A low-frequency load shedding method for a distributed new energy power source high-occupancy power system

Abstract

This invention discloses a low-frequency load shedding method for power systems with a high proportion of distributed renewable energy sources in the field of power system control technology. The method includes: collecting raw time-series data of active power and frequency of active load nodes in the target power system; processing a pre-acquired ARMAX model to obtain the inertial time constant of the target active load nodes and calculating the equivalent inertial time constant of the power system; determining the decrease in the equivalent inertial time constant of the power system under distributed renewable energy grid connection and selecting low-frequency load shedding parameters; calculating the total power deficit of the power system based on the equivalent inertial time constant, the calculated rate of change of the power system's inertial center frequency, and the active power loss caused by the disconnection of distributed renewable energy sources from the grid; evaluating the target active load nodes based on low-frequency load shedding evaluation indicators, determining the low-frequency load shedding sequence, and allocating the total power deficit to low-frequency load shedding rounds. This invention can improve the accuracy and effectiveness of low-frequency load shedding.

Description

Technical Field

[0001] This invention relates to a low-frequency load shedding method for a power system with a high proportion of distributed renewable energy sources, belonging to the field of power system control technology. Background Technology

[0002] Power system frequency is a key indicator for measuring the safe and stable operation of a power system. As the third line of defense for ensuring power system frequency stability, low-frequency load shedding can quickly disconnect loads when the system experiences a severe power deficit due to a fault, causing a sharp drop in frequency, thus preventing frequency collapse and maintaining frequency stability.

[0003] However, with the high proportion of distributed renewable energy sources integrated into the grid, a large number of distributed renewable energy sources have been added to the load side, profoundly changing the dynamic response characteristics and operating mechanisms of the power system. This poses a severe challenge to the adaptability and effectiveness of existing low-frequency load shedding strategies.

[0004] (1) Existing low-frequency load shedding methods cannot accurately obtain the inertial time constant of load nodes containing distributed new energy sources when calculating power deficit, nor can they calculate the power deficit caused by the disconnection of distributed power sources from the grid, resulting in inaccurate actual load shedding.

[0005] (2) The starting frequency and the allocated load reduction amount of each load reduction cycle in the existing low-frequency load reduction method are fixed, and the starting frequency is set too low, which cannot effectively prevent the rapid drop in frequency caused by the decrease in system inertia.

[0006] (3) Existing low-frequency load shedding methods do not take into account the distributed power sources in the load nodes when selecting load nodes to be cut off, resulting in a large number of distributed power sources being cut off during the load shedding process, which can easily increase the instability of the system and cause greater economic losses. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide a low-frequency load shedding method for power systems with a high proportion of distributed renewable energy sources, which solves the problems of inaccurate actual load shedding, inability to effectively prevent rapid frequency drop caused by system inertia, and large-scale disconnection of distributed power sources during the load shedding process in existing low-frequency load shedding methods.

[0008] To achieve the above objectives, the present invention is implemented using the following technical solution.

[0009] This invention proposes a low-frequency load shedding method for power systems with a high proportion of distributed renewable energy sources, comprising:

[0010] Collect raw time-series data of active power and frequency of active load nodes in the target power system;

[0011] Based on the original time-series data of the active power and frequency of the target active load node, the pre-acquired ARMAX model is processed to obtain the inertial time constant of the target active load node, and the equivalent inertial time constant of the power system is calculated based on the inertial time constant of the target active load node.

[0012] Based on the equivalent inertia time constant of the power system, determine the decrease of the equivalent inertia time constant of the power system under the grid connection of distributed new energy sources. Based on the decrease of the equivalent inertia time constant and the pre-established low-frequency load shedding strategy, select the corresponding low-frequency load shedding parameters.

[0013] When a power system experiences a power deficit fault, the total power deficit of the power system during the first round of low-frequency load shedding is calculated based on the equivalent inertial time constant of the power system, the calculated rate of change of the inertial center frequency of the power system, and the active power loss caused by the disconnection of distributed new energy sources from the grid.

[0014] Based on pre-established evaluation indicators for low-frequency load shedding of active load nodes, the target active load nodes are evaluated. Based on the evaluation results, the low-frequency load shedding sequence of the target active load nodes is determined. According to the low-frequency load shedding sequence and the low-frequency load shedding parameters, the total power deficit is allocated to the corresponding low-frequency load shedding rounds of the target active load nodes.

[0015] Further, the process of processing the pre-acquired ARMAX model based on the raw time-series data of the active power and frequency of the target active load node to obtain the inertial time constant of the target active load node includes:

[0016] Acquire and process the raw time-series data of the active power and frequency of the target active load node to obtain the time-series data of the change in active power and frequency of the target active load node;

[0017] Based on the ARMAX model, the time series data of the active power change is used as input, and the time series data of the frequency change is used as output. The deterministic part of the ARMAX model is used to characterize the transfer function of the active load node inertia response, and the order of the transfer function is determined by AIC criterion measurement.

[0018] Solve for the parameter vector to be identified in the ARMAX model, substitute the parameter vector to be identified into the ARMAX model, extract the dynamic part of the transfer function that characterizes the inertial response of the active load node, and obtain the discrete transfer function of the inertial response of the active load node.

[0019] The discrete transfer function is transformed into a continuous transfer function, and a unit step signal is applied to obtain the inertial time constant of the target active load node.

[0020] Furthermore, the formula for the pre-acquired ARMAX model is:

[0021] ;

[0022] ;

[0023] ;

[0024] ;

[0025] in, The time-series data of the frequency change of the target active load node at time t; The time series data of the change in active power of the target active load node at time t; This represents the noise component of the model. For backward displacement operator; , , These are the parameters to be identified in the ARMAX model; , , They are polynomials , , The order of the model; B(z) / A(z) is the deterministic part of the ARMAX model.

[0026] Furthermore, the formula for the equivalent inertial time constant of the power system is:

[0027] ;

[0028] in, The equivalent inertial time constant of the power system; The equivalent inertial time constant of power node i in the power system is obtained by directly statistically analyzing the inertial time constants of each synchronous generator on the power node. The inertial time constant of the active load node j is calculated; , These are the rated capacities of the power sources at power source node i and active load node j in the power system, respectively. , These represent the number of power source nodes and active load nodes in the power system, respectively. This refers to the total rated capacity of the power supply in the power system.

[0029] The formula for the decrease in the equivalent inertia time constant of the power system under distributed renewable energy grid connection is expressed as follows:

[0030] ;

[0031] in, This indicates the decrease in the equivalent inertia time constant of the power system under distributed renewable energy grid connection. The equivalent inertial time constant of the power system, It is the equivalent inertial time constant of the power system in the absence of distributed renewable energy sources.

[0032] Furthermore, the low-frequency load reduction strategy includes:

[0033] The basic cycle of low-frequency load shedding in the power system is set as several cycles;

[0034] When the first threshold At that time, the starting frequency, starting delay time, and load reduction amount allocated to several basic cycles of the power system are set according to the first preset rule;

[0035] When the second threshold When the first threshold is reached, the starting frequency, starting delay time, and load reduction amount allocated to several basic cycles of the power system are set according to the second preset rule.

[0036] when When the second threshold is reached, the starting frequency, starting delay time, and load reduction amount allocated to several basic cycles of the power system are set according to the third preset rule.

[0037] In addition to the aforementioned basic cycles, a special load reduction cycle is set up. The starting frequency of the special load reduction cycle is set to the first starting frequency, the starting delay time is set to the first delay time, and the allocated load reduction amount is the first percentage of the power system power deficit.

[0038] After the previous low-frequency load shedding cycle is completed, if the power system frequency Less than or equal to the starting value of the next round ,and Then the next low-frequency load shedding cycle will be initiated, in which... This is the starting value for low-frequency load shedding in the i-th round; if the power system frequency is different, it must be less than or equal to the starting value for the next round. If, after a delay, the system frequency is less than or equal to the first starting frequency, then a special round is initiated; if the power system frequency does not simultaneously meet the starting value for the next round, If the power system frequency is greater than the first starting frequency after the delay, the load shedding will end.

[0039] Furthermore, the calculation of the total power deficit of the power system during the first round of low-frequency load shedding, based on the equivalent inertial time constant of the power system, the calculated rate of change of the power system's inertial center frequency, and the active power loss caused by the disconnection of distributed renewable energy sources from the grid, includes:

[0040] The initial power deficit of the power system is estimated by calculating the rate of change of the inertial center frequency of the power system.

[0041] Based on the inertial time constant of the active load node, the rated capacity of the power supply, and the frequency, calculate the active power loss caused by the disconnection of distributed new energy power sources from the grid.

[0042] Based on the initial power deficit of the power system and the active power loss caused by the disconnection of the distributed new energy power source from the grid, the total power deficit of the power system during the first round of low-frequency load shedding is calculated.

[0043] Furthermore, the formula for calculating the inertial center frequency of the power system is:

[0044] ;

[0045] in, The inertial center frequency of the power system; Let i be the equivalent inertial time constant of power node i in the power system; Let be the inertial time constant of the active load node j; , These are the rated capacities of the power sources at power source node i and active load node j in the power system, respectively. , These represent the number of power source nodes and active load nodes in the power system, respectively. , These are the frequencies of power source node i and active load node j in the power system, respectively.

[0046] The formula for calculating the initial power deficit of the power system is as follows:

[0047] ;

[0048] in, This represents the initial power deficit of the power system. The equivalent inertial time constant of the power system; This refers to the total rated capacity of the power supply in the power system. The rated frequency of the power system; The rate of change of the inertial center frequency of the power system. The moment when a power deficit fault occurs in the power system;

[0049] The formula for calculating the active power loss caused by the disconnection of distributed renewable energy sources from the grid is as follows:

[0050] ;

[0051] in, This indicates that when the power system frequency drops to the frequency at which distributed renewable energy sources are disconnected from the grid. The active power loss caused by the disconnection of distributed renewable energy sources from the grid in the active load node j; , For the active load node j frequency to drop to Two moments before and after;

[0052] The total power deficit of the power system during the first round of low-frequency load shedding is expressed as follows:

[0053] ;

[0054] in, This refers to the total power deficit of the power system during the first round of low-frequency load shedding. This refers to the total active power loss caused by the disconnection of distributed renewable energy sources from the grid in active load nodes.

[0055] Furthermore, the evaluation indicators for low-frequency load shedding at active load nodes include the node's distributed renewable energy power penetration rate, node load shedding cost, and node frequency regulation effect coefficient.

[0056] The formula for the penetration rate of distributed new energy power sources at the nodes is:

[0057] ;

[0058] in, Given the distributed renewable energy penetration rate of load node j, load nodes with low distributed renewable energy penetration rates are preferentially selected for disconnection. , These represent the active power and load power of the distributed renewable energy source in load node j, respectively.

[0059] The formula for the node load reduction cost is:

[0060] ;

[0061] in, Given the unit load shedding cost of load node j, load nodes with lower unit load shedding costs are preferentially selected for shedding. , , The unit removal cost for Level 1, Level 2, and Level 3 loads, respectively; , , These represent the power of the primary, secondary, and tertiary loads in load node j, respectively. The cost of removing a unit power of distributed renewable energy source from load node j;

[0062] The formula for the node frequency modulation effect coefficient is:

[0063] ;

[0064] in, Given the frequency regulation effect coefficient of load node j, load nodes with smaller frequency regulation effect coefficients are preferentially selected for disconnection. Let j be the frequency of the active load node.

[0065] Furthermore, the evaluation of target active load nodes based on pre-established low-frequency load shedding evaluation indices, and the determination of the low-frequency load shedding sequence of target active load nodes based on the evaluation results, includes:

[0066] A standardized evaluation matrix is ​​established based on the low-frequency load shedding evaluation index of the active load node.

[0067] The weighting coefficients of various indicators of the load node are determined by using the entropy weight TOPSIS method.

[0068] Based on the low-frequency load shedding evaluation index of the active load node and the weighting coefficient, a weighting matrix is ​​constructed;

[0069] Based on the weighting matrix, calculate the positive and negative ideal solutions of the weighted low-frequency load reduction evaluation index values;

[0070] Based on the weighting matrix and the positive and negative ideal solutions, calculate the Euclidean distances from the load node to be evaluated to the positive and negative ideal solutions;

[0071] Based on the Euclidean distances from the load node to the positive and negative ideal solutions, the comprehensive evaluation value of the load node is calculated, and the low-frequency load shedding sequence of the target active load node is determined according to the comprehensive evaluation value of the load node.

[0072] Furthermore, the formula for the standardized evaluation matrix is:

[0073] ;

[0074] ;

[0075] Where Z is the evaluation matrix; For the elements in the matrix an n x 3 matrix Let be the standardized low-frequency load reduction evaluation index value of the j-th item of the i-th node; Let be the j-th low-frequency load shedding evaluation index value of the i-th node; n is the total number of load nodes;

[0076] The formula for the weighting coefficients of each indicator of the load node is as follows:

[0077] ;

[0078] in, , where is the weighting coefficient of the j-th low-frequency load shedding evaluation index for the load node; Let be the entropy value of the j-th low-frequency load shedding evaluation index of the load node;

[0079] The entropy value of the j-th low-frequency load shedding evaluation index of the load node The formula is:

[0080] ;

[0081] Where k is a constant, usually taken as... ; The weight of the j-th low-frequency load reduction evaluation index for the i-th node is given by the following formula:

[0082] ;

[0083] The formula for the weighting matrix is:

[0084] ;

[0085] Where V is the weighting matrix; Let j be the weighted standardized low-frequency load reduction evaluation index value of the i-th node, and its formula is:

[0086] ;

[0087] The formulas for the positive ideal solution and the negative ideal solution are:

[0088] ;

[0089] ;

[0090] Among them, A + The positive ideal solution represents the optimal value of the weighted low-frequency load reduction evaluation index; A - The negative ideal solution represents the worst value of the weighted low-frequency load reduction evaluation index.

[0091] The formula for the Euclidean distance from the load node to be evaluated to the positive and negative ideal solutions is:

[0092] ;

[0093] ;

[0094] in, Let be the Euclidean distance from the load node i to be evaluated to the positive ideal solution. Let be the Euclidean distance from the load node i to be evaluated to the negative ideal solution; This is the positive ideal solution for the weighted j-th low-frequency load reduction evaluation index value. The negative ideal solution for the weighted j-th low-frequency load reduction evaluation index value;

[0095] The formula for the comprehensive evaluation value of the load node is:

[0096] ;

[0097] in, CI is the comprehensive evaluation value of load node i. The larger the CI value, the more likely the corresponding load node will be cut off.

[0098] The beneficial effects achieved by this invention are as follows:

[0099] (1) By accurately evaluating the inertial time constant of the active node and the equivalent inertial time constant of the system, and monitoring the rate of change of the inertial center frequency of the system, the total power deficit of the system at the low-frequency load shedding start-up moment can be accurately calculated, thereby precisely controlling the load shedding amount and avoiding over-shearing and under-shearing.

[0100] (2) The action parameters of each round of low-frequency unloading are dynamically adjusted according to the inertia level of the system, so that the system can start emergency control more quickly in fault scenarios with low inertia and extremely fast frequency drop, avoiding the risk of deep frequency drop or even collapse due to response delay.

[0101] (3) By combining the output of the distributed power source of the active load node, the nodes with lower output of the distributed power source are selectively cut off during load shedding, ensuring that the power deficit of the system can be reduced with each load shedding operation. This solves the problem of the decrease in the proportion of actual controlled load due to the high penetration of distributed new energy sources, fundamentally ensuring the effectiveness of emergency control measures and reducing losses. Attached Figure Description

[0102] Figure 1 The flowchart illustrates a low-frequency load shedding method for a power system with a high proportion of distributed renewable energy sources, as provided by this invention.

[0103] Figure 2 This is a flowchart illustrating the implementation of the low-frequency load reduction method of the present invention. Detailed Implementation

[0104] The present invention will be further described below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and should not be used to limit the scope of protection of the present invention.

[0105] Example 1, such as Figure 1 As shown, this invention discloses a low-frequency load shedding method for a power system with a high proportion of distributed renewable energy sources, comprising:

[0106] Collect raw time-series data of active power and frequency of active load nodes in the target power system;

[0107] Based on the original time-series data of the active power and frequency of the target active load node, the pre-acquired ARMAX model is processed to obtain the inertial time constant of the target active load node, and the equivalent inertial time constant of the power system is calculated based on the inertial time constant of the target active load node.

[0108] Based on the equivalent inertia time constant of the power system, determine the decrease of the equivalent inertia time constant of the power system under the grid connection of distributed new energy sources. Based on the decrease of the equivalent inertia time constant and the pre-established low-frequency load shedding strategy, select the corresponding low-frequency load shedding parameters.

[0109] When a power system experiences a power deficit fault, the total power deficit of the power system during the first round of low-frequency load shedding is calculated based on the equivalent inertial time constant of the power system, the calculated rate of change of the inertial center frequency of the power system, and the active power loss caused by the disconnection of distributed new energy sources from the grid.

[0110] Based on pre-established evaluation indicators for low-frequency load shedding of active load nodes, the target active load nodes are evaluated. Based on the evaluation results, the low-frequency load shedding sequence of the target active load nodes is determined. According to the low-frequency load shedding sequence and the low-frequency load shedding parameters, the total power deficit is allocated to the corresponding low-frequency load shedding rounds of the target active load nodes.

[0111] A power system with a high proportion of distributed renewable energy sources refers to a power system in which a large number of distributed renewable energy sources, represented by distributed photovoltaic power, are connected to load feeders of different voltage levels in the distribution network. It is defined as a power system with a high proportion of distributed renewable energy sources when the penetration rate of distributed renewable energy sources exceeds 30%; the penetration rate is the proportion of the output of distributed renewable energy sources to the total load of the system.

[0112] The raw time-series data based on the active power and frequency of the target active load node are used to process the pre-acquired ARMAX model to obtain the inertial time constant of the target active load node, including:

[0113] Acquire and process the raw time-series data of the active power and frequency of the target active load node to obtain the time-series data of the change in active power and frequency of the target active load node;

[0114] Based on the ARMAX model, the time series data of the active power change is used as input, and the time series data of the frequency change is used as output. The deterministic part of the ARMAX model is used to characterize the transfer function of the active load node inertia response, and the order of the transfer function is determined by AIC criterion measurement.

[0115] Solve for the parameter vector to be identified in the ARMAX model, substitute the parameter vector to be identified into the ARMAX model, extract the dynamic part of the transfer function that characterizes the inertial response of the active load node, and obtain the discrete transfer function of the inertial response of the active load node.

[0116] The discrete transfer function is transformed into a continuous transfer function, and a unit step signal is applied to obtain the inertial time constant of the target active load node.

[0117] The formula for the pre-acquired ARMAX model is:

[0118] ;

[0119] ;

[0120] ;

[0121] ;

[0122] in, The time-series data of the frequency change of the target active load node at time t; The time series data of the change in active power of the target active load node at time t; This represents the noise component of the model. For backward displacement operator; , , These are the parameters to be identified in the ARMAX model; , , They are polynomials , , The order of the model; B(z) / A(z) is the deterministic part of the ARMAX model.

[0123] The formula for the equivalent inertial time constant of the power system is:

[0124] ;

[0125] in, The equivalent inertial time constant of the power system; The equivalent inertial time constant of power node i in the power system is obtained by directly statistically analyzing the inertial time constants of each synchronous generator on the power node. The inertial time constant of the active load node j is calculated; , These are the rated capacities of the power sources at power source node i and active load node j in the power system, respectively. , These represent the number of power source nodes and active load nodes in the power system, respectively. This refers to the total rated capacity of the power supply in the power system.

[0126] The formula for the decrease in the equivalent inertia time constant of the power system under distributed renewable energy grid connection is expressed as follows:

[0127] ;

[0128] in, This indicates the decrease in the equivalent inertia time constant of the power system under distributed renewable energy grid connection. The equivalent inertial time constant of the power system, The low-frequency load shedding strategies for power include:

[0129] The basic cycle of low-frequency load shedding in the power system is set as several cycles;

[0130] When the first threshold At that time, the starting frequency, starting delay time, and load reduction amount allocated to several basic cycles of the power system are set according to the first preset rule;

[0131] When the second threshold When the first threshold is reached, the starting frequency, starting delay time, and load reduction amount allocated to several basic cycles of the power system are set according to the second preset rule.

[0132] when When the second threshold is reached, the starting frequency, starting delay time, and load reduction amount allocated to several basic cycles of the power system are set according to the third preset rule.

[0133] In addition to the aforementioned basic cycles, a special load reduction cycle is set up. The starting frequency of the special load reduction cycle is set to the first starting frequency, the starting delay time is set to the first delay time, and the allocated load reduction amount is the first percentage of the power system power deficit.

[0134] After the previous low-frequency load shedding cycle is completed, if the power system frequency Less than or equal to the starting value of the next round ,and Then the next low-frequency load shedding cycle will be initiated, in which... This is the starting value for low-frequency load shedding in the i-th round; if the power system frequency is different, it must be less than or equal to the starting value for the next round. If, after a delay, the system frequency is less than or equal to the first starting frequency, then a special round is initiated; if the power system frequency does not simultaneously meet the starting value for the next round, If the power system frequency is greater than the first starting frequency after the delay, the load shedding will end.

[0135] The calculation of the total power deficit during the first round of low-frequency load shedding, based on the equivalent inertial time constant of the power system, the calculated rate of change of the power system's inertial center frequency, and the active power loss caused by the disconnection of distributed renewable energy sources from the grid, includes:

[0136] The initial power deficit of the power system is estimated by calculating the rate of change of the inertial center frequency of the power system.

[0137] Based on the inertial time constant of the active load node, the rated capacity of the power supply, and the frequency, calculate the active power loss caused by the disconnection of distributed new energy power sources from the grid.

[0138] Based on the initial power deficit of the power system and the active power loss caused by the disconnection of the distributed new energy power source from the grid, the total power deficit of the power system during the first round of low-frequency load shedding is calculated.

[0139] Before load shedding, distributed renewable energy sources in the power system will disconnect from the grid as the frequency drops. Therefore, the active power loss caused by this disconnection needs to be added when calculating the total power deficit of the system. For distributed renewable energy sources with low-frequency ride-through capability at node j, since the start frequency of the last load shedding round is higher than their disconnection frequency, the probability of distributed renewable energy sources with corresponding protection capabilities actively disconnecting from the grid during low-frequency load shedding is small. Therefore, during the entire low-frequency load shedding process, it is not necessary to estimate the power deficit caused by the disconnection of these distributed sources at corresponding times.

[0140] The formula for calculating the inertial center frequency of the power system is:

[0141] ;

[0142] in, The inertial center frequency of the power system; Let i be the equivalent inertial time constant of power node i in the power system; Let be the inertial time constant of the active load node j; , These are the rated capacities of the power sources at power source node i and active load node j in the power system, respectively. , These represent the number of power source nodes and active load nodes in the power system, respectively. , These are the frequencies of power source node i and active load node j in the power system, respectively.

[0143] The formula for calculating the initial power deficit of the power system is as follows:

[0144] ;

[0145] in, This represents the initial power deficit of the power system. The equivalent inertial time constant of the power system; This refers to the total rated capacity of the power supply in the power system. The rated frequency of the power system; The rate of change of the inertial center frequency of the power system. The moment when a power deficit fault occurs in the power system;

[0146] The formula for calculating the active power loss caused by the disconnection of distributed renewable energy sources from the grid is as follows:

[0147] ;

[0148] in, This indicates that when the power system frequency drops to the frequency at which distributed renewable energy sources are disconnected from the grid. The active power loss caused by the disconnection of distributed renewable energy sources from the grid in the active load node j; , For the active load node j frequency to drop to Two moments before and after;

[0149] The total power deficit of the power system during the first round of low-frequency load shedding is expressed as follows:

[0150] ;

[0151] in, This refers to the total power deficit of the power system during the first round of low-frequency load shedding. This refers to the total active power loss caused by the disconnection of distributed renewable energy sources from the grid in active load nodes.

[0152] The evaluation indicators for low-frequency load shedding at active load nodes include the node's distributed renewable energy power penetration rate, node load shedding cost, and node frequency regulation effect coefficient.

[0153] When selecting load nodes to be disconnected, based on the dual considerations of grid security and stability and control effectiveness, priority is given to disconnecting load nodes that do not contain renewable energy or have low renewable energy penetration. This can quickly reduce the system's active power deficit, effectively curb frequency decline, and also reduce damage to renewable energy power equipment. The formula for the distributed renewable energy penetration rate of the node is:

[0154] ;

[0155] in, Given the distributed renewable energy penetration rate of load node j, load nodes with low distributed renewable energy penetration rates are preferentially selected for disconnection. , These represent the active power and load power of the distributed renewable energy source in load node j, respectively.

[0156] According to the requirements of the "Design Code for Power Supply and Distribution Systems" standard, loads can be classified into first-level loads, second-level loads, and third-level loads according to their importance. The higher the load level, the greater the loss caused by load shedding. Considering that load nodes also contain distributed renewable energy sources, this part needs to be taken into account when calculating economic losses. The economic loss of load node j due to load shedding is expressed using the unit load shedding cost, and the formula for the node load shedding cost is:

[0157] ;

[0158] in, Given the unit load shedding cost of load node j, load nodes with lower unit load shedding costs are preferentially selected for shedding. , , The unit removal cost for Level 1, Level 2, and Level 3 loads, respectively; , , These represent the power of the primary, secondary, and tertiary loads in load node j, respectively. The cost of removing a unit power of distributed renewable energy source from load node j;

[0159] The load regulation effect can compensate for changes in load power when the system power balance is disrupted and frequency changes occur. This is especially true when the frequency drops. ,load The larger the value, the faster its active power absorption decreases. Therefore, priority should be given to removal. Smaller load nodes, retain Larger load nodes can fully utilize the load frequency regulation effect when the frequency drops, thereby reducing the active power absorbed by the load, which helps to reduce unbalanced power and quickly restore the steady-state frequency; the formula for the node frequency regulation effect coefficient is:

[0160] ;

[0161] in, Given the frequency regulation effect coefficient of load node j, load nodes with smaller frequency regulation effect coefficients are preferentially selected for disconnection. Let j be the frequency of the active load node.

[0162] The evaluation of target active load nodes based on pre-established low-frequency load shedding evaluation indices, and the determination of the low-frequency load shedding sequence of target active load nodes based on the evaluation results, includes:

[0163] A standardized evaluation matrix is ​​established based on the low-frequency load shedding evaluation index of the active load node.

[0164] The weighting coefficients of various indicators of the load node are determined by using the entropy weight TOPSIS method.

[0165] Based on the low-frequency load shedding evaluation index of the active load node and the weighting coefficient, a weighting matrix is ​​constructed;

[0166] Based on the weighting matrix, calculate the positive and negative ideal solutions of the weighted low-frequency load reduction evaluation index values;

[0167] Based on the weighting matrix and the positive and negative ideal solutions, calculate the Euclidean distances from the load node to be evaluated to the positive and negative ideal solutions;

[0168] Based on the Euclidean distances from the load node to the positive and negative ideal solutions, the comprehensive evaluation value of the load node is calculated, and the low-frequency load shedding sequence of the target active load node is determined according to the comprehensive evaluation value of the load node.

[0169] The formula for the standardized evaluation matrix is:

[0170] ;

[0171] ;

[0172] Where Z is the evaluation matrix; For the elements in the matrix an n x 3 matrix Let be the standardized low-frequency load reduction evaluation index value of the j-th item of the i-th node; Let be the j-th low-frequency load shedding evaluation index value of the i-th node; n is the total number of load nodes;

[0173] The formula for the weighting coefficients of each indicator of the load node is as follows:

[0174] ;

[0175] in, , where is the weighting coefficient of the j-th low-frequency load shedding evaluation index for the load node; Let be the entropy value of the j-th low-frequency load shedding evaluation index of the load node;

[0176] The entropy value of the j-th low-frequency load shedding evaluation index of the load node The formula is:

[0177] ;

[0178] Where k is a constant, usually taken as... ; The weight of the j-th low-frequency load reduction evaluation index for the i-th node is given by the following formula:

[0179] ;

[0180] The formula for the weighting matrix is:

[0181] ;

[0182] Where V is the weighting matrix; Let j be the weighted standardized low-frequency load reduction evaluation index value of the i-th node, and its formula is:

[0183] ;

[0184] The formulas for the positive ideal solution and the negative ideal solution are:

[0185] ;

[0186] ;

[0187] Among them, A + The positive ideal solution represents the optimal value of the weighted low-frequency load reduction evaluation index; A - The negative ideal solution represents the worst value of the weighted low-frequency load reduction evaluation index.

[0188] The formula for the Euclidean distance from the load node to be evaluated to the positive and negative ideal solutions is:

[0189] ;

[0190] ;

[0191] in, Let be the Euclidean distance from the load node i to be evaluated to the positive ideal solution. Let be the Euclidean distance from the load node i to be evaluated to the negative ideal solution; This is the positive ideal solution for the weighted j-th low-frequency load reduction evaluation index value. The negative ideal solution for the weighted j-th low-frequency load reduction evaluation index value;

[0192] The formula for the comprehensive evaluation value of the load node is:

[0193] ;

[0194] in, CI is the comprehensive evaluation value of load node i. The larger the CI value, the more likely the corresponding load node will be cut off.

[0195] In addition, before executing the load shedding action, the net load status of each active load node is first determined based on the load node sequence. The power flow of the active load node is checked through the directional power relay to see if it flows from the distribution network to the transmission network. If the power flows from the distribution network to the transmission network, the low-frequency load shedding device is locked, and the corresponding load node cannot be selected for shedding.

[0196] Example 2, based on the same inventive concept as Example 1, discloses a low-frequency load shedding method for a power system with a high proportion of distributed new energy power sources, the steps of which are as follows.

[0197] S1: Based on the capacity of the power sources in each node under the current power system operating status, estimate the inertial time constant of each node through power grid operation data and calculate the inertial time constant of the system. The process is as follows.

[0198] (1) For any active load node j in the power system, the frequency response process of node j can be expressed as:

[0199] ;

[0200] in, Let be the frequency change of node j; Let be the change in active power at node j; For the primary frequency-modulated active power increment of the power source in node j; Let be the equivalent damping coefficient of node j; Let be the inertial time constant of node j.

[0201] When the power system is subjected to small disturbances, the frequency fluctuates around the rated frequency. In this case, the frequency change of the node j to be estimated is only affected by the inertial response. It can be seen that node j contains transfer function G j (s):

[0202] ;

[0203] Among them, Gj (s) represents the nodes containing node j. The transfer function.

[0204] right Input a unit step signal And convert it into a time-domain expression:

[0205] ;

[0206] in, Let be the inertial time constant of node j; This is the time-domain expression for the frequency change.

[0207] right Differentiate, when When, the reciprocal of its derivative is :

[0208] ;

[0209] In summary, by obtaining the transfer function of the node frequency response, the inertial time constant can be obtained through the initial slope of its step response.

[0210] (2) Due to the complexity of noise and disturbance types in actual power grids, directly using the node j contained in the data is not feasible. transfer function G j (s) shows poor robustness in fitting. Therefore, a system identification method is adopted, which collects the input and output data of each active load node, constructs an equivalent discrete transfer function model using the ARMAX model, and then uses this model to extract the inertia.

[0211] 1) Data Acquisition and Preprocessing: By deploying measuring devices at each active load node in the power system, raw time-series data of active power and frequency at each active load node under small disturbances are collected. The steady-state operating values ​​are subtracted from the active power and frequency in the raw data to calculate the changes in active power and frequency. and The time-series data of active power change and frequency change are obtained; the processed node power change is used as input and the frequency change is used as output.

[0212] 2) Autoregressive Moving Average with exogenous inputs (ARMAX) is a mathematical model used for system identification and time series modeling. It extends the classic ARMA model by introducing external input variables, which can more accurately describe dynamic systems affected by external disturbances.

[0213] An ARMAX model can be represented as:

[0214] ;

[0215] ;

[0216] ;

[0217] ;

[0218] in, The output of the model at time t is the frequency change of node j; The input to the model at time t is the change in active power at node j. This represents the noise component of the model. For backward displacement operator; , , These are the parameters to be identified in the model; , , They are polynomials , , The order of the transfer function model is used. The deterministic part B(z) / A(z) of the ARMAX model is used to characterize the transfer function model of the research object.

[0219] 3) The Akaike Information Criterion (AIC) is used to determine the model order. This method addresses overfitting by adding a model complexity penalty term and uses the likelihood function to measure the fit of the system model. The Akaike Information Criterion (AIC) is a criterion for statistical model selection. Its core idea is to strike a balance between model goodness of fit and model complexity, avoid overfitting, and prioritize the model with the lowest AIC value.

[0220] AIC performance metrics are defined as follows:

[0221] ;

[0222] ;

[0223] ;

[0224] in, The AIC is the performance metric for an nth-order model. The smaller the AIC value, the better the model achieves a balance between fitting accuracy and complexity. The number of samples observed; The variance of the error after fitting the data to the nth-order model; The model order; The predicted value is calculated using the identification model; N is the number of samples.

[0225] 4) Parameter identification: Using the observed data, the parameter vectors in the model are identified. For the part to be identified, it is written in the following form:

[0226] ;

[0227] Extract the parameter vector that needs to be identified:

[0228] ;

[0229] Where θ is the parameter vector to be identified.

[0230] The input and output are respectively constructed into input-output matrices X and Y:

[0231] ;

[0232] ;

[0233] The objective function is determined as follows:

[0234] ;

[0235] right Find the partial derivatives and set them to 0:

[0236] ;

[0237] The least squares estimate of θ is obtained as follows:

[0238] ;

[0239] 5) Calculate the nodal inertia time constant, substitute the obtained parameter vector into the identification model, extract the part describing the deterministic dynamics of the system, and obtain the discrete transfer function:

[0240] ;

[0241] The discrete transfer function G(z) is transformed into a continuous transfer function G(s) using the bilinear transform method. By applying a unit step signal to G(s), the inertial time constant of the active load node can be calculated. .

[0242] (3) Calculate the equivalent inertial time constant of the power system :

[0243] ;

[0244] in, The equivalent inertial time constant of the power system; The equivalent inertial time constant of power node i in the power system is obtained by directly statistically analyzing the inertial time constants of each synchronous generator on the power node. The inertial time constant of the active load node j is calculated; , These are the rated capacities of the power sources at power source node i and active load node j in the power system, respectively. , These represent the number of power source nodes and active load nodes in the power system, respectively. This refers to the total rated capacity of the power supply in the power system.

[0245] S2: Determine the inertia level of the current distributed renewable energy grid-connected system and select the appropriate low-frequency load shedding parameters. The process is as follows:

[0246] The equivalent inertial time constant of the system in operation without distributed renewable energy sources is defined as follows: According to the current operating status of the power system ,pass and The ratio is used to determine the current system's inertia level:

[0247] ;

[0248] in, This indicates the decrease in the equivalent inertia time constant of the power system under distributed renewable energy grid connection. The equivalent inertial time constant of the power system, It is the equivalent inertial time constant of the power system in the absence of distributed renewable energy sources.

[0249] In accordance with the requirements of the "Technical Regulations for Automatic Low-Frequency Load Shedding in Power Systems", the low-frequency load shedding strategy in this embodiment is set up with a total of 4 basic wheels.

[0250] 1) When At that time, the starting frequencies of the power system for each round were set to 49.0Hz, 48.8Hz, 48.6Hz, and 48.4Hz, respectively, with a starting delay time of 0.2s for each round. The load reduction allocated to each round was 25%, 25%, 25%, and 25% of the calculated total power deficit, respectively.

[0251] 2) When The starting frequencies for each round of the power system are set to 49.2Hz, 49.0Hz, 48.8Hz, and 48.6Hz, respectively, with a starting delay of 0.2s for each round. The load reductions allocated to each round are 30%, 30%, 20%, and 20% of the calculated total power deficit, respectively.

[0252] 3) When The starting frequencies for each round of the power system are set to 49.4Hz, 49.2Hz, 49.0Hz, and 48.8Hz, respectively. The starting delay time for each round is 0.2s. The load reductions allocated to each round are 40%, 30%, 15%, and 15% of the calculated total power deficit, respectively.

[0253] 4) In addition, a special load reduction cycle is set. The starting frequency of the special cycle is set to 49.5Hz, the delay time is set to 10s, and the allocated load reduction amount is 10% of the power deficit.

[0254] S3: When a power deficit fault occurs in the power system, the initial power deficit and the increased active power loss due to the disconnection of distributed renewable energy sources are estimated as follows:

[0255] (1) Estimate the initial power deficit of the power system by measuring the rate of change of the inertial center frequency at the initial moment of the power system fault:

[0256] ;

[0257] ;

[0258] in, The inertial center frequency of the power system; Let i be the equivalent inertial time constant of power node i in the power system; Let be the inertial time constant of the active load node j; , These are the rated capacities of the power sources at power source node i and active load node j in the power system, respectively. , These represent the number of power source nodes and active load nodes in the power system, respectively. , These are the frequencies of power source node i and active load node j in the power system, respectively. This represents the initial power deficit of the power system. The equivalent inertial time constant of the power system; This refers to the total rated capacity of the power supply in the power system. The rated frequency of the power system; The rate of change of the inertial center frequency of the power system. The moment when a power deficit fault occurs in the power system

[0259] (2) Before the load shedding operation, distributed renewable energy sources in the system will disconnect from the grid as the frequency drops. Therefore, the active power loss caused by this disconnection needs to be added when calculating the total power deficit of the power system. The power system frequency drops to the disconnection frequency of the distributed renewable energy sources. Previously, the power supply capacity and inertia time constant in each active load node could be considered constant. The active power loss caused by the disconnection of distributed renewable energy sources from the grid in active load node j can be expressed as:

[0260] ;

[0261] in, , For the active load node j frequency to drop to Two moments before and after.

[0262] For distributed renewable energy sources with low-frequency ride-through capability at node j, since the start frequency of the last load shedding round of the existing low-frequency load shedding is higher than its disconnection frequency, the probability of distributed renewable energy sources with corresponding protection capabilities actively disconnecting from the grid during the low-frequency load shedding process is small. Therefore, during the entire low-frequency load shedding process, it is not necessary to estimate the power deficit caused by the disconnection of these distributed power sources at the corresponding time.

[0263] (3) When the power system experiences its first low-frequency load shedding operation, the total power deficit can be expressed as:

[0264] ;

[0265] in, This refers to the total power deficit of the power system during the first round of low-frequency load shedding. This refers to the total active power loss caused by the disconnection of distributed renewable energy sources from the grid in active load nodes.

[0266] S4: Establish low-frequency load shedding evaluation indices for active nodes. Based on these indices, use the entropy-weighted TOPSIS method to determine the load shedding sequence of active load nodes. Allocate the total load shedding of the power system to each load shedding round. The load shedding amount allocated in each round is determined by the indices. Select the appropriate load node for removal, as follows:

[0267] (1) Establish low-frequency load shedding evaluation index for active load nodes.

[0268] 1) Computing the penetration rate of distributed new energy power sources at the node.

[0269] When selecting load nodes to be disconnected, based on the dual considerations of grid security and stability and control effectiveness, priority is given to disconnecting load nodes that do not contain renewable energy or have low renewable energy penetration. This can quickly reduce the system's active power deficit, effectively curb frequency decline, and also reduce damage to renewable energy power equipment. The distributed renewable energy penetration rate of load node j can be expressed as:

[0270] ;

[0271] in, Given the distributed renewable energy penetration rate of load node j, priority should be given to cutting off load nodes with low distributed renewable energy penetration rates, which can improve load reduction efficiency. , These represent the active power and load power of the distributed renewable energy source in load node j, respectively.

[0272] 2) Calculate the cost of node load reduction.

[0273] According to the requirements of the "Design Code for Power Supply and Distribution Systems" standard, loads can be classified into primary, secondary, and tertiary loads based on their importance. The higher the load level, the greater the loss caused by load shedding. Furthermore, considering that load nodes may contain distributed renewable energy sources, this portion needs to be taken into account when calculating economic losses. The economic loss of load node j due to load shedding is expressed using the unit load shedding cost:

[0274] ;

[0275] in, For the unit load shedding cost of load node j, the preferred choice is... Cutting off load nodes with small values ​​can reduce economic losses; , , The unit removal cost for Level 1, Level 2, and Level 3 loads, respectively; , , These represent the power of the primary, secondary, and tertiary loads in load node j, respectively. The cost of removing a unit power of distributed renewable energy source from load node j.

[0276] 3) Calculate the node frequency regulation effect coefficient.

[0277] The load regulation effect can compensate for changes in load power when the system power balance is disrupted, causing frequency changes. Neglecting the effects of system voltage fluctuations, the relationship between system frequency and load active power is:

[0278] ;

[0279] in, This refers to the active power consumed by the load at the rated frequency of the power system. For loads that are proportional to the nth power of the power system frequency The proportion in; f is the load node frequency.

[0280] In general, loads in power systems that are directly proportional to the cube of the frequency change are few and their impact can be ignored. Differentiating the above equation yields the load regulation effect coefficient:

[0281] ;

[0282] in, This is the frequency modulation effect coefficient.

[0283] When the frequency decreases ,load The larger the value, the faster its active power absorption decreases. Therefore, priority should be given to removal. Smaller load nodes, retain Larger load nodes can fully utilize the load frequency regulation effect when the frequency drops, thereby reducing the active power absorbed by the load, which helps to reduce unbalanced power and quickly restore steady-state frequency.

[0284] The frequency regulation effect coefficient of load node j is:

[0285] ;

[0286] in, Given the frequency regulation effect coefficient of load node j, load nodes with smaller frequency regulation effect coefficients are preferentially selected for disconnection. Let j be the frequency of the active load node.

[0287] (2) Based on the established low-frequency load shedding evaluation indicators for load nodes, the load nodes are comprehensively evaluated using the entropy-weighted TOPSIS method to determine the order of load node shedding. The specific process is as follows:

[0288] 1) Establish an evaluation matrix.

[0289] The evaluation matrix is ​​obtained based on the calculation results of the three indicators of the established load nodes:

[0290] ;

[0291] in, Let X be the j-th low-frequency load reduction evaluation index value for the i-th node. After standardizing matrix X, we obtain matrix X. .

[0292] Elements in the evaluation matrix for:

[0293] ;

[0294] in, is the standardized low-frequency load shedding evaluation index value of the j-th item of the i-th node; n is the total number of load nodes.

[0295] 2) Determine the weights of various indicators of the load node using the entropy weight method.

[0296] The Entropy Weight TOPSIS method is an objective comprehensive evaluation method that combines the Entropy Weight Method and the TOPSIS (Technique for Order Preference by Similarity to Ideal Solution) method. It first uses the Entropy Weight Method to determine the objective weight of each evaluation index based on the dispersion of the data itself, and then uses the TOPSIS method to calculate the degree of similarity between each evaluation object and the ideal solution and to rank and optimize them.

[0297] For the j-th index, its entropy value is calculated as follows:

[0298] ;

[0299] Where k is a constant, usually taken as... ; The formula for calculating the weight of each standardized data point is as follows:

[0300] ;

[0301] The formula for calculating the weighting coefficients of each indicator is as follows:

[0302] ;

[0303] 3) Construct the weighting matrix.

[0304] After calculating the weight coefficients of each indicator using the entropy weight method, a weighting matrix is ​​constructed:

[0305] ;

[0306] in:

[0307] .

[0308] in, Let be the weighted standardized low-frequency load reduction evaluation index value of the j-th item of the i-th node.

[0309] 4) Calculate the ideal solution and the negative ideal solution.

[0310] For an indicator where "the larger the better," the ideal solution is the maximum value, and the negative ideal solution is the minimum value. For an indicator where "the smaller the better," the ideal solution is the minimum value, and the negative ideal solution is the maximum value. The ideal solution for the indicator proposed in this paper can be expressed as:

[0311] ;

[0312] ;

[0313] 5) Calculate the distance between the positive and negative ideal solutions.

[0314] Calculate the Euclidean distance from each load node to be evaluated to the positive / negative ideal solution. The distance from the node to be evaluated to the positive ideal solution is... The distance to the negative ideal solution is Their values ​​are as follows:

[0315] ;

[0316] ;

[0317] 6) Comprehensive evaluation value of load nodes

[0318] The overall evaluation value of each node is proportional to its proximity to the ideal solution and its distance from the negative ideal solution:

[0319] ;

[0320] 7) The order of removing load nodes.

[0321] Based on the comprehensive evaluation value (CI), all load nodes are sorted to obtain the load shedding order. The higher the CI value, the more suitable the node is to be disconnected.

[0322] In addition, before executing the load shedding action, the net load status of each active load node is first determined based on the load node sequence. The power flow of the active load node is checked through the directional power relay to see if it flows from the distribution network to the transmission network. If the power flows from the distribution network to the transmission network, the low-frequency load shedding device is locked, and the corresponding load node cannot be selected for shedding.

[0323] S5: After the previous low-frequency load shedding cycle is completed, if the power system frequency... Reach the starting value for the next round. ,and Then the next low-frequency load shedding cycle will be initiated, in which... This is the starting value for the i-th round of low-frequency load shedding; if the power system frequency recovers to less than or equal to 49.5Hz, a special load shedding round is initiated; if the power system frequency recovers to greater than 49.5Hz, and Then the load reduction will end.

[0324] like Figure 2 As shown, the flow of the low-frequency load shedding method of the present invention is as follows:

[0325] Obtain the equivalent inertial time constant of the power system under its current operating state. Assess the current inertia level of the system;

[0326] Based on the current inertia level of the power system and the pre-established low-frequency load shedding strategy, select the appropriate low-frequency load shedding parameters;

[0327] If the power system frequency Less than or equal to the frequency starting value of the first round of low-frequency load shedding. ,and Then, calculate the power deficit of the power system and allocate the power deficit of the power system to the load reduction of each round; start the low-frequency load reduction round and select the load nodes to be cut off based on the comprehensive evaluation value of the calculated load nodes;

[0328] After the previous low-frequency load shedding cycle is completed, if the power system frequency is less than or equal to the starting value of the next cycle, and If so, then the next low-frequency unloading cycle will be initiated;

[0329] After the previous low-frequency load shedding cycle is completed, if the power system frequency does not simultaneously meet the requirement of being less than or equal to the starting value of the next cycle, If, after a 10-second delay, the power system frequency is less than or equal to 49.5Hz, then a special wheel is activated.

[0330] After the previous low-frequency load shedding cycle is completed, if the power system frequency does not simultaneously meet the requirement of being less than or equal to the starting value of the next cycle, If the system frequency is greater than 49.5Hz after a 10-second delay, the load reduction will end.

[0331] In summary, the low-frequency load shedding method for power systems with a high proportion of distributed renewable energy sources proposed in this invention can achieve the following key technical effects. First, it significantly improves the speed and accuracy of grid frequency stability control under high-proportion renewable energy access. By accurately assessing the inertial time constant of active nodes and the equivalent inertial time constant of the power system, and monitoring the rate of change of the power system's inertial center frequency, it can accurately calculate the total power deficit of the power system at the start of low-frequency load shedding, thereby precisely controlling the load shedding amount and avoiding over-shearing and under-shearing. Second, based on the inertia level of the power system, the action parameters of each round of low-frequency load shedding are dynamically adjusted, enabling the power system to initiate emergency control more quickly in fault scenarios with low inertia and extremely rapid frequency drop, avoiding the risk of deep frequency drop or even collapse due to response lag. Finally, it improves the control objectives and execution effects of load shedding, enhancing the effectiveness of load shedding measures. By combining the output of distributed power sources at active load nodes, nodes with lower distributed power output are selectively disconnected during load shedding. This ensures that each load shedding operation reduces the power deficit in the system, solves the problem of the decrease in the proportion of actual controlled load during low-frequency load shedding caused by the high penetration of distributed renewable energy, fundamentally guarantees the effectiveness of emergency control measures, and reduces losses.

[0332] Those skilled in the art will understand that embodiments of this application can be provided as methods, systems, or computer program products. Therefore, this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application can take the form of a computer program product embodied on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0333] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart... Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0334] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0335] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0336] The embodiments of the present invention have been described above with reference to the accompanying drawings. However, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of the present invention without departing from the spirit and scope of the claims. All of these forms are within the protection scope of the present invention.

Claims

1. A low-frequency load shedding method for a power system with a high proportion of distributed renewable energy sources, characterized in that, include: Collect raw time-series data of active power and frequency of active load nodes in the target power system; Based on the original time-series data of the active power and frequency of the target active load node, the pre-acquired ARMAX model is processed to obtain the inertial time constant of the target active load node, and the equivalent inertial time constant of the power system is calculated based on the inertial time constant of the target active load node. Based on the equivalent inertia time constant of the power system, determine the decrease of the equivalent inertia time constant of the power system under the grid connection of distributed new energy sources. Based on the decrease of the equivalent inertia time constant and the pre-established low-frequency load shedding strategy, select the corresponding low-frequency load shedding parameters. When a power system experiences a power deficit fault, the total power deficit of the power system during the first round of low-frequency load shedding is calculated based on the equivalent inertial time constant of the power system, the calculated rate of change of the inertial center frequency of the power system, and the active power loss caused by the disconnection of distributed new energy sources from the grid. Based on pre-established evaluation indicators for low-frequency load shedding of active load nodes, the target active load nodes are evaluated. Based on the evaluation results, the low-frequency load shedding sequence of the target active load nodes is determined. According to the low-frequency load shedding sequence and the low-frequency load shedding parameters, the total power deficit is allocated to the corresponding low-frequency load shedding rounds of the target active load nodes.

2. The low-frequency load shedding method for a power system with a high proportion of distributed renewable energy sources according to claim 1, characterized in that, The raw time-series data based on the active power and frequency of the target active load node are used to process the pre-acquired ARMAX model to obtain the inertial time constant of the target active load node, including: Acquire and process the raw time-series data of the active power and frequency of the target active load node to obtain the time-series data of the change in active power and frequency of the target active load node; Based on the ARMAX model, the time series data of the active power change is used as input, and the time series data of the frequency change is used as output. The deterministic part of the ARMAX model is used to characterize the transfer function of the active load node inertia response, and the order of the transfer function is determined by AIC criterion measurement. Solve for the parameter vector to be identified in the ARMAX model, substitute the parameter vector to be identified into the ARMAX model, extract the dynamic part of the transfer function that characterizes the inertial response of the active load node, and obtain the discrete transfer function of the inertial response of the active load node. The discrete transfer function is converted into a continuous transfer function, and a unit step signal is applied to obtain the inertial time constant of the target active load node.

3. The low-frequency load shedding method for a power system with a high proportion of distributed renewable energy sources according to claim 2, characterized in that, The formula for the pre-acquired ARMAX model is: ； ； ； ； in, The time-series data of the frequency change of the target active load node at time t; The time series data of the change in active power of the target active load node at time t; This represents the noise component of the model. For backward displacement operator; , , These are the parameters to be identified in the ARMAX model; , , They are polynomials , , The order of the model; B(z) / A(z) is the deterministic part of the ARMAX model.

4. The low-frequency load shedding method for a power system with a high proportion of distributed renewable energy sources according to claim 1, characterized in that, The formula for the equivalent inertial time constant of the power system is: ； in, The equivalent inertial time constant of the power system; The equivalent inertial time constant of power node i in the power system is obtained by directly statistically analyzing the inertial time constants of each synchronous generator on the power node. The inertial time constant of the active load node j is calculated; , These are the rated capacities of the power sources at power source node i and active load node j in the power system, respectively. , These represent the number of power source nodes and active load nodes in the power system, respectively. This refers to the total rated capacity of the power supply in the power system. The formula for the decrease in the equivalent inertia time constant of the power system under distributed renewable energy grid connection is expressed as follows: ； in, This indicates the decrease in the equivalent inertia time constant of the power system under distributed renewable energy grid connection. The equivalent inertial time constant of the power system, It is the equivalent inertial time constant of the power system in the absence of distributed renewable energy sources.

5. The low-frequency load shedding method for a power system with a high proportion of distributed renewable energy sources according to claim 4, characterized in that, The low-frequency load reduction strategy includes: The basic cycle of low-frequency load shedding in the power system is set as several cycles; When the first threshold At that time, the starting frequency, starting delay time, and load reduction amount allocated to several basic cycles of the power system are set according to the first preset rule; When the second threshold When the first threshold is reached, the starting frequency, starting delay time, and load reduction amount allocated to several basic cycles of the power system are set according to the second preset rule. when When the second threshold is reached, the starting frequency, starting delay time, and load reduction amount allocated to several basic cycles of the power system are set according to the third preset rule. In addition to the aforementioned basic cycles, one special load reduction cycle is set up. The starting frequency of the special load reduction cycle is set to the first starting frequency, the starting delay time is set to the first delay time, and the allocated load reduction amount is the first percentage of the power system power deficit. After the previous low-frequency load shedding cycle is completed, if the power system frequency Less than or equal to the starting value of the next round ,and Then the next low-frequency load shedding cycle will be initiated, in which... This is the starting value for low-frequency load shedding in the i-th round; if the power system frequency is different, it must be less than or equal to the starting value for the next round. If, after a delay, the system frequency is less than or equal to the first starting frequency, then a special round is initiated; if the power system frequency does not simultaneously meet the starting value for the next round, If the power system frequency is greater than the first starting frequency after the delay, the load shedding will end.

6. The low-frequency load shedding method for a power system with a high proportion of distributed renewable energy sources according to claim 1, characterized in that, The calculation of the total power deficit during the first round of low-frequency load shedding, based on the equivalent inertial time constant of the power system, the calculated rate of change of the power system's inertial center frequency, and the active power loss caused by the disconnection of distributed renewable energy sources from the grid, includes: The initial power deficit of the power system is estimated by calculating the rate of change of the inertial center frequency of the power system. Based on the inertial time constant of the active load node, the rated capacity of the power supply, and the frequency, calculate the active power loss caused by the disconnection of distributed new energy power sources from the grid. Based on the initial power deficit of the power system and the active power loss caused by the disconnection of the distributed new energy power source from the grid, the total power deficit of the power system during the first round of low-frequency load shedding is calculated.

7. The low-frequency load shedding method for a power system with a high proportion of distributed renewable energy sources according to claim 6, characterized in that, The formula for calculating the inertial center frequency of the power system is: ； in, The inertial center frequency of the power system; Let i be the equivalent inertial time constant of power node i in the power system; Let be the inertial time constant of the active load node j; , These are the rated capacities of the power sources at power source node i and active load node j in the power system, respectively. , These represent the number of power source nodes and active load nodes in the power system, respectively. , These are the frequencies of power source node i and active load node j in the power system, respectively. The formula for calculating the initial power deficit of the power system is as follows: ； in, This represents the initial power deficit of the power system. The equivalent inertial time constant of the power system; This refers to the total rated capacity of the power supply in the power system. The rated frequency of the power system; The rate of change of the inertial center frequency of the power system. The moment when a power deficit fault occurs in the power system; The formula for calculating the active power loss caused by the disconnection of distributed renewable energy sources from the grid is as follows: ； in, This indicates that when the power system frequency drops to the frequency at which distributed renewable energy sources are disconnected from the grid. The active power loss caused by the disconnection of distributed renewable energy sources from the grid in the active load node j; , For the active load node j frequency to drop to Two moments before and after; The total power deficit of the power system during the first round of low-frequency load shedding is expressed as follows: ； in, This refers to the total power deficit of the power system during the first round of low-frequency load shedding. This refers to the total active power loss caused by the disconnection of distributed renewable energy sources from the grid in active load nodes.

8. The low-frequency load shedding method for a power system with a high proportion of distributed renewable energy sources according to claim 1, characterized in that, The evaluation indicators for low-frequency load shedding at active load nodes include the node's distributed renewable energy power penetration rate, node load shedding cost, and node frequency regulation effect coefficient. The formula for the penetration rate of distributed new energy power sources at the nodes is: ； in, Given the distributed renewable energy penetration rate of load node j, load nodes with low distributed renewable energy penetration rates are preferentially selected for disconnection. , These represent the active power and load power of the distributed renewable energy source in load node j, respectively. The formula for the node load reduction cost is: ； in, Given the unit load shedding cost of load node j, load nodes with lower unit load shedding costs are preferentially selected for shedding. , , The unit removal cost for Level 1, Level 2, and Level 3 loads, respectively; , , These represent the power of the primary, secondary, and tertiary loads in load node j, respectively. The cost of removing a unit power of distributed renewable energy source from load node j; The formula for the node frequency modulation effect coefficient is: ； in, Given the frequency regulation effect coefficient of load node j, load nodes with smaller frequency regulation effect coefficients are preferentially selected for disconnection. Let j be the frequency of the active load node.

9. The low-frequency load shedding method for a power system with a high proportion of distributed renewable energy sources according to claim 8, characterized in that, The evaluation of target active load nodes based on pre-established low-frequency load shedding evaluation indices, and the determination of the low-frequency load shedding sequence of target active load nodes based on the evaluation results, includes: A standardized evaluation matrix is ​​established based on the low-frequency load shedding evaluation index of the active load node. The weighting coefficients of various indicators of the load node are determined by using the entropy weight TOPSIS method. Based on the low-frequency load shedding evaluation index of the active load node and the weighting coefficient, a weighting matrix is ​​constructed; Based on the weighting matrix, calculate the positive and negative ideal solutions of the weighted low-frequency load reduction evaluation index values; Based on the weighting matrix and the positive and negative ideal solutions, calculate the Euclidean distances from the load node to be evaluated to the positive and negative ideal solutions; Based on the Euclidean distances from the load node to the positive and negative ideal solutions, the comprehensive evaluation value of the load node is calculated, and the low-frequency load shedding sequence of the target active load node is determined according to the comprehensive evaluation value of the load node.

10. The low-frequency load shedding method for a power system with a high proportion of distributed renewable energy sources according to claim 9, characterized in that, The formula for the standardized evaluation matrix is: ； ； Where Z is the evaluation matrix; For the elements in the matrix an n x 3 matrix Let be the standardized low-frequency load reduction evaluation index value of the j-th item of the i-th node; Let be the j-th low-frequency load shedding evaluation index value of the i-th node; n is the total number of load nodes; The formula for the weighting coefficients of each indicator of the load node is as follows: ； in, , where is the weighting coefficient of the j-th low-frequency load shedding evaluation index for the load node; Let be the entropy value of the j-th low-frequency load shedding evaluation index of the load node; The entropy value of the j-th low-frequency load shedding evaluation index of the load node The formula is: ； Where k is a constant, usually taken as... ; The weight of the j-th low-frequency load reduction evaluation index for the i-th node is given by the following formula: ； The formula for the weighting matrix is: ； Where V is the weighting matrix; Let j be the weighted standardized low-frequency load reduction evaluation index value of the i-th node, and its formula is: ； The formulas for the positive ideal solution and the negative ideal solution are: ； ； Among them, A + The positive ideal solution represents the optimal value of the weighted low-frequency load reduction evaluation index; A - The negative ideal solution represents the worst value of the weighted low-frequency load reduction evaluation index. The formula for the Euclidean distance from the load node to be evaluated to the positive and negative ideal solutions is: ； ； in, Let be the Euclidean distance from the load node i to be evaluated to the positive ideal solution. Let be the Euclidean distance from the load node i to be evaluated to the negative ideal solution; This is the positive ideal solution for the weighted j-th low-frequency load reduction evaluation index value. The negative ideal solution for the weighted j-th low-frequency load reduction evaluation index value; The formula for the comprehensive evaluation value of the load node is: ； in, CI is the comprehensive evaluation value of load node i. The larger the CI value, the more likely the corresponding load node will be cut off.

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