CN112134288A - Harmonic pollution power distribution network reconstruction method based on forward/backward scanning harmonic power flow - Google Patents
Harmonic pollution power distribution network reconstruction method based on forward/backward scanning harmonic power flow Download PDFInfo
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Abstract
Inputting load network data based on a harmonic pollution power distribution network reconstruction method of forward/backward scanning harmonic power flow; constructing a connection matrix, calculating the sum of each column, and judging whether a load network has an available tail end bus or not; determining the current and the flow direction of an end branch according to the load of the tail end bus from the tail end bus, then neglecting the tail end bus and a branch connected with the tail end bus, updating a connection matrix, and adding the neglected branch current to the corresponding sending tail end bus; according to the method of forward/backward scanning, the flow direction of the branch is determined while the annular structure is detected; the harmonic voltage drop of each bus relative to the first bus corresponds to the harmonic voltage of the first bus, and the harmonic voltage of the load network is obtained through calculation; from the angle of the load, calculating the harmonic voltage of the bus according to the connection load impedance of the appointed harmonic times; carrying out simulation analysis to obtain voltage total harmonic distortion; and reconstructing the power distribution network. The method considers the radial topology of the network, and has higher calculation efficiency compared with the prior method.
Description
Technical Field
The invention relates to the technical field of rapid reconstruction of a harmonic pollution power distribution network, in particular to a harmonic pollution power distribution network reconstruction method based on forward/backward scanning harmonic power flow.
Background
The power system load flow calculation is a common calculation in a power system, and can be used for calculating the steady-state operation state of a more complex power system network under various conditions. Including node voltage and power distribution levels, etc. By using the technology, whether overload conditions of all elements in the power system occur or not, whether all the voltage meets requirements or not, whether power distribution is reasonable or not, power loss conditions and the like can be checked. The Newton-Raphson power flow technology has important significance for designing a power system to be newly built and analyzing the transient state and the steady state of the power system.
Conventional harmonic analysis methods employ newton-raphson power flow methods, admittance matrices, or impedance matrices to determine the level of harmonic penetration in the power distribution system. These methods do not take into account the special topological characteristics of the power distribution system, such as radial and weak current configurations. Therefore, they require more computation time in computing the emissions for each harmonic order.
Document [1] Chinese patent "a harmonic current analysis method of a distributed power generation system" (CN103956735A) proposes a method for calculating the harmonic voltage distribution condition of all nodes in a system, and the method does not need iterative computation, can improve the computation speed and efficiency of the harmonic current analysis method, and overcomes the convergence problem of the harmonic current iterative computation. The harmonic power flow analysis method of the always-distributed power generation system proposed by the technical scheme of the document [1] has the defects that the efficiency of the calculation speed is only improved, and the calculation accuracy is low.
The document [2] Chinese patent "a calculation method of high-frequency harmonic current of an active power distribution network" (CN106655195A) provides a calculation method for obtaining the high-frequency harmonic current of the active power distribution network, and the method utilizes a high-frequency harmonic model and a superposition theorem in electrical engineering to accurately grasp the current distribution of the high-frequency harmonic, thereby being beneficial to better formulating harmonic treatment measures and reducing the harmonic treatment cost and the influence on a power system. The technical solution of document [2] has the disadvantages of low computational efficiency and limited application.
The document [3] Chinese patent "an uncertain harmonic power flow calculation method applicable to distributed power supply access" (CN106786608A) proposes a method for calculating uncertain harmonic power flow of distributed power supply access, the method has better containment on fluctuation data, and under the same operation purpose and condition, the calculation efficiency of the algorithm is far higher than that of a Monte Carlo method and is equivalent to that of a probabilistic power flow method. The technical solution of document [3] has the drawback that the uncertain information processing method cannot accurately describe all the uncertain information, and how to form a processing method that can be accurately described has a large research space.
The document [4] i.archiund-Aranda, r.o.mota-palomino.harmonic distribution networks [ C ]// International Conference on Harmonics & Quality of power. ieee,2010. harmonic emissions of the grid were calculated assuming that the only parallel device current sources in the grid were caused by non-linear loads. This assumption simplifies the harmonic calculation, using the current of the non-linear element to determine the current amplitude of the grid harmonic. The technical scheme of the document [3] simplifies harmonic calculation, determines the amplitude of the branch harmonic current by using the current of the nonlinear device, and has low calculation precision.
In document [5] Rajicic, Taleski R.two novel methods for radial and welky sampled network analysis [ J ]. Electric Power Systems Research,1998,48(2): p.79-87, an admittance summing method based on a "branch-by-branch calculation method" is proposed, which aims at node loads that can be expressed as constant admittance and is developed using a non-iterative method, which can take into account linear loads in a distribution network. The technical solution of document [5] has the drawback that manual numbering is used in each network configuration, which makes the method unusable for network reconfiguration.
Document [6] Lian K L, Noda T.A Time-Domain Harmonic Power-Flow Algorithm for organizing nonlinear phases-State Solutions [ J ]. Power Delivery IEEE Transactions on,2010,25(3): p.1888-1898. A Harmonic Power Flow calculation method implemented completely in the Time Domain is proposed. In essence, the method extends the time domain steady state method and takes into account the flow constraints and the total load in the flow calculation. The technical solution of document [6] has the disadvantage that it is suitable for the study of smaller systems, but is not well suited for the calculation of harmonic currents in some solutions and in many environments where harmonic current spectra of complex and variable harmonic current sources exist.
Document [7] Romero A, Zini H C, Ratta? G, et al, harmonic load-flow adaptive on the performance of the project [ J ]. Iet Generation Transmission & Distribution,2011,5(4):1. A HLF calculation method based on the probability theory is provided. The input is not probability but probability distribution, and the method is used for describing the uncertainty of the load size and composition. This method is classified as a frequency domain method. The technical solution of document [7] has the drawback that in the frequency domain analysis, the network under study is linear and time-invariant, and due to its nature, the frequency domain analysis requires the calculation of detailed information of a network, which needs to be clearly calculated for each frequency on a frequency band. Moreover, the information to be obtained is highly accurate.
A probabilistic harmonic power flow calculation method based on point estimation is proposed in the document [8] MohammadiM.Probalistic harmonic load flow using fast point estimate method [ J ] Generation, Transmission & Distribution, IET,2015,9(13): 1790-. When the method for analyzing the plurality of random variables with various types of probability distribution is popularized, the method is better than the previous point estimation method.
A new algorithm for calculating the power flow solution of a radial power distribution system is proposed in the document [9] Arenagira, Venkatesh B.harmonic load flow for radial distribution systems [ J ]. Journal of Engineering and Technology,2011,6(3):303-313. It uses a recursive algorithmic solution technique. The method adopts a novel dynamic data structure.
Document [10] Yuanyuanan Sun, Guibin Zhang, Wilsunxu, et al.A non-iterative harmonic Power flow method for AC/AC harmonic calculations [ J ].2008. document [11] Sun Y, Zhang G, Xu W, et al.A harmonic Coupled evaluation Matrix Model for AC/DC Converters [ J ]. IEEE Transactions on Power Systems,2007,22(4): p.1574-1582. A harmonic Power flow Model based on an Admittance Matrix is also proposed, taking the AC/DC converter into account in the Admittance Matrix of the system. The model transforms the time domain nonlinear properties of the converter into a frequency domain linear admittance matrix. The coupling between the harmonic voltage and the current of the converter can be expressed more accurately by this matrix and the result does not vary with the harmonic conditions of the system.
The technical scheme defects of the documents [8] to [11] are as follows: the effective parameters cannot be comprehensively considered, and meanwhile, the calculation speed and accuracy of the comprehensive Harmonic Load Flow (HLF) of the harmonic distortion level of the power distribution network need to be improved.
Disclosure of Invention
The method aims to solve the problems that all effective parameters cannot be comprehensively considered in the harmonic tide method in the prior art, and the calculation of the harmonic distortion horizontal speed of the power distribution network is slow, the accuracy is low and the like. The invention provides a harmonic pollution distribution network reconstruction method based on forward/backward scanning harmonic power flow, which considers the influence of a linear load and a sub-transmission transformer in calculation and is used for the reconfiguration problem needing multiple times of harmonic power flow iteration. The current flow of the network branch is calculated firstly, and data such as harmonic voltage, branch current and the like are obtained in forward/backward scanning, and meanwhile, the harmonic current can be calculated according to the method provided by the invention, and the radial topology can be verified at the same time. By calculating the branch current, the bus harmonic voltage can be obtained according to the method of the invention. The method considers the radial topology of the network, and has higher calculation efficiency compared with the prior method.
The technical scheme adopted by the invention is as follows:
the method for reconstructing the harmonic pollution power distribution network based on forward/backward scanning harmonic power flow comprises the following steps:
the method comprises the following steps: inputting load network data;
step two: constructing a connection matrix, calculating the sum of each column, and judging whether a load network has an available tail end bus or not;
step three: determining the current and the flow direction of an end branch according to the load of the tail end bus from the tail end bus, then neglecting the tail end bus and a branch connected with the tail end bus, updating a connection matrix, and adding the neglected branch current to the corresponding sending tail end bus;
step four: according to the method of forward/backward scanning, the flow direction of the branch is determined while the annular structure is detected;
step five: the harmonic voltage drop of each bus relative to the first bus corresponds to the harmonic voltage of the bus, so that the harmonic voltage of the load network is obtained through calculation;
step six: from the angle of the load, calculating the harmonic voltage of the bus according to the connection load impedance of the appointed harmonic times;
step seven: carrying out simulation analysis to obtain voltage total harmonic distortion;
step eight: to be provided with
And reconstructing the power distribution network for the target.
The invention discloses a harmonic pollution power distribution network reconstruction method based on forward/backward scanning harmonic tide, which has the following technical effects:
1) the special topological characteristic of the power distribution system is considered, the current flow of the network branch is determined, the radial topology of the network is verified simultaneously in the reconfiguration process, and the power flow direction of the network branch is determined. Compared with the traditional Newton-Raphson power flow technology, the method has the advantages of high efficiency, rapidness, accuracy and easiness in expansion in problem processing, and can solve other harmonic problems.
2) The influence of linear load modeling on a forward/backward formula of the harmonic power flow in the presence of the capacitor bank is considered, the harmonic impedance characteristics of the system are influenced by the linear load modeling in a harmonic analysis program, harmonic propagation in a network is changed, and the research accuracy can be improved by classifying linear load models.
Drawings
FIG. 1(1) is a schematic diagram of modeling an L-type network bus;
FIG. 1(2) is a schematic diagram of modeling an LC-type network bus;
FIG. 1(3) is a schematic diagram for modeling HC-type network bus;
fig. 1(4) is a schematic diagram for modeling an H-type network bus.
Fig. 2 is a schematic diagram of an IEEE standard 69 bus power distribution network.
FIG. 3 is a flow chart of a non-iterative harmonic power flow method based on forward/backward frequency sweeping.
Detailed Description
A harmonic pollution power distribution network reconstruction method based on forward/backward scanning harmonic power flow firstly needs to calculate the current flow of a network branch in the forward/backward scanning process. Then, in the forward sweep, the harmonic voltage of the node is calculated. The branch currents used in the backward sweep are calculated from the parallel device harmonic currents. Parallel devices in a capacitor compensation network include linear and non-linear loads and capacitor banks. In harmonic power flow, the harmonic currents of the nonlinear load are classified into known data for calculation. However, the linear load (capacitor bank) current must be calculated from known data. In nonlinear load modeling, it is assumed that the harmonic current at each harmonic order is a function of the fundamental current. Further, it is assumed that in a Medium Voltage (MV) distribution network, the harmonic voltage on the High Voltage (HV) side of the transformer in the HV/MV substation is 0.
The method for reconstructing the harmonic pollution power distribution network based on forward/backward scanning harmonic power flow comprises the following steps:
the method comprises the following steps: inputting load network data;
step two: constructing a connection matrix, calculating the sum of each column, and judging whether a load network has an available tail end bus or not;
step three: determining the current and the flow direction of an end branch according to the load of the tail end bus from the tail end bus, then neglecting the tail end bus and a branch connected with the tail end bus, updating a connection matrix, and adding the neglected branch current to the corresponding sending tail end bus;
step four: according to the method of forward/backward scanning, the flow direction of the branch is determined while the annular structure is detected;
step five: the harmonic voltage drop of each bus relative to the first bus corresponds to the harmonic voltage of the bus, so that the harmonic voltage of the load network is obtained through calculation;
step six: from the angle of the load, calculating the harmonic voltage of the bus according to the connection load impedance of the appointed harmonic times;
step seven: carrying out simulation analysis to obtain voltage total harmonic distortion;
step eight: to be provided with
And reconstructing the power distribution network for the target.
Considering the influence of linear load modeling on the forward/backward formula of the harmonic power flow in the presence of the capacitor bank, the modeling of the load network bus is classified as follows, as shown in fig. 1(1) -fig. 1 (4):
firstly, linear load L;
the capacitor compensates the linear load LC;
a nonlinear load HC compensated by the capacitor;
fourthly, nonlinear load H;
for the L, LC and HC buses, the current absorbed by the parallel devices is unknown; for a non-linear load H bus, the current absorbed by the parallel device is known; firstly, network harmonic currents of L, LC and HC buses are calculated, and the vector form of the network harmonic currents is as follows:
wherein:
harmonic current vectors of the buses L, LC, HC and H are respectively designated, and if the number of the buses of L type, LC type, HC type and H type is p, q, r and s respectively in the network of n buses, the harmonic current vectors of the buses L, LC, HC and H type are respectively designated
And I(h)Is p, q, r, s and n.
The invention proposes a method for simultaneously calculating branch currents and verifying radial topology, based on a connection matrix in which the sum of each column represents the total branch connected to the corresponding bus. Since the end bus is connected to only one branch, the end bus can be determined in this way;
starting from the end bus, determining the end branch current and flow direction according to the end bus load, i.e. determining the transmitting bus and the receiving bus of the end branch, then ignoring the end bus and its connected branches, updating the connection matrix, and adding the ignored branch currents to the corresponding transmitting end bus, where i and j indicate the transmitting end and receiving end buses of the branches, respectively:
wherein the content of the first and second substances,
and
respectively harmonic currents of bus i and bus j,
is the branching current of bus i between the bus being the transmit side and bus j being the receive side bus.
The process of determining the end branch current and flow direction based on the end bus load continues until the first bus is present. When network data is loaded, a connection matrix is first constructed and the sum of each column is calculated. And then judging whether an available end bus exists or not, if so, calculating the current and the flow direction of the end branch, then adding the branch current to the load of the sending end, removing the end bus and the connecting branch, calculating the sum of each column after finishing updating the connecting matrix, and judging whether the available end bus exists or not again. If no available port bus is available, it is determined whether all branches are considered, if all branches are considered, the topology is radial, and if not, the topology is not radial.
During reconstruction, a novel method is used for calculating branch current and judging the current flow direction to limit the radial operation of the network. There is no longer a terminal bus in the network and the program will check the configuration of the ring. The detection of the ring-shaped structure and the determination of the branch flow direction are performed simultaneously. In the forward/backward scanning method, the branch current direction is key information. Therefore, by calculating the branch current through the forward/backward scanning method, the bus harmonic voltage from the transmitting side bus to the receiving side bus is calculated:
wherein the content of the first and second substances,
neutralization
Respectively as a branch impedance and a branch current, V, between the transmit side bus i and the receive side bus ji (h)、
Harmonic voltages of bus i and bus j, respectively.
The harmonic voltage on the high-voltage side of the substation transformer in the high/medium voltage substation is set to 0, so the harmonic voltage drop of each bus relative to the first bus corresponds to its harmonic voltage. Thus, the network harmonic voltage V(h)Can be expressed in a matrix manner as:
[V(h)](n×1)＝[HA(h)](n×n)[I(h)](n×1) (5)
wherein: [ HA ](h)]Is a relationship matrix between the harmonic bus voltage vector and the system harmonic current vector. Thus, if the harmonic current is specified, the harmonic voltage can be determined.
For the L, LC, HC model, the bus voltage vector may be calculated from equation (6):
wherein:
and
corresponding to the L, LC and HC buses, the dimensions are (p + q + r) and (p + q + r) × s, respectively.
Wherein:
is a L dieThe harmonic voltage of the bus is shaped to be,
for the LC model bus harmonic voltage,
is the harmonic voltage of the bus of the HC model,
the total harmonic current of the model L, LC, HC and H.
For both the L and LC models, the bus harmonic voltage can be calculated from the connected load impedance for a specified harmonic order:
wherein:
is the impedance of the L-model,
impedance of the LC model.
For an LC bus, the equivalent impedance model and the linear load model of the capacitor bank must be considered in the desired harmonics
The current injected into the bus at each harmonic order has two components, including the capacitor bank current and the nonlinear load current. Thus, the bus harmonic voltage of the HC bus is calculated from the first component of the current injected into the bus. The capacitor bank voltage is:
wherein:
is the non-linear load current of the HC bus,
is the load impedance of the capacitor bank and,
harmonic voltages of the HC bus.
From a load perspective, the bus voltage vector is calculated according to equations (7) - (9):
wherein:
is a square matrix with dimension (p + q + r). Because the harmonic impedance model of the parallel devices consists of L, LC and capacitor banks in the HC bus, namely:
thus, the L, LC and HC harmonic currents for each harmonic order are calculated as follows:
according to the above equation (12-13), the harmonic current vector of the system is calculated, and the harmonic bus voltage vector is calculated. Dividing the impedance matrix into 3 defined sub-matrices
And
the proposed harmonic power flow method is more suitable for large-scale power distribution networks.
The Total Harmonic Distortion (THD) and the total network loss in the network bus are considered as network reconstruction evaluation indicators:
wherein: pLossIs the total power loss of the network, SATHD is the average THD, V of the networki h,
Is the voltage and current of the bus i with harmonic number h, Vi (1)Is the voltage of the bus i with the harmonic number of 1, n is the bus number, LTIs the apparent power of the system load, LiIs the apparent power of the bus i load, and m is the harmonic order.
Network reconfiguration is the process of changing the state of a connection or segment switch in order to improve network performance metrics. The goals of network reconfiguration are as follows:
wherein, PLoss-baseAnd SATHDbaseIs the total power loss of the underlying configuration and the network average THD. w is a1And w2Is addition of the corresponding objectThe weight factor. w is a1And w2Are assigned a base value of 0.5.
Example (b):
simulation experiments were conducted in an IEEE standard 69 bus radial distribution network, and the method proposed by the present invention was evaluated. The Total Harmonic Distortion (THD) and the total network loss in the network bus are regarded as evaluation indexes.
Wherein: pLossIs the total power loss of the network, SATHD is the average THD, V of the networki hIs the voltage of the bus i with the harmonic number h, n is the number of buses, LTIs the apparent power of the system load, LiIs the apparent power of the bus i load.
Example study network figure 2 shows a 12.66kV IEEE standard distribution network. The basic configuration of the system is a single supply point, 69 bus bars, 7 siding, 68 branches, 5 loops or connecting switches (switches 69-73), as shown in phantom. The total load of the basic configuration is 3802.19kW,2694.6 kvar. The network contains 2 capacitor banks, one for each bus 21 and 62, and has a size of 500 kvar.
Table 1 is the position of the nonlinear load. Table 2 shows data of the sub-transmission transformers. Table 3 is 2 common linear load models. The 3 non-linear load types are shown in table 4 assuming that their harmonic distributions are a function of the fundamental current.
TABLE 1 location of non-linear load
TABLE 2 sub-Transmission Transformer data
TABLE 32 common Linear load models
TABLE 4 harmonic spectra of nonlinear loads
There are several assumptions in this application to simplify the calculations: the nonlinear load is modeled as a current source per harmonic step, with constant amplitude and frequency spectrum; since the effects of the different harmonic orders are decoupled, it is assumed that the fundamental voltage is not affected by the harmonic voltage; the distribution network is assumed to be balanced, considering only three-phase loads.
The summary flow of the invention is shown in the attached figure 3:
load network data is input.
And constructing a connection matrix, calculating the sum of each column, and judging whether an available tail end bus exists or not.
From the end bus, the end branch current and flow direction are determined according to the end bus load. I.e. the transmit bus and the receive bus defining the end branches. Subsequently, the end bus and its connected branches are ignored, the connection matrix is updated, and the ignored branch currents are added to the respective transmit end buses.
According to the method of forward/backward scanning, the branch flow direction is determined while detecting the ring structure.
And the harmonic voltage drop of each bus relative to the 1 st bus corresponds to the harmonic voltage of the bus, so that the network harmonic voltage is calculated.
From the point of view of the load, the bus harmonic voltage is calculated from the connected load impedance of a specified harmonic order.
And (5) carrying out simulation analysis to obtain the total harmonic distortion of the voltage.
TABLE 5 verification result of harmonic power flow of bus distribution network
As can be seen from table 5, the simulation test verifies the effectiveness and correctness of the harmonic pollution power distribution network reconstruction method based on forward and backward scanning harmonic power flow.
TABLE 6 harmonic loss of the network under different conditions
Table 6 gives the network harmonic losses for the three cases. As predicted, high harmonic distortion of case1 (no load) and case2 (series RL) can lead to increased network harmonic losses. The linear load model, as a resistance-inductance impedance, in combination with the capacitor bank and sub-transmission transformers, will determine the impedance characteristics of the system. Harmonic resonance, on the other hand, is a function of the impedance characteristics of the system. Therefore, the linear load modeling has important significance in the power grid harmonic research.
In order to evaluate the application of the non-iterative harmonic power flow method of the forward/backward sweep frequency in the network reconstruction, three conditions are considered. The defined scheme is based on the following different linear load modeling: case 1: the linear load of the network is not considered in the harmonic power flow; case 2: the linear load of the network is considered as model 1 in table 1; case 3: the linear load of the network is considered as model 2 in table 1.
Network reconfiguration is the process of changing the state of a connection or segment switch in order to improve network performance metrics. The goals of network reconfiguration are as follows:
wherein, PLoss-baseAnd SATHDbaseIs the total power loss of the underlying configuration and the network average THD. w is a1And w2Are the weighting factors of the respective targets. w is a1And w2Are assigned a base value of 0.5.
To achieve 69 optimal configuration of the bus distribution network, an improved genetic algorithm (RGA) is employed. Furthermore, the effect of using this method in optimization time was evaluated compared to Direct Harmonic Analysis (DHA).
TABLE 7 comparison of calculated time results
Table 7 shows the comparison result between the calculation time and DHA of the proposed method, and it can be seen from table 7 that the method of the present invention has good performance, fast calculation speed, and reduced optimization time by 18.6%.
TABLE 8 optimization results
As shown in table 8, the linear load modeling method affects the optimal configuration of the network. The decision of the network operator is influenced. Furthermore, the results demonstrate the importance of the linear load modeling approach in harmonic studies. The voltage distribution of the network is improved in the case of 3 definitions compared to the basic configuration, as is the voltage THD of the network bus. Furthermore, the choice of linear load modeling methods in harmonic studies may change the optimal configuration of the network and thus may affect the decisions of the network operator.
Claims (7)
1. The method for reconstructing the harmonic pollution power distribution network based on forward/backward scanning harmonic power flow is characterized by comprising the following steps of:
the method comprises the following steps: inputting load network data;
step two: constructing a connection matrix, calculating the sum of each column, and judging whether a load network has an available tail end bus or not;
step three: determining the current and the flow direction of an end branch according to the load of the tail end bus from the tail end bus, then neglecting the tail end bus and a branch connected with the tail end bus, updating a connection matrix, and adding the neglected branch current to the corresponding sending tail end bus;
step four: according to the method of forward/backward scanning, the flow direction of the branch is determined while the annular structure is detected;
step five: the harmonic voltage drop of each bus relative to the first bus corresponds to the harmonic voltage of the bus, so that the harmonic voltage of the load network is obtained through calculation;
step six: from the angle of the load, calculating the harmonic voltage of the bus according to the connection load impedance of the appointed harmonic times;
step seven: carrying out simulation analysis to obtain voltage total harmonic distortion;
step eight: to be provided with
For the purpose, a power distribution network reconfiguration is performed.
2. The harmonic pollution power distribution network reconstruction method based on forward/backward scanning harmonic power flow according to claim 1, characterized in that: considering the influence of linear load modeling on the forward/backward formulation of the harmonic power flow in the presence of a capacitor bank, the modeling of the network bus is classified as follows:
firstly, linear load L;
the capacitor compensates the linear load LC;
a nonlinear load HC compensated by the capacitor;
fourthly, nonlinear load H;
for the L, LC and HC buses, the current absorbed by the parallel devices is unknown; for a non-linear load H bus, the current absorbed by the parallel device is known; firstly, network harmonic currents of L, LC and HC buses are calculated, and the vector form of the network harmonic currents is as follows:
wherein:
harmonic current vectors respectively referring to buses L, LC, HC and H, and in a network of n buses, if the number of L-type, LC-type, HC-type and H-type buses is p, q, r and s respectively, then
And I(h)Is p, q, r, s and n.
3. The harmonic pollution power distribution network reconstruction method based on forward/backward scanning harmonic power flow according to claim 1, characterized in that: a method for simultaneous calculation of branch currents and verification of radial topology is proposed, based on a connection matrix in which the sum of each column represents the total branch connected to the respective bus; since the side bus is connected to only one branch, the side bus can be determined in this way;
starting from the end bus, determining the end branch current and flow direction according to the end bus load, i.e. determining the transmitting bus and the receiving bus of the end branch, then ignoring the end bus and its connected branches, updating the connection matrix, and adding the ignored branch currents to the corresponding transmitting end bus, where i and j indicate the transmitting end and receiving end buses of the branches, respectively:
4. the harmonic pollution power distribution network reconstruction method based on forward/backward scanning harmonic power flow according to claim 1, characterized in that: this process continues until the first bus is present; after network data is loaded, firstly, a connection matrix is required to be constructed and the sum of each column is calculated; then judging whether an available end bus exists, if so, calculating the current and the flow direction of an end branch, then adding branch current to a sending end load, removing the end bus and a connecting branch, calculating the sum of each column after finishing updating of a connecting matrix, and judging whether the available end bus exists again; if no available port bus is available, it is determined whether all branches are considered, if all branches are considered, the topology is radial, and if not, the topology is not radial.
5. The harmonic pollution power distribution network reconstruction method based on forward/backward scanning harmonic power flow according to claim 1, characterized in that: in the reconstruction process, the bus harmonic voltage from the bus of the transmitting end to the bus of the receiving end is calculated by calculating the branch current through a forward/backward scanning method:
wherein the content of the first and second substances,
neutralization
Respectively as the branch impedance and branch current between the transmitting end bus i and the receiving end bus j;
setting the harmonic voltage of the high-voltage side of a transformer substation transformer in a high-voltage/medium-voltage transformer substation to be 0, so that the harmonic voltage drop of each bus relative to the first bus corresponds to the harmonic voltage of the bus; thus, the network harmonic voltage V(h)Can be expressed in a matrix manner as:
[V(h)](n×1)＝[HA(h)](n×n)[I(h)](n×1) (5)
wherein: [ HA ](h)]Is a relation matrix between a harmonic bus voltage vector and a system harmonic current vector; thus, if a harmonic current is specified, a harmonic voltage can be determined;
for the L, LC, HC model, the bus voltage vector may be calculated from equation (6):
wherein:
and
dimensions (p + q + r) and (p + q + r) × s corresponding to L, LC and HC buses, respectively;
for both the L and LC models, the bus harmonic voltage can be calculated from the connected load impedance for a specified harmonic order:
wherein:
for the L-model bus harmonic voltage,
for harmonic voltage of LC model bus；
For an LC bus, the equivalent impedance model and the linear load model of the capacitor bank must be considered in the desired harmonics
The current injected into the bus by each harmonic number has two components, including the capacitor bank current and the nonlinear load current; thus, the bus harmonic voltage of the HC bus is calculated from the first component of the current injected into the bus; the capacitor bank voltage is:
wherein:
is the non-linear load current of the HC bus,
is the load impedance of the capacitor bank and,
is the harmonic voltage of the HC bus;
from a load perspective, the bus voltage vector is calculated according to equations (7) - (9):
wherein
Is a square matrix with dimension (p + q + r); because the harmonic impedance model of the parallel devices consists of L, LC and capacitor banks in the HC bus, namely:
thus, the L, LC and HC harmonic currents for each harmonic order are calculated as follows:
calculating a harmonic current vector of the system according to the formula (12-13), and calculating a harmonic bus voltage vector; dividing the impedance matrix into 3 defined sub-matrices
The proposed harmonic power flow method is more suitable for large-scale power distribution networks.
6. The harmonic pollution power distribution network reconstruction method based on forward/backward scanning harmonic power flow according to claim 1, characterized in that: the Total Harmonic Distortion (THD) and the total network loss in the network bus are considered as network reconstruction evaluation indicators:
wherein P isLossIs the total power loss of the network, SATHD is the average THD, V of the networki hThe harmonic number of the bus i is hN is the number of buses, LTIs the apparent power of the system load, LiIs the apparent power of the bus i load.
7. The harmonic pollution power distribution network reconstruction method based on forward/backward scanning harmonic power flow according to claim 1, characterized in that: the goals of network reconfiguration are as follows:
wherein, PLoss-baseAnd SATHDbaseIs the total power loss and network average THD of the underlying configuration; w is a1And w2Are the weighting factors of the respective targets.
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