JP2010085163A - Current and power measurement apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a measurement apparatus for enabling a current measurement at the high current waveform accuracy, and enabling an effective power measurement for considering a current waveform. <P>SOLUTION: A current is detected by a current sensor 1, converted into a digital signal by an A/D converter 2, and loaded to a data acquisition register 3 by a sample signal from a sample signal generating circuit 7. The data loaded to the register 3 is loaded to a microprocessor 4, and processed. A V-cross timing detecting circuit 5 inputs AC power, and detects timing when the AC power crosses reference voltage. An oscillator 6 generates a frequency whose step-down value does not have a conjugate number relative a frequency of the AC power or which is a prime frequency or a prime multiple frequency. The sample signal generating circuit 7 transmits a zero-cross timing signal for indicating a change from a negative voltage to a positive voltage in the sample signal. The microprocessor 4 calculates a high-accuracy effective current, and calculates correct effective power and a power factor by utilizing a relationship between the sample number and a phase angle. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  In the present invention, the AC current sensor that is detected and sent by a large number of AC current sensors installed in large quantities of several tens or more is measured for each sensor, and the phase difference between the current value and the voltage is further measured. The present invention relates to a current and power measurement device that realizes accurate power calculation in consideration of the power factor by reflecting with high accuracy.

  Conventionally, the total current (electric power) measurement was good, but recently, as a measure against global warming, it has become necessary to grasp the power consumption situation in detail. Until now, it has been very difficult to simultaneously process and measure dynamically changing AC currents detected and sent by several tens or more AC current sensors, and the measuring apparatus has become expensive. It was. Conventionally, the load current is a sine wave current proportional to the voltage. However, in recent years, the power supply system of IT equipment is not necessarily a sine wave current.

There is a current detection device that measures a plurality of current sensors with respect to an AC current that dynamically changes the load current having such a waveform (see Patent Document 1).
This current detection device is a method of detecting the frequency of the power supply under measurement and finely sampling in synchronization with the frequency. However, since this apparatus performs calculation and determination processing while selecting a sensor, there is a problem that the timing at which the first sensor is selected deviates from the timing at which the last sensor is selected.

Therefore, there is a drawback that the phase difference between voltage and current cannot be detected. Similarly, there is a current measuring device of a type in which waveforms are recognized for a large number of sensors and sampled at a low frequency to improve accuracy (Japanese Patent Application No. 2007-271271 by the applicant of the present application).
Although the current measurement device of this application is accurate in current value measurement, there is a problem that only the power with a power factor of “1” can be found because the phase difference between the voltage and current of each sensor is not known.
JP-A-11-304852

  In both of the above-mentioned patent documents, the load current cannot be correctly measured, which is not necessarily a sine wave current that fluctuates dynamically. In addition, there is a problem that the active power cannot be measured as a product of a voltage corresponding to a distorted current waveform that is not necessarily a sine wave current. In addition, it is desired to measure current and active power at a low cost with a relatively simple configuration.

  The present invention has been made in view of the above circumstances, and is capable of accurately measuring a current by recognizing a current waveform with respect to a large amount of sensors and a dynamically changing current change that is not limited to a sine wave current. In addition, an object of the present invention is to provide a current and power measuring apparatus capable of measuring active power in consideration of a current waveform that is distorted with respect to voltage.

  In order to achieve the above-described object, the invention according to claim 1 is sufficient in comparison with the frequency of the AC power supply and the V cross timing detection unit that detects the timing at which the AC voltage is input and the AC voltage crosses the reference voltage. A transmitter that generates a frequency that is a high frequency, a step-down value with respect to the frequency of the AC power supply has no conjugate number, or a prime number and a multiple of the prime number, and a signal of the transmitter and a signal of the V cross timing detector A sample signal generating unit that inputs and outputs a zero cross timing signal in which the voltage is changed from negative to positive at a time interval that is stepped down N times by operating the counter with the signal of the transmission unit, and one or more AC current sensors A plurality of A / D conversion units provided corresponding to these, and an output of the A / D conversion unit provided corresponding to these A / D conversion units. Select the data acquisition register to be captured by the sample timing signal from the signal signal generation unit, select the data acquisition register, capture the contents of the data acquisition register, and use a sample period that does not have a conjugate number with respect to the period of the measurement current. The present invention is characterized by comprising a microprocessor that calculates an accurate effective current and uses the relationship between the number of samples in the cycle and the phase angle to calculate an accurate active power and a power factor.

  According to the present invention, with respect to a large number of current sensors (50 sensors or more), there is an advantage that a single device can accurately measure a current that is not necessarily a sine wave current and can be configured at a low price. .

  In addition, for any inquiry period (time) from the host device, the peak current value, effective current value, and active power of each sensor during that period can be notified to the host device.

Furthermore, for any inquiry period (time) from the host device, it is possible to notify the host device of the power factor value due to the phase shift of the voltage and current of each sensor during that period.
In addition, in response to an inquiry from the above device, the current waveform data for the immediately preceding cycle can be notified to the host device, and the frequency of the commercial power supply designated by the host device for overseas correspondence is as described above. Can do anything.

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of the present invention. In FIG. 1, reference numerals 1 to n denote AC current sensors including, for example, current transformers provided on a plurality of current lines not shown. The currents detected by the AC current sensors 1 _{1 to} 1n are converted into digital signals by the A / D converters 2 _{1 to} 2n, and sample timing signals from a sample signal generation circuit to be described later are sent to the data acquisition registers 3 _{1 to} 3n. It is taken in by. The data taken into the data acquisition registers 3 _{1 to} 3n is taken into the microprocessor 4 and processed as described later.

  Reference numeral 5 denotes a V cross timing detection circuit. The V cross timing detection circuit 5 detects the timing at which the AC power is input and the AC voltage crosses the reference voltage. Reference numeral 6 denotes a transmitter. The transmitter 6 has a sufficiently high frequency (approximately 1000 times or more) compared to the frequency of the AC power supply, and the value stepped down with respect to the frequency of the AC power supply has no conjugate number, prime number and prime number Which generates a frequency that is a multiple of.

  The signal from the transmitter 6 and the signal from the V cross timing detection circuit 5 are input to the sample signal generation circuit 7. Then, the sample signal generation circuit 7 sends out a zero cross timing signal in which the sample signal and the voltage change from negative to positive at a time interval stepped down N times by operating a counter (not shown) with the signal from the transmitter 6.

  The zero cross timing signal, the sample timing signal, and the V cross timing signal from the V cross timing detection circuit 5 are supplied to the microprocessor 4. Then, the microprocessor 4 calculates a high-accuracy effective current using a sample period having no conjugate number with respect to the period of the measurement current, and uses the relationship between the number of samples in the period and the phase angle to obtain an accurate value. The active power and power factor are calculated.

  In the embodiment of the present invention configured as described above, by selecting a prime number as a sampling frequency and sampling a prime number per second, it is the same as that sampled by the product of the prime number and the commercial AC power frequency. Use.

  Accordingly, if “359” is selected as a prime number and sampling is performed 359 times per second, a sample waveform can be obtained at equal intervals of 1/359 from one cycle of a commercial AC current waveform. In general, in order to obtain data with a resolution obtained by dividing one cycle into 1/359, if it is 50 Hz, it is necessary to sample at 359 × 50 = 17959 HZ = 17.95 KHZ. Even if 500 times more than 359 are sampled, since the conjugate number is “50”, the waveform is a rough waveform obtained by dividing the waveform into 1/10 equal parts.

  On the other hand, according to Shannon's sample theorem, the waveform can be reproduced by sampling at a frequency twice that of the rate of change of the AC current that changes dynamically. Even if the current changes for each cycle for a commercial power source of 50HZ or 60HZ, it may be sampled at 100 times or more than 120 times per second, so 359 times per second can be said to be a sufficient number of samples.

  Since recent IT devices often handle current only at a portion where the voltage is higher than the voltage of the sine wave, the current waveform is not a sine wave. For this reason, the active power cannot be calculated as the product of the phase shift amount and the two sine waves. In order to accurately calculate the active power, it is necessary to subdivide the waveform and integrate the value obtained by multiplying the voltage value and current value at the same timing.

  In the above description, it is described that one cycle can be subdivided into 359 equal parts, but the order of subdivision does not increase by 360 degrees / 359, but is a discrete order of multiples of 360 degrees / 359. However, if 359 samples are taken after 1 second, current data can be taken at 359 equally divided timings.

  On the other hand, since the relationship between the number of samples and the angle can be obtained by a calculation formula, the active power corresponding to the current waveform is obtained by multiplying the voltage corresponding to the angle. By dividing this active power by the product of the effective current and the peak voltage / √2, the power factor can be calculated for the distorted waveform.

  Hereinafter, an embodiment in which the above-described embodiment is realized by a program using a computer will be described with reference to FIG. 1 and Tables 1 to 3 shown below. Table 1 shows counters, registers, indicators and conversion tables in software processing common to program sequence control and sensors. Table 2 shows registers and memories corresponding to each sensor, and Table 3 shows counters corresponding to commands.

  The waveform storage memory address conversion table (s5) in Table 1 rearranges the measurement data in the order in which the angle advances from 0 degree to 360 degrees / 359 when a cycle waveform is drawn at a pitch of 1/359.

  For 50HZ, the calculation of F (n) = An * 50 * 360/359 is performed on A1 (first sample) to A359 (359th sample), and the value of F (An) is set to 360. The results of modulo calculation (MOD (F (An), 360)) are arranged in descending order of the angle, and a sample number, phase angle conversion table (s10), and a memory address conversion table are created.

For 60HZ, the calculation F (An) = An * 60 * 360/359 is used.
In the above calculation, for example, the phase angle conversion table (s10) and the waveform storage memory address conversion table (s5) up to the 16th sampling number are as shown in Table 4 and Table 5 following Table 4.

  The voltage conversion table (s7) is for obtaining a voltage corresponding to the current of the number of sampling times. In this table (s7), the maximum value of the voltage is “1”. Therefore, when the actual voltage is obtained, it is calculated by multiplying the value of the peak voltage register (s8).

The voltage conversion table (s7) is for A phase, B phase, and C phase for 50HZ and 60HZ, respectively.
For the 50HZ phase A, F (An) = An * 50 * 2π / 359 is calculated from A1 (first sample) to A359 (359th sample), and the value of F (An) is obtained. The SIN value (SIN (MOD (F (An), 2π))) obtained by modulo calculation with a value of 2π (MOD (F (An), 2π)) is calculated, and the SIN corresponding to the number of samples is calculated. Is a table of values.

For B phase of 50HZ, F (An) = An * 50 * 2π / 359-2π / 3
For C phase of 50HZ, F (An) = An * 50 * 2π / 359-4π / 3
For 60 HZ, the calculation of F (An) = An * 60 * 2π / 359 is used.
The memory in Table 2 can hold data corresponding to the address of the memory.
The counter of Table 3 uses a register as a counter function.

  In FIG. 1, a description will be given below of a case where the number of AC current sensors is 50 and the sampling frequency is 359 HZ with a commercial power source of 50 HZ.

  The zero-cross timing signal sent from the sample signal generation circuit 7 is generated at the time of zero-cross when the instruction from the microprocessor 4 changes from the negative of the latest AC input power source to the positive voltage. The sampling timing signal is generated at 1/359 second intervals from the zero cross timing. This is the same for 50HZ and 60HZ. The processing operation will be described below with reference to FIG. 1 and Tables 1 to 3 and the entire flowchart shown in FIG.

  (A). When the zero cross timing signal is detected, the commonly used sample number counter (s1) and sensor address register (s2) are cleared.

  (B). When waiting for the sample timing signal, the sample number counter (s1) is incremented by one.

  (C). The data is read from the data acquisition register 3 at the address indicated by the contents of the sensor address register (s2) and held in the data register (s3).

  (D). The current waveform storage memory indicator (s4) is checked, and the waveform storage memory (t1) area corresponding to the address indicated by the contents of the sensor address register (s2) is selected in the current-side waveform storage memory (t1).

  (E). Using the waveform storage memory address conversion table (s5), a conversion value corresponding to the contents of the sample number counter (s1) is obtained, and the conversion value is used as a memory address in the waveform storage memory (t1) area selected above. The contents of the data register (s3) are written.

  (F). Data in the peak value register (t2) corresponding to the contents of the sensor address register (s2) is read and the value is compared with the contents of the data register (s3).

  (G). If the content of the data register (s3) is small, proceed to the next. If the content of the data register (s3) is large, the content of the data register (s3) is written into the peak value register (t2), and the peak phase angle register (t3) corresponding to the content of the sensor address register (s2). ), The phase angle corresponding to the number of samples, which is the content of the sample number counter (s1), is converted by the phase angle conversion table (s10) and the value is written.

  (H). A value obtained by squaring the contents of the data register (s3) is added to the contents read from the current square accumulation register (t4) corresponding to the contents of the sensor address register (s2) and written to the current square accumulation register (t4). .

  (I). Based on the contents of the sensor address register (s2), it is determined which voltage conversion table (s7) to be used for each of A, B, C and phase groups from the sensor phase group management table (s6).

  (J). The value read from the active power accumulation register (t5) corresponding to the contents of the sensor address register (s2) is changed to the value of the data register (s3) and the contents of the sample number counter (t1) of the voltage conversion table (s7). The product of the corresponding address values is added and written to the active power accumulation register (t5).

  (K). It is checked whether or not the content of the sensor address register (s2) is “49” (maximum number of sensors). If it is not “49”, the content of the sensor address register (s2) is incremented by 1 and the processing returns to (c). . If “49”, the contents of the sensor address register (s2) are cleared and the process proceeds to the next step.

  (L). Whether the content of the sample number counter (s1) is “359” is checked. If it is “359”, the content of the sample number counter (s1) is cleared and the process proceeds to the next. If it is not “359”, the processing returns to (b).

  (M). The contents of the peak value register (t6) corresponding to the contents of the sensor address register (s2) are read out and compared with the contents of the peak value register (t2) corresponding to the contents of the sensor address register (s2). If the content of t2) is large, the content is written in the peak value memory (t6) for 1 second. Thereafter, the contents of the peak time register (t2) are cleared.

  (N). The content of the current square accumulation register (t4) corresponding to the content of the sensor address register (s2) is divided by “359”, and the square root value “A” of the result is 1 second corresponding to the content of the sensor address register (s2). It is added to the content of the effective current accumulation register (t8) and written to the effective current accumulation register (t8) for 1 second. The square root value “A” is stored in the power factor buffer A. Thereafter, the contents of the current square accumulation register (t4) are cleared.

  (O). When the content of the active power accumulation register (t5) corresponding to the content of the sensor address register (s2) is divided by “359”, the product “B” with the content of the peak voltage register (s8) is divided into the active power register (t9) for 1 second. ) And added to the active power accumulation register (t9) for 1 second. The product “B” is stored in the power factor buffer B. Thereafter, the contents of the active power accumulation register (t5) are cleared.

  (P). The contents of the power factor accumulation register (t7) for 1 second corresponding to the contents of the sensor address register (s2) obtained by dividing the value of the power factor buffer B by the product of the power factor buffer A and 1 / √2 And is written in the power factor accumulation register (t7) for 1 second.

  (Q). It is checked whether the content of the sensor address register (s2) is “49”. If it is not “49”, the content of the sensor address register (s2) is incremented by 1, and the process returns to the process (m). If “49”, the contents of the sensor address register (s2) are cleared and the process proceeds to the next A1.

  A1. It is checked whether a peak current value read command is received from the host device. If not, the content of the peak value reading second counter (u1) is incremented by 1 and the process proceeds to A3.

  A2. If it is, the contents of the sensor address register (s2) are cleared and the contents of the peak value register (t6) corresponding to the contents of the sensor address register (s2) from sensor addresses 0 to 49 are sent to the host device. The contents of the 1 second peak value register (t6) and the peak value reading second counter (u1) are cleared.

  A3. Check whether the effective current value read command is received from the host device. If not, the content of the effective current reading second counter (u2) is incremented by 1 and the process proceeds to A5.

  A4. If it is, the contents of the sensor address register (s2) are cleared, and the contents of the effective current accumulation register (t8) corresponding to the contents of the sensor address register (s2) from sensor addresses 0 to 49 are read out as the effective current. The value divided by the contents of the second counter (u2) is sent to the host device, and the contents of the contents of the effective current accumulation register (t8) and effective current reading second counter (u2) are cleared.

  A5. It is checked whether an active power read command is received from the host device. If not, the content of the active power read second counter (u3) is incremented by 1 and the process proceeds to A7.

  A6. If it is, the contents of the sensor address register (s2) are cleared and the contents of the active power accumulation register (t9) corresponding to the contents of the sensor address register (s2) from the sensor addresses 0 to 49 are changed to the active power. The value divided by the contents of the read second counter (u3) is sent to the host device, and the contents of the 1 second active power accumulation register (t9) and the active power read second counter (u3) are cleared.

  A7. Check if a power factor read command is received from the host device. If not, the content of the power factor read second counter (u4) is incremented by 1 and the process proceeds to A9.

  A8. If it is, the contents of the sensor address register (s2) are cleared, and the contents of the power factor accumulation register (t7) corresponding to the contents of the sensor address register (s2) from the sensor address 0 to 49 are read as the power factor. The value divided by the contents of the second counter (u4) is sent to the host device, and the contents of the one second power factor accumulation register (t7) and the power factor reading second counter (u4) are cleared.

  A9. Check whether a read command for the current waveform is received from the host device. If not, go to the next B1. If it is, the sensor address to be read specified by the command is set in the sensor address register (s2).

  A10. The current waveform storage memory indicator (s4) corresponding to the sensor address register (s2) is checked, and the data in the waveform storage memory (t1) that is not on the current side is sent to the host device in order from address 1 to address 359, and the sensor address The contents of the register (s2) are cleared.

B1. The microprocessor 4 calculates the peak voltage of the input power supply from the width of the V cross timing signal from the V cross timing detection circuit 5 and the value of V, and sets it in the peak voltage register (s8). Similarly to the current value, a method of measuring the voltage of the input power supply by A / D conversion may be used.
B2. The frequency of the commercial power supply is calculated from the cycle of the V cross timing signal and set in the frequency register (s9).

  B3. The microprocessor 4 calculates the timing at which the input power supply voltage switches from negative to positive from the width and period of the V cross timing signal from the V cross timing detection circuit 5 and informs the sample signal generator 7 of the zero cross timing. A method of detecting the zero cross timing by inputting the voltage of the input power supply to a commercially available comparator may be used.

  B4. The content of the sensor address register (s2) is incremented from “0” to “49”, the content of the peak phase angle register (t3) corresponding to the content of the sensor address register (s2) is checked, and 90 ° ± 58 ° Are classified into the A phase, 210 ° ± 58 ° as the B phase, and 330 ° ± 58 ° (272 ° to 28 °) as the C phase, and the sensor phase group management table (s6) is created. The power supply voltage input to the V cross timing detection circuit 5 is the A phase.

  For a large number of sensors, in addition to being able to measure current waveforms accurately and accurately measuring current fluctuations that change dynamically, not necessarily sinusoidal currents, effective power takes into account current waveforms that are distorted with respect to voltage. Can be measured.

The block block diagram which shows embodiment of this invention. FIG. 6 is a flowchart for explaining the operation of the embodiment.

Explanation of symbols

1 ₁ 1n ... AC current sensor 2 ₁ ~2n ... A / D converter 3 ₁ 3n ... data acquisition register 4 ... microprocessor 5 ... V-cross timing detection circuit 6 ... transmitter 7 ... sample signal generating circuit

Claims (1)

A V cross timing detection unit for inputting an AC power supply and detecting a timing at which the AC voltage crosses the reference voltage;
A transmitter that generates a frequency that is sufficiently high compared to the frequency of the AC power source, and that the value stepped down with respect to the frequency of the AC power source has no conjugate number or a prime number and a multiple of the prime number;
The signal of the transmitter and the signal of the V cross timing detector are input, and the counter is operated by the signal of the transmitter and the sample signal and the zero cross timing signal in which the voltage changes from negative to positive at the time interval stepped down N times are transmitted. A sample signal generator;
One or more AC current sensors;
A plurality of A / D converters provided corresponding to these,
A data acquisition register provided corresponding to these A / D conversion units, and for capturing the output of the A / D conversion unit with a sample timing signal from the sample signal generation unit;
Select the data acquisition register, capture the contents of the data acquisition register, calculate a high-accuracy effective current using a sample period that does not have a conjugate number with respect to the period of the measurement current, and the number of samples and phase angle of the period A current and power measuring apparatus comprising a microprocessor that calculates accurate active power and power factor by utilizing the above relationship.

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