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Method for monitoring electric network frequency

A power grid frequency and frequency measurement technology, applied to frequency measurement devices, etc., can solve problems such as frequency measurement errors

Inactive Publication Date: 2009-09-23
上海威能电力科技有限公司
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

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Problems solved by technology

[0002] Grid frequency is one of the important parameters monitored by power monitoring equipment. For three-phase voltage, the monitoring equipment usually selects one of the phases as the frequency monitoring signal. If the phase voltage is unexpectedly missing, the grid frequency monitoring will stop immediately. In addition, some power monitoring When the equipment has relatively large high-order harmonic content, frequency measurement errors will occur

Method used

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  • Method for monitoring electric network frequency

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Experimental program
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Effect test

Embodiment 1

[0024] The signal operation circuit described in Embodiment 1 first converts the weak current signal into a voltage signal with a resistor, and then uses an addition and subtraction circuit composed of an operational amplifier to perform the following operations on the three-phase voltage signal: U=UA+UB-UC, then three The phase voltage is synthesized into a voltage signal;

[0025] The amplification, shaping and input capture circuit described in Embodiment 1 first uses a general-purpose amplifying circuit composed of an operational amplifier to amplify the signal U by at least 10 times, and then uses two clamping diodes to intercept the amplified waveform to obtain an approximate square wave, and further The signal is shaped by the Schmitt trigger, and finally input to the I / O pin of the MCU / DSP with capture function; under the control of the MCU / DSP, the capture I / O can capture two adjacent rising edges (or Falling edge), and record its time interval, which is the signal pe...

Embodiment 2

[0037] The function of the signal conditioning circuit and A / D conversion described in Embodiment 2 is to first convert the weak current signal output by the voltage transformer into a voltage signal suitable for the input range of the A / D converter (including a conversion resistor and an amplifying circuit), and then input to the A / D converter (it can be the A / D converter on the MCU / DSP chip or an external serial or parallel interface A / D converter), under the control of the MCU / DSP, the three-phase voltage signal is in a certain Simultaneously collect and convert the digital signal sequence of the three-phase voltage: UA(n), UB(n), UC(n) at the same sampling frequency.

[0038] The digital signal operation described in the second embodiment is to perform the following operation on all corresponding sample point data of UA, UB, and UC to obtain a new sequence U(n)=UA(n)+UB(n)-UC(n).

[0039] The FIR low-pass filter described in Embodiment 2 can be designed by using window fun...

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Abstract

The invention relates to a method for monitoring electric network frequency, which is realized by the following steps of: (A) calculating voltage signals of A, B and C three-phase voltage subjected to mutual inductor conversion: U=UA+UB-UC; (b) performing the low-pass filtration of the calculated result signal U; and (C) measuring the frequency of the filtered signal. The method has the advantage that a monitoring device can still normally finish the function of measuring the electric network frequency under the conditions of any phase failure and harmonic interference.

Description

technical field [0001] The invention relates to a method for monitoring the frequency of a grid, in particular to a method which can still normally monitor the grid frequency when one or both phases of the three-phase voltage are missing and there is harmonic interference. Background technique [0002] Grid frequency is one of the important parameters monitored by power monitoring equipment. For three-phase voltage, the monitoring equipment usually selects one of the phases as the frequency monitoring signal. If the phase voltage is unexpectedly missing, the grid frequency monitoring will stop immediately. In addition, some power monitoring When the equipment has relatively large high-order harmonic content, frequency measurement errors will occur. [0003] With the continuous improvement of the demand for power monitoring, the requirement for complete monitoring of power parameters in the case of phase loss and harmonic interference is also becoming more and more prominent....

Claims

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Application Information

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IPC IPC(8): G01R23/02
Inventor 凌万水贾林壮
Owner 上海威能电力科技有限公司
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