Method for evaluating flexibility of five pumped storage units for new energy consumption

Abstract

The invention discloses a new energy consumption-oriented flexibility evaluation method for five pumped storage units, which comprises the following steps of: pre-establishing a system flexibility measurement index model which comprises the flexibility of a thermal power generating unit and the flexibility of different types of pumped storage units; a two-stage day-ahead scheduling optimization model including wind power, photovoltaic and thermal power units and pumped storage is constructed, the first stage of the model takes the minimum system operation cost under the new energy non-disturbance condition as the target, and the second stage of the model takes the minimum correction cost under the new energy output disturbance condition as the target; the new energy output uncertainty is represented by adopting an envelope boundary model, the bearable maximum new energy output disturbance range of the system under a given cost threshold value is determined by adjusting an uncertainty radius parameter, and the flexibility index of the system is calculated according to the maximum new energy output disturbance range. The method can achieve the unified evaluation of the flexibility characteristics of five pumped storage units, and reveals the rules of the improvement of the system flexibility and the enhancement of the new energy consumption capability of different unit types.

Description

Technical Field

[0001] This invention belongs to the field of power dispatching, specifically involving a method for evaluating the flexibility of five pumped storage units for new energy consumption. Background Technology

[0002] With the increasing scale of new energy sources connected to the grid, the proportion of coal-fired power units will further decrease in the future. How to rationally plan the flexibility and economy of the power system is a current challenge facing the new power system. Power system flexibility refers to the ability to quickly respond to uncertainties in balancing power supply and load demand while considering operational and economic constraints. Pumped storage (PHS) is a mature large-scale energy storage technology that plays an important role in improving grid flexibility. It features rapid start-up and shutdown, stable operation, and minimal impact from natural factors, and is therefore widely used for stable operation of power systems under conditions of high proportion of new energy grid connection. Different types of pumped storage units have their own operating characteristics, which determines the differences in their impact on system flexibility. However, existing research lacks a unified flexibility metric for constant-speed, variable-speed, ternary, and split-type pumped storage units to systematically quantify the flexibility characteristics of different units and their contribution to system flexibility. Summary of the Invention

[0003] Purpose of the invention: The purpose of this invention is to provide a method for evaluating the flexibility of five types of pumped storage units for new energy consumption. By establishing a system flexibility measurement index model, constructing a two-stage day-ahead scheduling optimization model, and introducing uncertainty envelope boundary analysis, this invention reveals the role of five types of pumped storage units (constant speed, doubly fed variable speed, full-frequency variable speed, ternary, and split type) in improving system flexibility and evaluates their ability to absorb new energy.

[0004] Technical solution: The present invention provides a method for evaluating the flexibility of five pumped storage units for new energy consumption, comprising the following steps:

[0005] A power system flexibility measurement index model is constructed, which includes the flexibility of thermal power units and the flexibility of pumped storage units. The contribution of different units to system flexibility is evaluated, thereby establishing a pumped storage flexibility evaluation method.

[0006] Simultaneously considering the operating characteristics of wind power, photovoltaic, thermal power units and five types of pumped storage units, a two-stage day-ahead dispatch model is constructed with the goal of minimizing the operating cost of the power system. The first stage of the dispatch model aims to minimize the operating cost of the power system under the condition of no disturbance from new energy sources, while the second stage aims to minimize the power system correction cost under the condition of uncertainty in the output of new energy sources.

[0007] An envelope boundary model is used to describe the uncertainty of renewable energy output. By adjusting the uncertainty radius parameter, the maximum range of renewable energy output disturbances that the power system can withstand under a given cost threshold is obtained, and the power system flexibility index is calculated accordingly.

[0008] Furthermore, the five types of pumped storage units include constant speed, doubly fed variable speed, full-frequency variable speed, ternary and separate pumped storage units.

[0009] Furthermore, the flexibility of the thermal power unit is determined by the unit's maximum and minimum output and its climbing ability. Its maximum upward flexibility and maximum downward flexibility at any given time are determined by the following formulas:

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[0011]

[0012] In the formula, , These represent the maximum upward and downward flexibility that a traditional thermal power unit can provide in time period t, respectively. , These represent the maximum and minimum output of a traditional thermal power unit, respectively. , These represent the upward and downward climbing capabilities of traditional thermal power units, respectively. This represents the power output of a traditional thermal power unit during time period t.

[0013] Furthermore, the flexibility of the pumped storage units is modeled according to the unit type, taking into account the unit's maximum and minimum reservoir capacity, maximum and minimum output, and ramp rate. The maximum upward and downward flexibility of constant-speed and variable-speed pumped storage units in time period t are determined by the following formulas:

[0014]

[0015]

[0016] In the formula, , These represent the maximum upward and downward flexibility that the pumped-storage unit can provide during time period t, respectively. , These represent the pumped-storage unit's ability to climb slopes uphill and downhill, respectively. This represents the power output of the pumped-storage unit during time period t in scenario s. , , , These represent the maximum and minimum power output of the pumped storage unit during power generation and pumping, respectively. , These represent the maximum and minimum water storage capacities of the pumped storage unit reservoir, respectively. This represents the reservoir capacity during time period t in scenario s. The conversion factor represents the mapping relationship between pumped storage capacity and flexibility.

[0017] For ternary and separate pumped storage units, they possess the characteristics of simultaneous pumping and power generation, with the pumping power remaining constant. The upward and downward flexibility provided by ternary and separate pumped storage units during time period t is determined by the following formula:

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[0020] In the formula: , .

[0021] Furthermore, the process for evaluating the contribution of different generating units to system flexibility is as follows:

[0022]

[0023] In the formula, , These represent the normalized flexibility index of traditional thermal power units and pumped storage units in time period t, respectively, i.e., their contribution to the system's flexibility.

[0024] The system flexibility index, obtained through normalization, measures the relative contribution of thermal power units and pumped storage units to system flexibility. Its calculation formula is as follows:

[0025]

[0026] In the formula, This indicates the overall system's flexibility. This indicates the operating status of pumped storage system during time period t under scenario s. This indicates the operating status of the thermal power unit during time period t.

[0027] Furthermore, the objective function of the two-stage day-ahead scheduling model includes the power generation cost, start-up and shutdown costs of thermal power units under normal operating conditions in the first stage, as well as the revenue from pumped storage; the second stage includes the adjustment costs of thermal power units and pumped storage under renewable energy disturbance scenarios.

[0028] In the formula, , These represent the marginal cost of generating electricity for thermal power units and the marginal revenue of pumped storage, respectively. , Let $\mathbf$ represent the marginal adjustment cost caused by the ramping of thermal power units and the system cost generated by the ramping adjustment of pumped storage in scenario $s$, respectively. This represents the power generation of the pumped-storage unit during time period t under normal operating conditions. This represents the start-up cost of a thermal power unit during time period t. Indicates the cost of the power system. , , , These represent the upward and downward adjustment amounts of thermal power units and pumped storage units during time period t under scenario s, respectively.

[0029] Furthermore, the first-stage constraints of the scheduling model are based on the following conditions:

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[0046] In the formula: , , , , , , These represent, respectively, the output of thermal power units, the predicted output of new energy sources, the output of pumped storage units, the transmission admittance of transmission lines, the voltage phase angle at node n, the voltage phase angle at node m, and the base load during time period t under normal operating conditions. , , , Let n represent the thermal power generation unit, the new energy power generation unit, the pumped storage unit, and the set of transmission lines from node n to node m, respectively. , Let represent the unit start-up cost of a thermal power unit and the start-up cost of a thermal power unit over a time period t, respectively. , These represent the power generation and pumping power of the pumped-storage unit during time period t under normal operating conditions. This represents the reservoir capacity during a time period t under normal operating conditions. , These represent the reservoir capacity at the beginning and end of the period under normal operating conditions, respectively. , These represent the discharge flow rate and the volume of water discarded during time period t under normal operating conditions, respectively. Indicates the inflow rate of the upstream reservoir. , These represent power generation efficiency and pumping efficiency, respectively. , These represent the power generation state variables and pumping state variables under normal operating conditions of the pumped-storage unit during time period t, respectively. This indicates the operating status of pumped storage under normal operating conditions during time period t.

[0047] Furthermore, the second-stage constraint of the scheduling model is the disturbance situation of new energy sources:

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[0078] In the formula: , , , , These represent the output of thermal power units during time period t in scenario s, the predicted output of new energy sources under disturbance, the output of pumped storage units, the voltage phase angle at node n, and the voltage phase angle at node m, respectively. , , , These represent the rotating reserve capacity of thermal power units and pumped storage units at the beginning and end of time period t, respectively. This indicates that the system's spinning reserve requirements are not considered for new energy sources. This represents the proportionality coefficient. , These represent the additional upward and downward reserve requirements after renewable energy power generation. , Let represent the binary state variables of power generation and water pumping in time period t under scenario s, respectively. , The reservoir capacity at the beginning and end of the time period in scenario s, respectively. , These represent the power generation and pumping power of the pumped-storage unit during time period t in scenario s, respectively. , These represent the outflow rate and the volume of water discarded during time period t in scenario s, respectively. , These represent the power generation state variables and pumping state variables during time period t in scenario s for pumped storage units.

[0079] Furthermore, the uncertainty radius parameter α characterizes the range of prediction deviation for new energy power:

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[0081] In the formula; α is the predicted value of the uncertain parameter θ, where α is the uncertain parameter.

[0082] Furthermore, the formula for measuring the flexibility of the power system is as follows:

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[0087] In the formula, “ "and" "These represent the upper and lower bounds of the potential uncertainty of new energy sources, respectively." The radius of uncertainty is unknown. , These represent wind power and photovoltaic power generation under basic operating conditions, respectively. Represents the cost threshold. , These represent the power output of the new energy unit under scenario s and the power output under normal operating conditions during time period t, respectively. , These represent the total cost of the power system and the cost of the first phase of the power system, respectively.

[0088] Beneficial Effects: Compared with the prior art, the beneficial effects of this invention are as follows: This invention proposes a unified system flexibility assessment method, which comprehensively considers the operating characteristics and system constraints of different types of pumped storage units, and realizes comparative analysis of the flexibility levels of multiple schemes; This invention constructs a two-stage day-ahead scheduling model with the goal of cost minimization, and considers the uncertainty of new energy sources through mixed integer linear programming (MILP) modeling and solving, thereby quantitatively assessing the flexibility level of systems containing different types of pumped storage units; This invention designs system flexibility assessment indicators for high-proportion new energy scenarios, which are used to quantify the regulation capacity of five types of pumped storage units, evaluate their effect on alleviating the start-up and ramp-up pressure of thermal power units, and assess the capacity for new energy absorption, thereby revealing the role of each type of pumped storage unit in improving system flexibility. Attached Figure Description

[0089] Figure 1 This is a flowchart of the present invention;

[0090] Figure 2 It is a six-node topology graph;

[0091] Figure 3 This is a schematic diagram showing the per-unit values ​​of load and renewable energy output;

[0092] Figure 4 This is a comparison chart of system flexibility under different six-node scenarios;

[0093] Figure 5 This is a schematic diagram of the start-up and shutdown of thermal power units under different cases with six nodes;

[0094] Figure 6 This is a comparison chart of system flexibility under different cases of IEEE 118 nodes. Detailed Implementation

[0095] The present invention will now be described in further detail with reference to the accompanying drawings.

[0096] like Figure 1 As shown, this invention proposes a method for evaluating the flexibility of five types of pumped storage units for new energy consumption, specifically including the following steps:

[0097] Step 1: Establish a system flexibility measurement index model, including the flexibility of thermal power units and the flexibility of pumped storage units.

[0098] (1.1) Constructing the flexibility of thermal power units: The flexibility of thermal power units is determined by the unit's maximum and minimum output and its climbing ability. Its maximum upward flexibility and maximum downward flexibility at any given time are determined by the following formulas:

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[0100]

[0101] In the formula: , These represent the maximum upward and downward flexibility that a traditional thermal power unit can provide in time period t, respectively. , These represent the maximum and minimum output of a traditional thermal power unit, respectively. , These represent the upward and downward climbing capabilities of traditional thermal power units, respectively. This represents the power output of a traditional thermal power unit during time period t.

[0102] (1.2) Constructing the flexibility of pumped storage: The flexibility of pumped storage units is modeled according to the unit type. Taking into account the maximum and minimum reservoir capacity, maximum and minimum output, and ramp rate of the unit, the maximum upward flexibility and maximum downward flexibility of constant-speed and variable-speed pumped storage in time period t are determined by the following formulas:

[0103]

[0104]

[0105] In the formula: , These represent the maximum upward and downward flexibility that the pumped-storage unit can provide during time period t, respectively. , These represent the pumped-storage unit's ability to climb slopes uphill and downhill, respectively. This represents the power output of the pumped-storage unit during time period t in scenario s. , , , These represent the maximum and minimum power output of the pumped storage unit during power generation and pumping, respectively. , These represent the maximum and minimum water storage capacities of the pumped storage unit reservoir, respectively. This represents the reservoir capacity during time period t in scenario s. is the conversion factor, which characterizes the mapping relationship between pumped storage capacity and flexibility.

[0106] For ternary and separate pumped storage units, they possess the characteristic of simultaneous pumping and power generation, with the pumping power remaining constant. The upward and downward flexibility provided by ternary and separate pumped storage units during time period t is determined by the following formula:

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[0109] In the formula: , .

[0110] (1.3) Building System Flexibility: To assess the contribution of different units to system flexibility, unit flexibility can be normalized in the following way:

[0111]

[0112] In the formula: , These represent the normalized flexibility index of traditional thermal power units and pumped storage units at time t, respectively, which is their contribution to the system's flexibility.

[0113] The system flexibility index, obtained through normalization, measures the relative contribution of thermal power units and pumped storage units to system flexibility. Its calculation formula is as follows:

[0114]

[0115] In the formula: This indicates the overall system's flexibility. This indicates the operating status of pumped storage system during time period t under scenario s. This indicates the operating status of the thermal power unit during time period t.

[0116] Step 2: Establish a two-stage day-ahead scheduling model with the goal of minimizing system operating costs; the first stage aims to minimize the day-ahead baseline operating cost under normal operating conditions without disturbance from new energy sources; the second stage aims to minimize the correction cost under the condition of considering disturbances in new energy output (scenario s).

[0117] The objective function includes the power generation cost, start-up and shutdown costs of thermal power units under normal operating conditions in the first stage, as well as the revenue from pumped storage. The second stage includes the adjustment costs of thermal power units and pumped storage under new energy disturbance scenarios.

[0118] In the formula: , These represent the marginal cost of generating electricity for thermal power units and the marginal revenue of pumped storage, respectively. , Let $\mathbf$ represent the marginal adjustment cost caused by the ramping of thermal power units and the system cost generated by the ramping adjustment of pumped storage in scenario $s$, respectively. This represents the power generation of the pumped-storage unit during time period t under normal operating conditions. This represents the start-up cost of a thermal power unit during time period t. Indicates the cost of the power system. , , , These represent the upward and downward adjustment amounts of thermal power units and pumped storage units during time period t under scenario s, respectively.

[0119] First-stage constraints:

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[0136] In the formula: , , , , , , These represent, respectively, the output of thermal power units, the predicted output of new energy sources, the output of pumped storage units, the transmission admittance of transmission lines, the voltage phase angle at node n, the voltage phase angle at node m, and the base load during time period t under normal operating conditions. , , , Let n represent the thermal power generation unit, the new energy power generation unit, the pumped storage unit, and the set of transmission lines from node n to node m, respectively. , Let represent the unit start-up cost of a thermal power unit and the start-up cost of a thermal power unit over a time period t, respectively. , These represent the power generation and pumping power of the pumped-storage unit during time period t under normal operating conditions. This represents the reservoir capacity during a time period t under normal operating conditions. , These represent the reservoir capacity at the beginning and end of the period under normal operating conditions, respectively. , These represent the discharge flow rate and the volume of water discarded during time period t under normal operating conditions, respectively. Indicates the inflow rate of the upstream reservoir. , These represent power generation efficiency and pumping efficiency, respectively. , These represent the power generation state variables and pumping state variables under normal operating conditions of the pumped-storage unit during time period t, respectively. This indicates the operating status of pumped storage under normal operating conditions during time period t.

[0137] Second-stage constraints:

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[0168] In the formula: , , , , These represent the output of thermal power units during time period t in scenario s, the predicted output of new energy sources under disturbance, the output of pumped storage units, the voltage phase angle at node n, and the voltage phase angle at node m, respectively. , , , These represent the rotating reserve capacity of thermal power units and pumped storage units at the beginning and end of time period t, respectively. This indicates that the system's spinning reserve requirements are not considered for new energy sources. This represents the proportionality coefficient. , These represent the additional upward and downward reserve requirements after renewable energy power generation. , Let represent the binary state variables of power generation and water pumping in time period t under scenario s, respectively. , The reservoir capacity at the beginning and end of the time period in scenario s, respectively. , These represent the power generation and pumping power of the pumped-storage unit during time period t in scenario s, respectively. , These represent the outflow rate and the volume of water discarded during time period t in scenario s, respectively. , These represent the power generation state variables and pumping state variables during time period t in scenario s for pumped storage units.

[0169] Step 3: Uncertainty analysis and system flexibility measurement.

[0170] An envelope boundary model is used to describe the uncertainty of renewable energy output, and the range of renewable energy power prediction deviation is characterized by setting an uncertainty radius parameter α.

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[0172] In the formula: It is the predicted value of the uncertain parameter θ, while α is the unknown uncertainty radius.

[0173] The formula for measuring the flexibility of a power system including pumped storage is as follows:

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[0178] In the formula: “ "and" "These represent the upper and lower bounds of the potential uncertainty of new energy sources, respectively." The radius of uncertainty is unknown. , These represent wind power and photovoltaic power generation under basic operating conditions, respectively. Represents the cost threshold. , These represent the power output of the new energy unit under scenario s and the power output under normal operating conditions during time period t, respectively. , These represent the total cost of the power system and the cost of the first phase of the power system, respectively.

[0179] In all tested systems, the proposed scheduling models, with or without pumped storage, remained feasible under given threshold conditions. The range of values ​​for the objective parameter α serves as an important basis for evaluating system flexibility, characterizing the system's operational status under different risk levels.

[0180] Step 4: Based on the above power system flexibility measurement formula, system flexibility... This is a nonlinear function, which needs to be linearized by converting it into a mixed-integer linear programming form. The linearization process is as follows:

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[0183] In the formula: As an auxiliary variable, This indicates whether unit r is activated during time period t (a binary variable), where μ is a continuous variable. represents an auxiliary variable whose continuous range of values ​​is limited by a lower bound of 0 and an upper bound of M, where M is a sufficiently large constant.

[0184] To verify the feasibility of this invention, the improved 6-bus system and the IEEE 118-bus system were used as examples to compare and analyze the impact of five types of pumped storage units on system flexibility. The simulation examples were performed using the MATLAB R2018b platform with the Gurobi solver to perform optimization calculations.

[0185] The improved six-node system includes 3 thermal power units, 7 transmission lines, and 3 load nodes, such as... Figure 2 As shown, one wind power unit and one photovoltaic unit are configured at node B1, with a total installed capacity of 140 MW, accounting for about 23% of the system peak load. Among them, the wind power installed capacity is 90 MW and the photovoltaic installed capacity is 50 MW. The system spinning reserve requirement is 8% of the system peak load, and the additional on / off reserve ratio coefficient for new energy is 10%. One pumped storage unit is configured at node B5. Figure 3 Hourly normalized per-unit curves for wind power output, photovoltaic power output, and system load are presented. The adjustable reservoir capacity of the pumped storage power station is 20 million m³. 3 The rated head of the unit is 300m.

[0186] To investigate the improvement in flexibility provided by available pumped storage, the following six cases were proposed for testing: Case 1: No pumped storage; Case 2: Pumped storage with only constant-speed pumped storage; Case 3: Pumped storage with only doubly-fed variable-speed pumped storage; Case 4: Pumped storage with only full-frequency variable-speed pumped storage; Case 5: Pumped storage with only separate pumped storage; Case 6: Pumped storage with only ternary pumped storage.

[0187] Six-node system: Figure 4 , Figure 5 The simulation results for the six-node system are provided by Figure 4 It is evident that the introduction of pumped storage can significantly enhance system flexibility. Figure 4 The horizontal lines representing the pumped storage unit's flexibility are as follows: Specifically, the ternary pumped storage unit can achieve power generation regulation across the entire power range and has the characteristic of simultaneous pumping and power generation, thus offering the highest flexibility. The full-frequency variable-speed pumped storage unit has the widest operating range for both power generation and pumping, and its flexibility is second only to the doubly-fed variable-speed pumped storage unit. The constant-speed pumped storage unit is limited by the constant power pumping capacity regulation of the reservoir, resulting in lower flexibility. The separate pumped storage unit is limited by its climbing ability, resulting in the lowest flexibility.

[0188] Figure 4 The left-hand diagonal filled bars represent the renewable energy absorption capacity, and the vertical filled bars represent the flexibility of thermal power units. The results show that without pumped storage, the renewable energy absorption capacity is limited (α = 0.150). To maintain system operation, G1 unit's frequent start-stop operations are restricted, G3 unit, due to its high flexibility, requires frequent adjustments to smooth power fluctuations, and G2 unit undertakes a large amount of ramp-up work, resulting in high operating costs. In this scenario, the renewable energy absorption capacity is at its lowest level. After pumped storage is connected to the grid, the system's regulation capacity is significantly improved; G2 unit no longer needs frequent ramp-up, and the output of G1 unit increases. In Case 2, after introducing constant-speed pumped storage, the online time of thermal power units increases, the number of start-stop operations decreases, peak-shaving pressure is alleviated, and system flexibility improves to 0.34. However, due to the limited power output adjustment range of constant-speed units and the fixed pumping power, the renewable energy absorption capacity is difficult to further improve, and the increase in α is not significant. In this case, the thermal power unit combination is similar to Case 1, but the frequent start-stop phenomenon of G2 unit is alleviated. The difference between Case 3 and Case 4 lies in the wider power regulation range of the full-frequency variable-speed pumped storage system. While both perform similarly in terms of unit combination, Case 4 offers greater flexibility than Case 3. Due to the variable pumping power, it significantly improves the renewable energy absorption capacity, resulting in a marked increase in α. Simultaneously, it reduces the online time of the high-cost G3 unit, allowing the low-cost G2 unit to remain online at all times, increasing the output of the G1 unit and reducing peak-shaving pressure. Cases 5 and 6 correspond to units capable of simultaneous pumping and power generation. Separate pumped storage systems have a smaller power regulation range and limited ramp-up capability, resulting in less online time for G1 and G3 units and a lower dispatch level for G1. Consequently, the flexibility and renewable energy absorption capacity of the thermal power units are lower than in Case 3. However, due to its simultaneous pumping and generation capability, its flexibility and absorption capacity are still superior to Case 2. In contrast, ternary pumped storage systems can achieve power generation regulation across the entire power range, significantly improving the dispatch and online time of the G1 unit. The system's flexibility and renewable energy absorption capacity reach a superior level, second only to Case 4.

[0189] The IEEE 118-node system: The improved IEEE 118-node system comprises 54 thermal power units, 186 lines, and 91 load nodes. The system includes four renewable energy generation units: two wind turbines and two photovoltaic power plants (located at nodes 15, 24, 54, and 96, respectively). The total installed capacity of renewable energy is 1175MW, of which 760MW is wind power and 415MW is photovoltaic. The output characteristic curves of the renewable energy units, the system spinning reserve requirement, and the renewable energy additional up / down reserve ratio coefficients are all the same as those of the six-node system. The system peak load is 5000MW. Pumped storage units are installed at the nodes with renewable energy generation, with a total installed capacity of 1200MW. The six case studies previously discussed in the six-node system are also compared and analyzed in this system.

[0190] Depend on Figure 6 It is evident that the introduction of pumped storage significantly improves the system's flexibility, and the improvement patterns of different types of units are consistent with the analysis conclusions of the six-node system mentioned earlier. Specifically, full-power variable frequency units have the most prominent advantages in terms of flexibility improvement and renewable energy absorption capacity, followed by ternary units, which possess full-power regulation characteristics and are effective in enhancing system regulation capabilities and alleviating pressure on thermal power units. Doubly fed variable speed and split-type units can also play a good regulatory role, but the improvement is relatively limited. Fixed-speed units, due to their limited power regulation range, have the smallest effect on flexibility improvement.

[0191] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for evaluating the flexibility of five types of pumped storage units for new energy consumption, characterized in that, The implementation process is as follows: A power system flexibility measurement index model is constructed, which includes the flexibility of thermal power units and the flexibility of pumped storage units. The contribution of different units to system flexibility is evaluated, thereby establishing a pumped storage flexibility evaluation method. Taking into account the operating characteristics of wind power, photovoltaic, thermal power units and five types of pumped storage units, a two-stage day-ahead dispatch model is constructed with the goal of minimizing the operating cost of the power system. The scheduling model aims to minimize the operating cost of the power system under the condition of no disturbance from new energy sources in the first stage, and to minimize the power system correction cost in the second stage, taking into account the uncertainty of new energy output. An envelope boundary model is used to describe the uncertainty of renewable energy output. By adjusting the uncertainty radius parameter, the maximum range of renewable energy output disturbances that the power system can withstand under a given cost threshold is obtained, and the power system flexibility index is calculated accordingly.

2. The method for evaluating the flexibility of five pumped storage units for new energy consumption according to claim 1, characterized in that, The five types of pumped storage units include constant speed, doubly fed variable speed, full-frequency variable speed, ternary, and separate pumped storage units.

3. The method for evaluating the flexibility of five pumped storage units for new energy consumption as described in claim 1, characterized in that, The flexibility of the thermal power unit is determined by the unit's maximum and minimum output and its climbing ability. Its maximum upward flexibility and maximum downward flexibility at any given time are determined by the following formulas: In the formula, , These represent the maximum upward and downward flexibility that a traditional thermal power unit can provide in time period t, respectively. , These represent the maximum and minimum output of a traditional thermal power unit, respectively. , These represent the upward and downward climbing capabilities of traditional thermal power units, respectively. This represents the power output of a traditional thermal power unit during time period t.

4. The method for evaluating the flexibility of five pumped storage units for new energy consumption as described in claim 1, characterized in that, The flexibility of the pumped storage units is modeled according to the unit type, taking into account the unit's maximum and minimum reservoir capacity, maximum and minimum output, and ramp rate. The maximum upward and downward flexibility of constant-speed and variable-speed pumped storage units in time period t are determined by the following formulas: In the formula, , These represent the maximum upward and downward flexibility that the pumped-storage unit can provide during time period t, respectively. , These represent the pumped-storage unit's ability to climb slopes uphill and downhill, respectively. This represents the power output of the pumped-storage unit during time period t in scenario s. , , , These represent the maximum and minimum power output of the pumped storage unit during power generation and pumping, respectively. , These represent the maximum and minimum water storage capacities of the pumped storage unit reservoir, respectively. This represents the reservoir capacity during time period t in scenario s. The conversion factor represents the mapping relationship between pumped storage capacity and flexibility. For ternary and separate pumped storage units, they possess the characteristics of simultaneous pumping and power generation, with the pumping power remaining constant. The upward and downward flexibility provided by ternary and separate pumped storage units during time period t is determined by the following formula: In the formula: , .

5. The method for evaluating the flexibility of five pumped storage units for new energy consumption according to claim 1, characterized in that, The process for assessing the contribution of different generating units to system flexibility is as follows: In the formula, , These represent the normalized flexibility index of traditional thermal power units and pumped storage units in time period t, respectively, i.e., their contribution to the system's flexibility. The system flexibility index, obtained through normalization, measures the relative contribution of thermal power units and pumped storage units to system flexibility. Its calculation formula is as follows: In the formula, This indicates the overall system's flexibility. This indicates the operating status of pumped storage system during time period t under scenario s. This indicates the operating status of the thermal power unit during time period t.

6. The method for evaluating the flexibility of five pumped storage units for new energy consumption according to claim 1, characterized in that, The objective function of the two-stage day-ahead scheduling model includes the power generation cost, start-up and shutdown costs of thermal power units under normal operating conditions in the first stage, as well as the revenue from pumped storage; the second stage includes the adjustment costs of thermal power units and pumped storage under renewable energy disturbance scenarios. In the formula, , These represent the marginal cost of generating electricity for thermal power units and the marginal revenue of pumped storage, respectively. , Let $\mathbf$ represent the marginal adjustment cost caused by the ramping of thermal power units and the system cost generated by the ramping adjustment of pumped storage in scenario $s$, respectively. This represents the power generation of the pumped-storage unit during time period t under normal operating conditions. This represents the start-up cost of a thermal power unit during time period t. Indicates the cost of the power system. , , , These represent the upward and downward adjustment amounts of thermal power units and pumped storage units during time period t under scenario s, respectively.

7. The method for evaluating the flexibility of five pumped storage units for new energy consumption according to claim 1, characterized in that, The first-stage constraints of the scheduling model are based on the following conditions: In the formula: , , , , , , These represent, respectively, the output of thermal power units, the predicted output of new energy sources, the output of pumped storage units, the transmission admittance of transmission lines, the voltage phase angle at node n, the voltage phase angle at node m, and the base load during time period t under normal operating conditions. , , , Let n represent the thermal power generation unit, the new energy power generation unit, the pumped storage unit, and the set of transmission lines from node n to node m, respectively. , Let represent the unit start-up cost of a thermal power unit and the start-up cost of a thermal power unit over a time period t, respectively. , These represent the power generation and pumping power of the pumped-storage unit during time period t under normal operating conditions. This represents the reservoir capacity during a time period t under normal operating conditions. , These represent the reservoir capacity at the beginning and end of the period under normal operating conditions, respectively. , These represent the discharge flow rate and the volume of water discarded during time period t under normal operating conditions, respectively. Indicates the inflow rate of the upstream reservoir. , These represent power generation efficiency and pumping efficiency, respectively. , These represent the power generation state variables and pumping state variables under normal operating conditions of the pumped-storage unit during time period t, respectively. This indicates the operating status of pumped storage under normal operating conditions during time period t.

8. The method for evaluating the flexibility of five pumped storage units for new energy consumption according to claim 1, characterized in that, The second-stage constraint of the scheduling model is the disturbance situation of new energy sources: In the formula: , , , , These represent the output of thermal power units during time period t in scenario s, the predicted output of new energy sources under disturbance, the output of pumped storage units, the voltage phase angle at node n, and the voltage phase angle at node m, respectively. , , , These represent the rotating reserve capacity of thermal power units and pumped storage units at the beginning and end of time period t, respectively. This indicates that the system's spinning reserve requirements are not considered for new energy sources. This represents the proportionality coefficient. , These represent the additional upward and downward reserve requirements after renewable energy power generation. , Let represent the binary state variables of power generation and water pumping in time period t under scenario s, respectively. , The reservoir capacity at the beginning and end of the time period in scenario s, respectively. , These represent the power generation and pumping power of the pumped-storage unit during time period t in scenario s, respectively. , These represent the outflow rate and the volume of water discarded during time period t in scenario s, respectively. , These represent the power generation state variables and pumping state variables during time period t in scenario s for pumped storage units.

9. The method for evaluating the flexibility of five pumped storage units for new energy consumption according to claim 1, characterized in that, The uncertainty radius parameter α characterizes the range of prediction deviation in new energy power: In the formula; α is the predicted value of the uncertain parameter θ, where α is the uncertain parameter.

10. The method for evaluating the flexibility of five pumped storage units for new energy consumption according to claim 1, characterized in that, The formula for measuring the flexibility of the power system is as follows: In the formula, " "and" "These represent the upper and lower bounds of the potential uncertainty of new energy sources, respectively." The radius of uncertainty is unknown. , These represent wind power and photovoltaic power generation under basic operating conditions, respectively. Represents the cost threshold. , These represent the power output of the new energy unit under scenario s and the power output under normal operating conditions during time period t, respectively. , These represent the total cost of the power system and the cost of the first phase of the power system, respectively.

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