Optical storage grid-connected and off-grid system cluster SOC balance control method

Abstract

The invention discloses an optical storage grid-connected and off-grid system cluster SOC (state of charge) equalization control method, which comprises the following steps: in a grid-connected mode, realizing active SOC equalization among subsystems through closed-loop control of charge and discharge power of a power grid; the active SOC equalization comprises a charging mode, a discharging mode and a standby mode; in the charging mode, executing balance control of less charging of the high-SOC subsystem; under the discharging mode, multi-discharging balance control of the high-SOC subsystem is executed; and under the standby mode, performing hedging active equalization control by using photovoltaic energy. Therefore, under the condition of high photovoltaic utilization rate, subsystem SOC balance management is realized.

Description

Technical Field

[0001] The present invention relates to the field of photovoltaic energy storage systems, and particularly to a method for SOC balancing control of a photovoltaic energy storage parallel and off-grid system cluster. Background Art

[0002] With the increasingly wide application of energy storage, the capacity of energy storage system clusters is also getting larger. Currently, there are mainly two methods: string type and centralized type. Among them, the string type energy storage system adopts the method of one cluster one management and AC coupling, which avoids battery parallel connection, has no BMS inter-cluster management, and is easier to achieve energy control, battery health management, safety monitoring, etc., with obvious advantages. The photovoltaic energy storage parallel and off-grid system combining energy storage and photovoltaic has a wide range of application scenarios. And the photovoltaic utilization rate of DC coupling of photovoltaic is 4% higher than that of AC coupling. In contrast, the photovoltaic energy storage parallel and off-grid system with DC coupling has better efficiency. However, in the actual application process of the optical cluster (DC coupling) parallel and off-grid system cluster, the following problems currently exist: 1. In an energy storage system cluster, the photovoltaic capacity configurations of each subsystem (photovoltaic energy storage system) are inconsistent. 2. Due to the AC coupling between energy storage subsystems, there is inevitably a SOC difference between each subsystem during operation. When switching from grid-connected operation to off-grid operation, due to the short board effect, the available discharge energy of the overall energy storage system will be reduced. 3. Currently, during the operation of the photovoltaic energy storage system cluster, the EMS only relies on the charge and discharge strategy and photovoltaic utilization rate, lacking research on the SOC balancing strategy for each subsystem under different operation modes. Summary of the Invention

[0003] In view of this, the purpose of the present invention is to provide a method for SOC balancing control of a photovoltaic energy storage parallel and off-grid system cluster, which realizes the SOC balancing management of subsystems under the condition of high photovoltaic utilization rate.

[0004] According to one aspect of the present invention, a method for SOC balancing control of a photovoltaic energy storage parallel and off-grid system cluster is provided, including: in the grid-connected mode, through the closed-loop control of the grid charge and discharge power, realizing the active SOC balance between each subsystem; the active SOC balance includes a charging mode, a discharging mode, and a standby mode; in the charging mode, implementing the balancing control of less charging for the high-SOC subsystem; in the discharging mode, implementing the balancing control of more discharging for the high-SOC subsystem; in the standby mode, using photovoltaic energy for hedging active balancing control.

[0005] Optionally, the control method in the charging mode includes the following steps:

[0006] Calculating the average charging power PrC of the subsystem according to the expected total charging power;

[0007] Calculating the available capacity rate of the system according to the average charging power PrC of the subsystem, and performing charging active balancing control when the available capacity rate of the system is less than 0.9;

[0008] The charging active equalization control includes calculating the average SOC of the subsystems, determining whether the SOC of each subsystem is greater than the average SOC of the subsystems, and for the subsystems with SOC greater than the average SOC of the subsystems, executing the charging power Pcn = SOC min / SOC t *(PrC - PVn); for the subsystems with SOC less than the average SOC of the subsystems, executing the charging power Pcn = PrC - PVn;

[0009] where SOC min is the minimum value of SOC in each subsystem; n is the number of subsystems; SOC t is the total SOC of the system; PVn is the photovoltaic power.

[0010] Optionally, the equalization control method in the charging mode further includes when the available capacity rate of the system is greater than 0.9, continuing to determine whether the average charging power PrC of the subsystems is greater than or equal to the photovoltaic power PVn, and for the subsystems with the average charging power PrC of the subsystems greater than or equal to the photovoltaic power PVn, executing the charging power Pcn = PrC - PVn; for the subsystems with the average charging power PrC of the subsystems less than the photovoltaic power PVn, executing the charging power Pcn = 0.

[0011] Optionally, the control method in the discharging mode includes the following steps:

[0012] When the available capacity rate of the system is less than 0.9, perform discharging active equalization control;

[0013] The discharging active equalization control includes calculating the average SOC of the subsystems, and determining whether the SOC of each subsystem is greater than the average SOC of the subsystems, and for the subsystems with SOC greater than the average SOC of the subsystems, executing the discharging power Pdn = Pmax; for the subsystems with SOC less than the average SOC of the subsystems, executing the discharging power Pdn = (PD - Pmax * m) / (n - m);

[0014] where PD is the expected total discharging power; Pmax is the maximum discharging power; m is the number of subsystems with SOC greater than the average SOC; n is the number of subsystems.

[0015] Optionally, the equalization control method in the discharging mode further includes when the available capacity rate of the system is greater than 0.9, executing the discharging power Pdn = PrD for each subsystem; where PrD is the average discharging power of the subsystems.

[0016] Optionally, the control method in the standby mode includes the following steps:

[0017] When the available capacity rate of the system is less than 0.9 and there is photovoltaic power access, it is judged whether the photovoltaic power PVx of the minimum SOC subsystem is less than the expected charging power PCx of the minimum SOC subsystem. If so, the hedging active equalization control is executed.

[0018] The hedging active equalization control includes discharging the subsystem with the maximum SOC, and the discharging power is Pdy = PCx - PVx - Pdn; charging the subsystem with the minimum SOC, and the charging power is Pcx = PCx - PVx; for other subsystems, when their photovoltaic power PVn is greater than the expected charging power PCn, they are discharged, and the discharging power is Pdn = PVn - PCn.

[0019] Wherein, PCn is the expected charging power of other subsystems; PVn is the photovoltaic power of other subsystems.

[0020] Compared with the prior art, the present invention can realize the SOC equalization management of subsystems under the condition of high photovoltaic utilization rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0022] Figure 1 : Overall control strategy;

[0023] Figure 2 : Flowchart of the control method in the charging mode;

[0024] Figure 3 : Flowchart of the control method in the discharging mode;

[0025] Figure 4 : Flowchart of the control method in the standby mode; DETAILED DESCRIPTION OF THE INVENTION

[0026] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0027] Figure 1 Illustrates an overall control strategy provided by an embodiment of the present invention, as Figure 1As shown, in the grid-connected mode, through the closed-loop control of the grid charge-discharge power, the active SOC balance among subsystems is achieved; the active SOC balance includes a charging mode, a discharging mode, and a standby mode; in the charging mode, an equalization control of less charging for subsystems with high SOC is executed; in the discharging mode, an equalization control of more discharging for subsystems with high SOC is executed; in the standby mode, the photovoltaic energy is used for hedging active equalization control. In the off-grid mode, the energy storage system acts as a voltage source and cannot independently adjust the output power, so no equalization management is performed.

[0028] Figure 2 The flowchart of the control method in the charging mode is shown, as Figure 2 shown, in the charging mode, the DC-side charging power value is ensured. Photovoltaic power is preferentially used for equalization and then for energy storage. When SOC < 100%, no photovoltaic power is abandoned. Subsystems with high SOC charge less; the specific control method includes the following steps: according to the expected total charging power, calculate the average charging power PrC of the subsystems; according to the average charging power PrC of the subsystems, calculate the available capacity rate of the system, and when the available capacity rate of the system is less than 0.9, perform charging active equalization control; the charging active equalization control includes calculating the average SOC of the subsystems and judging whether the SOC of each subsystem is greater than the average SOC of the subsystems, and for the subsystems with SOC greater than the average SOC of the subsystems, execute the charging power Pcn = SOC min / SOC t *(PrC - PVn); for the subsystems with SOC less than the average SOC of the subsystems, execute the charging power Pcn = PrC - PVn; where, SOC min is the minimum value of SOC in each subsystem; n is the number of subsystems; SOC t is the total SOC of the system; PVn is the photovoltaic power.

[0029] Furthermore, when the available capacity rate of the system is greater than 0.9, continue to judge whether the average charging power PrC of the subsystems is greater than or equal to the photovoltaic power PVn. For the subsystems with the average charging power PrC greater than or equal to the photovoltaic power PVn, execute the charging power Pcn = PrC - PVn; for the subsystems with the average charging power PrC less than the photovoltaic power PVn, execute the charging power Pcn = 0.

[0030] Figure 3 The flowchart of the control method in the discharging mode is shown, as Figure 3As shown, in the discharge mode, the AC-side discharge power value is ensured. Photovoltaic power is preferentially used for balancing and then for discharging. When the SOC < 100%, light is not abandoned. High-SOC systems discharge more, and low-SOC systems discharge less. The specific control method includes the following steps: When the available capacity rate of the system is less than 0.9, active discharge balancing control is performed; the active discharge balancing control includes calculating the average SOC of the subsystems and determining whether the SOC of each subsystem is greater than the average SOC of the subsystem. For the subsystems with SOC greater than the average SOC of the subsystem, the discharge power Pdn = Pmax is executed; for the subsystems with SOC less than the average SOC of the subsystem, the discharge power Pdn = (PD - Pmax*m) / (n - m) is executed; where PD is the expected total discharge power; Pmax is the maximum discharge power; m is the number of subsystems with SOC greater than the average SOC; n is the number of subsystems.

[0031] Furthermore, when the available capacity rate of the system is greater than 0.9, the discharge power Pdn = PrD is executed for each subsystem; where PrD is the average discharge power of the subsystem.

[0032] Figure 4 The flowchart of the control method in the standby mode is shown, as Figure 4 As shown, in the standby mode, the charging power and the discharge power are balanced. Photovoltaic power is preferentially used for balancing and then for energy storage. When the SOC < 100%, light is not abandoned. The photovoltaic energy is used for hedging. The specific control method includes the following steps: When the available capacity rate of the system is less than 0.9 and there is photovoltaic access, it is determined whether the photovoltaic power PVx of the subsystem with the minimum SOC is less than the expected charging power PCx of the subsystem with the minimum SOC. If so, the hedging active balancing control is executed; the hedging active balancing control includes discharging the subsystem with the maximum SOC, and the discharge power is Pdy = PCx - PVx - Pdn; charging the subsystem with the minimum SOC, and the charging power is Pcx = PCx - PVx; for other subsystems, when their photovoltaic power PVn is greater than the expected charging power PCn, they discharge, and the discharge power is Pdn = PVn - PCn; where Pdn is the discharge power of other subsystems; PCn is the expected charging power of other subsystems; PVn is the photovoltaic power of other subsystems.

[0033] It should be clear that the present application is not limited to the specific configurations and processes described above and shown in the figures. For the sake of brevity, the detailed description of known methods is omitted here. In the above embodiments, several specific steps are described and shown as examples. However, the method process of the present application is not limited to the specific steps described and shown. Those skilled in the art can make various changes, modifications, and additions, or change the order between the steps after understanding the spirit of the present application.

[0034] The functional blocks shown in the above-described structural block diagrams can be implemented as hardware, software, firmware, or a combination thereof. When implemented in hardware, it can be, for example, an electronic circuit, an application specific integrated circuit (ASIC), appropriate firmware, a plug-in, a functional card, and so on. When implemented in software, the elements of the present application are programs or code segments for performing the required tasks. The program or code segment can be stored in a machine-readable medium or transmitted via a data signal carried in a carrier wave over a transmission medium or a communication link. A "machine-readable medium" can include any medium that can store or transmit information. Examples of machine-readable media include electronic circuits, semiconductor memory devices, ROM, flash memory, erasable read only memory (EROM), floppy disks, compact disc read-only memory (CD-ROM), optical discs, hard disks, fiber optic media, radio frequency (RF) links, and so on. The code segment can be downloaded via a computer network such as the Internet, an intranet, and so on.

[0035] It should also be noted that the exemplary embodiments mentioned in the present application describe some methods or systems based on a series of steps or devices. However, the present application is not limited to the order of the above steps, that is, the steps can be executed in the order mentioned in the embodiments, or different from the order in the embodiments, or several steps can be executed simultaneously.

[0036] It should be understood that the protection scope of the present application is not limited thereto. Any person skilled in the art within the technical scope disclosed in the present application can easily think of various equivalent modifications or substitutions, and these modifications or substitutions should be covered within the protection scope of the present application.

Claims

1. A method for balancing the SOC of a photovoltaic and off-grid energy storage system cluster, characterized in that: include: In grid-connected mode, active SOC balancing is performed on each subsystem; The active SOC balancing includes active SOC balancing in charging mode, discharging mode and standby mode; In the charging mode, a balancing control method for less charging of the high SOC subsystem is executed; in the discharging mode, a balancing control method for more discharging of the high SOC subsystem is executed; In the standby mode, a balancing control method for hedging using photovoltaic energy is executed.

2. The method according to claim 1, characterized in that The equalization control method in the charging mode comprises the following steps: According to the expected total charging power, calculate the average charging power PrC of the subsystem; Calculate the system available capacity rate according to the subsystem average charging power PrC, and perform active charging balancing control when the system available capacity rate is less than 0.9; The active charging balancing control includes calculating the average SOC of the subsystems, and determining whether the SOC of each subsystem is greater than the average SOC of the subsystems, and executing the charging power Pcn=SOC for the subsystems whose SOC is greater than the average SOC of the subsystems. min / SOC t *(PrC-PVn); for a subsystem whose SOC is less than the average SOC of the subsystem, the charging power Pcn=PrC-PVn is executed; Among them, SOC min is the minimum value of SOC in each subsystem; n is the number of subsystems; SOC t is the total SOC of the system; PVn is the photovoltaic power.

3. The method according to claim 2, characterized in that The balancing control method under the charging mode also includes, when the system available capacity rate is greater than 0.9, continuing to judge whether the subsystem average charging power PrC is greater than or equal to the photovoltaic power PVn, and executing the charging power Pcn=PrC-PVn for the subsystem whose average charging power PrC is greater than or equal to the photovoltaic power PVn; and executing the charging power Pcn=0 for the subsystem whose average charging power PrC is less than the photovoltaic power PVn.

4. The method according to claim 2, characterized in that: The balance control method in the discharge mode comprises the following steps: When the available capacity rate of the system is less than 0.9, active discharge balancing control is performed; The active discharge balancing control includes calculating the average SOC of the subsystems, and judging whether the SOC of each subsystem is greater than the average SOC of the subsystems, and executing the discharge power Pdn=Pmax for the subsystems whose SOC is greater than the average SOC of the subsystems; and executing the discharge power Pdn=(PD-Pmax*m) / (nm) for the subsystems whose SOC is less than the average SOC of the subsystems; Wherein, PD is the expected total discharge power; Pmax is the maximum discharge power; m is the number of subsystems whose SOC is greater than the average SOC; and n is the number of subsystems.

5. The method according to claim 4, characterized in that The balancing control method in the discharge mode also includes executing a discharge power Pdn=PrD on each subsystem when the system available capacity rate is greater than 0.9; wherein PrD is an average discharge power of the subsystem.

6. The method according to claim 2, characterized in that The balance control method in the standby mode comprises the following steps: When the available capacity rate of the system is less than 0.9 and there is photovoltaic access, it is determined whether the photovoltaic power PVx of the minimum SOC subsystem is less than the expected charging power PCx ​​of the minimum SOC subsystem. If so, hedging active balancing control is performed; The hedging active balancing control includes discharging the subsystem with the largest SOC, and the discharge power is Pdy=PCx-PVx-Pdn; charging the subsystem with the smallest SOC, and the charging power is Pcx=PCx-PVx; in other subsystems, when the photovoltaic power PVn is greater than the expected charging power PCn, discharging is performed, and the discharge power is Pdn=PVn-PCn; Among them, PCn is the expected charging power of other subsystems; PVn is the photovoltaic power of other subsystems.

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