Method and system for matching capacity of new energy stations and networks considering transient overvoltage

Abstract

The present invention proposes a method and system for allocating the capacity of new energy stations to the grid considering transient overvoltage, which belongs to the technical field of calculation of grid capacity, including: simplifying the grid-connected hybrid station to obtain an equivalent model; calculating the initial value of the grid-connected ratio of each station based on the obtained equivalent model; calculating the stability condition of the phase-locked loop; when configuring the grid-connected converter according to the calculated initial value of the grid-connected ratio for any station, judging whether the phase-locked loop can remain stable after encountering a three-phase short circuit fault based on the stability condition of the phase-locked loop, and calculating the transient overvoltage of the station if it is unstable; when the transient overvoltage is lower than the safety threshold, maintaining the initial value of the grid-connected ratio; when the requirements are not met, deriving the grid-connected capacity ratio expression that meets the transient overvoltage constraint, and correcting the grid-connected ratio of the station to obtain the grid-connected capacity ratio and the grid-connected capacity ratio in any station.

Description

Technical Field

[0001] The present invention belongs to the technical field of grid capacity calculation, and in particular relates to a method and system for allocating capacity of new energy stations and grids considering transient overvoltage. Background Art

[0002] The statements in this section merely provide background information related to the present invention and do not necessarily constitute prior art.

[0003] New energy stations, which are facilities that generate electricity using renewable energy sources (such as wind, solar, hydro, and biomass), are a crucial component of driving energy transition. Renewable energy sources, such as wind and photovoltaics, have gradually shifted from incremental supplementary sources to primary power sources. In recent years, the combined installed capacity of wind and solar power has surpassed that of thermal power for the first time. This transformation is driving a fundamental restructuring of the power system, resulting in the emergence of a new power system characterized by a high proportion of renewable energy and power electronics.

[0004] The proportion of synchronous generators in new power systems has gradually decreased, significantly reducing their voltage support capabilities. Currently, the widely used grid-following (GFL) converters rely on phase-locked loops (PLLs) to achieve synchronous operation with the grid. PLLs are at risk of instability under low voltage conditions, and the grid-following converters lack the ability to actively support grid voltage, further worsening the transient voltage stability of the power system. The lack of voltage support capabilities at new energy stations has led to an increasing risk of a sharp increase in transient overvoltage when the system encounters a fault, which has become one of the key obstacles to the efficient absorption of new energy.

[0005] Grid-forming (GFM) control is gradually maturing. It can independently construct voltage and frequency, and has stronger stability under weak grid conditions. Grid-forming and grid-following control are beneficial for ensuring system voltage stability. However, the introduction of grid-forming makes the coupling characteristics of hybrid stations more complex, PLL stability is not easy to directly judge, and transient overvoltage is difficult to quantitatively evaluate. In addition, grid-forming converters are relatively expensive. For economic reasons, the grid-forming capacity ratio should be reduced as much as possible while meeting stability requirements. Therefore, solving the grid-following capacity ratio of each station in the renewable energy transmission system under the constraint of transient overvoltage is challenging.

[0006] During the research, the inventors discovered that the prior art discloses a technical solution for quantifying transient overvoltages in a new energy sending-end system. Under commutation failure, an equivalent circuit model of the sending-end system is constructed, including an LCC-HVDC DC system, a new energy unit, and an equivalent AC system at the sending end. Based on the equivalent circuit model of the sending-end system and the common coupling point, the node voltage equation is written to derive a voltage calculation formula at the common coupling point containing DC current and rectifier device advance trigger angle variables. The inverter turn-off angle is fitted, and the DC current and advance trigger angle of the DC system during the commutation failure are analyzed in stages to determine the time domain expression of the voltage amplitude under commutation failure. The partial derivative is calculated based on the time domain expression to obtain the maximum overvoltage moment and the maximum overvoltage value, and the transient overvoltage of the sending-end system under commutation failure is quantified. At this time, the dynamic coupling between the new energy and the DC system is accurately characterized, which can be applied to the quantification of transient overvoltages in the current DC transmission scenario of new energy stations.

[0007] The above scheme is a fully grid-following transmission system and does not consider the voltage support role of the grid-connected converter. Furthermore, the proposed method is only applicable to the analysis of commutation failure in DC transmission systems and cannot quantitatively assess transient overvoltages during short-circuit faults within the system.

[0008] In addition, the existing patent also discloses a grid power capacity configuration optimization scheme, which is based on the constraints of new energy grid connection stability, associates the corresponding technical indicators of the grid power supply, estimates and gives the initial configuration capacity of the grid power supply; selects the grid power access location as the high-voltage side and low-voltage side of the new energy station step-up transformer; verifies whether the grid power supply meets the constraint requirements based on the short-circuit ratio constraints of the new energy machine end and the grid connection point, the static safety constraints, and the transient stability constraints. If not, the access capacity is adjusted; if it is satisfied, the cost required for the current capacity is calculated based on the comprehensive unit price; compares the total cost of the corresponding capacity of the two access locations, and selects the economically optimal as the final configuration capacity.

[0009] The above scheme only proposes the constraints of the grid-type configuration, but does not propose an effective evaluation method for transient overvoltage. It cannot take into account the output characteristics of the grid-type converter and the PLL stability. The configured grid-type power supply capacity may not meet the transient overvoltage constraints under the condition of PLL instability. Summary of the Invention

[0010] To overcome the deficiencies of the above-mentioned prior art, the present invention provides a method for matching the capacity of new energy stations and grid-connected converters taking transient overvoltage into consideration, which is used to calculate the minimum capacity configuration of the grid-connected converters in the station under the condition of transient overvoltage constraints.

[0011] To achieve the above objectives, one or more embodiments of the present invention provide the following technical solutions:

[0012] First, a method for allocating the capacity of new energy stations to the grid considering transient overvoltage is disclosed, including:

[0013] Simplify the hybrid network station to obtain an equivalent model;

[0014] Based on the obtained equivalent model, the initial value of the grid ratio of each station is calculated;

[0015] Find the stability condition of the unlocking phase loop;

[0016] When configuring the grid-type converter at any station according to the calculated initial value of the grid-type ratio, the phase-locked loop stability condition is used to determine whether the phase-locked loop can remain stable after encountering a three-phase short-circuit fault. If it is unstable, the transient overvoltage of the station is calculated.

[0017] When the transient overvoltage is lower than the safety threshold U safe When the initial value of the grid-forming capacity ratio is maintained; when the requirements are not met, the grid-forming capacity ratio expression that meets the transient overvoltage constraint is derived, and the grid-forming capacity ratio of the station is corrected to obtain the grid-forming capacity ratio and the grid-following capacity ratio in any station.

[0018] As a further technical solution, the equivalent model is obtained by simplifying the hybrid network station, specifically including:

[0019] Modeling of the off-site topology of the renewable energy transmission system;

[0020] Modeling of internal converters in renewable energy transmission system stations;

[0021] Modeling of hybrid stations in the follow-up network;

[0022] Make assumptions about the series-parallel model;

[0023] Based on the above process, an equivalent model is obtained.

[0024] As a further technical solution, the following assumptions are made for the hybrid model:

[0025] Both grid-following and grid-forming converters switch to the low-throughput state during a fault, and enter the low-throughput recovery state after the fault is cleared;

[0026] The control mode delay after the fault occurs and clears is negligible;

[0027] During the fault period, the current loop adjustment process can be ignored when the phase-locked loop is used, and it is considered that the current loop has reached the command value;

[0028] The power angle of the grid-connected converter during the fault period is equal to the steady-state value before the fault.

[0029] As a further technical solution, the initial value of the grid ratio of each station is calculated based on the equivalent model obtained, including:

[0030] According to the simplified model of hybrid stations and the circuit superposition theorem, the grid connection point voltage of station i can be obtained;

[0031] Calculate the capacity ratio of a single station to the grid based on the grid connection point voltage of station i:

[0032] Calculate the initial value of the capacity ratio of each station and network based on the capacity ratio of a single station and network.

[0033] As a further technical solution, the capacity ratio of a single station to the network is calculated based on the grid connection point voltage of station i, specifically:

[0034] Calculate the capacity ratio of grid-connected converters based on the requirement of ensuring that the units do not go offline ;

[0035] Calculate the capacity ratio of grid-connected converters based on transient overvoltage constraints ;

[0036] When configuring the site network ratio, It should also be ensured that the new energy units do not disconnect from the grid during the fault and that the transient overvoltage is lower than the safety threshold after the fault is cleared.

[0037] As a further technical solution, it is possible to determine whether the PLL is unstable and calculate the transient overvoltage of the station. The calculation process is as follows:

[0038] Calculate the phase-lock angle error: Substitute the calculated PLL output phase angle into the phase angle expression to obtain the phase-lock angle error.

[0039] Based on the phase-locked angle error, the current loop output current before the fault is cleared, the grid-following output current and the internal impedance of the grid, the voltage amplitude expression is substituted to obtain the transient overvoltage calculation formula of station i.

[0040] Secondly, a capacity matching system for new energy stations and grids considering transient overvoltages is disclosed, including:

[0041] The equivalent model building module is configured to: simplify the hybrid network station to obtain an equivalent model;

[0042] The module for calculating the initial value of the network ratio of the following structures is configured to: calculate the initial value of the network ratio of the following structures of each station based on the obtained equivalent model;

[0043] The phase-locked loop stability condition solving module is configured to: solve the phase-locked loop stability condition;

[0044] The transient overvoltage calculation module is configured to: when configuring the grid-type converter at any station according to the calculated initial value of the grid-type ratio, determine whether the phase-locked loop can remain stable after encountering a three-phase short-circuit fault based on the phase-locked loop stability condition; if it is unstable, calculate the transient overvoltage of the station;

[0045] The capacity ratio calculation module is configured as follows: when the transient overvoltage is lower than the safety threshold U safe When the initial value of the grid-forming capacity ratio is maintained; when the requirements are not met, the grid-forming capacity ratio expression that meets the transient overvoltage constraint is derived, and the grid-forming capacity ratio of the station is corrected to obtain the grid-forming capacity ratio and the grid-following capacity ratio in any station.

[0046] One or more of the above technical solutions have the following beneficial effects:

[0047] This invention rationally simplifies the renewable energy transmission system based on the Thevenin equivalence and converter characteristics. It uses the circuit superposition theorem to calculate the initial value of the station's grid-type capacity ratio. Based on the model with the corrected initial value, it proposes a method for determining PLL stability and calculating the phase-lock angle when PLL is unstable. It also proposes a transient overvoltage verification formula that takes into account the phase-lock angle error. Based on the verification results, the station's grid-type capacity ratio is configured. This invention has theoretical and practical significance for the grid-type capacity ratio of renewable energy stations and can guide the design and operation of renewable energy transmission systems.

[0048] Advantages of additional aspects of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] The accompanying drawings, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0050] Figure 1 This is a schematic diagram of the topological structure of a new energy transmission system according to an embodiment of the present invention;

[0051] Figure 2 This is the control block diagram of the grid-type converter;

[0052] Figure 3 This is the control block diagram of the grid-following converter;

[0053] Figure 4 This is a schematic diagram of a hybrid network station i model according to an embodiment of the present invention;

[0054] Figure 5 This is a phasor relationship diagram of the instantaneous fault clearing according to an embodiment of the present invention;

[0055] Figure 6 The figure is a logic flow chart of an embodiment of the present invention. DETAILED DESCRIPTION

[0056] It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present invention belongs.

[0057] It should be noted that the terms used herein are for describing particular embodiments only and are not intended to limit the exemplary embodiments according to the present invention.

[0058] In the absence of conflict, the embodiments of the present invention and the features thereof may be combined with each other.

[0059] Example 1

[0060] This embodiment discloses a method for allocating the capacity of new energy stations and grids considering transient overvoltage, including:

[0061] Step 1: Based on the Thevenin equivalent and converter characteristics, the renewable energy transmission system is reasonably simplified to obtain an equivalent model;

[0062] Step 2: Use the circuit superposition theorem to calculate the initial value of the station network capacity ratio;

[0063] Step 3: Based on the model with the corrected initial value, a method for determining the PLL stability and a method for calculating the phase-locked angle when the PLL is unstable are proposed;

[0064] Step 4: Taking into account the phase-locked angle error, a transient overvoltage verification formula is proposed;

[0065] Step 5: Based on the verification results, configure the network capacity ratio of the station.

[0066] In step one: it is equivalent to the simplified model of the hybrid station; this equivalent model takes into account the topological structure of the renewable energy transmission system outside the station and the characteristics of the internal converter. At the same time, it is reasonably simplified based on the internal and external characteristics of the station and the needs of the research problems. It reduces the complexity and difficulty of analysis while more comprehensively reflecting the change process of the grid connection point voltage when a short-circuit fault occurs outside the station.

[0067] Due to varying terrain conditions, the topology of renewable energy transmission systems exhibits significant diversity. Furthermore, grid-following and grid-forming converters have numerous internal parameters and complex control characteristics. Therefore, we first simplify the renewable energy transmission system and make reasonable assumptions. The steps are as follows: Step (1-1) Modeling the off-site topology: Different landforms, such as mountainous, desert, and coastal regions, directly influence the layout of transmission corridors, resulting in topologies that may take on different forms, including long-chain, radial, or hybrid mesh configurations. Figure 1Represents the structural diagram of a new energy transmission system.

[0068] Assume that the renewable energy transmission system includes m renewable energy stations. After the renewable energy is connected to the grid, it is collected and transmitted to the receiving AC grid via the transmission line. The transmission line uses lumped parameters, ignoring the impedance effect of the station i outside the station, and only considering the system topology. The resistance value in the renewable energy transmission system is small and can be ignored. Therefore, the corresponding Thevenin reactance of the station i outside the station is obtained by the Thevenin equivalent: X i , the power supply is U i .

[0069] In this step, the topological structure outside the station is equivalent to X i and U i , the model constructed is Figure 4 middle right X i and U i .

[0070] Step (1-2) Modeling of the converter inside the station: The converter control mode can be divided into grid-forming control and grid-following control. The most commonly used control mode in the grid-forming type is virtual synchronous generator control, which is composed of Figure 2 As shown, it simulates the operating characteristics of the synchronous generator and can be equivalent to the amplitude , the output phase angle is The voltage source of the grid-following converter is Figure 3 As shown, it can be equivalent to a current source, and its output is:

[0071] (1)

[0072] Where: I T is the unit output current; is the current phase angle; is the reactive current; is the active current.

[0073] The formula (1) expresses I T 、 and 、 relationship, in Figure 3 、 Figure 4 And used in step (4-2).

[0074] Steps (1-3) Hybrid Station Modeling: Inside the station, the grid-connected and grid-connected converters are connected to the point of common coupling (PCC), which is then connected to the grid via transformers and lines. Without loss of generality, a grid-connected hybrid station i can be simplified as Figure 4 Model.

[0075] It should be noted that the hybrid station modeling steps (1-3) are implemented based on two parts. One part is the external modeling of the station, see step (1-1), and the other part is the internal converter modeling of the station, see step (1-2). If necessary, the three can be combined.

[0076] The base capacity of the system is S base , the total capacity of the converter at station i is n times the base capacity, that is, S base,i =n S base The total capacity of the grid-following type of station i is S GFL , the total output current is I L = I T ( S GFL / S base ); the total capacity of the network is S GFM , the output reactance is X GFM , calculated to the system capacity, X M = X GFM ( S base / S GFM ); the total reactance of the transmission line and transformer in the station is X L .

[0077] Steps (1-4) Hybrid model assumptions: (1) Both the grid-following and grid-forming converters switch to the low-throughput state during the fault period, and enter the low-throughput recovery state after the fault is cleared. Since these control strategies and the transient processes of each quantity are concentrated on the electromechanical transient scale, in order to study the impact of the output characteristics of the converter on transient overvoltage and improve the voltage assessment efficiency, the present invention ignores the influence of electromagnetic transient parameters and uses electromechanical transient model analysis. (2) Since the switching time between the low-throughput and low-throughput recovery modes is generally in the millisecond level, which is much less than the fault duration, it can be considered that the control mode delay after the fault occurs and is cleared can be ignored. (3) The current loop bandwidth is several times the phase-locked loop bandwidth. Therefore, when studying the phase-locked loop characteristics during the fault period, the current loop adjustment process can be ignored, and it is considered that the current loop has reached the command value, that is, I d = I d,ref , I q = I q,ref (4) Assuming that the current overload multiple of the grid-type converter is large, it can ensure that the UGFM remains basically unchanged; the inertia coefficient is also large, and the grid-type converter power angle The change is small in a short time, so it is considered that the and the steady-state value before the fault equal.

[0078] Step 2: Calculation method for the initial value of the capacity ratio of the grid: During the planning and construction period of the new energy transmission system, the proportion of each station in the system to the grid is unknown. Therefore, the voltage support role of other stations for the grid connection point of this station is ignored. First, calculate the initial value of the capacity ratio of station i to the grid.

[0079] Step (2-1) Calculate the grid connection point voltage: Based on the simplified model of the hybrid station (the model in the above steps (1-3)) and the circuit superposition theorem, the grid connection point voltage of station i can be obtained as:

[0080] (2)

[0081] Where: U 1 is the voltage amplitude at the grid connection point; is the grid connection point voltage phase angle; is the phase angle of the grid-type current loop; is the phase-locking angle, is the output voltage phase angle; U L 、 U M and U g They are the voltage amplitude components of the grid-following type, grid-forming type and equivalent power supply at the grid connection point, respectively:

[0082] (3)

[0083] Where: X M is the grid-type output reactance calculated into the system capacity; X i is the Thevenin equivalent reactance on the grid side; X L The total reactance of the transmission lines and transformers within the station; I L It is the total output current of the grid-following type; U GFM is the internal potential of the network; U i is the Thevenin equivalent power supply on the grid side.

[0084] Substituting Equation (3) into Equation (2) and decomposing it according to the phasor relationship, the voltage amplitude and phase angle are:

[0085] (4)

[0086] (5).

[0087] In this step, the grid connection point voltage is calculated using the simplified hybrid model and circuit superposition theorem, which can take into account the internal characteristics of the converter and fundamentally reveal the causes of transient overvoltage and the parameter influencing mechanism.

[0088] Step (2-2) calculates the ratio of a single station to the network capacity: let the network capacity ratio be = S GFM / n S base , then the network capacity ratio is At the same time, in order to ensure reliability, the initial value of the capacity ratio of station i is calculated based on the three-phase metallic short circuit near the grid side station .

[0089] The specific steps are as follows: Calculate the capacity ratio of the grid-connected converter based on the requirement of ensuring that the unit does not go offline :When a three-phase short circuit occurs, U i =0, X i =0. At this time, the grid type has no voltage support capability. U L =0. At the same time, the minimum grid connection point voltage of the new energy unit is set to Substituting each quantity into equations (3) and (4), we can calculate the capacity ratio of the grid-connected converter to ensure that the unit does not go offline. The minimum is:

[0090] (6)

[0091] Where: It is the network type output reactance; The minimum voltage at the grid connection point for the unit to operate without being disconnected from the grid; The total reactance of the transmission lines and transformers within the station; is the internal potential of the network.

[0092] Step (2-2-1) Calculate the capacity ratio of grid-connected converters based on transient overvoltage constraints :To simplify the initial value calculation process, it is assumed that the grid-type PLL can remain stable during the fault period. According to the low-throughput characteristics, the active current can be considered is 0, reactive current Reaching the maximum value Substituting it into formula (5) we can get . The fault is cleared instantly and recover, Decreases, and the phasor relationship is as follows Figure 5 shown.

[0093] At this time, the relationship between the quantities is obtained by the cosine theorem:

[0094] (7).

[0095] because , , then:

[0096] (8).

[0097] Let the transient overvoltage threshold be U safe Substituting each quantity into the above formula (8), we can get the proportion of network type in new energy station i: 2 minimum is:

[0098] (9)

[0099] Where: X GFM is the grid-forming output reactance; n is the multiple of the converter capacity in station i to the system capacity; X L The total reactance of the transmission lines and transformers within the station; X i is the Thevenin equivalent reactance on the grid side; I q,max is the maximum value of the grid-following reactive current; U i is the Thevenin equivalent power supply on the grid side; UGFM is the internal potential of the network.

[0100] When the grid is not overloaded and the voltage safety threshold U safe When taking 1.3pu, we can get:

[0101] (10).

[0102] Step (2-2-2) Configure the network ratio of a single station: When configuring the network ratio of a station, It should also be ensured that the new energy units do not disconnect from the grid during the fault and that the transient overvoltage is lower than the safety threshold after the fault is cleared. Therefore, the grid capacity ratio of station i is:

[0103] (11).

[0104] The calculation results obtained by this method can ensure that the station meets the constraints of maintaining the unit's grid connection and transient overvoltage after a short-circuit fault. In addition, the proportion of grid-connected capacity is minimized at this time, and the cost of building a hybrid station with grid-connected capacity is the lowest.

[0105] Step (2-3) calculates the initial value of the ratio of each station to the grid capacity, specifically including: step (2-3-1) ignoring the effects of other stations, calculate the grid capacity ratio of each station according to the above steps; step (2-3-2) taking into account the impedance and power supply of the grid-type converter inside the station, recalculate the Thevenin equivalent impedance and power supply outside station i, and obtain a new Thevenin equivalent model.

[0106] Step (2-3-3) is based on the model of step (2-3-2), and the method of step (2-2) is used to recalculate the network capacity ratio of each station, and obtain the initial value of the network ratio of each station. At this time, the initial value of the network capacity ratio of station i is , the impedance and power supply in the new equivalent model outside the station are X i 'and U i ', substituting into formula (3) we can get U L '、 U M 'and U g '.

[0107] Given the numerous internal parameters and complex structures of new energy stations, the sub-technical solution of this embodiment simplifies the analysis process and improves calculation speed. It can quickly calculate the grid capacity ratio that meets the transient overvoltage constraints of most stations. This new model, which takes into account the voltage support provided by other stations to the current station, is then developed. Based on this new model, the accuracy of the capacity ratio can be continuously improved.

[0108] Step 3: PLL stability judgment method: Under low voltage conditions during faults, PLL cannot always remain stable. From equations (4) and (5), we can see that the phase-locked angle This directly impacts transient overvoltages. Therefore, when configuring the grid converters at a station according to initial values, transient overvoltages may not meet requirements in the event of PLL instability. Further consideration is needed to determine the impact of PLL stability on the configuration ratio and verify that the initial configuration ratio meets transient overvoltage requirements.

[0109] Step (3-1) PLL stability condition solution: During the fault When it is established, the PLL can be considered stable, otherwise it is unstable. Substituting into formula (5) we can get:

[0110] (12).

[0111] Arrange the above formula and combine it with the trigonometric function and difference formula to get the U L The item is:

[0112] (13).

[0113] The above formula is Asin x -Bcos x =C form, introducing amplitude R and phase We can get:

[0114] (14).

[0115] Substituting the above formula (14) into formula (13) simplifies it to:

[0116] (15).

[0117] In order for the above equation to be solvable, it is necessary to satisfy:

[0118] (16).

[0119] Substituting equation (3) into the above equation, we can simplify equation (16) to obtain the solution condition as follows:

[0120] (17).

[0121] When there is a three-phase short circuit outside the station, U i '=0, the PLL steady-state condition can be simplified to:

[0122] (18).

[0123] Therefore, when station i encounters a three-phase short circuit fault, if the grid-following active current output in the station does not satisfy the above formula (18), there is no solution to formula (15), and there is no equilibrium point. , PLL becomes unstable.

[0124] This formula (18) can determine whether the PLL can remain stable when a three-phase short circuit occurs outside the station. Its form is simple and intuitively illustrates that the PLL stability is related to the grid-following type output active current, the grid-forming type internal potential and the reactance.

[0125] Step (3-2) PLL phase angle calculation method when it is unstable: Figure 3 From the grid-following control characteristics shown in the figure, we can see that the control equation of the PLL is:

[0126] (19)

[0127] Where: U 1,q is the q-axis component of the grid connection point voltage; k p is the proportionality coefficient; k i is the integration coefficient.

[0128] When the three-phase short circuit occurs, according to formula (2) and dq transformation, we can get U 1,q for:

[0129] (20)

[0130] Where: I d,ref It is the grid-following output current command value; X M is the grid-type output reactance calculated into the system capacity; X L The total reactance of the transmission lines and transformers within the station; X i ' is the equivalent reactance of the new model; U M ' is the voltage amplitude component of the grid type at the grid connection point under the new model; is the phase-locking angle; is the initial value of the phase angle of the network output voltage.

[0131] Substituting the above formula (20) into formula (19) we can obtain:

[0132] (twenty one).

[0133] The variable coefficient differential equation is transformed into a second-order constant coefficient linear differential equation. When the equilibrium point does not exist, the PLL phase diverges approximately in a power series monotonically changing manner, and in a short period of time, the PLL output phase angle The change is not significant. Therefore, in formula (21) The initial value before the fault can be used So formula (21) can be simplified as:

[0134] (twenty two)

[0135] (twenty three).

[0136] Therefore, the full solution of formula (22) is:

[0137] (twenty four).

[0138] in K 1 and K 2 can be obtained from the initial value and the initial value of the derivative respectively:

[0139] (25).

[0140] Based on the dynamic characteristics of the grid-following converter PLL, this method converts the variable coefficient differential equation into a constant coefficient differential equation, which greatly reduces the difficulty of solving and can obtain the analytical solution of the phase-locked angle when the PLL is unstable.

[0141] Step 4: Transient overvoltage calculation method: Station i is calculated according to the initial value When configuring a grid-type converter, the formula (18) is used to determine whether the PLL can remain stable after encountering a three-phase short-circuit fault. If it is unstable, its transient overvoltage needs to be verified. The following is a calculation method for the transient overvoltage when the PLL is unstable.

[0142] Step (4-1) Calculate the phase-lock angle error: At the moment of fault clearing, the grid voltage U i 'Restoration supports the voltage at the grid connection point. According to formula (5), Decreases instantly, and The phase-locked loop will not be able to mutate suddenly, which will cause errors and lead to inaccurate output current of the grid-following type, which may aggravate or alleviate transient overvoltage. Therefore, the value calculated when the PLL is unstable in the previous section is Substituting into formula (5) we can get .

[0143] Step (4-2) Calculate transient overvoltage: Before the fault is cleared, the output current of the current loop reaches the command value, that is, I T = IT,ref , and from formula (1) we can know The output current of the grid is proportional to its capacity ratio. The internal impedance of the network is inversely proportional to the network capacity. .

[0144] Substituting each quantity into formula (4), the transient overvoltage calculation formula of station i is:

[0145] (26)

[0146] Each quantity in the formula can be obtained from the internal parameters of the station and the control parameters of the converter respectively.

[0147] This transient overvoltage calculation formula can reflect the transient overvoltage generation mechanism and key influencing factors. It is applicable to the calculation of transient overvoltage under different converter characteristics and different grid capacity ratios.

[0148] Step 5: Follow the network capacity ratio method: Take station i as an example, in the follow the network ratio initial value On the basis of PLL stability, transient overvoltage is checked and the network ratio is corrected.

[0149] The specific steps are as follows: Step (5-1) Calculate the grid-following active current output instruction during the fault period when the station i encounters a three-phase short circuit fault based on the grid-following converter model and control parameters. I d,ref .Will I d = I d,ref Substitute into formula (18) to determine whether the PLL can remain stable.

[0150] Step (5-2) If equation (18) holds, the PLL is stable. The network capacity ratio of station i remains unchanged at the initial value, that is, .

[0151] If equation (18) is not true in step (5-3), the PLL loses stability. First, calculate the transient overvoltage when the PLL loses stability according to equation (24) in step 3. Then use the transient overvoltage calculation method in step 4 that takes into account the phase-locked loop error and PLL instability to verify the transient overvoltage. When the transient overvoltage is lower than the safety threshold U safe When unchanged; when the requirements are not met, the grid-type capacity ratio that meets the transient overvoltage constraint can be derived from formula (26) as formula (27), and the grid-type capacity ratio of station i is changed from Corrected to :

[0152] (27)

[0153] Where: X GFM is the grid-forming output reactance; n is the multiple of the converter capacity in station i to the system capacity; U i 'and X i 'Equivalent power and reactance for the new model; X L The total reactance of the transmission lines and transformers within the station; I T,ref and Output current and phase angle command values ​​for grid-following type; is the phase-locking angle; is the grid connection point voltage phase angle after correction; U safe is the voltage safety threshold; is the initial value of the phase angle of the network output voltage.

[0154] In this embodiment, the equation is used to solve the grid-type capacity ratio, which can take into account the grid-type output current characteristics and phase-locked loop error. At the same time, it can effectively ensure that the transient overvoltage of the station can still meet the safety threshold when the PLL is unstable. U safe requirements.

[0155] The same goes for step (5-4). Follow the above steps to configure the network ratios of the other (m-1) stations.

[0156] So far, the capacity ratio of grid-type converters considering transient overvoltage constraints in the new energy transmission system has been completed. The proportion of grid-type capacity in station i is , the proportion of network capacity is The total capacity of the network in the system is , the total capacity of the network type is .

[0157] For detailed implementation process, please refer to the attached Figure 6 As shown in the figure, the system is simplified based on the Thevenin equivalent and converter characteristics, the voltage amplitude and phase angle at the grid connection point of station i are calculated, and then the grid-connected ratio of a single station is configured based on the constraints of no unit disconnection and transient overvoltage. The initial value of the grid-connected capacity ratio outside station i is calculated to create a new model. The PLL within station i is determined to be stable. If so, the grid-connected capacity ratio remains unchanged at the initial value. The grid-connected capacity ratio and the grid-connected capacity ratio within station i are obtained. Other stations are configured according to the above steps to obtain the grid-connected capacity ratio of each station in the system. The PLL within station i is then determined to be stable. If not, the phase-locked angle is calculated, the transient overvoltage is solved, and the grid-connected capacity ratio is corrected.

[0158] Example 2

[0159] The purpose of this embodiment is to provide a computer device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor implements the steps of the above method when executing the program.

[0160] Example 3

[0161] The purpose of this embodiment is to provide a computer-readable storage medium.

[0162] A computer-readable storage medium stores a computer program, which, when executed by a processor, performs the steps of the above method.

[0163] Example 4

[0164] The purpose of this embodiment is to provide a system for allocating the capacity of new energy stations and networks taking transient overvoltage into consideration, including:

[0165] The equivalent model building module is configured to: simplify the hybrid network station to obtain an equivalent model;

[0166] The module for calculating the initial value of the network ratio of the following structures is configured to: calculate the initial value of the network ratio of the following structures of each station based on the obtained equivalent model;

[0167] The phase-locked loop stability condition solving module is configured to: solve the phase-locked loop stability condition;

[0168] The transient overvoltage calculation module is configured to: when configuring the grid-type converter at any station according to the calculated initial value of the grid-type ratio, determine whether the phase-locked loop can remain stable after encountering a three-phase short-circuit fault based on the phase-locked loop stability condition; if it is unstable, calculate the transient overvoltage of the station;

[0169] The capacity ratio calculation module is configured as follows: when the transient overvoltage is lower than the safety threshold U safe When the initial value of the grid-forming capacity ratio is maintained; when the requirements are not met, the grid-forming capacity ratio expression that meets the transient overvoltage constraint is derived, and the grid-forming capacity ratio of the station is corrected to obtain the grid-forming capacity ratio and the grid-following capacity ratio in any station.

[0170] Example 5

[0171] The purpose of this embodiment is to provide a computer program product containing instructions, which, when running on a computer, enables the computer to execute the methods and functions involved in any of the above embodiments.

[0172] The steps involved in the apparatus of the above embodiment correspond to those of the method embodiment 1. For detailed implementation, please refer to the relevant description of embodiment 1. The term "computer-readable storage medium" should be understood to mean a single medium or multiple media containing one or more instruction sets; it should also be understood to include any medium capable of storing, encoding, or carrying an instruction set for execution by a processor and causing the processor to perform any method of the present invention.

[0173] Those skilled in the art will appreciate that the modules or steps of the present invention described above can be implemented using a general-purpose computer device. Alternatively, they can be implemented using program code executable by a computing device, which can then be stored in a storage device and executed by the computing device. Alternatively, they can be fabricated into separate integrated circuit modules, or multiple modules or steps can be fabricated into a single integrated circuit module for implementation. The present invention is not limited to any specific combination of hardware and software.

[0174] Although the above describes the specific embodiments of the present invention in conjunction with the accompanying drawings, it is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art on the basis of the technical solution of the present invention without any creative work are still within the scope of protection of the present invention.

Claims

1. The capacity matching method of new energy stations and network considering transient overvoltage is characterized by: include: Simplify the hybrid network station to obtain an equivalent model; Based on the obtained equivalent model, the initial value of the grid ratio of each station is calculated; Find the stability condition of the unlocking phase loop; When configuring the grid-type converter for any station according to the calculated initial value of the grid-type ratio, the phase-locked loop stability condition is used to determine whether the phase-locked loop can remain stable after encountering a three-phase short-circuit fault. If it is unstable, the transient overvoltage of the station is calculated. The calculation process is as follows: Calculate the voltage phase angle: The control equation of the PLL is: （1） Where: U 1,q is the q-axis component of the grid connection point voltage; k p is the proportionality coefficient; k i is the integration coefficient; When three-phase short circuit occurs, U 1,q for: （2） Where: I d,ref It is the grid-following output current command value; X M is the grid-type output reactance calculated into the system capacity; X L The total reactance of the transmission lines and transformers within the station; X i ' is the equivalent reactance of the new model; U M ' is the voltage amplitude component of the grid type at the grid connection point under the new model; is the phase-locking angle; is the initial value of the phase angle of the network output voltage; Substituting the above formula (2) into formula (1) we can obtain: （3） In formula (3) Use its initial value before the failure Instead, formula (3) is simplified to: （4） （5） The analytical solution of the phase-locked angle when PLL becomes unstable is: (6), where and Obtained from the initial value and the initial value of the derivative respectively: (7), Substitute the calculated PLL output phase angle into the voltage phase angle expression to obtain the voltage phase angle; Substituting the voltage phase angle, the current loop output current before the fault is cleared, the grid-following output current, and the internal impedance of the grid into the voltage amplitude expression, the transient overvoltage calculation formula of station i is obtained; When the transient overvoltage is lower than the safety threshold U safe When the initial value of the grid-forming capacity ratio is maintained; when the requirements are not met, the grid-forming capacity ratio expression that meets the transient overvoltage constraint is derived, and the grid-forming capacity ratio of the station is corrected to obtain the grid-forming capacity ratio and the grid-following capacity ratio in any station.

2. The method for allocating capacity of new energy stations and networks considering transient overvoltage according to claim 1 is characterized in that: The equivalent model is obtained by simplifying the hybrid network station, specifically including: Modeling of the off-site topology of the renewable energy transmission system; Modeling of internal converters in renewable energy transmission system stations; Modeling of hybrid stations in the follow-up network; Make assumptions about the series-parallel model; Based on the above process, an equivalent model is obtained.

3. The method for allocating capacity of new energy stations and networks considering transient overvoltage according to claim 1 is characterized in that: Assumptions are made for the series-parallel model, including: Both grid-following and grid-forming converters switch to the low-throughput state during a fault, and enter the low-throughput recovery state after the fault is cleared; The control mode delay after the fault occurs and clears is negligible; During the fault period, the current loop adjustment process can be ignored when the phase-locked loop is used, and it is considered that the current loop has reached the command value; The power angle of the grid-connected converter during the fault period is equal to the steady-state value before the fault.

4. The method for allocating capacity of new energy stations and networks considering transient overvoltage according to claim 1 is characterized in that: Based on the equivalent model, the initial values ​​of the grid ratio of each station are calculated, including: According to the simplified model of hybrid stations and the circuit superposition theorem, the grid connection point voltage of station i can be obtained; Calculate the capacity ratio of a single station to the grid based on the grid connection point voltage of station i: Calculate the initial value of the capacity ratio of each station and network based on the capacity ratio of a single station and network.

5. The method for allocating capacity of new energy stations and networks considering transient overvoltage according to claim 4 is characterized in that: The capacity ratio of a single station to the network is calculated based on the grid connection point voltage of station i, specifically: Calculate the capacity ratio of grid-connected converters based on the requirement of ensuring that the units do not go offline; Calculate the capacity ratio of grid-connected converters based on transient overvoltage constraints; Configuration site i-structure network ratio hour, It should also be ensured that the new energy units do not disconnect from the grid during the fault and that the transient overvoltage is lower than the safety threshold after the fault is cleared.

6. The new energy station and network capacity matching system considering transient overvoltage is characterized by: include: The equivalent model building module is configured to: simplify the hybrid network station to obtain an equivalent model; The module for calculating the initial value of the network ratio of the following structures is configured to: calculate the initial value of the network ratio of the following structures of each station based on the obtained equivalent model; The phase-locked loop stability condition solving module is configured to: solve the phase-locked loop stability condition; The transient overvoltage calculation module is configured to: when configuring the grid-type converter at any station according to the calculated initial value of the grid-type ratio, determine whether the phase-locked loop can remain stable after encountering a three-phase short-circuit fault based on the phase-locked loop stability condition; if it is unstable, calculate the transient overvoltage of the station. The calculation process is as follows: Calculate the voltage phase angle: The control equation of the PLL is: （1） Where: U 1,q is the q-axis component of the grid connection point voltage; k p is the proportionality coefficient; k i is the integration coefficient; When three-phase short circuit occurs, U 1,q for: （2） Where: I d,ref It is the grid-following output current command value; X M is the grid-type output reactance calculated into the system capacity; X L The total reactance of the transmission lines and transformers within the station; X i ' is the equivalent reactance of the new model; U M ' is the voltage amplitude component of the grid type at the grid connection point under the new model; is the phase-locking angle; is the initial value of the phase angle of the network output voltage; Substituting the above formula (2) into formula (1) we can obtain: （3） In formula (3) Use its initial value before the failure Instead, formula (3) is simplified to: （4） （5） The analytical solution of the phase-locked angle when PLL becomes unstable is: (6), where and Obtained from the initial value and the initial value of the derivative respectively: (7), Substitute the calculated PLL output phase angle into the voltage phase angle expression to obtain the voltage phase angle; Substituting the voltage phase angle, the current loop output current before the fault is cleared, the grid-following output current, and the internal impedance of the grid into the voltage amplitude expression, the transient overvoltage calculation formula of station i is obtained; The capacity ratio calculation module is configured as follows: when the transient overvoltage is lower than the safety threshold U safe When the initial value of the grid-forming capacity ratio is maintained; when the requirements are not met, the grid-forming capacity ratio expression that meets the transient overvoltage constraint is derived, and the grid-forming capacity ratio of the station is corrected to obtain the grid-forming capacity ratio and the grid-following capacity ratio in any station.

7. A computer program product comprising a computer program, characterized in that When the computer program is executed by a processor, the method according to any one of claims 1 to 5 is implemented.

8. A computer device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein: When the processor executes the program, the steps of the method described in any one of claims 1 to 5 are implemented.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the program is executed by a processor, the steps of the method according to any one of claims 1 to 5 are performed.

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