Method for measuring torque ripple of permanent magnet motor, torque ripple measuring device, and method for manufacturing permanent magnet motor

Abstract

In the method for measuring the torque ripple of the permanent magnet motor according to the present disclosure, the permanent magnet motor is provided with: a stator having an iron core for guiding magnetic flux and a coil insulated from the iron core and capable of generating a rotating magnetic field; a rotor having a magnet for generating a magnetic flux, the rotor being fixed so as to be rotatable with respect to a stator for guiding the magnetic flux; and a speed detector for detecting the mechanical angular speed of the rotor, the method for measuring the torque ripple of the permanent magnet motor including a calculation step for calculating the torque ripple of the permanent magnet motor in a state in which the output shaft of the permanent magnet motor is not driven from the outside but is driven by the permanent magnet motor. Each angular acceleration obtained by differentiating the mechanical angular velocity detected by the velocity detector is decomposed into frequency components of an integer multiple of the number of times with respect to the rotation angle, and the frequency components are multiplied by the inertia moment to calculate a torque ripple.

Description

Technical Field

[0001] The present disclosure relates to a method of measuring torque ripple generated when a permanent magnet motor rotates. Background Art

[0002] In the torque pulsation measuring method disclosed in Patent Document 1 listed below, a torque sensor is provided between a test motor and a load motor as a measurement target, the test motor is rotated by the load motor, and the torque fluctuation generated at this time is measured.

[0003] In addition, in the torque pulsation measuring method disclosed in Patent Document 2 listed below, a load motor and a torque sensor are not used, and torque fluctuation is calculated based on a command value of a current supplied to a test motor controlled at a constant speed.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Publication No. 2005-188941

[0007] Patent Document 2: Japanese Patent Application Laid-Open No. 7-210221 Summary of the invention

[0008] Problem that the invention aims to solve

[0009] The method of Patent Document 1 requires a process of connecting the load motor and the torque sensor, which hinders improvement of productivity. In addition, there is a problem that the cost of a measuring device such as a torque sensor is required, which leads to an increase in production cost.

[0010] In the method of Patent Document 2, it is necessary to keep the speed constant to achieve measurement. When feedback control is performed as described in Patent Document 2, the deviation from the command speed is fed back to the torque, so speed changes are inevitably generated and constant speed control cannot be performed. When there is speed pulsation, a torque pulsation amount that depends on the inertia torque is generated, so there is a problem of measurement error of the torque pulsation.

[0011] The present disclosure is completed to solve the above-mentioned problems, and its purpose is to provide a torque pulsation measurement method, in which there is no need for mechanical connection between the load motor and the torque sensor relative to the permanent magnet motor, and the torque pulsation can be measured even in a state where constant speed control cannot be performed.

[0012] Means used to solve problems

[0013] In the torque pulsation measuring method of the permanent magnet motor disclosed in the present invention, the permanent magnet motor comprises: a stator having an iron core for guiding magnetic flux and a coil insulated from the iron core and capable of generating a rotating magnetic field; a rotor having a magnet for generating magnetic flux and being rotatably fixed relative to the stator for guiding magnetic flux; and a speed detector for detecting the mechanical angular velocity of the rotor. The torque pulsation measuring method includes a calculation step in which each angular acceleration obtained by differentiating the mechanical angular velocity detected by the speed detector is decomposed into frequency components of an integer multiple of the rotation angle when the output shaft of the permanent magnet motor is not driven from the outside but driven by the permanent magnet motor, and the frequency components are multiplied by the inertia moment to calculate the torque pulsation.

[0014] Furthermore, the method for manufacturing a permanent magnet motor of the present disclosure includes the step of determining whether the permanent magnet motor is good or not based on the torque ripple calculated using the torque ripple measuring method after assembling the permanent magnet motor.

[0015] In addition, in the torque pulsation measuring device of the permanent magnet motor disclosed in the present invention, the permanent magnet motor includes: a stator having an iron core for guiding magnetic flux and a coil insulated from the iron core and capable of generating a rotating magnetic field; a rotor having a magnet for generating magnetic flux and being rotatably fixed relative to the stator for guiding magnetic flux; and a speed detector for detecting the mechanical angular velocity of the rotor. The torque pulsation measuring device includes the following steps: calculating the inertial torque pulsation as follows: in a state where the output shaft of the permanent magnet motor is not driven from the outside but is driven by the permanent magnet motor, decomposing each angular acceleration obtained by differentiating the mechanical angular velocity detected by the speed detector into frequency components of an integer multiple with respect to the rotation angle, and multiplying by the inertial moment to obtain the inertial torque pulsation.

[0016] Effects of the Invention

[0017] According to the present disclosure, even when there is a speed change, the change in acceleration is frequency-converted in addition to the change in current, and the torque pulsation can be calculated using the inertia moment. Therefore, the torque pulsation can be measured without mechanically connecting the load motor and the torque sensor to the permanent magnet motor as the measurement object. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a diagram showing a control block of the torque pulsation measuring method according to the first embodiment.

[0019] Figure 2 1 is a schematic diagram showing a permanent magnet motor to be measured.

[0020] Figure 3 This is a diagram showing a signal output from an encoder serving as a position detector when the rotor is rotated in the positive direction.

[0021] Figure 4 This is a flowchart showing an example of the procedure of the torque pulsation measuring method.

[0022] Figure 5 This is a hardware configuration diagram of a control device that implements the torque pulsation measuring method of the first embodiment.

[0023] Figure 6 This is a diagram showing the operation flow of the torque pulsation measuring device according to the third embodiment. DETAILED DESCRIPTION

[0024] Hereinafter, the embodiments will be described with reference to the drawings. The same reference numerals are given to common or corresponding elements in the drawings, and the description thereof will be simplified or omitted.

[0025] Implementation method 1.

[0026] Figure 1 This is a diagram showing a control module of the torque pulsation measuring method according to the first embodiment. Figure 2 1 is a schematic diagram showing a permanent magnet motor (hereinafter referred to as a “motor”) Mt as a measurement object.

[0027] The motor Mt includes a stator 1 and a rotor 2. The stator 1 has an iron core 10 made of a laminated body through which a magnetic flux passes. The iron core 10 has a plurality of teeth 11 that are evenly arranged in the circumferential direction as the rotation direction and extend in the radial direction. Between adjacent teeth 11, three-phase windings 12 represented by a U-phase winding 12U, a V-phase winding 12V, and a W-phase winding 12W are provided through a predetermined connection. Insulators made of insulating paper 13 and resin are inserted between the windings 12 and the iron core 10 and between adjacent windings 12 to insulate each other.

[0028] The rotor 2 is arranged radially inside the stator 1. A magnet 21 is arranged on the radially outer surface of the rotor 2. A yoke 22 for passing magnetic flux is arranged on the inner circumference of the magnet 21. A shaft 23 is arranged at the center of the yoke 22 and is rotatably held by a bearing (not shown).

[0029] The rotor 2 is rotated by generating torque due to the attraction or repulsion between magnetic flux generated by energizing the winding 12 and magnetic flux generated by magnets 21 of the rotor 2 and by the attraction between magnetic flux generated by energizing the winding 12 and iron of the rotor 2 .

[0030] Regarding the d-axis current I in the d-axis and q-axis coordinate system rotating together with the rotor 2 d , q-axis current I q The size of the current I flowing through the U-phase winding 12U can be used U , the current I flowing through the V phase winding 12V V , the current I flowing through the W phase winding 12WW , and the electrical angle θ of the rotor 2 e , as shown in the following formula (1).

[0031] [Formula 1]

[0032]

[0033] The torque τ(t) generated by the motor Mt can be expressed using the d-axis current I d , q-axis current I q , Induction voltage constant K a , d-axis inductance L d , q-axis inductance L q , as shown in the following formula (2).

[0034] [Formula 2]

[0035]

[0036] In the above formula (2), N p is the number of pole pairs, which is a parameter determined when the motor Mt is designed. Figure 2 In the case of the motor Mt shown, the number of pole pairs N p is 5. Let the inertia moment of rotor 2 be J and the mechanical angular velocity be ω m When , the motion equation around the rotor 2 is expressed as follows (3).

[0037] [Formula 3]

[0038]

[0039] Here, τ ε (t) is a disturbance component, which is the loss torque generated in the sealing structure of the bearing or lubricant, and the torque generated by the attraction between the magnet and the iron between the rotor 2 and the stator 1. Among them, the component that changes depending on the rotation angle is called torque pulsation, which becomes the cause of instability in vibration, position, and speed control. It is known that the loss torque is usually speed-dependent, so it is not desirable to measure the torque pulsation in a state where there is a large speed change. Therefore, feedback control is performed so that the motor Mt can be operated in a manner that the mechanical angular velocity detected by the speed detector described later is kept as constant as possible.

[0040] The inertia moment J of the rotor 2 can be understood as a parameter of the motor Mt when designing the motor Mt. The inertia moment J is also called inertia. The induced voltage constant K can be obtained by solving the following equation (5): e The following formula (5) is obtained by making the rotor 2 rotate at ω without current flowing. r The d-axis current I d =0, and the q-axis current Iq is set to 0, and is set to the d-axis voltage V in the following equation (4): d = 0. In the following equations (4) and (5), Vq is the q-axis voltage.

[0041] [Formula 4]

[0042]

[0043] [Formula 5]

[0044] V q =ω r ×K e ···(5)

[0045] Next, the operation control state of the motor Mt in the present embodiment will be described.

[0046] The speed instruction unit 31 provides a predetermined operating speed ω o The speed calculation unit 32 differentiates the position signal input from the position detector 41 attached to the motor Mt and outputs a speed signal obtained by differentiation. The speed signal is equivalent to the actual speed. o The speed signal from the speed calculation unit 32 is subtracted, and the speed difference as the subtraction value is input to the torque command unit 33. The torque command unit 33 calculates the command torque so that acceleration is performed when the speed signal is slower than the command signal, and deceleration is performed when the speed signal is faster than the command signal. If the calculation in the torque command unit 33 is only proportional control, oscillation does not converge, so it is desirable to combine differential control and integral control.

[0047] The current control unit 34 calculates the q-axis current I that satisfies the command torque calculated by the torque command unit 33. q and d-axis current I d , the q-axis current I can be calculated q and d-axis current I d The U-phase current, V-phase current, and W-phase current of the inverter 42 are respectively equivalent to the switching instructions of the components of the inverter 42. The inverter 42 determines the duty ratio so as to become the current of each phase calculated by the current control unit 34, and applies the voltage supplied from the bus bar (not shown) to the motor Mt. The motor Mt generates a torque for acceleration or deceleration by applying the voltage, that is, by driving the current. The position of the motor Mt is detected by the position detector 41.

[0048] The current calculation unit 35 measures the drive current flowing through the motor Mt by the voltage application from the inverter 42, and applies feedback to the current control unit 34 so that the q-axis current I q and d-axis current I dbecomes the desired current.

[0049] As the position detector 41, for example, an encoder (not shown) can be used. The encoder outputs a signal of the A phase and a signal of the B phase according to the mechanical angular velocity of the rotor 2. The signal of the A phase is switched at a cycle of RES times while the rotor 2 rotates one revolution, and the signal of the B phase is switched at a cycle of RES times while the rotor 2 rotates one revolution. Figure 3 : is a diagram showing the signal output by the encoder when the rotor 2 is rotated in the positive direction. For example, when the rotor 2 rotates in the positive direction, when the time t0 of the fixed rotation angle has passed, the signal of the A phase changes from the low potential side to the high potential side. Thereafter, when the time t0 has further passed, the signal of the A phase changes from the high potential side to the low potential side. In addition, the signal of the B phase switches the high potential side and the low potential side with a time "t0÷2" offset relative to the signal of the A phase. In the present embodiment, after the signal of the A phase rises from the low potential side to the high potential side and the time "t0÷2" has passed, the signal of the B phase changes from the low potential side to the high potential side. In addition, after the signal of the A phase drops from the high potential side to the low potential side and the time "t0÷2" has passed, the signal of the B phase changes from the high potential side to the low potential side. The position detector 41 and the speed calculation unit 32 are equivalent to the speed detector. Feedback control is performed so that the mechanical angular velocity detected by the speed detector maintains a constant operating speed ω o .

[0050] The details of the current pulsation calculation unit 36, the speed pulsation calculation unit 37, and the torque pulsation calculation unit 38 represented by other control modules will be described later. In addition, the speed calculation unit 32, the torque command unit 33, the current control unit 34, the current calculation unit 35, the current pulsation calculation unit 36, the speed pulsation calculation unit 37, and the torque pulsation calculation unit 38 are functions calculated by the processor 30a executing a program stored in the memory 30b described later.

[0051] Next, the torque ripple measurement process (calculation step) will be described. Figure 4 This is a flowchart showing an example of the procedure of the torque pulsation measuring method.

[0052] First, the rotor 2 is rotated at a high speed (step S1). In step S1, a voltage V generated between the U-phase winding 12U fed by the U-phase power supply unit and the V-phase winding 12V fed by the V-phase power supply unit is measured. UV , and a voltage V generated between the V-phase winding 12V and the W-phase winding 12W via the W-phase power supply portion. Vw The voltage V generated between the W-phase winding 12W and the U-phase winding 12U WU According to V WU =-V UV -V VWThe d-axis voltage V is calculated using the measured voltage and the rotation angle of the rotor 2. d , so that the phase of the position detector 41 and the rotor 2 are matched so that V d In addition, when the phases of the position detector 41 and the rotor 2 are matched in advance using an absolute position detection sensor, such a phase matching step may not be necessary.

[0053] Next, the rotor 2 is rotated at a low speed (step S2). In step S2, the amplitude of the torque pulsation to be detected is assumed to be τ r , when the frequency of the torque pulsation with respect to the rotation angle as the mechanical angle is f, the rotation speed ω as the mechanical angular speed of the rotor 2 is m Determined as, the rotation speed ω m Satisfy m ×f<τ r relationship.

[0054] In steps S1 and S2 , no load for rotating the rotor 2 is attached to the rotor 2 , and the output shaft of the motor Mt is not driven from the outside but rotates in a self-propelled state driven by the motor Mt.

[0055] When the frequency with respect to the mechanical angle to be analyzed is denoted by f, it is preferable to select the number of signal switching times RES of the position detector 41 so that M in the following equation (6) becomes an integer.

[0056] When the frequency with respect to the mechanical angle to be analyzed is denoted by f, it is preferable to select the number of signal switching times RES of the position detector 41 so that M in the following equation (6) becomes an integer.

[0057] RES×4=f×M···(6)

[0058] In addition, when the rotation speed ω of the rotor 2 m When the speed command ω0 is sufficiently followed, the time required for one rotation is expressed by the following equation (7).

[0059] 2π÷ω0···(7)

[0060] Therefore, the time for the frequency f of the mechanical angle to be analyzed is expressed by the following equation (8), and therefore, the integral multiple of the time can be recorded.

[0061] 2π÷ω0÷f···(8)

[0062] At this time, when frequency components other than the frequency f for the mechanical angle to be analyzed are relatively large, it is desirable to determine the measurement time so as to be an integral multiple of these frequency components.

[0063] In addition, when the rotor 2 rotates in the direction opposite to the positive direction, the order of change of the A-phase signal and the B-phase signal is reversed. In this case, after the B-phase signal changes from the low potential side to the high potential side, the A-phase signal changes from the low potential side to the high potential side at the timing of time "t0÷2". Similarly, after the B-phase signal changes from the high potential side to the low potential side, the A-phase signal changes from the high potential side to the low potential side at the timing of time "t0÷2".

[0064] Next, the first calculation method of the rotation speed of the rotor 2 is described. When calculating the rotation speed, the number of times the A-phase signal switches from the low potential side to the high potential side, the number of times the A-phase signal switches from the high potential side to the low potential side, the number of times the B-phase signal switches from the low potential side to the high potential side, and the number of times the B-phase signal switches from the high potential side to the low potential side during a certain time Δt are measured. When the number of switching times during the time Δt is n times, the rotation speed ω of the rotor 2 m It can be obtained as shown in the following formula (9).

[0065] [Formula 6]

[0066]

[0067] The second calculation method of the rotation speed of the rotor 2 is described. The above-mentioned encoder signal can be used and the time interval Δt2 can be used to calculate the rotation speed of the rotor 2 as shown in the following formula (10), wherein the time interval Δt2 is the time interval from when the signal of the A phase changes from the low potential side to the high potential side or vice versa to when the signal of the B phase changes from the low potential side to the high potential side or vice versa.

[0068] [Formula 7]

[0069]

[0070] When there is sufficient signal change in the time interval of Δt in the above formula (9), the first calculation method of the rotation speed of the rotor 2 is effective, but when no sufficient signal change is observed in the time interval of Δt, it is impossible to capture the slight change in the rotation speed of the rotor. On the contrary, when the value of the speed calculation period Δt is increased, the speed feedback of the rotor is delayed and the speed stability is deteriorated, which is not preferred.

[0071] The magnitude of the torque ripple hardly changes depending on the rotation speed of the rotor 2. Consider the state in which the average loss torque and the motor Mt are balanced. When the speed amplitude is A, the relationship as shown in the following equation (11) holds.

[0072] [Formula 8]

[0073]

[0074] In the above equation (11), ω is the mechanical angular vibration frequency. When the above equation (11) is solved for the velocity amplitude A, the following equation (12) is obtained.

[0075] [Formula 9]

[0076]

[0077] According to the above formula (12), the faster the rotation speed of the rotor 2, the smaller the speed amplitude A. According to the resolution of the change in the rotation speed of the rotor 2 and the accuracy of the torque pulsation to be measured as the target, the relationship of the following formula (13) needs to be satisfied. Therefore, in order to ensure the measurement accuracy, it is preferable to slow down the rotation speed of the rotor 2.

[0078] [Formula 10]

[0079]

[0080] Next, in the speed pulsation calculation unit 37, a method for calculating the current torque pulsation as the pulsation of the rotation speed of the rotor 2 and the inertia torque pulsation as the pulsation of the acceleration is described. The speed within the speed calculation cycle is calculated according to the first calculation method or the second calculation method of the rotation speed of the rotor 2 at each time. Next, the obtained speed is differentiated within the analysis time, thereby the angular acceleration of the rotor 2 within the time can be calculated. In the differentiation of discrete values, it is desirable to use the center differential, and perform a calculation based on the center difference by dividing the difference between the value of the first point before the time to be calculated and the speed of the last point after the time to be calculated by twice the time interval. This is because the error can be significantly reduced compared with the forward differential and the backward differential, and when the forward differential and the backward differential are used, the time is offset from the center, but such a time offset does not occur in the case of the center differential.

[0081] As a second operation method for calculating the differential value, a method using Fourier transform is given. The measurement result of the rotation speed of the rotor 2 ω e (t) is expressed as shown in the following formula (14).

[0082] [Formula 11]

[0083]

[0084] Through Fourier transform, the coefficient A of each order component can be obtained k Here, T0 is the time of the analysis interval, N is the number of data points in the analysis interval, and i is an imaginary unit. The coefficient A from 1 to N ÷ 2 k It can be obtained using Fourier transform as shown in the following equation (15).

[0085] [Formula 12]

[0086]

[0087] Here, exp(ix) is an exponential function of a complex number, and has a relationship as shown in the following equation (16): i is an imaginary unit.

[0088] [Formula 13]

[0089] exp(ix)=cos(x)+i sin(x)···(1(6)

[0090] Regarding this calculation, as a method for obtaining the same result as the method using the above formula, a method of calculating components of each degree at high speed as a Cooley-Tukey type algorithm is widely known, and this algorithm can be used.

[0091] [Formula 14]

[0092]

[0093] Based on the relationship of the above formula (17), it is possible to calculate the components of each order of the angular acceleration of the rotor 2. In this case, even when the speed calculation cycle and the data acquisition cycle do not coincide with each other, the change in speed can be easily calculated.

[0094] Therefore, there is a remarkable effect that has not been achieved in the related art: the pulsation component of the inertial torque can be calculated by frequency-converting the variation of the angular acceleration.

[0095] Next, the current pulsation calculation unit 36 ​​measures the pulsation of torque generated by the motor Mt when the motor Mt is energized (step S3). The method of measuring the torque pulsation is described below. The d-axis current I is obtained using the above formula (1): d and q-axis current I q Using the known induction voltage constant K a , d-axis inductance L d , q-axis inductance L q The torque generated by the motor Mt at each time is calculated using the above formula (2).

[0096] In the same way as when the angular acceleration is calculated by the differential of the rotation speed of the rotor 2, the frequency component T of the torque generated by the motor Mt is calculated by dividing it into various order components as shown in the following equation (18): k .

[0097] [Formula 15]

[0098]

[0099] The frequency component T of the torque from 1 to N÷2 can be obtained by Fourier transform as shown in the following equation (19): k .

[0100] [Formula 16]

[0101]

[0102] Finally, the torque ripple τ generated by the attraction between the magnet and the iron between the rotor 2 and the stator 1 is obtained by the torque ripple calculation unit 38 using the above formula (3). ε By substituting the above equation (3) into the above equation (17) and the above equation (18), the following equation (20) is obtained.

[0103] [Formula 17]

[0104]

[0105] When the torque ripple τ ε When the above equation (20) is solved, the following equation (21) is obtained.

[0106] [Formula 18]

[0107]

[0108] Since exp(i×x) are orthogonal to each other, the torque ripple τ of the component orthogonal to the mechanical angle ε That is, components of the same frequency are added together. When the data of the torque pulsation of the desired number is analyzed within a time period K times the number of the torque pulsation of the desired number, the following equation (22) is obtained.

[0109] T K -J×A K ×i×2Kπ÷T0···(22)

[0110] At this time, the torque pulsation amplitude A can be expressed using the absolute value of the complex number as in the following equation (23): k .

[0111] |T K -J×A K ×i×2Kπ÷T0|···(23)

[0112] Figure 5 This is a hardware structure diagram of a control device 3 as a torque pulsation measuring device (also refer to Embodiment 3 described later) for implementing the above-mentioned torque pulsation measuring method. The control device 3 is equivalent to a computer capable of executing a torque pulsation measuring program, and can be implemented by a processing circuit. For example, the processing circuit has at least one processor 30a and at least one memory 30b.

[0113] When the processing circuit has at least one processor 30a and at least one memory 30b, each function of the control device 3 is implemented by software, firmware, or a combination of software and firmware. At least one of the software and firmware is described in the form of a program. At least one of the software and firmware is stored in at least one memory 30b. At least one processor 30a reads and executes the program stored in at least one memory 30b. At least one processor 30a is also called a central processing unit, a processing unit, a computing unit, a microprocessor, a microcomputer, or a DSP. For example, at least one memory 30b is a non-volatile or volatile semiconductor memory such as a RAM, a ROM, a flash memory, an EPROM, or an EEPROM, a magnetic disk, a floppy disk, an optical disk, a high-density disk, a mini disk, a DVD, or the like.

[0114] Furthermore, the processing circuit may be configured to include at least one dedicated hardware (not shown). In this case, the processing circuit may be implemented by, for example, a single circuit, a composite circuit, a programmed processor, a parallel programmed processor, an ASIC, an FPGA, or a combination thereof.

[0115] As described above, in this embodiment, since the pulsation component of the current is added to measure the torque pulsation, compared with the case where only the pulsation component of the inertia torque is calculated, the torque pulsation can be measured with high accuracy without the need for an external sensor and a load motor. In addition, compared with the case where only the pulsation of the current is used for calculation, the speed change contributes to the torque pulsation, so the torque pulsation can be measured with high accuracy without the need for an external sensor and a load motor.

[0116] In addition, the measurement of the torque pulsation as described above is performed in a process such as a factory test of the permanent magnet motor Mt after the permanent magnet motor Mt is assembled. At this time, it is possible to determine whether the permanent magnet motor Mt is good based on the measured torque pulsation, for example, based on the comparison result of the measured torque pulsation and a threshold value. Such a process of determining whether the permanent magnet motor Mt is good can constitute a method for manufacturing the permanent magnet motor Mt.

[0117] Implementation method 2.

[0118] The difference between the second embodiment and the first embodiment is that the d-axis current I d Constant. The following description will focus on this difference. By substituting the above formula (2) into I d (t) = I d , can be transformed as shown in the following formula (24).

[0119] [Formula 19]

[0120]

[0121] At this time, the torque τ(t) generated by the motor Mt depends only on I q (t), therefore, the frequency component of the torque generated by the motor Mt in the above equation (18) can be expressed as in the following equation (25).

[0122] [Formula 20]

[0123]

[0124] According to this embodiment, by making the d-axis current I d If the torque generated by the motor Mt is constant, the calculation of the torque generated by the motor Mt becomes easy, and the main cause of the measurement error of the torque pulsation can be reduced. As a result, the measurement accuracy of the torque pulsation can be improved.

[0125] In addition, when the d-axis current I d When it becomes 0, it does not depend on the d-axis inductance L d , q-axis inductance L q The torque pulsation can be obtained, and the calculation of the torque pulsation can be simplified, which is desirable. In addition, when the d-axis current flows, torque pulsation that depends on the higher harmonics of the induced voltage may be generated. Therefore, by making the d-axis current I d By making it 0, the generated torque ripple can be reduced and the measurement accuracy of the torque ripple can be improved.

[0126] Implementation method 3.

[0127] Figure 6 : is a diagram showing the operation flow of the torque pulsation measuring device according to Embodiment 3. Figure 6 The process shown is used to determine the torque ripple.

[0128] First, in step 1, the motor Mt is mounted on the torque pulsation measuring device (control device 3). Next, in step 2, the motor Mt is rotated by itself, and the voltage between the terminals of the motor Mt (for example, the line voltage between the U phase and the V phase) and the rotation speed are measured after the power supply is cut off. Next, in step 3, the induced voltage constant T is calculated by dividing the voltage measured in step 2 by the rotation speed. k It is also possible to calculate the speed in step 3 based on the cycle of voltage variation instead of measuring the speed in step 2, and use the calculated speed to calculate the induced voltage constant T k Next, in step 4, the motor Mt is rotated by a constant speed command. As in the first embodiment, the current and speed are acquired. Next, in step 5, as in the first embodiment, the induced voltage constant T calculated in step 3 is used. k The torque ripple is calculated by using the speed and current obtained in step 4. By performing the induced voltage constant T before step 5 kThe target torque variation can be measured quickly after step 4 by calculating the target torque variation after step 4. After the measurement is completed, the motor Mt is removed in step 6. In addition, steps 2 and 3 may be performed after step 5, but are preferably performed before step 5.

[0129] According to the present embodiment, a torque pulsation measuring device capable of measuring torque pulsation with high accuracy is obtained, similarly to the first embodiment.

[0130] Description of Reference Numerals

[0131] 1…stator, 10…iron core, 12…winding, 2…rotor, 21…magnet, 3…control device (torque ripple measuring device), 41…position detector (speed detector), J…moment of inertia

Claims

1. A method for measuring torque pulsation of a permanent magnet motor, The permanent magnet motor comprises: a stator having an iron core for guiding magnetic flux and a coil insulated from the iron core and capable of generating a rotating magnetic field; a rotor having a magnet for generating magnetic flux and rotatably fixed relative to the stator for guiding magnetic flux; and a speed detector for detecting a mechanical angular velocity of the rotor. in, The torque pulsation measurement method of the permanent magnet motor includes a calculation step, in which the following inertia torque pulsation is calculated. When the output shaft of the permanent magnet motor is not driven from the outside but is driven by the permanent magnet motor, each angular acceleration obtained by differentiating the mechanical angular velocity detected by the speed detector is decomposed into frequency components of an integer multiple of the rotation angle, and the frequency components are multiplied by the inertia moment to obtain the inertia torque pulsation.

2. The method for measuring torque pulsation of a permanent magnet motor according to claim 1, wherein: Feedback control is performed so that the mechanical angular velocity detected by the velocity detector maintains a specified constant velocity.

3. The method for measuring torque pulsation of a permanent magnet motor according to claim 1 or 2, wherein: The torque pulsation is calculated by adding the components of the same frequency as the current torque pulsation and the inertia torque pulsation, wherein the frequency components are decomposed into integer multiples of the rotation angle generated by the current flowing through the permanent magnet motor, and the current torque pulsation is calculated by multiplying the integer multiples of the frequency components by the induced voltage constant.

4. The method for measuring torque pulsation of a permanent magnet motor according to any one of claims 1 to 3, wherein: The permanent magnet motor is driven while keeping the d-axis current constant, and the torque ripple is calculated.

5. The method for measuring torque pulsation of a permanent magnet motor according to any one of claims 1 to 3, wherein: The permanent magnet motor is driven by setting the d-axis current to zero, and the torque ripple is calculated.

6. A method for manufacturing a permanent magnet motor, comprising the following steps: After the permanent magnet motor is assembled, whether the permanent magnet motor is good or not is determined based on the torque pulsation calculated using the torque pulsation measuring method according to any one of claims 1 to 3 .

7. A torque pulsation measuring device for a permanent magnet motor, The permanent magnet motor comprises: a stator having an iron core for guiding magnetic flux and a coil insulated from the iron core and capable of generating a rotating magnetic field; a rotor having a magnet for generating magnetic flux and rotatably fixed relative to the stator for guiding magnetic flux; and a speed detector for detecting a mechanical angular velocity of the rotor. in, The torque pulsation measuring device includes the following steps: calculating the inertia torque pulsation as follows: when the output shaft of the permanent magnet motor is not driven from the outside but is driven by the permanent magnet motor, decomposing each angular acceleration obtained by differentiating the mechanical angular velocity detected by the speed detector into frequency components of an integer multiple of the rotation angle, and multiplying the frequency components by the inertia moment to obtain the inertia torque pulsation.

8. The torque pulsation measuring device for a permanent magnet motor according to claim 7, wherein: Feedback control is performed so that the mechanical angular velocity detected by the velocity detector maintains a specified constant velocity.

9. The torque pulsation measuring device for a permanent magnet motor according to claim 7 or 8, wherein: The torque pulsation is calculated by adding the components of the same frequency of the electromagnetic torque pulsation and the inertia torque pulsation, wherein the frequency components are decomposed into integer multiples of the rotation angle generated by the current flowing through the permanent magnet motor, and the electromagnetic torque pulsation is calculated by multiplying the integer multiples of the frequency components by the induced voltage constant.

10. The torque pulsation measuring device for a permanent magnet motor according to any one of claims 7 to 9, characterized in that: The induced voltage constant was measured before and after the torque ripple was measured.

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