A joint active-reserve scheduling method based on safe intervals

Abstract

This invention discloses an active power-reserve joint dispatching method based on a safety interval. Step 1: Obtain the topology of a specified power system, the installed capacity of new energy sources and thermal power units, and the upper and lower limits of active power output of system nodes to construct a thermal stability safety domain. Step 2: Filter effective branches by injecting active power into nodes within the thermal stability safety domain. Step 3: Establish a set of safe and effective branches by performing relevant local boundary thermal stability checks on the effective branches using the following formula. Step 4: Determine whether a branch among the effective branches belongs to the set of safe and effective branches, and then construct an active power auxiliary dispatching model. Step 5: Verify the active power auxiliary dispatching model using a unit combination optimization algorithm and output the objective function for the extreme transmission scenario. This invention can improve the callability of day-ahead dispatching plans in power systems.

Description

Technical Field

[0001] This invention relates to the field of power system ancillary service dispatch optimization, and in particular to the problem of active power-reserve joint dispatch optimization method based on safety intervals. Background Technology

[0002] With the integration of new energy sources, the system is approaching its operational limits, leading to increasingly complex and diverse random factors that must be considered in power generation dispatch. The traditional power system model, which focuses solely on minimizing generation costs throughout the entire dispatch cycle, is no longer applicable. To better absorb new energy and improve system reliability, the power system needs to reserve reasonable standby capacity in day-ahead dispatch plans to mitigate power imbalances caused by new energy and load fluctuations. However, this often results in situations where, despite appropriate standby capacity being configured in day-ahead dispatch, the system may experience standby unavailability due to line flow constraints during actual dispatch if power fluctuations occur. Therefore, conducting research on active power-standby joint dispatch based on safety intervals is meaningful, as it can improve the availability of dispatch plans while balancing safety and economy. Summary of the Invention

[0003] To address the shortcomings of existing technologies, this invention primarily studies the active-reserve joint scheduling optimization problem based on safety intervals, which can improve the callability of day-ahead scheduling plans. Based on the thermal stability safety domain theory, transmission limit constraints are constructed for any branch in the system within the node injection space. Then, the effective branches—those experiencing "N-1" faults under specific operating conditions and those potentially overloaded under normal conditions—are analyzed. Finally, by setting transmission safety margins for each line, an economic scheduling model considering these margins is constructed.

[0004] The core content of this invention can be summarized as follows:

[0005] (1) A joint active-reserve scheduling method based on safe intervals is proposed. This method first constructs the mathematical relationship between the active power of the transmission line and the active power injected into the node, i.e., the safe interval model, and then selects the effective branch constraints that affect the feasibility of reserve dispatch based on the safe interval.

[0006] (2) In order to obtain a joint scheduling scheme of active power and reserve, this invention proposes a unit combination algorithm that considers the safety range under the premise of satisfying reserve restrictions, reserve constraints, safety constraints, unit output restrictions and ramp-up constraints, and schedules the unit combination in the system to obtain a feasible unit start-up and shutdown scheme and active power and reserve clearing plan.

[0007] To address the problems of the existing technology, the present invention adopts the following technical solution:

[0008] A joint active power-reserve scheduling method based on a safety interval, the joint scheduling method comprising the following steps:

[0009] Step 1: Obtain the topology of the specified power system, the installed capacity of new energy sources and thermal power units, and the upper and lower limits of active power output of system nodes to construct the thermal stability security domain; that is:

[0010]

[0011] Where: P ij Let i represent the power of branch l, with the first node being i and the last node being j. S is the maximum power constraint value for branch l. B Let f(x) = P be the set of branches, and let f(x) = P be other constraints that this set must satisfy.

[0012] Step 2: Filter effective branches by injecting active power into nodes in the thermal stability security domain;

[0013] Step 3: Establish a set of safe and effective branches by performing relevant local boundary thermal stability checks on the effective branches using the following formula;

[0014]

[0015] Step 4: Determine whether a branch in the effective branches belongs to the set of safe and effective branches, and then construct the active power auxiliary scheduling model: where:

[0016] When the node injection of an effective branch varies within Θ, if the maximum value P of the power flow in branch l... ijmax ;like If branch l is not found in the set of valid branches, then branch l belongs to the set of valid branches; otherwise, branch l does not belong to the set of valid branches.

[0017] P ijmax =max|P ij |

[0018]

[0019]

[0020]

[0021] Where: P ij Let i represent the power of branch l, with the first node being i and the last node being j. The maximum output of node i. B is the minimum output force of node i. ij θ represents the admittance value of branch l. i Let be the angle of attack of node i.

[0022] Step 5: Verify the active power auxiliary scheduling model using the unit combination optimization algorithm and output the objective function for the extreme transmission scenario:

[0023] maxβ

[0024] |P ij |≤β*P max

[0025] Specifically, the constraints on the power generation cost of the power system are as follows:

[0026] C(P)+S(z i,1 ,z i,2 ...,z i,t )≤obj*(1+σ)

[0027] β is the maximum transmission margin, P ij Let represent the power of branch l, with the first node being i and the last node being j. C(P) represents the unit output cost, S represents the start-up and shutdown cost, z represents the start-up and shutdown status of the unit, obj represents the objective function value of the traditional method, and σ is the maximum acceptable cost margin.

[0028] Furthermore, in step 2, the step of filtering valid branches is as follows:

[0029] The active power flow of branch l in the thermally stable safety domain is calculated using the following formula:

[0030]

[0031] Where: P ij Let B represent the power of branch l, with the first node being i and the last node being j. ij θ represents the admittance value of branch l. i Let θ be the angle of attack at node i. ij Let be the power angle difference of branch l.

[0032] The active power injection of all nodes in the thermally stable security domain is calculated using the following formula:

[0033]

[0034] in: This is the sensitivity coefficient. For P ij For θ i The partial derivative, For θ i For P k The partial derivative of x ij Let be the impedance value of branch l. Effective branches are selected by active power injection at all nodes: the effective branches are:

[0035] Θ={P|P m ≤P≤PM}

[0036] Where: Θ represents the effective branch set space.

[0037] Furthermore, step 5 involves verifying the active power auxiliary scheduling model using a unit combination optimization algorithm:

[0038] Constraints on the spinning reserve of the power system:

[0039]

[0040] in, D is the maximum active power output of unit i. t R represents the load level. t It is the active power reserve requirement for time period t;

[0041] Upper and lower limits constraints on active power output of the power system:

[0042] P i,min u i,t ≤p i,t ≤P i,max u i,t

[0043] Among them, P i,min and P i,max These are the upper and lower limits of active power output, u i,t The unit is in the powered-on state;

[0044] Minimum start-up and shutdown time constraints for thermal power units in the power system:

[0045]

[0046] in, and These refer to the start-up and shutdown times of thermal power units. and These are the minimum start-up and stop times, u i,t and u i,t-1 The start-up and stop states at time t and time t-1 are respectively;

[0047] The thermally stable safe domain power flow equation is obtained using the following formula:

[0048]

[0049] Q ij =-V i V j (G ij cosθ ij -B ij sinθ ij )+(B ij-b ij0 V i 2

[0050] Among them, P ij and Q ij G represents the active power and reactive power of branch l, respectively. ij and B ij The conductance and susceptance of branch l are respectively, V i Let θ be the voltage at node i. ij Let be the power angle difference of branch l.

[0051] Furthermore, the nonlinear terms in the power flow equations are linearized using the second-order cone method:

[0052]

[0053] x ij，1 =V i V j sinθ ij

[0054] x ij，2 =V i V j cosθ ij

[0055]

[0056] P ij =G ij x i -G ij x ij，2 -B ij x ij，1

[0057] Q ij =-G ij x ij，2 +B ij x ij，1 +(B ij -b ij0 )x i

[0058] (2x ij，1 ) 2 +(2x ij，2 ) 2 +(x i -x j ) 2 ≤(x i +x j ) 2

[0059] Where, xi x ij，1 and x ij，2 This is an intermediate auxiliary variable that is introduced.

[0060] Beneficial effects

[0061] Compared with the prior art, the beneficial effects of the present invention are:

[0062] To address the uncertainties arising from the integration of new energy sources, power system dispatching needs to consider reasonable power flow distribution. This includes not only whether day-ahead dispatching leads to line overload risks, but also the feasibility of intraday adjustment schemes. Therefore, this invention proposes a coordinated dispatching method for active power and reserve power that considers line transmission margins, based on the static security domain. By identifying effective branches prone to overload and generating safety interval constraints that take into account the range of unit output adjustment during reserve call-up, it can not only effectively solve the problem of reserve scheme availability verification, but also identify key factors affecting availability. Attached Figure Description

[0063] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments of this application and their descriptions are used to explain this application and do not constitute an undue limitation of this application.

[0064] Figure 1 The system structure diagram used in the numerical example analysis provided for this invention includes 5 generator sets, 15 lines and 11 load nodes, which is used to verify the effectiveness of the proposed method.

[0065] Figure 2 The new energy output prediction information provided by this invention is used to simulate power fluctuations in actual dispatching.

[0066] Figure 3 The unit output information provided by this invention is used to demonstrate the unit output information based on the safe zone scheduling method;

[0067] Figure 4 The two-dimensional safety domain diagram provided by this invention is used to illustrate the effective safety constraints, i.e., the effective branch constraints. It can be seen that there is a coupling relationship between the unit outputs, which means that the output of each unit cannot be determined individually.

[0068] Figure 5 The line power flow information provided by this invention is used to demonstrate the effectiveness of the proposed method. It can be seen that, for the scheduling plan obtained by the traditional unit combination method, although the total reserve capacity is sufficient, there is a high possibility that the reserve will be unavailable due to the limitation of line transmission capacity.

[0069] Figure 6 The flowchart of the joint scheduling method provided by the present invention. Detailed Implementation

[0070] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0071] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0072] As introduced in the background section, existing technologies are prone to problems in the coordinated scheduling of active power and reserve due to insufficient line transmission capacity, which prevents actual deployment. To solve the above problems, this application proposes an active power-reserve joint scheduling method based on safety intervals, which ensures the availability of scheduling results without significantly changing costs, and identifies the key factors affecting the scheduling.

[0073] like Figure 1-6 As shown, to better explain the mechanism of the boundary method proposed in this invention, the following sections will introduce the two aspects of effective branch selection and unit combination optimization algorithm.

[0074] 1. Valid branch selection

[0075] Power system thermal stability safety domain Ω THSR Defined in the node injection power space, it is the set of all operating points (complex power injections) that satisfy the system's thermal stability security constraints. Considering factors such as local reactive power balance in the transmission network, the thermal stability security constraints of a branch are mainly affected by its transmitted active power. In practice, the thermal stability security domain can be defined in the active power injection space of the node, as shown in the following equation.

[0076]

[0077] From Ω THSR As can be seen from the definition of (h), the key to solving the thermal stability security domain lies in establishing the mapping relationship between the active power injection of nodes and the active power flow of branches.

[0078] For high-voltage transmission systems, the following assumptions hold:

[0079] (1) The resistance of a transmission line is much smaller than its reactance, i.e., G ij ≈0.

[0080] (2) Under steady-state operation, the branch angle of the line is very small, therefore, sinθij ≈θ ij cosθ ij ≈1.

[0081] (3) Under steady-state operation, the voltage amplitude of the node is approximately maintained at 1.0 pu.

[0082] Under the above assumptions, the active power flow equations of the power system can be simplified to the following equation:

[0083]

[0084] By rearranging, the above equation can be transformed into the matrix shown below.

[0085] P=Bθ (3)

[0086] Transforming the above equation, we get:

[0087] θ=XP (4)

[0088] Correspondingly, the active power flow of branch l can be calculated by the following formula:

[0089]

[0090] According to equations (3) and (4), all nodes except the balancing node can be obtained:

[0091]

[0092] Taking the active power injection of all generating nodes and load nodes in the system, excluding the balancing machine, as the parameter space, and considering the variation range of node injection, the parameter space of the system can be expressed by the following formula:

[0093] Θ={P|P m ≤P≤P M} (7)

[0094] To ensure the system meets thermal stability safety constraints, all branches in the system need to be verified. Considering the large number of nodes and branches in a real large power grid, and the complexity and variability of operating modes, verifying the thermal stability safety constraints of all branches for each possible operating mode would involve an enormous workload. Typically, the injection at each node in the system varies within a certain range, i.e., Θ is a variable with a power of 2... nA hypercube with vertices. When node injection varies within Θ, not all branches in the system can reach their thermal stability limit. Therefore, this invention defines the branches that can reach the thermal stability limit after considering the range of node injection variation as effective branches. The combination of all effective branches is called the effective branch set, defined as shown in the following equation. During power grid operation, only the thermal stability safety constraints of the effective branches need to be verified. Correspondingly, when constructing the thermal stability safety domain of the system, only the local boundaries related to the effective branches need to be constructed.

[0095]

[0096] The basic process for determining whether a branch l belongs to the set of valid branches is as follows: Solve the optimization problem shown in the above equation to obtain the maximum power flow P of branch l when the node injection varies within Θ. ijmax If P ijmax ≥P l M If the condition is met, then branch l belongs to the set of valid branches; otherwise, branch l does not belong to the set of valid branches.

[0097] P ijmax =max|P ij |

[0098]

[0099]

[0100] P i m ≤P i ≤P i M

[0101] 2. Unit Combination Optimization Algorithm

[0102] (1) Rotational spare constraint:

[0103]

[0104] in, D is the maximum active power output of unit i. t R represents the load level. t It is the active power reserve requirement for time period t.

[0105] (2) Upper and lower limits of active power output constraints:

[0106] P i，min u i，t ≤p i，t ≤P i，max u i，t (11)

[0107] (3) Minimum start-up and shutdown time constraints for thermal power units:

[0108]

[0109] (4) Power flow equations:

[0110] P ij =G ij V i 2 -V i Y j (G ij cosθ ij +B ij sinθ ij (13)

[0111] Q ij =-V i V j (G ij cosθ ij -B ij sinθ ij )+(B ij -b ij0 V i 2 (14)

[0112] To handle the nonlinear terms in the power flow equations, this invention employs a second-order cone technique to linearize them, as detailed below:

[0113]

[0114] x ij，1 =V i V j sinθ ij (16)

[0115] x ij，2 =V i V j cosθ ij (17)

[0116]

[0117] P ij =G ij x i -G ij x ij，2 -B ij x ij，1 (19)

[0118] Q ij =-G ij x ij,2+B ij x ij，1 +(B ij -b ij0 )x i (20)

[0119] (2x ij，1 ) 2 +(2x ij，2 ) 2 +(x i -x j ) 2 ≤(x i +x j ) 2 (twenty one)

[0120] Where, x i x ij，1 and x ij，2 This is an intermediate auxiliary variable that is introduced.

[0121] (5) Objective function:

[0122] A target function for extreme transmission scenarios is constructed to ensure that the safety margin of effective branches is at a reasonable level. The specific target function is as follows:

[0123]

[0124] To balance economic efficiency, power generation cost constraints are established as follows:

[0125] C(P)+S(z i，1 , z i，2 ..., z i，t )≤obj*(1+σ) (23).

Claims

1. A joint active power-reserve scheduling method based on safe intervals, characterized in that, The joint scheduling method includes the following steps: Step 1: Obtain the topology of the specified power system, the installed capacity of new energy sources and thermal power units, and the upper and lower limits of active power output of system nodes to construct the thermal stability security domain; that is: Where: P ij This represents the power of branch l, with the first node being i and the last node being j. S is the maximum power constraint value for branch l. B Let f(x) be the set of branches, and P be other constraints that this set must satisfy. Step 2: Filter effective branches by injecting active power into nodes in the thermal stability security domain; Step 3: Establish a set of safe and effective branches by performing relevant local boundary thermal stability checks on the effective branches using the following formula; Step 4: Determine whether a branch in the effective branches belongs to the set of safe and effective branches, and then construct the active power auxiliary scheduling model: where: When the node injection of an effective branch varies within Θ, if the maximum value P of the power flow in branch l... ijmax If P ijmax ≥P l M If the condition is met, then branch l belongs to the set of valid branches; otherwise, branch l does not belong to the set of valid branches. P ijmax =max|P ij | P i m ≤P i ≤P i M Where: P ij Let i represent the power of branch l, with the first node being i and the last node being j. The maximum output of node i. B is the minimum output force of node i. ij θ represents the admittance value of branch l. i Let be the angle of attack at node i; Step 5: Verify the active power auxiliary scheduling model using the unit combination optimization algorithm and output the objective function for the extreme transmission scenario: maxβ |P ij |≤β*P max Specifically, the constraints on the power generation cost of the power system are as follows: C(P)+S(z i,1 ,With i,2 ...,With i,t )≤obj*(1+σ) β is the maximum transmission margin, P ij Let represent the power of branch l, with the first node being i and the last node being j. C(P) represents the unit output cost, S represents the start-up and shutdown cost, z represents the start-up and shutdown status of the unit, obj represents the objective function value of the traditional method, and σ is the maximum acceptable cost margin.

2. The active power-reserve joint scheduling method based on a safety interval according to claim 1, characterized in that, Step 2, the process of filtering valid branches: The active power flow of branch l in the thermally stable safety domain is calculated using the following formula: Where: P ij Let B represent the power of branch l, with the first node being i and the last node being j. ij θ represents the admittance value of branch l. i Let θ be the angle of attack at node i. ij The difference in power angle of branch l; The active power injection of all nodes in the thermally stable security domain is calculated using the following formula: in: This is the sensitivity coefficient. For P ij For θ i The partial derivative, For θ i For P k The partial derivative of x ij Let l be the impedance value of branch l; Valid branches are obtained by injecting active power into all nodes; the valid branches are: Θ={P|P m ≤P≤P M } Where: Θ represents the effective branch set space.

3. The active power-reserve joint scheduling method based on a safety interval according to claim 1, characterized in that, Step 5 involves verifying the active power auxiliary scheduling model using a unit combination optimization algorithm. Constraints on the spinning reserve of the power system: in, D is the maximum active power output of unit i. t R represents the load level. t It is the active power reserve requirement for time period t; Upper and lower limits constraints on active power output of the power system: P i,min in i,t ≤p i,t ≤P i,max in i,t Among them, P i,min and P i,max These are the upper and lower limits of active power output, u i,t The unit is in the powered-on state; Minimum start-up and shutdown time constraints for thermal power units in the power system: in, and These refer to the start-up and shutdown times of thermal power units. and These are the minimum start-up and stop times, u i,t and u i,t-1 The start-up and stop states at time t and time t-1 are respectively; The thermally stable safe domain power flow equation is obtained using the following formula: Among them, P ij and Q ij G represents the active power and reactive power of branch l, respectively. ij and B ij The conductance and susceptance of branch l are respectively, V i Let θ be the voltage at node i. ij Let be the power angle difference of branch l.

4. The active power-reserve joint scheduling method based on a safety interval according to claim 3, characterized in that, The nonlinear terms in the power flow equations are linearized using the second-order cone method: x ij，1 =V i V j sinθ ij x ij，2 =V i V j cosθ ij P ij =G ij x i -G ij x ij，2 -B ij x ij，1 Q ij =-G ij x ij,2 +B ij x ij，1 +(B ij -b ij0 )x i (2x ij，i ) 2 +(2x ij，2 ) 2 +(x i -x j ) 2 ≤(x i +x j ) 2 Where, x i x ij,1 and x ij,2 This is an intermediate auxiliary variable that is introduced.

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