CN103439545A - Analysis design method for reducing radiation interference of intelligent electric energy meter - Google Patents
Analysis design method for reducing radiation interference of intelligent electric energy meter Download PDFInfo
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Abstract
The invention discloses an analysis design method for reducing the radiation interference of an intelligent electric energy meter and provides a scheme which involves scientific and high-efficient fault and defect analyzing, problem solving and design improving. The method comprises the following steps: 1). beginning principle designing: drawing and selecting devices; 2). arranging a board, installing, and forming a prototype; 3). carrying out a battery power supply test; 4). determining whether the radiation interference of a high-frequency circuit exceeds a standard; 5). carrying out a first battery power supply test; 6). determining whether the radiation interference of a power supply circuit exceeds a standard; 7). carrying out a second battery power supply test; 8). determining whether the radiation interference of a metering circuit exceeds a standard; and 9). finishing. The method is designed by taking a national standard compulsorily executed in the industry as a criterion. By using the method, the capacity level of the design personnel of small and medium-sized electric energy meter manufacturers in analyzing, designing and improving radiation interference defects in a product designing process in a high-efficient and standard mode can be improved, the time, cost and labor for repeated examination can be reduced, the research and development cost can be saved, the research and development period can be shortened, and the product cost can be lowered.
Description
Technical field
The present invention relates to a kind of intelligent electric energy meter design cycle technical field, relate in particular to improving one's methods of the radiation interference analysis of causes of intelligent electric meter and the defect analysis of carrying out thus, optimal design.
Background technology
Intelligent electric energy meter is as the measuring products of electric energy metrical and charge calculation, not only require product to there is precise and stable metering performance, and require product that extremely strong anti-electromagnetic interference (EMI), the ability of shock resistance adverse environment resistant are arranged, guarantee that under any circumstance power information is correctly reliable, guarantee that electricity consumption, power supply both sides' interests are without prejudice.Intelligent electric energy meter mostly adopts singlechip technology to design, and electromagnetic interference (EMI) is to cause the one of the main reasons of intelligent electric energy meter fault or hydraulic performance decline.Simultaneously intelligent electric energy meter this must the least possible external release electromagnetic interference (EMI) when completing self function energy.The Electro Magnetic Compatibility that improves intelligent electric energy meter is to improve the key of its operational reliability, in the world using Electro Magnetic Compatibility as electrical and electronic product very important performance index and formulated must mandatory execution rules.The beginning of the nineties in last century, China was just to the Electro Magnetic Compatibility requirement to some extent of electronic electric energy meter, so far experienced the development of 4 basic versions, wherein the Main change of radio-frequency radiation immunity experiment is presented as that frequency range constantly enlarges, field intensity constantly strengthens, environmental unit requires to improve constantly.
Electromagnetic compatibility comprises electromagnetic interference (EMI) and two aspects of electromagnetic immunity.Generally speaking, to same intelligent electric energy meter, reduce its external electromagnetic interference (EMI), will strengthen its immunity to interference to external electromagnetic interference.Electromagnetic interference (EMI) (EMI) comprises the electromagnetic interference (EMI) that conducted EMI (low frequency electromagnetic interference), radial pattern electromagnetic interference (EMI) (high-frequency electromagnetic interference), static discharge (ESD), lightning surge produce etc.The wherein the most difficult control of radial pattern electromagnetic interference (EMI), because the frequency of radial pattern electromagnetic interference (EMI) is higher, the wavelength of energy is very short, and very short PCB layout or electric energy meter electric source transformer coil, current mutual inductor coil, voltage transformer (VT) coil etc. all may become dual-mode antenna.
From 2010, State Grid Corporation of China carries out the uniform bidding buying to electric energy meter and power information collecting device, the thing followed is also more and more higher to electric energy meter and power information collecting device supplier's requirement, supplier is carried out to on-the-spot audit marking, as the foundation of the assessment of bids.More and more higher along with EMC Requirements, now using artificial mains network, frequency spectrograph etc. and radio frequency conduction, radiation test, relevant equipment is as the major criterion of skill score in state net company, and electric energy meter and power information collecting device supplier will set up radio frequency conduction and radiation anti-interference test chamber in response to the situation infusion of financial resources.On the one hand, this type of comparison in equipment costliness, bring no small burden to supplier really.On the other hand, really to supplier, improve electric energy meter electromagnetism compatible design level and brought help.By testing laboratory, tested, the situation that electromagnetic interference (EMI) is exceeded standard can be solved by improving PCB design or principle design, replacing components and parts etc., thereby pass through smoothly while at state's network metering center, carrying out full Performance Detection, when obtaining and dividing than hi-tech, also avoid secondary or duplicate detection expense that repeatedly censorship produces.
The problem faced at present is: for middle-size and small-size electric energy meter manufacturer, the professional who does not have the EMC Design aspect, the article of relevant electric energy meter electromagnetism compatibility test rectification is also just judged the case as it stands, once radio frequency Conduction Interference or radiation interference, can't pass, only have measures such as rule of thumb taking to add magnetic bead, do not know where problem goes out actually.2010, the applicant's a three-phase radio-frequency card table newly developed was just because radiation interference is bigger than normal fails by the detection of the metering scientific research institute of provinceing, through censorship repeatedly yet by detection.So the applicant has strengthened the input in this field, comprise increase equipment, technician etc., improved gradually the level of electric energy meter electromagnetism compatible design and test.After this, the applicant constantly explores at work, attempts to form a technological means that is conducive to industry design effort.
Summary of the invention
The present invention is directed to above problem, a kind of analysis design method that reduces the intelligent electric energy meter radiation interference is provided, a kind of science has been proposed, efficiently fault, defect analysis, problem solve, improve the scheme of design, can improve the middle-size and small-size electric energy meter electric energy meter designer of manufacturer in product design process to the radiation interference defect carry out efficiently, the analysis of standard, design, improvement ability level; Reduce the time, expense, the labour that repeat censorship, save R & D Cost, shorten the R&D cycle, reduce cost of products.
Technical scheme of the present invention is: comprise the following steps:
1), start principle design; Drawing, select device;
2), fabric swatch, installation; Form model machine;
3), powered battery test; Described model machine is only used powered battery, advances microwave dark room and carries out Electromagnetic Interference Test, obtains the electromagnetic radiation intensity test curve figure mono-of described model machine;
4), high frequency circuit radiation disturbs the judgement that whether exceeds standard;
As without abnormal, continue lower step;
If any extremely, demarcate the abnormity point in described electromagnetic radiation intensity test curve figure mono-, read described abnormal point numerical value, as this numerical value be as described in the integral multiple of crystal oscillator frequency in intelligent electric meter, go step 4.1); As non-integral multiple, go step 4.2);
4.1), the MCU crystal oscillating circuit is improved or is changed the crystal oscillator device;
4.1.1), the model machine of improved crystal oscillating circuit inserted to microwave dark room carry out Electromagnetic Interference Test, obtain electromagnetic radiation intensity test curve figure mono-.1 of described model machine;
4.1.2) judgement;
As without abnormal, go step 5);
If any extremely, go step 4.2);
4.2), re-start fabric swatch or change device;
4.2.1), the judgement;
As without abnormal, go step 5);
If any extremely, return to step 1);
5), the Power supply test one; Disconnect the metering circuit of described intelligent electric meter, described model machine is advanced to microwave dark room and carry out Electromagnetic Interference Test, obtain the electromagnetic radiation intensity test curve figure bis-of described model machine;
6), the power circuit radiation interference judgement that whether exceeds standard;
As nothing is abnormal, abnormal point numerical value is less than national standard, goes step 7);
If any extremely, abnormal point numerical value is greater than national standard numerical value, goes step 6.1);
6.1), change transformer;
6.2), the judgement;
As without abnormal, go step 7);
If any extremely, continue;
6.2), install anti-interference device additional; The model machine that adds anti-interference device is inserted to microwave dark room and carry out Electromagnetic Interference Test, obtain electromagnetic radiation intensity test curve figure bis-.1 of described model machine;
6.3), the judgement;
As without abnormal, go step 7);
If any extremely, go step 1);
7), the Power supply test two; Access the metering circuit of described intelligent electric meter, described model machine is advanced to microwave dark room and carry out Electromagnetic Interference Test, obtain the electromagnetic radiation intensity test curve figure tri-of described model machine;
8), the metering circuit radiation interference judgement that whether exceeds standard;
As nothing is abnormal, abnormal point numerical value is less than national standard, goes step 9);
If any extremely, abnormal point numerical value is greater than national standard numerical value, goes step 8.1);
8.1), two input end signal lines of the differential amplifier of metering units are carried out to the multiple twin processing, to reduce common mode interference;
8.2), will carry out model machine after the multiple twin processing and advance microwave dark room and carry out Electromagnetic Interference Test, obtain electromagnetic radiation intensity test curve figure tri-.1 of described model machine;
8.3), the judgement;
As without abnormal, go step 9);
If any extremely, go step 8.4);
8.4), the judgement that whether exceeds standard of the crystal oscillating circuit radiation interference in metering circuit;
As do not exceed standard, go step 9);
As exceed standard, demarcate the abnormity point in described electromagnetic radiation intensity test curve figure tri-.1, read described abnormal point numerical value, as this numerical value be as described in the integral multiple of crystal oscillator frequency in crystal oscillating circuit in metering circuit, remove step 8.4.1); As non-integral multiple, go step 8.5);
8.4.1), the crystal oscillating circuit in metering circuit is improved or is changed the crystal oscillator device;
8.4.2), the model machine of the crystal oscillating circuit in the improved metering circuit inserted to microwave dark room carry out Electromagnetic Interference Test, obtain electromagnetic radiation intensity test curve figure tri-.2 of described model machine;
8.4.3) judgement;
As without abnormal, go step 9);
If any extremely, go step 8.5);
8.5), metering circuit is re-started fabric swatch or changes device;
8.5.1), the model machine of upper step improved inserted to microwave dark room carry out Electromagnetic Interference Test, obtain electromagnetic radiation intensity test curve figure tri-.3 of described model machine;
8.5.2), the judgement;
As without abnormal, go step 9);
If any extremely, return to step 1);
9), finish.
Described step 3) microwave dark room in comprises that rotary table, vertical antenna, the shielding for putting described model machine ask the test receiver with EMI; Described rotary table and vertical antenna are arranged on shielding and ask; Described vertical antenna connects described EMI test receiver; Described rotary table and described vertical antenna distance are 3 meters, and the range of described vertical antenna is apart from ground 1-4 rice; Described rotary table table surface height is 0.8 meter.
It is criterion that the national standard of the mandatory execution of industry is take in the present invention, from the technician's of basic unit workflow, has proposed the method for designing that intelligent electric meter avoids radiation interference to exceed standard in design process.From the product concept phase, after first sample has assembled, first by power supply, electric energy meter is not tested, but by lithium battery power supply, test the electromagnetic interference (EMI) intensity of this part, improve principle design, PCB design or the components and parts of this part while pinpointing the problems and change, meeting in the GB9254-2008 situation, reduce as far as possible its electromagnetic interference (EMI) intensity.The reason that so designer just can be underproof to radiation interference is got rid of, thereby know accurately it is which module is out of joint actually, avoid finding when design typification the final stage that comes into the market in wait have just been tested at product the underproof situation of radiation interference, now remodify again the design effort of PCB, not only can increase production cost, and can make product incur loss through delay and miss business opportunity, bring huge loss to enterprise.And then can improve the middle-size and small-size electric energy meter electric energy meter designer of manufacturer in product design process to the radiation interference defect carry out efficiently, the analysis of standard, design, improvement ability level; Reduce the time, expense, the labour that repeat censorship, save R & D Cost, shorten the R&D cycle, reduce cost of products.
The accompanying drawing explanation
Fig. 1 is dipole model of magnetic,
Fig. 2 is electric dipole model,
Fig. 3 is the structural representation of microwave dark room in the present invention,
Fig. 4 is the electromagnetic radiation intensity test curve figure mono-of the defect model machine in the present invention,
Fig. 5 is the electromagnetic radiation intensity test curve figure of the qualification model in the present invention,
Fig. 6 is the functional block diagram of single-phase intelligent ammeter in the present invention,
Fig. 7 is the structured flowchart of single-phase intelligent ammeter in the present invention,
Fig. 8 be in the present invention in power circuit primary and secondary between the structural representation of coupling capacitance,
Fig. 9 is process flow diagram of the present invention;
In figure, 1 is rotary table, the 2nd, and vertical antenna, the 3rd, barrier shield.
Embodiment
Method for designing of the present invention as shown in Figure 9, comprises the following steps:
1), start principle design; Drawing, select device;
2), fabric swatch, installation; Form model machine;
3), powered battery test; Described model machine is only used powered battery, advances microwave dark room and carries out Electromagnetic Interference Test, obtains the electromagnetic radiation intensity test curve figure mono-of described model machine, as shown in Figure 4;
4), high frequency circuit radiation disturbs the judgement that whether exceeds standard; The foundation of judgement is the horizontal fold line (being marked with GB9254) of top in Fig. 4,
As without abnormal, continue lower step;
If any extremely, demarcate the abnormity point in described electromagnetic radiation intensity test curve figure mono-, read described abnormal point numerical value, as this numerical value be as described in the integral multiple of crystal oscillator frequency in intelligent electric meter, go step 4.1); As non-integral multiple, go step 4.2); As near the abnormity point occurred 900M in Fig. 4;
4.1), the MCU crystal oscillating circuit is improved or is changed the crystal oscillator device;
4.1.1), the model machine of improved crystal oscillating circuit inserted to microwave dark room carry out Electromagnetic Interference Test, obtain electromagnetic radiation intensity test curve figure mono-.1 of described model machine;
4.1.2) judgement;
As without abnormal, go step 5);
If any extremely, go step 4.2);
4.2), re-start fabric swatch or change device (such as crystal oscillator ground wire, single chip circuit, telecommunication circuit etc.);
4.2.1), the judgement;
As without abnormal, go step 5);
If any extremely, return to step 1);
5), the Power supply test one; Disconnect the metering circuit (under electric power thus supplied, under the effect of power supply switch circuit, battery is idle) of described intelligent electric meter, described model machine is advanced to microwave dark room and carry out Electromagnetic Interference Test, obtain the electromagnetic radiation intensity test curve figure bis-of described model machine; It is multiple that this kind of defect has, the primary shown in the most typical Fig. 8 of being and secondary between the radiation that causes of the coupling capacitance phenomenon that exceeds standard; But also have other such as interference from power lead etc.
6), the power circuit radiation interference judgement that whether exceeds standard;
As nothing is abnormal, abnormal point numerical value is less than national standard (GB9254-2008), goes step 7);
If any extremely, abnormal point numerical value is greater than national standard (GB9254-2008), goes step 6.1);
6.1), change transformer;
6.2), the judgement;
As without abnormal, go step 7);
If any extremely, continue;
6.2), install anti-interference device additional; The model machine that adds anti-interference device is inserted to microwave dark room and carry out Electromagnetic Interference Test, obtain electromagnetic radiation intensity test curve figure bis-.1 of described model machine;
6.3), the judgement;
As without abnormal, go step 7);
If any extremely, go step 1);
7), the Power supply test two; Access the metering circuit of described intelligent electric meter, described model machine is advanced to microwave dark room and carry out Electromagnetic Interference Test, obtain the electromagnetic radiation intensity test curve figure tri-of described model machine;
8), the metering circuit radiation interference judgement that whether exceeds standard;
As nothing is abnormal, abnormal point numerical value is less than national standard (GB9254-2008), goes step 9);
If any extremely, abnormal point numerical value is greater than national standard (GB9254-2008), goes step 8.1);
8.1), two input end signal lines of the differential amplifier of metering units are carried out to the multiple twin processing, to reduce common mode interference;
8.2), will carry out model machine after the multiple twin processing and advance microwave dark room and carry out Electromagnetic Interference Test, obtain electromagnetic radiation intensity test curve figure tri-.1 of described model machine;
8.3), the judgement;
As without abnormal, go step 9);
If any extremely, go step 8.4);
8.4), the judgement that whether exceeds standard of the crystal oscillating circuit radiation interference in metering circuit; Because the work crystal oscillator of computation chip also can cause radiation to exceed standard, therefore need carry out separately to this one and get rid of flow process;
As do not exceed standard, go step 9);
As exceed standard, demarcate the abnormity point in described electromagnetic radiation intensity test curve figure tri-.1, read described abnormal point numerical value, as this numerical value be as described in the integral multiple of crystal oscillator frequency in crystal oscillating circuit in metering circuit, remove step 8.4.1); As non-integral multiple, go step 8.5);
8.4.1), the crystal oscillating circuit in metering circuit is improved or is changed the crystal oscillator device;
8.4.2), the model machine of the crystal oscillating circuit in the improved metering circuit inserted to microwave dark room carry out Electromagnetic Interference Test, obtain electromagnetic radiation intensity test curve figure tri-.2 of described model machine;
8.4.3) judgement;
As without abnormal, go step 9);
If any extremely, go step 8.5);
8.5), metering circuit is re-started fabric swatch or changes device (if need to change device here, is to change what device? such as: crystal oscillator ground wire, single chip circuit, communicating circuit etc.);
8.5.1), the model machine of upper step improved inserted to microwave dark room carry out Electromagnetic Interference Test, obtain electromagnetic radiation intensity test curve figure tri-.3 of described model machine;
8.5.2), the judgement;
As without abnormal, go step 9);
If any extremely, return to step 1);
9), finish, obtain the intelligent electric meter electromagnetic radiation intensity test curve figure as Fig. 5.
Preferably adopted following embodiment for microwave dark room in the present invention: comprise between rotary table for putting described model machine, vertical antenna, shielding and the EMI test receiver; During described rotary table and vertical antenna are arranged between shielding; Described vertical antenna connects described EMI test receiver; Described rotary table and described vertical antenna distance are 3 meters, and the range of described vertical antenna is apart from ground 1-4 rice; Described rotary table table surface height is 0.8 meter.(Fig. 5, receiver can be inner or outside between shielding);
But it should be noted that method of testing or equipment are not quite similar (as small-sized anechoic chamber,, 3 meters method microwave dark rooms, 6TEM cell etc.), but ultimate principle is similar.
Below further illustrate the present invention:
1, with single-phase intelligent electric energy meter (functional block diagram is as Fig. 6, and structured flowchart is as Fig. 7) for example, proved that magnetic dipole differential mode radiation model and electric dipole common mode radiation model are suitable for analyzing radiation interference and the anti-Interference Analysis of intelligent electric energy meter.
Because antenna is reciprocity, for same single-phase intelligent electric energy meter, reduce its external electromagnetic interference (EMI), will strengthen its immunity to interference to external electromagnetic interference, therefore from the radiation field intensity of analyzing electric energy meter, start with, research suppresses the electric energy meter electromagnetic radiation energy and strengthens the method for electromagnetism antijamming capability.
The external radiation interference of electric energy meter mainly contains the differential mode radiation interference and common mode radiation disturbs two kinds of forms.The differential mode radiation interference is produced by differential-mode current, and common mode radiation disturbs and produced by common mode current.
Differential-mode current refer to travel to and fro between between signal wire and return wire, electric current that the amplitude same phase is contrary, in the loop that it forms between signal wire and return wire, flow, this current loop has formed the differential mode radiation.When the girth of loop much smaller than signal wavelength and apart from the time, the differential mode radiation can be described by dipole model of magnetic.Interference current flows at (or between live wire and zero line of power lead) between signal wire and signal ground.The electric meter signal line mainly comprises master chip signal, computation chip signal, clock chip signal, lcd drive chip signal and communication chip (module) signal, in at present up-to-date scheme, SOC (the System on Chip) scheme that has much adopted integrated MCU (Micro Control Unit), metering, clock and liquid crystal drive to be integrated.In the electric meter signal circuit trace, the signal wire in circuit trace and its ground wire lean on very closely under normal circumstances, and the loop area of formation is very little, so the radiation of electric meter signal line differential mode interference can be described by dipole model of magnetic.In electric energy meter, the electric network source line is associated with its generation comprises power transformer and voltage, current sample part, and these also can form current loop and produce the differential mode radiation interference.The frequency range of testing due to radiation interference is 30MHZ～16HZ, its minimal wave length is λ min=3 * 10^8/10^9=0.3m, adopt the 3m method to be tested simultaneously, so meet equally the condition that the girth of loop is less than signal wavelength and a distance, so the differential mode radiation interference that power lead produces also can be described by dipole model of magnetic.
Common mode current refer to be present in signal wire with in return wire, electric current that phase place is identical.To one section wire that is connected with high-frequency current, when conductor length much smaller than signal wavelength and apart from the time, can think balanced current distribution on wire, common mode radiation can be described with electric dipole model.According to the analysis of above differential-mode current, the common mode radiation that electric meter signal line and power lead produce disturbs and also can describe with electric dipole model.As shown in Figure 1, 2.
2, respectively labor near field and the far-field characteristic of magnetic dipole differential mode radiation model and electric dipole common mode radiation model.
2.1, according to the Maxwell equation group, can derive the differential mode radiation field for (derivation is referring to document 1):
E
r＝0 (2)
E
θ＝0 (3)
In above formula, H is magnetic field intensity, and unit is A/m; E is electric field intensity, and unit is V/m; R is the distance of antenna to the field point, and unit is m; I is antenna current, and unit is A; Δ S is the small loop antenna area, and unit is m
2; η is the free space wave impedance, and numerical value is 377 Ω; K=2 π/λ is wave number, and unit is rad/m.
Getting amplitude obtains:
2.2, according to the Maxwell equation group, can derive the common mode radiation field and be:
H
r＝0 (14)
H
θ0 (15)
In above formula, H is magnetic field intensity, and unit is A/m; E is electric field intensity, and unit is V/m; R is the distance of antenna to the field point, and unit is m; I is antenna current, and unit is A; Δ l is antenna length, and unit is m; η is the free space wave impedance, and numerical value is 377 Ω; K=2 π/λ is wave number, and unit is rad/m.
Getting amplitude obtains:
2.3, when r<λ/2 π, be called near field.As r > during λ/2 π, be called far field.
Because the frequency range of testing is 30MHZ～1GHZ, its minimal wave length is λ
min3 * 10^8/10^9=0.3m, maximum wavelength is λ
max=3 * 10^8/ (3 * 10^7)=10m.
Therefore, the condition that meets far field is: r>λ
max/ 2 π=10/2 π=1.6 π;
The condition that meets near field is: r<λ
min/ 2 π=0.3/2 π=0.048 π;
Visible, adopt 3m method test electric energy meter radiation interference intensity can substantially meet far field condition, if the field distance is foreshortened in 4.8cm, also can substantially meet Near Field.
2.4 when r<<during λ/2 π,
2.4.1 formula (7), (8), (9) are approximately respectively following equation:
As can be seen here, near field region, square being inversely proportional to of the electric field intensity of magnetic dipole differential mode radiation model and distance, to signal frequency, be directly proportional, and magnetic field intensity is inversely proportional to the cube of a distance, irrelevant with signal frequency.
Wave impedance be defined as Z=|E|/| H|.When θ=90 °,
maximum, | H
θ| maximum, | H
r| be 0, simultaneously | H
r| denominator be | H
θ| therefore 1/2 of denominator, wave impedance maximum now.Therefore, the wave impedance of magnetic dipole differential mode radiation model near field region is:
As can be seen here, near field region, wave impedance, much smaller than the free space wave impedance, presents low impedance state, and the near field of small loop antenna is the Low ESR field, take magnetic field as main.
2.4.2 formula (16), (17), (18) are approximately respectively following equation:
As can be seen here, near field region, the electric field intensity of electric dipole common mode radiation model is inversely proportional to the cube of distance, with signal frequency, be inversely proportional to, and square being inversely proportional to of magnetic field intensity and a distance is irrelevant with signal frequency.
Wave impedance be defined as Z=|E|/| H|.When θ=90 °,
maximum, | E
θ| maximum, | E
r| be 0, simultaneously | E
r| denominator be | E
θ| therefore 1/2 of denominator, wave impedance minimum now.Therefore, the wave impedance of magnetic dipole differential mode radiation model near field region is:
As can be seen here, near field region, wave impedance, much larger than the free space wave impedance, presents high impedance status, and the near field of electrical dipole antenna is high impedance field, take electric field as main.
2.5 as r > > during λ/2 π,
2.5.1 formula (7), (8), (9) are approximately respectively following equation:
When θ=90 °,
with | H
θ| maximum, | H
r| be 0.Wave impedance is:
wave impedance equates with the free space wave impedance.Now, the magnetic field intensity of differential mode radiation and electric field intensity all with field apart from being inversely proportional to, to frequency square, loop current and loop area be directly proportional, but due to η=377>>1, so electromagnetic radiation mainly take electric field as main, magnetic field intensity can be ignored.
2.5.2 formula (16), (17), (18) are approximately respectively following equation:
When θ=90 °, | E
θ| and
maximum, | E
r| be 0.Wave impedance is:
wave impedance equates with the free space wave impedance.Now, the magnetic field intensity of common mode radiation and electric field intensity all with field apart from being inversely proportional to, to signal frequency, antenna current and antenna length, be directly proportional, but due to η=377>>1, so electromagnetic radiation mainly take electric field as main, magnetic field intensity can be ignored.
Document 1: Luo Yongchao.The Radiative EMI characteristic of PCB is diagnosed, is estimated and the research of inhibition method.Nanjing Normal University's master thesis, 2010.5
3. to analyzing at province metering institute electric energy meter disturbed test curve map.
Adopt 3m method test electric energy meter radiation interference intensity, because electric energy meter turntable height is 0.8m, add the electric energy meter oneself height, therefore can think that magnetic-dipole antenna and electrical dipole antenna height are at 1m.The receiving antenna height converts between 1m～4m, and electric energy meter is 3m apart from the horizontal range of receiving antenna.Therefore, the θ angle in Fig. 1 and Fig. 2 converts between 45 °～90 °, and angular range meets the 2nd all kinds of calculating of joint and approximate requirement.When θ=90 °, the radiation intensity maximum that differential-mode current and common mode current produce, now r=3m.
By Fig. 4 and Fig. 5, can be found out, when f<300MHz, radiation interference substrate radiation intensity presents not too regular parabolic shape; When f >=300MHz, radiation interference becomes an oblique line substantially, and minority frequency radiation intensity is larger with respect to substrate.
Now be analyzed as follows:
Make m=λ/2 π r, when f=300MHz, m
2=0.053, m
4=0.0028;
For formula (7),
R is certain, as f>during 300MHz, along with the increase gradually of frequency,
convergence is 1, so the time formula (7) strictly become formula (34).Differential mode radiation field intensity table of logarithm is shown:
20log|E|
dm?far=20log(ηπIΔS)-40logλ-20logr (41)
Because λ<1, so log λ<0, along with frequency increases gradually, the differential mode radiation field intensity strengthens gradually.But, due to the differential-mode current single spin-echo, as long as reasonable in design, differential mode radiation field intensity major part will be cancelled out each other.If design unreasonablely, will cause the differential mode radiation field intensity to increase, the circulation area is larger, and the differential mode radiation field intensity is larger.
Equally, r is certain, as f > during 300MHz, along with the increase gradually of frequency, formula (17) strictly becomes formula (39), and common mode radiation field intensity table of logarithm is shown:
20log|E|
cm?far=20log(ηIΔl)-20logλ-20log(2r) (42)
Because λ<1, so log λ<0, along with frequency increases gradually, the common mode radiation field intensity strengthens gradually.Because the common mode current phase place is identical, same point common mode radiation field intensity will superpose mutually.If design unreasonablely, will cause the common mode radiation field intensity to increase, the major part that common mode interference is radiation interference.
From above analysis, as f > during 300MHz, radiation interference becomes an oblique line substantially.
When f<300MHz, while along with signal frequency, dropping to 200MHz from 300MHz gradually, by can be calculated said circumstances, still substantially set up.Signal frequency drops to 30MHz from 200MHz gradually, and λ is increased to 10 gradually from 1.5, now just larger by above approximate error again.Now, in formula (7) and formula (17), the content in radical sign just can not be approximately 1.
Due to λ now > 1, the common mode radiation field intensity that the differential mode radiation field intensity meaned when enough hour of small loop antenna area formula (7) means with respect to formula (17) can be ignored substantially.
Order
?
So formula (43) is the para-curve that bottom is 3/4.This situation basic and Fig. 4 and Fig. 5 curves.Certainly, due to the increase along with signal λ, now, more and more near near field, can produce near-field effect, therefore now the radiation field intensity curve there will be some irregularly shaped.As non-microwave expert engineer, now radiation intensity quantitative test difficulty, can only qualitatively analyze much larger than the analysis more than 300MHZ.
From above analysis, the electric energy meter radiation interference is comprised of differential mode interference and common mode interference two parts, and the radiation interference analysis and modification also should be considered from these two aspects.
4. according to the concrete characteristics of single-phase intelligent electric energy meter, a kind of radiation interference of single-phase intelligent electric energy meter and the method for anti-Interference Analysis have been proposed.
Analysis according to the 1st joint, the 2nd joint and the 3rd joint, in conjunction with the characteristics of single-phase intelligent electric energy meter, the present invention proposes a kind of radiation interference of single-phase intelligent electric energy meter and the method for anti-Interference Analysis.
4.1 single-phase smart meter theory of constitution
Single-phase smart meter is comprised of equipment such as computation chip, high-speed data processor, the exchange of ESAM secure data, data-interfaces.Under the control of high-speed data processor, accurately obtain each real-time parameter of operation of power networks by computation chip, and according to requirements such as corresponding rates, data are processed, its result is kept in data-carrier store, and information is provided and carries out exchanges data to external interface at any time.Circuit in single-phase smart meter divides by its function, mainly contains power module, control module, metering module, communication module, memory module, display module etc.As shown in Figure 6, functional block diagram as shown in Figure 7 for its structured flowchart.
4.2 single-phase smart meter lithium battery
Single-phase smart meter all is furnished with the 3.6V lithium battery.During normal operation, battery is not worked.When grid cut-off, by lithium battery power supply, maintain the work of the unit such as microprocessor, storer, LCDs, infrared communication, so that can normal copy reading data.For electric energy meter, high-frequency signal also mainly concentrates on these parts.Therefore, can the radiation interference analysis be divided into to two parts by lithium battery and consider, 4.4 parts are shown in concrete analysis.
4.3 single-phase smart meter power transformer
The effect of single-phase smart meter power transformer is that line voltage is transformed to the electric energy meter operating voltage.Ideal transformer can only transmit the differential-mode current of alternation in theory and can not transmit common mode current, because the potential difference (PD) of common mode current at the Transformer Winding two ends is zero, can not on Transformer Winding, produce magnetic field.But real transformer is in the very little coupling capacitance of asking of primary and secondary winding, this electric capacity is between winding, to exist non-dielectric matter and physical clearance to cause, it provides a passage (seeing Fig. 8) through transformer for common mode current, therefore power transformer is also the part that must consider of radiation interference, and 4.4 parts are shown in concrete analysis.
4.4 radiation interference and anti-Interference Analysis and design improvement method
1) best method of inhibition radiation interference is again the design of PCB to be revised also to appropriate design again, if but when test find that radiation interference is defective, product now is design typification the final stage that comes into the market in wait often, remodify the design effort of PCB, not only can increase production cost, and can make product incur loss through delay and miss business opportunity.Therefore must establish the idea of " thing of considering when EMC is design, rather than the thing of considering during rectification ".
From Fig. 4 and Fig. 5, during 30MHZ, radiation interference intensity generally is no more than 25dBuV, and minimum radiation interference intensity is generally 10dBuV, and during 1GHZ, radiation interference intensity generally is no more than 40dBuV.Because State Grid Corporation of China has pattern standard, functional specification and the technical manual of unified intelligent electric energy meter, so the single-phase intelligent electric energy meter radiation interference test curve that each electric energy meter manufacturer produces is substantially like this.
2), owing to belonging to the relative high frequency part, the electromagnetic radiation that electric energy meter produces mainly concentrates on the unit such as microprocessor, storer, LCDs, infrared communication, clock unit.Therefore, in the product concept phase, after first sample has assembled, first by power supply, electric energy meter is not tested, but, by lithium battery power supply, test the electromagnetic interference (EMI) intensity of this part, improve principle design, PCB design or the components and parts of this part while pinpointing the problems and change, in the situation that meet the requirement of GB92542008, reduce as far as possible its electromagnetic interference (EMI) intensity.
At first consider the principle design part, for example the crystal oscillating circuit section processes, avoid the High-order Harmonic Generation amplitude that crystal oscillator frequency occurs to exceed standard etc.
Secondly, be also topmost be exactly that PCB routing is considered.Reduce the loop area that all high speed signals and clock signal wire form as far as possible, reduce differential mode interference; Make closely loop of signal wire, the high speed signal of adjacent layer is not transregional, reduces common mode interference; The necessary ground connection of shell of crystal oscillator etc.
Again, the device selection is also an important aspect.For example the paster optocoupler, in the situation that meet the communication baud rate requirement, select the optocoupler that speed is low as far as possible, because the rising edge of high speed photo coupling is trembled, more easily produces radiation interference.
3) after above part improvement designs and tested, first disconnect metering section, use Power supply to carry out the test of power supply unit radiation interference.
Power unit is mainly considered the following aspects: (1) transformer.According to 4.3 analyses, supplier should increase the gap between winding during design of transformer as far as possible, fills the space between winding with the material of low-k, to reduce the capacitor's capacity between winding simultaneously; (2), because electric energy meter is very high to cost and volume requirement, before transformer, do not install as far as possible the device of the interference of robust mould and common mode interference additional, but also need in case of necessity to install additional this class device; (3) power lead wiring.Because printed board sheet material is equivalent to capacitor dielectric, power and ground is distributed in the pros and cons of printed board, and power and ground wiring live width should suitably be widened, and ground wire should carry out the floor file processing, to reduce as far as possible appearance value etc.
4) after above part improvement designs and tested, the access metering section, re-use Power supply and carry out the test of metering units radiation interference.If occur, electromagnetic radiation exceeds standard, and now should mainly consider the improvement design of metering section.For using the SOC scheme, metering section is integrated among MCU.
Metering section is mainly considered voltage acquisition and current acquisition part.No matter voltage acquisition or current acquisition, be all collection signal to be delivered to the two ends of differential amplifier, so common mode inhibition is mainly to consider part.Mainly take following measures: (1) carries out multiple twin processing (common mode interference can be avoided, be reduced to twisted pair construction) by two lines of differential signal, to reduce as far as possible common mode interference.For adopting computation chip to be measured, also must carry out the processing of computation chip crystal oscillating circuit; (2) carry out low-pass filtering treatment at differential amplifier input two ends; (3) floor file processing of ground wire etc.
5) the contingency result caused due to the impact of the factors such as testing apparatus, environment, therefore preferably repeatedly test, so as to accomplish not omit, false-alarm not, guarantee that the design of product radiation interference meets the EMC requirement.
Claims (2)
1. an analysis design method that reduces the intelligent electric energy meter radiation interference, is characterized in that, comprises the following steps:
1), start principle design; Drawing, select device;
2), fabric swatch, installation; Form model machine;
3), powered battery test; Described model machine is only used powered battery, advances microwave dark room and carries out Electromagnetic Interference Test, obtains the electromagnetic radiation intensity test curve figure mono-of described model machine;
4), high frequency circuit radiation disturbs the judgement that whether exceeds standard;
As without abnormal, continue lower step;
If any extremely, demarcate the abnormity point in described electromagnetic radiation intensity test curve figure mono-, read described abnormal point numerical value, as this numerical value be as described in the integral multiple of MCU crystal oscillator frequency in intelligent electric meter, go step 4.1); As non-integral multiple, go step 4.2);
4.1), the MCU crystal oscillating circuit is improved or is changed the crystal oscillator device;
4.1.1), the model machine of improved crystal oscillating circuit inserted to microwave dark room carry out Electromagnetic Interference Test, obtain electromagnetic radiation intensity test curve figure mono-.1 of described model machine;
4.1.2) judgement;
As without abnormal, go step 5);
If any extremely, go step 4.2);
4.2), re-start fabric swatch or change device;
4.2.1), the judgement;
As without abnormal, go step 5);
If any extremely, return to step 1);
5), the Power supply test one; Disconnect the metering circuit of described intelligent electric meter, described model machine is advanced to microwave dark room and carry out Electromagnetic Interference Test, obtain the electromagnetic radiation intensity test curve figure bis-of described model machine;
6), the power circuit radiation interference judgement that whether exceeds standard;
As nothing is abnormal, abnormal point numerical value is less than national standard, goes step 7);
If any extremely, abnormal point numerical value is greater than national standard numerical value, goes step 6.1);
6.1), change transformer;
6.2), the judgement;
As without abnormal, go step 7);
If any extremely, continue;
6.2), install anti-interference device additional; The model machine that adds anti-interference device is inserted to microwave dark room and carry out Electromagnetic Interference Test, obtain electromagnetic radiation intensity test curve figure bis-.1 of described model machine;
6.3), the judgement;
As without abnormal, go step 7);
If any extremely, go step 1);
7), the Power supply test two; Access the metering circuit of described intelligent electric meter, described model machine is advanced to microwave dark room and carry out Electromagnetic Interference Test, obtain the electromagnetic radiation intensity test curve figure tri-of described model machine;
8), the metering circuit radiation interference judgement that whether exceeds standard;
As nothing is abnormal, abnormal point numerical value is less than national standard, goes step 9);
If any extremely, abnormal point numerical value is greater than national standard numerical value, goes step 8.1);
8.1), two input end signal lines of the differential amplifier of metering units are carried out to the multiple twin processing, to reduce common mode interference;
8.2), will carry out model machine after the multiple twin processing and advance microwave dark room and carry out Electromagnetic Interference Test, obtain electromagnetic radiation intensity test curve figure tri-.1 of described model machine;
8.3), the judgement;
As without abnormal, go step 9);
If any extremely, go step 8.4);
8.4), the judgement that whether exceeds standard of the crystal oscillating circuit radiation interference in metering circuit;
As do not exceed standard, go step 9);
As exceed standard, demarcate the abnormity point in described electromagnetic radiation intensity test curve figure tri-.1, read described abnormal point numerical value, as this numerical value be as described in the integral multiple of crystal oscillator frequency in crystal oscillating circuit in metering circuit, remove step 8.4.1); As non-integral multiple, go step 8.5);
8.4.1), the crystal oscillating circuit in metering circuit is improved or is changed the crystal oscillator device;
8.4.2), the model machine of the crystal oscillating circuit in the improved metering circuit inserted to microwave dark room carry out Electromagnetic Interference Test, obtain electromagnetic radiation intensity test curve figure tri-.2 of described model machine;
8.4.3) judgement;
As without abnormal, go step 9);
If any extremely, go step 8.5);
8.5), metering circuit is re-started fabric swatch or changes device;
8.5.1), the model machine of upper step improved inserted to microwave dark room carry out Electromagnetic Interference Test, obtain electromagnetic radiation intensity test curve figure tri-.3 of described model machine;
8.5.2), the judgement;
As without abnormal, go step 9);
If any extremely, return to step 1);
9), finish.
2. a kind of analysis design method that reduces the intelligent electric energy meter radiation interference according to claim 1, it is characterized in that described step 3) in microwave dark room comprise between rotary table for putting described model machine, vertical antenna, shielding and the EMI test receiver; During described rotary table and vertical antenna are arranged between shielding; Described vertical antenna connects described EMI test receiver; Described rotary table and described vertical antenna distance are 3 meters, and the range of described vertical antenna is apart from ground 1-4 rice; Described rotary table table surface height is 0.8 meter.
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