A method for evaluating equivalent stability of a new energy station

Abstract

A method for equivalent stability evaluation of new energy station, the method first equivalently regards the new energy station as an injected current source, establishes a multi-node network model containing synchronous generator, new energy station and infinite system; then, based on the node voltage equation, the system is simplified into an equivalent single-machine infinite system model through the elimination method, and the modified electromagnetic power expression of the synchronous generator after the new energy station is connected is derived; subsequently, the dynamic process of the active power of the new energy station recovering at a rate k after fault removal is analyzed, and its influence on the acceleration and deceleration areas in the swing of the power angle of the synchronous machine is analyzed; on this basis, a first swing and third swing transient power angle stability criterion is constructed with the recovery rate k as the variable; finally, the criterion is solved to obtain the safe allowable interval of the active power recovery rate k to ensure the transient stability of the system. The method provides an analysis tool for quantitatively evaluating the influence of new energy dynamics on the multi-swing stability of the system.

Description

Technical Field

[0001] This invention belongs to the field of power system stability control technology, and specifically relates to a method for evaluating the equivalent stability of new energy power plants. Background Technology

[0002] With the large-scale integration of new energy sources such as wind power and photovoltaics into the power grid, the stability characteristics of the power system have undergone fundamental changes. Traditional synchronous stability assessment methods rely on modeling the power generation units in the grid as models with fixed mechanical inertia and using classical transient stability analysis methods to assess the system's stability. However, new energy units are connected to the grid through power electronic equipment and do not possess traditional inertia. Their active power after a fault exhibits dynamic characteristics of gradually recovering at a certain rate, which renders traditional stability analysis methods inapplicable.

[0003] Therefore, there is an urgent need to design a method that can quantitatively analyze the impact of the active power recovery rate of new energy sources on the stability of the system's multiple swings. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides a method for evaluating the equivalent stability of new energy power plants, which incorporates the characteristics of new energy power generation into the traditional power grid stability analysis framework, thus solving the stability assessment problem brought about by large-scale new energy grid connection.

[0005] A method for assessing the equivalent stability of a new energy power station, the method specifically comprising:

[0006] Step 1: Establish a multi-node power network model including synchronous generator nodes, new energy power station grid connection nodes, and receiving-end infinite bus system nodes, wherein the new energy power station is equivalent to an injected current source;

[0007] Step 2: Based on the nodal voltage equations, the grid-connected nodes of the renewable energy power station and the receiving-end infinite bus system nodes are eliminated using the elimination method, leaving only the synchronous generator nodes. This yields the injection current correction model for the synchronous generator after it is connected to the renewable energy power station. The injection current correction model is as follows: ;in, This refers to the injection current of the synchronous generator when it is not connected to the new energy power station. This refers to the current increment generated at the synchronous machine terminals of the new energy power station;

[0008] Step 3: Based on the injected current correction model, derive the electromagnetic power correction formula for the synchronous machine under normal operating conditions: Among them, P e This refers to the electromagnetic power of the synchronous motor when it is not connected to the new energy power station. The electromagnetic power of the synchronous machine when connected to a new energy power station and operating normally, ΔP eThe electromagnetic power increment of the synchronous generator after connection to the new energy power station is denoted by δ, where δ is the power angle of the synchronous generator and E1 is the internal electromotive force of the synchronous generator. The phase angle for injecting current into the synchronous generator node. The phase angle that generates the current increment on the synchronous generator of the new energy power station;

[0009] Step 4: Simulate a transmission line fault in the system and disconnect the faulty component. At this point, the transmission line reactance is updated to... Repeat the elimination process described in step two to obtain the injection current correction model of the synchronous generator after the fault: ,in, , The current correction and increment generated at the synchronous motor terminals by wind power after a fault are calculated; therefore, the electromagnetic power correction formula for the synchronous motor instantaneously after the fault is cleared is derived: ,in, This refers to the electromagnetic power of the synchronizer moment after the fault is cleared. This refers to the electromagnetic power of the synchronous motor after a fault when wind power is not connected. This represents the instantaneous increase in the electromagnetic power of the synchronizing machine after the fault is cleared.

[0010] Step 5: During the active power recovery process of the renewable energy units after fault clearance, the current injected into the system by the renewable energy units is... Become The corrective electromagnetic power of the synchronizing machine from Gradually become Based on this dynamic process, the corrected motion equations for the equivalent OMIB system are established: Among them, M, , These are the moment of inertia, mechanical power, and corrected equivalent mechanical power of the synchronous generator, respectively.

[0011] Step Six: Based on the electromagnetic power correction formula and the equivalent OMIB system correction equation, analyze the impact of the active power recovery rate of the new energy unit on the stability of the synchronous machine's multi-pendulum power angle, and establish the stability criteria for the first pendulum and the third pendulum:

[0012] First stability criterion: S1≤S2, where S1 is the acceleration area during the first swing process at the critical cutting angle, and S2 is the maximum deceleration area during the first swing process at the critical cutting angle.

[0013] ;

[0014] in, The synchronous motor power angle at the moment the fault begins. To cut off the synchronous motor power angle during a fault; Y 12D' is the mutual impedance of the coefficient matrix of the node voltage equation; D' is the equivalent self-admittance after elimination; and B' is... The impedance angle;

[0015] ;

[0016] in, The synchronous motor power angle at the critical moment of instability. To reduce the synchronous motor power angle after the recovery rate is reduced; k is the recovery rate;

[0017] Third pendulum stability criterion: Set criterion S for the third pendulum. a ≤S b S a S is the acceleration area of ​​the third pendulum. b This represents the deceleration area of ​​the third pendulum.

[0018] ;

[0019] ;

[0020] in, To restore the electromagnetic power of the second pendulum to the corrected equivalent mechanical power after fault clearing at a slower recovery rate, the synchronous motor power angle is required. The synchronizing power angle at the end of the first pendulum stroke under a slower recovery rate;

[0021] Step 7: Based on the first stability criterion and the third pendulum stability criterion, determine the optimal active power recovery rate range for the new energy unit, wherein the optimal recovery rate range satisfies k min <k<k max The optimal recovery rate range must satisfy the following conditions: it must avoid both excessively fast recovery leading to S1>S2 causing initial swing instability, and excessively slow recovery leading to S... a >S b This caused the third swing to become unstable.

[0022] Preferably, the method for determining the optimal recovery rate interval in step seven is as follows: k max The solution is obtained from the stability criterion S1=S2 of the first pendulum; k min By the stability criterion S of the third pendulum a =S b The solution is obtained.

[0023] Preferably, it also includes a first pendulum angle stability criterion considering the overshoot during the active power recovery process of the new energy power station, specifically:

[0024] Make the overtuned surface S c1 =C1, from S1<S2- S c1 have to:

[0025] When the critical switching point is reached:

[0026] ;

[0027] When the machine power angle is switched earlier and the speed is recovered more quickly:

[0028] ;

[0029] Where C1 is a constant, The synchronous motor power angle is used to restore the electromagnetic power of the first pendulum to the corrected equivalent mechanical power after fault clearing under excessively fast recovery rate.

[0030] Preferably, it also includes a third pendulum angle stability criterion considering the overshoot during the active power recovery process of the new energy power station, specifically: let the overshoot surface S c2 =C2, when S a >S b - S c2 The third swing was unstable:

[0031] ;

[0032] Where C2 is a constant.

[0033] Preferably, in the third pendulum work angle stability criterion, the derivation and The specific method is as follows:

[0034] .

[0035] Preferably, the new energy power station is a wind farm or a photovoltaic power station, and the parameters of the injected current source include the current amplitude I. F With phase angle θ.

[0036] This invention provides a method for assessing the equivalent stability of renewable energy power plants. Based on the modeling concept of equating renewable energy power plants to injected current sources and converting them to the synchronous machine side, it achieves quantitative analysis of the transient stability of power systems containing renewable energy. This method, by deriving the corrected electromagnetic power expression for the synchronous machine after renewable energy integration, can reflect the impact of renewable energy active power recovery dynamics on the system power balance. Based on this, the constructed stability criterion covering the first and subsequent swings clarifies the quantitative relationship between the active power recovery rate and the stability of multiple swings. Furthermore, this method can ultimately output a safe range for the active power recovery rate of the system, thus providing a quantitative analytical method for tuning fault ride-through control parameters and assessing system stability at renewable energy power plants. Attached Figure Description

[0037] Appendix Figure 1This is a schematic diagram of a combined power plant system integrating a wind farm, provided in an embodiment of the present invention.

[0038] Appendix Figure 2 This is the equivalent circuit diagram of a wind farm connected to a dual-machine system after a fault, provided in an embodiment of the present invention.

[0039] Appendix Figure 3 This is a schematic diagram of a combined power plant system for wind farm integration after a fault, provided in an embodiment of the present invention.

[0040] Appendix Figure 4 This is the equivalent circuit diagram of a wind farm being integrated into a combined power plant system after a fault, provided in an embodiment of the present invention.

[0041] Appendix Figure 5 This is a schematic diagram of synchronous equivalent electromagnetic power recovery during the active power recovery period of a wind turbine, provided in an embodiment of the present invention.

[0042] Appendix Figure 6 This is a schematic diagram of the acceleration / deceleration area of ​​the first pendulum under the consideration of active recovery overshoot provided in an embodiment of the present invention.

[0043] in, Figure 2 Node 1 is the internal potential node of the synchronous generator; Node 2 is the grid connection point of the wind farm; Node 3 is the receiving-end large-scale system node; Detailed Implementation

[0044] To make the technical solution of the present invention easier to understand, a method for evaluating the equivalent stability of a new energy power station disclosed in the present invention will now be clearly and completely described in conjunction with embodiments and accompanying drawings.

[0045] A method for assessing the equivalent stability of new energy power plants is as follows:

[0046] like Figure 1 As shown, the synchronous generator is represented using a classical second-order model, and its internal potential is: A wind farm is considered a controlled "injected current source," with an output current of... The bus voltage of the infinite-voltage system at the receiving end is... Let the transient reactance of the synchronous generator (including the transformer) be jx. g The reactance of the transmission line is jx L The equivalent reactance of the receiving-end system (including the transformer) is jx s ;

[0047] like Figure 2 The equivalent circuit shown defines three nodes: node 1 (potential point within the synchronizing machine), node 2 (wind farm grid connection point), and node 3 (infinite bus system). The node voltage equations are established as follows:

[0048] ;

[0049] in, , , These are the injection currents at nodes 1 through 3, and Injecting current into wind power, , , These represent the node voltages of nodes 1 through 3. The elements of the admittance matrix are determined by the network parameters.

[0050] To simplify the system to an equivalent single-machine infinite (OMIB) model, nodes 2 and 3 need to be eliminated, retaining only node 1. That is, let , From the node voltage equation, the injected current at node 1 before connecting to the wind power source can be obtained: ; where Y 11 Y 22 Y 33 Y is the self-impedance of the coefficient matrix of the node voltage equation. 12 Y 21 Y 23 Y 32 The mutual impedance is the coefficient matrix of the node voltage equation.

[0051] After eliminating the wind power connection point and the receiving-end infinite system node, leaving only synchronous generator node 1, the injected current at the wind power connection node 1 is corrected as follows:

[0052] ;

[0053] in,

[0054] ;

[0055] To correct the current injected into node 1 after wind power is connected. To account for the current increment generated at the synchronous generator terminals by wind power, the electromagnetic power correction for the synchronous generator can be obtained as follows:

[0056] ;

[0057] Among them, P e This refers to the electromagnetic power of the synchronous motor when it is not connected to wind power. ΔP represents the electromagnetic power of the synchronous motor when connected to wind power and operating normally. e B is the increase in electromagnetic power of the synchronous machine after wind power is connected. impedance angle, The phase angle for injecting current into node 1. The phase angle at which the wind power generates an incremental current at the synchronous machine terminals.

[0058] like Figure 3 As shown, assuming a fault occurs on line 1 and is cleared, causing the line to be taken out of service, the circuit equivalent of the fault-prone structure is obtained as follows. Figure 4 The equivalent network shown here has the bookstore line reactance becoming... The node voltage equation after the fault is:

[0059] ;

[0060] Using the same elimination method, the corrected model of the injected current at node 1 after a fault, which is connected to wind power, is obtained:

[0061] ;

[0062] in, ; , , , The self-impedance and mutual impedance of the node voltage equations after a fault are given. , This refers to the current correction and increment generated at the synchronous machine terminals of the wind turbine after a fault.

[0063] The electromagnetic power of the synchronizer is as follows: (The value is missing from the original text.)

[0064] ;

[0065] in,, This refers to the electromagnetic power of the synchronizer moment after the fault is cleared. This refers to the electromagnetic power of the synchronous motor after a fault when wind power is not connected. This represents the instantaneous increase in the electromagnetic power of the synchronizing machine after the fault is cleared.

[0066] After the fault is cleared, as the wind turbine gradually returns to its normal active power output level, the current injected into the system by the wind turbine gradually decreases. Become ,Right now Gradually become The corrective electromagnetic power of the synchronizing machine from Gradually become ,in,

[0067] ;

[0068] angle( Let be the power angle between node 1 and the turbine injection current. This can be obtained by performing vector calculations on the system after the fault.

[0069] ;

[0070] angle( The value range of ) is (-90, 90°), and it is calculated... ,so( The range of values ​​for cos( ) is (90°, 270°). )<0. Similarly, cos( )<0.

[0071] Therefore, during the active power recovery process of the wind turbine, such as Figure 5 As shown, the corrected equivalent electromagnetic power will gradually return to the level when the wind turbine is at its normal output.

[0072] If the system is equivalent to an OMIB system, its modified equations of motion considering the influence of wind power are:

[0073] ;

[0074] in, , , These are the moment of inertia, mechanical power, and corrected equivalent mechanical power of the synchronous generator, respectively.

[0075] A small active power recovery rate in renewable energy units can make the first pendulum more stable, but it increases the risk of instability in the third pendulum. Therefore, this invention analyzes the impact of the recovery rate k on stability based on the equal area rule (EAC). The core lies in analyzing the changes in the acceleration and deceleration areas and establishing a stability criterion:

[0076] Stability criterion for the first swing: The acceleration area S1 during the fault is fixed, while the maximum deceleration area S2(k) after the fault is cleared varies with the recovery rate k. The condition for the stability of the first swing is that the acceleration area is not greater than the maximum deceleration area, i.e., S1≤S2.

[0077] in,

[0078] ;

[0079] Let S1 = S2, then we can solve for k (at this time, k is k). max ):

[0080] ;

[0081] Furthermore, when the machine cuts off the power angle earlier and recovers at a faster speed, the acceleration area and maximum deceleration area during the first swing are:

[0082] ;

[0083] ;

[0084] Depend on ,in , To determine the acceleration and deceleration areas at earlier start-up, the stability criterion for the first pendulum at the critical power angle at earlier start-up is obtained:

[0085] ;

[0086] To achieve a faster recovery rate during early turbine disconnection, in power systems with high wind power penetration, the active power recovery process of wind turbines is not an ideal zero-error step response. Influenced by their own control strategies (such as the dynamic characteristics of pitch control and torque control) and transient voltage fluctuations on the grid side, short-term overshoot often occurs after the active power output recovers to a set value. From the core analysis method of power angle stability derived above, wind turbine active power overshoot alters the equivalent mechanical power characteristics of the system during transient processes: the additional active power provided by the wind turbine during the overshoot phase directly affects the power balance relationship of the synchronous machine, causing changes in the acceleration or deceleration area compared to the scenario without overshoot, thereby affecting the swing trajectory and stability margin of the synchronous machine's power angle.

[0087] When the wind turbine recovers its active power output to the rated value at a certain recovery rate and then experiences overshoot for a short period of time, the impact on the stability of the initial swing is as follows: Figure 6 As shown. The maximum deceleration area decreases due to overshoot, thus reducing power angle stability, requiring a slower active power recovery rate to maintain power angle stability. The power angle stability condition for the first pendulum considering overshoot can be derived through formula derivation:

[0088] When the wind turbine recovers its active power output to the rated value at a certain recovery rate and then experiences overshoot for a short period of time, the impact on the stability of the initial swing is as follows: Figure 6 As shown. The maximum deceleration area decreases due to overshoot, thus reducing power angle stability, requiring a slower active power recovery rate to maintain power angle stability. The power angle stability condition for the first pendulum considering overshoot can be derived through formula derivation:

[0089] Make the overtuned surface S c1 =C1, from S1<S2- S c1 have to:

[0090] When the critical switching point is reached:

[0091] ;

[0092] When the machine power angle is switched earlier and the speed is recovered more quickly:

[0093] ;

[0094] Wherein, C1 is a constant, and its value ranges from 5% to 10% of the rated power of the synchronous machine; The synchronous motor power angle is used to restore the electromagnetic power of the first pendulum to the corrected equivalent mechanical power after fault clearing under excessively fast recovery rate.

[0095] Third pendulum stability criterion: While a slow recovery rate is beneficial for the stability of the initial pendulum swing, it may affect the stability of subsequent swings. Therefore, this invention focuses on the stability of the third pendulum swing and constructs a stability criterion for the third pendulum swing: S a ≥S b ;where S a S is the acceleration area of ​​the third pendulum. b This represents the deceleration area of ​​the third pendulum.

[0096] ;

[0097] ;

[0098] in, To restore the electromagnetic power of the second pendulum to the corrected equivalent mechanical power after fault clearing at a slower recovery rate, the synchronous motor power angle is required. The synchronizing power angle at the end of the first pendulum stroke under a slower recovery rate;

[0099] Depend on ;

[0100] Derivation and ;

[0101] Order: S a =S b Solving for k, we get k (at this point, k is k). min ):

[0102] ;

[0103] in: and Depend on All things can be uniquely determined by known quantities and can be expressed by known quantities.

[0104] According to the stability criteria of the first and third pendulums, the optimal active power recovery rate is k. min <k<k max .

[0105] Similarly, when considering the overshoot when the wind turbine resumes its active power output, the adjustment for the stability of the third pendulum angle is as follows:

[0106] Make the overtuned surface S c2 =C2, when S a >S b - S c2 The third swing was unstable:

[0107] ;

[0108] Where C2 is a constant.

[0109] It should be noted that for those skilled in the art, several improvements, substitutions, modifications and refinements can be made without departing from the principles and spirit of this invention, and these improvements, substitutions, modifications and refinements should also be considered within the scope of protection of this invention.

Claims

1. A method for evaluating the equivalent stability of a new energy power station, characterized in that, The method is specifically as follows: Step 1: Establish a multi-node power network model including synchronous generator nodes, new energy power station grid connection nodes, and receiving-end infinite bus system nodes, wherein the new energy power station is equivalent to an injected current source; Step 2: Based on the nodal voltage equations, the grid-connected nodes of the renewable energy power station and the receiving-end infinite bus system nodes are eliminated using the elimination method, leaving only the synchronous generator nodes. This yields the injection current correction model for the synchronous generator after it is connected to the renewable energy power station. The injection current correction model is as follows: ;in, This refers to the injection current of the synchronous generator when it is not connected to the new energy power station. This refers to the current increment generated at the synchronous machine terminals of the new energy power station; Step 3: Based on the injected current correction model, derive the electromagnetic power correction formula for the synchronous machine under normal operating conditions: Among them, P e This refers to the electromagnetic power of the synchronous motor when it is not connected to the new energy power station. The electromagnetic power of the synchronous machine when connected to a new energy power station and operating normally, ΔP e The electromagnetic power increment of the synchronous generator after connection to the new energy power station is denoted by δ, where δ is the power angle of the synchronous generator and E1 is the internal electromotive force of the synchronous generator. The phase angle for injecting current into the synchronous generator node. The phase angle that generates the current increment on the synchronous generator of the new energy power station; Step 4: Simulate a transmission line fault in the system and disconnect the faulty component. At this point, the transmission line reactance is updated to... Repeat the elimination process described in step two to obtain the injection current correction model of the synchronous generator after the fault: ,in, , The current correction and increment generated at the synchronous motor terminals by wind power after a fault are calculated; therefore, the electromagnetic power correction formula for the synchronous motor instantaneously after the fault is cleared is derived: ,in, This refers to the electromagnetic power of the synchronizer moment after the fault is cleared. This refers to the electromagnetic power of the synchronous motor after a fault when wind power is not connected. This represents the instantaneous increase in the electromagnetic power of the synchronizing machine after the fault is cleared. Step 5: During the active power recovery process of the renewable energy units after fault clearance, the current injected into the system by the renewable energy units is... Become The corrective electromagnetic power of the synchronizing machine from Gradually become Based on this dynamic process, the corrected motion equations for the equivalent OMIB system are established: Among them, M, , These are the moment of inertia, mechanical power, and corrected equivalent mechanical power of the synchronous generator, respectively. Step Six: Based on the electromagnetic power correction formula and the equivalent OMIB system correction equation, analyze the impact of the active power recovery rate of the new energy unit on the stability of the synchronous machine's multi-pendulum power angle, and establish the stability criteria for the first pendulum and the third pendulum: First stability criterion: S1≤S2, where S1 is the acceleration area during the first swing process at the critical cutting angle, and S2 is the maximum deceleration area during the first swing process at the critical cutting angle. ； in, The synchronous motor power angle at the moment the fault begins. To cut off the synchronous motor power angle during a fault; Y 12 D' is the mutual impedance of the coefficient matrix of the node voltage equation; D' is the equivalent self-admittance after elimination; B' is... The impedance angle; ； in, The synchronous motor power angle at the critical moment of instability. To reduce the synchronous motor power angle after the recovery rate is reduced; k is the recovery rate; Third pendulum stability criterion: Set criterion S for the third pendulum. a ≤S b S a S is the acceleration area of ​​the third pendulum. b This represents the deceleration area of ​​the third pendulum. ； ； in, To restore the electromagnetic power of the second pendulum to the corrected equivalent mechanical power after fault clearing at a slower recovery rate, the synchronous motor power angle is required. The synchronizing power angle at the end of the first pendulum stroke under a slower recovery rate; Step 7: Based on the first stability criterion and the third pendulum stability criterion, determine the optimal active power recovery rate range for the new energy unit, wherein the optimal recovery rate range satisfies k min <k<k max .

2. The method for equivalent stability assessment of a new energy power station as described in claim 1, characterized in that, The method for determining the optimal recovery rate interval in step seven is as follows: k max The solution is obtained from the stability criterion S1=S2 of the first pendulum; k min By the stability criterion S of the third pendulum a =S b The solution is obtained.

3. The method for equivalent stability assessment of a new energy power station as described in claim 1, characterized in that, It also includes a stability criterion for the first pendulum angle considering overshoot during the active power recovery process of the aforementioned new energy power station, specifically: Make the overtuned surface S c1 =C1, from S1<S2- S c1 have to: When the critical switching point is reached: ； When the machine power angle is switched earlier and the speed is recovered more quickly: ； Where C1 is a constant, The synchronous motor power angle is used to restore the electromagnetic power of the first pendulum to the corrected equivalent mechanical power after fault clearing under excessively fast recovery rate.

4. The method for equivalent stability assessment of a new energy power station as described in claim 1, characterized in that, It also includes a third pendulum angle stability criterion considering the overshoot during the active power recovery process of the new energy power station, specifically: let the overshoot surface S c2 =C2, when S a >S b - S c2 The third swing was unstable: ； Where C2 is a constant.

5. The method for equivalent stability assessment of a new energy power station as described in claim 1, characterized in that, In the third pendulum work angle stability criterion, the derivation and The specific method is as follows: 。 6. The method for equivalent stability assessment of a new energy power station as described in claim 1, characterized in that, The new energy power station is a wind farm or a photovoltaic power station, and the parameters of the injected current source include the current amplitude I. F With phase angle θ.

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