A method and system for analyzing fan access limits in a transient power angle stability scenario

Abstract

The application discloses a kind of wind turbine access limit analysis method and system under transient power angle stability situation, comprising: establishing equivalent model of double-fed wind generator access system;Deduce the system equivalent inertia and mechanical power expression under two situations of double-fed wind generator direct access power system and equivalent output replace generator;Analysis three-phase short-circuit fault on power system structure and electromagnetic power expression, deduce the expression of double-fed wind generator injected electromagnetic power before fault, during fault and after fault removal;Power system parameters, fault occurrence and removal time are input, on the basis of extended equal-area criterion formula is transformed to calculate, obtain the numerical relationship between wind turbine access amount and system acceleration area, system deceleration area;Wind turbine access amount initial value is drafted and gradually increases, judge the size relationship between system acceleration area and system deceleration area, obtain the critical access value of wind power of system.The application has higher accuracy.

Description

Technical Field

[0001] This invention relates to the field of wind power grid connection limit technology, specifically to a method and system for analyzing wind turbine grid connection limits under transient power angle stability scenarios. Background Technology

[0002] To ensure the continuous and reliable operation of the power system, research on the power system's ability to accept wind power under transient stability conditions is a prerequisite for subsequent research on the planning and optimization of new energy systems during the renewable energy transformation process. There are also relevant research results regarding wind power integration limits. Existing methods only consider the power flow transmission limit of the power system, neglecting the transient stability characteristics of the system's power angle and voltage, as well as the impact of wind power integration on the system's transient stability. This leads to inaccurate calculation results and may result in transient instability when achieving maximum wind power capacity grid connection, threatening the power supply security of the power system.

[0003] In view of the above, this application is hereby submitted. Summary of the Invention

[0004] The purpose of this invention is to provide a method and system for analyzing the wind turbine access limit under transient power angle stability scenarios. This addresses the research gap in the field of wind power access capacity limit calculation methods under the premise of power system transient stability. It solves the problem that existing wind power access limit calculation methods do not consider the transient stability characteristics of the system power angle and voltage, as well as the impact of wind power access on system transient stability. This avoids the risk of grid instability caused by inaccurate calculation of wind power access limit capacity, further improves the comprehensiveness and accuracy of wind power grid connection limit capacity assessment, and effectively improves the power supply reliability of the power system.

[0005] This invention is achieved through the following technical solution:

[0006] In a first aspect, the present invention provides a method for analyzing the limit of wind turbine connection under transient power angle stability scenarios, the method comprising:

[0007] Based on the power system structure, an equivalent model of the system including the doubly fed wind turbines is established.

[0008] Based on the equivalent model of the system with doubly fed wind turbines, we derive the expressions for the system's equivalent inertia and mechanical power in two cases: direct connection of doubly fed wind turbines to the power system and replacement of generators with equal output.

[0009] Based on the system's equivalent inertia and mechanical power expressions, the impact of three-phase short-circuit faults on the power system structure and electromagnetic power expressions is analyzed, and expressions for the electromagnetic power injected into the power system by the doubly-fed wind turbines before, during, and after the fault is cleared are derived.

[0010] Based on the expression for the injected electromagnetic power of a doubly fed wind turbine, and inputting power system parameters, fault occurrence and clearing times, the system is transformed and calculated based on the extended equal area rule formula to obtain the numerical relationship between the wind turbine connection quantity and the system acceleration area and system deceleration area.

[0011] The initial value of the wind turbine connection quantity is determined and gradually increased. The relationship between the acceleration area and the deceleration area of ​​the system is judged to obtain the critical wind power connection value of the system.

[0012] This invention analyzes the transient stability of wind turbine grid connection for both single-unit infinite bus systems and dual-unit systems, based on the extended equal-area rule, and proposes a method for calculating the wind turbine grid connection limit considering transient stability. First, an equivalent model of the system with a doubly-fed induction generator (DFIG) is established to analyze the impact of a three-phase short-circuit fault on the system structure and electromagnetic power expression. With a fixed system fault clearing time, a transformation calculation is performed based on the extended equal-area rule formula to obtain the numerical relationship between the wind turbine connection quantity and the system's acceleration and deceleration areas. When the system's deceleration area equals its acceleration area, the wind power connection quantity reaches a critical value. Considering two scenarios—direct wind turbine connection and wind power replacing synchronous generators with equal output—the connection limits of the doubly-fed induction generator (DFIG) in single-unit infinite bus systems and dual-unit systems are derived for each scenario. In all designed scenarios, the error between the calculated values ​​and simulation results is less than 1%, demonstrating the high accuracy of the proposed method for calculating the wind power connection limit under the premise of transient power angle stability.

[0013] Furthermore, based on the power system structure, an equivalent model of the system including doubly-fed wind turbines is established, including:

[0014] Based on the power system structure, the grid-connected equivalent system containing doubly fed wind turbines is divided into a single-unit infinite bus system and a dual-unit system.

[0015] Equivalent models were performed on the single-machine infinite bus system and the dual-machine system respectively to obtain the corresponding equivalent circuits;

[0016] Among them, the power system structure refers to the power system grid and installed capacity structure.

[0017] Furthermore, the equivalent models of systems with doubly-fed wind turbines include equivalent models of single-unit infinite bus systems with doubly-fed wind turbines and equivalent models of dual-unit systems with doubly-fed wind turbines.

[0018] Furthermore, based on the expression for the injected electromagnetic power of a doubly-fed induction generator (DFIG), and inputting power system parameters, fault occurrence and clearing times, a transformation calculation is performed on the extended equal-area rule formula to obtain the numerical relationship between the wind turbine connection quantity and the system acceleration area and deceleration area, including:

[0019] Input power system parameters, fault occurrence and clearing times, and set the initial grid connection power P of the doubly-fed wind turbine. w The power factor k of the doubly-fed wind turbine; power system parameters include the potential and impedance of the doubly-fed wind turbine, line impedance, transformer turns ratio and impedance in the power system;

[0020] Calculate the equivalent parameters of the power system and the equivalent electromagnetic power of the system before and after the fault occurs;

[0021] Based on the extended equal area rule formula, transformation calculations are performed to obtain the system acceleration area and the system deceleration area.

[0022] Furthermore, the formulas for calculating the system acceleration area and the system deceleration area are as follows:

[0023]

[0024]

[0025] In the formula, S add For the system acceleration area, S dec P is the deceleration area of ​​the system. e2 P is the power injected into the doubly-fed wind turbine side of the power system during a fault. e3 P is the power injected into the doubly-fed wind turbine side of the power system after the faulty line is disconnected. m The equivalent mechanical power of the power system is given by δ, where δ0 is the initial power angle of the power system, and δ b δ is the critical work angle of the force system. cut The power angle of the power system.

[0026] Furthermore, the formulas for calculating the initial power angle, critical power angle, and system power angle are as follows:

[0027]

[0028]

[0029]

[0030] In the formula, P m P is the equivalent mechanical power of the system. e2 To inject power into the doubly-fed wind turbine side of the power system during a fault, E k Z is the system equivalent inertia, E is the generator equivalent electromotive force, U is the step-down transformer bus voltage, and ω0 is the generator angular frequency; 11-1 and Z 12-1 These are the self-impedance and transfer impedance of the doubly-fed wind turbine generator side before the fault, respectively. 11-3 and Z 12-3These are the self-impedance and transfer impedance on the doubly-fed wind turbine side after the fault is cleared; and These are the pre-fault self-impedance angle and the transferred impedance angle, respectively; α 11-1 α 12-1 These are the complementary angles of the self-impedance angle and the transferred impedance angle before the fault, respectively; α 11-3 α 12-3 These are the complementary angles of the self-impedance angle and the transferred impedance angle after fault clearance, respectively; δ cut For fault clearing angle, δ b δ0 is the critical cutoff angle of the system, and δ0 is the initial power angle of the system; t cut and t fault These represent the fault clearing time and the fault occurrence time, respectively.

[0031] Furthermore, by determining the relationship between the system's acceleration area and deceleration area, the critical wind power access value of the system is obtained, including:

[0032] Initially, the system deceleration area was larger than the system acceleration area. As the number of wind turbines connected to the system increased, the system deceleration area gradually decreased, while the system acceleration area gradually increased.

[0033] When the deceleration area of ​​the system equals the acceleration area of ​​the system, the wind power access volume of the system reaches the critical value.

[0034] When the deceleration area of ​​the system is greater than the acceleration area of ​​the system, the wind power access volume of the system has not reached the critical value. The system returns to the calculation of the equivalent parameters of the power system and the wind turbine access volume of the system is increased.

[0035] Secondly, the present invention provides a wind turbine access limit analysis system under transient power angle stability scenarios, which uses the aforementioned wind turbine access limit analysis method under transient power angle stability scenarios; the system includes:

[0036] The equivalent model construction unit is used to establish an equivalent model of the power system, including the doubly fed wind turbines connected to the system, based on the power system structure.

[0037] The first expression derivation unit is used to derive the system equivalent inertia and mechanical power expressions for two cases: direct connection of the doubly fed wind turbine to the power system and replacement of the generator with equal output, based on the equivalent model of the system with the doubly fed wind turbine connected to the power system.

[0038] The second expression derivation unit is used to analyze the impact of three-phase short-circuit faults on the power system structure and electromagnetic power expression based on the system's equivalent inertia and mechanical power expression, and to deduce the expression of electromagnetic power injected into the power system by the doubly-fed wind turbine before, during, and after the fault is cleared.

[0039] The calculation unit is used to calculate the numerical relationship between the wind turbine connection amount and the system acceleration area and deceleration area based on the expression of the electromagnetic power injected by the doubly fed wind turbine, the power system parameters, the fault occurrence and clearing time, and the extended equal area rule formula.

[0040] The judgment unit is used to determine the initial value of the wind turbine connection quantity and gradually increase it, judge the relationship between the system acceleration area and the system deceleration area, and obtain the critical wind power connection value of the system.

[0041] Thirdly, the present invention also provides a computer device, including a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, it implements the above-mentioned method for wind turbine access limit analysis under transient power angle stability scenario.

[0042] Fourthly, the present invention provides a computer-readable storage medium storing a computer program, characterized in that the computer program, when executed by a processor, implements the above-described method for wind turbine access limit analysis under a transient power angle stability scenario.

[0043] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0044] This invention presents a method and system for analyzing the wind turbine grid connection limits under transient power angle stability scenarios. The invention analyzes the transient stability of wind turbine grid connection for both single-unit infinite bus systems and dual-unit systems based on the extended equal-area rule, and proposes a method for calculating the wind turbine grid connection limits considering transient stability. First, an equivalent model of the system with a doubly-fed induction generator (DFIG) is established to analyze the impact of a three-phase short-circuit fault on the system structure and electromagnetic power expression. With a fixed system fault clearing time, a transformation calculation is performed based on the extended equal-area rule formula to obtain the numerical relationship between the number of wind turbines connected and the system's acceleration and deceleration areas. Initially, the system's deceleration area is greater than its acceleration area. As the number of wind turbines connected increases, the system's deceleration area gradually decreases, while the system's acceleration area gradually increases. When the system's deceleration area equals its acceleration area, the wind turbine connection reaches a critical value. Considering two scenarios—direct wind turbine connection and wind power replacing synchronous generators with equal output—the grid connection limits for single-unit infinite bus systems and dual-unit systems with DFIGs are derived for each scenario. In all designed scenarios, the error between the calculated values ​​and the simulation results is less than 1%, proving that the wind power limit connection analysis method proposed in this invention under the premise of transient stability of the power angle has high accuracy. Attached Figure Description

[0045] The accompanying drawings, which are included to provide a further understanding of embodiments of the invention and form part of this application, do not constitute a limitation thereof. In the drawings:

[0046] Figure 1 This is a flowchart of a wind turbine connection limit analysis method under transient power angle stability scenario according to the present invention;

[0047] Figure 2 This is a structural diagram of a single-unit infinite bus system with a doubly fed wind turbine connected to the present invention;

[0048] Figure 3 This is the equivalent circuit diagram of the single-unit infinite bus system with a doubly fed wind turbine connected to the present invention;

[0049] Figure 4 This invention relates to a dual-machine system structure and equivalent circuit including a doubly-fed wind turbine. Figure 4 (a) is a structural diagram of a dual-unit system including a doubly-fed wind turbine. Figure 4 (b) is the equivalent circuit diagram of a dual-machine system with a doubly fed wind turbine connected;

[0050] Figure 5 The present invention includes the power characteristic curve of a doubly fed wind turbine connected to a single-unit infinite bus system;

[0051] Figure 6 The flowchart shows the calculation of the wind turbine connection limit under the premise of transient stability of the system of the present invention.

[0052] Figure 7 This is a power angle curve of the system in the single-machine infinite power system of the present invention when the wind turbine completely replaces the synchronous machine.

[0053] Figure 8 This is a diagram showing the system power angle curve in the scenario where the wind turbine is directly connected to a single-unit infinite power system according to the present invention.

[0054] Figure 9 This is a power angle curve of the system in the two-machine system of the present invention under the scenario of direct wind turbine connection;

[0055] Figure 10 This is a power angle curve of the system in the two-machine system of the present invention under the scenario of power replacement by wind turbine, etc.

[0056] Figure 11 This is a structural block diagram of a wind turbine access limit analysis system under transient power angle stability scenario according to the present invention. Detailed Implementation

[0057] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and accompanying drawings. The illustrative embodiments and descriptions of the present invention are only used to explain the present invention and are not intended to limit the present invention.

[0058] Existing wind turbine access limit analysis methods only consider the power flow transmission limit of the power system, without taking into account the transient stability characteristics of the system power angle and voltage, as well as the impact of wind power access on the system's transient stability. This leads to inaccurate calculation results and may cause transient instability when the maximum wind power capacity is connected to the grid, threatening the power supply security of the power system.

[0059] Therefore, addressing the research gap in the field of wind power grid connection capacity limit calculation methods under the transient stability premise of power systems, this invention treats doubly fed induction generators (DFIGs) as equivalent to a constant impedance model, dividing them into two scenarios: direct turbine grid connection and turbines replacing synchronous machines with equal output. Based on the extended equal area rule, a calculation method for the wind power grid connection limit under system transient stability constraints is further derived. Simultaneously, simulation models of a single-unit infinite bus system and a dual-unit system with DFIG grid connection are built in Matlab / Simulink software to verify the accuracy of the theoretical calculation results.

[0060] The key point of this invention lies in proposing a wind turbine grid-connection limit analysis method that considers the transient stability of the power grid. For the calculation of the maximum wind power grid-connection capacity of the power system under the premise of system transient stability, this invention equates the wind turbine to a constant impedance model and, by transforming the extended equal area rule formula, proposes a method for calculating the wind power grid connection limit under transient stability scenarios. This fills the research gap in existing wind power limit calculation methods that do not consider transient stability, effectively improving the accuracy of wind power grid connection limit calculation, providing guidance for wind power grid connection in practical engineering, effectively avoiding the potential grid instability risk caused by inaccurate grid connection limit calculation, and ensuring the power supply reliability of the power system. The core innovation of this invention is the inclusion of transient stability in the calculation of wind power grid connection limit capacity, providing guidance for accurately calculating wind power grid connection limits and wind power grid stability.

[0061] Example 1

[0062] like Figure 1 As shown, this invention provides a method for analyzing the limit of wind turbine connection under transient power angle stability scenarios. The method includes:

[0063] Step 1: Based on the power system structure, establish an equivalent model of the system including the doubly fed wind turbines connected to the system;

[0064] Step 2: Based on the equivalent model of the system with doubly fed wind turbines connected to the power system, derive the expressions for the equivalent inertia and mechanical power of the system in two cases: direct connection of the doubly fed wind turbines to the power system and replacement of the generator with the same output.

[0065] Step 3: Based on the system's equivalent inertia and mechanical power expressions, analyze the impact of three-phase short-circuit faults on the power system structure and electromagnetic power expressions, and deduce the expressions for the electromagnetic power injected by the doubly-fed wind turbines before, during, and after the fault is cleared.

[0066] Step 4: Based on the expression for the electromagnetic power injected by the doubly fed wind turbine, input the power system parameters, fault occurrence and clearing time, and perform transformation calculations based on the extended equal area rule formula to obtain the numerical relationship between the wind turbine connection amount and the system acceleration area and system deceleration area.

[0067] Step 5: Determine the initial value of the wind turbine connection quantity and gradually increase it; determine the relationship between the system acceleration area and the system deceleration area to obtain the critical wind power connection value of the system.

[0068] The specific details of this embodiment are as follows:

[0069] (1) Establish an equivalent model of the system including the doubly fed wind turbine generator.

[0070] First, based on the power system structure, the equivalent system with doubly fed wind turbines connected to the grid is divided into a single-unit infinite bus system and a dual-unit system. Second, equivalent models are performed for the single-unit infinite bus system and the dual-unit system respectively to obtain the corresponding equivalent circuits. Expressions for the power injected into the generator side before the fault, during the fault, and after the fault are proposed for the two models, which serve as the basis for the next step of transient stability analysis of wind turbine grid connection.

[0071] Among them, the power system structure refers to the power system grid and installed capacity structure.

[0072] Specifically, the equivalent models of systems with doubly-fed wind turbines include equivalent models of single-unit infinite bus systems with doubly-fed wind turbines and equivalent models of dual-unit systems with doubly-fed wind turbines.

[0073] 1) Equivalent model of a single-unit infinite bus system with a doubly-fed wind turbine connected

[0074] The structure diagram of a single-unit infinite bus system with a doubly-fed wind turbine is shown below. Figure 2 As shown. A doubly-fed induction generator (DFIG) has fast recovery characteristics, enabling it to quickly adjust its power to pre-fault levels after a fault is cleared. It maintains a essentially constant output power while rapidly clearing the fault. Therefore, in the equivalent simplified circuit, the DFIG can be represented as a constant negative impedance.

[0075]

[0076] Q w =P w tan(arccosk) (2)

[0077] Among them, U w P is the rated voltage of the DFIG connection point; w and Q w These represent the active and reactive power outputs of the DFIG, respectively; k is the power factor of the DFIG.

[0078] This invention considers the most severe three-phase short-circuit fault occurring at the beginning of the line. Since a three-phase short circuit is a symmetrical fault, the additional impedance at the fault point approaches zero. The simplified equivalent circuit diagrams of the system before and after fault clearance are as follows: Figure 3 As shown. Based on the grid connection method of wind turbines, there are two scenarios: direct connection to the power system at a certain ratio, and replacement of generators with equal output. Here, we will analyze the system's equivalent inertia and mechanical power expressions for these two scenarios respectively.

[0079] When the wind turbine is directly connected to the system, assuming the wind farm is connected from the generator side, the equivalent rotor motion equation on the generator side is:

[0080] E k =E k.G +E k.W +E k.S =H G P m.G +H W P W +E k.S (3)

[0081] P m =P m.G +P m.W (4)

[0082]

[0083] Among them, E k E is the equivalent inertia of the system. k.G E k.W and E k.S The inertia of the synchronous machine, DFIG, and infinite power supply, respectively; H G and H W P represents the inertial constants of the synchronous machine and the DFIG, respectively; m and P e These are the system's equivalent mechanical power and equivalent electromagnetic power, respectively.

[0084] When the output of a wind turbine or other power source replaces that of a generator, the expressions for the equivalent inertia and mechanical power of the system are:

[0085]

[0086] For simplified calculation, this invention ignores the resistance of the lines and transformers, considering only the impact of reactance on the system structure. Before the fault, the two circuits operated in parallel, and the power injected into the generator side was P. e1 The expression is:

[0087]

[0088]

[0089]

[0090] Among them, P e1 Z represents the power injected into the generator side before the fault, E is the equivalent electromotive force of the generator, and U is the bus voltage of the step-down transformer; 11-1 and Z 12-1 These are the self-impedance and transfer impedance on the generator side before the fault, respectively; x′ d x is the equivalent reactance of the generator. dT1 x is the equivalent impedance of the step-up transformer. dT2 x is the equivalent impedance of the step-down transformer. L Z represents the impedance of the transmission line. w The equivalent impedance of the fan; and These are the self-impedance angle and the transfer impedance angle before the fault, respectively, α 11-1 α 12-1 These are the complementary angles of the self-impedance angle and the transferred impedance angle before the fault, respectively; δ is the power angle of the power system.

[0091] During the fault, the line start end is directly grounded, and the power P injected into the generator side is... e2 Only the self-impedance part remains, and its expression is:

[0092]

[0093]

[0094] The meanings of the parameters in the formula are the same as above.

[0095] After the faulty line is disconnected, the double-circuit transmission line becomes a single-circuit line, and the power P injected into the generator side... e3 The expression is:

[0096]

[0097]

[0098]

[0099] In the formula, Z 11-3 and Z 12-3These are the self-impedance and transfer impedance on the doubly-fed wind turbine side after fault clearance; α 11-3 α 12-3 These are the complementary angles of the self-impedance angle and the transferred impedance angle after fault clearance, respectively; the meanings of the other parameters are the same as above.

[0100] 2) Equivalent model of a dual-machine system including a doubly-fed wind turbine

[0101] The structure and equivalent circuit of a dual-machine system including a doubly-fed wind turbine are as follows: Figure 4 As shown, Figure 4 (a) is a structural diagram of a dual-unit system including a doubly-fed wind turbine. Figure 4 (b) is the equivalent circuit diagram of a dual-unit system with a doubly-fed wind turbine connected. The wind turbine is connected from the S unit side. Consider that a permanent three-phase short-circuit fault occurs at the end of one of the lines closest to the S unit, and the additional impedance at the short-circuit point is zero.

[0102] The transient stability of the dual-generator system needs to be analyzed based on its equivalent single-generator infinitesimal model. By subtracting the rotor motion equations of the two generators, the equivalent rotor equations of the system can be obtained:

[0103]

[0104] Where, δ S and δ R δ represents the power angles of the left and right generators, respectively, and δ is the power angle difference between the two generators, the fluctuation of which can reflect the impact of wind power integration on the transient stability of the system; ω0 is the generator angular frequency, E k This is the equivalent inertia of the system.

[0105] In the case of direct connection of the wind turbine, the equivalent mechanical power P of the system is m and equivalent electromagnetic power P e The expressions are as follows:

[0106]

[0107]

[0108] Among them, E k.S E k.R and E k.W These are the inertia values ​​of generator S, generator R, and wind turbine, respectively; P mS P mR and P W These represent the power of generator S, generator R, and the wind turbine, respectively; P eS and P eR These are the electromagnetic powers of generator S and generator R, respectively.

[0109] When the output of the wind turbine replaces that of the synchronous generator, and the wind turbine replaces the output of the generators on both sides in proportion to the rated active power of the generator, the mechanical power expressions of the generators are as follows:

[0110]

[0111] Among them, P′ mS and P′ mR P represents the mechanical power of generator S and generator R respectively when the output of a wind turbine or other power source replaces that of a synchronous machine; NS and P NR These are the rated active power of generator S and generator R, respectively; the meanings of the other parameters are the same as above. The generator's moment of inertia will change with the change in mechanical power, and the system's equivalent power will also change accordingly.

[0112] The expressions for the injected power of the generators on both sides before the fault were as follows:

[0113]

[0114]

[0115]

[0116]

[0117]

[0118] In the formula, E1 and E2 are the equivalent electromotive forces of generator S and generator R, respectively; α 22-1 Z is the complementary angle of the self-impedance angle on the R side of the generator before the fault; 22-1 The self-impedance of the generator's R side before the fault; the meanings of the other parameters are the same as above.

[0119] The expressions for the injected power of the generators on both sides during a fault are as follows:

[0120]

[0121]

[0122]

[0123]

[0124] In the formula, α 11-2 α 22-2 These are the complementary angles of the self-impedance angles on the S and R sides of the generator during the fault; Z 11-2 and Z 22-2 The self-impedance of the generator's S-side and R-side during the fault; the meanings of the other parameters are the same as above.

[0125] After the fault is cleared, only the double-circuit line becomes a single-circuit line, and the system structure remains the same as before the fault.

[0126] (2) Transient stability analysis of the system including the wind turbine

[0127] The power characteristic curve of a single-unit infinite bus system containing a doubly-fed wind turbine is shown in the figure. Figure 5 As shown. According to the law of equal area, the system initially stabilizes at operating point a. After the fault occurs, the operating point jumps to P. e2 At the point corresponding to δ0 on the curve, the mechanical power of the system is greater than the electromagnetic power, and the generator rotor is subjected to an unbalanced torque with an accelerating effect, along P. e2 The curve accelerates to the right. cut The faulty line is disconnected at all times, at which point the system power angle is δ. cut The running point starts from P. e2 Jump to P e3 On the curve, the electromagnetic power is greater than the mechanical power, and the rotor experiences an unbalanced torque due to deceleration, along P. e3 In a deceleration curve, if the rotor speed decreases to the rated speed before reaching point b, the system has the ability to recover to a stable state. At this point, the deceleration imbalance torque still exists, and the rotor continues to decelerate to the left from this point until point c. At point c, the electromagnetic power and mechanical power of the system are balanced, but the rotor speed is already below the rated speed, and it continues to move to the left. When the rotor passes point c, due to the imbalance between electromagnetic and mechanical power, the rotor will regain an unbalanced torque that accelerates it, and it will reciprocate around the new equilibrium point c of the system after the fault is cleared, until it stabilizes at point c under the action of friction.

[0128] If the running point reaches P e3 With P m At point b, the synchronous machine speed has not yet dropped to the rated value. The rotor will be accelerated by the unbalanced torque again, and the operating point will continue to move to the right until the system becomes transiently unstable.

[0129] Based on the system electromagnetic power P before the fault e1 and mechanical power P m The intersection point a, and the electromagnetic power P after the fault is cleared. e3 and mechanical power P m From the intersection point b, the initial power angle δ0 and the critical power angle δ of the system can be calculated. b The value.

[0130]

[0131]

[0132] At the instant the fault occurs, δ0 is the initial value of the constant part of the differential expression (7), and the first-order initial value is:

[0133]

[0134] The system failure time is t. fault Substituting the initial value into equation (5) and solving the differential equation, we obtain the fault clearing angle δ. cut :

[0135]

[0136] For P respectively m and P e2 The difference and P e3 and P m Integral operations yield the expressions for the acceleration and deceleration areas of the system:

[0137]

[0138]

[0139] Furthermore, the formulas for calculating the system acceleration area and the system deceleration area are as follows:

[0140]

[0141]

[0142] In equations (28) to (35), S add For the system acceleration area, S dec P is the deceleration area of ​​the system. e2 P is the power injected into the doubly-fed wind turbine side of the power system during a fault. e3 P is the power injected into the doubly-fed wind turbine side of the power system after the faulty line is disconnected. m The equivalent mechanical power of the power system is given by δ, where δ0 is the initial power angle of the power system, and δ b δ is the critical power angle of the power system. cut This represents the power angle of the power system; the meanings of the other parameters are the same as above.

[0143] (3) Determine the wind power limit access capacity under transient stability premise

[0144] At fault clearing time t cutUnder certain conditions, the generator rotor speed needs to be reduced to the rated speed before the operating point reaches point b. That is, the power angle corresponding to point b is taken as the critical power angle for the generator to recover to a stable state. An initial value for the wind turbine connection is proposed, and its magnitude is gradually increased. If the power angle when the system recovers to stability is exactly equal to the power angle corresponding to point b, then the size of the deceleration area and the acceleration area of ​​the system are equal, which is the critical state of the system. By adjusting the wind power connection until the operating point reaches point b, the deceleration area is exactly equal to the acceleration area, that is, the areas calculated according to formulas (32) and (33) are equal, the critical wind power connection value of the system can be obtained. The calculation flowchart of the wind turbine connection limit under the premise of system transient stability is as follows: Figure 6 As shown. Figure 6 The calculation process is as follows:

[0145] Input power system parameters, fault occurrence and clearing time; power system parameters include the potential and impedance of the doubly fed wind turbine generator, line impedance, transformer ratio and impedance in the power system;

[0146] Set the initial input power P of the doubly-fed wind turbine. w and the power factor k of a doubly-fed wind turbine;

[0147] Calculate the equivalent parameters of the power system and the equivalent electromagnetic power of the system before and after the fault occurs;

[0148] Based on the extended equal area rule formula, transformation calculations are performed to obtain the system acceleration area and the system deceleration area;

[0149] Determine the relationship between the acceleration area and the deceleration area of ​​the system: initially, the deceleration area is larger than the acceleration area. As the number of wind turbines connected to the system increases, the deceleration area gradually decreases while the acceleration area gradually increases.

[0150] When the deceleration area of ​​the system equals the acceleration area of ​​the system, the wind power access volume of the system reaches the critical value.

[0151] When the deceleration area of ​​the system is greater than the acceleration area of ​​the system, the wind power access volume of the system has not reached the critical value. The system returns to the calculation of the equivalent parameters of the power system and the wind turbine access volume of the system is increased.

[0152] In practice, build the following in Matlab / Simulink respectively: Figure 2 and Figure 4The simulation model shown includes a power system with a doubly-fed induction generator (DFIG) wind turbine. The turbine parameters are identical in both systems, and it is a constant power factor control model with a power factor of 0.8, an inertia constant of 0.5s, and a turbine connection point voltage of 230kV. The system is set to experience a permanent three-phase short-circuit fault on the turbine connection side of one of the two circuits after 30 seconds of operation. The faulty circuit is disconnected 0.12 seconds after the fault occurs. The limit value for wind turbine connection at the critical instability of the system's power angle is sought by changing the wind power connection capacity.

[0153] (1) Standalone infinite system

[0154] In a single-machine infinite bus system, the synchronous machine has a rated active power of 320MW and an inertia constant of 3.14s. The parameters of the other components of the system are shown in Table 1.

[0155] Table 1 Parameters of each component in a single-machine infinite loop system

[0156]

[0157] A single-machine infinite power supply is also an infinite inertia source. According to formulas (32) and (33), since E k Infinity, the fault clearing angle δ in this system cut Since the initial power angle δ0 is approximately equal to the system's acceleration area, the system's power angle stability is relatively high. However, different DFIG connection methods still affect the equivalent electromagnetic and mechanical power values ​​of the system, thus influencing the system's power angle stability by changing the system's deceleration area. Therefore, the system inertia value can be set to a maximum value in the calculation to observe the changing trend of the wind power limit connection amount.

[0158] In scenarios where the output of a DFIG (Diverterless Radiator Induction Generator) replaces that of a synchronous motor, the system inertia is set to its maximum value. Supported by an infinite inertia source, when the wind turbine completely replaces the synchronous motor's output and the faulty line is disconnected, the system's power angle remains stable. The power angle curve of the system at this time is as follows: Figure 7 As shown.

[0159] In a scenario where a DFIG is directly connected to a single-unit infinite power system, with the system inertia set to the hundreds of millions and adjusted upwards, the wind turbine's ultimate input power eventually stabilizes at 429MW. If the turbine output exceeds this value, the system's electromagnetic power curve, after the faulty line is disconnected, will shift completely below the mechanical power curve, resulting in a negative deceleration area and system instability. The system power angle curve in this scenario is as follows: Figure 8 As shown, when the rated active power of the wind turbine is set to 429MW, the system power angle remains stable. Gradually increasing the wind turbine output until the turbine connection reaches 431MW, the system power angle curve diverges and oscillates until it becomes unstable.

[0160] (2) Dual-machine system

[0161] In the two-generator system, generator S has a rated active power of 320MW and an inertial constant of 7.314s; generator R has a rated active power of 411.8MW and an inertial constant of 9s; the parameters of other components in the system are shown in Table 2.

[0162] Table 2 Parameters of each component in a single-machine infinite loop system

[0163]

[0164] In the scenario of direct wind turbine connection to the system, the theoretical calculation yields a wind power connection limit of 539MW. For example... Figure 9 and Figure 10 As shown in the simulation model, when the wind turbine output is at the theoretical critical value, the power angle difference curve of the two generators diverges and oscillates, indicating that the system power angle has become unstable. To determine the access limit for direct grid connection of wind turbines, the wind turbine output was gradually reduced from 539MW until the wind turbine output reached 536MW, at which point the generator power angle difference curve could remain stable after the faulty line was disconnected.

[0165] (3) Results Analysis

[0166] Table 3 summarizes the calculation, simulation results, and errors of the wind power limit for each of the four scenarios under the critical steady-state of the power system's power angle.

[0167] Table 3. Calculation results and errors of wind power limit access under various scenarios.

[0168]

[0169] As shown in the table above, the error between the calculated value and the simulation result is less than 1% in all scenarios, proving that the wind power limit access analysis method proposed in this invention under the premise of transient stability of power angle has high accuracy.

[0170] This invention analyzes the transient stability of wind turbine grid connection for both single-unit infinite bus systems and dual-unit systems, based on the extended equal-area rule, and proposes a method for calculating the wind turbine grid connection limit considering transient stability. First, an equivalent model of the system with a doubly-fed induction generator (DFIG) is established to analyze the impact of a three-phase short-circuit fault on the system structure and electromagnetic power expression. With a fixed system fault clearing time, a transformation calculation is performed based on the extended equal-area rule formula to obtain the numerical relationship between the wind turbine connection quantity and the system's acceleration and deceleration areas. Initially, the system's deceleration area is greater than its acceleration area. As the wind turbine connection quantity increases, the system's deceleration area gradually decreases, while the system's acceleration area gradually increases. When the system's deceleration area equals its acceleration area, the wind power connection quantity reaches a critical value. Considering two scenarios—direct wind turbine connection and wind power replacing synchronous generators with equal output—the connection limits of the DFIG induction generator for single-unit infinite bus systems and dual-unit systems are derived for each scenario. In all designed scenarios, the error between the calculated values ​​and simulation results is less than 1%, demonstrating the high accuracy of the wind power limit connection quantity analysis method proposed in this invention under the premise of transient power angle stability.

[0171] Example 2

[0172] like Figure 11 As shown, the difference between this embodiment and Embodiment 1 is that this embodiment provides a wind turbine access limit analysis system under a transient power angle stability scenario. This system uses a wind turbine access limit analysis method under a transient power angle stability scenario from Embodiment 1. The system includes:

[0173] The equivalent model construction unit is used to establish an equivalent model of the power system, including the doubly fed wind turbines connected to the system, based on the power system structure.

[0174] The first expression derivation unit is used to derive the system equivalent inertia and mechanical power expressions for two cases: direct connection of the doubly fed wind turbine to the power system and replacement of the generator with equal output, based on the equivalent model of the system with the doubly fed wind turbine connected to the power system.

[0175] The second expression derivation unit is used to analyze the impact of three-phase short-circuit faults on the power system structure and electromagnetic power expression based on the system's equivalent inertia and mechanical power expression, and to deduce the expression of electromagnetic power injected into the power system by the doubly-fed wind turbine before, during, and after the fault is cleared.

[0176] The calculation unit is used to calculate the numerical relationship between the wind turbine connection amount and the system acceleration area and deceleration area based on the expression of the electromagnetic power injected by the doubly fed wind turbine, the power system parameters, the fault occurrence and clearing time, and the extended equal area rule formula.

[0177] The judgment unit is used to determine the initial value of the wind turbine connection quantity and gradually increase it, judge the relationship between the system acceleration area and the system deceleration area, and obtain the critical wind power connection value of the system.

[0178] The execution process of each unit can be carried out according to the steps of the wind turbine access limit analysis method under the transient power angle stability scenario in Example 1, and will not be described in detail in this example.

[0179] Meanwhile, the present invention also provides a computer device, including a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, it implements the above-mentioned method for wind turbine access limit analysis under transient power angle stability scenario.

[0180] Meanwhile, the present invention also provides a computer-readable storage medium storing a computer program, characterized in that the computer program, when executed by a processor, implements the above-mentioned method for wind turbine access limit analysis under transient power angle stability scenario.

[0181] Those skilled in the art will understand that embodiments of this application can be provided as methods, systems, or computer program products. Therefore, this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application can take the form of a computer program product embodied on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0182] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart... Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0183] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1The function specified in one or more boxes.

[0184] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0185] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for wind turbine interconnection limit analysis in transient power angle stability scenarios, characterized in that, The method includes: Based on the power system structure, an equivalent model of the system including the doubly fed wind turbines is established. Based on the equivalent model of the system with doubly fed wind turbines, the expressions for the system's equivalent inertia and mechanical power are derived for two cases: direct connection of the doubly fed wind turbine to the power system and replacement of the generator with equal output. Based on the equivalent inertia and mechanical power expressions of the system, the impact of three-phase short-circuit faults on the power system structure and electromagnetic power expressions is analyzed, and the expressions for the electromagnetic power injected by the doubly-fed wind turbines before, during, and after the fault is cleared are derived. Based on the expression for the injected electromagnetic power of a doubly fed wind turbine, and by inputting power system parameters, fault occurrence and clearing times, and transforming the extended equal area rule formula, the numerical relationship between the wind turbine connection quantity and the system acceleration area and deceleration area is obtained. The initial value of the wind turbine connection quantity is determined and gradually increased. The relationship between the acceleration area and the deceleration area of ​​the system is determined to obtain the critical wind power connection value of the system. Based on the expression for the injected electromagnetic power of a doubly-fed induction generator (DFIG), and inputting power system parameters, fault occurrence and clearing times, the system undergoes transformation calculations based on the extended equal-area rule formula to obtain the numerical relationship between the wind turbine connection quantity and the system acceleration area and deceleration area, including: Input power system parameters, fault occurrence and clearing time, and set the initial access power and power factor of the doubly-fed wind turbine; the power system parameters include the potential and impedance of the doubly-fed wind turbine, line impedance, transformer ratio and impedance in the power system; Calculate the equivalent parameters of the power system and the equivalent electromagnetic power of the system before and after the fault occurs; Based on the extended equal area rule formula, transformation calculations are performed to obtain the system acceleration area and the system deceleration area; The formulas for calculating the acceleration area and deceleration area of ​​the system are as follows: ； ； In the formula, To accelerate the area of ​​the system, For the system deceleration area, To inject power into the doubly-fed wind turbine side of the power system during a fault. To inject power into the power system on the doubly-fed wind turbine side after the faulty line is disconnected. Equivalent mechanical power of the power system The initial power angle of the power system. The critical work angle of the force system. To cut off the power angle of the power system.

2. The method for analyzing the limit of wind turbine connection under transient power angle stability scenario according to claim 1, characterized in that, Based on the power system structure, an equivalent model of the system including doubly-fed wind turbines is established, including: Based on the power system structure, the grid-connected equivalent system containing doubly fed wind turbines is divided into a single-unit infinite bus system and a dual-unit system. Equivalent models were performed on the single-machine infinite bus system and the dual-machine system respectively to obtain the corresponding equivalent circuits; The power system structure refers to the power system grid and installed capacity structure.

3. The method for analyzing the limit of wind turbine connection under transient power angle stability scenario according to claim 1, characterized in that, The equivalent model of the system with doubly fed wind turbines includes the equivalent model of a single-unit infinite bus system with doubly fed wind turbines and the equivalent model of a dual-unit system with doubly fed wind turbines.

4. The method for analyzing the limit of wind turbine connection under transient power angle stability scenario according to claim 1, characterized in that, The formulas for calculating the initial power angle, critical power angle, and system power angle are as follows: ； ； ； In the formula, The equivalent mechanical power of the system, To inject power into the doubly-fed wind turbine side of the power system during a fault. Here, E is the system's equivalent inertia, E is the generator's equivalent electromotive force, and U is the step-down transformer bus voltage. The generator's angular frequency; and These are the self-impedance and transfer impedance of the doubly-fed wind turbine side before the fault, respectively. and These are the self-impedance and transfer impedance on the doubly-fed wind turbine side after the fault is cleared; and These are the self-impedance angle and the transferred impedance angle before the fault, respectively. , These are the complementary angles of the self-impedance angle and the transferred impedance angle before the fault, respectively. , These are the complementary angles of the self-impedance angle and the transferred impedance angle after fault clearance; For fault removal angle, The critical cut-off angle of the system. The initial power angle of the system; and These represent the fault clearing time and the fault occurrence time, respectively.

5. The method for analyzing the limit of wind turbine connection under transient power angle stability scenario according to claim 1, characterized in that, Determining the relationship between the acceleration area and the deceleration area of ​​the system to obtain the critical wind power access value of the system includes: Initially, the system deceleration area was larger than the system acceleration area. As the number of wind turbines connected to the system increased, the system deceleration area gradually decreased, while the system acceleration area gradually increased. When the deceleration area of ​​the system equals the acceleration area of ​​the system, the wind power access volume of the system reaches the critical value. When the deceleration area of ​​the system is greater than the acceleration area of ​​the system, the wind power access volume of the system has not reached the critical value. The system returns to the calculation of the equivalent parameters of the power system and the wind turbine access volume of the system is increased.

6. A wind turbine connection limit analysis system under transient power angle stability scenario, characterized in that, The system uses a wind turbine connection limit analysis method under a transient power angle stability scenario as described in any one of claims 1 to 5; the system includes: The equivalent model construction unit is used to establish an equivalent model of the power system, including the doubly fed wind turbines connected to the system, based on the power system structure. The first expression derivation unit is used to derive the system equivalent inertia and mechanical power expressions for two cases: direct connection of the doubly fed wind turbine to the power system and replacement of the generator with equal output, based on the equivalent model of the system containing the doubly fed wind turbine. The second expression derivation unit is used to analyze the impact of three-phase short-circuit faults on the power system structure and electromagnetic power expression based on the equivalent inertia and mechanical power expression of the system, and to deduce the expression of electromagnetic power injected by the doubly-fed wind turbine before the fault, during the fault, and after the fault is cleared. The calculation unit is used to calculate the numerical relationship between the wind turbine connection amount and the system acceleration area and deceleration area based on the expression of the electromagnetic power injected by the doubly fed wind turbine, the power system parameters, the fault occurrence and clearing time, and the extended equal area rule formula. The judgment unit is used to determine the initial value of the wind turbine access quantity and gradually increase it, judge the relationship between the acceleration area and the deceleration area of ​​the system, and obtain the critical wind power access value of the system.

7. A computer device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the processor executes the computer program, it implements the wind turbine access limit analysis method under transient power angle stability scenario as described in any one of claims 1 to 5.

8. A computer-readable storage medium storing a computer program, characterized in that, When the computer program is executed by the processor, it implements the wind turbine access limit analysis method under transient power angle stability scenario as described in any one of claims 1 to 5.

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