Energy storage operation strategy optimization method considering charging and discharging losses and real-time electricity prices

Abstract

The present invention discloses a method for optimizing energy storage operation strategies that takes into account charging and discharging losses and real-time electricity prices. The method comprises the following steps: establishing an optimization model for user energy storage system operations; determining optimal charging and discharging periods based on electricity price curves; determining the charge and discharge states of the energy storage system during each period based on the optimal charging and discharging periods; converting the optimization model into a linear programming model based on the energy storage system charge and discharge states; and finally solving for an operation strategy that maximizes the operational efficiency of the energy storage system. The present invention converts the original model into a linear programming model, thereby simplifying an NP-hard combinatorial optimization problem into a linear optimization problem. This significantly improves the computational speed of the optimization process and can be conveniently run on resource-limited embedded industrial computers deployed on-site in energy storage systems.

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 social progress and improvements in people's living standards, electricity demand continues to grow, and the gap between peak and valley electricity demand is gradually widening. To encourage users to shift peak demand and fill valley demand, large industrial and commercial users in my country have generally implemented a two-part time-of-use electricity pricing policy. This widening gap between peak and valley electricity prices is particularly pronounced in economically developed provinces.

[0003] In recent years, falling lithium iron phosphate battery prices have led some commercial and industrial users to install and use lithium iron phosphate battery energy storage systems, seeking to profit from peak-valley arbitrage and reduced electricity demand. Although the cost of electrochemical energy storage is declining, the current mainstream lithium iron phosphate energy storage system remains expensive. Therefore, effective energy storage system planning and design, and particularly efficient utilization to minimize operating costs and maximize returns, remain pressing challenges.

[0004] The common operational control method used in current user-side energy storage systems is to set fixed charging and discharging periods. This statically specifies the charging and discharging status and power for specific periods within the energy storage EMS system. This statically configured operational strategy cannot adapt to dynamically changing electricity loads. When user load profiles change beyond the operational strategy's adaptability, or when time-of-use electricity prices fluctuate, a new operational strategy must be manually formulated.

[0005] To solve the above problems, those skilled in the art have proposed a solution that constructs 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 formulates an operating strategy based on the solution of the mathematical model. However, this type of solution still has the following defects: First, it does not fully consider the battery life loss caused by the charging and discharging process of the energy storage system and the resulting costs. Secondly, the constructed mathematical model is essentially a combinatorial optimization problem. If heuristic algorithms such as particle swarm optimization and annealing algorithms, or traditional search algorithms such as cutting plane method and branch and bound method are used for this type of optimization problem, 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 optimality. Summary of the Invention

[0006] This paper proposes an energy storage operation strategy optimization method that takes into account charging and discharging losses and real-time electricity prices. Its objectives are: 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 solutions of the present invention are as follows:

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

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

[0010] The objective function is to maximize the total net income from charging and discharging of the energy storage system. The total net income from charging and discharging is the sum of the charging and discharging income and the discharge subsidy during the operation period of the energy storage system, minus the charging and discharging depreciation costs. The charging and discharging income is a linearly related term, while the discharge subsidy and the charging and discharging depreciation costs are nonlinearly 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 nonlinearly related 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 conditions is a conditional constraint on the charging and discharging state of the energy storage system;

[0012] Step 2: Determine the optimal charging time period and the optimal discharging time period based on the electricity price curve; the optimal charging time period and the optimal discharging time period are time periods that meet the following conditions:

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

[0014] b) The electricity price during the optimal 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 and charging periods is greater than the comprehensive unit charge and discharge loss cost of the energy storage system;

[0018] Step 3: Based on the optimal charging time period and the optimal discharging time period obtained in step 2 and in combination with the load curve, the charge and discharge state of the energy storage system in each time period is determined. The charge and discharge state is divided into: chargeable, dischargeable, and neither charge nor discharge. Thus, each working period of the energy storage system is marked as: chargeable period, dischargeable period, or neither charge nor discharge period.

[0019] Step 4: Convert the optimization model in step 1 into a linear programming model based on the charge and discharge status of the energy storage system determined in step 3. Convert the nonlinear correlation terms in the objective function into linear correlation terms, narrow the constraint range of the charge and discharge power of the energy storage system in the corresponding time 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 operating efficiency of the energy storage system.

[0021] As a further improvement to the energy storage operation strategy optimization method that takes 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 The 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's charging and discharging operations in time period i; 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] Where, 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] Where 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, which is 1 when x is greater than or equal to 0 and 0 otherwise. sub The subsidy price per unit discharge volume.

[0033] As a further improvement to the energy storage operation strategy optimization method that takes into account charge and discharge losses and real-time electricity prices, the unit charge and discharge battery life loss cost is calculated as follows: Among them C bat is the initial purchase cost of the energy storage system battery, r is the capital discount rate, n is the battery life in years under the design working conditions of the energy storage system, Γ d The total throughput under the designed operating conditions for the energy storage system;

[0034] The total throughput under the design conditions 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 to the energy storage operation strategy optimization method that takes 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 power 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 period i, P batR is the rated charge and discharge power of the energy storage system;

[0037] (2) The charge constraint is: is the charge of the energy storage system in 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 neither charging nor discharging:

[0042] Where 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 charge constraint at the start and end times is: the charge of the energy storage system at the start time and the charge of the energy storage system at the end time 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 as follows: P gateM The maximum limit of electric power exchanged between the user's AC bus and the external public power grid, is the average value of the load electric power in period i in the load curve.

[0045] As a further improvement to the energy storage operation strategy optimization method that takes into account charging and discharging losses and real-time electricity prices, the calculation method for 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 of electricity price ρ i At time i, 1 kWh of electricity is charged and the electricity price is ρ j The total cost of 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; σ 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 refers to the cost of battery life loss per unit charge and discharge of the energy storage system.

[0048] As a further improvement to the energy storage operation strategy optimization method that takes into account charging and discharging losses and real-time electricity prices, the specific process of determining the optimal charging period and the optimal 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, lowest electricity price periods, and highest electricity price periods; the extremely low electricity price period refers to the period where its 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 where its 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 energy storage system's unit charge and discharge comprehensive loss cost, proceed to step 2-3. Otherwise, the system is marked as having no charge and discharge arbitrage opportunities, and the search for optimal discharge and charge periods ends.

[0051] Step 2-3: Find a period with the lowest electricity price, mark it as the best charging period, and set it as the 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 an extremely high electricity price period, 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 benchmark electricity price period; mark the period to be determined as the optimal discharge period; set the period to be determined as the benchmark electricity price period; jump to step 2-17;

[0058] Step 2-10: If the price difference between the price of the time period to be determined and the price of the benchmark electricity price period is greater than the unit charge and discharge comprehensive loss cost, then 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 optimal 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 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 2-16; otherwise, jump to step 2-17;

[0064] Step 2-16: Mark the period to be determined as an excellent charging period; set the period to be determined as a base electricity price period;

[0065] Step 2-17: If there are any undetermined electricity price periods in the extremely high electricity price period and the extremely low electricity price period after the base electricity price period, then execute step 2-5; otherwise, execute step 2-18;

[0066] Step 2-18: If there are any undetermined periods of electricity prices 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 closest to the benchmark electricity price period and not yet processed as the period to be determined;

[0068] Step 2-20: If the time period to be determined is an extremely high electricity price period, 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 price of the time period to be determined and the price of the benchmark electricity price period is greater than the unit charge and discharge comprehensive loss cost, then 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 of the benchmark electricity price period 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 period to be determined as the optimal charging period; set the period to be determined as the base electricity price period; and jump to step 2-18.

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

[0080] If the system is marked as having no charge / discharge arbitrage opportunities in step 2, the charge / discharge status is determined as follows: 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 as follows:

[0081] Step 3-1: In each adjacent interval dominated by an optimal charging period, mark 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 optimal charging period in the adjacent interval plus the combined unit charge and discharge loss cost of the energy storage system;

[0083] b. The electricity price during this period is less than the electricity price during the optimal forward discharge period in the 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, then 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, then 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 an optimal discharge period, mark the period that meets all of the following conditions as "dischargeable":

[0087] a. The electricity price during this period is greater than the electricity price during the optimal discharge period in the adjacent interval, minus the comprehensive unit charge and discharge loss cost 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 the adjacent interval plus the combined unit charge and discharge losses 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 the adjacent interval plus the comprehensive unit charge and discharge loss cost of the energy storage system;

[0090] The adjacent interval dominated by the said optimal discharge period: if an optimal discharge period has two adjacent optimal charge periods, then all periods between the two optimal charge periods constitute the adjacent interval dominated by the optimal discharge period; if an optimal discharge period has only one adjacent optimal charge period, then all periods between the optimal discharge period and the optimal charge 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 charging nor discharging, and the charge and discharge status marking process ends:

[0092] Condition 1: There are periods of time without charging or discharging status in the adjacent interval dominated by the optimal charging period, and the price difference between at least one of the periods of time without charging or discharging status and the price of the optimal discharging period before the adjacent interval is greater than the unit charge and discharge comprehensive loss cost, and the price difference between the period of time and the price of the optimal discharging period after the adjacent interval is greater than the unit charge and discharge comprehensive loss cost;

[0093] Condition 2: There are periods of time in the adjacent interval dominated by the optimal discharge period that are not marked as charging or discharging, and the price difference between at least one of the periods of time 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 period of time and the price of 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 discharge capacity of all adjacent intervals dominated by each optimal discharge period that meets condition 2 in step 3-3, and find the minimum capacity value among all charging and discharging capacities. If the minimum capacity value corresponds to an adjacent interval dominated by the optimal charging period, execute step 3-5; if the minimum capacity value corresponds to an adjacent interval dominated by the optimal discharge period, execute step 3-6.

[0095] Step 3-5: Mark the period of time in the adjacent interval dominated by the optimal charging period found in step 3-4, which has the electricity price closest to the optimal charging period in the adjacent interval and is not marked as charging or discharging, as "chargeable", and jump to step 3-3;

[0096] Step 3-6: Mark the period of time in the adjacent interval dominated by the optimal discharge period found in step 3-4, which has the electricity price closest to the optimal discharge period in the adjacent interval and is not marked with a charge or discharge state, as "dischargeable", and jump to step 3-3.

[0097] As a further improvement to 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 period i, It refers to the sum of the maximum allowable charging power of each period in the adjacent interval dominated by the optimal 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 the 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 to the energy storage operation strategy optimization method taking into account charging and discharging losses and real-time electricity prices, 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 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 discharge period or a non-charge period, the function value is 1; if time period i is a charge period, the function value is 0;

[0107] (3) For charge and discharge power constraints: If period i is a rechargeable period, the constraint is changed to If period i is a dischargeable period, the constraint is changed to If period i is a period of neither charging nor discharging, the constraint is changed to

[0108] (4) For the charge continuity constraint, if period i is a chargeable period, the constraint is directly set as If period i is a dischargeable period, the constraint is directly set as If period i is a period of neither charging nor discharging, 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 status of the energy storage system at each time period. It then processes the constructed optimization model based on this charge and discharge status, converting it into a linear programming model. This simplifies an NP-hard combinatorial optimization problem into a linear optimization problem, significantly improving the computational speed of the optimization process and enabling the method to be easily run on resource-limited embedded industrial computers deployed on-site with energy storage systems. This method can be applied to both time-of-use and real-time electricity pricing scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0112] Figure 2 is the load curve diagram;

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

[0114] Figure 4 is the electricity price curve;

[0115] Figure 5 A schematic diagram illustrating the relationship between the optimal charging period, the optimal discharging period, and 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 will be described in detail below with reference to the accompanying drawings. Obviously, the embodiments described are only a part of the embodiments of the present invention, rather than all the embodiments.

[0118] For industrial and commercial users equipped with behind-the-meter energy storage systems, local electricity prices typically fluctuate significantly between peak and valley levels, allowing energy storage systems to profit primarily through peak-valley arbitrage. At the same time, the high electricity loads of these industrial and commercial users also provide opportunities for the deployment and absorption of distributed generation. Even some enterprises, such as cement plants, paper mills, and glass factories, may have waste heat power generation equipment installed. Distributed generation and waste heat power generation within these enterprises are typically connected to the grid but not directly connected 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 the total net load, energy storage system, and AC bus. The total net load and energy storage system are connected to the AC bus, which is connected to the external public power grid through a main transformer. The total net load represents the total load after adding all the user's electricity load and self-generated power, 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 expressed 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, the charging power P is used batC After charging the energy storage system for Δt time, the added energy of the energy storage system 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 change of time is generally divided into N time periods (typically N is 96), the initial time is recorded as time 0, the end time is time N, the time period between time i and time i+1 is called time period i+1, the length of each time period is recorded as Δt, and the P on time period i is neat The average value is expressed as Thus, N consecutive Constitute the load curve for this period.

[0122] Usually used as Figure 3 The charge and discharge curve shown here represents the charge and discharge power P over a period of time (typically one day or 24 hours). bat The change of can also be divided into N periods. The period between time i and time i+1 is called period i+1. The P on period i 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 strategies taking into account charging and discharging losses and real-time electricity prices, comprising the following steps:

[0126] Step 1: Establish an optimization model for the operation of the user energy storage system. The optimization model includes an objective function and constraints. 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 from charging and discharging of the energy storage system. The total net income from charging and discharging is the sum of the charging and discharging income and the discharge subsidy during the operation period of the energy storage system, minus the charging and discharging depreciation costs. The charging and discharging income is a linearly related term, and the discharge subsidy and the charging and discharging depreciation costs are nonlinearly 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 nonlinearly 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 The 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's charging and discharging operations in time period i; 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] Where, 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] Where C bat_e The unit charge and discharge battery life loss cost of the energy storage system is calculated as follows: Among them C bat is the initial purchase cost of the energy storage system battery, r is the capital discount rate, n is the battery life in years under the design working conditions of the energy storage system, Γ d The total throughput under the design conditions of the energy storage system.

[0137] Furthermore, the total throughput under the design conditions 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, which is 1 when x is greater than or equal to 0 and 0 otherwise. sub The subsidy price per unit discharge volume (depending on the local government’s energy storage preferential policies).

[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. Among them, 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 period i, P batR is the rated charge and discharge power of the energy storage system.

[0144] (2) The charge constraint is: is the charge of the energy storage system in 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 neither charging nor discharging:

[0149] Where 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 charge constraint at the start and end times is: the charge of the energy storage system at the start time and the charge of the energy storage system at the end time 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 as follows: P gateM The maximum limit of electric power exchanged between the user's AC bus and the external public power grid, is the average value of the load electric power in period i in the load curve.

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

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

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

[0155] b) The electricity price during the optimal 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 charge and discharge 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 highest electricity price period and the electricity price in the lowest electricity price period 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 highest electricity price period and the electricity price in the lowest electricity price period is greater than the comprehensive loss cost per unit charge and discharge of the energy storage system, the highest electricity price period must be the excellent discharging period, and the lowest electricity price period must be the excellent charging period.

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

[0161]

[0162] in, Indicates that the energy storage system is under the condition of electricity price ρ i At time i, 1 kWh of electricity is charged and the electricity price is ρ j The total cost of 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; σ 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 refers to the cost of battery life loss per unit charge and discharge of 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, lowest electricity price periods, and highest electricity price periods. The extremely low electricity price period refers to a period where the electricity price is lower than the prices of the adjacent periods on both sides. The extremely high electricity price period refers to a period where the electricity price is higher than the 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. 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 lowest electricity price period, and 11-12 o'clock and 15-17 o'clock are the highest electricity price periods.

[0166] Step 2-2: If the price difference between the highest and lowest electricity prices is greater than the comprehensive loss cost per unit charge and discharge of the energy storage system, then proceed to step 2-3. Otherwise, the system is marked as having no charge and discharge arbitrage opportunities, and the search for the optimal discharge period and the optimal charge period ends.

[0167] Step 2-3: Find a period with the lowest electricity price, mark it as the best charging period, and set it as the 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 benchmark electricity price period, select the period that is temporally closest to the benchmark electricity price period and has not been processed as the period to be determined.

[0170] Step 2-6: If the time period to be determined is an extremely high electricity price period, 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 benchmark electricity price is greater than the unit charge and discharge comprehensive loss cost, then execute step 2-11; otherwise, jump to step 2-17.

[0175] 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.

[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; and 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, then execute step 2-16; otherwise, jump to step 2-17.

[0180] Step 2-16: Mark the period to be determined as an excellent charging period; set the period to be determined as a base electricity price 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, then 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 closest to the benchmark electricity price period and which has not been processed as the period to be determined.

[0184] Step 2-20: If the time period to be determined is an extremely high electricity price period, 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 base 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 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 2-25; otherwise, jump to step 2-18.

[0189] 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; and 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 in the period to be determined is less than the price in the period of the benchmark electricity price, 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 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.

[0194] Step 2-30: Mark the period to be determined as the optimal charging period; set the period to be determined as the base electricity price period; and jump to step 2-18.

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

[0196] If the system is marked as having no charge / discharge arbitrage opportunities in step 2, the charge / discharge status is determined as follows: 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 as follows:

[0197] Step 3-1: In each adjacent interval dominated by an optimal charging period, mark 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 optimal charging period in the adjacent interval plus the combined unit charge and discharge loss cost of the energy storage system;

[0199] b. The electricity price during this period is less than the electricity price during the optimal forward discharge period in the 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 , periods A and L are optimal charging periods, and periods G and Q are optimal discharging periods. According to the above definition, in this charge-discharge curve, periods A, B, C, D, E, F, and G constitute the adjacent interval dominated by the optimal charging period A; periods G, H, I, J, K, L, M, N, O, P, and Q constitute the adjacent interval dominated by the optimal charging period L.

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

[0204] a. The electricity price during this period is greater than the electricity price during the optimal discharge period in the adjacent interval, minus the comprehensive unit charge and discharge loss cost 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 the adjacent interval plus the combined unit charge and discharge losses 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 discharge period: if an excellent discharge period has two adjacent excellent charging periods, then all periods between the two excellent charging periods constitute the adjacent interval dominated by the excellent discharge period; if an excellent discharge period has only one adjacent excellent charging period, then all periods between the excellent discharge period and this excellent charging period constitute the adjacent interval dominated by the excellent discharge 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; 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 charging nor discharging, and the charge and discharge status marking process ends:

[0210] Condition 1: There are periods of unmarked charging and discharging status in the adjacent interval dominated by the excellent charging period, and the difference between the electricity price of at least one period of unmarked charging and discharging status and the price of the excellent discharging period in the adjacent interval forward is greater than the unit charging and discharging comprehensive loss cost, and at the same time, the difference between the electricity price of this period and the price of the excellent discharging period in the adjacent interval backward is greater than the unit charging and discharging comprehensive loss cost.

[0211] Condition 2: There are periods of unmarked charging and discharging status in the adjacent interval dominated by the excellent discharge period, and the difference between the electricity price of at least one period of unmarked charging and discharging status and the price of the excellent charging period in the adjacent interval forward is greater than the unit charging and discharging comprehensive loss cost, and at the same time, the difference between the electricity price of this period and the price of the excellent charging period in the adjacent interval backward 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 period i, It refers to the sum of the maximum allowable charging power of each period in the adjacent interval dominated by the optimal 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 period of time in the adjacent interval dominated by the optimal charging period found in step 3-4, which has the electricity price closest to the optimal charging period in the adjacent interval and is not marked with a charging or discharging state, as "chargeable", and jump to step 3-3.

[0220] Step 3-6: Mark the period of time in the adjacent interval dominated by the optimal discharge period found in step 3-4, which has the electricity price closest to the optimal discharge period in the adjacent interval and is not marked with a charge or discharge state, as "dischargeable", and jump to step 3-3.

[0221] Step 4: Convert the optimization model in step 1 into a linear programming model based on the charge and discharge status of the energy storage system determined in step 3. Convert the nonlinear correlation terms in the objective function into linear correlation terms, narrow the constraint range of the charge and discharge power of the energy storage system in the corresponding time 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 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 charge and discharge power constraints: If period i is a rechargeable period, the constraint is changed to If period i is a dischargeable period, the constraint is changed to If period i is a period of neither charging nor discharging, the constraint is changed to

[0226] (4) For the charge continuity constraint, if period i is a chargeable period, the constraint is directly set as If period i is a dischargeable period, the constraint is directly set as If period i is a period of neither charging nor discharging, 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 operating 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 generating the operation strategy. If neither the electricity price curve nor the load curve changes, step 5 is directly executed when generating the operation strategy.

[0231] Since this method greatly improves the computational speed of the optimization process by simplifying an NP-hard combinatorial optimization problem into a linear optimization problem, it can be easily run on resource-limited embedded industrial computers configured on-site in energy storage systems.

[0232] The following example uses a lithium iron phosphate energy storage system deployed at a cement plant in Guangdong Province as an example to briefly describe how the method described in this invention can be used to provide the system with an optimal charging and discharging strategy under a specific electricity price curve. This example aims to facilitate understanding and illustration of the method described in this invention. For simplicity, the cement plant's power distribution system has been intentionally simplified. For ease of description and graphical presentation, the commonly used 96-period load and charge / discharge curves have been 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 in FIG, 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 system is shown in Table 1.

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

[0236]

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

[0238] The cement plant's energy storage system design parameters include: maximum charge and discharge power of 5MW; maximum charge capacity of 10MWh; an allowable charge and discharge range of 5%-95%; both the energy storage system's charge and discharge efficiency are 92%; and the energy storage battery's unit charge and discharge lifespan degradation cost is 0.4 yuan / kWh.

[0239] The cement plant's estimated 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 time period. Under this net load curve, the energy storage system is allowed to operate at maximum charge and discharge power at all times. 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% by the end of the day, the process of calculating the energy storage charge and discharge strategy that maximizes the energy storage system's profit within the day using this method 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 charge and discharge 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] 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 neither charging nor 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 period.

[0255] Obviously, in the above optimization model, the charge continuity constraints of the objective function and the constraint function both depend on the charge and discharge state. Different charge and discharge 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 based on 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 charge and discharge 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 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 of 0:00-10:00, 12:00-14:00, and 19:00-24:00, 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 charge and discharge 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 slot 6, 5:00-6:00, charging:

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

[0277] Time slot 8, 7am-8am, 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] Time slot 20, 19:00-20:00, charging:

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

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

[0292] Time slot 23, 19:00-20:00, charging:

[0293] Time 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 operating efficiency of the energy storage system.

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

[0297] From 0:00 to 8:00, the energy storage system was charged at an average power of 1.22MW, using 9.78MWh of electricity, bringing the total charge of the energy storage system to 9.5MWh. The total revenue from charging and discharging during this period was (-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, releasing 3.28MWh of electricity, and the total charge to the energy storage system was 5.93MWh. The total charging and discharging revenue of the system during this period was 4,231 yuan.

[0300] From 11:00 to 12:00, the energy storage system discharged at a power of 5MW, discharging 5MW of electricity, and the total charge of the energy storage system was 0.5MWh. The total charging and discharging revenue of the system during this period was 7,800 yuan.

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

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

[0303] From 3:00 PM to 5:00 PM, the energy storage system discharged at an average power of 8.28 MW, discharging 8.28 MWh of electricity, leaving a total charge of 0.5 MWh. The total revenue from charging and discharging 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 exemplary embodiments described above, and that the present invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the present invention. The scope of the present invention is defined by the claims rather than the foregoing description.

Claims

1. A method for optimizing energy storage operation strategy taking into account charge and discharge losses and real-time electricity prices, characterized in that the steps include: Step 1: Establishing an optimization model for the operation of a user energy storage system. The optimization model includes an objective function and constraints, and the decision variable of the model is the charge and discharge power of the energy storage system in each time period. The objective function is to maximize the total net income from charging and discharging of the energy storage system. The total net income from charging and discharging is the sum of the charging and discharging income and the discharge subsidy during the operation period of the energy storage system, minus the charging and discharging depreciation costs. The charging and discharging income is a linearly related term, while the discharge subsidy and the charging and discharging depreciation costs are nonlinearly 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 nonlinearly related 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 conditions is a conditional constraint on the charging and discharging state of the energy storage system; The objective function constructed in step 1 is: ； in, The total net revenue from charging and discharging the energy storage system; For energy storage system in period The benefits gained from charging and discharging are positive benefits from charging and negative benefits from discharging. For the energy storage system Costs of energy storage life reduction caused by charging and discharging operations; Indicates that the energy storage system is in the period Discharge subsidy income obtained from discharge; is the total number of time periods in the optimization period; In the objective function The calculation method is: ； Where, For the period The charging and discharging power of the energy storage system is positive when charging and negative when discharging. For the period The electricity price, The length of a period; In the objective function The calculation method is: ； Where, 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, represents the unit step function, when If the function value is greater than or equal to 0, it is 1, otherwise it is 0. Subsidy price per unit discharge capacity; 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 exchanged between the user's AC bus and the external public power grid. (1) The charge and discharge power constraints are: , For the period The charging and discharging power of the energy storage system, is the rated charge and discharge power of the energy storage system; (2) The charge constraint is: , For the period The energy storage system charge, is the rated energy of the energy storage system, and 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 neither charging nor discharging: ; Where, The duration of a period. For the energy storage system charging efficiency, is the discharge efficiency of the energy storage system; (4) The charge constraints at the start and end times are: the charge of the energy storage system at the start time and the charge of the energy storage system at the end time are equal to their respective preset values, is the total number of time periods in the optimization period; (5) The total power exchanged between the user's AC bus and the external public power grid is constrained as follows: , The maximum limit of electric power exchanged between the user's AC bus and the external public power grid, The middle period of the load curve The average value of the load electric power; Step 2: Determine the optimal charging time period and the optimal discharging time period based on the electricity price curve; the optimal charging time period and the optimal discharging time period are time periods that meet the following conditions: a) The electricity price during the optimal discharge period is higher than the electricity prices during the adjacent periods on both sides; b) The electricity price during the optimal 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 and charging periods is greater than the comprehensive unit charge and discharge loss cost of the energy storage system; Step 3: Based on the optimal charging period and the optimal discharging period obtained in step 2, combined with the load curve, determine the charge and discharge state of the energy storage system in each period, wherein the charge and discharge state is divided into: chargeable, dischargeable, and neither charge nor discharge, so that each working period of the energy storage system is marked as: chargeable period, dischargeable period, or neither charge nor discharge period; Step 4: Convert the optimization model in step 1 into a linear programming model based on the charge and discharge status of the energy storage system determined in step 3. Convert the nonlinear correlation terms in the objective function into linear correlation terms, narrow the constraint range of the charge and discharge power of the energy storage system in the corresponding time 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 operating 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 according to claim 1 is characterized in that: The calculation method of the unit charge and discharge battery life loss cost is: ,in is the initial purchase cost of the energy storage system battery, is the funding discount rate, The lifespan of the battery under the design conditions of the energy storage system. The total throughput under the designed operating conditions for the energy storage system; The total throughput under the design conditions of the energy storage system is calculated as follows: , The number of cycles under the designed operating conditions for the energy storage system, is the designed charge and discharge depth of the energy storage system, is the rated energy of the energy storage system battery.

3. The energy storage operation strategy optimization method taking into account charging and discharging losses and real-time electricity prices according to claim 1 is characterized in that: The calculation method for the comprehensive loss cost per unit charge and discharge of the energy storage system is: ； in, Indicates that the energy storage system is Time period Charge 1kWh of electricity and charge at Time period The total cost of discharging 1 kWh of electricity; is the charging loss coefficient, and , Charging efficiency for energy storage systems; is the discharge loss coefficient, and , is the discharge efficiency of the energy storage system; It refers to the cost of battery life loss per unit charge and discharge of the energy storage system.

4. The energy storage operation strategy optimization method taking into account charging and discharging losses and real-time electricity prices according to claim 1 is 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, lowest electricity price periods, and highest electricity price periods; the extremely low electricity price period refers to the period where its 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 where its 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 energy storage system's unit charge and discharge comprehensive loss cost, proceed to step 2-3. Otherwise, the system is marked as having no charge and discharge arbitrage opportunities, and the search for optimal discharge and charge periods ends. Step 2-3: Find a period with the lowest electricity price, mark it as the best charging period, and set it as the 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 an extremely high electricity price period, 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 for 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; Skip to step 2-17; Step 2-10: If the price difference between the price of the time period to be determined and the price of the benchmark electricity price period is greater than the unit charge and discharge comprehensive loss cost, then execute step 2-11; otherwise, jump to step 2-17; 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; Skip to step 2-17; Step 2-12: If the base electricity price period is an optimal 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 for 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; Skip to step 2-17; 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, then execute step 2-16; otherwise, jump to step 2-17; Step 2-16: Mark the period to be determined as an optimal charging period; Set the period to be determined as the base electricity price period; Step 2-17: If there are any undetermined electricity price periods in the extremely high electricity price period and the extremely low electricity price period after the base electricity price period, then execute step 2-5; otherwise, execute step 2-18; Step 2-18: If there are any undetermined periods of electricity prices 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 closest to the benchmark electricity price period and not yet processed as the period to be determined; Step 2-20: If the time period to be determined is an extremely high electricity price period, 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 for the current benchmark electricity price period; Mark the period to be determined as an excellent discharge period; Set the period to be determined as the base electricity price period; Skip to step 2-18; Step 2-24: If the price difference between the price of the time period to be determined and the price of the benchmark electricity price period is greater than the unit charge and discharge comprehensive loss cost, then execute step 2-25; otherwise, jump to step 2-18; Step 2-25, marking the period to be determined as an excellent discharge period; Set the period to be determined as the base electricity price period; Skip 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 the best charging period; Set the period to be determined as the base electricity price period; Skip to step 2-18; Step 2-29: If the price difference between the price of the time period to be determined and the price of the benchmark electricity price period 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 period to be determined as an excellent charging period; Set the period to be determined as the base electricity price period; Skip to step 2-18.

5. The energy storage operation strategy optimization method taking into account charging and discharging losses and real-time electricity prices according to claim 4 is characterized in that: The specific process of step 3 is: If the system is marked as having no charge / discharge arbitrage opportunities in step 2, the charge / discharge status is determined as follows: 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 as follows: Step 3-1: In each adjacent interval dominated by an optimal charging period, mark the period that meets all of the following conditions as "chargeable": a. The electricity price during this period is less than the electricity price during the optimal charging period in the adjacent interval plus the combined unit charge and discharge loss cost of the energy storage system; b. The electricity price during this period is less than the electricity price during the optimal forward discharge period in the 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 an 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 optimal discharge period, mark the period that meets all of the following conditions as "dischargeable": a. The electricity price during this period is greater than the electricity price during the optimal discharge period in the adjacent interval, minus the comprehensive unit charge and discharge loss cost 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 the adjacent interval plus the combined unit charge and discharge losses 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 the adjacent interval plus the comprehensive unit charge and discharge loss cost of the energy storage system; The adjacent interval dominated by the optimal discharging period: if an optimal discharging period has two adjacent optimal charging periods, then all periods between the two optimal charging periods constitute the adjacent interval dominated by the optimal discharging period; If an optimal discharge period has only one adjacent optimal charge period, then all periods between the optimal discharge period and the optimal charge 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 charging nor discharging, and the charge and discharge status marking process ends: Condition 1: There are periods of time without charging or discharging status in the adjacent interval dominated by the optimal charging period, and the price difference between at least one of the periods of time without charging or discharging status and the price of the optimal discharging period before the adjacent interval is greater than the unit charge and discharge comprehensive loss cost, and the price difference between the period of time and the price of the optimal discharging period after the adjacent interval is greater than the unit charge and discharge comprehensive loss cost; Condition 2: There are periods of time in the adjacent interval dominated by the optimal discharge period that are not marked as charging or discharging, and the price difference between at least one of the periods of time 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 period of time and the price of 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 discharge capacity of all adjacent intervals dominated by each optimal discharge period that meets condition 2 in step 3-3, and find the minimum capacity value among all charging and discharging capacities. If the minimum capacity value corresponds to an adjacent interval dominated by the optimal charging period, execute step 3-5; if the minimum capacity value corresponds to an adjacent interval dominated by the optimal discharge period, execute step 3-6. Step 3-5: Mark the period of time in the adjacent interval dominated by the optimal charging period found in step 3-4, which has the electricity price closest to the optimal charging period in the adjacent interval and is not marked as charging or discharging, as "chargeable" and jump to step 3-3; Step 3-6: Mark the period of time in the adjacent interval dominated by the optimal discharge period found in step 3-4, which has the electricity price closest to the optimal discharge period in the adjacent interval and is not marked as a charge or discharge state, as "dischargeable" and jump to step 3-3.

6. The energy storage operation strategy optimization method taking into account charging and discharging losses and real-time electricity prices according to claim 5 is characterized in that: For an adjacent interval dominated by an excellent charging period, its charging capacity The calculation method is: ； ； in, It is the time period The maximum allowed charging power, It refers to the sum of the maximum allowable charging power of each period in the adjacent interval dominated by the optimal charging period. is the length of a period, is the rated charge and discharge power of the energy storage system, The middle period of the load curve The average value of the load electric power, 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 The calculation method is: ； ； in, It is the time period The maximum allowable discharge power, 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.

7. The energy storage operation strategy optimization method taking into account charging and discharging losses and real-time electricity prices according to claim 1 is characterized in that: The conversion process in step 4 includes: (1) For the nonlinear expression in the objective function , if the period For the charging period, , if the period is the discharge period, , if the period For the period of no charging or discharging, ; (2) For the nonlinear expression in the objective function , if the period The function value is 1 if the period is a discharge period or a non-charge period. It is the charging period, and the function value is 0; (3) For charge and discharge power constraints: , if the period is a charging period, then the constraint is changed to , if the period is the dischargeable period, then the constraint is changed to , if the period For a period of no charge or discharge, the constraint is changed to ; (4) For the charge continuity constraint, if the period is a charging period, then the constraint is directly set as , if the period is the dischargeable period, then the constraint is directly set as , if the period For a period of no charge or discharge, the constraint is directly set as .

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