Voltage-reactive compensation control strategy of construction power supply system for pumped storage based on hierarchical compensation principle

Abstract

A voltage-reactive power compensation control strategy of pumped storage construction power supply system based on hierarchical compensation principle is provided, which includes the steps of overall model, control variable, objective function, constraint condition and solution. For different typical power quality problems, hierarchical management is carried out from load side to network side. In the hierarchical management process, voltage, reactive current, reactive power, power factor and other parameters are used as basic criteria for compensation control switching. A multi-objective function model with minimum network loss, power factor and voltage deviation is further constructed. Considering the constraints of equipment and system operation, the optimal comprehensive compensation scheme of voltage-reactive power of pumped storage construction power supply system is obtained through NSGA-II iterative solution, so as to effectively solve the problems of large reactive power loss of distribution network line and unstable terminal voltage in pumped storage construction power supply system, and improve the power quality of the system.

Description

Technical Field

[0001] This invention belongs to the technical field of control strategy for pumped storage power supply systems, and relates to a voltage-reactive power compensation control strategy for pumped storage construction power supply systems based on the principle of graded compensation. Background Technology

[0002] In power supply systems, current focus is mostly on optimizing the coordinated operation of underlying equipment in the distribution network or addressing single power quality issues. However, the management of power supply for pumped storage power station construction is still in a relatively rudimentary stage. Comprehensive management strategies for typical power quality issues under multiple operating conditions in the power supply system for pumped storage power station construction, as well as the overall coordination and optimization of power quality, have not yet been considered. The hierarchical coordination and compensation control model and architecture urgently need further exploration. Summary of the Invention

[0003] The technical problem to be solved by this invention is to provide a voltage-reactive power compensation control strategy for pumped storage construction power supply system based on the principle of hierarchical compensation. This strategy involves voltage over-limit control and voltage-reactive power optimization control, over-limit judgment, global optimization and hierarchical coordination control, and supplementing over-limit correction with global optimization until the voltage and power of all nodes are within the normal range, thereby achieving system loss reduction and energy saving.

[0004] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a voltage-reactive power compensation control strategy for pumped storage construction power supply system based on the principle of graded compensation, which includes the following steps:

[0005] S1, the overall model, addresses the location and capacity determination issues of DG, capacitor banks, and OLTC equipment in the construction power supply system, and implements a multi-objective decision control scheme based on hierarchical coordination and compensation; the optimized control model for the pumped storage construction power supply system is represented as follows:

[0006] (1)

[0007] In the formula: Let be the overall objective function. , , For sub-objective functions; , These are the system and equipment-related constraints. These are the system decision variables and the system operating state variables, respectively; this model is an overall voltage-reactive power hierarchical coordinated optimization control model.

[0008] S2, control variables, including decision vector and state vector;

[0009] S2-1, Decision Vector This represents the decision vector of the optimization control model consisting of m control variables during the k-th hierarchical optimization control cycle; the decision vector xk includes the tap position of the OLTC. Number of capacitor banks switched The active and reactive power of SNOP and and ;

[0010] S2-2, State Vector This represents the state vector of the optimization control model consisting of m control variables during the k-th hierarchical optimization control cycle; the state vector... This includes the real-time active and reactive power of each node load. and Predicted power and Node voltage and branch current and power factor ;

[0011] S3, Objective function, the objective function F(x) of the hierarchical optimization model. k ,u k The plan consists of three levels of objective functions: F1(xk,uk,t) with the objective of optimal control of the distribution network voltage, F2(xk,uk,t) with the objective of optimal power factor of the construction power supply system, and F3(xk,uk,t). k ,u k The planning scheme F3(x) with the goal of minimizing the active power loss of the construction power supply system is t). k ,u k ,t);

[0012] S4, constraints, including power flow constraints, node voltage and branch current constraints, flexible interconnection device operation constraints, flexible transformer operation constraints, integrated reactive power compensation operation constraints, and power factor operation constraints;

[0013] S5, the solution includes loading real-time system data and models, initial power flow calculation, voltage over-limit judgment and correction, judgment and hierarchical management of typical power quality problems, power factor over-limit judgment and correction, global voltage-reactive power optimization and layer-by-layer iterative optimization.

[0014] In S2, the decision vector The maximum dimension is determined by the total number of DG power plants, feeders, and substations (CBs) and OLTCs in the distribution network, as well as the active and reactive power of SNOPs in the interconnected areas. The decision vector is determined during each optimization. The actual dimension is determined by the pre-decision method proposed at each level; state vector The maximum dimension is determined by the real-time and predicted active and reactive power of the loads at each node in the distribution network, the node voltage and branch current, and the power factor of the feeders and loads. The actual dimension of the state vector uk is determined by the pre-decision method proposed at each level during each optimization.

[0015] In S3, the hierarchical optimization model of the entire power supply system is represented as follows:

[0016] (1) Optimal voltage control objective of the construction power supply system:

[0017] (2)

[0018]

[0019] (2) Optimal power factor control objective of the construction power supply system:

[0020] (3)

[0021]

[0022] (3) Minimize active power loss in the construction power supply system:

[0023] (4)

[0024] .

[0025] In S4, (1) power flow constraints,

[0026] (5)

[0027] In the formula, , The active and reactive power injected into the generator at node i; , The active and reactive power injected into the load at node i; , Let the voltages at nodes i and j be . Let the electrical conductance be between node i and node j. The susceptance between node i and node j The phase angle difference between node i and node j;

[0028] (2) Node voltage and branch current constraints,

[0029] (6)

[0030] In the formula, and These are the upper and lower limits of the node voltage amplitude in the system; It is the current amplitude of branch ij. It is the upper limit of the current amplitude in branch ij;

[0031] (3) Operational constraints of flexible interconnection devices,

[0032] (7)

[0033] In the formula, and , respectively, are the operating losses of the i-side and j-side converters in the SNOP; k is the loss coefficient of the converter; This refers to the rated capacity of the SNOP converter;

[0034] (4) Operating constraints of flexible transformers

[0035] (8)

[0036] In the formula, The voltage on the high-voltage side of the flexible transformer is a constant. Let t be the turns ratio of the flexible transformer. The tap position at time t is an integer variable; This represents the difference in gear ratio between adjacent gears. , These are the maximum and minimum settings of the tap; The variable is 0 or 1. If it is 1, it indicates that the tap position of the on-load tap-changing transformer has changed. A value of 0 indicates that the tap position remains unchanged; This represents the maximum number of permissible operations for a flexible transformer.

[0037] (5) Comprehensive reactive power compensation operation constraints,

[0038] (9)

[0039] In the formula, The number of capacitor banks switched at node i during time period t; This refers to the reactive power generated by a single capacitor bank under rated voltage. This represents the maximum number of capacitor banks that can be switched at node i. It belongs to the 0,1 variable, and its 0,1 state indicates whether the capacitor bank at node i in time period t will be switched on or off in the next time. The maximum number of times a capacitor can be switched on and off in a group within 24 hours; , The upper and lower limits of the reactive power that the static var compensator at node i is allowed to output;

[0040] (6) Power factor operating constraints,

[0041] (10).

[0042] In S5, the solution process is as follows:

[0043] Step 1: Load the system's real-time data and model;

[0044] The system loads the electrical load information of the low-voltage distribution feeder terminal nodes and the medium-voltage distribution circuit information required for voltage-reactive power control, and collects real-time data and models. Specific content includes parameters such as voltage, current, active power, reactive power, and power factor on each distribution circuit bus, as well as the tap position, capacitor, and outgoing switch position signals of the flexible on-load tap changer.

[0045] Step 2, Initial power flow calculation;

[0046] Before performing reactive power and voltage optimization control of the construction power supply system, a power flow calculation is performed. The voltage calculated in this process is used as the basis for determining whether the voltage exceeds the limit in Step 3. The power calculated in this process is used as the basis for determining whether the power factor exceeds the limit in Step 5. The network loss calculated in this process is used as the initial network loss for reactive power optimization of the construction power supply system in Step 6.

[0047] Step 3, voltage over-limit judgment and correction;

[0048] Step 3-1: Determine whether there is a voltage over-limit based on the initial voltage value of each feeder operating independently. If all voltage nodes are within the normal range, the process ends.

[0049] Step 3-2: If there is a voltage limit violation, further analyze the degree of voltage limit violation and the cause of the violation.

[0050] Step 3-3: Determine whether the over-limit amount is within 10% based on the over-limit situation. If it exceeds 10%, there are many nodes with voltage over-limits. Further optimization algorithms need to be executed to constrain and correct the node voltage and branch power. When the requirements are met, the optimization iteration is exited.

[0051] Steps 3-4: If the voltage exceedance is within 10%, then the typical power quality problems will be addressed and the voltage exceedance will be eliminated in a tiered manner, from the load side to the grid side, i.e., in order of voltage level from low to high.

[0052] Step 4: Identification and graded management of typical power quality problems;

[0053] Step 4-1: Determine whether there is a large line impedance based on the collected information. If so, local compensation is achieved by configuring a comprehensive compensation power electronic device consisting of capacitor banks. The switching of capacitor banks is further controlled according to the change of the on-load tap changer to achieve a combination of various compensation capacities. The action value of the control device required to eliminate over-limit is estimated by pre-calculated initial voltage, and timely adjustments are made according to the terminal load working status or voltage changes. If not, proceed to the next step of judgment.

[0054] Step 4-2: Detect whether there is an inrush current or power surge in the distribution feeder based on real-time data of the line; if so, use a flexible on-load tap changer control scheme to continuously adjust the voltage and reactive power at the low-voltage distribution transformer level at the critical node to perform reactive power-voltage compensation for the load at the lower end of the transformer; if not, proceed to the next step of judgment.

[0055] Step 4-3: Based on the data from the distribution circuit bus, determine whether the power of different low-voltage distribution network feeders is unevenly distributed or exceeds the upper limit of the single-zone power threshold. At this time, due to the heavy load of the transformer area, the control device of a single area has reached the control constraint limit and cannot be further adjusted. Then, it seeks help from other areas of the same level. By configuring a power electronic flexible interconnection device, the power flow between multiple areas is regulated at the system level to adjust the uneven power distribution, realize reactive power and voltage regulation between multiple areas, and achieve voltage and reactive power balance regulation between multiple areas.

[0056] Step 5: Power factor exceeding limits judgment and correction;

[0057] If all power nodes are within the normal range, the process ends; if power exceeds the limit, further analyze the cause of the power exceedance and eliminate the power exceedance; refer to the judgment and correction of voltage exceedance, and comprehensively adjust through three aspects: power regulation of flexible interconnection device, flexible on-load tap changer position, compensation capacitor and reactor switching, and then correct the power factor according to real-time indicators and expected indicators to solve the situation of active and reactive power flow exceeding the limit.

[0058] Step 6: Global voltage-reactive power optimization;

[0059] When the node voltage and power factor of the system are within the normal range, the next step of global reactive power optimization calculation and operation is carried out. Based on the system's multi-objective function, including the requirements of the constraints, the optimization goal of minimizing the loss of the construction power supply system is achieved, thereby improving the economic efficiency of system operation.

[0060] Step 7: Iterate and optimize layer by layer until the termination condition is met and all node voltages and power are within the normal range;

[0061] The voltage and reactive power hierarchical coordinated control optimization of the power supply system for pumped storage power station construction is complex and has many constraints. It is a multi-dimensional nonlinear optimization model MOMINP. An improved non-dominated sorting genetic algorithm II (NSGA-II) with elitist strategy is selected to solve the MOMINP model.

[0062] The main beneficial effects of this invention are as follows:

[0063] This study considers multi-level and graded management of typical power quality problems such as long power supply radius, impulsive load access, non-uniform power distribution, or heavy load in transformer areas. Ultimately, it aims to achieve comprehensive voltage-reactive power control of the pumped storage power supply system through global reactive power optimization. This will solve the problems of large reactive power loss in the distribution network lines and unstable terminal voltage in the pumped storage power station construction power supply system, improve the reliability, stability, and economy of the power supply system, and improve the system's power quality.

[0064] First, voltage over-limit control is performed, followed by voltage reactive power optimization control; if the voltage is within acceptable limits, then power factor over-limit judgment and correction are performed.

[0065] Global voltage-reactive power optimization and layer-by-layer iterative global reactive power optimization are only performed when the voltage is within acceptable limits and there is no power factor exceeding the limit.

[0066] If voltage exceeds the limit, the degree of voltage exceedance is judged. If it is within the threshold of the exceedance node, typical power quality problems are judged and managed in stages, power factor exceedance is judged and corrected, and global voltage-reactive power optimization is performed to achieve hierarchical coordinated control.

[0067] If the hierarchical coordination fails due to a large number of nodes exceeding the threshold, global optimization is used to supplement the over-limit correction until the voltage and power of all nodes are within the normal range, thereby achieving system loss reduction and energy saving.

[0068] To address different typical power quality issues, a tiered approach is adopted, proceeding sequentially from the load side to the grid side. During this tiered approach, voltage, reactive current, reactive power, and power factor are comprehensively used as fundamental criteria for compensation control switching. Furthermore, a multi-objective function model is constructed, minimizing grid losses, power factor, and voltage deviation. Considering equipment and system operational constraints, the model is iteratively solved using NSGA-II to obtain the optimal voltage-reactive power compensation scheme for the pumped storage power supply system. This effectively solves the problems of high reactive power loss in the distribution network lines and unstable voltage at the end of the pumped storage power station construction power supply system, thereby improving the system's power quality. Attached Figure Description

[0069] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0070] Figure 1 This is a diagram of the voltage-reactive power hierarchical coordinated compensation control architecture optimized for the operation of this invention.

[0071] Figure 2 The flowchart shows the improved NSGA-II algorithm of this invention for solving the multi-objective MOMINP model. Detailed Implementation

[0072] like Figures 1-2 The present invention relates to a voltage-reactive power compensation control strategy for a pumped storage power supply system based on the principle of graded compensation, which includes the following steps:

[0073] S1, the overall model, addresses the location and capacity determination issues of DG, capacitor banks, and OLTC equipment in the construction power supply system, and implements a multi-objective decision control scheme based on hierarchical coordination and compensation; the optimized control model for the pumped storage construction power supply system is represented as follows:

[0074] (1)

[0075] In the formula: Let be the overall objective function. , , For sub-objective functions; , These are the system and equipment-related constraints. These are the system decision variables and the system operating state variables, respectively; this model is an overall voltage-reactive power hierarchical coordinated optimization control model.

[0076] S2, control variables, including decision vector and state vector;

[0077] S2-1, Decision Vector This represents the decision vector of the optimization control model consisting of m control variables during the k-th hierarchical optimization control cycle; the decision vector xk includes the tap position of the OLTC. Number of capacitor banks switched The active and reactive power of SNOP and and ;

[0078] S2-2, State Vector This represents the state vector of the optimization control model consisting of m control variables during the k-th hierarchical optimization control cycle; the state vector... This includes the real-time active and reactive power of each node load. and Predicted power and Node voltage and branch current and power factor ;

[0079] S3, Objective function, the objective function F(x) of the hierarchical optimization model. k ,u k The plan consists of three levels of objective functions: F1(xk,uk,t) with the objective of optimal control of the distribution network voltage, F2(xk,uk,t) with the objective of optimal power factor of the construction power supply system, and F3(xk,uk,t). k ,u k The planning scheme F3(x) with the goal of minimizing the active power loss of the construction power supply system is t). k ,u k ,t);

[0080] S4, constraints, including power flow constraints, node voltage and branch current constraints, flexible interconnection device operation constraints, flexible transformer operation constraints, integrated reactive power compensation operation constraints, and power factor operation constraints;

[0081] S5, the solution includes loading real-time system data and models, initial power flow calculation, voltage over-limit judgment and correction, judgment and hierarchical management of typical power quality problems, power factor over-limit judgment and correction, global voltage-reactive power optimization and layer-by-layer iterative optimization.

[0082] In the preferred scheme, in S2, the decision vector The maximum dimension is determined by the total number of DG power plants, feeders, and substations (CBs) and OLTCs in the distribution network, as well as the active and reactive power of SNOPs in the interconnected areas. The decision vector is determined during each optimization. The actual dimension is determined by the pre-decision method proposed at each level; state vector The maximum dimension is determined by the real-time and predicted active and reactive power of the loads at each node in the distribution network, the node voltage and branch current, and the power factor of the feeders and loads. The actual dimension of the state vector uk is determined by the pre-decision method proposed at each level during each optimization.

[0083] In the preferred scheme, in S3, the hierarchical optimization model of the entire power supply system is represented as follows:

[0084] (1) Optimal voltage control objective of the construction power supply system:

[0085] (2)

[0086]

[0087] (2) Optimal power factor control objective of the construction power supply system:

[0088] (3)

[0089]

[0090] (3) Minimize active power loss in the construction power supply system:

[0091] (4)

[0092] .

[0093] In the preferred scheme, in S4, (1) power flow constraints,

[0094] (5)

[0095] In the formula, , The active and reactive power injected into the generator at node i; , The active and reactive power injected into the load at node i; , Let the voltages at nodes i and j be . Let the electrical conductance be between node i and node j. The susceptance between node i and node j The phase angle difference between node i and node j;

[0096] (2) Node voltage and branch current constraints,

[0097] (6)

[0098] In the formula, and These are the upper and lower limits of the node voltage amplitude in the system; It is the current amplitude of branch ij. It is the upper limit of the current amplitude in branch ij;

[0099] (3) Operational constraints of flexible interconnection devices,

[0100] (7)

[0101] In the formula, and , respectively, are the operating losses of the i-side and j-side converters in the SNOP; k is the loss coefficient of the converter; This refers to the rated capacity of the SNOP converter;

[0102] (4) Operating constraints of flexible transformers

[0103] (8)

[0104] In the formula, The voltage on the high-voltage side of the flexible transformer is a constant. Let t be the turns ratio of the flexible transformer. The tap position at time t is an integer variable; This represents the difference in gear ratio between adjacent gears. , These are the maximum and minimum settings of the tap; The variable is 0 or 1. If it is 1, it indicates that the tap position of the on-load tap-changing transformer has changed. A value of 0 indicates that the tap position remains unchanged; This represents the maximum number of permissible operations for a flexible transformer.

[0105] (5) Comprehensive reactive power compensation operation constraints,

[0106] (9)

[0107] In the formula, The number of capacitor banks switched at node i during time period t; This refers to the reactive power generated by a single capacitor bank under rated voltage. This represents the maximum number of capacitor banks that can be switched at node i. It belongs to the 0,1 variable, and its 0,1 state indicates whether the capacitor bank at node i in time period t will be switched on or off in the next time. The maximum number of times a capacitor can be switched on and off in a group within 24 hours; , The upper and lower limits of the reactive power that the static var compensator at node i is allowed to output;

[0108] (6) Power factor operating constraints,

[0109] (10).

[0110] In the preferred solution, the solution process in S5 is as follows:

[0111] Step 1: Load the system's real-time data and model;

[0112] The system loads the electrical load information of the low-voltage distribution feeder terminal nodes and the medium-voltage distribution circuit information required for voltage-reactive power control, and collects real-time data and models. Specific content includes parameters such as voltage, current, active power, reactive power, and power factor on each distribution circuit bus, as well as the tap position, capacitor, and outgoing switch position signals of the flexible on-load tap changer.

[0113] Step 2, Initial power flow calculation;

[0114] Before performing reactive power and voltage optimization control of the construction power supply system, a power flow calculation is performed. The voltage calculated in this process is used as the basis for determining whether the voltage exceeds the limit in Step 3. The power calculated in this process is used as the basis for determining whether the power factor exceeds the limit in Step 5. The network loss calculated in this process is used as the initial network loss for reactive power optimization of the construction power supply system in Step 6.

[0115] Step 3, voltage over-limit judgment and correction;

[0116] Step 3-1: Determine whether there is a voltage over-limit based on the initial voltage value of each feeder operating independently. If all voltage nodes are within the normal range, the process ends.

[0117] Step 3-2: If there is a voltage limit violation, further analyze the degree of voltage limit violation and the cause of the violation.

[0118] Step 3-3: Determine whether the over-limit amount is within 10% based on the over-limit situation. If it exceeds 10%, there are many nodes with voltage over-limits. Further optimization algorithms need to be executed to constrain and correct the node voltage and branch power. When the requirements are met, the optimization iteration is exited.

[0119] Steps 3-4: If the voltage exceedance is within 10%, then the typical power quality problems will be addressed and the voltage exceedance will be eliminated in a tiered manner, from the load side to the grid side, i.e., in order of voltage level from low to high.

[0120] In the preferred scheme, Step 4 involves the identification and tiered management of typical power quality problems.

[0121] Step 4-1: Determine whether there is a large line impedance based on the collected information. If so, local compensation is achieved by configuring a comprehensive compensation power electronic device consisting of capacitor banks. The switching of capacitor banks is further controlled according to the change of the on-load tap changer to achieve a combination of various compensation capacities. The action value of the control device required to eliminate over-limit is estimated by pre-calculated initial voltage, and timely adjustments are made according to the terminal load working status or voltage changes. If not, proceed to the next step of judgment.

[0122] Step 4-2: Detect whether there is an inrush current or power surge in the distribution feeder based on real-time data of the line; if so, use a flexible on-load tap changer control scheme to continuously adjust the voltage and reactive power at the low-voltage distribution transformer level at the critical node to perform reactive power-voltage compensation for the load at the lower end of the transformer; if not, proceed to the next step of judgment.

[0123] Step 4-3: Based on the data from the distribution circuit bus, determine whether the power of different low-voltage distribution network feeders is unevenly distributed or exceeds the upper limit of the single-zone power threshold. At this time, due to the heavy load of the transformer area, the control device of a single area has reached the control constraint limit and cannot be further adjusted. Then, it seeks help from other areas of the same level. By configuring a power electronic flexible interconnection device, the power flow between multiple areas is regulated at the system level to adjust the uneven power distribution, realize reactive power and voltage regulation between multiple areas, and achieve voltage and reactive power balance regulation between multiple areas.

[0124] In the preferred scheme, Step 5: Power factor exceeding the limit judgment and correction;

[0125] If all power nodes are within the normal range, the process ends; if power exceeds the limit, further analyze the cause of the power exceedance and eliminate the power exceedance; refer to the judgment and correction of voltage exceedance, and comprehensively adjust through three aspects: power regulation of flexible interconnection device, flexible on-load tap changer position, compensation capacitor and reactor switching, and then correct the power factor according to real-time indicators and expected indicators to solve the situation of active and reactive power flow exceeding the limit.

[0126] Step 6: Global voltage-reactive power optimization;

[0127] When the node voltage and power factor of the system are within the normal range, the next step of global reactive power optimization calculation and operation is carried out. Based on the system's multi-objective function, including the requirements of the constraints, the optimization goal of minimizing the loss of the construction power supply system is achieved, thereby improving the economic efficiency of system operation.

[0128] Step 7: Iterate and optimize layer by layer until the termination condition is met and all node voltages and power are within the normal range;

[0129] The voltage and reactive power hierarchical coordinated control optimization of the power supply system for pumped storage power station construction is complex and has many constraints. It is a multi-dimensional nonlinear optimization model MOMINP. An improved non-dominated sorting genetic algorithm II (NSGA-II) with elitist strategy is selected to solve the MOMINP model.

[0130] Preferably, in the above architecture, voltage over-limit control is performed first, followed by voltage reactive power optimization control.

[0131] Preferably, if the voltage is qualified, Step 5 is performed to determine whether the power factor exceeds the limit. Step 6 and Step 7 are performed only if the voltage is qualified and the power factor does not exceed the limit.

[0132] Preferably, if there is a voltage over-limit, step 3 is performed to determine the degree of voltage over-limit. If it is within the threshold of the over-limit node, step 4, step 5, and step 6 are performed sequentially for hierarchical coordinated control.

[0133] Preferably, if hierarchical coordination fails due to a large number of out-of-limit nodes outside the threshold, global optimization is used to supplement the out-of-limit correction until the voltage and power of all nodes are within the normal range, thereby achieving system loss reduction and energy saving.

[0134] This study considers multi-level and graded management of typical power quality problems such as long power supply radius, impulsive load access, non-uniform power distribution, or heavy load in transformer areas. Ultimately, it aims to achieve comprehensive voltage-reactive power control of the pumped storage power supply system through global reactive power optimization. This will solve the problems of large reactive power loss in the distribution network lines and unstable terminal voltage in the pumped storage power station construction power supply system, improve the reliability, stability, and economy of the power supply system, and improve the system's power quality.

[0135] To address different typical power quality issues, a tiered approach is adopted, proceeding sequentially from the load side to the grid side. During this tiered approach, voltage, reactive current, reactive power, and power factor are comprehensively used as fundamental criteria for compensation control switching. Furthermore, a multi-objective function model is constructed, minimizing grid losses, power factor, and voltage deviation. Considering equipment and system operational constraints, the model is iteratively solved using NSGA-II to obtain the optimal voltage-reactive power compensation scheme for the pumped storage power supply system. This effectively solves the problems of high reactive power loss in the distribution network lines and unstable voltage at the end of the pumped storage power station construction power supply system, thereby improving the system's power quality.

[0136] The above embodiments are merely preferred technical solutions of the present invention and should not be considered as limitations on the present invention. The embodiments and features described in these embodiments can be arbitrarily combined without conflict. The scope of protection of the present invention should be limited to the technical solutions described in the claims, including equivalent substitutions of the technical features described in the claims. That is, equivalent substitutions and improvements within this scope are also within the scope of protection of the present invention.

Claims

1. A voltage-reactive power compensation control strategy for a pumped storage power supply system based on the principle of graded compensation, characterized in that, It includes the following steps: S1, the overall model, addresses the location and capacity determination issues of DG, capacitor banks, and OLTC equipment in the construction power supply system, and implements a multi-objective decision control scheme based on hierarchical coordination and compensation; the optimized control model for the pumped storage construction power supply system is represented as follows: (1) In the formula: Let be the overall objective function. , , For sub-objective functions; , These are the system and equipment-related constraints. These are system decision variables and system operating state variables, respectively. S2, control variables, including decision vector and state vector; S2-1, Decision Vector Including the tap position of OLTC Number of capacitor banks switched Active and reactive power of SNOP and ; S2-2, State Vector This includes the real-time active and reactive power of each node load. and Predicting active and reactive power and Node voltage and branch current and power factor ; S3, Objective function, the objective function of the hierarchical optimization model. (x k ,u k The objective function (t) consists of three levels: a planning scheme with the goal of optimal control of the distribution network voltage. (xk,uk,t) Planning scheme with the goal of optimizing the power factor of the construction power supply system. (x k ,u k Planning schemes that aim to minimize active power loss in the construction power supply system. (x k ,u k ,t); S4, constraints, including power flow constraints, node voltage and branch current constraints, flexible interconnection device operation constraints, flexible transformer operation constraints, integrated reactive power compensation operation constraints, and power factor operation constraints; S5, Solving, includes loading real-time system data and models, initial power flow calculation, voltage over-limit judgment and correction, judgment and hierarchical management of typical power quality problems, power factor over-limit judgment and correction, global voltage-reactive power optimization and layer-by-layer iterative optimization. In S5, the solution process is as follows: Step 1: Load the system's real-time data and model; Step 2, Initial power flow calculation; Step 3, voltage over-limit judgment and correction; Step 4: Identification and graded management of typical power quality problems; Step 5: Power factor exceeding limits judgment and correction; Step 6: Global voltage-reactive power optimization; Step 7: Iterate and optimize layer by layer until the termination condition is met and all node voltages and power are within the normal range; In the above solution, voltage over-limit control is performed first, and voltage reactive power optimization control is performed second. If the voltage is within acceptable limits, proceed to Step 5 to determine if the power factor exceeds the limit. Only if the voltage is within acceptable limits and the power factor does not exceed the limit will Step 6 and Step 7 be performed for global reactive power optimization. If voltage exceeds the limit, proceed to step 3 to determine the degree of voltage exceedance. If it is within the threshold of the exceedance node, proceed to step 4, step 5, and step 6 in sequence to perform hierarchical coordinated control. If the hierarchical coordination fails due to a large number of nodes exceeding the threshold, global optimization is used to supplement the over-limit correction until the voltage and power of all nodes are within the normal range, thereby achieving system loss reduction and energy saving.

2. The voltage-reactive power compensation control strategy for pumped storage construction power supply system based on the principle of graded compensation as described in claim 1, characterized in that: In S2, the decision vector The maximum dimension is determined by the total number of DG power plants, feeders, and substations (CBs) and OLTCs in the distribution network, as well as the active and reactive power of SNOPs in the interconnected areas. The decision vector is determined during each optimization. The actual dimension is determined by the pre-decision method proposed at each level; state vector The maximum dimension is determined by the real-time and predicted active and reactive power of the loads at each node in the distribution network, the node voltage and branch current, and the power factor of the feeders and loads. The actual dimension of the state vector uk is determined by the pre-decision method proposed at each level during each optimization.

3. The voltage-reactive power compensation control strategy for pumped storage construction power supply system based on the principle of graded compensation as described in claim 1, characterized in that: In S3, the hierarchical optimization model of the entire power supply system is represented as follows: (1) Optimal voltage control objective of the construction power supply system: （2） (2) Optimal power factor control objective of the construction power supply system: （3） (3) Minimize active power loss in the construction power supply system: （4） 。 4. The voltage-reactive power compensation control strategy for pumped storage construction power supply system based on the principle of graded compensation as described in claim 1, characterized in that: In S4, (1) power flow constraints, （5） In the formula, , The active and reactive power injected into the generator at node i; , The active and reactive power injected into the load at node i; , Let the voltages at nodes i and j be . Let the electrical conductance be between node i and node j. The susceptance between node i and node j The phase angle difference between node i and node j; (2) Node voltage and branch current constraints, （6） In the formula, and These are the upper and lower limits of the node voltage amplitude in the system; It is the current amplitude of branch ij. It is the upper limit of the current amplitude in branch ij; (3) Operational constraints of flexible interconnection devices, （7） In the formula, and , respectively, are the operating losses of the i-side and j-side converters in the SNOP; k is the loss coefficient of the converter; This refers to the rated capacity of the SNOP converter; (4) Operating constraints of flexible transformers （8） In the formula, The voltage on the high-voltage side of the flexible transformer is a constant. Let t be the turns ratio of the flexible transformer. The tap position at time t is an integer variable; This represents the difference in gear ratio between adjacent gears. , These are the maximum and minimum settings of the tap; The variable is 0 or 1. If it is 1, it indicates that the tap position of the on-load tap-changing transformer has changed. A value of 0 indicates that the tap position remains unchanged; This represents the maximum number of permissible operations for a flexible transformer. (5) Comprehensive reactive power compensation operation constraints, （9） In the formula, The number of capacitor banks switched at node i during time period t; This refers to the reactive power generated by a single capacitor bank under rated voltage. This represents the maximum number of capacitor banks that can be switched at node i. It belongs to the 0,1 variable, and its 0,1 state indicates whether the capacitor bank at node i in time period t will be switched on or off in the next time. The maximum number of times a capacitor can be switched on and off in a group within 24 hours; , The upper and lower limits of the reactive power that the static var compensator at node i is allowed to output; (6) Power factor operating constraints, （10）。 5. The voltage-reactive power compensation control strategy for pumped storage construction power supply system based on the principle of graded compensation as described in claim 1, characterized in that: Step 4-1: Determine whether there is a large line impedance based on the collected information. If so, local compensation is achieved by configuring a comprehensive compensation power electronic device consisting of capacitor banks. The switching of capacitor banks is further controlled according to the change of the on-load tap changer to achieve a combination of various compensation capacities. The action value of the control device required to eliminate over-limit is estimated by pre-calculated initial voltage, and timely adjustments are made according to the terminal load working status or voltage changes. If not, proceed to the next step of judgment. Step 4-2: Detect whether there is an inrush current or power surge in the distribution feeder based on real-time data of the line; if so, use a flexible on-load tap changer control scheme to continuously adjust the voltage and reactive power at the low-voltage distribution transformer level at the critical node to perform reactive power-voltage compensation for the load at the lower end of the transformer; if not, proceed to the next step of judgment. Step 4-3: Based on the data from the distribution circuit bus, determine whether the power of different low-voltage distribution network feeders is unevenly distributed or exceeds the upper limit of the single-zone power threshold. At this time, due to the heavy load of the transformer area, the control device of a single area has reached the control constraint limit and cannot be further adjusted. Then, it seeks help from other areas of the same level. By configuring a power electronic flexible interconnection device, the power flow between multiple areas is regulated at the system level to adjust the uneven power distribution, realize reactive power and voltage regulation between multiple areas, and achieve voltage and reactive power balance regulation between multiple areas.

6. The voltage-reactive power compensation control strategy for pumped storage construction power supply system based on the principle of graded compensation as described in claim 1, characterized in that: If all power nodes are within the normal range, the process ends; if power exceeds the limit, further analyze the cause of the power exceedance and eliminate the power exceedance; refer to the judgment and correction of voltage exceedance, and comprehensively adjust through three aspects: power regulation of flexible interconnection device, flexible on-load tap changer position, compensation capacitor and reactor switching, and then correct the power factor according to real-time indicators and expected indicators to solve the situation of active and reactive power flow exceeding the limit. When the node voltage and power factor of the system are within the normal range, the next step of global reactive power optimization calculation and operation is carried out. Based on the system's multi-objective function, including the requirements of the constraints, the optimization goal of minimizing the loss of the construction power supply system is achieved, thereby improving the economic efficiency of system operation.

7. The voltage-reactive power compensation control strategy for pumped storage construction power supply system based on the principle of graded compensation as described in claim 1, characterized in that: In S5, The system loads the electrical load information of the low-voltage distribution feeder terminal nodes and the medium-voltage distribution circuit information required for voltage-reactive power control, and collects real-time data and models. Specific content includes voltage, current, active power, reactive power, power factor parameters on each distribution circuit bus, as well as the tap position, capacitor, and outgoing switch position signals of the flexible on-load tap changer and reactor. Before performing reactive power and voltage optimization control of the construction power supply system, a power flow calculation is performed. The voltage calculated by the power flow is used as the basis for determining whether the voltage exceeds the limit in Step 3. The power calculated by the power flow is used as the basis for determining whether the power factor exceeds the limit in Step 5. The network loss calculated by the power flow is used as the initial network loss for reactive power optimization of the construction power supply system in Step 6. Step 3-1: Determine whether there is a voltage over-limit based on the initial voltage value of each feeder operating independently. If all voltage nodes are within the normal range, the process ends. Step 3-2: If there is a voltage limit violation, further analyze the degree of voltage limit violation and the cause of the violation. Step 3-3: Determine whether the over-limit amount is within 10% based on the over-limit situation. If it exceeds 10%, there are many nodes with voltage over-limits. Further optimization algorithms need to be executed to constrain and correct the node voltage and branch power. When the requirements are met, the optimization iteration is exited. Steps 3-4: If the voltage exceedance is within 10%, then the typical power quality problems will be addressed and the voltage exceedance will be eliminated in a tiered manner, from the load side to the grid side, i.e., in order of voltage level from low to high.

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