Flexible interconnection cooperative configuration method and device for AC / DC hybrid microgrid

Abstract

The invention provides a flexible interconnection cooperative configuration method and device for an AC / DC hybrid micro-grid, and belongs to the field of micro-grids. The method comprises the following steps: constructing an AC / DC hybrid micro-grid interconnected networking structure; wherein the voltage source converter divides the micro-grid into an alternating current area and a direct current area, and micro-grid interconnection is formed based on a direct current tie line; based on a networking structure and power supply and power utilization requirements, determining various operation strategies of an alternating current area and a direct current area of the micro-grid; a planning operation double-layer model of the micro-grid is constructed, and an upper-layer model of the planning operation double-layer model is used for planning an interconnection scheme, the capacity of each voltage source converter and the transmission capacity of a direct-current tie line; a lower-layer model of the planning operation double-layer model is used for determining the operation cost of the micro-grid based on multiple operation strategies; and solving the planning operation double-layer model based on simulated annealing and cone planning, and determining a configuration scheme. According to the invention, the networking planning cost can be reduced.

Description

Technical Field

[0001] The present invention relates to the field of microgrid technology, and in particular to a method and device for flexible interconnection and coordinated configuration of an AC / DC hybrid microgrid. Background Art

[0002] With the development of clean energy technology and the increase in residential electricity demand, the scale of renewable energy access represented by photovoltaics in the distribution network has continued to increase. As a result, microgrids, which aim to achieve flexible and efficient application of distributed power sources and solve the problem of grid connection of large numbers of distributed power sources in various forms, have also been widely used.

[0003] A microgrid is a small, integrated power system that can operate independently of a central power grid or be connected and work in conjunction with a central power grid. A microgrid typically includes distributed power sources, energy storage devices, energy conversion devices, and related load and monitoring protection systems. These components work together to meet power demand in a specific area while improving energy efficiency and system reliability. However, due to different load growth rates, in most areas of my country, on the one hand, there may be microgrids with both excess photovoltaic output and insufficient photovoltaic power supply in the distribution network. The former has problems such as abandonment of light and serious power reverse transmission. On the other hand, the transformer load rates of each microgrid are uneven. The transformers of light-loaded microgrids have low economic benefits, while the transformers of heavy-loaded microgrids have a higher risk of overheating and a shorter service life.

[0004] At present, power electronic devices such as converters can be used to realize the AC and DC regional operation of microgrids, and power mutual assistance between interconnected microgrids can be achieved through DC interconnection lines. However, the existing microgrid interconnection planning does not consider the transmission capacity configuration of DC interconnection lines, and does not consider the operation strategy of interconnected microgrid groups, resulting in high costs for existing interconnection planning. Summary of the invention

[0005] The embodiments of the present invention provide a method and device for flexible interconnection and coordinated configuration of an AC / DC hybrid microgrid to solve the problem of high cost in current microgrid interconnection planning.

[0006] In a first aspect, an embodiment of the present invention provides a method for flexible interconnection and coordinated configuration of an AC / DC hybrid microgrid, including:

[0007] Constructing a networking structure of AC / DC hybrid microgrid interconnection; wherein the voltage source converter divides the microgrid into an AC area and a DC area, and forms microgrid interconnection based on a DC tie line;

[0008] Based on the network structure and the demand for power supply and consumption, determine the various operation strategies for the AC and DC areas of the microgrid;

[0009] A two-layer model for planning and operation of the microgrid is constructed, wherein the upper layer model of the two-layer model is used to plan the interconnection scheme, the capacity of each voltage source converter and the transmission capacity of the DC tie line; the lower layer model of the two-layer model is used to determine the operation cost of the microgrid based on multiple operation strategies;

[0010] The two-level model of planning operation is solved based on simulated annealing and cone programming to determine the configuration scheme.

[0011] In a possible implementation, building a networking structure of AC / DC hybrid microgrid interconnection also includes:

[0012] Based on the position of the voltage source converter in the networking structure, a power flow model of the voltage source converter, a power flow balance model on the AC side, and a power flow balance model on the DC side are constructed.

[0013] In a possible implementation, the networking structure includes multiple microgrids, each of which includes a load device, an energy storage device, and a photovoltaic device;

[0014] The power flow model of the voltage source converter is:

[0015]

[0016] The power flow balance model on the AC side is:

[0017]

[0018] The power flow balance model on the DC side is:

[0019]

[0020] in, are the active power of the converter AC and DC ports flowing into and out of microgrid j at time t; loss is the loss coefficient of converter transmission; and are the active power flowing through the high-voltage side and low-voltage side of the microgrid j transformer at time t, ΔP j,DT is the internal transmission loss of transformer j; P j,t and Q j,t is the active power and reactive power of the AC side of microgrid j at time t; is the reactive power flowing through the microgrid j transformer at time t, and is the active power and reactive power of the conventional load on the AC side of microgrid j at time t; P j,t is the active power of the DC side of microgrid j at time t; is the active power generated by the photovoltaic device of microgrid j at time t; and is the discharging and charging power of the energy storage unit j in the microgrid at time t; is the active power injected into the DC side by the VSC at time t; and are the active power of conventional load and demand response load on the DC side of microgrid j at time t respectively; is the mutual aid power between microgrid j and microgrid i through the tie line at time t; n represents the number of microgrids connected to microgrid j.

[0021] In a possible implementation, the networking structure includes multiple microgrids;

[0022] Based on the network structure and the demand for power supply and consumption, various operation strategies for the AC and DC areas of the microgrid are determined, including:

[0023] Based on the output of photovoltaic equipment in the target microgrid and the power transfer balance relationship of the microgrid, the transfer mode of the target microgrid in the AC area and the transfer mode in the DC area are determined.

[0024] In one possible implementation, the upper model of the two-layer model for planning and operating is to minimize the sum of system investment cost, operation and maintenance cost, and operation cost as the objective function;

[0025] The lower model of the planning and operation two-layer model is based on the target operation strategy, with the minimum sum of the operation costs of the microgrid as the objective function; wherein the target operation strategy is any one of a plurality of operation strategies.

[0026] In a possible implementation, the upper model minF of the planned operation double-layer model is:

[0027] minF=C int +C M +C0;

[0028]

[0029]

[0030] C0=C P +C ess +C DR +C loss ;

[0031] Among them, C int is the total construction cost of the interconnection system; c VSC.int is the unit capacity construction cost of a single microgrid VSC in the interconnected system, S VSC,i The capacity of VSC installed for a single microgrid i in the interconnected system; x i-jis a 0-1 variable, x i-j 1 means that microgrid i and microgrid j are connected, x i-j 0 means that microgrid i and microgrid j are not connected; l i,j is the distance between microgrid i and microgrid j; c L.int E is the investment and installation cost of DC interconnection line per unit transmission power, j-i is the transmission capacity of the tie line between microgrid i and microgrid j, D is the number of microgrids configured with photovoltaic resources in the interconnected system, N is the total number of microgrids in the interconnected system; R(d,y) is the annual value conversion coefficient; is the unit capacity operation and maintenance cost of the microgrid VSC, C P The cost of purchasing and selling electricity to the superior power grid; C ess is the energy storage regulation cost; C DR To reduce the load regulation cost; C loss The network loss cost.

[0032] In one possible implementation, the operating costs of a microgrid include: transaction costs with the upper-level grid, charging and discharging costs of energy storage devices, demand response regulation costs, and network loss costs.

[0033] In one possible implementation, the minC0 of the lower model of the two-layer model is planned to be:

[0034] minC0=C P +C ess +C DR +C loss ;

[0035]

[0036]

[0037]

[0038]

[0039] Among them, D s is the total number of days in season s; is the electricity price at time t, is the transaction volume between microgrid d in season s and the upper-level power grid in period t, which is set to be positive when purchasing electricity from the upper-level power grid and negative when selling electricity to the upper-level power grid; α is the unit charging and discharging cost of the energy storage unit, is the charging and discharging power of the energy storage unit of microgrid d in time period t during season s, and η is the charging and discharging efficiency of the energy storage unit; is the compensation price for curtailing demand response, is the demand response amount that can be reduced by microgrid d in season s and period t; is the transformer loss cost, a d and b d is the distribution transformer loss coefficient of microgrid d; is the VSC transmission loss, χ loss is the VSC transmission loss coefficient, The power injected into the AC side of the VSC of microgrid d during period t in season s is: The VSC DC side injection power of microgrid d in time period t in season s is specified as and cannot be 1 at the same time; Δt is the duration of time period t, and D is the set of microgrids.

[0040] In one possible implementation, a two-level model is solved for planning operations based on simulated annealing and cone programming to determine a configuration solution, including:

[0041] Based on the simulated annealing algorithm, the upper model of the planning and operation double-layer model is solved to obtain the optimal microgrid interconnection scheme, the capacity configuration scheme of each voltage source converter, and the transmission capacity configuration scheme of the DC tie line;

[0042] Based on the optimal microgrid interconnection scheme, the capacity configuration scheme of each voltage source converter and the transmission capacity configuration scheme of the DC interconnection line, the cone programming algorithm is called to solve the lower model of the planning and operation two-layer model, and the result is passed to the upper model of the planning and operation two-layer model. The final configuration scheme is determined by iterative calculation.

[0043] In a second aspect, an embodiment of the present invention provides an AC / DC hybrid microgrid flexible interconnection collaborative configuration device, comprising:

[0044] A construction module is used to construct a networking structure of AC / DC hybrid microgrid interconnection; wherein the voltage source converter divides the microgrid into an AC area and a DC area, and forms a microgrid interconnection based on a DC tie line;

[0045] A strategy determination module is used to determine various operation strategies of the AC area and the DC area of ​​the microgrid based on the network structure and the power supply and power consumption requirements;

[0046] A model building module is used to build a two-layer model for planning and operating a microgrid, wherein the upper layer model of the two-layer model is used to plan the interconnection scheme, the capacity of each voltage source converter and the transmission capacity of the DC tie line; the lower layer model of the two-layer model is used to determine the operating cost of the microgrid based on multiple operating strategies;

[0047] The solution module is used to solve the two-layer model of planning operation based on simulated annealing and cone programming to determine the configuration plan.

[0048] The embodiment of the present invention provides a method and device for the flexible interconnection and collaborative configuration of an AC / DC hybrid microgrid, which forms a networking structure of an AC / DC hybrid microgrid interconnection by adopting a voltage source converter and a DC interconnection line. Next, based on the networking structure constructed above and the power supply and power consumption requirements, a variety of operating strategies for the AC area and the DC area of ​​the microgrid under different conditions, that is, a variety of transferable supply modes, are determined. Then, by constructing a two-layer model for planning and operation, the upper model is used to plan the interconnection scheme, the capacity of each voltage source converter and the transmission capacity of the DC interconnection line, and the lower model is used to determine the operating cost of the microgrid based on a variety of operating strategies. Finally, by solving the two-layer model for planning and operation using simulated annealing and cone programming, a configuration scheme is determined, which can greatly reduce the cost of microgrid interconnection planning. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0050] Figure 1 It is a flow chart for implementing the flexible interconnection and coordinated configuration method of AC / DC hybrid microgrids provided in an embodiment of the present invention;

[0051] Figure 2 This is an application scenario diagram of the AC / DC hybrid microgrid flexible interconnection collaborative configuration method provided by an embodiment of the present invention;

[0052] Figure 3 is a block diagram of a planning and operation double-layer model provided by an embodiment of the present invention;

[0053] Figure 4 is a schematic diagram of a two-layer model for solving planning operations provided by an embodiment of the present invention;

[0054] Figure 5 It is a schematic diagram of a distribution network topology structure of a certain place provided by an embodiment of the present invention;

[0055] Figure 6 This is a schematic diagram of photovoltaic power generation prediction output provided by an embodiment of the present invention;

[0056] Figure 7 is a schematic diagram of load prediction output provided by an embodiment of the present invention;

[0057] Figure 8 It is the transmission power of the DC tie line in spring and autumn and the transformer load rate of the heavy-load microgrid when two microgrids are interconnected provided by the embodiment of the present invention;

[0058] Fig. 9 It is the transmission power of the DC tie line in summer and the transformer load rate of the heavy-load microgrid when two microgrids are interconnected provided by the embodiment of the present invention;

[0059] Fig.10 It is the transmission power of the DC tie line in winter and the transformer load rate of the heavy-load microgrid when two microgrids are interconnected provided by the embodiment of the present invention;

[0060] Fig.11 The embodiment of the present invention provides the photovoltaic absorption rate of each microgrid;

[0061] Fig.12 The embodiment of the present invention provides the distribution transformer load rate before and after each microgrid is interconnected;

[0062] Fig.13 It is a structural schematic diagram of an AC / DC hybrid microgrid flexible interconnection and collaborative configuration device provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0063] In the following description, specific details such as specific system structures, technologies, etc. are provided for the purpose of illustration rather than limitation, so as to provide a thorough understanding of the embodiments of the present invention. However, it should be clear to those skilled in the art that the present invention may be implemented in other embodiments without these specific details. In other cases, detailed descriptions of well-known systems, devices, circuits, and methods are omitted to prevent unnecessary details from obstructing the description of the present invention.

[0064] In order to make the purpose, technical solutions and advantages of the present invention more clear, specific embodiments will be described below in conjunction with the accompanying drawings.

[0065] An AC / DC hybrid microgrid refers to a microgrid that contains both an AC bus and a DC bus, and can directly supply power to both AC and DC loads. A microgrid is an autonomous system that can achieve self-control, protection, and management. As a complete power system, it relies on its own control and management to achieve power balance control, system operation optimization, fault detection and protection, and power quality management.

[0066] Figure 1 The implementation flow chart of the flexible interconnection and coordinated configuration method of the AC / DC hybrid microgrid provided in the embodiment of the present invention is described in detail as follows:

[0067] S110. Construct a networking structure for interconnecting AC / DC hybrid microgrids.

[0068] The voltage source converter divides the microgrid into an AC area and a DC area, and forms microgrid interconnection based on DC interconnection lines.

[0069] By configuring voltage source converters (VSCs) and DC interconnection lines in each microgrid, a DC bus distributed topology structure is used as the networking structure for interconnecting microgrids.

[0070] VSC has two control degrees of freedom, which can control the magnitude and direction of active and reactive power.

[0071] like Figure 2 The diagram shows three interconnected microgrids, each of which includes an AC / DC voltage source converter, as well as load devices, energy storage devices, photovoltaic devices, and load-reducible devices in the DC area. Each microgrid is connected via a DC tie line.

[0072] Based on the interconnected networking structure of microgrids, a power flow model of microgrids can be established, including:

[0073] Voltage Source Converter Power Flow Model:

[0074]

[0075] Where: are the active power of the converter AC and DC ports flowing into and out of microgrid j at time t; loss is the loss coefficient of the converter transmission.

[0076] AC side power flow balance model:

[0077]

[0078] Where: and are the active power flowing through the high-voltage side and low-voltage side of the microgrid j transformer at time t, ΔP j,DT is the internal transmission loss of transformer j; P j,t and Q j,t is the active power and reactive power of the AC side of microgrid j at time t; is the reactive power flowing through the microgrid j transformer at time t, and is the active power and reactive power of the conventional load on the AC side of microgrid j at time t.

[0079] DC side power flow balance model:

[0080]

[0081] Where P j,t is the active power of the DC side of microgrid j at time t; is the active power generated by the photovoltaic device of microgrid j at time t; and is the discharging and charging power of the energy storage unit j in the microgrid at time t; is the active power injected into the DC side by the VSC at time t; and are the active power of conventional load and demand response load on the DC side of microgrid j at time t respectively; is the mutual aid power between microgrid j and microgrid i through the tie line at time t, When it is positive, it means that the power of microgrid i flows into microgrid j, otherwise it is negative; n represents the number of microgrids connected to microgrid j.

[0082] S120. Based on the network structure and the power supply and power consumption requirements, determine multiple operation strategies for the AC area and the DC area of ​​the microgrid.

[0083] The transfer mode of the target microgrid in the AC area and the transfer mode in the DC area can be determined based on the output of the photovoltaic equipment in the target microgrid and the power transfer balance relationship of the microgrid.

[0084] In this embodiment, the power transfer balance relationship of the microgrid can be determined first according to the photovoltaic power generation situation.

[0085] In some embodiments, if the photovoltaic output is insufficient, the power transfer balance equation of the current microgrid AC area is: Figure 2 The three interconnected microgrids in are taken as an example to illustrate, and microgrid No. 1 is set as microgrid A, microgrid No. 2 is set as microgrid B, and microgrid No. 3 is set as microgrid A.

[0086] ΔP AC =P PV1 +P H2 +…+P Hn ;

[0087] Among them, ΔP AC is the power shortage in the current microgrid AC area, P Hi is the transfer power provided by the i-th transfer mode, n is the total number of transfer modes that can be used in the current microgrid AC area when the photovoltaic output is insufficient.

[0088] There are four transfer modes in this case, namely:

[0089] Transfer mode 1 (H1): The AC area of ​​microgrid A is short of power supply, and the surplus PV output of microgrids B and C is transferred. The two interconnected microgrids transmit power to the DC area of ​​microgrid A through their respective DC interconnection lines, and then transmit it to the AC area through VSC. At this time, the transferred power P H1 for:

[0090]

[0091] Among them, χ loss is the VSC transmission loss coefficient; and The photovoltaic output of microgrid A is transferred to microgrid B and microgrid C respectively.

[0092] Transfer mode 2 (H2): The AC area of ​​microgrid A is underpowered, and the AC load is satisfied by purchasing electricity from the upper grid. The power is purchased from the upper grid and transmitted to the AC area of ​​microgrid A through the microgrid transformer. At this time, the transfer power P H2 for:

[0093]

[0094] in, is the amount of electricity purchased by microgrid A from the upper grid at time t; ΔP DT is the transformer transmission loss.

[0095] Transfer mode 3 (H3): The AC area is short of power supply, and the three microgrids call on internal resources (energy storage, demand response load) to meet the AC load power demand. Microgrid A calls on internal resources to transfer power through VSC; microgrids B and C call on internal resources to transfer power to the DC area of ​​microgrid A through their respective DC interconnection lines, and then transfer it to the AC area of ​​microgrid A through VSC. At this time, the transfer power P H3 for:

[0096]

[0097] in, is the energy storage discharge power of microgrid i at time t; The power of the demand response load (reducible load) is regulated by microgrid i at time t.

[0098] Transfer mode 4 (H4): The AC area is short of power supply, and the interconnected microgrid purchases power from the upper grid for transfer. Microgrid B and microgrid C purchase power from the upper grid, and transmit the power to the DC area of ​​microgrid A through their respective transformers, VSCs, and DC interconnection lines with microgrid A, and then transmit it to the AC area through VSCs. At this time, the transfer power P H4 for:

[0099]

[0100] in, is the amount of electricity purchased by microgrid i from the upper grid at time t. ΔP i,DT is the transformer loss of microgrid i at time t.

[0101] In some embodiments, if the photovoltaic output is insufficient, the power transfer to the DC area of ​​microgrid A is:

[0102] ΔP DC =P H5 +P H6 +P H7 ;

[0103] Among them, ΔP DC is the power shortage in the AC area of ​​microgrid A, P Hi The transfer power provided for the i-th transfer mode.

[0104] Transfer mode 5 (H5): When the DC area is short of power, the interconnected microgrids transfer power to the DC area of ​​microgrid A through their respective DC interconnection lines to meet the power demand of the DC load. At this time, the transferred power P H5 for:

[0105]

[0106] in, and The photovoltaic output of microgrid A is transferred to microgrid B and microgrid C respectively.

[0107] Transfer mode 6 (H6): The DC area of ​​microgrid A is underpowered, and it purchases electricity from the upper grid to meet the DC load demand. Microgrid A purchases electricity from the upper grid, transmits it to the AC area through the microgrid transformer, and then transmits it to the DC area through the VSC; microgrids B and C purchase electricity from the upper grid, and transmit power to the DC area of ​​microgrid A through their respective transformers, VSCs, and DC interconnection lines with microgrid A. At this time, the transfer power P H6 for:

[0108]

[0109] in, is the amount of electricity purchased by microgrid i from the upper grid at time t. ΔP i,DT is the transformer loss of microgrid i at time t.

[0110] Transfer mode 7 (H7): When the DC area is short of power, microgrid A and the interconnected microgrid call on internal resources (energy storage, demand response load) to transfer power to meet the DC load demand. Microgrid B and microgrid C call on internal resources to transfer power to the DC area of ​​microgrid A via their respective DC interconnection lines. At this time, the transferred power P H7 for:

[0111]

[0112] in, is the energy storage discharge power of microgrid i at time t; The power of the demand response load (reducible load) is regulated by microgrid i at time t.

[0113] In some embodiments, if microgrid A has excess photovoltaic output,

[0114] ΔP=P H8 +P H9 +P H10 ;

[0115] Where ΔP is the excess photovoltaic power of microgrid A, P Hi The transfer power provided for the i-th transfer mode.

[0116] Transfer mode 8 (H8): Microgrid A transmits excess PV output to the DC areas of microgrids B and C via DC interconnection lines AB and BC. At this time, the transfer power P H8 for:

[0117]

[0118] In the formula, and are the powers transmitted from microgrid A to microgrid B and microgrid C respectively.

[0119] Transfer mode 9 (H9): Microgrid A uses the excess photovoltaic power to charge the energy storage unit. At this time, the transfer power P H9 for:

[0120]

[0121] In the formula, is the energy storage charging power of microgrid A at time t.

[0122] Transfer mode 10 (H10): Microgrid A transmits excess photovoltaic power to the AC area through the VSC unit, and then sells power to the upper grid through the transformer. At this time, the transfer power P H10 for:

[0123]

[0124] In the formula, is the power output by microgrid A to the AC area through VSC at time t.

[0125] S130. Construct a two-layer model for planning and operation of microgrids.

[0126] Among them, the upper model of the planning and operation two-layer model is used to plan the interconnection scheme, the capacity of each voltage source converter and the transmission capacity of the DC interconnection line; the lower model of the planning and operation two-layer model is used to determine the operating cost of the microgrid based on multiple operating strategies.

[0127] In some embodiments, Figure 3 As shown in the figure, the upper model of the two-layer planning and operation model takes the minimum sum of system investment cost, operation and maintenance cost and operation cost as the objective function. The lower model of the two-layer planning and operation model takes the minimum sum of microgrid operation cost as the objective function according to the target operation strategy; wherein the target operation strategy is any one of multiple operation strategies.

[0128] In this embodiment, the operating costs of the microgrid include transaction costs with the upper-level power grid, charging and discharging costs of the energy storage device, demand response regulation costs, and network loss costs.

[0129] In this embodiment, the upper model minF of the planned operation double-layer model is:

[0130] minF=C int +C M +C0;

[0131]

[0132]

[0133] C0=C P +C ess +C DR +C loss ;

[0134] Among them, C int is the total construction cost of the interconnection system; c VSC.int is the unit capacity construction cost of a single microgrid VSC in the interconnected system, S VSC,i The capacity of VSC installed for a single microgrid i in the interconnected system; x i-j is a 0-1 variable, x i-j 1 means that microgrid i and microgrid j are connected, x i-j 0 means that microgrid i and microgrid j are not connected; l i,j is the distance between microgrid i and microgrid j; c L.int E is the investment and installation cost of DC interconnection line per unit transmission power, j-i is the transmission capacity of the tie line between microgrid i and microgrid j, D is the number of microgrids configured with photovoltaic resources in the interconnected system, N is the total number of microgrids in the interconnected system; R(d,y) is the annual value conversion coefficient; is the unit capacity operation and maintenance cost of the microgrid VSC, C PThe cost of purchasing and selling electricity to the superior power grid; C ess is the energy storage regulation cost; C DR To reduce the load regulation cost; C loss The network loss cost.

[0135] The lower model of the two-layer planning and operation model aims to minimize the sum of the distribution network operation costs, including the transaction costs with the upper power grid, the charging and discharging costs of the energy storage device, the demand response regulation costs and the network loss costs. The lower optimization model is established, and the objective function minC0 is:

[0136] minC0=C P +C ess +C DR +C loss ;

[0137]

[0138]

[0139]

[0140]

[0141] Among them, D s is the total number of days in season s; is the electricity price at time t, is the transaction volume between microgrid d in season s and the upper-level power grid in period t, which is set to be positive when purchasing electricity from the upper-level power grid and negative when selling electricity to the upper-level power grid; α is the unit charging and discharging cost of the energy storage unit, is the charging and discharging power of the energy storage unit of microgrid d in time period t during season s, and η is the charging and discharging efficiency of the energy storage unit; The compensation price for curtailing demand response, is the demand response amount that can be reduced by microgrid d in season s and period t; is the transformer loss cost, a d and b d is the distribution transformer loss coefficient of microgrid d; is the VSC transmission loss, χ loss is the VSC transmission loss coefficient, The power injected into the AC side of the VSC of microgrid d during period t in season s is: The VSC DC side injection power of microgrid d in time period t in season s is specified as and cannot be 1 at the same time; Δt is the duration of time period t, and D is the set of microgrids.

[0142] S140. Solve the planning operation double-layer model based on simulated annealing and cone programming to determine the configuration plan.

[0143] The simulated annealing algorithm is derived from the principle of solid annealing. It is a probability-based algorithm that heats the solid to a sufficiently high temperature and then slowly cools it. When heated, the particles inside the solid become disordered as the temperature rises, and the internal energy increases. When slowly cooled, the particles gradually become ordered, reaching an equilibrium state at each temperature, and finally reaching the ground state at room temperature, and the internal energy is reduced to a minimum.

[0144] Cone programming is a special mathematical optimization problem that extends the concepts of linear programming and quadratic programming to allow nonlinear constraints. Cone programming is widely used in engineering, economics, finance and other fields by solving the minimum or maximum value of a linear objective function under cone constraints.

[0145] In some embodiments, based on the idea of ​​interactive iterative nesting, the variable types and optimization requirements of the upper-level model and the lower-level model are comprehensively considered, and a hybrid optimization algorithm based on simulated annealing and cone programming is used to solve the planning model.

[0146] In this embodiment, based on the simulated annealing algorithm, the upper model of the planning and operation double-layer model is solved to obtain the optimal microgrid interconnection scheme, the capacity configuration scheme of each voltage source converter, and the configuration scheme of the transmission capacity of the DC tie line. Based on the optimal microgrid interconnection scheme, the capacity configuration scheme of each voltage source converter, and the configuration scheme of the transmission capacity of the DC tie line, the cone programming algorithm is called to solve the lower model of the planning and operation double-layer model, and the result is passed to the upper model of the planning and operation double-layer model, and iterative calculation is performed to determine the final configuration scheme.

[0147] Specific solution steps are as follows: Figure 4 As shown:

[0148] Step 1: Initialize simulated annealing, initialize parameters, set initial temperature and initial configuration scheme, and set SA iteration number G = 0;

[0149] Step 2: Generate a new microgrid interconnection plan and a capacity configuration plan for each microgrid VSC and tie line in the distribution network at the current temperature and pass it to the lower layer;

[0150] Step 3: The lower-layer model uses the cone programming algorithm to solve the lower-layer objective function according to the interconnection scheme and configuration scheme obtained in step 2, and passes the result to the upper layer;

[0151] Step 4: Calculate the fitness of the current planning scheme at the current temperature, and fully search the solution space at this temperature, repeating steps 2 to 4 for multiple rounds of iterations;

[0152] Step 5: Lower the temperature and reset the number of SA iterations G = 0; determine whether the convergence condition is met. If not, repeat steps 2 to 5 until the final temperature is reached;

[0153] Step 6: The convergence condition is met, the optimal configuration solution is obtained, and the solution is completed.

[0154] In order to prove the effectiveness of the flexible interconnection and coordinated configuration method of AC / DC hybrid microgrids provided by the present invention, a distribution network of a certain city is selected, and its topological structure and microgrid number are as follows: Figure 5 As shown, Figure 5 The middle node 1 is a communication node that interacts with the upper power grid, and the remaining nodes can be used as access nodes on the high-voltage side of each microgrid transformer. The present invention sets the minimum and maximum values ​​of the node voltage amplitude to 0.95 and 1.05 respectively, the load power factor on the AC side of the microgrid is 0.93, the transformer overload rate is 0.8, and the transformer ratio of the microgrid is 10kV / 400V. Taking into account the seasonal differences in photovoltaic power generation and AC and DC loads connected to the microgrid, typical daily data for four seasons with a time step of one hour for one year is selected as the prediction data for different loads and photovoltaic output in each microgrid. The timing curves of photovoltaic and load are shown as follows: Figure 6 and 7 As shown in the figure, the interconnection plan is set up for comparison before and after.

[0155] according to Figure 8-Figure 10 The schematic diagram of the DC interconnection line transmission power and the load rate of the overloaded microgrid 21 throughout the year when the two microgrids are interconnected shows that: after the interconnection optimization operation, the distribution transformer load rate of microgrid 21 decreases as a whole during the annual scheduling cycle, and during the peak power consumption periods of 12:00 and 20:00, the distribution transformer load rate of microgrid 21 can be reduced to below 0.8 through the power transfer of microgrid 20, avoiding the phenomenon of heavy or even overload operation of the microgrid, reducing the imbalance of the microgrid distribution transformer load, and indicating that the DC interconnection structure and interconnection transfer strategy can optimize the operation of the distribution network.

[0156] according to Fig.11 The photovoltaic absorption rate of each microgrid before and after interconnection shows that: due to the large photovoltaic installed capacity of each selected microgrid, the photovoltaic absorption rate of each microgrid did not exceed 80% before interconnection. After interconnection and transfer, the photovoltaic absorption rate of each microgrid has increased to a certain extent, and the improvement of microgrid 13 is the highest, reaching 41.5%. The load absorption photovoltaic rate of the selected microgrids finally reached more than 95%.

[0157] according to Fig.12The load rates of distribution transformers before and after the interconnection of each microgrid show that the load rates of distribution transformers of microgrids in each interconnected group in the distribution network before interconnection vary greatly. Taking microgrids 7, 8, and 9 as examples, the load rates of microgrids 7 and 9 are lower than 0.5, which are in a light-load state, while the load rate of microgrid 8 exceeds 0.8, which is seriously overloaded. Through interconnection planning, the load rate of distribution transformers of microgrid 8 during peak load periods is reduced, the utilization rate of distribution transformers of the two light-loaded microgrids is improved, and the load rate of distribution transformers in the interconnected microgrid group is balanced.

[0158] The annual comprehensive cost of the distribution network system before and after the interconnection planning is shown in Table 1 below.

[0159] Table 1

[0160]

[0161] Under the flexible interconnection planning and optimized operation of microgrids, the annual comprehensive cost of the system after interconnection planning was reduced by 1.1599 million yuan compared with before planning, and the annual comprehensive cost was reduced by 8.40%, indicating that the interconnection planning of microgrids can effectively improve the economy of the distribution network operation in the entire region. Among them, the annual energy storage charging and discharging cost and the annual demand response compensation cost increased by 101,000 yuan and 82,600 yuan respectively compared with before interconnection, but the annual electricity purchase cost was reduced by 1.4659 million yuan compared with before interconnection. This is because based on the DC interconnection line, the excess photovoltaic output of the microgrid can be transmitted across the microgrid, and during the peak period of electricity prices, the internal resources can be adjusted for transfer support, reducing the cost of electricity purchase. In addition, before and after the interconnection planning, the network loss cost of the system was reduced by 84,600 yuan. This is because the DC interconnection structure promotes the consumption of photovoltaic output between microgrids and reduces the loss of photovoltaic power generation in the main power grid.

[0162] The flexible interconnection and collaborative configuration method of the AC / DC hybrid microgrid provided by the present invention forms a networking structure of the interconnection of the AC / DC hybrid microgrid by adopting a voltage source converter and a DC interconnection line. Then, based on the networking structure constructed above and the demand for power supply and power consumption, multiple operation strategies for the AC area and the DC area of ​​the microgrid under different conditions, that is, multiple transferable supply modes, are determined. Then, by constructing a two-layer model for planning and operation, the upper model is used to plan the interconnection scheme, the capacity of each voltage source converter and the transmission capacity of the DC interconnection line, and the lower model is used to determine the operating cost of the microgrid based on multiple operation strategies. Finally, by solving the two-layer model for planning and operation using simulated annealing and cone programming, a configuration scheme is determined, thereby greatly reducing the cost of microgrid interconnection planning. In addition, the photovoltaic absorption efficiency of the microgrid can be improved, so that the transformer load rate of each microgrid is reduced.

[0163] It should be understood that the order of execution of the steps in the above embodiment does not necessarily mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiment of the present invention.

[0164] The following is an embodiment of the device of the present invention. For details not described in detail therein, reference may be made to the corresponding method embodiment described above.

[0165] Fig.13 The structure diagram of the AC / DC hybrid microgrid flexible interconnection and coordinated configuration device provided by an embodiment of the present invention is shown. For the convenience of explanation, only the part related to the embodiment of the present invention is shown, which is described in detail as follows:

[0166] like Fig.13 As shown, the AC / DC hybrid microgrid flexible interconnection collaborative configuration device 1300 includes:

[0167] A construction module 1310 is used to construct a networking structure of AC / DC hybrid microgrid interconnection; wherein the voltage source converter divides the microgrid into an AC area and a DC area, and forms a microgrid interconnection based on a DC tie line;

[0168] A strategy determination module 1320 is used to determine multiple operation strategies of the AC area and the DC area of ​​the microgrid based on the network structure and the power supply and power consumption requirements;

[0169] A model building module 1330 is used to build a two-layer model for planning and operating a microgrid, wherein the upper layer model of the two-layer model is used to plan the interconnection scheme, the capacity of each voltage source converter and the transmission capacity of the DC tie line; the lower layer model of the two-layer model is used to determine the operating cost of the microgrid based on multiple operating strategies;

[0170] The solution module 1340 is used to solve the planning operation double-layer model based on simulated annealing and cone programming to determine the configuration solution.

[0171] In one possible implementation, a model structure module 1310 is constructed to construct a voltage source converter power flow model, an AC side power flow balance model, and a DC side power flow balance model based on the position of the voltage source converter in the networking structure.

[0172] In a possible implementation, each microgrid includes a load device, an energy storage device, and a photovoltaic device;

[0173] The power flow model of the voltage source converter is:

[0174]

[0175] The power flow balance model on the AC side is:

[0176]

[0177] The power flow balance model on the DC side is:

[0178]

[0179] in, are the active power of the converter AC and DC ports flowing into and out of microgrid j at time t; loss is the loss coefficient of converter transmission; and are the active power flowing through the high-voltage side and low-voltage side of the microgrid j transformer at time t, ΔP j,DT is the internal transmission loss of transformer j; P j,t and Q j,t is the active power and reactive power of the AC side of microgrid j at time t; is the reactive power flowing through the microgrid j transformer at time t, and is the active power and reactive power of the conventional load on the AC side of microgrid j at time t; P j,t is the active power of the DC side of microgrid j at time t; is the active power generated by the photovoltaic device of microgrid j at time t; and is the discharging and charging power of the energy storage unit j in the microgrid at time t; is the active power injected into the DC side by the VSC at time t; and are the active power of conventional load and demand response load on the DC side of microgrid j at time t respectively; is the mutual aid power between microgrid j and microgrid i through the tie line at time t; n represents the number of microgrids connected to microgrid j.

[0180] In a possible implementation, the networking structure includes multiple microgrids;

[0181] The strategy determination module 1320 is used to determine the target microgrid's power transfer mode in the AC area and the power transfer mode in the DC area based on the output of the photovoltaic equipment in the target microgrid and the power transfer balance relationship of the microgrid.

[0182] In one possible implementation, the upper model of the two-layer model for planning and operating is to minimize the sum of system investment cost, operation and maintenance cost, and operation cost as the objective function;

[0183] The lower model of the planning and operation two-layer model is based on the target operation strategy, with the minimum sum of the operation costs of the microgrid as the objective function; wherein the target operation strategy is any one of a plurality of operation strategies.

[0184] In a possible implementation, the upper model minF of the planned operation double-layer model is:

[0185] minF=C int +C M +C0;

[0186]

[0187]

[0188] Among them, C int is the total construction cost of the interconnection system; c VSC.int is the unit capacity construction cost of a single microgrid VSC in the interconnected system, S VSC,i The capacity of VSC installed for a single microgrid i in the interconnected system; x i-j is a 0-1 variable, x i-j 1 means that microgrid i and microgrid j are connected, x i-j 0 means that microgrid i and microgrid j are not connected; l i,j is the distance between microgrid i and microgrid j; c L.int E is the investment and installation cost of DC interconnection line per unit transmission power, j-i is the transmission capacity of the tie line between microgrid i and microgrid j, D is the number of microgrids configured with photovoltaic resources in the interconnected system, N is the total number of microgrids in the interconnected system; R(d,y) is the annual value conversion coefficient; is the unit capacity operation and maintenance cost of the microgrid VSC, C P The cost of purchasing and selling electricity to the superior power grid; C ess is the energy storage regulation cost; C DR To reduce the load regulation cost; C loss The network loss cost.

[0189] In one possible implementation, the operating costs of a microgrid include: transaction costs with the upper-level grid, charging and discharging costs of energy storage devices, demand response regulation costs, and network loss costs.

[0190] In one possible implementation, the minC0 of the lower model of the two-layer model is planned to be:

[0191] minC0=C P +C ess +C DR +C loss ;

[0192]

[0193]

[0194]

[0195]

[0196] Among them, D s is the total number of days in season s; is the electricity price at time t, is the transaction volume between microgrid d in season s and the upper-level power grid in period t, which is set to be positive when purchasing electricity from the upper-level power grid and negative when selling electricity to the upper-level power grid; α is the unit charging and discharging cost of the energy storage unit, is the charging and discharging power of the energy storage unit of microgrid d in time period t during season s, and η is the charging and discharging efficiency of the energy storage unit; The compensation price for curtailing demand response, is the demand response amount that can be reduced by microgrid d in season s and period t; is the transformer loss cost, a d and b d is the distribution transformer loss coefficient of microgrid d; is the VSC transmission loss, χ loss is the VSC transmission loss coefficient, The power injected into the AC side of the VSC of microgrid d during period t in season s is: The VSC DC side injection power of microgrid d in time period t in season s is specified as and cannot be 1 at the same time; Δt is the duration of time period t, and D is the set of microgrids.

[0197] In a possible implementation, the solving module 1340 is used to solve the upper model of the planning and operation double-layer model based on a simulated annealing algorithm to obtain an optimal microgrid interconnection scheme, a capacity configuration scheme of each voltage source converter, and a configuration scheme of the transmission capacity of the DC tie line;

[0198] Based on the optimal microgrid interconnection scheme, the capacity configuration scheme of each voltage source converter and the transmission capacity configuration scheme of the DC interconnection line, the cone programming algorithm is called to solve the lower model of the planning and operation two-layer model, and the result is passed to the upper model of the planning and operation two-layer model. The final configuration scheme is determined by iterative calculation.

[0199] In the above embodiments, the description of each embodiment has its own emphasis. For parts that are not described or recorded in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0200] Those of ordinary skill in the art will appreciate that the templates, units, and algorithm steps of each example described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professional and technical personnel can use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of the present invention.

[0201] If the module / unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the present invention implements all or part of the processes in the above-mentioned embodiment method, and can also be completed by instructing the relevant hardware through a computer program. The computer program can be stored in a computer-readable storage medium. When the computer program is executed by the processor, it can implement the steps of the embodiment of the evaluation method for the adequacy of the distribution network in which each electric vehicle and distributed photovoltaic participate. Among them, the computer program includes computer program code, and the computer program code can be in source code form, object code form, executable file or some intermediate form. The computer-readable medium may include: any entity or device that can carry the computer program code, recording medium, U disk, mobile hard disk, disk, optical disk, computer memory, read-only memory, random access memory, electric carrier signal, telecommunication signal and software distribution medium.

[0202] The embodiments described above are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. Such modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included in the protection scope of the present invention.

Claims

1. A method for flexible interconnection and collaborative configuration of AC / DC hybrid microgrids, characterized in that: include: Constructing a networking structure of AC / DC hybrid microgrid interconnection; wherein the voltage source converter divides the microgrid into an AC area and a DC area, and forms microgrid interconnection based on a DC tie line; Based on the networking structure and the power supply and power consumption requirements, determine multiple operation strategies for the AC area and the DC area of ​​the microgrid; Constructing a two-layer model for planning and operating the microgrid, wherein the upper model of the two-layer model is used to plan the interconnection scheme, the capacity of each voltage source converter and the transmission capacity of the DC tie line; and the lower model of the two-layer model is used to determine the operating cost of the microgrid based on the multiple operating strategies; The planning operation double-layer model is solved based on simulated annealing and cone programming to determine the configuration scheme.

2. The AC / DC hybrid microgrid flexible interconnection collaborative configuration method according to claim 1 is characterized in that: The networking structure for constructing AC / DC hybrid microgrid interconnection also includes: Based on the position of the voltage source converter in the networking structure, a power flow model of the voltage source converter, a power flow balance model on the AC side, and a power flow balance model on the DC side are constructed.

3. The AC / DC hybrid microgrid flexible interconnection collaborative configuration method according to claim 2 is characterized in that: The networking structure includes multiple microgrids, each of which includes a load device, an energy storage device and a photovoltaic device; The voltage source converter power flow model is: The power flow balance model on the AC side is: The power flow balance model on the DC side is: in, are the active power of the converter AC and DC ports flowing into and out of microgrid j at time t; loss is the loss coefficient of converter transmission; and are the active power flowing through the high-voltage side and low-voltage side of the microgrid j transformer at time t, ΔP j,DT is the internal transmission loss of transformer j; P j,t and Q j,t is the active power and reactive power of the AC side of microgrid j at time t; is the reactive power flowing through the microgrid j transformer at time t, and is the active power and reactive power of the conventional load on the AC side of microgrid j at time t; P j,t is the active power of the DC side of microgrid j at time t; is the active power generated by the photovoltaic device of microgrid j at time t; and is the discharging and charging power of the energy storage unit j in the microgrid at time t; is the active power injected into the DC side by the VSC at time t; and are the active power of conventional load and demand response load on the DC side of microgrid j at time t respectively; is the mutual aid power between microgrid j and microgrid i through the tie line at time t; n represents the number of microgrids connected to microgrid j.

4. The AC / DC hybrid microgrid flexible interconnection collaborative configuration method according to claim 1, characterized in that: The networking structure includes multiple microgrids; The method of determining multiple operation strategies of the AC area and the DC area of ​​the microgrid based on the networking structure and the power supply and power consumption requirements includes: Based on the output of photovoltaic equipment in the target microgrid and the power transfer balance relationship of the microgrid, the transfer mode of the target microgrid in the AC area and the transfer mode in the DC area are determined.

5. The method for flexible interconnection and coordinated configuration of AC / DC hybrid microgrids according to claim 1, characterized in that: The upper model of the two-layer planning and operation model takes the minimum sum of system investment cost, operation and maintenance cost and operation cost as the objective function; The lower model of the planning and operation two-layer model is based on a target operation strategy, with the minimization of the sum of the operation costs of the microgrid as the objective function; wherein the target operation strategy is any one of the multiple operation strategies.

6. The method for flexible interconnection and coordinated configuration of AC / DC hybrid microgrids according to claim 5, characterized in that: The upper model minF of the two-layer model for planning and operation is: minF=C int +C M +C0; C0=C P +C ess +C DR +C loss ; Among them, C int is the total construction cost of the interconnection system; c VSC.int is the unit capacity construction cost of a single microgrid VSC in the interconnected system, S VSC,i The capacity of VSC installed for a single microgrid i in the interconnected system; x i-j is a 0-1 variable, x i-j 1 means that microgrid i and microgrid j are connected, x i-j 0 means that microgrid i and microgrid j are not connected; l i,j is the distance between microgrid i and microgrid j; c L.int E is the investment and installation cost of DC interconnection line per unit transmission power, j-i is the transmission capacity of the tie line between microgrid i and microgrid j, D is the number of microgrids configured with photovoltaic resources in the interconnected system, N is the total number of microgrids in the interconnected system; R(d,y) is the annual value conversion coefficient; is the unit capacity operation and maintenance cost of the microgrid VSC, C P The cost of purchasing and selling electricity to the superior power grid; C ess is the energy storage regulation cost; C DR To reduce the load regulation cost; C loss The network loss cost.

7. The method for flexible interconnection and coordinated configuration of AC / DC hybrid microgrids according to claim 5, characterized in that: The operating costs of the microgrid include: transaction costs with the upper-level power grid, charging and discharging costs of energy storage devices, demand response regulation costs and network loss costs.

8. The method for flexible interconnection and coordinated configuration of AC / DC hybrid microgrids according to claim 7, characterized in that: The lower model minC0 of the planned double-layer model is: minC0=C P +C ess +C DR +C loss ; Among them, D s is the total number of days in season s; is the electricity price at time t, is the transaction volume between microgrid d in season s and the upper-level power grid in period t, which is set to be positive when purchasing electricity from the upper-level power grid and negative when selling electricity to the upper-level power grid; α is the unit charging and discharging cost of the energy storage unit, is the charging and discharging power of the energy storage unit of microgrid d in time period t during season s, and η is the charging and discharging efficiency of the energy storage unit; is the compensation price for curtailing demand response, is the demand response amount that can be reduced by microgrid d in season s and period t; is the transformer loss cost, a d and b d is the distribution transformer loss coefficient of microgrid d; is the VSC transmission loss, χ loss is the VSC transmission loss coefficient, The power injected into the AC side of the VSC of microgrid d during period t in season s is: The VSC DC side injection power of microgrid d in time period t in season s is specified as and cannot be 1 at the same time; Δt is the duration of time period t, and D is the set of microgrids.

9. The method for flexible interconnection and coordinated configuration of AC / DC hybrid microgrids according to claim 1, characterized in that: The step of solving the two-layer model of the planning operation based on simulated annealing and cone programming to determine the configuration scheme includes: Based on the simulated annealing algorithm, the upper model of the planning and operation double-layer model is solved to obtain the optimal microgrid interconnection scheme, the capacity configuration scheme of each voltage source converter and the transmission capacity configuration scheme of the DC tie line; Based on the optimal microgrid interconnection scheme, the capacity configuration scheme of each voltage source converter and the configuration scheme of the transmission capacity of the DC interconnection line, the cone programming algorithm is called to solve the lower model of the planning and operation double-layer model, and the result is passed to the upper model of the planning and operation double-layer model, and iterative calculation is performed to determine the final configuration scheme.

10. An AC / DC hybrid microgrid flexible interconnection and collaborative configuration device, characterized in that: include: A construction module is used to construct a networking structure of AC / DC hybrid microgrid interconnection; wherein the voltage source converter divides the microgrid into an AC area and a DC area, and forms a microgrid interconnection based on a DC tie line; A strategy determination module is used to determine multiple operation strategies of the AC area and the DC area of ​​the microgrid based on the networking structure and the power supply and power consumption requirements; A model building module is used to build a two-layer model for planning and operating the microgrid, wherein the upper model of the two-layer model is used to plan the interconnection scheme, the capacity of each voltage source converter and the transmission capacity of the DC tie line; the lower model of the two-layer model is used to determine the operating cost of the microgrid based on the multiple operating strategies; The solution module is used to solve the two-layer model of the planning operation based on simulated annealing and cone programming to determine the configuration scheme.

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