Energy storage operation strategy optimization method considering charging and discharging loss and real-time electricity price

Abstract

The invention discloses an energy storage operation strategy optimization method considering charge and discharge loss and real-time electricity price, and the method comprises the steps: building a user energy storage system operation optimization model, and determining an excellent charging time period and an excellent discharging time period according to an electricity price curve, and determining the charging and discharging states of the energy storage system in each time period according to the excellent charging time period and the excellent discharging time period, converting the optimization model into a linear programming model according to the charging and discharging states of the energy storage system, and finally solving to obtain an operation strategy for maximizing the operation benefit of the energy storage system. According to the method, an original model is converted into a linear programming model, so that an NP-difficult combinatorial optimization problem is simplified into a linear optimization problem, the calculation speed of the optimization process is greatly improved, and the method can be conveniently operated on an embedded industrial personal computer with limited resources for on-site configuration of an energy storage system.

Description

Technical Field

[0001] The present invention belongs to the technical field of power systems, and in particular relates to an energy storage operation optimization method. Background Art

[0002] With the progress of society and the improvement of people's living standards, the demand for electricity continues to grow, and the difference between peak and valley electricity consumption is gradually expanding. In order to promote users to reduce peak load and fill valley load, large industrial and commercial users in my country generally implement a two-part time-of-use electricity price policy. In particular, in some economically developed provinces, the phenomenon of the gradual expansion of the difference between peak and valley electricity prices is particularly significant.

[0003] In recent years, the price of lithium iron phosphate batteries has fallen, causing some industrial and commercial users to install and use lithium iron phosphate battery energy storage systems to obtain economic benefits through peak-valley arbitrage and reduced electricity demand. Although the cost of electrochemical energy storage has a downward trend, the cost of the current mainstream lithium iron phosphate energy storage system is still relatively high. Therefore, how to effectively plan and design energy storage systems, especially how to efficiently use these energy storage systems to achieve the lowest operating cost and the highest operating profit, is an urgent problem to be solved.

[0004] In the energy storage system currently configured on the user side, the commonly used operation control method is to set a fixed charging and discharging period, that is, to statically specify the charging and discharging state and power of a specific period in the energy storage EMS system. This statically configured operation strategy cannot adapt to the dynamically changing power load. When the user load curve changes beyond the adaptation range of the operation strategy, or the time-of-use electricity price changes, a new operation strategy needs to be manually formulated.

[0005] To solve the above problems, technicians in this field have proposed a solution to build a mathematical model based on the design parameters of the energy storage system, the user load curve, the maximum exchange power between the user and the public distribution system, and the current time-of-use electricity price, and then dynamically formulate an operation strategy based on the solution results of the mathematical model. However, this type of solution still has the following defects: First, the battery life loss caused by the charging and discharging process of the energy storage system and the resulting costs are not fully considered. Secondly, the constructed mathematical model is essentially a combinatorial optimization problem. If heuristic algorithms such as particle swarm optimization and annealing algorithm are used for such optimization problems, or traditional search algorithms such as cutting plane method and branch and bound method, the solution efficiency is very low. On current mainstream desktop computers, depending on the complexity of the problem, the solution time usually takes several minutes to tens of minutes, and the solution given by the heuristic algorithm often cannot guarantee the global optimum. Summary of the invention

[0006] The present invention proposes an energy storage operation strategy optimization method taking into account charging and discharging losses and real-time electricity prices, the purpose of which is: 1. Considering the battery life loss cost during the optimization process. 2. Improving the model solution speed and ensuring the optimal solution.

[0007] The technical solution of the present invention is as follows:

[0008] A method for optimizing energy storage operation strategy taking into account charging and discharging losses and real-time electricity prices, comprising:

[0009] Step 1: Establishing a user energy storage system operation optimization model, wherein the optimization model includes an objective function and constraint conditions, and the decision variable of the model is the charge and discharge power of the energy storage system in each period;

[0010] The objective function is to maximize the total net income of charging and discharging of the energy storage system. The total net income of charging and discharging is the sum of the charging and discharging income and the discharge subsidy of the energy storage system during the operation period minus the charging and discharging impairment expenses, wherein the charging and discharging income is a linear correlation term, and the discharge subsidy and the charging and discharging impairment expenses are nonlinear correlation terms. The linear correlation term refers to a calculation expression that has a linear calculation relationship with the charging and discharging power of the energy storage system, and the nonlinear correlation term refers to a calculation expression that has a nonlinear calculation relationship with the charging and discharging power of the energy storage system;

[0011] The charge continuity constraint in the constraint condition is a conditional constraint on the charging and discharging state of the energy storage system;

[0012] Step 2: Determine the best charging time period and the best discharging time period according to the electricity price curve; the best charging time period and the best discharging time period refer to the time periods that meet the following conditions:

[0013] a) The electricity price during the best discharge period is higher than the electricity prices during the adjacent periods on both sides;

[0014] b) The electricity price during the best charging period is lower than the electricity price during the adjacent periods on both sides;

[0015] c) In the electricity price curve, there is at least one optimal charging period between two optimal discharging periods;

[0016] d) In the electricity price curve, there is at least one optimal discharging period between two optimal charging periods;

[0017] e) The price difference between any adjacent pair of optimal discharging time periods and optimal charging time periods is greater than the comprehensive unit charging and discharging loss cost of the energy storage system;

[0018] Step 3: According to the optimal charging time period and the optimal discharging time period obtained in step 2, combined with the load curve, the charging and discharging state of the energy storage system in each time period is determined, and the charging and discharging state is divided into: chargeable, dischargeable, and neither charge nor discharge, so that each working time period of the energy storage system is marked as: chargeable time period, dischargeable time period, or neither charge nor discharge time period;

[0019] Step 4: Convert the optimization model in step 1 into a linear programming model according to the charge and discharge state of the energy storage system determined in step 3: convert the nonlinear related terms in the objective function into linear related terms, narrow the constraint range of the charge and discharge power of the energy storage system in the corresponding period in the constraint conditions, and convert the conditional constraints in the constraint conditions into fixed constraints;

[0020] Step 5: Solve the linear programming model given in step 4 to obtain the operation strategy that maximizes the operation efficiency of the energy storage system.

[0021] As a further improvement of the energy storage operation strategy optimization method taking into account charging and discharging losses and real-time electricity prices, the objective function constructed in step 1 is:

[0022]

[0023] Among them, V total Total net revenue from charging and discharging the energy storage system; is the profit obtained by the energy storage system from charging and discharging in time period i, where charging is positive profit and discharging is negative profit; The cost of energy storage life loss caused by the energy storage system performing charging and discharging operations in time period i; It represents the discharge subsidy income obtained by the energy storage system during discharge in time period i; N is the total number of time periods in the optimization period.

[0024] As a further improvement of the energy storage operation strategy optimization method considering charging and discharging losses and real-time electricity prices, the objective function The calculation method is:

[0025]

[0026] In the formula, is the charging and discharging power of the energy storage system in time period i, which is positive during charging and negative during discharging, ρ i is the electricity price in period i, Δt is the length of a period;

[0027] In the objective function The calculation method is:

[0028]

[0029] In the formula, C bat_e The cost of depreciation of the unit charging and discharging battery life of the energy storage system;

[0030] In the objective function The calculation method is:

[0031]

[0032] Where ε(x) represents the unit step function. When x is greater than or equal to 0, the function value is 1, otherwise it is 0. sub The subsidy price per unit discharge amount.

[0033] As a further improvement of the energy storage operation strategy optimization method taking into account the charging and discharging losses and the real-time electricity price, the calculation method of the unit charging and discharging battery life loss cost is: Among them C bat is the initial purchase cost of the energy storage system battery, r is the capital discount rate, n is the life of the battery in years under the design conditions of the energy storage system, Γ d The total throughput under the design conditions for the energy storage system;

[0034] The total throughput under the design condition of the energy storage system is calculated as: Γ d =N d *D d *E batR , N d is the number of cycles under the designed operating conditions of the energy storage system, D d is the designed charge and discharge depth of the energy storage system, E batR is the rated energy of the energy storage system battery.

[0035] As a further improvement of the energy storage operation strategy optimization method taking into account charging and discharging losses and real-time electricity prices, the constraints of the optimization model include: charging and discharging power constraints, charge constraints, charge continuity constraints, start and end time charge constraints, and total electric power constraints exchanged between the user's AC bus and the external public power grid;

[0036] (1) The charge and discharge power constraints are: is the charging and discharging power of the energy storage system in time period i, P batR is the rated charging and discharging power of the energy storage system;

[0037] (2) The charge constraint is: is the charge of the energy storage system in time period i, E batR is the rated energy of the energy storage system, SOC MIN and SOC MAX are the minimum allowable state of charge and the maximum allowable state of charge of the energy storage system respectively;

[0038] (3) The charge continuity constraint is a conditional constraint, including the following three cases:

[0039] While charging:

[0040] When discharging:

[0041] When not charging or discharging:

[0042] In the formula, Δt is the duration of a period, η C is the charging efficiency of the energy storage system, η D is the discharge efficiency of the energy storage system;

[0043] (4) The load constraints at the start and end times are: the energy storage system load at the start time and the charge of the energy storage system at the end time They are equal to their respective preset values, and N is the total number of time periods in the optimization period;

[0044] (5) The total power exchanged between the user AC bus and the external public power grid is constrained to: P gateM The maximum limit of the electric power exchanged between the user's AC bus and the external public power grid. It is the average value of the load electric power in time period i in the load curve.

[0045] As a further improvement of the energy storage operation strategy optimization method taking into account the charging and discharging losses and the real-time electricity price, the calculation method of the unit charging and discharging comprehensive loss cost of the energy storage system is:

[0046]

[0047] in, Indicates that the energy storage system is under the condition that the electricity price is ρ i At time i, 1 kWh of electricity is charged and the electricity price is ρ j The total cost caused by releasing 1 kWh of electricity in time period j; σ C is the charging loss coefficient, and σ C =1-η C , η C is the charging efficiency of the energy storage system; D is the discharge loss coefficient, and σ D =1-η D , η D is the discharge efficiency of the energy storage system; C bat_e It is the cost of battery life loss per unit of charging and discharging in the energy storage system.

[0048] As a further improvement of the energy storage operation strategy optimization method taking into account the charging and discharging losses and the real-time electricity price, the specific process of determining the best charging period and the best discharging period is as follows:

[0049] Step 2-1, traverse the electricity price curve to find all extremely low electricity price periods, extremely high electricity price periods, minimum electricity price periods and maximum electricity price periods; the extremely low electricity price period refers to the period whose electricity price is lower than the electricity prices of the adjacent periods on both sides, the extremely high electricity price period refers to the period whose electricity price is higher than the electricity prices of the adjacent periods on both sides, the lowest electricity price period refers to the period with the lowest electricity price in the electricity price curve, and the highest electricity price period refers to the period with the lowest electricity price in the electricity price curve;

[0050] Step 2-2: If the price difference between the highest and lowest electricity prices is greater than the comprehensive loss cost per unit of charging and discharging of the energy storage system, then continue to step 2-3; otherwise, the system is marked as having no charging and discharging arbitrage opportunities, and the search for the best discharging period and the best charging period ends;

[0051] Step 2-3, find a period with the lowest electricity price, mark it as an excellent charging period, and set it as a base electricity price period;

[0052] Step 2-4, determine whether there is an extremely high electricity price period or an extremely low electricity price period after the base electricity price period, if so, execute step 2-5, otherwise jump to step 2-18;

[0053] Step 2-5, from the extremely high electricity price period and the extremely low electricity price period after the benchmark electricity price period, select the period that is closest to the benchmark electricity price period in time and has not been processed as the period to be determined;

[0054] Step 2-6: If the time period to be determined is a period of extremely high electricity prices, execute step 2-7; otherwise, jump to step 2-12;

[0055] Step 2-7: If the base electricity price period is an excellent discharge period, execute step 2-8; otherwise, jump to step 2-10;

[0056] Step 2-8: If the price of the time period to be determined is greater than the price of the base electricity price time period, execute step 2-9; otherwise, jump to step 2-17;

[0057] Step 2-9, cancel the optimal discharge period mark of the current base electricity price period; mark the period to be determined as the optimal discharge period; set the period to be determined as the base electricity price period; jump to step 2-17;

[0058] Step 2-10: If the price difference between the time period to be determined and the benchmark electricity price time period is greater than the unit charge and discharge comprehensive loss cost, execute step 2-11; otherwise, jump to step 2-17;

[0059] Step 2-11, mark the period to be determined as an excellent discharge period; set the period to be determined as a base electricity price period; jump to step 2-17;

[0060] Step 2-12: If the base electricity price period is an excellent charging period, execute step 2-13; otherwise, jump to step 2-15;

[0061] Step 2-13: If the price of the time period to be determined is less than the price of the benchmark electricity price time period, execute step 2-14; otherwise, jump to step 2-17;

[0062] Step 2-14, cancel the optimal charging period mark of the current base electricity price period; mark the period to be determined as the optimal charging period; set the period to be determined as the base electricity price period; jump to step 2-17;

[0063] Step 2-15: If the price difference between the time period to be determined and the benchmark electricity price time period is greater than the unit charge and discharge comprehensive loss cost, execute step 2-16; otherwise, jump to step 2-17;

[0064] Step 2-16, marking the period to be determined as an excellent charging period; setting the period to be determined as a base electricity price period;

[0065] Step 2-17: If there are any electricity price periods that have not been determined and processed in the extremely high electricity price period and the extremely low electricity price period after the base electricity price period, execute step 2-5; otherwise, execute step 2-18;

[0066] Step 2-18: If there are undetermined electricity price periods in the extremely high electricity price period and the extremely low electricity price period before the base electricity price period, then execute step 2-19; ​​otherwise, the search for the optimal discharge period and the optimal charge period ends;

[0067] Step 2-19, from the extremely high electricity price period and the extremely low electricity price period before the benchmark electricity price period, select the electricity price period that is closest to the benchmark electricity price period and has not been determined as the period to be determined;

[0068] Step 2-20: If the time period to be determined is a period of extremely high electricity prices, execute step 2-21; otherwise, jump to step 2-26;

[0069] Step 2-21, if the base electricity price period is an excellent discharge period, execute step 2-22, otherwise jump to step 2-24;

[0070] Step 2-22: If the price of the time period to be determined is greater than the price of the base electricity price time period, execute step 2-23; otherwise, jump to step 2-18;

[0071] Step 2-23, cancel the optimal discharge period mark of the current base electricity price period; mark the period to be determined as the optimal discharge period; set the period to be determined as the base electricity price period; jump to step 2-18;

[0072] Step 2-24: If the price difference between the time period to be determined and the benchmark electricity price time period is greater than the unit charge and discharge comprehensive loss cost, execute step 2-25; otherwise, jump to step 2-18;

[0073] Step 2-25, mark the period to be determined as an excellent discharge period; set the period to be determined as a base electricity price period; jump to step 2-18;

[0074] Step 2-26: If the base electricity price period is an excellent charging period, execute step 2-27; otherwise, jump to step 2-29;

[0075] Step 2-27, if the price of the time period to be determined is less than the price of the benchmark electricity price time period, execute step 2-28, otherwise jump to step 2-18;

[0076] Step 2-28, cancel the optimal charging period mark of the current base electricity price period; mark the period to be determined as the optimal charging period; set the period to be determined as the base electricity price period; jump to step 2-18;

[0077] Step 2-29, if the price difference between the price of the time period to be determined and the price difference between the time period of the benchmark electricity price is greater than the unit charge and discharge comprehensive loss cost, then execute step 2-30, otherwise jump to step 2-18;

[0078] Step 2-30, mark the time period to be determined as an excellent charging time period; set the time period to be determined as a base electricity price time period; jump to step 2-18.

[0079] As a further improvement of the energy storage operation strategy optimization method taking into account charging and discharging losses and real-time electricity prices, the specific process of step 3 is:

[0080] If the system is marked as having no charging and discharging arbitrage opportunities in the previous step 2, the charging and discharging status is determined in the following manner: if the energy storage system charge at the set end time is greater than the energy storage system charge at the start time, all time periods are marked as "chargeable"; if the energy storage system charge at the set end time is less than the energy storage system charge at the start time, all time periods are marked as "dischargeable"; in other cases, all time periods are marked as "neither charging nor discharging"; otherwise, the charging and discharging status is determined according to the following steps:

[0081] Step 3-1: In each adjacent interval dominated by an optimal charging period, mark the status of the period that meets all of the following conditions as "chargeable":

[0082] a. The electricity price during this period is less than the electricity price during the best charging period in this adjacent interval plus the comprehensive loss cost per unit charge and discharge of the energy storage system;

[0083] b. The electricity price during this period is less than the electricity price during the best forward discharge period in this adjacent interval minus the comprehensive unit charge and discharge loss cost of the energy storage system;

[0084] c. The electricity price during this period is less than the electricity price during the optimal backward discharge period in the adjacent interval minus the comprehensive unit charge and discharge loss cost of the energy storage system;

[0085] The adjacent interval dominated by the optimal charging period means that if an optimal charging period has two adjacent optimal discharging periods, all periods between the two optimal discharging periods constitute the adjacent interval dominated by the optimal charging period; if an optimal charging period has only one adjacent optimal discharging period, all periods between the optimal charging period and the optimal discharging period constitute the adjacent interval dominated by the optimal charging period;

[0086] Step 3-2: In each adjacent interval dominated by the best discharge period, mark the status of the period that meets all the following conditions as "dischargeable":

[0087] a. The electricity price during this period is greater than the electricity price during the best discharge period in this adjacent interval minus the comprehensive loss cost of unit charging and discharging of the energy storage system;

[0088] b. The electricity price during this period is greater than the electricity price during the optimal forward charging period in this adjacent interval plus the comprehensive unit charging and discharging loss cost of the energy storage system;

[0089] c. The electricity price during this period is greater than the electricity price during the optimal backward charging period in this adjacent interval plus the comprehensive unit charging and discharging loss cost of the energy storage system;

[0090] The adjacent interval dominated by the said optimal discharge period: if a certain optimal discharge period has two adjacent optimal charging periods, then all periods between the two optimal charging periods constitute the adjacent interval dominated by the optimal discharge period; if a certain optimal discharge period has only one adjacent optimal charging period, then all periods between the optimal discharge period and the optimal charging period constitute the adjacent interval dominated by the optimal discharge period;

[0091] Step 3-3: If there is an adjacent interval dominated by an optimal charging period that satisfies the following condition 1, or if there is an adjacent interval dominated by an optimal discharging period that satisfies the following condition 2, then execute step 3-4; otherwise, all remaining periods not marked with charge and discharge status are marked as neither charge nor discharge, and the charge and discharge status marking process ends:

[0092] Condition 1: There are periods of unmarked charging and discharging status in the adjacent interval dominated by the optimal charging period, and the price difference between the electricity price of at least one period of unmarked charging and discharging status and the price of the optimal discharging period in the adjacent interval is greater than the unit charging and discharging comprehensive loss cost, and the price difference between the electricity price of this period and the price of the optimal discharging period in the adjacent interval is greater than the unit charging and discharging comprehensive loss cost;

[0093] Condition 2: There are periods of unmarked charge and discharge status in the adjacent interval dominated by the optimal discharge period, and the price difference between the electricity price of at least one period of unmarked charge and discharge status and the price of the optimal charging period in the adjacent interval is greater than the unit charge and discharge comprehensive loss cost, and the price difference between the electricity price of this period and the optimal charging period in the adjacent interval is greater than the unit charge and discharge comprehensive loss cost;

[0094] Step 3-4, calculate the charging capacity of all adjacent intervals dominated by each optimal charging period that meets condition 1 in step 3-3, and the discharging capacity of all adjacent intervals dominated by each optimal discharging period that meets condition 2 in step 3-3, and find the minimum capacity value among all charging capacities and discharging capacities. If the minimum capacity value corresponds to the adjacent interval dominated by the optimal charging period, execute step 3-5; if the minimum capacity value corresponds to the adjacent interval dominated by the optimal discharging period, execute step 3-6;

[0095] Step 3-5, mark the time period whose electricity price is closest to the best charging time period in the adjacent interval dominated by the best charging time period found in step 3-4 and is not marked with a charging or discharging state as "chargeable", and jump to step 3-3;

[0096] Step 3-6: Mark the time period whose electricity price is closest to the best discharge time period in the adjacent interval dominated by the best discharge time period found in step 3-4 and whose charge and discharge status is not marked as "dischargeable", and jump to step 3-3.

[0097] As a further improvement of the energy storage operation strategy optimization method taking into account charging and discharging losses and real-time electricity prices:

[0098] For an adjacent interval dominated by an optimal charging period, its charging capacity Q CA The calculation method is:

[0099]

[0100] in, is the maximum allowed charging power for time period i, It refers to the sum of the maximum allowable charging power of each period in the adjacent interval dominated by the best charging period, Δt is the length of a period, P batR is the rated charge and discharge power of the energy storage system, is the average value of load power in period i in the load curve, P gateM The maximum limit of electric power exchanged between the user's AC bus and the external public power grid;

[0101] For an adjacent interval dominated by an excellent discharge period, its discharge capacity Q DA The calculation method is:

[0102]

[0103] in, is the maximum allowable discharge power in time period i, It refers to the sum of the maximum allowable discharge powers of each time period in the adjacent interval dominated by the optimal discharge time period.

[0104] As a further improvement of the energy storage operation strategy optimization method taking into account the charging and discharging losses and the real-time electricity price: the conversion process in step 4 includes:

[0105] (1) For the nonlinear expression in the objective function If time period i is a charging period, If time period i is a dischargeable time period, If time period i is a period of neither charging nor discharging,

[0106] (2) For the nonlinear expression in the objective function If time period i is a dischargeable time period or a non-charge-neither-discharge time period, the function value is 1; if time period i is a chargeable time period, the function value is 0;

[0107] (3) For charging and discharging power constraints: If time period i is a rechargeable time period, the constraint is changed to If time period i is a dischargeable time period, the constraint is changed to If time period i is a non-charging and non-discharging period, the constraint is changed to

[0108] (4) For the charge continuity constraint, if time period i is a chargeable time period, the constraint is directly set as If time period i is a dischargeable time period, the constraint is directly set as If time period i is a non-charging and non-discharging period, the constraint is directly set as

[0109] Compared with the prior art, the present invention has the following beneficial effects:

[0110] The method of the present invention first determines the charge and discharge state of the energy storage system in each time period, and then processes the constructed optimization model according to the charge and discharge state, converting it into a linear programming model, thereby simplifying an NP-hard combinatorial optimization problem into a linear optimization problem, greatly improving the calculation speed of the optimization process, so that the method can be conveniently run on an embedded industrial computer with limited resources configured on-site in the energy storage system. The method can be applied to both time-of-use electricity price scenarios and real-time electricity price scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0111] Figure 1 A simplified diagram of the electricity logic structure of industrial and commercial users equipped with user-side energy storage;

[0112] Figure 2 is the load curve diagram;

[0113] Figure 3 It is the charge and discharge curve diagram;

[0114] Figure 4 It is the electricity price curve;

[0115] Figure 5 A schematic diagram for illustrating the relationship between the optimal charging period, the optimal discharging period and the adjacent intervals;

[0116] Figure 6 This is the estimated net load curve of a cement plant on a certain day. DETAILED DESCRIPTION

[0117] The technical solution of the present invention is described in detail below in conjunction with the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments.

[0118] For industrial and commercial users equipped with user-side energy storage systems, the local electricity price generally has a large difference between peak and valley prices, and the energy storage system mainly makes profits through peak-valley arbitrage. At the same time, the large electricity load of these industrial and commercial users also provides opportunities for the configuration and consumption of distributed power generation. Even some cement plants, paper mills, glass plants and other enterprises may be equipped with waste heat power generation equipment. The distributed power generation and waste heat power generation in these enterprises usually adopt the mode of connecting to the grid but not connecting to the grid.

[0119] like Figure 1 As shown in Figure 1, the electricity consumption logic structure of such industrial and commercial users equipped with user-side energy storage consists of total net load, energy storage system and AC bus. The total net load and energy storage system are connected to the AC bus, and the AC bus is connected to the external public power grid through the main transformer. Among them, the total net load represents the total load after all the user's electricity loads and self-generated power are added together, P neat Represents the load electric power between the total net load and the AC bus, and the flow from the bus to the load is defined as the positive direction. gateRepresents the total electric power exchanged between the user's AC bus and the external public power grid. It is stipulated that the flow from the external public power grid to the AC bus is the positive direction, and P gateM Represents the maximum limit of the electric power exchanged between the user's AC bus and the external public power grid. bat Represents the charging and discharging power of the energy storage system, and the direction of flow to the energy storage system, i.e., the charging direction, is defined as the positive direction. For the convenience of expression, the power size of the energy storage system when charging is represented as P batC , P batC =P bat ; The power of the energy storage system when discharging is expressed as P batD , P batD =|P bat |=-P bat .P neat , P gate and P bat The relationship between the three is: gate =P neat +P bat .

[0120] Furthermore, using η C Indicates the charging efficiency of the energy storage system, then the charging power P batC After charging the energy storage system for Δt time, the energy storage system charge energy increase value is: P batC *η C *Δt. Use η D To express the discharge efficiency of the energy storage system, the discharge power P is used. batD After discharging the energy storage system for Δt time, the energy storage system charge energy reduction value is:

[0121] Usually used as Figure 2 The load curve shown is used to represent the load power P within a period of time (typically one day or 24 hours). neat The period is generally divided into N time periods (typically N is 96), with the initial time being 0 and the end time being N. The time period between time i and time i+1 is called time period i+1, and the length of each time period is Δt. neat The average value is expressed as Thus, N consecutive This constitutes the load curve for this period.

[0122] Usually used as Figure 3 The charge and discharge curve shown is used to represent the charge and discharge power P within a period of time (typically one day or 24 hours). bat The change of can also be divided into N time periods. The time period between time i and time i+1 is called time period i+1. The P bat The average value is expressed as Thus, N consecutive The charge and discharge curves during this period are formed.

[0123] In this method, it is agreed that the load curve and the charging curve have the same time division method for a period of time (typically one day or 24 hours), that is, the start time is the same, the end time is the same, and the equal fraction N is also the same.

[0124] A continuous period of time with equal electricity prices is defined as an electricity price period. All electricity price periods within a period (typically a day or 24 hours) constitute a Figure 4 The electricity price curve is shown.

[0125] A method for optimizing energy storage operation strategy taking into account charging and discharging losses and real-time electricity prices, comprising:

[0126] Step 1: Establish a user energy storage system operation optimization model, wherein the optimization model includes an objective function and constraint conditions, and the decision variable of the model is the charge and discharge power of the energy storage system in each time period.

[0127] The objective function is to maximize the total net income of charging and discharging of the energy storage system. The total net income of charging and discharging is the sum of the charging and discharging income and the discharge subsidy of the energy storage system during the operation period minus the charging and discharging depreciation expenses, wherein the charging and discharging income is a linearly related term, and the discharge subsidy and the charging and discharging depreciation expenses are non-linearly related terms. The linearly related term refers to a calculation expression that has a linear calculation relationship with the charging and discharging power of the energy storage system, and the non-linearly related term refers to a calculation expression that has a nonlinear calculation relationship with the charging and discharging power of the energy storage system.

[0128] Specifically, the objective function is:

[0129]

[0130] Among them, V total Total net revenue from charging and discharging the energy storage system; is the profit obtained by the energy storage system from charging and discharging in time period i, where charging is positive profit and discharging is negative profit; The cost of energy storage life loss caused by the energy storage system performing charging and discharging operations in time period i; It represents the discharge subsidy income obtained by the energy storage system during discharge in time period i; N is the total number of time periods in the optimization period.

[0131] In the objective function The calculation method is:

[0132]

[0133] In the formula, is the charging and discharging power of the energy storage system in time period i, which is positive during charging and negative during discharging, ρ i is the electricity price in period i, and Δt is the length of a period.

[0134] In the objective function The calculation method is:

[0135]

[0136] In the formula, C bat_e It is the life loss cost of the unit charging and discharging battery of the energy storage system, and its calculation method is: Among them C bat is the initial purchase cost of the energy storage system battery, r is the capital discount rate, n is the life of the battery in years under the design conditions of the energy storage system, Γ d The total throughput under design conditions for the energy storage system.

[0137] Furthermore, the total throughput under the design condition of the energy storage system is calculated as: Γ d =N d *D d *E batR , N d is the number of cycles under the designed operating conditions of the energy storage system, D d is the designed charge and discharge depth of the energy storage system, E batR is the rated energy of the energy storage system battery.

[0138] In engineering calculations, for the sake of convenience, the cost can be allocated to the charging process and the discharging process. Then the unit charging life loss cost of the energy storage battery and the unit discharging life loss cost of the energy storage battery can be expressed as

[0139] In the objective function The calculation method is:

[0140]

[0141] Where ε(x) represents the unit step function. When x is greater than or equal to 0, the function value is 1, otherwise it is 0. sub The subsidy price per unit discharge volume (depending on the local government’s preferential energy storage policy).

[0142] The constraints of the optimization model include: charging and discharging power constraints, charge constraints, charge continuity constraints, start and end time charge constraints, and total power constraints exchanged between the user's AC bus and the external public power grid. The charge continuity constraint is a conditional constraint on the charging and discharging state of the energy storage system.

[0143] (1) The charge and discharge power constraints are: is the charging and discharging power of the energy storage system in time period i, P batR is the rated charging and discharging power of the energy storage system.

[0144] (2) The charge constraint is: is the charge of the energy storage system in time period i, E batR is the rated energy of the energy storage system, SOC MIN and SOC MAX They are the minimum allowable state of charge and the maximum allowable state of charge of the energy storage system respectively.

[0145] (3) The charge continuity constraint is a conditional constraint, including the following three cases:

[0146] While charging:

[0147] When discharging:

[0148] When not charging or discharging:

[0149] In the formula, Δt is the duration of a period, η C is the charging efficiency of the energy storage system, η D is the discharge efficiency of the energy storage system.

[0150] (4) The load constraints at the start and end times are: the energy storage system load at the start time and the charge of the energy storage system at the end time They are equal to their respective preset values, and N is the total number of time periods in the optimization period.

[0151] (5) The total power exchanged between the user AC bus and the external public power grid is constrained to: P gateM The maximum limit of the electric power exchanged between the user's AC bus and the external public power grid. It is the average value of the load electric power in time period i in the load curve.

[0152] It can be seen that in the currently constructed model, the expressions of the objective function and the constraints contain nonlinear parts caused by the different charging and discharging states during the time periods, which makes the solution of the optimization model essentially an NP-hard combinatorial optimization problem.

[0153] Step 2: Determine the best charging time period and the best discharging time period according to the electricity price curve. The best charging time period and the best discharging time period refer to the time periods that meet the following conditions:

[0154] a) The electricity price during the best discharge period is higher than the electricity prices during the adjacent periods on both sides;

[0155] b) The electricity price during the best charging period is lower than the electricity price during the adjacent periods on both sides;

[0156] c) In the electricity price curve, there is at least one optimal charging period between two optimal discharging periods;

[0157] d) In the electricity price curve, there is at least one optimal discharging period between two optimal charging periods;

[0158] e) The price difference between any adjacent pair of optimal discharging periods and optimal charging periods is greater than the comprehensive unit charging and discharging loss cost of the energy storage system.

[0159] Based on the above definition, it is not difficult to infer that when the price difference between the electricity price in the period with the highest electricity price and the electricity price in the period with the lowest electricity price is less than or equal to the comprehensive loss cost per unit charge and discharge of the energy storage system, there must be no excellent charging period and excellent discharging period in the electricity price curve; conversely, if the price difference between the electricity price in the period with the highest electricity price and the electricity price in the period with the lowest electricity price is greater than the comprehensive loss cost per unit charge and discharge of the energy storage system, the period with the highest electricity price must be the excellent discharging period, and the period with the lowest electricity price must be the excellent charging period.

[0160] The calculation method of the comprehensive loss cost per unit charge and discharge of the energy storage system is as follows:

[0161]

[0162] in, Indicates that the energy storage system is under the condition that the electricity price is ρ i At time i, 1 kWh of electricity is charged and the electricity price is ρ j The total cost caused by releasing 1 kWh of electricity in time period j; σ C is the charging loss coefficient, and σ C =1-η C , η C is the charging efficiency of the energy storage system; D is the discharge loss coefficient, and σ D =1-η D , η D is the discharge efficiency of the energy storage system; C bat_e It is the cost of battery life loss per unit of charging and discharging in the energy storage system.

[0163] According to the above definition, the specific process of determining the optimal charging period and the optimal discharging period is as follows:

[0164] Step 2-1, traverse the electricity price curve to find all extremely low electricity price periods, extremely high electricity price periods, minimum electricity price periods and maximum electricity price periods. The extremely low electricity price period refers to the period when its electricity price is lower than the electricity price of the adjacent periods on both sides, the extremely high electricity price period refers to the period when its electricity price is higher than the electricity price of the adjacent periods on both sides, the lowest electricity price period refers to the period with the lowest electricity price in the electricity price curve, and the highest electricity price period refers to the period with the lowest electricity price in the electricity price curve.

[0165] For example Figure 4 The electricity price curve shows that 0-8 o'clock, 12-14 o'clock and 19-24 o'clock are periods of extremely low electricity prices, 11-12 o'clock and 15-17 o'clock are periods of extremely high electricity prices, 0-8 o'clock is the period of lowest electricity prices, and 11-12 o'clock and 15-17 o'clock are both periods of highest electricity prices.

[0166] Step 2-2: If the price difference between the highest electricity price and the lowest electricity price is greater than the comprehensive loss cost per unit of charging and discharging of the energy storage system, continue to step 2-3; otherwise, the system is marked as having no charging and discharging arbitrage opportunities, and the search for the best discharging period and the best charging period ends.

[0167] Step 2-3: Find a period with the lowest electricity price, mark it as an excellent charging period, and set it as a base electricity price period.

[0168] Step 2-4: Determine whether there is an extremely high electricity price period or an extremely low electricity price period after the base electricity price period. If so, execute step 2-5; otherwise, jump to step 2-18.

[0169] Step 2-5: From the extremely high electricity price period and the extremely low electricity price period after the reference electricity price period, the period that is closest to the reference electricity price period in time and has not been processed is selected as the period to be determined.

[0170] Step 2-6: If the time period to be determined is a period of extremely high electricity prices, execute step 2-7; otherwise, jump to step 2-12.

[0171] Step 2-7: If the base electricity price period is an excellent discharge period, execute step 2-8; otherwise, jump to step 2-10.

[0172] Step 2-8: If the price of the time period to be determined is greater than the price of the base electricity price time period, execute step 2-9; otherwise, jump to step 2-17.

[0173] Step 2-9, cancel the optimal discharge period mark of the current base electricity price period; mark the period to be determined as the optimal discharge period; set the period to be determined as the base electricity price period; jump to step 2-17.

[0174] Step 2-10: If the price difference between the price of the time period to be determined and the price difference between the time period of the base electricity price is greater than the unit charge and discharge comprehensive loss cost, execute step 2-11; otherwise, jump to step 2-17.

[0175] Step 2-11, mark the time period to be determined as an excellent discharge time period; set the time period to be determined as a base electricity price time period; jump to step 2-17.

[0176] Step 2-12: If the base electricity price period is an optimal charging period, execute step 2-13; otherwise, jump to step 2-15.

[0177] Step 2-13: If the price of the time period to be determined is less than the price of the benchmark electricity price time period, execute step 2-14; otherwise, jump to step 2-17.

[0178] Step 2-14, cancel the optimal charging period mark of the current base electricity price period; mark the period to be determined as the optimal charging period; set the period to be determined as the base electricity price period; jump to step 2-17.

[0179] Step 2-15: If the price difference between the price of the time period to be determined and the price difference between the time period of the benchmark electricity price is greater than the unit charge and discharge comprehensive loss cost, execute step 2-16; otherwise, jump to step 2-17.

[0180] Step 2-16: Mark the time period to be determined as an excellent charging time period; set the time period to be determined as a base electricity price time period.

[0181] Step 2-17: If there are any electricity price periods that have not been determined and processed in the extremely high electricity price period and the extremely low electricity price period after the base electricity price period, execute step 2-5; otherwise, execute step 2-18.

[0182] Step 2-18: If there are undetermined electricity price periods in the extremely high electricity price period and the extremely low electricity price period before the base electricity price period, execute step 2-19; ​​otherwise, the search for the optimal discharge period and the optimal charge period ends.

[0183] Step 2-19: From the extremely high electricity price period and the extremely low electricity price period before the benchmark electricity price period, select the electricity price period that is closest to the benchmark electricity price period and has not been processed as the period to be determined.

[0184] Step 2-20: If the time period to be determined is a period of extremely high electricity prices, execute step 2-21; otherwise, jump to step 2-26.

[0185] Step 2-21: If the base electricity price period is an excellent discharge period, execute step 2-22; otherwise, jump to step 2-24.

[0186] Step 2-22: If the price of the time period to be determined is greater than the price of the reference electricity price time period, execute step 2-23; otherwise, jump to step 2-18.

[0187] Step 2-23, cancel the optimal discharge period mark of the current base electricity price period; mark the period to be determined as the optimal discharge period; set the period to be determined as the base electricity price period; jump to step 2-18.

[0188] Step 2-24: If the price difference between the time period to be determined and the reference electricity price time period is greater than the unit charge and discharge comprehensive loss cost, execute step 2-25; otherwise, jump to step 2-18.

[0189] Step 2-25, mark the time period to be determined as an excellent discharge time period; set the time period to be determined as a base electricity price time period; jump to step 2-18.

[0190] Step 2-26: If the base electricity price period is an optimal charging period, execute step 2-27; otherwise, jump to step 2-29.

[0191] Step 2-27: If the price of the time period to be determined is less than the price of the benchmark electricity price time period, execute step 2-28; otherwise, jump to step 2-18.

[0192] Step 2-28, cancel the optimal charging period mark of the current base electricity price period; mark the period to be determined as the optimal charging period; set the period to be determined as the base electricity price period; jump to step 2-18.

[0193] Step 2-29: If the price difference between the time period to be determined and the reference electricity price time period is greater than the unit charge and discharge comprehensive loss cost, execute step 2-30; otherwise, jump to step 2-18.

[0194] Step 2-30, mark the time period to be determined as an excellent charging time period; set the time period to be determined as a base electricity price time period; jump to step 2-18.

[0195] Step 3: According to the optimal charging time period and the optimal discharging time period obtained in step 2, combined with the load curve, the charging and discharging state of the energy storage system in each time period is determined, and the charging and discharging state is divided into: chargeable, dischargeable, and neither charge nor discharge, so that each working time period of the energy storage system is marked as: chargeable time period, dischargeable time period, or neither charge nor discharge time period.

[0196] If the system is marked as having no charge-discharge arbitrage opportunities in the previous step 2, the charge-discharge status is determined in the following manner: if the energy storage system charge at the set end time is greater than the energy storage system charge at the start time, all time periods are marked as "chargeable"; if the energy storage system charge at the set end time is less than the energy storage system charge at the start time, all time periods are marked as "dischargeable"; in other cases, all time periods are marked as "neither charge nor discharge". Otherwise, the charge-discharge status is determined in the following steps:

[0197] Step 3-1: In each adjacent interval dominated by an optimal charging period, mark the status of the period that meets all of the following conditions as "chargeable":

[0198] a. The electricity price during this period is less than the electricity price during the best charging period in this adjacent interval plus the comprehensive loss cost per unit charge and discharge of the energy storage system;

[0199] b. The electricity price during this period is less than the electricity price during the best forward discharge period in this adjacent interval minus the comprehensive unit charge and discharge loss cost of the energy storage system;

[0200] c. The electricity price during this period is less than the electricity price during the optimal backward discharge period in the adjacent interval minus the comprehensive unit charge and discharge loss cost of the energy storage system;

[0201] The adjacent interval dominated by the excellent charging period means: if an excellent charging period has two adjacent excellent discharging periods, then all periods between the two excellent discharging periods constitute the adjacent interval dominated by the excellent charging period; if an excellent charging period has only one adjacent excellent discharging period, then all periods between the excellent charging period and this excellent discharging period constitute the adjacent interval dominated by the excellent charging period.

[0202] like Figure 5 , time periods A and L are excellent charging time periods, and time periods G and Q are excellent discharging time periods. According to the above definition, in the charge and discharge curve, time periods A, B, C, D, E, F, and G constitute the adjacent interval dominated by the excellent charging time period A; time periods G, H, I, J, K, L, M, N, O, P, and Q constitute the adjacent interval dominated by the excellent charging time period L.

[0203] Step 3-2: In each adjacent interval dominated by the best discharge period, mark the status of the period that meets all the following conditions as "dischargeable":

[0204] a. The electricity price during this period is greater than the electricity price during the best discharge period in this adjacent interval minus the comprehensive loss cost of unit charging and discharging of the energy storage system;

[0205] b. The electricity price during this period is greater than the electricity price during the optimal forward charging period in this adjacent interval plus the comprehensive unit charging and discharging loss cost of the energy storage system;

[0206] c. The electricity price during this period is greater than the electricity price during the optimal backward charging period in this adjacent interval plus the comprehensive unit charging and discharging loss cost of the energy storage system.

[0207] The adjacent interval dominated by the excellent discharging period: if an excellent discharging period has two adjacent excellent charging periods, then all periods between the two excellent charging periods constitute the adjacent interval dominated by the excellent discharging period; if an excellent discharging period has only one adjacent excellent charging period, then all periods between the excellent discharging period and this excellent charging period constitute the adjacent interval dominated by the excellent discharging period.

[0208] like Figure 5 , time periods A and L are excellent charging time periods, and time periods G and Q are excellent discharging time periods. According to the above definition, in the charge and discharge curve, time periods A, B, C, D, E, F, G, H, I, J, K, and L constitute the adjacent interval dominated by the excellent discharge time period G; and time periods L, M, N, O, P, and Q constitute the adjacent interval dominated by the excellent discharge time period Q.

[0209] Step 3-3: If there is an adjacent interval dominated by an optimal charging period that satisfies the following condition 1, or if there is an adjacent interval dominated by an optimal discharging period that satisfies the following condition 2, then execute step 3-4; otherwise, all remaining periods not marked with charge and discharge status are marked as neither charge nor discharge, and the charge and discharge status marking process ends:

[0210] Condition 1: There are time periods without marked charging and discharging status in the adjacent interval dominated by the optimal charging time period, and the price difference between the electricity price of at least one time period without marked charging and discharging status and the price of the optimal discharging time period in the adjacent interval forward is greater than the unit charging and discharging comprehensive loss cost, and at the same time, the price difference between the electricity price of this time period and the price of the optimal discharging time period in the adjacent interval backward is greater than the unit charging and discharging comprehensive loss cost.

[0211] Condition 2: There are time periods without marked charging and discharging status in the adjacent interval dominated by the optimal discharge time period, and the price difference between the electricity price of at least one time period without marked charging and discharging status and the price of the optimal charging time period forward in the adjacent interval is greater than the unit charging and discharging comprehensive loss cost, and at the same time, the price difference between the electricity price of this time period and the price of the optimal charging time period backward in the adjacent interval is greater than the unit charging and discharging comprehensive loss cost.

[0212] Step 3-4, calculate the charging capacity of all adjacent intervals dominated by the optimal charging period that meets condition 1 in step 3-3, and the discharge capacity of all adjacent intervals dominated by the optimal discharge period that meets condition 2 in step 3-3, and find the minimum capacity value among all charging capacities and discharge capacities. If the minimum capacity value corresponds to the adjacent interval dominated by the optimal charging period, execute step 3-5; if the minimum capacity value corresponds to the adjacent interval dominated by the optimal discharge period, execute step 3-6.

[0213] For an adjacent interval dominated by an optimal charging period, its charging capacity Q CA The calculation method is:

[0214]

[0215] in, is the maximum allowed charging power for time period i, It refers to the sum of the maximum allowable charging power of each period in the adjacent interval dominated by the best charging period, Δt is the length of a period, P batR is the rated charge and discharge power of the energy storage system, is the average value of load power in period i in the load curve, p gateM It is the maximum limit of electric power exchanged between the user's AC bus and the external public power grid.

[0216] For an adjacent interval dominated by an excellent discharge period, its discharge capacity Q DA The calculation method is:

[0217]

[0218] in, is the maximum allowable discharge power in time period i, It refers to the sum of the maximum allowable discharge powers of each time period in the adjacent interval dominated by the optimal discharge time period.

[0219] Step 3-5: Mark the time period whose electricity price is closest to the best charging time period in the adjacent interval dominated by the best charging time period found in step 3-4 and whose charging and discharging status is not marked as "chargeable", and jump to step 3-3.

[0220] Step 3-6: Mark the time period whose electricity price is closest to the best discharge time period in the adjacent interval dominated by the best discharge time period found in step 3-4 and whose charge and discharge status is not marked as "dischargeable", and jump to step 3-3.

[0221] Step 4: Convert the optimization model in step 1 into a linear programming model according to the charge and discharge state of the energy storage system determined in step 3: convert the nonlinear related terms in the objective function into linear related terms, narrow the constraint range of the charge and discharge power of the energy storage system in the corresponding period in the constraint conditions, and convert the conditional constraints in the constraint conditions into fixed constraints.

[0222] Specifically:

[0223] (1) For the nonlinear expression in the objective function If time period i is a charging period, If time period i is a dischargeable time period, If time period i is a period of neither charging nor discharging,

[0224] (2) For the nonlinear expression in the objective function If time period i is a dischargeable time period or a non-charge-neither-discharge time period, the function value is 1; if time period i is a chargeable time period, the function value is 0.

[0225] (3) For charging and discharging power constraints: If time period i is a rechargeable time period, the constraint is changed to If time period i is a dischargeable time period, the constraint is changed to If time period i is a non-charging and non-discharging period, the constraint is changed to

[0226] (4) For the charge continuity constraint, if time period i is a chargeable time period, the constraint is directly set as If time period i is a dischargeable time period, the constraint is directly set as If time period i is a non-charging and non-discharging period, the constraint is directly set as

[0227] By concretizing the nonlinear expressions in the objective function and constraints caused by different charging and discharging states into linear expressions, the combinatorial optimization problem is ultimately simplified to a linear optimization problem.

[0228] Step 5: Solve the linear programming model given in step 4 to obtain the operation strategy that maximizes the operation efficiency of the energy storage system.

[0229] Preferably, the simplex method is used to solve the linear programming model.

[0230] Furthermore, if the electricity price curve or the load curve changes, steps 2 to 5 are executed once when the operation strategy is generated; if neither the electricity price curve nor the load curve changes, step 5 is directly executed when the operation strategy is generated.

[0231] Since this method greatly improves the calculation speed of the optimization process by simplifying an NP-hard combinatorial optimization problem into a linear optimization problem, this method can be easily run on an embedded industrial computer with limited resources configured on-site in the energy storage system.

[0232] The following takes the lithium iron phosphate energy storage system configured in a cement plant in Guangdong Province as an example to briefly describe how to use the method of the present invention to provide the optimal charging and discharging operation strategy of the energy storage system under a specific electricity price curve. The purpose of this embodiment is to better understand and illustrate the method of the present invention. For simplicity, the transformation and distribution system of the cement plant is purposefully simplified. For the convenience of description and graphical display, the commonly used 96-period load curve and charge-discharge curve are simplified to 24-period curves.

[0233] The power logic diagram of a cement plant equipped with an energy storage system is as follows: Figure 1 As shown, the limit of power exchange between the cement plant and the external public power grid is limited by the rated capacity of the main transformer, which is 25MW.

[0234] The time-of-use electricity price for 110kV line power supply in Guangdong Province's two-part electricity price is shown in Table 1.

[0235] Table 1: Time-of-use electricity price list for power supply of 110kV lines.

[0236]

[0237] The local cement plant provides a subsidy of 0.2 yuan per kilowatt-hour for user-side energy storage based on the discharge volume.

[0238] The design parameters of the cement plant energy storage system are as follows: maximum charge and discharge power 5MW; maximum charge capacity 10MWh; allowable charge and discharge range 5%-95%; energy storage system charging efficiency and discharge efficiency are both 92%; energy storage battery unit charge and discharge life depreciation cost 0.4 yuan / kWh.

[0239] The cement plant's net load curve for a certain day is as follows Figure 6 shown.

[0240] To simplify the calculation process, the selected net load curve has a load greater than 5MW and less than 20MW in each period. Under such a net load curve, the energy storage system is allowed to operate at the maximum charging and discharging power at any time. Assuming that the initial SOC of the energy storage system at the beginning of the day is 5%, and the SOC of the energy storage system is required to be 5% at the end of the day, the process of using this method to calculate the energy storage charging and discharging strategy that maximizes the benefits of the energy storage system on that day is as follows:

[0241] Step 1: Establish a user energy storage system operation optimization model.

[0242] The objective function is:

[0243]

[0244] Because of different charging and discharging states, the calculation method of the summation term is different. Each period has two possibilities: charging and discharging. The above objective function has 2 9 = 512 possible combinations.

[0245] The constraints include:

[0246] (1) Charge and discharge power constraints:

[0247] (2) The charge constraint is:

[0248] (3) The charge continuity constraint is a conditional constraint:

[0249] While charging:

[0250] When discharging:

[0251] When not charging or discharging:

[0252] (4) Charge constraints at start and end times:

[0253] (5) Constraints on the total electric power exchanged between the user's AC bus and the external public power grid:

[0254] according to Figure 6 The net load curve shown in Figure 2 shows that the interactive power constraint between the external public grid and the energy storage system will not affect the charging and discharging power of the energy storage system. Figure 6 Under the net load curve shown, the energy storage system can charge and discharge at maximum power in each time period.

[0255] Obviously, in the above optimization model, the charge continuity constraints of the objective function and the constraint function both depend on the charging and discharging state. Different charging and discharging states have different expression forms. Such optimization problems are combinatorial optimization problems, which are difficult to solve.

[0256] Step 2: Determine the optimal charging time and the optimal discharging time according to the electricity price curve.

[0257] The best charging times include: 0:00-8:00; 12:00-14:00; 19:00-24:00;

[0258] The best discharge times include: 11-12 o'clock; 15-17 o'clock.

[0259] Step 3: Determine the charging and discharging status of the energy storage system in each time period.

[0260] The charging time periods include: 0:00-10:00; 12:00-14:00; 19:00-24:00;

[0261] The available discharge periods include: 10-12 o'clock; 14-19 o'clock.

[0262] Step 4: Convert the optimization model in step 1 into a linear programming model according to the charge and discharge state of the energy storage system determined in step 3.

[0263] The rewritten objective function is:

[0264]

[0265]

[0266] Charge and discharge power constraints: For the charging periods from 0:00 to 10:00, 12:00 to 14:00, and 19:00 to 24:00, the power constraint expression is: For the dischargeable periods from 10:00 to 12:00 and from 14:00 to 19:00, the power constraint expression is:

[0267] The charge continuity constraint is a conditional constraint: select the corresponding constraint formula for different time periods.

[0268] Because the charging and discharging status of each time period has been determined, the charge of the energy storage system at each moment in the charge continuity constraint can be refined as follows:

[0269] The initial time is 0:

[0270] Period 1, 0:00-1:00, charging:

[0271] Period 2, 1:00-2:00, charging:

[0272] Period 3, 2:00-3:00, charging:

[0273] Period 4, 3:00-4:00, charging:

[0274] Period 5, 4:00-5:00, charging:

[0275] Time period 6, 5:00-6:00, charging:

[0276] Time slot 7, 6:00-7:00, charging:

[0277] Time slot 8, 7:00-8:00, charging:

[0278] Time slot 9, 8:00-9:00, charging:

[0279] Time slot 10, 9:00-10:00, charging:

[0280] Period 11, 10:00-11:00, discharge:

[0281] Period 12, 11:00-12:00, discharge:

[0282] Time slot 13, 12:00-1:00, charging:

[0283] Period 14, 13:00-14:00, Charging:

[0284] Period 15, 14:00-15:00, discharge:

[0285] Period 16, 15:00-16:00, discharge:

[0286] Period 17, 16:00-17:00, discharge:

[0287] Period 18, 17:00-18:00, discharge:

[0288] Period 19, 18:00-19:00, discharge:

[0289] Period 20, 19:00-20:00, Charging:

[0290] Period 21, 19:00-20:00, Charging:

[0291] Period 22, 19:00-20:00, Charging:

[0292] Period 23, 19:00-20:00, Charging:

[0293] Period 24, 19:00-20:00, Charging:

[0294] Other constraints remain unchanged.

[0295] Step 5: Solve the linear programming model given in step 4 to obtain the operation strategy that maximizes the operation efficiency of the energy storage system.

[0296] Linear programming problems can be solved quickly and easily using the classic simplex method. For this example, it only takes 0.047 seconds to find the optimal solution using the simplex method using EXCEL software on an ordinary desktop computer. The final operating strategy is:

[0297] From 0:00 to 8:00, the energy storage system is charged with an average power of 1.22MW. The charging process uses 9.78MWh of electricity, and the energy storage system is charged to 9.5MWh. The total charging and discharging income of the system during this period is (-4500) yuan.

[0298] 8:00-10:00, no charging and no discharging;

[0299] From 10:00 to 11:00, the energy storage system discharged at an average power of 3.28MW, discharged 3.28MWh of electricity, and the energy storage system charge was 5.93MWh; the total charging and discharging income of the system during this period was 4,231 yuan;

[0300] From 11:00 to 12:00, the energy storage system discharges at a power of 5MW, discharging 5MW of electricity, and the energy storage system charge is 0.5MWh; the total charging and discharging income of the system during this period is 7,800 yuan;

[0301] From 12:00 to 14:00, the energy storage system was charged at an average power of 4.89MW, using 9.78MWh of electricity, and the energy storage system was charged to a total capacity of 9.5MWh. The total revenue from charging and discharging of the system during this period was (-6359) yuan.

[0302] 14:00-15:00, no charging and no discharging;

[0303] From 15:00 to 17:00, the energy storage system discharged at an average power of 8.28MW, discharged 8.28MWh of electricity, and the energy storage system charge was 0.5MWh; the total charging and discharging income of the system during this period was 12,917 yuan;

[0304] 17:00-24:00, no charging or discharging.

[0305] Within 24 hours, through two charges and two discharges, the total charging and discharging income of the energy storage system was 14,089 yuan.

[0306] It should be noted that it is obvious to those skilled in the art that the present invention is not limited to the details of the above exemplary embodiments, and that the present invention can be implemented in other specific forms without departing from the spirit or essential features of the present invention. The scope of the present invention is defined by the claims rather than the above description.

Claims

1. A method for optimizing energy storage operation strategy taking into account charging and discharging losses and real-time electricity prices, characterized in that the steps include: Step 1: Establishing a user energy storage system operation optimization model, wherein the optimization model includes an objective function and constraint conditions, and the decision variable of the model is the charge and discharge power of the energy storage system in each period; The objective function is to maximize the total net income of charging and discharging of the energy storage system. The total net income of charging and discharging is the sum of the charging and discharging income and the discharge subsidy of the energy storage system during the operation period minus the charging and discharging impairment expenses, wherein the charging and discharging income is a linear correlation term, and the discharge subsidy and the charging and discharging impairment expenses are nonlinear correlation terms. The linear correlation term refers to a calculation expression that has a linear calculation relationship with the charging and discharging power of the energy storage system, and the nonlinear correlation term refers to a calculation expression that has a nonlinear calculation relationship with the charging and discharging power of the energy storage system; The charge continuity constraint in the constraint condition is a conditional constraint on the charging and discharging state of the energy storage system; Step 2: Determine the best charging time period and the best discharging time period according to the electricity price curve; the best charging time period and the best discharging time period refer to the time periods that meet the following conditions: a) The electricity price during the best discharge period is higher than the electricity prices during the adjacent periods on both sides; b) The electricity price during the best charging period is lower than the electricity price during the adjacent periods on both sides; c) In the electricity price curve, there is at least one optimal charging period between two optimal discharging periods; d) In the electricity price curve, there is at least one optimal discharging period between two optimal charging periods; e) The price difference between any adjacent pair of optimal discharging time periods and optimal charging time periods is greater than the comprehensive unit charging and discharging loss cost of the energy storage system; Step 3: According to the optimal charging time period and the optimal discharging time period obtained in step 2, combined with the load curve, the charging and discharging state of the energy storage system in each time period is determined, and the charging and discharging state is divided into: chargeable, dischargeable, and neither charge nor discharge, so that each working time period of the energy storage system is marked as: chargeable time period, dischargeable time period, or neither charge nor discharge time period; Step 4: Convert the optimization model in step 1 into a linear programming model according to the charge and discharge state of the energy storage system determined in step 3: convert the nonlinear related terms in the objective function into linear related terms, narrow the constraint range of the charge and discharge power of the energy storage system in the corresponding period in the constraint conditions, and convert the conditional constraints in the constraint conditions into fixed constraints; Step 5: Solve the linear programming model given in step 4 to obtain the operation strategy that maximizes the operation efficiency of the energy storage system.

2. The energy storage operation strategy optimization method taking into account charging and discharging losses and real-time electricity prices as claimed in claim 1 is characterized in that: The objective function constructed in step 1 is: Among them, V total Total net revenue from charging and discharging the energy storage system; is the profit obtained by the energy storage system from charging and discharging in time period i, where charging is positive profit and discharging is negative profit; The cost of energy storage life loss caused by the energy storage system performing charging and discharging operations in time period i; It represents the discharge subsidy income obtained by the energy storage system during discharge in time period i; N is the total number of time periods in the optimization period.

3. The energy storage operation strategy optimization method taking into account charging and discharging losses and real-time electricity prices as claimed in claim 1 is characterized in that: In the objective function The calculation method is: In the formula, is the charging and discharging power of the energy storage system in time period i, which is positive during charging and negative during discharging, ρ i is the electricity price in period i, Δt is the length of a period; In the objective function The calculation method is: In the formula, C bat_e The cost of depreciation of the unit charging and discharging battery life of the energy storage system; In the objective function The calculation method is: Where ε(x) represents the unit step function. When x is greater than or equal to 0, the function value is 1, otherwise it is 0. sub The subsidy price per unit discharge amount.

4. The energy storage operation strategy optimization method taking into account charging and discharging losses and real-time electricity prices as claimed in claim 3 is characterized in that: The calculation method of unit charge and discharge battery life loss cost is: Among them C bat is the initial purchase cost of the energy storage system battery, r is the capital discount rate, n is the life of the battery in years under the design conditions of the energy storage system, Γ d The total throughput under the design conditions for the energy storage system; The total throughput under the design condition of the energy storage system is calculated as: Γ d =N d *D d *E batR , N d is the number of cycles under the designed operating conditions of the energy storage system, D d is the designed charge and discharge depth of the energy storage system, E batR is the rated energy of the energy storage system battery.

5. The energy storage operation strategy optimization method taking into account charging and discharging losses and real-time electricity prices as claimed in claim 3 is characterized in that: The constraints of the optimization model include: charging and discharging power constraints, charge constraints, charge continuity constraints, start and end time charge constraints, and total power constraints exchanged between the user's AC bus and the external public power grid; (1) The charge and discharge power constraints are: is the charging and discharging power of the energy storage system in time period i, P batR is the rated charging and discharging power of the energy storage system; (2) The charge constraint is: is the charge of the energy storage system in time period i, E batR is the rated energy of the energy storage system, SOC MIN and SOC MAX are the minimum allowable state of charge and the maximum allowable state of charge of the energy storage system respectively; (3) The charge continuity constraint is a conditional constraint, including the following three cases: While charging: When discharging: When not charging or discharging: In the formula, Δt is the duration of a period, η C is the charging efficiency of the energy storage system, η D is the discharge efficiency of the energy storage system; (4) The load constraints at the start and end times are: the energy storage system load at the start time and the charge of the energy storage system at the end time They are equal to their respective preset values, and N is the total number of time periods in the optimization period; (5) The total power exchanged between the user AC bus and the external public power grid is constrained to: P gateM The maximum limit of the electric power exchanged between the user's AC bus and the external public power grid. It is the average value of the load electric power in time period i in the load curve.

6. The energy storage operation strategy optimization method taking into account charging and discharging losses and real-time electricity prices as claimed in claim 1, characterized in that: The calculation method of the comprehensive loss cost per unit charge and discharge of the energy storage system is as follows: in, Indicates that the energy storage system is under the condition that the electricity price is ρ i At time i, 1 kWh of electricity is charged and the electricity price is ρ j The total cost caused by releasing 1 kWh of electricity in time period j; σ C is the charging loss coefficient, and σ C =1-η C , η C is the charging efficiency of the energy storage system; D is the discharge loss coefficient, and σ D =1-η D , η D is the discharge efficiency of the energy storage system; C bat_e It is the cost of battery life loss per unit of charging and discharging in the energy storage system.

7. The method for optimizing energy storage operation strategy taking into account charging and discharging losses and real-time electricity prices according to claim 1, characterized in that: The specific process of determining the optimal charging period and the optimal discharging period is as follows: Step 2-1, traverse the electricity price curve to find all extremely low electricity price periods, extremely high electricity price periods, minimum electricity price periods and maximum electricity price periods; the extremely low electricity price period refers to the period whose electricity price is lower than the electricity prices of the adjacent periods on both sides, the extremely high electricity price period refers to the period whose electricity price is higher than the electricity prices of the adjacent periods on both sides, the lowest electricity price period refers to the period with the lowest electricity price in the electricity price curve, and the highest electricity price period refers to the period with the lowest electricity price in the electricity price curve; Step 2-2: If the price difference between the highest and lowest electricity prices is greater than the comprehensive loss cost per unit of charging and discharging of the energy storage system, then continue to step 2-3; otherwise, the system is marked as having no charging and discharging arbitrage opportunities, and the search for the best discharging period and the best charging period ends; Step 2-3, find a period with the lowest electricity price, mark it as an excellent charging period, and set it as a base electricity price period; Step 2-4, determine whether there is an extremely high electricity price period or an extremely low electricity price period after the base electricity price period, if so, execute step 2-5, otherwise jump to step 2-18; Step 2-5, from the extremely high electricity price period and the extremely low electricity price period after the benchmark electricity price period, select the period that is closest to the benchmark electricity price period in time and has not been processed as the period to be determined; Step 2-6: If the time period to be determined is a period of extremely high electricity prices, execute step 2-7; otherwise, jump to step 2-12; Step 2-7: If the base electricity price period is an excellent discharge period, execute step 2-8; otherwise, jump to step 2-10; Step 2-8: If the price of the time period to be determined is greater than the price of the base electricity price time period, execute step 2-9; otherwise, jump to step 2-17; Step 2-9, cancel the optimal discharge period mark of the current benchmark electricity price period; Mark the period to be determined as an excellent discharge period; set the period to be determined as a base electricity price period; Jump to step 2-17; Step 2-10: If the price difference between the time period to be determined and the benchmark electricity price time period is greater than the unit charge and discharge comprehensive loss cost, execute step 2-11; otherwise, jump to step 2-17; Step 2-11, marking the period to be determined as an excellent discharge period; setting the period to be determined as a base electricity price period; Jump to step 2-17; Step 2-12: If the base electricity price period is an excellent charging period, execute step 2-13; otherwise, jump to step 2-15; Step 2-13: If the price of the time period to be determined is less than the price of the benchmark electricity price time period, execute step 2-14; otherwise, jump to step 2-17; Step 2-14, cancel the optimal charging period mark of the current base electricity price period; mark the period to be determined as the optimal charging period; The period to be determined is set as the base electricity price period; Jump to step 2-17; Step 2-15: If the price difference between the time period to be determined and the benchmark electricity price time period is greater than the unit charge and discharge comprehensive loss cost, execute step 2-16; otherwise, jump to step 2-17; Step 2-16, marking the time period to be determined as an excellent charging time period; The period to be determined is set as the base electricity price period; Step 2-17: If there are any electricity price periods that have not been determined and processed in the extremely high electricity price period and the extremely low electricity price period after the base electricity price period, execute step 2-5; otherwise, execute step 2-18; Step 2-18: If there are undetermined electricity price periods in the extremely high electricity price period and the extremely low electricity price period before the base electricity price period, then execute step 2-19; ​​otherwise, the search for the optimal discharge period and the optimal charge period ends; Step 2-19, from the extremely high electricity price period and the extremely low electricity price period before the benchmark electricity price period, select the electricity price period that is closest to the benchmark electricity price period and has not been determined as the period to be determined; Step 2-20: If the time period to be determined is a period of extremely high electricity prices, execute step 2-21; otherwise, jump to step 2-26; Step 2-21, if the base electricity price period is an excellent discharge period, execute step 2-22, otherwise jump to step 2-24; Step 2-22: If the price of the time period to be determined is greater than the price of the base electricity price time period, execute step 2-23; otherwise, jump to step 2-18; Step 2-23, cancel the optimal discharge period mark of the current benchmark electricity price period; Mark the period to be determined as an excellent discharge period; The period to be determined is set as the base electricity price period; Jump to step 2-18; Step 2-24: If the price difference between the time period to be determined and the benchmark electricity price time period is greater than the unit charge and discharge comprehensive loss cost, execute step 2-25; otherwise, jump to step 2-18; Step 2-25, marking the time period to be determined as an excellent discharge time period; The period to be determined is set as the base electricity price period; Jump to step 2-18; Step 2-26: If the base electricity price period is an excellent charging period, execute step 2-27; otherwise, jump to step 2-29; Step 2-27, if the price of the time period to be determined is less than the price of the benchmark electricity price time period, execute step 2-28, otherwise jump to step 2-18; Step 2-28, cancel the optimal charging period mark for the current base electricity price period; Mark the period to be determined as an excellent charging period; The period to be determined is set as the base electricity price period; Jump to step 2-18; Step 2-29, if the price difference between the price of the time period to be determined and the price difference between the time period of the benchmark electricity price is greater than the unit charge and discharge comprehensive loss cost, then execute step 2-30, otherwise jump to step 2-18; Step 2-30, marking the time period to be determined as an excellent charging time period; The period to be determined is set as the base electricity price period; Skip to step 2-18.

8. The method for optimizing energy storage operation strategy taking into account charging and discharging losses and real-time electricity prices as claimed in claim 7, characterized in that: The specific process of step 3 is: If the system is marked as having no charge-discharge arbitrage opportunity in the previous step 2, the charge-discharge status is determined in the following manner: if the energy storage system charge at the set end time is greater than the energy storage system charge at the start time, all time periods are marked as "chargeable"; if the energy storage system charge at the set end time is less than the energy storage system charge at the start time, all time periods are marked as "dischargeable"; in other cases, all time periods are marked as "neither charge nor discharge"; otherwise, the charge-discharge status is determined according to the following steps: Step 3-1: In each adjacent interval dominated by an optimal charging period, mark the status of the period that meets all the following conditions as "chargeable": a. The electricity price during this period is less than the electricity price during the best charging period in this adjacent interval plus the comprehensive loss cost per unit charge and discharge of the energy storage system; b. The electricity price during this period is less than the electricity price during the best forward discharge period in this adjacent interval minus the comprehensive unit charge and discharge loss cost of the energy storage system; c. The electricity price during this period is less than the electricity price during the optimal backward discharge period in the adjacent interval minus the comprehensive unit charge and discharge loss cost of the energy storage system; The adjacent interval dominated by the optimal charging period means that if a certain optimal charging period has two adjacent optimal discharging periods, then all periods between the two optimal discharging periods constitute the adjacent interval dominated by the optimal charging period; If a certain optimal charging period has only one adjacent optimal discharging period, then all periods between the optimal charging period and the optimal discharging period constitute the adjacent interval dominated by the optimal charging period; Step 3-2: In each adjacent interval dominated by an excellent discharge period, mark the status of the period that meets all the following conditions as "dischargeable": a. The electricity price during this period is greater than the electricity price during the best discharge period in this adjacent interval minus the comprehensive loss cost of unit charging and discharging of the energy storage system; b. The electricity price during this period is greater than the electricity price during the optimal forward charging period in this adjacent interval plus the comprehensive unit charging and discharging loss cost of the energy storage system; c. The electricity price during this period is greater than the electricity price during the optimal backward charging period in this adjacent interval plus the comprehensive unit charging and discharging loss cost of the energy storage system; The adjacent interval dominated by the optimal discharge period: if a certain optimal discharge period has two adjacent optimal charging periods, then all periods between the two optimal charging periods constitute the adjacent interval dominated by the optimal discharge period; If a certain optimal discharge period has only one adjacent optimal charging period, then all periods between the optimal discharge period and the optimal charging period constitute the adjacent interval dominated by the optimal discharge period; Step 3-3: If there is an adjacent interval dominated by an optimal charging period that satisfies the following condition 1, or if there is an adjacent interval dominated by an optimal discharging period that satisfies the following condition 2, then execute step 3-4; otherwise, all remaining periods not marked with charge and discharge status are marked as neither charge nor discharge, and the charge and discharge status marking process ends: Condition 1: There are periods of unmarked charging and discharging status in the adjacent interval dominated by the optimal charging period, and the price difference between the electricity price of at least one period of unmarked charging and discharging status and the price of the optimal discharging period in the adjacent interval is greater than the unit charging and discharging comprehensive loss cost, and the price difference between the electricity price of this period and the price of the optimal discharging period in the adjacent interval is greater than the unit charging and discharging comprehensive loss cost; Condition 2: There are periods of unmarked charge and discharge status in the adjacent interval dominated by the optimal discharge period, and the price difference between the electricity price of at least one period of unmarked charge and discharge status and the price of the optimal charging period in the adjacent interval is greater than the unit charge and discharge comprehensive loss cost, and the price difference between the electricity price of this period and the optimal charging period in the adjacent interval is greater than the unit charge and discharge comprehensive loss cost; Step 3-4, calculate the charging capacity of all adjacent intervals dominated by each optimal charging period that meets condition 1 in step 3-3, and the discharging capacity of all adjacent intervals dominated by each optimal discharging period that meets condition 2 in step 3-3, and find the minimum capacity value among all charging capacities and discharging capacities. If the minimum capacity value corresponds to the adjacent interval dominated by the optimal charging period, execute step 3-5; if the minimum capacity value corresponds to the adjacent interval dominated by the optimal discharging period, execute step 3-6; Step 3-5, mark the time period whose electricity price is closest to the best charging time period in the adjacent interval dominated by the best charging time period found in step 3-4 and is not marked with a charging or discharging state as "chargeable", and jump to step 3-3; Step 3-6, mark the time period whose electricity price is closest to the excellent discharge time period in the adjacent interval dominated by the excellent discharge time period found in step 3-4 and is not marked with a charge or discharge state as "dischargeable", and jump to step 3-3.

9. The energy storage operation strategy optimization method taking into account charging and discharging losses and real-time electricity prices as claimed in claim 8, characterized in that: For an adjacent interval dominated by an optimal charging period, its charging capacity Q CA The calculation method is: in, is the maximum allowed charging power for time period i, It refers to the sum of the maximum allowable charging power of each period in the adjacent interval dominated by the best charging period, Δt is the length of a period, P batR is the rated charge and discharge power of the energy storage system, is the average value of load power in period i in the load curve, P gateM The maximum limit of electric power exchanged between the user's AC bus and the external public power grid; For an adjacent interval dominated by an excellent discharge period, its discharge capacity Q DA The calculation method is: in, is the maximum allowable discharge power in time period i, It refers to the sum of the maximum allowable discharge powers of each time period in the adjacent interval dominated by the optimal discharge time period.

10. The energy storage operation strategy optimization method taking into account charging and discharging losses and real-time electricity prices as claimed in claim 5, characterized in that: The conversion process in step 4 includes: (1) For the nonlinear expression in the objective function If time period i is a charging period, If time period i is a dischargeable time period, If time period i is a period of neither charging nor discharging, (2) For the nonlinear expression in the objective function If time period i is a dischargeable time period or a non-charge-neither-discharge time period, the function value is 1; if time period i is a chargeable time period, the function value is 0; (3) For charging and discharging power constraints: If time period i is a rechargeable time period, the constraint is changed to If time period i is a dischargeable time period, the constraint is changed to If time period i is a non-charging and non-discharging period, the constraint is changed to (4) For the charge continuity constraint, if time period i is a chargeable time period, the constraint is directly set as If time period i is a dischargeable time period, the constraint is directly set as If time period i is a non-charging and non-discharging period, the constraint is directly set as

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