert AC power to DC power through rectification, instead of a DC voltage source. Or, a structure can be used that controls a DC / DC converter to different voltages based on a DC voltage source with a specific voltage.

[0053] As a structural example, the control unit 10 includes a current command value calculation unit 11, a voltage command value calculation unit 12, a PWM signal generation unit 14, a coordinate transformation unit 13, an angular velocity calculation unit 15, and a magnet temperature estimation unit 40.

[0054] The coordinate transformation unit 13 takes into input the current information (current detection value) flowing through the PM motor 20 obtained by the current detection unit 50 and the motor electrical angle detection value obtained by the angle sensor 60, and converts it from the three-phase UVW axis to the dq axis as defined later, and outputs the d-axis current detection value (d-axis current value) and the q-axis current detection value (q-axis current value).

[0055] The angular velocity calculation unit 15 takes into input the electric motor electrical angle detection value obtained by the angle sensor 60 and outputs the electrical angular velocity.

[0056] The current command value calculation unit 11 inputs the speed command value or torque command value, and outputs the d-axis current command value and the q-axis current command value.

[0057] The d-axis current command value, q-axis current command value, d-axis current detection value, q-axis current detection value, and electrical angular velocity are input to the voltage command value calculation unit 12, and based on these values, a d-axis voltage command value and a q-axis voltage command value (q-axis voltage value) are generated.

[0058] The PWM signal generation unit 14 receives the d-axis voltage command value and the q-axis voltage command value, and based on these values, outputs a PWM signal for controlling the on / off of the switching elements constituting the inverter 30.

[0059] At Figure 1 , the rotational speed command value and the torque command value are shown in the control unit 10, but may be configured to be obtained from, for example, an upper control system or other control systems not shown.

[0060] <Structural Example of PM Motor 20>

[0061] Figure 2 is a diagram schematically showing the structure of the PM motor 20. The PM motor 20 includes a stator 21 and a rotor 22 provided on the inner peripheral side of the stator 21. The stator 21 has a plurality of stator poles 28 with windings (coils) 25 wound around a stator core (stator iron core) 26. The rotor 22 has permanent magnets (PMs) 27.

[0062] Figure 2 An example is shown in which the number of poles (also referred to as the number of slots) of the stator 21 is 6 and the number of poles of the rotor 22 is 2. The number of poles of the stator 21 and the rotor 22 can be freely selected, and the structure may be such that the number of poles of the stator 21 and the rotor 22 are equal, or the structure may be such that the number of poles of the stator 21 and the rotor 22 are different. In addition, it does not matter whether the connection of the plurality of windings is in parallel or in series. In the present embodiment, as an example of the PM motor 20 constituted by three-phase windings, the windings 25 of the opposing stator poles 28 are connected in series to form one phase and are described.

[0063] By passing a current through the winding 25, based on the principle of an electromagnet, the stator pole 28 generates a magnetic pole, and the polarity (N pole, S pole) is changed according to the current direction of the winding 25. In the present embodiment, when a positive DC current is passed through the winding 25, the stator pole 28 becomes an S pole, and the rotational angle (rotational angle position) of the rotor 22 when the N pole of the permanent magnet 27 of the rotor 22 is attracted is defined as zero degrees. Further, hereinafter, the rotational angle position of the rotor is denoted as the rotor position θd. When there are a plurality of stator poles 28, one of the stator poles 28 is defined as a reference position. In the present embodiment, the one located at Figure 2The winding 25 on the right (the winding closest to phase U) will be used as a reference position for explanation. In this application, the direction of counterclockwise rotation of rotor 22 is defined as forward rotation.

[0064] In the processing of the motor control device 100, the rotor position θd of the rotor 22 of the PM motor 20 is used as information, and the structure for detecting position information is described as follows: a rotary transformer, encoder, etc., which are angle sensors 60, are used. Of course, a structure can also be obtained by sensorless control using a position estimation unit, which outputs the estimated rotation angle position of the PM motor 20 based on the current flowing through the PM motor 20 and the applied voltage applied to the PM motor 20.

[0065] <Explanation of coordinate axes>

[0066] The definition of coordinate axes is explained here. Figure 3 This 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 of UVW are configured with an electrical angular phase difference of 120 degrees. The main magnetic flux direction of the permanent magnets provided in the rotor 22 is defined as the d-axis, and the dq-axis, which is formed by the d-axis and the q-axis, which advances electrically 90 degrees (electrical angle 90 degrees) from the d-axis in the rotational direction, is defined. This dq-axis is a rotating coordinate system. The definition of the d-axis can also be referred to as the rotational angular position where the magnetic flux of the permanent magnet 27 linked with the reference winding 25 is at its maximum.

[0067] <Inverter 30>

[0068] Next, we will refer to Figure 4 The block diagram shown illustrates the structure of the inverter 30 and the current detection unit 50. Figure 4 This is a block diagram showing the structure of the inverter 30 and the current detection unit 50.

[0069] like Figure 4 As shown, the inverter 30 includes an inverter module 131, a DC voltage source 120, and a gate drive circuit 123. Here, the output of the DC voltage source 120 is a DC voltage Edc.

[0070] Inverter module 131 includes switching elements 32a to 32f (e.g., semiconductor switching elements such as IGBTs or MOS-FETs) and return diodes connected in parallel with them. Switching elements 32a to 32f are collectively referred to as "switching elements 32".

[0071] A parallel resistor 135 is connected in series with the DC voltage source 120. This is used to protect the switching element 32 from excessive current flow.

[0072] Two sets of switching elements 32 are connected in series, and these switching elements 32 constitute the upper and lower arms of each phase. Figure 4 In the example, the upper and lower arms of phase U are composed of switching elements 32a and 32b, the upper and lower arms of phase V are composed of switching elements 32c and 32d, and the upper and lower arms of phase W are composed of switching elements 32e and 32f. The connection points of the upper and lower arms of each phase are connected to the PM motor 20.

[0073] Gate drive circuit 123 receives from Figure 1 The PWM signal generation unit 14 outputs a pulsed drive signal (details described later), and outputs drive signals 34a to 34f based on this pulsed drive signal. The method for generating the drive signal can use known techniques. Figure 5 One example is shown below.

[0074] Figure 5 This is a diagram representing the AC voltage command value and the triangular wave carrier signal used to generate the drive signal. For example... Figure 5 As shown, based on the relationship between the triangular wave carrier signal and the voltage command values ​​of each phase, the drive signal Gp for the upper arm and the drive signal Gn for the lower arm, as shown in the figure, are generated.

[0075] In inverter module 131, switching control is performed on each switching element 32 based on the aforementioned drive signals 34a to 34f.

[0076] Depending on the switching state of the upper and lower arms, the voltage of each phase of the inverter 30 becomes either DC voltage Edc or zero voltage. Because the inverter 30 switches at a frequency sufficiently high to match the AC voltage appearing in the PM motor 20, the output voltage of each phase of the inverter 30 can be freely adjusted by changing the switching ratio (duty cycle) of the upper and lower arms. That is, a three-phase AC voltage of any frequency can be applied to the PM motor 20, thereby enabling variable speed drive and torque control of the PM motor 20.

[0077] <Current Detection Unit 50>

[0078] The current detection unit 50 detects the current flowing through phases U and W of the three-phase AC current flowing from the inverter 30 to the PM motor 20, and outputs the results as AC current detection values ​​Iu and Iw. While it can detect the AC current of all phases, according to Kirchhoff's first law, if two phases of the three-phase current can be detected, the remaining phase can be calculated from the detected two phases. For example, a current detection unit 50, such as a current transformer (CT), can be installed in the lower arm of the inverter module 131.

[0079] As the current detection unit 50, for example, a phase shunt current method can be adopted. In this phase shunt current method, a shunt resistor is added to the lower arm of the inverter module 130 to replace the CT, and the current flowing through each phase of the inverter 30 is detected based on the current flowing through the shunt resistor. A single shunt current detection method can also be adopted to replace the current detection unit 50 or be added to the current detection unit 50. This single shunt current detection method detects the current on the AC side of the inverter 30 based on the DC current flowing through the shunt resistor 135 added to the DC side of the inverter 30. The single shunt current detection method utilizes the phenomenon that the current flowing through the shunt resistor 135 changes with time according to the energization state of the switching element 32 constituting the inverter 30.

[0080] <Driving method of PM motor 20>

[0081] When driving a motor having a permanent magnet 27 in the rotor 22, if a magnetic flux generated by the winding 25 is generated at a position that advances 90 electrical degrees in the rotational direction with respect to the magnetic flux of the permanent magnet 27, the maximum torque can be obtained with the minimum current. By driving in this way, there is an effect of not only realizing the miniaturization and light weight of the motor but also miniaturizing the inverter 30.

[0082] Among the above d-axis and q-axis, the d-axis can be called the magnet flux axis, and the q-axis can be called the winding flux axis. Appropriately controlling the current on the q-axis is particularly important. The current flowing through the motor is decomposed into a magnetic field component and a torque component on the rotating coordinate axes. In order to control the rotational speed or torque of the motor, the phase and magnitude of the voltage are controlled. Generally, this is called vector control. In addition, as a driving method of the PM motor, control is performed on the dq-axis, but a known coordinate conversion technique can be used to convert the three phases from the UVW axis to the dq-axis.

[0083] As the voltage command value calculation unit 12, for example, there are the structures and methods described in Japanese Patent Laid-Open No. 2005-39912. Figure 6 The structural example of the voltage command value calculation unit 12 when using this structure is shown.

[0084] By Figure 6 the voltage command value calculation unit 12 in inputs the d-axis and q-axis current command values (Id * and Iq * ) calculated by the current command value calculation unit 11 and the electrical angular velocity ωe, and performs vector operations as shown in Equation (1) and Equation (2), thereby obtaining the d-axis voltage command value Vd ＊ and the q-axis voltage command value Vq ＊ .

[0085] Vd ＊ = R × Id ＊＊-ωe×Lq×Iq ＊＊ _ fil …(1)

[0086] Vq ＊ =R×Iq ＊＊ +ωe×Ld×Id ＊＊ _ fil +ωe×Ke…(2)

[0087] In addition, in equations (1) and (2), R represents the winding resistance value of each phase of the PM motor 20 (motor), Ld represents the d-axis inductance, Lq represents the q-axis inductance, and Ke represents the induced voltage constant.

[0088] To make the current on the dq axis flow according to the command, use Figure 6 The structure of the d-axis current controller 114a and the q-axis current controller 114b in the diagram. Figure 6 In the d-axis current controller 114a of the circuit structure, the subtractor 91d receives the d-axis current command value Id. * Subtract the DC-axis current detection value Idc from the middle. Proportional transducers 92c and 92d multiply the result of this subtraction by the specified gains Kp_acrd and Ki_acrd, respectively. Integrator 94c takes the output of proportional transducer 92d, i.e., "Ki_acrd × (Idc)". * The integral is performed using "-Idc". Adder 90b adds the product result of proportionalizer 92c to the integral result of integrator 94c, and uses this sum as the d-axis current command value Id. ** Output.

[0089] Similarly, in the q-axis current controller 114b, the subtractor 91e takes the q-axis current command value Iq. * Subtract the qc-axis current detection value Iqc from the middle. Proportionals 92e and 92f multiply the subtraction result by the gains Kp_acrq and Ki_acrq, respectively. Integrator 94d takes the output of proportional 92f, i.e., "Ki_acrq×(Iqc)", as the result. * The integral is performed using "-Iqc". Adder 90c adds the product result of proportionalizer 92e to the integral result of integrator 94c, and uses this sum as the q-axis current command value Iq. ** Output is then produced. Thus, the d-axis current controller 14a and the q-axis current controller 14b each constitute a proportional-integral arithmetic unit.

[0090] In multipliers 92g and 92i, the winding resistance R of each phase of the PM motor 20 is multiplied by Id. ** andIq ** Find the first term on the right side of equations (1) and (2).

[0091] In the second term on the right-hand side of equations (1) and (2), the d-axis and q-axis current command values ​​(Idf) ** and Iqf ** ) is achieved through the use of Figure 6 The filter circuits 98a and 98b in the middle control the current command values ​​(Iq) for the q-axis and d-axis. ** 、Id ** The value is obtained by filtering. In multipliers 92h and 92j, the q-axis inductance Lq and the d-axis inductance Ld are respectively related to Idf. ** and Iqf ** Multiply by the electrical angular velocity ωe, and also by the electrical angular velocity ωe, to obtain the second term on the right side of equations (1) and (2). In addition, multiplier 92k multiplies the electrical angular velocity ωe by the inductance Ld of the d-axis, to obtain the third term on the right side of equation (2).

[0092] Subtractor 91f calculates the d-axis voltage command value Vd in equation (1) by subtracting the output of multiplier 92h from the output of multiplier 92g. * Adder 90d calculates the sum of the outputs of multipliers 92i, 92j, and 92k to obtain the q-axis voltage command value Vq in equation (2). * .

[0093] Figure 6 The advantage of this circuit structure example is that, in the voltage command value calculation unit 12, the d-axis current controller 114a and the q-axis current controller 114b are connected in series to the voltage calculation; and it includes first-order hysteresis filters (low-pass filters) 98a and 98b with a cutoff frequency comparable to the electrical time constant of the motor. Since an inverse model of the motor is thus established, even when the operation cycle of the control unit 10 is limited, it can still achieve the effect of ideal vector control.

[0094] <Technical Issues in Improving Torque Accuracy>

[0095] Although the motor control device 100 controls the speed or torque of the PM motor 20 to the desired value, in the drive of the PM motor, when the temperature of the magnet changes, the magnetic flux changes according to the temperature. Therefore, there is a problem that the torque accuracy deteriorates when no response is performed.

[0096] When the magnet temperature can be measured, torque accuracy can be improved by adjusting the current command value based on the temperature. However, due to durability and production issues, it is difficult to directly connect a temperature sensor to the magnet present inside the rotor. Therefore, estimating the magnet temperature is an effective countermeasure. Regarding the estimation of magnet temperature, for example, there are structures and methods described in Patent Document 1 (Japanese Patent Application Laid-Open No. 2021-2949) and Patent Document 2 (Japanese Patent Application Laid-Open No. 2021-16226).

[0097] In Patent Document 1, as described in the Technical Problems section, the following problem exists: Since the change in magnetic flux caused by the change in magnet temperature has a current dependence that varies depending on the d-axis current and the q-axis current, the estimated value of the change in magnet magnetic flux will be incorrect when the d-axis current and the q-axis current are not zero, and the estimated value of magnet temperature will also be incorrect.

[0098] Furthermore, Patent Document 2 has the following problem: when estimating the magnet temperature based on the magnet flux, a table showing the correspondence between the magnet flux, d-axis current, q-axis current, and magnet temperature is used, and the current dependence of the flux variation due to temperature changes is also considered to estimate the magnet temperature. However, because a table with three parameter inputs is used, the amount of data in the table increases, resulting in a large measurement operation time for creating the table and a heavy processing load for the table reference. The method for solving this problem will be described below.

[0099] <Concept of the Invention>

[0100] In this invention, the d-axis flux variation, which is the difference between the d-axis flux and the d-axis flux reference value, is first calculated. Then, based on the d-axis current value and the q-axis current value, the d-axis flux variation is corrected to a variation equivalent to when the d-axis current is zero. The magnet flux reference value is calculated based on the q-axis current value, and the estimated magnet temperature is calculated based on the corrected d-axis flux variation and the magnet flux reference value.

[0101] <Summary of the magnet temperature estimation operation in this invention>

[0102] The q-axis voltage equation under steady-state conditions, when neglecting the differential terms and taking the average value of each value, can be expressed by the following equation.

[0103] Vq ＊ =Vdrop_q+ωe×Ψd…(3)

[0104] Here, the q-axis voltage command value Vq * The components are: electrical angular velocity ωe, d-axis magnetic flux Ψd, and q-axis voltage drop component Vdrop_q. Vdrop_q is the velocity electromotive force (induced voltage) of ωeΨd and the q-axis voltage command value Vq. * The difference between them, and is the overall voltage drop component on the q-axis, including the voltage drop caused by the winding resistance, the voltage drop at the switching element 32, the error voltage caused by the dead time, and the error voltage caused by the PWM method. The d-axis flux Ψd can be expressed by the following formula.

[0105] Ψd=Ld×Id+Ψd0…(4)

[0106] Here, Ld is the d-axis inductance, Id is the d-axis current value, and Ψd0 is the magnetic flux. As can be seen from equation (4), when Id is zero, the d-axis flux Ψd becomes the magnetic flux Ψd0.

[0107] Next, use Figure 7 This section provides a summary of the magnet temperature estimation process. Figure 7 This is a graph showing the relationship between the d-axis flux and the corresponding d-axis current under a certain q-axis current. In equation (4), the d-axis inductance Ld and the magnetic flux Ψd0 vary according to the d-axis current value Id and the q-axis current value Iq. Therefore, the value of the d-axis flux Ψd varies not only with the d-axis current but also with the q-axis current. Figure 4 The d-axis flux curve changes with the q-axis current value.

[0108] First, the d-axis flux reference value Ψd_std is pre-measured and stored as a reference temperature. This is equivalent to measuring and storing... Figure 7 The d-axis flux curve is obtained at the reference temperature. However, as mentioned above, the d-axis flux also varies with the q-axis current value Iq. Therefore, the d-axis flux is measured relative to the d-axis current value Id and the q-axis current value Iq and stored as Ψd_std.

[0109] Next, the procedure for estimating the magnet temperature will be explained. When the estimated magnet temperature differs from the reference temperature, such as... Figure 7 As shown, the d-axis flux curve at the estimated time differs from the d-axis flux curve at the reference temperature. In motors using magnets like neodymium magnets, where the flux increases as the magnet temperature decreases, if the estimated magnet temperature is lower than the reference temperature, then as... Figure 7 As shown, the estimated d-axis flux curve shifts towards the positive direction of the d-axis flux axis relative to the d-axis flux curve at the reference temperature. Conversely, when the estimated magnet temperature is higher than the reference temperature, the estimated d-axis flux curve shifts towards the negative direction of the d-axis flux axis relative to the d-axis flux curve at the reference temperature.

[0110] Since the d-axis current value Id and the q-axis current value Iq are controlled according to the torque command value or the speed command value during simulation, it is impossible to measure all d-axis flux curves during simulation. Therefore, firstly, the d-axis flux Ψd under the d-axis current value Id and the q-axis current value Iq during simulation is calculated by the following formula (5).

[0111] Ψd=(Vq ＊ -Vdrop_q) / ωe…(5)

[0112] The q-axis voltage drop component Vdrop_q includes the voltage drop caused by various factors, but if only the voltage drop caused by the total resistance component of the winding, cable, switching element 32, etc., which is the most dominant, is considered, it can be calculated by the following formula (6).

[0113] Vdrop_q=Rall×Iq…(6)

[0114] Here, Rall is the total resistance value including the windings, cables, switching element 32, etc. The total resistance value Rall can be obtained by measurement or calculated based on the conductor cross-sectional area and length of the windings and cables, as well as the current and voltage characteristics of the switching element.

[0115] Based on the estimated d-axis current and q-axis current, calculate the pre-stored d-axis magnetic flux reference value Ψd_std. Then, calculate the d-axis magnetic flux variation ΔΨd using the following formula (7).

[0116] ΔΨd=Ψd―Ψd_std…(7)

[0117] The d-axis flux variation ΔΨd exhibits a current dependence that varies with the d-axis current value Id and the q-axis current value Iq. This is primarily because changes in magnet temperature lead to changes in magnet flux, which in turn alters the magnetic flux density of the iron core inside the motor, resulting in changes in inductance. Therefore, when estimating magnet temperature based on the d-axis flux variation ΔΨd, its current dependence must be considered.

[0118] Therefore, the d-axis flux variation ΔΨd under the estimated d-axis current value Id and q-axis current value Iq is corrected so that this d-axis flux variation ΔΨd is equivalent to the d-axis flux variation ΔΨd0 when Id is zero. The corrected d-axis flux variation is set as the corrected d-axis flux variation ΔΨd_cmp. ΔΨd_cmp is calculated based on ΔΨd, Id, and Iq. Preferably, the difference between ΔΨd_cmp and ΔΨd0 is small.

[0119] The calculation method for ΔΨd_cmp based on ΔΨd, Id, and Iq is explained. First, the ratio of ΔΨd0 to ΔΨd calculated under two pre-existing temperature conditions is recorded as the correction coefficient K. The correction coefficient K is represented by the following formula (8).

[0120] K=ΔΨd0 / ΔΨd…(8)

[0121] Since ΔΨd0 varies with the q-axis current value Iq, and ΔΨd varies with the d-axis current value Id and the q-axis current value Iq, the correction coefficient K is recorded relative to the d-axis current value Id and the q-axis current value Iq.

[0122] When estimating, ΔΨd_cmp is calculated by the following equation (9).

[0123] ΔΨd_cmp=ΔΨd×K…(9)

[0124] When the two temperature conditions for determining the correction factor K are consistent with the reference temperature and the estimated temperature, ΔΨd_cmp and ΔΨd0 are consistent. However, when the two temperature conditions for determining the correction factor K are different from the reference temperature and the estimated temperature, ΔΨd_cmp and ΔΨd0 are inconsistent. Nevertheless, regardless of the choice of the two temperature conditions, since the correction factor K, which is the ratio of ΔΨd0 to ΔΨd, is almost constant, the difference between ΔΨd_cmp and ΔΨd0 is small even when the two temperature conditions for determining the correction factor K are inconsistent with the reference temperature and the estimated temperature.

[0125] Therefore, based on the d-axis flux variation ΔΨd, the corrected d-axis flux variation ΔΨd_cmp, which is equivalent to the d-axis flux variation ΔΨd0 when Id is zero, can be calculated.

[0126] Next, based on the estimated q-axis current value Iq, the magnetic flux at the reference temperature, i.e., the magnetic flux reference value Ψd0_std, is calculated. The d-axis magnetic flux, i.e., the magnetic flux at which the d-axis current value Id is zero, varies with the q-axis current value Iq. The magnetic flux reference value Ψd0_std can be measured and stored in advance at the reference temperature, or it can be obtained from the data in the d-axis flux reference value Ψd_std when the d-axis current value Id is zero.

[0127] Finally, the estimated magnet temperature Tm_est is calculated based on the corrected d-axis flux variation ΔΨd_cmp and the magnet flux reference value Ψd0_std. The ratio of ΔΨd_cmp to Ψd0_std, i.e., the flux variation ratio KΨ, is calculated by the following formula (10).

[0128] KΨ=ΔΨd_cmp / Ψd0_std…(10)

[0129] The estimated magnet temperature is calculated based on the relationship between the flux change rate KΨ and the magnet temperature. This can be achieved by pre-changing the magnet temperature, measuring the flux change rate KΨ, or calculating and storing the flux change rate KΨ using electromagnetic field simulation, and presenting the correspondence between the flux change rate KΨ and the magnet temperature as a table. Alternatively, the magnet temperature can be calculated using a mathematical formula with the flux change rate KΨ as input.

[0130] The above provides an overview of the magnet temperature estimation operation in this invention. Next, the structure and operation of the magnet temperature estimation unit 40 will be described in detail.

[0131] <Structure and Operation of the Magnet Temperature Estimation Unit>

[0132] Figure 8 This is a control block diagram of the magnet temperature estimation unit 40. Figure 9 This is a block diagram including the voltage sensor 70 that measures the output voltage of the measurement inverter 30. The operation when estimating the magnet temperature during the driving of the motor will be described below.

[0133] Calculate the magnet temperature estimated value Tm_est based on the q-axis voltage value Vq, the electrical angular velocity ωe, the d-axis current value Id, and the q-axis current value Iq. The details of each block will be described later.

[0134] First, the d-axis current value and the q-axis current value can be the d-axis current detection value and the q-axis current detection value as in the connection of Figure 1 , or can be the d-axis current command value and the q-axis current command value based on the command value. In addition, the q-axis voltage value can be the q-axis voltage command value as in the connection of Figure 1 , or can be the structure where the output voltage of the inverter 30 is measured using the voltage sensor 70 as shown in Figure 9 , the voltage detection value is input to the control unit 10, and the voltage detection value is converted from the three-phase UVW axis to the dq axis by the coordinate conversion unit 13a, so as to obtain the d-axis voltage detection value and the q-axis voltage detection value, and thus the q-axis voltage value is set as the q-axis voltage detection value.

[0135] The d-axis flux change amount calculation unit 41 calculates the d-axis flux change amount ΔΨd based on the q-axis voltage value Vq, the electrical angular velocity ωe, the d-axis current value Id, and the q-axis current value Iq. ΔΨd is the difference between the d-axis flux Ψd at the time of estimation and the d-axis flux reference value Ψd_std which is the d-axis flux at the reference temperature.

[0136] Next, in the d-axis flux change amount correction unit, based on the d-axis current value Id and the q-axis current value Iq, the d-axis flux change amount ΔΨd is corrected to the d-axis flux change amount ΔΨd0 corresponding to when Id is zero, and the corrected d-axis flux change amount ΔΨd_cmp is calculated.

[0137] In the magnet flux reference value calculation unit 43, the magnet flux reference value Ψd0_std is calculated based on the q-axis current value Iq.

[0138] Finally, in the magnet temperature calculation unit 44, the magnet temperature estimated value Tm_est is calculated based on the corrected d-axis flux change amount ΔΨd_cmp and the magnet flux reference value Ψd0_std.

[0139] The structure and operation of the d-axis flux change amount calculation unit <d-axis flux change amount operation unit structure and operation>

[0140] Figure 10This is a control block diagram of the d-axis flux change calculation unit 41. The d-axis flux calculation unit 411 uses the q-axis voltage value Vq, electrical angular velocity ωe, and q-axis current value Iq as inputs to calculate the d-axis flux Ψd.

[0141] One method for calculating the d-axis flux Ψd is based on equations (5) and (6). Furthermore, as shown in equation (6), by adding not only the voltage drop caused by all resistance components Rall in the voltage drop component to Vdrop_q, but also the nonlinear voltage drop component relative to the q-axis current value Iq of the switching element 32 to Vdrop_q, the calculation accuracy of the d-axis flux Ψd can be improved. In this case, a table or mathematical expression is used, taking the q-axis current value Iq as input and the voltage drop of the switching element 32 as output. Furthermore, methods can be based on the q-axis current value Iq, Figure 10 The d-axis current value Id (not shown), DC voltage Edc, and switching frequency fsw (which are inputs to the d-axis flux calculation unit 411) are used to calculate the error voltage caused by the dead time and the error voltage caused by the PWM method, and these are added to Vdrop_q.

[0142] The d-axis flux reference value calculation unit 412 calculates the d-axis flux reference value Ψd_std at the reference temperature based on the d-axis current value Id and the q-axis current value Iq. The calculation method is unrestricted as long as the d-axis flux reference value Ψd_std can be calculated from the d-axis current value Id and the q-axis current value Iq.

[0143] As an example of the method for calculating the d-axis flux reference value Ψd_std, it can be configured as follows: the d-axis flux is calculated in advance by measuring the d-axis flux relative to the d-axis current value Id and the q-axis current value Iq, or by using electromagnetic field simulation, and stored; a table of Ψd_std with Id and Iq as parameters is created and used during estimation. Alternatively, it can be configured as follows: the relationship between the d-axis flux reference value Ψd_std and the d-axis current value Id and the q-axis current value Iq is converted into a mathematical expression and used during estimation. As an example of using a mathematical expression, it can be configured as follows: the relationship between the d-axis inductance Ld_std at the reference temperature and the d-axis current value Id and the q-axis current value Iq is stored in advance, and the d-axis flux reference value Ψd_std is calculated by the following formula (11).

[0144] Ψd_std=Ld_std×Id+Ψd0_std…(11)

[0145] Furthermore, during the motor drive process, when the magnet temperature can be regarded as the reference temperature, the d-axis flux Ψd output by the d-axis flux calculation unit at this time can be stored as a d-axis flux reference value Ψd_std relative to the d-axis current value Id and the q-axis current value Iq at this time, the table of Ψd_std is updated, and the mathematical formula used to calculate Ψd_std is updated.

[0146] Finally, the d-axis flux variation calculation unit 41 calculates the d-axis flux variation ΔΨd based on equation (7) and the difference between the d-axis flux Ψd and the d-axis flux reference value Ψd_std.

[0147] Figure 11 The diagram shows an example of the relationship between the d-axis flux reference value Ψd_std, stored as a table or mathematical formula in the d-axis flux reference value calculation unit 412, and the d-axis current value Id and the q-axis current value Iq. For example... Figure 11 As shown, in a magnet motor designed to generate a flux that weakens the magnet flux as the d-axis current increases in the negative direction, the d-axis flux decreases as the d-axis current value increases in the negative direction.

[0148] Furthermore, the d-axis flux also varies depending on the q-axis current value. If the magnet flux or the d-axis inductance is kept constant when calculating the reference value of the d-axis flux, the variation ΔΨd of the d-axis flux will introduce errors, and the estimated value of the magnet temperature will also be inaccurate. By pre-storing the reference value Ψd_std of the d-axis flux that varies with the d-axis current and q-axis current, and performing calculations based on the d-axis current value Id and the q-axis current value Iq during estimation, the variation ΔΨd of the d-axis flux can be calculated accurately.

[0149] <Structure and Operation of the Magnet Flux Reference Value Calculation Unit>

[0150] The magnet flux reference value calculation unit 43 calculates the magnet flux reference value Ψd0_std based on the q-axis current value Iq. Figure 12 An example of the relationship between the q-axis current value Iq and the magnet flux reference value Ψd0_std is shown. In the magnet flux reference value calculation unit 43, as long as the magnet flux reference value Ψd0_std can be calculated based on the q-axis current value Iq, the calculation method is not limited.

[0151] As an example of the calculation method of the magnet flux reference value Ψd0_std, it can be configured as follows: Measure in advance the magnet flux reference value Ψd0_std with respect to the q-axis current value Iq at the reference temperature, or calculate the magnet flux reference value Ψd0_std with respect to the q-axis current value Iq at the reference temperature by electromagnetic field simulation, and store it. Create a table of Ψd0_std with Iq as a parameter and use this table during estimation. Alternatively, it can be configured to convert the relationship between the magnet flux reference value Ψd0_std and the q-axis current value Iq into a mathematical formula and use this mathematical formula during estimation. In addition, the magnet flux reference value Ψd0_std and the reference d-axis flux Ψd_std stored in the d-axis flux reference value calculation unit 412 have the same flux value when the d-axis current value Id is zero. Therefore, when calculating the reference d-axis flux Ψd_std in the d-axis flux reference value calculation unit 412, the flux value when the d-axis current value Id is zero can be calculated and used as the output of the magnet flux reference value calculation unit 43, that is, the magnet flux reference value Ψd0_std.

[0152] <Structure and operation of the d-axis flux variation correction unit>

[0153] Figure 13 It is the control block diagram of the d-axis flux variation correction unit 42. Based on the d-axis current value Id and q-axis current value Iq at the time of estimation, calculate the corrected d-axis flux variation ΔΨd_cmp equivalent to the d-axis flux variation ΔΨd0 when Id is zero according to the d-axis flux variation ΔΨd. The correction coefficient calculation unit 421 takes the d-axis current value Id and q-axis current value Iq as inputs to calculate the correction coefficient K. The correction coefficient calculation unit 421 only needs to be able to calculate the correction coefficient K according to the d-axis current value Id and q-axis current value Iq, and the calculation method is not limited.

[0154] As an example of the calculation method of the correction coefficient K, it can be configured as follows: Based on ΔΨd0 and ΔΨd measured or calculated by electromagnetic field simulation for the d-axis current value Id and q-axis current value Iq under two pre-existing temperature conditions, calculate and store the correction coefficient K according to Equation (8), create a table of the correction coefficient K with Id and Iq as parameters, and use this table during estimation. Alternatively, the relationship between the correction coefficient K and the d-axis current value Id and q-axis current value Iq can be converted into a mathematical formula and used during estimation.

[0155] Finally, the d-axis flux variation correction unit 42 calculates the corrected d-axis flux variation ΔΨd_cmp according to Equation (9).

[0156] Figure 14An example is shown showing the relationship between the correction coefficient K, stored as a table or mathematical formula in the correction coefficient calculation unit 421, and the corresponding d-axis current value Id and q-axis current value Iq. The correction coefficient K is the ratio of the d-axis flux variation ΔΨd to the d-axis flux variation ΔΨd0 when Id is zero; therefore, on the straight line where the d-axis current value Id is zero, the correction coefficient K is 1. Although the characteristics of a motor vary depending on its structure, in the case of a motor where the absolute value of the d-axis flux variation ΔΨd increases as the d-axis current increases in the negative direction, such as... Figure 14 As shown, the correction factor K decreases as the d-axis current increases in the negative direction. Furthermore, since the d-axis flux variation ΔΨd also changes with the q-axis current, the correction factor K also becomes a value that varies with the q-axis current.

[0157] Although the structure of the correction coefficient K, which is the ratio of ΔΨd0 to ΔΨd, has been explained, other correction methods can be used to calculate ΔΨd_cmp based on ΔΨd, Id, and Iq. Regardless of the correction method used, it is sufficient to calculate ΔΨd_cmp, which is equivalent to ΔΨd0.

[0158] <Structure and Operation of the Magnet Temperature Calculation Unit>

[0159] Figure 15 This is a control block diagram of the magnet temperature calculation unit 44. The estimated magnet temperature Tm_est is calculated based on the corrected d-axis flux variation ΔΨd_cmp and the magnet flux reference value Ψd0_std. First, the ratio of ΔΨd_cmp to Ψd0_std, i.e., the flux change ratio KΨ, is calculated based on equation (10). Next, in the magnet temperature conversion unit 441, the estimated magnet temperature Tm_est is calculated based on the relationship between the flux change ratio KΨ and the magnet temperature.

[0160] This can be achieved by pre-changing the magnet temperature, measuring the magnetic flux change rate KΨ, or calculating and storing the magnetic flux change rate KΨ using electromagnetic field simulation, and then presenting the correspondence between the magnetic flux change rate KΨ and the magnet temperature as a table. Alternatively, the magnet temperature can be calculated using a mathematical formula with the magnetic flux change rate KΨ as input.

[0161] Figure 16 An example is shown illustrating the relationship between the flux change ratio KΨ, stored as a table or mathematical formula in the magnet temperature conversion unit 441, and the corresponding estimated magnet temperature Tm_est. When the flux change ratio KΨ is zero, the flux change due to the magnet temperature change is zero; therefore, the estimated magnet temperature Tm_est is equal to the reference magnet temperature. The flux change ratio for temperature changes varies depending on the temperature characteristics of the magnet. In cases like neodymium magnets, where the magnet flux decreases as temperature increases, such as... Figure 16As shown, there exists a relationship that the estimated magnet temperature decreases as the rate of change of magnetic flux increases in the positive direction.

[0162] Although the structure for calculating the ratio of the corrected d-axis flux variation ΔΨd_cmp to the magnet flux reference value Ψd0_std, i.e., the flux variation ratio KΨ, has been explained, and the magnet temperature estimation value Tm_est has been calculated by the magnet temperature conversion unit 441, other calculation methods can be used to calculate Tm_est based on ΔΨd_cmp and Ψd0_std.

[0163] <Effects of the Invention>

[0164] In the structure and operation of the magnet temperature estimation of the present invention, the following characteristic is utilized: the ratio of the d-axis flux variation ΔΨd0 when Id is zero to the magnet flux reference value Ψd0_std is determined almost uniquely based on the difference between the reference temperature and the magnet temperature at the estimation time. If a d-axis flux variation ΔΨd, which is different from the d-axis flux variation ΔΨd0 when Id is zero, is directly used for magnet temperature estimation, an estimation temperature error will occur. Therefore, a corrected d-axis flux variation ΔΨd_cmp, which is equivalent to the d-axis flux variation ΔΨd0 when Id is zero, is used. Furthermore, if the magnet flux reference value Ψd0_std is set to constant for magnet temperature estimation, an estimation temperature error will occur. Therefore, the value calculated based on the q-axis current value Iq is used as Ψd0_std. By correcting ΔΨd to ΔΨd_cmp, which is equivalent to ΔΨd0, and calculating Ψd0_std based on the q-axis current value Iq, the current dependence of the d-axis flux variation ΔΨd caused by temperature change can be appropriately corrected, thereby improving the accuracy of magnet temperature estimation.

[0165] Furthermore, since the d-axis flux variation ΔΨd is corrected based on two parameters, the d-axis current value Id and the q-axis current value Iq, and the magnet flux reference value Ψd0_std is calculated based on the q-axis current value Iq, the required adjustment workload, time, and estimated processing workload are significantly reduced compared to the method of directly calculating the magnet temperature using three parameters, namely the d-axis current value Id, the q-axis current value Iq, the d-axis flux Ψd, or the magnet flux, as inputs.

[0166] Next, we will explain how to improve the accuracy of the magnet temperature estimate by correcting ΔΨd to ΔΨd_cmp, which is equivalent to ΔΨd0, and by calculating Ψd0_std based on the q-axis current value Iq.

[0167] Figure 17This is a control block diagram showing an example of the structure of a magnet temperature estimation unit when the d-axis flux variation correction unit is not included and the magnet flux reference value is set to a constant. In the absence of the d-axis flux variation correction unit, the magnet flux reference value calculation unit 43a outputs a fixed magnet flux reference value. The d-axis flux variation calculation unit 41a is the same as the d-axis flux variation calculation unit 41.

[0168] Figure 18 This section shows an example of the magnet temperature estimation error in the magnet temperature estimation section when the d-axis flux variation correction unit is not included and the magnet flux reference value is set to a constant. This is the estimation result when the true magnet temperature value at the estimation time is set to a value different from the reference temperature, and the estimation temperature error obtained by subtracting the true magnet temperature value at the estimation time from the estimated magnet temperature value relative to the rotational speed and torque is plotted. Since the magnet flux reference value is kept constant without correcting for the d-axis flux variation, a large estimation error of 100°C occurs. In particular, in the high torque region where the q-axis current is large, the error in the magnet flux reference value becomes larger, and the magnet temperature estimation value also exhibits a large error.

[0169] Figure 19 This is a control block diagram showing a structural example of a magnet temperature estimation unit without the d-axis flux variation correction unit. Although the d-axis flux variation correction unit is absent, the magnet flux reference value calculation unit 43b is the same as the magnet flux reference value calculation unit 43, and the d-axis flux variation calculation unit 41a is the same as the d-axis flux variation calculation unit 41.

[0170] Figure 20 An example of magnet temperature estimation error in the magnet temperature estimation section without the d-axis flux variation correction unit is shown. The conditions and plotting method of the true magnet temperature during estimation are the same as those for... Figure 18 Same. With Figure 18 In contrast, calculating the magnet flux reference value based on the q-axis current reduces the estimated temperature error. However, because the d-axis flux variation ΔΨd, which differs from the d-axis flux variation ΔΨd0 when Id is zero, is directly used for magnet temperature estimation, an estimated temperature error of approximately 20°C is introduced.

[0171] Figure 21 An example of the magnet temperature estimation result obtained by the magnet temperature estimation unit 40 is shown. By correcting ΔΨd to ΔΨd_cmp, which is equivalent to ΔΨd0, and calculating Ψd0_std based on the q-axis current value Iq, the current dependence of the d-axis magnetic flux variation ΔΨd caused by temperature change can be appropriately corrected, thereby reducing the estimated temperature error to about 5°C.

[0172] <Modification of Example 1>

[0173] In the above description, the correction coefficient K and the magnet flux reference value Ψd0_std are calculated by separate arithmetic units. According to equations (9) and (10), the flux change ratio KΨ is expressed by equation (12).

[0174] KΨ=ΔΨd×K / Ψd0_std…(12)

[0175] Here, K / Ψd0_std can be integrated into a conversion coefficient Kt, and the conversion coefficient Kt can be calculated based on the d-axis current value and the q-axis current value. Figure 22 The diagram shows the control block diagram of the part that calculates the flux change ratio based on the d-axis flux variation in this case. The conversion coefficient calculation unit 45 calculates the conversion coefficient Kt based on equation (12) and multiplies it by the d-axis flux variation ΔΨd, thereby calculating the flux change ratio KΨ.

[0176] [Example 2]

[0177] Embodiment 2 of the present invention will be described. Structures common to Embodiment 1 will be given the same reference numerals, and detailed descriptions thereof will be omitted.

[0178] Except for the following aspects, the structure of this embodiment can be the same as that of Embodiment 1. This embodiment relates to a control unit 10, which includes a unit that uses information about a magnet temperature estimation value estimated by the magnet temperature estimation unit 40.

[0179] A technical problem with electric motors containing permanent magnets in the rotor is thermal demagnetization of the permanent magnets. When the temperature of the permanent magnet rises above a certain level, it can sometimes lead to irreversible demagnetization. When the permanent magnet is demagnetized, it is difficult to control the motor speed or torque to the desired value. In addition, the current flowing through the motor or inverter may sometimes increase in order to ensure torque generation.

[0180] Figure 23 This is a block diagram illustrating the structure of the control unit 10a according to Embodiment 2 of the present invention. The control unit 10a of Embodiment 2 includes a unit that uses information estimated using magnet temperature.

[0181] exist Figure 23 The structure shown includes a torque command value limiting unit 16, a d-axis current command value limiting unit 17 that limits the d-axis current command value, and a q-axis current command value limiting unit 18 that limits the q-axis current command value. For speed command values ​​and torque commands obtained from the control unit 10a, or from a higher-level control system or other control system not shown, the torque command value limiting unit 16 limits the torque command value based on a magnet temperature estimation value estimated by the magnet temperature estimation unit 40.

[0182] Figure 24This diagram illustrates a structural example of the torque command value limiting unit 16, the d-axis current command value limiting unit 17, and the q-axis current command value limiting unit 18. The estimated magnet temperature value, estimated by the magnet temperature estimation unit 40, is input to the command limit value calculation unit 101. The command limit value calculation unit 101 outputs the command limit value based on the input estimated magnet temperature value.

[0183] For example, when the estimated magnet temperature, which poses no risk of thermal demagnetization, is below the judgment threshold Th, the command limit value is set to the same value as when the magnet temperature is sufficiently low. If the estimated magnet temperature exceeds the judgment threshold Th, the command limit value is reduced and output. When the estimated magnet temperature is high and the risk of thermal demagnetization is high, the command limit value can be set to zero, thereby setting the motor output to zero.

[0184] Command value limiter 102 limits the maximum and minimum values ​​of torque command value, d-axis current command value, or q-axis current command value based on command value limit values. Here, however, the limit values ​​for the maximum and minimum values ​​can be set as absolute values ​​with different signs as command value limit values. Alternatively, it can include a command value limit calculation unit for the maximum value and a command value limit calculation unit for the minimum value, setting the limit values ​​for the maximum and minimum values ​​to different values.

[0185] Therefore, by configuring a unit that includes information on the estimated magnet temperature value estimated by the magnet temperature estimation unit 40, thermal demagnetization of the permanent magnet of the PM motor and excessive increase in the current flowing through the PM motor or inverter 30 can be prevented in advance. That is, a highly reliable motor control device can be provided. Here, it can be configured to include at least one of the torque command value limiting unit 16, the d-axis current command value limiting unit 17, and the q-axis current command value limiting unit 18. Although thermal demagnetization of the permanent magnet of the PM motor and excessive increase in the current flowing through the PM motor or inverter 30 can be prevented in advance by a single command value limiting unit, multiple command value limiting units can be included for the purpose of ensuring redundancy or gradually reducing the output.

[0186] Furthermore, in the absence of a unit for estimating the permanent magnet temperature of the PM motor, the continuous rated output is sometimes set to a small value with a margin relative to the maximum output to prevent thermal demagnetization. In this embodiment, in the case of a unit that limits the command value and suppresses the output based on the estimated magnet temperature, the continuous rated output can be set by minimizing the margin relative to the maximum output. That is, the continuous rated output can be improved while keeping the motor structure the same.

[0187] [Example 3]

[0188] Embodiment 3 of the present invention will be described. Structures common to Embodiments 1 and 2 are given the same reference numerals, and their detailed descriptions are omitted.

[0189] Except for the following aspects, the structure of this embodiment can be the same as that of Embodiment 1. This embodiment relates to a control unit 10b, which includes a unit that uses information about a magnet temperature estimation value estimated by the magnet temperature estimation unit 40.

[0190] When the torque of a motor with permanent magnets in its rotor is controlled to the desired value, changes in the magnet's temperature cause a change in magnetic flux, resulting in a deterioration in torque accuracy without any intervention. Taking the installation of a motor control unit in an electric vehicle system as an example, this deterioration in torque accuracy can lead to problems such as reduced ride comfort and decreased accuracy of autonomous driving.

[0191] Figure 25 This is a block diagram showing the structure of the control unit 10b according to Embodiment 3 of the present invention. The control unit 10b of Embodiment 3 includes a current command value calculation unit 11a, which calculates the d-axis current command value and the q-axis current command value by using the magnet temperature estimation value estimated by the magnet temperature estimation unit 40 as input, in addition to the torque command value.

[0192] The current command value calculation unit 11a calculates the d-axis current command value and the q-axis current command value, so that when the magnet temperature is at the reference temperature, the difference between the torque command value and the actual torque of the motor is reduced. When the magnet temperature differs from the reference temperature, a torque error will occur. Therefore, the d-axis current command value and the q-axis current command value are calculated based on the estimated magnet temperature and the torque command value, so that the torque error caused by the change in magnet temperature is reduced.

[0193] Therefore, by configuring a unit that has information on the estimated value of the magnet temperature estimated by the magnet temperature estimation unit 40, the deterioration of torque accuracy caused by changes in magnet temperature can be reduced, thereby providing a motor control device with high torque accuracy.

[0194] As described above, the system includes: a q-axis voltage value calculation unit that calculates the q-axis voltage value based on a measured voltage value of the magnet motor or a voltage command value calculated to make the torque or current of the magnet motor match the command value; a d-axis flux variation calculation unit that calculates the difference between the d-axis flux and the d-axis flux reference value, i.e., the d-axis flux variation, using the q-axis voltage value, electrical angular velocity, d-axis current value, and q-axis current value as inputs; and a d-axis flux variation correction unit that corrects the d-axis flux variation based on the d-axis current value and the q-axis current value. The system includes a d-axis flux variation calculation unit that calculates the magnet flux reference value based on the q-axis current value, and a magnet temperature calculation unit that calculates the magnet temperature estimate based on the corrected d-axis flux variation and the magnet flux reference value. This corrects the current dependence of the flux variation caused by temperature changes when estimating the magnet temperature, improves the magnet temperature estimation accuracy, and reduces the load and time required for prior adjustment and the processing load during estimation.

[0195] This invention is not limited to the embodiments described above, but also includes various modifications. For example, the above embodiments are detailed descriptions provided to facilitate understanding of the invention and are not required to have all the structures described.

[0196] Furthermore, the aforementioned structures, functions, processing units, and processing procedures can be partially or entirely implemented in hardware, for example, by designing integrated circuits. Alternatively, the aforementioned structures and functions can be implemented in software by having a processor interpret and execute programs that perform their respective functions.

[0197] Furthermore, the signal and information lines shown are taken into account as necessary for the description, but are not limited to showing all the control and information lines necessary for the product. Additionally, each of the aforementioned structures, functions, processing units, and processes does not necessarily need to be physically located in the same place, and some may be located, for example, via a network or cloud through communication.

[0198] Furthermore, although the motor is described as having an inner rotor structure with the rotor located inside the stator, it could also have an outer rotor structure. Additionally, the motor could be a radial clearance motor or an axial clearance motor. Besides a PMSM, a synchronous motor or SRM equipped with magnets could also be used.

[0199] Label Explanation

[0200] 10, 10a, 10b Control Section

[0201] 11.11a Current Command Value Calculation Unit

[0202] 12 Voltage Command Value Calculation Unit

[0203] 13 Coordinate Transformation Department

[0204] 14 PWM signal generation unit

[0205] 15 Angular Velocity Calculation Unit

[0206] 16 Torque Command Value Limiting Section

[0207] 17d-axis current command value limiting section

[0208] 18q-axis current command value limiting section

[0209] 20PM electric motor

[0210] 27 permanent magnet

[0211] 30 inverter

[0212] 40 Magnet Temperature Estimation Section

[0213] 41d-axis flux variation calculation unit

[0214] 42d-axis flux variation correction unit

[0215] 43 Magnet flux reference value calculation unit

[0216] 44 Magnet Temperature Calculation Unit

[0217] 45 Conversion Coefficient Calculation Section

[0218] 50 Current Detection Unit

[0219] 60-degree angle sensor

[0220] 70 Voltage Sensor

[0221] 100 motor control device

[0222] 101 Instruction Limit Value Arithmetic Unit

[0223] 102 instruction value limiter

[0224] 411d-axis flux processing unit

[0225] 412d-axis flux reference value calculation unit

[0226] 421 Correction Coefficient Calculation Unit

[0227] 441 Magnet Temperature Conversion Department.

Claims

1. An electric motor control device, comprising a control unit for controlling an electric motor having a permanent magnet, characterized in that, The control unit includes a magnet temperature estimation unit. The magnet temperature estimation unit takes into account: a q-axis voltage value calculated based on either the motor's speed command value or the motor's torque command value, or a voltage detection value of the motor; an electrical angular velocity calculated based on the motor's electrical angle; and d-axis and q-axis current values ​​calculated based on the motor's voltage detection value or the motor's current detection value, or based on the command value, and estimates the temperature of the permanent magnet. The magnet temperature estimation unit includes: The d-axis flux variation calculation unit takes the q-axis voltage value, the electrical angular velocity, the d-axis current value, and the q-axis current value as input, and calculates the difference between the d-axis flux and the d-axis flux reference value, i.e., the d-axis flux variation; the d-axis flux variation correction unit calculates the corrected d-axis flux variation based on the d-axis current value and the q-axis current value. A magnet flux reference value calculation unit calculates a magnet flux reference value based on the q-axis current value; and The magnet temperature calculation unit calculates the estimated magnet temperature of the permanent magnet based on the corrected d-axis magnetic flux variation and the magnet magnetic flux reference value.

2. The motor control device according to claim 1, characterized in that, The d-axis flux variation calculation unit includes: a d-axis flux calculation unit that inputs the q-axis voltage value, the electrical angular velocity, and the q-axis current value, and calculates the d-axis flux; and a d-axis flux reference value calculation unit that inputs the d-axis current value and the q-axis current value, and calculates the d-axis flux reference value. The variation in d-axis magnetic flux is calculated based on the difference between the d-axis magnetic flux and the reference value of d-axis magnetic flux.

3. The motor control device according to claim 1, characterized in that, The d-axis flux variation correction unit includes a correction coefficient calculation unit, which takes the d-axis current value and the q-axis current value as inputs and calculates the correction coefficient. The d-axis flux variation correction unit calculates the corrected d-axis flux variation based on the d-axis flux variation and the correction coefficient.

4. The motor control device according to claim 1, characterized in that, The magnet temperature calculation unit includes a magnet temperature conversion unit, which inputs the magnetic flux change ratio calculated based on the corrected d-axis magnetic flux variation and the magnet magnetic flux reference value, and calculates the estimated magnet temperature value.

5. The motor control device according to any one of claims 1 to 4, characterized in that, The control unit includes a command value limiter that limits the maximum and minimum values ​​of the torque command value, the d-axis current value, or the q-axis current value based on the estimated magnet temperature.

6. The motor control device according to any one of claims 1 to 4, characterized in that, The control unit includes a current command value calculation unit, which calculates the d-axis current command value and the q-axis current command value based on the torque command value and the estimated magnet temperature.

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