Motor characteristic test method

Abstract

To provide a motor characteristic test device and a motor characteristic test method that can conduct an accurate characteristic test of a motor even if the motor has relatively small output.SOLUTION: A motor characteristic test device has a structure in which a test motor and a load motor are arranged opposite to each other, and rotation shafts of the test motor and load motor are mechanically connected by coupling with a torque meter therebetween, wherein an inverter is connected to each of the test motor and the load motor, and the load motor has a rotation angle sensor. The rotation angle sensor has a larger outer diameter than that of the test motor, and a signal from the rotation angle sensor is output to the inverter of the test motor so as to enable vector control of the test motor.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a motor characteristic testing device and a motor characteristic testing method. [Background technology]

[0002] In recent years, the use of electric vehicles has been expanding in order to reduce CO2 emissions. Such electrification is not limited to the automotive field, but has also spread to various industries and products, and there is a demand for the development of highly efficient motors with a wide range of output power. In order to achieve higher motor efficiency, various motor designs or motor materials are repeatedly prototyped and evaluated in search of motors with low energy loss. In relation to such evaluations, for example, Patent Document 1 discloses a motor testing device that tests the rotation state of a motor when a load is applied by a load device.

[0003] In particular, for magnetic materials such as magnets and electromagnetic steel sheets for motors, motors are often prototyped to evaluate whether the motor characteristics predicted by numerical simulations based on the material characteristics can actually be obtained. In addition, the characteristics of prototype motors (hereinafter referred to as "test motors") are sometimes evaluated as part of the material characteristic evaluation of new magnetic materials. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2019-215164 A Summary of the Invention [Problem to be solved by the invention]

[0005] Here, the structure, type, and output of the test motor are often determined according to the characteristics of the developed material. Therefore, the output of the test motor is diverse. However, in the past, it was difficult to evaluate test motors with various output ranges with high accuracy using one test device. If different test devices were prepared according to the output range, the cost of evaluating the test motor would increase significantly. In addition, information on the rotation angle is required to control the test motor for evaluation and rotate it appropriately, but many test motors do not have a rotation angle. In addition, the detection accuracy of the rotation angle sensor depends on the number of pulses per rotation of the rotating shaft, and the size of the rotation angle sensor generally becomes large for products with a large number of pulses. In particular, when evaluating a test motor with a low output, there is a limit to the size of the rotation angle sensor that can be directly installed on the test motor. Therefore, it was difficult to evaluate a test motor with a low output with high accuracy.

[0006] The present disclosure has been made in consideration of the above-described circumstances, and aims to provide a motor characteristic testing device and a motor characteristic testing method that enable high-precision characteristic testing even for motors with relatively small output. [Means for solving the problem]

[0007] (1) A motor characteristic testing device according to an embodiment of the present disclosure, A motor characteristic test device in which a test motor and a load motor are arranged opposite to each other, the test motor and the load motor have rotating shafts mechanically connected by a coupling via a torque meter, the test motor and the load motor are each connected to an inverter, and the load motor has a rotation angle sensor, The rotation angle sensor has an outer diameter larger than that of the sample motor, and a signal from the rotation angle sensor is output to an inverter of the sample motor so that vector control of the sample motor is possible.

[0008] (2) As an embodiment of the present disclosure, In the motor characteristic testing device described in (1), the torque meter has two measurement ranges, one of which is 1 / 10 or less of the other measurement range.

[0009] (3) As an embodiment of the present disclosure, In the motor characteristic testing device according to (1) or (2), the coupling has a bellows structure.

[0010] (4) A motor characteristic testing method according to an embodiment of the present disclosure, A motor characteristic testing method using the motor characteristic testing device according to any one of (1) to (3), a step of increasing the rotation speed stepwise by controlling the rotation speed of the load motor and measuring the load torque at each rotation speed by the torque meter before mechanically connecting the rotating shaft of the test motor and the rotating shaft of the load motor by the coupling; and providing a correction as an offset amount to a torque value measured after the test motor and the rotating shaft of the load motor are mechanically connected by the coupling based on the measured load torque, The step of measuring the load torque performs 0 Arms control with a predetermined voltage being applied from a DC power supply to the inverter of the test motor.

[0011] (5) As an embodiment of the present disclosure, In the motor characteristic testing method according to (4), a step of controlling the rotational speed of the load motor and controlling the output of the sample motor to sweep in a stepped manner by the signal, thereby acquiring the characteristics of the sample motor in a map form; a step of releasing the mechanical connection between the rotating shaft of the test motor and the rotating shaft of the load motor, increasing the rotation speed of the load motor stepwise, and measuring the load torque at each rotation speed by the torque meter; and correcting the characteristics of the test motor obtained in the form of a map based on the load torque measured by mechanically disconnecting the rotating shaft. Effect of the Invention

[0012] According to the present disclosure, it is possible to provide a motor characteristic testing device and a motor characteristic testing method that enable high-precision characteristic testing even for motors with relatively low output. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a diagram illustrating an example of the configuration of a motor characteristic test device according to an embodiment of the present disclosure. [Diagram 2] FIG. 2 is a diagram illustrating another configuration example of a motor characteristic test device according to an embodiment of the present disclosure. [Diagram 3] FIG. 3 is a diagram illustrating a state of a motor characteristic test device when measuring the offset of a torque meter in a motor characteristic test method according to an embodiment of the present disclosure. [Figure 4] FIG. 4 is a diagram illustrating a stepwise change in the rotation speed in a motor characteristic testing method according to an embodiment of the present disclosure. [Diagram 5] FIG. 5 is a diagram illustrating the measurement results of the offset amount of the torque meter. [Figure 6] FIG. 6 is a diagram illustrating an example of the offset amount of a torque meter measured in a motor characteristic test. [Figure 7] FIG. 7 is a diagram illustrating the core dimensions of the motor evaluated in the examples. [Figure 8] FIG. 8 is a diagram showing the relationship between the motor characteristics evaluated in the examples and the magnetic properties of the iron core material. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, a motor characteristic testing device and a motor characteristic testing method according to an embodiment of the present disclosure will be described with reference to the drawings. In each drawing, the same or corresponding parts are given the same reference numerals. In the following description of the embodiment, the description of the same or corresponding parts will be omitted or simplified as appropriate.

[0015] Fig. 1 is a diagram showing the configuration of a motor characteristic test device according to this embodiment. A test motor and a load motor are arranged facing each other. Here, the test motor is a motor that is a prototype test piece. The load motor is a motor provided in the motor characteristic test device that applies a load to the test motor in a test (characteristic evaluation).

[0016] The motor characteristic test device has a structure in which the rotating shafts of the test motor and the load motor are mechanically connected by a coupling via a torque meter. In other words, the rotating shafts of both motors are mechanically linked by a coupling via a torque meter. A DC power supply and an inverter are provided for each of the load motor and the test motor, and it is possible to control the current supply to the motors separately. In addition, a power meter is provided between the inverter and the test motor in order to measure the input power to the test motor. The motor characteristic test device may include, as other components, a control unit that provides a motor control command value, a temperature measuring system and a cooling system for temperature management, etc. The control unit is, for example, composed of a computer. The control unit may not only provide a motor control command value, but may also control the entire motor characteristic test device, and may execute the processing of the motor characteristic test method described later. In addition, the motor characteristic test device may be configured to include a transmission as shown in FIG. 2 in order to adjust the relationship between the torque and the rotation speed according to the test (evaluation).

[0017] Here, as shown in FIG. 1, the load motor is provided with a rotation angle sensor having a larger outer diameter than the test motor. Here, the outer diameter is the diameter of the outer circle of the load motor, the test motor, and the rotation angle sensor, which are cylindrical with the rotation axis as the center. The rotation angle sensor is configured to output a signal including information on the detected rotation angle to both the test motor control inverter (the inverter for the test motor) and the load motor control inverter (the inverter for the load motor). The accuracy of the rotation angle sensor is indicated by an index such as the number of pulses per rotation, and generally, the larger the outer diameter, the larger the number of pulses. In addition, generally, the test motor with small output tends to be small in size. Therefore, it is preferable to use a rotation angle sensor with a large outer diameter, but if a large rotation angle sensor is directly provided on a test motor with small output (small size), energy loss occurs due to mechanical resistance, which makes it difficult to test the motor characteristics with high accuracy. In the motor characteristic test device according to this embodiment, a rotation angle sensor with a larger outer diameter than the test motor is provided on a relatively large load motor. In addition, the motor characteristic test device according to this embodiment can execute vector control of the test motor using the signal from the rotation angle sensor of the load motor, eliminating the need to directly attach a rotation angle sensor to the test motor. This makes it possible to detect the rotation angle of a test motor with low output with high accuracy, which results in a highly accurate characteristic test.

[0018] As an alternative method, a rotation angle sensor that matches the size of the test motor may be attached to the test motor. However, this is not preferable because it may result in measurement errors for reasons explained below.

[0019] First, it is known that the motor torque (T) of a rotary synchronous motor is expressed by the following formula.

[0020]

number

[0021] Here, P n is the number of poles. ais the flux linkage. i a is the current. L d is the d-axis inductance. L q is the q-axis inductance. Additionally, β is the current lead angle. The control accuracy of the current lead angle (β) is affected by the measurement error of the rotation angle sensor. The rotation angle sensor measures the mechanical angle. In motor control, the error of the rotation angle sensor becomes a control error of the electrical angle. The relationship between the mechanical angle and the electrical angle is expressed by the following formula.

[0022]

number

[0023] Here, θ E is the electrical angle [deg]. Also, θ M is the mechanical angle [deg]. From the relational equation between the mechanical angle and the electrical angle, we can see that the more poles the test motor has, the larger the error in the electrical angle due to the measurement error in the mechanical angle will be. For example, motors for drones often use an outer rotor type motor structure, and are often designed with multiple poles. As an example, a motor for an aerial photography drone may have an outer diameter of about 40 mm, but a multiple pole configuration of 14 or more poles. In the case of 14 poles, if the rotation angle sensor generates a measurement error of 1 [deg] of the mechanical angle, it will result in an electrical angle error of 7 [deg]. From the motor torque equation, for example, a motor with a difference between the d-axis inductance and the q-axis inductance of 0 will generate a measurement error of 0.75%.

[0024] Generally, motor characteristic tests include motor efficiency η (%) as an evaluation item. Motor efficiency η (%) is calculated by η = (Pout / Pin) x 100 (%), where Pout (W) is the motor output and Pin (W) is the motor input. Here, the motor input Pin (W) is given by the effective value of the three-phase power measured by a power meter (see Figure 1). Also, the motor output Pout (W) is calculated by Pout (W) = T (Nm) x N (rpm) x (2π / 60). Here, T is the motor torque, and N is the motor rotation speed.

[0025] The torque error of 0.75% explained as an example is directly reflected in the error of the motor efficiency η, so it is very important to control the current advance angle with high accuracy. Therefore, rather than using a rotation angle sensor that matches the size of the test motor, it is preferable to use a rotation angle sensor that has a relatively large outer diameter, i.e., a large number of pulses per rotation and high measurement accuracy. By using the motor characteristic test device according to this embodiment, the signal from a rotation angle sensor that is sufficiently large and has high resolution and is provided on the load motor can be used to control the test motor, so that large measurement errors in the test can be prevented. Here, the type of rotation angle sensor can be a resolver, an encoder, etc., but is not limited to a specific type.

[0026] Here, the motor characteristic test device may be provided with a torque meter with small error accuracy. However, if the maximum rated torque is large, minute torque changes may not be detected with high accuracy. This is because the accuracy guarantee by the torque meter manufacturer is often set for the maximum rated torque. Replacing the torque meter every time the test motor to be tested is replaced requires labor, cost, and time. Therefore, it is preferable that the torque meter has two measurement ranges, one of which is 1 / 10 or less of the other measurement range. As an example, a torque meter having a first range of 20 Nm corresponding to the maximum output of the motor characteristic test device and a second range of 2 Nm, which is 1 / 10 of the first range, as measurement ranges may be used. As a specific example, a dual-rated torque meter such as 4503B from Kisra may be used.

[0027] In addition, the coupling is not limited to a specific type, and can be selected based on the diameter of the rotating shaft. However, if the test motor is manufactured by reusing a commercially available product, there may be cases where the rotating shaft of the test motor cannot be precisely aligned with the rotating shaft of the load motor. For this reason, it is preferable that the coupling has a bellows structure that can absorb the misalignment of the shafts and mechanically connect the rotating shafts.

[0028] Next, a motor characteristic test method using the motor characteristic test device according to this embodiment will be described. As described above, the motor characteristic test device according to this embodiment makes it possible to detect the rotation angle of even a test motor with a small output with high accuracy. In the motor characteristic test method according to this embodiment, the offset amount of the torque meter is further specified and corrected, thereby enabling even more accurate characteristic testing.

[0029] First, before mechanically connecting the rotating shafts of the test motor and the load motor by a coupling, the load motor is driven to gradually increase the rotation speed, and the load torque is measured by a torque meter at each rotation speed. Before mechanically connecting the rotating shaft, the motor characteristic test device is in the state shown in Figure 3. Figure 4 shows an example of a stepwise change in the rotation speed. A positive rotation speed indicates a forward rotation. A negative rotation speed indicates a reverse rotation state. Figure 5 shows an example of the load torque measured at each rotation speed. As shown by the curve plotted with a circle in Figure 5, torque is detected at a non-zero rotation speed even though the rotating shafts of the test motor and the load motor are not connected and the inverter for driving the test motor is OFF. In other words, a torque sensor offset amount symmetrical with respect to the origin, centered on 0 rpm, is observed. The main cause of this torque sensor offset amount is thought to be the mechanical resistance of the torque meter itself.

[0030] Furthermore, as shown by the triangular curve in Figure 5, the torque sensor offset amount becomes even larger when the inverter for driving the test motor is turned from OFF to ON and measurement is performed. The reason for the increase in the torque sensor offset amount is thought to be the effect of noise from the inverter for driving the test motor affecting the torque meter. In actual testing (evaluation), the test motor is affected by the offset when the inverter for driving the test motor is ON. For this reason, it is preferable to measure the torque sensor offset amount when the inverter for driving the test motor is ON. Specifically, it is preferable to perform 0 Arms control while a specified voltage is applied from a DC power supply to the inverter of the test motor and measure the torque sensor offset amount. 0 Arms control is performed by applying a specified voltage to the inverter of the test motor (i a ) is a control that makes the effective value of zero.

[0031] Based on the load torque measured in this way, a process is executed to provide a correction as an offset to the torque value measured after mechanically connecting the rotating shafts of the test motor and the load motor via a coupling. By identifying and correcting the offset thought to be caused by the mechanical resistance of the torque meter, it becomes possible to perform characteristic tests (motor characteristic evaluation) with even higher accuracy.

[0032] Next, the load motor controls the rotation speed, and the output of the test motor is controlled to sweep in a stepped manner according to the signal from the rotation angle sensor, thereby obtaining the characteristics of the test motor in a map form. Here, "obtaining the characteristics of the test motor in a map form" means, for example, mapping the rotation speed on the horizontal axis and the torque on the vertical axis, and measuring the motor characteristics by identifying correlations, etc. The state in which the output of the test motor sweeps in a stepped manner refers to the state in which the rotation speed changes in stages, as shown in Figure 4.

[0033] After acquiring the characteristics of the test motor in a map form, the mechanical connection between the rotating shaft of the test motor and the load motor is released, the rotation speed is increased stepwise by the load motor, and the load torque is measured by the torque meter at each rotation speed. The stepwise increase in the rotation speed may be as shown in Figure 4. At this time, the motor characteristic test device is in a state where the test motor is not rotating, but the inverter is ON. Figure 6 shows an example of the torque offset amount based on the load torque measured after the mechanical connection of the rotating shaft is released. In the example of Figure 6, after holding one rotation speed for about 10 seconds, eight torque measurements are performed every second, and the torque offset amount obtained in each measurement is plotted. Therefore, multiple plots are seen for each level of rotation speed. As mentioned above, correction (primary correction) for the offset amount thought to be due to the mechanical resistance of the torque meter has been performed, but as shown in Figure 6, a small amount of offset (the absolute value is very small compared to the value shown in Figure 5) has occurred. The effect of the temperature dependency of the mechanical loss is thought to be the cause of the offset even after the primary correction. When comprehensively measuring and evaluating motor characteristics in a map format, measurements are taken at over 1,000 points while changing measurement conditions, and in some cases the motor continues to rotate for around six hours. In particular, it is expected that the temperature of the bearings will differ significantly from the initial state (room temperature). By correcting the characteristics of the test motor obtained in a map format based on the load torque, which is thought to be the effect of the temperature dependency of mechanical loss, it becomes possible to perform characteristic testing with even higher precision.

[0034] As described above, the motor characteristic test device and motor characteristic test method according to the present embodiment, by using the above-mentioned configuration and process, make it possible to perform highly accurate characteristic tests even on motors with relatively low output. Furthermore, the motor characteristic test device and motor characteristic test method according to the present embodiment can perform highly accurate characteristic evaluations on motors of a wide variety of types and output ranges. This makes it possible to suppress capital investment in test equipment and reduce the costs associated with evaluating sample motors, which is essential for developing highly efficient motors.

[0035] Although the embodiments of the present disclosure have been described based on the drawings, it should be noted that those skilled in the art can easily make various modifications or corrections based on the present disclosure. For example, the functions included in each component can be rearranged so as not to cause logical inconsistencies, and multiple components can be combined into one or divided. The embodiments of the present disclosure can also be realized as a program executed by a processor included in the device or a storage medium on which a program is recorded. It should be understood that these are also included in the scope of the present disclosure.

[0036] The effects of the present disclosure will be specifically described below based on examples (experimental examples); however, the present disclosure is not limited to these examples.

[0037] (Example) In this embodiment, the motor characteristic test method was carried out by a motor characteristic test device having the configuration shown in Fig. 1. Here, the test motor was smaller than the load motor, with the outer diameter of the test motor being 42 mm and the outer diameter of the rotation angle sensor (encoder) of the load motor being 63 mm. In other words, the outer diameter of the test motor was 2 / 3 of the outer diameter of the load motor. In this embodiment, a rotation angle sensor manufactured by BEI Sensors with the model number "H25D-SS-975-T3-ABZC-28V / V-SM20-S" was used. The number of pulses was 975 / revolution.

[0038] The number of poles of the test motor is 14 poles of the outer rotor. The magnet used is a Nd sintered magnet. A stator core having the shape shown in FIG. 7 was manufactured by punching and crimping lamination using five types of core materials with different magnetic properties. The properties of the five types of core materials (A to E) are shown in Table 1. Next, a test motor was assembled using the stator core having the above shape, and the motor properties were evaluated. Here, the motor properties were evaluated five times each by the conventional method (comparative example) of attaching a rotation angle sensor to the test motor and the motor property test method (example) described as the above embodiment. The motor properties of the comparative example and example were evaluated for each of the test motors using the five types of core materials (A to E). Here, the test motor and the rotation angle sensor were attached and removed each time an evaluation was performed. The voltage applied to the inverter was fixed at 30 V, the carrier frequency was 17.5 kHz, and the current advance angle β was 0 deg, and the test motor was PWM inverter controlled. The test motor was driven at a rotation speed of 1000 rpm up to 10000 rpm in 1000 rpm increments. A current was applied from 2.5 Arms to 25.0 Arms in 2.5 Arms increments. The characteristics of the test motor were obtained in a map form. FIG. 8 shows the relationship between the magnetic properties of the iron core material and the maximum efficiency and maximum torque, which are representative motor characteristics. Here, the standard deviation is σ, and the error bars of the motor characteristic values ​​are shown at 1σ. Among the data in FIG. 8, those related to the embodiment are summarized in Table 2, and those related to the comparative example are summarized in Table 3. In Tables 2 and 3, each of the evaluated test motors is distinguished by the iron core material (A to E) as an identifier. The iron core materials (A to E) are the same as those listed in Table 1. In general, the lower the iron loss of the iron core material, the higher the maximum efficiency of the motor. In general, the higher the magnetic flux density of the iron core material, the higher the maximum torque. Both the comparative example and the embodiment showed such a tendency. However, in the comparative example, the measured values ​​of the motor characteristics were not stable and had large variations. The variations in the measured values ​​in the comparative example are thought to be due to the influence of mechanical loss in the rotation angle sensor, and it is thought that the variations in the installation accuracy for each evaluation were reflected in the evaluation results.As can be seen from the correlation between the magnetic properties of the iron core material and the motor properties and the size of the error bars, highly accurate property testing is possible by using the motor property testing device and motor property testing method according to this embodiment.

[0039] [Table 1]

[0040] [Table 2]

[0041] [Table 3]

Claims

1. A motor characteristic test method using a motor characteristic test device in which a test motor and a load motor are arranged opposite to each other, the test motor and the load motor have rotating shafts mechanically connected by a coupling via a torque meter, the test motor and the load motor are each connected to an inverter, and the load motor has a rotation angle sensor, a step of increasing the rotation speed stepwise by controlling the rotation speed of the load motor and measuring the load torque at each rotation speed by the torque meter before mechanically connecting the rotating shaft of the test motor and the rotating shaft of the load motor by the coupling; and providing a correction as an offset amount to a torque value measured after the test motor and the rotating shaft of the load motor are mechanically connected by the coupling based on the measured load torque, The step of measuring the load torque includes performing 0 Arms control in a state where a predetermined voltage is applied from a DC power supply to the inverter of the test motor, A motor characteristic testing method, wherein the rotation angle sensor has an outer diameter larger than that of the test motor, and a signal from the rotation angle sensor is output to an inverter of the test motor so as to enable vector control of the test motor.

2. a step of controlling the rotational speed of the load motor and controlling the output of the sample motor to sweep in a stepped manner by the signal, thereby acquiring the characteristics of the sample motor in a map form; a step of releasing the mechanical connection between the rotating shaft of the test motor and the rotating shaft of the load motor, increasing the rotation speed of the load motor stepwise, and measuring the load torque at each rotation speed by the torque meter; and correcting the characteristics of the test motor acquired in the form of a map based on the load torque measured by disconnecting the mechanical connection of the rotating shaft.

3. 3. The motor characteristic testing method according to claim 1, wherein the torque meter has two measurement ranges, one of the measurement ranges being equal to or smaller than 1 / 10 of the other measurement range.

4. 3. The motor characteristic testing method according to claim 1, wherein the coupling has a bellows structure.

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