JPH0275966A - Electronic watthour meter - Google Patents

Abstract

PURPOSE:To measure an active power and a reactive power in a wide range by arithmetically processing the voltage signal and the current signal with a Fourier transformation. CONSTITUTION:An analog voltage signal 1 in a system to be measured is inputted to an A/D converter 3 through a sample-and-hold circuit 2, then inputted to a high speed Fourier transform device (FET) 4 in the manner of making the real and imaginary parts of the output digital signal to be zero. The real and imaginary parts resulted from the Fourier transformation are inputted to multipliers 5,8 and 16,14 respectively, and each output of the multipliers 5,8 are subtracted in a subtracting device 6. Also an analog current signal 10 in the system to be measured is similarly processed in order of the sample- and-hold circuit 11, A/D converter 12, FFT 13, and the real and imaginary parts resulted from the Fourier transformation are inputted to the multipliers 14,16 and 5,8 respectively, and each output of the multipliers 14,16 are added in an adding device 17. Then, by means of integrating the output of the subtracting device 6 in an integrating circuit 7, the active power data 9 are obtained, and the reactive power data 18 can be obtained if the output of the adding device 17 is integrated in the integrating circuit 15.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to an electronic watt-hour meter, and particularly to an electronic watt-hour meter that measures reactive energy as well as active energy.

[Prior Art] Conventionally, this type of electronic watt-hour meter has a configuration not shown in FIG. 2.

Voltage signal 30 and current signal 38 are analog signals indicating the voltage and r4 current of the system under test, respectively.

The voltage signal 30 is sampled and bolded at a predetermined clock cycle in a sampled and bolded circuit 31, and then converted into a digital signal in an analog-to-digital converter (ADC) 32.

Here, in order to correct the offset that occurs in the process of digitizing the voltage signal 30, the voltage signal of the 0 multiplier 34 is passed through a digital filter (high-pass filter) 33 and then sent to a multiplier 34 and a phase shift circuit 36. The output signal corresponds to the product of the voltage signal and the current signal, and by integrating this in the m calculation circuit 35, data (active power data) 37 indicating the amount of active power is obtained. The phase shift circuits 36 and 44 are a pair of all-pass type circuits (so-called 90-degree phase difference circuits) in which the phase difference approximates 90 degrees in a predetermined bandwidth.

Here, the bandwidth in which the phase difference approximates 90 degrees is set to include from the fundamental law of the power supply frequency to the desired harmonic, and the 90 degree phase difference is approximated within the approximation band based on the measurement error limit of reactive power. Calculating the error limits, phase shift circuits 36 and 44
It is necessary to determine the circuit order of

Further, as for the current signal 38, the sample and hold circuit 39 and the analog-to-digital converter (AD
C) 40, digital filter (high pass filter) 4
After processing in the order of 1, the multiplier 34 and the phase shift circuit 44
sent to. By multiplying the Okayama force signals of the phase shift circuits 36 and 44 by a multiplier 42 and integrating this by an integrating circuit 43, data indicating reactive power amount (reactive power data) 45 is obtained.
get.

[Problems to be Solved by the Invention] The conventional electronic watt-hour meter described above has a configuration that includes a filter and a phase shift circuit. There are drawbacks such as measurement errors due to deviation from the phase difference and narrow measurement bandwidth due to circuit scale limitations.

An object of the present invention is to eliminate the above-mentioned drawbacks and provide an electronic watt-hour meter that can measure active power and reactive power with a small circuit scale, less error, and a wide measurement bandwidth.

[Means for Solving the Problems] An electronic watt-hour meter according to the present invention receives a voltage signal and a current signal indicating the voltage and current of a measurement target, and generates active power data and reactive power data indicating active power and reactive power. In an electronic watt-hour meter that obtains, the voltage signal is Fourier-transformed to obtain first transformed real part data representing the real part of the frequency component of the voltage signal and imaginary part of the frequency component of the voltage signal. and a first transformed imaginary part data representing
Fourier transform means for Fourier transforming the current signal, and second transformed real part data representing the real part of the frequency component of the current signal and second transformed real part data representing the imaginary part of the frequency component of the current signal. a second Fourier transform means that outputs the transformed imaginary part data, and multiplies the first transformed real part data and the second transformed real part data, and outputs the multiplied result. a first multiplier for outputting a first multiplication result signal representing the first multiplication result; and a first multiplier for multiplying the first converted imaginary part data by the second converted imaginary part data and representing the multiplied result. a second multiplication means for outputting a second multiplication result signal; and a subtraction means for subtracting the second multiplication result signal from the first multiplication result signal and outputting a subtraction result signal representing the subtracted result. and a first integrating means for integrating the subtraction result signal and outputting the integrated result as the active power data, the first converted imaginary part data and the second converted real part. a third multiplication means for multiplying the first converted real part data and the second converted imaginary part data by outputting a third multiplication result signal representing the multiplied result; and a fourth multiplication means for outputting a fourth multiplication result signal representing the multiplied result; and a fourth multiplication means for adding the third multiplication result signal and the fourth multiplication result signal; and a second integrating means that integrates the addition result signal and outputs the integrated result as the reactive power data.

[Example] Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of an electronic power meter according to an embodiment of the present invention.

The voltage signal 1 and the current signal 10 are analog signals indicating the voltage and current of the system under test, respectively.

The voltage signal 1 is sampled and held at a predetermined clock cycle in the sample bold circuit 2, and then converted into an analog signal.
It is converted into a digital signal by a digital converter (ADC) 3, and the result is sent to a fast Fourier transformer (FFT) 4 with the real part and imaginary part set to 0, and the real part and imaginary part of the Fourier transform result are multiplied, respectively. The respective outputs of multiplier 5.8 are further sent to subtractor 6.
is subtracted by

The other current signal 10 is also generated by the sample bold circuit 11 and the analog-to-digital converter (ADC) as described above.
12, Fast Fourier Transform (FFT) 13, and the real and imaginary parts of the Fourier transform result are processed in the order of multiplier 14. 16 and 5.8, and the respective outputs of multipliers 14.16 are further added together in adder 17. The output of the subtracter 6 is integrated by an integration circuit 7 to obtain data 9 indicating the amount of active power (active power data). Similarly, the output of the adder 17 is integrated by the integration circuit 15 to obtain data (reactive power data) 18 indicating the amount of reactive power.

Now, as a specific example of offset suppression that occurs in the process of digitizing voltage and current signals, let us consider measuring the power of 2nd to 7th harmonic components of a 50 Hz commercial power supply. When the real part is the result of sampling the voltage and current at 16 points at 800 Hz, and the fast Fourier transform (FFT) is performed with the imaginary part set to 0, the frequency is OHZ, 50
Hz, 100Hz, 1
50 Hz, 200 Hz.

Eight complex frequency components of 250 Hz, 300 Hz, and 350 Hz are obtained. 8 obtained in this way
The complex frequency component of the point is expressed as the voltage real part V ro+V
rl, ”” V r? , voltage imaginary part V H6, Vth,
...V 17, voltage real part I,. +ll+...I,
F, and voltage imaginary part 11o, I-th...II7.

Here, the offset that occurs in the process of digitizing voltage and current signals is a DC component (frequency 0Hz), so the power from the fundamental signal to the 7th harmonic excluding the frequency component of OHz is the effective power = Σ (V1*I r
kV+kl+h).

Reactive power=Σ(vrkIIk+vlkIrk), and by integrating these, active power amount and reactive power amount are obtained, and offset can be easily suppressed.

[Effects of the Invention] As explained above, the present invention does not require a special circuit for offset cancellation, so it is possible to reduce the circuit scale, and at the same time, it does not require a pair of phase shift circuits as in the conventional case. Furthermore, the circuit size can be reduced, there is no error due to deviation from the phase difference of 90°, and active power and reactive power can be measured with little error over a wide band up to 1/2 of the sampling period. be.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of an electronic watt-hour meter according to an embodiment of the present invention, and FIG. 2 is a block diagram showing the configuration of a conventional electronic watt-hour meter. 1... Voltage signal, 2... Sample hold circuit, 3
...Analog-to-digital converter (ADC), 4...
・°Fast Fourier transformer (FFT), 5... Multiplier, 6... Subtractor, 7... Integration circuit, 8... Multiplier, 9... Active power data, 10... Current No. 18, 1
1... Sample bold circuit, 12... Analog
Digital converter (ADC), 13... Fast Fourier transformer (FPT), 14... Multiplier, 15... Integration circuit, 16... Multiplier, 17... Adder, 18...
・Reactive power data.

Claims (1)

[Claims] 1. In an electronic watt-hour meter that receives a voltage signal and a current signal indicating the voltage and current of a measurement target and obtains active power data and reactive power data indicating active power and reactive power, The voltage signal is Fourier transformed, and first transformed real part data representing the real part of the frequency components of the voltage signal and first transformed imaginary part data representing the imaginary part of the frequency components of the voltage signal. and a first Fourier transform means for Fourier transforming the current signal to output second transformed real part data representing the real part of the frequency component of the current signal and imaginary data of the frequency component of the current signal. a second Fourier transform means outputting second transformed imaginary part data representing a part; and multiplying the first transformed real part data and the second transformed real part data; a first multiplier that outputs a first multiplication result signal representing the multiplied result; and a first multiplier that multiplies the first converted imaginary part data and the second converted imaginary part data; a second multiplier that outputs a second multiplication result signal representing the multiplied result; and a subtraction result that subtracts the second multiplication result signal from the first multiplication result signal and represents the subtracted result. subtraction means for outputting a signal; first integration means for integrating the subtraction result signal and outputting the integrated result as the active power data; and the first converted imaginary part data and the second a third multiplication means for multiplying the first converted real part data by the converted real part data and outputting a third multiplication result signal representing the multiplied result; a fourth multiplier that multiplies the converted imaginary part data and outputs a fourth multiplication result signal representing the multiplication result; the third multiplication result signal and the fourth multiplication result signal; and a second integrating means for integrating the addition result signals and outputting the integrated result as the reactive power data. An electronic watt-hour meter characterized by: