JPH0638084B2 - Distorted wave AC characteristics measuring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an effective value voltage of a distorted wave alternating current containing a harmonic component,
The present invention relates to a digital arithmetic measurement device that measures RMS current, power, and power factor with high accuracy.

[Prior art]

In recent years, in a light controller used for dimming in a drawing room at home or an electric heater used in a kitchen, a thyristor element is used for power control, and a part of the AC waveform is cut to change the conduction angle. The power is adjusted by controlling the power.

When the power is adjusted by using the thyristor as a switching element, the current is remarkably distorted, that is, a so-called distorted wave alternating current, which is generated by cutting a part of each steady waveform.

RMS voltage of such distorted wave AC, which is remarkably distorted,
When measuring the rms value current, the method of calculating each rms value of the distorted wave alternating current from the change in the electrical resistance due to the temperature change of the platinum wire by converting it to the amount of heat using a resistance change element such as a platinum wire It is customary. In addition, a method of using a Hall element to obtain the electric power value of the distorted wave AC by an analog amount is used.

However, neither method is sufficient for obtaining highly accurate measurement results. Moreover, there has been a problem that it is not possible to sufficiently cope with the digitization of data, the incorporation into an automatic control system, the centralized management of electric power, the long-distance data transmission, etc., which have been rapidly required in recent years.

[Object of the Invention]

The present invention has been made in view of the above problems, particularly significant distortion, for example, the effective value voltage of the distorted wave AC such that a part of the waveform is cut, the effective value current, the active power,
It is an object of the present invention to provide a characteristic measuring instrument capable of measuring a characteristic value of a distorted wave AC such as a power factor with high accuracy by a simple operation.

[Structure of Invention]

In order to achieve the above object, the configuration of the characteristic measuring apparatus of the digital arithmetic type of the present invention is such that a synchronizing signal generation for generating a synchronizing signal synchronized with the fundamental wave component of a distorted wave AC including a fundamental wave component and a harmonic wave component. A circuit, a means for determining whether or not a sync signal is obtained, a sampling time setting means for setting a sampling time corresponding to an integral multiple of the cycle of the sync signal, and a sampling frequency setting means for setting a preset sampling frequency. A sampling means for sampling the instantaneous value of the distorted wave alternating current at a time interval shorter than the fundamental wave period; an A / D conversion circuit for converting the output of the sampling means into a digital signal and outputting the digital signal; And a calculating means for calculating the characteristic value of the distorted wave alternating current based on the Until the sampling time, it was sampled by the sampling means,
When it is determined that the synchronization signal cannot be obtained, the sampling means performs sampling until the number of times of sampling is reached.

The characteristic value of the distorted wave alternating current of the present invention, the effective voltage,
It refers to the effective value current, power and power factor, and in carrying out the present invention, a desired characteristic value is appropriately selected from among them and implemented.

The calculation of the characteristic value of the present invention is (1) the effective value of the voltage (2) Effective value of current (3) Active power (4) Apparent power is P ₂ = V · I (VA) (5) Reactive power is (6) Power factor (However, P ₂ is the apparent power).

Here, v ₁ and v _{2 to} v _N are the respective data values of the voltage data 20a, i _{1 to} i _N are the respective data values of the current data 20b, N is the number of the respective data of the voltage data 20a and the current data 20b, According to the quantization theory, in the case of a sine wave waveform, the number of samples per cycle is three.

For example, if the fundamental wave is 50 Hz and the harmonics up to 2 kHz are the measurement target, the cycle of 2 kHz is 500 μsec, and according to the quantization theory, the minimum number of samples per cycle of 2 kHz is 3, so the sampling interval Is 167 (50
0 μ sec ÷ 3) μ sec, and the number of samples is 120 (3 when the sampling time is one week of the fundamental wave).
Number of pieces x 2000Hz ÷ 50Hz). A sampling interval of about 100 μsec is set for an ordinary distorted waveform, which is practically sufficient. That is, the preset harmonic in the constituent elements of the present invention refers to 2 kHz in the above example.

By setting the sampling time, that is, a value that is an integral multiple of the fundamental wave period, so that a range of about 3 to 10 can be selected, the measurement error is further reduced.

Depending on the distorted waveform, the sync signal may not be obtained. At this time, it is not preferable for practical use that measurement becomes impossible. Therefore, in the program of the device of the present invention, when the synchronization signal cannot be obtained, the sampling time is set to 10 times the fundamental wave period (200 msec at 50 cycles), and the sampling number is 2000 (200 msec ÷ 0.1 mse).
The characteristic value should be calculated as c). In this case, it takes some time for measurement and calculation.

That is, the sampling number when the asynchronous signal in the constituent elements of the present invention is not obtained is, in the above example, a sampling cycle of 100 μsec and a sampling number of 20.
Indicates 00. Even if the synchronization signal cannot be obtained, it is generally possible to predict and confirm the basic frequency in advance, and therefore it is possible to preset the harmonics that determine the frequency of the sampling pulse.

〔Example〕

Hereinafter, the present invention will be described in detail with reference to an embodiment with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG. 2 is a waveform diagram of the distorted wave AC measured in FIG.

In FIG. 1, reference numeral 1 denotes a converter, which includes a pair of voltage-voltage converters (hereinafter abbreviated as PT) 2a and 2b and a pair of current-voltage converters (hereinafter abbreviated as CT) 3a and 3b, respectively. The corresponding input voltage or input current is converted into a voltage of a predetermined magnification and output. In the embodiment shown in FIG. 1, a single-phase three-wire type AC 100V having an A phase and a B phase is used as a power source to be measured of a distorted wave AC. That is, the power supply voltage on the A phase side is supplied to PT2a and the power supply current is supplied to CT3a, and the power supply voltage on the B phase side is supplied to PT2b and the power supply current is C.
It is given to T3b respectively.

Reference numerals 4a, 4b, 4c and 4d denote attenuators (hereinafter abbreviated as ATT), which attenuate the input voltage from the converter 1 according to the attenuation rate (input range switching signal) designated by the input range switching switch 5. The outputs of the attenuators 4a and 4c are given to the analog switch 6a, and the outputs of the attenuators 4b and 4d are given to the analog switch 6b. Each analog switch 6
Among the input signals on the A-phase side and the B-phase side, a and 6b output the signal of one of the designated phases based on the switching signal of the microprocessor 8.

Reference numeral 10 is a synchronizing signal generating circuit, which is provided with the output of the attenuator 4a, that is, the voltage signal on the A phase side as shown in FIG. 2 (X), and is synchronized with the cycle of the fundamental wave component of the power source to be measured. The sync signal 11 is output.

The operation of the synchronizing signal generating circuit 10 will be described in detail with reference to FIG. 2. As shown in FIG. 2 (X), the first threshold value, V _H, and the second threshold value lower than the first threshold value V _H are used. Threshold and V _L
A Schmitt type comparator circuit in which is set is built in, and as shown in FIG. 2 (Y), from when the value of the voltage signal exceeds the first threshold value V _H until it reaches the second threshold value V _L. The comparator circuit described above is turned on, and conversely, the comparator circuit is turned off from the second threshold value V _L until the next first threshold value V _H is reached. By repeating such operations, for example, the voltage signal, that is, the synchronization signal 11 synchronized with the cycle of the fundamental wave component of the power source to be measured is output from the rising time interval of the synchronization signal. The synchronization signal 11 may be output based on the current signal on the A phase side as shown in FIG. 2 (Z). In this case, the output of the attenuator 4b may be given to the synchronizing signal generating circuit 10.

Reference numeral 12 denotes a cycle setting circuit, which sets a sampling time To corresponding to an integral multiple of the cycle of the synchronizing signal 11, for example, double as shown in FIG. That is, when a pulse 14 having a predetermined period output from a counter timer controller (hereinafter abbreviated as CTC) 13 incorporated in the microprocessor 8 is input, for example, a pulse interval of 100 μsec, the cycle setting circuit is pulsed only for the sampling time To. 14 is output as a conversion command signal 16 to the A / D converters 15a and 15b. This pulse 14
The pulse width is usually about 2 to 4 μsec.

When each of the A / D converters 15a and 15b receives the conversion command signal 16, it starts A / D conversion, and immediately before that, the hold signals 17a and 17b (hereinafter, EOC1 and
EOC2) is output to the corresponding sample hold circuits 18a and 18b. In addition, this EOC
1 and EOC2 continue to be output until the A / D conversion is completed.

When the hold signals 17a and 17b are input, the sample and hold circuits 18a and 18b convert the instantaneous values (analog values) of the corresponding voltage and current signals into the A / D converter 15 respectively.
a and 15b, and the A / D converters 15a and 15b convert the corresponding 12-bit parallel digital signals. When the conversion is completed, the EOC1 and EOC2 are respectively set to the voltage LOW level and sent to the microprocessor (hereinafter abbreviated as processor) 8 as voltage data 20a and current data 20b, respectively. EOC1, EOC2
Is output to the processor 8 via the OR gate of 21a, so that both 15a and 15b become the voltage LOW level only when the conversion is completed, and the output signal of 21 is used as an interrupt signal.

The interrupt signal 21 is output to the processor 8 to store the above-mentioned digitized voltage data 20a and current data 20b in the memory incorporated in the processor 8. The processor 8 has a function IC 22 and a CP for controlling this function IC.
It has a built-in calculation means formed of U or the like, and calculates a desired characteristic value according to a calculation routine under the program control of the CPU.

When the above calculation in the processor 8 is completed, the calculation result is transferred to the display control CPU 23 and the binary number is set to 1
After being converted into a decimal number, the display data 25 is displayed on the display unit 25.
Output to. The display unit 25 calculates results based on the display data 24. In this embodiment, the effective values of voltage and current, active power,
Displays the power factor in decimal. Further, the processor 8 monitors each data of the voltage data 20a and the current data 20b, and when detecting that the data is incorrect, it outputs an error signal 27 and displays an error display on the data error display unit 28. Order. 29 is a measurement mode switch,
The measurement mode of A-phase, B-phase or A-phase + B-phase of the power source to be measured shown in FIG. 1 is set.

FIG. 3 is a flowchart showing the main program of the CPU incorporated in the processor 8, and FIG. 4 is a flowchart showing the data sampling control.

The operation of the present invention will be described with reference to FIGS. 3 and 4.

Whether power is turned on in step S1 as shown in FIG.
Alternatively, when the reset switch is operated in step S2, the process proceeds to step S3, and the functions IC22, CTC13, etc. are initialized. In step S4, the measurement mode switch 29
Determine the preset measurement mode according to the operation. In step S5, the presence / absence of the synchronization signal 11 is discriminated to determine whether the sampling method is synchronous or asynchronous. That is, when the synchronization signal 11 is obtained, step S
6, the processing proceeds to S7, and the sampling by the synchronous method is executed. On the contrary, when the synchronization signal 11 cannot be obtained, the processing proceeds to step S8 and the sampling by the asynchronous method is executed.

Next, the synchronous and asynchronous sampling will be described in detail with reference to FIG. 4 showing the case where the measurement mode is set to the A phase + B phase.

First, in step S5, when it is determined that the synchronization signal 11 is obtained, the process proceeds to step S6, and the number of cycle settings of the cycle setting DIP switch built in the cycle setting circuit 12 is read. That is, it is read that the set cycle number is 2, for example, as shown in FIG. Of course, this cycle setting DIP switch is 2
It can be set to an appropriate integer other than, for example, 3 to 10, and the sampling time To is determined by the value of the set cycle number and the cycle of the synchronization signal 11. In the above example, the sampling time To is set as follows. That is, if the power supply frequency of the power supply to be measured is 50 Hz, In step T1, the CTC 13 is driven to drive the predetermined pulse 1
4 is generated.

At step T2, at the same time as the reading of the synchronizing signal 11, the pulse 14 having a pulse interval of 100 μsec is outputted to the cycle setting circuit 12 at step T3. In step T4, the analog switches 6a and 6b are instructed to switch the power source to be measured to the A phase side. In step T5, analog voltage of phase A, sampling by holding current, and A
Although / D conversion is performed, no program is actually required.

That is, at this time, when the pulse 14 is output from the CTC as described in FIG. 1, each A / D converter 15a, 15
From b, corresponding sample hold circuits 18a and 18b
Hold signals (EOC1, EOC2) 17a, 17b
Is output, the analog values of the input voltage and current are sampled and then converted into digital data. When the digital conversion is completed, a conversion end signal, that is, an interrupt signal (EOC) 21 is given from the A / D converters 15a and 15b to the processor 8 at step T6, and the voltage data on the A phase side digitally converted at step T7. 20a
And the current data 20b are stored in the memory. Step T
At 8, the analog switches 6a and 6b are instructed to switch the power source to be measured to the B-phase side. From step T9 to step T11, the same operation as that performed for the A phase is performed for the B phase, and the data is stored in the memory area given to the B phase.

Subsequently, in step T12, the signal cycle of the sync signal 11 output from the sync signal generation circuit 10 is monitored, and whether the signal cycle of the sync signal 11 has passed the time corresponding to the number of cycles 2, that is, the sampling time To. To determine
If the sampling time To has not been reached, the process returns to step T4 to continue sampling of the A phase and the B phase.
In addition, the sampling time T from the start of sampling
When o has passed, the process proceeds to step S9 to end the sampling operation.

Next, asynchronous sampling will be described. That is, if it is determined in step S5 that it is an asynchronous type, in step T13, the CTC 13 outputs the pulse 14 having a pulse interval of 100 μsec to the cycle setting circuit 12. At step T14, the analog switches 6a and 6b are instructed to switch the power source to be measured to the A phase side. Step T15
Then, the cycle setting circuit 12 gives the pulse 14 as it is to the respective A / D conversion circuits 15a and 15b as the control signal 16, processes the data in the same manner as in the step T5, and completes the digital conversion in the step T16. The conversion circuits 15a and 15b supply the (EOC) signal 21 to the microprocessor and store the voltage data 20a and the current data 20b on the A phase side, which are digitally converted in step T17, in the memory.

In step T18, the analog switches 6a and 6b are instructed to switch the power source to be measured to the phase B side, and step T18 is executed.
In 19 to T21, the same operation as in steps T15 to T17 is executed for the B phase and stored in the memory area given to the B phase data.

In step T22, the number of times of sampling is monitored, and the number of times of sampling is less than or equal to a predetermined number, for example, 2000.
If the number of times is less than or equal to the number of times, the process returns to step T14 again to continue sampling on the A phase side and the B phase side. Here, when the number of sampling times reaches 2000, the sampling ends and the process proceeds to step S9. If the number of samplings is set to a large number, the accuracy improves, but the measurement time and the calculation time become longer. In the case of 50 Hz, 2000 times requires a measurement time of 0.2 seconds.

Referring to FIG. 3 again, when the sampling is completed as described above, in step S9, each data value of the voltage data and the current data stored in the memory is corrected according to the input range of the input range changeover switch 5. In step S10, the function IC22 is started to calculate each characteristic value of the measured contrast. In step S11, the calculation result is transferred to the display control CPU 22, and the process returns to step S4 to repeat the measurement operation.

Next, the operation of displaying the calculation result will be described. In the display control CPU 22, when an interrupt signal is input from the processor 8 as shown in step S12, step S1
In 3, the calculation result is received. Since this operation result is a binary number, it is converted to a decimal number in step S14. In step S15, the display data 24 converted into a decimal number is output and the display unit 25 is instructed to display the calculation result.
Returning to step 12, the display operation is repeated by the transfer signal of the next calculation result.

〔The invention's effect〕

As described above, according to the present invention, a distorted wave alternating current including a fundamental wave component and a harmonic wave component is provided with a synchronizing signal generating circuit that synchronizes with the cycle of the fundamental wave component, and when a synchronizing signal is obtained, a preset harmonic wave is obtained. A sampling pulse having a frequency of sampling at least three times from one cycle is given to the sampling means a plurality of times of sampling times of the fundamental wave period, and if a synchronization signal is not obtained, a preset sampling number is given to the sampling means. Since it is applied, even in the case of a distorted alternating current with a significantly distorted waveform,
The characteristic value can be measured with high accuracy by a simple operation.

That is, since the distorted wave AC characteristic measuring apparatus of the present invention can calculate each characteristic value with a digital value with high accuracy, the calculation results are not limited to the use of the measuring device and the calculation results are directly transferred to another central control unit. Since it is possible to easily realize a monitoring system for effectively remotely monitoring and recording electric power and the like, it is possible to meet the demands of a highly industrialized society and an information society.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a waveform diagram of a distorted wave AC of a power source to be measured measured in FIG. 1, and FIG. 3 is a main memory of a CPU incorporated in a microprocessor. FIG. 4 is a flowchart showing a program, and FIG. 4 is a flowchart showing data sampling control. 1 ... Converter, 2a, 2b ... Voltage-voltage converter, 3
a, 3b ... Current-voltage converter, 4a-4d ... Attenuator, 5 ... Input range selector switch, 6a, 6b ... Analog switch, 8 ... Microprocessor, 10 ...
Sync signal generation circuit, 12 ... Cycle setting circuit, 13 ...
... CTC, 15a, 15b ... A / D converter, 22 ...
Function IC, 23 ... Display control CPU, 25 ...
Display unit, 28 ... Data error display unit, 29 ... Input range selector switch.

Claims (1)

[Claims] 1. A synchronization signal generation circuit for generating a synchronization signal synchronized with the fundamental wave component of a distorted wave alternating current including a fundamental wave component and a harmonic component, and means for determining whether or not the synchronization signal is obtained. Sampling time setting means for setting a sampling time corresponding to an integer multiple of the cycle of the synchronizing signal, sampling number setting means for setting a preset sampling frequency, and an instantaneous value of the distorted wave AC for a time shorter than the fundamental wave cycle. Sampling means for sampling at intervals, an A / D conversion circuit for converting the output of the sampling means into a digital signal and outputting the digital signal, and an arithmetic means for calculating the characteristic value of the distorted wave AC based on the digital data are provided. If it is determined that the synchronization signal is obtained, the sampling means performs sampling until the sampling time is reached. Perform ring, also to the case where it is determined that the synchronization signal can not be obtained reaches the number of samplings, the strain wave AC testing apparatus characterized by performing sampling by the sampling means.