Torque measurement circuit for electric motor and method for calculating electric motor torque

Abstract

To provide a motor torque measurement circuit and a motor torque calculation method that can calculate torque with high reliability with a simpler configuration.SOLUTION: The present motor torque measurement circuit calculates a first torque current value of the motor from an actual measured value of a U-phase current, an actual measured value of a V-phase current, and a calculated value of a W-phase current calculated from these actual measured values, calculates a second torque current value of the motor from the actual measured value of the V-phase current, an actual measured value of the W-phase current, and a calculated value of the U-phase current calculated from these actual measured values, calculates a third torque current value of the motor from the actual measured value of the W-phase current, the actual measured value of the U-phase current, and a calculated value of the V-phase current calculated from these actual measured values, and when the difference between the maximum torque current value and the minimum torque current value, of the first torque current value, the second torque current value, and the third torque current value, is within an allowable range, notifies an upper device of a current value indicating the torque of the motor determined based on the calculated torque current values.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a motor torque measurement circuit and a motor torque calculation method. [Background Art]

[0002] In devices using an electric motor, torque is measured for controlling the electric motor (see, for example, Patent Documents 1 and 2). [Prior Art Documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Unexamined Patent Publication No. Hei 9-005383 [Patent Document 2] Japanese Unexamined Patent Publication No. 2018-129957 [Summary of the Invention] [Problem to be Solved by the Invention]

[0004] In motor torque calculation, the circuits for calculating the motor torque are duplexed, and highly reliable torque is calculated by comparing the torques calculated by the respective duplexed circuits. When such a configuration is adopted, for example, two ammeters are provided for each of the U-phase, V-phase, and W-phase power lines of the drive current supplied to the motor. However, the duplexed circuit makes it difficult to reduce the size of the device equipped with the electric motor and leads to an increase in the manufacturing cost of the device.

[0005] One aspect of the disclosed technology aims to provide a motor torque measurement circuit and a motor torque calculation method that can calculate highly reliable torque with a simpler configuration. [Means for Solving the Problem]

[0006] One aspect of the disclosed technology is exemplified by the following motor torque measurement circuit. The motor torque measurement circuit comprises a U-phase power line, a V-phase power line, and a W-phase power line that supply a three-phase AC drive current to the motor; a first measurement unit that measures the current flowing through the U-phase power line; a second measurement unit that measures the current flowing through the V-phase power line; a third measurement unit that measures the current flowing through the W-phase power line; and a calculation unit. The calculation unit calculates a calculated value for the W-phase current from the measured value of the U-phase current measured by the first measurement unit and the measured value of the V-phase current measured by the second measurement unit, and calculates a first torque current value indicating the torque of the motor from the measured value of the U-phase current, the measured value of the V-phase current and the calculated value of the W-phase current, and calculates a calculated value for the U-phase current from the measured value of the V-phase current and the measured value of the W-phase current measured by the third measurement unit, and calculates a second torque current value indicating the torque of the motor from the measured value of the V-phase current, the measured value of the W-phase current and the calculated value of the U-phase current The current value is calculated, and the current value of the V phase is calculated from the measured value of the W phase current and the measured value of the U phase current. A third torque current value indicating the torque of the motor is calculated from the measured value of the W phase current, the measured value of the U phase current and the calculated value of the V phase current. If the difference between the maximum torque current value and the minimum torque current value among the first torque current value, the second torque current value and the third torque current value is within the allowable range, the current value indicating the torque of the motor, determined based on the first torque current value, the second torque current value and the third torque current value, is notified to the higher-level device.

[0007] In the torque measurement circuit of the above-mentioned electric motor, when calculating the torque current value, the measured values ​​of two of the three phases are used, and the value of the remaining phase is calculated from the measured values ​​of the two phases. Then, the first torque current value, the second torque current value, and the third torque current value are calculated. In each of the current values, the phases of the calculated current values ​​are different. The torque measurement circuit for the motor described above determines the current value indicating the torque of the motor based on the torque current value calculated when the difference between the torque current values ​​calculated using these three different methods is within an acceptable range. This allows for the calculation of a highly reliable torque with a simpler configuration, without duplicating the measurement units provided for each phase.

[0008] Here, the calculation unit may include a first circuit for calculating the first torque current value, a second circuit for calculating the second torque current value, and a third circuit for calculating the third torque current value. Furthermore, if the difference between the maximum torque current value and the minimum torque current value among the first, second, and third torque current values ​​calculated by different circuits is within an acceptable range, the calculation circuit may notify a higher-level device of a current value indicating the torque of the electric motor, determined based on the first, second, and third torque current values.

[0009] When the first, second, and third torque current values ​​are calculated using the same circuit, an error in that circuit will equally affect the first, second, and third torque current values, potentially leading to a situation where a torque current value different from the motor's torque is not detected. In the above-mentioned motor torque measurement circuit, by separating the circuits used to calculate each torque current value, even if an error occurs in one of the circuits, causing the torque current value calculated by that circuit to be incorrect, the other torque current values ​​will not be affected by that error. Therefore, the above-mentioned motor torque measurement circuit can prevent incorrectly calculated torque current values ​​from being treated as representing the motor's torque.

[0010] The torque measurement circuit for the electric motor may include a U-phase power line, a V-phase power line, and a W-phase power line that supply a three-phase AC drive current to the electric motor; a first measurement unit that measures the current flowing through the U-phase power line; a second measurement unit that measures the current flowing through the V-phase power line; a first measurement unit that measures the current flowing through the W-phase power line; a sensor that measures the torque of the electric motor; and a calculation unit. The calculation unit then calculates a fourth torque current value indicating the torque of the motor from the measured value of the U-phase current measured by the first measurement unit, the measured value of the V-phase current measured by the second measurement unit, and the measured value of the W-phase current measured by the third measurement unit. It then converts the measured value indicating the torque of the motor measured by the sensor into a fifth torque current value indicating the measured value. If the difference between the fourth torque current value and the fifth torque current value is within an acceptable range, the calculation unit may notify the higher-level device of the current value indicating the torque of the motor determined based on the fourth and fifth torque current values. The torque measurement circuit for the motor determines the torque current value indicating the torque of the motor when the difference between the torque current value calculated from the current value supplied to the motor and the torque current value indicating the torque measured by the sensor is within an acceptable range. In the torque measurement circuit for the motor, it is not necessary to duplicate the sensor that measures the torque of the motor, so a more reliable torque can be calculated with a simpler configuration.

[0011] In the above-described torque measurement circuit for the electric motor, the calculation unit may store in the memory the correspondence between the measured value of the sensor and the fourth torque current value calculated when the electric motor is outputting the torque measured by the sensor, and by referring to the memory, convert the measured value indicating the torque of the electric motor measured by the sensor into the fifth torque current value indicating the measured value. By using the above correspondence, the torque measurement circuit for the electric motor can be made to have the same value when the fourth torque current value and the fifth torque current value indicate the same torque.

[0012] The disclosed technology can also be understood from the perspective of the method for calculating the torque of an electric motor. [Effects of the Invention]

[0013] According to the disclosed technology, reliable torque can be calculated with a simpler configuration. [Brief explanation of the drawing]

[0014] [Figure 1] Figure 1 shows an example of a motor torque measurement circuit according to this embodiment. [Figure 2] Figure 2 is a first diagram showing an example of the processing flow of the motor torque measurement process using the torque measurement circuit according to the embodiment. [Figure 3] Figure 3 is a second diagram showing an example of the processing flow of the motor torque measurement process using the torque measurement circuit according to the embodiment. [Figure 4] Figure 4 shows an example of a torque measurement circuit related to a comparative example. [Figure 5] Figure 5 shows an example of a torque measurement circuit according to the first modified example. [Figure 6] Figure 6 shows an example of a torque measurement circuit according to the second modified example. [Figure 7] Figure 7 illustrates the first correspondence between torque current value and measured torque value. [Figure 8] Figure 8 illustrates a second correspondence between torque current values ​​and measured torque values. [Modes for carrying out the invention]

[0015] <Embodiment> Embodiments will be described below with reference to the drawings. FIG. 1 is a diagram showing an example of a torque measurement circuit 100 for a motor 30 according to an embodiment. The torque measurement circuit 100 includes a power circuit 20, a motor 30, and a torque calculation circuit 10. The torque calculation circuit 10 includes three-phase to two-phase conversion circuits 11a, 11b, 11c, rotational coordinate conversion circuits 12a, 12b, 12c, and control circuits 13a, 13b, 13c. When the three-phase to two-phase conversion circuits 11a, 11b, 11c are not distinguished from one another, they are also referred to as the three-phase to two-phase conversion circuit 11. When the rotational coordinate conversion circuits 12a, 12b, 12c are not distinguished from one another, they are also referred to as the rotational coordinate conversion circuit 12. When the control circuits 13a, 13b, 13c are not distinguished from one another, they are also referred to as the control circuit 13. The torque measurement circuit 100 is an example of "a torque measurement circuit for an electric motor". The torque calculation circuit 10 is an example of a "calculation unit".

[0016] The power circuit 20 supplies a three-phase alternating current drive current to the motor 30 via a U-phase power line 21, a V-phase power line 22, and a W-phase power line 23. Through the U-phase power line 21, a U-phase current is supplied from the power circuit 20 to the motor 30. Through the V-phase power line 22, a V-phase current is supplied from the power circuit 20 to the motor 30. Through the W-phase power line 23, a W-phase current is supplied from the power circuit 20 to the motor 30.

[0017] The U-phase power line 21 is provided with an ammeter 51 that measures the current value of the U-phase current flowing through the U-phase power line 21. The V-phase power line 22 is provided with an ammeter 52 that measures the current value of the V-phase current flowing through the V-phase power line 22. The W-phase power line 23 is provided with an ammeter 53 that measures the current value of the W-phase current flowing through the W-phase power line 23.

[0018] The motor 30 is, for example, an alternating current motor. The motor 30 operates by receiving the drive current supplied from the power circuit 20. The torque of the output shaft of the motor 30 is controlled in accordance with the drive current supplied from the power circuit 20. The motor 30 is an example of an "electric motor".

[0019] A U-phase branch wiring 41 is connected to the ammeter 51, which inputs the U-phase current value measured by the ammeter 51 to the three-phase to two-phase conversion circuits 11a and 11c. A V-phase branch wiring 42 is connected to the ammeter 52, which inputs the V-phase current value measured by the ammeter 52 to the three-phase to two-phase conversion circuits 11a and 11b. A W-phase branch wiring 43 is connected to the ammeter 53, which inputs the W-phase current value measured by the ammeter 53 to the three-phase to two-phase conversion circuits 11b and 11c. The ammeter 51 is an example of the "first measurement unit". The ammeter 52 is an example of the "second measurement unit". The ammeter 53 is an example of a "third measuring unit".

[0020] The three-phase to two-phase conversion circuit 11 is a circuit that converts three-phase AC to two-phase AC. The three-phase to two-phase conversion circuit 11a receives the current values ​​of the U-phase and V-phase measured by ammeters 51 and 52, respectively. The three-phase to two-phase conversion circuit 11a calculates the current value of the W-phase from the input current values ​​of the U-phase and V-phase. The three-phase to two-phase conversion circuit 11a converts the three-phase AC, based on the input current values ​​of the U-phase and V-phase and the calculated current value of the W-phase, into two-phase AC. The three-phase to two-phase conversion circuit 11a inputs the current values ​​of the α-phase Iα(U&V) and the β-phase Iβ(U&V), which have been converted to two phases, into the rotational coordinate conversion circuit 12a.

[0021] The three-phase to two-phase conversion circuit 11b receives the V-phase current value and the W-phase current value measured by ammeters 52 and 53, respectively. The three-phase to two-phase conversion circuit 11b calculates the U-phase current value from the input V-phase current value and W-phase current value. The three-phase to two-phase conversion circuit 11b converts the three-phase AC, which is based on the input V-phase current value, the W-phase current value, and the calculated U-phase current value, into a two-phase AC. The three-phase to two-phase conversion circuit 11b inputs the converted α-phase current value Iα(V&W) and β-phase current value Iβ(V&W) into the rotational coordinate conversion circuit 12b.

[0022] The three-phase to two-phase conversion circuit 11c receives the W-phase current value and the U-phase current value measured by ammeters 53 and 51, respectively. The three-phase to two-phase conversion circuit 11c calculates the V-phase current value from the input W-phase current value and U-phase current value. The three-phase to two-phase conversion circuit 11c converts the three-phase AC, which is based on the input W-phase current value, the U-phase current value, and the calculated V-phase current value, into a two-phase AC. The three-phase to two-phase conversion circuit 11c inputs the converted α-phase current value Iα(W&U) and β-phase current value Iβ(W&U) into the rotational coordinate conversion circuit 12c.

[0023] The rotary coordinate transformation circuit 12 receives two-phase AC power converted from three-phase AC by the three-phase to two-phase conversion circuit 11. The rotary coordinate transformation circuit 12 performs a rotary coordinate transformation on the input two-phase AC power to determine the current values ​​of the d-axis and q-axis. Here, the current value of the d-axis represents the excitation current value of the motor 30, and the current value of the q-axis represents the torque current value of the motor 30. The rotary coordinate transformation circuit 12 then inputs the determined excitation current value and torque current value to the control circuit 13.

[0024] The rotational coordinate transformation circuit 12a inputs the excitation current value Id(U&V) and torque current value Iq(U&V), obtained by converting the α-phase current value Iα(U&V) and β-phase current value Iβ(U&V) input from the three-phase two-phase conversion circuit 11a, into the control circuit 13a. The rotational coordinate transformation circuit 12b inputs the excitation current value Id(V&W) and torque current value Iq(V&W), obtained by converting the α-phase current value Iα(V&W) and β-phase current value Iβ(V&W) input from the three-phase two-phase conversion circuit 11b, into the control circuit 13b. The rotational coordinate transformation circuit 12c inputs the excitation current value Id(W&U) and torque current value Iq(W&U), obtained by converting the α-phase current value Iα(W&U) and β-phase current value Iβ(W&U) input from the three-phase two-phase conversion circuit 11c, into the control circuit 13c.

[0025] The control circuit 13 can be considered, for example, as a computer having an arithmetic unit, memory, etc. Control circuits 13a and 13b are connected by connection bus B1. Control circuits 13b and 13c are connected by connection bus B2.

[0026] Control circuit 13 determines whether all of the torque current values ​​Iq(U&V), torque current values ​​Iq(V&W), and torque current values ​​Iq(W&U) match. Control circuit 13a inputs Iq(U&V) from the rotation coordinate transformation circuit 12a to control circuit 13b via connection bus B1. Control circuit 13c inputs torque current values ​​Iq(W&U) from the rotation coordinate transformation circuit 12c to control circuit 13b via connection bus B2. Control circuit 13b inputs torque current values ​​Iq(V&W) from the rotation coordinate transformation circuit 12b to control circuit 13a via connection bus B1. Control circuit 13b also... The torque current value Iq(V&W) input from the coordinate transformation circuit 12b is input to the control circuit 13c via the connecting bus B2.

[0027] Control circuit 13a determines whether the torque current value Iq(U&V) input from the rotation coordinate transformation circuit 12a matches the torque current value Iq(V&W) input from control circuit 13b. Control circuit 13c determines whether the torque current value Iq(W&U) input from the rotation coordinate transformation circuit 12c matches the torque current value Iq(V&W) input from control circuit 13b. Control circuit 13b determines whether the torque current value Iq(V&W) input from the rotation coordinate transformation circuit 12b matches the torque current value Iq(U&V) input from control circuit 13a. Control circuit 13b further determines whether the torque current value Iq(V&W) input from the rotation coordinate transformation circuit 12b matches the torque current value Iq(W&U) input from control circuit 13c.

[0028] In the above process, each of the control circuits 13a, 13b, and 13c made a determination as to whether all of the torque current values ​​Iq(V&W) and Iq(W&U) matched. However, the determination as to whether all of the torque current values ​​Iq(V&W) and Iq(W&U) matched may be made by any one of the control circuits 13. For example, control circuit 13b may make the determination as to whether all of the torque current values ​​Iq(V&W) and Iq(W&U) match, and the determination by control circuits 13a and 13b may be omitted.

[0029] Here, if all of the torque current values ​​Iq(V&W) and Iq(W&U) match, the control circuit 13 determines the calculated torque current value as the torque current value representing the torque of the motor 30. The control circuit 13 may also notify a higher-level device such as a PLC or servo driver of the determined torque current value as information indicating the torque of the motor 30. Furthermore, if all of the torque current values ​​Iq(V&W) and Iq(W&U) do not match, the control circuit 13 may, for example, notify a higher-level device that it was not possible to accurately calculate the torque of the motor 30.

[0030] The three-phase to two-phase conversion circuit 11a, the rotational coordinate conversion circuit 12a, and the control circuit 13a are examples of the "first circuit". The three-phase to two-phase conversion circuit 11b, the rotational coordinate conversion circuit 12b, and the control circuit 13b are examples of the "second circuit". The three-phase to two-phase conversion circuit 11c, the rotational coordinate conversion circuit 12c, and the control circuit 13c are examples of the "third circuit".

[0031] Figures 2 and 3 show an example of the processing flow for torque measurement of the motor 30 by the torque measurement circuit 100 according to the embodiment. The following description of an example of the processing flow for torque measurement of the motor 30 will refer to Figures 2 and 3.

[0032] In S1, the three-phase to two-phase conversion circuit 11a obtains the current value of the U-phase from ammeter 51 and the current value of the V-phase from ammeter 52. In S2, the three-phase to two-phase conversion circuit 11a calculates the current value of the W-phase from the current values ​​of the U-phase and V-phase obtained in S1.

[0033] In S3, a first torque current value representing the torque of the motor 30 is calculated using the three-phase current values ​​obtained in S1 (U-phase current value and V-phase current value) and the W-phase current value calculated in S2. The three-phase to two-phase conversion circuit 11a converts the three-phase current values ​​obtained in S1 (U-phase current value and V-phase current value) and the W-phase current value calculated in S2 into two-phase current values ​​Iα(U&V) and Iβ(U&V) and inputs them to the rotational coordinate conversion circuit 12a. The rotational coordinate conversion circuit 12a generates a first torque current value Iq(U&V) representing the torque of the motor 30 based on the input current values ​​Iα(U&V) and Iβ(U&V). The rotational coordinate conversion circuit 12a inputs the generated first torque current value Iq(U&V) to the control circuit 13a.

[0034] In S4, the three-phase to two-phase conversion circuit 11b obtains the V-phase current value from ammeter 52 and the W-phase current value from ammeter 53. In S5, the three-phase to two-phase conversion circuit 11b calculates the U-phase current value from the V-phase current value obtained in S4 and the W-phase current value.

[0035] In S6, a torque current value representing the torque of the motor 30 is calculated using the three-phase current values ​​obtained in S4 (V-phase current value, W-phase current value) and the U-phase current value calculated in S5. The three-phase to two-phase conversion circuit 11b converts the three-phase current values ​​obtained in S4 (V-phase current value, W-phase current value) and the U-phase current value calculated in S5 into two-phase current values ​​Iα(V&W) and Iβ(V&W) and inputs them to the rotational coordinate conversion circuit 12b. The rotational coordinate conversion circuit 12b generates a second torque current value Iq(V&W) representing the torque of the motor 30 based on the input current values ​​Iα(V&W) and Iβ(V&W). The rotational coordinate conversion circuit 12b inputs the generated second torque current value Iq(V&W) to the control circuit 13b.

[0036] In S7, the three-phase to two-phase conversion circuit 11c obtains the W-phase current value from ammeter 53 and the U-phase current value from ammeter 51. In S8, the three-phase to two-phase conversion circuit 11c calculates the V-phase current value from the W-phase current value and the U-phase current value obtained in S7.

[0037] In S9, a torque current value representing the torque of the motor 30 is calculated using the three-phase current values ​​obtained in S7 (W-phase current value and U-phase current value) and the V-phase current value calculated in S8. The three-phase to two-phase conversion circuit 11c converts the three-phase current values ​​obtained in S7 (W-phase current value and U-phase current value) and the V-phase current value calculated in S8 into two-phase current values ​​Iα(W&U) and Iβ(W&U) and inputs them to the rotational coordinate conversion circuit 12c. The rotational coordinate conversion circuit 12c generates a third torque current value Iq(W&U) representing the torque of the motor 30 based on the input current values ​​Iα(W&U) and Iβ(W&U). The rotational coordinate conversion circuit 12c inputs the generated third torque current value Iq(W&U) to the control circuit 13c.

[0038] In S10, the control circuit 13b determines whether the first torque current value Iq(U&V) calculated in S3, the second torque current value Iq(V&W) calculated in S6, and the third torque current value Iq(W&U) calculated in S9 match. If they match (YES in S10), the process proceeds to S11. If they do not match (NO in S10), the process proceeds to S12.

[0039] In S11, the control circuit 13b determines that the torque current values ​​calculated in S3, S6, and S9 are the same, and therefore determines these calculated torque current values ​​to be the torque current values ​​representing the torque of the motor 30. For example, the control circuit 13b may notify the higher-level device of information including the determined torque current values ​​as a feedback signal.

[0040] In S12, the control circuit 13b determines that it could not correctly calculate the torque current value of the motor 30 because the torque current values ​​calculated in S3, S6, and S9 did not match, and outputs an error. Examples of error outputs include the output of an alarm sound, the display of an error message on a display device, and notification to a higher-level device.

[0041] <Comparative Example> Here, in order to verify the effects of the embodiment, a comparative example will be described. Figure 4 is a diagram showing an example of a torque measurement circuit 500 according to the comparative example. The drive current from the power circuit 520 is supplied to the motor 530 via the U-phase power line 521, the V-phase power line 522, and the W-phase power line 523. In the torque measurement circuit 500, two ammeters are placed on each power line: ammeters 551 and 551a on the U-phase power line 521, ammeters 552 and 552a on the V-phase power line 522, and ammeters 553 and 553a on the W-phase power line 523.

[0042] The current values ​​of the U-phase measured by ammeter 551, the V-phase measured by ammeter 552, and the W-phase measured by ammeter 553 are input to the three-phase to two-phase conversion circuit 511a. The current values ​​of the U-phase measured by ammeter 551a, the V-phase measured by ammeter 552a, and the W-phase measured by ammeter 553a are input to the three-phase to two-phase conversion circuit 511b.

[0043] The three-phase to two-phase conversion circuit 511a converts the input three-phase current values ​​of U-phase, V-phase, and W-phase into two-phase current values ​​Iα_1 and Iβ_1, and inputs the converted two-phase current values ​​to the rotational coordinate conversion circuit 512a. The three-phase to two-phase conversion circuit 511b converts the input three-phase current values ​​of U-phase, V-phase, and W-phase into two-phase current values ​​Iα_2 and Iβ_2, and inputs the converted two-phase current values ​​to the rotational coordinate conversion circuit 512b.

[0044] The rotational coordinate transformation circuit 512a converts the current values ​​Iα_1 and Iβ_1 into the d-axis current value Id_1 and the q-axis current value Iq_1 by performing a rotational coordinate transformation. Here, the d-axis current value Id_1 is the current value that represents the excitation current value of the motor 530, and is therefore also called the excitation current value Id_1. Similarly, the q-axis current value Iq_1 is the current value that represents the torque of the motor 530, and is therefore also called the torque current value Iq_1. The rotational coordinate transformation circuit 512a inputs the excitation current value Id_1 and the torque current value Iq_1 to the control circuit 513a.

[0045] The rotational coordinate transformation circuit 512b converts the current values ​​Iα_2 and Iβ_2 into the d-axis current value Id_2 and the q-axis current value Iq_2 by performing a rotational coordinate transformation. Here, the d-axis current value Id_2 is the current value that represents the excitation current value of the motor 530, and is therefore also called the excitation current value Id_2. Similarly, the q-axis current value Iq_2 is the current value that represents the torque of the motor 530, and is therefore also called the torque current value Iq_2. The rotational coordinate transformation circuit 512b inputs the excitation current value Id_2 and the torque current value Iq_2 to the control circuit 513b.

[0046] Control circuits 513a and 513b determine whether the torque current value Iq_1 calculated by the rotational coordinate transformation circuit 512a matches the torque current value Iq_2 calculated by the rotational coordinate transformation circuit 512b. For example, control circuit 513b inputs the torque current value Iq_2 input from the rotational coordinate transformation circuit 512b to control circuit 513a. Then, the rotational coordinate transformation circuit 512a determines whether the torque current value Iq_1 calculated by the rotational coordinate transformation circuit 512a matches the torque current value Iq_2 input from control circuit 513b.

[0047] In the comparative example, the torque current value representing the torque of the motor 530 is calculated using the measured current values ​​of the U-phase, V-phase, and W-phase. Therefore, the ammeters placed on the U-phase power line 521, V-phase power line 522, and W-phase power line 523 are duplicated. In other words, in the comparative example, in addition to the ammeters 551, 552, and 553 used to drive the motor 530, ammeters 551a, 552a, and 553a are added for torque calculation. In the comparative example, the addition of ammeters 551a, 552a, and 553a increases the number of circuit blocks in the torque measurement circuit 500, making it difficult to make the torque measurement circuit 500 compact and leading to increased manufacturing costs.

[0048] On the other hand, in the torque measurement circuit 100 according to this embodiment, one ammeter is provided for each of the U-phase power line 21, V-phase power line 22, and W-phase power line 23. These ammeters were originally installed for the control of the motor 30 and have been repurposed for the torque measurement circuit 100. In other words, ammeters 51, 52, and 53 are not ammeters added specifically for the torque measurement circuit 100. Therefore, according to this embodiment, the increase in circuit blocks within the torque measurement circuit 100 is suppressed.

[0049] In this embodiment, two of the three phases of the three-phase AC (U, V, and W) are measured by an ammeter, and the current values ​​of the other phases are calculated using the measured current values ​​of the two phases. Then, a first torque current value of the motor 30 is calculated using the measured current values ​​of the U and V phases, and the W phase current value calculated based on the measured current values ​​of the U and V phases. A second torque current value of the motor 30 is calculated using the measured current values ​​of the V and W phases, and the U phase current value calculated based on the measured current values ​​of the V and W phases. A third torque current value of the motor 30 is calculated using the measured current values ​​of the W and U phases, and the V phase current value calculated based on the measured current values ​​of the W and U phases. These values ​​are then compared.

[0050] In other words, in this embodiment, when calculating the first torque current value, the current value of the W phase is used as redundant data; when calculating the second torque current value, the current value of the U phase is used as redundant data; and when calculating the third torque current value, the current value of the V phase is used as redundant data. Then, by comparing these first, second, and third torque current values, if the same torque current value can be calculated regardless of which of the U, V, or W phase current values ​​is used as redundant data, the calculated torque current value is determined to be the torque current value representing the torque of the motor 30.

[0051] Therefore, according to this embodiment, even without duplicating the ammeters provided on the U-phase power line 21, V-phase power line 22, and W-phase power line 23, a highly reliable torque of the motor 30 can be calculated by comparing torque current values ​​calculated using three different calculation methods. In other words, in this embodiment, the torque current value of the motor 30 can be calculated using the ammeters 51, 52, and 53 used to drive the motor 30, without arranging additional ammeters on the U-phase power line 21, V-phase power line 22, and W-phase power line 23. This makes it easy to miniaturize the torque measurement circuit 100 and suppress increases in manufacturing costs.

[0052] Here, we consider the case where the torque current values ​​Iq(U&V), Iq(V&W), and Iq(W&U) are all calculated using the same path (for example, the three-phase two-phase conversion circuit 11a and the rotating coordinate conversion circuit 12a). In this case, even if an error occurs in the three-phase two-phase conversion circuit 11a, the torque current values ​​Iq(U&V), Iq(V&W), and Iq(W&U) are all affected by the error in the three-phase two-phase conversion circuit 11a. Therefore, even if a difference arises between the torque current value that represents the actual torque of the motor 30 and the calculated torque current value due to the effect of the error, the torque current values ​​Iq(U&V), Iq(V&W), and Iq(W&U) may be equal. In other words, if the torque current values ​​Iq(U&V), Iq(V&W), and Iq(W&U) are all calculated using the same method, there is a risk that any difference between the calculated torque current values ​​and the torque current values ​​representing the torque of the motor 30 may be overlooked.

[0053] On the other hand, in this embodiment, the torque current value Iq(U&V) with the W phase as redundant data is calculated by the three-phase to two-phase conversion circuit 11a and the rotational coordinate conversion circuit 12a, the torque current value Iq(V&W) with the U phase as redundant data is calculated by the three-phase to two-phase conversion circuit 11b and the rotational coordinate conversion circuit 12b, and the torque current value Iq(W&U) with the V phase as redundant data is calculated by the three-phase to two-phase conversion circuit 11c and the rotational coordinate conversion circuit 12c. In other words, the torque current values ​​Iq(U&V), Iq(V&W), and Iq(W&U) are calculated by different paths.

[0054] Therefore, according to this embodiment, for example, if an error occurs in the three-phase to two-phase conversion circuit 11a and the torque current value Iq(U&V) becomes different from the torque current value that indicates the actual torque of the motor 30, the torque current value Iq(U&V) will be different from the torque current values ​​Iq(V&W) and Iq(W&U). Therefore, even if there is a difference between the calculated torque current value and the torque current value that indicates the torque of the motor 30, this difference can be detected. This is possible. In other words, in this embodiment, if an incorrect torque current value is calculated, the possibility of that incorrect torque current value being considered to represent the torque of the motor 30 is suppressed as much as possible.

[0055] <First variation> In the embodiment, a highly reliable torque current value of the motor 30 was calculated using three control circuits: control circuit 13a, control circuit 13b, and control circuit 13c. The first modified example describes a modified example in which a highly reliable torque current value of the motor 30 is calculated using two control circuits. Components identical to those in the embodiment are denoted by the same reference numerals, and their descriptions are omitted.

[0056] Figure 5 shows an example of a torque measurement circuit 100a according to the first modified example. The torque measurement circuit 100a includes a torque calculation circuit 10a instead of the torque calculation circuit 10. The torque calculation circuit 10a includes three-phase to two-phase conversion circuits 111a, 111b, rotational coordinate conversion circuits 112a, 112b, and control circuits 113a, 113b.

[0057] In the torque measurement circuit 100a, the U-phase current value measured by the ammeter 51 is input to the three-phase to two-phase conversion circuit 111a and the three-phase to two-phase conversion circuit 111b. The V-phase current value measured by the ammeter 52 is input to the three-phase to two-phase conversion circuit 111a and the three-phase to two-phase conversion circuit 111b. The W-phase current value measured by the ammeter 53 is input to the three-phase to two-phase conversion circuit 111a and the three-phase to two-phase conversion circuit 111b. In other words, in the first modified example, the measured current values ​​of the U-phase, V-phase, and W-phase are input to both the three-phase to two-phase conversion circuit 111a and the three-phase to two-phase conversion circuit 111b.

[0058] The three-phase to two-phase conversion circuit 111a calculates the current value of the W phase based on the measured current values ​​of the U phase and V phase. Then, the three-phase to two-phase conversion circuit 111a generates the current value of the α phase Iα(U&V) and the current value of the β phase Iβ(U&V) by converting the measured current values ​​of the U phase and V phase, and the current value of the W phase calculated from the measured current values ​​of the U phase and V phase.

[0059] The three-phase to two-phase conversion circuit 111a further calculates the current value of the U phase based on the measured current values ​​of the V phase and W phase. Then, the three-phase to two-phase conversion circuit 111a generates the current value of the α phase Iα(V&W) and the current value of the β phase Iβ(V&W) by converting them to two phases using the measured current values ​​of the V phase and W phase, and the current value of the W phase calculated from the measured current values ​​of the V phase and W phase.

[0060] The three-phase to two-phase conversion circuit 111a inputs the generated current values ​​Iα(U&V), Iβ(U&V), Iα(V&W), and Iβ(V&W) to the rotational coordinate conversion circuit 112a.

[0061] The three-phase to two-phase conversion circuit 111b calculates the current value of the U phase based on the measured current values ​​of the V phase and W phase. Then, the three-phase to two-phase conversion circuit 111b generates the current value of the α phase Iα(V&W) and the current value of the β phase Iβ(V&W) by converting them to two phases using the measured current values ​​of the V phase and W phase, and the current value of the U phase calculated from the measured current values ​​of the V phase and W phase.

[0062] The three-phase to two-phase conversion circuit 111b further calculates the current value of the V phase based on the measured current values ​​of the W phase and U phase. Then, the three-phase to two-phase conversion circuit 111b generates the current value of the α phase Iα(W&U) and the current value of the β phase Iβ(W&U) converted to two phases using the measured current values ​​of the W phase and U phase, and the current value of the V phase calculated from the measured current values ​​of the W phase and U phase.

[0063] The three-phase to two-phase conversion circuit 111a inputs the generated current values ​​Iα(V&W), Iβ(V&W), Iα(W&U), and Iβ(W&U) to the rotational coordinate conversion circuit 112b. Let it.

[0064] The rotational coordinate transformation circuit 112a performs a rotational coordinate transformation on the current values ​​Iα(U&V) and Iβ(U&V) input from the three-phase to two-phase conversion circuit 11a to calculate the excitation current value Id(U&V) and torque current value Iβ(U&V). The rotational coordinate transformation circuit 112a also performs a rotational coordinate transformation on the current values ​​Iα(V&W) and Iβ(V&W) input from the three-phase to two-phase conversion circuit 11a to calculate the excitation current value Id(V&W) and torque current value Iβ(V&W). The rotational coordinate transformation circuit 112a inputs the calculated excitation current value Id(U&V), torque current value Iq(U&V), excitation current value Id(V&W), and torque current value Iq(V&W) to the control circuit 113a.

[0065] The rotational coordinate transformation circuit 112b performs a rotational coordinate transformation on the current values ​​Iα(V&W) and Iβ(V&W) input from the three-phase to two-phase conversion circuit 11b to calculate the excitation current value Id(V&W) and torque current value Iβ(V&W). The rotational coordinate transformation circuit 112b also performs a rotational coordinate transformation on the current values ​​Iα(W&U) and Iβ(W&U) input from the three-phase to two-phase conversion circuit 11b to calculate the excitation current value Id(W&U) and torque current value Iβ(W&U). The rotational coordinate transformation circuit 112b inputs the calculated excitation current value Id(V&W), torque current value Iq(V&W), excitation current value Id(W&U), and torque current value Iq(W&U) to the control circuit 113b.

[0066] The control circuit 113a inputs the torque current values ​​Iq(U&V) and Iq(V&W) input from the rotation coordinate transformation circuit 112a to the control circuit 113b. The control circuit 113b determines whether all of the torque current values ​​Iq(U&V) and Iq(V&W) input from the control circuit 113a, and the torque current values ​​Iq(V&W) and Iq(W&U) input from the rotation coordinate transformation circuit 112b match.

[0067] Furthermore, the control circuit 113b inputs the torque current values ​​Iq(V&W) and Iq(W&U) input from the rotation coordinate transformation circuit 112b to the control circuit 113a. The control circuit 113a determines whether all of the torque current values ​​Iq(V&W) and Iq(W&U) input from the control circuit 113b, and the torque current values ​​Iq(U&V) and Iq(V&W) input from the rotation coordinate transformation circuit 112a match.

[0068] In the first modified example, the measured values ​​of the U-phase, V-phase, and W-phase are input to both the three-phase to two-phase conversion circuits 111a and 111b. In the three-phase to two-phase conversion circuit 111a, for example, the current value of the W-phase is calculated from the measured current values ​​of the U-phase and V-phase, and the current value of the α-phase Iα(U&V) and the current value of the β-phase Iβ(U&V) are calculated. That is, the current values ​​of the α-phase and β-phase are calculated using the W-phase current value as redundant data. In this way, in the first modified example, similar to the embodiment, the current values ​​of the α-phase and β-phase are calculated using one of the three phases as redundant data. Then, the control circuits 113a and 113b determine whether the torque current values ​​calculated using one of the three phases as redundant data match, and if they match, the torque current value is adopted as the torque current value indicating the torque of the motor 30. In other words, in the first modified example, as in the embodiment, it is possible to calculate the torque of the motor 30 with high reliability without duplicating the ammeters provided on each of the U-phase power line 21, V-phase power line 22, and W-phase power line 23. ru.

[0069] <Second variation> The embodiments and the first modified example described above describe a method for calculating the torque of a motor 30 with high reliability based on the current values ​​of the U-phase, V-phase, and W-phase of the drive current supplied to the motor 30. The second modified example describes a method for calculating the torque of a motor 30 with high reliability by using a torque measuring sensor to measure the torque of the motor 30 in combination.

[0070] Figure 6 shows an example of a torque measurement circuit 100b according to a second modification. The torque measurement circuit 100b includes a torque calculation circuit 10b instead of a torque calculation circuit 10. The torque calculation circuit 10b includes a three-phase to two-phase conversion circuit 211, a rotary coordinate conversion circuit 212, an input circuit 14, a current value conversion circuit 15, and control circuits 213a and 213b. In the second modification, a torque measurement sensor 31 is provided to measure the torque value of the motor 30. The measured torque value measured by the torque measurement sensor 31 is input to the input circuit 14 via a sensor cable 44. The torque measurement sensor 31 is an example of a "sensor".

[0071] The input circuit 14 is, for example, an interface with the sensor cable 44. The input circuit 14 has a connection port that accepts the connection of the sensor cable 44. The input circuit 14 causes the measured torque value input from the torque measurement sensor 31 to be input to the current value conversion circuit 15. The current value conversion circuit 15 calculates a measured torque current value Iq_s that represents the measured torque value input from the input circuit 14, and inputs the calculated measured torque current value Iq_s to the control circuit 213b.

[0072] Here, the unit of the torque current value is (A) and the unit of the measured torque value is (Nm). Therefore, the correspondence between the torque current value and the measured torque value is used to convert from the measured torque value to the measured torque current value.

[0073] Figure 7 illustrates the first correspondence between torque current values ​​and measured torque values. Figure 7 illustrates a state in which multiple torque current values ​​and measured torque values ​​are measured in relation to the torque command value from a higher-level device. In Figure 7, measured values ​​are marked with circles for torque current values ​​and diamonds for measured torque values. In Figure 7, the solid line graph shows the torque current values, and the dashed-dotted line graph shows the measured torque values.

[0074] By measuring multiple torque current values ​​and measured torque values ​​relative to the torque command value, and applying the least squares method, the following approximate equations (1) and (2) are obtained.

number

[0075] From equations (1) and (2), we can obtain the following equation (3).

number

[0076] The current value conversion circuit 15 stores equation (3) in its memory beforehand, and by using equation (3) stored in the memory, it can calculate the measured torque current value Iq_s from the measured torque value. Equation (3) is an example of a correspondence.

[0077] Next, another example of calculating the measured torque current value Iq_s using the current value conversion circuit 15 will be described with reference to Figure 8. Figure 8 is a diagram illustrating a second correspondence between the torque current value and the measured torque value. The vertical axis in Figure 8 represents the torque current value (A) or the measured torque value (Nm). The horizontal axis in Figure 8 represents the torque command value (Nm) for the motor 30. In Figure 8, the solid line graph represents the torque current value, and the dashed-dotted line graph represents the measured torque value.

[0078] In Figure 8, if we consider (X[n], Z[n]) as the origin, the torque current values ​​are as follows: Equation (4) holds true.

number

[0079] Furthermore, in Figure 8, if we consider (X[n], Z[n]) as the origin, the following equation (5) holds for the measured torque value.

number

[0080] From equations (4) and (5), we can see that the following equation (6) holds true.

number

[0081] The current value conversion circuit 15 can also calculate the measured torque current value Iq_s from the measured torque value by pre-storing equation (6) in the memory unit and using equation (6) stored in the memory unit. Equation (6) is an example of a "correspondence relationship".

[0082] Returning to Figure 6, the current values ​​of the U, V, and W phases measured by ammeters 51, 52, and 53 are input to the three-phase to two-phase conversion circuit 211. The three-phase to two-phase conversion circuit 211 converts the three-phase AC current, based on the input current values ​​of the U, V, and W phases, into a two-phase AC. That is, unlike the three-phase to two-phase conversion circuit 11, the three-phase to two-phase conversion circuit 211 uses measured values ​​for all three phases: U, V, and W. The three-phase to two-phase conversion circuit 211 inputs the current value Iα_i of the α phase and the current value Iβ_i of the β phase, which have been converted to two phases, into the rotational coordinate conversion circuit 212.

[0083] The rotational coordinate transformation circuit 212 inputs the excitation current value Id_i and torque current value Iq_i, which are obtained by transforming the α-phase current value Iα_i and β-phase current value Iβ_i input from the three-phase to two-phase transformation circuit 211, to the control circuit 213a.

[0084] Control circuit 213a inputs the torque current value Iq_i, which is input from the rotation coordinate transformation circuit 212, to control circuit 213b. Control circuit 213b then inputs the measured torque current value Iq_s, which is input from the current value transformation circuit 15, to control circuit 213a.

[0085] Control circuit 213a determines whether the torque current value Iq_i input from the rotation coordinate transformation circuit 212 matches the measured torque current value Iq_s input from control circuit 213b. Control circuit 213b determines whether the measured torque current value Iq_s input from the current value transformation circuit 15 matches the torque current value Iq_i input from control circuit 213a. If either control circuit 213a or control circuit 213b determines that they match, it determines the calculated torque current value as the current value representing the torque of the motor 30. If either control circuit 213a or control circuit 213b determines that they do not match, it notifies a higher-level device of an error, for example.

[0086] According to the second modified example, reliable torque calculation becomes possible by comparing the torque current value calculated based on the current measured by ammeters 51, 52, and 53 with the measured torque current value indicating the torque measured by the torque measurement sensor 31.

[0087] Furthermore, since the units of the torque current value and the measured torque value are different, it is not possible to directly convert the measured torque value to the torque current value. Therefore, in the second modified example, such a conversion is made possible by using the correspondence relationship explained with reference to Figures 7 and 8. As a result of this conversion being possible in the second modified example, it becomes possible to calculate torque with high reliability using the torque current value and the measured torque value.

[0088] In the embodiments described above, the current values ​​of the currents flowing through the U-phase power line 21, V-phase power line 22, and W-phase power line 23 were measured by ammeters 51, 52, and 53. However, the current values ​​of the currents flowing through the U-phase power line 21, V-phase power line 22, and W-phase power line 23 may be measured by other means. For example, the voltages of the U-phase power line 21, V-phase power line 22, and W-phase power line 23 may be measured, and the current values ​​of the currents flowing through the U-phase power line 21, V-phase power line 22, and W-phase power line 23 may be calculated from the measured voltages.

[0089] In the embodiments described above, the torque calculation circuit 10 calculated and compared the torque current values ​​Iq(U&V), Iq(V&W), and Iq(W&U). However, the calculation and comparison of the torque current values ​​Iq(U&V), Iq(V&W), and Iq(W&U) may also be performed by means other than the torque calculation circuit 10, for example, by software processing by a processor.

[0090] In the embodiments described above, the torque current value representing the torque of the motor 30 was determined when the torque current values ​​Iq(U&V), Iq(V&W), and Iq(W&U) coincided. However, the torque current values ​​Iq(U&V), Iq(V&W), and Iq(W&U) do not need to coincide precisely. For example, the torque current value representing the torque of the motor 30 may be determined if the difference between the maximum and minimum torque current values ​​among Iq(U&V), Iq(V&W), and Iq(W&U) is within a predetermined allowable range. The predetermined allowable range can be appropriately determined according to the desired measurement accuracy of the torque.

[0091] The embodiments and variations described above can be combined in various ways.

[0092] <Note 1> A U-phase power line (21), a V-phase power line (22), and a W-phase power line (23) supply a three-phase AC drive current to the electric motor (30), A first measuring unit (51) for measuring the current flowing through the U-phase power line (21), A second measuring unit (52) for measuring the current flowing through the V-phase power line (22), A third measuring unit (53) for measuring the current flowing through the W-phase power line (23), It comprises a calculation unit (10, 10a), The calculation unit (10, 10a) is The measured value of the U-phase current measured by the first measuring unit and the measured value of the V-phase current measured by the second measuring unit are used to calculate the W-phase current. From the measured value of the U-phase current, the measured value of the V-phase current, and the calculated value of the W-phase current, a first torque current value indicating the torque of the electric motor is calculated. The measured value of the V-phase current and the measured value of the W-phase current measured by the third measuring unit are used to calculate the U-phase current. From the measured value of the current in the V phase, the measured value of the current in the W phase, and the calculated value of the current in the U phase, A second torque current value indicating the torque of the aforementioned electric motor is calculated, The measured value of the current in the W phase and the measured value of the current in the U phase are used to calculate the current in the V phase. From the measured value of the W-phase current, the measured value of the U-phase current, and the calculated value of the V-phase current, a third torque current value indicating the torque of the motor is calculated. If the difference between the maximum torque current value and the minimum torque current value among the first, second, and third torque current values ​​is within the allowable range, the current value indicating the torque of the electric motor, determined based on the first, second, and third torque current values, is notified to the higher-level device. Torque measurement circuit for electric motor (100, 100A).

[0093] <Note 2> A U-phase power line (21), a V-phase power line (22), and a W-phase power line (23) supply a three-phase AC drive current to the electric motor (30), A first measuring unit (51) for measuring the current flowing through the U-phase power line (21), A second measuring unit (52) for measuring the current flowing through the V-phase power line (22), A third measuring unit (53) for measuring the current flowing through the W-phase power line (23), A sensor (31) for measuring the torque of the electric motor (30), It comprises a calculation unit (10b) and, The calculation unit (10b) is, From the measured value of the U-phase current measured by the first measuring unit, the measured value of the V-phase current measured by the second measuring unit, and the measured value of the W-phase current measured by the third measuring unit, a fourth torque current value indicating the torque of the electric motor is calculated. The measured value representing the torque of the electric motor, measured by the sensor, is converted into a fifth torque current value representing the measured value. If the difference between the fourth torque current value and the fifth torque current value is within the allowable range, the current value indicating the torque of the electric motor, determined based on the fourth torque current value and the fifth torque current value, is notified to the higher-level device. Torque measurement circuit for electric motor (100b). [Explanation of symbols]

[0094] 10. Torque calculation circuit 11. Three-phase to two-phase conversion circuit 11a Three-phase to two-phase conversion circuit 11b. Three-phase to two-phase conversion circuit 11c ·· Three-phase to two-phase conversion circuit 12. Rotational Coordinate Transformation Circuit 12a Rotational Coordinate Transformation Circuit 12b Rotational Coordinate Transformation Circuit 12c ··Rotational coordinate transformation circuit 13. Control Circuit 13a Control Circuit 13b. Control circuit 13c control circuit 14. Input Circuit 15. Current Value Conversion Circuit 20. Power Circuit 21...U phase power line 22...V phase power line 23...W phase power line 30 motor 31. Torque measurement sensor 41··U Phase Branch Wiring 42V phase branch wiring 43-W phase branch wiring 44. Sensor Cable 51...Ammeter 52...Ammeter 53...Ammeter 100 Torque Measurement Circuit 100A Torque Measurement Circuit 100b Torque measurement circuit 111a ··Three-phase to two-phase conversion circuit 111b · Three-phase to two-phase conversion circuit 112a Rotational Coordinate Transformation Circuit 112b Rotational Coordinate Transformation Circuit 113a Control Circuit 113b Control Circuit 211. Three-phase to two-phase conversion circuit 212. Rotational Coordinate Transformation Circuit 213a Control Circuit 213b Control Circuit 500 Torque Measurement Circuit 520 Power Circuit 530 motor 521...U phase power line 522...V phase power line 523...W phase power line 541··U Phase Branch Wiring 542··V-phase branch wiring 543··W phase branch wiring 511a Three-phase to two-phase conversion circuit 511b · Three-phase to two-phase conversion circuit 512a Rotational Coordinate Transformation Circuit 512b Rotational Coordinate Transformation Circuit 513a Control Circuit 513b Control Circuit 551...Ammeter 552...Ammeter 553...Ammeter B1 connecting bus B2 connecting bus

Claims

1. U-phase power lines, V-phase power lines, and W-phase power lines that supply three-phase AC drive current to the electric motor, A first measuring unit for measuring the current flowing through the U-phase power line, A second measuring unit for measuring the current flowing through the V-phase power line, A third measuring unit for measuring the current flowing through the W-phase power line, It comprises a calculation unit, The calculation unit, A first circuit calculates a W-phase current from the measured value of the U-phase current measured by the first measuring unit and the measured value of the V-phase current measured by the second measuring unit, converts the three-phase AC based on the measured value of the U-phase current, the measured value of the V-phase current, and the calculated value of the W-phase current into a two-phase AC, and performs a rotational coordinate transformation on the converted two-phase current values ​​to calculate a first torque current value indicating the torque of the electric motor. A second circuit calculates a U-phase current from the measured value of the V-phase current and the measured value of the W-phase current measured by the third measuring unit, converts the three-phase AC based on the measured value of the V-phase current, the measured value of the W-phase current, and the calculated value of the U-phase current into a two-phase AC, and performs a rotational coordinate transformation on the converted two-phase current values ​​to calculate a second torque current value indicating the torque of the motor. The circuit includes a third circuit that calculates a V-phase current from the measured W-phase current and the measured U-phase current, converts the three-phase AC based on the measured W-phase current, the measured U-phase current, and the calculated V-phase current into a two-phase AC, and performs a rotational coordinate transformation on the converted two-phase current values ​​to calculate a third torque current value indicating the torque of the motor, The first circuit, the second circuit, and the third circuit are all different circuits. If the difference between the maximum and minimum torque current values ​​among the first, second, and third torque current values ​​calculated by different circuits is within an acceptable range, the current value indicating the torque of the electric motor, determined based on the first, second, and third torque current values, is notified to the higher-level device. Torque measurement circuit for an electric motor.

2. U-phase power lines, V-phase power lines, and W-phase power lines that supply three-phase AC drive current to the electric motor, A first measuring unit for measuring the current flowing through the U-phase power line, A second measuring unit for measuring the current flowing through the V-phase power line, A third measuring unit for measuring the current flowing through the W-phase power line, A sensor for measuring the torque of the electric motor, It comprises a calculation unit, The calculation unit, From the measured value of the U-phase current measured by the first measuring unit, the measured value of the V-phase current measured by the second measuring unit, and the measured value of the W-phase current measured by the third measuring unit, a fourth torque current value indicating the torque of the electric motor is calculated. The correspondence between the measured value of the sensor and the fourth torque current value calculated when the electric motor is outputting the torque measured by the sensor is stored in the memory unit. Referencing the memory unit, the measured value representing the torque of the electric motor measured by the sensor is converted into a fifth torque current value representing the measured value. If the difference between the fourth torque current value and the fifth torque current value is within the allowable range, the current value indicating the torque of the electric motor, determined based on the fourth torque current value and the fifth torque current value, is notified to the higher-level device. Torque measurement circuit for an electric motor.

3. The three-phase AC current, consisting of the measured U-phase and V-phase current values ​​and the W-phase current value calculated from the measured U-phase and V-phase current values, is converted to a two-phase AC current, and a rotational coordinate transformation is performed on the converted two-phase current values ​​to calculate a first torque current value representing the torque of the motor in the first circuit. Of the aforementioned drive current, the measured V-phase and W-phase current values ​​and the U-phase current value calculated from the measured V-phase and W-phase current values ​​are used to convert the three-phase AC into a two-phase AC, and a rotational coordinate transformation is performed on the converted two-phase current values ​​to calculate a second torque current value representing the torque of the motor in a second circuit different from the first circuit. The three-phase AC current, consisting of the measured W-phase and U-phase current values ​​and the V-phase current value calculated from the measured W-phase and U-phase current values, is converted to a two-phase AC current, and a rotational coordinate transformation is performed on the converted two-phase current values ​​to calculate a third torque current value representing the torque of the motor in a third circuit different from the first and second circuits. If the difference between the maximum and minimum torque current values ​​among the first, second, and third torque current values ​​calculated by different circuits is within an acceptable range, the current value indicating the torque of the electric motor, determined based on the first, second, and third torque current values, is notified to the higher-level device. Method for calculating the torque of an electric motor.

4. The fourth torque current value is calculated from the measured current values ​​of the U-phase, V-phase, and W-phase currents supplied to the motor. The correspondence between the measured value of the sensor that measures the torque of the electric motor and the fourth torque current value calculated when the electric motor is outputting the torque measured by the sensor is stored in the storage unit. Referencing the memory unit, the torque value of the electric motor measured by the sensor is converted into a current value to calculate a fifth torque-current value. If the difference between the fourth torque current value and the fifth torque current value is within the allowable range, the current value indicating the torque of the electric motor, determined based on the fourth torque current value and the fifth torque current value, is notified to the higher-level device. Method for calculating the torque of an electric motor.

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