JP2856398B2 - Electronic watt-hour meter - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronic watt-hour meter, and more particularly, to an electronic watt-hour meter that measures reactive power as well as active power.

[Conventional technology]

A conventional electronic power meter of this type receives a voltage signal indicating a voltage in a measured system and a current signal indicating a current, and integrates a multiplication result of the two signals to obtain a signal indicating an active power amount. Further, a signal indicating the amount of reactive power is obtained by delaying the phase angle of the voltage signal by 90 degrees and integrating the result of multiplication of the voltage signal and the current signal. To delay the phase angle of the voltage signal, the frequency of the power supply (for example, for commercial power,
A phase shifter for one frequency is used that delays the voltage phase by 90 degrees at 50 or 60 Hz.

[Problems to be solved by the invention]

In the conventional electronic watt-hour meter described above, the phase shifter used in the reactive power measuring section is 90% at only one frequency of the power supply frequency.
Since a phase shift transition is provided, the current signal (or voltage signal) has many harmonics as well as the fundamental frequency of the power supply frequency, as in the case of a measured system using a control switching element such as a thyristor. When the phase shifter includes the phase shifter, the phase shift angle given to the harmonic component by the phase shifter deviates from 90 degrees, and there is a problem that a measurement error of the reactive power increases.

An object of the present invention is to provide an electronic watt-hour meter that eliminates the above-described problems and can accurately measure reactive power even in a system under measurement that generates harmonics.

[Means for solving the problem]

The watt hour meter according to the present invention includes: an active power measuring unit that receives a voltage signal and a current signal indicating a voltage and a current to be measured and integrates a multiplication result of the two signals; And a reactive power measuring means for integrating a result of multiplication of a pair of output signals obtained by passing both signals through the phase shift circuit.

〔Example〕

 Next, the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing a first embodiment of the present invention. The voltage signal and the current signal are analog signals indicating the voltage and current of the measured system, respectively. The voltage signal is sampled and held by the sample and hold circuit 1 at a predetermined clock cycle, then converted into a digital signal by an analog-digital converter (ADC) 3 and sent to the multiplier 5 and the phase shift circuit 7. Similarly, the current signal is converted into a digital signal through the sample and hold circuit 2 and the ADC 4 and sent to the multiplier 5 and the phase shift circuit 8. The output signal of the multiplier 5 corresponds to the product of the voltage signal and the current signal, and the integrated signal is integrated by the integration circuit 9 to obtain data (active power data) indicating the active power amount. The phase shifters 7 and 8 are
This is a pair of all-pass circuits in which the phase difference is approximated to 90 degrees in a predetermined bandwidth (so-called 90-degree phase shift circuit). A bandwidth where the phase difference approximates 90 degrees is set so as to include from the fundamental wave of the power supply frequency to the harmonic of the desired order, and the approximation of the 90-degree phase shift within the approximation band from the measurement error limit of the reactive power. By calculating the error limit, the circuit order of the phase shift circuits 7 and 8 is determined. Therefore, if the digitized voltage signal and current signal are passed through the phase shift circuits 7 and 8, respectively, a relative phase difference substantially equal to 90 degrees is provided not only to the fundamental component but also to the harmonic component of both signals. be able to. Phase shift circuit 7
And 8 are multiplied by a multiplier 6 and multiplied by an integrating circuit 10 to obtain data (reactive power data) indicating a reactive power amount.

Although the present embodiment can be realized in an analog form, by digitizing, the circuit size can be reduced, and variations in characteristics and changes over time can be reduced. Even when the power supply frequency includes not only the fundamental wave but also the harmonics, the digitization and the above-mentioned phase shift processing cause the phase shift angle of the harmonic components to deviate from 90 degrees and the error in the measurement of the reactive power The problem that the conventional wattmeter has is that it becomes large does not occur. Therefore, highly accurate measurement of reactive power becomes possible.

FIG. 2 is a block diagram showing a second embodiment of the present invention. This embodiment is similar to the first embodiment (see FIG. 1).
It has a configuration in which filters 11 and 12 are inserted after ADCs 3 and 4, respectively. The filters 11 and 12 are high-pass filters for correcting an offset generated in the process of digitizing the voltage signal and the current signal. That is, when digitized by the analog-digital converter (ADC) 3, a DC component may be generated in the digital signal, and this may be an offset. The filters 11 and 12 are filters that pass only high-frequency components of the digital signal, and thereby can remove a DC component that causes an offset from the digital signal. Thereby, it is possible to prevent a measurement error due to the offset from occurring.

〔The invention's effect〕

As described above, the present invention provides a 90-degree phase difference not only to the fundamental wave of both the voltage and current signals but also to the harmonic components, thereby accurately converting the reactive power to the system under measurement that generates harmonics. There is an effect that an electronic wattmeter that can be measured can be realized.

[Brief description of the drawings]

1 and 2 are block diagrams of an embodiment of the present invention. 1,2 ... sample and hold circuit, 3,4 ... analog-digital converter (ADC), 5,6 ... multiplier, 7,8 ... phase shift circuit, 9,10 ... integration circuit, 1, 12 ... Filter.

Continuation of the front page (72) Inventor Hidetake Nakamura 5-33-1, Shiba, Minato-ku, Tokyo NEC Corporation (72) Inventor Shigeo Fushimi 5-33-1, Shiba, Minato-ku, Tokyo NEC Corporation (72) Inventor Masatoshi Komatsu 5-33-1, Shiba, Minato-ku, Tokyo NEC Corporation (56) References JP-A-58-182563 (JP, A) JP-A-54-128771 (JP, A) JP-A-60-202367 (JP, A) JP-A-52-6569 (JP, A) JP-A-61-270668 (JP, A) JP-A-57-111460 (JP, A) JP-A-62 122331 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G01R 21/00 G01R 21/133 G01R 22/00 G01R 23/20 C

Claims (2)

(57) [Claims] An active power measuring means for receiving a voltage signal and a current signal indicating a voltage and a current to be measured and integrating a multiplication result of the two signals; A pair of phase shift circuits for providing a relative phase difference substantially equal to 90 degrees within a frequency band including the signals, and integrating the results of multiplication of a pair of output signals for obtaining the two signals through the phase shift circuits; An electronic watt-hour meter comprising: a reactive power measuring means for converting the voltage signal and the current signal in analog form into digital signals, respectively, as a multiplication input of the active power measuring means; and An electronic watt-hour meter as an input to the phase shift circuit of the power measuring means. 2. An electronic watt-hour meter according to claim 2, wherein a high-pass filter for removing a DC component from said digital signal is interposed at a stage preceding said phase shift circuit.