AU2013201595B2

AU2013201595B2 - Method and apparatus for harmonic state estimation in power system

Info

Publication number: AU2013201595B2
Application number: AU2013201595A
Authority: AU
Inventors: Wei Cai; Chun Deng; Huimin He; Xiaojiang Liu; Juan SUO; Jianwei Wang; Honggeng Yang
Original assignee: State Grid Corp of China SGCC; North China Electric Power Research Institute Co Ltd
Current assignee: State Grid Corp of China SGCC; North China Electric Power Research Institute Co Ltd
Priority date: 2012-03-20
Filing date: 2013-03-12
Publication date: 2014-08-14
Anticipated expiration: 2033-03-12
Also published as: CN103323688B; AU2013201595A1; CN103323688A

Abstract

Embodiments of the present invention provide a method and an apparatus for harmonic state estimation in a power system. The method 5 comprises: collecting network topology structure information corresponding to a power system; collecting measurement point position information in the power system; collecting measurement point harmonic information in the power system; performing network topology observability analysis according to the network topology structure information, the measurement point to position information and the measurement point harmonic information so as to determine an observable range in the current power system; determining harmonic state parameters corresponding to the current power system according to the observable range in the power system. The present invention realizes optimal configuration of measurement points upon demands of 15 different users and solves the problems in the prior art of complicated algorithm, great amount of computation and the neglect that the measurement device has an ability to measure the voltage and current at the same time by introducing a suspicious harmonic injection node into the observability analysis logical judgment method and using a recursive algorithm to realize 20 the whole-network analysis. S101 collecting network topology structure information corresponding to a power system collecting measurement point position information in the power S102~ system collecting measurement point harmonic information in the power S103 -- system performing network topology observability analyis according to the network topology structure information, the measurement point S104 position information and the measurement point harmonic information so as to determine an observable range in the current ower s stem S105 determining harmonic state parameters corresponding to the current power system according to the observable range in the power system

Description

METHOD AND APPARATUS FOR HARMONIC STATE ESTIMATION IN POWER SYSTEM This application claims priority from Chinese Application No. 5 201210073739.6 filed on 20 March 2012, the contents of which are to be taken as incorporated herein by this reference. FIELD OF THE INVENTION The present invention relates to the field of power system planning, 1o especially to an optimal configuration to a power system, and more particularly to a method and an apparatus for harmonic state estimation in a power system. BACKGROUND OF THE INVENTION 1s In recent years, with the rapid development of modem industries and wide applications of power electronic technologies, harmonics generated by a large number of power electronic apparatuses, nonlinear fluctuating loads and various variable velocity variable frequency drives pollute the power system more and more seriously, and threaten safe and economical 20 operations of various electrical apparatuses in a power grid. Therefore, the analysis and research on the harmonic of the power system are of great importance in practice. The key of the Harmonic State Estimation (HSE) technology lies in the analysis on network observability and the optimal configuration for a 25 measurement device. Since a quality of HSE is a function of a measurement number and a measurement device installing position, the configuration of a large number of harmonic measuring instruments may of course increase a redundancy of measurement data, and improve precision of estimated results, but meanwhile greatly increases investment cost; on the contrary, if the 1 number of measuring instruments is too small, the observable range for the harmonic state estimation is too limited, which thus cannot realize effective observation. In addition, the observability analysis is a fundamental basis for the configuration of a harmonic measurement device, and is dependent on the 5 number, position and type of measurement values, and a network topology, so the appropriate selection of the position where the harmonic measuring device is installed is of great significance. As far back as 1989, Heydt el al. firstly proposed that a minimum condition number method for coefficient matrix is used to configure a 1o harmonic measurement point, but it is obviously difficult for the minimum condition number constraint method to obtain an optimal measurement point. There are other scholars who proposed that a sequence analysis based on minimum variance criteria method is used to realize the optimal configuration for measurement points, but this method requires massive is calculation, and tends to be influenced by system parameters. Additionally, some other scholars proposed that a genetic algorithm which is used to perform the optimal configuration for measurement points. An optimal solution can be obtained by such an algorithm, but its number of iterations is relatively large and the speed of convergence is low. 20 The adoption of the above HSE measurement point configuring method to perform the optimal configuration of the power system and the harmonic state estimation generally has the following disadvantages that: (1) the algorithm is complicated and the amount of computation is great; (2) it is necessary to solve the rank of a measurement matrix, the computation 25 quantity of the process for obtaining the rank is great and increases with an index of a matrix dimension, and the practical effect in a large-scale network is poor; (3) all of the algorithms ignore that the measurement device has a capability of measuring a voltage and a current at the same time.

The discussion of documents, acts, materials, devices, articles and the like is included in this specification solely for the purpose of providing a context for the present invention. It is not suggested or represented that any or all of these matters formed part of the prior art base or were common 5 general knowledge in the field relevant to the present invention as it existed before the priority date of each claim of this application. Where the terms "comprise", "comprises", "comprised" or "comprising" are used in this specification (including the claims) they are to be interpreted as specifying the presence of the stated features, integers, steps or 10 components, but not precluding the presence of one or more other features, integers, steps or components, or group thereof. SUMMARY OF THE INVENTION The embodiment of the present invention provides a method and a 15 system for harmonic state estimation in a power system, which realizes the optimal configuration of measurement points upon demands of different users and solves the problems in the prior art of complicated algorithm, great amount of computation and the neglect that the measurement device has a capability of measuring the voltage and current at the same time by 20 introducing a suspicious harmonic injection node into the observability analysis logical judgment method and using a recursive algorithm to realize the whole network analysis. In one aspect of the present invention, there is provided a method for harmonic state estimation in a power system, comprising: collecting a 25 network topology structure information corresponding to the power system, the network topology structure information comprising a network adjacent matrix and a harmonic node admittance matrix; collecting a measurement point position information in the power system; collecting a measurement point harmonic information in the power system, the measurement point harmonic information including a harmonic voltage measurement value and a harmonic current measurement value; performing network topology observability analysis according to the network topology structure information, the measurement point position information and the 5 measurement point harmonic information so as to determine an observable range in the current power system; and determining harmonic state parameters corresponding to the current power system according to the observable range in the power system. In another aspect of the present invention, there is provided an 10 apparatus for harmonic state estimation in a power system, comprising: a network topology structure collecting device for collecting network topology structure information corresponding to a power system, the network topology structure information including a network adjacent matrix and a harmonic node admittance matrix; a measurement point position collecting device for 15 collecting measurement point position information in the power system; a measurement point harmonic collecting device for collecting measurement point harmonic information in the power system, the measurement point harmonic information including a harmonic voltage measurement value and a harmonic current measurement value; an observability analysis device for 20 performing network topology observability analysis according to the network topology structure information, the measurement point position information and the measurement point harmonic information so as to determine an observable range in the current power system; and a harmonic parameter determining device for determining harmonic state parameters corresponding 25 to the current power system according to the observable range in the power system. The advantageous effects of the present invention are in that: due to the adoption of logical operations, the whole amount of computation is small, the operation for obtaining the rank of the measurement matrix required by the

A

traditional observability analysis method is not necessary, which is more evident during the optimal configuration for the multi-node network measurement point; the suspicious harmonic injection node is introduced into the observability logical analysis, which greatly increases the number of the 5 network state observable nodes, the increasing in the suspicious harmonic injection nodes corresponds to addition of several equation sets in a measurement equation, such that the number of solvable node voltages greatly increases; the present invention is suitable for the practical situation where the current grid measurement device has the harmonic voltage and 10 current measurements at the same time, and can be used for the harmonic state estimation of separated networks with small measurement points. BRIEF DESCRIPTION OF THE DRAWINGS 4a In order to more clearly describe the technical solutions of the embodiments of the present invention or the prior art, the drawings, which are needed to be used in the descriptions of the embodiments or the prior art, are briefly introduced as follows. Obviously, the drawings described s hereinafter just illustrate some embodiments of the present invention, and a person skilled in the art can obtain other drawings based on these drawings without paying a creative effort. Fig.1 is a flowchart of a method for harmonic state estimation in a power system provided by an embodiment of the present invention; 10 Fig.2 is a specific flowchart of the step S104 shown in Fig.1; Fig.3 is a flowchart of a second embodiment of a method for harmonic state estimation in a power system provided by an embodiment of the present invention; Fig.4 is a structural block diagram of an apparatus for harmonic state 15 estimation in a power system provided by an embodiment of the present invention; Fig.5 is a structural block diagram of an observability analysis device 400 shown in Fig.4; Fig.6 is structural block diagram of the second embodiment of the 20 apparatus for harmonic state estimation in a power system provided by an embodiment of the present invention; Fig.7 is a structural schematic diagram of a simple network with 6 nodes and 6 branches in an embodiment of the present invention; Fig.8 is a structural schematic diagram of an IEEE-14-nodes network in 25 an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS The technical solutions of embodiments of the present invention will be clearly and completely described as follows with reference to the drawings of embodiments of the present invention. Apparently, the described embodiments are just a part of embodiments of the present invention rather than all the embodiments. Based on the embodiments of the present invention, any other embodiment obtained by a person skilled in the art 5 without paying a creative effort shall fall within the protection scope of the present invention. The observability analysis method, referring to judge an ability to determine a bus state by using existing measurement data under the precondition of giving the network topology structure and the measurement 1o configuration, is below introduced firstly. A mathematical model for harmonic state estimation is expressed as Z=HX+e wherein X is an undetermined nx 1 dimensional state vector, Z is an mx 1 dimensional measurement vector, H is an mxn dimensional measurement 15 matrix for correlating the measurement value with a state variable, which is related to a topology structure of the power system, the fundamental admittance matrix, and the measurement configuration solutions of the system, and E is an mx 1 dimensional measurement error vector caused by random noise, converter errors and communication problems. 20 The measurement matrix represents the relationship between the measurement vector and the estimated state variable. If what is estimated is a node harmonic voltage, the measurement equation has the following three situations. a. If the measurement item is a harmonic node injection current IN, the 25 measurement equation expressed by the harmonic node voltage UN and the harmonic node-node admittance matrix YNN is that: IN(h) = YNN (h)UN(h) b. If the measurement item is a harmonic node voltage, there is: UN(h)= IUN(h) wherein I is a unit matrix with diagonal elements being 1. c. If the measurement item is a harmonic branch current measurement IL, the measurement equation expressed by the harmonic node voltage UN and the harmonic branch-node admittance matrix YLN is that 5 ILN(h) = 1',(h)UN (h) The measurement value of the harmonic state estimation is wherein: a. the state of a self-measurement bus is completely observable, that is Vr, =UV, b. when the local side voltage is observable or measurable, the branch 10 measurement makes the state of an opposite side bus interconnected with the present measurement branch observable, that is as such, the branch current measurement is used for correlating the current voltage observable nodes and the unobservable nodes; 15 c. when the node voltages at two ends of the branch are observable, the branch current is observable, that is I, = -Y( )+VY wherein Ygo is half of a line-to-ground admittance, and Yy is a corresponding element in the node-node admittance matrix. 20 Since there are many nodes being non-harmonic current injection nodes in the system, such as non-industrial load bus, and an equivalent node of a three-winding transformer (generated during modeling) whose bus injection current can be deemed to be 0, such a condition provides a basis for the logical analysis on observability in a whole power system network. 25 Fig.1 is a structural block diagram of a method for harmonic state estimation in a power system. From Fig.1, it can be known that the method comprises: S101: collecting network topology structure information corresponding to a power system, the network topology structure information including a '7 network adjacent matrix and a harmonic node admittance matrix. In the present invention, for convenience of explanation and analysis, the related variables of the power system are selected as follows. (1) In the power system, the connection relationship between buses can 5 be expressed by the network adjacent matrix. A network with n nodes can be expressed by an n xn order square matrix A, which indicates the connection relationship between buses, wherein Ai indicates the connection relationship between the node i with other nodes in the network. The number of non-zero elements in A, is the number of nodes connected with the node i. The element 10 in the i-th row and j-th column is aij. If aij is 1, the node i is connected directly with the node j. If aij is 0, the node i is not connected directly with the nodej. The matrix A can be written as A=[A A 2 ... An ]T, wherein a row vector Ai indicates the connection relationship between the i-th node and other nodes. Fig.7 is a structural schematic diagram of a simple network with 15 6 nodes and 6 branches of an embodiment of the present invention. "A" in Fig.7 indicates the installation positions of the measurement device. The network adjacent matrix as shown in Fig.7 is as follows: Al 1 0 0 0 0

A

2 1 1 1 0 1 0 A= 3 0 1 1 1 1 0

A

4 0 0 1 1 0 0

A

5 0 1 1 0 1 1

_A

6 _0 0 0 0 1 _ The network adjacent matrix is used for the observability analysis of the 20 power system. (2) The harmonic node admittance matrix Y is an n xn order sparse matrix. If the node i is not connected with the nodej, Yij=O; otherwise, Yij is the harmonic admittance of the ij branch. The harmonic node admittance is used for the calculation of the harmonic state estimation. 25 S102: collecting measurement point position information in the power system. In the present invention, since the measurement point can

R

simultaneously provide the harmonic voltage and the harmonic current, for the measurement point at the i side of the ij branch, the related variables are selected as follows. (1) An n xI vector U is used to represent the measurement nodes and the 5 observable nodes. When the node i is observable or is the measurement node, the corresponding matrix element ui is 1, otherwise the corresponding matrix element ui is 0. If all the elements in the matrix U are 1, it is indicated that the whole network state is observable. Fig.7 can be expressed as V =[k us us u 4 us u1]=[1 1 0 0 0 O]f 10 (2) An n xn square matrix I is used to represent the branch current measurement. If a monitor is installed at the i-j branch close to the node i side, Ii, l. Fig.7 can be expressed as 1,~ ~0 1 0 0 0 0 12 0 1 0 0 0 13 0 0 0 0 0 0 1, 0 0 0 0 0 0 15 0 0 0 0 0 0 16 0 0 0 0 0 0 (3) An n xI matrix K is used to indicate whether or not the node is a 15 suspicious harmonic current injection node. If the node i is a suspicious harmonic current injection node, Ki is 0, otherwise Ki is 1. Fig.7 can be expressed as

K

T

=[K K K K4 K =[I 1 0 1 0f S103: collecting measurement point harmonic information in the power 20 system, the measurement point harmonic information including a harmonic voltage measurement value and a harmonic current measurement value. An n x1 order vector V is used to represent the harmonic voltage measurement value, wherein vi indicates the measurement voltage of the node i. 25 A kx3 order vector M is used to represent the harmonic current a measurement value, wherein mij and mr, 2 respectively represent number of the first node and number of the last node of the branches where the measurement points are located, and min 3 represents the measurement current value. 5 S104: performing network topology observability analysis according to the network topology structure information, the measurement point position information and the measurement point harmonic information so as to determine the observable range in the current power system. Fig.2 is a specific flowchart of the step S104. From Fig.2, it can be 10 known that the step specifically comprises the following steps. S201: traversing the nodes in the power system according to the harmonic node admittance matrix, the measurement point position information and the measurement point harmonic information corresponding to the power system. 15 For a specific power system, the traversed nodes herein are initial observable nodes. For example, if a certain node is provided with a monitor, the node is directly observable. The observable nodes obtained by recursion in the subsequent steps comprise the directly observable nodes provided with monitors, and also comprises indirectly observable nodes obtained by these 20 observable nodes. Therefore, the number of observable nodes obtained by recursion finally is greater than the original number of observable nodes. S202: traversing opposite nodes in all branches connected with the node according to the harmonic node admittance matrix, the measurement point position information and the measurement point harmonic information 25 corresponding to the power system. The step of performing the analysis of observability of the network topology on the opposite nodes specifically comprises: S203: judging whether or not the current measurement exists on the branch connected with the opposite nodes, if so, the step S205 is executed; IAi otherwise, the step S204 is executed; S204: the opposite nodes being observable. S205: judging whether or not there is only one unobservable opposite node among the opposite nodes of all branches connected with the node, if so, 5 the step S206 is executed; otherwise, the step S202 is executed. If a node is provided with a monitor, the node can be directly observable initially, and other nodes are unobservable. In the process of traversing recursion, the unobservable nodes become observable gradually due to satisfying some conditions. When traversing to the node nl, its opposite 1o nodes may have the situation where only one node is unobservable. S206: judging whether or not the node is the non-harmonic current injection node, if the node is the non-harmonic current injection node, the step S204 is executed; otherwise, the step S202 is executed; S207: generating the observable range of the power system according to is the observability of all the nodes and the opposite nodes. An embodiment of the step S104 is shown as follows. (1) providing U1 = U'I+U', ,the non-zero element ui is processed to be logic "1" during the operation, which indicates that the corresponding node voltage i is observable. Step (2) is performed for each of the newly added 20 nodes. (2) for the newly added observable nodes i, an intersection of the corresponding elements in U and Ai is obtained, and then Ii is updated, expressed in a mathematical relationship as I,=UnA" . This step is used for updating the branch current. 25 (3) providing C, = A, I, if the number of non-zero elements in Ci is 1, the column number where the non-zero element is located is m. If Km is also 1 at the same time, the node m voltage is observable. That is, if the node i is the non-harmonic current injection node and the currents in the branches connected with the node i except for the i-m branch are observable, the point 11 m voltage is observable, that is Urn = (4) the steps (2) and (3) constitute a recursion algorithm. When a new observable node is added, new observable nodes are searched around by taking the newly added node as a starting point. Such a process is repeated 5 until the topology analysis stops when the node is the suspicious harmonic current injection node or the number of currents of known branches is insufficient. At this time, the network is not completely observable. (5) if all the elements in U are 1, all of the node voltages are observable. S 105: determining harmonic state parameters corresponding to the 10 current power system according to the observable range in the power system. Fig.3 is a flowchart of a second embodiment of a method for harmonic state estimation in a power system provided by the embodiment of the present invention. From Fig.3, it can be known that the step S105 specifically comprises: 15 S305: re-numbering according to the observable range in the power system, so as to form the observable network comprising only the observable nodes. For the practical situation where the measurement devices in the current grid are deployed dispersedly, the observable analyzing method in the above S104 can be used to solve the network state with the measurement 20 points being separated or the network being not completely observable. Numbers of the observable nodes are column numbers of all non-zero elements in U. S306: establishing a network node equation according to the observable network. The original nodes and numbers may be inconsecutive, which is not 25 beneficial to the subsequent processing. Therefore, the original nodes are re-numbered by any numbering way as long as consecutive node numbers are formed, and the new and old node numbers can be converted mutually. Meanwhile, all the data (including V M, K) related to the node numbers are replaced with new node numbers to re-constitute a n-nodes system. The 1-1 reconstructed network may have a plurality of isolated electrical islands, and correspondingly, the admittance matrix parameters may also change. For a certain order of harmonic, there is: Z=HX+e Z = I,, H =Y,, 5~ Y wherein X is an undetermined nx 1 dimensional voltage vector, Z is an mx1 dimensional measurement vector, H is an mxn dimensional measurement matrix for correlating the measurement value with the voltage vector, which is related to the topology structure of the system, the harmonic 10 admittance matrix, and the measurement configuration solution of the system, and c is an mx 1 dimensional measurement error vector caused by random noise, converter errors and communication problems, Vm is a voltage measurement, Im is a current measurement, IL is an harmonic current injection measurement, and IL= 0 for a determined non-harmonic current 15 injection node. S307: determining the harmonic state parameters according to the network node equation, the harmonic state parameters including the current value and the voltage value of the node. In the present embodiment, the least square method is used to solve an 20 optimal approximate solution. That is:

H

T

Z = H T HX wherein HTis a transposed matrix of H. The equation set is to solve the undetermined voltage vector X. From the node equation: I =YX 25 each node current injection can be solved, thereby determining the position of a harmonic source, wherein Y is a node admittance matrix, and I is a node current injection vector. From Fig.3, it can be known that besides the above steps, the method for harmonic state estimation in a power system provided by the embodiment of the present invention further comprises: 5 S308: adding measurement point position information on different branches of the power system upon different demands. The measurement device in the current practical grid has the function of voltage and current measurements at the same time. The traditional optimal configuration method for measurement points only takes into consideration 1o that the measurement device only has the voltage measurement or current measurement, thereby being not suitable in the practical grid. For the practical situation where the number of the measurement devices in the grid and the investment cost are limited, in the method provided in the present invention, the configuration of the newly added measurement points can be 15 performed on the basis of the topology observability analysis method. The newly added measurement points will increase the number, and the increased number is related to the position of the measurement device. Meanwhile, the main load type, the voltage level and the size of capacity of each bus are different. 20 In the present embodiment, a weighted multi-objective mathematical model is constructed as follows: maxM=max +S, +A 3 7) In the equation, M is target values of newly added observable nodes, n is the number of newly added observable nodes, V is a voltage level factor, S is 25 a load capacity (pre-unit value), T is a load type value factor, and A is a weighting coefficient of a corresponding index, which can be appropriately adjusted according to different requirements of different power grid enterprises. 14 The addition of the measurement devices on different branches differently influences the observability of the system. Firstly, a measurement device is firstly added on a certain branch on which it is possible to add the measurement device, and then the network topology analysis is performed to s analyze its observability, to calculate an objective function value of the weighted multi-objective mathematical model. Different branches are selected to obtain different objective function values, and the branch with a maximum value of the weighted multi-objective mathematical model is a branch optimal for installing the newly added measurement point. It is 1o possible to continuously add measurement points on the basis of the newly added n measurement points, and the added n+1 measurement points are also optimal. The importance of the newly added measurement points is ordered upon different demands, and important users concerned by power grid enterprises can be brought into the observable range or the observability of 15 whole grid with the optimal configuration can be realized. For a system with N buses, P measurement devices, M possible installation points and Q devices to be installed, the whole-grid observability can be realized just by at most Q(2M+1-Q)12 times of network topology analysis and a minute amount of operation of the target value. 20 Fig.4 is a structural block diagram of an apparatus for harmonic state estimation in a power system provided by an embodiment of the present invention. From Fig.4, it can be seen that the apparatus comprises a network topology structure collecting device 100 for collecting network topology structure information corresponding to a power system, the network topology 25 structure information including a network adjacent matrix and a harmonic node admittance matrix. In the present invention, for convenience of explanation and analysis, the related variables of the power system are selected as follows. (1) In the power system, the connection relationship between buses can

I,,

be expressed by the network adjacent matrix. A network with n nodes can be expressed by an n xn order square matrix A, which indicates the connection relationship between buses, wherein A, indicates the connection relationship between the node i with other nodes in the network. The number of non-zero 5 elements in A, is the number of nodes connected with the node i. The element in the i-th row and j-th column is aij. If aij is 1, the node i is connected directly with the node j. If aij is 0, the node i is not connected directly with the nodej. The matrix A can be written as A=[A I A 2 ... An ]T, wherein a row vector Ai indicates the connection relationship between the i-th node and 10 other nodes. Fig.7 is a structural schematic diagram of a simple network with 6 nodes and 6 branches of an embodiment of the present invention. "A" in Fig.7 indicates the installation positions of the measurement device. The network adjacent matrix as shown in Fig.7 is as follows: 4 1 0 0 0 0

A

2 1 1 1 0 1 0 A= 3 01 1 1 1 0

A

4 0 0 1 1 0 0

A

5 0 1 1 0 1 1

A

6 0 0 0 0 1 _ 1s The network adjacent matrix is used for the observability analysis of the power system. (2) The harmonic node admittance matrix Y is an n xn order sparse matrix. If the node i is not connected with the nodej, Yij=O; otherwise, Yij is the harmonic admittance of the ij branch. The harmonic node admittance 20 matrix is used for the calculation of the harmonic state estimation. The apparatus further comprises a measurement point position collecting device 200 for collecting measurement point position information in the power system. In the present invention, since the measurement point can simultaneously provide the harmonic voltage and the harmonic current, 25 for the measurement point at the i side of the ij branch, the related variables are selected as follows. 1t (1) An n xI vector U is used to represent the measurement nodes and the observable nodes. When the node i is observable or is the measurement node, the corresponding matrix element ui is 1, otherwise the corresponding matrix element ui is 0. If all the elements in the matrix U are 1, the whole network 5 state is observable. Fig.7 can be expressed as = u2 us u4 U, uf KI, =[ 1 0 0 0 (2) An n xn square matrix I is used to represent the branch current measurement. If a monitor is installed at the i-j branch close to the node i side, Iij=l. Fig.7 can be expressed as I,~ ~0 1 0 0 0 0 I2 0 1 0 0 0 13 0 0 0 0 0 0 14 0 0 0 0 0 0 15 0 0 0 0 0 0 10 - -0 0 0 0 0 0 (3) An nx1 matrix K is used to indicate whether or not the node is a suspicious harmonic current injection node. If the node i is a suspicious harmonic current injection node, Ki is 0, otherwise Ki is 1. Fig.7 can be expressed as 1s K

T

=[K K2 K K K K ] =[O I 1 0 1 O] The apparatus further comprises a measurement point harmonic collecting device 300 for collecting measurement point harmonic information in the power system, the measurement point harmonic information including a harmonic voltage measurement value and a harmonic current measurement 20 value. An n x] order vector V is used to represent the harmonic voltage measurement value, wherein vi indicates the measurement voltage of the node i. A kx3 order vector M is used to represent the harmonic current 25 measurement value, wherein mij and mi, 2 respectively represent number of 17 the first node and number of the last node of the branches where the measurement points are located, and mO represents the measurement current value. The apparatus further comprises an observability analyzing device 400 5 for performing network topology observability analysis according to the network topology structure information, the measurement point position information and the measurement point harmonic information so as to determine the observable range in the current power system. Fig.5 is a structural block diagram of the observability analyzing device 10 400. From Fig.5, it can be known that the device comprises: A first traversing device 401, for traversing the nodes in the power system according to the harmonic node admittance matrix, the measurement point position information and the measurement point harmonic information corresponding to the power system; 15 For a specific power system, the traversed nodes herein are initial observable nodes. For example, if a certain node is provided with a monitor, the node is directly observable. The observable nodes obtained by recursion in the subsequent steps include the directly observable node provided with the monitor, and also includes indirectly observable nodes obtained by these 20 observable nodes. Therefore, the number of observable nodes obtained by recursion finally is greater than the original number of observable nodes; A second traversing device 402 for traversing opposite nodes in all branches connected with the node according to the harmonic node admittance matrix, the measurement point position information and the 25 measurement point harmonic information corresponding to the power system; An analyzing device 403 for performing the analysis of observability of the network topology on the opposite nodes, the analyzing device 403 comprises: 18 A first judging device 4301 for judging whether or not a current measurement exists on a branch connected with an opposite node; A first observability outputting device 4032 for outputting the opposite node as being observable if the first judging device judges that the current 5 measurement exists on the branch connected with the opposite node; A second judging device 4033 for judging whether or not there is only one unobservable opposite node among the opposite nodes of all branches connected with the node when there is no current measurement on the branch connected with the opposite nodes; 10 If a node is provided with a monitor, the node can be directly observable initially, and other nodes are unobservable. In the process of traversing recursion, the unobservable nodes become observable gradually due to satisfying some conditions. When traversing to the node n 1, its opposite nodes may have the situation where only one node is unobservable; is A second observability outputting device 4034 for outputting the observable opposite nodes on the current branch when the second judging device judges that there is only one unobservable opposite node among the opposite nodes of all branches connected with the node and the node is the non-harmonic current injection node; 20 An observable range outputting device 4035 for generating the observable range of the power system according to the observability of all the nodes and the opposite nodes; A specific embodiment of the observability analysis device 400 is shown as follows: 25 (1) providing U' = U'I+U , the non-zero element ui is processed to be logic "1" during the operation, which indicates that the corresponding node voltage i is observable. Step (2) is performed for each of the newly added nodes; (2) for the newly added observable nodes i, an intersection of the 19 corresponding elements in U and Ai is obtained, and then Ii is updated, expressed in a mathematical relationship as I = U , A, . This step is used for updating the branch current; (3) providing C, = A, - I, if the number of non-zero elements in Ci is 1, s the column number where the non-zero element is located is m. If Km is also 1 at the same time, the node m voltage is observable. That is, if the node i is the non-harmonic current injection node and the currents in the branches connected with the node i except for the i-m branch are observable, the point m voltage is observable, that is U, = I. 10 (4) the steps (2) and (3) constitute a recursion algorithm. When a new observable node is added, new observable nodes are searched around by taking the newly added node as a starting point. Such a process is repeated until the topology analysis stops when the node is the suspicious harmonic current injection node or the amount of currents of known branches is 15 insufficient. At this time, the network is not completely observable; (5) if all the elements in U are 1, all of the node voltages are observable; A harmonic parameter determining device 500 for determining harmonic state parameters corresponding to the current power system according to the observable range in the power system; Fig.6 is a structural 20 block diagram of a second embodiment of the apparatus for harmonic state estimation in a power system provided by the embodiment of the present invention; From Fig.6, it can be known that the harmonic parameter determining device specifically comprises: A numbering device 501 for re-numbering according to the observable 25 range in the power system, so as to form the observable network only comprising the observable nodes; For the practical situation where the measurement devices in the current grid are deployed dispersedly, the above observability analyzing method can be used to solve the network state with the measurement points being separated or the network being not completely observable. Numbers of the observable nodes are the column numbers of all non-zero elements in U; An equation establishing device 502 for establishing a network node equation according to the observable network; The original nodes and s numbers may be inconsecutive, which is not beneficial to the subsequent processing; Therefore, the original nodes are re-numbered by any numbering way as long as consecutive node numbers are formed, and the new and old node numbers can be converted mutually; Meanwhile, all the data (including V M, K) related to the node numbers are replaced with new node numbers to 1o re-constitute a n-nodes system; The reconstructed network may have a plurality of isolated electrical islands, and correspondingly, the admittance matrix parameters may also change; For a certain order of harmonic, there is: Z = HX + e Z = I,, H =Y, 15 wherein X is an undetermined nxl dimensional voltage vector, Z is an mx1 dimensional measurement vector, H is an mxn dimensional measurement matrix for correlating the measurement value with the voltage vector, which is related to the topology structure of the system, the harmonic admittance matrix, and the measurement configuration solutions of the 20 system, and e is an mx 1 dimensional measurement error vector caused by random noise, converter errors and communication problems, Vm is a voltage measurement, Im is a current measurement, IL is an harmonic current injection measurement, and IL= 0 for a determined non-harmonic current injection node; 25 A harmonic state parameter determining device 503 for determining the harmonic state parameters according to the network node equation, the harmonic state parameters including the current value and the voltage value

II

of the node. In the present embodiment, the least square method is used to solve an optimal approximate solution. That is:

H

T

Z=H

T

HX s wherein HT is a transposed matrix of H. The equation set is to solve the undetermined voltage vector X. From the node equation: I =YX it is possible to solve each node current injection, thereby determining 10 the position of a harmonic source, wherein Y is a node admittance matrix, and I is a node current injection vector. From Fig.6, it can be known that besides the above devices, the apparatus for harmonic state estimation in a power system provided by the embodiment of the present invention further comprises: 15 a measurement point adding device 600 for adding measurement point position information on different branches of the power system upon different demands. The measurement device in the current practical grid has the function of voltage and current measurements at the same time. The traditional optimal 20 configuration method for measurement points only takes into consideration that the measurement device only has the voltage measurement or current measurement, thereby not being suitable in the practical grid. For the practical situation where the number of the measurement devices in the grid and the investment cost are limited, in the method provided in the present 25 invention, the configuration of the newly added measurement point can be performed on the basis of the topology observability analysis method so as to realize the optimal configuration of the network measurement points. The newly added measurement point will increase the number of the network observable bus, the increases number is related to the position of the measurement device. Meanwhile, the main load type, the voltage level and the size of capacity of each bus are different. In the present embodiment, a weighted multi-objective mathematical model is constructed as follows: max M = max (V, +,AS, +A ) 5 In the equation, M is target values of newly added observable nodes, n is the number of newly added observable nodes, Vi is a voltage level factor, S is a load capacity (pre-unit value), T, is a load type value factor, and 2 is a weighting coefficient of a corresponding index, which can be appropriately 1o adjusted according to different requirements of different power grid enterprises. The addition of the measurement device on different branches differently influences the observability of the system. Firstly, a measurement device is firstly added on a certain branch on which it is possible to add the 15 measurement device, and then the network topology observability analysis is performed, to calculate an objective function value of the weighted multi-objective mathematical model. Different branches are selected to obtain different objective function values, and the branch with a maximum value of the weighted multi-objective mathematical model is a branch 20 optimal for installing the newly added measurement point. It is possible to continuously add measurement points on the basis of the newly added n measurement points, and the added n+l measurement points are also optimal. The importance of the newly added measurement points is ordered upon different demands, and important users concerned by power grid enterprises 25 can be brought into the observable range or the observability of whole grid with the optimal configuration can be realized. For a system with N buses, P measurement devices, M possible installation points and Q devices to be installed, the whole-grid observability can be realized only by at most Q(2M+1-Q)12 times of network topology analysis and a minute amount of operation of the target value. The method and apparatus for harmonic state estimation in a power system provided by the embodiment of the present invention are introduced 5 below in details in connection with the specific embodiments. The description is made by taking the IEEE-14-nodes network shown in Fig.8 as an example. By taking the IEEE-14-nodes as shown in Fig.8 as an example, it is assumed that all the nodes except for the nodes 4, 5, 6 and 14 are 1o non-harmonic current injection nodes, and the observability analysis with/without consideration of the non-harmonic current injection node is shown in Table 1. From Table 1, it can be known that in the method and apparatus for harmonic state estimation in a power system provided by the embodiment of the present invention, due to the consideration of the 15 non-harmonic injection node, the number of observable nodes greatly increases. Table 1 observable nodes with observable nodes without consideration of the initial measurement consideration of the on-harmonic inj ectio non-harmonic injection node node 2-3 13-14 11-6 3-4 2 3 4 6 7 8 9 10 11 13 14 2346 1113 14 In Fig.8, the harmonic source is on the nodes 4, 5, 6 and 14, nodes 7 and 20 8 are non-harmonic current injection nodes, and the harmonic injection current with other equivalent load nodes can be obtained after the harmonic state estimation for the whole grid. Tables 2 and 3 are the optimal configuration results and its time for measurement point under the IEEE-14 nodes. As shown, the time required to 25 perform optimal configuration according to the method provided by the 24 present invention is greatly less than that in the traditional method of the prior art, and the time of optimal configuration is substantially unrelated to the number of the added devices. In order to verify the influence of the number of nodes on the calculation time, analysis is performed by taking a 5 practical power grid at some place as an example. The practical power grid comprises in total 12 220kV transformer substations, 38 110kV transformer substations, 92 bus sections, 34 three-winding transformers and 126 nodes. During modeling, a three-winding transformer will generate an equivalent node. Under the circumstance of normal operation, a transformer only 1o generates a small amount of harmonics, which can be to be a non-harmonic current injection node. The buses without any equivalent load will be deemed non-harmonic current injection nodes, with a total number of 34. The optimal configuration time is 0.016s, which indicates that the number of nodes has very small influence on the optimal calculation time. 15 Table 2 initial the time/s measurementnumber of selected branch points added devices 1 1-5 0.016 2 1-53-4 0.016 non 3 1-53-4 11-6 0.016 1-5 3-4 11-6 9-14 0.016 8 8-7 12-13 2-1 10-7 1 11-6 0.016 5-4 2 11-6 1-2 0.016 14-13 3 11-6 1-28-7 0.016 6 11-6 1-2 8-7 9-10 3-2 0.016 12-6 2-3 1 1-5 0.016 13-14 2 1-5 8-7 0.016 11-6 3 1-5 8-79-10 0.016 3-4 4 1-5 8-7 9-10 12-6 0.016 Table 3 initial the time/s measurement number of selected branch points added devices 1 1-5 0.05 2 1-5 3-4 0.45 non 3 1-53-4 11-6 0.87 8 1-5 3-4 11-6 9-14 3.54 8-7 12-13 2-1 10-7 1 11-6 0.06 5-4 2 11-6 1-2 0.75 14-13 3 11-6 1-2 8-7 0.93 11-6 1-2 8-7 9-10 3-2 2.88 6 12-6 2-3 1 1-5 0.08 13-14 2 1-5 8-7 0.82 11-6 3 1-5 8-79-10 1.33 3-4 4 1-5 8-7 9-10 12-6 15.625 Analysis is performed by taking a practical power grid at some place as an example. The practical power grid comprises in total 12 220kV transformer substations, 38 110kV transformer substations, 92 bus sections, s 34 three-winding transformers and 126 nodes. During modeling, a three-winding transformer will generate an equivalent node. Under the circumstance of normal operation, a transformer only generates a small amount of harmonics, which can be deemed to be a non-harmonic current injection node. The buses without any equivalent load will be deemed to non-harmonic current injection nodes, with a total number of 34. The addition of the non-harmonic current injection nodes increases the solving condition and enlarges the network observable range. Table 4 is a configuration result of the power grid system at some place. The above result indicates that the present invention can be surely used for practical use. 15 Table 4 the number selected numbers of added observable of added branches nodes devices 1 28-32 28,32 2 107-123 107,123,122,128 3 6-18 5,15,18 4 30-35 30,35,40 5 72-73 71,72,73 6 82-79 82,79,67,78 7 61-63 61,63,49,115,130,70,68 8 60-58 60,58,83,57 9 12-56 12,56,8 10 41-37 41,37,36 To sum up, the embodiments of the method provide a method and a system for harmonic state estimation in a power system. By introducing the idea of recursion into the observability logical judgment, the whole-grid 5 traversing is realized. Meanwhile, by adopting the condition that a part of the nodes in the network are non-harmonic current injection nodes, the observable range of the network is greatly enlarged. The present invention has the following advantages: (1) due to the adoption of logical operation, the whole amount of 1o computation is small, the operation for solving the rank of the measurement matrix required by the traditional observability analysis method is not necessary, which is more evident during the optimal configuration for the multi-node network measurement point; (2) the suspicious harmonic injection node is introduced into the 15 observability logical analysis, which greatly increases the number of the network state observable nodes, the increase of the suspicious harmonic injection nodes corresponding to adding several equation sets in a measurement equation, such that the number of solvable node voltages greatly increases; 20 (3) the preference observation of important bus or user is realized upon demands under the circumstance of the whole optimal configuration, which can obtain a satisfied result and have strong flexibility; (4) the present invention is suitable for the practical situation where the current grid measurement device has the harmonic voltage and current 5 measurements at the same time, and can be used for the harmonic state estimation of network with a small number of separated measurement points. The principle and implementations of the present invention are described through specific embodiments of the present invention. The descriptions of the above embodiments are just for the understanding of the 1o methods and the key ideas of the present invention. Meanwhile, a person skilled in the art may modify the embodiments and the application scope based on the ideas of the present invention. In conclusion, the contents of the specification shall not be construed as limitations to the present invention.

Claims

1. A method for harmonic state estimation in a power system, comprising: 5 collecting a network topology structure information corresponding to the power system, the network topology structure information including a network adjacent matrix and a node admittance matrix; collecting a measurement point position information in the power system; 10 collecting a measurement point harmonic information in the power system, the measurement point harmonic information including a harmonic voltage measurement value and a harmonic current measurement value; performing network topology observability analysis according to the network topology structure information, the measurement point position 15 information and the measurement point harmonic information so as to determine an observable range in the current power system; and determining harmonic state parameters corresponding to the current power system according to the observable range in the power system. 20

2. The method according to claim 1, wherein the step of performing network topology observability analysis according to the network topology structure information, the measurement point position information and the measurement point harmonic information so as to determine an observable range in the current power system comprising: 25 traversing nodes in the power system according to the harmonic node admittance matrix, the measurement point position information and the measurement point harmonic information corresponding to the power system; traversing opposite nodes in all branches connected with the nodes according to the harmonic node admittance matrix, the measurement point position information and the measurement point harmonic information corresponding to the power system; and performing network topology observability analysis on the opposite 5 nodes.

3. The method according to claim 2, wherein the step of performing network topology observability analysis on the opposite nodes comprising: judging whether or not a current measurement exists on a branch 10 connected with an opposite node; if a current measurement exists on a branch connected with the opposite node, the opposite node is observable.

4. The method according to claim 3, wherein the step of performing 15 network topology observability analysis on the opposite nodes further comprising: judging whether or not there is only one unobservable opposite node among the opposite nodes of all branches connected with the node when there is no current measurement on the branches connected with the opposite 20 nodes; when it is judged that there is only one unobservable opposite node among the opposite nodes of all branches connected with the node and the node is a non-harmonic current injection node, the opposite node on the current branch is observable. 25

5. The method according to any one of claims 1 to 4, wherein the step of determining harmonic state parameters corresponding to the current power system according to the observable range in the power system comprising: re-numbering according to the observable range in the power system, so in as to form an observable network only comprising the observable nodes; establishing a network node equation according to the observable network; determining the harmonic state parameters according to the network 5 node equation, the harmonic state parameters including a current value and a voltage value of the node.

6. The method according to any one of claims 1 to 5, further comprising: 10 adding measurement point position information on different branches of the power system upon different demands.

7. The method according to claim 6, wherein the step of adding measurement point position information on different branches of the power 15 system upon different demands is executed by following equation: maxM = max (Y +4Si +2T) wherein M is target values of newly added observable nodes, n is the number of newly added observable nodes, Vi is a voltage level factor, Si is a load capacity, Ti is a load type value factor, and ) is a weighting coefficient of 20 a corresponding index.

8. An apparatus for harmonic state estimation in a power system, comprising: a network topology structure collecting device for collecting network 25 topology structure information corresponding to a power system, the network topology structure information including a network adjacent matrix and a harmonic node admittance matrix; a measurement point position collecting device for collecting measurement point position information in the power system; 31 a measurement point harmonic collecting device for collecting measurement point harmonic information in the power system, the measurement point harmonic information including a harmonic voltage measurement value and a harmonic current measurement value; 5 an observability analysis device for performing network topology observability analysis according to the network topology structure information, the measurement point position information and the measurement point harmonic information so as to determine an observable range in the current power system; and 10 a harmonic parameter determining device for determining harmonic state parameters corresponding to the current power system according to the observable range in the power system.

9. The apparatus according to claim 8, wherein the observability 15 analysis device comprising: a first traversing device for traversing nodes in the power system according to the harmonic node admittance matrix, the measurement point position information and the measurement point harmonic information corresponding to the power system; 20 a second traversing device for traversing opposite nodes in all branches connected with the nodes according to the harmonic node admittance matrix, the measurement point position information and the measurement point harmonic information corresponding to the power system; and an analysis device for performing network topology observability 25 analysis on the opposite nodes.

10. The apparatus according to claim 8 or claim 9, wherein the analysis device comprising: a first judging device for judging whether or not a current measurement I?) exists on a branch connected with a opposite node; a first observability outputting device for outputting the opposite node as being observable when the first judging device judges that the current measurement exists on the branch connected with the opposite node. 5

11. The apparatus according to claim 10, wherein the analyzing device further comprising: a second judging device for judging whether or not there is only one unobservable opposite node among the opposite nodes of all branches 10 connected with the node when there is no current measurement on the branches connected with the opposite nodes; a second observability outputting device for outputting, when the second judging device judges that there is only one unobservable opposite node among the opposite nodes of all branches connected with the node and 15 the node is a non-harmonic current injection node, the opposite nodes on the current branch as being observable; an observability range outputting device for generating the observable range of the power system according to the observabilities of all the nodes and the opposite nodes. 20

12. The apparatus according to any one of claims 8 to 11, wherein the harmonic parameter determining device comprising: a numbering device for re-numbering according to the observable range in the power system, so as to form a observable network only comprising the 25 observable nodes; an equation establishing device for establishing a network node equation according to the observable network; a harmonic state parameter determining device for determining harmonic state parameters according to the network node equation, the 33 harmonic state parameters including a current value and a voltage value of the node.

13. The apparatus according to any one of claims 8 to 12, wherein the 5 apparatus further comprising: a measurement point adding device for adding measurement point position information on different branches of the power system upon different demands. 10

14. The apparatus according to claim 13, wherein the measurement point adding device operates by following equation: maxM =max Y (i+S +S+S T) wherein M is target values of newly added observable nodes, n is the number of newly added observable nodes, V is a voltage level factor, Si is a 15 load capacity, Ti is a load type value factor, and ) is a weighting coefficient of a corresponding index.

15. A method for harmonic state estimation substantially as herein described with reference to any one of the embodiments illustrated in the 20 accompanying drawings.

16. An apparatus for harmonic state estimate substantially as herein described with reference to any one of the embodiments illustrated in the accompanying drawings.