JPH01224675A - Electronic watthour meter - Google Patents

Abstract

PURPOSE:To accurately measure the reactive electric energy of even a system to be measured which generates higher harmonics by providing a couple of phase shifting circuits generating a relative phase difference which is substantially equal to 90 deg. in a prescribed frequency band. CONSTITUTION:A voltage signal and a current signal are sampled and held by sample and hold circuits 1 and 2 at a prescribed clock period and converted by A/D converters 3 and 4 into digital signals, which are sent to a multiplier 5 and phase shifting circuits 7 and 8. The output signal of the multiplier 5 corresponds to the product of the voltage signal and current signal and is integrated by an integrating circuit 9 to obtain data indicating active electric energy. The circuits 7 and 8 are a couple of entire-band passing type circuits whose phase difference is approximated to 90 deg. with prescribed band width. Thus, the digitized voltage signal and current signal are passed through the circuits 7 and 8 to generate the relative phase difference which is substantially equal to 90 deg. as to not only the basic wave components of both signals, but also even higher harmonic components; and the output signals of the circuits 7 and 8 are multiplied by a multiplier 6 and integrated by an integration circuit 10 to obtain reactive power data.

Description

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

[Conventional technology]

Conventional electronic wattmeters of this type receive both a voltage signal indicating the voltage and a current signal indicating the current in the system being measured, and generate a signal indicating the active energy amount by integrating the multiplication results of both signals. 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 multiplication results of this and the current signal. To delay the phase angle of the voltage signal, a -frequency phase shifter is used that delays the voltage phase by 90 degrees at the frequency of the power supply (for example, 50 or 60 Hz for commercial power).

[Problem that the invention seeks to solve]

In the above-mentioned conventional electronic watt-hour meter, the phase shifter used in the reactive power measuring section has a power supply frequency of 90%.
For example, in the case of a system under test that uses controlled switching elements such as thyristors, the current signal (or voltage signal) contains not only the fundamental wave of the power supply frequency but also many of its harmonics. If it is included, the phase shift angle that the phase shifter gives to the harmonic component will deviate from 90 degrees, resulting in a problem that the measurement error of reactive power will increase.

SUMMARY OF THE INVENTION An object of the present invention is to provide an electronic watt-hour meter that eliminates the above-mentioned problems and can accurately measure reactive power even in systems under test that generate harmonics.

[Means for solving problems]

The watt-hour meter of the present invention includes an active power measuring means that receives a voltage signal and a current signal indicating the voltage and current of a measurement target and integrates the multiplication results of the two signals, and The reactive power measuring means has a pair of phase shift circuits that give a relative phase difference equal to , and integrates the multiplication results of a pair of output signals obtained by passing both of the above signals through the phase shift circuit.

〔Example〕

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

FIG. 1 is a block diagram showing a first embodiment of the present invention. The voltage signal and current signal are analog signals indicating the voltage and current of the system under test, respectively.

The voltage signal is sampled and held at a predetermined clock cycle in the sample and hold circuit 1, and then converted into an analog signal.
It is converted into a digital signal by a digital converter (ADC) 3 and sent to a multiplier 5 and a phase shift circuit 7. Similarly, the current signal is transmitted to the sample hold circuit 2 and the ADC 4.
The signal is converted into a digital signal and sent to a multiplier 5 and a phase shift circuit 8. The output signal of the multiplier 5 corresponds to the product of the voltage signal and the current signal, and by integrating this in the integration circuit 9, data indicating the amount of active power (active power data) is obtained. The phase shifters 7 and 8 are a pair of all-pass type circuits (so-called 90 degree
degree phase shift difference circuit). Set the bandwidth in which the phase difference approximates 90 degrees to include from the fundamental wave of the power supply frequency to the harmonics of the desired order, and also approximate the 90 degree phase shift difference within the approximation band from the measurement error limit of reactive power. Calculate the error limit and
The circuit orders of phase shift circuits 7 and 8 are determined. Therefore, by passing the digitized voltage signal and current signal through the phase shift circuits 7 and 8, respectively, a relative phase difference substantially equal to 90 degrees is given to not only the fundamental wave component but also the harmonic component of both signals. be able to.

By multiplying the power signals of both the phase shift circuits 7 and 8 by the multiplier 6 and integrating the multiplied signals by the integrating circuit 10, data indicating the amount of reactive power (reactive power data) is obtained.

Although this embodiment can be implemented in an analog format, by digitizing it, the circuit size can be made smaller and variations in characteristics and changes over time can be reduced.

FIG. 2 is a block diagram showing a second embodiment of the invention. This embodiment is based on A in the first embodiment (see Fig. 1).
After DC3 and 4, filters 11 and 1, respectively.
It has a configuration with 2 inserted. The filters 11 and 12 are high-pass filters for correcting offsets that occur during the digitization process of voltage and current signals. This can prevent measurement errors caused by offsets.

〔Effect of the invention〕

As explained above, the present invention provides a 90 degree phase difference not only to the fundamental wave but also to the harmonic components of both voltage and current signals, thereby accurately controlling reactive power even in the system under test that generates harmonics. This has the effect of realizing an electronic watt-hour meter that can measure energy.

[Brief explanation of the drawing]

1 and 2 are block diagrams of embodiments of the present invention.

Claims (3)

[Claims] (1) Active power measuring means that receives a voltage signal and a current signal indicating the voltage and current of the measurement target and integrates the multiplication results of both signals, and a relative phase difference that is substantially equal to 90 degrees within a predetermined frequency band. and reactive power measuring means for integrating the multiplication results of the pair of output signals obtained by passing both the signals through the phase shift circuit. Power meter. (2) The voltage signal and the current signal in analog format are each converted into digital signals to be used as multiplication inputs of the active power measuring means and as inputs of the phase shift circuit of the reactive power measuring means. The electronic watt-hour meter described in (1). (3) The electronic watt-hour meter according to claim (2), further comprising a filter for suppressing offset components generated in the process of conversion after conversion into a digital signal.