New energy grid-connected optimization control method based on multi-constraint check

Abstract

The invention provides a new energy grid-connected optimization control method based on multi-constraint check, and the method comprises the steps: taking a system net rack after new energy is connected to a power grid as a research object, considering the static safety constraint, static stability constraint, transient stability constraint and MRSCR constraint of each node in the system, comprehensively analyzing the maximum active power output of the new energy of the whole system and each node, and calculating the optimal power output of the new energy. And if some new energy units or stations do not meet any one of the constraint conditions, performing differential control on the active power output of the new energy units or stations in a targeted manner, and maximizing the active power output of the new energy as far as possible under the condition of meeting all the constraint conditions.

Description

Technical Field

[0001] The present invention relates to the technical field of new energy planning and operation, and particularly to a new energy grid-connected optimization control method based on multi-constraint checking. Background Art

[0002] The multi-station short-circuit ratio (MRSCR) of new energy is an index for evaluating the voltage strength of the AC power grid accessed by new energy. The larger the MRSCR, the stronger the grid framework of the AC power grid accessed by new energy. The smaller the MRSCR, it indicates that there is a scenario where new energy is incorporated into a weak AC power grid in a local area, and problems such as static voltage instability, transient overvoltage, and sub / super-synchronous oscillation may occur. Currently, the national mandatory standard GB38755-2019 "Power System Safety and Stability Guide" clearly requires that the short-circuit ratio of new energy power stations should reach a reasonable level. Therefore, in order to make the MRSCR reach a reasonable index, the most commonly used means in the power grid currently is to control the output of new energy, thereby increasing the MRSCR.

[0003] However, with the large-scale grid connection of new energy, the existing method of directly "equalizing" and uniformly controlling the output of new energy in a certain area according to the MRSCR index will limit the transmission limit of the new energy transmission channel and restrict the consumption capacity of new energy. Moreover, the MRSCR index only represents the static voltage stability of the new energy grid connection point. For the power grid, various safety and stability constraints such as static security, static stability, and transient stability of the power grid after the access of new energy also need to be considered. Only by comprehensively considering the MRSCR index and various safety and stability constraint conditions can the active power output of new energy be reasonably controlled. Moreover, in order to make new energy output as much as possible, the present invention proposes a new energy grid-connected optimization control method based on multi-constraint checking, that is, instead of "one-size-fits-all" restricting the output of new energy, but "differentiating" the control of the output of new energy according to the MRSCR level and safety and stability constraint conditions of new energy accessing the power grid, thereby optimizing the active power control method of new energy and improving the consumption level of new energy. Summary of the Invention

[0004] The purpose of the present invention is to provide a new energy grid-connected optimization control method based on multi-constraint checking to solve the problems raised in the above background art.

[0005] The present invention is achieved through the following technical solutions:

[0006] A new energy grid-connected optimization control method based on multi-constraint checking, the method includes the following steps:

[0007] Step S1: Detect the voltage of each node in the system, the line power flow, the power angles and active power outputs of each generator before the new energy is connected to the grid. After the new energy is incorporated into the grid, first conduct a static security constraint check under the regional maximum load or the maximum sectional power flow. Scan all the lines in the network under normal conditions and N-1 fault conditions and perform static analysis one by one after N-1 opening until both the node voltage and the line power flow meet the critical requirements of static security constraints;

[0008] Step S2: After the static security constraint check is completed, conduct a static stability check. Check whether the static stability inequality constraint conditions are met after the new energy is connected under normal conditions and fault conditions, and adjust the active power output of the new energy units until the load margin of the new energy station at a certain output state is exactly equal to the minimum load margin;

[0009] Step S3: After the static stability check is completed, conduct a transient stability check. Scan the system for various large disturbance faults, monitor the voltage of each load bus node and the power angles of each unit, and adjust the active power output of the new energy units until the voltage at the load bus meets the critical constraints of transient voltage and transient power angle;

[0010] Step S4: After the transient stability check is completed, finally conduct an MRSCR check. Calculate the ratio of the short-circuit capacity at the connection point of the new energy station in the whole network to the equivalent power of the new energy considering the influence of other new energy stations for each new energy station in the network, and adjust the active power output of the new energy unit until the short-circuit ratio of each new energy unit meets the requirement of being greater than or equal to 1.5.

[0011] Specifically, step S1 further includes:

[0012] Taking the active power output of the new energy station as the optimization object and aiming at maximizing the upper bound of the allowable output of the new energy to construct an objective function; specifically as follows:

[0013] This objective function is to maximize the active power output of the new energy under a certain operation mode in the optimized system. Considering that the new energy in the system is generally connected in a centralized manner and the new energy collection areas are generally far apart, the active power output of the new energy varies with its centralized installation location, so the new energy in different collection areas is calculated separately. Then the objective function is:

[0014]

[0015] In the formula, D is the total number of new energy collection areas included in the system, d represents a certain collection area, P w (d) is the wind power active power output of collection area d under a certain operation mode, P pv (d) is the photovoltaic active power output of collection area d under a certain operation mode.

[0016] Specifically, the step S1 specifically includes:

[0017] The static security constraints for new - energy grid connection operation include:

[0018] Under normal conditions, the node voltage change ΔU 0 and transmission line power change ΔP L0 ;

[0019] Under fault conditions, the node voltage change ΔU f , transmission line power change ΔP Lf and generator power change ΔP Gf . Due to the existence of ΔU and ΔP, the voltages of all nodes, the power flows of all lines, and the powers of all generators in the whole system will fluctuate, and there is a risk that the node voltages and line transmission powers exceed the limits. Therefore, under normal conditions, the voltage change of the node needs to meet the constraint: U min ≤U 0 +ΔU 0 ≤U max ;

[0020] The change in the active power flow of the line needs to meet the constraint: -P max ≤P L0 +ΔP L0 ≤P max ;

[0021] Under fault conditions, the voltage change of the node needs to meet the constraint:

[0022] The change in the active power flow of the line needs to meet the constraint:

[0023] The change in the power of the generator needs to meet the constraint:

[0024] In the formula, U 0 is the voltage value of a certain node in the system under normal conditions before new - energy grid connection, U min is the minimum static voltage of a certain node under normal conditions, U max is the maximum static voltage of a certain node under normal conditions, P L0 is the actual active power transmission value of a certain line in the system under normal conditions before new - energy grid connection, P max is the maximum active power transmitted by the line, U f is the voltage value of a certain node in the system under fault conditions before new - energy grid connection, is the minimum static voltage of a certain node under fault conditions, is the maximum static voltage of a certain node under fault conditions, P Lf is the actual active power transmission value of a certain line in the system under fault conditions before new - energy grid connection, is the maximum active power transmitted by the line in case of a fault, P Gf is the active power value generated by a certain generator in the system before the new energy is connected to the grid in case of a fault, is the maximum active power generated by the generator in case of a fault, is the minimum active power generated by the generator in case of a fault.

[0025] Specifically, the step S1 further specifically includes:

[0026] Judge whether the requirements of static security are met through the inequality constraints of static security. If it is met and the margin is large, the new energy output can be continuously increased and the output of conventional units can be reduced until both the node voltage and line power flow meet the critical requirements of static security constraints;

[0027] If it is not met, locate the new energy unit output that specifically causes the node voltage or line power flow to exceed the limit, that is, find the new energy station with the largest influencing factor, and then adjust the active power output of this new energy unit until both the node voltage and line power flow meet the critical requirements of static security constraints.

[0028] Specifically, the step S2 specifically includes:

[0029] The commonly used static voltage stability and security indicators after the new energy is centrally connected to the grid include the load margin indicator. That is, when the system operates near the nose point of the P-V curve, the corresponding load margin indicator is zero, indicating that the system is at the critical point of static stability. For the new energy access problem, the load margin indicator method is used to verify whether the static stability constraints are met after the new energy is connected. Its inequality constraint equation is:

[0030]

[0031] In the formula, λ max represents the load margin under a certain output state of the new energy station, λ req is the minimum load margin that must be met, V represents the bus voltage of the new energy connection point, and θ represents the bus angle of the new energy connection point.

[0032] Specifically, the step S2 further specifically includes:

[0033] Check whether the static stability inequality constraint conditions are met after the new energy is connected under normal conditions and N-1 fault conditions. If it is met and the margin is large, the new energy output can be continuously increased and the output of conventional units can be reduced until the load margin under a certain output state of this new energy station is exactly equal to the minimum load margin;

[0034] If not satisfied, locate the output of the new energy unit that specifically causes its load margin to be less than the minimum load margin, and then adjust the active power output of this new energy unit until the load margin under a certain output state of this new energy station is exactly equal to the minimum load margin.

[0035] Specifically, step S3 specifically includes:

[0036] After the new energy is connected to the power grid in a concentrated manner, the transient stability constraints specifically include voltage transient stability constraints and power angle stability constraints. The transient voltage stability constraint is based on the reduction amplitude of the voltage after a fault and can be expressed as:

[0037]

[0038] In the formula, N is the set of nodes, V crit is the limit value of the voltage reduction amplitude, T crit is the time threshold, t 1 represents the moment of t 1 time, t 2 represents the moment of t 2 time;

[0039] The power angle stability constraint can be expressed as:

[0040] |δ k,i (t) - δ k,j (t)| ≤ δ max , i ≠ j, i ∈ G, j ∈ G, k ∈ C

[0041] In the formula, t ∈ [0, T], T is the time period of the transient process under study, δ max is the allowable upper limit value of the power angle swing, δ k,i (t) is the power angle of any i-th unit under fault conditions, δ k,j (t) is the power angle of any j-th unit under fault conditions, k represents k pre-faults, G represents the set of generators in the system, and C represents the set of pre-faults.

[0042] Specifically, step S3 specifically includes:

[0043] If during the transient process after being disturbed, the load bus voltage can meet the requirement of recovering above 0.8 p.u. within 10 s, and the power angle stability requirements of each unit are met and the margin is large, then the new energy output can be continuously increased and the output of conventional units can be reduced until the voltage at the load bus meets the critical constraints of transient voltage and transient power angle;

[0044] If not satisfied, locate the output of the new energy unit that specifically causes the voltage at the load bus not to meet the requirements or the power angle to become unstable, and then adjust the active power output of this new energy unit until the voltage at the load bus meets the critical constraints of transient voltage and transient power angle.

[0045] Specifically, step S4 specifically includes:

[0046] Multi - Renewable - Energy - Source Short - Circuit Ratio (MRSCR) i is defined as the ratio of the short - circuit capacity at the grid - connection point of a renewable - energy source power station to the equivalent power of the renewable - energy source considering the influence of other renewable - energy source power stations:

[0047]

[0048] In the formula, S aci is the short - circuit capacity at the busbar of the grid - connection point of the renewable - energy source power station; P aci is the output of the renewable - energy source power station; Z ij and Z ii respectively represent the mutual impedance and self - impedance at the grid - connection point of the renewable - energy source power station.

[0049] Specifically, step S4 specifically includes:

[0050] Conduct MRSCR verification, calculate the ratio of the short - circuit capacity at the grid - connection point of each renewable - energy source power station in the whole network to the equivalent power of the renewable - energy source considering the influence of other renewable - energy source power stations, and verify whether the short - circuit ratio of each renewable - energy generator set meets the requirement of being greater than 1.5. If it meets and the margin is large, the output of the renewable - energy source can be further increased and the output of the conventional generator set can be reduced until the short - circuit ratio of the renewable - energy generator set is exactly equal to the critical value of 1.5;

[0051] If it does not meet the requirement, find the renewable - energy source power station with the largest influencing factor, and then adjust the active power output of this renewable - energy generator set until the short - circuit ratio of each renewable - energy generator set meets the requirement of being greater than or equal to 1.5.

[0052] Compared with the prior art, the beneficial effects achieved by the present invention are as follows:

[0053] The present invention provides an optimized control method for renewable - energy grid connection based on multi - constraint verification. This method considers various safety and stability constraint conditions of the power grid while taking into account the MRSCR index. Through systematic static - security, static - stability, and transient - stability verification, it realizes comprehensive monitoring and analysis of the power - grid operation state. Through multi - dimensional constraint coupling optimization, on the premise of ensuring power - grid safety, it significantly improves the renewable - energy accommodation level and power - grid power - supply reliability. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the following - described drawings are only the preferred embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0055] Figure 1 It is a schematic flow diagram of an optimization control method for new - energy grid connection based on multi - constraint verification.

[0056] Figure 2 It is a schematic diagram of the main grid of a power grid with a high proportion of new energy access. Specific implementation manners

[0057] In order to make the objectives, technical solutions and advantages of the present invention more apparent, exemplary embodiments according to the present invention will be described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments of the present invention. It should be understood that the present invention is not limited by the exemplary embodiments described herein. Based on the embodiments of the present invention described herein, all other embodiments obtained by those skilled in the art without creative efforts shall fall within the protection scope of the present invention.

[0058] In the following description, numerous specific details are given to provide a more thorough understanding of the present invention. However, it is obvious to those skilled in the art that the present invention can be implemented without one or more of these details. In other instances, some well - known technical features are not described in order to avoid obscuring the present invention.

[0059] It should be understood that the present invention can be implemented in different forms and should not be construed as limited to the embodiments presented herein. On the contrary, providing these embodiments will make the disclosure thorough and complete, and will fully convey the scope of the present invention to those skilled in the art.

[0060] The purpose of the terms used herein is only to describe specific embodiments and is not a limitation of the present invention. When used herein, the singular forms "a", "an" and "the" are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the terms "comprising" and / or "including", when used in this specification, determine the presence of the described features, integers, steps, operations, elements and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or groups. When used herein, the term "and / or" includes any and all combinations of the related listed items.

[0061] To thoroughly understand the present invention, detailed structures will be presented in the following description to explain the technical solutions proposed by the present invention. The optional embodiments of the present invention are described in detail below. However, in addition to these detailed descriptions, the present invention can also have other implementation manners.

[0062] See Figure 1 , an optimization control method for new - energy grid connection based on multi - constraint verification, the method includes the following steps:

[0063] Step S1: Detect the voltage of each node, line power flow, power angle and active power output information of each generator in the system before the new energy is connected to the grid. After the new energy is incorporated into the grid, first conduct a static security constraint check under the regional maximum load or maximum section power flow. Scan all lines in the network in the normal mode and N-1 fault conditions and conduct static analysis one by one after N-1 opening until both the node voltage and line power flow meet the critical requirements of static security constraints.

[0064] Step S2: After the static security constraint check is completed, conduct a static stability check. Check whether the inequality constraints of static stability are met after the new energy is connected in the normal mode and fault conditions, and adjust the active power output of the new energy units until the load margin of the new energy station at a certain output state is exactly equal to the minimum load margin.

[0065] Step S3: After the static stability check is completed, conduct a transient stability check. Scan the system for various large disturbance faults, monitor the voltage of each load bus node and the power angle of each unit, and adjust the active power output of the new energy units until the voltage at the load bus meets the critical constraints of transient voltage and transient power angle.

[0066] Step S4: After the transient stability check is completed, finally conduct an MRSCR check. Calculate the ratio of the short-circuit capacity at the new energy station connection point of all new energy stations in the network to the equivalent power of the new energy considering the influence of other new energy stations, and adjust the active power output of the new energy units until the short-circuit ratio of each new energy unit meets the requirement of being greater than or equal to 1.5.

[0067] Exemplarily, the present invention takes the system network framework after the new energy is connected to the grid as the research object, considers the static security constraints, static stability constraints, transient stability constraints and MRSCR constraints of each node in the system, comprehensively analyzes the maximum active power output of the new energy in the whole system and each node. If some new energy units or stations do not meet any of the constraint conditions, "differentiated" control is carried out on the active power output of these new energy units or stations. The core goal of this optimal control method is: to maximize the active power output of the new energy as much as possible under the condition of meeting all constraint conditions.

[0068] Specifically, the step S1 further includes:

[0069] Taking the active power output of the new energy station as the optimization object and constructing an objective function with the goal of maximizing the upper bound of the allowable output of the new energy; specifically as follows:

[0070] The objective function is to maximize the active power output of new energy under a certain operation mode in the system. Considering that new energy in the system is generally connected in a centralized manner and the new energy collection areas are generally far apart, the active power output of new energy varies with its centralized installation location. Therefore, the new energy in different collection areas is calculated separately, and the objective function is as follows:

[0071]

[0072] In the formula, D is the total number of new energy collection areas included in the system, d represents a certain collection area, P w (d) is the active power output of wind power in collection area d under a certain operation mode, and P pv (d) is the active power output of photovoltaic power in collection area d under a certain operation mode.

[0073] Specifically, step S1 specifically includes:

[0074] The static security constraints for the grid-connected operation of new energy include:

[0075] Under normal conditions, the node voltage change ΔU 0 and transmission line power change ΔP L0 caused by the grid-connected operation of new energy;

[0076] Under fault conditions, the node voltage change ΔU f , transmission line power change ΔP Lf and generator power change ΔP Gf . Due to the existence of ΔU and ΔP, the node voltages, line power flows, and generator powers of the entire system will fluctuate, and there is a risk of node voltage and line transmission power exceeding the limits. Therefore, under normal conditions, the voltage change of the node needs to meet the constraint: U min ≤U 0 +ΔU 0 ≤U max ;

[0077] The change in the active power flow of the line needs to meet the constraint: -P max ≤P L0 +ΔP L0 ≤P max ;

[0078] Under fault conditions, the voltage change of the node needs to meet the constraint:

[0079] The change in the active power flow of the line needs to meet the constraint:

[0080] The change in the power of the generator needs to meet the constraint:

[0081] In the formula, U0 is the voltage value at a certain node in the system under normal conditions before new energy grid connection, U min is the minimum static voltage at a certain node under normal conditions, U max is the maximum static voltage at a certain node under normal conditions, P L0 is the actual transmitted active power value of a certain line in the system under normal conditions before new energy grid connection, P max is the maximum active power transmitted by the line, U f is the voltage value at a certain node in the system under fault conditions before new energy grid connection, is the minimum static voltage at a certain node under fault conditions, is the maximum static voltage at a certain node under fault conditions, P Lf is the actual transmitted active power value of a certain line in the system under fault conditions before new energy grid connection, is the maximum active power transmitted by the line under fault conditions, P Gf is the active power value generated by a certain generator in the system under fault conditions before new energy grid connection, is the maximum active power generated by the generator under fault conditions, is the minimum active power generated by the generator under fault conditions.

[0082] Specifically, step S1 further specifically includes:

[0083] Judge whether the requirements of static security are met through the inequality constraints of static security. If it is met and the margin is large, the new energy output can be continuously increased and the output of conventional units can be reduced until both the node voltage and line power flow meet the critical requirements of static security constraints;

[0084] If it is not met, locate the new energy unit output that specifically causes the node voltage or line power flow to exceed the limit, that is, find the new energy station with the largest influence factor, and then adjust the active power output of the new energy unit until both the node voltage and line power flow meet the critical requirements of static security constraints.

[0085] Specifically, step S2 specifically includes:

[0086] Common static voltage stability and security indicators after new energy is centrally connected to the power grid include the load margin index. That is, when the system operates near the nose point of the P-V curve, the corresponding load margin index is zero, indicating that the system is at the critical point of static stability. For the new energy access problem, the load margin index method is used to verify whether the static stability constraints are met after new energy access. Its inequality constraint equation is:

[0087]

[0088] In the formula, λ maxIndicates the load margin under a certain output state of the new energy power station, λ req Is the minimum load margin that must be met. V represents the bus voltage at the new energy grid connection point, and θ represents the bus angle at the new energy grid connection point. Static stability needs to be verified separately under steady-state conditions and after faults.

[0089] Specifically, step S2 further includes:

[0090] Under normal conditions and N-1 faults, verify whether the static stability inequality constraint conditions are met after the new energy is connected. If they are met and the margin is large, the new energy output can be increased and the conventional unit output can be reduced until the load margin under a certain output state of the new energy power station is exactly equal to the minimum load margin;

[0091] If not, locate the output of the new energy unit that specifically causes its load margin to be less than the minimum load margin, and then adjust the active power output of this new energy unit until the load margin under a certain output state of the new energy power station is exactly equal to the minimum load margin.

[0092] Specifically, step S3 includes:

[0093] The transient stability constraints after the centralized connection of new energy to the power grid specifically include voltage transient stability constraints and power angle stability constraints. The transient voltage stability constraint is based on the voltage reduction amplitude after the fault and can be expressed as:

[0094]

[0095] In the formula, N is the set of nodes, V crit Is the voltage reduction amplitude limit value, T crit Is the time threshold, t 1 Represents time t 1 At moment t 2 Represents time t 2 At moment;

[0096] The power angle stability constraint can be expressed as:

[0097] |δ k,i (t) - δ k,j (t)| ≤ δ max , i ≠ j, i ∈ G, j ∈ G, k ∈ C

[0098] In the formula, t ∈ [0, T], T is the transient process time period under study, δ max Is the allowable upper limit value of the power angle swing, δ k,i (t) is the power angle of any i-th unit under fault conditions, δ k,j (t) is the power angle of any j-th unit under fault conditions, k represents k pre-contingency faults, G represents the set of generators in the system, and C represents the set of pre-contingency faults.

[0099] Exemplarily, according to the "Guideline for the Evaluation of Voltage Stability in Power Systems", the transient voltage stability criterion is that during the transient process after the power system is disturbed, the load bus voltage can recover above 0.8 p.u. within 10 s.

[0100] The transient power angle stability constraint has two meanings, that is, the maximum power angle difference during the power angle swing of each unit in the network does not exceed a certain limit, such as 180°; the power angle swings of each unit show a trend of decaying oscillation and finally tend to be stable.

[0101] Specifically, the step S3 specifically includes:

[0102] If during the transient process after being disturbed, the load bus voltage can meet the requirement of recovering above 0.8 p.u. within 10 s, and the power angle stability requirements of each unit and the margin is large, then the new energy output can be continuously increased and the output of conventional units can be reduced until the voltage at the load bus meets the critical constraints of transient voltage and transient power angle;

[0103] If not, locate the new energy unit output that specifically causes the voltage at the load bus not to meet the requirements or the power angle instability, and then adjust the active power output of the new energy unit until the voltage at the load bus meets the critical constraints of transient voltage and transient power angle.

[0104] Specifically, the step S4 specifically includes:

[0105] Multi-station short-circuit ratio MRSCR of new energy i It is defined as the ratio of the short-circuit capacity at the connection point of the new energy station to the equivalent power of the new energy considering the influence of other new energy stations:

[0106]

[0107] In the formula, S aci is the short-circuit capacity at the bus of the connection point of the new energy station, P aci is the output of the new energy station; Z ij and Z ii respectively represent the mutual impedance and self-impedance at the connection point of the new energy station;

[0108] Exemplarily, for the multi-station short-circuit ratio index of new energy, in actual operation, the critical short-circuit ratio is used as the basis for judging the system stability margin and provides a reference for calculating the system transmission limit. That is, for a specific new energy collection system, ensure that the system can operate stably when above this critical short-circuit ratio value. Currently, the multi-station short-circuit ratio index of new energy takes the short-circuit ratio at the machine terminal of the new energy greater than 1.5, that is, the multi-station short-circuit ratio constraint of new energy is:

[0109] MRSCR i≥1.5

[0110] Specifically, step S4 specifically includes:

[0111] Perform MRSCR verification, calculate the ratio of the short-circuit capacity at the grid connection point of the new energy power stations across the network to the equivalent power of the new energy after considering the influence of other new energy power stations, and verify whether the MRSCR of each new energy unit meets the requirement of being greater than 1.5. If it meets and has a large margin, the new energy output can be further increased and the conventional unit output can be reduced until the short-circuit ratio of the new energy unit is exactly equal to the critical value of 1.5;

[0112] If it does not meet the requirement, find the new energy power station with the largest influencing factor, and then adjust the active power output of this new energy unit until the short-circuit ratio of each new energy unit meets the requirement of being greater than or equal to 1.5.

[0113] Exemplarily, please refer to Figure 2 , taking a power grid with a high proportion of new energy access as an example. This power grid mainly has 7 wind power / solar photovoltaic centralized access areas, namely regions A, B, C, D, E, F, and G.

[0114] Exemplarily, in this application, the "differentiated" optimization control method of the present invention is compared with other commonly used differentiated control methods to analyze the influence of different control strategies on the new energy consumption capacity of the power grid. For the control scheme, we set the following:

[0115] The differentiated control scheme of this method: Perform MRSCR and security and stability constraint verification according to the actual situation, and optimize the control output.

[0116] Other differentiated control schemes: Adopt specific limits or relatively simple control strategies, emphasizing the output optimization of different new energy power stations, but not considering the global optimum, specifically including: Differentiated control based on a single short-circuit ratio (MRSCR); Regional hierarchical control based on static security constraints (differentially adjusting the output according to the power grid partition).

[0117] The uniform control scheme is to control the new energy across the network by reducing the output in the same proportion to ensure that the machine-side short-circuit ratios of all new energy power stations are qualified and meet the security and stability requirements.

[0118] The calculation results after taking control measures are shown in the following table:

[0119]

[0120] Comparison and explanation

[0121] 1. Control coincidence rate:

[0122] The maximum control simultaneity rate of the differential control method of the present invention is 56%. Compared with 53%, 51% of other differential controls and 47.3% of uniform control, it shows a higher concurrent accommodation capacity. This means that this method can support more new energy power generation access during the peak period of power demand.

[0123] 2. Percentage of new energy restriction:

[0124] In terms of new energy restriction, the restriction percentage of the differential control scheme of the present invention is only 13.8%, which is significantly lower than 18.5%, 15.5% of other differential control methods and 22.6% of uniform control. The lower the restriction percentage means higher power grid accommodation capacity.

[0125] 3. Optimized output:

[0126] The differential control method of the present invention can optimize the output of each new energy station to the greatest extent by accurately analyzing the characteristics and operating status of each new energy station. Other differential control methods are usually based on relatively simple limits and fail to fully tap the potential of new energy, thus affecting the overall accommodation efficiency.

[0127] From the comparison results, it can be seen that the "differential" optimized control method of the present invention shows more excellent performance in the research of the maximum active power output of new energy. Compared with the traditional uniform control and other differential control methods, using the method of the present invention can not only improve the new energy simultaneity rate, but also significantly reduce the restriction level and enhance the new energy accommodation capacity of the power grid, with higher application value.

[0128] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A new energy grid-connected optimization control method based on multi-constraint verification, characterized in that: The method comprises the following steps: Step S1: Detect the voltage of each node, line flow, power angle and active output information of each generator of the system before the new energy is connected to the grid. After the new energy is connected to the grid, perform static safety constraint verification under the maximum load or maximum cross-section flow of the region, scan the entire network line in normal mode and N-1 fault conditions, and perform static analysis after N-1 disconnection one by one until the node voltage or line flow meets the critical requirements of static safety constraints; Step S2: After the static safety constraint check is completed, a static stability check is performed to verify whether the static stability inequality constraint conditions are met after the new energy is connected in a normal mode and under fault conditions, and the active output of the new energy unit is adjusted until the load margin of the new energy station under a certain output state is exactly equal to the minimum load margin; Step S3: After the static stability check is completed, a transient stability check is performed, the system is scanned for various large disturbance faults, the voltage of each load bus node and the power angle of each unit are monitored, and the active output of the new energy unit is adjusted until the voltage at the load bus meets the critical constraints of the transient voltage and transient power angle; Step S4: After the transient stability check is completed, the MRSCR check is finally carried out. The ratio of the short-circuit capacity of the new energy station grid connection point and the new energy equivalent power after considering the influence of other new energy stations is calculated for the new energy stations in the entire network, and the active output of the new energy unit is adjusted until the short-circuit ratio of each new energy unit meets the requirement of being greater than or equal to 1.

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2. The method for optimizing the grid connection of renewable energy based on multi-constraint verification according to claim 1 is characterized in that: The step S1 further comprises: The active output of new energy stations is taken as the optimization object, and the objective function is constructed with the goal of maximizing the upper limit of the allowable output of new energy; the details are as follows: The objective function is to optimize the maximum active output of new energy under a certain operation mode in the system. Considering that new energy is generally connected in a centralized manner in the system and the distance between each collection area of ​​new energy is generally far, the active output of new energy varies with the location of its centralized installation. Therefore, the new energy in different collection areas is calculated separately, and the objective function is: Where D is the total number of new energy collection areas included in the system, d represents a certain collection area, P w (d) is the wind power active output in the collection area d under a certain operation mode, P pv (d) is the photovoltaic active output of the collection area d under a certain operation mode.

3. The new energy grid-connected optimization control method based on multi-constraint verification according to claim 2 is characterized in that: The step S1 specifically includes: Static safety constraints for new energy grid-connected operation include: Under normal conditions, the node voltage change ΔU0 and transmission line power change ΔP caused by the grid-connected operation of new energy L0 ; Node voltage change ΔU under fault conditions f , Transmission line power change ΔP Lf and generator power change ΔP Gf , due to the existence of ΔU and ΔP, the voltage of each node in the whole system, the power flow of each line and the power of each generator will fluctuate, and there is a risk of exceeding the limit of node voltage and line transmission power. Therefore, under normal conditions, the voltage change of the node must meet the constraint: U min ≤U0+ΔU0≤U max ; The active power flow change of the line must meet the constraints: -P max ≤P L0 +ΔP L0 ≤P max ; The voltage change of the node under fault conditions must satisfy the constraints: The active power flow change of the line must meet the constraints: The power change of the generator must satisfy the constraints: Where U0 is the voltage value of a node in the system before the new energy is connected to the grid in normal mode, U min is the minimum static voltage of a node under normal conditions, U max is the maximum static voltage of a node under normal conditions, P L0 P is the actual active power value transmitted by a certain line in the system under normal conditions before the new energy is connected to the grid. max is the maximum active power transmitted by the line, U f is the voltage value of a node in the system before the new energy is connected to the grid. is the minimum static voltage of a node under fault conditions, is the maximum static voltage of a node under fault conditions, P Lf It is the actual active power value transmitted in a certain line in the system before the new energy is connected to the grid. is the maximum active power transmitted by the line under fault conditions, P Gf It is the active power value of a generator in the system before it is connected to the grid. The maximum active power generated by the generator in the event of a fault. The minimum active power generated by the generator in the event of a fault.

4. The method for optimizing the control of renewable energy grid connection based on multi-constraint verification according to claim 3 is characterized in that: The step S1 further specifically includes: The inequality constraints of static safety are used to determine whether the requirements of static safety are met. If they are met and the margin is large, the output of new energy units can be increased and the output of conventional units can be reduced until the node voltage or line flow meets the critical requirements of the static safety constraints; If it is not satisfied, the output of the new energy unit that causes the node voltage or line flow to exceed the limit is located, that is, the new energy station with the largest influencing factor is found, and then the active output of the new energy unit is adjusted until the node voltage or line flow meets the critical requirements of the static safety constraint.

5. The method for optimizing the grid connection of renewable energy based on multi-constraint verification according to claim 4 is characterized in that: The step S2 specifically includes: The commonly used static voltage stability safety indicators after the centralized access of new energy to the power grid include the load margin index, that is, when the system operates near the nose of the PV curve, the corresponding load margin index is zero, indicating that the system is at the critical point of static stability. For the problem of new energy access, the load margin index method is used to verify whether the static stability constraints are met after the access of new energy. The inequality constraint equation is: l max (V,θ)≥λ req In the formula, λ max Indicates the load margin of a new energy station under a certain output state, λ req is the minimum load margin that must be met, V represents the bus voltage at the renewable energy grid connection point, and θ represents the bus angle at the renewable energy grid connection point.

6. The method for optimizing the control of renewable energy grid connection based on multi-constraint verification according to claim 5, characterized in that: The step S2 specifically includes: After verifying the access of new energy in normal mode and under N-1 fault conditions, determine whether the static stability inequality constraint conditions are met. If they are met and the margin is large, the output of new energy can be increased and the output of conventional units can be reduced until the load margin of the new energy station under a certain output state is exactly equal to the minimum load margin; If it is not satisfied, the output of the new energy unit that causes its load margin to be less than the minimum load margin is located, and then the active output of the new energy unit is adjusted until the load margin of the new energy station under a certain output state is exactly equal to the minimum load margin.

7. The method for optimizing the control of renewable energy grid connection based on multi-constraint verification according to claim 6, characterized in that: The step S3 specifically includes: The transient stability constraints after the centralized access of new energy to the power grid specifically include voltage transient stability constraints and power angle stability constraints. The transient voltage stability constraints are based on the voltage reduction after the fault and can be expressed as: Where N is the node set, V crit is the voltage reduction limit, T crit is the time threshold, t1 represents time t1, and t2 represents time t2; The power angle stability constraint can be expressed as: |d k,i (t)-d k,j (t)|≤δ max ,i≠j,i∈G,j∈G,k∈C Where t∈[0,T], T is the time period of the transient process under study, δ max is the upper limit of the power angle swing, δ k,i (t) is the power angle of any i-th unit under fault conditions, δ k,j (t) is the power angle of any j-th unit under fault conditions, k represents k anticipated faults, G represents the set of generators in the system, and C represents the set of anticipated faults.

8. The method for optimizing the control of renewable energy grid connection based on multi-constraint verification according to claim 7, characterized in that: The step S3 specifically includes: If, in the transient process after being disturbed, the load bus voltage can meet the requirement of recovering to above 0.8pu within 10s and the power angle of each unit is stable and has a large margin, the output of new energy units can be increased and the output of conventional units can be reduced until the voltage at the load bus meets the critical constraints of transient voltage and transient power angle; If it is not satisfied, the output of the new energy unit that causes the voltage at the load bus to not meet the requirements or the power angle to be unstable is located, and then the active output of the new energy unit is adjusted until the voltage at the load bus meets the critical constraints of transient voltage and transient power angle.

9. The method for optimizing the control of renewable energy grid connection based on multi-constraint verification according to claim 8, characterized in that: The step S4 specifically includes: New energy multi-station short circuit ratio MRSCR i It is defined as the ratio of the short-circuit capacity of the grid-connected point of the new energy station to the equivalent power of the new energy after considering the impact of other new energy stations: In the formula, S aci is the short-circuit capacity of the busbar at the grid connection point of the new energy station, P aci For the output of new energy stations, Z ij , Z ii They respectively represent the mutual impedance and self-impedance at the grid connection point of the new energy station.

10. The method for optimizing the control of renewable energy grid connection based on multi-constraint verification according to claim 9, characterized in that: The step S4 specifically includes: Conduct MRSCR verification, calculate the ratio of the short-circuit capacity of the grid-connected points of the new energy stations in the entire network to the equivalent power of new energy after considering the impact of other new energy stations, and verify whether the short-circuit ratio of each new energy unit meets the requirement of being greater than 1.

5. If it does, the output of new energy units can be increased and the output of conventional units can be reduced until the short-circuit ratio of the new energy units is exactly equal to the critical value of 1.5; If it is not satisfied, find out the new energy station with the largest influencing factor, and then adjust the active output of the new energy unit until the short-circuit ratio of each new energy unit meets the requirement of being greater than or equal to 1.5.

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