AC / DC system power flow overload emergency control method based on VSC-HVDC sensitivity analysis

Abstract

The invention discloses an AC / DC system power flow overload emergency control method based on VSC-HVDC sensitivity analysis, and relates to the technical field of AC / DC system static safety and stability control, and the method comprises the steps: obtaining a VSC-HVDC control method and an operation mode in an AC system, converting a to-be-converted AC line into a VSC-HVDC line, and obtaining an AC / DC system structure; establishing a power sensitivity calculation formula of the VSC-HVDC to an alternating current line based on the alternating current and direct current system structure; converting the power sensitivity calculation formula into a line matrix form, and establishing a power sensitivity matrix for the whole line of the system; performing optimization problem calculation based on the power sensitivity matrix to obtain an optimal adjustment value; and verifying emergency control of the line overload problem according to the optimal adjustment value to obtain an optimal control parameter of the VSC-HVDC. According to the method, power optimization is carried out on the overload lines by adjusting the power of the VSC, all the lines are ensured to be kept in a safe operation state, and the method plays an important role in avoiding long-time overload of the lines.

Description

Technical Field

[0001] The present invention relates to the technical field of static safety and stability control of AC and DC systems, in particular to an AC and DC system power flow overload emergency control method based on VSC-HVDC sensitivity analysis. Background Art

[0002] The rapid development of large-scale renewable energy generation RPGs is gradually replacing traditional synchronous generators and redistributing power flows in modern power systems. The access of RPGs to AC power grids, which are mostly located in remote areas, has put forward new demands on power transmission and may cause line overload and tripping of power grids, threatening the safe and stable operation of power grids. In modern power systems, long-term overload of interconnected transmission lines may cause power grid failures, thereby causing large-scale power outages. In order to alleviate transmission line overload, traditional methods solve optimal power flow OPF and safety constrained optimal power flow SCOPF based on power system models to optimize system operation scenarios. Optimal power flow OPF is a method for power system operation and planning that aims to minimize the desired goal while ensuring that all constraints are met to achieve the optimal state of control variables. Safety constrained optimal power flow SCOPF pays more attention to safety constraints to ensure that the stability and reliability of the power system are maintained after a single fault occurs. Previous studies have proposed methods to alleviate overloads through generation scheduling and load reduction, but these methods often require longer response times and greater economic costs. In addition, the complexity of power system models and safety constraints increases the time required to solve the optimal power flow OPF problem, hindering the ability to respond quickly to power system faults or overloads.

[0003] In order to meet the time requirements of emergency control after a fault occurs, the sensitivity method can be used to linearize the system constraints. The sensitivity method can directly analyze how specific parameters affect the operating state without iterative calculation of the power network equations; the transmission line has a certain overload capacity under different overload durations depending on the load conditions before the fault; due to the complexity of system operation and the variability of renewable energy and load, it becomes challenging to accurately predict the system overload after a fault occurs, so the ex ante optimization solution is not applicable and must rely on real-time emergency control; with the advancement of DC transmission technology, new power electronic equipment such as high-voltage direct current HVDC systems provide better controllability and lower operating costs, making them more applicable in emergency control applications.

[0004] In the method of using VSC-HVDC in combination with sensitivity analysis to alleviate AC line overload, it is usually necessary to calculate the sensitivity of the DC line to the AC system, predict and analyze the line power changes, and thus achieve corrective control of the overloaded line. However, the above sensitivity-based emergency control method only focuses on the overloaded line and cannot determine the safety of other lines during the optimization process. At the same time, the sensitivity calculation is only a small-scale calculation for the problem line, and the sensitivity cannot be used to optimize the global power flow distribution of the system. Summary of the invention

[0005] In view of the above-mentioned problems, the present invention is proposed.

[0006] Therefore, the problem to be solved by the present invention is how to provide an emergency control method for quickly alleviating line overload and optimizing global power flow based on AC-DC power sensitivity analysis after a system failure, so as to restore line overload under different fault scenarios and optimize power flow distribution.

[0007] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0008] In a first aspect, an embodiment of the present invention provides an AC / DC system power flow overload emergency control method based on VSC-HVDC sensitivity analysis, which includes obtaining a control method and an operating mode of a VSC-HVDC in an AC system, and converting an AC line to be converted into a VSC-HVDC line to obtain an AC / DC system structure; establishing a power sensitivity calculation formula of VSC-HVDC to an AC line based on the AC / DC system structure; converting the power sensitivity calculation formula into a line matrix form to establish a power sensitivity matrix for the entire line of the system; performing optimization problem calculation based on the power sensitivity matrix to obtain an optimal adjustment value; verifying the emergency control of the line overload problem according to the optimal adjustment value to obtain the optimal control parameters of the VSC-HVDC.

[0009] As a preferred solution of the AC / DC system power flow overload emergency control method based on VSC-HVDC sensitivity analysis of the present invention, the VSC-HVDC control method includes the following steps: the current equation of the VSC in the dq reference system decouples the control of the d-axis and the q-axis, and the specific formula is as follows:

[0010]

[0011] Where d, q and ref are the reference of d-axis, q-axis and signal respectively; u d and i d are the d-axis voltage and current of VSC respectively; u q and i q are the q-axis voltage and current of VSC respectively; u d.ref and uq.ref are the d-axis and q-axis voltages of the pulse width modulation (PWM) reference; R and L are the resistance and inductance of the phase reactor, respectively.

[0012] As a preferred scheme of the AC / DC system power flow overload emergency control method based on VSC-HVDC sensitivity analysis described in the present invention, wherein: the operation mode of VSC-HVDC includes normal mode and emergency mode; the normal mode means that under normal operation mode, the VSC-HVDC interconnection helps to transmit planned power and maintain terminal voltage; the emergency mode means that when a disturbance occurs, the VSC-HVDC switches to the emergency mode, and the VSC-HVDC line provides power flow adjustment and transient support.

[0013] As a preferred solution of the AC / DC system power flow overload emergency control method based on VSC-HVDC sensitivity analysis described in the present invention, wherein: the power sensitivity calculation formula of VSC-HVDC to AC line refers to combining the linear power flow equation of the system under study with graph theory, considering the system voltage parameters, and calculating the sensitivity of node injection power to line power; the power sensitivity calculation formula of VSC-HVDC to AC line includes the following steps: obtaining the network node voltage equation based on the mathematical model of the power grid, and the specific formula is as follows:

[0014] I N =Y N U N

[0015] Among them, I N The column vector of the node injected current; U N is the node voltage column vector; Y N is the node admittance matrix; based on the network node voltage equation, the relationship between the network branch current and the branch voltage is obtained, and the specific formula is as follows:

[0016]

[0017] Among them, I B is the branch current column vector; U B is the branch voltage column vector; Y B is the branch admittance matrix; A is the node association matrix; define the network correlation coefficient matrix C(λ), the specific formula is as follows:

[0018]

[0019] According to the relationship between the network branch current and the branch voltage and the network correlation coefficient matrix C(λ), the linear combination of the injected current of each node is obtained. The specific formula is as follows:

[0020] I k,B =λk-1 I 1,N +…+λ k-i I i,N +…+λ k-n I n,N

[0021] Among them, λ k-i is the current I of branch k in the network correlation coefficient matrix C(λ) k,B The injected current I i,N In order to obtain the relationship between line power and node injection power, the branch current vector I k,B Multiply the voltage on both sides of , the specific formula is as follows:

[0022]

[0023] Among them, U k,B is the starting voltage vector of line k; U i,N is the voltage vector of node i; rewrite the above formula into the form of P+jQ, expand the vector into its real part and imaginary part, and get the following formula:

[0024]

[0025] Among them, θ k,B is the phase angle of the voltage at the starting end of branch k; θ i,N is the phase angle of the voltage at node i; P k,B is the active power at the starting end of branch k; Q k,B is the reactive power at the starting end of branch k; k-i,a and λ k-i,b are the relevant parameters λ k-i The real and imaginary parts of the transmission line are: In the emergency control to eliminate the active power overload of the transmission line, only the active power of the control node is adjusted without changing the reactive power, and the following relationship is obtained:

[0026]

[0027] By substituting into the power equation for calculation, the power sensitivity β between the power variable of line k and the injected power variable of node i is obtained: k-i as follows:

[0028]

[0029] Among them, β k-i is the power sensitivity between the power variable of line k and the injected power variable of node i.

[0030] As a preferred scheme of the AC / DC system power flow overload emergency control method based on VSC-HVDC sensitivity analysis described in the present invention, wherein: converting the power sensitivity calculation formula into a line matrix form means taking into account that the number of DC lines and AC lines in the actual system is greater, and the lines are closely connected, and will affect each other during the power adjustment process. Therefore, in order to realize the prediction of global power, the power sensitivity calculation formula is converted into a line matrix form, and a power sensitivity matrix for the entire system line is established.

[0031] As a preferred solution of the AC / DC system power flow overload emergency control method based on VSC-HVDC sensitivity analysis of the present invention, the establishment of the power sensitivity matrix for the entire system line includes the following steps: after replacing the AC line with the VSC-HVDC line, recalculating the network correlation coefficient matrix, the specific formula is as follows:

[0032]

[0033] Among them, C * (λ) is the value recalculated after the introduction of VSC-HVDC. By substituting the updated λ into the power sensitivity calculation formula, the sensitivity matrix S of the node injection power in the system including VSC-HVDC is obtained. m×n , the specific formula is as follows:

[0034]

[0035] Where m is the number of AC lines in the system; n is the number of system nodes; assuming that the xth DC line is connected between node i and node j, the power sensitivity of the DC line to other AC lines is calculated as follows:

[0036] Sen DC,x =S[:,j]-S[:,i]

[0037] Among them, Sen DC,x is the power sensitivity of the x-th DC line relative to the AC line; S[:,j] and S[:,i] are the matrices S m×n The jth and ith columns of the DC line are adjusted by ΔP DC,x After that, the power P of the AC line is calculated by the following formula:

[0038]

[0039] Where ΔP m is the power change of the mth AC line; P0 is the initial power value of the AC line; according to the power P of the AC line, after adjusting the DC power, the power of the AC line is calculated.

[0040] As a preferred solution of the AC / DC system power flow overload emergency control method based on VSC-HVDC sensitivity analysis of the present invention, wherein: performing optimization problem calculation based on the power sensitivity matrix means that according to the power sensitivity matrix, the parameter variation range and operation constraints of the DC and AC lines in the actual system are considered, and the optimization problem is solved with the minimum absolute amount of adjusted power as the optimization objective function to obtain the optimal adjustment value; obtaining the optimal adjustment value includes the following steps: using the power sensitivity matrix to calculate the sensitivity of the DC line power to the AC line power, and prioritizing the DC lines in the following manner:

[0041]

[0042] Among them, b k 1 is the sensitivity of the first DC line to the kth AC line; x is the number of candidate DC lines; to evaluate whether the AC transmission line will be overloaded, the active power flow after the line fault is calculated. Assuming that the k line is overloaded, the transmission power after the overload is P ka , overload ΔP k The specific formula is as follows:

[0043] ΔP k =P ka -P kmax

[0044] Among them, P kmax is the rated power limit of the line; in order to achieve power dispatch and eliminate the overload ΔP on the transmission line by adjusting the power of the DC line k , solve the following optimization problem, the objective function of the optimization problem is as follows:

[0045]

[0046] Where ΔP DC,m , P DC,m , as well as are the power variation, actual power, minimum power and maximum power of the mth DC line respectively; ε is a small constant; P k and P kmax are the actual power and maximum power of the kth AC line respectively; L is the set of all AC lines; by solving the objective function of the optimization problem, the sensitivity-based VSC-HVDC power adjustment is obtained.

[0047] In the second aspect, in order to further solve the safety problems existing in the static safety and stability control of AC and DC systems, the present invention provides an AC and DC system power flow overload emergency control system based on VSC-HVDC sensitivity analysis, which includes: a structure acquisition module, which is used to obtain the control method and operation mode of VSC-HVDC in the AC system, convert the AC line to be converted into a VSC-HVDC line, and obtain the AC and DC system structure; a sensitivity calculation module, which is used to establish a power sensitivity calculation formula of VSC-HVDC to the AC line based on the AC and DC system structure; a matrix conversion module, which is used to convert the power sensitivity calculation formula into a line matrix form, and establish a power sensitivity matrix for the entire line of the system; an optimal calculation module, which is used to solve the optimization problem based on the power sensitivity matrix, with the minimum absolute amount of adjusted power as the optimization objective function, and obtain the optimal adjustment value; a verification module, which is used to verify whether the line overload problem can be controlled in real time within the required time according to the optimal adjustment value, and obtain the optimal control parameters of VSC-HVDC.

[0048] In a third aspect, an embodiment of the present invention provides a computer device, comprising a memory and a processor, wherein the memory stores a computer program, wherein: when the computer program is executed by the processor, any step of the AC / DC system power flow overload emergency control method based on VSC-HVDC sensitivity analysis as described in the first aspect of the present invention is implemented.

[0049] In a fourth aspect, an embodiment of the present invention provides a computer-readable storage medium having a computer program stored thereon, wherein: when the computer program is executed by a processor, any step of the method for emergency control of AC / DC system power flow overload based on VSC-HVDC sensitivity analysis as described in the first aspect of the present invention is implemented.

[0050] Beneficial effects of the present invention: The present invention proposes an emergency control method for power flow overload of an AC / DC system based on VSC-HVDC sensitivity analysis, which is feasible for quickly alleviating the problem of line overload through VSC-HVDC after a system failure, and optimizing VSC and global power flow; considering saving transmission corridor space, VSC-HVDC lines are used to directly replace AC lines and connected to two bus terminals; multiple DC converters are deployed to enhance the system's global power optimization capability; a sensitivity matrix is ​​derived based on the admittance matrix before the system failure, and the impact of multiple VSC-HVDC lines on the AC line power is quantified without power measurement and redundant calculation, and its accuracy is verified; in various fault scenarios, the power of the overloaded line is optimized by adjusting the power of the VSC, while ensuring that all lines in the system remain in a safe operating state, which plays an important role in avoiding long-term line overload in variable operating scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work. Among them:

[0052] Figure 1 This is an overall flow chart of the AC / DC system power flow overload emergency control method based on VSC-HVDC sensitivity analysis in Example 1.

[0053] Figure 2 Schematic diagram of the basic control framework of VSC-HVDC in Example 1.

[0054] Figure 3 This is a schematic diagram of the structure of the computer device in Example 3.

[0055] Figure 4 Schematic diagram of VSC-HVDC interconnection between two load areas in the power grid in Example 4. DETAILED DESCRIPTION

[0056] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the accompanying drawings.

[0057] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein, and those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0058] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The term "in one embodiment" that appears in different places in this specification does not necessarily refer to the same embodiment, nor does it refer to a separate or selective embodiment that is mutually exclusive with other embodiments.

[0059] Example 1

[0060] Reference Figure 1 and Figure 2 , which is the first embodiment of the present invention, and provides an AC / DC system power flow overload emergency control method based on VSC-HVDC sensitivity analysis.

[0061] The existing methods of using VSC-HVDC to alleviate AC line overload in combination with sensitivity analysis have the following main problems: the sensitivity-based emergency control method only focuses on the overloaded line and cannot determine the safety of other lines during the optimization process; at the same time, the sensitivity calculation is only a small-scale calculation for the problem line, and the sensitivity cannot be used to optimize the global power flow distribution of the system.

[0062] The present application provides an effective solution to the above-mentioned problems. Next, multiple embodiments will be combined to explain in detail how to implement the AC / DC system power flow overload emergency control method based on VSC-HVDC sensitivity analysis.

[0063] Figure 1 The overall flow chart of the AC / DC system power flow overload emergency control method based on VSC-HVDC sensitivity analysis is shown, including:

[0064] S1: Acquire a control method and an operation mode of a VSC-HVDC in an AC system, and convert the AC line to be converted into a VSC-HVDC line to obtain an AC / DC system structure.

[0065] Preferably, the control method of VSC-HVDC comprises the following steps: VSC-HVDC is an important device in an AC / DC hybrid power grid, used to convert active power between the two sides of the AC system, and the current equation of VSC in the dq reference system decouples the control of the d-axis and the q-axis, so that the active power and the reactive power can be adjusted more independently. The current equation of VSC in the dq reference system is as follows:

[0066]

[0067] Where d, q and ref are the reference of d-axis, q-axis and signal respectively; u d and i d are the d-axis voltage and current of VSC respectively; u q and i q are the q-axis voltage and current of VSC respectively; u d.ref and u q.ref are the d-axis and q-axis voltages of the pulse width modulation (PWM) reference; R and L are the resistance and inductance of the phase reactor, respectively.

[0068] Furthermore, the VSC controller adopts the traditional proportional-integral PI control method, where the basic control framework of VSC-HVDC is as follows Figure 2 As shown in Figure 2, VSC-HVDC can independently control and quickly adjust active power, which helps to restore the power system after a power outage. Figure 2 In the control structure shown, the operator will need to adjust the active power ΔP dcEnter the VSC-HVDC controller to quickly alleviate system power flow overload issues.

[0069] Preferably, the operation mode of the VSC-HVDC includes a normal mode and an emergency mode.

[0070] Specifically, the normal mode refers to the normal operating mode, in which the VSC-HVDC interconnection helps to transmit the planned power and maintain the terminal voltage. The power flow is determined by the system dispatcher. In this mode, the VSC-HVDC in the power grid can participate in safety-constrained economic dispatch as a controllable resource, thereby enhancing the flexibility of the system.

[0071] Specifically, emergency mode means that when a disturbance occurs, such as a load change or line interruption, the VSC-HVDC switches to emergency mode; the VSC-HVDC line can provide rapid power flow adjustment and transient support to help mitigate the impact of disturbances and prevent large-scale power outages in the power grid. For example, the power flow of the HVDC line can be quickly increased or decreased to reduce the burden on parallel AC interconnection lines, or to balance the supply and demand in a load area that has lost a large amount of power supply from the external power grid.

[0072] It should be noted that it is not easy to build new transmission lines and substations in large-scale power grids. Therefore, it is chosen to convert some AC lines into VSC-HVDC lines to enhance the capacity and resilience of the grid; the operating mode of VSC-HVDC in the AC system is divided into normal mode and emergency mode, so as to cope with possible operating conditions of the AC and DC systems.

[0073] Preferably, since power regulation in the prior art mostly relies on traditional AC lines, which have a slow adjustment speed and affect the overall stability of the network, the present invention converts some AC lines into VSC-HVDC lines, thereby enhancing the grid capacity and improving the grid's response capability; compared with traditional AC systems, VSC-HVDC can provide faster and more accurate power regulation and control, especially in emergency mode, by quickly increasing or decreasing power flow, it can significantly reduce the pressure of system overload and avoid large-scale power outages.

[0074] S2: Based on the AC / DC system structure, a calculation formula for the power sensitivity of VSC-HVDC to the AC line is established.

[0075] Preferably, establishing a calculation formula for the power sensitivity of VSC-HVDC to AC lines means combining the linear power flow equation of the system under study with graph theory in order to study the power sensitivity between the VSC-HVDC lines and the AC lines, comprehensively considering the system voltage parameters, and calculating the sensitivity of the node injection power to the line power; in addition, the sensitivity of the embedded VSC-HVDC lines is also determined for optimizing the emergency control of line overload.

[0076] It should be noted that the power sensitivity calculation formula is intended to linearize the relationship between DC power and system AC power, and to improve the accuracy and speed of grid line power flow prediction to cope with all possible abnormal operation scenarios.

[0077] Specifically, establishing a calculation formula for the power sensitivity of VSC-HVDC to the AC line includes the following steps: obtaining a network node voltage equation based on a mathematical model of the power grid, and the specific formula is as follows:

[0078] I N =Y N U N

[0079] Among them, I N The column vector of the node injected current; U N is the node voltage column vector; Y N is the node admittance matrix.

[0080] Based on the network node voltage equation, the relationship between the network branch current and branch voltage is obtained. The specific formula is as follows:

[0081]

[0082] Among them, I B is the branch current column vector; U B is the branch voltage column vector; Y B is the branch admittance matrix; A is the node association matrix.

[0083] Define the network correlation coefficient matrix C(λ), the specific formula is as follows:

[0084]

[0085] According to the relationship between the network branch current and branch voltage and the network correlation coefficient matrix C(λ), the linear combination of the injected current of each node is obtained. Taking line k as an example, the linear combination of the injected current of each node, that is, the branch current vector I k,B The specific formula is as follows:

[0086] I k,B =λ k-1 I 1,N +…+λ k-i I i,N +…+λ k-n I n,N

[0087] Among them, λ k-i is the current I of branch k in the network correlation coefficient matrix C(λ) k,B The injected current I i,NThe related parameters between .

[0088] In order to obtain the relationship between line power and node injection power, the branch current vector I k,B Multiply the voltage on both sides of , the specific formula is as follows:

[0089]

[0090] Among them, U k,B is the starting voltage vector of line k; U i,N is the voltage vector of node i.

[0091] Rewrite the above formula into the form of P+jQ, expand the vector into its real part and imaginary part, and get the following formula:

[0092]

[0093] Among them, θ k,B is the phase angle of the voltage at the starting end of branch k (in radians); θ i,N is the phase angle of the voltage at node i (in radians); P k,B is the active power at the starting end of branch k (unit: MW); Q k,B is the reactive power at the starting end of branch k (unit: MVar); k-i,a and λ k-i,b are the relevant parameters λ k-i The real and imaginary parts of the voltage and power of the branches and nodes all use their respective per-unit values.

[0094] In the emergency control to eliminate the active power overload of the transmission line, since only the active power of the control node is adjusted without changing its reactive power, the reactive power part of the injection node is set to 0, and the real part of the above formula is taken to obtain the following relationship:

[0095]

[0096] By substituting into the power equation for calculation, the power sensitivity β between the power variable of line k and the injected power variable of node i is obtained: k-i as follows:

[0097]

[0098] Among them, β k-i is the power sensitivity between the power variable of line k and the injected power variable of node i.

[0099] Preferably, by establishing a calculation formula for the sensitivity of VSC-HVDC to AC line power, the present invention can more accurately predict power flow changes, especially in multi-line and multi-node power grids, and can adjust power distribution in real time. This sensitivity-based adjustment method is more efficient than the simple power adjustment method in the prior art, and can quickly respond and optimize power scheduling under complex power grid operating conditions.

[0100] S3: Convert the power sensitivity calculation formula into a line matrix form and establish a power sensitivity matrix for the entire line of the system.

[0101] Preferably, converting the power sensitivity calculation formula into a line matrix form means taking into account that in an actual system, there are more DC lines and AC lines, and the lines are closely connected, and they will affect each other during the power adjustment process. Therefore, it is necessary to fully consider the global power of the system for adjustment to achieve a global optimal state and avoid other lines from exceeding the limit during local adjustment. Therefore, in order to realize the prediction of global power, it is necessary to convert the power sensitivity calculation formula into a line matrix form and establish a power sensitivity matrix for all lines of the system.

[0102] It should be noted that the power sensitivity calculated according to the power sensitivity calculation formula represents the sensitivity of the injected power of the representative node to the line power. In order to use the VSC-HVDC's ability to quickly adjust power to adjust the power of adjacent lines and thus share the load of overloaded lines, it is necessary to calculate the sensitivity of the VSC-HVDC power to the line power. From the perspective of the AC system, the impedance of the VSC-HVDC line is independent of the power flow distribution, because the HVDC components are decoupled through the converter station. Therefore, the VSC-HVDC line can be regarded as a boundary, and the power on both sides is fully controllable. The power sensitivity of the AC line relative to the VSC-HVDC line can be calculated using the power sensitivity calculation formula.

[0103] Specifically, establishing the power sensitivity matrix for the entire system line includes the following steps: After replacing the AC line with the VSC-HVDC line, the network correlation coefficient matrix needs to be recalculated. The specific formula is as follows:

[0104]

[0105] Among them, C * (λ) is the value recalculated after the introduction of VSC-HVDC.

[0106] By substituting the updated λ into the power sensitivity calculation formula, the sensitivity matrix S of the node injection power in the system including VSC-HVDC is obtained: m×n , the specific formula is as follows:

[0107]

[0108] Wherein, m is the number of AC lines in the system; n is the number of system nodes.

[0109] Assuming that the xth DC line is connected between nodes i and j, increasing the DC line power means increasing the output power of node i and the input power of node j at the same time, so the power sensitivity of the DC line to other AC lines can be calculated as follows:

[0110] Sen DC,x =S[:,j]-S[:,i]

[0111] Among them, Sen DC,x is the power sensitivity of the x-th DC line relative to the AC line, which is a column vector containing m rows; S[:,j] and S[:,i] are matrices S m×n The j-th and i-th columns of .

[0112] In linear networks, the superposition principle can be applied, so the power adjustment ΔP after the xth DC line DC,x After that, the power P of the AC line can be calculated by the following formula:

[0113]

[0114] Where ΔP m is the power change of the mth AC line; P0 is the initial power value of the AC line.

[0115] According to the power P of the AC line, the power of the AC line can be calculated after adjusting the DC power. However, since there may be a deviation between the calculated value and the actual value, a margin needs to be introduced in the optimization programming to ensure the reliability of the result.

[0116] Preferably, through the power sensitivity matrix, the system can fully consider the mutual influence between DC and AC lines, avoid the impact of local overload problems on global stability, and compared with the simple combination method of the prior art, the present invention can accurately adjust the power grid on a global scale, maximize the avoidance of line overload, and reduce the possible overload risk of other lines.

[0117] S4: Calculate the optimization problem based on the power sensitivity matrix to obtain the optimal adjustment value.

[0118] Preferably, calculating the optimization problem based on the power sensitivity matrix means taking into account the parameter variation range and operating constraints of the DC and AC lines in the actual system according to the power sensitivity matrix, taking the minimum absolute amount of adjusted power as the optimization objective function, solving the optimization problem, and obtaining the optimal adjustment value, thereby providing an economical optimal solution for eliminating system overload power and ensuring global stability.

[0119] Specifically, obtaining the optimal adjustment value includes the following steps: Considering a group of candidate VSC-HVDC lines, whose DC power can be rescheduled, for a specific AC line, increasing the power of some DC lines may increase the power of the AC line, and reducing the power of other DC lines may also increase the power of the AC line. Therefore, the sensitivity of the DC line power to the AC line power is calculated using the power sensitivity matrix, such as the sensitivity of the DC line to the AC line k, and the DC lines are prioritized as follows:

[0120]

[0121] Among them, b k 1 is the sensitivity of the first DC line to the kth AC line; x is the number of candidate DC lines; it can be seen that by setting P DC,x The DC power of the xth VSC-HVDC can be increased by 1dc -P DC,M Or reduce P DC,M+1 -P DC,x To reduce the power of the kth AC line, there are obviously many scheduling strategies to alleviate the overload of the AC line, but the most effective way is to adjust the power of the leftmost or rightmost DC line.

[0122] In order to evaluate whether the AC transmission line will be overloaded, the active power flow after the line fault is calculated. Assuming that the k line is overloaded, the transmission power after the overload is P ka , overload ΔP k The specific formula is as follows:

[0123] ΔP k =P ka -P kmax

[0124] Among them, P kmax is the rated power limit of the line, that is, the maximum capacity of the line.

[0125] In order to achieve efficient power dispatch and eliminate overload ΔP on the transmission line by adjusting the power of the DC line k , we need to solve the following optimization problem, the objective function of the optimization problem is as follows:

[0126]

[0127] Where ΔP DC,m , P DC,m , as well as are the power change, actual power, minimum power and maximum power of the mth DC line respectively; ε is a small constant used to indicate the threshold of power change; P k and P kmax are the actual power and maximum power of the kth AC line respectively; L is the set of all AC lines.

[0128] In AC-DC systems, changing the generator output has low sensitivity and poor economy. In contrast, it is more practical and faster to transfer overload power flow by adjusting DC control parameters. Therefore, by solving the objective function of the optimization problem, the sensitivity-based VSC-HVDC power adjustment amount is obtained to reduce the risk of power flow overload.

[0129] Preferably, the emergency mode of VSC-HVDC can respond quickly when a disturbance occurs, quickly adjust power, and prevent large-scale power outages caused by system overload. In particular, the present invention ensures that the system can quickly resume stable operation in the event of load changes or line interruptions through the optimized VSC-HVDC control strategy, thus avoiding the problem of insufficient fault response capability of traditional power grids.

[0130] S5: Verify the emergency control of the line overload problem according to the optimal adjustment value to obtain the optimal control parameters of the VSC-HVDC.

[0131] Specifically, obtaining the optimal control parameters of VSC-HVDC means verifying whether it is possible to implement real-time emergency control of the line overload problem within the required time based on the obtained sensitivity-based VSC-HVDC power adjustment amount, so that the system maintains safe and stable operation, and the adjustment amount is minimized, thereby obtaining the optimal control parameters of VSC-HVDC.

[0132] In summary, the present invention proposes an emergency control method for power flow overload of AC / DC systems based on VSC-HVDC sensitivity analysis, which is feasible for quickly alleviating the problem of line overload through VSC-HVDC after a system failure, and optimizing VSC and global power flow; considering saving transmission corridor space, VSC-HVDC lines are used to directly replace AC lines and connected to two bus terminals; multiple DC converters are deployed to enhance the system's global power optimization capability; a sensitivity matrix is ​​derived based on the admittance matrix before the system failure, and the impact of multiple VSC-HVDC lines on the AC line power is quantified without power measurement and redundant calculation, and its accuracy is verified; in various fault scenarios, the power of the overloaded line is optimized by adjusting the power of the VSC, while ensuring that all lines in the system remain in a safe operating state, which plays an important role in avoiding long-term line overload in variable operating scenarios.

[0133] Embodiment 2 is an embodiment of the present invention, which provides an AC / DC system power flow overload emergency control system based on VSC-HVDC sensitivity analysis, including: a structure acquisition module, used to obtain the control method and operation mode of VSC-HVDC in the AC system, convert the AC line to be converted into a VSC-HVDC line, and obtain the AC / DC system structure; a sensitivity calculation module, used to establish a power sensitivity calculation formula of VSC-HVDC to the AC line based on the AC / DC system structure; a matrix conversion module, used to convert the power sensitivity calculation formula into a line matrix form, and establish a power sensitivity matrix for the entire line of the system; an optimal calculation module, used to solve the optimization problem based on the power sensitivity matrix, with the minimum absolute amount of adjusted power as the optimization objective function, and obtain the optimal adjustment value; a verification module, used to verify whether the line overload problem can be controlled in real time within the required time according to the optimal adjustment value, and obtain the optimal control parameters of VSC-HVDC.

[0134] Embodiment 3 is an embodiment of the present invention, which is different from the previous embodiment in that:

[0135] like Figure 3 As shown, if the function is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, or the part that contributes to the prior art or the part of the technical solution, can be embodied in the form of a software product, which is stored in a storage medium and includes several instructions for a computer device (which can be a personal computer, a server, or a network device, etc.) to perform all or part of the steps of the method described in each embodiment of the present invention. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), disk or optical disk and other media that can store program codes.

[0136] The logic and / or steps represented in the flowchart or otherwise described herein, for example, can be considered as an ordered list of executable instructions for implementing logical functions, and can be embodied in any computer-readable medium for use by an instruction execution system, device or apparatus (such as a computer-based system, a system including a processor, or other system that can fetch instructions from an instruction execution system, device or apparatus and execute instructions), or in conjunction with such instruction execution systems, devices or apparatuses. For the purposes of this specification, "computer-readable medium" can be any device that can contain, store, communicate, propagate or transmit a program for use by an instruction execution system, device or apparatus, or in conjunction with such instruction execution systems, devices or apparatuses.

[0137] More specific examples of computer-readable media (a non-exhaustive list) include the following: an electrical connection with one or more wires (electronic device), a portable computer disk case (magnetic device), a random access memory (RAM), a read-only memory (ROM), an erasable and programmable read-only memory (EPROM or flash memory), an optical fiber device, and a portable compact disk read-only memory (CDROM). In addition, the computer-readable medium may even be a paper or other suitable medium on which the program is printed, since the program may be obtained electronically, for example, by optically scanning the paper or other medium, followed by editing, deciphering or, if necessary, processing in another suitable manner, and then stored in a computer memory.

[0138] It should be understood that the various parts of the present invention can be implemented by hardware, software, firmware or a combination thereof. In the above-mentioned embodiments, a plurality of steps or methods can be implemented by software or firmware stored in a memory and executed by a suitable instruction execution system. For example, if implemented by hardware, as in another embodiment, it can be implemented by any one of the following technologies known in the art or their combination: a discrete logic circuit having a logic gate circuit for implementing a logic function for a data signal, a dedicated integrated circuit having a suitable combination of logic gate circuits, a programmable gate array (PGA), a field programmable gate array (FPGA), etc.

[0139] Example 4 is an embodiment of the present invention, which provides an AC / DC system power flow overload emergency control method based on VSC-HVDC sensitivity analysis. In order to verify the beneficial effects of the present invention, scientific demonstration is carried out through simulation experiments.

[0140] This example simulates by selecting a test system, including load area I and load area II. Figure 4 The figure shows a schematic diagram of the VSC-HVDC interconnection between two load areas in the power grid. It can be seen from the figure that in the system load area, compared with the original AC lines, some AC lines are replaced by VSC-HVDC lines, and then when fault a or fault b occurs, power can be transmitted through multiple AC and DC lines, so that the system has more flexible power regulation capabilities, ensuring that all lines in the system remain in a safe operating state, which is important for avoiding long-term line overload in variable operating scenarios.

[0141] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. An AC / DC system power flow overload emergency control method based on VSC-HVDC sensitivity analysis, characterized by: include: Obtaining a control method and an operation mode of a VSC-HVDC in an AC system, and converting an AC line to be converted into a VSC-HVDC line to obtain an AC-DC system structure; A power sensitivity calculation formula of VSC-HVDC to AC line is established based on the AC / DC system structure; Convert the power sensitivity calculation formula into a line matrix form to establish a power sensitivity matrix for the entire line of the system; Performing optimization calculation based on the power sensitivity matrix to obtain an optimal adjustment value; The emergency control of the line overload problem is verified according to the optimal adjustment value, and the optimal control parameters of the VSC-HVDC are obtained.

2. The method for emergency control of AC / DC power flow overload based on VSC-HVDC sensitivity analysis according to claim 1, characterized in that: The VSC-HVDC control method comprises the following steps: The current equation of the VSC in the dq reference frame decouples the control of the d-axis and q-axis. The specific formula is as follows: Where d, q and ref are the reference of d-axis, q-axis and signal respectively; u d and i d are the d-axis voltage and current of VSC respectively; u q and i q are the q-axis voltage and current of VSC respectively; u d.ref and u q.ref are the d-axis and q-axis voltages of the pulse width modulation (PWM) reference; R and L are the resistance and inductance of the phase reactor, respectively.

3. The method for emergency control of power flow overload of AC / DC system based on VSC-HVDC sensitivity analysis according to claim 2, characterized in that: The operation modes of VSC-HVDC include normal mode and emergency mode; The normal mode refers to the normal operation mode in which the VSC-HVDC interconnection helps to transmit the planned power and maintain the terminal voltage; The emergency mode means that when a disturbance occurs, the VSC-HVDC switches to the emergency mode, and the VSC-HVDC line provides power flow adjustment and transient support.

4. The method for emergency control of power flow overload of AC / DC system based on VSC-HVDC sensitivity analysis according to claim 3, characterized in that: The formula for calculating the power sensitivity of VSC-HVDC to AC lines is to combine the linear power flow equation of the system under study with graph theory, consider the system voltage parameters, and calculate the sensitivity of node injection power to line power; The formula for calculating the power sensitivity of the VSC-HVDC to the AC line includes the following steps: Based on the mathematical model of the power grid, the network node voltage equation is obtained. The specific formula is as follows: I N =Y N U N Among them, I N The column vector of the node injected current; U N is the node voltage column vector; Y N is the node admittance matrix; Based on the network node voltage equation, the relationship between the network branch current and the branch voltage is obtained. The specific formula is as follows: Among them, I B is the branch current column vector; U B is the branch voltage column vector; Y B is the branch admittance matrix; A is the node association matrix; Define the network correlation coefficient matrix C(λ), the specific formula is as follows: According to the relationship between the network branch current and the branch voltage and the network correlation coefficient matrix C(λ), the linear combination of the injected current of each node is obtained. The specific formula is as follows: I k,B =λ k-1 I 1,N +…+λ k-i I i,N +…+λ k-n I n,N Among them, λ k-i is the current I of branch k in the network correlation coefficient matrix C(λ) k,B The injected current I i,N The related parameters between In order to obtain the relationship between line power and node injection power, the branch current vector I k,B Multiply the voltage on both sides of , the specific formula is as follows: Among them, U k,B is the starting voltage vector of line k; U i,N is the voltage vector of node i; Rewrite the above formula into the form of P+jQ, expand the vector into its real part and imaginary part, and get the following formula: Among them, θ k,B is the phase angle of the voltage at the starting end of branch k; θ i,N is the phase angle of the voltage at node i; P k,B is the active power at the starting end of branch k; Q k,B is the reactive power at the starting end of branch k; k-i,a and λ k-i,b are the relevant parameters λ k-i The real and imaginary parts of In the emergency control to eliminate the active power overload of the transmission line, only the active power of the control node is adjusted without changing the reactive power, and the following relationship is obtained: By substituting into the power equation for calculation, we can obtain the power sensitivity β between the power variable of line k and the injected power variable of node i. k-i as follows: Among them, β k-i is the power sensitivity between the power variable of line k and the injected power variable of node i.

5. The method for emergency control of AC / DC power flow overload based on VSC-HVDC sensitivity analysis according to claim 4, characterized in that: Converting the power sensitivity calculation formula into a line matrix form means that in the actual system, the number of DC lines and AC lines is greater, and the lines are closely connected, and they will affect each other during the power adjustment process. Therefore, in order to realize the prediction of global power, the power sensitivity calculation formula is converted into a line matrix form, and a power sensitivity matrix for the entire system line is established.

6. The method for AC / DC system power flow overload emergency control based on VSC-HVDC sensitivity analysis according to claim 5, characterized in that: The establishment of a power sensitivity matrix for all lines of the system comprises the following steps: After replacing the AC line with the VSC-HVDC line, the network correlation coefficient matrix is ​​recalculated. The specific formula is as follows: Among them, C * (λ) is the value recalculated after the introduction of VSC-HVDC; By substituting the updated λ into the power sensitivity calculation formula, the sensitivity matrix S of the node injection power in the system including VSC-HVDC is obtained: m×n , the specific formula is as follows: Where m is the number of AC lines in the system; n is the number of system nodes; Assuming that the xth DC line is connected between nodes i and j, the power sensitivity of the DC line to other AC lines is calculated as follows: Sen DC,x =S[:,j]-S[:,i] Among them, Sen DC,x is the power sensitivity of the x-th DC line relative to the AC line; S[:,j] and S[:,i] are the matrices S m×n The j-th and i-th columns of ; After the xth DC line power adjustment ΔP DC,x After that, the power P of the AC line is calculated by the following formula: Among them, ΔP m is the power change of the mth AC line; P0 is the initial power value of the AC line; According to the power P of the AC line, the power of the AC line is calculated after adjusting the DC power.

7. The method for emergency control of power flow overload of AC / DC system based on VSC-HVDC sensitivity analysis according to claim 6, characterized in that: Calculating the optimization problem based on the power sensitivity matrix means solving the optimization problem based on the power sensitivity matrix, taking into account the parameter variation range and operation constraints of the DC and AC lines in the actual system, and taking the minimum absolute amount of adjusted power as the optimization objective function to obtain the optimal adjustment value; The obtaining of the optimal adjustment value comprises the following steps: The power sensitivity matrix is ​​used to calculate the sensitivity of the DC line power to the AC line power and prioritize the DC lines as follows: Among them, b k 1 is the sensitivity of the first DC line to the kth AC line; x is the number of candidate DC lines; In order to evaluate whether the AC transmission line will be overloaded, the active power flow after the line fault is calculated. Assuming that the k line is overloaded, the transmission power after the overload is P ka , overload ΔP k The specific formula is as follows: ΔP k =P ka -P kmax Among them, P kmax is the rated power limit of the line; In order to achieve power dispatch and eliminate overload ΔP on the transmission line by adjusting the power of the DC line k , solve the following optimization problem, the objective function of the optimization problem is as follows: Among them, ΔP DC,m , P DC,m , as well as are the power variation, actual power, minimum power and maximum power of the mth DC line respectively; ε is a small constant; P k and P kmax are the actual power and maximum power of the kth AC line respectively; L is the set of all AC lines; By solving the objective function of the optimization problem, the sensitivity-based VSC-HVDC power adjustment is obtained.

8. An AC / DC system power flow overload emergency control system based on VSC-HVDC sensitivity analysis, based on the AC / DC system power flow overload emergency control method based on VSC-HVDC sensitivity analysis according to any one of claims 1 to 7, characterized in that: include, A structure acquisition module is used to acquire the control method and operation mode of VSC-HVDC in the AC system, convert the AC line to be converted into a VSC-HVDC line, and obtain the AC-DC system structure; A sensitivity calculation module is used to establish a power sensitivity calculation formula of VSC-HVDC to AC lines based on the AC / DC system structure; The matrix conversion module is used to convert the power sensitivity calculation formula into a line matrix form and establish a power sensitivity matrix for the entire line of the system; An optimal calculation module is used to solve the optimization problem based on the power sensitivity matrix and take the minimum absolute amount of adjusted power as the optimization objective function to obtain the optimal adjustment value; The verification module is used to verify whether the line overload problem can be controlled in real time within the required time according to the optimal adjustment value, so as to obtain the optimal control parameters of the VSC-HVDC.

9. A computer device comprising a memory and a processor, wherein the memory stores a computer program, wherein: When the processor executes the computer program, the steps of the method for emergency control of AC / DC system power flow overload based on VSC-HVDC sensitivity analysis according to any one of claims 1 to 7 are implemented.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the method for emergency control of AC / DC system power flow overload based on VSC-HVDC sensitivity analysis according to any one of claims 1 to 7 are implemented.

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