A method and system for transient power angle stability discrimination of a distributed phase modifier

Abstract

The application discloses a kind of distributed phase modifier transient power angle stability discrimination method and system, it is related to distributed phase modifier technical field, the method includes: considering the control switching process in the process of new energy failure, determine the power angle characteristics of phase modifier under different fault types after failure and during failure;System energy function is constructed based on the power angle characteristics of the phase modifier;The stability margin of the power angle of the phase modifier is calculated based on the system energy function;The critical cut-off angle of system power angle stability is determined based on the power angle stability margin of the phase modifier;In the limit cut-off time, the transient power angle stability of the phase modifier is discriminated based on the critical cut-off angle of system power angle stability.The application considers new energy control switching when discriminating the transient power angle stability of the phase modifier, improves the accuracy of discrimination, compared with existing time-domain simulation method, greatly reduce the amount of calculation.

Description

Technical Field

[0001] This invention relates to the field of distributed synchronous condenser technology, and in particular to a method and system for determining the transient power angle stability of a distributed synchronous condenser considering the switching of new energy sources. Background Technology

[0002] To address the transient overvoltage problem in renewable energy sources, distributed synchronous condensers (DCCs) have been applied in renewable energy power plants. However, the large-scale integration of renewable energy sources poses a risk of power angle instability to DCCs installed in these plants after system failures. Therefore, it is urgent to study transient power angle stability analysis methods for DCCs and to reveal their transient power angle stability mechanism.

[0003] Existing methods for analyzing the transient power angle stability of distributed synchronous condensers often simplify the network by eliminating nodes or making equivalent changes to the circuit, failing to consider the voltage characteristics at the renewable energy grid connection point. However, the voltage at the renewable energy grid connection point directly affects the switching of its control strategy. Without considering the switching of renewable energy control strategies, the transient power angle stability of the system cannot be determined. Summary of the Invention

[0004] Based on this, the purpose of this invention is to provide a method and system for determining the transient power angle stability of a distributed synchronous condenser that takes into account the switching of new energy sources, thereby improving the accuracy of transient power angle stability determination.

[0005] To achieve the above objectives, the present invention provides the following solution:

[0006] A method for determining the transient power angle stability of a distributed synchronous condenser includes:

[0007] Considering the control switching process during new energy failure, determine the camera power angle reduction characteristics for different failure types after and during the failure.

[0008] Construct the system energy function based on the power angle characteristics of the camera adjuster;

[0009] Calculate the stability margin of the synchronous condenser's power angle based on the system energy function;

[0010] The critical cut-off angle for system power angle stability is determined based on the power angle stability margin of the synchronous condenser.

[0011] By setting a limit cut-off time, the transient power angle stability of the synchronous condenser is determined based on the critical cut-off angle for system power angle stability.

[0012] To achieve the above objectives, the present invention also provides the following solution:

[0013] A distributed synchronous condenser transient power angle stability determination system includes:

[0014] The module for determining the power angle characteristics of the condenser is used to consider the control switching process during the fault process of new energy, and to determine the power angle characteristics of the condenser under different fault types after and during the fault.

[0015] The system energy function construction module is used to construct the system energy function based on the power angle characteristics of the condenser.

[0016] The synchronous condenser angle stability margin calculation module is used to calculate the synchronous condenser angle stability margin based on the system energy function.

[0017] The system power angle stability critical cut-off angle determination module is used to determine the system power angle stability critical cut-off angle based on the synchronous condenser's power angle stability margin.

[0018] The discrimination module is used to determine the transient power angle stability of the synchronous condenser based on the critical cut-off angle for system power angle stability at a set limit cut-off time.

[0019] According to specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0020] This invention first considers the control switching process during renewable energy source failures, analyzing the reduced camera power angle characteristics under different failure types after and during the failure. Second, based on the camera power angle characteristics, a system energy function is constructed to obtain the camera power angle stability margin expression. Then, the transient power angle stability margin of the camera is calculated, and the limiting cutoff angle is obtained. Finally, a distributed camera transient power angle stability discrimination method is proposed, determining whether the camera will experience power angle instability at a set limiting cutoff time. This invention considers renewable energy source control switching when discriminating the transient power angle stability of the camera, improving the accuracy of the discrimination and significantly reducing the computational load compared to existing time-domain simulation methods. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 A flowchart of the distributed synchronous condenser transient power angle stability determination method provided in this invention;

[0023] Figure 2 The overall flowchart of the distributed synchronous condenser transient power angle stability discrimination method provided by the present invention;

[0024] Figure 3 A schematic diagram of a new energy transmission system model including a synchronous condenser;

[0025] Figure 4 A schematic diagram for solving the critical cut-off angle of a distributed synchronous condenser;

[0026] Figure 5 For distributed synchronous condensers δ c Solution diagram. Detailed Implementation

[0027] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] The purpose of this invention is to provide a method and system for determining the transient power angle stability of a distributed synchronous condenser that takes into account the switching of new energy sources, thereby improving the accuracy of transient power angle stability determination.

[0029] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0030] Example 1

[0031] like Figures 1-2 As shown, the distributed synchronous condenser transient power angle stability determination method provided by the present invention includes the following steps:

[0032] S1: Consider the control switching process during the new energy failure process, and determine the camera power angle characteristics to be adjusted according to different failure types after and during the failure.

[0033] S2: Construct a system energy function based on the power angle characteristics of the synchronous condenser; the system energy function includes the system energy function after the fault and the energy function during the fault.

[0034] S3: Calculate the power angle stability margin of the condenser based on the system energy function.

[0035] S4: Determine the critical cut-off angle for system power angle stability based on the power angle stability margin of the condenser.

[0036] S5: At the set limit cut-off time, the transient power angle stability of the synchronous condenser is determined based on the critical cut-off angle for system power angle stability.

[0037] Furthermore, step S1 specifically includes:

[0038] To address the transient power angle stability problem of distributed synchronous condensers, a new energy transmission system via AC lines is established, such as... Figure 3As shown. Obtain the rotor inertia time constant T of the synchronous condenser. J Adjusting the camera transient reactance X d 'With transformer reactance X T Their sum is X sc Adjust the internal potential E of the camera sc The internal potential E of the receiving end system s Obtain the sum of the system transformer reactance and the line reactance, X. L (X L =X L1 +0.5X L2 +X L3 ), Active current output of new energy source I wp With reactive current I wq New energy active power control parameter K p2 Reactive power control parameter K q1 .

[0039] Figure 2 In the middle, δ s For the rotor angle, δ sc To adjust the relative position angle of the rotor between the camera and the receiving-end system, U b δ represents the voltage amplitude at the wind turbine's grid connection point. b The voltage at the grid connection point and the relative angle between the voltage and the system are the following parameters. To adjust the camera's output current, To adjust the camera output current This represents the total line current. At the sending end of the system, the current emitted by the synchronous condenser will be... along as well as Normal decomposition into active current Its amplitude is I scp reactive current

[0040] (1) Dynamic characteristics of distributed synchronous condensers after a fault

[0041] Taking the voltage at point b as a reference, i.e., δ s =-δ b At this point, the relative angle between the synchronous condenser rotor angle and the voltage at point b is defined as Δδ. sc Then we have Δδ sc =δ sc -δ b At this time, the active current emitted by the synchronous condenser is:

[0042]

[0043] Suppose that the synchronous condenser injects reactive current I into node b. scq In the positive direction, that is, when node b sends reactive current to the synchronous condenser, I scqSince the value is negative, the reactive current injected by the synchronous condenser into node b is:

[0044]

[0045] At the receiving end of the system, the total current It can be decomposed into reactive current. active current Its amplitude is I w +I scp .

[0046] First, consider that new energy sources only generate active current, that is... and In phase, according to phasor relations, we can obtain:

[0047]

[0048] U b =E s cosδ b +I scq X L (4)

[0049] If we consider that new energy sources also generate reactive power, then the current will be... along as well as Normal decomposition into active current Its amplitude is I wp reactive current Its amplitude is I wq Equation (4) can then be updated to:

[0050] U b =E s cosδ b +(I scq +I wq )X L (5)

[0051] Substituting equation (1) into equation (3) and replacing I with Iwp, we get:

[0052]

[0053] Substituting equation (2) into equation (5), we get:

[0054]

[0055] After sorting, we can get U b expression:

[0056]

[0057] Based on the camera's output power:

[0058]

[0059] Then we can obtain P sc The expression is:

[0060]

[0061] in:

[0062]

[0063] sinδ b Approximately δ b sinΔδ sc Approximately Δδ sc Then we can obtain:

[0064]

[0065] δ sc When it changes, we can obtain P. sc The expression is:

[0066]

[0067] set up

[0068]

[0069] Then we can obtain

[0070] P sc =k1cos(cδ) sc +d)sin(aδ sc +b)+k2sin(2aδ sc +2b)+k3sin(aδ sc +b) (15)

[0071] (2) Dynamic characteristics of distributed synchronous condensers during faults

[0072] Suppose a fault occurs at the beginning of line L2. Since the faulty renewable energy source has switched to low-voltage ride-through control, during the fault period X... L for:

[0073]

[0074] In the formula, X Δ Additional impedance for asymmetrical short circuit, single-phase short circuit X Δ(1) Two-phase short circuit X Δ(2) Two-phase short-circuit ground X Δ(20) The additional impedances are as follows:

[0075]

[0076] Furthermore, the control equation for the new energy source to enter the low-voltage ride-through phase during the fault is as follows:

[0077] I wpf =K p1 U b +K p2 I wp (18)

[0078] I wqf =K q1 (0.9-U b )+K q2 I wq (19)

[0079] In the formula, K p1 K p2 K is the active current control coefficient. q1 K q2 This is the reactive current control coefficient. In practical engineering, K is usually considered. p1 =0, and reactive power priority control is adopted, that is, when the total output current reaches the upper limit, the active current is reduced so that the reactive current satisfies equation (19).

[0080] Based on the previous derivation, equation (8) can be simplified to:

[0081]

[0082] Substituting into the reactive power formula for wind turbines, we can obtain...

[0083]

[0084] In the formula, e = X sc E s / (X sc +X L ), g = X L E sc / (X sc +X L h = X L X sc / (X sc +X L ), which can be solved to obtain:

[0085]

[0086] Similarly, substitute equation (18) into the expressions b and d of equation (14) to replace the original I. wp The expression can be obtained as:

[0087]

[0088] Substituting equation (22) into equation (9), we obtain the expression for the synchronous condenser power angle characteristic during the fault period when the wind power enters the low voltage ride-through control state:

[0089]

[0090] As can be seen from equation (24), compared with equation (15), the reactive component of the wind turbine causes changes in k1, k2, and k3, while the active component causes changes in b and d.

[0091] Furthermore, step S2 specifically includes:

[0092] The energy functions after and during the fault of the synchronous condenser are constructed using equations (15) and (24) respectively. The system potential energy is obtained by integrating equation (15), and the system kinetic energy is obtained by integrating equation (24).

[0093] During steady-state operation, the synchronous condenser does not output active power, meaning Esc and Ub are in phase. According to the system phasor relationship, at this time, we have: sinδ b =I w X L / E s sinδ b Approximately δ b Then we can obtain:

[0094]

[0095] In the formula, δ scs To adjust the rotor's relative position angle when the camera is in steady state, then for any position after the fault, δ sc The potential energy of the corresponding system is:

[0096]

[0097] Among them, W sc Let W be the potential energy function. sc |δ sc For δ sc The system potential energy function value at the equilibrium point. Substituting equation (25) into equation (26), we can obtain the system potential energy function value at the equilibrium point as: W sc |δ scs :

[0098]

[0099] Therefore, the energy function can be obtained as follows:

[0100]

[0101]

[0102] In the formula V k (ωsc V represents the kinetic energy of the phase converter rotor. p (δ sc ) represents the system's potential energy.

[0103] At the time of fault clearing, the total system energy is:

[0104]

[0105] In the formula, δ scc The relative angle between the synchronous condenser and the system at the moment of fault clearing, ω scc Adjust the relative angular velocity of the camera rotor at the moment of fault clearing.

[0106] After the fault ends, the total energy in the system remains unchanged (considering the energy dissipated by system damping, the system eventually returns to steady state), that is, the system after the fault has:

[0107] V P (δ scc )+V K (ω scc ) = V P (δ sc )+V K (ω sc (31)

[0108] If the system absorbs all the energy accumulated during the synchronous condenser malfunction after the fault is cleared: kinetic energy V k (ω scc )+potential energy V p (δ scc The maximum potential energy V was not reached. p (δ scu If the system remains stable, then the power angle will remain stable; otherwise, power angle instability will occur.

[0109] Note: The energy function is the basis for the transient stability margin in the technical solution.

[0110] Further calculations were performed on the total system energy during the failure.

[0111]

[0112] In the formula, when the fragrance rotor is at δ sc At this point, the system potential energy function value is:

[0113]

[0114] Substituting equation (25) into equation (33), we get W scf |δ scs , will δ scc Substituting into equation (33), we can obtain W. scf |δ sccThen, the total kinetic energy V obtained by the synchronous condenser during the fault period can be obtained by equation (32). k (ω scc ). δ scc Substituting into equation (26) yields V. p (δ scc ).

[0115] Furthermore, steps S3-S4 specifically include:

[0116] For the fault clearing angle δ scc The transient stability margin expression can be obtained by subtracting the total energy of the system at the time of fault clearance from the maximum potential energy of the system after the fault.

[0117] η(δ scc ) = V P (δ scu )-V K (ω scc )-V P (δ scc (34)

[0118] like Figure 4 As shown, when η(δ) scc When δ = 0, the system reaches the stability boundary, and at this point δ scc The critical cutoff angle for system power angle stability, i.e., δ sclim .

[0119] Furthermore, step S5 specifically includes:

[0120] According to the "Technical Guidelines for Power Systems" (GB / T38969-2020), the system fault clearing time t is determined based on different fault locations. c At this point, according to the equation of motion of the synchronous condenser rotor:

[0121]

[0122] In the formula, δ sc The relative position angle of the rotors between the adjusting camera and the receiving end system is given by t, where t is time, ω is the electrical angular velocity of the adjusting camera rotor, and ω0 is the rated electrical angular velocity of the system, all in rad / s. J To adjust the camera's inertial time constant, the dimension is s; P m The power of the prime mover is approximately zero, P. scf denoted as the active power output of the synchronous condenser during a fault, expressed in per-unit values; D is the damping coefficient of the synchronous condenser.

[0123] Set the initial value of ω to ω0, and δ sc The initial value is δ scs Starting from t=0, the improved Euler method (35) is used to calculate until t cAt the end of the time (the fault end time required by the standard), the calculation result δ is obtained. sc (t c ), denoted as δ c ,like Figure 5 As shown.

[0124] Compare δ c With δ sclim If δ c Less than δ sclim In this scenario, adjusting the camera's angle of attack will stabilize the scene. If δ c Less than δ sclim In this scenario, adjusting the camera's power angle will cause instability.

[0125] Example 2

[0126] In order to implement the method corresponding to Embodiment 1 above and achieve the corresponding functions and technical effects, a distributed synchronous condenser transient power angle stability discrimination system is provided below.

[0127] The system includes:

[0128] The module for determining the power angle characteristics of the condenser is used to consider the control switching process during the fault process of new energy, and to determine the power angle characteristics of the condenser for different fault types after and during the fault.

[0129] The system energy function construction module is used to construct the system energy function based on the power angle characteristics of the condenser.

[0130] The synchronous condenser power angle stability margin calculation module is used to calculate the synchronous condenser power angle stability margin based on the system energy function.

[0131] The system power angle stability critical cut-off angle determination module is used to determine the system power angle stability critical cut-off angle based on the power angle stability margin of the condenser.

[0132] The discrimination module is used to discriminate the transient power angle stability of the synchronous condenser based on the critical cut-off angle for system power angle stability at a set limit cut-off time.

[0133] Furthermore, the discrimination module specifically includes:

[0134] The synchronous condenser rotor motion equation acquisition unit is used to acquire the synchronous condenser rotor motion equation.

[0135] The calculation unit is used to calculate the fault clearing angle up to the set limit clearing time based on the motion equation of the synchronous condenser rotor using the improved Euler method.

[0136] The first discrimination unit is used to determine the transient power angle stability of the synchronous condenser when the fault clearing angle at the set limit clearing time is less than the critical clearing angle for system power angle stability.

[0137] The second discrimination unit is used to determine the transient power angle instability of the synchronous condenser when the critical cut-off angle for system power angle stability is less than the fault cut-off angle at the set limit cut-off time.

[0138] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the systems disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the descriptions are relatively simple; relevant parts can be referred to the method section.

[0139] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. Furthermore, those skilled in the art will recognize that, based on the ideas of the present invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A method for determining the transient power angle stability of a distributed synchronous condenser, characterized in that, include: Considering the control switching process during new energy failure, determine the camera power angle reduction characteristics for different failure types after and during the failure. A system energy function is constructed based on the power angle characteristics of the synchronous condenser; the system energy function includes the system energy function after the fault and the energy function during the fault. Calculate the stability margin of the synchronous condenser's power angle based on the system energy function; The critical cut-off angle for system power angle stability is determined based on the power angle stability margin of the synchronous condenser. At a set limit cut-off time, the transient power angle stability of the synchronous condenser is determined based on the critical cut-off angle for system power angle stability; specifically, this includes: obtaining the synchronous condenser rotor motion equation; Based on the rotor motion equation of the synchronous condenser, the fault clearing angle at the set limit clearing time is calculated using the improved Euler method. When the fault clearing angle at the set limit clearing time is less than the critical clearing angle for system power angle stability, the transient power angle of the synchronous condenser is determined to be stable. When the critical clearing angle for system power angle stability is less than the fault clearing angle at the set limit clearing time, the transient power angle of the synchronous condenser is determined to be unstable.

2. The distributed synchronous condenser transient power angle stability determination method according to claim 1, characterized in that, The expression for the power angle characteristic of the adjusting camera after a fault is: Among them, P sc To adjust the camera's output power, δ sc To adjust the relative position angle of the rotor between the camera and the receiving system, a, b, c, k1, k2, and k3 are all intermediate variables; E s E is the internal potential of the receiving-end system. sc To adjust the internal potential of the camera, X L X is the sum of the system transformer reactance and the line reactance. sc I is the sum of the transient reactance of the synchronous condenser and the reactance of the transformer. wp I wq These are the active current and reactive current output from new energy sources, respectively. The expression for the synchronous condenser's power angle characteristic during a fault is: e=X sc E s / (X sc +X L ),g=X L E sc / (X sc +X L ),h=X L X sc / (X sc +X L ) Among them, P scf E is the active power output of the synchronous condenser during a fault. sc To adjust the internal potential of the camera, K q1 K q2 I is the reactive current control coefficient. wq The reactive current output during the steady-state operation of the new energy source is given by g, h, e, and d. f b f All are intermediate variables.

3. The distributed synchronous condenser transient power angle stability determination method according to claim 2, characterized in that, The expression for the system energy function after a fault is: The expression for the energy function during a fault is: in, This represents the system potential energy after the fault is cleared. The kinetic energy of the synchronous condenser rotor after the fault is cleared, δ scc For fault clearing angle, ω scc Adjust the relative angular velocity of the camera rotor at the moment of fault clearing. For the system potential energy, To adjust the kinetic energy of the camera rotor, To adjust the relative angular velocity of the rotor during camera transients, ω sc To adjust the relative angular velocity of the rotor during the transient state of the camera, δ scs To adjust the relative position angle of the rotor when the camera is in steady state, Equilibrium point δ scs The value of the system's potential energy function. Equilibrium point δ scs The value of the system's potential energy function.

4. The distributed synchronous condenser transient power angle stability determination method according to claim 1, characterized in that, The expression for the stability margin of the synchronous condenser's power angle is: in, To adjust the camera's power angle stability margin, δ scc For fault removal angle, This represents the maximum potential energy of the system after the fault. To adjust the kinetic energy of the camera rotor after the fault is cleared. This represents the system potential energy after the fault is cleared. The relative power angle between the camera and the system after a fault, δ scc For fault clearing angle, ω scc Adjust the relative angular velocity of the camera rotor at the moment of fault clearing.

5. The distributed synchronous condenser transient power angle stability determination method according to claim 1, characterized in that, The expression for the motion equation of the synchronous condenser rotor is as follows: Where, δ sc The relative position angle of the rotors between the adjusting camera and the receiving end system is given by t, where t is time, ω is the electrical angular velocity of the adjusting camera rotor, and ω0 is the rated electrical angular velocity of the system. J To adjust the camera's inertial time constant, P m P is the power of the prime mover. scf D is the active power output of the synchronous condenser during the fault period, and D is the damping coefficient of the synchronous condenser.

6. A distributed synchronous condenser transient power angle stability discrimination system, characterized in that, include: The module for determining the power angle characteristics of the condenser is used to consider the control switching process during the fault process of new energy, and to determine the power angle characteristics of the condenser under different fault types after and during the fault. The system energy function construction module is used to construct the system energy function based on the power angle characteristics of the condenser. The synchronous condenser angle stability margin calculation module is used to calculate the synchronous condenser angle stability margin based on the system energy function. The system power angle stability critical cut-off angle determination module is used to determine the system power angle stability critical cut-off angle based on the synchronous condenser's power angle stability margin. The discrimination module is used to discriminate the transient power angle stability of the synchronous condenser based on the critical cut-off angle for system power angle stability at a set limit cut-off time. The discrimination module specifically includes: The synchronous condenser rotor motion equation acquisition unit is used to acquire the synchronous condenser rotor motion equation. The calculation unit is used to calculate the fault clearing angle up to the set limit clearing time based on the motion equation of the synchronous condenser rotor using the improved Euler method. The first discrimination unit is used to determine the transient power angle stability of the synchronous condenser when the fault clearing angle at the set limit clearing time is less than the critical clearing angle for system power angle stability. The second discrimination unit is used to determine the transient power angle instability of the synchronous condenser when the critical cut-off angle for system power angle stability is less than the fault cut-off angle at the set limit cut-off time.

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