A method and terminal for searching operating boundaries of a flexible direct current transmission system

Abstract

The present invention provides a method and terminal for searching the operating boundary of a flexible direct current transmission system, including: initializing a steady-state model of the flexible direct current transmission system, constructing the voltage equations and operating constraints of each node in the flexible direct current transmission system; constructing an operating boundary search model for the flexible direct current transmission system, converting the problem of determining the operating domain of the flexible direct current transmission system into an optimization problem of the upper and lower limits of the output active power and reactive power; constructing an operating condition set of the flexible direct current transmission system, and using the operating boundary search model to calculate the upper and lower limits of the output power under different conditions in the operating condition set, and obtaining the operating boundary of the flexible direct current transmission system. The present invention obtains the upper and lower limits of the output power of the flexible direct current transmission system by optimizing the calculation, and then directly determines the operating boundary of the system, avoids determining the operating range by point-by-point verification, effectively saves calculation overhead, and intuitively gives the system operating area, providing a reference for system planning and operation scheduling.

Description

Technical Field

[0001] The present invention relates to the technical field of flexible direct current power transmission systems, and in particular to a method and a terminal for searching operating boundaries of flexible direct current power transmission systems. Background Art

[0002] In recent years, flexible DC transmission technology has been widely used in scenarios such as asynchronous networking and offshore wind power transmission. my country has built several demonstration projects of flexible DC transmission systems in Nanhui, Shanghai, Nan'ao, Shantou, Zhoushan, Zhejiang, Xiamen, Fujian, and Rudong, Jiangsu, which are of great significance to promoting the development of flexible DC transmission technology.

[0003] The flexible DC transmission system has the ability to operate in four quadrants of output power. Its output active power and reactive power can be flexibly adjusted according to the system's transmission and reception needs, but its output upper and lower boundaries are limited by many factors such as voltage stability and current limit.

[0004] At present, most of the research on the output power control of flexible direct current transmission systems is aimed at a given operating condition, and the output limit capacity of the system under the current operating condition is determined by a step-by-step iterative verification method. The calculation overhead is extremely large, and it is impossible to intuitively and comprehensively determine the current system operating state margin. Therefore, this application studies a search method for the operating boundary of a flexible direct current transmission system, which determines the system operating boundary by solving the upper and lower limits of the system output power, effectively improving the calculation efficiency and providing a reference for system planning and operation scheduling. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a method and terminal for searching the operating boundary of a flexible direct current transmission system, which can directly determine the operating boundary of the flexible direct current transmission system, avoid determining the operating range through point-by-point verification, effectively save calculation overhead, and provide a reference for system planning and operation scheduling.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0007] A method for searching operating boundaries of a flexible direct current transmission system comprises the following steps:

[0008] S1. Initialize the steady-state model of the flexible DC transmission system and construct the voltage equations and operation constraints of each node in the flexible DC transmission system;

[0009] S2. Construct an operation boundary search model for the flexible DC transmission system, and transform the operation domain determination problem of the flexible DC transmission system into an optimization problem of the upper and lower limits of the output active power and reactive power;

[0010] S3. Construct an operating condition set of the flexible DC power transmission system, and use the operating boundary search model to calculate the upper and lower limits of the output power under different conditions in the operating condition set to obtain the operating boundary of the flexible DC power transmission system.

[0011] In order to solve the above technical problems, another technical solution adopted by the present invention is:

[0012] A flexible direct current transmission system operation boundary search terminal includes a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor implements the following steps when executing the computer program:

[0013] S1. Initialize the steady-state model of the flexible DC transmission system and construct the voltage equations and operation constraints of each node in the flexible DC transmission system;

[0014] S2. Construct an operation boundary search model for the flexible DC transmission system, and transform the operation domain determination problem of the flexible DC transmission system into an optimization problem of the upper and lower limits of the output active power and reactive power;

[0015] S3. Construct an operating condition set of the flexible DC power transmission system, and use the operating boundary search model to calculate the upper and lower limits of the output power under different conditions in the operating condition set to obtain the operating boundary of the flexible DC power transmission system.

[0016] The beneficial effects of the present invention are as follows: the present invention provides a method and a terminal for searching the operating boundaries of a flexible direct current transmission system. By constructing a steady-state model of the flexible direct current transmission system, and constructing voltage equations and operating constraints of each node in the flexible direct current transmission system based on the steady-state model, the problem of determining the operating domain of the system is converted into an optimization problem of the upper and lower limits of the output power in combination with the operating boundary search model of the flexible direct current transmission system. Then, an operating condition set of the flexible direct current system is constructed, and the upper and lower limits of the output power under different operating conditions are calculated by using the operating boundary search model, so as to directly determine the operating boundary of the system, avoid determining the operating range by point-by-point verification, effectively save calculation overhead, and intuitively provide the system operating area, providing a reference for system planning and operation scheduling. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is an overall flow chart of a method for searching operating boundaries of a flexible direct current transmission system according to an embodiment of the present invention;

[0018] Figure 2 It is a system structure diagram of the flexible DC transmission system;

[0019] Figure 3 It is the equivalent circuit diagram of the flexible DC transmission system at the fundamental frequency;

[0020] Figure 4 It is a specific flow chart of a method for searching operating boundaries of a flexible direct current transmission system according to an embodiment of the present invention;

[0021] Figure 5 It is the output side operation boundary of the flexible DC transmission system in the present invention;

[0022] Figure 6 It is a structural schematic diagram of a flexible direct current transmission system operation boundary search terminal according to an embodiment of the present invention.

[0023] Description of labels:

[0024] 1. A terminal for searching operating boundaries of a flexible direct current transmission system; 2. A memory; 3. A processor. DETAILED DESCRIPTION

[0025] In order to explain the technical content, achieved objectives and effects of the present invention in detail, the following is an explanation in combination with the implementation modes and the accompanying drawings.

[0026] Please refer to Figures 1 to 5 , a method for searching operating boundaries of a flexible direct current transmission system, comprising the steps of:

[0027] S1. Initialize the steady-state model of the flexible DC transmission system and construct the voltage equations and operation constraints of each node in the flexible DC transmission system;

[0028] S2. Construct an operation boundary search model for the flexible DC transmission system, and transform the operation domain determination problem of the flexible DC transmission system into an optimization problem of the upper and lower limits of the output active power and reactive power;

[0029] S3. Construct an operating condition set of the flexible DC power transmission system, and use the operating boundary search model to calculate the upper and lower limits of the output power under different conditions in the operating condition set to obtain the operating boundary of the flexible DC power transmission system.

[0030] From the above description, it can be seen that the beneficial effects of the present invention are: by constructing a steady-state model of a flexible direct current transmission system, and constructing the voltage equations and operating constraints of each node in the flexible direct current transmission system based on the steady-state model, combined with the operating boundary search model of the flexible direct current transmission system, the problem of determining the operating domain of the system is converted into an optimization problem of the upper and lower limits of the output power, and then a set of operating conditions of the flexible direct current system is constructed, and the operating boundary search model is used to calculate the upper and lower limits of the output power under different operating conditions, thereby directly determining the operating boundary of the system, avoiding determining the operating range by point-by-point verification, effectively saving calculation overhead, and intuitively giving the system operating area, providing a reference for system planning and operation scheduling.

[0031] Furthermore, the voltage equations and operation constraints of each node constructed in S1 are specifically:

[0032] The voltage equation groups between the virtual connection points of the upper and lower bridge arms, the output points, the common connection points, and the equivalent nodes of the feed-in end system in the flexible direct current transmission system are respectively constructed, and the voltage constraints and current constraints of the voltage equation groups are constructed.

[0033] From the above description, it can be seen that the voltage equation group and its operation constraints of each node in the flexible DC transmission system are constructed so that the boundary search model can be optimized and constrained according to the voltage equation group and the operation constraints, ensuring that a stable and accurate system operation boundary is obtained in the future.

[0034] Furthermore, constructing the voltage equation and operation constraints of each node in S1 specifically includes the following steps:

[0035] S11, construct the voltage equation group to obtain formula (1):

[0036]

[0037] Wherein, diff is the virtual connection point of the upper and lower bridge arms of the flexible DC transmission system at the fundamental frequency, v is the output point of the flexible DC transmission system, PCC is the common connection point between the flexible DC transmission system and the feed-in system, sys is the equivalent node of the feed-in system of the flexible DC transmission system, arm is the bridge arm of the flexible DC transmission system, T is the converter transformer of the flexible DC transmission system, U is the node voltage, P is the active power, Q is the reactive power, Z is the impedance, j is the imaginary unit, a dot above a letter indicates a phasor, and no dot above a letter indicates a conventional variable;

[0038] S12. Calculate the real part and imaginary part of the phase quantity in formula (1) to obtain formulas (2), (3) and (4):

[0039]

[0040]

[0041]

[0042] Wherein, d is the d-axis component of the output point voltage of the flexible DC transmission system, q is the q-axis component of the output point voltage of the flexible DC transmission system, R is the resistance, and X is the reactance;

[0043] S13. Construct the voltage constraint of the virtual connection point of the upper and lower bridge arms voltage of the flexible DC transmission system, as shown in the following formula (5):

[0044]

[0045] Among them, U dc is the DC side capacitor voltage of the flexible DC transmission system;

[0046] S14. Construct the voltage constraint of the output point of the flexible DC transmission system, as shown in formula (6):

[0047] U min ≤U v ≤U max (6);

[0048] Among them, U min is the voltage lower limit of the output point of the flexible DC transmission system, U max The voltage upper limit of the output point of the flexible DC transmission system;

[0049] S15. Construct the current constraint of the output point of the flexible DC transmission system, as shown in formula (7):

[0050]

[0051] Among them, I max It is the upper limit of current at the output point of the flexible DC transmission system.

[0052] From the above description, it can be seen that the voltage equation group of each node of the flexible DC transmission system and the voltage and current constraints of the output point are constructed so that they can be subsequently substituted into the boundary search model to obtain the upper and lower boundaries under various working conditions.

[0053] Furthermore, the operation boundary search model of the flexible DC transmission system includes an output upper limit optimization model and an output lower limit optimization model. In S2, the operation domain determination problem of the flexible DC transmission system is converted into an upper and lower limit optimization problem of output active power and reactive power, specifically:

[0054] S21, construct the output upper limit optimization model to obtain formula (8):

[0055]

[0056] Among them, Q v，max is the output reactive upper limit of the flexible DC transmission system, st is the abbreviation of subject to, and st(2)-(7) indicates that the output upper limit optimization model must satisfy the above formulas (2)-(7);

[0057] S22, construct the output lower limit optimization model to obtain formula (9):

[0058]

[0059] Among them, Q v，min It is the lower limit of output reactive power of flexible DC transmission system.

[0060] From the above description, it can be seen that the operation domain problem of the flexible DC transmission system is transformed into the optimization problem of the upper and lower limits of the output active power and reactive power, and the output upper limit optimization model and the output lower limit optimization model are constructed. Both models satisfy the above formulas (2)-(7), and P = P v The known quantity is substituted into the optimization model for optimization solution, and the known quantity is determined by the operating condition set of step S3 to ensure the accuracy of the solution.

[0061] Furthermore, the S3 specifically includes the following steps:

[0062] S31, construct the operating condition set, and obtain formula (10):

[0063] Set1 = {P v |P min ≤P v ≤P max} (10);

[0064] Wherein, Set1 is the operating condition set, P max is the upper limit of the output active power of the flexible DC transmission system, P min is the lower limit of the output active power of the flexible DC transmission system;

[0065] S32, the operating conditions of the operating condition set are substituted into the output upper limit optimization model and the output lower limit optimization model one by one, and the upper and lower limits of the output reactive power of the flexible DC transmission system are respectively obtained, and the operating boundary of the flexible DC transmission system is obtained according to the upper and lower limits, as shown in the following formula (11):

[0066]

[0067] Among them, Set2 is the upper operating boundary set of the flexible DC transmission system, and Set3 is the lower operating boundary set of the flexible DC transmission system.

[0068] From the above description, it can be seen that by substituting all operating conditions into the optimization model to solve the upper and lower limit boundaries of all operating conditions, the operating boundary of the system can be directly determined, avoiding the determination of the operating range through point-by-point verification, effectively saving calculation overhead, and intuitively giving the system operating area.

[0069] Please refer to Figure 6 , a flexible direct current transmission system operation boundary search terminal, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor implements the following steps when executing the computer program:

[0070] S1. Initialize the steady-state model of the flexible DC transmission system and construct the voltage equations and operation constraints of each node in the flexible DC transmission system;

[0071] S2. Construct an operation boundary search model for the flexible DC transmission system, and transform the operation domain determination problem of the flexible DC transmission system into an optimization problem of the upper and lower limits of the output active power and reactive power;

[0072] S3. Construct an operating condition set of the flexible DC power transmission system, and use the operating boundary search model to calculate the upper and lower limits of the output power under different conditions in the operating condition set to obtain the operating boundary of the flexible DC power transmission system.

[0073] From the above description, it can be seen that the beneficial effects of the present invention are: based on the same technical concept, in conjunction with the above-mentioned flexible direct current transmission system operation boundary search method, a flexible direct current transmission system operation boundary search terminal is provided, by constructing a steady-state model of the flexible direct current transmission system, and constructing the voltage equations and operation constraints of each node in the flexible direct current transmission system based on the steady-state model, combined with the operation boundary search model of the flexible direct current transmission system, the problem of determining the operation domain of the system is converted into an optimization problem of the upper and lower limits of the output power, and then a set of operating conditions of the flexible direct current system is constructed, and the operation boundary search model is used to calculate the upper and lower limits of the output power under different operating conditions, thereby directly determining the operation boundary of the system, avoiding determining the operation range by point-by-point verification, effectively saving calculation overhead, and intuitively giving the system operation area, providing a reference for system planning and operation scheduling.

[0074] Furthermore, the voltage equations and operation constraints of each node constructed in S1 are specifically:

[0075] The voltage equation groups between the virtual connection points of the upper and lower bridge arms, the output points, the common connection points, and the equivalent nodes of the feed-in end system in the flexible direct current transmission system are respectively constructed, and the voltage constraints and current constraints of the voltage equation groups are constructed.

[0076] From the above description, it can be seen that the voltage equation group and its operation constraints of each node in the flexible DC transmission system are constructed so that the boundary search model can be optimized and constrained according to the voltage equation group and the operation constraints, ensuring that a stable and accurate system operation boundary is obtained in the future.

[0077] Furthermore, constructing the voltage equation and operation constraints of each node in S1 specifically includes the following steps:

[0078] S11, construct the voltage equation group to obtain formula (1):

[0079]

[0080] Wherein, diff is the virtual connection point of the upper and lower bridge arms of the flexible DC transmission system at the fundamental frequency, v is the output point of the flexible DC transmission system, PCC is the common connection point between the flexible DC transmission system and the feed-in system, sys is the equivalent node of the feed-in system of the flexible DC transmission system, arm is the bridge arm of the flexible DC transmission system, T is the converter transformer of the flexible DC transmission system, U is the node voltage, P is the active power, Q is the reactive power, Z is the impedance, j is the imaginary unit, a dot above a letter indicates a phasor, and no dot above a letter indicates a conventional variable;

[0081] S12. Calculate the real part and imaginary part of the phase quantity in formula (1) to obtain formulas (2), (3) and (4):

[0082]

[0083]

[0084]

[0085] Wherein, d is the d-axis component of the output point voltage of the flexible DC transmission system, q is the q-axis component of the output point voltage of the flexible DC transmission system, R is the resistance, and X is the reactance;

[0086] S13. Voltage constraints of the virtual connection points of the upper and lower bridge arms of the flexible DC transmission system are as follows:

[0087]

[0088] Among them, U dc is the DC side capacitor voltage of the flexible DC transmission system;

[0089] S14. Construct the voltage constraint of the output point of the flexible DC transmission system, as shown in formula (6):

[0090] U min ≤U v ≤U max (6);

[0091] Among them, U min is the voltage lower limit of the output point of the flexible DC transmission system, U max The voltage upper limit of the output point of the flexible DC transmission system;

[0092] S15. Construct the current constraint of the output point of the flexible DC transmission system, as shown in formula (7):

[0093]

[0094] Among them, I maxIt is the upper limit of current at the output point of the flexible DC transmission system.

[0095] From the above description, it can be seen that the voltage equation group of each node of the flexible DC transmission system and the voltage and current constraints of the output point are constructed so that they can be subsequently substituted into the boundary search model to obtain the upper and lower boundaries under various working conditions.

[0096] Furthermore, the operation boundary search model of the flexible DC transmission system includes an output upper limit optimization model and an output lower limit optimization model. In S2, the operation domain determination problem of the flexible DC transmission system is converted into an upper and lower limit optimization problem of output active power and reactive power, specifically:

[0097] S21, construct the output upper limit optimization model to obtain formula (8):

[0098]

[0099] Among them, Q v，max is the output reactive upper limit of the flexible DC transmission system, st is the abbreviation of subject to, and st(2)-(7) indicates that the output upper limit optimization model must satisfy the above formulas (2)-(7);

[0100] S22, construct the output lower limit optimization model to obtain formula (9):

[0101]

[0102] Among them, Q v，min It is the lower limit of output reactive power of flexible DC transmission system.

[0103] From the above description, it can be seen that the operation domain problem of the flexible DC transmission system is transformed into the optimization problem of the upper and lower limits of the output active power and reactive power, and the output upper limit optimization model and the output lower limit optimization model are constructed. Both models satisfy the above formulas (2)-(7), and P = P v The known quantity is substituted into the optimization model for optimization solution, and the known quantity is determined by the operating condition set of step S3 to ensure the accuracy of the solution.

[0104] Furthermore, the S3 specifically includes the following steps:

[0105] S31, construct the operating condition set, and obtain formula (10):

[0106] Set1 = {P v |P min ≤P v ≤P max} (10);

[0107] Wherein, Set1 is the operating condition set, P max is the upper limit of the output active power of the flexible DC transmission system, P min is the lower limit of the output active power of the flexible DC transmission system;

[0108] S32, the operating conditions of the operating condition set are substituted into the output upper limit optimization model and the output lower limit optimization model one by one, and the upper and lower limits of the output reactive power of the flexible DC transmission system are respectively obtained, and the operating boundary of the flexible DC transmission system is obtained according to the upper and lower limits, as shown in the following formula (11):

[0109]

[0110] Among them, Set2 is the upper operating boundary set of the flexible DC transmission system, and Set3 is the lower operating boundary set of the flexible DC transmission system.

[0111] From the above description, it can be seen that by substituting all operating conditions into the optimization model to solve the upper and lower limit boundaries of all operating conditions, the operating boundary of the system can be directly determined, avoiding the determination of the operating range through point-by-point verification, effectively saving calculation overhead, and intuitively giving the system operating area.

[0112] The present invention provides a method and terminal for searching the operating boundary of a flexible direct current transmission system, which is suitable for determining the operating boundary of a flexible direct current transmission system, and can intuitively provide the operating domain of the system, providing a reference for system planning and operation scheduling. The following is a detailed description in conjunction with an embodiment.

[0113] Please refer to Figure 1 , Embodiment 1 of the present invention is:

[0114] A method for searching the operating boundary of a flexible DC transmission system, such as Figure 1 As shown, the steps include:

[0115] S1. Initialize the steady-state model of the flexible DC transmission system and construct the voltage equations and operation constraints of each node in the flexible DC transmission system;

[0116] S2. Construct an operation boundary search model for the flexible DC transmission system, and transform the operation domain determination problem of the flexible DC transmission system into an optimization problem of the upper and lower limits of the output active power and reactive power;

[0117] S3. Construct an operating condition set of the flexible DC transmission system, and use an operating boundary search model to calculate the upper and lower limits of the output power under different conditions in the operating condition set to obtain the operating boundary of the flexible DC transmission system.

[0118] That is, in this embodiment, by constructing a steady-state model of the flexible DC transmission system, and constructing the voltage equations and operating constraints of each node in the flexible DC transmission system based on the steady-state model, combined with the operating boundary search model of the flexible DC transmission system, the problem of determining the operating domain of the system is converted into an optimization problem of the upper and lower limits of the output power, and then a set of operating conditions of the flexible DC system is constructed, and the operating boundary search model is used to calculate the upper and lower limits of the output power under different operating conditions, thereby directly determining the operating boundary of the system, avoiding determining the operating range through point-by-point verification, effectively saving calculation overhead, and intuitively giving the system operating area, providing a reference for system planning and operation scheduling.

[0119] Embodiment 2 of the present invention is:

[0120] A method for searching operating boundaries of a flexible direct current transmission system is provided. Based on the above-mentioned first embodiment, in this embodiment, the voltage equations and operating constraints of each node constructed in step S1 are specifically as follows:

[0121] The voltage equations between the virtual connection points of the upper and lower bridge arms, the output points, the common connection points, and the equivalent nodes of the feed-in end system in the flexible DC transmission system are respectively constructed, and the voltage constraints and output current constraints of the voltage equations are constructed. That is, by constructing the voltage equations and their operation constraints of each node in the flexible DC transmission system, the boundary search model can be optimized and constrained according to the voltage equations and operation constraints, so as to ensure that a stable and accurate system operation boundary is obtained in the future. In this embodiment, it can be specifically refined into the following steps:

[0122] S11. Construct the voltage equation group and obtain formula (1):

[0123]

[0124] Wherein, diff is the virtual connection point of the upper and lower bridge arms of the flexible DC transmission system at the fundamental frequency, v is the output point of the flexible DC transmission system, PCC is the common connection point between the flexible DC transmission system and the feed-in system, sys is the equivalent node of the feed-in system of the flexible DC transmission system, arm is the bridge arm of the flexible DC transmission system, T is the converter transformer of the flexible DC transmission system, U is the node voltage, P is the active power, Q is the reactive power, Z is the impedance, j is the imaginary unit, a dot above the letter indicates a phasor, and no dot above the letter indicates a conventional variable.

[0125] S12. Calculate the real part and imaginary part of the phase quantity in formula (1) to obtain formulas (2), (3) and (4):

[0126]

[0127]

[0128]

[0129] Wherein, d is the d-axis component of the output point voltage of the flexible DC transmission system, q is the q-axis component of the output point voltage of the flexible DC transmission system, R is the resistance, and X is the reactance.

[0130] S13. Construct the voltage constraint of the virtual connection point of the upper and lower bridge arms voltage of the flexible DC transmission system, as shown in the following formula (5):

[0131]

[0132] S14. Construct the voltage constraint of the output point of the flexible DC transmission system, as shown in formula (6):

[0133] U min ≤U v ≤U max (6);

[0134] Among them, U min is the voltage lower limit of the output point of the flexible DC transmission system, U max The voltage upper limit of the output point of the flexible DC transmission system;

[0135] S15. Construct the current constraint of the output point of the flexible DC transmission system, as shown in formula (7):

[0136]

[0137] Among them, I max It is the upper limit of current at the output point of the flexible DC transmission system.

[0138] That is, step S1 as a whole constructs a voltage equation group of each node of the flexible DC transmission system and voltage and current constraints of the output point, so as to subsequently substitute them into the boundary search model to obtain the upper and lower boundaries under various working conditions.

[0139] Among them, in this embodiment, the operation boundary search model of the flexible DC transmission system includes an output upper limit optimization model and an output lower limit optimization model, and the operation domain determination problem of the flexible DC transmission system is converted into an upper and lower limit optimization problem of output active power and reactive power in step S2, specifically:

[0140] S21. Construct an output upper limit optimization model and obtain formula (8):

[0141]

[0142] Among them, Q v，maxis the output reactive upper limit of the flexible DC transmission system, st is the abbreviation of subject to, and st(2)-(7) means that the output upper limit optimization model must satisfy the above formulas (2)-(7).

[0143] S22. Construct an output lower limit optimization model and obtain formula (9):

[0144]

[0145] Among them, Q v，min It is the lower limit of output reactive power of flexible DC transmission system.

[0146] That is, step S2 transforms the operation domain problem of the flexible DC transmission system into the optimization problem of the upper and lower limits of the output active power and reactive power, and constructs an output upper limit optimization model and an output lower limit optimization model. Both models satisfy the above formulas (2)-(7), and P=P v Substitute the known quantity into the optimization model for optimization solution, and the known quantity is determined by the operating condition set Set1 of step S3 to ensure the accuracy of the solution.

[0147] Therefore, step S3 is specifically as follows:

[0148] According to the operating condition set, all operating conditions are substituted into the output upper limit optimization model and the output lower limit optimization model one by one to obtain the upper and lower limits of the output power of the flexible DC transmission system under all operating conditions, which specifically includes the following steps:

[0149] S31. Construct an operating condition set and obtain formula (10):

[0150] Set1 = {P v |P min ≤P v ≤P max} (10);

[0151] Among them, Set1 is the operating condition set, P max is the upper limit of the output active power of the flexible DC transmission system, P min It is the lower limit of the output active power of the flexible DC transmission system.

[0152] S32, the operating conditions of the operating condition set are input into the output upper limit optimization model and the output lower limit optimization model one by one, and the upper and lower limits of the output reactive power of the flexible DC transmission system are obtained respectively, and the operating boundary of the flexible DC transmission system is obtained according to the upper and lower limits, as shown in the following formula (11):

[0153]

[0154] Among them, Set2 is the upper operating boundary set of the flexible DC transmission system, and Set3 is the lower operating boundary set of the flexible DC transmission system.

[0155] That is, in step S3, by substituting all operating conditions into the optimization model to solve the upper and lower limit boundaries of all operating conditions, the operating boundary of the system can be directly determined, avoiding the determination of the operating range through point-by-point verification, effectively saving calculation overhead, and intuitively giving the system operating area.

[0156] Please refer to Figures 2 to 5 , Embodiment 3 of the present invention is:

[0157] A method for searching operating boundaries of a flexible direct current transmission system is provided. Based on the above-mentioned second embodiment, in this embodiment, Figure 2 is a system structure diagram of the flexible direct current transmission system of the present invention, Figure 2 Middle U p is the upper arm voltage of the flexible DC transmission system, U n is the lower arm voltage of the flexible DC transmission system, SM1~SMn are submodules of the flexible DC transmission system (composed of n submodules), U sm For each submodule, the output voltage, K T is the commutation transformation ratio of the flexible DC transmission system; Figure 3 is the equivalent circuit diagram of the flexible DC transmission system at the fundamental frequency. According to the circuit principle of the equivalent circuit diagram, Figure 4 The specific flow chart for determining the operating boundary is shown in the figure. First, a flexible DC transmission system model is constructed, and the voltage equations between the nodes in the system are initialized. According to formulas (1)-(4), the voltage equations between the virtual connection points of the upper and lower bridge arms, the output points, the common connection points, and the equivalent nodes of the feed-in end system in the flexible DC transmission system are respectively constructed, and the real and imaginary parts are calculated respectively. Then, the voltage constraints and current constraints of the output points of the flexible DC transmission system are constructed according to formulas (5)-(7).

[0158] Secondly, according to formulas (8)-(9), the output upper limit optimization model and output lower limit optimization model of the flexible DC transmission system are constructed respectively.

[0159] Then, according to formula (10), the active operating condition set of the flexible DC transmission system is constructed, and the upper and lower limits of the reactive output power under different operating conditions are calculated using the output upper limit optimization model and the output lower limit optimization model constructed above. After traversing all the operating condition sets, the operating boundary of the flexible DC transmission system is obtained.

[0160] In this embodiment, the output side operation domain of the flexible DC transmission system finally obtained by using the flexible DC transmission system operation boundary search method proposed in the present invention is as follows: Figure 5As shown, the method proposed in the present invention can not only directly determine the operating boundary of the system, avoid determining the operating range through point-by-point verification, and effectively save calculation overhead, but also intuitively give the system operating area, providing a reference for system planning and operation scheduling.

[0161] Please refer to Figure 6 , Embodiment 4 of the present invention is:

[0162] A flexible direct current transmission system operation boundary search terminal 1 includes a memory 2, a processor 3, and a computer program stored in the memory 2 and executable on the processor 3. In this embodiment, when the processor 3 executes the computer program, the steps of any one of the above-mentioned embodiments 1 to 3 are implemented.

[0163] In summary, the present invention provides a method and terminal for searching the operating boundaries of a flexible direct current transmission system, which obtains the upper and lower limits of the output power of the flexible direct current transmission system through optimization calculation, and then directly determines the operating boundaries of the system, avoiding determining the operating range through point-by-point verification, effectively saving calculation overhead, and intuitively giving the system operating area, providing a reference for system planning and operation scheduling.

[0164] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent transformations made using the contents of the present invention's specification and drawings, or directly or indirectly applied in related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A method for searching operating boundaries of a flexible direct current transmission system, characterized in that: Includes steps: S1. Initialize the steady-state model of the flexible DC transmission system and construct the voltage equations and operation constraints of each node in the flexible DC transmission system; S2. Construct an operation boundary search model for the flexible DC transmission system, and transform the operation domain determination problem of the flexible DC transmission system into an optimization problem of the upper and lower limits of the output active power and reactive power; S3, constructing an operating condition set of the flexible direct current power transmission system, and using the operating boundary search model to calculate the upper and lower limits of the output power under different conditions in the operating condition set, to obtain the operating boundary of the flexible direct current power transmission system; The voltage equations and operation constraints of each node constructed in S1 are specifically: Constructing voltage equations between virtual connection points of upper and lower bridge arms, output points, common connection points, and equivalent nodes of the feed-in terminal system in the flexible direct current transmission system respectively, and constructing voltage constraints and current constraints of the voltage equations; The voltage equations and operation constraints of each node are constructed in S1, which specifically includes the following steps: S11, construct the voltage equation group to obtain formula (1): (1)； Wherein, diff is the virtual connection point of the upper and lower bridge arms of the flexible DC transmission system at the fundamental frequency, v is the output point of the flexible DC transmission system, PCC is the common connection point between the flexible DC transmission system and the feed-in system, sys is the equivalent node of the feed-in system of the flexible DC transmission system, arm is the bridge arm of the flexible DC transmission system, T is the converter transformer of the flexible DC transmission system, U is the node voltage, P is the active power, Q is the reactive power, Z is the impedance, j is the imaginary unit, a dot above a letter indicates a phasor, and no dot above a letter indicates a conventional variable; S12. Calculate the real part and imaginary part of the phase quantity in formula (1) to obtain formulas (2), (3) and (4): (2)； (3)； (4)； Wherein, d is the d-axis component of the output point voltage of the flexible DC transmission system, q is the q-axis component of the output point voltage of the flexible DC transmission system, R is the resistance, and X is the reactance; S13. Construct the voltage constraint of the virtual connection point of the upper and lower bridge arms voltage of the flexible DC transmission system, as shown in the following formula (5): (5)； Among them, U dc is the DC side capacitor voltage of the flexible DC transmission system; S14. Construct the voltage constraint of the output point of the flexible DC transmission system, as shown in formula (6): (6)； Among them, U min is the voltage lower limit of the output point of the flexible DC transmission system, U max The voltage upper limit of the output point of the flexible DC transmission system; S15. Construct the current constraint of the output point of the flexible DC transmission system, as shown in formula (7): (7)； Among them, I max It is the upper limit of current at the output point of the flexible DC transmission system.

2. A method for searching operating boundaries of a flexible direct current transmission system according to claim 1, characterized in that: The operation boundary search model of the flexible DC power transmission system includes an output upper limit optimization model and an output lower limit optimization model. In S2, the operation domain determination problem of the flexible DC power transmission system is converted into an upper and lower limit optimization problem of output active power and reactive power, which is specifically: S21, construct the output upper limit optimization model to obtain formula (8): (8)； Among them, Q v，max is the output reactive power upper limit of the flexible DC transmission system, st is the abbreviation of subject to, and st(2)-(7) indicates that the output upper limit optimization model must satisfy the above formulas (2)-(7); S22, construct the output lower limit optimization model to obtain formula (9): (9)； Among them, Q v，min It is the lower limit of output reactive power of flexible DC transmission system.

3. A method for searching operating boundaries of a flexible direct current transmission system according to claim 2, characterized in that: The S3 specifically includes the following steps: S31, construct the operating condition set and obtain formula (10): (10)； Wherein, Set1 is the operating condition set, P max is the upper limit of the output active power of the flexible DC transmission system, P min is the lower limit of the output active power of the flexible DC transmission system; S32, the operating conditions of the operating condition set are substituted into the output upper limit optimization model and the output lower limit optimization model one by one, and the upper and lower limits of the output reactive power of the flexible DC transmission system are respectively obtained, and the operating boundary of the flexible DC transmission system is obtained according to the upper and lower limits, as shown in the following formula (11): (11)； Among them, Set2 is the upper operating boundary set of the flexible DC transmission system, and Set3 is the lower operating boundary set of the flexible DC transmission system.

4. A flexible direct current transmission system operation boundary search terminal, executing a flexible direct current transmission system operation boundary search method according to any one of claims 1 to 3, characterized in that: The invention comprises a memory, a processor and a computer program stored in the memory and executable on the processor, wherein the processor implements the following steps when executing the computer program: S1. Initialize the steady-state model of the flexible DC transmission system and construct the voltage equations and operation constraints of each node in the flexible DC transmission system; S2. Construct an operation boundary search model for the flexible DC transmission system, and transform the operation domain determination problem of the flexible DC transmission system into an optimization problem of the upper and lower limits of the output active power and reactive power; S3, constructing an operating condition set of the flexible direct current power transmission system, and using the operating boundary search model to calculate the upper and lower limits of the output power under different conditions in the operating condition set, to obtain the operating boundary of the flexible direct current power transmission system; The voltage equations and operation constraints of each node constructed in S1 are specifically: Constructing voltage equations between virtual connection points of upper and lower bridge arms, output points, common connection points, and equivalent nodes of the feed-in terminal system in the flexible direct current transmission system respectively, and constructing voltage constraints and current constraints of the voltage equations; The voltage equations and operation constraints of each node are constructed in S1, which specifically includes the following steps: S11, construct the voltage equation group to obtain formula (1): (1)； Wherein, diff is the virtual connection point of the upper and lower bridge arms of the flexible DC transmission system at the fundamental frequency, v is the output point of the flexible DC transmission system, PCC is the common connection point between the flexible DC transmission system and the feed-in system, sys is the equivalent node of the feed-in system of the flexible DC transmission system, arm is the bridge arm of the flexible DC transmission system, T is the converter transformer of the flexible DC transmission system, U is the node voltage, P is the active power, Q is the reactive power, Z is the impedance, j is the imaginary unit, a dot above a letter indicates a phasor, and no dot above a letter indicates a conventional variable; S12. Calculate the real part and imaginary part of the phase quantity in formula (1) to obtain formulas (2), (3) and (4): (2)； (3)； (4)； Wherein, d is the d-axis component of the output point voltage of the flexible DC transmission system, q is the q-axis component of the output point voltage of the flexible DC transmission system, R is the resistance, and X is the reactance; S13. Construct the voltage constraint of the virtual connection point of the upper and lower bridge arms voltage of the flexible DC transmission system, as shown in the following formula (5): (5)； Among them, U dc is the DC side capacitor voltage of the flexible DC transmission system; S14. Construct the voltage constraint of the output point of the flexible DC transmission system, as shown in formula (6): (6)； Among them, U min is the voltage lower limit of the output point of the flexible DC transmission system, U max The voltage upper limit of the output point of the flexible DC transmission system; S15. Construct the current constraint of the output point of the flexible DC transmission system, as shown in formula (7): (7)； Among them, I max It is the upper limit of current at the output point of the flexible DC transmission system.

5. The flexible direct current transmission system operation boundary search terminal according to claim 4, characterized in that: The operation boundary search model of the flexible DC power transmission system includes an output upper limit optimization model and an output lower limit optimization model. In S2, the operation domain determination problem of the flexible DC power transmission system is converted into an upper and lower limit optimization problem of output active power and reactive power, which is specifically: S21, construct the output upper limit optimization model to obtain formula (8): (8)； Among them, Q v，max is the output reactive power upper limit of the flexible DC transmission system, st is the abbreviation of subject to, and st(2)-(7) indicates that the output upper limit optimization model must satisfy the above formulas (2)-(7); S22, construct the output lower limit optimization model to obtain formula (9): (9)； Among them, Q v，mix It is the lower limit of output reactive power of flexible DC transmission system.

6. A flexible direct current transmission system operation boundary search terminal according to claim 5, characterized in that: The S3 specifically includes the following steps: S31, construct the operating condition set and obtain formula (10): (10)； Wherein, Set1 is the operating condition set, P max is the upper limit of the output active power of the flexible DC transmission system, P min is the lower limit of the output active power of the flexible DC transmission system; S32, the operating conditions of the operating condition set are substituted into the output upper limit optimization model and the output lower limit optimization model one by one, and the upper and lower limits of the output reactive power of the flexible DC transmission system are respectively obtained, and the operating boundary of the flexible DC transmission system is obtained according to the upper and lower limits, as shown in the following formula (11): (11)； Among them, Set2 is the upper operating boundary set of the flexible DC transmission system, and Set3 is the lower operating boundary set of the flexible DC transmission system.

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