Multi-source cooperative fault recovery control method for electricity-gas integrated energy system

Abstract

The invention relates to the technical field of comprehensive energy systems, and particularly discloses a multi-source cooperative fault recovery control method for an electricity-gas comprehensive energy system, which aims at minimizing the sum of weighted power-loss load capacity, weighted gas-loss load capacity and network loss. A remote controllable switch of a power distribution network, opening and closing of a pipeline valve in a natural gas network and distributed energy output of an electricity-gas integrated energy system are used as control variables, corresponding constraint conditions are constructed for the power distribution network, the natural gas network and electrical coupling equipment, and a multi-source cooperative fault recovery problem is constructed. And an optimal recovery strategy is obtained by solving the multi-source collaborative fault recovery problem. According to the method, the characteristics of flexibility and coordination of the power-gas internet and the pipeline storage characteristic of the gas network are fully utilized, the power and gas load recovery state and the output of each distributed energy source are optimized in time, the system source load fluctuation can be effectively resisted, continuous supply of key loads is guaranteed, and the new energy utilization rate is increased.

Description

Technical Field

[0001] The present invention relates to the technical field of integrated energy systems, and particularly to a multi-source collaborative fault recovery control method for an electricity-gas integrated energy system. Background Technique

[0002] With the continuous growth of energy demand, new energy power generation such as wind power and photovoltaic power will gradually occupy the main position in the future power supply structure. At the same time, due to the economic and efficient characteristics of natural gas power generation, the rapidly increasing installed capacity of gas-fired turbines (GFTs) and the increasingly popular power-to-gas (P2G) technology have laid a solid foundation for building a tightly coupled electricity-gas integrated energy system (EGIES). The coupling of the distribution network and the natural gas network for overall unified planning and operation can not only utilize the fast response characteristics of gas-fired turbines to suppress and regulate the fluctuations of new energy outputs such as wind power, but also convert excess electric energy into natural gas through P2G for energy supply or storage, significantly improving the grid connection and consumption capacity of new energy.

[0003] However, with the large-scale combined application of energy such as electric energy and natural gas and the intensive construction of urban pipeline networks, against the background of frequent extreme weather events and unforeseen accidents globally, the safe operation of the power and natural gas systems is facing unprecedented severe tests, and the risk of large-scale power outages and gas outages caused by EGIES failures is increasing. Therefore, it is urgently necessary to conduct in-depth research on the fault recovery strategy of EGIES.

[0004] As an important part of the electricity-gas integrated energy system, the research on its fault recovery has been relatively mature. According to the IEEE1547-2003 standard, distributed power sources can be used to divide the power outage area into islands for load recovery. Some literature considers that in the single-source island recovery mode, the power generation resources are limited during the recovery process, and through distribution network reconfiguration or island integration, the collaborative effect of multiple types of power sources in the recovery is strengthened and the spatial penetration ability of the power sources is improved, thereby improving the system resilience and load recovery effect.

[0005] Based on this, the concept of multi-source collaborative restoration of the distribution network can be borrowed to propose a theoretical framework for multi-source collaborative fault restoration of EGIES, giving full play to the advantages of the flexible and variable network topology structure of the distribution network and the electro-gas bidirectional coupling characteristics, and realizing a collaborative restoration mechanism for multi-energy coupling and complementarity of EGIES in the spatio-temporal dimension. At present, there are few literatures on the fault restoration of integrated energy systems. And most of the existing research literatures are based on the steady-state power flow model of the natural gas network, that is, natural gas is instantaneously transmitted in the pipeline. In actual situations, different from the near-light-speed propagation of electric energy in the power system, the flow velocity of natural gas is much slower, which means that the supply-demand balance of natural gas in the gas network is not achieved instantaneously, but there is a certain time delay. Utilizing this characteristic, natural gas can be temporarily stored in the pipeline, and this dynamic storage effect is usually referred to as the "pipe storage" effect. The existing research has not deeply explored the role played by this flexible resource in fault restoration. Summary of the Invention

[0006] The present invention provides a multi-source collaborative fault restoration control method for an electro-gas integrated energy system, and the technical problem to be solved is: how to consider the dynamic storage effect of natural gas and perform fault restoration on the electro-gas integrated energy system.

[0007] To solve the above technical problems, the present invention provides a multi-source collaborative fault restoration control method for an electro-gas integrated energy system, including the steps of:

[0008] Determine the network structure of the electro-gas integrated energy system, which includes a distribution network, a natural gas network, and electrical coupling devices coupling the distribution network and the natural gas network;

[0009] Determine the specific location where a fault occurs in the electro-gas integrated energy system and the expected fault restoration time;

[0010] Based on the current network structure, the specific location where a fault occurs, and the expected fault restoration time, construct a multi-source collaborative fault restoration problem; the objective function of the multi-source collaborative fault restoration problem is to minimize the sum of the weighted power loss load, the weighted gas loss load, and the network loss, with the remotely controllable switches of the distribution network, the opening and closing of pipeline valves in the natural gas network, and the distributed energy output of the electro-gas integrated energy system as control variables. The constraint conditions of the multi-source collaborative fault restoration problem include the constraints on the distribution network, the constraints on the natural gas network considering the dynamic pipe storage effect of the gas network, and the constraints on the electrical coupling devices;

[0011] Solve the multi-source collaborative fault restoration problem to obtain the control variable settings for each time period;

[0012] Control the electro-gas integrated energy system with the control variable settings for each time period within the expected fault restoration time.

[0013] Furthermore, the distribution network includes power source nodes, electrical load nodes, and distribution lines. Each power source node and electrical load node are connected by distribution lines. The power source nodes include new energy generating units and energy storage devices; the natural gas network includes gas source nodes, gas load nodes, compressors, and natural gas pipelines. The gas source nodes, gas load nodes, and compressors are connected by natural gas pipelines; the electrical coupling device includes a gas turbine for gas-to-electricity conversion and a power-to-gas device for electricity-to-gas conversion. The gas turbine and the power-to-gas device are connected between the electrical load node and the gas load node; the distributed energy of the electricity-gas integrated energy system includes the power source node, the gas source node, the gas turbine, and the power-to-gas device.

[0014] Furthermore, the objective function is constructed as: minf = wf1 + f2, where f represents the objective function value, f1 represents the first sub-function, f2 represents the second sub-function, w represents the weight coefficient of the first sub-function f1, min represents minimization, the first sub-function f1 is the sum of the weighted power loss load and the weighted gas loss load, and the second sub-function f2 is the network loss.

[0015] Furthermore, the first sub-function f1 is equal to The second sub-function f2 is equal to T is the set of all time periods during the restoration process, L is the set of all electrical load nodes; D is the set of all gas load nodes; P i,t represents the load of electrical load node i at time period t; γ i represents the weight coefficient of P i,t ; ω i,t represents the restoration state of electrical load node i at time period t, ω i,t = 1 indicates that electrical load node i has been restored to power supply, otherwise it means that electrical load node i has not been restored; Q j,t represents the load of gas load node j at time period t; λ j represents the weight coefficient of Q j,t ; ζ j,t represents the restoration state of gas load node j at time period t, ζ j,t = 1 indicates that gas load node j has been restored to gas supply, otherwise it means that gas load node j has not been restored; represents the network loss of the distribution network at time period t; Δt represents the duration of the scheduling time period.

[0016] Furthermore, the constraints on the distribution network include the output power constraints of new energy generating units, the state constraints of electrical load nodes, the electrical network topology constraints, and the operation constraints of the distribution network;

[0017] The output power constraint of the new energy generating unit is that the output power of the new energy generating unit in each time period is greater than 0 and does not exceed the predicted output power of the new energy generating unit in that time period;

[0018] The state constraint of the electrical load node is that the restoration state of each electrical load node can only change once during the entire restoration process;

[0019] The electrical network topology constraint is that the topology of the electrical network satisfies a radial network;

[0020] The distribution network operation constraint is to make the distribution network satisfy the power flow constraint of the radial network power flow model.

[0021] Furthermore, the electrical network topology constraint is specifically:

[0022]

[0023] Among them, E is the set of lines between electrical load node p and electrical load node q. Electrical load nodes include power source nodes, electrical load nodes, and gas turbines, O pq and O qp are 0-1 integer variables representing the relationship between electrical load node p and electrical load node q. If O pq =1 and O qp =0, it means that electrical load node p is the parent node of electrical load node q. If O pq =0 and O qp =1, it means that electrical load node q is the parent node of electrical load node p; Ω(p) represents all electrical load nodes connected to electrical load node p, and L m represents the set of nodes excluding the balancing node, and m represents the power source node serving as the balancing node.

[0024] Furthermore, the constraints on the natural gas network considering the dynamic gas storage effect of the gas network include the gas source node output constraint, the gas load node state constraint, the natural gas storage constraint, the natural gas network power flow constraint, the gas load node balance constraint, the gas pressure constraint, the pipeline flow constraint, and the compressor branch constraint;

[0025] The gas source node output constraint is that the gas production of each gas source node in each time period is between the maximum and minimum values of the gas intake of the gas source node;

[0026] The gas load node state constraint is that the restoration state of each gas load node can only change once during the entire restoration process;

[0027] The natural gas storage constraint is that the natural gas storage volume after the restoration stage is the same as the initial value;

[0028] The natural gas network power flow constraint is that for natural gas pipelines without compressors, their flow rate and gas pressure satisfy:

[0029]

[0030] Among them, φc,t and φ d,t are the air pressures at the starting point and the ending point of the pipeline (c, d) at time period t, respectively, and represent the gas flow rates flowing into and out of the pipeline (c, d) at time period t. D is the pipeline diameter, C is the gas temperature, R is the molar gas constant, Z is the gas compressibility factor, ρ is the standard gas density, μ is the gas friction factor, sgn cd,t (φ c,t , φ d,t ) represents the air flow direction of the pipeline. When φ c,t > φ d,t then sgn cd,t (φ c,t , φ d,t ) = 1. When φ c,t < φ d,t then sgnc d,t (φ c,t , φ d,t ) = -1, represents the magnitude of the average flow rate of the pipeline (c, d) at time period t.

[0031] Furthermore, the constraints on the natural gas network considering the dynamic pipeline storage effect of the gas network also include gas load node balance constraints, air pressure constraints, pipeline flow constraints, and compressor branch constraints;

[0032] The gas load node balance constraint is:

[0033]

[0034] where, is the gas flow rate output by the power - to - gas device v at time period t; is the natural gas flow rate consumed by the gas turbine k at time period t, represents the gas flow rate of the gas source node k at time period t, represents the gas load of the gas load node c at time period t. I(cd) = c means that natural gas flows into the pipeline (c, d) through the gas load node c; O(cd) = d means that natural gas flows out of the pipeline (c, d) through the gas load node d;

[0035] The air pressure constraint is that the air pressure φ c,t of each gas load node at time period t is between the minimum air pressure and the maximum air pressure

[0036] The pipeline flow constraint is that the flow rate of each pipeline (c, d) at time period t does not exceed the maximum pipeline flow rate

[0037] The constraints of the compressor branch are that the flow rate and air pressure of each pipeline (c, d) in the t period satisfy:

[0038]

[0039] where τ cd is the compressor compression coefficient; u cd,t is a 0-1 variable, and u cd,t = 1 indicates that the pipeline (c, d) is working properly in the t period, otherwise u cd,t = 0.

[0040] Furthermore, the constraints on the electrical coupling equipment include gas-to-electricity constraints and electricity-to-gas constraints;

[0041] The gas-to-electricity constraint is is the active power generated by the gas turbine k in the t period, is the power generation efficiency of the gas turbine, is the natural gas flow consumed by the gas turbine k in the t period, and G is the lower calorific value of natural gas;

[0042] The electricity-to-gas constraint is is the electricity-to-gas efficiency, is the active power generated by the electricity-to-gas device v in the t period, is the amount of natural gas generated by the electricity-to-gas device v in the t period.

[0043] Furthermore, the multi-source collaborative fault recovery problem is solved to obtain the control variable settings in each period, specifically including:

[0044] The square term in the natural gas network power flow constraint is incrementally linearized using the incremental linearization method, thereby transforming the multi-source collaborative fault recovery problem into a linear programming problem;

[0045] A linear solver is used to solve the multi-source collaborative fault recovery problem.

[0046] The multi-source collaborative fault recovery control method for the electric-gas integrated energy system provided by the present invention aims to minimize the sum of the weighted power loss load, the weighted gas loss load and the network loss, and takes the remote controllable switch of the distribution network, the opening and closing of the pipeline valve in the natural gas network and the distributed energy output of the electric-gas integrated energy system as the control variables, and constructs corresponding constraints for the distribution network, the natural gas network and the electrical coupling equipment, wherein the constraints of the natural gas network take into account the dynamic storage effect of natural gas, constructs a multi-source collaborative fault recovery problem, and obtains the optimal recovery strategy by solving the multi-source collaborative fault recovery problem. The present invention makes full use of the flexible and cooperative characteristics of the electric-gas interconnected network and the pipeline storage characteristics of the gas network, optimizes the recovery status of the electric and gas loads and the output size of each distributed energy source in time, and can effectively resist the fluctuation of system source and load, ensure the continuous supply of key loads and improve the utilization rate of new energy. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 is an example diagram of the network structure of the electric-gas integrated energy system provided by an embodiment of the present invention;

[0048] Figure 2 It is a flow chart of a multi-source collaborative fault recovery control method for an electric-gas integrated energy system provided by an embodiment of the present invention;

[0049] Figure 3 This is a result diagram of the effect of gas network storage on gas turbine output under scenario 1 provided by an embodiment of the present invention;

[0050] Figure 4 This is a diagram showing the partial gas load recovery of a faulty pipeline in the gas network under scenario 1 provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0051] The following specifically illustrates the implementation mode of the present invention in conjunction with the accompanying drawings. The embodiments are provided for illustrative purposes only and cannot be understood as limiting the present invention. The accompanying drawings are provided for reference and illustration only and do not constitute a limitation on the scope of patent protection of the present invention, because many changes can be made to the present invention without departing from the spirit and scope of the present invention.

[0052] The network structure of an electric-gas integrated energy system (EGIES) includes a power distribution network, a natural gas network, and electrical coupling devices that couple the power distribution network and the natural gas network. The power distribution network includes power source nodes, electrical load nodes, and distribution lines, and each power source node and electrical load node are connected by distribution lines. The power source nodes include new energy generating units (such as wind turbine units, photovoltaic power stations, etc.) and energy storage devices (such as battery energy storage systems BESS). The electrical load nodes are classified into primary electrical loads (the highest priority, such as hospitals, emergency facilities), secondary electrical loads (the second highest priority),... ordinary electrical loads (the lowest priority) according to their importance (priority order during restoration). The natural gas network includes gas source nodes, gas load nodes, compressors, and natural gas pipelines, and the gas source nodes, gas load nodes, and compressors are connected by natural gas pipelines. Similarly, the gas load nodes are classified into primary gas loads (the highest priority), secondary gas loads (the second highest priority),... ordinary gas loads (the lowest priority) according to their importance (priority order during restoration). When there are only two levels of gas load nodes, they are classified into important gas loads (high priority) and ordinary gas loads (low priority). The electrical coupling devices include gas-fired turbines (GFT) for gas-to-electricity conversion and power-to-gas devices (P2G) for electricity-to-gas conversion. The gas-fired turbines and power-to-gas devices are connected between the electrical load nodes and the gas load nodes, generally between ordinary electrical loads and ordinary gas loads. The distributed energy sources of the electric-gas integrated energy system include power source nodes, gas source nodes, gas-fired turbines, and power-to-gas devices.

[0053] An example of the topological structure of an electric-gas integrated energy system is shown as Figure 1 follows, where the electrical load nodes are represented by E plus a serial number, the gas load nodes are represented by N plus a serial number, the gas source nodes are represented by W plus a serial number, and the new energy power source nodes are represented by WT plus a serial number. When the EGIES fails due to extreme disasters, the faulty components in the power grid and the gas network are indicated by the faulty power grid components and the faulty gas network components respectively in Figure 1 respectively.

[0054] After the EGIES fails due to extreme disasters, the primary goal of system restoration is to ensure the energy supply of important loads and avoid significant economic losses. This paper assumes that the communication automation equipment remains normal during the fault, and the dispatching center can control the opening and closing of remote controllable switches in the power system, pipeline valves in the natural gas network, and the output of distributed energy sources, so that the power outage and gas outage areas after the fault can quickly resume supply using local resources. To effectively enhance the collaborative ability between distributed power sources, this paper considers constructing a multi-source collaborative restoration model for EGIES by utilizing the flexible and variable characteristics of the power distribution network topology and the dynamic gas storage effect of the gas network.

[0055] Specifically, the multi-source collaborative fault restoration control method for the electric-gas integrated energy system provided by the embodiments of the present invention, as shown in the flowchart of Figure 2 follows, includes the steps:

[0056] Determine the network structure of the integrated electricity-gas energy system, which includes a distribution network, a natural gas network, and electrical coupling devices that couple the distribution network and the natural gas network;

[0057] Determine the specific location of the fault and the expected fault recovery time in the integrated electricity-gas energy system;

[0058] Construct a multi-source collaborative fault recovery problem based on the current network structure, the specific location of the fault, and the expected fault recovery time; specifically, the objective function of the multi-source collaborative fault recovery problem is to minimize the sum of the weighted power loss load, the weighted gas loss load, and the network loss, with the remote controllable switches of the distribution network, the opening and closing of pipeline valves in the natural gas network, and the distributed energy output of the integrated electricity-gas energy system as control variables. The constraint conditions of the multi-source collaborative fault recovery problem include the constraints on the distribution network, the constraints on the natural gas network considering the dynamic gas storage effect, and the constraints on the electrical coupling devices;

[0059] Solve the multi-source collaborative fault recovery problem to obtain the control variable settings for each time period;

[0060] Control the integrated electricity-gas energy system with the control variable settings for each time period within the expected fault recovery time.

[0061] 1. Objective Function

[0062] During system faults, in order to supply energy to important loads for as long as possible and reduce network losses caused by changes in the network structure during the recovery process. The optimization objective of this fault recovery model is divided into two parts. The first part is to minimize the weighted power loss load and the weighted gas loss load, and the second part is to minimize the sum of network losses for each time period, which are expressed as follows:

[0063]

[0064] Among them, f1 represents the first sub-function, f2 represents the second sub-function, min represents minimization, T is the set of all time periods during the recovery process, L is the set of all electrical load nodes; D is the set of all gas load nodes; P i,t represents the load of electrical load node i at time t; γ i represents the weight coefficient of P i,t ; ω i,t represents the recovery status of electrical load node i at time t, ω i,t =1 indicates that electrical load node i has been restored to power, otherwise it means that electrical load node i has not been restored; Q j,t represents the load of gas load node j at time t; λ j represents the weight coefficient of Q j,tThe weight coefficient; ζ j,t Indicates the restoration status of the gas load node j at time t, ζ j,t ζ = 1 indicates that the gas supply to the gas load node j has been restored, otherwise it means that the gas load node j has not been restored; Represents the network loss of the distribution network at time t; Δt represents the duration of the scheduling period.

[0065] According to the primary and secondary relationships of the objective function, the objective functions of the two parts are combined through the weight coefficient. The selection of different weight coefficients determines different restoration schemes. The weight value of the first part should not be too small. According to experience, the weight value w of the first part in this paper is taken as 10, and its specific objective function is shown in Equation (3):

[0066] minf = wf1 + f2 (3)

[0067] w represents the weight coefficient of the first sub-function f1, and f represents the value of the objective function.

[0068] 2. Distribution network operation model

[0069] The constraints on the distribution network include the output constraints of new energy generating units, the state constraints of electrical load nodes, the electrical network topology constraints, and the distribution network operation constraints.

[0070] (1) Output constraints of new energy generating units

[0071] In this paper, the main power source of the distribution network is high-penetration new energy generation. The output scheduling of new energy at each moment is restricted by the predicted available power generation, that is, the output power of the new energy generating unit at each time period is greater than 0 and does not exceed the predicted output of the new energy generating unit at that time period. It is expressed by the formula:

[0072]

[0073] Among them, Represents the actual output power of the new energy generating unit at the electrical load node i at time t, Represents the predicted output of the new energy generating unit at time t.

[0074] (2) State constraints of electrical load nodes

[0075] To ensure the power supply reliability and the power consumption quality of users, this paper stipulates that the restoration status of each electrical load node can only change once during the restoration process. The constraints are as follows:

[0076]

[0077] (3) Electrical network topology constraints

[0078] During the fault recovery process, this paper selects to connect the distribution network into a large island through network reconfiguration of the distribution network. The topological structure of the distribution network must satisfy a radial network, which can be represented by the constraint conditions related to graph theory:

[0079]

[0080] Among them, E is the set of lines between electrical load node p and electrical load node q. Electrical load nodes include power source nodes, electrical load nodes, and gas turbines, O pq and O qp are 0-1 integer variables representing the relationship between electrical load node p and electrical load node q. If O pq =1 and O qp =0, it means that electrical load node p is the parent node of electrical load node q. If O pq =0 and O qp =1, it means that electrical load node q is the parent node of electrical load node p; Ω(p) represents all electrical load nodes connected to electrical load node p, L m represents the set of nodes excluding the balancing node, and m represents the power source node as the balancing node.

[0081] Equation (6) describes the correlation between the line operating state and the nodes at both ends of the line. For non-balancing nodes, the number of its parent nodes is strictly limited to a single node. As the system reference point, the balancing node has zero parent nodes.

[0082] (4) Distribution network operation constraints

[0083] This paper adopts the DistFlow power flow model that satisfies the radial network of the distribution network and introduces the line switch state variable to obtain the following power flow constraints:

[0084]

[0085] l pq,t u p,t =(P pq,t ) 2 +(Q pq,t ) 2 (9)

[0086] Among them, P pq,t and Q pq,t are the active power and reactive power flowing out from electrical load node p and flowing to electrical load node q on line (p,q) at time t, respectively; P qh,t and Q qh,t are the active power and reactive power flowing out from electrical load node q and flowing to electrical load node h on line (q,h) at time t, respectively; and The active power and reactive power injected by distributed power sources (new energy units, gas turbines, energy storage, etc.) at the electrical load node q during the t period; r pq , x pq The resistance and reactance on the line (p, q) respectively; l pq,t Is the square of the amplitude of the current on the line (p, q) during the t period; P q,t And Q q,t The load amounts of the electrical load nodes p and q during the t period respectively, ω q,t , ω q,t Represent the restoration states of the electrical load nodes p and q during the t period (refer to ω i,t ); α pq,t Is a 0-1 integer variable representing the state of the line (p, q) during the t period, α pq,t = 1 indicates that the line is closed, otherwise α pq,t = 0; M is a constant of infinity; m pq Is the evaluation parameter of the line (p, q). When the line (p, q) is normally connected, the value of m pq Is 0, otherwise it is infinity; u p,t , u q,t Are the squared values of the voltage amplitudes of the electrical load nodes p and q during the t period respectively.

[0087] The line capacity, voltage, and current in the distribution network part need to satisfy the following constraints:

[0088]

[0089]

[0090] Among them, And Are the upper and lower limits of the voltage of the electrical load node p, taking 0.95 times and 1.05 times of the standard voltage respectively; Is the maximum current allowed to pass through the line (p, q).

[0091] 3. Natural gas network operation model

[0092] This paper adopts the quasi-steady state power flow equation of natural gas considering dynamic gas storage. The operation constraints of the natural gas system mainly include the gas source node output constraint, the gas load node state constraint, the natural gas storage constraint, and the natural gas network power flow constraint.

[0093] (1) Gas source node output constraint

[0094] The gas production volume Of the gas source node j during the t period needs to satisfy:

[0095]

[0096] Among them, and are the maximum and minimum values of the gas intake at the gas source node j, respectively.

[0097] (2) Gas load node status constraint

[0098] Similar to the electric load node status constraint, the restoration status of each gas load node can only change once during the entire restoration process, which is expressed by the formula:

[0099]

[0100] (3) Natural gas pipeline storage constraint

[0101] Different from the rapid transmission of electric energy, the flow velocity of natural gas in pipelines is relatively slow, usually at the level of 10 meters per second, with obvious inertia and time-delay characteristics. This characteristic leads to a difference in the flow rates at the inlet and outlet of the pipeline, and the difference is stored in the pipeline in the form of pipeline storage, making the natural gas pipeline equivalent to an energy storage unit in the power system. For the pipeline storage volume in the pipeline, the following formula is used to describe it:

[0102]

[0103] Among them, the subscripts c and d are used to represent the gas load nodes at both ends of a pipeline (flowing from gas load node c to d), and Q cd,t is the volume of gas stored in the pipeline (c, d) at time t, φ c,t and φ d,t are the gas pressures at the starting point and the ending point of the pipeline (c, d) at time t, respectively. and are the gas flow rates flowing into and out of the pipeline (c, d) at time t, D is the pipeline diameter, C is the gas temperature, R is the molar gas constant, Z is the gas compressibility factor, and ρ is the standard gas density.

[0104] It should be clear here that Equation (16) and Equation (17) describe the gas network storage relationship from different perspectives. Equation (16) describes the relationship between the storage gas volume at a certain moment and the gas pressures at both ends of the pipeline; Equation (17) depicts the storage capacity of the gas network pipeline from the time dimension.

[0105] Since the adjustment measures of the natural gas system are quite limited, in order to rationally utilize the dynamic storage of the gas network and maintain the gas pressure stability, it is considered that the pipeline storage volume after the restoration stage is the same as the initial value:

[0106]

[0107] (4) Natural gas network power flow constraint

[0108] For the natural gas pipeline (c, d) without a compressor, the following constraints exist for the flow rate and gas pressure:

[0109]

[0110] Among them, sgn cd,t (φ c,t , φ d,t ) is the gas flow direction of the pipeline (c, d), is the average flow rate of the pipeline (c, d) at time t, and μ is the gas friction factor.

[0111] (5) Gas load node balance constraint

[0112] For the natural gas load node equation containing the power-to-gas equipment and gas turbine:

[0113]

[0114] Among them, is the gas flow rate output by the power-to-gas equipment v at time t; is the natural gas flow rate consumed by the gas turbine k at time t, is the gas flow rate of the gas source node k at time t, is the gas load of the gas load node c at time t. I(cd) = c means that natural gas flows into the pipeline (c, d) through the gas load node c; O(cd) = d means that natural gas flows out of the pipeline (c, d) through the gas load node d.

[0115] (6) Gas pressure constraint

[0116] During the recovery process, the gas pressure φ of each node in the natural gas system at time t c,t all need to meet the corresponding gas pressure range:

[0117]

[0118] Among them, and are the maximum and minimum values of the gas pressure of the gas load node c respectively.

[0119] (7) Pipeline flow constraint

[0120] When natural gas is transmitted in the pipeline, its flow rate at time t should also meet the corresponding flow constraint:

[0121]

[0122] Among them, is the maximum value of the pipeline flow rate.

[0123] (8) Compressor branch constraint

[0124] For natural gas pipelines (c, d) containing compressors, the following constraints apply to the flow rate and gas pressure:

[0125]

[0126] Among them, τ cd is the compression coefficient of the compressor; u cd,t is a binary variable. When u cd,t = 1, it means that the pipeline (c, d) is operating normally; otherwise, u cd,t = 0.

[0127] 4. Coupling device constraints

[0128] EGIES realizes two-way coupling through gas turbines and power-to-gas devices. The constraints on electrical coupling devices include power-to-electricity constraints and power-to-gas constraints.

[0129] Gas generators consume natural gas to produce heat and convert heat energy into electrical energy. The corresponding power-to-electricity constraint is:

[0130]

[0131] Among them, is the active power output by gas turbine k at time t, is the power generation efficiency of gas turbine k, and G is the lower calorific value of natural gas.

[0132] Power-to-gas devices consume electrical energy to electrolyze water and synthesize methane. The corresponding power-to-gas constraint is:

[0133]

[0134] Among them, is the power-to-gas efficiency, is the active power output by power-to-gas device v at time t, is the amount of natural gas generated by power-to-gas device v at time t.

[0135] For the non-linear equation (19) in the flow rate constraint of the gas distribution network pipeline, there are square terms on both sides of the equal sign, which increases the difficulty of solving using a solver. Regarding the square of the average pipeline flow rate and the square of the gas pressure in constraint (19), this paper adopts the incremental linearization method to linearly approximate each square term. The entire model is transformed into a linear programming problem, and then commercial solvers such as CPLEX can be used for solving. Taking the non-linear equation f(x) = x 2 defined in a certain interval as an example, the specific process of the incremental linearization method is as follows:

[0136] (1) Determine the appropriate number of linearization segments c-1 to ensure a balance between linearization accuracy and solution computational complexity.

[0137] (2) Calculate the value of each segment point within the range of x.

[0138] (3) Obtain the value of f(x) corresponding to each segment point.

[0139] (4) f(x) = x 2 It can be approximated by the following formula:

[0140]

[0141] Among them, ψ is the segment point set, δ i is a continuous variable with a value range of 0-1, indicating the position on the i-th segment interval, θ i It is a 0-1 variable used to ensure the continuity of filling each interval during the piecewise linearization process.

[0142] In summary, the multi-source collaborative fault recovery control method for the electric-gas integrated energy system provided by the embodiment of the present invention aims to minimize the sum of the weighted power loss load, the weighted gas loss load and the network loss, and takes the remote controllable switch of the distribution network, the opening and closing of the pipeline valve in the natural gas network and the distributed energy output of the electric-gas integrated energy system as the control variables, and constructs corresponding constraints for the distribution network, the natural gas network and the electrical coupling equipment, wherein the constraints of the natural gas network take into account the dynamic storage effect of natural gas, constructs a multi-source collaborative fault recovery problem, and obtains the optimal recovery strategy by solving the multi-source collaborative fault recovery problem. The present invention makes full use of the flexible and cooperative characteristics of the electric-gas interconnected network and the pipeline storage characteristics of the gas network, optimizes the recovery status of the electric and gas loads and the output size of each distributed energy source in time, and can effectively resist the fluctuation of system source and load, ensure the continuous supply of key loads and improve the utilization rate of new energy.

[0143] In order to prove the effectiveness and superiority of the fault recovery method proposed in this paper, this paper uses the regional EGIES formed by coupling the improved IEEE13-node standard distribution system and the 7-node natural gas network as a research example for simulation analysis. In the figure, the thin solid line represents the distribution network feeder branch operating in normal mode, the dotted line represents the tie line branch, which is disconnected in normal operation, and the thick solid line represents the natural gas network branch. Two distributed wind power generation devices and a storage power station are configured in the distribution system, and the natural gas network is configured with two gas sources and two compressors. The distribution network and the natural gas network are bidirectionally coupled through a gas turbine and an electric-to-gas device. The grid structure of the test system is shown in the attached figure. Figure 1 shown.

[0144] By comparing various design scenarios, the advantages of the electric-gas interconnected system considering the dynamic gas network storage effect in improving the load restoration effect are analyzed. The scenario design is as follows:

[0145] Scenario 1, which is the restoration strategy used in this paper. When faults occur in some lines or pipelines of the power grid and gas network, coordinated restoration considering the electric-gas bidirectional coupling and the gas network storage effect is carried out.

[0146] Scenario 2, only considering the electric-gas interconnected system bidirectional coupling and multi-source coordinated restoration, without considering the gas network storage.

[0147] Scenario 3, without considering the electric-gas coupling, the distribution network and the natural gas network independently carry out fault restoration.

[0148] Scenario 4, without considering multi-source coordination, the distribution network part is only divided into single islands by single source for restoration.

[0149] The objective function values under different scenarios are shown in Table 1, and the restoration results of different scenarios are shown in Table 2. The influence results of the gas network storage on the gas turbine output under Scenario 1 are as Figure 3 shown, and the gas load restoration of the faulty pipeline part of the gas network under Scenario 1 is as Figure 4 shown.

[0150] Table 1 Objective function values under different scenarios

[0151]

[0152] Table 2 Comparison of restoration results of different scenarios

[0153]

[0154] From Table 1, Table 2, Figure 3 , Figure 4 it can be seen that the system load restoration value of the method proposed in this paper is the highest. Scenario 1 considers the multi-source coordinated restoration of the electric-gas system interconnection. The natural gas in the normal pipeline part can be coupled with the distribution network through GFT to provide more abundant electric energy support for the distribution network. Some electric energy in the distribution network can also be converted into natural gas through P2G to restore the natural gas load of the downstream faulty part. And Scenario 1 considers the dynamic cache of the gas network, making the system load restoration situation less affected by the fluctuation of new energy output. Most of the important loads of the distribution network and the gas distribution network have maintained long-term supply. Therefore, the overall weighted restoration volume of Scenario 1 is the largest, which is 78560.61.

[0155] In Scenario 2, only considering the energy storage devices in the distribution network can suppress the fluctuations of wind power output to a small extent. The load and gas intake volume of the natural gas system can only achieve real-time power balance, and it is impossible to optimize the system restoration strategy in the time dimension by using the buffering effect of the gas network, resulting in a more likely load shedding phenomenon when the wind power fluctuates. Therefore, the important load restoration rate in this scenario is lower than that in Scenario 1, and the objective function value is also slightly lower, about 92.62% of the objective function value in Scenario 1. In Scenario 3, due to the lack of consideration of the electricity-gas coupling, there are double limitations: the natural gas in the normal network part cannot be converted into electric energy, and the downstream gas load isolated due to pipeline failures cannot be restored. So the gas load restoration volume is the lowest, and the load restoration value is about 74.64% of the objective function in Scenario 1. Moreover, due to the lack of power-to-gas equipment to consume the excess electric energy, the utilization rate of wind power is also the lowest. In Scenario 4, due to the inability to achieve the coordination of multiple sources in the spatial dimension, the system's ability to resist source-load fluctuations is limited, and the overall restoration value is 14% lower than that of the method in this paper.

[0156] Through comprehensive comparison, it shows the effectiveness of the method proposed in the present invention in prolonging the critical load restoration time, resisting the fluctuations of new energy output, and enhancing the system resilience.

[0157] According to the experimental results shown in Table 1, Table 2, Figure 3 and Figure 4 it can be seen that the effects and advantages of the present invention are as follows:

[0158] 1) Considering the dynamic pipe storage characteristics of the gas network, it enriches and deepens the research on the fault restoration of the integrated electricity-gas energy system;

[0159] 2) Utilizing this flexible resource of the gas network storage, the restoration strategy can be flexibly adjusted in the time dimension, ensuring the long-term supply of critical loads, maximizing the weighted load restoration volume, effectively resisting the impact of source-load fluctuations on the load restoration effect during the fault process, and enhancing the system resilience;

[0160] 3) Utilizing the characteristics of distribution network reconfiguration and multi-source collaborative complementarity of electricity-gas coupling, strengthening the coupling and connection of multiple sources in space and time, improving the reliability and flexibility of energy supply, and enhancing the utilization rate of new energy and the load restoration effect.

[0161] The above embodiments are the preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement methods and are all included in the protection scope of the present invention.

Claims

1. A multi-source collaborative fault recovery control method for an electric-gas integrated energy system, characterized in that: Includes steps: Determining a network structure of an electric-gas integrated energy system, the network structure comprising a power distribution network, a natural gas network, and an electrical coupling device coupling the power distribution network and the natural gas network; Determine the specific location of the fault in the electric-gas integrated energy system and the expected fault recovery time; A multi-source collaborative fault recovery problem is constructed based on the current network structure, the specific location of the fault and the expected fault recovery time; the objective function of the multi-source collaborative fault recovery problem is to minimize the sum of the weighted power loss load, the weighted gas loss load and the network loss, with the remote controllable switches of the distribution network, the opening and closing of the pipeline valves in the natural gas network and the distributed energy output of the electric-gas integrated energy system as the control variables. The constraints of the multi-source collaborative fault recovery problem include constraints on the distribution network, constraints on the natural gas network considering the dynamic pipe storage effect of the gas network and constraints on the electrical coupling equipment; Solve the multi-source collaborative fault recovery problem and obtain the control variable settings in each time period; The electric-gas integrated energy system is controlled by setting control variables for each time period within the expected fault recovery time.

2. The multi-source coordinated fault recovery control method for an electric-gas integrated energy system according to claim 1 is characterized in that: The distribution network includes power supply nodes, electric load nodes and distribution lines. Each power supply node and electric load node is connected through a distribution line. The power supply node includes a new energy generator set and an energy storage device. The natural gas network includes a gas source node, a gas load node, a compressor, and a natural gas pipeline. The gas source node, the gas load node and the compressor are connected through a natural gas pipeline. The electrical coupling device includes a gas turbine for gas-to-electricity and an electric-to-gas device for electric-to-gas. The gas turbine and the electric-to-gas device are connected between the electric load node and the gas load node. The distributed energy of the electric-gas integrated energy system includes the power supply node, the gas source node, the gas turbine, and the electric-to-gas device.

3. The multi-source coordinated fault recovery control method for an electric-gas integrated energy system according to claim 2 is characterized in that: The objective function is constructed as: minf=wf1+f2, wherein f represents the objective function value, f1 represents the first sub-function, f2 represents the second sub-function, w represents the weight coefficient of the first sub-function f1, min represents minimization, the first sub-function f1 is the sum of the weighted power loss load and the weighted gas loss load, and the second sub-function f2 is the network loss.

4. The multi-source coordinated fault recovery control method for an electric-gas integrated energy system according to claim 3 is characterized in that: The first subfunction f1 is equal to The second subfunction f2 is equal to T is the set of all time periods in the recovery process, L is the set of all electric load nodes; D is the set of all gas load nodes; P i,t represents the load of the electric load node i in period t; γ i Indicates P i,t The weight coefficient of i,t represents the recovery state of the electric load node i in period t, ω i,t =1 indicates that the power supply of the electric load node i has been restored, otherwise it means that the power supply of the electric load node i has not been restored; Q j,t represents the load of gas load node j in period t; j Indicates Q j,t The weight coefficient of j,t represents the recovery state of gas load node j in period t, ζ j,t =1 indicates that the gas supply to gas load node j has been restored, otherwise it indicates that the gas supply to gas load node j has not been restored; Represents the network loss of the distribution network in period t; Δt represents the length of the scheduling period.

5. The multi-source coordinated fault recovery control method for an electric-gas integrated energy system according to claim 4 is characterized in that: The constraints on the distribution network include the output constraints of new energy generators, the state constraints of electric load nodes, the topology constraints of the electrical network and the operation constraints of the distribution network; The output constraint of the new energy generator set is that the output power of the new energy generator set in each period is greater than 0 and does not exceed the predicted output of the new energy generator set in the period; The electric load node state constraint is that the recovery state of each electric load node can only change once during the entire recovery process; The electrical network topology constraint is that the topology of the electrical network satisfies a radial network; The distribution network operation constraint is to make the distribution network meet the power flow constraint of the radial network power flow model.

6. The multi-source coordinated fault recovery control method for an electric-gas integrated energy system according to claim 5 is characterized in that: The electrical network topology constraints are specifically: Where E is the line set between the electric load node p and the electric load node q. The electric load node includes the power supply node, the electric load node and the gas turbine. pq and O qp is a 0-1 integer variable representing the relationship between the load node p and the load node q. pq =1 and O qp =0 means that the electric load node p is the parent node of the electric load node q. pq =0 and O qp =1 indicates that the electric load node q is the parent node of the electric load node p; Ω(p) indicates all the electric load nodes connected to the electric load node p, L m represents a node set that does not include a balancing node, and m represents a power node that serves as a balancing node.

7. The multi-source coordinated fault recovery control method for an electric-gas integrated energy system according to claim 6 is characterized in that: The constraints on the natural gas network considering the dynamic pipeline storage effect of the gas network include gas source node output constraints, gas load node state constraints, natural gas pipeline storage constraints, natural gas network flow constraints, gas load node balance constraints, gas pressure constraints, pipeline flow constraints and compressor branch constraints; The gas source node output constraint is that the gas production of each gas source node in each time period is between the maximum and minimum values ​​of the gas intake of the gas source node; The gas load node state constraint is that the recovery state of each gas load node can only change once during the entire recovery process; The natural gas pipeline inventory constraint is that the natural gas pipeline inventory after the recovery phase is the same as the initial value; The natural gas network flow constraint is that for a natural gas pipeline without a compressor, its flow and pressure satisfy: Among them, φ c,t and φ d,t are the air pressure at the start and end of the pipeline (c, d) during period t, and represents the gas flow in and out of the pipeline (c, d) during period t, D is the pipeline diameter, C is the gas temperature, R is the molar gas constant, Z is the gas compressibility coefficient, ρ is the standard gas density, μ is the gas friction factor, sgn cd,t (φ c,t ,φ d,t ) represents the airflow direction of the pipeline. When φ c,t >φ d,t Then sgn cd,t (φ c,t ,φ d,t )=1, when φ c,t <φ d,t Then sgn cd,t (φ c,t ,φ d,t )=﹣1, Represents the average flow rate of pipeline (c, d) during period t.

8. The multi-source coordinated fault recovery control method for an electric-gas integrated energy system according to claim 7 is characterized in that: The constraints on the natural gas grid considering the dynamic pipeline storage effect of the gas grid also include gas load node balance constraints, gas pressure constraints, pipeline flow constraints and compressor branch constraints; The gas load node balance constraint is: in, is the gas flow rate produced by the power-to-gas device v during period t; is the natural gas flow consumed by gas turbine k during period t, represents the gas flow rate of the gas source node k during period t, represents the gas load of gas load node c in period t, I(cd)=c means that natural gas flows into pipeline (c, d) through gas load node c; O(cd)=d means that natural gas flows out of pipeline (c, d) through gas load node d; The air pressure constraint is that the air pressure of each air load node in period t is within the minimum air pressure to the maximum air pressure; The pipeline flow constraint is that the flow of each pipeline in time period t does not exceed the maximum pipeline flow; The compressor branch constraint is that the flow rate and pressure of each pipeline in period t satisfy: Among them, τ cd is the compression coefficient of the compressor; u cd,t is a 0-1 variable, u cd,t =1 means that the pipeline (c, d) works normally during period t, otherwise u cd,t =0.

9. The multi-source coordinated fault recovery control method for an electric-gas integrated energy system according to claim 8 is characterized in that: Constraints on electrical coupling equipment include gas-to-electricity constraints and electric-to-gas constraints; The gas-to-electricity constraint is is the active power generated by gas turbine k during period t, is the gas turbine power generation efficiency, is the natural gas flow consumed by gas turbine k during period t, G is the lower calorific value of natural gas; The power-to-gas constraint is is the power-to-gas efficiency, is the active power generated by the power-to-gas device v during period t, is the amount of natural gas generated by the power-to-gas device v during period t.

10. The multi-source coordinated fault recovery control method of the electric-gas integrated energy system according to claim 9 is characterized in that: Solve the multi-source collaborative fault recovery problem and obtain the control variable settings in each period, including: The square term in the natural gas grid power flow constraint An incremental linearization method is used to perform incremental linearization, thereby converting the multi-source collaborative fault recovery problem into a linear programming problem; A linear solver is used to solve the multi-source collaborative fault recovery problem.

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