A gravity energy storage charging and discharging method using piecewise linearization approximation

Abstract

The application discloses a gravity energy storage charging and discharging method using piecewise linearization approximation, and establishes a double-tower type gravity energy storage system according to the structure of an actual gravity energy storage system; the double-tower type gravity energy storage system comprises a hollow cylindrical tower and a central tower located at the center of the hollow cylindrical tower; according to the increased gravity potential energy when bricks are moved from the hollow cylindrical tower to the central tower, the height difference of the tower after charging, the height difference of the tower before charging, the height of the central tower after charging, the volume of the bricks lifted by the energy storage system, the charging power of the current period, the volume of the bricks dropped by the energy storage system and the discharging power and volume of the current period, a nonlinear double-tower model of the gravity energy storage output is established, and is then converted into a mixed integer linear programming model; the nonlinear double-tower model of the gravity energy storage output is solved, the gravity energy storage charging and discharging control is controlled according to the solving result, and can participate in dispatching, and can be configured on the power generation side and the power grid side in a large scale, and has a relatively low unit cost.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of efficient energy storage technology in power systems, and in particular to a gravity energy storage charging and discharging method using piecewise linearization approximation. BACKGROUND

[0002] With the increasing penetration of renewable energy, the volatility and intermittency of renewable energy pose great challenges to the safe operation of power systems. Energy storage systems have excellent regulation performance and can hedge against the uncertainty of renewable energy, cope with load fluctuations and equipment failures, and promote the consumption of renewable energy. Traditional energy storage technologies have their own limitations, such as high configuration cost of electrochemical energy storage, geographical environment constraints of pumped storage, and high self-discharge rate of flywheel energy storage. A new type of gravity energy storage has gradually developed in recent years. Gravity energy storage technology is free from geographical environment constraints and can be deployed on a large scale on the power generation side and the power grid side, with lower unit cost and great potential for future development.

[0003] Gravity energy storage has been applied in some demonstration projects after a period of construction and development, but there is still little research on the detailed process of gravity energy storage charging and discharging. The specific action characteristics of gravity energy storage and the corresponding energy storage parameters are not clear. As a new energy storage technology, gravity energy storage is still in its early stages of research, and there is no specific operation model to describe its output characteristics, making it impossible to control the charging and discharging. SUMMARY

[0004] The present application aims to provide a gravity energy storage charging and discharging method using piecewise linearization approximation, which conducts detailed research on the action process of gravity energy storage, establishes a nonlinear double-tower model of gravity energy storage output, and converts the nonlinear double-tower model of gravity energy storage output into a mixed integer linear programming model to analyze the action characteristics of gravity energy storage and achieve control of gravity energy storage charging and discharging.

[0005] To achieve the above purpose, the technical solution adopted by the present application is as follows:

[0006] A gravity energy storage charging and discharging method using piecewise linearization approximation, comprising the following steps:

[0007] Step 1: Establish a double-tower gravity energy storage system according to the structure of the actual gravity energy storage system; the double-tower gravity energy storage system includes a hollow cylindrical tower and a central tower located at the center of the hollow cylindrical tower; the central tower is denoted as tower a, and the hollow cylindrical tower is denoted as tower b;

[0008] Step 2: according to the increased gravitational potential energy of moving the bricks from the hollow cylindrical tower to the central tower, the height difference of the tower after charging, the height difference of the tower before charging, the height of the central tower after charging, the volume of the bricks lifted by the energy storage system and the feasible region of the charging power in the current period, the discharged power and the volume in the current period, a nonlinear double-tower model of the gravity energy storage output is established;

[0009] Step 3: the nonlinear double-tower model of the gravity energy storage output is converted into a mixed integer linear programming model; the nonlinear double-tower model of the gravity energy storage output is solved, and the charging and discharging control of the gravity energy storage is performed according to the solving result.

[0010] Further improvement of the application is that the increased gravitational potential energy of moving the bricks from the hollow cylindrical tower to the central tower is calculated by the following formula:

[0011] p ch η ch T=Nm unit gh ab (3)

[0012] In the formula, p ch is the charging power of the gravity energy storage, η ch is the charging efficiency of the gravity energy storage, g is the acceleration of gravity, T is the time required for lifting N bricks from the hollow cylindrical tower to the central tower, m unit is the mass of a single brick, and h ab is the height difference between the two towers.

[0013] Further improvement of the application is that the height difference of the tower after charging is calculated by the following formula:

[0014]

[0015] In the formula, Δh ab is the change amount of the height difference between the two towers, Δh1 is the height change of tower a in time Δt, Δh2 is the height change of tower b in time Δt, X a is the number of bricks per layer of tower a, and X b is the number of bricks per layer of tower b.

[0016] Further improvement of the application is that the height difference of the tower before charging is calculated by the following formula:

[0017]

[0018] In the formula, h ab is the height difference of the tower before charging, X a is the number of bricks per layer of tower a, X b is the number of bricks per layer of tower b, and h a is the height of the central cylindrical tower. is the maximum height of the central tower.

[0019] The present application is further improved in that the height of the central tower after charging is calculated by the following formula:

[0020]

[0021] wherein h 'a is the height of the central tower after charging, is the maximum height of the central tower, X a is the number of bricks per floor of the tower a, X b is the number of bricks per floor of the tower b, V unit is the volume of each brick, p ch is the charging power of the gravity energy storage, η ch is the charging efficiency of the gravity energy storage, ΔT is the minimum time scale of day-ahead scheduling, S unit is the bottom area of a single brick, g is the acceleration of gravity, h a is the height of the central cylindrical tower, m unit m unit is the mass of a single brick.

[0022] The present application is further improved in that the volume of the bricks lifted by the energy storage system is calculated by the following formula:

[0023]

[0024] wherein, is the height of the tower a at the previous moment, is the height of the tower a at the current moment, X a is the number of bricks per floor of the tower a, S unit is the bottom area of a single brick, is the maximum height of the central tower, X b is the number of bricks per floor of the tower b, V unit is the volume of each brick, p ch is the charging power of the gravity energy storage, η ch is the charging efficiency of the gravity energy storage, ΔT is the minimum time scale of day-ahead scheduling, m unit is the mass of a single brick, g is the acceleration of gravity;

[0025] the charging power of the current period is calculated by the following formula:

[0026]

[0027] wherein, is the expression of the charging power of the current period, is the height of the tower a at the previous moment, The brick volume lifted by the energy storage system in the current period, and the discharge power in the current period is calculated by the following formula:

[0028] The further improvement of the present application is that the brick volume lowered by the energy storage system and the discharge power in the current period is calculated by the following formula:

[0029] The brick volume lowered by the energy storage system The brick volume lowered by the energy storage system is calculated by the following formula:

[0030]

[0031] In the formula, The height of tower a at the previous moment, The height of tower a at the current moment, a The number of bricks per floor of tower a, unit The bottom area of a single brick, The maximum height of the central tower, b The number of bricks per floor of tower b, unit The volume of each brick, m unit The mass of a single brick, g is the acceleration of gravity, η dis The gravity energy storage discharge power;

[0032] The discharge power in the current period The discharge power in the current period is calculated by the following formula:

[0033]

[0034] In the formula, The expression of the discharge power in the current period, and the minimum time scale of day-ahead scheduling is ΔT.

[0035] The further improvement of the present application is that the feasible region of the volume is calculated by the following formula:

[0036]

[0037] In the formula, The brick volume lowered by the energy storage system, and the height of tower a at the previous moment, a The number of bricks per floor of tower a, unit The bottom area of a single brick, The height of tower a at the previous moment, The maximum height of the central tower, b The number of bricks per floor of tower b.

[0038] The further improvement of the present application is that the nonlinear double-tower model of the gravity energy storage output is converted into a mixed integer linear programming model by using the piecewise linearization approximation method.

[0039] Compared with the prior art, the present application has the beneficial effects that:

[0040] In the present application, according to the structure of the actual gravity energy storage system, a double-tower gravity energy storage system is established; the double-tower gravity energy storage system includes a hollow cylindrical tower and a central tower located in the center of the hollow cylindrical tower; according to the increased gravitational potential energy of moving the bricks from the hollow cylindrical tower to the central tower, the height difference of the tower after charging, the height difference of the tower before charging, the height of the central tower after charging, the volume of the bricks lifted by the energy storage system, and the feasible region of the charging power of the current period, the volume of the bricks dropped by the energy storage system and the discharge power of the current period, a nonlinear double-tower model of the gravity energy storage output is established; the nonlinear double-tower model of the gravity energy storage output is converted into a mixed integer linear programming model; the nonlinear double-tower model of the gravity energy storage output is solved, and the charging and discharging control of the gravity energy storage is carried out according to the solving result, and can participate in the dispatching, can be configured in large scale on the power generation side and the power grid side, the unit cost is low, and the problems of traditional energy storage modes such as electrochemical energy storage, pumped storage, flywheel energy storage, etc. are overcome. Limited by geographical environment and cost factors.

[0041] Further, in the case that the specific action characteristics and parameters of the gravity energy storage are not clear, the present application carries out fine calculation on the action process of the gravity energy storage, uses the piecewise linearization approximation method, i.e. uses one-dimensional function set to piecewise linearize the double-variable nonlinear function, converts the nonlinear double-tower model of the gravity energy storage output into a mixed integer linear programming model, analyzes the action characteristics of the gravity energy storage, and can study the influence of the energy storage parameters on the energy storage effect. BRIEF DESCRIPTION OF DRAWINGS

[0042] Figure 1 Fig. 3 is a three-view diagram of the double-tower gravity energy storage according to the present application; wherein (a) is a front view, (b) is a top view;

[0043] Figure 2 Fig. 4 is a schematic diagram of the volume change in the process of charging the gravitational potential energy;

[0044] Figure 3 Fig. 5 is a graph of the volume of the lifted bricks changing with the charging power and the height of the central tower;

[0045] Figure 4 Fig. 6 is a three-dimensional curve of the volume of the dropped bricks dynamically changing with the discharge power and the height of the central tower. DETAILED DESCRIPTION

[0046] The present application will be further described below in conjunction with the drawings, but the content of the present application is not limited to this.

[0047] The present application selects volume as the research object according to the dynamic operation characteristics of gravity energy storage, carries out calculus on the gravity bricks at a single moment, calculates the analytical expression of the central tower height, energy storage output and the number of brick movements, and analyzes the action characteristics of the gravity energy storage by modeling the charging and discharging process of the gravity energy storage, using piecewise linearization of a two-variable nonlinear function to finely model the action process of the gravity energy storage, and studying the influence of energy storage parameters on the energy storage effect.

[0048] The gravity energy storage charging and discharging method using piecewise linearization approximation of the present application comprises the following steps:

[0049] Step 1: According to the structure of the actual gravity energy storage system, the structure of the double-tower gravity energy storage system is established.

[0050] According to the structure and working principle of the double-tower gravity energy storage system, a model is established. The specific process is: the crane hoists the brick pile into the central tower from the peripheral hollow cylindrical tower, and stores the electric energy in the gravitational potential energy of the central tower; the bricks uniformly descend from the central tower to the peripheral hollow cylindrical tower to drive the generator rotor to generate electricity, and convert the gravitational potential energy into electric energy. The front view and top view of the gravity energy storage system are shown in Figs. Figure 1 (a) and (b), Figure 1 In the figures, the bottom area of a single brick is S unit , the central tower is denoted as tower a, and the surrounding hollow cylindrical tower is denoted as tower b, the number of bricks per layer of tower a / b is X a / X b , the height of the central cylindrical tower of the brick pile is h a , the bottom area is X a S unit , the height of the surrounding hollow cylindrical tower is h b , the volume of each brick is V unit , the bottom area is X b S unit , and the volume of the central tower is:

[0051]

[0052] In the formula, is the volume of tower a at time t, is the height of tower a at time t, and T is the set of time in a day.

[0053] Step 2: According to the principle of gravity energy storage of gravitational potential energy and kinetic energy conversion, the charging and discharging process of the gravity energy storage is modeled, comprising the following steps:

[0054] Step 2.1: According to the principle of conversion of gravitational potential energy and kinetic energy in the process of gravitational energy storage and charging and discharging, the conversion of gravitational potential energy and kinetic energy is realized by the lifting of each brick, and the remaining capacity of gravitational potential energy is stored in the central tower. The gravitational potential energy of the tower is the sum of the gravitational potential energy of each layer of bricks, and the mass of a single brick is m unit , the height of the brick is h unit , the gravitational potential energy of the tower is (X a m unit gh a )(1+h a / h unit ) / 2, see Figure 2 :

[0055] Figure 2 The part indicated by the arrow represents the part of lifting the brick, which is transferred from the hollow cylindrical tower b to the central tower a. The time required for N bricks to be lifted from the surrounding hollow cylindrical tower to the central tower is T, and the volume lifting speed is NV unit / T. In time Δt, tower a is raised from height h a to h 'a , tower b is raised from height h b to h 'b , and the volume of the brick moving is:

[0056]

[0057] The increased gravitational potential energy is the electrical energy absorbed by the system multiplied by the charging efficiency, which is:

[0058] p ch η ch T=Nm unit gh ab (3)

[0059] In the formula, p ch is the charging power of the gravitational energy storage, η ch is the charging efficiency of the gravitational energy storage, g is the acceleration of gravity, which is 9.8 m / s 2 , and h ab is the height difference between the two towers.

[0060] Step 2.2: Calculate the expression of the height difference h 'ab of the tower after charging. First, multiply the volume moved by the brick with the increased gravitational potential energy of the system on both sides of the equation:

[0061] V unit p ch η ch Δt=X a S unit m unit gh abΔh1 (4)

[0062] Based on the principle that the collective variation of the two towers is equal, i.e. the bricks added to tower a come from the bricks reduced in tower b, we have:

[0063] X a S unit Δh1=X b S unit Δh2 (5)

[0064]

[0065] The height of the two towers increases and decreases respectively, so the increment of the height difference of the gravity storage tower is equal to the sum of the height variations of the two towers, which is:

[0066]

[0067] In the formula, Δh ab is the variation of the height difference of the two towers.

[0068] Substitute the sum of the height variations of the two towers Δh ab in formula (7) into formula (4) to obtain:

[0069]

[0070] Integrate the above formula within the minimum time scale ΔT of the day-ahead dispatch, and substitute the upper and lower limits of the integral, and then the expression of the tower height difference h 'ab after charging can be obtained, which is:

[0071]

[0072]

[0073]

[0074] Step 2.3: Calculate the expression of the original tower height difference h ab :

[0075] Based on the fact that the total number of bricks in the gravity storage system is constant, the total volume of the two towers at any time is equal; in the height dimension, i.e. the equivalent height of the two towers remains unchanged, which is equal to the maximum height of the central tower in numerical value When tower a is at the highest, the height of tower b is zero, and all the bricks are used to pile up tower a:

[0076]

[0077] The expression of the original tower height difference h ab is:

[0078]

[0079] where the height difference of the original tower is the height difference of the tower before charging.

[0080] Step 2.4: Calculate the height of the central tower after charging h 'a The expression for h

[0081]

[0082] Step 2.5: Calculate the volume of the brick raised by the energy storage after time T at time t and the charging power in the current period The expression for V

[0083] According to the formula for the volume of a cylinder, the volume of the brick raised by the energy storage after time T at time t V is the height increase of the tower a multiplied by its base area, which depends on the height of the tower a at the previous time and the charging power in the current period The volume of the brick raised V is:

[0084]

[0085] The charging power P depends on the height of the tower a at the previous time and the volume of the brick raised in the current period V is:

[0086]

[0087] where is the expression for the charging power in the current period.

[0088] Step 2.6: Calculate the volume of the brick lowered by the energy storage after time T at time t and the charging power in the current period The expression for V

[0089]

[0090]

[0091] where η dis is the discharge power of the gravitational energy storage, is the expression for the discharge power in the current period.

[0092] Step 2.7: Calculate the feasible region of the volume V

[0093] Unlike traditional energy storage, the central tower height is not zero after releasing all the energy, on the contrary, the inner and outer tower height is the same at this time. It can be seen that the volume of the falling brick is limited by the current height of the central tower during the discharge of the gravity energy storage, and the feasible region of the falling volume is:

[0094]

[0095] According to the dynamic operation characteristics of gravity energy storage, the volume is selected as the research object, the integral of the brick movement process at a single time is carried out, the analytical expressions of the central tower height, energy storage output and the number of brick movements are derived, and a nonlinear double tower model describing the output of gravity energy storage is established. That is, according to the increased gravitational potential energy calculated in step 2.1, the height difference of the tower after charging calculated in step 2.2, the height difference of the original tower calculated in step 2.3, the height of the central tower after charging calculated in step 2.4, the volume of the brick lifted by the energy storage system calculated in step 2.5, the charging power of the current period, the volume of the brick descended by the energy storage system calculated in step 2.6, the discharging power of the current period and the feasible region of the volume calculated in step 2.7, a nonlinear double tower model of the output of gravity energy storage is established.

[0096] Step 3: Use piecewise linearization approximation method to convert the nonlinear double tower model of gravity energy storage output into a mixed integer linear programming model; determine the height interval of the tower, and approximate the output power of gravity energy storage according to piecewise linearization.

[0097] Due to the special structure design and function of gravity energy storage, both formula (16) in step 2.5 and formula (18) in step 2.6 are two-dimensional nonlinear equations, so the following steps are used to linearize the above gravity energy storage model.

[0098] Step 3.1: Determine the interval of the height h of tower a:

[0099]

[0100]

[0101]

[0102]

[0103] In the formula, h is the state of the i-th sub-interval of h, 1 is h falling in it, 0 is h falling in other positions, and h i h is the height value of the i-th sub-interval of h. There is only one h enables, uniquely determines the interval of the height h of tower a, and lays the foundation for linearizing the power p based on the given h.

[0104] Step 3.2: Piecewise linearization approximation of the gravity storage output power:

[0105] According to the idea of piecewise linearization of one-dimensional function, p = g i (q) Linearization process is:

[0106]

[0107]

[0108]

[0109]

[0110]

[0111] In the formula, q i,j is the volume of the brick in the ith sub-interval of h and the jth sub-interval of q, is a two-dimensional 0-1 variable, the state of the ith sub-interval of h and the jth sub-interval of q, i.e. the height h i of the tower a, i,j the state of the moving brick volume q i at the time, is 1, which represents that at this time period, the gravity storage tower a is at the height h i,j , and the moving brick volume is q (2) , which is 0, i.e. the gravity storage is in other states.

[0112] In the two-dimensional 0-1 matrix z (1) , only one is 1, and it is consistent with the one-dimensional 0-1 matrix z (1) , which determines the sub-interval of the height of tower a, z (2) , and the volume interval of the moving brick is solved on the basis of z (1) . Only one q i,j is not zero and its value is equal to q, which is to linearize the variable value to accurately represent the volume of the moving brick. Piecewise linearization of the gravity storage output power is achieved by using linear interpolation, taking the charging power expression as an example, the charging power is linearized as:

[0113]

[0114] The original nonlinear problem is reconstructed by a linearization method, the double-tower gravity energy storage model is converted into a mixed integer linear programming model, a commercial solver such as Cplex, Gorubi can be called to solve, and gravity energy storage charging and discharging control is carried out according to the solving result. When the gravity energy storage is used as an independent energy storage device on the power generation side, it can participate in the day-ahead energy market, and can use the price peak-valley difference and the flexible adjustment characteristics of the energy storage to arbitrage. The gravity energy storage charging and discharging method proposed in the application can participate in the day-ahead scheduling of the gravity energy storage power station.

[0115] In order to make the purpose, technical scheme and advantages of the embodiments of the application more clear, further demonstrate the advantages of the application, the volume of the lifting brick changes with the charging power and the height of the central tower, and the volume of the descending brick changes with the discharging power and the dynamic change of the height of the central tower are simulated, see Figure 3 The gravity energy storage charges and discharges by lifting and descending huge bricks, and the number of bricks moved per hour depends on the current height of the central tower and the output power. When the charging power is zero, it is proved that the gravity energy storage does not move, so the volume of the lifting brick is zero, which conforms to the physical reality; when the height of the central tower is fixed, the volume of the lifting brick per unit time increases with the increase of the charging power. It should be noted that when the height of the central tower approaches the lowest point (the height of the two towers is the same), due to the continuous decrease of the difference between the inner and outer towers, based on the formula of work done by gravity, the volume of the lifting brick rapidly increases to realize the same power output. Therefore, with the continuous decrease of the height of the central tower, the gravity energy storage can lift more bricks from the hollow tower to the central tower per unit time.

[0116] Referring to Figure 4 , the intersection of the vertical power axis section and the three-dimensional curve is found, and when the discharging power is zero, the gravity energy storage remains static, and the volume of the descending brick is zero at any height. The intersection of the vertical height axis section and the three-dimensional curve is found, and when the height of the central tower is the same, the volume of the descending brick increases with the increase of the discharging power. It should be noted that the size of the discharging power of the gravity energy storage affects the trend of the curve of the volume of the brick changing with the height of the tower, that is, the intersection of the vertical power axis section and the surface in Figure 4 .

[0117] The application is directed to a new gravity energy storage method, through fine modeling of the gravity energy storage action process, using piecewise linearization of a two-variable nonlinear function, obtaining a mixed integer linear programming model of the gravity energy storage output, analyzing the action characteristics of the gravity energy storage, and studying the influence of the energy storage parameters on the energy storage effect. Compared with traditional energy storage methods such as electrochemical energy storage, pumped storage, flywheel energy storage, etc., the application is directed to gravity energy storage, which is free from geographical environment restrictions and can be configured on the power generation side and the power grid side on a large scale at a relatively low unit cost. The model performs calculus on the gravity bricks at a single time according to the dynamic operation characteristics of the gravity energy storage, calculates the central tower height, the energy storage output and the number of brick movements, and uses piecewise linearization of a two-variable nonlinear function for solving. The gravity energy storage charging and discharging method in the application has strong universality and comprehensiveness.

Claims

1. A gravity-based energy storage charging and discharging method using a piecewise linearization approximation, characterized in that, Includes the following steps: Step 1: Based on the structure of the actual gravity energy storage system, establish a dual-tower gravity energy storage system; The twin-tower gravity energy storage system includes a hollow cylindrical tower and a central tower located at the center of the hollow cylindrical tower; the central tower is denoted as tower a, and the hollow cylindrical tower is denoted as tower b. Step 2: Based on the gravitational potential energy increase from moving bricks from the hollow cylindrical tower to the central tower, the height difference of the towers after charging, the height difference of the towers before charging, the height of the central tower after charging, the volume of bricks lifted by the energy storage system, the charging power during the current period, the volume of bricks lowered by the energy storage system, and the feasible region of the discharge power and volume during the current period, establish a nonlinear dual-tower model for gravity energy storage output. Step 3: Transform the nonlinear dual-tower model of gravity energy storage output into a mixed-integer linear programming model; The nonlinear dual-tower model of gravity energy storage output is solved, and the charging and discharging control of gravity energy storage is based on the solution results; The increased brick volume due to energy storage system Calculated using the following formula: In the formula, The height of tower a at the previous moment. Let X be the current height of tower a. a S represents the number of bricks per floor of tower a. unit The base area of ​​a single brick. X is the maximum height of the central tower. b V represents the number of bricks per floor of tower b. unit p is the volume of each brick. ch For gravity-based energy storage charging power, η ch Let ΔT be the gravity energy storage charging efficiency, and m be the minimum time scale for day-ahead scheduling. unit Let g be the mass of a single brick, and g be the acceleration due to gravity. Current charging power Calculated using the following formula: In the formula, The expression for the charging power during the current time period. The height of tower a at the previous moment. ΔT represents the volume of bricks raised during the current period, and ΔT is the smallest time scale for day-ahead scheduling.

2. The gravity energy storage charging and discharging method using piecewise linearization approximation according to claim 1, characterized in that, The increase in gravitational potential energy when moving the bricks from the hollow cylindrical tower to the central tower is calculated using the following formula: p ch η ch T=Nm unit g ab (3) In the formula, p ch For gravity-based energy storage charging power, η ch Let g be the gravity-based energy storage charging efficiency, g be the gravitational acceleration, T be the time required for N bricks to be lifted from the hollow cylindrical tower to the central tower, and m be the time. unit For the mass of a single brick, h ab This represents the height difference between the two towers.

3. The gravity energy storage charging and discharging method using piecewise linearization approximation according to claim 1, characterized in that, The height difference of the towers after charging is calculated using the following formula: In the formula, Δh ab Let X represent the change in height difference between the two towers, where Δh1 is the change in height of tower a within time Δt, and Δh2 is the change in height of tower b within time Δt. a Let X be the number of bricks per floor of tower a. b This represents the number of bricks per floor of tower b.

4. The gravity energy storage charging and discharging method using piecewise linearization approximation according to claim 1, characterized in that, The height difference of the towers before charging is calculated using the following formula: In the formula, h ab X represents the height difference of the tower before charging. a Let X be the number of bricks per floor of tower a. b h represents the number of bricks per floor of tower b. a The height of the central cylindrical tower. This is the maximum height of the central tower.

5. The gravity energy storage charging and discharging method using piecewise linearization approximation according to claim 1, characterized in that, The height of the central tower after charging is calculated using the following formula: In the formula, h 'a The height of the central tower after charging. X is the maximum height of the central tower. a Let X be the number of bricks per floor of tower a. b V represents the number of bricks per floor of tower b. unit p is the volume of each brick. ch For gravity-based energy storage charging power, η ch For gravity energy storage charging efficiency, ΔT is the minimum time scale for day-ahead scheduling, and S unit Let g be the base area of ​​a single brick, g be the acceleration due to gravity, and h be the acceleration due to gravity. a The height of the central cylindrical tower is in meters. unit The mass of a single brick.

6. The gravity energy storage charging and discharging method using piecewise linearization approximation according to claim 1, characterized in that, The volume of bricks that decreased in the energy storage system and the discharge power during the current period: The volume of bricks reduced by the energy storage system Calculated using the following formula: In the formula, The height of tower a at the previous moment. Let X be the current height of tower a. a S represents the number of bricks per floor of tower a. unit The base area of ​​a single brick. X is the maximum height of the central tower. b V represents the number of bricks per floor of tower b. unit Let m be the volume of each brick. unit Let g be the mass of a single brick, g be the acceleration due to gravity, and η be the acceleration due to gravity. dis This refers to the power of gravity-stored energy discharge. Current period discharge power Calculated using the following formula: In the formula, Let ΔT be the expression for the discharge power during the current period, where ΔT is the minimum time scale for day-ahead scheduling.

7. The gravity energy storage charging and discharging method using piecewise linearization approximation according to claim 1, characterized in that, The feasible region of the volume is calculated using the following formula: In the formula, X represents the volume of bricks that decrease in the energy storage system. a S represents the number of bricks per floor of tower a. unit The base area of ​​a single brick. The height of tower a at the previous moment. X is the maximum height of the central tower. b This represents the number of bricks per floor of tower b.

8. The gravity energy storage charging and discharging method using piecewise linearization approximation according to claim 1, characterized in that, The nonlinear dual-tower model of gravity energy storage output is transformed into a mixed-integer linear programming model by using the piecewise linearization approximation method.

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