Measuring device and measurement method

Abstract

To provide a measuring device and a measurement method that measure the frequency component in a high frequency range of electric power with good accuracy.SOLUTION: The above problem can be solved by a measuring device (1) or the like that is provided with a processor (10), and that connects to a current sensor (2) and measures the frequency component of electric power of a measurement object (4). The processor (10) acquires correction data for correcting the phase characteristic of the current sensor (2), acquires the voltage data of the measurement object (4) and the current data of the measurement object (4) detected by the current sensor in sequence of time, corrects the voltage data and / or the current data on the basis of the correction data so as to shift the relative phases of the voltage data and current data, and determines the voltage and current frequency components on the basis of the voltage data and current data after correction. The measuring device (1) is constituted to measure the frequency component of the active power and / or reactive power on the basis of the voltage and current frequency components.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a measuring device and a measuring method, and particularly to a measuring device and a measuring method for measuring the frequency components of electric power.

Background Art

[0002] A power measuring device obtains power by time-series integration averaging of the product value of a voltage and a current sampled from a measurement object. At this time, the frequency characteristics of the measurement system have a great influence on the measurement accuracy. For example, a phase error occurs due to the sensing unit, circuit unit, or propagation delay characteristics of the cable length of a current sensor that measures current. Patent Document 1 describes a technique for correcting this phase error. Also, in a measurement system provided with a band filter in the signal input unit, the frequency characteristics of the band filter affect the measurement accuracy. Patent Document 2 describes a technique for correcting an error due to such frequency characteristics.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the power measurement method based on the integrated average of the product of the above-mentioned voltage and current, power including all frequency components can be measured. However, in recent years, for more detailed power analysis, there has been a demand for measuring devices and measurement methods for measuring power for each frequency component. With the spread of new power semiconductors (SiC, GaN), the frequencies used in AC sources such as the switching frequency of power inverters have become higher, and there is a demand for measuring devices that can accurately measure the frequency components of power including the high-frequency region. Also, when the current waveform flowing through the measurement target is a non-sinusoidal waveform such as a triangular wave or a rectangular wave, the waveform itself contains harmonic components such as the third harmonic (for example, 11% in the case of a triangular wave), the fifth harmonic (4% for the same), and the seventh harmonic (2% for the same). Therefore, analysis including the high-frequency region is required. However, there has been a problem that as the frequency increases, the phase error due to the delay characteristics of the current sensor increases, and the measurement accuracy of the frequency components in the high-frequency region decreases. For example, in the case of a power inverter that switches at 300V 30A 100kHz and the loss of the reactor is 1%, the power loss of the reactor is 0.09kW, and the phase difference between the voltage and the current is 89.43°. If there is a 0.1° voltage-current phase error in the measuring device at 100kHz, the loss that should originally be 0.09kW will be measured as 0.0738kW, which is 18% different from the true value.

[0005] Fig. 6 shows the frequency characteristics of a general current sensor. Fig. 6(a) shows the frequency characteristics of the magnitude of the current detected by the current sensor, with the frequency on the horizontal axis and the error from the true value of the magnitude (level) of the detected current on the vertical axis. Fig. 6(b) shows the frequency characteristics of the phase of the current detected by the current sensor, with the frequency on the horizontal axis and the phase difference between the detected phase and the true value on the vertical axis. It can be seen that the error 60 in the magnitude of the current remains relatively small even in the frequency region exceeding 100kHz, while the phase error 61 becomes significant in the high-frequency region of 10kHz or more. From this, it can be understood that suppressing the phase error is essential for improving the measurement accuracy in the measurement of the frequency components of power including the high-frequency region.

[0006] The present invention has been made in view of the above-described problems, and an object thereof is to provide a measuring device and a measuring method for accurately measuring the frequency components of power in a high-frequency region.

Means for Solving the Problems

[0007] The above-described problem is solved by a measuring device including a processor and connected to a current sensor to measure the frequency components of the power of a measurement target, wherein the processor acquires correction data for correcting the phase characteristics of the current sensor, acquires time-series voltage data of the measurement target and current data of the measurement target detected by the current sensor, corrects at least one of the voltage data and the current data so as to shift the phase between the voltage data and the current data based on the correction data, obtains the frequency components of the voltage and the current based on the corrected voltage data and current data, and is configured to obtain and output the frequency components of at least one of the active power and the reactive power based on the frequency components of the voltage and the current.

[0008] That is, by obtaining and outputting the frequency components of the power based on the voltage data and the current data corrected based on the correction data for correcting the phase characteristics of the current sensor, it is possible to suppress a decrease in measurement accuracy due to a phase error and accurately measure the frequency components of the power in the high-frequency region.

[0009] Here, it is desirable that the measuring device further includes a display device for displaying the frequency components of the power. By displaying the obtained frequency components of the power numerically or graphically on the screen of the display device, it becomes possible to grasp at a glance the power situation in each frequency region.

[0010] Further, it is desirable that the current sensor is detachably attachable to the measuring device, and the processor is configured to acquire correction data from the current sensor. By configuring the current sensor to carry correction data for a phase error specific to the sensor and the measuring device to acquire the correction data, it becomes possible to automatically perform correction according to the frequency characteristics of the current sensor.

[0011] Further, it is desirable that the measuring device further includes a connector for detachably attaching the current sensor. Thereby, it becomes possible to easily replace the current sensor according to the measurement object and the power analysis content.

[0012] Furthermore, it is desirable that the frequency component of the power obtained by the measuring device includes a frequency region of 10 kHz or more. Since the phase error of the current sensor becomes significant in the frequency region of 10 kHz or more, according to the present invention, it is possible to suppress a decrease in measurement accuracy due to the phase error of the frequency component of 10 kHz or more and accurately measure the frequency component of the power in the high-frequency region.

[0013] Furthermore, the above problems can also be solved by a method for implementing each function of the above-described processor.

Advantages of the Invention

[0014] According to the measuring device and the measuring method according to the present invention, it is possible to provide a measuring device and a measuring method for accurately measuring the frequency component of the power in the high-frequency region.

Brief Description of the Drawings

[0015]

Figure 1

Figure 2

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Figure 5

Figure 6

Embodiments for Carrying Out the Invention

[0016] Hereinafter, specific examples of embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic configuration diagram showing a configuration when measuring the power of a measurement target 4 using a power frequency component measurement device 1 and a current sensor 2 according to an embodiment of the present invention. The measurement device 1 and the current sensor 2 can be detachably attached by a connector 16 of the measurement device 1 and a connector 21 of the current sensor 2. Thereby, it becomes possible to easily replace the current sensor 2 according to the measurement target 4 and the power analysis content.

[0017] One end of the electric wire that is the measurement target 4 is connected to an AC source such as a power inverter, and the other end is connected to a load. The current sensor 2 measures the current of the measurement target 4 flowing from the AC source to the load. The current flowing through the measurement target 4 may be single-phase or polyphase. In this embodiment, for the sake of simplicity of explanation, single-phase measurement will be described. In the case of polyphase, the frequency components of the power are obtained for each phase, and the obtained powers are summed for each frequency component to obtain the frequency components of the power of the entire polyphase line.

[0018] The current sensor 2 is a sensor that detects the magnitude of the current flowing through the measurement target 4 and outputs an analog signal representing the detected current magnitude. The current sensor 2 includes a memory 20 and a connector 21. The memory 20 stores correction data for correcting the phase characteristics of the current sensor 2. The details of the content of the correction data will be described later. An analog signal line and a digital signal line are connected to the connector 21. By connecting the connector 21 to the connector 16 of the measurement device 1, an analog signal representing the magnitude of the current of the measurement target 4 detected via the analog signal line and correction data are transmitted via the digital signal line.

[0019] The measuring device 1 has a function of obtaining an analog signal representing the magnitude of the current of the measurement target 4 detected by the current sensor 2 and an analog voltage signal of the measurement target 4 from the probe 3 connected to the measurement target 4, and calculating at least one of the active power and the reactive power of the measurement target 4. The measuring device 1 includes a processor 10, an input device 11, a display device 12, a memory 13, ADCs (analog-to-digital converters) 14 and 15, and a connector 16 connected to the processor 10. The input of the ADC 15 is connected to the probe 3 connected to the measurement target 4, and the output is connected to the processor 10. An analog signal line and a digital signal line are connected to the connector 16. The digital signal line is connected to the processor 10 directly or via a data bus or the like, and the analog signal line is connected to the processor 10 via the ADC 14. Note that, a anti-aliasing filter (AAF) for preventing aliasing errors generated during sampling or data decimation, and a range circuit for limiting the voltage range of the input signal to the measuring device 1 may be provided in front of the ADCs 14 and 15.

[0020] The processor 10 receives data from the input device 11, the memory 13, the ADCs 14 and 15, and the connector 16, executes a program for calculating the frequency components of the power recorded in the memory 13, obtains at least one of the frequency components of the active power and the reactive power of the measurement target 4, and outputs the text and graph of the obtained frequency components to the display device 12. Note that, the obtained frequency components are not limited to the output to the display device, and may be outputted to the outside of the measuring device 1 by wire or wirelessly from an external output terminal (not shown), or may be outputted by being stored in an external storage device (not shown) provided inside or outside the measuring device 1.

[0021] The input device 11 is a device having a function of acquiring data from the user of the measuring device 1 or an external device, and can be composed of a keyboard, a mouse, a touch panel, an I / O interface, etc. The display device 12 is a device that receives the power data requested by the measuring device 1, converts it into a visual image, and outputs it, and can be composed of a liquid crystal display, an EL display, etc. The memory 13 has a function of recording programs and digital data, and can be composed of a ROM, a RAM, an HDD, a flash memory, etc. A program for calculating the frequency components of the power of the measurement target 4 is stored in the memory 13 by the processor 10. Note that DFT (Discrete Fourier Transform) or FFT (Fast Fourier Transform) can be used for the calculation of the frequency components.

[0022] The ADCs 14 and 15 have a function of converting an analog signal into a digital signal. The ADC 14 receives an analog signal representing the magnitude of the current flowing through the measurement target 4, which is detected by the current sensor 2 and acquired via the connector 16, converts it into digital current data, and outputs it to the processor 10. The ADC 15 converts the magnitude of the analog voltage signal of the measurement target 4 from the probe 3 into digital voltage data and outputs it to the processor 10.

[0023] Next, correction data for correcting the phase characteristics of the current sensor 2 will be described with reference to FIG. 3. FIG. 3 is a graph showing the magnitude of the phase error between the measured value and the true value with respect to the frequency component, with the frequency on the horizontal axis and the phase error on the vertical axis. The current sensor 2 of the present embodiment has a frequency characteristic as shown by line 61 in FIG. 3. As is clear from the figure, a phase delay 63 of 16° occurs at 300 kHz. This phase delay 63 corresponds to a time difference of 16° / 360° / 300 kHz = 148 ns. The correction data is composed of the time difference between the voltage and the current corresponding to the phase error. That is, the content of the correction data stored in the memory 20 of the current sensor 2 is 148 ns. The processor 10 of the measuring device 1 performs correction to shift the time so that the current data advances 148 ns with respect to the voltage data based on this correction data, thereby compensating for the phase delay 63. Since the current sensor 2 has a phase characteristic with a constant group delay in a practical measurement frequency band, the phase delay of frequency components other than 300 kHz can also be compensated by the above-described correction, and it is possible to obtain voltage data and current data with the phase error suppressed as shown by line 62. Note that the correction data is not limited to the above-described time difference, and can be appropriately set, such as being composed of a predetermined frequency and the amount of phase error at that frequency.

[0024] Next, a specific example of an embodiment of the measurement method according to the present invention will be described with reference to the drawings. FIG. 2 is an operation flowchart of the measuring device 1. The measuring device 1 implements the measurement method shown in the flowchart by executing a program stored in the memory 13 by the processor 10.

[0025] First, the processor 10 acquires correction data for correcting the phase characteristics of the current sensor 2 (step 50). Since the phase characteristics are unique to the current sensor, by storing the correction data in the memory 20 of the current sensor 2 as in this embodiment and having the processor 10 acquire the correction data from the current sensor 2, it becomes possible to automatically perform phase correction according to the frequency characteristics of the current sensor 2. However, the acquisition of the correction data is not limited to acquisition from the memory 20 of the current sensor 2. It can be appropriately changed, such as acquiring from a user or an external device via the input device 11, acquiring correction data pre-stored in the memory 13 of the measurement device 1 in advance, or measuring the phase delay of the current sensor 2 to acquire the correction data.

[0026] Next, the processor 10 acquires time-series voltage data of the measurement target 4 and current data of the measurement target 4 detected by the current sensor 2 (step 51). More specifically, the ADC 14 repeatedly samples the current of the measurement target 4, the ADC 15 repeatedly samples the voltage of the measurement target 4, and the processor 10 acquires the current data and voltage data obtained by the sampling and records them in the memory 13 together with the sampling time. As a result, time-series voltage data and time-series current data are stored in the memory 13. Note that the sampling may be performed periodically or repeatedly at arbitrary timings.

[0027] Next, the processor 10 corrects at least one of the voltage data and the current data so as to shift the phase between the voltage data and the current data based on the correction data (step 52). As described above, the correction data is composed of the time difference between the voltage and the current corresponding to the phase error. Therefore, the processor 10 corrects the sampling time so that the sampling times of the current data and the voltage data acquired in step 51 are relatively shifted by the amount of the time difference. At this time, the sampling time of the current data may be advanced by the amount of the time difference, or the sampling time of the voltage data may be delayed by the amount of the time difference. Further, both the current data and the voltage data may be corrected so that the sampling times of both data are relatively shifted by the amount of the time difference. When the correction data is composed of other than the time difference between the voltage and the current corresponding to the phase error, the processor calculates the time difference from the correction data, and corrects the sampling time of the current data or the voltage data so as to be relatively shifted by the amount of the time difference.

[0028] Note that step 51 (data acquisition) and step 52 (phase correction) may be performed simultaneously and in parallel. That is, for each sampling, the acquired current data and voltage data may be recorded in the memory 13 together with the sampling time corrected based on the correction data, so that the corrected time-series voltage data and current data are stored in the memory 13.

[0029] Next, the processor 10 obtains the frequency components of the voltage U and the current I based on the corrected voltage data and current data (step 53). More specifically, a DFT or FFT is performed on the corrected time-series voltage data and current data recorded in the memory 13 to calculate the frequency components of the voltage U and the current I of the measurement target 4. Further, from the frequency components of the voltage U and the current I of the measurement target 4, the frequency component of the phase difference θ between the voltage U and the current I of the measurement target 4 is obtained. The range of the frequency components to be obtained can be arbitrarily set, but in the measuring device 1 of the present embodiment, a frequency region of 10 kHz or higher can be included. This is because the phase error caused by the current sensor 2, which becomes significant in the high-frequency region of 10 kHz or higher, is suppressed by the correction in step 52, and highly accurate data can be obtained.

[0030] Next, the processor 10 obtains at least one of the frequency components of the active power P and the reactive power Q based on the frequency components of the voltage and the current (step 54). More specifically, from the frequency components of the voltage U, the current I, and the phase difference θ obtained in step 53, the active power P = UIcosθ and / or the reactive power Q = UIsinθ are calculated for each frequency component to obtain the frequency component of one or both of the active power P and the reactive power Q. Note that the active power P may be obtained by multiplying the real components of the voltage U and the current I. More specifically, when the real components in the FFT calculation results of the waveforms of the voltage U and the current I of the measurement target 4 are Urj and Irj (j = 0 to N / 2, where N is the number of FFT points), respectively, 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 the current I. More specifically, when the imaginary components in the FFT calculation results of the waveforms of the voltage U and the current I of the measurement target 4 are Uij and Iij (j = 0 to N / 2, where N is the number of FFT points), respectively, the frequency component Qj of the reactive power can be obtained from Uij*Iij. Note that the frequency of the obtained active power Pj or reactive power Qj can be obtained by multiplying j by the sampling frequency (= 1 / sampling period).

[0031] Finally, the frequency components of the power of the measurement target 4 obtained (at least one of the active power P and the reactive power Q) are displayed on the display device 12 (step 55). FIG. 4 shows an example of the display of the frequency components of the active power P. On the screen of the display device 12, the frequency is taken on the horizontal axis and the active power P is taken on the vertical axis. The frequency components are divided into five frequency regions 70 to 75, and a bar graph showing the integrated value of the active power P for each region is displayed. In addition to the display of the frequency components of the active power P, a frequency graph of the reactive power Q with the frequency on the horizontal axis and the reactive power Q on the vertical axis, showing the integrated value of the reactive power Q for each frequency region, may be displayed on the screen of the display device 12 as the same or a separate graph as the active power P. Further, instead of the bar graph, the frequency components of the active power P or the reactive power Q may be displayed as a line graph, or instead of or together with the graph, the values of the active power P or the reactive power Q may be displayed. In this way, by displaying the frequency components of the obtained power on the screen of the display device in the form of a graph or numerical values, it becomes possible to grasp at a glance the power situation in each frequency region.

[0032] FIG. 5 is an explanatory diagram showing the effects of the present invention. FIG. 5(a) shows the frequency components of the voltage U, current I, power factor cosθ, and active power P obtained based on the voltage data and current data before correction according to the present invention, and FIG. 5(b) shows the frequency components of the voltage U, current I, power factor cosθ, and active power P obtained based on the data after correction according to the present invention, shown for each frequency region. In each figure, the solid line indicates the measured value of the frequency component based on the voltage data and current data acquired by the processor 10, and the broken line indicates the true value.

[0033] As is apparent from Fig. 5(a), the measured values and true values of the voltage U and current I obtained based on the voltage data and current data before correction agree well regardless of the frequency range. In contrast, the measured values and true values of the power factor cosθ and the active power P do not agree in the high-frequency range. As described above, this is because the error in the magnitude of the current or voltage remains relatively small even in the high-frequency range, while the phase error becomes significant in the high-frequency range. On the other hand, as is apparent from Fig. 5(b), it can be seen that the frequency components of the voltage U, current I, power factor cosθ, and active power P obtained based on the corrected data agree well between the measured values and the true values from the low-frequency range to the high-frequency range. Thus, the measuring apparatus and measuring method according to the present invention make it possible to provide a measuring apparatus and measuring method that accurately measure the frequency components of power in the high-frequency range.

[0034] As described above, the invention made by the inventors of the present application has been specifically described based on the embodiments. However, it goes without saying that the present invention is not limited thereto and can be variously modified without departing from the gist thereof. For example, in the above-described embodiments, the case where the current flowing through the measurement target 4 is single-phase has been described as an example. In the case of polyphase, current sensors 2, probes 3, connectors 16, 21, and ADCs 14, 15 are provided for each phase, and steps 50 to 54 are executed for each phase to obtain the frequency components of the power (at least one of the active power and the reactive power), and the powers of each obtained phase are totaled for each frequency component, whereby the frequency components of the power flowing through the measurement target 4 can be measured.

Description of Reference Numerals

[0035] 1 Measuring apparatus 2 Current sensor 3 Probe 4 Measurement target 10 Processor 11 Input device 12 Display device 13, 20 Memory 14, 15 ADC 16, 21 Connector

Claims

1. A measuring device comprising a processor and connected to a current sensor to measure the frequency components of the power of a measurement target, wherein the processor, acquires correction data for correcting the phase characteristics of the current sensor, acquires time-series voltage data of the measurement target and current data of the measurement target detected by the current sensor, corrects at least one of the voltage data and the current data so as to shift the phases of the voltage data and the current data based on the correction data, obtains frequency components of voltage and current based on the corrected voltage data and current data, obtains and outputs frequency components of at least one of active power and reactive power based on the frequency components of the voltage and the current is configured as follows, measuring device.

2. The measuring device according to claim 1, further comprising a display device for displaying the frequency components of the power.

3. The current sensor is detachably attachable to the measuring device, the processor is configured to acquire the correction data from the current sensor, measuring device according to claim 1.

4. The measuring device according to claim 3, further comprising a connector for detachably attaching the current sensor.

5. The measuring device according to claim 1, wherein the frequency components of the power include a frequency range of 10 kHz or more.

6. A measuring method for measuring the frequency components of the power of a measurement target, comprising: a step in which a processor acquires correction data for correcting the phase characteristics of a current sensor; a step in which the processor acquires time-series voltage data of the measurement target and current data of the measurement target detected by the current sensor; a step in which the processor corrects at least one of the voltage data and the current data so as to shift the phases of the voltage data and the current data based on the correction data; a step in which the processor obtains frequency components of voltage and current based on the corrected voltage data and current data; a step in which the processor obtains and outputs frequency components of at least one of active power and reactive power based on the frequency components of the voltage and the current; A measuring method including.

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