Reactive voltage optimization control method for electricity-gas interconnection integrated energy system

Abstract

The invention discloses a reactive voltage optimization control method for an electricity-gas interconnection integrated energy system, belongs to the technical field of power system optimization control, and is used for solving the technical problem that the reactive power optimization method in the prior art neglects the reactive power output characteristics of a new energy unit and a coupling element. According to the invention, after the reactive power output of the new energy unit and the coupling element gas turbine is considered in the electric-gas interconnection integrated energy system IEGS, the system voltage deviation is effectively reduced; it is proved that combined dispatching of the gas turbine and the P2G can improve the absorption capacity of the wind turbine generator of the system, and the economic cost is reduced. According to the method, the reactive voltage optimization model of the electrical-pneumatic interconnected integrated energy system is converted into the mixed integer second-order cone programming model by using the second-order cone relaxation method, so that the solving precision and rate are ensured.

Description

Technical Field

[0001] The present invention belongs to the technical field of power system optimization control, and in particular relates to a reactive voltage optimization control method for an electric-gas interconnected integrated energy system taking into account the reactive support capabilities of new energy units and coupling elements. Background Art

[0002] In recent years, due to the depletion of fossil fuels and the environmental problems they bring, renewable energy sources such as wind power and photovoltaics are gradually becoming the main source of energy supply in my country. [1-2] However, due to the randomness and volatility of wind power and photovoltaic power, and the current supporting smart grid and energy storage technology are not yet mature, the problem of wind and solar power abandonment is serious. In recent years, how to improve the new energy consumption capacity has become a research hotspot. [3-4] On the other hand, with the continuous advancement of energy internet strategy and green energy transformation [5] The Integrated Electricity-Gas System (IEGS), which can realize the complementarity of multiple energy sources, has developed rapidly. [6] .

[0003] At present, the research on IEGS focuses on economic dispatch, expansion planning, etc. For example, the multi-energy flow calculation model built for the electric-gas IES system can effectively realize the coordinated operation between different energy sources, thereby optimizing the performance and efficiency of the overall system. [7] ; In order to deal with the contradiction between the high operating cost of P2G and wind power consumption, a multi-objective fuzzy weighted method can be used to coordinate the comprehensive cost of the system and the level of wind power consumption. [8] ; The IEGS economic dispatch model with P2G carbon trading incentive mechanism proves that P2G has a positive effect on wind curtailment and low-carbon electricity [9] However, the above-mentioned DC power flow model, which focuses on economy, ignores the voltage and current constraints in the power grid and the impact of the reactive output of new energy units on the voltage of the power system. As the proportion of new energy in the power system continues to increase, its uncertainty and the two-way flow of power flow will bring greater challenges and complexity to the reactive voltage optimization of the power system.

[0004] At present, the research on reactive power optimization of power systems in single or multiple energy networks mainly focuses on reactive power compensation technology, reactive power supply characteristics, and reactive load demand response. [10-12] For example, by adjusting the tap position of the transformer and the reactive power compensation equipment, static and dynamic reactive power compensation can be performed on the urban power grid with multiple voltage levels.

[13] ; Based on the upper and lower limits of active and reactive output of distributed generation, OLTC and shunt capacitors are used to achieve dynamic reactive power optimization of distribution network.

[14] However, the above studies mainly focus on additional reactive power compensation and reactive power output of new energy. In fact, as a bridge connecting the power system and the natural gas system, the gas turbine itself has a certain reactive power compensation capability.

[15] However, the current reactive power optimization methods all ignore the reactive power output characteristics of new energy units and coupling elements.

[0005] Therefore, a new technical solution is urgently needed in the prior art to solve this problem. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide a reactive voltage optimization control method for an electric-gas interconnected integrated energy system to solve the technical problem that the reactive power optimization methods in the prior art all ignore the reactive output characteristics of new energy units and coupling elements.

[0007] A reactive voltage optimization control method for an electric-gas interconnected integrated energy system comprises the following steps, which are performed in sequence:

[0008] Step 1: According to the composition and structure of the electricity-gas interconnection system, establish the IEGS model of the electricity-gas interconnection integrated energy system;

[0009] Step 2: Taking into account the constraints of the power grid, gas grid and coupling elements, taking the system comprehensive cost and voltage deviation as the optimization target, the IEGS reactive power and voltage optimization model of the electricity-gas interconnected integrated energy system is established;

[0010] Step 3: Use the second-order cone relaxation method to transform the IEGS reactive power and voltage optimization model of the electricity-gas interconnected integrated energy system into a mixed integer convex optimization problem for solution, and obtain the operating results under the optimal coupling condition, thereby realizing the reactive power and voltage optimization control of the electricity-gas interconnected integrated energy system.

[0011] The electricity-gas interconnected comprehensive energy system model is an electricity-gas comprehensive energy system model that includes power-to-gas P2G, gas turbines, wind power, photovoltaics and compressors. Establishing the electricity-gas interconnected comprehensive energy system model includes power system modeling, natural gas system modeling and coupling element modeling.

[0012] The power system is modeled as follows:

[0013] a. The power grid used in the electricity-gas interconnected integrated energy system is the distribution network, and the node active and reactive equations are established as follows:

[0014]

[0015] Where P j,t and Q j,t are the active injection power and reactive injection power of node j at time t respectively; P jp,t and Qjp,t are the active power and reactive power flowing through branch jp at time t; P ij,t and Q ij,t are the active power and reactive power flowing from node i to node j at time t; I ij,t is the current flowing through branch ij at time t; r ij represents the resistance of branch ij; x ij represents the reactance of branch ij; u i,t 、u j,t are the amplitude of the voltage at node i and node j at time t respectively;

[0016] b. To ensure the safe operation of the power system, the following constraints are imposed:

[0017] |I ij,t |≤I ij,max (2);

[0018] u j,min ≤u j,t ≤u j,max (3);

[0019] In the formula, I ij,max is the maximum value of the current flowing through branch ij; u j,min and u j,max are the minimum and maximum values ​​of the voltage at node j.

[0020] The constraints of the power system are as follows:

[0021] 1) The power balance constraints are as follows:

[0022]

[0023] Where: P e,j,t , P PV,j,t , P PW,j,t and P GT,j,t are the active power injected into node j by the upper grid, photovoltaic unit, wind turbine unit and gas turbine at time t; P L,j,t and P P2G,j,t are the active power consumed by the j-node load and the P2G equipment at time t; Q e,j,t , Q PV,j,t , Q PW,j,t and Q GT,j,t are the reactive power injected into node j by the upper grid, photovoltaic unit, wind turbine unit and gas turbine at time t; Q L,j,t and Q P2G,j,t are the reactive power consumed by the j-node load and the power-to-gas P2G equipment at time t, respectively;

[0024] 2) The active and reactive output constraints of photovoltaic units are as follows:

[0025]

[0026] Where: P PV,j,t , Q PV,j,t are the active and reactive power injected into node j by the PV system at time t; P PV,t,MPPT is the active power of the photovoltaic unit working at the MPPT maximum power point tracking point at time t; S PV is the installed capacity of the photovoltaic unit;

[0027] 3) The active-reactive output constraints of wind turbines are as follows:

[0028]

[0029] Where: P PW,j,t and Q PW,j,t P is the active power and reactive power injected into node j by the wind turbine at time t; PW,f,t and Q PW,f,t is the predicted active power and reactive power of the wind turbine at time t;

[0030] 4) The power purchase constraints are as follows:

[0031] 0≤P e,j,t ≤P e,j,max (19);

[0032] Where P e,j,t P is the power purchased by node j from the upper grid at time t; e,j,max The maximum value of the purchased power.

[0033] The natural gas system is modeled as follows:

[0034] a. According to the Weymouth equation, in the dispatching period t, the natural gas pipeline flow equation is expressed as:

[0035]

[0036] Where W mn,t is the gas flow rate of pipeline mn at time t; S mn is a directional parameter. If the pressure at node m is greater than that at node n, it is 1, otherwise it is -1. mn is the pipeline equation parameter, which is related to the pipeline temperature, length, diameter and friction;

[0037] b. The energy consumption of the compressor and the pipeline inlet flow rate are expressed as:

[0038]

[0039] Wmn,t =W kn,t +W cp,t (7);

[0040] Where W cp,t , W kn,t and W mn,t are the energy consumption of the compressor, the natural gas flow rate at the inlet and the natural gas flow rate at the pipeline at time t respectively; m,t and π k,t are the air pressures at node m and node k at time t; k cp is the compression ratio; Z H is the intrinsic constant of natural gas; T k,t is the natural gas temperature at time t.

[0041] The constraints of the natural gas system are as follows:

[0042] 1) Natural gas power balance constraints are as follows:

[0043]

[0044] Where: W g,m,t is the natural gas supply at node m at time t; W load,m,t is the gas load at node m at time t; W GT,m,t is the natural gas consumption of the gas turbine at node m at time t; W mn,t is the gas flow from node m to node n; set R is the set of natural gas nodes, and set B is the set of natural gas pipelines;

[0045] 2) The pipeline flow constraints are as follows:

[0046] W mn,min ≤W mn,t ≤W mn,max (twenty one);

[0047] Where: W mn,t is the gas flow rate of pipeline mn at time t; W mn,min and W mn,max are the minimum and maximum values ​​of the gas flow in pipeline mn respectively;

[0048] 3) The node pressure constraints are as follows:

[0049]

[0050] Where: π n,min and π m,min are the minimum gas pressures at n nodes and m nodes respectively; π n,max and π m,max is the maximum value of the gas pressure at the n-node and the m-node;

[0051] 4) The gas source output constraints are as follows:

[0052] W g,m,min ≤W g,m,t ≤W g,m,max (twenty three);

[0053] Where: W g,m,t W is the gas supply of the gas source at time t; g,m,max The maximum value of the gas supply from the gas source; W g,m,min It is the minimum value of gas supply from the gas source;

[0054] 5) Compressor constraints are as follows:

[0055]

[0056] Where: k cp,min and k cp,max They are the minimum and maximum values ​​of the compressor outlet pressure and transformation ratio at time t respectively.

[0057] The coupling element is modeled as follows:

[0058] a. Power-to-gas (P2G) modeling:

[0059] The technical principle of P2G is a two-step chemical reaction: first, water is electrolyzed to generate hydrogen and oxygen, and then the generated hydrogen reacts with carbon dioxide to synthesize methane, which is then fed into the natural gas network for supply or storage as a component of synthetic natural gas. On the one hand, a large amount of carbon dioxide is consumed in the process of synthesizing methane, which has environmental benefits; on the other hand, P2G is equivalent to artificially increasing the load of the power system, which can absorb the surplus of renewable energy power generation in the power system;

[0060] The amount of hydrogen produced by electrolysis of water is calculated by the following formula:

[0061]

[0062] In the formula, is the hydrogen produced during the electrolysis of water at time t; P pw,t is the wind power consumed for water electrolysis at time t; is the efficiency of the chemical reaction, which is taken as 0.7; LHV is the lower heating value of hydrogen, which is taken as 3.5kW·h / m 3 ;

[0063] The electrical energy consumed by power-to-gas (P2G) is calculated by the following formula:

[0064] P P2G,j,t =W P2G,j,t HGV / η P2G (9);

[0065] Where PP2G,j,t is the power consumed by the P2G device at node j at time t; W P2G,j,t is the amount of natural gas produced by the power-to-gas (P2G) equipment at node j at time t; HGV is the high calorific value of natural gas, which is 9.88kW·h / m 3 ; η P2G is the conversion efficiency of the power-to-gas (P2G) equipment, which is taken as 0.6;

[0066] b. Gas turbine modeling:

[0067] Gas turbines consume natural gas and generate electricity. The specific energy relationship is as follows:

[0068] P GT,j,t =η GT W GT,j,t HGV (10);

[0069] Where W GT,j,t is the amount of natural gas consumed by the gas turbine at node j at time t; η GT is the conversion efficiency of the gas turbine, which is taken as 0.75.

[0070] The constraints of the coupling element are as follows:

[0071] 1) The gas turbine output constraints are as follows:

[0072]

[0073] Where: P GT,j,t and Q GT,j,t P is the active and reactive power injected into node j by the gas turbine at time t; GT,j,max and Q GT,j,max The maximum value of active power and reactive power injected into the gas turbine at node j;

[0074] 2) The constraints of the power-to-gas (P2G) unit are as follows:

[0075]

[0076] Where: P P2G,j,t and Q P2G,j,t is the active and reactive power consumed by the power-to-gas P2G unit at node j at time t; P P2G,j,max and Q P2G,j,max is the maximum value of active and reactive power consumed by the power-to-gas P2G unit at node j; P P2G,j,min and Q P2G,j,min It is the minimum value of active and reactive power consumed by the power-to-gas P2G unit at node j.

[0077] The establishment of the IEGS reactive power and voltage optimization model for the electricity-gas interconnected integrated energy system is as follows;

[0078] In order to take into account both voltage deviation and economic cost, a voltage deviation penalty coefficient is introduced to transform the multi-objective problem into a single-objective problem for easy solution. The IEGS comprehensive cost F is defined as the sum of the system comprehensive cost and the projection of the voltage deviation in the economic dimension:

[0079]

[0080] Where: f1 is the projection of voltage deviation in the economic dimension; f2 is the comprehensive cost of the system;

[0081]

[0082] Where: U j,t is the voltage of node j at time t, and the voltage amplitude of node 1 is set as the voltage reference value, that is, U1 = 1p.u.; δ1 is the voltage penalty coefficient to ensure that the values ​​of each item in the objective function are of the same order of magnitude; G bus is a node set;

[0083] f2=C1+C2+C3+C4+C5 (13);

[0084] Where: C1 and C2 are the electricity purchase cost and gas purchase cost respectively, C3, C4 and C5 are the operating costs of power-to-gas (P2G), gas turbine and compressor respectively. The specific formula is as follows:

[0085]

[0086] Where: F e is the electricity purchase cost, P e,j,t F is the power purchased by node j at time t; g is the gas purchase cost, W g,m,t is the gas purchase volume of node m at time t;

[0087]

[0088] Where: P GT,j,t is the operating power of the gas generator set at node j at time t; F GT is the gas turbine operating cost, which is 70 yuan / MW·h; P P2G,j,t is the operating power of the power-to-gas P2G device at node j at time t; F P2G is the unit operating cost of the power-to-gas (P2G) device, which is 800 yuan / MW; P COM,m,t F is the operating power of the compressor at node m at time t; COM is the unit operating cost of the electric compressor, which is 300 yuan / MW·h.

[0089] The second-order cone relaxation method used in step 3 is to transform f1 in the IEGS reactive power and voltage optimization model of the electricity-gas interconnected integrated energy system into a mixed integer second-order cone programming problem, as follows:

[0090]

[0091] In the formula, u j,t is a new variable introduced for power flow constraints in the distribution network, and u j,t =U j,t 2 .

[0092] Through the above design scheme, the present invention can bring the following beneficial effects:

[0093] 1. The present invention realizes that after the reactive output of the new energy unit and the coupling element gas turbine is considered in the electricity-gas interconnected integrated energy system IEGS, the system voltage deviation is effectively reduced.

[0094] 2. The present invention proves that the joint dispatch of gas turbines and power-to-gas (P2G) can improve the system's wind turbine absorption capacity and reduce economic costs.

[0095] 3. The present invention uses the second-order cone relaxation method to transform the reactive voltage optimization model of the electricity-gas interconnected integrated energy system into a mixed integer second-order cone programming model, thereby ensuring the solution accuracy and speed. BRIEF DESCRIPTION OF THE DRAWINGS

[0096] The present invention is further described below with reference to the accompanying drawings and specific embodiments:

[0097] Figure 1 This is a flow chart of a reactive voltage optimization control method for an electricity-gas interconnected integrated energy system according to the present invention;

[0098] Figure 2 A topological diagram of an electrically interconnected integrated energy system consisting of an IEEE 33-node power system and a 7-node natural gas system in an embodiment of the present invention;

[0099] Figure 3 A photovoltaic unit predicted output diagram in an embodiment of the present invention;

[0100] Figure 4 A wind power prediction output diagram in an embodiment of the present invention;

[0101] Figure 5 It is a daily power curve diagram of the system electricity-gas load in an embodiment of the present invention;

[0102] Figure 6 This is a schematic diagram of reactive power output and consumption of a unit in scenario 1 in an embodiment of the present invention;

[0103] Figure 7 This is a schematic diagram of reactive power output and consumption of a unit in scenario 2 in an embodiment of the present invention;

[0104] Figure 8 A schematic diagram of voltage magnitude at each moment of the power system in an embodiment of the present invention;

[0105] Fig. 9 A schematic diagram showing a comparison of reactive power output of a gas generator set in an embodiment of the present invention;

[0106] Fig.10 This is a schematic diagram of the amount of electricity consumed by the power-to-gas equipment in an embodiment of the present invention. DETAILED DESCRIPTION

[0107] In order to make the objectives, technical solutions and advantages of the present invention more clear, the embodiments of the present invention are described in further detail below.

[0108] Example 1

[0109] A reactive power voltage optimization control method for an electric-gas interconnected integrated energy system, see Figure 1 , the method comprises the following steps:

[0110] 101: Based on the analysis of the composition and structure of the electricity-gas interconnection system, a comprehensive energy system model of electricity-gas interconnection is established;

[0111] 102: Taking into account the constraints of the power grid, gas grid and coupling elements, the reactive power and voltage optimization model of the electricity-gas interconnected integrated energy system is established with the system comprehensive cost and voltage deviation as the optimization target;

[0112] 103: Using the second-order cone relaxation technique, the reactive power and voltage optimization model of the electricity-gas interconnected integrated energy system is transformed into a mixed integer convex optimization problem for solution;

[0113] 104: Simulate the IEEE 33-node power grid and 7-node natural gas grid coupled system.

[0114] Embodiment 1 of the present invention takes into account the reactive support capability of the new energy units and the coupling elements through the above steps 101 to 104, so as to reduce the overall system cost and voltage deviation.

[0115] Example 2

[0116] The scheme in Example 1 is further introduced in combination with the following specific calculation formula and examples, as described below:

[0117] 201: Considering the reactive output of new energy and coupling elements, a model of an integrated power-to-gas energy system including power-to-gas (P2G), gas turbines, wind power, photovoltaics and compressors is constructed.

[0118] 1) Power system modeling

[0119] The power grid used in the electricity-gas interconnected integrated energy system is the distribution network, and the node active and reactive equations are established as follows:

[0120]

[0121] Where P j,t and Q j,t are the active injection power and reactive injection power of node j at time t respectively; P jp,t and Q jp,t are the active power and reactive power flowing through branch jp at time t; P ij,t and Q ij,t are the active power and reactive power flowing from node i to node j at time t; I ij,t is the current flowing through branch ij at time t; r ij represents the resistance of branch ij; x ij represents the reactance of branch ij; u i,t 、u j,t are the amplitudes of the voltage at node i and node j at time t respectively.

[0122] To ensure the safe operation of the power system, the following constraints must be met:

[0123] |I ij,t |≤I ij,max (2);

[0124] u j,min ≤u j,t ≤u j,max (3);

[0125] In the formula, I ij,max is the maximum value of the current flowing through branch ij; u j,min and u j,max are the minimum and maximum values ​​of the voltage at node j.

[0126] 2) Natural gas system modeling

[0127] According to the Weymouth equation, within the scheduling period t, the natural gas pipeline flow equation can be expressed as:

[0128]

[0129]

[0130] Where W mn,t is the gas flow rate of pipeline mn at time t; S mn is a directional parameter. If the pressure at node m is greater than that at node n, it is 1, otherwise it is -1.mn are the pipe equation parameters, which are related to the physical properties of the pipe, such as temperature, length, diameter and friction.

[0131] The energy consumption of the compressor and the pipeline inlet flow rate are expressed as:

[0132]

[0133] W mn,t =W kn,t +W cp,t (7);

[0134] Where W cp,t , W kn,t and W mn,t are the energy consumption of the compressor, the natural gas flow rate at the inlet and the natural gas flow rate at the pipeline at time t respectively; m,t and π k,t are the air pressures at node m and node k at time t; k cp is the compression ratio; Z H is the intrinsic constant of natural gas; T k,t is the natural gas temperature at time t.

[0135] 3) Coupling element modeling

[0136] a. P2G modeling

[0137] The technical principle of power-to-gas is a two-step chemical reaction: first, water is electrolyzed to generate hydrogen and oxygen, and then the generated hydrogen reacts with carbon dioxide to synthesize methane, which is then fed into the natural gas network for supply or storage as a component of synthetic natural gas. On the one hand, a large amount of carbon dioxide is consumed in the process of synthesizing methane, which has good environmental benefits; on the other hand, power-to-gas is equivalent to artificially increasing the load of the power system, which can absorb the surplus of renewable energy generation in the power system.

[0138] The amount of hydrogen produced by electrolysis of water is calculated by the following formula:

[0139]

[0140] In the formula, is the hydrogen produced during the electrolysis of water at time t; P pw,t is the wind power consumed for water electrolysis at time t; is the efficiency of the chemical reaction, which is taken as 0.7; LHV is the lower heating value of hydrogen, which is taken as 3.5kW·h / m 3 The power consumed by P2G is calculated by the following formula:

[0141] P P2G,j,t =W P2G,j,t HGV / η P2G (9);

[0142] Where P P2G,j,t is the power consumed by the P2G device at node j at time t; W P2G,j,t is the amount of natural gas produced by the power-to-gas (P2G) equipment at node j at time t; HGV is the high calorific value of natural gas, which is 9.88kW·h / m 3 ; η P2G is the conversion efficiency of the power-to-gas (P2G) device, which is taken as 0.6.

[0143] b. Gas Turbine Modeling

[0144] Gas turbines consume natural gas and generate electricity. The specific energy relationship is as follows:

[0145] P GT,j,t =η GT W GT,j,t HGV (10);

[0146] Where W GT,j,t is the amount of natural gas consumed by the gas turbine at node j at time t; η GT is the conversion efficiency of the gas turbine, which is taken as 0.75.

[0147] 202: Considering the power flow constraints of the power system and the natural gas system, an optimal dispatch model is established with the goal of minimizing voltage deviation and system comprehensive cost;

[0148] The objective function of the IEGS reactive voltage optimization model includes two parts: minimizing voltage deviation and comprehensive cost. In order to take into account the voltage deviation and economic cost in IEGS, the voltage deviation penalty coefficient is introduced to transform the multi-objective problem into a single-objective problem for easy solution. The IEGS comprehensive cost is defined as the sum of the system comprehensive cost and the projection of the voltage deviation in the economic dimension:

[0149]

[0150] Where: f1 is the projection of voltage deviation in the economic dimension; f2 is the comprehensive cost of the system.

[0151]

[0152] Where: U j,t is the voltage of node j at time t, and the voltage amplitude of node 1 is set as the voltage reference value, that is, U1 = 1p.u.; δ1 is the voltage penalty coefficient to ensure that the values ​​of each item in the objective function are of the same order of magnitude; G bus A collection of nodes.

[0153] f2=C1+C2+C3+C4+C5 (13);

[0154] In the formula: C1 and C2 are the electricity purchase cost and gas purchase cost respectively; C3, C4 and C5 are the operating costs of power-to-gas (P2G), gas turbine and compressor respectively.

[0155]

[0156] Where: F e is the electricity purchase cost, P e,j,t F is the power purchased by node j at time t; g is the gas purchase cost, W g,m,t is the gas purchase volume of node m at time t.

[0157]

[0158] Where: P GT,j,t is the operating power of the gas generator set at node j at time t; F GT is the gas turbine operating cost, which is 70 yuan / MW·h; P P2G,j,t is the operating power of the power-to-gas P2G device at node j at time t; F P2G is the unit operating cost of the power-to-gas (P2G) device, which is 800 yuan / MW; P COM,m,t F is the operating power of the compressor at node m at time t; COM is the unit operating cost of the electric compressor, which is 300 yuan / MW·h.

[0159] The power system constraints are as follows:

[0160] 1) The power balance constraints are as follows:

[0161]

[0162] Where: P e,j,t , P PV,j,t , P PW,j,t and P GT,j,t are the active power injected into node j by the upper grid, photovoltaic unit, wind turbine unit and gas turbine at time t; P L,j,t and P P2G,j,t are the active power consumed by the j-node load and the P2G equipment at time t; Q e,j,t , Q PV,j,t , Q PW,j,t and Q GT,j,t are the reactive power injected into node j by the upper grid, photovoltaic unit, wind turbine unit and gas turbine at time t; Q L,j,t and Q P2G,j,t They are the reactive power consumed by the j-node load and the power-to-gas P2G equipment at time t respectively.

[0163] 2) The photovoltaic active-reactive output constraints are as follows:

[0164]

[0165] Where: P PV,j,t , Q PV,j,t are the active and reactive power injected into node j by the PV system at time t; P PV,t,MPPT is the active power of the photovoltaic unit working at the MPPT maximum power point tracking point at time t; S PV is the installed capacity of the photovoltaic unit.

[0166] 3) The wind power active-reactive output constraints are as follows:

[0167]

[0168] Where: P PW,j,t and Q PW,j,t P is the active power and reactive power injected into node j by the wind turbine at time t; PW,f,t and Q PW,f,t is the predicted active power and reactive power of the wind turbine at time t.

[0169] 4) The power purchase constraints are as follows:

[0170] 0≤P e,j,t ≤P e,j,max (19);

[0171] Where P e,j,t P is the power purchased by node j from the upper grid at time t; e,j,max The maximum value of the purchased power.

[0172] The natural gas system constraints are as follows:

[0173] 1) Natural gas power balance constraints are as follows:

[0174]

[0175] Where: W g,m,t is the natural gas supply at node m at time t; W load,m,t is the gas load at node m at time t; W GT,m,t is the natural gas consumption of the gas turbine at node m at time t; W mn,t is the gas flow from node m to node n; set R is the set of natural gas nodes, and set B is the set of natural gas pipelines.

[0176] 2) The pipeline flow constraints are as follows:

[0177] W mn,min ≤W mn,t ≤W mn,max (twenty one);

[0178] Where: W mn,t is the gas flow rate of pipeline mn at time t; W mn,min and W mn,max are the minimum and maximum values ​​of the gas flow in pipeline mn respectively.

[0179] 3) The node pressure constraints are as follows:

[0180]

[0181] Where: π n,min and π m,min are the minimum gas pressures at n nodes and m nodes respectively; π n,max and π m,max is the maximum value of the gas pressure at the n-node and the m-node.

[0182] 4) The gas source output constraints are as follows:

[0183] W g,m,min ≤W g,m,t ≤W g,m,max (twenty three);

[0184] Where: W g,m,t W is the gas supply of the gas source at time t; g,m,max The maximum value of the gas supply from the gas source; W g,m,min It is the minimum value of gas supply volume.

[0185] 5) Compressor constraints are as follows:

[0186]

[0187] Where: k cp,min and k cp,max They are the minimum and maximum values ​​of the compressor outlet pressure and transformation ratio at time t respectively.

[0188] The coupling element constraints are as follows:

[0189] 1) The gas turbine output constraints are as follows:

[0190]

[0191] Where: P GT,j,t and Q GT,j,t P is the active and reactive power injected into node j by the gas turbine at time t; GT,j,max and Q GT,j,max The maximum value of active power and reactive power injected into the gas turbine at node j.

[0192] 2) The constraints of P2G units are as follows:

[0193]

[0194] Where: P P2G,j,t and Q P2G,j,t is the active and reactive power consumed by the power-to-gas P2G unit at node j at time t; P P2G,j,max and Q P2G,j,max is the maximum value of active and reactive power consumed by the power-to-gas P2G unit at node j; P P2G,j,min and Q P2G,j,min It is the minimum value of active and reactive power consumed by the power-to-gas P2G unit at node j.

[0195] 203: The mixed-integer nonlinear optimization problem is transformed into a mixed-integer second-order cone programming model using the second-order cone relaxation technique;

[0196] The IEGES reactive power voltage optimization problem established by this method is a mixed integer nonlinear optimization problem. In order to ensure the accuracy and speed of the solution, it is necessary to use the second-order cone relaxation technology to convert it into a mixed integer second-order cone programming model for easy solution.

[0197] In view of the power flow constraints of the distribution network, a new variable l is first introduced ij,t =I 2ij,t ,u ij,t =U 2ij,t , then formula (1) will be transformed into:

[0198]

[0199] It is transformed into a second-order cone relaxation, and the specific process is as follows:

[0200]

[0201]

[0202] In addition, for the nonlinear constraint of the gas grid flow (4), if the incremental piecewise linearization method is used, there is often a disadvantage of large errors. The second-order cone relaxation method can also be used to deal with this constraint, as shown in formula (30):

[0203]

[0204] At this point, through the second-order cone relaxation transformation, f1 in the IEGS reactive power and voltage optimization model established above is transformed into a mixed integer second-order cone programming problem, as follows:

[0205]

[0206] The IEGS reactive power and voltage optimization model established by this method is a nonlinear model. The power flow constraints in the power system and the pipeline flow equations in the natural gas system are first converted through the second-order cone relaxation method to adapt to the CPLEX solution environment, and then large-scale solutions are performed through the YALMIP toolbox.

[0207] Example 3

[0208] The following is a specific example of a reactive power voltage optimization control method for an electric-gas interconnected integrated energy system according to an embodiment of the present invention. This example takes an electric interconnected integrated energy system consisting of an IEEE 33-node power system and a 7-node natural gas system as the research object. Figure 2 As shown, see the following description:

[0209] The IEEE 33-node power system of Example 3 has a total of 33 nodes, 32 branches, a reference voltage of 12.66 kV, a reference power of 10 MW, and a node voltage safety range of 0.95 to 1.05 pu. Node 5 is set as a gas turbine connected to node 2 of the gas grid, node 14 is set as a wind turbine, nodes 7, 20, and 30 are set as photovoltaic units, and node 1 is connected to the upper power grid. Set up an electric-to-gas device, the input end is connected to node 18 of the power system, and the output end is connected to node 7 of the natural gas system. The 7-node natural gas system has 2 natural gas sources W1 and W2, 1 compressor, and 5 natural gas pipelines.

[0210] The maximum output power of PV1, PV2 and PV3 is set to 800KW; the maximum output power of the gas turbine is set to 4MW. Figure 3 , wind turbine output forecast Figure 4 , IEGS electric-gas load daily output curve see Figure 5 .

[0211] In order to verify the impact of the proposed IEGS reactive voltage optimization strategy on the distribution network voltage, the following two scenarios are set for comparative analysis.

[0212] Scenario 1: The coupling between the electrical and gas systems is not considered, and each system operates independently.

[0213] Scenario 2: Considering the coupling between the electrical and gas systems, each system operates under optimal coupling conditions.

[0214] The reactive power output and consumption of system units in scenario 1 and scenario 2 are as follows: Figure 6 and Figure 7As shown. In scenario 1, from 08:00 to 20:00, the output of wind turbines is small, and the reactive power of the system is mainly borne by the upper power grid, gas turbines and photovoltaic units. Since the additional reactive power output of the coupling element gas turbine in the system is not considered in scenario 1, the reactive power output of the system during this period is insufficient, resulting in the voltage exceeding the lower limit; while from 22:00 to 08:00, due to the large output of wind turbines and the small system load during this period, the output of wind turbines cannot be absorbed, so that the flow direction of the system changes and the system voltage exceeds the upper limit. In scenario 2, since the coordinated operation of the power system and the natural gas system is considered, the power system and the natural gas system become a whole, and the gas purchase cost of the gas turbine from the natural gas system remains unchanged. During the period of 08:00 to 20:00 when the time-of-use electricity price is high, the gas turbine generates more reactive power, and the coupling element itself has certain reactive regulation characteristics, which can provide more reactive support for the system to increase the voltage. During the period from 21:00 to 06:00, the system load is relatively small and the wind turbines provide relatively large power, which is absorbed by the P2G equipment, thereby reducing the system voltage and improving the voltage over-limit situation.

[0215] The voltage of the power system at each moment is as follows Figure 8 This method sets the node voltage safety range to 0.95-1.05pu. In scenario 1, it can be seen that the voltage meets the conditions at 07:00, 08:00, and 11:00-13:00, and the voltage exceeds the safety range in the remaining time periods. It can be seen that the voltage in each time period in scenario 2 is improved, so that the voltage of the power system in each time period is always kept within the safety range.

[0216] Comparison of reactive power output of gas generator sets Fig. 9 As shown in the figure, the results of the power-to-gas equipment absorbing the surplus electricity are as follows Fig.10 As shown, it can be found that the power-to-gas equipment is in operation from 21:00 to 06:00, converting the electricity that cannot be absorbed by the power system into natural gas, storing it in the natural gas system, and converting it into electricity through the gas unit during the peak load period of the power system.

[0217] The comprehensive cost of IEGS under scenarios 1 and 2 is shown in Table 1. As can be seen from the table, the power purchase cost C1 of the distribution network in scenario 2 is reduced by 48,900 yuan compared with scenario 1, because during the period of high power purchase prices, the reactive power demand of the distribution network is mainly borne by gas turbines and wind turbines, thereby reducing the reactive power purchased from the upper power grid; since gas turbines consume more natural gas to provide reactive power to the distribution network, the gas purchase cost C2 of scenario 2 is increased compared with scenario 1; scenario 1 does not consider the coupling between the electricity and gas systems, so the operating cost C3 of P2G is 0; the operating power of the gas turbine in scenario 2 is higher than that in scenario 1, so the operating cost C4 of the gas turbine is higher than that in scenario 1; scenario 2 considers the coupling between the electricity and gas systems. In the stage of large wind power output, the P2G unit converts its unabsorbed wind power into natural gas for storage, the gas in the natural gas network increases, and the operating power of the compressor increases, so the compressor operating cost C5 increases.

[0218] Table 1 Comparison of comprehensive costs under various scenarios

[0219]

[0220] The above results show that after considering the reactive power output of new energy units and coupling element gas turbines in IEGS, the system voltage deviation is effectively reduced. The joint dispatch of gas turbines and P2G can improve the system wind turbine absorption capacity and reduce economic costs. Applying the second-order cone relaxation method to the model of the present invention can ensure the solution accuracy and speed.

[0221] Those skilled in the art will appreciate that the accompanying drawing is only a schematic diagram of a preferred embodiment, and the serial numbers of the embodiments of the present invention are only for description and do not represent the advantages or disadvantages of the embodiments.

[0222] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

[0223] References:

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Claims

1. A reactive voltage optimization control method for an electricity-gas interconnected integrated energy system, characterized by: The method comprises the following steps, and the following steps are performed in sequence: Step 1: According to the composition and structure of the electricity-gas interconnection system, establish the IEGS model of the electricity-gas interconnection integrated energy system; Step 2: Taking into account the constraints of the power grid, gas grid and coupling elements, taking the system comprehensive cost and voltage deviation as the optimization target, the IEGS reactive power and voltage optimization model of the electricity-gas interconnected integrated energy system is established; Step 3: Use the second-order cone relaxation method to transform the IEGS reactive power and voltage optimization model of the electricity-gas interconnected integrated energy system into a mixed integer convex optimization problem for solution, and obtain the operating results under the optimal coupling condition, thereby realizing the reactive power and voltage optimization control of the electricity-gas interconnected integrated energy system.

2. The method for optimizing reactive power and voltage in an electric-gas interconnected integrated energy system according to claim 1 is characterized in that: The electricity-gas interconnected comprehensive energy system model is an electricity-gas comprehensive energy system model that includes power-to-gas P2G, gas turbines, wind power, photovoltaics and compressors. Establishing the electricity-gas interconnected comprehensive energy system model includes power system modeling, natural gas system modeling and coupling element modeling.

3. The method for optimizing reactive power and voltage in an electric-gas interconnected integrated energy system according to claim 2 is characterized in that: The power system is modeled as follows: a. The power grid used in the electricity-gas interconnected integrated energy system is the distribution network, and the node active and reactive equations are established as follows: Where P j,t and Q j,t are the active injection power and reactive injection power of node j at time t respectively; P jp,t and Q jp,t are the active power and reactive power flowing through branch jp at time t; P ij,t and Q ij,t are the active power and reactive power flowing from node i to node j at time t; I ij,t is the current flowing through branch ij at time t; r ij represents the resistance of branch ij; x ij represents the reactance of branch ij; u i,t 、u j,t are the amplitude of the voltage at node i and node j at time t respectively; b. To ensure the safe operation of the power system, the following constraints are imposed: |I ij,t |≤I ij,max (2); in j,min in j,t in j,max (3); In the formula, I ij,max is the maximum value of the current flowing through branch ij; u j,min and u j,max are the minimum and maximum values ​​of the voltage at node j.

4. The method for optimizing reactive power and voltage in an electric-gas interconnected integrated energy system according to claim 3 is characterized in that: The constraints of the power system are as follows: 1) The power balance constraints are as follows: Where: P e,j,t , P PV,j,t , P PW,j,t and P GT,j,t are the active power injected into node j by the upper grid, photovoltaic unit, wind turbine unit and gas turbine at time t; P L,j,t and P P2G,j,t are the active power consumed by the j-node load and the P2G equipment at time t; Q e,j,t , Q PV,j,t , Q PW,j,t and Q GT,j,t are the reactive power injected into node j by the upper grid, photovoltaic unit, wind turbine unit and gas turbine at time t; Q L,j,t and Q P2G,j,t are the reactive power consumed by the j-node load and the power-to-gas P2G equipment at time t, respectively; 2) The active and reactive output constraints of photovoltaic units are as follows: Where: P PV,j,t , Q PV,j,t are the active and reactive power injected into node j by the PV system at time t; P PV,t,MPPT is the active power of the photovoltaic unit working at the MPPT maximum power point tracking point at time t; S PV is the installed capacity of the photovoltaic unit; 3) The active-reactive output constraints of wind turbines are as follows: Where: P PW,j,t and Q PW,j,t P is the active power and reactive power injected into node j by the wind turbine at time t; PW,f,t and Q PW,f,t is the predicted active power and reactive power of the wind turbine at time t; 4) The power purchase constraints are as follows: 0≤P e,j,t ≤P e,j,max (19); Where P e,j,t P is the power purchased by node j from the upper grid at time t; e,j,max The maximum value of the purchased power.

5. The method for optimizing reactive power and voltage in an electricity-gas interconnected integrated energy system according to claim 2 is characterized by: The natural gas system is modeled as follows: a. According to the Weymouth equation, in the dispatching period t, the natural gas pipeline flow equation is expressed as: Where W mn,t is the gas flow rate of pipeline mn at time t; S mn is a directional parameter. If the pressure at node m is greater than that at node n, it is 1, otherwise it is -1. mn is the pipeline equation parameter, which is related to the pipeline temperature, length, diameter and friction; b. The energy consumption of the compressor and the pipeline inlet flow rate are expressed as: IN mn,t =In kn,t +W cp,t (7); Where W cp,t , W kn,t and W mn,t are the energy consumption of the compressor, the natural gas flow rate at the inlet and the natural gas flow rate at the pipeline at time t respectively; m,t and π k,t are the air pressures at node m and node k at time t; k cp is the compression ratio; Z H is the intrinsic constant of natural gas; T k,t is the natural gas temperature at time t.

6. The method for optimizing reactive power and voltage in an electricity-gas interconnected integrated energy system according to claim 5 is characterized in that: The constraints of the natural gas system are as follows: 1) Natural gas power balance constraints are as follows: Where: W g,m,t is the natural gas supply at node m at time t; W load,m,t is the gas load at node m at time t; W GT,m,t is the natural gas consumption of the gas turbine at node m at time t; W mn,t is the gas flow from node m to node n; set R is the set of natural gas nodes, and set B is the set of natural gas pipelines; 2) The pipeline flow constraints are as follows: IN mn,min ≤In mn,t ≤In mn,max (21); Where: W mn,t is the gas flow rate of pipeline mn at time t; W mn,min and W mn,max are the minimum and maximum values ​​of the gas flow in pipeline mn respectively; 3) The node pressure constraints are as follows: Where: π n,min and π m,min are the minimum gas pressures at n nodes and m nodes respectively; π n,max and π m,max is the maximum value of the gas pressure at the n-node and the m-node; 4) The gas source output constraints are as follows: IN g,m,min ≤In g,m,t ≤In g,m,max (23); Where: W g,m,t W is the gas supply of the gas source at time t; g,m,max The maximum value of the gas supply from the gas source; W g,m,min It is the minimum value of gas supply from the gas source; 5) Compressor constraints are as follows: Where: k cp,min and k cp,max They are the minimum and maximum values ​​of the compressor outlet pressure and transformation ratio at time t respectively.

7. The method for optimizing reactive power and voltage in an electricity-gas interconnected integrated energy system according to claim 2 is characterized by: The coupling element is modeled as follows: a. Power-to-gas (P2G) modeling: The technical principle of P2G is a two-step chemical reaction: first, water is electrolyzed to generate hydrogen and oxygen, and then the generated hydrogen reacts with carbon dioxide to synthesize methane, which is then fed into the natural gas network for supply or storage as a component of synthetic natural gas. On the one hand, a large amount of carbon dioxide is consumed in the process of synthesizing methane, which has environmental benefits; on the other hand, P2G is equivalent to artificially increasing the load of the power system, which can absorb the surplus of renewable energy power generation in the power system; The amount of hydrogen produced by electrolysis of water is calculated by the following formula: In the formula, is the hydrogen produced during the electrolysis of water at time t; P pw,t is the wind power consumed for water electrolysis at time t; is the efficiency of the chemical reaction, which is taken as 0.7; LHV is the lower heating value of hydrogen, which is taken as 3.5kW·h / m 3 ; The electrical energy consumed by power-to-gas (P2G) is calculated by the following formula: P P2G,j,t =W P2G,j,t ·HGV / η P2G (9); Where P P2G,j,t is the power consumed by the P2G device at node j at time t; W P2G,j,t is the amount of natural gas produced by the power-to-gas (P2G) equipment at node j at time t; HGV is the high calorific value of natural gas, which is 9.88kW·h / m 3 ; η P2G is the conversion efficiency of the power-to-gas (P2G) equipment, which is taken as 0.6; b. Gas turbine modeling: Gas turbines consume natural gas and generate electricity. The specific energy relationship is as follows: P GT,j,t =η GT W GT,j,t ·HGV (10); Where W GT,j,t is the amount of natural gas consumed by the gas turbine at node j at time t; η GT is the conversion efficiency of the gas turbine, which is taken as 0.

75.

8. The method for optimizing reactive power and voltage in an electricity-gas interconnected integrated energy system according to claim 7 is characterized by: The constraints of the coupling element are as follows: 1) The gas turbine output constraints are as follows: Where: P GT,j,t and Q GT,j,t P is the active and reactive power injected into node j by the gas turbine at time t; GT,j,max and Q GT,j,max The maximum value of active power and reactive power injected into the gas turbine at node j; 2) The constraints of the power-to-gas (P2G) unit are as follows: Where: P P2G,j,t and Q P2G,j,t is the active and reactive power consumed by the power-to-gas P2G unit at node j at time t; P P2G,j,max and Q P2G,j,max is the maximum value of active and reactive power consumed by the power-to-gas P2G unit at node j; P P2G,j,min and Q P2G,j,min It is the minimum value of active and reactive power consumed by the power-to-gas P2G unit at node j.

9. The method for optimizing reactive power and voltage in an electricity-gas interconnected integrated energy system according to claim 1 is characterized by: The establishment of the IEGS reactive power and voltage optimization model for the electricity-gas interconnected integrated energy system is as follows; In order to take into account both voltage deviation and economic cost, a voltage deviation penalty coefficient is introduced to transform the multi-objective problem into a single-objective problem for easy solution. The IEGS comprehensive cost F is defined as the sum of the system comprehensive cost and the projection of the voltage deviation in the economic dimension: Where: f1 is the projection of voltage deviation in the economic dimension; f2 is the comprehensive cost of the system; Where: U j,t is the voltage of node j at time t, and the voltage amplitude of node 1 is set as the voltage reference value, that is, U1 = 1p.u.; δ1 is the voltage penalty coefficient to ensure that the values ​​of each item in the objective function are of the same order of magnitude; G bus is a node set; f2=C1+C2+C3+C4+C5 (13); Where: C1 and C2 are the electricity purchase cost and gas purchase cost respectively, C3, C4 and C5 are the operating costs of power-to-gas (P2G), gas turbine and compressor respectively. The specific formula is as follows: Where: F e is the electricity purchase cost, P e,j,t F is the power purchased by node j at time t; g is the gas purchase cost, W g,m,t is the gas purchase volume of node m at time t; Where: P GT,j,t is the operating power of the gas generator set at node j at time t; F GT is the gas turbine operating cost, which is 70 yuan / MW·h; P P2G,j,t is the operating power of the power-to-gas P2G device at node j at time t; F P2G is the unit operating cost of the power-to-gas (P2G) device, which is 800 yuan / MW; P COM,m,t F is the operating power of the compressor at node m at time t; COM is the unit operating cost of the electric compressor, which is 300 yuan / MW·h.

10. The method for optimizing reactive power and voltage in an electricity-gas interconnected integrated energy system according to claim 9 is characterized in that: The second-order cone relaxation method used in step 3 is to transform f1 in the IEGS reactive power and voltage optimization model of the electricity-gas interconnected integrated energy system into a mixed integer second-order cone programming problem, as follows: In the formula, u j,t is a new variable introduced for power flow constraints in the distribution network, and u j,t =U j,t 2 .

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