A distribution network fault recovery method based on active control of distributed generation

Abstract

The present invention provides a distribution network fault recovery method based on active control of distributed power sources, comprising the following steps: first, using terminal equipment to collect parameters such as voltage amplitude and phase angle of each node of the distribution network, active load, reactive load, initial active output, initial reactive output, and initial switch state of distributed power sources in real time; when a fault occurs in the distribution network, disconnect the adjacent switches of the fault section to isolate the fault, and use the operating parameters at this time to calculate the state combination of the new segment switches and the connecting switches, and then formulate a separation and closing operation sequence plan; before each execution of the connecting switch closing operation, calculate the optimal control point of the distributed power source upstream of the closing point according to the preset closing time; adjust the power control reference value of each distributed power source, and then perform the closing operation. The present invention is easy to implement, can suppress the closing voltage fluctuation in the distribution network fault recovery process to the greatest extent, and effectively improve the safety and reliability of the new energy power system.

Description

Technical Field

[0001] The present invention relates to the technical field of renewable energy power generation control, and in particular to a distribution network fault recovery method based on active control of distributed power sources. Background Art

[0002] Fault recovery refers to the process of restoring the power-off load to the greatest extent possible while ensuring system safety through a series of means after a fault occurs and the grid is isolated. Network reconstruction is the main means of fault recovery for radial distribution networks. However, limited by the constraints of branch capacity and node voltage, network reconstruction often faces the problem of node voltage fluctuation or even exceeding the limit. With the increasingly severe global energy crisis and environmental pollution problems, the proportion of distributed power sources such as wind power and photovoltaics connected to the distribution network has increased year by year, causing the traditional distribution network to gradually transform into an active distribution network. Distributed power sources have flexible power regulation capabilities and can provide effective support for fault recovery of distribution networks. However, due to the uncertainty of wind and light output, the regulation capability of distributed power sources has significant dynamic characteristics. How to make full use of the flexible control capabilities of distributed power sources and effectively cooperate with network reconstruction has become the key to fault recovery of distribution networks.

[0003] In view of the fault recovery problem of distribution networks containing distributed generation, existing research is devoted to the establishment and solution of fault recovery models, but in general, network reconstruction and island division are used as means of fault recovery, mainly for solving the static switch state combination that satisfies the objective function. Network reconstruction is essentially the closing and unclosing of the network. First, the tie switch is closed to form a ring network, and then a certain segment switch on the ring network is opened to restore its radial structure, so as to realize line load transfer without power loss to users. However, if the voltage difference between the nodes on both sides of the tie switch is large, a large circulating current will be generated in the electromagnetic ring network after the ring is closed, and the impact current generated at the moment of closing the ring may cause equipment overload and affect the correct action of protection. Under the influence of the constant outlet voltage of the distribution network substation, the impact component in the closing current is transmitted to the downstream feeder, causing the voltage of each node to fluctuate or even exceed the limit. Most of the existing methods only perform steady-state safety verification on the switch state. A small number of literatures consider the steady-state and transient safety constraints of the closing operation during the reconstruction process, but they all focus on ensuring that the closing current does not exceed the limit, pay less attention to the voltage problem in the closing process, and lack active suppression means.

[0004] The common practice now is to introduce reactors or energy storage equipment, and give priority to disconnecting distributed power sources with large capacity, poor excitation control or close to the closing point during the closing and opening operations. However, this also weakens the supporting role of distributed power sources to the distribution network, which is not conducive to fault recovery of the distribution network.

[0005] In summary, how to reduce or even suppress the transient voltage fluctuation of the closed loop during the recovery process after a distribution network fault as much as possible to ensure the safety of distributed power sources and the reliability of the power system has become an urgent problem that technicians in this field need to solve. Summary of the invention

[0006] In view of the deficiencies of the above-mentioned prior art, the present invention provides a distribution network fault recovery method based on active control of distributed power sources, so as to reduce the loop voltage fluctuation during the power grid fault recovery process and improve the power supply safety and reliability during the fault recovery process of the new energy power system.

[0007] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0008] A distribution network fault recovery method based on active control of distributed power sources is used to perform distribution network fault recovery control after disconnecting adjacent switches in a faulty section of the distribution network when a fault occurs, and comprises the following steps:

[0009] S1. Obtaining node operation parameters of each node of the distribution network when a failure occurs in the distribution network;

[0010] S2. Before performing the tie switch closing operation on the closing point in the distribution network after the fault, the intersection between the feasible power set and the power controllable range of each distributed power source upstream of the closing point is calculated and determined according to the node operation parameters of each node of the distribution network, and then the optimal control point of the distributed power source upstream of the closing point is calculated;

[0011] S3. Send the optimal control point to the corresponding distributed power source, adjust the power control reference value of each distributed power source, and then perform the closing operation according to the formulated closing operation plan.

[0012] In the above-mentioned distribution network fault recovery method based on active control of distributed power sources, preferably, the node operating parameters include the node's voltage amplitude, voltage phase angle value, active load, reactive load, initial active output of the distributed power source, initial reactive output and initial switch state.

[0013] In the above-mentioned distribution network fault recovery method based on active control of distributed power sources, preferably, in step S2, the calculation of the optimal control point of the distributed power source includes the following steps:

[0014] S201, determine the power controllable range of each distributed power source upstream of the closing point; compile a serial number for each distributed power source from the closing point to the distribution network substation node, then take the initial value of the distributed power source serial number i as 1, and execute step S202;

[0015] S202, calculate the feasible power set Φ of the i-th distributed generation g,i ;

[0016] S203, determine the feasible power set Φ of the i-th distributed power source g,i Whether there is an intersection with its power controllable range; if there is a feasible power intersection, execute step S204; if there is no feasible power intersection, execute step S205;

[0017] S204, calculating the optimal control point of the i-th distributed power source when there is a feasible power intersection, as the calculation result of the optimal control point of the distributed power source, and executing step S206;

[0018] S205, using the closed-loop voltage non-periodic component coefficient optimization model to solve the optimal control point of the ith distributed power source when there is no feasible power intersection; then, determine whether the ith distributed power source is the distributed power source closest to the distribution network substation node; if so, determine the optimal control point of the ith distributed power source when there is no feasible power intersection as the calculation result of the optimal control point of the distributed power source, and execute step S206; if not, let i be incremented by 1, return to execute step S202, and continue to search and calculate the optimal control point of the distributed power source;

[0019] S206. Stop searching and complete the calculation of the optimal control point of the distributed power source.

[0020] In the above-mentioned distribution network fault recovery method based on active control of distributed generation, preferably, in step S202, the feasible power set Φ of the i-th distributed generation is g,i The calculation method is as follows:

[0021] S221, before closing, based on the forward-backward substitution method and the collected node voltage phase angle value, construct the voltage amplitude U of the closing node a on one side of the i-th distributed generation a,ol Regarding the active power P of the i-th distributed generation g,i , reactive power Q g,i Function:

[0022] U a,ol =f a (P g,i ,Q g,i );

[0023] S222, let the phase of the non-periodic component coefficient of the closed-loop voltage be 0, and derive the voltage amplitude U of the closed-loop node b on one side of the i-th distributed generation b,ol Regarding the active power P of the i-th distributed generation g,i , reactive power Q g,i Function U b,ol =f b (P g,i ,Q g,i ), and bring it into the function U a,ol =f a(P g,i ,Q g,i ), and the reactive power Q of the i-th distributed generation is obtained g,i The equation is:

[0024]

[0025] In the formula, A, B, and C are the coefficients of the equation;

[0026] S223, for the i-th distributed generation reactive power Q g,i Solve the equation to obtain the feasible power set Φ of the i-th distributed generation g,i for:

[0027]

[0028] In the above-mentioned distribution network fault recovery method based on active control of distributed power sources, preferably, in step S204, when there is a feasible power intersection, the optimal control point of the i-th distributed power source is calculated according to the following method:

[0029] S241, determining the relationship between the feasible power set of the i-th distributed power source and its power controllable range; if the two sets intersect, executing step S242; if the two sets are tangent, executing step S243;

[0030] S242, substitute the reactive power controllable range of the i-th distributed generation into the feasible power set to solve the two active power solutions of the i-th distributed generation in

[0031] If the i-th distributed generation is energy storage, the active control reference value P g,i,ref The values ​​are:

[0032]

[0033] Where P g,i,t is the active power output by the i-th distributed generation at time t;

[0034] If the i-th distributed generation is a wind turbine or photovoltaic, its active power control reference value P g,i,ref The values ​​are:

[0035]

[0036] Where P g,i,t,mpp is the maximum power operating point of the i-th distributed generation at time t;

[0037] Then, execute step S244;

[0038] S243, substitute the reactive power controllable range of the i-th distributed power source into the feasible power set to solve the unique active power solution of the i-th distributed power source

[0039] Then the active power control reference value P of the i-th distributed generation is g,i,ref The values ​​are:

[0040]

[0041] Then, execute step S244;

[0042] S244, the active power control reference value P of the i-th distributed power source g,i,ref Substitute the feasible power set and calculate the corresponding reactive power control reference value to determine the optimal control point:

[0043]

[0044] In the above-mentioned distribution network fault recovery method based on active control of distributed power sources, preferably, in step S205, the optimization model of the non-periodic component coefficient of the closed-loop voltage of the i-th distributed power source is:

[0045] Objective function F i To minimize the absolute value of the non-periodic component of the closed-loop voltage:

[0046]

[0047] In the formula, is the function of the non-periodic component coefficient of the closed-loop voltage with respect to the active and reactive power of the ith distributed generation when the source load power other than the ith distributed generation power is constant;

[0048] For the objective function F i , the constraints include:

[0049] Constraints 1) Constraints on the controllable range of power of the i-th distributed generation:

[0050]

[0051] Where P g,i,t is the active output of the ith distributed generation at time t; P g,i,max , P g,i,min are the upper and lower limits of the active power output of the i-th distributed generation; Q g,i,max , Q g,i,min are the upper and lower limits of the reactive power output of the i-th distributed generation respectively;

[0052] Constraint 2) Node voltage constraint:

[0053] U i,min ≤Ui ≤U i,max ;

[0054] Where U i is the voltage amplitude of the node to which the i-th distributed generation is connected; U i,min , U i,max They are the lower and upper limits of node voltage allowed in the distribution network respectively;

[0055] Constraint 3) Branch current constraint:

[0056] I ij ≤I ij,max ;

[0057] In the formula, I ij ,I ij,max The flow through branch L ij The current amplitude and the maximum current value allowed to flow; branch L ij It is the branch between the nodes to which the i-th distributed generation and its next adjacent distributed generation j are connected.

[0058] In the above-mentioned distribution network fault recovery method based on active control of distributed power sources, preferably, the non-periodic component coefficient of the closed-loop voltage of the i-th distributed power source is:

[0059]

[0060] Where, ω is the system angular frequency; t 0 is the preset closing time, I ab,i,m is the peak value of the closed-loop current flowing between the closing nodes a and b on both sides of the i-th distributed power source, θ ab,i is the initial phase angle of the closing current flowing between the closing nodes a and b on both sides of the i-th distributed power source, and:

[0061]

[0062] In the formula, R eq , L eq are the equivalent resistance and equivalent inductance of the additional passive ring network respectively; U a,ol (P g,i ,Q g,i ), U b,ol are the voltage amplitudes of the two closing nodes a and b before closing respectively; δ a,o1 , δ b,ol They are the initial phase angles of the voltage at the two closing nodes a and b before closing.

[0063] In the above-mentioned distribution network fault recovery method based on active control of distributed power sources, preferably, in step S205, the specific method for calculating the optimal control point of the i-th distributed power source when there is no feasible power intersection is: solving the optimization model of the non-periodic component coefficient of the closed-loop voltage of the i-th distributed power source through the particle swarm algorithm, and obtaining the distributed power source power value that minimizes the absolute value of the non-periodic component coefficient of the closed-loop voltage, that is, the optimal control point of the i-th distributed power source when there is no feasible power intersection.

[0064] In the above-mentioned distribution network fault recovery method based on active control of distributed power sources, preferably, in step S3, the manner of adjusting the power control reference value of each distributed power source is:

[0065] If a new optimal control point with feasible power intersection or an optimal control point without feasible power intersection is calculated for a certain distributed power source, the new optimal control point with feasible power intersection or the new optimal control point without feasible power intersection is adjusted to the power control reference value of the distributed power source; otherwise, the original power control reference value of the distributed power source is maintained.

[0066] Compared with the prior art, the present invention has the following beneficial effects:

[0067] 1. The prior art determines the fault recovery and reconstruction process based on the condition that the closed-loop current does not exceed the limit, fails to consider the voltage fluctuation during the closed-loop process, and lacks active suppression measures, which may not only affect the normal operation of the load, but also threaten the safety of the distributed power supply. Compared with the prior art, the present invention fully considers the impact of the closed-loop voltage fluctuation during the distribution network fault recovery process, and uses the active control of the distributed power supply power to suppress the closed-loop voltage fluctuation before performing the closing operation, which can effectively improve the stability of the source and load and ensure the power supply reliability during the system fault recovery process.

[0068] 2. Some existing technologies use reactors or energy storage devices, and give priority to disconnecting large-capacity distributed power sources with poor excitation control or close to the closing point during the closing and opening operations to avoid voltage fluctuations. This is not only costly and complex to regulate, but also limits the normal operation of distributed power sources and their support for the distribution network. Compared with the existing technology, the present invention constructs a feasible power set of distributed power sources that suppresses the closing voltage fluctuations, and considers the intersection of the feasible power set of distributed power sources and their power controllable range, searches for distributed power sources upstream of the closing point one by one, and optimally controls their active and reactive power, which can suppress the closing voltage fluctuations to the greatest extent while ensuring the safety of distributed power sources. BRIEF DESCRIPTION OF THE DRAWINGS

[0069] In order to make the purpose, technical solution and advantages of the invention more clear, the present invention will be further described in detail below with reference to the accompanying drawings, in which:

[0070] Figure 1 It is a flow chart of a distribution network fault recovery method based on active control of distributed power sources of the present invention.

[0071] Figure 2 This is an example diagram of a distribution network topology with distributed power sources.

[0072] Figure 3 It is a calculation flow chart of the optimal control point of distributed power supply in the distribution network fault recovery method of the present invention.

[0073] Figure 4 Yes Figure 2 The example system shown is a waveform diagram of node voltage and branch current of a closed-loop branch when the prior art method is used to perform distribution network fault recovery.

[0074] Figure 5 Yes Figure 2 The example system shown is a waveform diagram of node voltage and branch current of a closed-loop branch when the distribution network fault recovery method of the present invention is adopted. DETAILED DESCRIPTION

[0075] The present invention is further described in detail below with reference to the accompanying drawings.

[0076] In view of the deficiencies of the above-mentioned prior art, the present invention provides a distribution network fault recovery method based on active control of distributed power sources, which fully considers the impact of the output of each distributed power source on the voltage fluctuation of the fault recovery loop, constructs a feasible power set of distributed power sources that suppresses the voltage fluctuation of the loop, and calculates the optimal control point of the distributed power source based on the intersection of the feasible power set and the power controllable range, thereby suppressing the voltage fluctuation of the loop during the distribution network fault recovery process to the greatest extent and improving the power supply safety of the new energy power system during the fault recovery process. At the same time, the present invention can effectively suppress the voltage fluctuation during the fault recovery loop process by implementing the optimal power control of the distributed power source before each closing of the switch during the distribution network fault recovery process, improve the source-load stability, and ensure the power supply reliability during the fault recovery process.

[0077] The present invention is based on the distribution network fault recovery method of the distributed power source active control, and its process is as follows: Figure 1 As shown, the specific steps include:

[0078] S1. Obtain node operation parameters of each node of the distribution network when a failure occurs in the distribution network.

[0079] In a specific implementation, the terminal device can be used to collect parameters such as voltage amplitude, voltage phase angle, active load, reactive load, initial active output of distributed power source, initial reactive output and initial switch state of each node of the distribution network in real time as node operation parameters. When a fault occurs in the distribution network, according to the conventional fault handling scheme in the prior art, the adjacent switches of the fault section will be disconnected to isolate the fault, and the node operation parameters at the time of the fault will be used to calculate the new state combination of the section switch and the connecting switch, and then formulate a closing operation plan for fault recovery. At the same time, since the node operation parameters of each node are collected when the distribution network is working, it is easy to obtain the node operation parameters of each node of the distribution network when a fault occurs in the distribution network.

[0080] S2. Before performing the tie switch closing operation on the closing point in the distribution network after a fault, the intersection between the feasible power set and the power controllable range of each distributed power source upstream of the closing point is calculated and determined according to the node operating parameters of each node in the distribution network, and then the optimal control point of the distributed power source upstream of the closing point is calculated.

[0081] In this process, the influence of the output of each distributed power source on the voltage fluctuation of the fault recovery loop is fully considered, the feasible power set of distributed power sources that can suppress the voltage fluctuation of the loop is determined, and the optimal control point of the distributed power source is calculated based on the intersection of the feasible power set and the power controllable range, so as to suppress the voltage fluctuation of the loop during the fault recovery process of the distribution network to the greatest extent.

[0082] S3. Send the optimal control point to the corresponding distributed power source, adjust the power control reference value of each distributed power source, and then perform the closing operation according to the formulated closing operation plan.

[0083] Through the above method, the present invention searches for distributed power sources upstream of the closing point one by one before restoring the circuit breaker after a distribution network fault, and optimally controls the distributed power sources based on the intersection of the feasible power set and the power controllable range to suppress voltage fluctuations during the closing process, thereby effectively improving source-load stability and ensuring power supply reliability during the fault recovery process.

[0084] Figure 2 This is an example diagram of the topology of a distribution network with distributed generation. B1, B4, and B10 are 3 different 110kV 10kV busbars. The short-circuit impedances of the main transformers T1 and T2 are (0.01106+j0.0416)Ω and (0.01112+j0.04178)Ω, respectively. The power supply of the two 110kV substations B1 and B4 is taken from the same 220kV substation. The rated frequency of the system is 50Hz. The 10kV lines L1~L4 are overhead lines of the same model, with positive sequence resistance and reactance of 0.170 and 0.336Ω / km, respectively. Nodes B2 and B3 are connected to energy storage and double-fed asynchronous wind turbines DFIG, respectively.

[0085] In specific implementation, in step S2, the calculation process of the optimal control point of the distributed power source is as follows: Figure 3 As shown, the following steps are included:

[0086] S201, determine the power controllable range of each distributed power source upstream of the closing point; compile a serial number for each distributed power source from the closing point to the distribution network substation node, then take the initial value of the distributed power source serial number i as 1, and execute step S202;

[0087] S202, calculate the feasible power set Φ of the i-th distributed generation g,i ;

[0088] S203, determine the feasible power set Φ of the i-th distributed power source g,i Whether there is an intersection with its power controllable range; if there is a feasible power intersection, execute step S204; if there is no feasible power intersection, execute step S205;

[0089] S204, calculating the optimal control point of the i-th distributed power source when there is a feasible power intersection, as the calculation result of the optimal control point of the distributed power source, and executing step S206;

[0090] S205, using the closed-loop voltage non-periodic component coefficient optimization model to solve the optimal control point of the ith distributed power source when there is no feasible power intersection; then, determine whether the ith distributed power source is the distributed power source closest to the distribution network substation node; if so, determine the optimal control point of the ith distributed power source when there is no feasible power intersection as the calculation result of the optimal control point of the distributed power source, and execute step S206; if not, let i be incremented by 1, return to execute step S202, and continue to search and calculate the optimal control point of the distributed power source;

[0091] S206. Stop searching and complete the calculation of the optimal control point of the distributed power source.

[0092] Such a processing flow is to successively search for distributed power sources upstream of the closing point, and optimally control the distributed power sources based on the intersection of the feasible power set and the power controllable range to suppress voltage fluctuations during the closing process.

[0093] In the processing of the above steps S201 to S206, when specifically implemented, in step S201, the controllable power range of each distributed power source upstream of the closing point can be determined based on data such as network parameters of the distribution network and collected load information.

[0094] In specific implementation, in step S202, the feasible power set Φ of the i-th distributed power source is g,i The calculation method is as follows:

[0095] S221, before closing, based on the forward-backward substitution method and the collected node voltage phase angle value, construct the voltage amplitude U of the closing node a on one side of the i-th distributed generation a,ol Regarding the active power P of the i-th distributed generation g,i , reactive power Q g,i Function:

[0096] U a,ol =f a (P g,i ,Q g,i );

[0097] S222, let the phase of the non-periodic component coefficient of the closed-loop voltage be 0, and derive the voltage amplitude U of the closed-loop node b on one side of the i-th distributed generation b,ol Regarding the active power P of the i-th distributed generation g,i , reactive power Q g,i Function U b,ol =f b (P g,i ,Q g,i ), and bring it into the function U a,ol =f a (P g,i ,Q g,i ), and the reactive power Q of the i-th distributed generation is obtained g,i The equation is:

[0098]

[0099] In the formula, A, B, and C are the coefficients of the equation.

[0100] For example, Figure 2 As an example of the distribution network topology structure shown in the figure, assume that the current first distributed power source is the double-fed asynchronous wind turbine DFIG in the system, and the closing nodes on both sides of the double-fed asynchronous wind turbine DFIG are nodes B3 and B5 respectively; 35,i =-ωt 0 Substitute θ 35,i As a function of the voltage amplitudes at nodes B3 and B5, we can obtain:

[0101]

[0102] In the formula, θ 35,i is the initial phase angle of the closing current flowing between the closing nodes B3 and B5; ω is the system angular frequency; t 0 is the preset closing time; U 3,ol is the voltage amplitude of node B3 before closing, U 5,ol is the voltage amplitude of node B5 before closing; m is obtained by the following formula:

[0103]

[0104] In the formula, R eq , L eq are the equivalent resistance and equivalent inductance of the additional passive ring network respectively;

[0105] Will U 3,ol About U 5,ol Substitute the function into the function U a,ol =f a (P g,i ,Q g,i ), we can get the reactive power Q of the i-th distributed generation: g,i The equation is:

[0106]

[0107] Taking the doubly-fed asynchronous wind turbine DFIG connected to node B3 as the first distributed power source as an example, the active power P of the first distributed power source can be obtained: g,1 , reactive power Q g,1 The quadratic equation of :

[0108]

[0109] In the formula,

[0110]

[0111] Where U 1 is the voltage amplitude of the power node B1; R 12 , X 12 are the resistance and reactance of branch L1 respectively; R 23 , X 23 are the resistance and reactance of branch L2 respectively; P L2 , Q L2 are the active load and reactive load of node B2 respectively; P L3 , Q L3 are the active load and reactive load of node B3 respectively.

[0112] S223, for the i-th distributed generation reactive power Q g,i Solve the equation to obtain the feasible power set Φ of the i-th distributed generation g,i for:

[0113]

[0114] Based on solving the above equations and obtaining the values ​​of coefficients A, B, and C, the feasible power set Φ of the i-th distributed generation can be obtained. g,i .

[0115] In specific implementation, in step S204, when there is a feasible power intersection, the optimal control point of the i-th distributed power source is calculated according to the following method:

[0116] S241. Determine the relationship between the feasible power set of the i-th distributed power source and its power controllable range; if the two sets intersect (i.e., the intersection of the two sets contains multiple elements), execute step S242; if the two sets are tangent (i.e., the intersection of the two sets contains only one element), execute step S243.

[0117] S242, substitute the reactive power controllable range of the i-th distributed generation into the feasible power set to solve the two active power solutions of the i-th distributed generation in

[0118] If the i-th distributed generation is energy storage, the active control reference value P g,i,ref The values ​​are:

[0119]

[0120] Where P g,i,t is the active power output by the i-th distributed generation at time t;

[0121] If the i-th distributed generation is a wind turbine or photovoltaic, its active power control reference value P g,i,ref The values ​​are:

[0122]

[0123] Where P g,i,t,mpp is the maximum power operating point of the i-th distributed generation at time t;

[0124] Then, execute step S244.

[0125] S243, substitute the reactive power controllable range of the i-th distributed power source into the feasible power set to solve the unique active power solution of the i-th distributed power source

[0126] Then the active power control reference value P of the i-th distributed generation is g,i,ref The values ​​are:

[0127]

[0128] Then, execute step S244.

[0129] S244, the active power control reference value P of the i-th distributed power source g,i,ref Substitute the feasible power set and calculate the corresponding reactive power control reference value to determine the optimal control point:

[0130]

[0131] In specific implementation, in step S205, the optimization model of the non-periodic component coefficient of the closed-loop voltage of the i-th distributed power source is:

[0132] Objective function F i To minimize the absolute value of the non-periodic component of the closed-loop voltage:

[0133]

[0134] In the formula, When the source load power other than the i-th distributed generation power is constant, the coefficient of the non-periodic component of the closed-loop voltage is a function of the active and reactive power of the i-th distributed generation.

[0135] For the objective function F i , the constraints include:

[0136] Constraints 1) Constraints on the controllable range of power of the i-th distributed generation:

[0137]

[0138] Where P g,i,t is the active output of the ith distributed generation at time t; P g,i,max , P g,i,min are the upper and lower limits of the active power output of the i-th distributed generation; Q g,i,max , Q g,i,min are the upper and lower limits of the reactive power output of the i-th distributed generation respectively;

[0139] Constraint 2) Node voltage constraint:

[0140] U i,min ≤U i ≤U i,max ;

[0141] Where U i is the voltage amplitude of the node to which the i-th distributed generation is connected; U i,min , U i,max They are the lower and upper limits of node voltage allowed in the distribution network respectively;

[0142] Constraint 3) Branch current constraint:

[0143] I ij ≤I ij,max ;

[0144] In the formula, I ij ,I ij,max The flow through branch L ijThe current amplitude and the maximum current value allowed to flow; branch L ij It is the branch between the nodes to which the i-th distributed generation and its next adjacent distributed generation j are connected.

[0145] In specific implementation, in steps S202 and S205, the non-periodic component coefficient of the closed-loop voltage of the i-th distributed power source is:

[0146]

[0147] Where, ω is the system angular frequency; t 0 is the preset closing time, I ab,i,m is the peak value of the closed-loop current flowing between the closing nodes a and b on both sides of the i-th distributed power source, θ ab,i is the initial phase angle of the closing current flowing between the closing nodes a and b on both sides of the i-th distributed power source, and:

[0148]

[0149] In the formula, R eq , L eq are the equivalent resistance and equivalent inductance of the additional passive ring network respectively; U a,ol (P g,i ,Q g,i ), U b,ol are the voltage amplitudes of the two closing nodes a and b before closing, and the i-th distributed generation is distributed on the feeder where the closing node a is located. U a,ol (P g,i ,Q g,i ) can be derived based on the forward-backward method and the collected node voltage phase angle value; δ a,o1 , δ b,ol They are the initial phase angles of the voltage at the two closing nodes a and b before closing.

[0150] During specific implementation, in step S205, the specific method for calculating the optimal control point of the i-th distributed power source when there is no feasible power intersection is: solving the optimization model of the non-periodic component coefficient of the closed-loop voltage of the i-th distributed power source through the particle swarm algorithm, and obtaining the distributed power source power value that minimizes the absolute value of the non-periodic component coefficient of the closed-loop voltage, which is the optimal control point of the i-th distributed power source when there is no feasible power intersection.

[0151] In the specific implementation, in step S3, the method of adjusting the power control reference value of each distributed power source is: if a new optimal control point with a feasible power intersection or an optimal control point without a feasible power intersection is calculated for a certain distributed power source, then the new optimal control point with a feasible power intersection or the optimal control point without a feasible power intersection is adjusted to the power control reference value of the distributed power source; otherwise, the original power control reference value of the distributed power source is maintained.

[0152] like Figure 2 Taking the example system shown as an example, the rated powers of energy storage and double-fed asynchronous wind turbine DFIG are 2MW and 1.5MW respectively. The line lengths and load parameters are shown in Table 1 and Table 2 respectively. The current wind speed is 14.9m / s, the output of the double-fed asynchronous wind turbine DFIG is 1.966MW, and the output of energy storage is 0.815MW. Branch L8 fails at 1s, and the contact switch of branch L7 is closed to transfer the B9 load, and then the contact switch of branch L3 is closed at 4s.

[0153] Figure 4 Shows the Figure 2 The example system shown is a waveform diagram of node voltage and branch current of a closed-loop branch when the prior art method is used to perform distribution network fault recovery; wherein, Figure 4 (a) is the voltage waveform of node B3 of the closed-loop branch at this time. Figure 4 (b) is the current waveform of branch L3 of the closed loop branch at this time. Figure 4 As shown, if the existing technical method is used to perform distribution network fault recovery and no active control of distributed power sources is taken, the voltage of node B3 at the moment of ring closing rises from 10.4kV to 11.1kV within 25ms, exceeding the upper limit of the allowable voltage of the distribution network. At the same time, the maximum value of the impact current of branch L3 reaches 96A.

[0154] Table 1 Line length

[0155]

[0156] Table 2 Load power

[0157]

[0158] Figure 5 Shows the Figure 2 The example system shown is a waveform diagram of node voltage and branch current of a closed-loop branch when the distribution network fault recovery method of the present invention is adopted; wherein, Figure 5 (a) is the voltage waveform of node B3 of the closed-loop branch at this time. Figure 5 (b) is the current waveform of branch L3 of the closed loop branch at this time. Figure 5As shown in FIG. 1 , by using the method disclosed in the present invention, it can be calculated that the optimal operating point of the double-fed asynchronous wind turbine DFIG is 1.38MW of active power and 0.76Mvar of reactive power. After adjusting the power of the double-fed asynchronous wind turbine DFIG before closing, the line voltage of the B3 node, the effective value of the branch L3 current, and the active and reactive power of the double-fed asynchronous wind turbine DFIG are as follows: Figure 5 As shown. At 3.5s, the active power of the double-fed asynchronous wind turbine DFIG is changed from 1.966MW to 1.38MW, and the reactive power output is changed to 0.76Mvar. At the moment of closing the loop, the voltage of node B3 rises steadily from 10.42kV to 10.68kV. The maximum current of branch L3 is only 72A. It can be seen that the optimal operating point of the active and reactive power data of the double-fed asynchronous wind turbine DFIG is controlled by the method of the present invention, which effectively suppresses the closing voltage fluctuation during the fault recovery process.

[0159] To sum up, the distribution network fault recovery method based on active control of distributed power sources in the present invention fully considers the influence of the output of each distributed power source on the fault recovery loop voltage fluctuation, constructs a feasible power set of distributed power sources that suppresses the loop voltage fluctuation, and calculates the optimal control point of the distributed power source based on the intersection of the feasible power set and the power controllable range, thereby improving the source-load stability, suppressing the loop voltage fluctuation in the distribution network fault recovery process to the greatest extent, and improving the power supply safety and reliability in the fault recovery process of the new energy power system.

[0160] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described with reference to the preferred embodiments of the present invention, it should be understood by those skilled in the art that various changes may be made in form and details without departing from the spirit and scope of the present invention as defined in the appended claims.

Claims

1. A distribution network fault recovery method based on active control of distributed power sources, characterized in that: The method is used to perform distribution network fault recovery control after disconnecting the adjacent switches of the fault section when a distribution network fault occurs, and includes the following steps: S1. Obtaining node operation parameters of each node of the distribution network when a failure occurs in the distribution network; S2. Before performing the tie switch closing operation on the closing point in the distribution network after the fault, the intersection between the feasible power set and the power controllable range of each distributed power source upstream of the closing point is calculated and determined according to the node operation parameters of each node of the distribution network, and then the optimal control point of the distributed power source upstream of the closing point is calculated; the calculation of the optimal control point of the distributed power source includes the following steps: S201, determine the power controllable range of each distributed power source upstream of the closing point; compile a serial number for each distributed power source from the closing point to the distribution network substation node, then take the initial value of the distributed power source serial number i as 1, and execute step S202; S202, calculate the feasible power set Φ of the i-th distributed generation g,i ; S203, determine the feasible power set Φ of the i-th distributed power source g,i Whether there is an intersection with its power controllable range; if there is a feasible power intersection, execute step S204; if there is no feasible power intersection, execute step S205; S204, calculating the optimal control point of the i-th distributed power source when there is a feasible power intersection, as the calculation result of the optimal control point of the distributed power source, and executing step S206; Among them, when there is a feasible power intersection, the optimal control point of the i-th distributed generation is calculated as follows: S241, determining the relationship between the feasible power set of the i-th distributed power source and its power controllable range; if the two sets intersect, executing step S242; if the two sets are tangent, executing step S243; S242, substitute the reactive power controllable range of the i-th distributed generation into the feasible power set to solve the two active power solutions of the i-th distributed generation in If the i-th distributed generation is energy storage, the active control reference value P g,i,ref The values ​​are: Where P g,i,t is the active power output by the i-th distributed generation at time t; If the i-th distributed generation is a wind turbine or photovoltaic, its active power control reference value P g,i,ref The values ​​are: Where P g,i,t,mpp is the maximum power operating point of the i-th distributed generation at time t; Then, execute step S244; S243, substitute the reactive power controllable range of the i-th distributed power source into the feasible power set to solve the unique active power solution of the i-th distributed power source Then the active power control reference value P of the i-th distributed generation is g,i,ref The values ​​are: Then, execute step S244; S244, the active power control reference value P of the i-th distributed power source g,i,ref Substitute the feasible power set and calculate the corresponding reactive power control reference value to determine the optimal control point: A, B, C are the reactive power Q of the i-th distributed generation g,i The coefficients of the equation; S205, using the closed-loop voltage non-periodic component coefficient optimization model to solve the optimal control point of the ith distributed power source when there is no feasible power intersection; then, determine whether the ith distributed power source is the distributed power source closest to the distribution network substation node; if so, determine the optimal control point of the ith distributed power source when there is no feasible power intersection as the calculation result of the optimal control point of the distributed power source, and execute step S206; if not, let i be incremented by 1, return to execute step S202, and continue to search and calculate the optimal control point of the distributed power source; S206, stop searching and complete the calculation of the optimal control point of the distributed power source; S3. Send the optimal control point to the corresponding distributed power source, adjust the power control reference value of each distributed power source, and then perform the closing operation according to the formulated closing operation plan.

2. The method for distribution network fault recovery based on active control of distributed power sources according to claim 1 is characterized in that: The node operation parameters include the voltage amplitude, voltage phase angle, active load, reactive load, initial active output, initial reactive output and initial switch state of the node.

3. The method for distribution network fault recovery based on active control of distributed power sources according to claim 1 is characterized in that: In step S202, the feasible power set Φ of the i-th distributed generation g,i The calculation method is as follows: S221, before closing, based on the forward-backward substitution method and the collected node voltage phase angle value, construct the voltage amplitude U of the closing node a on one side of the i-th distributed generation a,ol Regarding the active power P of the i-th distributed generation g,i , reactive power Q g,i Function: U a,ol =f a (P g,i ,Q g,i ); S222, let the phase of the non-periodic component coefficient of the closed-loop voltage be 0, and derive the voltage amplitude U of the closed-loop node b on one side of the i-th distributed generation b,ol Regarding the active power P of the i-th distributed generation g,i , reactive power Q g,i Function U b,ol =f b (P g,i ,Q g,i ), and bring it into the function U a,ol =f a (P g,i ,Q g,i ), and the reactive power Q of the i-th distributed generation is obtained g,i The equation is: In the formula, A, B, and C are the coefficients of the equation; S223, for the i-th distributed generation reactive power Q g,i Solve the equation to obtain the feasible power set Φ of the i-th distributed generation g,i for:

4. The method for distribution network fault recovery based on active control of distributed power sources according to claim 1 is characterized in that: In step S205, the optimization model of the non-periodic component coefficient of the closed-loop voltage of the i-th distributed power source is: Objective function F i To minimize the absolute value of the non-periodic component of the closed-loop voltage: In the formula, is the function of the non-periodic component coefficient of the closed-loop voltage with respect to the active and reactive power of the ith distributed generation when the source load power other than the ith distributed generation power is constant; P g,i , Q g,i are the active power and reactive power of the i-th distributed generation respectively; For the objective function F i , the constraints include: Constraints 1) Constraints on the controllable range of power of the i-th distributed generation: Where P g,i,t is the active output of the ith distributed generation at time t; P g,i,max , P g,i,min are the upper and lower limits of the active power output of the i-th distributed generation; Q g,i,max , Q g,i,min are the upper and lower limits of the reactive power output of the i-th distributed generation respectively; Constraint 2) Node voltage constraint: IN i,min ≤U i ≤U i,max ; Where U i is the voltage amplitude of the node to which the i-th distributed generation is connected; U i,min , U i,max They are the lower and upper limits of node voltage allowed in the distribution network respectively; Constraint 3) Branch current constraint: I ij ≤I ij,max ; In the formula, I ij ,I ij,max The flow through branch L ij The current amplitude and the maximum current value allowed to flow; branch L ij It is the branch between the nodes to which the i-th distributed generation and its next adjacent distributed generation j are connected.

5. The method for distribution network fault recovery based on active control of distributed power sources according to claim 3 or 4, characterized in that: The non-periodic component coefficient of the closed-loop voltage of the i-th distributed generation is: Where ω is the system angular frequency; t0 is the preset closing time, I ab,i,m is the peak value of the closed-loop current flowing between the closing nodes a and b on both sides of the i-th distributed power source, θ ab,i is the initial phase angle of the closing current flowing between the closing nodes a and b on both sides of the i-th distributed power source, and: In the formula, R eq , L eq are the equivalent resistance and equivalent inductance of the additional passive ring network respectively; U a,ol (P g,i ,Q g,i ), U b,ol are the voltage amplitudes of the two closing nodes a and b before closing respectively; δ a,o1 , δ b,ol They are the initial phase angles of the voltage at the two closing nodes a and b before closing.

6. The method for distribution network fault recovery based on active control of distributed power sources according to claim 4, characterized in that: In step S205, the specific method for calculating the optimal control point of the i-th distributed power source when there is no feasible power intersection is: solving the optimization model of the non-periodic component coefficient of the closed-loop voltage of the i-th distributed power source through the particle swarm algorithm, and obtaining the distributed power source power value that minimizes the absolute value of the non-periodic component coefficient of the closed-loop voltage, which is the optimal control point of the i-th distributed power source when there is no feasible power intersection.

7. The method for distribution network fault recovery based on active control of distributed power sources according to claim 1, characterized in that: In step S3, the method of adjusting the power control reference value of each distributed power source is: If a new optimal control point with feasible power intersection or an optimal control point without feasible power intersection is calculated for a certain distributed power source, the new optimal control point with feasible power intersection or the new optimal control point without feasible power intersection is adjusted to the power control reference value of the distributed power source; otherwise, the original power control reference value of the distributed power source is maintained.

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