JP2022091420A - Measuring device, measuring method, and power converter - Google Patents

Abstract

To improve accuracy in measuring a frequency of an AC voltage waveform.SOLUTION: A measuring device comprises: a measuring unit 90 for an AC voltage waveform; first detection units 31, 33 that detect first cross time when the AC voltage waveform crosses a first threshold and a first measured value of the AC voltage waveform at the first cross time; second detection units 32, 34 that detect second cross time when the AC voltage waveform crosses a second threshold and a second measured value of the AC voltage waveform at the second cross time; an estimation unit 40 that estimates reference cross time when a measured value of the AC voltage waveform crosses a reference value between the first cross time and the second cross time; and a calculation unit 91 that calculates a frequency of the AC voltage waveform by using a time interval of the reference cross time. The measuring unit 90 has a first analog-digital converter that detects the AC voltage waveform within a first voltage detection range, and a second analog-digital converter that detects the AC voltage waveform within a second voltage detection range.SELECTED DRAWING: Figure 2

Description

The present disclosure relates to a measuring device, a measuring method and a power conversion device.

Conventionally, there is known a frequency measuring device that counts a clock of one cycle of a waveform of a frequency measurement target signal by a counter and obtains a frequency from the count value (see, for example, Patent Document 1).

Japanese Unexamined Patent Publication No. 6-11526

FIG. 1 is a timing chart for explaining an example of a frequency measurement method using a frequency measurement device (hereinafter, referred to as “frequency measurement device 1”) in a comparative mode. The frequency measuring device 1 acquires the measured value ws of the AC voltage waveform wm by sampling the analog AC voltage waveform wm. The measured value ws represents a time-series sample value of the AC voltage waveform wm. The frequency measuring device 1 generates one square wave w0 by comparing the measured value ws with one threshold value (0 in this case). When the frequency of the AC voltage waveform wm is, for example, the rated frequency of 50 Hz, the period of the square wave w0 is expected to be 20 ms (= 1/50). The frequency measuring device 1 measures the frequency fm of the AC voltage waveform wm by detecting the falling or rising edge (zero cross point) of one square wave w0 and measuring the detected falling or rising cycle.

However, in this measurement method, in principle, the detection time of the zero cross point varies at 1/2 width of the sampling cycle of the AC voltage waveform wm (for example, 0.25 ms width when the sampling cycle is 0.5 ms). As a result, the measured frequency fm may vary with respect to the set frequency fs of the AC voltage waveform wm. Further, if at least one of the amplitude and the offset of the AC voltage waveform wm fluctuates, the frequency fm may not be measured appropriately.

The present disclosure provides a measuring device, a measuring method, and a power conversion device having improved measurement accuracy of the frequency of an AC voltage waveform.

In one aspect of the disclosure,
A measuring unit that measures AC voltage waveforms,
A first detection unit that detects a first cross time at which the measured value of the AC voltage waveform crosses the first threshold and a first measured value of the AC voltage waveform at the first cross time.
A second detector that detects a second cross time at which the measured value of the AC voltage waveform crosses a second threshold value lower than the first threshold value and a second measured value of the AC voltage waveform at the second cross time. When,
An estimation unit that estimates a reference cross time in which the measured value of the AC voltage waveform crosses the reference value between the first measurement value and the second measurement value between the first cross time and the second cross time. When,
A calculation unit for calculating the frequency of the AC voltage waveform using the time interval of the reference cross time is provided.
The measuring unit detects the AC voltage waveform in the first voltage detection range and outputs the first digital measurement value, and detects the AC voltage waveform in the second voltage detection range. It has a second analog-digital converter that outputs a second digital measurement.
The first voltage detection range is wider than the second voltage detection range and includes the second voltage detection range.
A measuring device is provided in which the second voltage detection range includes a voltage range corresponding to a numerical range from the first threshold value to the second threshold value.

According to one aspect of the present disclosure, it is possible to improve the measurement accuracy of the frequency of the AC voltage waveform.

It is a timing chart for demonstrating an example of the frequency measurement method by the frequency measuring apparatus in one comparative form. It is a figure which shows the structural example of the frequency measuring apparatus in 1st Embodiment. It is a figure for demonstrating the 1st cross time, the 2nd cross time, a positive measured value and a negative measured value. It is a timing chart which shows an example of the estimation process of zero cross time. It is a timing chart which shows an example of a frequency calculation process. It is a figure which shows an example of the simulation result of the frequency measurement method by the frequency measuring apparatus in one comparative form. It is a figure which shows an example of the simulation result of the frequency measurement method by the frequency measuring apparatus in 1st Embodiment. It is a figure which shows the structural example of the frequency measuring apparatus in 2nd Embodiment. It is a timing chart for demonstrating an example of the frequency measurement method by the frequency measuring apparatus in 2nd Embodiment. It is a figure which shows the structural example of the frequency measuring apparatus in 3rd Embodiment. It is a figure which shows an example of the measured value of the AC voltage waveform when the amplitude is a normal value, and the offset amount is zero. It is a figure which shows an example of the measured value of the AC voltage waveform when the amplitude is lowered to 20% of the normal value, and the offset amount is zero. It is a figure which shows an example of the measured value of the AC voltage waveform when the amplitude is a normal value, and there is an offset amount of 10% of the normal value of an amplitude. It is a figure which shows the structural example of the instantaneous voltage measuring part which measures an AC voltage waveform. It is a figure which illustrates the 1st voltage detection range and the 2nd voltage detection range. It is a figure which shows an example of the waveform of the 2nd digital measurement value which is output from the 2nd ADC in which the AC voltage waveform wm which exceeds the 2nd voltage detection range is input.

Hereinafter, embodiments according to the present disclosure will be described with reference to the drawings. In addition, "greater than or equal to" and "greater than or equal to" may be read interchangeably, and "less than or equal to" and "less than" may be read interchangeably.

FIG. 2 is a diagram showing a configuration example of the frequency measuring device according to the first embodiment. The frequency measuring device 100 shown in FIG. 2 is a device that measures the frequency of the AC voltage waveform wm in the power transmission line 3 of the system 4. The frequency measuring device 100 may be a single device connected to the power transmission line 3, or may be built in a device 2 (for example, a power conditioner (PCS)) connected to the system 4. The PCS is a device including a conversion circuit 5 that converts DC power generated by a solar panel or the like into AC power, and outputs the converted AC power to a power transmission line 3. The conversion circuit 5 may be a circuit that converts DC or AC input power into AC power having an AC voltage waveform wm, or converts AC power having an AC voltage waveform wm into DC or AC output power. It may be a circuit.

The frequency measuring device 100 outputs (provides), for example, the measured frequency of the AC voltage waveform wm by display, communication, or the like, or outputs (provides) to a predetermined control such as power conversion or abnormality detection. In order to improve the function of such an application, it may be required to measure the frequency of the AC voltage waveform wm with high accuracy.

The frequency measuring device 100 includes a frequency measuring circuit 101 that measures the frequency of the AC voltage waveform wm, and is a device that outputs the frequency measured by the frequency measuring circuit 101. The frequency measurement circuit 101 includes a measurement unit 90, a detection unit 30, an estimation unit 40, a calculation unit 91, and a change unit 110.

The frequency measurement circuit 101 includes, for example, a memory and a processor (for example, a CPU (Central Processing Unit)). The configuration of a part or all of the measurement unit 90, the detection unit 30, the estimation unit 40, the calculation unit 91, and the change unit 110 is realized by operating the processor by the program stored in the memory. A part or all of the configuration of the calculation unit 91 and the like may be formed by FPGA (Field Programmable Gate Array).

Hereinafter, each configuration of the frequency measuring device 100 shown in FIG. 2 will be described with reference to FIGS. 3, 4, and 5.

The measuring unit 90 measures the AC voltage waveform wm, and acquires, for example, the measured value ws of the AC voltage waveform wm by sampling the analog AC voltage waveform wm at a constant sampling cycle. The measured value ws represents a time-series sample value of the AC voltage waveform wm. The measuring unit 90, for example, converts an analog AC voltage waveform wm into a digital value by sampling it with an analog-digital converter at a constant sampling cycle, thereby converting the AC voltage waveform wm into a time-series measured value ws (waveform). Data) is acquired.

The measuring unit 90 has, for example, an instantaneous voltage measuring unit 10 and a square wave conversion unit 20.

The instantaneous voltage measuring unit 10 measures the instantaneous voltage (measured value ws in time series) for each sampling of the AC voltage waveform wm by sampling the analog AC voltage waveform wm with an analog-digital converter at a constant sampling cycle. do.

As shown in FIG. 3, the square wave conversion unit 20 generates the first square wave w1 by comparing the magnitude of the measured value ws of the AC voltage waveform wm with the positive threshold value th1, and the measured value of the AC voltage waveform wm. The second square wave w2 is generated by comparing the magnitude of ws and the negative threshold th2. For example, when the measured value wm becomes the positive threshold th1 or more, the square wave conversion unit 20 switches the level of the first square wave w1 to the first level (high level in this example), and the measured value wm is a positive threshold. When it becomes less than th1, the level of the first square wave w1 is switched to the second level (low level in this example). Similarly, when the measured value wm becomes the negative threshold value th2 or more, the square wave conversion unit 20 switches the level of the second square wave w2 to the first level (high level in this example), and the measured value wm becomes negative. When it becomes less than the threshold value th2, the level of the second square wave w2 is switched to the second level (low level in this example). The positive threshold value th1 is an example of a first threshold value set higher than a predetermined reference value R. The negative threshold value th2 is an example of a second threshold value lower than the first threshold value, and is a threshold value set lower than the predetermined reference value R. The reference value R is zero in this example.

The detection unit 30 detects when the measured value ws of the AC voltage waveform wm crosses a predetermined threshold value (cross time) and the measured value ws of the AC voltage waveform wm at the crossing time. The detection unit 30 detects the first cross time at which the measured value of the AC voltage waveform wm crosses the positive threshold th1 and the positive measured value wsp of the AC voltage waveform wm at the first cross time. The first detection unit and the second detection for detecting the second cross time at which the measured value ws of the AC voltage waveform wm crosses the negative threshold th2 and the negative measured value wsn of the AC voltage waveform wm at the second cross time. Has a part. The detection unit 30 has at least one of a first rising detection unit 31 and a first falling detection unit 33 as an example of the first detection unit. The detection unit 30 has at least one of a second rise detection unit 32 and a second fall detection unit 34 as an example of the second detection unit. The positive measured value wsp is an example of the first measured value of the AC voltage waveform at the first cross time. The negative measured value wsn is an example of the second measured value of the AC voltage waveform at the second cross time.

The first rise detection unit 31 detects the first rise time at which the measured value ws of the AC voltage waveform wm becomes the positive threshold th1 or more and the positive measured value ws of the AC voltage waveform wm at the first rise time. .. The first rise time is an example of the first cross time.

The second rise detection unit 32 detects the second rise time at which the measured value ws of the AC voltage waveform wm becomes the negative threshold th2 or more and the negative measured value ws of the AC voltage waveform wm at the second rise time. .. The second rise time is an example of the second cross time.

The first falling detection unit 33 sets the first falling time at which the measured value ws of the AC voltage waveform wm is less than the positive threshold value th1 and the positive measured value ws of the AC voltage waveform wm at the first falling time. Is detected. The first fall time is an example of the first cross time.

The second falling detection unit 34 sets the second falling time at which the measured value ws of the AC voltage waveform wm is less than the negative threshold value th2 and the negative measured value ws of the AC voltage waveform wm at the second falling time. Is detected. The second fall time is an example of the second cross time.

In the estimation unit 40, the measured value ws of the AC voltage waveform wm crosses zero between the positive measured value wsp and the negative measured value wsn between the first cross time and the second cross time t ₀ . To estimate. FIG. 4 shows a case where the measured value ws estimates a _zero crossing time t0 that crosses zero between a positive measured value wsp and a negative measured value wsn between the first fall time and the second fall time. Is illustrated. Zero between the positive and negative measurements wsp is an example of the reference value R between the first and second measurements. The zero cross time t ₀ is an example of the reference cross time when the measured value of the AC voltage waveform crosses the reference value R.

The estimation unit 40 has at least one of a first correction calculation unit 41 and a second correction calculation unit 42. The first correction calculation unit 41 estimates the rising zero crossing time, which is the time when the measured value ws crosses zero between the positive measured value and the negative measured value between the second rising time and the first rising time. This is an example of the first estimation unit. The second correction calculation unit 42 is a standing time when the measured value ws crosses zero between the positive measured value th1 and the negative measured value th2 between the first falling time and the second falling time. This is an example of the second estimation unit that estimates the falling zero cross time. The rising zero cross time is the rising reference cross time when the measured value of the AC voltage waveform crosses the reference value between the first measured value and the second measured value between the second rising time and the first rising time. This is an example. The fall zero cross time is the time when the measured value of the AC voltage waveform crosses the reference value between the first measured value and the second measured value between the first fall time and the second fall time. This is an example of the falling reference cross time.

The calculation unit 91 measures the frequency of the AC voltage waveform wm using the time interval of the _zero cross time t0. The calculation unit 91 has, for example, a period calculation unit 50 and a frequency calculation unit 60.

The cycle calculation unit 50 calculates the cycle of the AC voltage waveform wm using the time interval of the _zero cross time t0. For example, as shown in FIG. 5, one time interval T ₁ sandwiched between two adjacent zero cross times t ₀₁ and t ₀₂ corresponds to one cycle of the AC voltage waveform wm (t ₀₁ <t ₀₂ ). Therefore, the cycle calculation unit 50 calculates one cycle of the AC voltage waveform wm by, for example, measuring one time interval T ₁ sandwiched between two adjacent zero cross times t ₀₁ and t ₀₂ .

As shown in FIG. 5, the sum of the two time intervals T ₁ and T ₂ sandwiched between the three adjacent zero cross times t ₀₁ , t ₀₂ , and t ₀₃ corresponds to two cycles of the AC voltage waveform wm (t). ₀₁ <t ₀₂ <t ₀₃ ). Therefore, for example, the cycle calculation unit 50 divides the total of (n-1) time intervals sandwiched between n adjacent zero cross times t ₀ by (n-1) to obtain an AC voltage waveform wm. One cycle may be calculated. n represents an integer of 2 or more.

The cycle calculation unit 50 has, for example, at least one of a rising cycle calculation unit 51 and a falling cycle calculation unit 52. The rising cycle calculation unit 51 calculates the rising cycle of the AC voltage waveform wm using the time interval of the rising zero cross time estimated by the first correction calculation unit 41. The fall cycle calculation unit 52 calculates the fall cycle of the AC voltage waveform wm using the time interval of the fall zero cross time estimated by the second correction calculation unit 42. FIG. 5 illustrates the calculation of the fall cycle.

The frequency calculation unit 60 calculates the frequency of the AC voltage waveform wm by calculating the reciprocal of the cycle of the AC voltage waveform wm calculated by the cycle calculation unit 50. The frequency calculation unit 60 has, for example, at least one of a rising frequency calculation unit 61 and a falling frequency calculation unit 62.

The rising frequency calculation unit 61 calculates the rising frequency fu of the AC voltage waveform wm by calculating the reciprocal of the rising cycle calculated by the rising cycle calculation unit 51. The fall frequency calculation unit 62 calculates the fall frequency fd of the AC voltage waveform wm by calculating the reciprocal of the fall cycle calculated by the fall cycle calculation unit 52. FIG. 5 illustrates the calculation of the falling frequency fd.

When the cycle (frequency) of the AC voltage waveform wm fluctuates frequently, the AC voltage waveform wm is measured every time the zero cross time t ₀ is detected in that the cycle (frequency) of the AC voltage waveform wm is measured with high accuracy. It is preferable to calculate one cycle and frequency of.

As described above, according to the first embodiment, for example, in the case of FIG. 4, the first fall time and the second fall time are detected by using the positive threshold value th1 and the negative threshold value th2. By using the positive threshold th1 and the negative threshold th2, even if the sampling cycle of the AC voltage waveform wm is not relatively short (even if the sampling frequency is not relatively high), two falling edges with a relatively short time interval are used. The time (first fall time and second fall time) can be detected. Then, the fall zero cross time, which is the time point at which the measured value ws crosses zero between the positive measured value wsp and the negative measured value wsn between the first fall time and the second fall time, is estimated. .. Since the fall zero cross time is estimated from two fall times with relatively short time intervals, the estimation accuracy of the fall zero cross time is improved. Then, since the falling frequency fd of the AC voltage waveform wm is calculated using the time interval of the falling zero cross time estimated in this way, the measurement accuracy of the falling frequency fd is improved. The same can be considered when measuring the rising frequency fu, and the measurement accuracy of the rising frequency fu is improved.

If it is not necessary to measure the rising frequency fu in the first embodiment, the first rising detection detection unit 31, the second rising detection detection unit 32, the first correction calculation unit 41, the rising cycle calculation unit 51, and the rising frequency calculation unit 61 may be omitted. Similarly, in the first embodiment, if the measurement of the falling frequency fd is unnecessary, the first falling detection unit 33, the second falling detection unit 34, the second correction calculation unit 42, and the falling cycle calculation unit 52 And the falling frequency calculation unit 62 may be omitted.

In FIG. 4, the measuring unit 90 is used once or more between the first fall time and the fall zero cross time t ₀ , and once or more between the fall zero cross time t ₀ and the second fall time. , The measured value ws of the AC voltage waveform wm is acquired by sampling the AC voltage waveform wm. As a result, the detection accuracy of the fall zero cross time t ₀ is improved, so that the measurement accuracy of the fall frequency fd is also improved.

Similarly, the measuring unit 90 samples the AC voltage waveform wm at least once between the second rise time and the rise zero cross time and at least once between the rise zero cross time and the first rise time. Acquires the measured value ws of the AC voltage waveform wm. As a result, the detection accuracy of the rising zero cross time is improved, so that the measurement accuracy of the rising frequency fu is also improved.

In this way, the measuring unit 90 samples the AC voltage waveform wm at least once between the first cross time and the zero cross time and at least once between the zero cross time and the second cross time. , It is preferable to acquire the measured value ws of the AC voltage waveform wm. In other words, the measuring unit 90 samples the AC voltage waveform wm at least once between the first cross time and the zero cross time and at least once between the zero cross time and the second cross time. It is preferable to set a positive threshold th1 and a negative threshold th2.

It is preferable that the positive threshold value th1 and the negative threshold value th2 have the same absolute value. As a result, the number of samplings between the first crossing time and the zero crossing time and the number of samplings between the zero crossing time and the second crossing time can be made substantially the same. As a result, the detection accuracy of the zero cross time is improved, so that the measurement accuracy of the frequency of the AC voltage waveform wm is also improved.

In FIG. 4, for example, the first falling detection unit 33 may detect the timing at which the falling edge of the first square wave w1 is detected as the _first falling time t1. For example, the second falling detection unit 34 may detect the timing at which the falling edge of the second square wave w2 is detected as the _second falling time t2.

The first fall detection unit 33 detects the measured value at the _first fall time t1 among the plurality of measured values ws as _a positive measured value v1. The _second falling detection unit 34 detects the measured value at the _second falling time t2 among the plurality of measured values ws as a negative measured value v2.

The second correction calculation unit 42 performs a fall zero cross by performing an interpolation calculation using the first fall time t ₁ , the second fall time t ₂ , the positive measured value v ₁ and the negative measured value v ₂ . Estimate time t ₀ . For example, when the first fall time t ₁ is set to 0, the second correction calculation unit 42 performs an interpolation calculation using the calculation formula “t ₀ = −v ₁ · t ₂ / (v ₂ − v ₁ )”. , It is possible to estimate the falling zero crossing time t ₀ where the measured value ws crosses zero. Similarly, the first correction calculation unit 41 can estimate the rise zero cross time by performing an interpolation calculation using the first rise time, the second rise time, the positive measured value, and the negative measured value.

FIG. 6 is a diagram showing an example of a simulation result of a frequency measurement method (when measuring frequency fm using one threshold value (= 0)) by a frequency measuring device in one comparative mode. FIG. 7 is a diagram showing an example of a simulation result of the frequency fm measured using the threshold values of the above-mentioned frequency measuring method (two positive and negative) by the frequency measuring device in the first embodiment. In the case of FIG. 6, the measured frequency fm deviates from the actual set frequency fs, whereas in the case of FIG. 7, the measured frequency fm is the same as the actual set frequency fs. Was done.

In FIG. 2, the frequency measurement circuit 101 includes a change unit 110. The changing unit 110 changes the first threshold value th1 and the second threshold value th2 according to at least one of the amplitude A and the offset amount B of the AC voltage waveform wm. As a result, even if at least one of the amplitude A and the offset amount B fluctuates due to some factor, the first threshold value th1 and the second threshold value th2 can be adjusted to appropriate values according to the fluctuations, so that alternating current can be obtained. The measurement accuracy of the frequency of the voltage waveform wm is improved.

FIG. 11 is a diagram showing an example of the measured value ws of the AC voltage waveform wm when the amplitude A is a normal value and the offset amount B is zero. The changing unit 110 or the instantaneous voltage measuring unit 10 detects the amplitude A and the offset amount B based on the plurality of measured values ws. The respective detection methods of the amplitude A and the offset amount B may be any known method. The changing unit 110 or the instantaneous voltage measuring unit 10 detects the amplitude A by, for example, detecting the peak values of a plurality of measured values wm. The changing unit 110 or the instantaneous voltage measuring unit 10 detects the offset amount B, for example, by integrating a plurality of measured values wm or applying a low-pass filter.

In the example shown in FIG. 11, when the normal value of the amplitude A and the state without the offset amount B are detected, the change unit 110 sets the first threshold value th1 to the first default value "+0.2". Then, the second threshold value th2 is set to the second default value "-0.2".

FIG. 12 is a diagram showing an example of the measured value ws of the AC voltage waveform wm when the amplitude A drops to 20% of the normal value and the offset amount B is zero. The changing unit 110 changes the difference Δth between the first threshold value th1 and the second threshold value th2 according to the magnitude of the amplitude A. For example, the changing unit 110 decreases the difference Δth as the amplitude A becomes smaller, and increases the difference Δth as the amplitude A increases.

By changing the difference Δth according to the magnitude of the amplitude A, the relative positions (magnitudes) of the first threshold value th1 and the second threshold value th2 with respect to the amplitude A change significantly before and after the amplitude A changes. Can be suppressed. Therefore, even if the amplitude A fluctuates due to some factor, the difference Δth can be adjusted to an appropriate value according to the magnitude of the amplitude A, so that the measurement accuracy of the frequency of the AC voltage waveform wm is improved.

The changing unit 110 may change the difference Δth according to the magnitude of the amplitude A so that the ratio (A / Δth) of the difference Δth to the amplitude A becomes constant. As a result, the relative positions (magnitudes) of the first threshold value th1 and the second threshold value th2 with respect to the amplitude A are substantially maintained before and after the amplitude A changes. Therefore, even if the amplitude A fluctuates due to some factor, the difference Δth can be adjusted to a more appropriate value according to the magnitude of the amplitude A, so that the measurement accuracy of the frequency of the AC voltage waveform wm is further improved.

The changing unit 110 may change the first threshold value th1 and the second threshold value th2 at the same rate of change as the rate of change of the amplitude A, respectively. As a result, the ratio of the difference Δth to the amplitude A becomes constant before and after the change in the amplitude A, so that the measurement accuracy of the frequency of the AC voltage waveform wm is further improved.

FIG. 12 illustrates a state in which the amplitude A is reduced to 20% of the normal value. When this state is detected, the changing unit 110 changes the first threshold value th1 from "+0.2" to "+0.04 (= + 0.2 × 20%)" and sets the second threshold value th2 to "-0. Change from 2 "to" -0.04 (= -0.2 x 20%) ". That is, the changing unit 110 changes the first threshold value th1 and the second threshold value th2 at the same rate of change as the rate of change of the amplitude A, respectively. As a result, the difference Δth is changed from the default value “0.4” to “0.08 (= 0.4 × 20%)”. In FIG. 11, the ratio (A / Δth) of the difference Δth to the amplitude A is 0.4 (= 0.4 / 1.0). On the other hand, also in FIG. 12, the ratio (A / Δth) of the difference Δth to the amplitude A is 0.4 (= 0.08 / 0.2). That is, the difference Δth is changed according to the magnitude of the amplitude A so that the ratio of the difference Δth to the amplitude A becomes constant.

The changing unit 110 may change the first threshold value th1 and the second threshold value th2 after the amount of change in the amplitude A exceeds the first predetermined amount. In other words, the changing unit 110 does not have to change the first threshold value th1 and the second threshold value th2 until the amount of change in the amplitude A exceeds the first predetermined amount. As a result, the change of the first threshold value th1 and the second threshold value th2 can be stopped until the change amount of the amplitude A exceeds the first predetermined amount, so that a dead zone in which the first threshold value th1 and the second threshold value th2 do not change is provided. be able to. As a result, for example, it is possible to suppress a decrease in frequency measurement accuracy due to an excessive change in the first threshold value th1 and the second threshold value th2.

FIG. 13 is a diagram showing an example of the measured value ws of the AC voltage waveform wm when the amplitude A is a normal value and there is an offset amount B of 10% of the normal value of the amplitude A. The changing unit 110 changes the reference value R, the first threshold value th1 and the second threshold value th2, respectively, with the same offset amount as the offset amount B of the AC voltage waveform wm. As a result, the relative positions (magnitudes) of the reference value R, the first threshold value th1 and the second threshold value th2 with respect to the waveform represented by the plurality of measured values wm are substantially maintained before and after the offset amount B changes. To. Therefore, even if the offset amount B fluctuates due to some factor, the reference value R, the first threshold value th1 and the second threshold value th2 can be adjusted to appropriate values according to the magnitude of the offset amount B, and thus the AC voltage. The measurement accuracy of the frequency of the waveform wm is improved.

For example, it is assumed that the offset amount B changes from "zero (FIG. 11)" to "+0.1 (FIG. 13)". When the change unit 110 detects this change, the reference value R is changed from "zero" to "+0.1", the first threshold value th1 is changed from "+0.2" to "+0.3", and the first threshold value is changed. 2 Change the threshold value th2 from "-0.2" to "-0.1".

The changing unit 110 may change the reference value R, the first threshold value th1 and the second threshold value th2, respectively, after the offset amount B of the AC voltage waveform wm exceeds the second predetermined amount. In other words, the changing unit 110 does not have to change the reference value R, the first threshold value th1 and the second threshold value th2 until the offset amount B of the AC voltage waveform wm exceeds the second predetermined amount. As a result, the change of the reference value R, the first threshold value th1 and the second threshold value th2 can be stopped until the offset amount B exceeds the second predetermined amount, so that the reference value R, the first threshold value th1 and the second threshold value th2 can be stopped. Can be provided with a dead zone that does not change. As a result, for example, it is possible to suppress a decrease in frequency measurement accuracy due to an excessive change in the reference value R, the first threshold value th1 and the second threshold value th2.

FIG. 14 is a diagram showing a configuration example of an instantaneous voltage measuring unit that measures an AC voltage waveform. The instantaneous voltage measuring unit 10 shown in FIG. 14 includes a first analog-digital converter 11 (first ADC 11), a second analog-digital converter 12 (second ADC 12), a first protection circuit 13, a second protection circuit 14, and a second. It has a 1-voltage dividing circuit 15 and a 2nd voltage dividing circuit 16.

The first voltage dividing circuit 15 and the second voltage dividing circuit 16 are circuits that divide the analog AC voltage waveform wm by a resistor or the like, respectively, and the analog AC voltage waveform wm having a relatively large amplitude A is relatively small. It is converted into an analog AC voltage waveform wm having an amplitude A and output.

The first protection circuit 13 is a circuit for preventing an analog voltage exceeding the first voltage detection range D1 from being input to the first ADC 11. The first voltage detection range D1 represents a range of analog input voltages that can be detected by the first ADC 11. The first protection circuit 13 uses, for example, the AC voltage waveform wm divided by the first voltage divider circuit 15 between the power supply voltage (positive power supply voltage "+ VCS1" and the negative power supply voltage "-VCC1"" of the first ADC 11. It is a diode clamp circuit that clamps to the potential difference) by a plurality of diodes.

The second protection circuit 14 is a circuit for preventing an analog voltage exceeding the second voltage detection range D2 from being input to the second ADC 12. The second voltage detection range D2 represents the range of analog input voltage that can be detected by the second ADC 12. The second protection circuit 14 uses, for example, the AC voltage waveform wm divided by the second voltage divider circuit 16 between the power supply voltage of the second ADC 12 (positive power supply voltage "+ VCS2" and negative power supply voltage "-VCC2". It is a diode clamp circuit that clamps to the potential difference) by a plurality of diodes.

The negative power supply voltages "-VCC1" and "-VCC2" may be replaced with zero (ground voltage).

The first ADC 11 detects the analog AC voltage waveform wm in the first voltage detection range D1 and outputs the first digital measured value ws1. The second ADC 12 detects the analog AC voltage waveform wm in the second voltage detection range D2 and outputs the second digital measured value ws2. The first digital measured value ws1 and the second digital measured value ws2 are both examples of the above-mentioned measured value ws which are digital values.

FIG. 15 is a diagram illustrating a first voltage detection range and a second voltage detection range. The first voltage detection range D1 is wider than the second voltage detection range D2 and includes the second voltage detection range D2. As a result, the first ADC 11 can detect the AC voltage waveform wm in a wider range than the second ADC 12.

However, at least one of the amplitude A and the offset B of the AC voltage waveform wm may fluctuate due to some factor.

For example, in FIG. 11, due to fluctuations in at least one of the amplitude A and the offset B, the maximum value or the minimum value of the first digital measurement value ws1 output from the first ADC 11 is between the first threshold value th1 and the second threshold value th2. There may be a transition from the outside to the inside of the numerical range Ed1. In this case, since the first digitally measured value ws1 does not cross the first threshold value th or the second threshold value th, the frequency of the AC voltage waveform wm cannot be measured by using the first digitally measured value ws1.

To prevent this, as shown in FIG. 15, the second ADC 12 measures the AC voltage waveform wm in the second voltage detection range D2 including the voltage range Ea. The voltage range Ea is an analog voltage range corresponding to the numerical range Ed2 (see FIG. 12) between the first threshold th1 and the second threshold th2. The numerical range Ed2 is narrower than the numerical range Ed1. Since the second voltage detection range D2 includes the analog voltage range Ea, the maximum value and the minimum value of the second digital measurement value ws2 output from the second ADC 12 are in the numerical range Ed2 even if they transition to the inside of the numerical range Ed1. If it does not transition to the inside of, the first threshold th1 and the second threshold th2 are crossed. Therefore, by using the second digital measured value ws2, it is possible to measure the frequency of the AC voltage waveform wm.

As described above, the presence or absence of the above-mentioned change unit 110 by including the voltage range Ea corresponding to the numerical range Ed2 between the first threshold value th1 and the second threshold value th2 in the second voltage detection range D2 of the second ADC 12. Regardless of this, the measurement accuracy of the frequency of the AC voltage waveform wm can be improved.

Since the second voltage detection range D2 is narrower than the first voltage detection range D1, the voltage range targeted by the second ADC 12 is narrower than the voltage range targeted by the first ADC 11. Therefore, even if the resolution of the second ADC 12 is equal to or lower than the resolution of the first ADC 11, the voltage detection accuracy of the second ADC 12 can be ensured. Resolution is expressed in number of bits. By adopting the second ADC 12 whose resolution is lower than that of the first ADC 11, for example, the circuit scale of the second ADC 12 can be reduced while ensuring the voltage detection accuracy of the second ADC 12.

The second voltage detection range D2 is (1 / N) times the first voltage detection range D1 (N is a number larger than 1), and the number of bits obtained by subtracting the resolution of the second ADC 12 from the resolution of the first ADC 11 is defined as X. .. At this time, if X is a value rounded down to the nearest whole number of -log ₂ (1 / N), the circuit scale of the second ADC 12 can be reduced while ensuring the voltage detection accuracy of the second ADC 12.

For example, in FIG. 15, it is assumed that the second voltage detection range D2 is (1/4) times the first voltage detection range D1 (N = 4). In this case, since "-log ₂ (1/4) = 2.43", the number of bits X that can be lowered as the resolution of the second ADC 12 is determined in order to secure the voltage detection accuracy and reduce the circuit scale at the same time. It becomes 2. In the case of X = 2, assuming that the resolution of the first ADC 11 is, for example, 12 bits, the resolution of the second ADC 12 may be 10 bits or more.

In FIG. 14, the instantaneous voltage measuring unit 10 may switch whether the digital measured value used for measuring the frequency fm of the AC voltage waveform wm is the first digital measured value ws1 or the second digital measured value ws2. .. Thereby, for example, even if an abnormality occurs in either of the first ADC 11 and the second ADC 12, the frequency fm can be measured by using the ADC in which the abnormality has not occurred.

Even if the instantaneous voltage measuring unit 10 uses the first digital measured value ws1 for detecting the amplitude A of the AC voltage waveform wm and the second digital measured value ws2 for measuring the frequency fm of the AC voltage waveform wm. good. As a result, the frequency measuring device 100 can not only measure the frequency fm but also detect the amplitude A. At this time, even if the first voltage detection range D1 is set to a range equal to or higher than the amplitude rated value of the AC voltage waveform wm, and the second voltage detection range D2 is set to a range less than the amplitude rated value of the AC voltage waveform wm. good. At this time, when there are voltage dividing circuits 15 and 16 as shown in FIG. 14, the first voltage detection range D1 and the second voltage detection range D2 are defined by the amplitude rated value of the AC voltage waveform wm after voltage division. For example, in FIG. 15, the first voltage detection range D1 may be set in the range of ± 120% of the amplitude rated value, and the second voltage detection range D2 may be set in the range of ± 30% of the amplitude rated value. In this case, the second voltage detection range D2 corresponds to (1/4) times the first voltage detection range D1.

FIG. 16 is a diagram showing an example of a waveform of a second digital measured value ws2 output from a second ADC 12 in which an AC voltage waveform wm exceeding the second voltage detection range D2 is input. When the second voltage detection range D2 is set to a range smaller than the amplitude rated value of the AC voltage waveform wm, the waveform of the second digitally measured value ws2 becomes close to a trapezoidal wave as shown in FIG. However, even in such a waveform, the frequency fm can be measured by the second digital measured value ws2 crossing the first threshold value th1 and the second threshold value th2.

The instantaneous voltage measuring unit 10 switches whether the digital measured value used for measuring the frequency fm is the first digital measured value ws1 or the second digital measured value ws2 according to the amplitude A of the AC voltage waveform wm. May be. In this case, the amplitude A is an amplitude detected value detected based on a plurality of first digital measured values ws1 output from the first ADC 11, but is acquired by another means such as an external device of the frequency measuring device 100. It may be a value.

For example, in FIG. 15, when the amplitude A is outside the second voltage detection range D2, the instantaneous voltage measurement unit 10 uses the first digital measurement value ws1 for measuring the frequency fm, and the amplitude A is the second voltage detection range. When inside D2, the second digital measurement value ws2 may be used to measure the frequency fm. Thereby, the digital measured value of the first digital measured value ws1 and the second digital measured value ws2, whichever is appropriate for the measurement of the frequency fm, can be used according to the fluctuation of the amplitude A.

For example, the detection unit 30 (see FIG. 2) has a time at which the first digitally measured value ws1 crosses the first threshold value th1 and the second threshold value th2 that define the numerical range Ed1 shown in FIG. The first digital measured value ws1 can be detected. On the other hand, the detection unit 30 has a time at which the second digital measurement value ws2 crosses the first threshold value th1 and the second threshold value th2 that define the numerical range Ed2 shown in FIG. 12, and the second digital measurement value at each time. It can detect ws2.

In response to the request signal from the external device of the frequency measuring device 100, the instantaneous voltage measuring unit 10 sets the digital measured value used for measuring the frequency fm as the first digital measured value ws1 or the second digital measured value ws2. You may switch whether to do it. This makes it possible to measure the frequency fm by using the ADC required by the external device.

For example, in FIG. 15, when the amplitude A of the AC voltage waveform wm transitions from the outside to the inside of the second voltage detection range D2, the instantaneous voltage measuring unit 10 sets the digital measurement value used for detecting the amplitude A to the first digital. The measured value ws1 may be switched to the second digital measured value ws2. As a result, even if the first digital measurement value ws1 cannot be used for detecting the amplitude A due to the transition of the amplitude A from the outside to the inside of the second voltage detection range D2, the second digital measurement value is used for detecting the amplitude A. It becomes possible to use ws2. For example, in FIG. 11, when the instantaneous voltage measuring unit 10 detects that the first digital measured value ws1 has transitioned from the outside to the inside of the numerical range Ed1, the amplitude A has transitioned from the outside to the inside of the second voltage detection range D2. It is determined that it has been done.

For example, in FIG. 15, when the amplitude A of the AC voltage waveform wm transitions from the inside to the outside of the second voltage detection range D2, the instantaneous voltage measuring unit 10 sets the digital measurement value used for detecting the amplitude A to the second digital. The measured value ws2 may be switched to the first digital measured value ws1. As a result, even if the second digital measurement value ws2 cannot be used for detecting the amplitude A due to the transition of the amplitude A from the inside to the outside of the second voltage detection range D2, the first digital measurement value is used for detecting the amplitude A. It becomes possible to use ws1. For example, in FIG. 12, when the instantaneous voltage measuring unit 10 detects that the second digital measured value ws2 has transitioned from the inside to the outside of the numerical range Ed2, the amplitude A has transitioned from the inside to the outside of the second voltage detection range D2. It is determined that it has been done.

FIG. 8 is a diagram showing a configuration example of the frequency measuring device according to the second embodiment. FIG. 9 is a timing chart for explaining an example of the frequency measurement method by the frequency measuring device in the second embodiment. In the second embodiment, the description of the same configuration as that of the first embodiment will be omitted by referring to the above description. The frequency measuring device 200 shown in FIG. 8 includes an average frequency measuring circuit 201, and the average frequency measuring circuit 201 includes a frequency measuring circuit 101 (FIG. 2) and an averaging circuit 70.

The calculation unit 91 in the frequency measurement circuit 101 has an averaging circuit 70 that calculates the frequency of the AC voltage waveform vm by averaging the falling frequency fd and the rising frequency fd. The averaging circuit 70 calculates the sum of the falling frequency fd and the rising frequency fd by the adder 71, and divides the sum by 2 by the divider 72 to average the falling frequency fd and the rising frequency fd. Calculate the value (average frequency of AC voltage waveform vm).

By calculating the frequency of the AC voltage waveform vm in this way, the accuracy of the frequency value by averaging is improved. In addition, since the rising zero cross time and the falling zero cross time are reflected in the calculation of the frequency of the AC voltage waveform vm at the timing shifted by half a cycle (see FIG. 9), the frequency measurement accuracy is improved and the measurement is performed. The time response speed is improved.

FIG. 10 is a diagram showing a configuration example of the frequency measuring device according to the third embodiment. In the third embodiment, the description of the same configuration as that of the first embodiment or the second embodiment will be omitted by referring to the above description. The frequency measuring device 300 shown in FIG. 10 includes an average frequency measuring circuit 301. The average frequency measurement circuit 301 detects the average frequency of the three-phase AC voltage waveform Vm. The average frequency measurement circuit 301 includes a plurality of frequency measurement circuits 101a, 101b, 101c having the same circuit configuration as the frequency measurement circuit 101 (FIG. 2), and an averaging circuit 80.

The measurement unit 90 in the frequency measurement circuit 101a measures the phase voltage (A phase voltage) of the AC voltage waveform wm of the A phase in the transmission line 3, and the estimation unit 40 in the frequency measurement circuit 101a is a zero cross of the A phase voltage. Estimate the time. The calculation unit 91 in the frequency measurement circuit 101a calculates the frequency of the A-phase voltage using the time interval of the zero-cross time of the A-phase voltage. Similarly, the frequency measurement circuit 101b calculates the frequency of the B-phase voltage, and the frequency measurement circuit 101c calculates the frequency of the C-phase voltage. The average frequency measurement circuit 301 includes an averaging circuit 80 as a calculation unit that calculates the frequency (three-phase average frequency) of the AC voltage waveform Vm by averaging the frequencies of the phase voltages of a plurality of phases. The averaging circuit 80 calculates the sum of the frequencies of the A-phase voltage, the B-phase voltage, and the C-phase voltage by the adder 81, and divides the sum by 3 by the divider 82 to obtain the three-phase average frequency. calculate. As a result, the accuracy of the frequency value by averaging is improved, and the zero cross time of each phase voltage is reflected in the frequency calculation at the timing shifted by one-third cycle, so that the temporal response speed of the measurement is increased. improves.

Alternatively, the measuring unit 90 in the frequency measuring circuit 101a measures the AB line voltage (AB phase voltage of the AC waveform) between the A-phase power transmission line 3 and the B-phase power transmission line 3, and the frequency measuring circuit 101a. The estimation unit 40 in the estimation unit estimates the zero cross time of the AB line voltage. The calculation unit 91 in the frequency measurement circuit 101a calculates the frequency of the AB line voltage using the time interval of the zero cross time of the AB line voltage. Similarly, the frequency measurement circuit 101b calculates the frequency of the BC line voltage, and the frequency measurement circuit 101c calculates the frequency of the CA line voltage. The average frequency measurement circuit 301 includes an averaging circuit 80 as a calculation unit that calculates the frequency (three-phase average frequency) of the AC voltage waveform Vm by averaging the frequencies of the three line voltages. The averaging circuit 80 calculates the sum of the frequencies of the AB line voltage, the BC line voltage, and the CA line voltage by the adder 81, and divides the sum by 3 by the divider 82 to obtain three phases. Calculate the average frequency. As a result, the accuracy of the frequency value by averaging is improved, and the zero cross time of each line voltage is reflected in the frequency calculation at the timing shifted by one-third cycle, so that the time response speed of the measurement is increased. improves.

The average frequency measurement circuit 301 may include a plurality of average frequency measurement circuits 201a, 201b, 201c having the same circuit configuration as the average frequency measurement circuit 201 (FIG. 8), and an averaging circuit 80.

Although the measuring device, the measuring method, and the power conversion device have been described above by the embodiment, the present invention is not limited to the above embodiment. Various modifications and improvements, such as combinations and substitutions with some or all of the other embodiments, are possible within the scope of the present invention.

For example, the reference value between the first and second measurements (in other words, the reference value between the first and second thresholds) is not limited to zero and can be positive or negative. good. Further, both the first threshold value and the second threshold value may be positive values or negative values.

Further, the measuring device is not limited to a dedicated device for measuring a frequency, and may be a device having a function of measuring a frequency. Examples of the measuring device having a frequency measuring function include a power meter, a smart meter, and a PMU (Phasor Measurement Unit). Further, the measuring device having a frequency measuring function may be provided in a grid interconnection device such as a grid interconnection protection relay (protection relay).

The power conversion device provided with the measuring device is not limited to the PCS that uses sunlight, a storage battery, a fuel cell, or the like. Power converters equipped with measuring devices include EV chargers, UPS (rectifier side connected to the grid or inverter side connected to the load), rectifiers, general-purpose inverters (inverter for driving motors, etc.), and self-excited type. Alternatively, a separately-excited SVC (Static Var Compensator), a self-excited STATCOM (Static Synchron Compensator), a frequency converter (a device that mutually converts 50Hz and 60Hz), etc. be.

For example, the PCS uses the measured frequency for output control such as a system protection function (frequency decrease relay, frequency increase relay, independent operation detection) specified in the system interconnection regulation, a frequency-Watt function of a smart inverter, and the like. For example, if the UPS has a function of regenerating power to the system on the rectifier side, the measured frequency is used to control the power regeneration, and in the case of a parallel drive type with the system voltage on the inverter side, it is measured. The frequency is used for synchronous input control for inverter output in the event of a system side power failure. The rectifier and the general-purpose inverter use the measured frequency to control the power regeneration, for example, when the system has a function of regenerating the power. The SVC and STATCOM use, for example, the measured frequency for system protection functions (frequency drop relay, frequency rise relay, isolated operation detection) in the grid interconnection regulations. The frequency converter uses, for example, the measured frequency for output control of a basic device. The grid interconnection protection relay uses, for example, the measured frequency for the grid protection function (frequency drop relay, frequency rise relay, independent operation detection) specified in the grid interconnection regulation. Power meters, smart meters and PMUs monitor, for example, the measured frequency.

The voltage value measured by the first ADC whose voltage detection range is set to a range larger than the rated voltage is, for example, for controlling the device (voltage amplitude detection, effective value detection, instantaneous value detection, etc.) and for device protection (for device protection (voltage amplitude detection, effective value detection, instantaneous value detection, etc.). For system protection (ground fault overvoltage relay, overvoltage relay, undervoltage relay, etc.), for weighing, measurement or monitoring (power meter, smart meter, etc.) If) used for.

2 Equipment 3 Transmission line 4 system 5 Conversion circuit 10 Instantaneous voltage measuring unit 11 1st analog-digital converter 12 2nd analog-digital converter 13 1st protection circuit 14 2nd protection circuit 15 1st voltage divider circuit 16 2nd Voltage divider circuit 20 Square wave conversion unit 30 Detection unit 31 First rise detection unit 32 Second rise detection unit 33 First fall detection unit 34 Second fall detection unit 40 Estimating unit 50 Period calculation unit 60 Frequency calculation unit 70, 80 Averager circuit 71,81 Adder 72,82 Divider 90 Measuring unit 91 Computing unit 100, 200, 300 Frequency measuring device 101, 101a, 101b, 101c Frequency measuring circuit 110 Change unit 201, 201a, 201b, 201c, 301 Average frequency measurement circuit A A amplitude B Offset amount

Claims (12)

A measuring unit that measures AC voltage waveforms,
A first detection unit that detects a first cross time at which the measured value of the AC voltage waveform crosses the first threshold and a first measured value of the AC voltage waveform at the first cross time.
A second detector that detects a second cross time at which the measured value of the AC voltage waveform crosses a second threshold value lower than the first threshold value and a second measured value of the AC voltage waveform at the second cross time. When,
An estimation unit that estimates a reference cross time in which the measured value of the AC voltage waveform crosses the reference value between the first measurement value and the second measurement value between the first cross time and the second cross time. When,
A calculation unit for calculating the frequency of the AC voltage waveform using the time interval of the reference cross time is provided.
The measuring unit detects the AC voltage waveform in the first voltage detection range and outputs the first digital measurement value, and detects the AC voltage waveform in the second voltage detection range. It has a second analog-digital converter that outputs a second digital measurement.
The first voltage detection range is wider than the second voltage detection range and includes the second voltage detection range.
The second voltage detection range is a range including a voltage range corresponding to a numerical range from the first threshold value to the second threshold value. The measuring device according to claim 1, wherein the resolution of the second analog-to-digital converter is equal to or lower than the resolution of the first analog-digital converter. The measuring device according to claim 2, wherein the resolution of the second analog-to-digital converter is lower than the resolution of the first analog-to-digital converter. The second voltage detection range is (1 / N) times the first voltage detection range (N is a number larger than 1), and the second analog-to-digital conversion is performed from the resolution of the first analog-digital converter. Assuming that the number of bits obtained by subtracting the resolution of the device is X,
X is the value rounded down to the nearest whole number of -log ₂ (1 / N).
The measuring device according to claim 3. The method according to any one of claims 1 to 4, wherein the measuring unit switches whether the digital measured value used for measuring the frequency is the first digital measured value or the second digital measured value. Measuring device. The measuring unit
The first digital measurement is used to detect the amplitude of the AC voltage waveform.
The second digital measurement is used to measure the frequency.
The measuring device according to any one of claims 1 to 5. The measuring unit switches between the first digital measured value and the second digital measured value as the digital measured value used for measuring the frequency according to the amplitude of the AC voltage waveform. The measuring device according to 6. When the amplitude of the AC voltage waveform is outside the second voltage detection range, the measuring unit uses the first digital measurement value for measuring the frequency, and the amplitude of the AC voltage waveform is the second voltage. The measuring device according to claim 7, wherein the second digital measured value is used for measuring the frequency when it is inside the detection range. The measuring unit switches whether the digital measured value used for measuring the frequency is the first digital measured value or the second digital measured value in response to a request signal from an external device of the measuring device. , The measuring device according to any one of claims 1 to 6. The measuring unit
When the amplitude of the AC voltage waveform transitions from the outside to the inside of the second voltage detection range, the digital measurement value used for detecting the amplitude of the AC voltage waveform is measured from the first digital measurement value to the second digital measurement. Switch to value,
When the amplitude of the AC voltage waveform transitions from the inside to the outside of the second voltage detection range, the digital measurement value used for detecting the amplitude of the AC voltage waveform is measured from the second digital measurement value to the first digital measurement. The measuring device according to any one of claims 1 to 9, which switches to a value. The measuring device according to any one of claims 1 to 10 and a conversion circuit are provided.
The conversion circuit is a power conversion device that converts input power into AC power having the AC voltage waveform, or converts AC power having the AC voltage waveform into output power. It is a measurement method performed by a measuring device.
The AC voltage waveform is measured by the measuring unit,
The first cross time at which the measured value of the AC voltage waveform crosses the first threshold value and the first measured value of the AC voltage waveform at the first cross time are detected.
The second cross time at which the measured value of the AC voltage waveform crosses the second threshold value lower than the first threshold value and the second measured value of the AC voltage waveform at the second cross time are detected.
The reference cross time at which the measured value of the AC voltage waveform crosses the reference value between the first measured value and the second measured value between the first cross time and the second cross time is estimated.
Using the time interval of the reference cross time, the frequency of the AC voltage waveform is calculated.
The measuring unit detects the AC voltage waveform in the first voltage detection range and outputs the first digital measurement value, and detects the AC voltage waveform in the second voltage detection range. It has a second analog-digital converter that outputs a second digital measurement.
The first voltage detection range is wider than the second voltage detection range and includes the second voltage detection range.
The measurement method, wherein the second voltage detection range includes a voltage range corresponding to a numerical range from the first threshold value to the second threshold value.

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