Method for shutdown discharge of all-vanadium redox flow battery system

Abstract

The invention discloses a shutdown discharge method for an all-vanadium redox flow battery system. The all-vanadium redox flow battery system comprises an all-vanadium redox flow battery, a battery management system and an energy storage converter, the all-vanadium redox flow battery comprises a galvanic pile, an electrolyte, an electrolyte circulating pump and positive and negative storage tanks, the battery management system and the energy storage converter are independently and electrically connected with the all-vanadium redox flow battery; the battery management system is in communication connection with the energy storage converter through a communication protocol; after the all-vanadium redox flow battery system is shut down, when the SOC value of the all-vanadium redox flow battery is smaller than SOC3, shutdown discharging is not needed; and when the SOC value of the all-vanadium redox flow battery is greater than or equal to SOC3, the battery management system issues a discharging instruction to control the energy storage converter to discharge at constant power until the voltage of the all-vanadium redox flow battery is reduced to cut-off voltage V, and the battery management system issues a discharging stopping instruction to control the energy storage converter to stop discharging.

Description

Technical Field

[0001] The present application relates to a method for shutdown discharge of a vanadium redox flow battery system, belonging to the technical field of electrochemical energy storage. Background Art

[0002] The vanadium redox flow battery has the advantages of flexible design (complete decoupling of power and capacity), long service life, free site selection, safety, environmental protection, high residual value, and controllable resources, and is mainly applicable to large-scale and medium- to long-term energy storage scenarios.

[0003] There is a large amount of pipeline and electrolyte inside the vanadium redox flow battery system. After the battery system shuts down, a certain amount of electrolyte will inevitably remain in the stack, and the leakage current formed is converted into heat, resulting in an increase in the electrolyte temperature. When the flow battery system shuts down while being charged, the remaining electrical energy in the stack will be released in the form of leakage. At this time, the electrolyte no longer flows, causing the stack temperature to rise rapidly. Once the temperature exceeds the tolerance range of the stack material, it will inevitably cause irreversible damage to the stack material and then burn out the stack. Therefore, dealing with the energy in the stack during the shutdown of the flow battery system is a key technology for protecting the stack and extending the battery life.

[0004] The current treatment method is to make the height of the stack higher than the liquid level of the liquid storage tank. After the electrolyte pump of the battery system stops running, the liquid in the stack flows back into the liquid storage tank due to gravity. At this time, there is almost very little remaining electrolyte in the stack. The above method has a certain effect, but there are also deficiencies. The stack needs to be placed at a high position, which makes the stack maintenance difficult in the later stage of the project, and there are high requirements for the height space, making it very difficult to implement in actual projects. Another feasible solution is to avoid the problem that the remaining liquid forms a closed loop in the stack, and under the action of the stack voltage, a large leakage current in the stack generates a large amount of heat in a short time, causing destructive ablation of the stack component materials. After the battery system stops, it is necessary to release the electrical energy in the stack back to the power grid. At this time, if the series-connected stack discharges at a low power, the discharge time will be long, which will have a certain impact on the utilization rate of the energy storage system. If the series-connected stack discharges at a high power during shutdown, although the discharge time is short, multiple energy storage systems discharging at a high power simultaneously will have a greater impact on the power grid power flow distribution, and the electrical energy of the stack cannot be completely discharged, which also has a certain impact on the life of the stack. Therefore, it is particularly important to adjust the stack discharge power and discharge cut-off voltage according to the state of charge of the battery after shutdown, and to control the shutdown discharge duration of the battery system and the discharge depth of the stack. Summary of the Invention

[0005] According to one aspect of the present application, a method for shutdown discharge of a vanadium redox flow battery system is provided. Aiming at the phenomenon that "after the battery system shuts down, since a part of the electrolyte remains in the battery stack, if the state of charge (SOC) value of the battery is high at this time, the remaining liquid forms a closed loop in the stack, and under the action of the stack voltage, the leakage current in the stack is large, and a large amount of heat is generated by the current in a short time, causing destructive ablation of the constituent materials of the stack", the problem of heat generation of the residual electrolyte in the stack, which affects the power flow distribution of the energy storage system when the shutdown discharge time is too long and affects the stack life when the discharge time is too short, is solved.

[0006] The present application adopts the following technical solutions:

[0007] A method for shutdown discharge of a vanadium redox flow battery system, the vanadium redox flow battery system includes a vanadium redox flow battery, a battery management system, and an energy storage converter;

[0008] The vanadium redox flow battery includes a stack, an electrolyte, an electrolyte circulation pump, and positive and negative electrode storage tanks;

[0009] The battery management system and the energy storage converter are independently electrically connected to the vanadium redox flow battery;

[0010] The battery management system is communicatively connected to the energy storage converter through the Modbus_TCP communication protocol;

[0011] After the vanadium redox flow battery system shuts down and the electrolyte circulation pump stops running, when the SOC value of the vanadium redox flow battery is less than SOC 3 , there is no need for shutdown discharge; when the SOC value of the vanadium redox flow battery is greater than or equal to SOC 3 , the battery management system issues a discharge command to control the energy storage converter to discharge at a constant power until the voltage of the vanadium redox flow battery drops to the cut-off voltage V, and then the battery management system issues a stop discharge command to control the energy storage converter to stop discharging;

[0012] Among them, SOC 3 is 0 to 20%, the discharge power is set to Pdischarge, and the value of Pdischarge is less than the rated power P of the vanadium redox flow battery N .

[0013] The battery management system collects the battery voltage, charge and discharge current, and real-time detects the SOC of the battery, and controls the start and stop of the electrolyte circulation pump and the charge and discharge of the energy storage converter, etc. When the electrolyte pump of the battery system stops circulating, at this time the battery management system detects the SOC of the battery, and according to the size of the battery SOC at this time, controls the discharge power of the energy storage converter and the battery discharge cut-off voltage. The cut-off voltage V is 0.5 to 1n, where n is the total number of battery series connections.

[0014] In this application, the SOC value is calculated by the battery management system provided by the battery manufacturer.

[0015] After the all-vanadium liquid flow battery system is shut down, when SOC 3 ≤SOC<SOC 2 When Pdischarge>P N / 2, where SOC 2 20-75%;

[0016] When SOC 2 ≤SOC<SOC 1 When P N / 3<Pdischarge≤P N / 2, where SOC 1 75-100%;

[0017] When SOC ≥ SOC 1 When Pdischarge≤P N / 3.

[0018] Optionally, the battery management system includes: a central processing unit, a data acquisition and storage module, a voltage, current, flow, pressure, temperature and other transmission modules, a charging protection module, a discharging protection module, a single-cell protection module, an HMI display module, an RJ45 and a wireless communication module.

[0019] The battery management system is a collection of electronic devices used to monitor, evaluate and protect the operating status of the battery, including: monitoring and transmitting the operating status information of the battery system, such as battery voltage, current, electrolyte temperature and protection amount, evaluating and calculating the battery's state of charge SOC, and protecting the safety of the battery system.

[0020] The battery management system can achieve the following functions:

[0021] Limit setting of operating parameters of all-vanadium liquid flow battery system: The operating parameter limits can be set on the display interface of the battery management system. The battery management system can also complete real-time monitoring of the operating status of the battery system, as follows:

[0022] ①Analog measurement function: It can measure battery string voltage, charge and discharge current, temperature and other parameters in real time. The battery management system can optimize and correct analog measurement to meet the requirements of battery safety, reliability, stable operation and service life.

[0023] ②Battery management system alarm function: When a battery system fails, it can display and upload various fault information.

[0024] ③ Battery management system protection function: When the battery system is running, if abnormalities occur in battery voltage, current, temperature, etc., the battery management system can upload fault information through communication with a third party.

[0025] ④ Self-diagnosis function: The battery management system has a self-diagnosis function. It self-diagnoses the internal and external communication status of the battery management system, whether the analog quantity acquisition and control functions are normal, etc.

[0026] ⑤ Operating status display function: The battery management system can display various operating data and working status of the battery system, such as various analog quantities, alarm and protection information, etc.

[0027] Optionally, the all-vanadium redox flow battery includes at least 1 battery pack and a battery management system and an energy storage converter that match its quantity.

[0028] Optionally, the battery pack includes 1 stack or at least 2 series-connected stacks.

[0029] Optionally, the all-vanadium redox flow battery system further includes 1 local monitoring system and 1 energy management system;

[0030] The energy management system is electrically connected to the local monitoring system;

[0031] The local monitoring system is electrically connected to the battery management system.

[0032] The beneficial effects that this application can produce include:

[0033] The method for shutdown and discharge of the all-vanadium redox flow battery system provided by this application can improve the energy efficiency of the all-vanadium redox flow battery system and extend the service life of the battery stack. Description of the Drawings

[0034] Figure 1 Schematic diagram of the control architecture of the energy system including the all-vanadium redox flow battery system in the embodiment of this application

[0035] Figure 2 Schematic diagram of the functions of the battery management system in the embodiment of this application.

[0036] Figure 3 Flow chart of the shutdown and discharge of the all-vanadium redox flow battery system in the embodiment of this application. Detailed Description of the Embodiments

[0037] The following describes this application in detail with reference to the embodiments, but this application is not limited to these embodiments.

[0038] Unless otherwise specified, the raw materials in the embodiments of this application are all purchased through commercial channels.

[0039] Embodiment 1

[0040] The schematic diagram of the energy system control architecture including a vanadium redox flow battery system is as follows Figure 1 As shown, the energy management system is the overall dispatcher of the energy storage system. It issues active power and reactive power commands to the local monitoring system according to external demands. The local monitoring system distributes the total power based on the total power demand of the energy management system and the status of each battery system, and issues it to each battery management system. Each set of battery management controls the charging power and discharging power of the energy storage converter, charging or discharging commands, starting or stopping commands of the energy storage converter, etc. At the same time, the important parameters of the energy storage converter and the important operation data of each battery system also need to be uploaded to the energy management system through the local monitoring system.

[0041] Among them, each vanadium redox flow battery system has a rated power of 250 kW and is composed of 8 stacks in series. The system DC voltage range is 0 - 750 V, and the maximum working current is 650 A. The battery management system collects parameters such as the total voltage, total current, pipeline flow rate, pressure, positive and negative electrolyte temperatures, positive and negative storage tank liquid levels, and voltage of each stack, open circuit voltage, etc. The battery management system communicates with the energy storage converter through the Modbus_TCP communication protocol. The battery management system acts as the client station, and the energy storage converter acts as the server station.

[0042] The method for the vanadium redox flow battery system to stop and discharge is as follows: When the battery system stops, if the SOC of the battery system > 75%, the battery management system issues a stop and discharge command to the energy storage converter with a discharge power of 60 kW, and controls the energy storage converter to discharge. When the total battery voltage drops to 320 V, stop the stop and discharge operation. If 50% < SOC < 75% at this time, the battery management system issues a stop and discharge command to the energy storage converter with a discharge power of 100 kW, and controls the energy storage converter to discharge. When the total battery voltage drops to 400 V, stop the stop and discharge operation. If 20% < SOC < 55% at this time, the battery management system issues a stop and discharge command to the energy storage converter with a discharge power of 250 kW, and controls the energy storage converter to discharge. When the total battery voltage drops to 450 V, stop the stop and discharge operation. If the SOC of the battery < 20% at this time, the battery energy storage system does not need to stop and discharge.

[0043] The above are only several embodiments of the present application and do not impose any form of limitation on the present application. Although the present application is disclosed as above with preferred embodiments, it is not intended to limit the present application. Any person skilled in the art, without departing from the scope of the technical solution of the present application, makes some changes or modifications using the disclosed technical content, which are equivalent to equivalent implementation cases and all fall within the scope of the technical solution.

Claims

1. A method for discharging a vanadium liquid flow battery system during shutdown. It is characterized in that The all-vanadium liquid flow battery system includes an all-vanadium liquid flow battery, a battery management system, and an energy storage converter; The all-vanadium liquid flow battery comprises a battery stack, an electrolyte, an electrolyte circulation pump, and positive and negative electrode storage tanks; The battery management system and the energy storage converter are independently and electrically connected to the all-vanadium liquid flow battery; The battery management system is connected to the energy storage converter via the Modbus_TCP communication protocol; When the all-vanadium redox flow battery system shuts down and the electrolyte circulation pump stops running, when the SOC value of the all-vanadium redox flow battery is less than SOC 3 , there is no need to shut down and discharge; when the SOC value of the all-vanadium redox flow battery is greater than or equal to SOC 3 , the battery management system issues a discharge command to control the energy storage converter to discharge at a constant power until the voltage of the all-vanadium redox flow battery drops to the cut-off voltage V, and then the battery management system issues a stop discharge command to control the energy storage converter to stop discharging; Among them, SOC 3 is 0 to 20%, the power of discharging is set as Pdischarge, and the value of Pdischarge is less than the rated power P of the all-vanadium redox flow battery N .

2. The method according to claim 1, It is characterized in that After the all-vanadium redox flow battery system shuts down, when SOC 3 ≤SOC<SOC 2 , Pdischarge>P N / 2, where SOC 2 is 20 to 75%; When the SOC 2 ≤SOC < SOC 1 When, P N / 3 < Pdischarge ≤ P N / 2, where SOC 1 is 75 to 100%; When SOC ≥ SOC 1 , Pdischarge ≤ P N / 3.

3. The method according to claim 2, It is characterized in that V1 <V2<V3。 4. The method according to claim 1, It is characterized in that The structure of the battery management system includes: a central processing unit, a data acquisition and storage module, a voltage, current, flow, pressure, temperature and other transmission modules, a charging protection module, a discharging protection module, a single-cell protection module, an HMI display module, an RJ45 and a wireless communication module.

5. The method according to claim 1, It is characterized in that The all-vanadium liquid flow battery comprises at least one battery group and a battery management system and an energy storage converter matching the number of battery groups.

6. The method according to claim 5, It is characterized in that The battery pack includes one battery stack or at least two battery stacks connected in series.

7. The method according to claim 5, It is characterized in that The all-vanadium liquid flow battery system also includes an on-site monitoring system and an energy management system; The energy management system is electrically connected to the local monitoring system; The local monitoring system is electrically connected to the battery management system.

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