Centralized energy storage grouping coordination control method and system considering health degree of battery

Abstract

The invention discloses a centralized energy storage grouping coordination control method and a centralized energy storage grouping coordination control system considering the health degree of a battery, and belongs to a recycling technology under the condition of different battery life losses, and the method comprises the following steps of: dividing a centralized energy storage system consisting of batteries in different health states into two subsystems; the two subsystems are respectively used for undertaking a negative charging task and a discharging task, the two subsystems can be mutually converted, and when the adjusting power of one subsystem is insufficient, part or all of the battery packs of the other energy storage subsystem are selected to temporarily undertake corresponding adjusting tasks, so that the power adjusting requirement of energy storage is met. According to the invention, a centralized energy storage operation mode of different battery health states is constructed to break through an energy sharing barrier, so that output of a new energy station can be coordinated and net load fluctuation of a power grid can be stabilized; and secondly, a dynamic charging and discharging safety margin is set based on the health degree of the batteries, so that a grouping coordination control strategy considering different health states of the batteries is put forward, and the problem brought by inconsistency of the batteries to operation regulation and control is solved.

Description

Technical Field

[0001] The present invention relates to a large-scale centralized energy storage technology composed of batteries, and in particular to a centralized energy storage grouping coordination control method taking battery health into account. Background Art

[0002] Centralized energy storage utilizes the temporal and spatial complementary characteristics between different regulation needs, and uses time and space multiplexing to improve the utilization of energy storage itself. Taking the configuration of centralized energy storage in a cluster of new energy stations as the object, a scheduling strategy for energy storage to participate in primary and secondary frequency regulation auxiliary services is proposed. Taking grid-side energy storage as the research object, the transaction model and mechanism of energy storage participating in peak regulation and frequency regulation services are realized through blockchain technology. Taking user-side resource sharing as the object, two-layer management of user-side resources is realized based on the energy sharing cloud system. However, most of the above studies are based on the perspective of a single subject, namely power source, power grid, and user, and have not yet broken the energy sharing barriers between different participating subjects, making it difficult to adapt to the regulation needs of different application scenarios under the future evolution of the power grid form. Therefore, it is urgent to study the energy storage operation model that takes into account the interests of multiple parties. In addition, in order to promote the sustainable development of energy storage, its economic organization method also needs further research.

[0003] With the arrival of the retirement tide of new energy vehicles in my country, a large number of batteries have entered the recycling stage. The use of retired batteries to build energy storage has not only improved the economy of large-scale centralized energy storage, but also reduced the huge pressure of retired batteries on the social ecological environment, and to a certain extent promoted the development of the new energy vehicle industry. However, the inconsistency of the health status and charge status of retired power batteries leads to an obvious "short board effect" in the process of energy storage charging and discharging, which increases the frequency of system maintenance and operation and maintenance costs, and reduces the overall operating life and efficiency of the system. Therefore, it is urgent to study the reasonable differentiated power allocation strategy to control the charging and discharging of energy storage in response to the inconsistency of battery health status, so as to overcome the "short board effect" and improve the overall operating efficiency.

[0004] Existing technologies include: In order to solve the problems of low operating efficiency and difficult control of cascade utilization energy storage systems, a segmented control strategy based on the rain flow counting method is proposed. Taking the coordinated output of wind farms with retired power batteries as the application scenario, a coordinated control strategy for differentiated energy storage modes is proposed. In order to solve the problem of simultaneous retirement of batteries in cascade utilization energy storage systems with multi-branch topology, a control strategy of preferential output of some battery clusters and joint output of all battery clusters is proposed based on the imbalance of battery health status. For the application scenario of cascade utilization energy storage in photovoltaic storage charging stations, an energy optimization control strategy considering the battery health assessment model within the life cycle of cascade utilization is proposed. The above research results are mainly aimed at the cascade utilization of retired batteries in a single application scenario. At the same time, in the process of operation and regulation of retired power batteries, there is a lack of consideration of the dynamic changes in health.

[0005] Based on the above analysis, in order to improve the utilization of energy storage and solve the economic dilemma in the large-scale development of energy storage, the present invention proposes a centralized energy storage group coordination control strategy that takes into account the health of retired batteries. In order to cope with the adjustments to energy storage brought about by the evolution of future power grid forms, a new centralized energy storage operation mode is proposed, which can not only meet the requirements of assisting new energy sites to adjust their output plans, but also reduce the fluctuations caused by the net load of the power grid; in order to improve the economy of large-scale centralized energy storage, the dynamic safety margin of the battery is set on the basis of considering the dynamic evaluation of the battery health throughout the life cycle, and further proposes a battery energy storage group coordination control strategy for different health levels. Finally, an example analysis is carried out through the actual situation in a certain area in northwest my country, and the final results verify the practicability of the strategy, and at the same time verify that the strategy has more competitive advantages than existing strategies. Summary of the invention

[0006] Purpose of the invention: In view of the above-mentioned deficiencies in the prior art, the present invention provides a centralized energy storage group coordination control method and system taking into account battery health.

[0007] Technical solution: A centralized energy storage group coordination control method taking battery health into account. This method divides the centralized energy storage system composed of batteries in different health states into two subsystems, which are used to undertake negative charging tasks and discharging tasks respectively. The two subsystems can be converted into each other. When the regulation power of a subsystem is insufficient, part or all of the battery groups of another energy storage subsystem will be selected to temporarily undertake the corresponding regulation tasks to meet the power regulation needs of energy storage.

[0008] The method adopts a group coordination control strategy and specifically includes:

[0009] S1. Calculate the health and available capacity of each battery, and divide the battery packs into charging battery pack units and discharging battery pack units according to the health of each battery pack;

[0010] S2. Calculate the regulation requirements of multiple scenarios and determine the number of charge and discharge response groups;

[0011] S3. Calculate the dynamic capacity and health of each battery pack according to the charge and discharge power response of each battery pack and the dynamic safety margin of charge and discharge, including allocating power to each battery pack according to the charge and discharge safety margin, and calculating the capacity attenuation and health of the battery pack after participating in the demand response;

[0012] This process is repeated until the correction of each time period in the total scheduling cycle is completed;

[0013] S4, conversion of charging and discharging unit groups. During the operation of cascade utilization energy storage, when a battery group with a charge state reaching the upper and lower limits of the threshold appears in the charging and discharging unit group, the battery group reaching the upper and lower limits of the threshold is converted into a state, that is, the charging battery group reaching the upper limit of the threshold is converted into a discharging unit, and the discharging battery group reaching the lower limit of the threshold is converted into a charging unit.

[0014] Further, step S2 includes calculating the multi-scenario regulation requirements and determining the number of response groups of charging and discharging batteries;

[0015] The adjustment requirements of multiple scenarios include:

[0016] 1) Scenario 1: Energy storage participates in the output plan of new energy stations, and the power regulation requirements are as follows:

[0017]

[0018] in, They represent the load forecast value, new energy output forecast value and conventional unit output at time t respectively. represents the power regulation demand of energy storage participating in the output plan of new energy stations at time t, where Indicates charging. Indicates discharge;

[0019] 2) Scenario 2: Energy storage is used to smooth out grid net load fluctuations. The power regulation requirements are as follows:

[0020]

[0021] In the formula, They represent the actual load value and the actual output value of new energy at time t respectively. represents the power regulation demand of energy storage to smooth the net load fluctuation of the power grid at time t, where Indicates charging. Indicates discharge;

[0022] Combining the above scenarios 1) and 2), the net power regulation requirements of energy storage in multiple scenarios are obtained: for:

[0023]

[0024] Furthermore, the total capacity of energy storage participating in multi-scenario regulation needs is obtained. for:

[0025]

[0026] in, t0 Indicates the initial time of the scheduling period.

[0027] Furthermore, the calculation of step S3 includes:

[0028] S31. Battery health

[0029] Set the battery health to S OH It is defined as the ratio of the amount of electricity discharged from the battery at the rated rate from a fully charged state to the cut-off voltage to the nominal capacity of the battery. The formula is:

[0030]

[0031] Among them, C A is the actual measured battery capacity, C N is the nominal discharge capacity of a new battery;

[0032] S32. Establish a dynamic health model for battery capacity loss

[0033] Battery DOD under actual operating conditions bat The DOD of the battery will change with the change of system operation. bat The corresponding maximum number of cycles is uniformly converted into the equivalent number of cycles under full charge and discharge conditions. By summing up, the equivalent number of cycles N' of the battery in the operating cycle can be obtained:

[0034]

[0035] Among them, N D (1) is the maximum number of cycles corresponding to the battery when the discharge depth is 100%; N D (DOD bat,k ) is the battery at the depth of discharge DOD bat,k The maximum number of cycles corresponding to ;

[0036] Therefore, the energy storage battery single discharge capacity loss index Z is established as:

[0037]

[0038] The depth of discharge at time t in a known cycle is DOD. bat According to the discharge amount at the corresponding time, it can be known that the discharge capacity loss E at time t loss (t) should be expressed as:

[0039] E loss (t)=-Z·P bat (t)Δt,(P bat (t)<0)

[0040] Where: P bat (t) represents the charging and discharging power of the energy storage at time t, and P bat (t)<0;

[0041] The dynamic health of each battery pack is obtained based on the capacity loss of the energy storage battery during the charging and discharging process, as shown below:

[0042]

[0043] In the formula, S OH (t) represents the health of the battery pack at time t, E bess Indicates the rated capacity of the battery pack;

[0044] S33. Calculate the charge and discharge power output limit of the safety margin

[0045] Considering the characteristics of the single cells of retired batteries, the attenuation of battery life is estimated according to the capacity loss index. Retired batteries with similar health are combined in series and parallel. The capacity attenuation model per unit time period can obtain the corresponding attenuation δ:

[0046]

[0047] The state of charge safety margin of the cascade energy storage system is set according to the capacity attenuation of the battery, specifically:

[0048]

[0049] Among them, soc' min 、soc' max Indicates the battery state of charge safety margin, soc min 、soc max Indicates the safety margin of the state of charge of the battery during initial application;

[0050] Based on the current state of charge of the energy storage, the energy storage charge and discharge factor is introduced to limit the charge and discharge power of the energy storage, which is divided into a discharge factor and a charge factor;

[0051] The discharge influencing factor of energy storage is expressed as:

[0052] λ dis =max{(1-soc / W dis ),0}

[0053]

[0054] Among them, W dis It represents the measurement parameter of energy storage discharge, which is set according to the normal working range and warning working range of the energy storage device. dis is an intermediate variable. When soc is less than W dis When dis =0; when soc is greater than W dis When dis <0; is the adjustment coefficient; f dis is the influence factor of the current soc value on discharge;

[0055] Energy storage charging influencing factors:

[0056] λ ch =min{(1-soc / W ch ),0}

[0057]

[0058] Among them, W ch It represents the measurement parameter of energy storage charging, which is set according to the normal working range and warning working range of the energy storage device. ch is an intermediate variable. When soc is less than W ch When ch =0; when soc is greater than W ch When ch <0; is the adjustment coefficient; f ch is the impact factor of the current soc value on charging;

[0059] Based on the current state of charge of the energy storage and considering the charge and discharge factors of the energy storage, the charge and discharge safety margin of the energy storage can be obtained, and the following expression exists:

[0060]

[0061] Among them, P bat_lim Indicates the charging and discharging power limit of energy storage, P ch_max Indicates the maximum charging power of energy storage, P dis_max Indicates the maximum discharge power of the energy storage.

[0062] Furthermore, the battery health and available capacity are calculated using methods including its capacity attenuation coefficient, operating temperature, and charge and discharge depth.

[0063] The present invention also provides a centralized energy storage group coordination control system that takes battery health into account, including a memory, a processor, and a computer program stored in the memory, and the processor executes the computer program to implement the above-mentioned centralized energy storage group coordination control method that takes battery health into account.

[0064] A computer-readable storage medium stores a computer program / instruction, which implements the above method when executed by a processor.

[0065] Beneficial effects: In order to further improve the operation cycle of large-scale centralized energy storage and achieve full life cycle coverage of batteries under different battery life loss levels, the present invention proposes a centralized energy storage group coordination control strategy that takes into account battery health. First, a centralized energy storage operation mode with different battery health states is constructed to break the energy sharing barrier, so that it can not only coordinate the output of new energy stations but also smooth the net load fluctuation of the power grid; secondly, a dynamic charging and discharging safety margin is set based on the battery health, so as to propose a group coordination control strategy that takes into account different battery health states to cope with the challenges brought by battery inconsistency to operation and regulation. The simulation results of the example show that the proposed strategy meets the multi-scenario regulation requirements of the power grid and the power station while improving the economy of the centralized energy storage power station and extending the cycle life of the battery. In addition, the group coordination control strategy implemented based on the present invention enables the battery group used in the charging and discharging stages to have a considerable charging and discharging capacity, improves the orderliness of the charging and discharging state of the battery group used in each stage, and avoids the charging and discharging unit group from entering an extreme operating state due to insufficient charging and discharging capacity. At the same time, the group coordination control strategy proposed in the present invention carries out group operation according to the health of the batteries, realizing "deep charging and deep discharging of batteries with high health, shallow charging and shallow discharging of batteries with low health", improving the operational flexibility of cascade energy storage, avoiding the "short board effect" of each battery unit, and improving the energy utilization rate of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0066] Figure 1 It is a schematic diagram of the centralized energy storage scenario setting;

[0067] Figure 2 It is the relationship diagram between cycle life and discharge depth of second-use battery;

[0068] Figure 3 It is a topological diagram of the grouped battery energy storage system;

[0069] Figure 4 is a group coordination control flow chart of the present invention;

[0070] Figure 5 It is the predicted and actual wind power output in the northwest region on a certain day in the embodiment;

[0071] Figure 6 It is the predicted and actual load situation of the northwest region on a certain day in the embodiment;

[0072] Figure 7 It is the output of thermal power units and energy storage under multi-scenario regulation requirements;

[0073] Figure 8 is a net load comparison diagram of an embodiment;

[0074] Fig. 9 It is the SOC curve of each battery pack under group coordinated control;

[0075] Fig.10 It is the SOC curve of each battery pack under the equal sharing strategy;

[0076] Fig.11 It is the SOC curve of each echelon of battery utilization under the proportional allocation strategy;

[0077] Fig.12 This is a comparison chart of the number of charge and discharge conversions for different strategies;

[0078] Fig.13 This is a comparison chart of the maximum DOD of batteries used in different tiers under different control strategies;

[0079] Fig.14 It is a comparison chart of the changes in the health of the energy storage system before and after setting the dynamic safety margin;

[0080] Fig.15 Whether to set up a comparative analysis chart of the impact of SOH on battery capacity attenuation. DETAILED DESCRIPTION

[0081] In order to explain the technical solution provided by the present invention in detail, a further introduction is given below in conjunction with the accompanying drawings of the specification.

[0082] 1. Scenario settings for centralized energy storage under different battery health conditions

[0083] The scenario settings of centralized energy storage that meets different regulation requirements of multiple participants and in various scenarios under different battery health conditions are as follows: Figure 1 As shown in the figure. In this scenario, energy storage can not only smooth out the net load fluctuation of the power grid, but also coordinate the output plan of new energy stations. Figure 1 It can be seen that the frequent changes in regulation requirements between multiple scenarios increase the frequency of charge and discharge conversion of energy storage batteries and reduce the cycle life of retired batteries. At the same time, due to the different health levels of different batteries in the cascade utilization energy storage system, the regulation effect of the energy storage system will be far from expected. To solve this complex problem, it is necessary to consider combining retired batteries with different health levels with the regulation requirements in multiple scenarios so that the energy storage system can dynamically allocate its own charge and discharge power.

[0084] 2. Multi-scenario adjustment demand model

[0085] Scenario 1: Energy storage participates in the output plan of new energy stations. The power regulation requirements are as follows:

[0086]

[0087] in, They respectively represent the load forecast value, new energy output forecast value and conventional unit output at time t. represents the power regulation demand of energy storage participating in the output plan of new energy stations at time t, where Indicates charging. Indicates discharge.

[0088] Scenario 2: Energy storage is used to smooth out grid net load fluctuations. The power regulation requirements are as follows:

[0089]

[0090] In the formula, They respectively represent the actual load value and the actual output value of new energy at time t. represents the power regulation demand of energy storage to smooth the net load fluctuation of the power grid at time t, where Indicates charging. Indicates discharge.

[0091] Combining Scenario 1 and Scenario 2, we can derive the net power regulation requirements of energy storage in multiple scenarios. for:

[0092]

[0093] Furthermore, the total capacity of energy storage participating in multi-scenario regulation needs is obtained. for

[0094]

[0095] Wherein, t0 represents the initial time of the scheduling period.

[0096] 3. Characterization of battery health throughout the entire life cycle

[0097] 3.1 Battery Health

[0098] The health of the battery in energy storage is an important indicator that affects its charge and discharge performance. As the number of charge and discharge times of the battery pack increases, the health of the battery pack gradually decreases and its life gradually decays. OH It is defined as the ratio of the amount of electricity discharged from the battery at the rated rate from a fully charged state to the cut-off voltage to the nominal capacity of the battery, expressed as

[0099]

[0100] Among them, C A is the actual measured battery capacity, C N is the nominal discharge capacity of a new battery.

[0101] When the battery health is less than 0.8, it cannot be used in some scenarios (such as electric vehicles) and needs to be retired. At this time, retired power batteries still have a relatively high available capacity. They can be disassembled, sorted, and reassembled for large-scale energy storage. Certain technical means are used to extend the operating life of retired power batteries and improve their safety. They can be used again in energy storage scenarios that do not require high capacity performance. The health limit of retired power batteries is [50%, 80%].

[0102] 3.2 Dynamic health model considering battery capacity loss

[0103] The cycle life of the battery is related to multiple factors such as temperature and discharge depth. The present invention focuses on the discharge depth DOD. bat In order to determine the impact of retired battery cycle life, retired lithium batteries are selected as energy storage batteries for cascade utilization. The power function method is used to fit the cycle life and discharge depth of retired lithium batteries, as shown in formula (6). The fitting results are shown in Figure 2 As shown. Through the curve relationship between cycle life and discharge depth, the capacity loss index of the second-use battery for one discharge is determined, and then according to the discharge amount of the second-use battery, the capacity loss caused by one discharge of the second-use battery is obtained, and then the capacity loss of the second-use battery in one operation cycle is calculated. According to its capacity loss, the dynamic health of the retired battery can be calculated.

[0104]

[0105] Where: N D is the cycle life of retired batteries, DOD bat is the discharge depth of the retired battery.

[0106] However, in actual operation, the battery DOD bat The present invention uses the equivalent cycle life method to calculate the different DOD values ​​in the actual operation of the battery. bat The corresponding maximum number of cycles is converted into full charge and discharge state (DOD bat =1), the equivalent cycle number N' of the battery in the operating cycle can be obtained by summing:

[0107]

[0108] Among them, N D (1) is the maximum number of cycles corresponding to the battery when the discharge depth is 100%; N D (DOD bat,k ) is the battery at the depth of discharge DOD bat,k The maximum number of cycles corresponding to .

[0109] Therefore, the single discharge capacity loss index Z of the energy storage battery is established as:

[0110]

[0111] The depth of discharge at time t in a known cycle is DOD. bat According to the discharge amount at the corresponding time, it can be known that the discharge capacity loss E at time t loss (t) should be expressed as:

[0112] E loss (t)=-Z·P bat (t)Δt,(P bat (t)<0) (9)

[0113] Where: P bat (t) represents the charging and discharging power of the energy storage at time t, and P bat (t)<0. The dynamic health of each battery pack is obtained based on the capacity loss of the energy storage battery during the charging and discharging process, as shown in formula (10):

[0114]

[0115] In the formula, S OH (t) represents the health of the battery pack at time t, E bess Indicates the rated capacity of the battery pack.

[0116] 4. Consider the charging and discharging power output limit with safety margin

[0117] When batteries are used in energy storage systems, their initial capacities are similar but inconsistent. In order to improve the reliability of system operation, the characteristics of the single cells of retired batteries need to be considered. The attenuation of battery life is estimated based on the capacity loss index, and retired batteries with similar health are combined in series and parallel. The corresponding attenuation δ can be obtained from the capacity attenuation model per unit time period in formula (9):

[0118]

[0119] The state of charge safety margin of the cascade energy storage system is set according to the capacity decay of the battery, specifically:

[0120]

[0121] Among them, soc′ min , soc′ max Indicates the battery state of charge safety margin, soc min 、soc maxIndicates the state of charge safety margin of the battery when it is initially used. Within the state of charge safety margin of the energy storage, in order to prevent over-discharge of the energy storage, the discharge of the energy storage is suppressed when the state of charge is low; in order to avoid overcharging of the energy storage, the charging power of the energy storage is suppressed when the state of charge of the energy storage is very high. Based on the current state of charge of the energy storage, the energy storage charge and discharge factor is introduced to limit the charge and discharge power of the energy storage, which is divided into the discharge factor and the charge factor.

[0122] 1) Discharge influencing factors of energy storage

[0123] λ dis =max{(1-soc / W dis ),0} (13)

[0124]

[0125] Among them, W dis It represents the measurement parameter when the energy storage is discharged, and is set according to the normal working range and the early warning working range of the energy storage device. dis =0.3;λ dis is an intermediate variable. When soc is less than W dis When dis =0; when soc is greater than W dis When dis <0; is the adjustment coefficient; f dis is the influence factor of the current soc value on discharge.

[0126] 2) Energy storage charging influencing factors

[0127] λ ch =min{(1-soc / W ch ),0} (15)

[0128]

[0129] Among them, W ch It represents the metric parameter when the energy storage is charged, and is set according to the normal working range and the warning working range of the energy storage device. In this embodiment, W is selected ch =0.7;λ ch is an intermediate variable. When soc is less than W ch When ch =0; when soc is greater than W ch When ch <0; is the adjustment coefficient; f ch It is the influence factor of current soc value on charging.

[0130] Based on the current state of charge of the energy storage and considering the charging and discharging factors of the energy storage, the charging and discharging safety margin of the energy storage can be obtained.

[0131]

[0132] Among them, P bat_lim Indicates the charging and discharging power limit of energy storage, P ch_max Indicates the maximum charging power of energy storage, P dis_max Indicates the maximum discharge power of the energy storage.

[0133] 5. Grouping control strategy for different battery health status

[0134] 5.1 Grouped battery energy storage system topology

[0135] Combination Figure 1 Based on the operation mode of centralized energy storage, the entire retired battery energy storage system can be divided into two subsystems, one system is responsible for charging and the other is responsible for discharging. In order to meet the regulation requirements, the two subsystems can be temporarily converted, that is, when the regulation power of a subsystem is insufficient, part (or all) of the battery packs of another energy storage subsystem will be selected to temporarily undertake the corresponding regulation tasks to meet the power regulation requirements of energy storage. In the grouping mode, the topology of the retired battery energy storage system is as follows: Figure 3 As shown:

[0136] 5.2 Group coordination control strategy

[0137] In order to reduce the number of charge and discharge conversions of battery packs under the multi-scenario regulation requirements of multiple participants and improve the overall cycle life of the centralized energy storage system, a group coordination control strategy is used to allocate power between different battery packs. Assume that there are n battery packs in the cascade energy storage system, the number of battery packs in the charging unit group is k, the number of battery packs in the discharging unit group is m, and k+m=n is satisfied. The group coordination control process is as follows: Figure 4 As shown. Among them, p lim,j Indicates the limit charge and discharge power of the charge and discharge battery pack, [S OHmin ,S OHmax ] represents the health range of each battery pack, and [SOCmin, SOCmax] represents the available capacity range of each battery pack.

[0138] According to the above control flow chart, the group coordination control is summarized into the following four stages:

[0139] Phase 1: Calculate the health and available capacity of each battery, and group and combine the battery packs according to their health: The available capacity and health of retired batteries can be calculated through their capacity attenuation coefficient, operating temperature, charge and discharge depth, etc.; group and combine battery packs with similar health and initial available capacity into charging battery pack units and discharging battery pack units.

[0140] The second stage: Calculate the regulation requirements of multiple scenarios and determine the number of charge and discharge response groups: Calculate the regulation requirements of multiple scenarios according to equations (1)-(3), and further calculate the number of charge and discharge battery response groups.

[0141] The third stage: According to the charge and discharge power response of each battery group, the dynamic capacity and health are calculated in combination with the dynamic safety margin of charge and discharge: the power of each retired battery group is allocated according to the charge and discharge safety margin set in this article; the capacity attenuation and health of the battery group after participating in the demand response are calculated. This is repeated until the correction of each period in the total dispatch cycle is completed.

[0142] The fourth stage: conversion of charging and discharging unit groups: During the operation of cascade utilization energy storage, when a battery group with SOC (state of charge) reaching the upper and lower limits of the threshold appears in the charging and discharging unit group, the battery group reaching the upper and lower limits of the threshold is converted into a state, that is, the charging battery group reaching the upper limit of the threshold is converted into a discharging unit, and the discharging battery group reaching the lower limit of the threshold is converted into a charging unit.

[0143] 6. Example verification

[0144] 6.1 Related parameter settings

[0145] This embodiment selects the predicted output and actual output of a certain day in the annual historical data of a wind farm with an installed capacity of 50MW in the northwest region, such as Figure 5 . And select the forecast load and actual load on the same day, such as Figure 6 Since retired batteries generally have a remaining capacity of 65%-80% and have a high utilization value

[14] , the centralized energy storage system is configured with 6 groups of batteries with a rated capacity of 15MWh each, and their initial SOH values ​​are 0.55, 0.60, 0.65, 0.70, 0.75, and 0.80; according to the battery grouping coordination control strategy of the present invention, the three retired battery groups with SOH values ​​of 0.55, 0.60, and 0.70 are set as charging units; and the three retired battery groups with SOH values ​​of 0.65, 0.75, and 0.80 are set as discharging units.

[0146] 6.2 Verification of the effectiveness of group coordination control strategy

[0147] 6.2.1 Analysis of energy storage requirements for multi-scenario regulation

[0148] The second-hand battery uses energy storage to participate in assisting new energy stations to adjust their output plans in a shared manner and to reduce the net load fluctuations generated by the power grid. The total output of thermal power units and energy storage is adjusted as follows: Figure 7 As shown in the figure, the comparison of net load is as follows Figure 8 shown.

[0149] Depend on Figure 7 Combination Figure 5 and Figure 6 It can be seen that in the time period of 8:00-12:00, the wind power output is small and the load demand is large. At this time, the capacity of the energy storage cannot meet the total power demand of the regulation. In order to meet the power regulation demand, thermal power units are required to participate in coordinating the output of new energy sites, and the thermal power units have a large output. In the time periods of 0:00-3:00, 14:00-18:00, and 22:00-24:00, the wind power output is large and the load is small. At this time, the energy storage charging and discharging power is the main one, and the thermal power units have only a small output to meet the energy balance of the energy storage in a scheduling cycle, indicating that the energy storage meets the regulation needs of tracking the output plan of the new energy site. Further, by Figure 8 It can be seen that with the participation of energy storage, the net load fluctuation of the power grid has been smoothed to a certain extent, achieving the effect of peak shaving and valley filling. Therefore, energy storage, a new energy storage operation mode, meets the regulation needs of multiple scenarios.

[0150] 6.2.2 Analysis of SOC changes of each battery pack under the group coordination control strategy

[0151] Based on the total demand for energy storage in various scenarios at different time periods, combined with the operating characteristics and constraints of energy storage itself, the cascade utilization of energy storage is grouped and coordinated. The SOC change curve of each cascade utilization battery group is as follows: Fig. 9 shown.

[0152] Depend on Fig. 9It can be seen that according to the group coordination control strategy proposed in the present invention, 6 groups of echelon utilization batteries alternately participate in the regulation requirements of multiple scenarios, so that some echelon utilization battery groups are in a charging state for a long time, and the other part is in a discharging state for a long time (as shown in the figure, groups 1, 2, and 3 are in one state, and groups 4, 5, and 6 are in another state). For the part beyond the charging and discharging capacity of the echelon utilization battery group, the battery group with flexible charge and discharge conversion participates in the regulation requirements of multiple scenarios, as shown in the 4 circles in the figure. The group coordination control strategy enables the charging and discharging echelon utilization battery group to have a considerable charging and discharging capacity, improves the orderliness of the charging and discharging state of each echelon utilization battery group, and avoids the charging and discharging unit group from entering an extreme operating state due to insufficient charging and discharging capacity. At the same time, the group coordination control strategy proposed in the present invention is grouped and put into operation according to the health of the battery, realizing "deep charging and deep discharging of batteries with high health, and shallow charging and shallow discharging of batteries with low health", improving the operational flexibility of the echelon utilization energy storage, avoiding the "short board effect" of each battery unit, and improving the energy utilization rate of the battery.

[0153] 6.3 Control effect comparison

[0154] In order to verify the feasibility of the proposed group coordination control strategy, the power sharing strategy commonly used in the engineering field and the proportional allocation strategy commonly used in the academic field are selected for comparison with the group control strategy proposed in this paper. The effects of the three control strategies are compared from three aspects: the SOC change curve of each echelon battery pack, the number of charge and discharge conversions of each echelon battery pack, and the discharge depth of each echelon battery pack.

[0155] 6.3.1 Comparison of SOC changes of each battery pack under different strategies

[0156] The proportional allocation strategy allocates power in each period according to the available capacity ratio of each battery pack, and the power balancing strategy distributes the power demand of each period to each battery pack according to the regulation requirements of multiple scenarios. Under these two control strategies, each battery pack unit of the cascade utilization energy storage participates in the regulation requirements of multiple scenarios, and the SOC change curves of each battery pack are as follows: Fig.10 , 11 shown.

[0157] Depend on Fig.10 and Fig.11 It can be seen that under the proportional allocation and equal sharing control strategies, each battery pack is involved in the power regulation requirements in multiple scenarios, and all battery pack units perform charging and discharging tasks at the same time until the battery SOC reaches the threshold for charging and discharging conversion. Figure 8In contrast, when each battery pack is charged and discharged at the same time, the SOC of each battery pack maintains the same change trend, causing some battery packs to enter extreme operating states due to insufficient charging and discharging capabilities. The inconsistency of retired battery packs is ignored, increasing the "short board effect" of retired batteries.

[0158] 6.3.2 Comparison of charge and discharge conversion times of each battery pack under different strategies

[0159] The number of battery pack charge and discharge conversions is the main technical indicator that affects the operating efficiency and operating life of each battery pack for cascade utilization. Frequent battery charge and discharge state conversion will increase battery operating losses and reduce the cycle life of the cascade utilization battery pack. The test cycle of multi-scenario regulation demand is extended to 6 scheduling cycles to obtain the difference between the number of charge and discharge cycles of the cascade utilization battery pack unit under three different control strategies. The comparison results under different strategies are shown in the figure below. Fig.12 shown.

[0160] Depend on Fig.12 It can be seen that under the power sharing strategy and the proportional allocation strategy, the battery pack units of the cascade utilization energy storage are in working state during the period when the power regulation demand in multiple scenarios is not 0, and the maximum number of charge and discharge state conversions can reach 78 times and 118 times respectively. Under the group coordination control strategy, the maximum number of charge and discharge conversions of the cascade utilization battery is 38 times, which greatly reduces the number of charge and discharge conversions and prolongs the cycle life of the retired battery units.

[0161] 6.3.3 Comparison of battery discharge depth under different strategies

[0162] There are large differences in the health of each battery unit in the cascade utilization energy storage. In order to reduce the impact of the inconsistency of each battery unit and avoid the "short board effect" of the battery unit as much as possible, the charging and discharging power of different retired battery groups should be reasonably allocated according to their health. The maximum discharge depth of each battery group under different control strategies is as follows: Fig.13 shown.

[0163] Depend on Fig.13 It can be seen that under the proportional allocation strategy and the equal distribution strategy, each battery unit has the same charge and discharge operation, but its discharge depth is small, which is 25% of the group coordination control strategy, so that each battery group in the cascade energy storage will frequently charge and discharge at low power, increasing the number of charge and discharge switching of each battery group, affecting the service life of the battery. The group coordination optimization method proposed in this paper performs group coordination control according to the health of each retired battery, optimizes its output based on the health of each battery group, avoids disorderly and frequent switching of charge and discharge states, reduces the inconsistency of each retired battery, and prolongs the cycle life of the cascade energy storage.

[0164] 6.4 Analysis of Battery Health Under Dynamic Safety Margin

[0165] On the basis of the above analysis, in order to detect the impact of dynamic charge and discharge safety margin on the health of cascade utilization energy storage, the relationship between the life and health of cascade utilization energy storage is simulated and analyzed before and after the dynamic safety margin is set. Fig.14 shown.

[0166] Depend on Fig.14 It can be seen that after the charge and discharge cycle reaches 1400 times, the life loss rate of the cascade utilization energy storage is lower than that without considering the dynamic charge and discharge safety margin when the charge and discharge cycle reaches 2500 times. After the charge and discharge cycle reaches 2500 times, the life decay rate in the two cases has a large difference. Within the life cycle of the cascade utilization energy storage, considering the dynamic charge and discharge safety margin, the cycle life of the cascade utilization energy storage increases by 7.8%, indicating that the dynamic charge and discharge safety margin setting proposed by the present invention is conducive to reducing the operating loss of the cascade utilization energy storage and improving its cycle life.

[0167] 6.5 Analysis of the impact of health on battery capacity attenuation

[0168] The cycle life of energy storage batteries in cascade utilization is basically different, resulting in different capacity attenuation during the charge and discharge process of energy storage battery packs in cascade utilization, further increasing the inconsistency of the battery pack. In order to monitor the impact of dynamic health on the capacity attenuation of cascade utilization energy storage systems, the following Fig.15 The simulation analysis is shown.

[0169] Depend on Fig.15 It can be seen that after the number of cycles reaches 1400, there is a significant difference in the capacity loss of the cascade utilization energy storage with and without considering the health. The capacity attenuation without considering the health is greater than the capacity attenuation with considering the health, and as the number of cycles increases, the difference in capacity attenuation continues to increase. This shows that during the reorganization and charging and discharging process of retired battery cells, considering the health of the battery pack can reduce the inconsistency of each battery pack and improve the cycle life of the battery.

[0170] The present invention aims at optimizing the control of battery packs in multiple application scenarios under the conditions of battery recycling, reducing net load fluctuations in the power grid, and assisting new energy stations in adjusting output. Based on the battery health, a group optimization control model considering the dynamic safety margin of charging and discharging is proposed. Through the above embodiments, the present invention has the following significant effects and improvements:

[0171] (1) Centralized energy storage that takes into account different battery health states can meet the regulation needs of multiple scenarios, including coordinating the peak-to-valley difference of new energy stations by nearly 15%, and smoothing out 7.8% of net load fluctuations. In addition, centralized energy storage based on retired batteries achieves full life cycle coverage of retired batteries, reducing the huge pressure of retired batteries on the social ecological environment.

[0172] (2) The proposed coordinated control strategy for battery grouping in cascade utilization can greatly reduce the number of charge and discharge switching of each battery group while meeting the regulation requirements of multiple scenarios. Compared with the power balancing strategy and the proportional allocation strategy, the maximum charge and discharge switching times of the battery group are reduced by 51.28% and 67.8% respectively.

[0173] (3) After considering the dynamic safety margin of charge and discharge, the cycle life of the battery packs in each tier is significantly extended. In terms of the multi-scenario adjustment requirements of the present invention, the cycle life is increased by 7.8%.

[0174] (4) Considering the health factor during battery grouping and charging and discharging makes the operation of each battery group more gentle, reduces the capacity loss of each battery group during the charging and discharging process, and at the same time, makes the health of each battery group tend to be consistent, reducing the inconsistency of each retired battery group.

[0175] In order to further improve the engineering feasibility of the group coordination control strategy for different battery health states, the energy storage benefit allocation problem under different battery health states will be further explored to further develop the economic sustainability research of battery energy storage with heterogeneous health states.

Claims

1. A centralized energy storage group coordination control method taking battery health into account, characterized in that: The method divides the centralized energy storage system composed of batteries in different health states into two subsystems, which are used to undertake negative charging tasks and discharging tasks respectively, and the two subsystems can be converted into each other. When the adjustment power of a subsystem is insufficient, part or all of the battery groups of another energy storage subsystem will be selected to temporarily undertake the corresponding adjustment tasks to meet the power adjustment requirements of energy storage; The method adopts a group coordination control strategy and specifically includes: S1. Calculate the health and available capacity of each battery, and divide the battery packs into charging battery pack units and discharging battery pack units according to the health of each battery pack; S2. Calculate the regulation requirements of multiple scenarios and determine the number of charge and discharge response groups; S3. Calculate the dynamic capacity and health of each battery pack according to the charge and discharge power response of each battery pack and the dynamic safety margin of charge and discharge, including allocating power to each battery pack according to the charge and discharge safety margin, and calculating the capacity attenuation and health of the battery pack after participating in the demand response; This process is repeated until the correction of each time period in the total scheduling cycle is completed; S4, conversion of charging and discharging unit groups. During the operation of cascade utilization energy storage, when a battery group with a charge state reaching the upper and lower limits of the threshold appears in the charging and discharging unit group, the battery group reaching the upper and lower limits of the threshold is converted into a state, that is, the charging battery group reaching the upper limit of the threshold is converted into a discharging unit, and the discharging battery group reaching the lower limit of the threshold is converted into a charging unit.

2. The centralized energy storage group coordination control method according to claim 1 is characterized in that: Step S2 includes calculating the multi-scenario regulation requirements and determining the number of response groups of charging and discharging batteries; The adjustment requirements of multiple scenarios include: 1) Scenario 1: Energy storage participates in the output plan of new energy stations, and the power regulation requirements are as follows: in, They represent the load forecast value, new energy output forecast value and conventional unit output at time t respectively. represents the power regulation demand of energy storage participating in the output plan of new energy stations at time t, where Indicates charging. Indicates discharge; 2) Scenario 2: Energy storage is used to smooth out grid net load fluctuations. The power regulation requirements are as follows: In the formula, They represent the actual load value and the actual output value of new energy at time t respectively. represents the power regulation demand of energy storage to smooth the net load fluctuation of the power grid at time t, where Indicates charging. Indicates discharge; Combining the above scenarios 1) and 2), the net power regulation requirements of energy storage in multiple scenarios are obtained: for: Furthermore, the total capacity of energy storage participating in multi-scenario regulation needs is obtained. for: Wherein, t0 represents the initial time of the scheduling cycle.

3. The centralized energy storage group coordination control method according to claim 1 is characterized in that: The calculation of step S3 includes: S31. Battery health Set the battery health to S OH It is defined as the ratio of the amount of electricity discharged from the battery at the rated rate from a fully charged state to the cut-off voltage to the nominal capacity of the battery. The formula is: Among them, C A is the actual measured battery capacity, C N is the nominal discharge capacity of a new battery; S32. Establish a dynamic health model for battery capacity loss Battery DOD under actual operating conditions bat The DOD of the battery will change with the change of system operation. bat The corresponding maximum number of cycles is uniformly converted into the equivalent number of cycles under full charge and discharge conditions. By summing up, the equivalent number of cycles N' of the battery in the operating cycle can be obtained: Among them, N D (1) is the maximum number of cycles corresponding to the battery when the discharge depth is 100%; N D (DOD bat,k ) is the battery at a depth of discharge (DOD) bat,k The maximum number of cycles corresponding to ; Therefore, the energy storage battery single discharge capacity loss index Z is established as: The depth of discharge at time t in a known cycle is DOD. bat According to the discharge amount at the corresponding time, it can be known that the discharge capacity loss E at time t loss (t) should be expressed as: E loss (t)=-Z·P bat (t)Δt,(P bat (t)<0) Where: P bat (t) represents the charging and discharging power of the energy storage at time t, and P bat (t)<0; The dynamic health of each battery pack is obtained based on the capacity loss of the energy storage battery during the charging and discharging process, as shown below: In the formula, S OH (t) represents the health of the battery pack at time t, E bess Indicates the rated capacity of the battery pack; S33. Calculate the charge and discharge power output limit of the safety margin Considering the characteristics of the single cells of retired batteries, the attenuation of battery life is estimated according to the capacity loss index. Retired batteries with similar health are combined in series and parallel. The capacity attenuation model per unit time period can obtain the corresponding attenuation δ for: The state of charge safety margin of the cascade energy storage system is set according to the capacity attenuation of the battery, specifically: Among them, soc' min 、soc' max Indicates the battery state of charge safety margin, soc min 、soc max Indicates the safety margin of the state of charge of the battery during initial application; Based on the current state of charge of the energy storage, the energy storage charge and discharge factor is introduced to limit the charge and discharge power of the energy storage, which is divided into discharge factor and charge factor; The discharge influencing factor of energy storage is expressed as: λ dis =max{(1-soc / W dis ),0} Among them, W dis It represents the measurement parameter of energy storage discharge, which is set according to the normal working range and warning working range of the energy storage device. dis is an intermediate variable. When soc is less than W dis When dis =0; when soc is greater than W dis When dis <0; is the adjustment coefficient; f dis is the influence factor of the current soc value on discharge; The influencing factors of energy storage charging are: l ch =min{(1-soc / W ch ),0} Among them, W ch It represents the measurement parameter of energy storage charging, which is set according to the normal working range and warning working range of the energy storage device. ch is an intermediate variable. When soc is less than W ch When ch =0; when soc is greater than W ch When ch <0; is the adjustment coefficient; f ch is the impact factor of the current soc value on charging; Based on the current state of charge of the energy storage and considering the charge and discharge factors of the energy storage, the charge and discharge safety margin of the energy storage can be obtained, and the following expression exists: Among them, P bat_lim Indicates the charging and discharging power limit of energy storage, P ch_max Indicates the maximum charging power of energy storage, P dis_max Indicates the maximum discharge power of the energy storage.

4. The centralized energy storage group coordination control method according to claim 1 is characterized in that: The battery health and available capacity are calculated using methods including capacity attenuation coefficient, operating temperature, and charge and discharge depth.

5. A centralized energy storage group coordination control system taking battery health into account, characterized in that: The method comprises a memory, a processor and a computer program stored in the memory, wherein the processor executes the computer program to implement the method according to any one of claims 1 to 4.

6. A computer-readable storage medium having a computer program / instruction stored thereon, characterized in that: When the computer program / instructions are executed by a processor, the method according to any one of claims 1 to 4 is implemented.

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