Power system emergency control method considering large disturbance and wind power low-pass cascade concurrency

Abstract

The invention discloses a power system emergency control method considering large disturbance and wind power low-pass cascade concurrency, and belongs to the field of power system frequency safety emergency control. Firstly, a power grid multi-resource emergency control full response analysis model considering a wind power wake flow effect and an emergency control resource output characteristic is established, an improved full response analysis method is proposed on the basis, and system frequency response dynamic analysis description under multiple cascade disturbances is realized. And secondly, a control mode of on-line analysis, instant calculation and real-time matching considering wind power low-voltage crossing is provided, dynamic correction of a system frequency safety index is realized, and a system emergency control strategy is rapidly and accurately obtained on the basis. According to the power system emergency control method provided by the invention, a new thought can be provided for solving the frequency safety problem of the system in a large disturbance and wind power low-crossing cascade concurrence scene in the power system, and safe and stable operation of the power system is facilitated.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of power system frequency safety emergency control, and relates to a power system emergency control method considering large disturbance and wind power low penetration coincidence. BACKGROUND

[0002] After a large active power loss occurs in a power system, in order to protect the frequency safety of the system and prevent low-frequency load shedding, emergency control measures need to be taken after the disturbance occurs to quickly make up for the power loss of the system to prevent the rapid drop of the frequency. This process is called frequency safety emergency control and belongs to the second line of defense of the power system. At present, there are many mature explorations on the second line of defense, which have made great contributions to the safe and stable operation of the system.

[0003] With the large-scale access of wind power and other new energy, synchronous units have been gradually replaced by new energy units in the power generation position in the power system. The support characteristics of new energy units to the power grid are significantly different from those of synchronous units, which makes the frequency dynamic response process of the power system more complex when it suffers from large disturbances. If a single large disturbance occurs in the power system, accompanied by voltage reduction, such as a three-phase short-circuit fault, a large area of new energy low-voltage penetration (low penetration) will easily occur near the fault. After the low-voltage penetration of new energy, there are two stages of power loss and recovery, which will cause the system to withstand multiple compound power shocks after the disturbance occurs, resulting in the risk of secondary frequency drop or overshoot, such as the analysis of the possibility of wind power low-voltage penetration triggering low-frequency defense and its impact by Liu Yang et al. in “Liu Yang, Wang Congying, Xia Deming, et al. Analysis and measures of the impact of large-area wind power low-voltage penetration on power grid frequency caused by power grid fault [J]. Power System Technology, 2021, 45(09): 3505-3514.”. The previous researches mostly focused on the emergency control problem of the system under single disturbance, such as the emergency control strategy of AC / DC hybrid power grid frequency considering the frequency modulation capability of wind power in the sending end proposed by Liu Yishi et al. in “Liu Yishi, Chai Yongning, Liu Chao, et al. Frequency emergency control strategy of AC / DC hybrid power grid considering frequency modulation capability of wind power in sending end [J]. Power System Automation, 2025, 49(08): 97-109.”, but it cannot solve the frequency safety and stability problem of the system under compound cascading disturbance.

[0004] Therefore, in order to better protect the frequency safety of the power system with high proportion of new energy access, it is necessary to study the frequency safety emergency control strategy of the system under wind power low penetration. SUMMARY

[0005] In view of the above problems existing in the prior art, the present application proposes a power system frequency safety emergency control method considering large disturbance and wind power low penetration concurrent, which strives to maintain the frequency safety of the system after a cascade disturbance occurs and ensures that the system does not occur low-frequency load shedding. The present application includes two parts, the first part: a power grid multi-resource emergency control full-response analysis model considering the wake effect of wind power and the output characteristics of emergency control resources is established, and on this basis, an improved full-response analysis method is proposed to realize the dynamic analysis and description of the system frequency response under multiple cascade disturbances. The full-response model established in the first part accurately reflects the frequency safety index, which provides the basis for the second part of the application. The second part: a "online analysis, instant calculation, real-time matching" control mode considering wind power low penetration is proposed to realize the dynamic correction of the system frequency safety index, and on this basis, the system emergency control strategy is quickly and accurately obtained. The present application provides a new idea for solving the frequency safety problem of the system under the cascade concurrent scene of large disturbance and wind power low penetration in the power system, and helps the safe and stable operation of the power system.

[0006] In the establishment of the full-response analysis model in part one, due to the high-order and nonlinear characteristics of the frequency response model, in order to facilitate the analysis of the model, the different response resources in the model need to be aggregated first to reduce the order of the model. Secondly, in order to facilitate the analysis of the model, the output characteristics of the frequency response resources are fitted into the governor characteristics, i.e. a first-order inertia link, by using the least square method. At the same time, in the frequency response model, the output size of the frequency response resources is coupled with the system frequency, which is not convenient for analyzing the frequency change curve of the system. At the same time, the emergency control focuses on the size of the lowest point of the system frequency after the disturbance, and the time from the disturbance to the lowest point of the system frequency is very short, so the power and frequency can be decoupled in an open-loop manner to facilitate the analysis of the frequency safety index of the system. The traditional frequency response analysis model assumes that the system is running in the initial state when the system is disturbed. Therefore, when the system is subjected to multiple cascade disturbances, the frequency curve after analysis will deviate seriously. Therefore, an improved full-response frequency response model is proposed to accurately analyze the system frequency response process under complex disturbances.

[0007] In part two, an emergency control mode and model considering wind power low penetration are constructed. Since the full-response model considering wind power low penetration adopts an open-loop method to realize the input of system frequency, this will cause deviation of the lowest point of the system frequency after analysis. Further, it will cause deviation of the control strategy formulated. To solve this problem, a "online analysis, instant calculation, real-time matching" control mode is proposed to correct the frequency safety index of the system and ensure the accuracy of the control strategy formulated. Further, a corresponding control model is established based on this control mode, and the control objective is to minimize the total control cost of the power system, and the constraint conditions include the output size constraint of the emergency control resources and the frequency safety constraint.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0009] An emergency control method for power systems considering large disturbances and concurrent low-voltage wind power cascading includes the following steps:

[0010] S1 analyzes the emergency control process for power system frequency security considering large disturbances and concurrent low-voltage wind power transmission, and provides specific means for solving the emergency control of power systems with large disturbances and concurrent wind power transmission according to this invention. Specifically:

[0011] In emergency control, to effectively curb the system frequency decline rate, fast-response emergency control resources are generally used to inject active power into the system, with a response time between 0.1s and 0.2s. This time span typically falls within the wind turbine low-voltage recovery period. Simultaneously, due to communication limitations, the control delays of different emergency control resources vary, resulting in multiple power surges to the system during the emergency control phase. Therefore, under this disturbance condition, the power system will experience M+N+2 power surges (M represents the output of M emergency resources, N represents the N stages of wind turbine low-voltage recovery, and 2 represents the power surges caused by the large disturbance and the wind turbine low-voltage recovery, respectively). Each power surge causes a sudden change in system frequency. To understand the system frequency change process, a full-response analysis method is needed to analyze and process the data to determine the lowest frequency point under different power surges.

[0012] The purpose of frequency safety emergency control is to minimize the control cost of the system while ensuring its frequency safety. Essentially, it is an optimization problem. Therefore, this invention will establish suitable control modes and optimal control models based on the proposed full response analysis method, i.e., S2, to ensure the frequency safety of the system under cascading disturbances, i.e., S3, S4, and S5.

[0013] S2. Establish a full-response analytical model for multi-resource emergency control of the power grid, considering the wind wake effect and the output characteristics of emergency control resources, to accurately analyze the frequency dynamics of the system. Specifically:

[0014] S2.1. As can be seen from the analysis of S1, the frequency security emergency control of large disturbances and wind power low-voltage concurrent will cause the power system to be subjected to M+N+2 different power surges, and the types of these power surges are not the same. In order to accurately reflect the frequency security index of the system under these different power surges, it is necessary to establish a full response frequency response model of the power system.

[0015] S2.2, the frequency response model is characterized by high order and nonlinearity. To facilitate analytical processing of the frequency response model, it is necessary to aggregate the different response resources in the frequency response model to reduce the order of the frequency response model. The power system frequency response model includes four parts: frequency response resources (conventional units), emergency control resources, disturbances, and resource inertia.

[0016] Specifically, conventional generating units generally include hydroelectric generators, gas turbine generators, and thermal power generators. To reduce the order of their frequency response model, a branch-normalized gain method is used to aggregate multiple units of the same type into a single unit. The parameters for hydroelectric, nuclear, and thermal power generators are as follows: , , . The parameters are those of the frequency response model of the hydroelectric generator. These are the parameters for the frequency response model of the gas turbine unit. These are the parameters of the thermal power unit. Each parameter is obtained by combining the results using formulas (1), (2), and (3).

[0017] (1)

[0018] (2)

[0019] (3)

[0020] In the formula, , and Hydroelectric motors ,gas turbine and thermal power The capacity ratio coefficient for the unit cluster. , and For hydroelectric motors ,gas turbine and thermal power The adjustment coefficient. Indicates the first Parameters of the Taiwan hydroelectric generator unit This refers to the number of hydropower units. Indicates the first Parameters of Taiwan thermal power units This refers to the number of hydropower units. Indicates the first Parameters of the Taiwan hydroelectric generator unit This refers to the number of hydropower units.

[0021] Emergency control resources include energy storage, DC power, and interruptible loads. They have advantages such as large response capacity, rapid output, and high controllability, and are widely used in power system emergency control to quickly fill system power gaps and prevent low-frequency load shedding.

[0022] Emergency control resources' participation in the power system frequency response includes two parts: delay time and output dynamics. Let the key parameters be... , These are the time constant and delay time of the output characteristics of the emergency control resources, respectively. The corresponding unit parameters are obtained by aggregating them using formula (4).

[0023] (4)

[0024] In the formula, To control resources in an emergency The capacity size. To control the amount of resources in an emergency.

[0025] In the aggregated multi-resource system frequency response model, the power output of wind power low-voltage transmission and emergency control resources is not related to the system frequency. Therefore, the power surges caused by both can be regarded as disturbances experienced by the system.

[0026] The inertial time constant, droop coefficient, and gain coefficient in the aggregated system frequency response model can be calculated by formulas (5), (6), and (7), respectively.

[0027] (5)

[0028] (6)

[0029] (7)

[0030] In the formula, , and The first The first type of resource The magnitude of the inertia of each unit, the proportion of its single-unit capacity in this type of resource, and the descent coefficient. For the first The size of the resource class, This represents the total capacity of the system. and These are the types of resources that can provide inertia and the number of resources in each type.

[0031] As can be seen from S2.2, in the multi-resource aggregation frequency response model constructed at this time, the power output characteristic transfer functions of hydropower units, gas turbine units, and thermal power units are relatively high-order.

[0032] To facilitate analytical processing of the model, the output characteristics of the conventional unit are fitted to the characteristics of the unit's governor using the least squares method, i.e., the first-order inertial element. Therefore, the output expression of the conventional unit can be represented by formula (8).

[0033] (8)

[0034] In the formula, and These are the fitted gain coefficient and time constant of the conventional unit, respectively. This represents the output variation of conventional generating units.

[0035] S2.4, after reducing the frequency response model order via S2.3, decouples the output of the frequency response resource from the system frequency, allowing for the analytical acquisition of the system's frequency change curve. Simultaneously, emergency control focuses on the magnitude of the system's lowest frequency point after a disturbance. Since the time from the disturbance's occurrence to the system reaching its lowest frequency is very short, an open-loop approach can be used to decouple power and frequency, thus constructing a low-order frequency response open-loop model.

[0036] (9)

[0037] (10)

[0038] After a power system experiences a power disturbance, the change in system frequency can be expressed by formula (9). Integrating both sides of the formula yields the system frequency change formula, as shown in formula (10). Where, For the power system in The power surges that are constantly encountered include those caused by disturbances, low-voltage wind power, and power surges from emergency control resources. This represents the magnitude of the frequency change input into the system after the loop is opened. This represents the frequency deviation caused by the preceding disturbance.

[0039] S2.5 After decoupling power and frequency in the system's frequency response model via S2.4, the system's full response model can be constructed.

[0040] Traditional analytical frequency response models assume that the system operates in its initial state when disturbed. Therefore, when the system suffers multiple cascading disturbances, the analyzed frequency response curve will be severely deviated.

[0041] In circuit theory, the dynamic response of a system is divided into two categories: zero-state response and zero-input response. This approach considers both the dynamic changes caused by external disturbances and the dynamic changes in the system's internal "inertia" after the disturbance, thus accurately reflecting the changes in system parameters. Based on this idea, this paper constructs the following full-response model using the superposition theorem.

[0042] a) Zero-state response;

[0043] Substituting equation (10) into equation (8), we obtain the output power of the frequency response resource, as shown in equation (11):

[0044] (11)

[0045] The zero-state response is caused by external disturbances to the system, so its expression can be represented by formula (12).

[0046] (12)

[0047] In the formula, and These are the output power of the frequency response resource and the zero-state response output power of the system, respectively. This represents the inverse Laplace change. The frequency magnitude of the input frequency response and This refers to the power surge of the system.

[0048] b) Zero-input response;

[0049] The zero-input response of a system refers to the dynamic process caused by its own "energy" when it is not subjected to external shocks. In power systems, this is mainly reflected in the speed governor and the rotor.

[0050] Speed ​​controller side:

[0051] (13)

[0052] Rotor side:

[0053] (14)

[0054] In the formula, The total output of conventional and new energy units. For frequency response resources in The amount of resources output at any given moment.

[0055] When the system is subjected to a large disturbance causing wind power to undercut, it will be subject to step, first-order inertial and slope disturbances, as shown in formula (15).

[0056] (15)

[0057] In the formula, , These represent the magnitudes of the step disturbance and the inertial disturbance, respectively. Let be the slope of the step disturbance. It is a step function. and They are respectively and The cumulative magnitude of the power surge at any given moment.

[0058] Based on formula (15), and combined with formulas (9) and (10), the frequency of the system input after open loop is generated. As shown in formula (16);

[0059] (16)

[0060] Based on the above formulas, the frequency of the system can be obtained, as shown in formulas (17) and (18):

[0061] (17)

[0062] (18)

[0063] In the formula, and They are respectively and Regular units at any time The magnitude of the output force. and They are respectively for and The frequency of the time system.

[0064] S3 analyzes and considers the dynamic process of system frequency under low-voltage wind power, and derives the formulas for the frequency change process of the power system at each stage, laying the foundation for the establishment of subsequent control modes and control models.

[0065] Based on the S2 full response model, the dynamic frequency process of the system considering wind power low-voltage ride-through is analyzed, and the corresponding frequency change formula is derived. The power system considering wind power low-voltage ride-through includes five stages: initial disturbance stage, wind turbine low-voltage ride-through stage, emergency control stage, wind turbine recovery stage, and wind turbine low-voltage ride-through termination stage.

[0066] S3.1, Derivation of the system frequency response process under the initial disturbance stage. From 0- During the period, the system was subjected to a step disturbance. As can be seen from formula (18), the system frequency at this time is as shown in formula (19).

[0067] (19)

[0068] S3.2, Derivation of the system frequency response process during the low-frequency ride-through phase of the wind turbine. From - During the period, the system was subjected to a step disturbance. From formulas (12), (17) and (18), it can be seen that the system frequency at this time is as shown in formula (20).

[0069] (20)

[0070] S3.3, Derivation of the system frequency response process during the emergency control phase. From - During the period, the system is subjected to N first-order inertial disturbances. As can be seen from formulas (12) and (18), the system frequency at this time is as shown in formula (21).

[0071] (twenty one)

[0072] S3.4, Derivation of the system frequency response process during the wind turbine recovery phase. From... - During the period, the system was subjected to M ramp disturbances. From formulas (12) and (18), we can see that the system frequency at this time is as shown in formula (22).

[0073] (twenty two)

[0074] S3.5, Derivation of the system frequency response process during the wind turbine recovery phase. From - During this period, the wind power low-voltage transmission ended, and the system experienced a step disturbance. As can be seen from formula (22), the system frequency at this time is as shown in formula (23).

[0075] (twenty three)

[0076] S4 establishes an emergency control mode for the power system that considers large disturbances and concurrent wind power generation, providing an effective framework for the effective implementation of the control strategy derived in S5.

[0077] Based on the dynamic process of power system emergency control frequency during wind power low-voltage ride-through analyzed in S3, an emergency control mode for the power system considering large disturbances and concurrent wind power generation is established. Specifically:

[0078] The full-response model considering low-voltage wind power transmission described in S2 uses an open-loop approach to input the system frequency, which leads to a deviation in the lowest point of the analyzed system frequency. This, in turn, causes deviations in the formulated control strategy. To address this issue, a control mode of "online analysis, real-time calculation, and real-time matching" is proposed.

[0079] The proposed control mode has a control cycle of 15 minutes, and online analysis is performed at the beginning of the control cycle to check frequency safety indicators. To correct the minimum allowed frequency point, first calculate the control strategy under a specific disturbance, then input the control strategy into the system simulation model to obtain the minimum frequency point at this time. And use formula (24) to calculate the percentage deviation of the lowest frequency point. .like ( If it is a very small number, then the frequency security index The frequency index remains unchanged; instead, it is updated using formula (25). Repeat the above process until the condition is met. Then, output the current... .

[0080] (twenty four)

[0081] (25)

[0082] The real-time calculation phase lasts for the last 5 minutes of the control cycle, and it is based on the frequency safety index under the corresponding disturbance, corrected by the online analysis phase. The system calculates control strategies and generates control decision tables. Real-time matching is performed when a disturbance occurs; the corresponding control decision is then executed to protect system frequency security.

[0083] If no disturbance occurs in the system during the control cycle, the generated control decision table will be archived, and the generation of the control decision table for the next cycle will continue.

[0084] S5. Establish an emergency control model for the power system that considers large disturbances and concurrent wind power generation, so as to quickly and accurately determine emergency control strategies for the power system that take into account large disturbances and concurrent wind power low-voltage transmission.

[0085] Based on the emergency control model established in S4, an emergency control model for the power system considering large disturbances and concurrent wind power generation is established and applied to the "online analysis" and "real-time calculation" stages of the control mode. The specific emergency control model is as follows:

[0086] The objective function of the power system emergency control model is shown in formula (26);

[0087] (26)

[0088] In the formula, This represents the total control cost of the power system. , and These represent the control costs for DC power, energy storage, and load shedding, respectively. , and These represent the sizes of emergency control commands for DC, energy storage, and load shedding, respectively.

[0089] The constraints of the power system emergency control model are as follows:

[0090] a) Constraints on the amount of emergency control resources output;

[0091] (27)

[0092] (28)

[0093] (29)

[0094] Emergency control resource output has upper and lower limits, thus constraints (28), (29), and (30) were constructed. , and The sizes of emergency control commands for DC, energy storage, and load shedding are specified separately.

[0095] b) Frequency security constraints;

[0096] (30)

[0097] After a power system is disturbed, the lowest point of the system frequency should be at Therefore, constraints (30) are constructed to ensure the frequency security of the system.

[0098] The above model can be combined with specific scenario information and MATLAB can be used to solve the control strategies under various disturbances.

[0099] The beneficial effects of this invention are:

[0100] This invention establishes an improved full-response analysis model that takes into account the zero-state response and zero-input response of the power system, enabling analysis of power system frequency changes after multiple cascaded power surges of different types. It proposes an "online analysis, real-time calculation, and real-time matching" control mode considering wind power low-voltage ride-through, achieving dynamic correction of system frequency safety indicators. Based on this, it quickly and accurately derives emergency control strategies for the system, providing a new and scalable approach for emergency control considering wind power low-voltage ride-through. Attached Figure Description

[0101] Figure 1 A diagram illustrating the emergency control process for power systems experiencing large disturbances and concurrent low-voltage wind power surges, provided by this invention.

[0102] Figure 2 This is a comparison chart of the zero-state response analysis proposed in this invention and the zero-state response analysis of traditional methods;

[0103] Figure 3 A schematic diagram of the control mode of "online analysis, instant calculation, and real-time matching" provided by the present invention;

[0104] Figure 4 A simplified diagram of the emergency control process for power systems experiencing large disturbances and concurrent low-voltage wind power surges, provided for the purposes of this invention;

[0105] Figure 5 The diagram shows the frequency variation of the full response model, simulation model, and traditional model under perturbation proposed in this invention.

[0106] Figure 6 Frequency variation diagram after the implementation of the emergency control strategy for the system under large disturbances and concurrent low-voltage wind power provided by the present invention. Detailed Implementation

[0107] The present invention will be further illustrated below with reference to specific implementation examples.

[0108] This invention proposes an emergency control method for power system frequency security considering large disturbances and concurrent wind power low-voltage ride-through. This method aims to maintain frequency security after cascading disturbances and prevent low-frequency load shedding. The invention comprises two parts. The first part establishes a full-response analytical model for multi-resource emergency control of the power grid, considering wind wake effects and the output characteristics of emergency control resources. Based on this, an improved full-response analysis method is proposed to dynamically and analytically characterize the system frequency response under multiple cascading disturbances. The full-response model established in the first part accurately reflects the frequency security indicators, providing the foundation for the second part of the invention. The second part proposes an "online analysis, real-time calculation, and real-time matching" control mode considering wind power low-voltage ride-through, enabling dynamic correction of system frequency security indicators and rapidly and accurately deriving the system's emergency control strategy. This invention provides a new approach to solving the frequency security problem of power systems under cascading scenarios of large disturbances and concurrent wind power low-voltage ride-through, contributing to the safe and stable operation of power systems.

[0109] In establishing a partial full-response analytical model, due to the high-order and nonlinear characteristics of the frequency response model, it is necessary to first aggregate different response resources in the model to reduce the model order in order to facilitate analytical processing. Secondly, to facilitate analytical processing, the output characteristics of the frequency response resources are fitted to the characteristics of the unit governor using the least squares method, i.e., a first-order inertial element. Meanwhile, in the frequency response model, the output magnitude of the frequency response resources is coupled with the system frequency, making it difficult to analytically obtain the system's frequency change curve. Furthermore, emergency control focuses on the magnitude of the minimum frequency point after the system is disturbed, and the time from the occurrence of the disturbance to the system frequency reaching the minimum point is very short. Therefore, an open-loop approach can be used to decouple power and frequency to facilitate the analysis of the system's frequency safety indicators. Traditional frequency response analytical models assume that the system is operating in its initial state when disturbed. Therefore, when the system suffers multiple cascading disturbances, the analyzed frequency curve will be severely deviated. To address this, an improved full-response frequency response model is proposed to accurately analyze the system frequency response process under complex disturbances.

[0110] In Part Two, an emergency control mode and model considering wind power low-voltage ride-through were constructed. Because the full-response model considering wind power low-voltage ride-through uses an open-loop approach to input the system frequency, this can lead to deviations in the analyzed minimum system frequency. This, in turn, can cause deviations in the formulated control strategy. To address this issue, a control mode of "online analysis, real-time calculation, and real-time matching" is proposed to correct the system's frequency safety indicators and ensure the accuracy of the formulated control strategy. Furthermore, a corresponding control model is established based on this control mode. The control objective is to minimize the total control cost of the power system, with constraints including emergency control resource output size constraints and frequency safety constraints.

[0111] This embodiment provides an emergency control method for power systems that considers large disturbances and concurrent low-voltage wind power cascading, including the following steps:

[0112] S1: This paper analyzes the emergency control process for power system frequency security considering large disturbances and concurrent low-voltage wind power transmission, and provides specific methods for solving the emergency control of power systems under large disturbances and concurrent wind power transmission. Specifically:

[0113] In emergency control, to effectively curb the system frequency drop rate, emergency control resources with faster response times are generally used to inject active power into the system. Their response time is between 0.1s and 0.2s, typically falling within the wind power low-voltage recovery period. However, due to communication limitations, different emergency control resources have varying control delays, leading to multiple power surges to the system during the emergency control phase. Therefore, under this disturbance, the power system will experience M+N+2 power surges (M represents the output of M emergency resources, N represents the N stages of wind turbine low-voltage recovery, and 2 represents the power surges caused by the large disturbance and the wind power low-voltage recovery, respectively). Therefore, the entire power change process of the emergency control system considering wind power low-voltage recovery is as follows: Figure 1 As shown.

[0114] Under each power surge, the system frequency will change abruptly. To understand the process of the system frequency change, it is necessary to use the full response analysis method to analyze and process the data, so as to find the lowest frequency point of the system under different power surges.

[0115] The purpose of frequency safety emergency control is to minimize the control cost of the system while ensuring its frequency safety. Essentially, it is an optimization problem. Therefore, this invention will establish suitable control modes and optimal control models based on the proposed full response analysis method, i.e., S2, to ensure the frequency safety of the system under cascading disturbances, i.e., S3, S4, and S5.

[0116] S2. Establish a full-response analytical model for multi-resource emergency control of the power grid, considering the wind wake effect and the output characteristics of emergency control resources, to accurately analyze the frequency dynamics of the system. Specifically:

[0117] S2.1, as analyzed in S1, shows that the frequency security emergency control due to large disturbances and concurrent low-voltage wind power surges will cause the power system to experience M+N+2 different power surges, and these power surges are not of the same type. In order to accurately reflect the frequency security indicators of the system under these different power surges, it is necessary to establish a full-response frequency response model of the power system.

[0118] S2.2, the frequency response model is characterized by high order and nonlinearity. To facilitate analytical processing of the frequency response model, it is necessary to aggregate the different response resources in the frequency response model to reduce the order of the frequency response model. The power system frequency response model includes four parts: frequency response resources (conventional units), emergency control resources, disturbances, and resource inertia.

[0119] Specifically, conventional generating units generally include hydroelectric generators, gas turbine generators, and thermal power generators. To reduce the order of their frequency response model, a branch-normalized gain method is used to aggregate multiple units of the same type into a single unit. The parameters for hydroelectric, nuclear, and thermal power generators are as follows: , , . The parameters are those of the frequency response model of the hydroelectric generator. These are the parameters for the frequency response model of the gas turbine unit. These are the parameters of the thermal power unit. Each parameter is obtained by combining the results using formulas (1), (2), and (3).

[0120] Emergency control resources include energy storage, DC power, and interruptible loads. They have advantages such as large response capacity, rapid output, and high controllability, and are widely used in power system emergency control to quickly fill system power gaps and prevent low-frequency load shedding.

[0121] Emergency control resources' participation in the power system frequency response includes two parts: delay time and output dynamics. Let the key parameters be... , These are the time constant and delay time of the output characteristics of the emergency control resources, respectively. The corresponding unit parameters are obtained by aggregating them using formula (4).

[0122] In the aggregated multi-resource system frequency response model, the power output of wind power low-voltage transmission and emergency control resources is not related to the system frequency. Therefore, the power surges caused by both can be regarded as disturbances experienced by the system.

[0123] The inertial time constant, droop coefficient, and gain coefficient in the aggregated system frequency response model can be calculated by formulas (5), (6), and (7), respectively.

[0124] As can be seen from S2.2, in the multi-resource aggregation frequency response model constructed at this time, the power output characteristic transfer functions of hydropower units, gas turbine units, and thermal power units are relatively high-order.

[0125] To facilitate analytical processing of the model, the output characteristics of the conventional unit are fitted to the characteristics of the unit's governor using the least squares method, i.e., the first-order inertial element. Therefore, the output expression of the conventional unit can be represented by formula (8).

[0126] S2.4, after reducing the frequency response model order via S2.3, allows for the decoupling of the output power of the frequency response resources from the system frequency, enabling the analytical acquisition of the system's frequency variation curve. Simultaneously, emergency control focuses on the magnitude of the system's lowest frequency point after a disturbance. Since the time from the disturbance's occurrence to the system reaching its lowest frequency is very short, an open-loop approach can be used to decouple power and frequency, thus constructing a low-order frequency response open-loop model.

[0127] After a power system experiences a power disturbance, the change in system frequency can be expressed by formula (9). Integrating both sides of the formula yields the system frequency change formula, as shown in formula (10). Where, For the power system in The power surges that are constantly encountered include those caused by disturbances, low-voltage wind power, and power surges from emergency control resources. This represents the magnitude of the frequency change input into the system after the loop is opened.

[0128] S2.5 After decoupling power and frequency in the system's frequency response model via S2.4, the system's full response model can be constructed.

[0129] Traditional analytical frequency response models assume the system operates in its initial state when disturbed. Therefore, when the system experiences multiple cascading disturbances, the analytical frequency curve will deviate significantly. In circuit theory, the dynamic response process of a system is divided into two categories: zero-state response and zero-input response. This considers both the dynamic changes caused by external disturbances and the dynamic changes in the system's internal "inertia" after being disturbed, thus accurately reflecting the changes in system parameters. Based on this idea, this paper constructs the following total response model using the superposition theorem.

[0130] Li Zifeng et al., in their paper "Zifeng Li, Litao Guo, Samson S. Yu, Mingli Zhang, YupengRen, Na Zhang, Weidong Li, An efficient full-response analytical model for probabilistic production simulation in fast frequency response reserveplanning, Energy, Volume 273, 2023, 127268," adopted... Figure 2 The method shown in (a) analyzes the zero-state response, ignoring the frequency effects caused by the aforementioned perturbations. This invention employs... Figure 2 The following zero-state response was obtained by analyzing the method shown in (b).

[0131] a) Zero-state response;

[0132] Substituting formula (10) into formula (8), we obtain the output power of the frequency response resource, as shown in formula (11).

[0133] The zero-state response is caused by external disturbances to the system, so its expression can be represented by formula (12).

[0134] b) Zero-input response;

[0135] The zero-input response of a system refers to the dynamic process caused by its own "energy" when it is not subjected to external shocks. In power systems, this is mainly reflected in the speed governor and the rotor.

[0136] When the system is subjected to a large disturbance causing wind power to undercut, it will be subject to step, first-order inertial and slope disturbances, as shown in formula (15).

[0137] Based on formula (15), and combined with formulas (9) and (10), the frequency of the system input after open loop is generated. As shown in formula (16);

[0138] Based on the above formulas, the frequency of the system can be obtained, as shown in formulas (18) and (19).

[0139] S3 analyzes and considers the dynamic process of system frequency under low-voltage wind power, and derives the formulas for the frequency change process of the power system at each stage, laying the foundation for the establishment of subsequent control modes and control models.

[0140] Based on the S2 full response model, the dynamic frequency process of the system considering wind power low-voltage ride-through is analyzed, and the corresponding frequency change formula is derived. The power system considering wind power low-voltage ride-through includes five stages: initial disturbance stage, wind turbine low-voltage ride-through stage, emergency control stage, wind turbine recovery stage, and wind turbine low-voltage ride-through termination stage.

[0141] S3.1, Derivation of the system frequency response process under the initial disturbance stage. From 0- During the period, the system was subjected to a step disturbance. As can be seen from formula (18), the system frequency at this time is as shown in formula (19).

[0142] S3.2, Derivation of the system frequency response process during the low-frequency ride-through phase of the wind turbine. From - During the period, the system was subjected to a step disturbance. From formulas (12), (17) and (18), it can be seen that the system frequency at this time is as shown in formula (20).

[0143] S3.3, Derivation of the system frequency response process during the emergency control phase. From - During the period, the system is subjected to N first-order inertial disturbances. As can be seen from formulas (12) and (18), the system frequency at this time is as shown in formula (21).

[0144] S3.4, Derivation of the system frequency response process during the wind turbine recovery phase. From... - During the period, the system was subjected to M ramp disturbances. From formulas (12) and (18), we can see that the system frequency at this time is as shown in formula (22).

[0145] S3.5, Derivation of the system frequency response process during the wind turbine recovery phase. From - During this period, the wind power low-voltage transmission ended, and the system experienced a step disturbance. As can be seen from formula (22), the system frequency at this time is as shown in formula (23).

[0146] S4 establishes an emergency control mode for the power system that considers large disturbances and concurrent wind power generation, providing an effective framework for the effective implementation of the control strategy derived in S5.

[0147] Based on the dynamic process of power system emergency control frequency during wind power low-voltage ride-through analyzed in S3, an emergency control mode for the power system considering large disturbances and concurrent wind power generation is established, such as... Figure 3 As shown, specifically:

[0148] The full-response model considering low-voltage wind power transmission described in S2 uses an open-loop approach to input the system frequency, which leads to a deviation in the lowest point of the analyzed system frequency. This, in turn, causes deviations in the formulated control strategy. To address this issue, a control mode of "online analysis, real-time calculation, and real-time matching" is proposed.

[0149] The proposed control mode has a control cycle of 15 minutes, and online analysis is performed at the beginning of the control cycle to check frequency safety indicators. The correction of the (system's lowest permissible frequency point) involves first calculating the control strategy under a specific disturbance, and then inputting the control strategy into the power system simulation model corresponding to the full response model to obtain the current lowest frequency point. And use formula (24) to calculate the percentage deviation of the lowest frequency point. .like ( If the value is 0.0001, then the frequency security index... The frequency index remains unchanged; instead, it is updated using formula (25). Repeat the above process until the condition is met. Then, output the current... .

[0150] If no disturbance occurs in the system during the control cycle, the generated control decision table will be archived, and the generation of the control decision table for the next cycle will continue.

[0151] S5. Establish an emergency control model for the power system that considers large disturbances and concurrent wind power generation, so as to quickly and accurately determine emergency control strategies for the power system that take into account large disturbances and concurrent wind power low-voltage transmission.

[0152] Based on the emergency control model established by S4, an emergency control model for the power system considering large disturbances and concurrent wind power generation is established and applied to the "online analysis" and "real-time calculation" stages of the control mode.

[0153] The objective function of the power system emergency control model is shown in formula (26);

[0154] The constraints of the power system emergency control model are as follows:

[0155] a) Constraints on the output of emergency control resources, as shown in formulas (27) to (29);

[0156] b) Frequency security constraints, as shown in formula (30);

[0157] After a power system is disturbed, the lowest point of the system frequency should be at Therefore, constraints (31) are constructed to ensure system frequency security.

[0158] The effectiveness of the proposed method was verified using MATLAB software. The improved full response analysis method, compared with traditional full response analysis methods and simulation methods, was used to analyze the system frequency response under the same large disturbance. The emergency control process of the power system is as follows: Figure 4 As shown, where It is 0.15. It is 0.3. It is (0.3.x). It is 0.1 pu. It is 0.25 pu. For (0.3-x)pu, The slope is 0.05. The slope is 0.025. , , , , .

[0159] The results are as follows Figure 5As shown, it can be seen that the system frequency response curves obtained by the proposed improved full-response analysis method and the simulation method are basically consistent. However, the frequency curves derived by the traditional full-response analysis method in the paper "Zifeng Li, Litao Guo, Samson S. Yu, Mingli Zhang, Yupeng Ren, Na Zhang, Weidong Li, An efficient full-response analytical model for probabilistic production simulation in fast frequency response reserveplanning, Energy, Volume 273, 2023, 127268" show obvious errors. This demonstrates the effectiveness and superiority of this invention.

[0160] Secondly, the effectiveness of the proposed control strategy was verified. After the disturbance, the output of the emergency control resources DC, energy storage, and load shedding were 0.1 pu, 0.024258 pu, and 0 pu, respectively. This is because the system's control objective is to minimize the total control cost, while the control costs of DC, energy storage, and load shedding increase sequentially; therefore, the output of DC, energy storage, and load shedding also increase sequentially. After adopting the emergency control measures, the system frequency curve is as follows: Figure 6 As shown, the system's minimum frequency is 49.5 Hz, which meets the requirement that the system will not experience low-frequency load shedding, thus ensuring the system's frequency safety.

[0161] The above embodiments are merely illustrative of the implementation methods of the present invention, but should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the protection scope of the present invention.

Claims

1. An emergency control method for power systems considering large disturbances and concurrent low-voltage power line-through, characterized in that, The power system emergency control method includes the following steps: S1 analyzes the emergency control process for power system frequency security considering large disturbances and concurrent wind power low-voltage ride-through. Under this disturbance, the power system is subjected to M+N+2 power surges, where M represents the output of M emergency resources, N represents the N stages of wind turbine low-voltage ride-through recovery, and 2 represent the power surges caused by the large disturbance and the wind power low-voltage ride-through, respectively. Under each power surge, the system frequency undergoes a sudden change. Using the full-response analytical method, the lowest frequency point under different power surges is obtained. S2. Establish a full-response analytical model for multi-resource emergency control of the power grid that considers the wake effect of wind power and the output characteristics of emergency control resources, and use it to analyze the frequency dynamic process of the power system. S3, analyze and consider the dynamic process of system frequency under low-voltage wind power, and derive the formulas for the power system frequency change process at each stage. Based on the S2-based full-response analytical model for emergency control of multiple power grid resources, the frequency dynamic process of the power system considering wind power low-voltage ride-through is analyzed, and the frequency change formula is obtained. The power system considering wind power low-voltage ride-through includes the initial disturbance stage, the wind turbine low-voltage ride-through stage, the emergency control stage, the wind turbine recovery stage, and the wind turbine low-voltage ride-through termination stage. S4 establishes an emergency control model for the power system that considers large disturbances and concurrent wind power generation, thus creating a framework for the implementation of the control strategy derived in S5. It adopts a control mode that features online analysis, real-time calculation, and real-time matching. S5, based on the power system emergency control model established in S4, establishes a power system emergency control model that considers large disturbances and concurrent wind power generation. This model is used in the online analysis and real-time calculation stages of the control mode to obtain a power system emergency control strategy that considers large disturbances and concurrent wind power low-voltage transmission.

2. The emergency control method for a power system considering large disturbances and concurrent low-voltage power transmission according to claim 1, characterized in that, Specifically, S2 is: S2.1, large disturbances and concurrent low-voltage wind power will cause the power system to be subjected to M+N+2 different power surges. In order to reflect the frequency security index of the power system under different power surges, a full-response frequency response model of the power system is established. S2.2, aggregate the different response resources in the full-response frequency response model; the full-response frequency response model includes four parts: frequency response resources, emergency control resources, disturbances, and resource inertia, wherein the frequency response resources are determined by the conventional unit; specifically: The conventional generating units include hydroelectric units, gas turbine units, and thermal power units. A branch-standardized gain method is used to aggregate multiple units of the same type into a single unit. The parameters for hydroelectric, nuclear, and thermal power units are as follows: , , ; The parameters are those of the frequency response model of the hydroelectric generator. These are the parameters for the frequency response model of the gas turbine unit. These are the parameters for thermal power units; The emergency control resources include energy storage, DC power, and interruptible loads. The participation of emergency control resources in the power system frequency response includes two parts: delay time and output dynamics. Let the key parameters be... , These are the time constant and delay time of the output characteristics of the emergency control resources, respectively; using formula (4), the corresponding unit parameters are aggregated; (4) ； In the formula, To control resources in an emergency The capacity size; To urgently control the quantity of resources; In the aggregated full-response frequency response model, the power surge caused by wind power low-voltage transmission and emergency control resource output can both be regarded as disturbances experienced by the power system. The inertial time constant, droop coefficient and gain coefficient in the aggregated full response frequency response model are calculated by formulas (5), (6) and (7), respectively; (5) ； (6) ； (7) ； In the formula, , and The first The first type of resource The magnitude of the inertia of each unit, the proportion of its single-unit capacity in this type of resource, and the droop coefficient; For the first The size of the resource class, This refers to the total capacity of the system. and These are the types of resources that can provide inertia and the number of resources in each type. S2.3, the output characteristics of the conventional unit are fitted to the characteristics of the unit speed governor using the least squares method, that is, the first-order inertial element; then the output expression of the conventional unit is expressed by formula (8); (8) ； In the formula, and These are the fitted gain coefficient and time constant of the conventional unit, respectively; This refers to the output variation of conventional generating units; S2.4 After reducing the order of the full-response frequency response model through S2.3, the output of the frequency response resource is decoupled from the system frequency, and the frequency change curve of the power system is obtained analytically. An open-loop approach is adopted to decouple power and frequency, thereby constructing a low-order frequency response open-loop model. (9) ； (10) ； In the formula, For the power system in The power surges that are constantly encountered include those caused by disturbances, low-voltage wind power transmission, and emergency control resources. This refers to the magnitude of the frequency change input into the system after the loop is opened; This represents the frequency deviation caused by the preceding disturbance. After the power system is subjected to power disturbance, the change in system frequency is expressed by formula (9). By integrating the left and right sides of the formula, the formula for the change in power system frequency is obtained, as shown in formula (10). S2.5 After decoupling power and frequency in the system's frequency response model via S2.4, the system's full response model is constructed. a) Zero-state response; Substituting equation (10) into equation (8), we obtain the output power of the frequency response resource, as shown in equation (11): (11) ； The zero-state response is caused by external disturbances to the system, and its expression is given by formula (12); (12) ； In the formula, and These are the output power of the frequency response resource and the zero-state response output power of the system, respectively. Indicates the inverse Laplace change; The frequency magnitude of the input frequency response and This is the power surge of the system; b) Zero-input response; In power systems, zero-input response is manifested on both sides of the speed governor and the rotor; When the power system is subjected to a large disturbance causing wind power to undercut, it can perform emergency control and withstand step, first-order inertial and slope disturbances, as shown in formula (15). (15) ； In the formula, , These represent the magnitudes of the step disturbance and the inertial disturbance, respectively. The slope of the step disturbance; It is a step function. and They are respectively and The cumulative magnitude of the power surge at any given moment; Based on formula (15), and combined with formulas (9) and (10), the frequency of the system input after open loop is generated. As shown in formula (16); (16) ； Based on the above formulas, the frequency of the power system is obtained, as shown in formulas (17) and (18): (17) ； (18) ； In the formula, and They are respectively and Regular units at any time The magnitude of the output force; and They are respectively for and The frequency of the time system.

3. The emergency control method for a power system considering large disturbances and concurrent low-voltage wind power transmission as described in claim 2, characterized in that, In S 2.2, each parameter is obtained by combining formulas (1), (2) and (3); (1) ； (2) ； (3) ； In the formula, , and Hydroelectric motors ,gas turbine and thermal power The capacity ratio of the generator cluster; , and For hydroelectric motors ,gas turbine and thermal power The adjustment coefficient; Indicates the first Parameters of the Taiwan hydroelectric generator unit This refers to the number of hydropower units; Indicates the first Parameters of Taiwan thermal power units This refers to the number of hydropower units; Indicates the first Parameters of the Taiwan hydroelectric generator unit This refers to the number of hydropower units.

4. The emergency control method for a power system considering large disturbances and concurrent low-voltage wind power transmission as described in claim 3, characterized in that, In S2.5, the zero-input response specifically refers to: Speed ​​controller side: (13) ； Rotor side: (14) ； In the formula, The total output of conventional and new energy units; For frequency response resources in The amount of resources output at any given moment.

5. The emergency control method for a power system considering large disturbances and concurrent low-voltage wind power transmission as described in claim 4, characterized in that, Specifically, S3 is: S3.1, Derivation of the system frequency response process under the initial disturbance stage; from 0- During this period, the power system experienced a step disturbance. From formula (18), we can see that the system frequency at this time is as shown in formula (19). (19) ； S3.2, Derivation of the system frequency response process during the low-frequency ride-through phase of the wind turbine; from - During this period, the power system experienced a step disturbance. From formulas (12), (17) and (18), it can be seen that the system frequency at this time is as shown in formula (20); (20) ； S3.3, Derivation of the system frequency response process during the emergency control phase; from - During this period, the power system is subjected to N first-order inertial disturbances. From formulas (12) and (18), it can be seen that the system frequency at this time is as shown in formula (21). (21) ； S3.4, Derivation of the system frequency response process during the wind turbine recovery phase; from - During the period, the power system was subjected to M ramp disturbances. From formulas (12) and (18), it can be seen that the system frequency at this time is as shown in formula (22). (22) ； S3.5, Derivation of the system frequency response process during the wind turbine recovery phase; from - During this period, the low-voltage ride-through of wind power ended, and the power system experienced a step disturbance. As can be seen from formula (22), the system frequency at this time is as shown in formula (23); (23)。 6. The emergency control method for a power system considering large disturbances and concurrent low-voltage wind power transmission as described in claim 5, characterized in that, Specifically, S4 is: The control cycle of the aforementioned control mode is 15 minutes, and the online analysis involves performing frequency safety indicators at the beginning of the control cycle. The correction, among which This is the lowest frequency allowed by the system. First, the control strategy under a specific disturbance is calculated. Then, the control strategy is input into the power system simulation model corresponding to the full response model to obtain the minimum frequency point at this time. And use formula (24) to calculate the percentage deviation of the lowest frequency point. ; like ,in If it is a very small number, then the frequency security index The frequency index remains unchanged; instead, it is updated using formula (25). Repeat the above process until the condition is met. Then, output the current... ; (24) ； (25) ； The real-time calculation phase lasts for the last 5 minutes of the control cycle, and it is based on the frequency safety index under the corresponding disturbance, corrected by the online analysis phase. The system calculates control strategies and generates control decision tables; in real time, when a disturbance occurs, it matches and executes the corresponding control decision to protect the system frequency security. If no disturbance occurs in the power system during the control cycle, the generated control decision table will be archived, and the generation of the control decision table for the next cycle will continue.

7. The emergency control method for a power system considering large disturbances and concurrent low-voltage wind power transmission as described in claim 6, characterized in that, In S4, It is 0.0001.

8. The emergency control method for a power system considering large disturbances and concurrent low-voltage wind power transmission as described in claim 7, characterized in that, Specifically, S5 is: The objective function of the power system emergency control model is shown in formula (26); (26) ； In the formula, This represents the total control cost of the power system. , and These are the control costs for DC, energy storage, and load shedding, respectively. , and These represent the sizes of emergency control commands for DC, energy storage, and load shedding, respectively. The constraints of the power system emergency control model are as follows: a) Constraints on the amount of emergency control resources output; (27) ； (28) ； (29) ； Emergency control resource output has upper and lower limits, thus constraints (28), (29) and (30) were constructed; among them , and The magnitude of emergency control commands for DC, energy storage, and load shedding are specified separately. b) Frequency security constraints; (30) ； After a power system is disturbed, the lowest point of the system frequency should be at Therefore, constraint (30) is constructed to ensure the frequency security of the system; The power system emergency control model can combine specific scenario information and use MATLAB to solve the control strategies under various disturbances.

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