JPH03279871A - Reactive power measuring instrument - Google Patents

Abstract

PURPOSE:To eliminate the need to use an analog integrator by storing digitized data temporarily, and generating a difference in read timing among respective signals and delaying either of a current signal and a voltage signal by an electric angle of pi/2. CONSTITUTION:Analog signals which show the AC voltage and AC current at a terminal to be measured are inputted through a voltage signal input circuit 11 and a current signal input circuit 21. A period measuring means 4 measures the periods of the analog signals. The two inputted analog signals are converted into two digital data, which are written in a 1st storage circuit 31 and a 2nd storage circuit 32 with clock signals synchronized with the sampling periods of 1st and 2nd A/D converters 12 and 22. Then an arithmetic circuit 3 reads data corresponding to the voltage and data corresponding to a current which is delayed in phase by the electric angle pi/2 out of the digital data stored in the storage circuits 31 and 32 and calculates the means value of the time integration of their product.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention is applied to a measuring means for measuring AC reactive power.

〔overview〕

The present invention provides a reactive power measurement device that temporarily stores digitized current and voltage signals, and differentiates the readout timing of each signal so that either the current signal or the voltage signal is converted into an electrical angle of π/2. By providing a delay of , it is possible to eliminate the need to use an analog integrator as a delay element.

[Conventional example]

In the conventional measuring means, as shown in FIG. 3, one of an analog signal representing an alternating voltage or an analog signal representing an alternating current is applied from the end to be measured via a voltage signal input circuit 11 and a current signal input circuit 21. The analog integrator 6
A phase delay corresponding to a quarter of the signal period is caused by passing through the signal, and the calculation result in the calculation circuit 7 is displayed as reactive power.

[Problem to be solved by the invention]

However, such a conventional device requires an expensive filter, and has the drawback that it is technically difficult to realize a filter that accurately generates a phase delay over a wide range of frequency bands.

The present invention aims to eliminate such drawbacks and provides a reactive power measuring device that does not include an analog integrator as a component.

[Means to solve the problem]

The present invention comprises: a first input circuit that inputs an analog signal representing an alternating current voltage at the end to be measured; a second input circuit that inputs an analog signal representing an alternating current at the end to be measured; In a power measuring device equipped with an arithmetic circuit that calculates reactive power from a value input to an input circuit, the two input circuits each sample an input analog signal at a predetermined period and convert it into digital data. The arithmetic circuit includes an analog-to-digital conversion circuit, and the arithmetic circuit includes:
A memory circuit temporarily stores this digital data, and from the digital data stored in this memory circuit, data corresponding to the voltage and data corresponding to the current whose phase is delayed by an electrical angle π/2 are read out. and means for calculating a time-integrated average of the product.

Further, the storage circuits are two first-in, first-out storage circuits connected to the outputs of the two input circuits, and in which writing is performed using clock signals synchronized with the clock signals of the analog-to-digital conversion circuits, respectively,
The calculating means may include means for supplying, as read clock signals, clock signals whose starting times differ from each other by the one-fourth cycle to the two first-in, first-out storage circuits.

[For production]

Instantaneous values of current and voltage input manually as analog signals are sampled at a period that satisfies the sampling theorem and converted into digital signals, and each is temporarily stored in a memory circuit at the same timing. Data corresponding to an instantaneous voltage value and data corresponding to an instantaneous current value with a phase difference of π/4 electrical angle from the phase of this instantaneous voltage value are read out from the contents of this storage circuit at the same timing, and a plurality of data are read out at the same timing. The average value of the product of the two data read over the period of is calculated. This calculation result is displayed as reactive power.

〔Example〕

Hereinafter, one embodiment of the present invention will be described based on the drawings.

First, the configuration of this embodiment will be explained based on FIG. As shown in FIG. 1, this embodiment consists of a first input circuit 1 that inputs an analog signal representing the AC voltage at the end to be measured, and a second input circuit 1 to manually input the analog signal representing the AC current at the end to be measured. The first input circuit 1 includes a circuit 2, an arithmetic circuit 3, a period measuring means 4 for measuring the period of an input analog signal, and a display 5 for displaying the calculation result of the arithmetic circuit 3. , a voltage signal input circuit 11, and a first analog-to-digital converter 12 that samples the output of the voltage signal input circuit 11 at a predetermined sampling period and converts it into digital data. The arithmetic circuit 3 includes a signal input circuit 21 and a second analog-to-digital converter 22 that samples the output of the current signal input circuit 21 at a predetermined sampling period and converts it into digital data. a first storage circuit 31 that temporarily stores digital data converted by the converter 12; and a second analog-to-digital converter 22.
a second storage circuit 32 that temporarily stores digital data converted by the first storage circuit 31 and a second storage circuit 32;
The data corresponding to the voltage is read out from the data temporarily stored in the data, and the data corresponding to the current having a phase difference corresponding to a quarter of the signal period with respect to this voltage is read out according to the measurement result of the period measuring means 4. It includes a clock generation section 34 that generates a clock signal, and includes a first storage circuit 31 and a second storage circuit 3.
Find the product of the data read from 2, and calculate multiple pieces of this product (
and a calculation unit 33 that calculates the average value of the sum of the number of signals included in at least one period or more of the input analog signal and which is an integral multiple of the period.

Next, the operation of this embodiment will be explained based on FIGS. 1 and 2.

An analog signal representing the AC voltage at the end to be measured and an analog signal representing the AC current are input via the voltage signal input circuit 11 and the current signal input circuit 21 (step Sl).
. On the other hand, the period of this analog signal is measured by the period measuring means 4 (step S2).

The instantaneous values of the two analog signals input in step S1 are sampled at a predetermined period by the first analog-to-digital converter 12 and the second analog-to-digital converter 22, and these two sampled values are converted into two digital data. (Step S3), each of these two digital data is written into the first storage circuit 31 and the second storage circuit 32 using a clock signal synchronized with the sampling period of the two analog-digital converters 12 and 22 (Step S4) . N + of the analog signal input to the first storage circuit 31 and the second storage circuit 32
Digital data for a period of 0.25 (N is 1.2.3) is written (step 35).
).

The stored contents of the first storage circuit 31 are read using a clock signal having the same timing as the write clock signal, and a clock having a timing that is equivalent to a period of -4 of the period of the analog signal with respect to the write clock signal. Step S6) to read out the contents stored in the second storage circuit 32 using the signal, calculate the product of the two read digital data, and calculate the number of pieces of this product (the number included in one or more periods of the input analog signal). ) is calculated (step S7), and the result of this calculation is displayed on the display 5 (step 38).

The present invention can be carried out by using a first-in-first-out storage circuit or a digital delay element in either the first storage circuit or the second storage circuit constituting this embodiment, and using data that has been A/D converted for the rest. . In this case, the information can be displayed on the display in real time.

[Effects of the Invention] As explained above, the present invention eliminates the filter as a means for delaying one of the input amounts and uses a memory instead, so it has the effect of reducing costs and the ability to input data over a wide range of frequency bands. This has the effect that the device can be realized without any technical difficulties.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the configuration of an embodiment of the present invention. Configuration diagram. FIG. 2 is a flowchart showing the operation of the embodiment of the present invention. FIG. 3 is a block configuration diagram showing the configuration of a conventional example. 1...First input circuit, 2...Second human power circuit, 3.7
... Arithmetic circuit, 4... Period measuring means, 5... Display, 6... Analog integrator, 11... Voltage signal input circuit, 12... First analog-to-digital converter, 21
. . . Current signal input circuit, 22 . Department.

Claims (1)

[Claims] 1. A first input circuit into which an analog signal representing an alternating current voltage at the end to be measured is input; and a second input circuit into which an analog signal representing an alternating current at the end to be measured is input. , a power measuring device comprising an arithmetic circuit that calculates reactive power from values input to the two input circuits, each of the two input circuits has a digital signal that is sampled at a predetermined period from an input analog signal. The arithmetic circuit includes a storage circuit that temporarily stores this digital data, and converts the digital data stored in the storage circuit into data corresponding to voltage and electrical angle π/2. 1. A reactive power measuring device comprising: means for reading out data corresponding to a current whose phase is delayed by a certain amount, and calculating a time-integrated average of the product thereof. 2. The memory circuits are two first-in, first-out memory circuits that are connected to the outputs of the two input circuits and are written using clock signals that are synchronized with the clock signals of the analog-to-digital conversion circuits, respectively, and perform the calculation. 2. The reactive power measuring device according to claim 1, wherein the means includes means for supplying, as readout clock signals, clock signals whose starting times differ from each other by the one-fourth period to the two first-in, first-out storage circuits.