CN105391059A - Distributed power generation system state estimation method based on current measurement transformation - Google Patents

Abstract

The invention discloses a distributed power generation system state estimation method based on current measurement transformation. First branch power measurement, node power measurement and power pseudo measurement are converted to a real part and a virtual part of branch current; branch current of an equivalent node is obtained according to the characteristic and type of a distributed power supply; a measurement matrix and an information matrix are built, and singular value decomposition is performed on the information matrix to obtain a corresponding inverse matrix; the amount of current of each branch is used as the state quantity, a least squares estimation criterion is adopted to perform state estimation, and the branch current is corrected; according to the updated branch current, and a backward iterative method is utilized to solve a voltage vector of each node; and the node voltage that is obtained is utilized to perform measurement transformation, the branch circuit is corrected, voltage of each node is obtained, and the steps are repeated till the condition of convergence is satisfied. The distributed power generation system state estimation method based on current measurement transformation has relatively fast arithmetic speed of an algorithm, can well process power measurement, adopts the state estimation algorithm with singular value decomposition, and can identify a state-unobservable area, thereby solving the ill-conditioned problem of a system.

Description

A kind of distributed generation system method for estimating state based on current measurement conversion

Technical field

The invention belongs to technical field of power systems, particularly relate to a kind of distributed generation system method for estimating state based on current measurement conversion.

Background technology

Along with the development of intelligent distribution network, distributed power source constantly will access power distribution network, proposes new requirement to power distribution network safe and reliable operation, and to carry out state estimation to distribution system be the prerequisite realizing power distribution network intelligent scheduling.Under the observable prerequisite of keeping system, state estimation can improve the precision of data according to the redundancy of metric data, estimate the electric information not having measuring equipment place, compare with Load flow calculation, state estimation is the former expansion and continuity, result of calculation is also more accurate, so the infiltration carrying out analysis distribution formula power supply by studying the State Estimation for Distribution Network containing distributed power source has great importance on the impact that state of electric distribution network is estimated.

After power distribution network access distributed power source, the system of multiple feed will be become by single power supply, the trend of power distribution network also will change, need to carry out necessary adjustment to state of electric distribution network algorithm for estimating, in addition, the access of distributed power source adds the measurement amount of distribution system, will produce active influence to the precision improving state of electric distribution network estimation.For the Different Effects that different distributed electrical Source Types access distribution brings, need for himself characteristic, research is adapted to the state estimation algorithm of distributed generation system.For the control of intelligent distribution network and operation provide security evaluation basis.On the other hand, consider electric power system due to test leakage amount or other reasons cause not observable time, how Ill-conditioned System carries out state estimation, is directly connected to POWER SYSTEM STATE assess effectiveness.

Summary of the invention

For Power system state estimation to the deficiency to process Ill-conditioned System problem, the present invention proposes a kind of distributed generation system method for estimating state based on current measurement conversion, Ill-conditioned System state estimation problem can be solved on the one hand, carry out grid-connected process to distributed power source is access grid-connected on the one hand, realize the state estimation of distributed generation system.

The present invention is such realization, a kind of distributed generation system method for estimating state based on current measurement conversion, and concrete steps comprise:

First, measured by branch power, the pseudo-measurement amount of node power amount side and power is converted to real part and the imaginary part of branch current, and asks the branch current of its equivalent node according to the characteristic of distributed power source and type;

Then, build calculation matrix and information matrix, adopt singular value decomposition method to its corresponding inverse matrix of information matrix;

Then, using the magnitude of current of each branch road as quantity of state, adopt least-squares estimation criterion to carry out state estimation, revise branch current;

Then, according to the branch current after renewal, offspring's method is utilized to solve the voltage vector of each node;

Finally, recycle the node voltage of trying to achieve and do Transformed Measurement, revise branch current, try to achieve each node voltage, so repeatedly until meet the condition of convergence.

Further, adopt least-squares estimation criterion to carry out state estimation, revise the method for branch current, concrete steps comprise:

First, based on least squares theory, the estimated value being state variable with electric current both sides amount rectangular be expressed as:

$\hat{x}={\left(H^T{R}^{-1}H\right)}^{-1}{H}^T{R}^{-1}z$

With B=H ^tr ^-1h is as the information matrix of measurement equation.Singular value decomposition is adopted to process information matrix:

B＝USV ^T

B ^-1＝VS ^-1U ^T

If s-matrix diagonal element is all greater than 0, then system mode is objective.If diagonal element exists non-positive number, then represent that system is ill, exists unobservable region.

Then, after trying to achieve current status amount, the quantity of power according to following each node of formula correction is measured.

$P+jQ={\stackrel{\·}{U}}^{k-1}\·{\left({\stackrel{\·}{I}}^k\right)}^{*}$

Then, according to the structure of power distribution network, utilize offspring's method to solve the voltage of each node.

${\stackrel{\·}{U}}_i^k={\stackrel{\·}{U}}_j^k-\mathrm{\Δ}{\stackrel{\·}{U}}_{ij}^k$

Then, judge whether convergence according to the condition of convergence, when meeting the condition of convergence, iteration terminates.

$max\left|U_i^k-U_i^{k-1}\right|<\mathrm{\&epsiv;}$

If do not meet the condition of convergence, then carry out next round iteration according to formula:

${\hat{x}}^{(k+1)}={\left({\mathrm{VS}}^{-1}{U}^T\right)}^{-1}{H}^T{R}^{-1}z$

The described distributed generation system method for estimating state based on current measurement conversion, specifically comprises the processing method of distributed power source:

(1) when carrying out state estimation to the electric power system containing distributed power source, need to set up different computation models and processing scheme according to distributed electrical Source Type.According to different distributed power sources generating attribute and the impact of grid-connected generation, distributed power source can be divided into 4 interior joint types, be respectively: PQ node, PQ (V) node, PV node and I node.According to the difference of distributed electrical Source Type, process respectively;

(2) to PQ node, regarded conventional load node and considered, and be directly converted into magnitude of current measurement by changed power formula;

(3) to PQ (V) node, distributed power source due to PQ (V) node type keeps meritorious power invariability, and the reactive power exported and voltage have relation, therefore be converted into PQ node when each iteration, and be translated into magnitude of current measurement according to changed power formula.And each new magnitude of voltage that basis obtains before iteration is revised the reactive power exported.

(4) to PV node, due to PV node type distributed power source keep active power and node voltage amplitude constant, therefore PQ node is converted into when iteration, active power measurement amount is constant, reactive power measurement amount is got 0.5 or 0.8 according to power factor and is asked for, and is then translated into the magnitude of current according to horse-power formula and measures; And each after iteration, adopt the method for superposition offset current to make up node voltage and copy and measure unequal voltage with voltage and copy difference.

(5) when PV node occurs that reactive power is more real, the reactive power of PV node is set as the reactive power upper limit of generator, in iteration after this, this node is converted to PQ nodes for state and estimates, and no longer consider that voltage copies poor impact.

The distributed generation system method for estimating state based on current measurement conversion of invention, to on the basis of state estimation algorithm, it is improved on the one hand, propose the method for estimating state for all kinds of distributed electrical source node, four class distributed electrical source nodes are discussed respectively, propose the processing policy of this four category node in state estimation, make algorithm more have applicability; On the other hand, introduce unusual decomposition strategy, use singular value decomposition method information matrix to be treated to the product of orthogonal matrix, diagonal matrix S and orthogonal matrix, realize the state estimation to Ill-conditioned System.And due to only a singular value decomposition need be carried out to information matrix in an iterative process, save program runtime.

Accompanying drawing explanation

Fig. 1 is the basic step of a kind of distributed generation system method for estimating state based on current measurement conversion that the present invention proposes;

Fig. 2 is the flow chart of a kind of distributed generation system method for estimating state based on current measurement conversion that the present invention proposes;

Fig. 3 is the weak ring power distribution network of IEEE36 node containing distributed power source that the embodiment of the present invention provides;

Embodiment

In order to make object of the present invention, technical scheme and advantage clearly understand, below in conjunction with embodiment, the present invention is further elaborated.Should be appreciated that specific embodiment described herein only in order to explain the present invention, be not intended to limit the present invention.

See Fig. 1, the present invention proposes a kind of distributed generation system method for estimating state based on current measurement conversion.

Step S1, measures branch power, and node power amount side and the pseudo-measurement amount of power are converted to real part and the imaginary part of branch current;

Step S2, asks the branch current of its equivalent node according to the characteristic of distributed power source and type;

Step S3, builds calculation matrix and information matrix, and carries out singular value decomposition to information matrix and ask its corresponding inverse matrix;

Step S4, using the magnitude of current of each branch road as quantity of state, adopts least-squares estimation criterion to carry out state estimation, revises branch current;

Step S5, according to the branch current after renewal, utilizes offspring's method to solve the voltage vector of each node;

Step S6, recycles the node voltage of trying to achieve and does Transformed Measurement, revise branch current, try to achieve each node voltage, so repeatedly until meet the condition of convergence.

The branch current method of its equivalent node is asked to be according to the characteristic of distributed power source and type:

Distributed power source is divided into four kinds of node types, i.e. PQ node, PQ (V) node, PV node and I node; The distributed power source of PQ node type, in state estimation algorithm, needs to be converted into current measurement by power conversion formula; The reactive power that the distributed power source of PQ (V) node type exports is relevant with node voltage, first first converts it to PQ node, and asks its current measurement; The distributed power source of PV node type converts PQ node to, and ask its current measurement, the method being converted to current measurement is: active power measures constant, and it is 0.5 or 0.8 get steady state value that reactive power measures by power factor, then just can calculate the measurement of its node load Injection Current.Injection reactive power if there is PV node is out-of-limit, and so the idle injection of PV node is set as the idle output upper limit of generator, in iteration after this, this node adds computing as PQ node, need not consider the impact that voltage magnitude difference band comes; The distributed power source of I node type only needs directly to measure as negative load current in state estimation.

According to formula, unusual decomposition is carried out to information matrix:

B＝H ^TR ^-1H

B＝USV ^T

B ^-1＝VS ^-1U ^T

Information matrix B is decomposed into row orthogonal matrix U (m × n), according to BB the most at last ^tthe diagonal matrix S that forms of non-negative square root and the product of orthogonal matrix V (n × n), and ask its unusual decomposition inverse matrix;

Utilize offspring's method solve the voltage vector of each node process in, first measure according to following each quantity of power of formula correction.

$P+jQ={\stackrel{\&CenterDot;}{U}}^{k-1}\&CenterDot;{\left({\stackrel{\&CenterDot;}{I}}^k\right)}^{*}$

Then according to the structure of power distribution network, offspring's method is utilized to solve the voltage of each node.

${\stackrel{\&CenterDot;}{U}}_i^k={\stackrel{\&CenterDot;}{U}}_j^k-\mathrm{\&Delta;}{\stackrel{\&CenterDot;}{U}}_{ij}^k$

In process to its node voltage of distributed power source node regulation:

Constant active power can be exported to the distributed power source of PQ (V) node type, but the reactive power exported is relevant with node voltage, before each state estimation iteration, the idle needs of output of PQ (V) node are revised according to the magnitude of voltage obtained after each iteration, then combine the active power recorded to measure, convert thereof into load current and measure.

To PV node after each iteration, the voltage magnitude of node and given voltage magnitude measure can be unequal, adopt the method for superposition offset current to make up the next impact of this voltage magnitude difference band, make the voltage magnitude of PV node equal with given voltage magnitude measuring value.

When adopting least square method to solve quantity of state, because distributed power source is as real-time measurement amount access common node, it is more much smaller than the error in measurement of the puppet measurement obtained by load prediction when not connecing distributed power source to make the error in measurement of this node, so the load bus to access distributed power source, the selection of weight should be rethought, suitably increase distributed power source and site weight.

As the flow chart that Fig. 2 is the distributed generation system method for estimating state based on current measurement conversion.

If Fig. 3 is the weak ring power distribution network of IEEE36 node containing distributed power source that the embodiment of the present invention provides, when there is looped network situation in power distribution network, by looped network tie lines information response in measurement function and Jacobian matrix, and increase the branch current quantity of state between two closed loop points.

System voltage reference value gets 6.062kV, and apparent power fiducial value gets 100kVA, and iteration precision selects 10-5, and node 16 and 22, node 24 and 29 form two looped networks, the weak ring distribution net work structure figure containing distributed power source according to Fig. 3.The distributed electrical Source Type and the parameter that access IEEE36 weak ring power distribution network node system in example are as shown in table 1.

Table 1 accesses the distributed electrical Source Type of weak ring power distribution network

For fuel cell, transducer parameters: P _n=600kW, ρ _min=0.75;

For asynchronous wind generating, reactive-load compensation capacitor parameter: Q _n-Unit=40kvar, U _n=6.062kV

Choosing asynchronous wind generating, to access this weak ring power distribution network be that example is analyzed, and the absolute error of the state estimation and measuring value that system A phase partial branch active power listed by table 2 compares.

As can be seen from Table 2, branch road 10,12,19 and 24 does not have branch power metric data, except the state estimation absolute error of branch road 19 is slightly large, the state estimation absolute error of other four branch roads is all within 1%, the branch power information that can obtain not having installation measurement equipment place by state estimation is described, and precision is higher.Average to measurement absolute error and state estimation absolute error, can obtain measuring mean absolute error is 1.816%, and state estimation mean absolute error is 1.557%, improves the precision of state estimation after adding asynchronous wind generating.

The absolute error of table 2A phase branch road active power state estimated value and measuring value compares

Claims (8)

1. based on a distributed generation system method for estimating state for current measurement conversion, it is characterized in that, the described distributed generation system method for estimating state based on current measurement conversion comprises:

Step S1, measures branch power, and node power amount side and the pseudo-measurement amount of power are converted to real part and the imaginary part of branch current;

Step S2, asks the branch current of its equivalent node according to the characteristic of distributed power source and type;

Step S3, builds calculation matrix and information matrix, and carries out singular value decomposition to information matrix and ask its corresponding inverse matrix;

Step S4, using the magnitude of current of each branch road as quantity of state, adopts least-squares estimation criterion to carry out state estimation, revises branch current;

Step S5, according to the branch current after renewal, utilizes offspring's method to solve the voltage vector of each node;

Step S6, recycles the node voltage of trying to achieve and does Transformed Measurement, revise branch current, try to achieve each node voltage, so repeatedly until meet the condition of convergence.

2., as claimed in claim 1 based on the distributed generation system method for estimating state of current measurement conversion, it is characterized in that, in step S2, ask the branch current method of its equivalent node as follows according to the characteristic of distributed power source and type:

Distributed power source is divided into four kinds of node types, i.e. PQ node, PQ (V) node, PV node and I node; The distributed power source of PQ node type, in state estimation algorithm, needs to be converted into current measurement by power conversion formula; The reactive power that the distributed power source of PQ (V) node type exports is relevant with node voltage, first first converts it to PQ node, and asks its current measurement; The distributed power source of PV node type converts PQ node to, and asks its current measurement; The distributed power source of I node type only needs directly to measure as negative load current in state estimation.

3. as claimed in claim 1 based on the distributed generation system method for estimating state of current measurement conversion, it is characterized in that, step S3 carries out singular value decomposition to information matrix and asks the method for its corresponding inverse matrix to be:

According to formula:

B＝H ^TR ^-1H

B＝USV ^T

B ^-1＝VS ^-1U ^T

Information matrix B is decomposed into row orthogonal matrix U (m × n), according to BB ^tthe diagonal matrix S that forms of non-negative square root and the product of orthogonal matrix V (n × n), and ask its unusual decomposition inverse matrix.

4., as claimed in claim 1 based on the distributed generation system method for estimating state of current measurement conversion, it is characterized in that, the method that step S5 utilizes offspring's method to solve the voltage vector of each node is:

(1) measure according to following each quantity of power of formula correction.

(2) according to the structure of power distribution network, offspring's method is utilized to solve the voltage of each node.

。

5., as claimed in claim 1 based on the distributed generation system method for estimating state of current measurement conversion, it is characterized in that, revise branch current in step S6, the method for trying to achieve each node voltage is:

(1) distributed power source of PQ (V) node type can export constant active power, but the reactive power exported is relevant with node voltage, before each state estimation iteration, the idle needs of output of PQ (V) node are revised according to the magnitude of voltage obtained after each iteration, then combine the active power recorded to measure, convert thereof into load current and measure.

(2) PV node after each iteration, the voltage magnitude of node and given voltage magnitude measure can be unequal, adopt the method for superposition offset current to make up the next impact of this voltage magnitude difference band, make the voltage magnitude of PV node equal with given voltage magnitude measuring value.

6., as claimed in claim 1 based on the distributed generation system method for estimating state of current measurement conversion, it is characterized in that, when adopting least square method to solve quantity of state, the choosing method of weight:

Distributed power source is as real-time measurement amount access common node, it is more much smaller than the error in measurement of the puppet measurement obtained by load prediction when not connecing distributed power source to make the error in measurement of this node, so the load bus to access distributed power source, the selection of weight should be rethought, suitably increase distributed power source and site weight.

7. the distributed power source of PV node type as claimed in claim 2 converts PQ node to, and asks its current measurement method, and it is characterized in that, the method being converted to current measurement comprises:

Active power measures constant, and it is 0.5 or 0.8 get steady state value that reactive power measures by power factor, then just can calculate the measurement of its node load Injection Current.

8. revise branch current as claimed in claim 5, try to achieve the method for each node voltage, it is characterized in that, PV node is carried out to the conversion method of current measurement:

After each iteration, the injection reactive power if there is PV node is out-of-limit, and so the idle injection of PV node is set as the idle output upper limit of generator, in iteration after this, this node adds computing as PQ node.