Torque pulsation measuring method and device for permanent magnet motor, and manufacturing method of permanent magnet motor

Abstract

The present disclosure provides a torque pulsation measurement method for a permanent magnet motor provided with a stator that has an iron core guiding magnetic flux and a coil insulated from the iron core and capable of generating a rotating magnetic field, a rotor that has a magnet generating magnetic flux and that is rotatably fixed to the stator guiding magnetic flux, and a velocity detector that detects the mechanical angular velocity of the rotor. The torque pulsation measurement method includes a calculation step for calculating, in a state in which an output shaft of the permanent magnet motor is not driven from outside and is driven by the permanent magnet motor, torque pulsation by decomposing each angular acceleration obtained by differentiating the mechanical angular velocity detected by the velocity detector into a frequency component of an order that is an integral multiple of a rotation angle and multiplying the frequency component by an inertia moment.

Description

[Technical Field]

[0001] The present disclosure relates to a method for measuring torque pulsations that occur when a permanent magnet motor rotates. [Background technology]

[0002] In the torque pulsation measurement method disclosed in Patent Document 1 below, a torque sensor is placed between the test motor to be measured and the load motor, the test motor is rotated by the load motor, and the torque fluctuations that occur during this rotation are measured.

[0003] Furthermore, the torque pulsation measurement method disclosed in Patent Document 2 below calculates torque fluctuations from the command value of the current passed through a test motor controlled to a constant speed, without using a load motor or torque sensor. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-188941 [Patent Document 2] Japanese Patent Application Publication No. 7-210221 Summary of the Invention [Problem to be solved by the invention]

[0005] The method of Patent Document 1 requires a process for connecting a load motor and a torque sensor, which hinders productivity improvement. In addition, there is a problem in that the cost of measuring devices such as torque sensors is required, which leads to an increase in production costs.

[0006] In the method of Patent Document 2, maintaining a constant speed is a necessary condition for achieving measurement. When performing feedback control as described in Patent Document 2, deviations from the command speed are fed back to the torque, which inevitably causes speed fluctuations and makes constant speed control impossible. When speed pulsation exists, torque pulsation dependent on inertia torque occurs, which causes the problem of torque pulsation measurement errors.

[0007] The present disclosure has been made to solve the above-mentioned problems, and aims to provide a torque pulsation measurement method that does not require mechanical connection of a load motor or torque sensor to a permanent magnet motor, and that can measure torque pulsation even when constant speed control is not possible. [Means for solving the problem]

[0008] The torque pulsation measurement method for a permanent magnet motor according to the present disclosure includes a permanent magnet motor including an iron core that conducts magnetic flux, a stator that is insulated from the iron core and has coils capable of generating a rotating magnetic field, a rotor that has magnets that generate magnetic flux and is rotatably fixed relative to the stator that conducts magnetic flux, and a speed detector that detects the mechanical angular velocity of the rotor. The torque pulsation measurement method includes a calculation step of, while the output shaft of the permanent magnet motor is not driven from an external source but is driven by the permanent magnet motor itself, differentiating the mechanical angular velocity detected by the speed detector to obtain angular accelerations, decomposing the angular accelerations into frequency components of orders that are integer multiples of the rotation angle, and multiplying the results by the moment of inertia to calculate torque pulsation. The rotation angle generated by the current flowing through the permanent magnet motor is decomposed into frequency components of integer multiples, and this is multiplied by an induced voltage constant to calculate the current torque pulsation. The torque pulsation is then calculated by adding together the components of the inertial torque pulsation with the same frequency.

[0009] Furthermore, the method for manufacturing a permanent magnet motor according to the present disclosure includes a step of, after assembling the permanent magnet motor, determining whether the permanent magnet motor is good or bad based on torque pulsation calculated using the torque pulsation measurement method.

[0010] The torque pulsation measurement device for a permanent magnet motor according to the present disclosure includes a permanent magnet motor including an iron core that conducts magnetic flux, a stator that is insulated from the iron core and has a coil capable of generating a rotating magnetic field, a rotor that has a magnet that generates magnetic flux and is rotatably fixed to the stator that conducts magnetic flux, and a speed detector that detects the mechanical angular velocity of the rotor. The torque pulsation measurement device includes, in a state in which the output shaft of the permanent magnet motor is not driven from outside but is driven by the permanent magnet motor itself, a process of differentiating the mechanical angular velocity detected by the speed detector to obtain angular accelerations, decomposing the angular accelerations into frequency components of orders that are integer multiples of the rotation angle, and multiplying the frequency components by the moment of inertia to calculate inertial torque pulsation. The rotation angle generated by the current flowing through the permanent magnet motor is decomposed into frequency components of integer multiples, and this is multiplied by the induced voltage constant to calculate the electromagnetic torque pulsation. Torque pulsation is then calculated by adding together the components of the inertial torque pulsation with the same frequency. [Effects of the Invention]

[0011] According to the present disclosure, even when speed fluctuations are present, torque pulsation can be calculated by converting the frequency of acceleration fluctuations in addition to current fluctuations and utilizing the moment of inertia. Therefore, torque pulsation can be measured without mechanically connecting a load motor or torque sensor to the permanent magnet motor being measured. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 2 is a diagram showing a control block of the torque pulsation measuring method according to the first embodiment. [Figure 2] FIG. 1 is a schematic diagram showing a permanent magnet motor to be measured. [Figure 3] FIG. 10 is a diagram showing a signal output by an encoder serving as a position detector when the rotor is rotated in the forward direction. [Figure 4] 1 is a flowchart illustrating an example of a procedure of a torque pulsation measuring method. [Figure 5] 1 is a hardware configuration diagram of a control device that implements a torque pulsation measuring method according to a first embodiment. [Figure 6] FIG. 10 is a diagram showing an operation flow of the torque pulsation measuring device according to the third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, embodiments will be described with reference to the drawings. Common or corresponding elements in the various drawings will be denoted by the same reference numerals, and descriptions thereof will be simplified or omitted.

[0014] Embodiment 1 Fig. 1 is a diagram showing a control block of a torque pulsation measuring method according to embodiment 1. Fig. 2 is a schematic diagram showing a permanent magnet motor (hereinafter referred to as "motor") Mt that is the object of measurement.

[0015] The motor Mt includes a stator 1 and a rotor 2. The stator 1 has an iron core 10 made of laminated layers that allow magnetic flux to pass through. The iron core 10 has a plurality of teeth 11 that are evenly arranged in the circumferential direction, which is the direction of rotation, and each extending radially. Three-phase windings 12, represented by a U-phase winding 12U, a V-phase winding 12V, and a W-phase winding 12W, are provided between adjacent teeth 11 through predetermined connections. Insulators made of insulating paper 13 or resin are inserted between the windings 12 and the iron core 10 and between adjacent windings 12 to insulate them from each other.

[0016] The rotor 2 is provided radially inside the stator 1. A magnet 21 is provided on the radially outer surface of the rotor 2. A yoke 22 for passing magnetic flux is provided on the inner periphery of the magnet 21. A shaft 23 is provided at the center of the yoke 22, and is rotatably held by a bearing (not shown).

[0017] The magnetic flux generated by passing current through the winding 12 attracts and repels the magnetic flux created by the magnet 21 of the rotor 2, and the magnetic flux generated by passing current through the winding 12 also attracts the iron of the rotor 2, generating torque and causing the rotor 2 to rotate.

[0018] The d-axis current I in the d-axis and q-axis coordinate system that rotates with rotor 2 d , q-axis current I qThe magnitude of the current I flowing through the U-phase winding 12U is U , the current I flowing through the V-phase winding 12V V , the current I flowing through the W-phase winding 12W W and the electrical angle θ of rotor 2 e Using this, it can be expressed as the following equation (1).

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[0019] The torque τ(t) generated by the motor Mt is calculated by the d-axis current I d , q-axis current I q , induced voltage constant K a , d-axis inductance L d , q-axis inductance L q Using this, it can be expressed as in the following equation (2).

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[0020] In the above formula (2), N p is the number of pole pairs, which is a parameter determined when designing the motor Mt. In the case of the motor Mt shown in Figure 2, the number of pole pairs N p is 5. The moment of inertia of rotor 2 is J, and the mechanical angular velocity is ω m Then, the equation of motion around the rotor 2 is expressed as the following equation (3).

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[0021] where τ ε(t) is a disturbance component, and is made up of loss torque generated by the bearings, lubricant sealing structures, etc., and torque generated by the attraction between the magnet and iron between the rotor 2 and stator 1. Of these, the component that varies depending on the rotation angle is called torque pulsation, and causes vibration and instability in position and speed control. Since loss torque is generally known to be speed-dependent, it is not desirable to measure torque pulsation when there are large speed fluctuations. Therefore, feedback control is performed so that the motor Mt is operated so that the mechanical angular speed detected by the speed detector (described below) remains as constant as possible.

[0022] The moment of inertia J of the rotor 2 can be grasped as a parameter of the motor Mt when designing the motor Mt. The moment of inertia J is also called inertia. The induced voltage constant K e is the rotor 2 with no current flowing. r By rotating at a speed of d 0, q-axis current I q is set to 0, and the d-axis voltage V d = 0, the following equation (5) is derived and can be found by solving it. In the following equations (4) and (5), Vq is the q-axis voltage.

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[0023] Next, the operational control state of the motor Mt in this embodiment will be described.

[0024] The speed command unit 31 sets a predetermined operating speed ω o The operating speed corresponds to the rotation speed. The speed calculation unit 32 differentiates the position signal input from the position detector 41 attached to the motor Mt, and outputs the speed signal obtained by the differentiation. The speed signal corresponds to the actual speed. The command speed ω from the speed command unit 31 oThe speed signal from the speed calculation unit 32 is subtracted from this, and the speed difference obtained by the subtraction is input to the torque command unit 33. The torque command unit 33 calculates a command torque so that the motor accelerates when the speed signal is slower than the command signal, and decelerates when the speed signal is faster than the command signal. If the calculation in the torque command unit 33 is only proportional control, the motor will oscillate and not converge, so it is desirable to combine it with differential control or integral control.

[0025] The current control unit 34 controls the q-axis current I so as to satisfy the command torque calculated by the torque command unit 33. q and d-axis current I d Calculate the calculated q-axis current I q and d-axis current I d The U-phase current, V-phase current, and W-phase current that can realize the above are calculated. Each phase current corresponds to a switching command for the elements of the inverter 42. The inverter 42 determines a duty ratio so that each phase current becomes the one calculated by the current control unit 34, and applies a voltage supplied from a bus (not shown) to the motor Mt. The motor Mt generates torque that accelerates or decelerates due to the applied voltage, i.e., the drive current. The position of the motor Mt is detected by a position detector 41.

[0026] The current calculation unit 35 measures the drive current flowing through the motor Mt due to the voltage applied from the inverter 42, and calculates the q-axis current I q and d-axis current I d A feedback is applied to the current control section 34 so that the desired current is obtained.

[0027] The position detector 41 may be, for example, an encoder (not shown). The encoder outputs an A-phase signal and a B-phase signal according to the mechanical angular velocity of the rotor 2. The A-phase signal switches every RES cycles while the rotor 2 rotates once, and the B-phase signal switches every RES cycles while the rotor 2 rotates once. FIG. 3 shows the signals output by the encoder when the rotor 2 rotates in the forward direction. For example, when the rotor 2 rotates in the forward direction, the A-phase signal changes from low potential to high potential after a time t0 corresponding to a certain rotation angle. After that, when time t0 further elapses, the A-phase signal changes from high potential to low potential. The B-phase signal switches between high potential and low potential with a time delay of "t0÷2" from the A-phase signal. In this embodiment, after the A-phase signal rises from the low potential side to the high potential side, the B-phase signal changes from the low potential side to the high potential side at the timing when the time "t0÷2" has elapsed. Also, after the A-phase signal falls from the high potential side to the low potential side, the B-phase signal changes from the high potential side to the low potential side at the timing when the time "t0÷2" has elapsed. The position detector 41 and the speed calculation unit 32 correspond to a speed detector. The mechanical angular speed detected by this speed detector is a constant operating speed ω o Feedback control is used to maintain this.

[0028] The details of the current pulsation calculation unit 36, speed pulsation calculation unit 37, and torque pulsation calculation unit 38 represented in the other control blocks will be described later. The speed calculation unit 32, torque command unit 33, current control unit 34, current calculation unit 35, current pulsation calculation unit 36, speed pulsation calculation unit 37, and torque pulsation calculation unit 38 are functions that are calculated by the processor 30a executing programs stored in the memory 30b, which will be described later.

[0029] Next, the procedure for measuring torque pulsation (calculation step) will be described. Fig. 4 is a flowchart showing an example of the procedure for measuring torque pulsation.

[0030] First, the rotor 2 is rotated at high speed (step S1). In step S1, a voltage V is generated between the U-phase winding 12U connected to the U-phase power supply and the V-phase winding 12V connected to the V-phase power supply. UV and the voltage V generated between the V-phase winding 12V and the W-phase winding 12W connected to the W-phase power supply. VW Measure the voltage V generated between the W-phase winding 12W and the U-phase winding 12U. WU is V WU =-V UV -V VW The d-axis voltage V can be calculated using the measured voltage and the rotation angle of the rotor 2. d Calculate V d The phase of the position detector 41 and the rotor 2 are aligned so that the phase difference is small. Note that if the phase of the position detector 41 and the rotor 2 is aligned in advance using an absolute position detection sensor, this phase alignment step may be unnecessary.

[0031] Next, the rotor 2 is rotated at a low speed (step S2). In step S2, the magnitude of the amplitude of the torque pulsation to be detected is set as τ r , where f is the frequency of torque pulsation relative to the rotation angle, which is the mechanical angle, and ω is the rotation speed, which is the mechanical angular velocity of rotor 2. m But, ω m ×f<τ r The rotation speed ω m Determine. In steps S1 and S2, no load is attached to the rotor 2 to rotate 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.

[0032] When the frequency for the mechanical angle to be analyzed is f, the number of signal switching times RES of the position detector 41 should be selected so that M in the following equation (6) is an integer.

[0033] When the frequency for the mechanical angle to be analyzed is f, the number of signal switching times RES of the position detector 41 should be selected so that M in the following equation (6) is an integer. RES×4=f×M (6)

[0034] In addition, for the speed command ω0, the rotation speed ω of rotor 2 m When the rotation is sufficiently moving, the time required for one rotation is expressed by the following equation (7). 2π÷ω0 (7)

[0035] Therefore, the time of frequency f for the mechanical angle to be analyzed is expressed by the following equation (8), and the time of an integer multiple of this can be recorded. 2π÷ω0÷f···(8)

[0036] In this case, if frequency components other than the frequency f for the mechanical angle to be analyzed are included in large quantities, it is desirable to determine the measurement time so that it is also an integer multiple of those frequency components.

[0037] When the rotor 2 rotates in the opposite direction to the forward direction, the order in which the A-phase signal and the B-phase signal change is reversed. In this case, after the B-phase signal changes from low potential to high potential, the A-phase signal changes from low potential to high potential after the time "t0 ÷ 2" has elapsed. Similarly, after the B-phase signal changes from high potential to low potential, the A-phase signal changes from high potential to low potential after the time "t0 ÷ 2" has elapsed.

[0038] Next, a first calculation method for the rotation speed of the rotor 2 will be described. To calculate the rotation speed, the number of times that the A-phase signal switches from low potential to high potential, the A-phase signal switches from high potential to low potential, the B-phase signal switches from low potential to high potential, and the B-phase signal switches from high potential to low potential, which occur during a certain time period Δt, is counted. If the number of switches during the time period Δt is n, then the rotation speed ω of the rotor 2 is calculated as follows: m can be calculated as in the following equation (9).

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[0039] We will now explain the second method for calculating the rotational speed of the rotor 2. Using the encoder signals described above, the time interval Δt2 from when the A-phase signal changes from low potential to high potential, or vice versa, until the B-phase signal changes from low potential to high potential, or vice versa, can be used to calculate the rotational speed using the following equation (10):

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[0040] If there is a sufficient change in the signal during the time interval Δt in equation (9) above, the first calculation method for the rotational speed of rotor 2 is effective, but if there is not a sufficient change in the signal during the time interval Δt, it will not be possible to capture minute changes in the rotational speed of the rotor. Conversely, if the value of the speed calculation period Δt is increased, a delay will occur in the rotor speed feedback, which will worsen speed stability, and is therefore not desirable.

[0041] The magnitude of torque pulsation changes little depending on the rotational speed of rotor 2. Consider a state in which the average loss torque and motor Mt are balanced. If the speed amplitude is taken as A, the relationship shown in the following equation (11) holds.

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[0042] In the above equation (11), ω is the mechanical angular frequency. Solving the above equation (11) for the velocity amplitude A gives the following equation (12).

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[0043] According to the above equation (12), the faster the rotation speed of the rotor 2, the smaller the speed amplitude A. The relationship in the following equation (13) must be satisfied depending on the resolution of the fluctuations in the rotation speed of the rotor 2 and the target accuracy of the torque pulsation to be measured. Therefore, to ensure measurement accuracy, it is preferable to slow down the rotation speed of the rotor 2.

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[0044] Next, we will explain how the speed pulsation calculation unit 37 calculates the current torque pulsation, which is the pulsation of the rotational speed of the rotor 2, and the inertia torque pulsation, which is the pulsation of the acceleration. The speed in the speed calculation cycle is calculated using either the first or second calculation method for the rotational speed of the rotor 2 at each time. The angular acceleration of the rotor 2 at that time can then be calculated by differentiating the obtained speed at the analysis time. When differentiating discrete values, it is desirable to use central differentiation, in which the difference between the speed value one point before the time to be calculated and the speed value one point after the time to be calculated is divided by twice the time interval. This is because it can reduce errors compared to forward and backward differentiation, and because forward and backward differentiation result in time shifting from the center, whereas central differentiation does not.

[0045] A second calculation method for calculating the differential value is a method using Fourier transform. e (t) is expressed as the following equation (14).

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[0046] By Fourier transform, coefficient A for each order component k Here, T0 is the time of the analysis interval, N is the number of data points in the analysis interval, and i is the imaginary unit. Coefficient A from 1 to N÷2 k can be obtained by using Fourier transform as shown in the following equation (15).

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[0047] Here, exp(ix) is the exponential function of a complex number, and has the relationship shown in the following equation (16), where i is the imaginary unit.

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[0048] This calculation can be performed using the Cooley-Tukey algorithm, which is a widely known method for quickly calculating components of each order, and can obtain the same results as the method using the above equation.

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[0049] From the relationship in equation (17) above, it is possible to calculate the components of each order of the angular acceleration of the rotor 2. In this case, even if the speed calculation period and the data acquisition period do not match, it is possible to easily calculate the change in speed.

[0050] Therefore, by converting the frequency of the fluctuations in angular acceleration, it is possible to calculate the pulsating component of the inertia torque, which is a remarkable effect not available in the past.

[0051] Next, the current pulsation calculation unit 36 ​​measures the torque pulsation generated by the motor Mt by energizing the motor Mt (step S3). The method for measuring the torque pulsation will be described below. Using the above formula (1), the d-axis current I d and q-axis current I q Calculate the known induced voltage constant K a , d-axis inductance L d , q-axis inductance L q Using the above equation (2), the torque value generated by the motor Mt at each time is calculated.

[0052] As in the case of calculating the angular acceleration by differentiating the rotational speed of the rotor 2, the frequency component T of the torque generated by the motor Mt is calculated by dividing it into each order component as shown in the following equation (18). k Calculate.

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[0053] Finally, the torque pulsation calculation unit 38 calculates the torque pulsation τ generated by the mutual attraction between the magnet and the iron between the rotor 2 and the stator 1. ε The method for calculating the above will be explained using the above formula (3). By substituting the above formulas (17) and (18) into the above formula (3), the following formula (20) is obtained.

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[0054] The above equation (20) is used to calculate the torque pulsation τ ε When solving, the following equation (21) is obtained.

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[0055] Since exp(i×x) are mutually orthogonal, the torque pulsation τ of the component orthogonal to the mechanical angle ε In other words, components of the same frequency are added together. To determine the torque pulsation of the desired order, the following equation (22) is obtained by analyzing data over a period of time that is K times the order of the torque pulsation to be determined. T K -J×A K ×i×2Kπ÷T0···(22)

[0056] At this time, the amplitude of the torque pulsation A k can be expressed as the following equation (23) using the absolute value of a complex number. |T K -J×A K ×i×2Kπ÷T0|···(23)

[0057] 5 is a hardware configuration diagram of a control device 3 serving as a torque pulsation measuring device (see also the third embodiment described later) that implements the torque pulsation measuring method. The control device 3 corresponds to a computer capable of executing a torque pulsation measuring program and can be realized by a processing circuit. For example, the processing circuit includes at least one processor 30a and at least one memory 30b.

[0058] When the processing circuit includes at least one processor 30a and at least one memory 30b, each function of the control device 3 is realized by software, firmware, or a combination of software and firmware. At least one of the software and firmware is written as a program. At least one of the software and firmware is stored in at least one memory 30b. The at least one processor 30a reads and executes the program stored in the at least one memory 30b. The at least one processor 30a is also called a central processing unit, processing unit, arithmetic unit, microprocessor, microcomputer, or DSP. For example, the at least one memory 30b may be a non-volatile or volatile semiconductor memory such as RAM, ROM, flash memory, EPROM, or EEPROM, a magnetic disk, a flexible disk, an optical disk, a compact disk, a minidisk, or a DVD.

[0059] The processing circuitry may also be configured to include at least one dedicated hardware (not shown), which may be implemented, for example, as a single circuit, multiple circuits, a programmed processor, parallel programmed processors, an ASIC, an FPGA, or a combination thereof.

[0060] As described above, in this embodiment, torque pulsation is measured by adding a current pulsation component, so torque pulsation can be measured with higher accuracy without requiring an external sensor or load motor, compared to when only the inertia torque pulsation component is calculated. Furthermore, speed fluctuations also contribute to torque pulsation, so torque pulsation can be measured with higher accuracy without requiring an external sensor or load motor, compared to when calculation is performed using only current pulsation.

[0061] The torque pulsation measurement described above is performed after the permanent magnet motor Mt is assembled, during a process such as a shipping test of the permanent magnet motor Mt. At that time, the quality of the permanent magnet motor Mt can be determined based on the measured torque pulsation, for example, based on the results of comparing the measured torque pulsation with a threshold value. This process of determining the quality of the permanent magnet motor Mt can constitute a manufacturing method for the permanent magnet motor Mt.

[0062] Embodiment 2 In the second embodiment, the d-axis current I d The difference from the first embodiment is that I is constant. This difference will be mainly explained below. d (t)=I d By substituting the above, it can be transformed into the following equation (24).

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[0063] At this time, the torque τ(t) generated by the motor Mt is I q Since the frequency component of the torque generated by the motor Mt in the above equation (18) is time-dependent only on (t), it can be expressed as in the following equation (25).

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[0064] According to this embodiment, the d-axis current I dBy keeping constant, it becomes easier to calculate the magnitude of the torque generated by the motor Mt, and it is possible to reduce the causes of errors in measuring torque pulsation, thereby improving the accuracy of measuring torque pulsation.

[0065] Furthermore, the d-axis current I d When is set to 0, the d-axis inductance L d and q-axis inductance L q This is desirable because it allows torque pulsation to be calculated independently of d-axis current I, and the calculation of torque pulsation can be simplified. d By setting ≠0, the torque pulsation that occurs can be reduced, and the measurement accuracy of the torque pulsation can be improved.

[0066] Embodiment 3 6 is a diagram showing the operation flow of the torque pulsation measuring device according to embodiment 3. In this embodiment, torque pulsation is measured according to the procedure shown in FIG.

[0067] First, in step 1, the motor Mt is attached to the torque pulsation measuring device (control device 3). Next, in step 2, the motor Mt is rotated under its own power, 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 The speed is not measured in step 2, but is calculated in step 3 from the period of the voltage fluctuation, and the calculated speed is used 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 k The torque pulsation is calculated using the speed and current obtained in step 4. The induced voltage constant T kBy performing the calculation of before step 5, the target torque fluctuation can be measured quickly after step 4. Once the measurement is completed, the motor Mt is removed in step 6. Note that steps 2 and 3 may be performed after step 5, but it is preferable to perform them before step 5.

[0068] According to this embodiment, a torque pulsation measuring device capable of measuring torque pulsation with high accuracy, similar to the first embodiment, can be obtained. [Explanation of symbols]

[0069] REFERENCE SIGNS LIST 1... stator, 10... iron core, 12... winding, 2... rotor, 21... magnet, 3... control device (torque pulsation measuring device), 41... position detector (speed detector), J... moment of inertia

Claims

1. A torque pulsation measurement method for a permanent magnet motor including: a stator having an iron core that conducts magnetic flux and a coil that is insulated from the iron core and can generate a rotating magnetic field; a rotor having a magnet that generates magnetic flux and that is fixed to the stator that conducts magnetic flux so as to be rotatable; and a speed detector that detects a mechanical angular velocity of the rotor, a calculating step of calculating an inertial torque pulsation obtained by decomposing each angular acceleration obtained by differentiating the mechanical angular velocity detected by the velocity detector into frequency components of orders of integer multiples of the rotation angle and multiplying the frequency components by a moment of inertia, while the output shaft of the permanent magnet motor is not driven from an external source but is driven by the permanent magnet motor itself; A torque pulsation measurement method for a permanent magnet motor, in which the rotation angle generated by the current flowing through the permanent magnet motor is decomposed into frequency components of integer multiples, and then this is multiplied by an induced voltage constant to calculate current torque pulsation. The current torque pulsation is calculated by adding together the components of the inertia torque pulsation having the same frequency.

2. 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 speed detector is maintained at a designated constant velocity.

3. A method for measuring torque pulsation of a permanent magnet motor as described in claim 1, in which the permanent magnet motor is driven with a constant d-axis current and torque pulsation is calculated.

4. 2. The method for measuring torque pulsation of a permanent magnet motor according to claim 1, wherein the permanent magnet motor is driven with the d-axis current set to 0, and torque pulsation is calculated.

5. A method for manufacturing a permanent magnet motor, comprising: a step of, after assembling the permanent magnet motor, determining whether the permanent magnet motor is good or bad based on torque pulsation calculated using the torque pulsation measurement method according to any one of claims 1 to 4.

6. A torque pulsation measuring device for a permanent magnet motor, comprising: a stator having an iron core that conducts magnetic flux and a coil that is insulated from the iron core and can generate a rotating magnetic field; a rotor having a magnet that generates magnetic flux and that is fixed rotatably relative to the stator that conducts magnetic flux; and a speed detector that detects the mechanical angular velocity of the rotor, a step of calculating an inertial torque pulsation obtained by decomposing each angular acceleration obtained by differentiating the mechanical angular velocity detected by the velocity detector into frequency components of orders of integer multiples of the rotation angle and multiplying the frequency components by a moment of inertia, while the output shaft of the permanent magnet motor is not driven from an external source but is driven by the permanent magnet motor itself; A torque pulsation measuring device for a permanent magnet motor that calculates torque pulsation by decomposing the rotation angle generated by the current flowing through the permanent magnet motor into frequency components of integer multiples and multiplying these by an induced voltage constant to calculate electromagnetic torque pulsation and adding together the components of the inertial torque pulsation with the same frequency.

7. 7. The torque pulsation measuring device for a permanent magnet motor according to claim 6, wherein feedback control is performed so that the mechanical angular velocity detected by said speed detector is maintained at a designated constant velocity.

8. A torque pulsation measuring device for a permanent magnet motor as described in claim 6 or claim 7, characterized in that the induced voltage constant is measured before measuring the torque pulsation.

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