CN102832970B - Power line state monitoring method and device - Google Patents

Abstract

The invention provides a monitoring method of a power transmission line state in a power line communication system, wherein the monitoring method comprises the following steps: S1. a node A performs framing on the known training sequence and to-be-sent data modulated by an OFDM (orthogonal frequency division multiplexing) technology, and sends signals into a power line through a coupler for transmission; S2. a node B receives sent signals through the coupler, modulates the received signals by utilizing the known training sequence, and extracts transmission data; S3. the node B obtains transmission channel frequency response or impact response by utilizing the known training sequence; S4. the node B analyzes the channel frequency response, extracts relevant information of the transmission line, and obtains the variation information of basic parameters of the transmission line through analyzing the relevant information so as to calculate the channel parameters; and S5. the node B estimates and forecasts the channel state of the power transmission line according to channel parameter variation. According to the method provided by the invention, the state information of the power line can be monitored in real time, and a data collecting device and a communication system are not required to be arranged out of the power transmission line, and the monitoring method of the power transmission line state in the power line communication system has the advantages of good stability, low cost, and the like.

Description

A kind of method of power line status monitoring and device thereof

Technical field

The invention belongs to power line status monitoring technical field, particularly a kind of method of the electric line communication system transmission line status monitoring based on OFDM technology and device thereof.

Background technology

In electrical power transmission system, because middle and long distance power transmission line is exposed on the ground, is subject to the boisterous impacts such as wind and frost sleet, the aging of circuit can be caused.The aging meeting of circuit causes the transmission usefulness of power line to reduce, and produces more energy dissipation, causes mains supply unstable, even can produce potential safety hazard.For this reason, the monitoring for power line is very important in electrical power transmission system, and the method for the technology that various antagonism power line is aging and detection power line status is all suggested and applies.

Detection at present to power line ageing state, when high pressure and ultra high voltage, mainly configure various property sensor at transmission node place, for transmission line even external environment state monitor in real time, or by analyzing line status the impedance variation of transfer wire.The pre-Optical Fiber Transmission nodal information laid in power line is utilized to be used for wireline inspection to Central Control Room.For mid & low-voltage line, because circuit is more and complicated, the mode of artificial line walking often can only be adopted to carry out detecting and safeguarding.But, being on a grand scale or being in high-risk danger zone when monitoring electrical network, all greatly can increase for sensor network and the laying of fiber optic network and the cost of maintenance, the great expense incurred of electrical network can be caused, and mesolow circuit is inherently difficult to lay the auxiliary optical fiber of communication and transducer; The method real-time of impedance analysis is also lower simultaneously, and also need extra special instrument, flexibility is inadequate.

Along with the development of the communication technology, power line communication achieves significant progress, receives extensive attention, and compared with other various net control communication plans, its advantage is: cost is low, extension is wide, easy construction, a line are dual-purpose.

Summary of the invention

(1) technical problem that will solve

The technical problem to be solved in the present invention is: how to utilize power line transmission channel to provide a kind of method and device of transmission line status monitoring.

(2) technical scheme

In order to solve the problem, the invention provides the monitoring method of electric power transfer line states in a kind of electric line communication system, comprise the following steps: signal by known training sequence and the data framing to be sent that utilizes OFDM technology to modulate, and is sent into power line by coupler and transmitted by S1, node A; S2, Node B are received by coupler and send signal, utilize known training sequence demodulated received signal, extract transmission data; S3, Node B utilize known training sequence to obtain transmission channel frequency response or impulse response; S4, Node B analyze channel frequency response, extract the relevant information of transmission line, are drawn the change information of transmission line basic parameter, to calculate channel parameter by the change analyzing relevant information; S5, Node B carry out estimating and forecasting according to channel parameter change to power transmission line channel status.

Preferably, described training sequence comprises time-domain training sequence, frequency domain training sequence.

Preferably, described OFDM framing mode comprises ZP-OFDM, CP-OFDM and TDS-OFDM.

Preferably, in step S4, described relevant information comprises that frequency plot between poor, the adjacent extreme value of frequency interval between the amplitude of the maximum of channel frequency response, minimizing amplitude, phase place, position, adjacent extreme value is poor, the cycle of phase response.

Preferably, in step S4, described transmission line basic parameter comprises the relative dielectric constant ε of dielectric between conductor _r, relative permeability μ _r, angle of loss, electrical length l.

Preferably, in step S5, describedly estimating and forecasting is carried out to power transmission line channel status comprise following corresponding relation according to channel parameter change: between conductor, the relative dielectric constant of the dielectric ambient temperature residing for voltage ageing or transmission line representing transmission line that diminishes raises, relative permeability diminishes the magnetic ageing that represents transmission line or cause medium to there occurs deformation heterogeneous due to the change of pressure, and the increase of angle of loss represents that transmission line creates voltage ageing or changes the loss caused due to external environment.

Preferably, according to time-domain training sequence, then represent that the impulse response of channel is estimated by the convolution of training sequence and receiving sequence, then obtain channel frequency response through discrete Fourier transform (DFT) (DFT) conversion; According to frequency domain training sequence, then represent that the frequency response of channel is estimated by receiving sequence and the business of the discrete Fourier transform (DFT) (DFT) sending sequence.

Present invention also offers the device of transmission line status monitoring in a kind of power communication system, this device comprises: data generating unit, for generation of the data of required transmission; The data of generation are carried out OFDM modulation for the demand according to system by signal madulation unit, and known training pilot tone and OFDM symbol are carried out combine, framing, output to coupler unit; Coupler unit, transmits to power line for the signal coupling exported by signal madulation unit, or processes for being received and be transferred to signal demodulation unit by the signal coupling on power line; Signal demodulation unit, for being undertaken the signal received from coupling unit synchronous and demodulating the training sequence carried; Channel frequency response estimation unit, utilize receive with known pilot frequency sequence carry out channel frequency response estimate, obtain frequency response parameter; Linear electrical parameter computing unit, by the change of relevant information in analysis frequency response parameter and analysis frequency response curve, obtains and estimates the change of transmission line basic parameter; Transmission line states prediction unit, carries out Macro or mass analysis to the basic parameter change of transmission line, draws the prediction to line status and monitoring.

(3) beneficial effect

The present invention utilizes power line communication technology, propose a kind of based on the electric line communication system transmission line status monitoring of OFDM technology, the method for maintenance and device, utilize power transmission line collection, transmission and analysis circuit ageing state, Real-Time Monitoring power line status information, without the need to layout data harvester and communication system again beyond transmission line, reduce cost, effectively make use of abundant existing power line network resource, meet the requirement creating conservation-minded society.

Description of the invention provides in order to example with for the purpose of describing, and is not exhaustively or limit the invention to disclosed form.Many modifications and variations are obvious for the ordinary skill in the art.Selecting and describing embodiment is in order to principle of the present invention and practical application are better described, and enables those of ordinary skill in the art understand the present invention thus design the various embodiments with various amendment being suitable for special-purpose.

Accompanying drawing explanation

With reference to the accompanying drawings and further describe the present invention in conjunction with example.Wherein:

Fig. 1 is the monitoring method flow chart according to the embodiment of the present invention.

Fig. 2 sends according to the system of the embodiment of the present invention one and receives block diagram.

Fig. 3 is the frame structure of the TDS-OFDM according to the embodiment of the present invention one.

Fig. 4 is the topology diagram of the node according to the embodiment of the present invention.

Fig. 5 is the dynamic impedance circuit diagram of the transmission line according to the embodiment of the present invention.

Fig. 6 is power line cross section according to the embodiment of the present invention and equivalent capacity schematic diagram.

Fig. 7 is the power line capacitive coupling schematic diagram according to the embodiment of the present invention.

Fig. 8 is the variation diagram according to power line transmission channel magnitude response curve in the embodiment of the present invention one.

Fig. 9 is the frame structure of the CP-OFDM according to the embodiment of the present invention two.

Figure 10 is the variation diagram according to power line transmission channel magnitude response curve in the embodiment of the present invention two.

Figure 11 is the frame structure of the ZP-OFDM according to the embodiment of the present invention three.

Figure 12 is the variation diagram according to power line transmission channel magnitude response curve in the embodiment of the present invention three.

Figure 13 is the variation diagram according to power line transmission channel magnitude response curve in the embodiment of the present invention four.

Figure 14 is the variation diagram according to power line transmission channel phase response curve in the embodiment of the present invention four.

Figure 15 is the installation drawing of the monitoring method for carrying out system transfers line states in power line transmission system based on OFDM technology according to the embodiment of the present invention.

Embodiment

Below in conjunction with drawings and Examples, the specific embodiment of the present invention is described in further detail.Following examples for illustration of the present invention, but are not used for limiting the scope of the invention.

Embodiment one

Embodiment one gives the scheme of the present invention's proposition for carrying out a kind of embodiment of system communications line status monitoring and maintenance in power line transmission system based on TDS-OFDM technology.

Present embodiment is for the typical multicarrier operation pattern of one of PLC system, and design parameter is as follows: carrier mode Z=3780, and transmitting terminal planisphere mapping mode is 16QAM, and frame head mode PN945, FEC code check is 0.4.

As shown in Figure 2, according to embodiment of the present invention monitoring and the method safeguarding the systematic electricity line states described in the present embodiment, as shown in Figure 3, its concrete steps are as follows for the topological structure of node:

Signal by known training sequence and the data framing to be sent that utilizes TDS-OFDM technology to modulate, and is sent into power line transmission by coupler by S1, node A;

In the present embodiment, data to be sent, first through FEC coding, then carry out the symbol X that 16QAM constellation mapping obtains frequency domain _k, every 3780 frequency domain symbol X _kforming an OFDM symbol, is the IDFT(IFFT of 3780 through length) by each frequency domain symbol X _ktransform on time domain corresponding subcarrier; In time domain, symbol lengths be 420 the PN sequence front end that is placed in OFDM symbol carry out framing as frame head, then frame structure utilizes root-raised cosine pulse to carry out time domain molding filtration as shown in Figure 4 and the bandwidth of signal is limited, and carries out the transmission of signal to the signal processed after carrying out up-conversion and power amplification.

S2, Node B are received by coupler and send signal, utilize known training sequence demodulated received signal, extract transmission data;

In the present embodiment, Node B by coupler Received signal strength from power line, the signal received by down-conversion, through root-raised cosine pulse bandwidth filtering and sampling; Data after sampling are corresponding carries out synchronous, channel estimating and FFT.

S3, Node B utilize known training sequence to obtain transmission channel frequency response;

In the present embodiment, after carrying out signal and be synchronous, just can carry out channel frequency response and have estimated.The known PN sequence (time-domain training sequence) due to one section with good autocorrelation is inserted in step sl as frame head, and we utilize PN sequence as channel monitoring signal.For each signal frame, the PN sequence received and local PN sequence are carried out relevant impulse response h (t) that just can obtain channel.Again DFT is carried out to impulse response sequence, obtain frequency response H (f) of channel.

Concrete principle is as follows:

Power line channel can carry out modeling with a multipath function, and impulse response is as follows:

$h\left(t\right)=\underset{i=1}{\overset{N}{\mathrm{\Σ}}}{g}_i\·\mathrm{\δ}(t-{\mathrm{\τ}}_i)---\left(1\right)$

Wherein, g _ibe the attenuation parameter in each footpath, its expression formula and connotation will hereafter make an explanation from transmission line theory.

S (n) when supposing primary signal waiting for transmission, the noise of additivity is n (n), and so the sampling of Received signal strength can be expressed as:

$y\left(n\right)=s\left(n\right)\⊗h\left(n\right)+n\left(n\right)=\underset{i=1}{\overset{N}{\mathrm{\Σ}}}{g}_{i}s(n-{\mathrm{\τ}}_i)+n\left(n\right)---\left(2\right)$

Because PN sequence has good autocorrelation, the impulse response of channel estimates to be expressed as the relevant of Received signal strength and known PN sequence:

h(n)=R _py(n) （3）

And then do Fourier transform, the frequency response function of channel can be obtained.

S4, Node B analysis frequency respond, and extract key message to calculate channel parameter;

Concrete, modeling is carried out to the channel of power line, the general multipath model adopting description time domain specification, analyze according to transmission line theory, when mesolow power line is as data transmission channel, can adopt traditional two wires uniform transmission line model (bilinear model) Approximate Equivalent, namely signal of communication transmits between the two phases, but not single-phase-center line mode.

Distributed parameter line is regarded as and is composed in series by the lumped parameter power circuit of many infinitely small length Δ x, as shown in Figure 5.

Wherein, u (t, x), u (t, t+ Δ x) represent x and x+ Δ x place instantaneous voltage respectively; I (t, x), i (t, x+ Δ x) represent x and x+ Δ x place current instantaneous value respectively; R ₀, G ₀, L ₀, C ₀resistance, leakage conductance, inductance, the line capacitance of representation unit length respectively.

By the transfer function of the known power line channel multipath model of formula (1) be:

$H\left(f\right)=\underset{i=1}{\overset{N}{\mathrm{\Σ}}}{g}_i\·e^{-j2\mathrm{\π}{\mathrm{f\τ}}_i}---\left(4\right)$

Wherein attenuation parameter α (f) is Line Attenuation constant, l _ifor signal transmission is passed through path, a _ireflect network topology structure, be called weight coefficient, it is comprehensive at the catadioptric Overlay of each node in path that it is that Signal transmissions is passed through, relevant with line parameter circuit value, number of nodes, branch road connected mode etc.

Provide the computational methods of mesolow power line basic parameter below, the sectional view of power line is as Fig. 6.In formula, c ₀for the light velocity in vacuum; μ ₀=4 π 10 ^-7h/m is permeability of vacuum, ε ₀=10 ^-9/ 36 π F/m are permittivity of vacuum; σ _c, μ ₀be respectively conductor conductivity and relative permeability; μ _r, ε _r, σ _rbe respectively the relative permeability of dielectric between conductor, relative dielectric constant and conductivity; Tan δ is the angle of loss of dielectric between conductor.

$R_0=\sqrt{\frac{{\mathrm{\μ}}_0{\mathrm{\μ}}_{0}f}{\mathrm{\π}{\mathrm{\σ}}_c{r}^2}}\left[\frac{(D/2r)}{\sqrt{{(D/2r)}^2-1}}\right](\mathrm{\Ω}/m)---\left(5\right)$

$L_0=\frac{{\mathrm{\μ}}_r{\mathrm{\μ}}_0}{\mathrm{\π}}{\mathrm{Cosh}}^{-1}\left(\frac{D}{2r}\right)+\frac{R_0}{2\mathrm{\πf}}(H/m)---\left(6\right)$

$C_0=\frac{{\mathrm{\π\ϵ}}_r{\mathrm{\ϵ}}_0}{{\mathrm{Cosh}}^{-1}(D/2r)}(F/m)---\left(7\right)$

G ₀=2πfC ₀tanδ(S/m) （8）

$\mathrm{\γ}=\mathrm{\α}+\mathrm{j\β}=\sqrt{(R+\mathrm{j\ωL})(G+\mathrm{j\ωC})}---\left(9\right)$

Generally, owing to there is decay and coupling, need to revise resistance per unit length, electric capacity and inductance:

The total resistance value of unit length is:

R _tot=X _R·R ₀（10）

Wherein X _rit is correction factor.

Capacitive coupling schematic diagram as shown in Figure 7, in order to simplify calculating, can use its equivalent capacitance value of circuit counting shown in Fig. 8:

$C_{\mathrm{tot}}=\frac{{3C}_{\mathrm{cab}}}{2}+\frac{C_{\mathrm{con}}}{2}---\left(11\right)$

C _cabc above being exactly ₀, for capacitance between unit length of conductor and screen, ε _ccfor the dielectric constant of dielectric between conductor and screen.

The equivalent leakage conductance of unit length is:

$G_{\mathrm{tot}}=G_0\·\frac{C_{\mathrm{tot}}}{C_0}---\left(12\right)$

Can find by analysis, be subject to external force, variations in temperature when circuit or cause the change of the dielectric constant of the insulator of transmission line, magnetic permeability, decay factor and electrical length due to self aging, thus when causing distributed constant to change, can there is corresponding change in the frequency response curve of circuit.

In the present embodiment, extract the DIELECTRIC CONSTANT ε that key message is insulator medium in transmission line with the channel parameter calculated _r;

For the multipath effect of power transmission line, the mesohigh of employing, the mode of middle and long distance classics, parameter is as following table:

Multipath is numbered	1	2	3	4	5	6
							Equivalent length/m	200	221	242	259	266	530
Weight coefficient	0.54	0.275	-0.15	0.08	-0.03	-0.02

The basic parameter adopted in emulation is as following table:

Basic parameter title	Symbol	Numerical value or interval
			Heart yearn radius	r	1.22mm
Heart yearn spacing	D	4.04mm
			The light velocity in vacuum	c	3×10 8m/s
The relative dielectric constant of medium	ε r	[3.5,4]
			Dielectric constant in vacuum	ε 0	8.85×10 -12F/m
The relative permeability of medium	μ r	[0.7,1.3]

Magnetic permeability in vacuum	μ 0	4π×10 -7H/m
			The conductivity of conductor	σ	5.76×10 7S/m
The current displacement angle of medium	tanδ	[10 -3,10 -2]

In this Application Example, we choose difference on the frequency between the numerical value of the maximum of the amplitude-response curve of transmission channel and minimum as key message for predicting the change of the dielectric constant of insulator medium in transmission line.

When the numerical value difference on the frequency become between large and minimum of the maximum of the amplitude-response curve of transmission channel becomes large, we can analyze the DIELECTRIC CONSTANT ε of insulator medium in transmission line _rreduce, namely illustrate that ambient temperature residing for transmission line raises or that transmission line occurs is aging.

As Fig. 9 shows identical transmission line at different conditions from the amplitude-response curve of 1 ~ 100MHz, can see that the difference on the frequency that solid line increases between (△ A), minimum compared to the numerical value of maximum on the amplitude-response curve of dotted line channel also becomes large (d2>d1) simultaneously, therefore we judge the DIELECTRIC CONSTANT ε of insulator medium in transmission line according to the change of key message _rreduce, thus the ambient temperature of estimation residing for transmission line raises or transmission line there occurs aging.

S5, Node B carry out estimating and forecasting according to channel parameter change to power transmission line channel status, it can be used as data to be transmitted to be sent to power line network by coupler, and to be forwarded by other node or other modes pass to control station.

The change of the difference on the frequency therefore between the size variation and minimum of maximum on the amplitude-response curve that we pass through analysis channel, just can analyze the change of the dielectric constant of the insulator medium of transmission line.And the reduction of dielectric constant, often just reflect the rising of the aging of transmission line or ambient temperature, thus just can have comparatively in time the state of transmission line and judge accurately and monitor.

Embodiment two

Embodiment two gives the scheme of the present invention's proposition for carrying out the monitoring of system transfers line states and a kind of embodiment of maintenance based on CP-OFDM technology in power line transmission system.

Present embodiment is for the typical multicarrier operation pattern of one of PLC system, and design parameter is as follows: carrier mode Z=3780, and transmitting terminal planisphere mapping mode is 64QAM, FEC code check is 0.4.

As shown in Figure 2, according to embodiment of the present invention monitoring and the method safeguarding the systematic electricity line states described in the present embodiment, its concrete steps are as follows:

Signal by known training sequence and the data framing to be sent that utilizes OFDM technology to modulate, and is sent into power line transmission by coupler by S1, node A;

In the present embodiment, data to be sent, first through FEC coding, then carry out the symbol X that 64QAM constellation mapping obtains frequency domain _k, specific frequency-domain pilot sequence is inserted into original frequency domain symbol X _kthe middle means as channel estimating, the position of wherein inserting is through well-designed and fixing.

Wherein the inserted mode of frequency-domain pilot sequence common are block (Block) pilot tone and dressing (Comb) pilot tone two kinds, wherein Block mode is used for by all subcarriers in OFDM symbol periodically transmitting pilot tone, and Comb mode uses a subset of sub-clutter to transmit pilot tone.

Then every 3780 new frequency domain symbols forming an OFDM symbol, is the IDFT(IFFT of 3780 through length) by each frequency domain symbol X _ktransform on time domain corresponding subcarrier, then frequency-domain pilot sequence has just been fixed on specific subcarrier; In time domain, the front end that rear 420 symbol sebolic addressings getting IDFT are placed in OFDM symbol forms Cyclic Prefix (CP) and carries out framing as frame head, then utilize root-raised cosine pulse to carry out time domain molding filtration the bandwidth of signal is limited, after up-conversion and power amplification are carried out to the signal processed, carry out the transmission of signal.

S2, Node B are received by coupler and send signal, demodulated received signal, extract transmission data;

S3, Node B utilize known training sequence to obtain transmission channel frequency response (or channel impulse response);

Ofdm system receiving terminal, through A/D and low pass filter, removes Cyclic Prefix, carries out DFT to received signal, if there is no ISI, then

Y(k)=X(k)H(k)+I(k)+W(k) （13）

This example, to the certainty Channel Modeling of quasistatic, is discussed to the channel estimating of ofdm system during being intended to an OFDM information symbol, so save the subscript index of OFDM information symbol sequence n in above formula.In formula, Y (k) represents the Received signal strength value at a receiving terminal kth subcarrier place, H (k) represents the channel frequency characteristic value at a kth subcarrier place, W (k) represents frequency domain Jiaxing white Gaussian noise, and I (k) represents the ICI component that an ofdm system kth carrier wave place participates in.After receiving terminal carries out FFT process to received signal, the pilot tone that system utilizes frequency domain to insert carries out channel estimating.

LS criterion lower channel estimated result:

$H_{\mathrm{LS}}=X_p^{-1}{Y}_p---\left(14\right)$

Then carry out interpolation according to pilot sub-carrier estimated value, just can obtain the channel estimation value that all subcarriers go out.Common interpolating method has two-dimentional MMSE interpolation, piecewise linear interpolation, piecewise polynomial fitting, interpolation and low pass interpolation etc. based on DFT.

S4, Node B analysis frequency respond, and extract key message to calculate channel parameter;

In the present embodiment, extract the magnetic permeability μ that key message is insulator medium in transmission line with the channel parameter calculated _r;

Concrete theory deduction refers to Application Example one, and classical multipath model used herein is different from Application Example one, and parameter is as following table:

Multipath is numbered	1	2	3	4	5
						Equivalent length/m	300	350	370	450	510
Weight coefficient	0.26	0.05	-0.03	0.25	-0.35

In this Application Example, we choose difference on the frequency between the numerical value of the maximum of the amplitude-response curve of transmission channel and minimum as key message for predicting the change of the magnetic permeability of insulator medium in transmission line.

When the numerical value of the maximum of the amplitude-response curve of transmission channel diminishes and difference on the frequency between minimum becomes large, we can analyze the magnetic permeability μ of insulator medium in transmission line _rreduce, namely illustrate that transmission line receives the interference of intense electromagnetic field or creates magnetic ageing.

As Figure 11 shows identical transmission line at different conditions from the amplitude-response curve of 1 ~ 100MHz, can see that the difference on the frequency that solid line reduces between (△ A), minimum compared to the numerical value of maximum on the amplitude-response curve of dotted line channel but becomes greatly (d2>d1), therefore we judge the magnetic permeability μ of insulator medium in transmission line according to the change of key message _rreduce, thus estimate that residing for transmission line, environment has the stronger interference of electromagnetic field or transmission line to there occurs magnetic ageing.

S5, Node B carry out estimating and forecasting according to channel parameter change to power transmission line channel status, it can be used as data to be transmitted to be sent to power line network by coupler, and to be forwarded by other node or other modes pass to control station.

The change of the difference on the frequency therefore between the numerical value change and minimum of maximum on the amplitude-response curve that we pass through analysis channel, just can analyze the change of the magnetic permeability of the insulator medium of transmission line.And the reduction of magnetic permeability, often just reflect the aging of transmission line, thus just can have comparatively in time the state of transmission line and judge accurately and monitor.

Embodiment three

Embodiment three gives the scheme of the present invention's proposition for carrying out the monitoring of system transfers line states and a kind of embodiment of maintenance based on ZP-OFDM technology in power line transmission system.

Present embodiment is for the typical multicarrier operation pattern of one of PLC system, and design parameter is as follows: carrier mode Z=3780, and transmitting terminal planisphere mapping mode is 256QAM, FEC code check is 0.6.

As shown in Figure 2, according to embodiment of the present invention monitoring and the method safeguarding the systematic electricity line states described in the present embodiment, its concrete steps are as follows:

Signal by known training sequence and the data framing to be sent that utilizes OFDM technology to modulate, and is sent into power line transmission by coupler by S1, node A;

In the present embodiment, data to be sent, first through FEC coding, then carry out the symbol X that 256QAM constellation mapping obtains frequency domain _k, specific frequency-domain pilot sequence is inserted into original frequency domain symbol X _kthe middle means as channel estimating, the position of wherein inserting is through well-designed and fixing.

Similarly, the inserted mode of frequency-domain pilot sequence common are block (Block) pilot tone and dressing (Comb) pilot tone two kinds.

Then every 3780 new frequency domain symbols forming an OFDM symbol, is the IDFT(IFFT of 3780 through length) by each frequency domain symbol X _ktransform on time domain corresponding subcarrier, then frequency-domain pilot sequence has just been fixed on specific subcarrier; In time domain, the front end 420 0 sequences being placed in OFDM symbol forms prefix (ZP) and carries out framing as frame head, then utilize root-raised cosine pulse to carry out time domain molding filtration the bandwidth of signal is limited, after up-conversion and power amplification are carried out to the signal processed, carry out the transmission of signal.

S2, Node B are received by coupler and send signal, demodulated received signal, extract transmission data;

S3, Node B utilize known training sequence to obtain transmission channel frequency response (or channel impulse response);

Ofdm system receiving terminal, through A/D and low pass filter, removes prefix, carries out DFT to received signal, if there is no ISI, then such as formula (24).

After receiving terminal carries out FFT process to received signal, the pilot tone that system utilizes frequency domain to insert carries out channel estimating.

With H under LMMSE criterion _pfor variable minimizes following formula:

min{(Y _p-X _pH _p) ^H(Y _p-X _pH _p)} （15）

Be multiple Gaussian Profile in CIR tap and additive noise, and under the two separate precondition, the channel estimation results of LMMSE criterion is:

${\hat{H}}_{\mathrm{LMMSE}}=R_{\mathrm{HH}}{(R_{\mathrm{HH}}+\frac{\mathrm{\β}}{\mathrm{SNR}}I)}^{-1}{\hat{H}}_{\mathrm{LS}}---\left(16\right)$

Then carry out interpolation according to pilot sub-carrier estimated value, just can obtain the channel estimation value that all subcarriers go out.Common interpolating method has two-dimentional MMSE interpolation, piecewise linear interpolation, piecewise polynomial fitting, interpolation and low pass interpolation etc. based on DFT.

S4, Node B analysis frequency respond, and extract key message to calculate channel parameter;

In the present embodiment, extract the loss angle δ that key message is insulator medium in transmission line with the channel parameter calculated;

Concrete theory deduction refers to Application Example one, and classical multipath model used herein is different from Application Example one, and parameter is as following table:

Multipath is numbered	1	2	3	4
					Equivalent length/m	150	188	264	397
Weight coefficient	0.4	-0.4	-0.8	-1.5

In this Application Example, the numerical value change that we choose the maximum of the amplitude-response curve of transmission channel as key message for predicting the change of the loss angle δ of insulator medium in transmission line.

The difference on the frequency become between large and extreme value when the numerical value of the maximum of the amplitude-response curve of transmission channel is constant, the loss angle δ that we can analyze insulator medium in transmission line increases, and namely illustrates that transmission line creates voltage ageing or changes the loss caused due to external environment.

As Figure 12 shows identical transmission line at different conditions from the amplitude-response curve of 1 ~ 100MHz, can see that solid line increases (△ A), difference on the frequency between minimum constant (d2>d1) compared to the numerical value of maximum on the amplitude-response curve of dotted line channel, therefore according to the change of key message, we judge that the loss angle δ of insulator medium in transmission line increases, thus estimate that transmission line creates voltage ageing or changes the loss caused due to external environment.

S5, Node B carry out estimating and forecasting according to channel parameter change to power transmission line channel status, it can be used as data to be transmitted to be sent to power line network by coupler, and to be forwarded by other node or other modes pass to control station.

Therefore the difference on the frequency when we are increased by the numerical value analyzing the maximum of the amplitude-response curve of the transmission channel of channel while between extreme value is constant, just can analyze the increase of loss angle, thus just can have the aging conditions of transmission line and judge comparatively accurately and monitor.

Embodiment four

Embodiment four gives the scheme of the present invention's proposition for carrying out the monitoring of system transfers line states and a kind of embodiment of maintenance based on TDS-OFDM technology in power line transmission system.

Present embodiment is for the typical multicarrier operation pattern of one of PLC system, and design parameter is as follows: carrier mode Z=3780, and transmitting terminal planisphere mapping mode is 64APSK, FEC code check is 0.4.

As shown in Figure 2, according to embodiment of the present invention monitoring and the method safeguarding the systematic electricity line states described in the present embodiment, as shown in Figure 3, its concrete steps are as follows for the topological structure of node:

Signal by known training sequence and the data framing to be sent that utilizes TDS-OFDM technology to modulate, and is sent into power line transmission by coupler by S1, node A;

In the present embodiment, data to be sent, first through FEC coding, then carry out the symbol X that 16QAM constellation mapping obtains frequency domain _k, every 3780 frequency domain symbol X _kforming an OFDM symbol, is the IDFT(IFFT of 3780 through length) by each frequency domain symbol X _ktransform on time domain corresponding subcarrier; In time domain, symbol lengths be 420 the PN sequence front end that is placed in OFDM symbol carry out framing as frame head, then frame structure utilizes root-raised cosine pulse to carry out time domain molding filtration as shown in Figure 4 and the bandwidth of signal is limited, and carries out the transmission of signal to the signal processed after carrying out up-conversion and power amplification.

S2, Node B are received by coupler and send signal, utilize known training sequence demodulated received signal, extract transmission data;

In the present embodiment, Node B by coupler Received signal strength from power line, the signal received by down-conversion, through root-raised cosine pulse bandwidth filtering and sampling; Data after sampling are corresponding carries out synchronous, channel estimating and FFT.

S3, Node B utilize known training sequence to obtain transmission channel frequency response;

In the present embodiment, after carrying out signal and be synchronous, just can carry out channel frequency response and have estimated.The known PN sequence (time-domain training sequence) due to one section with good autocorrelation is inserted in step sl as frame head, and we utilize PN sequence as channel monitoring signal.For each signal frame, the PN sequence received and local PN sequence are carried out relevant impulse response h (t) that just can obtain channel.Again DFT is carried out to impulse response sequence, obtain frequency response H (f) of channel.

S4, Node B analysis frequency respond, and extract key message to calculate channel parameter;

In the present embodiment, extract the DIELECTRIC CONSTANT ε that key message is insulator medium in transmission line with the channel parameter calculated _rwith magnetic permeability μ _r.

Concrete theory deduction refers to Application Example one, and classical two-path model parameter used herein sees the following form:

Multipath is numbered	1	2
			Equivalent length/m	20	25
Weight coefficient	0.5	0.3

In this Application Example, our difference on the frequency chosen between the numerical value of the maximum of the amplitude-response curve of transmission channel, minimum coordinates the periodicity of phase response curve special frequency channel scope as key message for change or the change due to the aging line electricity length caused while predicting the dielectric constant of insulator medium in transmission line and magnetic permeability.

It is substantially constant that difference on the frequency between the minimum of the amplitude-response curve of transmission channel becomes numerical value that is large, maximum, and we can analyze the DIELECTRIC CONSTANT ε of insulator medium in transmission line _rreduce magnetic permeability μ simultaneously _rreduce, coordinate the larger change of the phase response number of cycles within the scope of certain frequency, can the above-mentioned analysis of aided verification, the increase of line electricity length that transmission line creates voltage ageing and magnetic ageing and may cause thus is namely described.

As Figure 13 shows identical transmission line at different conditions from the amplitude-response curve of 1 ~ 100MHz, can see that solid line has larger increase compared to the difference on the frequency on the amplitude-response curve of dotted line channel greatly, between substantially constant, the minimum of the numerical value of minimum value, as Figure 14 shows the phase response curve under corresponding conditions, can see that phase cycling becomes large, therefore we judge the DIELECTRIC CONSTANT ε of insulator medium in transmission line according to the change of key message _rreduce magnetic permeability μ simultaneously _rreduce, thus estimate that transmission line creates voltage ageing and magnetic ageing, and the increase of the line electricity length caused thus.

Embodiment five

The present embodiment provide the present invention propose for carrying out the monitoring of system transfers line states and the device of maintaining method based on OFDM technology in power line transmission system.

With reference to accompanying drawing 15, based on background technology and the above-mentioned description about the power line transmission system based on OFDM technology, the present invention proposes to be used for carrying out the monitoring of system transfers line states and the device of maintaining method based on OFDM technology in power line transmission system, comprise: node A(contains data generating unit, signal madulation unit, coupling unit), Node B (containing coupling unit, signal demodulation unit, channel frequency response estimation unit, linear electrical parameter computing unit, transmission line states prediction unit).

Each Elementary Function and signal annexation are described below:

1) data generating unit, for generation of the data bit transmitted needed for power line monitoring system.

2) signal madulation unit, for the data of generation to be carried out the modulation of OFDM according to the demand of system, more known training pilot tone and OFDM symbol are combined, framing, outputs to coupling unit, for transmission.

3) coupler unit, the signal coupling to be sent exported for signal madulation unit transmits to power line, or is got off to process by the Signal reception on power line for signal demodulation unit;

4) signal demodulation unit, for being undertaken the signal received from coupling unit synchronous and demodulating the training sequence carried;

5) channel frequency response estimation unit, the frequency response utilizing known pilot sequence to carry out channel is estimated, obtains frequency response parameter.

6) linear electrical parameter computing unit, by the change of the key message such as spacing change, phase information in analysis frequency response curve between the minimizing amplitude of maximum value, change in location and extreme value, obtain relative dielectric constant ε transmission line basic parameter being comprised to dielectric between conductor _r, relative permeability μ _r, the change of angle of loss δ is estimated.。

7) transmission line states prediction unit, carries out Macro or mass analysis to the basic parameter change of transmission line, draws the prediction to line status and monitoring.

With reference to accompanying drawing 15, at start node A, first data generating unit produces data to be sent, through Channel Modulation unit, data to be sent and training pilot tone are processed, produce ofdm signal and framing, be sent on power transmission line through coupling unit, in Node B, by coupling unit by Signal reception to channel demodulation unit, carry out synchronous and after demodulating the training pilot tone of carrying to the received signal, at channel frequency response estimation unit, the known frequency response of training pilot tone to channel is utilized to estimate, linear electrical parameter computing unit utilizes the frequency response obtained to estimate to estimate the change of the basic parameter of transmission line, Macro or mass analysis is carried out in the basic parameter change of last transmission line states prediction unit to transmission line, draw the prediction to line status and monitoring.

Can find out, node A and Node B are a kind of differentiation functionally, and any node can have the function of these two nodes, can call corresponding unit as required for the status predication of transmission line and Signal transmissions in concrete application.

Claims (8)

1. a method for power transmission line status monitoring, is characterized in that, comprises the following steps:

Signal by known training sequence and the data framing to be sent that utilizes OFDM technology to modulate, and is sent into power line by coupler and is transmitted by S1, node A;

S2, Node B are received by coupler and send signal, utilize known training sequence demodulated received signal, extract transmission data;

S3, Node B utilize known training sequence to obtain transmission channel frequency response;

S4, Node B analyze channel frequency response, extract the relevant information of transmission line, are drawn the change information of transmission line basic parameter, to calculate channel parameter by the change analyzing relevant information;

Described relevant information comprises that frequency plot between poor, the adjacent extreme value of frequency interval between the amplitude of the maximum of channel frequency response, minimizing amplitude, phase place, position, adjacent extreme value is poor, the cycle of phase response;

Described transmission line basic parameter comprises the relative dielectric constant ε of dielectric between conductor _r, relative permeability μ _r, angle of loss, electrical length l;

Described channel parameter comprises the loss angle δ of insulator medium in the magnetic permeability of insulator medium in the dielectric constant of insulator medium in transmission line, transmission line and transmission line;

S5, Node B carry out estimating and forecasting according to channel parameter change to power transmission line channel status.

2. the method for claim 1, is characterized in that:

Described training sequence comprises time-domain training sequence, frequency domain training sequence.

3. the method for claim 1, is characterized in that:

Described OFDM framing mode comprises ZP-OFDM, CP-OFDM and TDS-OFDM.

4. the method for claim 1, is characterized in that:

In step S5, describedly estimating and forecasting is carried out to power transmission line channel status comprise following corresponding relation according to channel parameter change: between conductor, the dielectric constant of the dielectric ambient temperature residing for voltage ageing or transmission line representing transmission line that diminishes raises, magnetic permeability diminishes the magnetic ageing that represents transmission line or cause medium to there occurs deformation heterogeneous due to the change of pressure, and the increase of angle of loss represents that transmission line creates voltage ageing or changes the loss caused due to external environment.

5. method as claimed in claim 2, is characterized in that:

According to time domain known training sequence, then represent that the impulse response of channel is estimated by the convolution of known training sequence and receiving sequence, then obtain channel frequency response through discrete Fourier transform (DFT) DFT conversion; According to frequency domain known training sequence, then directly represent that the frequency response of channel is estimated with the business of the discrete Fourier transform (DFT) DFT of receiving sequence and known training sequence.

6. the monitoring device of transmission line state in power communication system, it is characterized in that, this device comprises:

Data generating unit, for generation of data waiting for transmission;

The data of generation are carried out OFDM modulation for the demand according to system by signal madulation unit, and known training pilot tone and OFDM symbol are carried out combine, framing, output to coupler unit;

Coupler unit, transmits to power line for the signal coupling exported by signal madulation unit, or processes for being received and be transferred to signal demodulation unit by the signal coupling on power line;

Signal demodulation unit, for being undertaken the signal received from coupling unit synchronous and demodulating the training sequence carried;

Channel frequency response estimation unit, utilize receive with known pilot frequency sequence carry out channel frequency response estimate, obtain frequency response parameter;

Linear electrical parameter computing unit, by the change of relevant information in analysis frequency response parameter and analysis frequency response curve, obtains and estimates the change of transmission line basic parameter;

Transmission line states prediction unit, carries out Macro or mass analysis to the basic parameter change of transmission line, draws the prediction to line status and monitoring.

7. monitoring device as claimed in claim 6, is characterized in that:

In frequency response curve described in linear electrical parameter computing unit, relevant information comprises: spacing, phase place between the maximum amplitude of frequency response curve, minimum amplitude, position, extreme value.

8. monitoring device as claimed in claim 6, is characterized in that:

Described in linear electrical parameter computing unit, transmission line basic parameter comprises: the relative dielectric constant ε of dielectric between conductor _r, relative permeability μ _r, angle of loss δ, electrical length l.