Power system instability control method and device based on saddle node bifurcation sensitivity

Abstract

The invention discloses an electric power system instability control method and device based on saddle node bifurcation sensitivity, and the method comprises the steps: carrying out the load flow calculation of an electric power system before a fault, so as to determine the initial steady-state values of an algebraic variable and a state variable at a balance point; constructing a balance point calculation model based on the current relation of the power supply steady-state model, the load steady-state model and the alternating current network of the power system after the fault occurs; parameterizing fault parameters of the balance point calculation model according to the fault type, iteratively solving the balance point calculation model based on the initial steady-state value by using a homotopy method, and judging whether a balance point exists or not; and if the balance point does not exist, the sensitivity of the homotopy parameters at the saddle node bifurcation point to the operation parameters is solved, a plurality of operation parameters with the maximum sensitivity are selected to be adjusted until the homotopy parameters corresponding to the saddle node bifurcation point are larger than a preset threshold value, and the power system after the fault has the balance point again and is restored to be stable. According to the invention, the calculation time and calculation resources of the balance point are saved.

Description

Technical Field

[0001] The present application relates to the technical field of power system control, and particularly to a power system instability control method and device based on the sensitivity of saddle-node bifurcation points. Background Art

[0002] The power grid structure is gradually becoming more complex, the operation mode is tending to be diversified, the power system is subjected to more frequent disturbances, and the operating state is approaching its stable operation limit. Therefore, it is very necessary to judge and locate the reasons for system instability based on the analysis of the operating point of the system after being disturbed, and to formulate control strategies.

[0003] At present, the acquisition of the equilibrium point information of the power system after being disturbed mainly depends on time-domain simulation, which requires a large amount of time and computing resources. In addition, for the control of system instability, traditionally, it mainly relies on adjusting the output of generators after system grouping, lacking an analytical guiding basis. Therefore, at present, there is an urgent need to explore a more efficient equilibrium point calculation method and a more accurate basis for formulating control strategies. Summary of the Invention

[0004] The present application provides a power system instability control method and device based on the sensitivity of saddle-node bifurcation points, which are used to improve the technical problems that the existing technology relies on time-domain simulation to obtain the equilibrium point information of the power system after being disturbed, resulting in high time cost and large consumption of computing resources, and that the existing instability control methods rely on adjusting the output of generators after system grouping and lack an analytical guiding basis.

[0005] In view of this, the first aspect of the present application provides a power system instability control method based on the sensitivity of saddle-node bifurcation points, including:

[0006] Performing a power flow calculation on the power system before a fault occurs, and determining the initial steady-state values of algebraic variables and state variables at the equilibrium point according to the power flow calculation results;

[0007] Constructing an equilibrium point calculation model based on the power source steady-state model, load steady-state model and current relationship of the AC network of the power system after a fault occurs;

[0008] Parametrizing the fault parameters in the equilibrium point calculation model according to the fault type, and using the homotopy method to iteratively solve the equilibrium point calculation model based on the initial steady-state values of algebraic variables and state variables, and determining whether there is an equilibrium point;

[0009] If there is no equilibrium point, then solving the sensitivity of the homotopy parameter at the saddle-node bifurcation point to the operating parameters of the power system, and selecting a plurality of operating parameters with the largest sensitivity for adjustment until the homotopy parameter corresponding to the saddle-node bifurcation is greater than a preset threshold, so that the power system after the fault re-exists an equilibrium point and resumes stability.

[0010] Optionally, when the power source is a synchronous generator set, the steady-state model of the power source is:

[0011]

[0012] where V x and represent the x-axis component and y-axis component of the stator voltage respectively; is the power angle of the generator; R a represents the stator resistance; and represent the x-axis component and y-axis component of the generator current respectively; X d and X q represent the synchronous reactance of the d-axis and q-axis respectively; D is the damping coefficient, F is the system frequency; K represents the regulator gain coefficient; K A represents the voltage regulator gain coefficient; K V represents the proportional-integral coefficient; V ref represents the reference value of the voltage; Y ref is the reference value of the opening of the water gate; K GW is the speed gain coefficient; V x and V y represent the x-axis component and y-axis component of the grid-connected point voltage respectively.

[0013] Optionally, the steady-state model of the load is:

[0014]

[0015] where P L0 and Q L0 are the active power and reactive power absorbed by the load under steady-state conditions of the power system respectively; V0 is the node voltage of the load under steady state; I Lx and I Ly represent the x-axis component and y-axis component of the load current respectively; , , are the proportions occupied by the constant impedance part, constant current part and constant power part in all active loads respectively; , , are the proportions occupied by the constant impedance part, constant current part and constant power part in all reactive loads respectively.

[0016] Optionally, the current relationship of the AC network is:

[0017]

[0018] where and are the generator output current and load current at node i respectively; Yij is the mutual admittance between node i and node j; is the voltage phasor of node j; n is the number of nodes in the power system.

[0019] Optionally, when the fault is that the tie line between node p and node q is cut off, the parameterized fault parameter is the impedance between node p and node q;

[0020] When the fault is a sudden increase or decrease in load, the parameterized fault parameter is the load change;

[0021] When the generator output suddenly increases or decreases, the parameterized fault parameter is the generator output change.

[0022] Optionally, the sensitivity of the homotopy parameter at the saddle-node bifurcation point to the operating parameters of the power system includes:

[0023] Performing a first-order Taylor expansion on the equilibrium point calculation model to obtain the first-order Taylor expansion of the equilibrium point calculation model;

[0024] Based on the characteristic that the Jacobian matrix at the saddle-node bifurcation point is singular, calculating the left eigenvector according to the Jacobian matrix in the first-order Taylor expansion;

[0025] Multiplying each term in the equilibrium point calculation model by the left eigenvector to obtain the sensitivity of the homotopy parameter at the saddle-node bifurcation point to the operating parameters.

[0026] The second aspect of this application provides a power system instability control device based on the sensitivity of the saddle-node bifurcation point, including:

[0027] A power flow calculation unit, configured to perform power flow calculation on the power system before a fault occurs, and determine the initial steady-state values of algebraic variables and state variables at the equilibrium point according to the power flow calculation results;

[0028] A model construction unit, configured to construct an equilibrium point calculation model based on the power supply steady-state model, load steady-state model, and current relationship of the AC network of the power system after a fault occurs;

[0029] A judgment unit, configured to parameterize the fault parameters in the equilibrium point calculation model according to the fault type, use the homotopy method to iteratively solve the equilibrium point calculation model based on the initial steady-state values of algebraic variables and state variables, and judge whether there is an equilibrium point;

[0030] A parameter adjustment unit, configured to, if there is no equilibrium point, solve the sensitivity of the homotopy parameter at the saddle-node bifurcation point to the operating parameters of the power system, select several operating parameters with the largest sensitivity for adjustment, until the homotopy parameter corresponding to the saddle-node bifurcation is greater than a preset threshold, so that the power system after the fault re-exists an equilibrium point and resumes stability.

[0031] Optionally, when the fault is that the tie line between node p and node q is cut off, the parameterized fault parameter is the impedance between node p and node q;

[0032] When the fault is a sudden increase or decrease in load, the parameterized fault parameter is the load change amount;

[0033] When the output of the generator suddenly increases or decreases, the parameterized fault parameter is the change amount of the generator output.

[0034] The third aspect of the present application provides an electronic device, which includes a processor and a memory;

[0035] The memory is used to store program code and transmit the program code to the processor;

[0036] The processor is used to execute any one of the power system instability control methods based on the sensitivity of the saddle-node bifurcation point in the first aspect according to the instructions in the program code.

[0037] The fourth aspect of the present application provides a computer-readable storage medium, which is used to store program code, and when the program code is executed by a processor, it implements any one of the power system instability control methods based on the sensitivity of the saddle-node bifurcation point in the first aspect.

[0038] It can be seen from the above technical solutions that the present application has the following advantages:

[0039] The power system instability control method based on the sensitivity of the saddle-node bifurcation point of the present application directly solves the algebraic equation under the steady state of the system, avoids solving complex differential equations, saves a large amount of time and computing resources; uses the homotopy method to iteratively solve the equilibrium point calculation model, and has better convergence; compared with the traditional method that relies on adjusting the generator output after system grouping, the present application can provide an analytical guidance basis for instability control, and can determine the adjustment direction and control effectiveness of each adjustable operating parameter. Description of the Drawings

[0040] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained according to these drawings.

[0041] Figure 1 It is a schematic flowchart of a power system instability control method based on the sensitivity of the saddle-node bifurcation point provided by an embodiment of the present application;

[0042] Figure 2 It is a time-domain simulation diagram of the relative power angles of all generators in the power system after being disturbed;

[0043] Figure 3 It is a homotopy curve diagram of the power system after being disturbed;

[0044] Figure 4 It is the sensitivity of the homotopy parameter to the generator output at the saddle-node bifurcation point after the power system is disturbed;

[0045] Figure 5 It is a time-domain simulation diagram of the relative power angles of all generators in the power system after control measures are taken;

[0046] Figure 6 It is a homotopy curve diagram after control measures are taken;

[0047] Figure 7 It is a time-domain simulation diagram of the relative power angles of all generators in the power system under the critical stable state;

[0048] Figure 8 It is a homotopy curve diagram under the critical stable state;

[0049] Figure 9 It is the sensitivity of the homotopy parameter to the generator output at the saddle-node bifurcation point of the power system under the critical stable state;

[0050] Figure 10 It is a time-domain simulation diagram of the relative power angles of the generators after the output of the generators at 38 nodes is reduced by 20 MW under the critical state;

[0051] Figure 11 It is a homotopy curve diagram after the output of the generators at 38 nodes is reduced by 20 MW under the critical state;

[0052] Figure 12 It is a time-domain simulation diagram of the relative power angles of the generators after the output of the generators at 31 nodes is reduced by 20 MW under the critical state;

[0053] Figure 13 It is a homotopy curve diagram after the output of the generators at 31 nodes is reduced by 20 MW under the critical state;

[0054] Figure 14 It is a structural schematic diagram of a power system instability control device based on the sensitivity of the saddle-node bifurcation point provided by an embodiment of the present application. Specific implementation manner

[0055] To enable those skilled in the art to better understand the solution of this application, the following will clearly and completely describe the technical solution in the embodiments of this application in conjunction with the accompanying drawings in the embodiments of this application. Obviously, the described embodiments are only a part of the embodiments of this application, rather than all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the scope of protection of this application.

[0056] For ease of understanding, please refer to Figure 1 , this application embodiment provides a power system instability control method based on the sensitivity of saddle-node bifurcation points, including:

[0057] Step 110: Perform a power flow calculation on the power system before a fault occurs, and determine the initial steady-state values of algebraic variables and state variables at the equilibrium point according to the power flow calculation results;

[0058] Before a fault occurs, perform a power flow calculation on the power system, and reverse-deduce the numerical values of each variable under the target operating conditions according to the power flow calculation results, so as to determine the initial steady-state values of algebraic variables and state variables at the equilibrium point of the power system before the fault. Algebraic variables include the voltage, current, active power, reactive power, etc. of each node, and state variables include the generator rotor angle, rotor speed, excitation voltage, mechanical power, etc.

[0059] Step 120: Construct an equilibrium point calculation model based on the power source steady-state model, load steady-state model, and current relationship of the AC network of the power system after a fault occurs;

[0060] Derive the expressions of the power source and load under steady state according to the dynamic element model in the power system, and combine them with the equations of the network to construct a complete equilibrium point calculation model. In this step, it is necessary to construct the equilibrium point calculation model of the entire system. The following takes the commonly used dynamic element model as an example to introduce the modeling and processing methods. Considering the simplicity and convenience of derivation and expression, the subscript i of the node is ignored. The power source model takes the most commonly used synchronous generator set in the current power system as an example. The synchronous generator set adopts a sixth-order model, and uses the frequency after the system is disturbed to replace the original power frequency , so as to obtain the steady-state model of the synchronous generator set under steady state:

[0061] (1)

[0062] In the formula: and respectively represent the d-axis component and q-axis component of the stator voltage; and respectively represent the d-axis component and q-axis component of the generator current; represents the stator resistance; and denote the synchronous reactance of d-axis and q-axis respectively; The new reference frequency The electrical angular velocity of the system after the disturbance; and are the mechanical power and electromagnetic power of the generator's prime mover respectively; D is the damping coefficient, and F is the system frequency; is the excitation potential, output by the excitation system, and its expression is as follows:

[0063] (2)

[0064] Where: Represents the regulator gain coefficient; Indicates the voltage regulator gain coefficient; represents the proportional integral coefficient; Indicates the reference value of voltage; Indicates additional excitation input; Indicates the terminal voltage.

[0065] Taking the turbine as an example, the prime mover mechanical power in formula (1) is It can be calculated by the following formula:

[0066] (3)

[0067] Where: is the reference value of the sluice gate opening; is the speed gain coefficient.

[0068] The electromagnetic power in formula (1) It can be determined by the equation at the grid connection point:

[0069] (4)

[0070] in and Represents the generator current Axis components and Axis component; and Represents the generator terminal voltage Axis components and Axis component; V x and They represent the x-axis component and y-axis component of the grid connection point voltage respectively.

[0071] Since equation (1) is based on the dq coordinate system, in order to convert it to the xy coordinate system with the grid point equation, the following conversion relationship is satisfied:

[0072] (5)

[0073] (6)

[0074] Where: is the generator power angle;

[0075] Substituting equations (2), (3), (4), (5), and (6) into equation (1) can form the steady-state model of the synchronous generator set after disturbance:

[0076] (7)

[0077] The load model adopts the ZIP model and considers the relationship between load node power, voltage and current, which is:

[0078] (8)

[0079] Where: and are the active power and reactive power absorbed by the load under steady-state conditions of the power system; is the node voltage of the load in steady state; and Represents the load current Axis components and Axis component; 、 、 are the proportions of the constant impedance part, constant current part and constant power part in all active loads respectively; 、 、 are the proportions of the constant impedance part, constant current part and constant power part in all reactive loads respectively; and are the derivatives of the active power and reactive power of the node with respect to frequency. The grid equation of the load node is as follows:

[0080] (9)

[0081] Where, P L and Q L are the active load and reactive load of the node respectively.

[0082] Substituting equation (8) into equation (9) can form the steady-state model after the load is disturbed:

[0083] (10)

[0084] Where, L DP and L DQ They are active frequency factor and reactive frequency factor respectively.

[0085] Current relationship combined with the AC network:

[0086] (11)

[0087] Where and are the generator output current and load current at node i respectively; Y ij is the mutual admittance between node i and node j; is the voltage phasor of node j.

[0088] By combining equations (7), (8), (10) and (11), it can be abbreviated as:

[0089] (12)

[0090] In the formula: represents the vector composed of all generator output current phasors; represents the vector composed of all load current phasors; is the admittance matrix; is the vector composed of all node voltages; represents the equations related to all generator nodes; F is the system frequency; is the voltage phasor of node i; is the generator power angle of node i; represents the equations related to all load nodes; is the current phasor of load node j.

[0091] To ensure the well-posedness of the equation, a node is specified as the voltage phase reference node, and its phase remains unchanged before and after the perturbation. There is:

[0092] (13)

[0093] In the formula: and represent the x-axis component and y-axis component of the voltage of reference node k respectively, represents the voltage phase angle of reference node k;

[0094] Equations (12) and (13) constitute the equilibrium point calculation model of the entire power system, which can be abbreviated as:

[0095] (14)

[0096] Where represents all the unknown state variables in equations (12) and (13).

[0097] Step 130: Parameterize the fault parameters in the equilibrium point calculation model according to the fault type, and use the homotopy method to iteratively solve the equilibrium point calculation model based on the initial steady-state values of the algebraic variables and state variables to determine whether there is an equilibrium point;

[0098] When the power system is disturbed, the homotopy method is used to iteratively solve the equilibrium point calculation model, and the homotopy parameter is introduced to characterize the continuous change of the disturbance. The initial steady-state values of the algebraic variables and state variables solved in Step 110 are the starting points of the iteration, that is, after the fault occurs, the evolution starts from the initial steady-state values. Taking the example that a tie line between node p and node q is removed, the fault parameter parameterized by the removal of the tie line between node p and node q is the impedance between node p and node q, and the admittance matrix in Equation (14) is modified as follows:

[0099] (15)

[0100] where 、 、 、 represent the self-admittance of node p, the self-admittance of node q, the mutual admittance between nodes pq, and the mutual admittance between nodes qp after the fault, respectively; 、 、 、 are the self-admittance of node p, the self-admittance of node q, the mutual admittance between nodes pq, and the mutual admittance between nodes qp before the fault, respectively; and are the impedance of the tie line between nodes p and q and the shunt admittance to the ground, respectively. Equation (15) can be abbreviated as:

[0101] (16)

[0102] For Equation (16), obviously, corresponds to the equilibrium point calculation model of the power system before the disturbance, corresponds to the equilibrium point calculation model of the disturbed power system (i.e., the power system after the fault occurs). If the homotopy method can obtain the equilibrium point manifold at , then the equilibrium point of the disturbed system exists.

[0103] It should be noted that the fault parameterization processes corresponding to other fault types are similar to the above process, except that the parameterized fault parameters are different. The fault parameter parameterized by the removal of the tie line between p and q is the impedance between pq, the fault parameter parameterized by the sudden increase or decrease of the load is the load change amount, and the fault parameter parameterized by the sudden increase or decrease of the generator output is the generator output change amount.

[0104] Step 140: If there is no equilibrium point, solve the sensitivity of the homotopy parameter at the saddle-node bifurcation point to the operating parameters of the power system, select several operating parameters with the largest sensitivity for adjustment until the homotopy parameter corresponding to the saddle-node bifurcation is greater than the preset threshold, so that the post-fault power system has an equilibrium point again and returns to stability;

[0105] For the case where there is no equilibrium point, the saddle-node bifurcation point in the unstable state can be pulled to a new saddle-node bifurcation point (corresponding ) by adjusting the operating parameters of the power system (such as generator output, reactive power compensation, etc.), so that the homotopy curve intersects with the straight line. Considering the adjustable operating parameters, rewrite Equation (16) in the following form:

[0106] (17)

[0107] where p represents the adjustable operating parameter. The first-order Taylor expansion of Equation (17) is as follows:

[0108] (18)

[0109] At the saddle-node bifurcation point, the Jacobian matrix is singular. Therefore, there exists a left eigenvector corresponding to a zero eigenvalue, such that:

[0110] (19)

[0111] Therefore, multiplying each term of Equation (17) by the left eigenvector , the calculation formula for the sensitivity of the homotopy parameter at the saddle-node bifurcation point to the adjustable operating parameter can be obtained:

[0112] (20)

[0113] After calculating the sensitivity of the homotopy parameter at the saddle-node bifurcation point obtained according to Equation (20) to the adjustable operating parameter, sort each sensitivity. Since the sensitivity change shows a linear relationship, when the system approaches the saddle-node bifurcation point, the deviation between the obtained sensitivity value and the actual value is small. Based on this characteristic, when adjusting the adjustable parameters to construct an equilibrium point, it is not possible to make a large adjustment to a single operating parameter alone, but multiple operating parameters with higher sensitivity should be selected for adjustment. Three operating parameters with the largest sensitivity values can be selected, and by adjusting these operating parameters, the system load margin can be increased, thereby realizing the right shift of the saddle-node bifurcation point. When the homotopy parameter at the saddle-node bifurcation point is slightly greater than 1, the homotopy curve intersects with the The straight lines re - generate intersections, and at this time, the adjusted system equilibrium point exists.

[0114] This application directly solves the algebraic equations under the system steady state, avoiding the solution of complex differential equations, saving a large amount of time and computing resources; using the homotopy method for iterative solution, it has better convergence and lower requirements for the initial value; compared with the traditional method that relies on adjusting the generator output after system grouping, this method can provide an analytical guiding basis for instability control.

[0115] To verify the accuracy and effectiveness of the post - fault power system instability control method based on the sensitivity of the saddle - node bifurcation point proposed in this application, the accuracy of this method is verified on the IEEE39 - bus system. The pre - disturbance system frequency is 50Hz, and the following disturbances are set: A three - phase short - circuit fault occurs on the 6 - side of node 6 at t = 0.1s (5 cycles) on line 6 - 11 and is removed at t = 0.2s (10 cycles). The time - domain simulation results of the system after the disturbance are as Figure 2 shown, and the homotopy curve diagram of the system after the disturbance is as Figure 3 shown. After the disturbance, the relative power angles between the generator groups (blue boxes) at nodes 30 and 37, the generator groups (green boxes) at nodes 31 and 39, and the generator groups (red boxes) at nodes 32, 33, 34, 35, 36, and 38 continuously increase, and the system shows oscillatory out - of - step. The corresponding to the saddle - node bifurcation point indicates that the main reason for the system instability at this time is that there is no equilibrium point in the system after being disturbed.

[0116] Taking the adjustment of the generator active power output as an example, the homotopy parameter at the saddle - node bifurcation point can be obtained according to the above process for the sensitivity of the active power P G as shown in Figure 4 .

[0117] At t = 0.3s (15 cycles), that is, 0.1s (5 cycles) after the disturbance, the following measures are taken:

[0118] (1) Increase the output of the generators at nodes 37 and 30 by 100MW and 50MW respectively;

[0119] (2) Decrease the output of the generators at nodes 32 and 34 by 100MW and 50MW respectively.

[0120] After taking the control measures, the corresponding to the saddle - node bifurcation point of the homotopy curve indicates that the system has an equilibrium point. At this time, the relative power angles of all network generators fluctuate within a small range and then tend to fixed values, and the system returns to stability. The corresponding time - domain simulation results and homotopy curve diagrams are as Figure 5 and 6As shown. It should be noted that, compared with the traditional method of roughly adjusting the output according to the overall change rate of the power angle of the generator group, the method proposed in this application provides an analytical control basis, ensuring the effectiveness of the subsequent control strategy formulation.

[0121] To further prove that this application is different from the traditional method of adjusting according to the generator group, at t = 0.3 s (15 cycles), that is, 0.1 s (5 cycles) after the disturbance occurs, only the following adjustments are made:

[0122] (1) Increase the output of the generator at node 37 by 90 MW;

[0123] (2) Decrease the output of the generator at node 32 by 90 MW.

[0124] Make the system just in the critical stable state. The time-domain simulation results corresponding to the system in the critical stable state are as Figure 7 shown. At this time, the corresponding at the saddle-node bifurcation point of the homotopy curve, as Figure 8 shown. At this time, recalculate the homotopy parameter at the saddle-node bifurcation point for the sensitivity of the active power P G to as Figure 9 shown.

[0125] It can be seen from Figure 9 that: Although the generator at node 38 is in the group with the fastest power angle change, in fact, increasing the output of this generator is more beneficial to the rapid stability of the system after being disturbed. On the contrary, if the output of this generator is reduced, the stability of the system will be damaged; Similarly, the generators at nodes 31 and 39 are in the group with a relatively fast power angle change, but in fact, increasing the output of this generator is more beneficial to the rapid stability of the system after being disturbed. Further, it can be seen from the analytical results that under the same output adjustment, increasing the output of the generator at node 39 can make the system stable faster. On the contrary, reducing the output of the generator at node 39 will make the system unstable faster. The following will prove this based on this.

[0126] The time-domain simulation results and the homotopy curve corresponding to reducing the output of the generator at node 38 by 20 MW in the critical stable state are respectively as Figure 10 and Figure 11 shown. The system gradually shows oscillatory out-of-step. The corresponding at the saddle-node bifurcation point of the homotopy curve, as Figure 11 shown.

[0127] Similarly, when reducing the generator output at node 39 by 10 MW under the critical state, the system gradually experiences oscillatory instability. While under the same conditions, the generator output at node 31 needs to be reduced by 20 MW for the system to exhibit a similar instability phenomenon. The corresponding time-domain simulation results and homotopy curves after reducing the generator output at node 31 by 20 MW under the critical state are respectively as Figure 12 and Figure 13 shown. The corresponding to the saddle-node bifurcation point of the homotopy curve.

[0128] Combined with Figure 11 and Figure 13 , it can be seen that different from the traditional control according to generator grouping, the proposed analytical method in this application can determine the adjustment direction and control effectiveness of each generator.

[0129] The above is an embodiment of a power system instability control method based on saddle-node bifurcation point sensitivity provided by this application. The following is an embodiment of a power system instability control device based on saddle-node bifurcation point sensitivity provided by this application.

[0130] Please refer to Figure 14 . A power system instability control device based on saddle-node bifurcation point sensitivity provided by an embodiment of this application includes:

[0131] A power flow calculation unit 210, configured to perform power flow calculation on the power system before a fault occurs, and determine the initial steady-state values of algebraic variables and state variables at the equilibrium point according to the power flow calculation results;

[0132] A model construction unit 220, configured to construct an equilibrium point calculation model based on the power source steady-state model, load steady-state model, and current relationship of the AC network of the power system after a fault occurs;

[0133] A judgment unit 230, configured to parameterize the fault parameters in the equilibrium point calculation model according to the fault type, and iteratively solve the equilibrium point calculation model based on the initial steady-state values of algebraic variables and state variables by using the homotopy method, and judge whether there is an equilibrium point;

[0134] A parameter adjustment unit 240, configured to, if there is no equilibrium point, solve the sensitivity of the homotopy parameter at the saddle-node bifurcation point to the operating parameters of the power system, select several operating parameters with the largest sensitivity for adjustment until the homotopy parameter corresponding to the saddle-node bifurcation is greater than a preset threshold, so that the power system after the fault re-exists an equilibrium point and resumes stability.

[0135] Furthermore, when the fault is that the tie line between node p and node q is removed, the parameterized fault parameter is the impedance between node p and node q;

[0136] When the fault is a sudden increase or decrease in load, the parameterized fault parameter is the load change amount;

[0137] When the output of the generator suddenly increases or decreases, the parameterized fault parameter is the change amount of the generator output.

[0138] An embodiment of the present application further provides an electronic device, which includes a processor and a memory;

[0139] The memory is used to store program code and transmit the program code to the processor;

[0140] The processor is used to execute the power system instability control method based on the saddle-node bifurcation point sensitivity in the foregoing method embodiment according to the instructions in the program code.

[0141] An embodiment of the present application further provides a computer-readable storage medium, which is characterized in that the computer-readable storage medium is used to store program code, and when the program code is executed by a processor, the power system instability control method based on the saddle-node bifurcation point sensitivity in the foregoing method embodiment is implemented.

[0142] Those skilled in the art can clearly understand that for the convenience and brevity of description, the specific working processes of the above-described devices and units can refer to the corresponding processes in the foregoing method embodiments, and will not be elaborated herein.

[0143] The terms "first", "second", "third", "fourth", etc. (if any) in the specification of the present application and the above drawings are used to distinguish similar objects, and do not have to be used to describe a specific order or sequence. In addition, the terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device that includes a series of steps or units does not have to be limited to those steps or units clearly listed, but may include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0144] It should be understood that in this application, "at least one (item)" means one or more, and "a plurality" means two or more. "And / or" is used to describe the association relationship of associated objects, indicating that there can be three relationships. For example, "A and / or B" can mean: only A exists, only B exists, and both A and B exist at the same time. Among them, A and B can be singular or plural. The character " / " generally indicates that the associated objects before and after are in an "or" relationship. "At least one (or more) of the following" or its similar expressions refer to any combination of these items, including any combination of single items (or more) or plural items (or more). For example, at least one (or more) of a, b, or c can mean: a, b, c, "a and b", "a and c", "b and c", or "a and b and c", where a, b, and c can be single or multiple.

[0145] In several embodiments provided in this application, it should be understood that the disclosed devices and methods can be implemented in other ways. For example, the device embodiments described above are merely illustrative. For example, the division of the units is only a logical function division. In actual implementation, there can be other division methods. For example, multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the displayed or discussed coupling or direct coupling or communication connection between each other can be through some interfaces. The indirect coupling or communication connection of the devices or units can be in electrical, mechanical or other forms.

[0146] The units described as separate components may or may not be physically separated. The components displayed as units may or may not be physical units, that is, they can be located in one place, or they can be distributed to multiple network units. Some or all of the units can be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0147] In addition, in each embodiment of this application, the functional units can be integrated in a processing unit, or each unit can exist physically alone, or two or more units can be integrated in one unit. The above integrated units can be implemented in the form of hardware or in the form of software functional units.

[0148] When the integrated unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of this application, in essence, or the part that contributes to the prior art, or all or part of this technical solution, can be embodied in the form of a software product. This computer software product 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 execute all or part of the steps of the methods described in various embodiments of this application. The foregoing storage medium includes: various media that can store program codes, such as USB flash drives, mobile hard disks, read-only memories (English full name: Read-Only Memory, English abbreviation: ROM), random access memories (English full name: Random Access Memory, English abbreviation: RAM), magnetic disks, or optical discs.

[0149] As described above, the above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit them; although this application has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments or perform equivalent replacements for some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of various embodiments of this application.

Claims

1. A power system instability control method based on the sensitivity of saddle-node bifurcation points, characterized in that, including: Performing a power flow calculation on the power system before a fault occurs, and determining the initial steady-state values of algebraic variables and state variables at the equilibrium point according to the power flow calculation results; Constructing an equilibrium point calculation model based on the power source steady-state model, load steady-state model, and current relationship of the AC network of the power system after a fault occurs; Parametrizing the fault parameters in the equilibrium point calculation model according to the fault type, and using the homotopy method to iteratively solve the equilibrium point calculation model based on the initial steady-state values of algebraic variables and state variables, and determining whether there is an equilibrium point; If there is no equilibrium point, then solving the sensitivity of the homotopy parameter at the saddle-node bifurcation point to the operating parameters of the power system, and selecting several operating parameters with the largest sensitivity for adjustment until the homotopy parameter corresponding to the saddle-node bifurcation is greater than a preset threshold, so that the power system after the fault has an equilibrium point again and returns to stability.

2. The power system instability control method based on the sensitivity of the saddle-node bifurcation point according to claim 1, wherein When the power source is a synchronous generator set, the power source steady-state model is: where, V x and represent the x-axis component and y-axis component of the stator voltage respectively; is the power angle of the generator; R a represents the stator resistance; and represent the x-axis component and y-axis component of the generator current respectively; X d and X q represent the synchronous reactance of the d-axis and q-axis respectively; D is the damping coefficient, F is the system frequency; K represents the regulator gain coefficient; K A represents the voltage regulator gain coefficient; K V represents the proportional integral coefficient; V ref represents the reference value of the voltage; Y ref is the reference value of the opening of the water gate; K GW is the speed gain coefficient; V x and V y represent the x-axis component and y-axis component of the grid-connected point voltage respectively.

3. The power system instability control method based on the sensitivity of the saddle-node bifurcation point according to claim 2, wherein The load steady-state model is: where P L0 and Q L0 are the active power and reactive power absorbed by the load under steady-state conditions of the power system, respectively; V0 is the nodal voltage of the load under steady state; I Lx and I Ly represent the x-axis component and y-axis component of the load current, respectively; , , are the proportions of the constant impedance part, constant current part, and constant power part in all active loads, respectively; , , are the proportions of the constant impedance part, constant current part, and constant power part in all reactive loads, respectively.

4. The power system instability control method based on the sensitivity of the saddle-node bifurcation point according to claim 3, wherein The current relationship of the AC network is: In the formula, and are the output current of the generator and the load current at node i respectively; Y ij is the mutual admittance between node i and node j; is the voltage phasor of node j; n is the number of nodes in the power system.

5. The power system instability control method based on the sensitivity of the saddle-node bifurcation point according to claim 1, characterized in that When the fault is that the tie line between node p and node q is removed, the parametrized fault parameter is the impedance between node p and node q; When the fault is a sudden increase or decrease in load, the parametrized fault parameter is the load change amount; When the generator output suddenly increases or decreases, the parametrized fault parameter is the generator output change amount.

6. The power system instability control method based on the sensitivity of the saddle-node bifurcation point according to claim 1, wherein The solving of the sensitivity of the homotopy parameter at the saddle-node bifurcation point to the operating parameters of the power system includes: Performing a first-order Taylor expansion on the equilibrium point calculation model to obtain the first-order Taylor expansion formula of the equilibrium point calculation model; Based on the characteristic that the Jacobian matrix is singular at the saddle-node bifurcation point, calculating the left eigenvector according to the Jacobian matrix in the first-order Taylor expansion formula; Multiplying each term in the equilibrium point calculation model by the left eigenvector to obtain the sensitivity of the homotopy parameter at the saddle-node bifurcation point to the operating parameters.

7. A power system instability control device based on the sensitivity of saddle-node bifurcation points, characterized in that, including: A power flow calculation unit for performing a power flow calculation on the power system before a fault occurs, and determining the initial steady-state values of algebraic variables and state variables at the equilibrium point according to the power flow calculation results; A model construction unit for constructing an equilibrium point calculation model based on the power source steady-state model, load steady-state model, and current relationship of the AC network of the power system after a fault occurs; A judgment unit for parametrizing the fault parameters in the equilibrium point calculation model according to the fault type, and using the homotopy method to iteratively solve the equilibrium point calculation model based on the initial steady-state values of algebraic variables and state variables, and determining whether there is an equilibrium point; A parameter adjustment unit for, if there is no equilibrium point, solving the sensitivity of the homotopy parameter at the saddle-node bifurcation point to the operating parameters of the power system, and selecting several operating parameters with the largest sensitivity for adjustment until the homotopy parameter corresponding to the saddle-node bifurcation is greater than a preset threshold, so that the power system after the fault has an equilibrium point again and returns to stability.

8. The power system instability control device based on the sensitivity of the saddle-node bifurcation point according to claim 7, characterized in that, including: When the fault is that the tie line between node p and node q is removed, the parametrized fault parameter is the impedance between node p and node q; When the fault is a sudden increase or decrease in load, the parametrized fault parameter is the load change amount; When the generator output suddenly increases or decreases, the parametrized fault parameter is the generator output change amount.

9. An electronic device, characterized in that, The device includes a processor and a memory; The memory is used for storing program codes and transmitting the program codes to the processor; The processor is used for executing the power system instability control method based on the sensitivity of the saddle-node bifurcation point according to the instructions in the program codes, as described in any one of claims 1-6.

10. A computer-readable storage medium, characterized in that, The computer-readable storage medium is used for storing program codes, and when the program codes are executed by a processor, the power system instability control method based on the sensitivity of the saddle-node bifurcation point as described in any one of claims 1-6 is implemented.

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