Method for operating a battery energy storage system

Abstract

The invention relates to a method for operating a battery energy storage system, wherein the battery energy storage system is formed from a plurality of battery modules, wherein, in a first operating phase, the battery energy storage system is used to output energy and is recharged after an energy output, wherein the first operating phase is ended as soon as an end-of-life criterion is reached, wherein the battery energy storage system has residual energy after the first operating phase, wherein, in a second operating phase, the residual energy present in the battery energy storage system is used to output energy, wherein the energy is output in the same manner as in the first operating phase.

Description

[0001] Description

[0002] Method for operating a battery energy storage system

[0003] The invention relates to a method for operating a battery energy storage system (BESS), wherein the battery energy storage system is formed from a plurality of battery modules, wherein in a first operating phase the battery energy storage system is used to release energy and to be recharged after an energy release, wherein the first operating phase is terminated as soon as an EoL criterion is reached, wherein the battery energy storage system has residual energy after the first operating phase.

[0004] The invention further relates to a battery energy storage system.

[0005] Battery energy storage systems (BESS) are becoming increasingly important in electrical power systems. This is becoming even more important as the integration of fluctuating renewable energy sources such as solar and wind power increases. When generating electricity, it is important to consider that these renewable sources fluctuate over time. With the ability to supply or absorb large amounts of power in milliseconds, batteries are indeed very well suited for controlling or limiting the ramp rate, as well as for frequency regulation, load balancing, etc. However, since energy capacity remains an important cost factor, it is crucial to correctly size the battery or battery capacity for the application.

[0006] Grid-scale battery energy storage systems (BESS) typically consist of multiple battery modules operating or interconnected in parallel or series. During normal BESS operation, a possible difference in the charging and / or discharging of different BESS units can lead to an imbalance between them; i.e., they would have different states of charge (SoCs). State of charge imbalance can also occur if a BESS or a series of BESSs are disconnected and then reconnected, e.g., due to a fault or normal maintenance.

[0007] Battery modules usually contain lithium-ion cells. Lithium-ion cells made with a liquid or solid electrolyte, or conventional lithium-ion batteries made as solid-state batteries, reach the end of their lifespan after a certain period of cyclical and calendar stress, which is often referred to as the End of Life (EoL). The lithium-ion cells are assembled into the battery module using either serial or parallel wiring. This type of wiring is used to increase the voltage, on the one hand, and to increase the maximum current, on the other. Battery modules made of this type are used within a large stationary energy storage system. In this case, however, serial wiring is usually used to increase the overall voltage.

[0008] The service life of a lithium-ion cell is determined after a certain period of use or after a certain period of use during cyclic loading. Once the lithium-ion cell or battery module reaches the end of its service life, an initial operating phase is completed. However, the battery module may still have residual energy.

[0009] Currently, lithium-ion cells are recycled when they reach their end of life after a certain calendar and cyclical load. However, lithium-ion batteries must be electrically discharged before further recycling to ensure operational and process reliability. It is important that the total cell voltage of a battery module is 0V. The residual energy otherwise contained could be released during mechanical recycling, which is carried out by shredding and direct recycling, and cause damage to the system and, in the worst case, even pose a danger to people. Furthermore, the residual energy should be used for reasons of sustainability.

[0010] The steps described below are usually carried out by a battery module recycler. Since the battery recycler usually has no information about the battery module, the polarity of the battery module poles is determined in a first step. In a second step, the battery module voltage is measured using a multimeter in order to determine the current state of charge of the battery module. The discharge current and the discharge time are then defined. In a further step, the battery module is connected to an electronic load using a specifically adapted connector and discharged. This step is usually carried out manually. With newer discharge test benches, this is partially automated.

[0011] In the next step, the battery module is discharged to a final module voltage of 0V using an electronic load. However, due to electrochemical processes inside the cell, considerable heat is generated during discharge to a battery voltage of 0V. To avoid excessive stress on the cells during this stage, the battery module temperature is monitored using temperature measurements or a thermal imaging camera mounted above the battery module to be discharged.

[0012] As soon as a final module voltage of 0V is measured at the terminals of the cell module, the discharge process is terminated by the electronic load. However, it is possible that the battery module voltage would relax after the electronic load was removed. Therefore, a short-circuit bridge must be attached to the cell module. This ensures that the battery module voltage cannot relax during storage until the battery module is actually recycled. In a further step, the external short-circuit bridge is removed before it is sent for final recycling, and the module is sent to a shredding process, etc.

[0013] The disadvantage of this approach is that the entire process must be monitored, which can lead to high personnel costs. Furthermore, the energy still stored in a battery module is essentially made available to the recycling plant operator free of charge during discharge. A single battery module may still have several kWh of residual energy stored, which is not financially considered by the BESS operator. Furthermore, specific adapters must be available to short-circuit the battery module after discharge.

[0014] It is therefore desirable to provide a better method for this purpose .

[0015] This is where the invention comes in, the object of which is to provide a method that is cost-effective and safe.

[0016] This object is achieved by a method for operating a battery energy storage system, wherein the battery energy storage system is formed from a plurality of battery modules, wherein in a first operating phase the battery energy storage system is used to release energy and to be recharged or to absorb energy again after an energy release, wherein the first operating phase is ended as soon as an EoL criterion is reached, wherein the battery energy storage system has residual energy and residual capacity after the first operating phase, wherein in a second operating phase the residual energy present in the battery energy storage system is used to release energy, wherein the energy is released as in the first operating phase.

[0017] The object is also achieved by a battery energy storage system comprising a plurality of battery modules, wherein the energy storage system is designed to carry out the method according to the invention.

[0018] The new process is more cost-effective, more resource-efficient, safer, simpler and easier to use.

[0019] The invention is based on the idea of ​​still utilising the residual energy in the individual battery modules. The deep discharge of the battery module in a BESS is initiated with the aid of a software function. According to the invention, it is not necessary to remove the battery module because the battery module is properly cooled during discharge. If the system or individual battery modules reach their EoL criterion, the operator of the system can automatically discharge or deep discharge the respective battery module. This is done, for example, by pressing a button, entering an input on a control panel, entering a command, a HW bridge or similar. No electronic load is used for this discharge; instead, the infrastructure already provided by the BESS is used in the form of an inverter.This means that the residual electrical energy in the battery module is fed into the power grid with the help of the inverter and paid to the operator.

[0020] Temperature monitoring during the discharge of residual energy is carried out using the temperature sensors already installed in the battery module. Therefore, additional temperature monitoring is not required.

[0021] According to the invention, the discharge process is carried out until a cell voltage or module voltage of 0V is reached. As soon as 0V is reached, the two battery module poles are short-circuited. This short circuit is carried out using an internal short-circuit circuit on the BMS PCB. This bridge can be triggered either manually (setting a jumper) or via software. A design of this bridge for a high current or a high short-circuit power does not have to be taken into account, since the module is short-circuited as soon as a residual voltage of 0.00V is reached. This means that the switching is carried out by a circuit internally mapped on the BMS PCB.

[0022] Advantageous further developments are specified in the subclaims.

[0023] In the following, an embodiment of the invention is explained in more detail with reference to the following figures.

[0024] The above-described properties, features and advantages of this invention, as well as the manner in which they are achieved, will become clearer and more clearly understood in connection with the following description of the embodiments, which are explained in more detail in connection with the drawings.

[0025] Identical components or components with the same function are marked with the same reference symbols.

[0026] Exemplary embodiments of the invention are described below with reference to the drawings. These are not intended to represent the exemplary embodiments to scale; rather, where useful for explanation, the drawings are presented in a schematic and / or slightly distorted form. For supplements to the teachings immediately apparent in the drawings, reference is made to the relevant prior art.

[0027] FIG 1 shows a flow diagram of the method according to the invention

[0028] FIG 2 schematic representation of a conventional battery arrangement

[0029] FIG 3 schematic representation of a battery arrangement according to the invention in normal operation

[0030] FIG 4 schematic representation of the battery arrangement according to the invention in a so-called recycling mode.

[0031] Figure 1 shows a flow chart of the method according to the invention.

[0032] Grid-scale battery energy storage systems (BESS) typically consist of multiple battery modules operating in parallel or series. The battery modules include lithium-ion cells constructed with liquid or solid electrolytes, or conventional lithium-ion batteries constructed as solid-state batteries.

[0033] After a certain period of cyclical and cyclical stress, these battery modules reach the end of their service life, which is often referred to as End of Life (EoL). The lithium-ion cells are assembled into the battery module using either serial or parallel wiring. This type of wiring is used to increase the voltage, on the one hand, and to increase the maximum current, on the other. Such battery modules are used within a large stationary energy storage system. In this case, however, serial wiring is usually used to increase the overall voltage.

[0034] The service life of a lithium-ion cell is determined after a certain period of use or after a certain period of use during cyclic loading. Once the lithium-ion cell or battery module reaches the end of its service life, an initial operating phase is completed.

[0035] In the first operating phase, the battery energy storage system releases energy and is recharged after an energy release, whereby the first operating phase is terminated as soon as an EoL criterion is reached, whereby the battery energy storage system has residual energy after the first operating phase.

[0036] As soon as the EoL criterion is reached, a so-called recycling mode is initiated in process step 1, which is carried out either by a software or a hardware circuit.

[0037] After the first process step 1, the second process step 2 follows, in which an internal monitoring function for the battery module as well as for a cell undervoltage is adjusted, whereby, strictly speaking, the control parameters are adjusted.

[0038] Subsequently, in the next process step 3, the module temperature or the cell temperature limits for monitoring deep discharge are set.

[0039] In the next process step 4, the BESS system discharges the battery modules and feeds the remaining energy back into the grid until the module voltage reaches OV.

[0040] This process step 4 thus begins a second operating phase in which the residual energy present in the battery energy storage system is used to release energy, with the energy being released as in the first operating phase. The battery energy storage system has an inverter connected to the battery modules, with the energy being released to the inverter in the first operating phase. In the second operating phase, the energy is also released to the inverter.

[0041] In the next process step 5 the module voltage of OV is reached.

[0042] The second operating phase is followed by a third operating phase, in which the battery modules have two battery module poles. In the third operating phase, the two battery module poles are short-circuited. This is illustrated in process step 6 in Figure 1.

[0043] The short circuit of the two battery module poles occurs via an internal short circuit.

[0044] In the next process step 7, the battery module is removed from a rack or container and transported to a recycling facility.

[0045] Figures 2 to 4 show a schematic representation of a battery arrangement 8, which can also be referred to as a battery energy storage system. The battery arrangement 8 comprises a battery 9. The battery 9 is part of an arrangement which includes cells, a pack, a rack and a container (not shown) and is connected to an inverter 10. A voltmeter 11 for measuring an electrical voltage is arranged between the battery 9 and the inverter 10. Figure 2 shows a conventional design of a system without a so-called “recycling mode”. The cells, pack, rack and container are operated conventionally. Frequency stabilization, energy removal, etc. can be carried out with the battery arrangement 8. According to the prior art, the cells, pack, rack and container must be dismantled and subjected to the corresponding conventional process. Figure 3 shows a battery arrangement 8 according to the invention.The difference between the embodiment according to Figure 3 and Figure 4 is that the battery 9 can be short-circuited via a switch 12. The system shown in Figure 3 is therefore designed in a so-called "recycling mode". The system or battery arrangement 8 can be operated as usual without disrupting the function of the modes described with reference to Figure 2. The short-circuit via the switch 9 impairs the operation of the system or battery arrangement in one case. It must also be ensured by a software function or hardware (for example a jumper, a seal or a short-circuit bridge) that the short-circuit using switch 9 cannot be carried out in this state (battery voltage > 0V).

[0046] Figure 4 shows the inventive battery arrangement from Figure 3 with a closed switch 9. The cells, modules, pack, rack, and container are discharged to a voltage of 0V using the existing inverter. At the same time, monitoring is performed to prevent critical system states.

[0047] If the battery voltage is equal to 0V, switch 9 is closed to short-circuit the batteries. The short circuit can occur at the cell, pack, module, rack, or container level. Advantageously, the short circuit can occur at the module level, as this unit is easier to transport.

[0048] Although the invention has been illustrated and described in detail by the preferred embodiment, the invention is not limited to the disclosed examples and other variants can be derived by the person skilled in the art without departing from the scope of the invention.

Claims

Patent claims 1. Method for operating a battery energy storage system, wherein the battery energy storage system is formed from a plurality of battery modules, wherein in a first operating phase the battery energy storage system is used to deliver energy and to be recharged after an energy release, wherein the first operating phase is ended as soon as an EoL criterion is reached, wherein the battery energy storage system has residual energy after the first operating phase, wherein in a second operating phase the residual energy present in the battery energy storage system is used to deliver energy, wherein the energy release takes place as in the first operating phase.

2. The method according to claim 1, wherein the battery energy storage system comprises an inverter connected to the battery modules and the energy is delivered to the inverter in the first operating phase, wherein the energy is also delivered to the inverter in the second operating phase.

3. Method according to claim 1 or 2, wherein the second operating phase is started manually or automatically. 4 . Method according to one of the preceding claims, wherein the inverter is connected to a power grid.

5. The method according to any one of the preceding claims, wherein the second operating phase continues until a residual voltage of 0 V is reached in the battery modules.

6. The method according to claim 5, wherein the second operating phase is followed by a third operating phase, wherein the battery modules have two battery module poles, wherein in the third operating phase the two battery module poles are short-circuited.

7. Method according to claim 6, wherein the short circuit of the two battery module poles is effected via an internal short circuit.

8. Method according to claim 6 or 7, wherein after the short circuit the battery modules are prepared for removal.

9. The method according to claim 8, wherein the battery modules are recycled after removal.

10. Battery energy storage system comprising a plurality of battery modules, wherein the energy storage system is designed to carry out the method according to one of claims 1 to 9.

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