CN101539596A - Method for monitoring electric network frequency - Google Patents
Method for monitoring electric network frequency Download PDFInfo
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- CN101539596A CN101539596A CN200810034943A CN200810034943A CN101539596A CN 101539596 A CN101539596 A CN 101539596A CN 200810034943 A CN200810034943 A CN 200810034943A CN 200810034943 A CN200810034943 A CN 200810034943A CN 101539596 A CN101539596 A CN 101539596A
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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
The present invention relates to a kind of monitoring method of mains frequency, relate in particular to a kind of appointing and lack one mutually or appoint scarce two-phase, have simultaneously under the situation of harmonic interference, still can normally finish the method for monitoring electric network frequency at three-phase voltage.
Background technology
Mains frequency is one of important parameter of apparatus of electrical monitoring equipment monitoring, for three-phase voltage, watch-dog is usually selected wherein one as the frequency monitoring signal, the disappearance if this phase voltage meets accident, then monitoring electric network frequency stops immediately, and some apparatus of electrical monitoring equipment the frequency measurement mistake can occur under the bigger situation of higher harmonic content in addition.
Along with improving constantly of power monitoring demand, under the situation of phase shortage and harmonic interference, still can the requirement that parameters of electric power carries out complete monitoring also be become increasingly conspicuous.Because the situation of A, B, C three-phase generation phase shortage is at random, and harmonic interference is the common interference that apparatus of electrical monitoring equipment will be faced, therefore, provide a kind of to lack a phase or two phase voltages, under the situation of harmonic interference, the method that still can normally finish monitoring electric network frequency is an apparatus of electrical monitoring equipment frequency monitoring function important technological problems to be solved simultaneously.
Summary of the invention
The technical issues that need to address of the present invention have provided a kind of method of monitoring electric network frequency, can satisfy the demand that apparatus of electrical monitoring equipment still can normally be monitored mains frequency under phase shortage and harmonic interference situation.
In order to solve the problems of the technologies described above, the present invention realizes by following steps:
(a) A, B, the voltage signal of C three-phase voltage after the mutual inductor conversion carry out computing: U=UA+UB-UC;
(b) operation result signal U is carried out low-pass filtering;
(c) filtered signal is carried out frequency measurement.
Compared with prior art, the invention has the beneficial effects as follows: make watch-dog have under any phase shortage and harmonic interference situation, still can normally finish the function of grid frequency measurement.
Description of drawings
Fig. 1 is the signal processing flow synoptic diagram of embodiments of the invention one;
Fig. 2 is the signal processing flow synoptic diagram of embodiments of the invention two.
Embodiment
Below in conjunction with accompanying drawing and embodiment the present invention is described in further detail:
The present invention realizes by following steps:
(a) A, B, the voltage signal of C three-phase voltage after the mutual inductor conversion carry out computing: U=UA+UB-UC;
(b) operation result signal U is carried out low-pass filtering;
(c) filtered signal is carried out frequency measurement.
In described step (a), to the signal operation that three-phase voltage carries out, described signal operation process can be finished by signal computing circuit, also can finish computing to digital signal in A/D conversion back;
In described step (b), described low-pass filter acts on the voltage signal after the computing, if signal operation adopts mimic channel to finish, low-pass filtering can be an analog filter, if the digital signal of signal operation after the A/D conversion carried out, then filtering can be adopted the FIR wave filter of numerical approach.
In described step (c), if the method that adopts mimic channel to carry out signal operation and filtering, then frequency measurement is that the square wave after the shaping is caught frequency measurement to amplification; If the employing numerical approach, then frequency measurement is by the identification of digital signal zero passage, interpolation, and the method for computation period is finished frequency measurement.
The specific embodiment of the present invention has two kinds:
Adopt analog form when (1) system does not have the voltage monitoring function, comprise voltage transformer (VT), signal computing circuit, amplification shaping and input capture circuit;
Adopt digital form when (2) system has the voltage monitoring function, comprise voltage transformer (VT), signal conditioning circuit and A/D conversion, digital signal computing, FIR low-pass filter, zero passage identification calculated rate;
Embodiment one and example two described voltage transformer (VT) are used for outside three-phase voltage (220V or 100V) is converted to the inner weak current signal of apparatus of electrical monitoring equipment;
Embodiment one described signal computing circuit, be voltage signal with the weak current conversion of signals at first with resistance, the adder and substracter circuit that adopts operational amplifier to form then carries out following computing: U=UA+UB-UC to three-phase voltage signal, and then three-phase voltage synthesizes one road voltage signal;
Embodiment one described amplification shaping and input capture circuit, the general amplifying circuit that at first adopts operational amplifier to form amplifies at least 10 times to signal U, use the later waveform intercepting of diode pair amplification of two clamping actions to obtain approximate square wave then, further by Schmidt trigger to signal shaping, be input to the I/O pin that MCU/DSP has capturing function at last; Under the control of MCU/DSP, catch I/O and can capture two adjacent rising edges (or negative edge), and write down its time interval, be the signal period, further obtain frequency.Typical circuit as shown in Figure 1.
In described step (a), the three-phase voltage simulating signal has been finished following computing U=UA+UB-UC.Because UA, UB, UC are that frequency is identical, differ 120 ° sine (cosine) signal, close poor eliminate indigestion formula according to trigonometric function and prove that easily signal U after the computing is and UA, UB, voltage signal that the UC frequency is identical.
In described step (b), the voltage signal after the computing is carried out low-pass filtering, to remove harmonic interference.Further, filtered signal is amplified common more than 10 times, and use stabilivolt (or diode) that the part that exceeds logic high in the waveform and be lower than logic low is cut out, become the approximate square-wave signal that to catch measurement.Adopt Schmidt trigger pairing approximation square-wave signal to carry out shaping at last, to reduce error.
In described step (c), what the square-wave signal after the shaping was imported into MCU or DSP catches the I/O pin, and the function that its rising edge to pin level (or negative edge) is caught timing can be finished the mensuration of square-wave cycle (frequency).
Do not influence the technical matters of frequency monitoring when appointing a scarce phase or two phase voltages in order to solve, the invention provides and pass through signal operation, and the signal after the computing carried out the influence that the method for frequency monitoring avoids phase shortage to bring, it is characterized in that signal operation, signal operation is the key that guarantees to finish under the phase shortage situation normal frequency measurement, promptly still can obtain the voltage signal identical with mains frequency under the phase shortage situation arbitrarily by linear operation UA+UB-UC.Simultaneously for to avoid the influence of harmonic wave to frequency monitoring, wave filter provided by the invention to it is characterized in that the signal after the UA+UB-UC computing is carried out low-pass filtering, and, can obviously reduce equipment cost, improve plant efficiency not to three-phase voltage filtering respectively.
Because most apparatus of electrical monitoring equipment have the three-phase voltage monitoring function, promptly has the link of three-phase voltage signal being carried out the A/D conversion, in this case, the present invention adopts identical mechanism to provide a kind of numerical approach to finish frequency monitoring under any phase shortage situation and the harmonic interference, can further significantly reduce equipment cost, this method may further comprise the steps:
(A) A, B, C three-phase voltage are converted to light current through mutual inductor and press signal, and signal condition is after A/D is converted to the digital signal sequences of three-phase voltage: UA (n), UB (n), UC (n)
(B) UA, UB, all corresponding sampling point data of UC are carried out following computing and are obtained new voltage signal sequence U (n)=UA (n)+UB (n)-UC (n), and to adopt passband be that the FIR low-pass filter of 0 ~ 80Hz carries out filtering to U (n).
(C) by zero crossing identification and linear interpolation method, finish the calculating of signal period and frequency.
In described step (A), finish the discrete sampling and the digitized process of three-phase voltage by hardware circuits such as mutual inductor, signal condition, A/D conversion and MCU/DSP.
In described step (B), digital signal sequences is finished linear computing U (n)=UA (n)+UB (n)-UC (n), because UA, UB, UC are that frequency is identical, differ 120 ° sine (cosine) signal, prove that easily burst U (n) after the computing is and UA, UB, voltage signal that the UC frequency is identical.Adopting passband in addition is that the FIR low-pass filter of 0 ~ 80Hz carries out filtering to digital signal sequences U (n), to remove harmonic interference.Because digital signal is to finish frequency measurement with the method for zero crossing identification, therefore requires wave filter to have linear phase characteristic, must adopt the FIR wave filter.
In described step (C), filtered Serial No. U (n) is carried out zero crossing identification, promptly search for two consecutive point of opposite in sign in the Serial No., and between these 2, calculate relative precise zero points position by approach based on linear interpolation, at last according to a plurality of signal calculated cycles at zero point and frequency.
It is the voltage signal (comprising transfer resistance and amplifying circuit) that the weak current signal of voltage transformer (VT) output at first is converted to suitable A/D converter input range that embodiment two described signal conditioning circuits and A/D change its effect, be input to A/D converter (can be that A/D converter also can be external serial or parallel interface A/D converter on the MCU/DSP sheet) then, under the control of MCU/DSP, three-phase voltage signal is gathered the digital signal sequences that is converted to three-phase voltage: UA (n), UB (n), UC (n) simultaneously with certain sample frequency.
Embodiment two described digital signal computings are UA, UB, all corresponding sampling point data of UC to be carried out following computing obtain new sequence U (n)=UA (n)+UB (n)-UC (n).
Embodiment two described FIR low-pass filters can adopt THE DESIGN OF WINDOW FUNCTION method or the design of other method for designing, and its passband is below the 80Hz, and stopband is more than the 120Hz, adopts the FIR wave filter on about 40 ~ 60 rank usually.This wave filter acts on signal U (n), to remove the interference of harmonic wave to influence, the especially higher hamonic wave of frequency measurement.
Embodiment two described zero passage identification calculated rates are that filtered U (n) sequence is scanned, identification obtains two sampling points before and after the zero passage, and the method for using these two linear interpolation of sampling point obtains near the more accurate position of signal zero (0 o'clock, function y=sin (x) is similar to y=x); Adopt and use the same method, can calculate a series of null position according to U (n) sequence, thereby calculate the signal period, further obtain frequency.Typical circuit as shown in Figure 2.
Claims (4)
1. the method for a monitoring electric network frequency, realize by following steps:
(a) A, B, the voltage signal of C three-phase voltage after the mutual inductor conversion carry out computing: U=UA+UB-UC;
(b) operation result signal U is carried out low-pass filtering;
(c) filtered signal is carried out frequency measurement.
2. the method for monitoring electric network frequency according to claim 1, in described step (a), to the signal operation that three-phase voltage carries out, described signal operation process can be finished by signal computing circuit, also can finish computing to digital signal in A/D conversion back.
3. the method for monitoring electric network frequency according to claim 1, in described step (b), described low-pass filter acts on the voltage signal after the computing, if signal operation adopts mimic channel to finish, low-pass filtering can be an analog filter, if the digital signal of signal operation after the A/D conversion carried out, then filtering can be adopted the FIR wave filter of numerical approach.
4. the method for monitoring electric network frequency according to claim 1, in described step (c), if the method that adopts mimic channel to carry out signal operation and filtering, then frequency measurement is to amplifying, the square wave after the shaping is caught frequency measurement; If the employing numerical approach, then frequency measurement is by the identification of digital signal zero passage, interpolation, and the method for computation period is finished frequency measurement.
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| CN200810034943A CN101539596A (en) | 2008-03-21 | 2008-03-21 | Method for monitoring electric network frequency |
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Cited By (13)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102062809A (en) * | 2010-11-10 | 2011-05-18 | 电子科技大学 | Method for capturing and locking voltage zero-crossing point of power grid |
| CN102253281A (en) * | 2011-04-26 | 2011-11-23 | 江苏斯菲尔电气股份有限公司 | Method for measuring power grid frequency by resisting harmonic interference and automatically changing phase based on software |
| CN102539912A (en) * | 2011-12-21 | 2012-07-04 | 上海市电力公司 | Mains frequency detection method for load monitor |
| CN101865951B (en) * | 2009-12-23 | 2012-08-08 | 中国航空工业集团公司第六三一研究所 | Anti-interference frequency measuring method |
| CN102749508A (en) * | 2011-04-20 | 2012-10-24 | 北京德威特继保自动化科技股份有限公司 | Frequency measurement device and method |
| CN103048539A (en) * | 2012-12-28 | 2013-04-17 | 南京工程学院 | Accurate acquisition device and method of power frequency in audio forensics |
| CN103197158A (en) * | 2013-03-26 | 2013-07-10 | 深圳市英威腾电气股份有限公司 | Three-phase power grid phase loss detection method and circuit |
| CN104007312A (en) * | 2014-06-20 | 2014-08-27 | 西南大学 | Signal frequency real-time measuring method based on low-frequency square signal frequency prediction |
| CN104483547A (en) * | 2014-11-27 | 2015-04-01 | 广东电网有限责任公司电力科学研究院 | Method and system for filtering power signal |
| CN104569581A (en) * | 2015-01-30 | 2015-04-29 | 湖南大学 | Multi-level set and single-cycle estimation method of power grid frequency measuring |
| CN106405230A (en) * | 2016-08-23 | 2017-02-15 | 北京德威特继保自动化科技股份有限公司 | Frequency measuring method and apparatus |
| CN109470934A (en) * | 2018-11-02 | 2019-03-15 | 广州绰立科技有限公司 | The detection method and its detection system of input phase failure |
| CN111896807A (en) * | 2020-08-05 | 2020-11-06 | 威胜集团有限公司 | Fundamental wave frequency measuring method, measuring terminal and storage medium |
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2008
- 2008-03-21 CN CN200810034943A patent/CN101539596A/en active Pending
Cited By (20)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN101865951B (en) * | 2009-12-23 | 2012-08-08 | 中国航空工业集团公司第六三一研究所 | Anti-interference frequency measuring method |
| CN102062809A (en) * | 2010-11-10 | 2011-05-18 | 电子科技大学 | Method for capturing and locking voltage zero-crossing point of power grid |
| CN102749508A (en) * | 2011-04-20 | 2012-10-24 | 北京德威特继保自动化科技股份有限公司 | Frequency measurement device and method |
| CN102749508B (en) * | 2011-04-20 | 2015-08-12 | 北京德威特继保自动化科技股份有限公司 | Frequency measuring equipment and method |
| CN102253281A (en) * | 2011-04-26 | 2011-11-23 | 江苏斯菲尔电气股份有限公司 | Method for measuring power grid frequency by resisting harmonic interference and automatically changing phase based on software |
| CN102539912B (en) * | 2011-12-21 | 2014-10-08 | 上海市电力公司 | Mains frequency detection method for load monitor |
| CN102539912A (en) * | 2011-12-21 | 2012-07-04 | 上海市电力公司 | Mains frequency detection method for load monitor |
| CN103048539A (en) * | 2012-12-28 | 2013-04-17 | 南京工程学院 | Accurate acquisition device and method of power frequency in audio forensics |
| CN103197158A (en) * | 2013-03-26 | 2013-07-10 | 深圳市英威腾电气股份有限公司 | Three-phase power grid phase loss detection method and circuit |
| CN103197158B (en) * | 2013-03-26 | 2015-09-16 | 深圳市英威腾电气股份有限公司 | A kind of three phase network method for detecting open phase and circuit |
| CN104007312A (en) * | 2014-06-20 | 2014-08-27 | 西南大学 | Signal frequency real-time measuring method based on low-frequency square signal frequency prediction |
| CN104007312B (en) * | 2014-06-20 | 2017-01-18 | 西南大学 | Signal frequency real-time measuring method based on low-frequency square signal frequency prediction |
| CN104483547A (en) * | 2014-11-27 | 2015-04-01 | 广东电网有限责任公司电力科学研究院 | Method and system for filtering power signal |
| CN104569581A (en) * | 2015-01-30 | 2015-04-29 | 湖南大学 | Multi-level set and single-cycle estimation method of power grid frequency measuring |
| CN106405230A (en) * | 2016-08-23 | 2017-02-15 | 北京德威特继保自动化科技股份有限公司 | Frequency measuring method and apparatus |
| CN106405230B (en) * | 2016-08-23 | 2019-04-12 | 北京德威特电气科技股份有限公司 | Frequency measurement method and device |
| CN109470934A (en) * | 2018-11-02 | 2019-03-15 | 广州绰立科技有限公司 | The detection method and its detection system of input phase failure |
| CN109470934B (en) * | 2018-11-02 | 2021-06-25 | 广州绰立科技有限公司 | Input phase loss detection method and detection system thereof |
| CN111896807A (en) * | 2020-08-05 | 2020-11-06 | 威胜集团有限公司 | Fundamental wave frequency measuring method, measuring terminal and storage medium |
| CN111896807B (en) * | 2020-08-05 | 2023-03-14 | 威胜集团有限公司 | Fundamental wave frequency measuring method, measuring terminal and storage medium |
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Open date: 20090923 |