CN106130042B - A kind of neutral point voltage flexible control method for improving active compensation technology - Google Patents
A kind of neutral point voltage flexible control method for improving active compensation technology Download PDFInfo
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Abstract
Herein caused by analysis system normal operation in the mechanism of neutral point voltage, propose a kind of flexible control method for the neutral point voltage for improving active compensation technology, this method utilizes the iteration thought of calculus of finite differences, according to the size and phase place change of neutral point voltage, the size and phase of Injection Current are controlled simultaneously, it is zero that neutral point voltage, which can not only accurately be controlled, and neutral point voltage can also be controlled to the desired value of any non-zero, can be on the premise of system earth mode not be changed, the asymmetrical voltage of quick compensation system.This method breaches the limitation to the frequent measurement of electrical network parameter, the parameter over the ground of system need to only be measured once, in the case of power network unusual fluctuation, it can be still updated to original electrical network parameter in algorithm and be iterated circulation, can there is fast convergence rate, the size that Injection Current can be adjusted simultaneously and phase, the change for adapting to system architecture, parameter.
Description
Technical field
The present invention relates to during a kind of resonant earthed system normal operation voltage to neutral control new method, specifically
It is that the thought voltage to neutral based on calculus of finite differences carries out Flexible Control.
Background technology
China's medium voltage distribution network mainly in a manner of small current neutral grounding based on, conventional has neutral by arc extinction coil grounding side
Two kinds of formula and isolated neutral mode.Because three-phase overhead transmission line is typically using the frame that do not replace in both earthing modes
And if in view of might have the unsymmetrical arrangement of single-phase high voltage load, voltage transformer and compensating electric capacity and non-in circuit
The presence of complete mutually power supply, causing three relatively parameter unbalances so that neutral point voltage is present, and in neutral point through disappearing
In arc coil earthed system, due to the input of arc suppression coil so that zero sequence impedance increase, the degree of asymmetry of power network is exaggerated, it is special
Yi Fashengyin tunings are improper not when power network degree of asymmetry is larger causes resonance overvoltage, and higher neutral point voltage can to match somebody with somebody
The safety and reliability of power network is a greater impact.
The method of more commonly used limitation neutral point voltage is by increasing coupling capacitor and filling arc suppression coil
Appropriate off-resonance point operation is put to realize.Increase coupling capacitor makes three-phase ground capacitance equal, it is necessary to increase equipment
Input, and when line construction, parameter change, capacitor can not change therewith immediately, in some instances it may even be possible to can increase power network
Three-phase imbalance.The operation of arc suppression coil off-resonance point can not be inherently eliminated asymmetrical voltage, and its inhibition is limited.
Active compensation technology compensation neutral point voltage be the method newly proposed in recent years, it first with the degree of asymmetry of power network, phase voltage,
Power network total capacitance theoretical calculation goes out the size of Injection Current, then injects the electric current that the theoretical calculation obtains to neutral point, reaches
The purpose of neutral point voltage control, the method is to be directly injected into the electric current that theoretical calculation obtains, it is impossible to which voltage to neutral is carried out
Flexible Control, and system insulating resistance is have ignored, and when system architecture, parameter change, voltage to neutral
Control effect has a great influence.
The content of the invention
Technical problem：Technical problem solved by the invention is to propose a kind of neutral point voltage for improving active compensation technology
Flexible control method, a certain initial current is injected to neutral point, using the thought of calculus of finite differences, by the size for controlling Injection Current
And phase, finally realize the Flexible Control of neutral point voltage.This method breaches traditional active compensation neutral point voltage technology
Can not accurate Injection Current limitation, need to only measure once to the parameter over the ground of system, it is still available in the case of power network unusual fluctuation
Original electrical network parameter, without to the power network after unusual fluctuation, parameter measures again over the ground, simplifying that conventional method repeatedly measures can institute
The inconvenience brought, it is well practicality to have.
Technical scheme：To solve above technical problem, the present invention proposes a kind of neutral point electricity for improving active compensation technology
Flexible control method is pressed, its particular content is：
A certain current known first is injected to neutral point, obtains the size and phase angle of the neutral point voltage after Injection Current, so
Electrical network parameter is combined afterwards, and each increment for needing Injection Current size and phase angle is calculated using calculus of finite differences thought successive ignition
Increment, electric current corresponding to injection finally realize the Flexible Control of neutral point voltage, and methods described step includes：
Step a:Using A phase supply voltages as reference vector, if
Wherein, CΣ=CA+CB+CCFor the total direct-to-ground capacitance of system,For the total insulation conductance of system, L is
Arc suppression coil inductance；According to network system total capacitance, the arc suppression coil inductance of input, total conductance parameter value calculation Y over the ground over the ground
With phase angle beta；
Step b：Inject all known initial current of phase and amplitude
Wherein, ρ is overhead transmission line power network degree of asymmetry, and scope is 0.5%~1.5% in engineering, and average ρav=
1%,For supply voltage, C∑For power network total capacitance；
Step c：If it is zero to suppress neutral point voltage, A=0, B=0 are set；Measure the neutral point voltage after Injection Current
Size and phase obtain A(k)And B(k), then Δ A(k)With Δ B(k)For：
Formula (2), A(k)And B(k)The real and imaginary parts of the actually measured neutral point voltage of respectively corresponding k circulation；
Step d:Judge max | Δ A(k),ΔB(k)| ＜ ε, wherein ε are that the error of function value is less than given feasible value.
If judging to set up, adjust successfully；If judgement is invalid, below step is carried out；
Step e：CalculateMatrix：
Wherein
MatrixIn element H(k)、N(k)、M(k)、L(k)Should correspond to I in the value of the electric current of injections (k)WithWhen,
Obtained by formula (4)；
Step f：Solve update equation formula：
Obtain correctionWith Δ Is '(k), thus obtain revisedAnd Is (k+1):
As new injected value of current, step c is substituted into again, by successive ignition, until neutral point voltage is zero.
It is as follows for the iterative method thought in above-mentioned steps, its principle：
For first order nonlinear algebraic equation
F (x)=0 (7)
If its Exact Solutions is x(*), and x(k)For its approximate solution, Δ x(k)To be poor between them, i.e.,
x(*)=x(k)+Δx(k) (8)
Formula (8) is substituted into formula (7), had
F(x(k)+Δx(k))=0 (9)
Formula (9) is in x(k)Place is launched into Taylor series, obtains
Omit Δ x in formula (10)(k)Square and the above it is every, and only take its linear segment, obtain
F(x(k))+F'(x(k))Δx(k)=0 (11)
Formula (11) is referred to as update equation, can be solved using it
Δx(k)=-[F'(x(k))]-1F(x(k)) (12)
And by Δ x(k)Referred to as correction.
If x(k)It is suitable to choose, then x(k)+Δx(k)Compare x(k)Closer to Exact Solutions, and make
x(k+1)=x(k)+Δx(k) (13)
Its difference between Exact Solutions is Δ x(k+1), i.e.,
x(*)=x(k+1)+Δx(k+1) (14)
Then, repeat said process, i.e., change k into k+1 in formula (9)~formula (14), it is closer so as to draw
In the x of Exact Solutions(k+2).If the initial value chosen is suitable, above-mentioned iterative process is repeated, is up to obtaining sufficiently exact solution
Only, and can be with | F (x(k)) | ＜ ε, ε are that the error of function value is less than given feasible value, as convergent criterion, its
Iterative process can illustrate its geometric meaning with Fig. 2.
Beneficial effect：A kind of neutral point voltage control method for improving active compensation technology proposed by the present invention, can not only
Accurate to control neutral point voltage be zero, and can also control the neutral point voltage can be not changing to the desired value of any non-zero
On the premise of system earthing mode, the asymmetrical voltage of quick compensation system.When this method efficiently solves power network unusual fluctuation, tradition side
Method needs the problem of frequently measurement electrical network parameter, and the parameter over the ground of system need to only be measured once, in the case of power network unusual fluctuation,
It can be still updated to original electrical network parameter in algorithm and be iterated circulation, speed responsive is fast, disclosure satisfy that electrical network parameter, structure
Change, adaptability are stronger.
Brief description of the drawings
System architecture sketch when Fig. 1 is power network normal operation.
Fig. 2 is calculus of finite differences iterative process convergence graph.
Fig. 3 is Flexible Control Injection Current size and phase flow chart.
Embodiment
Structure diagram during neutral by arc extinction coil grounding system normal operation is shown refering to Fig. 1.In figureRespectively A, B, C three-phase mains voltage,For neutral point voltage, L is arc suppression coil inductance, CA、CB、CCRespectively
For A, B, C three phase capacitance, rA、rB、rCFor A, B, C three phase isolated resistance,For the equivalent current of injection.
The voltage on the basis of A phase supply voltages, can be obtained by Kirchhoff's current law (KCL)：
Then neutral point voltageFor：
C in formula (2)Σ=CA+CB+CC,α=ej120；
Order
If ignoring the influence of system insulating resistance, can obtain
In formula (4) For supply voltage.
Meanwhile if order
Its (5), which are substituted into (2), to be obtained：
It can be obtained by formula (6)
OrderAccording to linear segment is only taken in calculus of finite differences, it can show that update equation formula is
In formula (9), have
Formula (9) can be write as
Wherein Δ Is '(k)=Δ Is (k)/Is (k)。
In formula (11), matrixIn element H(k)、N(k)、M(k)、L(k)It in the On The Current Value of injection is I to bes (k)With
When, it is calculated by formula (10), for formula (11), can obtain correctionWith Δ Is '(k), so as to draw
Then, repeat said process, i.e., change k into k+1 in formula (11)~formula (12), it is closer so as to draw
In the x of Exact Solutions(k+2)。
If the initial value chosen is suitable, above-mentioned iterative process is repeated, untill sufficiently exact solution is obtained, and
Can be with max | Δ A(k),ΔB(k)| ＜ ε, ε are that the error of function value is less than given feasible value, as convergent criterion.
Arbitrary size and the electric current of phase are injected in theory, are updated in algorithm, its iterative process is all convergent, but is examined
Consider the influence of calculation error in practice and measurement error, and reduce iterations, initial Injection Current should close to exact value,
Specific prediction is as follows：
Because present invention is generally directed to overhead transmission line power network, degree of asymmetry ρ scopes in engineering are 0.5%~1.5%, are taken
Average value ρav=1%, then further according to supply voltageWith the power network total capacitance C measured∑Initial Injection Current is predicted, it is
Exemplified by suppressing neutral point voltage and be zero, specific regulation process is as follows：
The first step：According to network system total capacitance, the arc suppression coil inductance of input, total conductance parameter value calculation over the ground over the ground
Amplitude Y and phase angle beta, the purpose is to combine the size and phase of Injection Current, calculateMatrix, k are iterative cycles number；
Second step：Inject the electric current of prediction
3rd step：It is zero to suppress neutral point voltage, then puts A=0, B=0；
4th step：The size and phase of neutral point voltage after measurement Injection Current obtain A(k)And B(k), wherein A(k)And B(k)The real and imaginary parts of the actually measured neutral point voltage of respectively corresponding k circulation, i.e. Δ A(k)=A-A(k)、ΔB(k)=
B-B(k), judge max | Δ A(k),ΔB(k)| ＜ ε, if judging to set up, adjust successfully；If judgement is invalid, walk below
Suddenly；
5th step：According to formula (10) calculating matrixMiddle each element；
6th step：Obtained according to formula (11)With Δ Is '(k), so as to obtainAnd Is (k+1), as new note
Enter current value, be updated to FOUR EASY STEPS, can be achieved to control neutral point voltage is zero.
Regulation flow process figure refers to Fig. 3.
Claims (4)
1. a kind of neutral point voltage flexible control method for improving active compensation technology, it is characterised in that first neutral to power distribution network
Point injects a certain current known, obtains the size and phase angle of the neutral point voltage after Injection Current, then in conjunction with electrical network parameter, profit
Be calculated with calculus of finite differences successive ignition needs the increment of Injection Current size and the increment of phase angle every time, electric current corresponding to injection,
The final Flexible Control for realizing neutral point voltage, step are as follows：
Step a:Using A phase supply voltages as reference vector, if
Wherein, CΣ=CA+CB+CCFor the total direct-to-ground capacitance of system,For the total insulation conductance of system, L is extinguishing arc
Coil inductance；According to network system total capacitance, the arc suppression coil inductance of input, over the ground total conductance parameter value calculation Y and phase over the ground
Angle beta；
Step b：Inject all known initial current of phase and amplitude
Step c：If it is zero to suppress neutral point voltage, sets its real and imaginary parts and meet A=0, B=0；After measuring Injection Current
The size and phase of neutral point voltage obtain A(k)And B(k), then the difference DELTA A of its size and phase(k)With Δ B(k)For：
Wherein, A(k)And B(k)The real and imaginary parts of the actually measured neutral point voltage of respectively corresponding k circulation；
Step d:Judge max | Δ A(k),ΔB(k)| ＜ ε, wherein ε are that the error of function value is less than given feasible value；If sentence
It is broken into vertical, then adjusts successfully；If judgement is invalid, below step is carried out；
Step e：CalculateMatrix：
Step f：Solve update equation formula
Obtain correctionWith Δ Is'(k), thus obtain revisedAnd Is (k+1):
As new injected value of current, step c is substituted into again, by successive ignition, until neutral point voltage is zero.
2. a kind of neutral point voltage flexible control method for improving active compensation technology as claimed in claim 1, its feature exist
In all known initial Injection Current of phase and amplitude described in step bMissed in view of calculation error in practice and measurement
The influence of difference, and iterations is reduced, initial Injection Current is calculated by formula (6)：
In formula (6)For overhead transmission line power network degree of asymmetry, α=ej120,For supply voltage, C∑For power network
Total capacitance；Due to overhead transmission line power network degree of asymmetry ρ, scope is 0.5%~1.5% in engineering, and average ρav=1%.
3. a kind of neutral point voltage flexible control method for improving active compensation technology as claimed in claim 1, its feature exist
In, if step c control neutral point voltage to the desired value of any non-zero, can be on the premise of system earth mode not be changed, soon
The asymmetrical voltage of fast compensation system.
4. a kind of neutral point voltage flexible control method for improving active compensation technology as claimed in claim 1, its feature exist
In described in step eMatrix, its computational methods are as follows：
MatrixIn element H(k)、N(k)、M(k)、L(k)Should be that to correspond to value be I in the electric current of injections (k)WithWhen, by above formula
(7) obtain.
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