CN101718820B - Power distribution transformer monitoring terminal and method for calculating current complex power precision thereof - Google Patents
Power distribution transformer monitoring terminal and method for calculating current complex power precision thereof Download PDFInfo
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Abstract
The invention relates to a method for improving calculation current and complex power precision of a power distribution transformer monitoring terminal, including: dividing a three-phase current into two paths after the three-phase current passes a current transformer (CT), not amplifying one path, and amplifying the other path by ten times, then entering an analog-to-digital converter (AD) for sampling, finally performing a fast Fourier translation (FFT) calculation according to the conversion result and selecting an appropriate group of current data; setting an initial phase different of the three-phase voltage and the three-phase current which is an asynchrony phase difference obtained according to the phase difference of the voltage and the current at the maximum spectral line through the FFT calculation when an analog-to-digital conversion (ACD) is entered, and calculating the complex power through compensation of the phase error. The measuring precision of the three-phase current and the complex power is increased by adopting the fast Fourier transform FFT algorithm. The functions of measuring, monitoring, communication and meter reading are integrated into one body and the precision of calculating the current and the complex power of the power distribution transformer monitoring terminal is increased.
Description
Technical field
The method of electric current and complex power precision is calculated in the raising that the present invention relates to a kind of distribution transformer monitoring terminal.
Background technology
Along with the continuous development of science and technology, to the demand of electric power energy and qualitatively, all have higher requirement from quantity.Electric system is a convenient management; Usually in certain area coverage; For example a residential quarter or an office block are provided with the continuous data of various measuring terminals in the concentrator pickup area, and monitoring and the control of distributing transformer monitoring equipment to the operation of power networks situation will be set.But the metering of present most distributing transformer monitoring equipment, monitoring, communication, meter-reading module all are separately designs; Though can concentrate placement; Unified management, but still need lay various communication line between each equipment guaranteeing mutual back work and coordination, and each equipment all will dispose special communication interface circuit and is connected with the upload control main website; Cause resource to repeat, and it keeps in repair and maintenance difficulties is big, cost is high, reliability is low.Simultaneously present most monitoring terminals adopt single-chip microcomputer, single channel A/D to add the data acquisition and processing (DAP) circuit that multi-way switch is formed, and generally adopt the computing method of time domain.Along with people's is to the improve of electric power monitoring system performance requirement, and the deficiency on the performance that this structure is brought is then more and more obvious.Mainly comprise following three aspects: (1) in the signal processing circuit of in the past measuring three-phase current, no matter the size of electric current directly gets into the A/D module and samples, and causes bigger measuring error; (2) owing to adopt the computing method of frequency domain, counting of Fast Fourier Transform (FFT) FFT sampling is also increasingly high, makes SF and calculated amount improve greatly, and the circuit that common single-chip microcomputer and A/D converter are formed can't satisfy the requirement of system performance; (3) non-synchronous sampling of three-phase voltage and three-phase current has caused the measuring error of voltage and current phase differential, and the error that causes calculating complex power is bigger, when particularly proceeding to higher hamonic wave and analyzing, can cause the very big error of calculation.
Summary of the invention
In order to address the above problem, the purpose of this invention is to provide a kind of method that can improve distribution transformer monitoring terminal calculating electric current and complex power precision.
The present invention realizes through following technical scheme:
The method of electric current and complex power precision is calculated in the raising of distribution transformer monitoring terminal:
After three-phase current Ia, Ib, Ic are through current transformer CT; In described signal conditioning circuit; Respectively three-phase Ia, Ib, Ic are divided into two-way, the one tunnel does not amplify it, and another road is amplified ten times to it; The analog-to-digital conversion module ADC that gets into said digital signal processor DSP then samples, and at last carries out fast Flourier FFT according to the transformation result of the analog-to-digital conversion module ADC of said digital signal processor DSP and calculates and select one group of suitable current data;
Set three-phase voltage and three-phase current initial phase difference is
after three-phase voltage and three-phase current pass through the analog-to-digital conversion module ADC conversion of said digital signal processor DSP simultaneously; Calculate through FFT FFT, obtain the phase differential
of voltage and current at maximum spectral line place obtain three-phase voltage and three-phase current because of mutual inductor, circuit and the asynchronous phase error that causes of analog-to-digital conversion module ADC
that gets into said digital signal processor DSP through compensation of phase error
calculating complex power.
Three-phase voltage passes through current transformer CT through voltage transformer (VT) and three-phase current, is connected with the signal input part of signal conditioning circuit respectively, and the signal output part of signal conditioning circuit is connected with the interior analog-to-digital conversion module ADC of said digital signal processor DSP.
Effect of the present invention:
(1) the present invention adopts the digital signal processor DSP chip as CPU; Can accomplish the accurate measurement to three-phase voltage, three-phase current, complex power, to the monitoring of various pulsed quantities and quantity of state, it is fast to have processing speed; Volume is little; Maintenance, maintenance difficulties is low, effectively reduces the investment of total system, and tangible economic benefit is arranged.
(2) the present invention adopts the Fast Fourier Transform (FFT) fft algorithm to improve the measuring accuracy of three-phase current and complex power; Its measurement result has improved the precision of frequency analysis; Substation transformer is monitored in real time,, improve the reliability of system to realize the real-time monitoring and control of system.
Description of drawings
Fig. 1 is the hardware principle block diagram of distribution transformer monitoring terminal.
Fig. 2 is the conditioning module circuit theory diagrams of three-phase current, three-phase voltage.
Fig. 3 is the process flow diagram of metering three-phase current, three-phase voltage.
Fig. 4 is the external expansion interface schematic diagram of the serial peripheral equipment interface SPI of digital signal processor DSP.
Embodiment
Describe the present invention with reference to the accompanying drawings.
Fig. 1 is a hardware principle block diagram of the present invention.It includes power management module (2), active crystal oscillator module (3) and the watchdog module (4) of digital signal processor DSP (1) and relative set; Behind three-phase voltage U a, Ub, Uc process voltage transformer pt (5) and three-phase current Ia, Ib, the Ic process current transformer CT (6), the analog-to-digital conversion module ADC that gets into said digital signal processor DSP through signal conditioning circuit (7) respectively samples; The serial communication interface SCI of said digital signal processor DSP is connected with the general packet radio service GPRS network communication module (9) that is used for controlling center (8) communication; The internal integrated circuit I of said digital signal processor DSP
2The C bus is connected with clock chip RX8025 (11) with the exterior storage chip 24C64EEPROM (10) that is used to store all kinds of parameters and data respectively; The serial peripheral equipment interface SPI of said digital signal processor DSP is connected with external expansion interface chip SC16IS752 (12); Expand two asynchronous serial communication interface UARTA and UARTB respectively through described external expansion interface chip SC16IS752; Said asynchronous serial communication interface UARTA is connected with RS485 (14) interface through level transferring chip MAX485 (13), and said asynchronous serial communication interface UARTB is connected with line of electric force low pressure carrier wave meter-reading module (15); Be respectively arranged with at the general purpose digital quantity input/output port GPIO of said digital signal processor DSP and be used to control the energy supply control module (16) that general packet radio service GPRS module resets; Keysheet module (17); Be used to show the LCD MODULE LCD (18) of each item continuous data and parameter; Various pulsed quantity input signals (19) and quantity of state input signal (20) are used for the digital quantity output circuit (24) of pilot relay group (23) action through the digital quantity input circuit (22) of photoelectrical coupler (21) input and through photoelectrical coupler.
Keyboard circuit is made up of the six press keys switch; One end ground connection of each button, the other end links to each other with the general purpose input/output port GPIO of digital signal processor DSP, and receives 3.3V through pull-up resistor; When button was not pressed, it was logical one that digital signal processor DSP reads key assignments; When button was pressed, it was logical zero that digital signal processor DSP reads key assignments.LCD MODULE LCD adopts the Chinese dot matrix type graph lcd module OCM12864 of 128*64, and the lattice pixels of LCD is arranged continuously, and row and column does not all have empty separated in arranging, can character display, Chinese character and continuous figure.The LCD MODULE WV is 3.3V, has 8 normal data buses, and 6 control lines and power lead need combine keyboard to accomplish demonstration work by digital signal processor DSP.
As shown in Figure 2; When using transformer monitoring terminal of the present invention to be used to measure three-phase voltage and three-phase current; Because the variation range of three-phase voltage U a, Ub, Uc is smaller; So only need it is converted into the needed voltage 1.5～3.3V of digital signal processor DSP through voltage transformer pt, voltage follower, the analog-to-digital conversion module ADC that can get into said digital signal processor DSP samples.But the variation range of three-phase current Ia, Ib, Ic is bigger; Need change to tens amperes from several milliamperes; Therefore after three-phase current Ia, Ib, Ic are through current transformer CT; The first via is not amplified it, directly gets into said digital signal processor DSP through voltage follower and handles, and the second the tunnel amplifies 10 times of said digital signal processor DSPs of entering through operational amplifier handles.
As shown in Figure 3; Three-phase current and three-phase voltage are changed through the analog-to-digital conversion module ADC that at first gets into said digital signal processor DSP after the above-mentioned processing; Carry out Fast Fourier Transform (FFT) FFT according to the transformation result of the analog-to-digital conversion module ADC of said digital signal processor then, obtain the complex phase amount of three-phase current and three-phase voltage.When the scope of three-phase current at several amperes between tens amperes the time, select the measured current data of the first via; When the scope of three-phase current is between several milliamperes to several amperes, select the second tunnel measured current data.After this kind processing, improved the measuring accuracy of electric current significantly.
Three-phase current, three-phase voltage are because mutual inductor, circuit and the asynchronous phase error that causes of analog-to-digital conversion module ADC that gets into said digital signal processor DSP; So the present invention improves the precision of calculating complex power through the method for compensation of phase error; So-called complex power S=P+jQ; Wherein S representes complex power, and P representes active power, and Q representes reactive power.Concrete computation process is following:
The frequency of setting three-phase voltage U a is identical with the frequency of three-phase current Ia, the initial phase of Ua be the initial phase of
Ia be
initial phase difference
promptly
Then complex power is
in theory wherein
be the conjugate complex number of
; Promptly
P is an active power, and Q is a reactive power.
After three-phase voltage U a and three-phase current Ia pass through the analog-to-digital conversion module ADC conversion of said digital signal processor DSP simultaneously; Calculate through FFT FFT, obtain both phase differential at maximum spectral line place can obtain for
Ua and Ia because of mutual inductor, circuit and the asynchronous phase error that causes of analog-to-digital conversion module ADC
that gets into said digital signal processor DSP then the complex power of reality should be
When not response external order of long period appears in the general packet radio service GPRS network communication module that is used for the controlling center communication of distribution transformer monitoring terminal; In the time of perhaps can not special circumstances such as normally closing through AT order; This moment is through the power supply of the general purpose digital quantity input/output port GPIO control energy supply control module force disconnect GPRS module of said digital signal processor DSP; Restart then, activate the GPRS module again.
The quantity of state collection of distribution transformer monitoring terminal mainly is real-time collection position state and other status informations, should write down current remote signalling state, writes down remote signalling displacement information again; The pulsed quantity collection mainly is the pulse of gathering electric energy meter output, and calculates electric flux according to electric energy meter pulse constant and mutual inductor ratio.Because pulsed quantity and quantity of state all are switching values, so with both input interface circuit Unified Treatment, the present invention has designed the digital-quantity input interface circuit of four-way.The forceful electric power signal of outside input at first carries out electrical isolation and buffering through photoelectrical coupler; Reduce power surges, suppress spike pulse and interference of noise, the general purpose input/output port GPIO that then weak electric signal of its output is sent into digital signal processor DSP detects.
It is remote control that the control command that distant place main website issues is accepted at the substation transformer terminal, and the controlled variable that perhaps issues according to main website is controlled according to user power utilization situation at that time, operates exit relay and carries out corresponding action.Two groups of actuating mechanisms are arranged in the relay, can realize normally opened contact, normally closed contact through being connected to different lead-out terminals.During no control action, photoelectric coupling circuit is not worked, and triode is in cut-off state, makes relay keep original state to prevent malfunction.
In central controlled occasion, the point that need carry out communication is a lot, and often has only one or two as the microcontroller serial port of control maincenter, in order to realize the control to multiple spot, need expand serial ports.Owing to have only one or two asynchronous serial communication interface SCI in the said digital signal processor DSP sheet; Can't satisfy the demand of on-scene communication fully; Therefore expand two asynchronous serial communication interface UARTA and UARTB through the serial peripheral equipment interface SPI of said digital signal processor DSP through external expansion interface chip SC16IS752; Said asynchronous serial communication interface UARTA is through one of level transferring chip MAX485 expansion and RS485 interface, and said asynchronous serial communication interface UARTB expands a low voltage power line carrier meter-reading module.
Claims (2)
1. the method for electric current and complex power precision is calculated in the raising of distribution transformer monitoring terminal, it is characterized in that:
After three-phase current Ia, Ib, Ic are through current transformer CT; In described signal conditioning circuit; Respectively three-phase Ia, Ib, Ic are divided into two-way, the one tunnel does not amplify it, and another road is amplified ten times to it; The analog-to-digital conversion module ADC that gets into said digital signal processor DSP then samples, and at last carries out fast Flourier FFT according to the transformation result of the analog-to-digital conversion module ADC of said digital signal processor DSP and calculates and select one group of suitable current data;
Set three-phase voltage and three-phase current initial phase difference is
after three-phase voltage and three-phase current pass through the analog-to-digital conversion module ADC conversion of said digital signal processor DSP simultaneously; Calculate through FFT FFT, obtain the phase differential
of voltage and current at maximum spectral line place obtain three-phase voltage and three-phase current because of mutual inductor, circuit and the asynchronous phase error that causes of analog-to-digital conversion module ADC
that gets into said digital signal processor DSP through compensation of phase error
calculating complex power.
2. the method for electric current and complex power precision is calculated in the raising of distribution transformer monitoring terminal according to claim 1; It is characterized in that: three-phase voltage passes through current transformer CT through voltage transformer (VT) and three-phase current; Be connected with the signal input part of signal conditioning circuit respectively, the signal output part of signal conditioning circuit is connected with the interior analog-to-digital conversion module ADC of said digital signal processor DSP.
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| CN102095925B (en) * | 2010-12-31 | 2013-03-06 | 江苏省电力公司电力科学研究院 | Electronic reactive power meter based on Walsh transformation algorithm |
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| CN103278687A (en) * | 2012-09-28 | 2013-09-04 | 天津学子电力设备科技有限公司 | Power distribution network phase recognition device based on gprs (general packet radio service) |
| CN102946260B (en) * | 2012-12-04 | 2014-08-13 | 湖南大学 | Automatic meter reading system and communication link quality detecting method thereof |
| CN103033717A (en) * | 2012-12-28 | 2013-04-10 | 安徽中兴继远信息技术股份有限公司 | Oversampling distribution transformer terminal |
| CN103323723B (en) * | 2013-07-18 | 2015-08-12 | 中国海洋石油总公司 | A kind of offshore power grid distribution end apparatus for monitoring energy resource and monitoring method |
| CN105116263A (en) * | 2015-09-18 | 2015-12-02 | 成都比善科技开发有限公司 | Intelligent power monitoring device |
| US9843335B2 (en) * | 2015-12-29 | 2017-12-12 | Schweitzer Engineering Laboratories, Inc. | Supervision of input signal channels |
| CN106645926B (en) * | 2016-12-29 | 2019-11-08 | 国网智能科技股份有限公司 | A method for measuring and calculating the power of three-phase AC circuit |
| CN107831361A (en) * | 2017-10-27 | 2018-03-23 | 深圳华讯角度生物医疗电子科技有限公司 | A kind of power measurement instruments |
| CN110687483A (en) * | 2019-10-26 | 2020-01-14 | 湖北民族大学 | On-line monitoring and fault diagnosis device for high-voltage distribution transformers |
| CN111650433A (en) * | 2020-04-01 | 2020-09-11 | 国家电网有限公司 | Distribution transformer terminal power consumption measurement circuit and distribution transformer terminal |
| CN111541303A (en) * | 2020-05-07 | 2020-08-14 | 瑞壳科技（上海）有限公司 | A power monitoring system |
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