Measurement device, measurement method, and measurement program

Abstract

This measurement device is capable of power analysis of an measurement object provided with a motor and an inverter for controlling the motor. This measurement device comprises a current acquisition unit (31) that acquires current data of a measurement object, a voltage acquisition unit (32) that acquires voltage data of the measurement object, a power spectrum analysis unit (33) that obtains and outputs a frequency component of at least one of active power and reactive power on the basis of the acquired voltage data and current data, a frequency band setting unit (41) configured to be capable of setting the frequency band of ringing power, a power integration unit (42) that calculates a power integrated value of the set frequency band using the frequency component of at least one of active power and reactive power output by the power spectrum analysis unit (33), and a display control unit (34) that displays the calculation result of the power integration unit (42) on a display (15).

Description

Measuring device, measuring method, and measurement program

[0001] The present invention relates to a measuring device, a measuring method, and a measurement program.

[0002] Conventionally, a motor drive system that drives a motor by an inverter is known. Such a motor drive system is mounted on various devices including EV vehicles and is widely used.

[0003] Among the power supplied from the inverter to the motor, the fundamental wave power directly contributes to the rotational force, and the other high-frequency components are lost as ineffective energy such as heat, sound, and vibration. Therefore, in the development of a motor drive system, reduction of power loss is important, and a power measuring device is used to analyze the factors (see, for example, Patent Document 1).

[0004] Japanese Patent Application Laid-Open No. 2013-124915

[0005] In recent years, in order to achieve carbon neutrality, the miniaturization and weight reduction of the motor drive system have been promoted. In order to achieve higher efficiency of the inverter, the power devices used in the inverter are changing from IGBTs to SiC, GaN, etc., and the rising time of switching tends to be faster. Along with such changes, it is expected that the specifications and functions required for the measuring devices used in development will also change, and a measuring device that can provide useful power data for development is required.

[0006] The present invention has been made in view of such circumstances, and an object thereof is to provide a measuring device, a measuring method, and a measurement program that can provide power data useful for the development of a motor drive system.

[0007] One aspect of the present invention is a measuring device capable of power analysis of a target to be measured, comprising a motor and an inverter for controlling the motor, the measuring device comprising: current acquisition means for acquiring current data of the target to be measured; voltage acquisition means for acquiring voltage data of the target to be measured; power spectrum analysis means for determining and outputting at least one frequency component of active power and reactive power based on the acquired voltage data and current data; frequency band setting means configured to set the frequency band of ringing power; power integration means for calculating a power integrated value of the set frequency band using at least one frequency component of active power and reactive power output by the power spectrum analysis means; and display control means for displaying the calculation result of the power integration means on a display means.

[0008] One aspect of the present invention is a measurement method capable of power analysis of a target to be measured, comprising a motor and an inverter for controlling the motor, wherein a computer performs the following steps: acquiring current data of the target to be measured; acquiring voltage data of the target to be measured; determining and outputting at least one frequency component of active power and reactive power based on the acquired voltage data and current data; configuring the ringing power frequency band to be settable; calculating a power integrated value of the set frequency band using at least one frequency component of the active power and reactive power; and displaying the power integrated value on a display means.

[0009] One aspect of the present invention is a measurement program for causing a computer to function as the above-mentioned measuring device.

[0010] The present invention has the effect of providing power data useful for the development of motor drive systems.

[0011] This figure shows a schematic configuration of a measurement system according to one embodiment of the present invention. This is a functional configuration diagram showing an example of the functions of a measurement device according to one embodiment of the present invention. This is a flowchart showing an example of the processing procedure for power spectrum analysis performed by a power spectrum analysis unit according to one embodiment of the present invention. This figure shows an example of a power spectrum screen according to one embodiment of the present invention. This figure shows an example of a setting screen according to one embodiment of the present invention. This is a flowchart showing an example of the power integration processing procedure performed by a power integration unit according to one embodiment of the present invention. This figure shows an example of the display of POA value and OA value according to one embodiment of the present invention. This figure shows an example of an equivalent circuit of a motor drive system. This figure shows an example of frequency characteristics when a simulation is performed using the equivalent circuit shown in Figure 9, where (a) is the frequency characteristics of voltage, (b) is the frequency characteristics of impedance, and (c) is the frequency characteristics of current. This figure is for explaining the fundamental frequency, carrier frequency, and ringing frequency. This figure is for explaining the relationship between carrier frequency and ringing power. This figure is for explaining the relationship between carrier frequency and inverter efficiency influence.

[0012] Hereinafter, an embodiment of the measuring device, measuring method, and measuring program according to the present invention will be described with reference to the drawings. The measuring device according to this embodiment is a device that can be widely applied to the power analysis of equipment, and in particular, as shown in Figure 1, it has a power analysis function that is suitable for the power analysis of a motor drive system 50 comprising a motor 6 and an inverter 5 that controls the motor 6.

[0013] As described above, in recent years, power devices used in the inverter 5 of the motor drive system 50 are changing to SiC, GaN, etc., and the switching rise time is becoming faster. The inventors have found that, with the increase in switching speed in such inverters 5, ringing power (ringing power generated by cable inductance, etc.) is being generated in frequency bands that had not been previously considered. The measuring device 10 according to this embodiment was invented based on this new finding and can provide ringing power in a visually apparent manner. Before going into a detailed description of the measuring device 10 below, ringing power will be explained.

[0014] Figure 9 shows the equivalent circuit 60 for one phase of the motor. As shown in Figure 9, the equivalent circuit 60 for one phase of the motor 6 can be represented by the inductance component of the cable 4 connecting the inverter 5 and the motor 6 shown in Figure 1, the inductance component of the motor 6, and the capacitance component.

[0015] Figure 10 shows an example of frequency characteristics when a simulation is performed using the equivalent circuit 60, where (a) shows the voltage frequency characteristics, (b) shows the impedance frequency characteristics, and (c) shows the current frequency characteristics. From the voltage frequency characteristics shown in Figure 10(a), it can be seen that when SiC and GaN are used as power devices, higher frequency components are included compared to when IGBTs are used. Furthermore, it was found that these high-frequency components of the voltage cause current to flow in a high-frequency band that was not considered when IGBTs were used.

[0016] In other words, in the conventional case where IGBTs were used as power devices, as shown in Figure 11, it was sufficient to focus on the fundamental frequency band dependent on the motor rotation speed and the power frequency component at the carrier frequency. In contrast, with the replacement of IGBTs with new power devices such as SiC and GaN, and the resulting increase in switching speed, it was found that current flows at the resonance point between the motor's capacitance component and the cable inductance. As a result, new insights were gained, indicating that ringing power (power loss) occurs in an even higher frequency band than before (approximately several hundred kHz to several tens of MHz).

[0017] The inventors found that, as shown in Figure 12, the ringing power increases as the carrier frequency increases; as shown in Figure 13, the efficiency impact on the inverter increases as the carrier frequency increases; and the ringing power occurs in a frequency band independent of the carrier frequency.

[0018] Based on these new findings, understanding the extent of this ringing power is crucial in developing a more efficient motor drive system 50 (see Figure 1). The measuring device 10 according to this embodiment enables the measurement of this ringing power.

[0019] Figure 1 is a diagram showing the schematic configuration of a measurement system 1 according to one embodiment of the present invention. As shown in Figure 1, the measurement system 1 measures the power of the cable 4 connecting the inverter 5 and the motor 6 in the motor drive system 50 which is the object of measurement. In this embodiment, for the sake of simplicity, the explanation will be given using the case where the motor 6 is a single-phase motor as an example, but in the case of a multi-phase system, the frequency components of the power of the entire multi-phase line can be determined by determining the frequency components of the power for each phase and summing up the determined power for each frequency component.

[0020] The measurement system 1 comprises a measuring device 10, a current sensor 2, and a voltage sensor 3. The current sensor 2 measures the current flowing from the inverter 5 to the motor 6 and outputs an analog current signal to the measuring device 10 corresponding to the magnitude of the measured current. The voltage sensor 3, for example, measures the line voltage of the motor 6 and outputs an analog voltage signal to the measuring device 10 corresponding to the magnitude of the measured voltage.

[0021] The measuring device 10 includes, for example, an A / D converter 11, an A / D converter 12, a data processing circuit 13, an input operation unit 14, and a display 15. The measuring device 10 may also include a communication interface, an external interface, etc.

[0022] The A / D converter 11 converts the analog current signal input from the current sensor 2 into a digital current signal by sampling it at a predetermined sampling period and outputs it. The A / D converter 12 converts the analog voltage signal input from the voltage sensor 3 into a digital voltage signal by sampling it at a predetermined sampling period and outputs it. On the signal input side of the A / D converters 11 and 12, known devices such as an anti-aliasing filter (AAF) to prevent aliasing errors that occur during sampling and data decimation, a range circuit to limit the voltage range of the input signal to the data processing circuit 13, and an amplifier to amplify the signal may be provided. Sampling may be performed periodically as described above, or it may be performed repeatedly at any timing.

[0023] The data processing circuit 13 is a computer, and for example, it includes a CPU (Central Processing Unit: processor), main memory, secondary storage (secondary storage: memory), etc. The data processing circuit 13 can be implemented using, for example, a microcomputer, FPGA (Field-Programmable Gate Array), PLC (Programmable Logic Controller), etc.

[0024] The secondary storage device is a non-transitor computer-readable storage medium. Examples of secondary storage devices include semiconductor memory, such as flash memory and SSDs (Solid State Drives). Other examples of secondary storage devices include magnetic disks (HDDs), optical disks (CD-ROMs, DVD-ROMs, etc.), and magneto-optical disks. The secondary storage device stores programs and data for realizing the various functions of the data processing circuit 13, which will be described later. The secondary storage device also stores phase correction data, which will be described later. The secondary storage device may also store various data acquired by the measuring device 10. Multiple secondary storage devices may be provided, and programs and data for realizing the functions described later may be divided and stored in each secondary storage device.

[0025] The input operation unit 14 is a man-machine interface for the user to input instructions to the measuring device 10. Examples of the input operation unit 14 include various buttons, dial buttons, and a touch panel. The display 15 is, for example, a liquid crystal display and displays data processed by the data processing circuit 13 and judgment results.

[0026] Figure 2 is a functional configuration diagram showing an example of the functions of the measuring device 10. As shown in Figure 2, the measuring device 10 includes a storage unit 30, a current acquisition unit 31, a voltage acquisition unit 32, a power spectrum analysis unit 33, a display control unit 34, and a partial overall value calculation unit (POA value calculation unit) 35.

[0027] These various functions are realized, for example, by a data processing circuit 13. For example, a series of processes for realizing these various functions are stored in secondary memory in the form of a program, and the CPU reads this program into main memory and performs information processing and calculations to realize the various functions. The program may be pre-installed in secondary memory, provided in a state where it is stored on a non-temporary computer-readable storage medium, or distributed via wired or wireless communication means.

[0028] The memory unit 30 stores various correction data used in the power spectrum analysis unit 33 and the POA value calculation unit 35, which will be described later. The memory unit 30 stores current data and voltage data acquired by the current acquisition unit 31 and the voltage acquisition unit 32, as well as analysis results from the power spectrum analysis unit 33 and calculation results from the POA value calculation unit 35.

[0029] The current acquisition unit 31 acquires current data of the object to be measured. For example, the current acquisition unit 31 acquires the digital current signal output from the A / D converter 11. The voltage acquisition unit 32 acquires voltage data of the object to be measured. For example, the voltage acquisition unit 32 acquires the digital voltage signal output from the A / D converter 12. The acquired current data and voltage data are stored in the storage unit 30, for example, linked to the sampling time.

[0030] The power spectrum analysis unit 33 uses the acquired current data and voltage data, or the current data and voltage data stored in the storage unit 30, to determine the frequency component of at least one of the active power and reactive power. An example of the analysis process performed by the power spectrum analysis unit 33 will be described below with reference to Figure 3. Figure 3 is a flowchart showing an example of the processing procedure for the power spectrum analysis process performed by the power spectrum analysis unit 33.

[0031] First, the power spectrum analysis unit 33 compensates for the phase error (SA1) by correcting the sampling time associated with the current data and voltage data based on the phase correction data.

[0032] For example, due to the phase characteristics of the current sensor 2, a time error occurs between the sampled voltage data and current data. Therefore, it is necessary to compensate for this time error. Phase correction data consists of, for example, the time difference between voltage and current corresponding to the phase error, and is stored in advance in the memory unit 30. The power spectrum analysis unit 33 uses the phase correction data stored in the memory unit 30 to correct the sampling time so that the sampling times of the voltage data and current data are shifted relative to each other by the amount of the time difference.

[0033] In this case, the power spectrum analysis unit 33 may advance the sampling time of the current data by the amount of the time difference, or delay the sampling time of the voltage data by the amount of the time difference. Furthermore, both the current data and the voltage data may be corrected so that the sampling times of both data are shifted relative to each other by the amount of the time difference. If the correction data consists of something other than the time difference between voltage and current corresponding to the phase error, the power spectrum analysis unit 33 calculates the time difference from the correction data and corrects the sampling times of the current data and voltage data so that they are shifted relative to each other by the amount of the time difference. The correction data is not limited to the time difference described above, but can be set as appropriate, for example, by consisting of a predetermined frequency and the amount of phase error at that frequency.

[0034] Next, the power spectrum analysis unit 33 applies a window function to the phase-corrected current data and voltage data (SA2). Examples of window functions include a square window, Hanning window, and flat-top window. Subsequently, the frequency components of the voltage and current are calculated by performing an FFT (Fast Fourier Transform) or DFT (Discrete Fourier Transform) on the current data and voltage data after applying the window function (SA3).

[0035] Next, the power spectrum analysis unit 33 performs amplitude correction on the voltage frequency component and the current frequency component using a window function (SA4). Specifically, the power spectrum analysis unit 33 performs amplitude correction by applying a window function by multiplying the voltage frequency component and the current frequency component by a predetermined correction value.

[0036] Next, the power spectrum analysis unit 33 uses the frequency components of the amplitude-corrected voltage U and the frequency components of the current I to calculate the frequency component of at least one of the active power P and reactive power Q (SA5).

[0037] Specifically, the power spectrum analysis unit 33 calculates the active power P = UIcosθ and / or reactive power Q = UIsinθ for each frequency component from the frequency components of voltage U, current I, and phase difference θ, and determines the frequency components of one or both of the active power P and reactive power Q. The active power P may also be obtained by multiplying the real components of voltage U and current I.

[0038] More specifically, when the real components in the FFT calculation results of the voltage waveform and current waveform are Urj and Irj (j = 0 to N / 2, where N is the number of FFT points), the frequency component Pj of the active power can be obtained from Urj * Irj. Similarly, the frequency component Qj of the reactive power may be obtained by multiplying the imaginary components of the voltage U and current I. More specifically, when the imaginary components in the FFT calculation results of the voltage waveform and current waveform are Uij and Iij (j = 0 to N / 2, where N is the number of FFT points), the frequency component Qj of the reactive power can be obtained from Uij * Iij. By multiplying j by the sampling frequency (= 1 / sampling period), the frequency of the obtained active power Pj or reactive power Qj can be determined. The processing procedure of the power spectrum analysis unit 33 described above is just one example and is not limited thereto. That is, as long as the frequency components of the power can be obtained, other known methods can be appropriately adopted.

[0039] Returning to Figure 2, the display control unit 34 displays the analysis results of the power spectrum analysis unit 33 on the display 15. Figure 4 shows an example of the power spectrum screen. The power spectrum screen displays a bar graph with frequency on the horizontal axis and active power P on the vertical axis, showing the value of active power P at each frequency. In addition to displaying the frequency components of active power P, the frequency components of reactive power Q, with frequency on the horizontal axis and reactive power Q on the vertical axis, showing the value of reactive power Q at each frequency, may also be displayed on the display 15 as the same or a separate graph as that of active power P. Alternatively, the frequency components of active power P and reactive power Q may be displayed as line graphs instead of bar graphs.

[0040] The display control unit 34 displays various setting screens related to the POA value calculation unit 35 (described later), the partial overall value (POA value) calculated by the POA value calculation unit 35, and the like on the display 15.

[0041] The POA value calculation unit 35 includes a frequency band setting unit 41 and a power integration unit 42. The frequency band setting unit 41 sets the frequency band for calculating the POA value. Here, the frequency band setting unit 41 is configured to be able to set the frequency band of ringing power. The frequency band setting unit 41 sets the frequency band, for example, based on frequency band information input from the input operation unit 14. The frequency band information can be input by the user through a setting screen (UI) displayed on the display 15.

[0042] Figures 5 and 6 show examples of setting screens displayed on the display 15. As shown in Figure 5, the setting screen is provided with input buttons BT1 and BT2 that allow the user to switch on / off the functions for calculating the overall value (OA value) and POA value. When the POA value calculation function is set to ON using input button BT2 and the range setting button BT3 is pressed, the setting screen shown in Figure 6 is displayed. The setting screen shown in Figure 6 is configured so that the user can directly input the lower limit value f1 and the upper limit value f2 of the frequency band for calculating the POA value. When an arbitrary frequency is input by the user on this setting screen, the frequency band setting unit 41 sets the input frequency band.

[0043] As shown in FIG. 4, when a power spectrum screen is displayed on the display 15, a bar 40 for specifying a frequency band for calculating the POA value may be displayed on the power spectrum screen. Thereby, the user can easily specify a desired frequency band by a simple operation of moving the bar 40 while checking the actually measured power spectrum.

[0044] The power integration unit 42 calculates an integrated power value (POA value) by integrating the power values in the frequency band set by the frequency band setting unit 41. Hereinafter, the arithmetic processing by the power integration unit 42 will be described with reference to FIG. 7. FIG. 7 is a flowchart showing an example of the procedure of the power integration process executed by the power integration unit 42.

[0045] First, the power integration unit 42 calculates the sum of the powers (power integration value) in the frequency band by simply adding the power values in the frequency band set by the frequency band setting unit 41 (SB1).

[0046] Subsequently, the final POA value is calculated by correcting the calculated power integration value (SB2). The correction is for reducing the influence of the window function and amplitude correction used when the power integration unit 33 calculates the frequency components of the power. Specifically, the final POA value is calculated by multiplying the power integration value calculated in step SB1 by a correction value by a window function such as a Hanning window or a flat top. For example, the POA value is calculated by the following formula (1).

[0047]

[0048] In the above formula (1), f1 is the lower limit value of the frequency band, f2 is the upper limit value of the frequency band, P(f) is the power value at each frequency, and Hf is the correction value related to the window function.

[0049] For the OA value, in the above formula (1), 0 may be set as f1 and infinity may be set as f2.

[0050] The POA value and OA value calculated by the POA value calculation unit 35 are displayed on the display 15 by the display control unit 34. Figure 8 shows an example of the display of the POA value and OA value. In Figure 8, the POA value for the frequency band specified by the bar 40 is shown together with the OA value. The analysis results from the power spectrum analysis unit 33 and the integrated results calculated by the POA value calculation unit 35 may be transmitted to other devices (for example, other measuring devices or data management devices) via a communication interface (not shown).

[0051] Next, the flow of the measurement method using the measurement system 1 according to this embodiment will be described. First, the current flowing through the cable 4 is detected by the current sensor 2, and an analog current signal is output to the measuring device 10. The phase voltage of the motor 6 is detected by the voltage sensor 3, and an analog voltage signal is output to the measuring device 10.

[0052] The analog current signal is converted into a digital current signal (current data) by the A / D converter 11 of the measuring device 10 and output to the data processing circuit 13. The analog voltage signal is converted into a digital current signal (voltage data) by the A / D converter 12 of the measuring device 10 and output to the data processing circuit 13.

[0053] The data processing circuit 13 obtains the frequency components of power by performing power spectrum analysis based on current data and voltage data. The specific processing details are explained using Figure 3. As a result, the display 15 displays a power spectrum screen as illustrated in Figure 4. If the POA function is turned on, the data processing circuit 13 calculates the POA value by integrating the power values ​​in the frequency band specified by the user and then applying corrections. If the OA function is turned on, it calculates the OA value. The data processing circuit 13 displays the calculated POA value and OA value on the display 15 (see Figure 8).

[0054] As described above, this embodiment includes a power spectrum analysis unit 33 for analyzing the frequency components of power, a frequency band setting unit 41 configured to set the frequency band of ringing power, a power integration unit 42 that calculates the power integrated value of the set frequency band using at least one of the frequency components of active power and reactive power output by the power spectrum analysis unit 33, and a display control unit 34 that displays the calculation result of the power integration unit 42 on the display 15.

[0055] This allows the user to easily understand how much active power exists in the frequency band set by the frequency band setting unit 41 by checking the integrated power (POA) value displayed on the display 15. In other words, by setting only the ringing frequency band by the frequency band setting unit 41, power in the frequency bands related to the fundamental wave and carrier wave is excluded, and only the power value related to ringing is extracted, and its integrated value (POA) can be obtained. Since ringing power (power loss due to ringing) is an important factor that affects motor efficiency and inverter efficiency, this can provide the user with information useful for developing the motor drive system 50.

[0056] The measuring device 10 includes an input operation unit 14 for the user to set the frequency band for calculating the integrated power value, and the frequency band setting unit 41 sets the frequency band based on the frequency band information input from the input operation unit 14. This allows the user to arbitrarily set the frequency band for calculating the POA value. As a result, by changing the specified frequency band, the user can obtain POA values ​​related to the fundamental wave, POA values ​​related to the carrier frequency, and POA values ​​related to the ringing frequency, respectively, and can utilize this data for development.

[0057] The present inventors have described the invention in detail based on embodiments, but it goes without saying that the present invention is not limited thereto and can be modified in various ways without departing from its essence. For example, in the above-described embodiment, the case in which the current flowing through the cable 4 is single-phase was used as an example, but in the case of multi-phase, a current sensor 2 and a voltage sensor 3 may be provided for each phase, and power spectrum analysis may be performed for each phase. The POA value may be calculated for each phase, or the values ​​for all phases may be added together.

[0058] 1: Measurement system 2: Current sensor 3: Voltage sensor 4: Cable 5: Inverter 6: Motor 10: Measurement device 11: A / D converter 12: A / D converter 13: Data processing circuit 14: Input operation unit 15: Display 30: Memory unit 31: Current acquisition unit 32: Voltage acquisition unit 33: Power spectrum analysis unit 34: Display control unit 35: POA value calculation unit 40: Bar 41: Frequency band setting unit 42: Power integration unit 50: Motor drive system 60: Equivalent circuit BT1: Input button BT2: Input button BT3: Range setting button

Claims

1. A measuring device capable of power analysis of a target to be measured, comprising a motor and an inverter for controlling the motor, the measuring device comprising: current acquisition means for acquiring current data of the target to be measured; voltage acquisition means for acquiring voltage data of the target to be measured; power spectrum analysis means for determining and outputting at least one frequency component of active power and reactive power based on the acquired voltage data and current data; frequency band setting means configured to set the frequency band of ringing power; power integration means for calculating a power integrated value of the set frequency band using at least one frequency component of active power and reactive power output by the power spectrum analysis means; and display control means for displaying the calculation result of the power integration means on a display means.

2. The measuring device according to claim 1, further comprising an input operation means for a user to set the frequency band for calculating the integrated power value, wherein the frequency band setting means sets the frequency band based on the frequency band information input from the input operation means.

3. The measuring device according to claim 2, wherein the display control means simultaneously displays a power spectrum screen including at least one frequency component of the active power and the reactive power, and a setting screen for the user to input the frequency band information.

4. The measuring device according to claim 2, wherein the display control means causes the display means to display a power spectrum screen including at least one frequency component of the active power and the reactive power, and displays a bar on the power spectrum screen for the user to input the frequency band information.

5. A measurement method capable of power analysis of a target to be measured, comprising a motor and an inverter for controlling the motor, wherein a computer performs the following steps: acquiring current data of the target to be measured; acquiring voltage data of the target to be measured; determining and outputting at least one frequency component of active power and reactive power based on the acquired voltage data and current data; configuring the ringing power frequency band to be settable; calculating a power integrated value of the set frequency band using at least one frequency component of the active power and reactive power; and displaying the power integrated value on a display means.

6. A measurement program for causing a computer to function as a measuring device according to any one of claims 1 to 4.

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