A method and terminal for describing steady-state operation domain of flexible direct current transmission system

Abstract

The present invention provides a method and terminal for characterizing the steady-state operation domain of a flexible direct current transmission system, including: initializing a steady-state model of the flexible direct current transmission system, constructing voltage equations, power equations and constraints of each node in the flexible direct current transmission system; constructing an operating condition set of the flexible direct current transmission system, substituting any condition in the operating condition set into the voltage equation and the power equation to obtain a steady-state solution of the system, and determining the rationality of the steady-state solution according to the constraints; traversing all conditions in the operating condition set, and outputting all reasonable steady-state solutions to obtain a steady-state operation domain of the flexible direct current transmission system. The present invention can intuitively give the steady-state operation domain of the flexible direct current transmission system under steady-state conditions, assist in judging the operation margin of the flexible direct current transmission system, and can adjust and flexibly characterize the operation domain in a systematic manner, providing a reference for planning and operation personnel.

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 characterizing a steady-state operation domain of a flexible direct current power transmission system. Background Art

[0002] With the rapid development of power electronics technology, flexible DC transmission technology has been used in practical projects such as asynchronous system interconnection and new energy transmission. Thanks to the use of insulated gate bipolar transistors with controllable conduction channels, flexible DC transmission has the characteristics of independent regulation of active and reactive power, no need for reactive power compensation, and no commutation failure. With the topology of modular multi-level converters in series, the flexible DC transmission system can obtain a more ideal output waveform, which is one of the main directions for the development of DC transmission technology in the future.

[0003] Theoretically, the flexible DC transmission system has the ability to flexibly adjust power in four quadrants, and its ideal operating domain is a unit circle. However, in actual operation, due to the constraints of voltage stability, voltage amplitude, and current limit, its actual operating domain does not present an ideal circular shape. In addition, most of the existing relevant research results study the output boundary of the flexible DC transmission system for a specific operating condition, and do not give the upper and lower limits of the system's steady-state operation under all possible conditions. For this reason, it is necessary to study a method for characterizing the steady-state operating domain of the flexible DC transmission system to provide a reference for planning and operation personnel. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a method and terminal for characterizing the steady-state operation domain of a flexible direct current transmission system, so as to intuitively judge the operation margin of the flexible direct current transmission system under the current working conditions and provide a reference for planning and operation personnel.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is: a method for characterizing the steady-state operation domain of a flexible direct current transmission system, comprising the steps of:

[0006] S1. Initialize the steady-state model of the flexible DC transmission system, and construct the voltage equation, power equation and constraint conditions of each node in the flexible DC transmission system;

[0007] S2. constructing an operating condition set of the flexible DC power transmission system, substituting any operating condition in the operating condition set into the voltage equation and the power equation to obtain a steady-state solution of the system, and determining the rationality of the steady-state solution according to the constraint conditions;

[0008] S3. Traverse all the operating conditions in the operating condition set, and output all reasonable steady-state solutions to obtain the steady-state operating domain of the flexible direct current transmission system.

[0009] In order to solve the above technical problems, another technical solution adopted by the present invention is: a terminal for characterizing the steady-state operation domain of a flexible direct current transmission system, 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:

[0010] S1. Initialize the steady-state model of the flexible DC transmission system, and construct the voltage equation, power equation and constraint conditions of each node in the flexible DC transmission system;

[0011] S2. constructing an operating condition set of the flexible direct current transmission system, substituting any operating condition in the operating condition set into the voltage equation and the power equation to obtain a steady-state solution of the system, and determining the rationality of the steady-state solution according to the constraint conditions;

[0012] S3. Traverse all the operating conditions in the operating condition set, and output all reasonable steady-state solutions to obtain the steady-state operating domain of the flexible direct current transmission system.

[0013] The beneficial effects of the present invention are as follows: the present invention provides a method and terminal for characterizing the steady-state operating domain of a flexible direct current transmission system, which can intuitively provide the steady-state operating domain of the flexible direct current transmission system under steady-state conditions, assist in judging the operating margin of the flexible direct current transmission system, and can flexibly characterize the operating domain according to the system mode of adjustment, providing a reference for planning and operation personnel. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is an overall flow chart of a method for characterizing a steady-state operation domain of a flexible direct current transmission system according to an embodiment of the present invention;

[0015] Figure 2 It is a system structure diagram of the flexible DC transmission system;

[0016] Figure 3 It is the equivalent circuit diagram of the flexible DC transmission system;

[0017] Figure 4 It is a specific flow chart of steady-state operation domain characterization of a method for characterizing steady-state operation domain of a flexible direct current transmission system according to an embodiment of the present invention;

[0018] Figure 5 It is the output side operation domain of the flexible DC transmission system in the present invention;

[0019] Figure 6 It is a structural schematic diagram of a terminal for depicting a steady-state operation domain of a flexible direct current transmission system according to an embodiment of the present invention.

[0020] Description of labels:

[0021] 1. A terminal for characterizing the steady-state operation domain of a flexible direct current transmission system; 2. Memory; 3. Processor. DETAILED DESCRIPTION

[0022] 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.

[0023] Please refer to Figures 1 to 5 , a method for characterizing a steady-state operation domain of a flexible direct current transmission system, comprising the steps of:

[0024] S1. Initialize the steady-state model of the flexible DC transmission system, and construct the voltage equation, power equation and constraint conditions of each node in the flexible DC transmission system;

[0025] S2. constructing an operating condition set of the flexible direct current transmission system, substituting any operating condition in the operating condition set into the voltage equation and the power equation to obtain a steady-state solution of the system, and determining the rationality of the steady-state solution according to the constraint conditions;

[0026] S3. Traverse all the operating conditions in the operating condition set, and output all reasonable steady-state solutions to obtain the steady-state operating domain of the flexible direct current transmission system.

[0027] From the above description, it can be seen that the beneficial effects of the present invention are: it can intuitively give the steady-state operating domain of the flexible DC transmission system under steady-state conditions, assist in judging the operating margin of the flexible DC transmission system, and can flexibly characterize the operating domain according to the system mode of adjustment, providing a reference for planning and operation personnel.

[0028] Furthermore, the voltage equation, power equation and constraint conditions of each node constructed in S1 are specifically as follows:

[0029] A voltage equation group and a power equation group are respectively constructed between the common connection point between the flexible direct current transmission system and the feed-in end system and the output point of the flexible direct current transmission system, and voltage constraints of the voltage equation group and current constraints of the power equation group are constructed.

[0030] From the above description, it can be seen that a set of equations for current and power between nodes is constructed in order to solve and obtain a steady-state solution.

[0031] Furthermore, constructing the voltage equation, power equation and constraint conditions of each node in S1 specifically includes the following steps:

[0032] S11, construct the voltage equation group to obtain formula 1:

[0033]

[0034] 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, sys is the feed-in end 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;

[0035] Calculate the phasor in formula 1 according to the real part and imaginary part respectively, and get formula 2:

[0036]

[0037] Among them, U vd is the d-axis component of the output point voltage of the flexible DC transmission system, U vq 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;

[0038] S12, construct the power equation group to obtain Formula 3:

[0039]

[0040] Among them, PCC is the common connection point between the flexible DC transmission system and the feed-in end system;

[0041] S13. The voltage of the upper and lower bridge arms of the flexible DC transmission system is as follows:

[0042]

[0043] Among them, U p is the upper bridge arm voltage, U n is the lower bridge arm voltage, U dc is the DC side capacitor voltage;

[0044] The voltage constraint of the virtual connection point of the upper and lower bridge arms is obtained as shown in Formula 5:

[0045]

[0046] S14. Construct the current constraint on the output side of the flexible DC transmission system, as shown in Formula 6:

[0047]

[0048] Among them, I max is the upper limit of current on the output side of the flexible DC transmission system;

[0049] S15. Construct the voltage constraint on the output side of the flexible DC transmission system, as shown in Formula 7:

[0050] U min ≤U v ≤U max ;

[0051] Among them, U min is the voltage lower limit on the output side of the flexible DC transmission system, U max It is the voltage upper limit on the output side of the flexible DC transmission system.

[0052] From the above description, it can be seen that a set of quadratic equations for voltage and power are constructed respectively, and the voltage and current constraints are combined so that the steady-state solution of the system can be obtained by substituting the operating conditions into the operating conditions later. The upper and lower bridge arms of the flexible DC transmission system are composed of a group of sub-modules connected in series. Under steady-state conditions, the bridge arm voltage is the sum of the capacitor voltages of all sub-modules put into operation. Therefore, the upper and lower bridge arm voltages are both greater than or equal to 0.

[0053] Furthermore, the S2 is specifically:

[0054] According to the upper and lower limits of the active power and reactive power of the flexible direct current transmission system, all possible operating condition sets are obtained by permutations and combinations, and any condition in the operating condition set is substituted into the voltage equation group and the power equation group to solve the steady-state solution, and the rationality of the steady-state solution and the satisfaction of the constraint conditions are judged.

[0055] From the above description, it can be seen that all possible operating conditions within the upper and lower limits of active and reactive power of the flexible DC transmission system are arranged to ensure that all reasonable steady-state solutions can be obtained later to draw the steady-state operation domain and provide a reference for planning and operation personnel.

[0056] Furthermore, the S2 specifically includes the following steps:

[0057] S21, construct the operating condition set to obtain Formula 8:

[0058]

[0059] Wherein, Set is the set of operating conditions, S max is the apparent power upper limit on the output side of the flexible DC transmission system;

[0060] S22, substituting any operating condition in the operating condition set into the voltage equation group and the power equation group, and then solving to obtain the voltage and power variables of each node of the flexible DC transmission system, and checking whether the result meets the operating constraints, specifically:

[0061] If the voltage and power variables are real solutions and satisfy the constraints, it is considered that the operating condition belongs to the steady-state operation domain of the flexible DC transmission system.

[0062] From the above description, it can be seen that when any working condition is substituted into the above-constructed voltage equation and power equation, since both the voltage equation and the power equation are quadratic equations, the steady-state solution obtained may have complex roots, that is, an unreasonable solution. Therefore, it is necessary to determine whether the steady-state solution is a real solution in order to obtain a reasonable steady-state solution.

[0063] Please refer to Figure 6 , a terminal for describing a steady-state operation domain of a flexible direct current transmission system, 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:

[0064] S1. Initialize the steady-state model of the flexible DC transmission system, and construct the voltage equation, power equation and constraint conditions of each node in the flexible DC transmission system;

[0065] S2. constructing an operating condition set of the flexible direct current transmission system, substituting any operating condition in the operating condition set into the voltage equation and the power equation to obtain a steady-state solution of the system, and determining the rationality of the steady-state solution according to the constraint conditions;

[0066] S3. Traverse all the operating conditions in the operating condition set, and output all reasonable steady-state solutions to obtain the steady-state operating domain of the flexible direct current transmission system.

[0067] 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 method for characterizing the steady-state operating domain of a flexible direct current transmission system, a terminal for characterizing the steady-state operating domain of a flexible direct current transmission system is provided, which can intuitively give the steady-state operating domain of the flexible direct current transmission system under steady-state conditions, assist in judging the operating margin of the flexible direct current transmission system, and can flexibly characterize the operating domain according to the system mode of adjustment, providing a reference for planning and operation personnel.

[0068] Furthermore, the voltage equation, power equation and constraint conditions of each node constructed in S1 are specifically as follows:

[0069] A voltage equation group and a power equation group are respectively constructed between the common connection point between the flexible direct current transmission system and the feed-in end system and the output point of the flexible direct current transmission system, and voltage constraints of the voltage equation group and current constraints of the power equation group are constructed.

[0070] From the above description, it can be seen that a set of equations for current and power between nodes is constructed in order to solve and obtain a steady-state solution.

[0071] Furthermore, constructing the voltage equation, power equation and constraint conditions of each node in S1 specifically includes the following steps:

[0072] S11, construct the voltage equation group to obtain formula 1:

[0073]

[0074] 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, sys is the feed-in end 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;

[0075] Calculate the phasor in formula 1 according to the real part and imaginary part respectively, and get formula 2:

[0076]

[0077] Among them, U vd is the d-axis component of the output point voltage of the flexible DC transmission system, U vq 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;

[0078] S12, construct the power equation group to obtain Formula 3:

[0079]

[0080] Among them, PCC is the common connection point between the flexible DC transmission system and the feed-in end system;

[0081] S13. The voltage of the upper and lower bridge arms of the flexible DC transmission system is as follows:

[0082]

[0083] Among them, U p is the upper bridge arm voltage, U n is the lower bridge arm voltage, U dc is the DC side capacitor voltage;

[0084] The voltage constraint of the virtual connection point of the upper and lower bridge arms is obtained as shown in Formula 5:

[0085]

[0086] S14. Construct the current constraint on the output side of the flexible DC transmission system, as shown in Formula 6:

[0087]

[0088] Among them, I maxis the upper limit of current on the output side of the flexible DC transmission system;

[0089] S15. Construct the output side voltage constraint of the flexible DC transmission system, as shown in Formula 7:

[0090] U min ≤U v ≤U max ;

[0091] Among them, U min is the voltage lower limit on the output side of the flexible DC transmission system, U max It is the voltage upper limit on the output side of the flexible DC transmission system.

[0092] From the above description, it can be seen that a set of quadratic equations for voltage and power are constructed respectively, and the voltage and current constraints are combined so that the steady-state solution of the system can be obtained by substituting the operating conditions into the operating conditions later. The upper and lower bridge arms of the flexible DC transmission system are composed of a group of sub-modules connected in series. Under steady-state conditions, the bridge arm voltage is the sum of the capacitor voltages of all sub-modules put into operation. Therefore, the upper and lower bridge arm voltages are both greater than or equal to 0.

[0093] Furthermore, the S2 is specifically:

[0094] According to the upper and lower limits of the active power and reactive power of the flexible direct current transmission system, all possible operating condition sets are obtained by permutations and combinations, and any condition in the operating condition set is substituted into the voltage equation group and the power equation group to solve the steady-state solution, and the rationality of the steady-state solution and the satisfaction of the constraint conditions are judged.

[0095] From the above description, it can be seen that all possible operating conditions within the upper and lower limits of active and reactive power of the flexible DC transmission system are arranged to ensure that all reasonable steady-state solutions can be obtained later to draw the steady-state operation domain and provide a reference for planning and operation personnel.

[0096] Furthermore, the S2 specifically includes the following steps:

[0097] S21, construct the operating condition set to obtain Formula 8:

[0098]

[0099] Wherein, Set is the set of operating conditions, S max is the apparent power upper limit on the output side of the flexible DC transmission system;

[0100] S22, substituting any operating condition in the operating condition set into the voltage equation group and the power equation group, and then solving to obtain the voltage and power variables of each node of the flexible DC transmission system, and checking whether the result meets the operating constraints, specifically:

[0101] If the voltage and power variables are real solutions and satisfy the constraints, it is considered that the operating condition belongs to the steady-state operation domain of the flexible DC transmission system.

[0102] From the above description, it can be seen that when any working condition is substituted into the above-constructed voltage equation and power equation, since both the voltage equation and the power equation are quadratic equations, the steady-state solution obtained may have complex roots, that is, an unreasonable solution. Therefore, it is necessary to determine whether the steady-state solution is a real solution in order to obtain a reasonable steady-state solution.

[0103] Please refer to Figure 1 , Embodiment 1 of the present invention is:

[0104] A method for describing a steady-state operation domain of a flexible direct current transmission system comprises the following steps:

[0105] S1. Initialize the steady-state model of the flexible DC transmission system, and construct the voltage equation, power equation and constraint conditions of each node in the flexible DC transmission system;

[0106] S2. Construct an operating condition set of the flexible DC transmission system, substitute any operating condition in the operating condition set into the voltage equation and the power equation to obtain a steady-state solution of the system, and determine the rationality of the steady-state solution according to the constraint conditions;

[0107] S3. Traverse all operating conditions in the operating condition set and output all reasonable steady-state solutions to obtain the steady-state operating domain of the flexible DC transmission system.

[0108] That is, in this embodiment, the steady-state operating domain of the flexible DC transmission system under steady-state conditions can be intuitively given to assist in judging the operating margin of the flexible DC transmission system, and the operating domain can be flexibly characterized according to the system mode of adjustment, providing a reference for planning and operation personnel.

[0109] Embodiment 2 of the present invention is:

[0110] A method for describing a steady-state operation domain of a flexible direct current transmission system is provided. Based on the above-mentioned first embodiment, in this embodiment, in step S1, a voltage equation, a power equation and constraints of each node are constructed, specifically:

[0111] The voltage equations and power equations between the common connection point between the flexible DC transmission system and the feed-in system and the output point of the flexible DC transmission system are respectively constructed, and the voltage constraints of the voltage equations and the current constraints of the power equations are constructed so as to obtain a steady-state solution in the subsequent solution. In this embodiment, the following steps are specifically included:

[0112] S11. Construct the voltage equation group and obtain formula 1:

[0113]

[0114] 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, sys is the feed-in end 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;

[0115] Calculate the phasor in formula 1 according to the real part and imaginary part respectively, and get formula 2:

[0116]

[0117] Among them, U vd is the d-axis component of the output point voltage of the flexible DC transmission system, U vq 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;

[0118] S12. Construct the power equation group and obtain Formula 3:

[0119]

[0120] Among them, PCC is the common connection point between the flexible DC transmission system and the feed-in end system;

[0121] S13. The voltage of the upper and lower bridge arms of the flexible DC transmission system is as follows:

[0122]

[0123] Among them, U p is the upper bridge arm voltage, U n is the lower bridge arm voltage, U dc is the DC side capacitor voltage;

[0124] The voltage constraints of the virtual connection points of the upper and lower bridge arms are obtained as follows:

[0125]

[0126] S14. Construct the current constraint on the output side of the flexible DC transmission system, as shown in Formula 6:

[0127]

[0128] Among them, I max is the upper limit of current on the output side of the flexible DC transmission system;

[0129] S15. Construct the voltage constraint on the output side of the flexible DC transmission system, as shown in Formula 7:

[0130] U min ≤U v ≤U max ;

[0131] Among them, U min is the voltage lower limit on the output side of the flexible DC transmission system, U max It is the voltage upper limit on the output side of the flexible DC transmission system.

[0132] That is, in this embodiment, a quadratic equation system of voltage and power is constructed respectively, and combined with the voltage and current constraints, which is used to subsequently substitute into the working conditions to obtain the steady-state solution of the system, where Figure 3 As shown in the figure, the upper and lower bridge arms of the flexible DC transmission system are composed of a group of sub-modules connected in series. Under steady-state conditions, the bridge arm voltage is the sum of the capacitor voltages of all sub-modules put into operation. Therefore, the upper and lower bridge arm voltages are both greater than or equal to 0.

[0133] In addition, in this embodiment, step S2 is specifically as follows:

[0134] According to the upper and lower limits of the active power and reactive power of the flexible DC transmission system, all possible operating condition sets are obtained by permutations and combinations. Any condition in the operating condition set is substituted into the voltage equation group and the power equation group to solve the steady-state solution, and the rationality of the steady-state solution and the satisfaction of the constraints are judged. That is, all possible operating conditions within the upper and lower limits of the active and reactive power of the flexible DC transmission system are arranged to ensure that all reasonable steady-state solutions can be obtained later, so as to draw the steady-state operation domain and provide a reference for planning and operation personnel.

[0135] Specifically, the following steps are included:

[0136] S21. Construct an operating condition set and obtain Formula 8:

[0137]

[0138] Among them, Set is the operating condition set, S max is the apparent power upper limit on the output side of the flexible DC transmission system;

[0139] S22, substituting any operating condition in the operating condition set into the voltage equation group and the power equation group, and then solving to obtain the voltage and power variables of each node of the flexible DC transmission system, and checking whether the result meets the operating constraints, specifically:

[0140] If the voltage and power variables are real solutions and meet the constraints, the operating condition is considered to be within the steady-state operation domain of the flexible DC transmission system.

[0141] That is, in this embodiment, any operating condition is substituted into the above-constructed voltage equation and power equation. Since the voltage equation and the power equation are both quadratic equations, the steady-state solution obtained may have complex roots, that is, an unreasonable solution. Therefore, it is necessary to determine whether the steady-state solution is a real solution in order to obtain a reasonable steady-state solution.

[0142] Please refer to Figures 2 to 5 , Embodiment 3 of the present invention is:

[0143] A method for describing a steady-state operation domain 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 3 is the equivalent circuit diagram of the flexible DC transmission system. According to the circuit principle of the equivalent circuit diagram, Figure 4 The steady-state operation domain shown in the figure depicts a specific process flow chart. First, the voltage equations between nodes in the flexible DC transmission system are initialized and constructed.

[0144] Secondly, the voltage equations of the nodes in the flexible DC transmission system are constructed according to Formula 1 and Formula 2, the power equations of the nodes in the flexible DC transmission system are constructed according to Formula 3, the voltage constraints of the virtual connection points of the upper and lower bridge arms of the flexible DC transmission system are constructed according to Formula 4 and Formula 5, the current constraints on the output side of the flexible DC transmission system are constructed according to Formula 6, and the voltage constraints on the output side of the flexible DC transmission system are constructed according to Formula 7.

[0145] Then, according to Formula 8, a set of operating conditions of the flexible DC transmission system is constructed, and each operating condition in the set of operating conditions of the flexible DC transmission system is substituted into the above voltage equation and power equation, and then the voltage and power variables of each node of the flexible DC transmission system are solved, and it is checked whether the results meet the voltage constraints and current constraints. At the same time, it is judged whether the solved voltage and power variables are real solutions. If they meet the voltage constraints and current constraints and are real solutions, the voltage and power variables are judged to be reasonable, that is, the operating condition is considered to belong to the steady-state operation domain of the flexible DC transmission system.

[0146] Finally, determine whether all operating conditions in the operating condition set have been substituted into the voltage equation and the power equation for solution. If all operating conditions have not been traversed, obtain the voltage and power variables under other conditions and check their rationality until the traversal is completed. Then, the steady-state operating domain of the flexible DC transmission system can be output.

[0147] In this embodiment, the output side operation domain of the flexible DC transmission system obtained by using the method for describing the steady-state operation domain of the flexible mainstream power transmission system proposed in the present invention is as follows: Figure 5As shown, it can be seen that the operating domain of the output side of the flexible DC transmission system is not an ideal unit circle, but an arc-like shape with "concave on top and convex on bottom". The upper boundary of the operating domain is mainly limited by the voltage constraints of the virtual connection points of the upper and lower bridge arms and the voltage constraints on the output side of the flexible DC transmission system, while the lower boundary of the operating domain is mainly limited by the current constraints on the output side of the flexible DC transmission system.

[0148] Please refer to Figure 6 , Embodiment 4 of the present invention is:

[0149] A terminal 1 for characterizing a steady-state operation domain of a flexible direct current transmission system 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.

[0150] In summary, the method and terminal for characterizing the steady-state operating domain of a flexible direct current transmission system provided by the present invention can intuitively provide the steady-state operating domain of the flexible direct current transmission system under steady-state conditions, assist in judging the operating margin of the flexible direct current transmission system, and can flexibly characterize the operating domain according to the system mode of adjustment, providing a reference for planning and operation personnel.

[0151] 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 describing the steady-state operation domain 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 equation, power equation and constraint conditions of each node in the flexible DC transmission system, specifically: Constructing a voltage equation group and a power equation group between a common connection point between the flexible direct current transmission system and the feed-in end system and an output point of the flexible direct current transmission system respectively, and constructing a voltage constraint of the voltage equation group and a current constraint of the power equation group; The specific steps include: S11, construct the voltage equation group to obtain formula 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, sys is the feed-in end 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; Calculate the phasor in formula 1 according to the real part and imaginary part respectively, and get formula 2: ； Among them, U vd is the d-axis component of the output point voltage of the flexible DC transmission system, U vq 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; S12, construct the power equation group to obtain Formula 3: ； Among them, PCC is the common connection point between the flexible DC transmission system and the feed-in end system; S13. The voltage of the upper and lower bridge arms of the flexible DC transmission system is as follows: ； Among them, U p is the upper bridge arm voltage, U n is the lower bridge arm voltage, U dc is the DC side capacitor voltage; The voltage constraint of the virtual connection point of the upper and lower bridge arms is obtained as shown in Formula 5: ； S14. Construct the current constraint on the output side of the flexible DC transmission system, as shown in Formula 6: ； Among them, I max is the upper limit of current on the output side of the flexible DC transmission system; S15. Construct the voltage constraint on the output side of the flexible DC transmission system, as shown in Formula 7: ； Among them, U min is the voltage lower limit on the output side of the flexible DC transmission system, U max is the voltage upper limit on the output side of the flexible DC transmission system; S2. constructing an operating condition set of the flexible direct current transmission system, substituting any operating condition in the operating condition set into the voltage equation and the power equation to obtain a steady-state solution of the system, and determining the rationality of the steady-state solution according to the constraint conditions; S3. Traverse all the operating conditions in the operating condition set, and output all reasonable steady-state solutions to obtain the steady-state operating domain of the flexible direct current transmission system.

2. A method for describing a steady-state operation domain of a flexible direct current transmission system according to claim 1, characterized in that: The S2 is specifically: According to the upper and lower limits of the active power and reactive power of the flexible direct current transmission system, all the operating condition sets are obtained by permutations and combinations, and any condition in the operating condition set is substituted into the voltage equation group and the power equation group to solve the steady-state solution, and the rationality of the steady-state solution and the satisfaction of the constraint conditions are judged.

3. A method for describing a steady-state operation domain of a flexible direct current transmission system according to claim 2, characterized in that: The S2 specifically includes the following steps: S21, construct the operating condition set to obtain Formula 8: ； Wherein, Set is the set of operating conditions, S max is the apparent power upper limit on the output side of the flexible DC transmission system; S22, substituting any operating condition in the operating condition set into the voltage equation group and the power equation group, and then solving to obtain the voltage and power variables of each node of the flexible DC transmission system, and checking whether the result meets the operating constraints, specifically: If the voltage and power variables are real solutions and satisfy the constraints, it is considered that the operating condition belongs to the steady-state operation domain of the flexible DC transmission system.

4. A terminal for describing a steady-state operation domain of a flexible direct current transmission system, executing a method for describing a steady-state operation domain of a flexible direct current transmission system as claimed in 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 equation, power equation and constraint conditions of each node in the flexible DC transmission system, specifically: Constructing a voltage equation group and a power equation group between a common connection point between the flexible direct current transmission system and the feed-in end system and an output point of the flexible direct current transmission system respectively, and constructing a voltage constraint of the voltage equation group and a current constraint of the power equation group; The specific steps include: S11, construct the voltage equation group to obtain formula 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, sys is the feed-in end 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; Calculate the phasor in formula 1 according to the real part and imaginary part respectively, and get formula 2: ； Among them, U vd is the d-axis component of the output point voltage of the flexible DC transmission system, U vq 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; S12, construct the power equation group to obtain Formula 3: ； Among them, PCC is the common connection point between the flexible DC transmission system and the feed-in end system; S13. The voltage of the upper and lower bridge arms of the flexible DC transmission system is as follows: ； Among them, U p is the upper bridge arm voltage, U n is the lower bridge arm voltage, U dc is the DC side capacitor voltage; The voltage constraint of the virtual connection point of the upper and lower bridge arms is obtained as shown in Formula 5: ； S14. Construct the current constraint on the output side of the flexible DC transmission system, as shown in Formula 6: ； Among them, I max is the upper limit of current on the output side of the flexible DC transmission system; S15. Construct the voltage constraint on the output side of the flexible DC transmission system, as shown in Formula 7: ； Among them, U min is the voltage lower limit on the output side of the flexible DC transmission system, U max is the voltage upper limit on the output side of the flexible DC transmission system; S2. constructing an operating condition set of the flexible direct current transmission system, substituting any operating condition in the operating condition set into the voltage equation and the power equation to obtain a steady-state solution of the system, and determining the rationality of the steady-state solution according to the constraint conditions; S3. Traverse all the operating conditions in the operating condition set, and output all reasonable steady-state solutions to obtain the steady-state operating domain of the flexible direct current transmission system.

5. A terminal for describing a steady-state operation domain of a flexible direct current transmission system according to claim 4, characterized in that: The S2 is specifically: According to the upper and lower limits of the active power and reactive power of the flexible direct current transmission system, all the operating condition sets are obtained by permutations and combinations, and any condition in the operating condition set is substituted into the voltage equation group and the power equation group to solve the steady-state solution, and the rationality of the steady-state solution and the satisfaction of the constraint conditions are judged.

6. A terminal for describing a steady-state operation domain of a flexible direct current transmission system according to claim 5, characterized in that: The S2 specifically includes the following steps: S21, construct the operating condition set to obtain Formula 8: ； Wherein, Set is the set of operating conditions, S max is the apparent power upper limit on the output side of the flexible DC transmission system; S22, substituting any operating condition in the operating condition set into the voltage equation group and the power equation group, and then solving to obtain the voltage and power variables of each node of the flexible DC transmission system, and checking whether the result meets the operating constraints, specifically: If the voltage and power variables are real solutions and satisfy the constraints, it is considered that the operating condition belongs to the steady-state operation domain of the flexible DC transmission system.

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