Lithium battery pack charging and discharging management method and system

Abstract

The invention relates to a lithium battery pack charging and discharging management method and system, and belongs to the field of battery pack charging and discharging. The method is applied to an energy storage system comprising a container lithium battery pack, the lithium battery pack comprises i parallel branches, i is a positive integer smaller than or equal to n, and n is the number of branches; the method comprises the following steps: when i is from 1 to n / 2, the charge-discharge multiplying power Ci of a branch is gradually reduced; and when i is from n / 2 to n, the charge-discharge multiplying power Ci of the branch is gradually increased. The thermal safety and the service life of the container lithium battery pack are improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery pack charging and discharging, and in particular relates to a lithium battery pack charging and discharging management method and system. Background Art

[0002] With the large-scale access of photovoltaic and wind energy to the grid, energy storage systems have become an indispensable and important part of the operation of the power grid, and container energy storage systems based on lithium battery packs are a typical representative of them. The introduction of container lithium battery energy storage systems into the power grid can directly manage the demand side, quickly charge the unit when the load is low, and quickly discharge it during peak hours, thereby reducing the load difference between peaks and valleys and the peak-to-valley difference between day and night, effectively improving the stability of the power system operation; at the same time, traditional energy supply and energy consumption entities such as power plants and users can use the electricity price difference between peaks and valleys to obtain benefits and improve the economic efficiency of operation. Under the premise of cooperating with distributed power generation, it can effectively reduce energy costs. Container lithium battery energy storage systems are widely used.

[0003] However, container lithium battery energy storage systems are generally placed outdoors, and the battery packs are placed very densely. Heat accumulation is easy to form during the charging and discharging process, causing the temperature inside the container to rise significantly and causing temperature inconsistencies between batteries, thereby affecting the charging and discharging performance of the battery pack. It also brings the risk of thermal runaway of the battery pack, posing a huge thermal safety hazard. The thermal safety issue during the operation of the container lithium battery energy storage system is one of the problems that need to be solved.

[0004] In addition, the energy storage system includes multiple energy storage branches, and any energy storage branch includes energy storage batteries and DC / DC converters connected in series. The output ends of each energy storage branch and the output end of the photovoltaic system are respectively connected to the DC side of the inverter, and the AC side of the inverter is connected to the AC power grid. The controller is respectively connected to each energy storage branch in the energy storage system to control the charging and discharging process of each energy storage branch.

[0005] In actual applications, the controller will obtain the total power to be allocated of the energy storage system in any control cycle, and then allocate the total power to be allocated in each energy storage branch according to the SOC value of the energy storage battery in each energy storage branch, and control the charging and discharging process of the corresponding energy storage branch according to the allocated power corresponding to each energy storage branch.

[0006] In the prior art, the total power to be allocated is allocated among the energy storage branches in each control cycle, which may easily lead to the energy storage branches being unable to effectively respond to power allocation instructions because their own shared power is greater than the corresponding limit value, thereby causing the entire photovoltaic storage system to be unable to meet actual application requirements. In addition, the thermal risk caused by the temperature rise of the battery pack is not considered when meeting the limit. Therefore, the power allocation of each energy storage branch to the thermal safety risk of the battery pack is also a problem that needs to be solved. Summary of the invention

[0007] The object of the present invention is to provide a lithium battery pack charge and discharge management method and system, thereby improving the thermal safety and life of the container lithium battery pack.

[0008] A lithium battery pack charge and discharge management method is applied to an energy storage system including a container lithium battery pack, wherein the lithium battery pack includes i parallel branches, i is a positive integer less than or equal to n, and n is the number of branches; The method comprises: When i changes from 1 to n / 2, the branch charge and discharge rate C i gradually decrease; When i changes from n / 2 to n, the branch charge and discharge rate C i Gradually increasing.

[0009] Optionally, the output end of the energy storage system is connected to the power grid via a DC / AC inverter; it also includes a photovoltaic or wind energy system, and the output end of the photovoltaic or wind energy system is also connected to the DC side of the DC / AC inverter.

[0010] Optionally, n is divisible by 4.

[0011] A lithium battery pack charge and discharge management method is applied to an energy storage system including a controller and a container lithium battery pack, wherein the lithium battery pack includes i parallel branches, i is a positive integer less than or equal to n, n is the number of branches, and each branch includes M batteries connected in series and in parallel, and M is a positive integer; The method comprises: The controller obtains the total charge and discharge power of the lithium battery pack in the current control cycle and the operating power of the lithium battery pack of each branch in the previous control cycle; Wherein, the total charge and discharge power is the set power of the lithium battery pack in the current control cycle; the operating power of the lithium battery pack in the previous control cycle is the sum of the charge and discharge powers of each branch in the previous control cycle; The adjusted power is the set power minus the operating power; Allocating the adjusted power to each of the branches to obtain the charge and discharge power of each of the branches in the current control cycle; The controller controls the charging and discharging of the corresponding branch based on the charging and discharging power of the current control cycle of each branch.

[0012] Optionally, allocating the adjusted power to each branch is specifically: When i changes from 1 to n / 2, the branch charge and discharge rate C i gradually decrease; When i changes from n / 2 to n, the branch charge and discharge rate C i Gradually increase; The divided adjustment power P allocated to each branch i =Ci * , where a is an integer between 1 and M, and V ia is the terminal voltage of the a-th battery in the i-th branch, in Vol ia and SOC is the remaining capacity of the a-th battery in the i-th branch; The adjustment power = .

[0013] Optionally, the output terminal of the energy storage system is connected to the power grid via a DC / AC inverter, and the output terminals of the photovoltaic and / or wind energy systems are also connected to the DC side of the DC / AC inverter.

[0014] Optionally, the specific method of allocating the adjustment power to each branch is as follows: Set a high charge-discharge rate A1, a nominal charge-discharge rate A2, and a low charge-discharge rate A3; A1 is in the range of 1.2C - 5C, A2 is in the range of 0.8C - 1.2C, and A3 is in the range of 0.1C - 0.8C, where C is the current that can fully charge or discharge the battery in 1 hour; When x belongs to the interval [1, i], the charge-discharge rate C of the branch x is the high charge-discharge rate A1, and the sub-adjustment power HP allocated to the high-discharge-rate branch x = C x * ; When x belongs to the interval [i, j], the charge-discharge rate C of the branch x is the low charge-discharge rate A3, and the sub-adjustment power LP allocated to the low-discharge-rate branch x = C x * ; When x belongs to the interval [j, n], the charge-discharge rate C of the branch x is the nominal charge-discharge rate A2, and the sub-adjustment power NP allocated to the nominal-discharge-rate branch x = C x * ; where 1 < i < j < n, x and j are integers, V xa is the terminal voltage of the a-th battery in the x-th branch, in Vol xa and SOC is the remaining capacity of the a-th battery in the x-th branch; The adjustment power = + .

[0015] Optionally, A1 > A2 > A3.

[0016] Optionally, 2(i - 1) < (j - i).

[0017] Optional, 1.6(i-1)<(nj).

[0018] Beneficial technical effects: Firstly, the high charging rate branches of the container lithium battery pack are concentrated on one side to avoid heat accumulation of the entire lithium battery pack, thereby improving the thermal safety of the container lithium battery pack and avoiding overheating or damage or power limitation of the lithium battery pack due to concentrated temperature rise.

[0019] Secondly, since the charging rate at the end of the lithium battery pack is large, it is convenient to maintain or replace the battery at the end.

[0020] Thirdly, since there are controlled differences in the charging rates of multiple adjacent branches, the charging current of each branch is controlled, thereby avoiding imbalance in charging current between branches caused by excessive charging current in some branches and too small charging current in some branches.

[0021] Fourthly, by dividing the battery into high charge and discharge rate branches, nominal charge and discharge rate branches, and low charge and discharge rate branches, the number of high charge and discharge rate branches is reduced, thereby avoiding too many branches charging and discharging at high rates at the same time, thereby improving the overall life of the battery pack. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Various other advantages and benefits will become apparent to those of ordinary skill in the art by reading the detailed description of the preferred embodiments below. The accompanying drawings are only for the purpose of illustrating the preferred embodiments and are not to be considered as limiting the present invention. Moreover, the same reference symbols are used throughout the accompanying drawings to represent the same components. In the accompanying drawings: Figure 1 This is a schematic diagram of a lithium battery pack connected to the network according to an embodiment of the present invention.

[0023] Figure 2 This is a front view of a lithium battery pack according to an embodiment of the present invention.

[0024] Figure 3 Schematic diagram of charging rate distribution of a lithium battery pack according to an embodiment of the present invention.

[0025] Figure 4 Schematic diagram of battery charging and discharging time and temperature rise according to an embodiment of the present invention. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical scheme and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0027] It should be noted that, in this article, the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, an element defined by the sentence "comprises a ..." does not exclude the existence of other identical elements in the process, method, article or device including the element.

[0028] Embodiment 1 like Figure 1 As shown, a lithium battery pack charge and discharge management method according to an embodiment of the present invention is applied to an energy storage system including a container lithium battery pack, and the output end of the energy storage system is connected to the power grid via a DC / AC inverter. Optionally, a photovoltaic or wind energy system is also included, and the output end of the photovoltaic or wind energy system is also connected to the DC side of the DC / AC inverter. Optionally, the lithium battery pack charge and discharge management method provided in an embodiment of the present invention is applied to an energy storage system that can obtain relevant parameters of power conversion devices such as lithium battery packs and inverters, and also includes a controller that runs a preset control program and controls the operating state of the lithium battery pack. It can also be applied to other controllers in a power supply system composed of an energy storage system, a photovoltaic system, and an inverter. Of course, in some cases, it can also be applied to servers on the network side.

[0029] Optionally, the lithium battery pack includes i parallel branches, where i is a positive integer less than or equal to n, and n is the number of branches and is divisible by 4.

[0030] Optionally, each branch includes multiple batteries and DC / DC converters connected in series, and each branch is connected to the DC side of the DC / AC inverter through a DC / DC converter. In actual applications, the charging and discharging power thresholds corresponding to different states of the lithium battery pack are different, and the DC / DC converter also corresponds to its own power threshold. Therefore, during the charging and discharging process of the lithium battery pack, the actual charging and discharging power used cannot be greater than the aforementioned two thresholds.

[0031] like Figure 2-Figure 4 As shown, the i parallel branches of the container lithium battery pack are arranged from left to right or from right to left. The lithium battery packs are highly densely arranged, which easily forms heat accumulation during the charging and discharging process, causing the temperature in the container to rise significantly. The method of this embodiment includes: When i changes from 1 to n / 2, the branch charge and discharge rate C i gradually decrease; When i changes from n / 2 to n, the branch charge and discharge rate C i Gradually increasing.

[0032] exist Figure 3In the figure, the charge and discharge ratio of branch 1-4 is: C1>C2>C3>C4, and the charge and discharge ratio of branch 5-8 is: C5 <C6<C7<C8。

[0033] Through the above method steps, the branch charge and discharge rates at both ends of the container lithium battery pack are higher than the charge and discharge rates of the middle branch. Since the air flow at both ends is good, heat dissipation is convenient and heat accumulation is not easy to form, thus improving the thermal safety of the container lithium battery pack.

[0034] Embodiment 2 This embodiment is an improvement on the first embodiment.

[0035] A lithium battery pack charge and discharge management method is applied to an energy storage system including a controller and a container lithium battery pack, wherein the output end of the energy storage system is connected to a power grid via a DC / AC inverter, and the output end of a photovoltaic and / or wind energy system is also connected to the DC side of the DC / AC inverter. The lithium battery pack comprises i parallel branches, i is a positive integer less than or equal to n, n is the number of branches, and each branch comprises M batteries connected in series and in parallel, and M is a positive integer.

[0036] Optionally, n is divisible by 4.

[0037] Optionally, n is greater than 10.

[0038] Optionally, M is greater than or equal to 12.

[0039] The method comprises: The controller obtains the total charge and discharge power of the lithium battery pack in the current control cycle and the operating power of the lithium battery pack of each branch in the previous control cycle; Wherein, the total charge and discharge power is the set power of the lithium battery pack in the current control cycle; the operating power of the lithium battery pack in the previous control cycle is the sum of the charge and discharge powers of each branch in the previous control cycle; The adjusted power is the set power minus the operating power; Allocating the adjusted power to each branch. It can be understood that each branch adds the adjusted power allocated between the branches on the basis of the charge and discharge power of the previous control cycle to obtain the charge and discharge power of each branch in the current control cycle; The controller controls the charging and discharging of the corresponding branch based on the charging and discharging power of the current control cycle of each branch; The allocation of the adjusted power to each branch is specifically: When i changes from 1 to n / 2, the branch charge and discharge rate C i gradually decrease; When i changes from n / 2 to n, the branch charge and discharge rate C i Gradually increase; The divided adjustment power P allocated to each branch i =C i * , where a is an integer between 1 and M, V ia is the terminal voltage of the ath battery in the ith branch, Vol ia is the remaining capacity of the ath battery in the ith branch; The adjusted power = .

[0040] Through the above method steps, on the first hand, the charge and discharge rate of the branch at the end of the container lithium battery pack is higher than the charge and discharge rate of the middle branch. Since the air circulation at both ends is good, heat dissipation is convenient and heat accumulation is not easy to form, thereby improving the thermal safety of the container lithium battery pack and avoiding overheating or damage or power limitation of the lithium battery pack due to concentrated temperature rise; on the second hand, since the charge rate at the end of the lithium battery pack is large, it is convenient to maintain or replace the battery at the end; on the third hand, since there is a controlled difference in the charge rate of adjacent branches, the charging current of each branch is controlled, avoiding the imbalance of charging current between branches caused by excessive charging current of some branches and excessive charging current of some branches.

[0041] Embodiment 3 This embodiment is an improvement on the first or second embodiment.

[0042] A lithium battery pack charge and discharge management method is applied to an energy storage system including a controller and a container lithium battery pack, the output end of the energy storage system is connected to the DC side of a DC / AC inverter, the AC side of the DC / AC inverter is connected to a power grid, the output end of a photovoltaic and / or wind energy system is connected to the DC side of the DC / AC inverter, the lithium battery pack includes i parallel branches, i is a positive integer less than or equal to n, n is the number of branches, each branch includes M batteries connected in series and in parallel, and M is a positive integer.

[0043] Optionally, the controller is disposed in a centralized control cabinet inside the container, or the controller is disposed in a control room.

[0044] Optionally, n is greater than 20.

[0045] Optionally, M is greater than or equal to 8.

[0046] The method comprises: The controller obtains the total charge and discharge power of the lithium battery pack in the current control cycle and the operating power of the lithium battery pack of each branch in the previous control cycle; Wherein, the total charge and discharge power is the set power of the lithium battery pack in the current control cycle; the operating power of the lithium battery pack in the previous control cycle is the sum of the charge and discharge powers of each branch in the previous control cycle; Adjust the power to be the set power minus the operating power; Distribute the adjusted power to each of the branches. It can be understood that the charge and discharge power of each branch in the previous control period is superimposed with the adjusted power distributed among the branches to obtain the charge and discharge power of each branch in the current control period; The controller controls the charge and discharge of the corresponding branch based on the charge and discharge power of each branch in the current control period; The specific method of distributing the adjusted power to each of the branches is as follows: Set a high charge and discharge rate A1, a nominal charge and discharge rate A2, and a low charge and discharge rate A3; Optionally, A1 > A2 > A3; Optionally, A1 is in the range of 1.2C - 5C, A2 is in the range of 0.8C - 1.2C, and A1 is in the range of 0.1C - 0.8C, where C is the current that can fully charge or discharge the battery in 1 hour; When x belongs to the interval [1, i], the charge and discharge rate C of the branch x is the high charge and discharge rate A1, and the sub-adjusted power HP distributed to the high discharge rate branch x = C x * ; When x belongs to the interval [i, j], the charge and discharge rate C of the branch x is the low charge and discharge rate A3, and the sub-adjusted power LP distributed to the low discharge rate branch x = C x * ; When x belongs to the interval [j, n], the charge and discharge rate C of the branch x is the nominal charge and discharge rate A2, and the sub-adjusted power NP distributed to the nominal discharge rate branch x = C x * ; where 1 < i < j < n, x and j are integers, V xa is the terminal voltage of the a-th battery in the x-th branch, and Vol xa is the remaining capacity of the a-th battery in the x-th branch; The adjusted power = + .

[0047] Optionally, 2(i - 1) < (j - i).

[0048] Optionally, 3(i - 1) < (j - i).

[0049] Optionally, 4(i - 1) < (j - i).

[0050] Optional, 1.2(i-1)<(nj).

[0051] Optional, 1.4(i-1)<(nj).

[0052] Optional, 1.6(i-1)<(nj).

[0053] Optional, 1.8(i-1)<(nj).

[0054] Optional, 2(i-1)<(nj).

[0055] Optional, 3(i-1)<(nj).

[0056] Optional, i<0.05n.

[0057] Optional, i<0.1n.

[0058] Optional, i<0.12n.

[0059] Optional, i<0.14n.

[0060] Optional, i<0.16n.

[0061] Optional, i<0.17n.

[0062] Optional, i<0.18n.

[0063] Optional, i<0.19n.

[0064] Optional, i<0.2n.

[0065] Optional, i<0.25n.

[0066] Optional, i<0.3n.

[0067] Optional, i<0.4n.

[0068] Through the above method steps, on the first hand, the branches with high charging rates of the container lithium battery pack are concentrated on one side to avoid heat accumulation of the entire lithium battery pack, thereby improving the thermal safety of the container lithium battery pack and avoiding overheating or damage or power limitation of the lithium battery pack due to concentrated temperature rise; on the second hand, since the charging rate at the end of the lithium battery pack is large, it is convenient to maintain or replace the battery at the end; on the third hand, since there are controlled differences in the charging rates of multiple adjacent branches, the charging current of each branch is controlled, avoiding the imbalance of charging current between branches caused by excessive charging current of some branches and excessive charging current of some branches; on the fourth hand, by dividing the high charging and discharging rate branches, the nominal charging and discharging rate branches and the low charging and discharging rate branches, the number of high charging and discharging rate branches is reduced, avoiding too many branches from charging and discharging at a high rate at the same time, and improving the overall life of the battery pack.

[0069] Those of ordinary skill in the art will appreciate that the units and algorithm steps of each example described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, computer software, or a combination of the two. In order to clearly illustrate the interchangeability of hardware and software, the composition and steps of each example have been generally described in terms of function in the above description. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professional and technical personnel can use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of the present invention.

[0070] It should be noted that the serial numbers of the embodiments of the present invention are only for description and do not represent the advantages or disadvantages of the embodiments.

[0071] The above are only preferred embodiments of the present invention, and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention specification and drawings, or directly or indirectly applied in other related technical fields, and any combination of embodiments or schemes are also included in the patent protection scope of the present invention.

Claims

1. A lithium battery pack charge and discharge management method, characterized in that: Applicable to an energy storage system including a container lithium battery pack, the lithium battery pack includes i parallel branches, i is a positive integer less than or equal to n, and n is the number of branches; The method comprises: When i changes from 1 to n / 2, the branch charge and discharge rate C i gradually decrease; When i changes from n / 2 to n, the branch charge and discharge rate C i Gradually increasing.

2. The method according to claim 1, characterized in that The output end of the energy storage system is connected to the power grid via a DC / AC inverter; it also includes a photovoltaic or wind energy system, and the output end of the photovoltaic or wind energy system is also connected to the DC side of the DC / AC inverter.

3. The method according to claim 1, characterized in that n is divisible by 4.

4. A lithium battery pack charge and discharge management method, applied to an energy storage system including a controller and a container lithium battery pack, wherein the lithium battery pack comprises i parallel branches, i is a positive integer less than or equal to n, n is the number of branches, and each branch comprises M batteries connected in series and in parallel, M is a positive integer; characterized in that: The method comprises: The controller obtains the total charge and discharge power of the lithium battery pack in the current control cycle and the operating power of the lithium battery pack of each branch in the previous control cycle; Wherein, the total charge and discharge power is the set power of the lithium battery pack in the current control cycle; the operating power of the lithium battery pack in the previous control cycle is the sum of the charge and discharge powers of each branch in the previous control cycle; The adjusted power is the set power minus the operating power; Allocating the adjusted power to each of the branches to obtain the charge and discharge power of each of the branches in the current control cycle; The controller controls the charging and discharging of the corresponding branch based on the charging and discharging power of the current control cycle of each branch.

5. The lithium battery pack charge and discharge management method according to claim 4, characterized in that: The allocation of the adjusted power to each branch is specifically: When i changes from 1 to n / 2, the branch charge and discharge rate C i gradually decrease; When i changes from n / 2 to n, the branch charge and discharge rate C i Gradually increase; The divided adjustment power P allocated to each branch i =C i * , where a is an integer between 1 and M, V ia is the terminal voltage of the ath battery in the ith branch, Vol ia is the remaining capacity of the ath battery in the ith branch; The adjusted power = .

6. The lithium battery pack charge and discharge management method according to claim 4, characterized in that: The output end of the energy storage system is connected to the power grid via a DC / AC inverter, and the output end of the photovoltaic and / or wind energy system is also connected to the DC side of the DC / AC inverter.

7. The lithium battery pack charge and discharge management method according to claim 4, characterized in that: The allocation of the adjusted power to each branch is specifically: Set the high charge and discharge rate A1, the nominal charge and discharge rate A2, and the low charge and discharge rate A3; A1 is 1.2C-5C, A2 is 0.8C-1.2C, A1 is 0.1C-0.8C, C is the current that can fully charge or discharge the battery in 1 hour; When x belongs to the interval [1,i], the branch charge and discharge rate C x For high charge and discharge rate A1, the high discharge rate branch is allocated with the adjusted power HP x =C x * ; When x belongs to the interval [i,j], the branch charge and discharge rate C x For low charge and discharge rate A3, the low discharge rate branch is allocated a divided adjustment power LP x =C x * ; When x belongs to the interval [j,n], the branch charge and discharge rate C x The nominal charge and discharge rate A2, the nominal discharge rate branch distribution power NP x =C x * ; where 1 < i < j < n, x and j are integers, V xa is the terminal voltage of the a-th battery in the x-th branch, Vol xa is the remaining capacity of the a-th battery in the x-th branch; The adjusted power = + .

8. The lithium battery pack charge and discharge management method according to claim 7, characterized in that: A1>A2>A3.

9. The lithium battery pack charge and discharge management method according to claim 7, characterized in that: 2(i-1)<(ji).

10. The method according to claim 7, characterized in that 1.6(i-1)<(nj).

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