Current measurement method, current measurement system, and program

Abstract

To accurately measure a d-axis current and a q-axis current of an AC motor using a current sensor having a high-pass characteristic.SOLUTION: A current measurement method uses a plurality of current sensors 11 to 13 that detect currents of at least two phases among three-phase currents Iu to Iw, that have a high-pass characteristic and flow in an AC motor, and an angle sensor that detects a rotation angle θ of the AC motor. The current measurement method acquires a sine component sinθ and a cosine component cosθ of the rotation angle θ on the basis of an output signal of the angle sensor, and applies filtering processing using a filter having a frequency characteristic equivalent to the high-pass characteristic of the current sensors 11 to 13 to the sine component sinθ and the cosine component cosθ. Then, the current measurement method measures currents Id and Iq of a d-axis and a q-axis, respectively, on the basis of a synthesized value θc of the rotation angle obtained by synthesizing the sine component sin(θc) and the cosine component cos(θc) after filtering processing, and the detected values of the three-phase currents Iu to Iw.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a current measurement method, a current measurement system, and a program for measuring current. [Background Art]

[0002] Patent Document 1 discloses a current detection device in which an integration circuit is connected to a coil. [Prior Art Documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-153646 [Summary of the Invention] [Problems to be Solved by the Invention]

[0004] When measuring the current of an AC motor, it is also possible to detect the three-phase current flowing through the AC motor using the above-described current detection device, and measure the d-axis current and q-axis current of the AC motor based on the detected current values.

[0005] However, when using a current sensor having high-pass characteristics as in the above-described current detection device, in the low frequency band, the lower the frequency of the three-phase current is, the more the phase angle of the detected three-phase current advances, and this phase error causes a problem that measurement accuracy decreases.

[0006] The present invention has been made in view of such problems, and an object thereof is to accurately measure the d-axis current and q-axis current of an AC motor using a current sensor having high-pass characteristics. [Means for Solving the Problems]

[0007] According to one aspect of the present invention, a current measurement method is a method for measuring the currents of the d axis and q axis in an AC motor using a plurality of current sensors having high-pass characteristics and detecting the currents of at least two phases of the three-phase current flowing through the AC motor, and an angle sensor that detects the rotation angle of the AC motor. This current measurement method includes an acquisition step of acquiring the sine and cosine components of the rotation angle based on the output signals of the angle sensors, and a processing step of applying filtering to the sine and cosine components using a filter having frequency characteristics corresponding to the high-pass characteristics of the current sensors. Furthermore, the current measurement method includes a measurement step of measuring the currents of the d axis and q axis based on a composite value of the rotation angle obtained by combining the sine and cosine components after filtering and the detected values ​​of the three-phase currents obtained by the plurality of current sensors. [Effects of the Invention]

[0008] According to this embodiment, by applying a frequency characteristic filter corresponding to the high-pass characteristics of the current sensor to the sinusoidal and cosine components of the rotation angle, the combined value obtained by synthesizing the sinusoidal and cosine components of the rotation angle is adjusted to account for the low-frequency phase error caused by the current sensor.

[0009] Therefore, by converting the three-phase current into d-axis and q-axis currents using a composite value of rotation angles that takes phase errors into account, the phase errors included in the detected values ​​of the three-phase current are canceled out by the composite value of rotation angles, thereby reducing the measurement errors of the d-axis and q-axis currents.

[0010] Thus, according to this embodiment, the d-axis current and q-axis current of an AC motor can be accurately measured using a current sensor having high-frequency pass-through characteristics. [Brief explanation of the drawing]

[0011] [Figure 1] Figure 1 shows the configuration of the current measurement system in the first embodiment. [Figure 2A]Figure 2A shows an example of the amplitude gain frequency characteristics of a current sensor and a high-pass filter (HPF) section having equivalent high-pass characteristics. [Figure 2B] Figure 2B shows the phase frequency characteristics corresponding to the amplitude gain frequency characteristics shown in Figure 2A. [Figure 3] Figure 3 is a flowchart showing the current measurement method in the first embodiment. [Figure 4] Figure 4 is a diagram illustrating the measurement error caused by the current measurement system. [Figure 5A] Figure 5A shows modified examples of the amplitude gain frequency characteristics of a current sensor and an HPF section having equivalent high-pass characteristics. [Figure 5B] Figure 5B shows the phase frequency characteristics corresponding to the modified example shown in Figure 5A. [Figure 6] Figure 6 shows the configuration of the current measurement system in the second embodiment. [Modes for carrying out the invention]

[0012] Embodiments of the present invention will be described below with reference to the attached drawings. Throughout this specification, the same or equivalent elements will be denoted by the same reference numerals.

[0013] (First Embodiment) Figure 1 shows the configuration of the current measurement system in the first embodiment.

[0014] The current measurement system 1 is a measurement system for measuring the current in the d-axis and q-axis coordinate systems of an AC motor. In the first embodiment, the currents in the d-axis and q-axis are measured based on the three-phase current flowing between the motor 2, which is an AC motor, and the inverter 3. The three-phase current referred to here is the alternating current of the three phases: U-phase, V-phase, and W-phase.

[0015] The current measurement system 1 comprises current sensors 11 to 13, resolvers 20, AD converters 31 to 36, and a processing unit 40.

[0016] The current sensors 11 to 13 are a plurality of sensors that detect the three-phase current flowing to the motor 2. The current sensors 11 to 13 each have a high-pass characteristic where attenuation increases relative to an amplitude gain in a high-frequency band that is substantially constant, as the frequency of the alternating current approaches zero in a low-frequency band.

[0017] The current sensors 11 to 13 are implemented by, for example, an inexpensive AC current sensor or a flexible current sensor. In the first embodiment, each of the current sensors 11 to 13 includes a Rogowski coil 10A for detecting alternating current, and an integrating circuit 10B that integrates the induced current flowing in the Rogowski coil 10A.

[0018] The current sensor 11 detects a U-phase alternating current, and outputs the detected signal to an AD converter 31 as a detection value of the U-phase current Iu. The current sensor 12 detects a V-phase alternating current, and outputs the detected signal to an AD converter 32 as a detection value of the V-phase current Iv. The current sensor 13 detects a W-phase alternating current, and outputs the detected signal to an AD converter 33 as a detection value of the W-phase current Iw. In this way, the current sensors 11 to 13 output the detection values of the three-phase currents Iu to Iw to the AD converters 31 to 33.

[0019] The resolver 20 functions as an angle sensor that detects the rotation angle of the motor 2. In the first embodiment, the resolver 20 includes one primary winding disposed on a rotor side of the motor 2, a signal source that excites the primary winding, and two secondary windings disposed on a stator side of the motor 2.

[0020] Further, the resolver 20 outputs an excitation signal Vex supplied from the signal source to the primary winding, a sine detection signal Vsin flowing in one of the secondary windings, and a cosine detection signal Vcos flowing in the other of the secondary windings, to the AD converters 34 to 36 respectively.

[0021] The excitation signal Vex, the sine detection signal Vsin and the cosine detection signal Vcos described above are each represented by the following formulas (1) to (3).

[0022]

number

[0023] The AD converters 31 to 36 convert the output signals of the current sensors 11 to 13 and the three output signals of the resolver 20 from analog signals to digital signals. Each of the AD converters 31 to 36 transmits the converted output signal to the processing unit 40.

[0024] The processing unit 40 transforms the three-axis coordinate system of U-phase, V-phase, and W-phase into a two-axis coordinate system of d-axis and q-axis. Specifically, the processing unit 40 measures the d-axis and q-axis currents in the motor 2 based on the output signals of the resolver 20 and the output signals of the current sensors 11 to 13.

[0025] The processing unit 40, for example, uses the Park transformation formula shown in equation (4) below to calculate the measured values ​​of the d-axis current Id and the q-axis current Iq using the three-phase currents Iu to Iw indicated by the output signals of the current sensors 11 to 13 and the rotation angle θ of the motor 2.

[0026]

number

[0027] The processing unit 40 is composed of one or more hardware or software components. In the first embodiment, the processing unit 40 is composed of hardware consisting of digital circuits. For example, the processing unit 40 is a computer composed of a processor, ROM (Read Only Memory), RAM (Random Access Memory), a mass storage device, an input / output interface, and a bus connecting these components.

[0028] Examples of processors include CPUs (Central Processing Units) and MPUs (Micro Processor Units). Examples of mass storage devices include HDDs (Hard Disk Drives) and SSDs (Solid State Drives).

[0029] The processing unit 40 of the first embodiment includes a synchronous detection unit 41, HPF units 42A and 42B, a rotation angle calculation unit 43, and a coordinate transformation unit 44.

[0030] The synchronous detection unit 41 functions as an acquisition means for acquiring the sinusoidal component sinθ and the cosine component cosθ of the rotation angle θ based on the output signal of the resolver 20, which is an angle sensor.

[0031] Specifically, the synchronous detection unit 41 of the first embodiment acquires the excitation signal Vex, the sine detection signal Vsin, and the cosine detection signal Vcos as the output signals of the resolver 20. The synchronous detection unit 41 then multiplies the sine detection signal Vsin and the cosine detection signal Vcos by the excitation signal Vex to extract the sine component sinθ and the cosine component cosθ of the rotation angle θ.

[0032] The synchronous detection unit 41 transmits the extracted sine component sinθ to the HPF unit 42A and the cosine component cosθ to the HPF unit 42B.

[0033] The HPF sections 42A and 42B function as processing means that apply filtering to the sine component sinθ and the cosine component cosθ using filters having frequency characteristics corresponding to the high-pass characteristics of the current sensors 11 to 13.

[0034] HPF sections 42A and 42B each have equivalent high-pass filters. HPF section 43A applies the above filtering process to the sine component sinθ, and similarly, HPF section 43B applies the above filtering process to the cosine component cosθ.

[0035] The HPF sections 42A and 42B transmit the sine component sin(θc) and cosine component cos(θc) after filtering to the rotation angle calculation section 43, respectively.

[0036] The rotation angle calculation unit 43 combines the sine component sin(θc) and the cosine component cos(θc) after filtering to obtain the combined value θc of the rotation angle. In the first embodiment, the rotation angle calculation unit 43 calculates the combined value θc of the rotation angle using the following equation (5).

[0037]

number

[0038] The rotation angle calculation unit 43 transmits the calculated composite value θc of the rotation angles to the coordinate transformation unit 44. In this way, the composite value θc of the rotation angles is obtained by combining the sine component sin(θc) and the cosine component cos(θc) after filtering.

[0039] The coordinate transformation unit 44 functions as a measuring means for measuring the currents of the d axis and q axis based on the combined value of the rotation angles θc and the detected values ​​of the three-phase currents Iu to Iw detected by the current sensors 11 to 13.

[0040] Specifically, the coordinate transformation unit 44 of the first embodiment substitutes the above composite value θc for the rotation angle θ of the motor 2 in equation (4) above, and substitutes the detected values ​​of the current sensors 11 to 13 for the three-phase currents Iu to Iw, to calculate the measured values ​​of the d-axis current Id and the q-axis current Iq.

[0041] The coordinate transformation unit 44 then outputs the calculated d-axis current Id and q-axis current Iq values. Subsequently, the processing unit 40 estimates the torque value T of the motor 2 using the measured values ​​of the d-axis current Id and q-axis current Iq, for example, as shown in equation (6) below.

[0042]

number

[0043] Although the processing unit 40 illustrated in Figure 1 is composed of digital circuits, the processing unit 40 may be composed of analog circuits instead of digital circuits. Furthermore, although each of the current sensors 11 to 13 is provided with an integrating circuit 10B, the current measurement system 1 may be configured so that the function of the integrating circuit 10B is performed by the processing unit 40.

[0044] Furthermore, while Figure 1 illustrates an example in which the three-phase currents Iu to Iw flowing through the motor 2 are detected using three current sensors 11 to 13, it is also possible to obtain the detected values ​​of the three-phase currents Iu to Iw using only two current sensors.

[0045] Specifically, the three-phase currents Iu to Iw have the relationship shown in equation (7), so the current value of the other phase can be determined using the current values ​​of at least two phases.

[0046]

number

[0047] Thus, by using two current sensors that detect the currents of at least two of the three-phase currents Iu to Iw flowing through the motor 2, the detected values ​​of the three-phase currents Iu to Iw can be obtained according to equation (7) above. Here, in addition to the current values ​​detected by the current sensors, the calculated value of the other phase obtained using the detected values ​​of two phases is also referred to as the detected value.

[0048] Next, the frequency characteristics of the current sensors 11 to 13 and the HPF sections 42A and 42B will be described with reference to Figures 2A and 2B.

[0049] Figure 2A shows an example of the amplitude gain frequency characteristics of the current sensors 11 to 13 and the HPF sections 42A and 42B. Figure 2B shows the phase frequency characteristics corresponding to the amplitude gain frequency characteristics shown in Figure 2A.

[0050] Figures 2A and 2B show the frequency response of a filter designed with a cutoff frequency of 1.5 Hz, an order of 2, and a Q value of 0.7.

[0051] As shown in Figure 2A, the amplitude gain is constant in the high-frequency band where the frequency of the three-phase current is higher than approximately 1.5 Hz, and in the low-frequency band where the frequency is lower than approximately 1.5 Hz, the amplitude gain decreases as the frequency decreases.

[0052] Thus, the current sensors 11 to 13 of the first embodiment have a high-frequency pass-through characteristic in which the amplitude gain is sharply attenuated at low frequencies.

[0053] As shown in Figure 2B, the phase frequency characteristics of the current sensors 11 to 13 having the high-pass characteristics shown in Figure 2A show that the phase advances rapidly as the frequency decreases in the low-frequency range. This large phase error in the low-frequency range leads to increased measurement errors for the d-axis current Id and the q-axis current Iq.

[0054] As a countermeasure, in the first embodiment, the frequency characteristics (filter characteristics) of the HPF sections 42A and 42B are both designed to have frequency characteristics equivalent to the high-pass characteristics of the current sensors 11 to 13 shown in Figures 2A and 2B.

[0055] As a specific example, the frequency characteristics of the HPF sections 42A and 42B are adjusted so that the specified parameters used to define the frequency characteristics, such as the cutoff frequency, order, and Q value, are equivalent to the specified parameters of the current sensors 11 to 13.

[0056] Next, the operation of the current measurement system 1 will be explained with reference to Figure 3.

[0057] Figure 3 is a flowchart showing an example of the processing procedure for the current measurement method using the current measurement system 1.

[0058] In step S1, the current sensors 11 to 13 detect the three-phase currents Iu to Iw flowing through the motor 2.

[0059] In step S2, the processing unit 40 obtains the sine component sinθ and cosine component cosθ of the rotation angle θ of the motor 2 based on the output signal of the resolver 20. Specifically, the synchronous detection unit 41 of the processing unit 40 extracts the sine component sinθ and cosine component cosθ using the excitation signal Vex, the sine detection signal Vsin, and the cosine detection signal Vcos included in the output signal of the resolver 20.

[0060] In step S3, the processing unit 40 uses HPF sections 42A and 42B as filters having frequency characteristics corresponding to the high-pass characteristics of the current sensors 11 to 13 to filter the sine component sinθ and the cosine component cosθ.

[0061] Specifically, in the processing unit 40, the sine component sinθ is input to the HPF unit 42A, and the filtered sine component sin(θc) is output from the HPF unit 42A. At the same time, the cosine component cosθ is input to the HPF unit 42B, and the filtered cosine component cos(θc) is output from the HPF unit 42B.

[0062] In step S4, the processing unit 40 combines the sine component sin(θc) and the cosine component cos(θc) after filtering to obtain the combined value θc of the rotation angle. Specifically, the rotation angle calculation unit 43 of the processing unit 40 calculates the combined value θc of the rotation angle according to, for example, equation (5) above.

[0063] In step S5, the processing unit 40 acquires the combined value θc of the rotation angle obtained by combining the sine component sin(θc) and cosine component cos(θc) after filtering, and the detected values ​​of the three-phase currents Iu to Iw detected by the current sensors 11 to 13. Then, the processing unit 40 measures the currents Id and Iq of the d axis and q axis based on the acquired combined value θc of the rotation angle and the detected values ​​of the three-phase currents Iu to Iw.

[0064] Specifically, the coordinate transformation unit 44 of the processing unit 40 calculates the measured values ​​of the d-axis current Id and the q-axis current Iq by substituting the combined value θc and the detected values ​​of the current sensors 11 to 13 into the rotation angle θ and the three-phase currents Iu to Iw in equation (4) above. Subsequently, the processing unit 40 estimates the torque of the motor 2 based on the calculated measured values, for example using equation (6) above.

[0065] Once step S5 is completed, the series of processing steps for the current measurement method shown in Figure 3 is finished.

[0066] Next, the accuracy of the measurement results obtained by the current measurement system 1 will be explained with reference to Figure 4.

[0067] Figure 4 shows the measurement error of the d-axis current Id calculated by the processing unit 40. In Figure 4, the horizontal axis represents the frequency of the three-phase currents Iu to Iw, and the vertical axis represents the measurement error. The measurement error is based on the measurement results of an ideal current measurement system in which no phase error occurs due to the current sensors 11 to 13.

[0068] Figure 4 shows the frequency characteristics of the measurement error in the current measurement system 1 according to the first embodiment, represented by a solid line, and the frequency characteristics of the measurement error in a typical configuration in which only the HPF sections 42A and 42B of the current measurement system 1 are removed, represented by a dashed line.

[0069] In the first embodiment, the combined value θc of the rotation angle is adjusted by the HPF sections 42A and 42B so that the phase error included in the detected values ​​of the three-phase currents Iu to Iw is reduced in the low frequency range. As a result, as shown in Figure 4, the measurement error in the first embodiment is smaller in the low frequency range compared to the measurement error in a typical configuration.

[0070] Figure 4 shows the frequency characteristics with respect to the measurement error of the d-axis current Id, and the q-axis current Iq exhibits similar frequency characteristics. Therefore, by arranging HPF sections 42A and 42B between the synchronous detection section 41 and the rotation angle calculation section 43, the measurement errors of the d-axis current Id and q-axis current Iq are reduced in the low-frequency range.

[0071] Next, the effects and benefits of the first embodiment will be described.

[0072] The current measurement method of the first embodiment measures the currents in the d axis and q axis of the motor 2 using a plurality of current sensors 11 to 13 that detect the three-phase currents Iu to Iw flowing through the motor 2 as an AC motor, and a resolver 20 that functions as an angle sensor that detects the rotation angle θ of the motor 2. The current sensors 11 to 13 that detect the three-phase currents Iu to Iw have high-pass characteristics as shown in Figures 2A and 2B.

[0073] The current measurement method described above includes an acquisition step (S2) of acquiring the sinusoidal component sinθ and cosine component cosθ of the rotation angle θ based on the output signal of the resolver 20, and a processing step (S3) of applying filtering to the sinusoidal component sinθ and cosine component cosθ using a filter having a frequency characteristic corresponding to the high-pass characteristics of the current sensors 11 to 13. Furthermore, the current measurement method includes a measurement step (S5) of measuring the currents of the d axis and q axis based on the combined value θc of the rotation angle obtained by combining the sinusoidal component sin(θc) and cosine component cos(θc) after filtering, and the detected values ​​of the three-phase currents Iu to Iw detected by the multiple current sensors 11 to 13.

[0074] Furthermore, the program of the first embodiment causes a computer that acquires the output signals of the multiple current sensors 11 to 13 and the output signal of the resolver 20 to execute the acquisition step (S2), processing step (S3), and measurement step (S5) described above.

[0075] Furthermore, the current measurement system 1 of the first embodiment includes a plurality of current sensors 11 to 13, a resolver 20, a synchronous detection unit 41, HPF units 42A and 42B, and a coordinate transformation unit 44.

[0076] In the current measurement system 1 described above, the synchronous detection unit 41 functions as an acquisition means to acquire the sinusoidal component sinθ and cosine component cosθ of the rotation angle based on the output signal of the resolver 20. The HPF units 42A and 42B function as processing means to apply filtering to the sinusoidal component sinθ and cosine component cosθ using filters having frequency characteristics corresponding to the high-pass characteristics of the current sensors 11 to 13. Furthermore, the coordinate transformation unit 44 functions as a measurement means to measure the currents of the d axis and q axis based on the combined value θc of the rotation angle obtained by combining the filtered sin(θc) and cosine component cos(θc), and the detected values ​​of the three-phase currents Iu to Iw detected by the multiple current sensors 11 to 13.

[0077] With these configurations, the sinusoidal component sinθ and cosine component cosθ of the rotation angle are filtered using a frequency characteristic corresponding to the high-pass characteristics of the current sensors 11 to 13. As a result, the combined value θc of sin(θc) and cosine component cos(θc) of the rotation angle after filtering is affected by the low-frequency phase error caused by the current sensors 11 to 13.

[0078] Therefore, when converting three-phase currents Iu to Iw into d-axis and q-axis currents Id and Iq using the combined value θc of the rotation angle, which takes phase error into account, the phase error included in the detected values ​​of the three-phase currents Iu to Iw is canceled out by the combined value θc of the rotation angle. Thus, the measurement errors of the d-axis current Id and q-axis current Iq can be reduced.

[0079] Thus, according to the first embodiment, the d-axis current Id and q-axis current Iq of the motor 2 can be accurately measured using current sensors 11 to 13 having high-frequency pass-through characteristics.

[0080] Furthermore, the current sensors 11 to 14 of the first embodiment include a Rogowski coil 10A.

[0081] By employing the Rogowski coil 10A, it becomes possible to pass the current sensors 11 to 13 through even when the space between the three wires connected to the motor 2 is narrow. For example, in a drive unit integrating the motor 2 and inverter 3, even when the gap between the wires is narrow, it becomes possible to arrange the current sensors 11 to 13 in a ring around each wire.

[0082] Furthermore, by employing the Rogowski coil 10A, it becomes easier to give flexibility to the current sensors 11 to 13, thereby reducing the risk of damaging surrounding components when passing each of the current sensors 11 to 13 between the wires.

[0083] Furthermore, in the current measurement method of the first embodiment, the acquisition step (S2), processing step (S3), and measurement step (S5) are performed by one or more hardware devices.

[0084] This configuration allows for accurate measurement of the d-axis current Id and q-axis current Iq in real time. Therefore, it becomes possible to control the torque of motor 2 based on the measured values ​​of the d-axis current Id and q-axis current Iq, and to detect abnormalities in motor 2 and immediately stop motor 2.

[0085] Furthermore, in the current measurement method of the first embodiment, the hardware that performs the acquisition step (S2), processing step (S3), and measurement step (S5) is a digital circuit, as shown in Figure 1.

[0086] This configuration eliminates the need for analog circuits, simplifying signal processing. Therefore, it is possible to simplify the circuit configuration of the hardware while reducing the number of potential points where malfunctions may occur.

[0087] On the other hand, analog circuits may be used instead of digital circuits as the hardware that performs the acquisition step (S2), processing step (S3), and measurement step (S5). In this case, since sampling errors caused by digital processing do not occur, the decrease in measurement accuracy can be suppressed compared to digital circuits.

[0088] Furthermore, in the current measurement method of the first embodiment, the acquisition step (S2), processing step (S3), and measurement step (S5) may be performed by software instead of hardware.

[0089] This configuration eliminates the need for hardware. Therefore, the cost of implementing the current measurement method can be reduced compared to using hardware.

[0090] In the first embodiment, examples of the high-frequency pass characteristics of the current sensors 11 to 13 and the HPF sections 42A and 42B are shown in Figures 3A and 3B, but the high-frequency pass characteristics are not limited to these.

[0091] Next, modified examples of the high-frequency pass characteristics of the current sensors 11 to 13 and the HPF sections 42A and 42B will be described with reference to Figures 5A and 5B.

[0092] Figure 5A shows another example of the amplitude gain frequency characteristics of the current sensors 11 to 13 and the HPF sections 42A and 42B. Figure 5B shows the phase frequency characteristics corresponding to the amplitude gain frequency characteristics shown in Figure 5A.

[0093] Figures 5A and 5B show the frequency response of a filter designed with a cutoff frequency of 10 Hz, an order of 1, and a Q value of 0.5.

[0094] As shown in Figure 5A, the amplitude gain is constant in the high-frequency band above approximately 10 Hz, and decreases as the frequency decreases in the low-frequency band below approximately 10 Hz.

[0095] As shown in Figure 5B, the phase frequency characteristics of the current sensors 11 to 13 having the high-pass characteristics shown in Figure 5A also show that the phase advances as the frequency decreases in the low-frequency range.

[0096] In this modified example, the frequency characteristics of the HPF sections 42A and 42B are designed to be equivalent to the high-pass characteristics of the current sensors 11 to 13 shown in Figures 5A and 5B. Specifically, the frequency characteristics of the HPF sections 42A and 42B are designed to be equivalent to the specified parameters of the current sensors 11 to 13.

[0097] Next, the configuration of the second embodiment will be described with reference to Figure 6.

[0098] Figure 6 shows the configuration of the current measurement system 1A of the second embodiment.

[0099] Current measurement system 1A replaces the resolver 20, AD converters 33 to 36, and processing unit 40 that constitute current measurement system 1 shown in Figure 1 with a rotary encoder 21 and a processing unit 40A. Processing unit 40A replaces the synchronous detection unit 41 of processing unit 40 with a pulse conversion unit 41A and a separation unit 41B.

[0100] The other components of the current measurement system 1A are the same as those of the current measurement system 1 of the first embodiment. Therefore, only the rotary encoder 21, pulse conversion unit 41A, and separation unit 41B, which differ from those of the first embodiment, will be described here.

[0101] The rotary encoder 21 functions as an angle sensor that detects the rotation angle of the motor 2.

[0102] The rotary encoder 21 has a known configuration and includes, for example, a light-emitting unit having one or more light-emitting elements, a disk having slits for A-phase signals, B-phase signals, and Z-phase signals and rotating with the rotation axis of the motor 2, and a light-receiving unit for detecting light passing through the disk. The rotary encoder 21 outputs A-phase signals, B-phase signals, and Z-phase signals of a pulse train, respectively.

[0103] The pulse conversion unit 41A and the separation unit 41B function as acquisition means for acquiring the sinθ and cosine component cosθ of the rotation angle θ based on the output signal of the rotary encoder 21.

[0104] The pulse conversion unit 41A converts the A-phase signal, B-phase signal, and Z-phase signal into the rotation angle θ of the motor 2. The pulse conversion unit 41A outputs the converted rotation angle θ to the separation unit 41B.

[0105] The separation unit 41B separates the rotation angle θ output from the pulse conversion unit 41A into a sine component sinθ and a cosine component cosθ. The separation unit 41B outputs the separated sine component sinθ and cosine component cosθ to the HPF units 42A and 42B, respectively.

[0106] Thus, by employing the rotary encoder 21, the sine component sinθ and the cosine component cosθ of the rotation angle θ of the motor 2 can be obtained, similar to the first embodiment.

[0107] As a result, in the HPF sections 42A and 42B, a frequency characteristic filter corresponding to the high-pass characteristics of the current sensors 11 to 13 is applied to the sine component sinθ and the cosine component cosθ. Then, in the rotation angle calculation section 43, the composite value θc of the rotation angle is calculated by combining the filtered sine component sin(θc) and the cosine component cos(θc).

[0108] Therefore, in the second embodiment as in the first embodiment, the phase error component of the three-phase currents Iu to Iw detected by the current sensors 11 to 13 is suppressed by the composite value θc of the rotation angle. This makes it possible to accurately measure the d-axis current Id and the q-axis current Iq.

[0109] Although various embodiments of the present invention have been described above, these embodiments only represent a portion of the applications of the present invention, and are not intended to limit the technical scope of the present invention to the specific configurations of the above embodiments.

[0110] For example, in the above embodiment, a resolver 20 and a rotary encoder 21 were given as examples of angle sensors, but the sensor is not limited to these, as long as it detects the rotation angle θ of the motor 2.

[0111] Furthermore, although the Rogowski coil 10A was given as an example of the current sensor 11 to 13 in the above embodiment, it is not limited to these as long as it has high-frequency pass-through characteristics. [Explanation of symbols]

[0112] 1. 1A Current Measurement System 10A Logoski Coil 11-13 Current Sensor 20. Resolver (angle sensor) 21. Rotary Encoder (Angle Sensor) 40, 40A Processing Unit (Hardware) 41 Synchronous detection unit (acquisition means) 41A, 41B Pulse conversion unit, separation unit (acquisition means) 42A, 42B HPF section (processing means) 44 Coordinate transformation unit (measurement means) S2, S3, S5 (Acquisition step, Processing step, Measurement step)

Claims

1. A current measurement method for measuring the d-axis and q-axis currents in an AC motor, using a plurality of current sensors having high-frequency pass characteristics and detecting the currents of at least two phases of the three-phase current flowing through the AC motor, and an angle sensor that detects the rotation angle of the AC motor, An acquisition step of acquiring the sine and cosine components of the rotation angle based on the output signal of the angle sensor, A processing step of applying a filter to the sine component and the cosine component using a filter having a frequency characteristic corresponding to the high-pass characteristics of the current sensor, A measurement step in which the currents of the d axis and q axis are measured based on the combined value of the rotation angle obtained by combining the sinusoidal and cosine components after the filtering process and the detected values ​​of the three-phase current obtained by the plurality of current sensors, A method for measuring current, including the measurement of current.

2. A current measurement method according to claim 1, The current sensor includes a Rogowski coil, Current measurement method.

3. A current measurement method according to claim 1 or claim 2, The acquisition step, the processing step, and the measurement step are performed by one or more hardware devices. Current measurement method.

4. A current measurement method according to claim 3, The aforementioned one or more hardware components are analog circuits. Current measurement method.

5. A current measurement method according to claim 3, The aforementioned one or more hardware components are digital circuits. Current measurement method.

6. A current measurement method according to claim 1 or claim 2, The acquisition step, the processing step, and the measurement step are performed by software. Current measurement method.

7. Multiple current sensors having high-frequency pass-through characteristics, which detect the current of at least two phases of the three-phase current flowing through an AC motor, An angle sensor for detecting the rotation angle of the AC motor, An acquisition means for acquiring the sine and cosine components of the rotation angle based on the output signal of the angle sensor, A processing means for applying filtering to the sine component and the cosine component using a filter having a frequency characteristic corresponding to the high-pass characteristics of the current sensor, A measuring means for measuring the currents of the d axis and q axis based on the combined value of the rotation angle obtained by combining the sinusoidal and cosine components after the filtering process and the detected values ​​of the three-phase current obtained by the plurality of current sensors, A current measurement system including a current measurement system.

8. A computer that acquires output signals from multiple current sensors having high-frequency pass characteristics and detecting at least two phases of the three-phase current flowing through an AC motor, and output signals from an angle sensor that detects the rotation angle of the AC motor, An acquisition step of acquiring the sine and cosine components of the rotation angle based on the output signal of the angle sensor, A processing step of applying a filter to the sine component and the cosine component using a filter having a frequency characteristic corresponding to the high-pass characteristics of the current sensor, A measurement step of measuring the currents in the d-axis and q-axis of the AC motor based on the combined value of the rotation angle obtained by combining the sine and cosine components after the filtering process and the output signals of the plurality of current sensors, A program to execute.

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