SE2150539A1

SE2150539A1 - A system

Info

Publication number: SE2150539A1
Application number: SE2150539A
Authority: SE
Inventors: Callum Hoare
Original assignee: Northvolt Ab
Priority date: 2021-04-28
Filing date: 2021-04-28
Publication date: 2022-10-29
Also published as: WO2022229276A1

Abstract

The present invention relates to controller (21) for an energy storage system, ESS, (20) comprising an external grid input/output connection, a load output, an AC/DC inverter, a control circuitry (PLC), a common DC bus and a communication interface. The controller is configured o: communicate with a plurality of battery packs (22a-e) to receive information related to charge status for each battery pack, balance the plurality of battery packs based on the received charge status for each pack to reduce a difference in charge status between the battery packs below a predetermined level; and transmit instructions to connect the plurality of battery packs o the common DC bus. The present invention also relates to a battery pack and an energy storage system.

Description

Confidential A SYSTEl\/l TECHNICAL FIELD The present disclosure relates to the field of battery systems comprising one or more packs, and more particular to modular battery systems for electric applications. BACKGROUND Traditionally large Energy Storage, ES, is provided in containers solutions, as illustrated in Figure 1. The energy storage solution comprises a predetermined amount of battery cells arranged in battery strings and interconnected by fixed cabling, which requires long installation times.

Different applications may require energy storage with different energy capacity and power. Also, the physical location of the energy storage may differ over time, and container solutions requires special equipment to relocate.

Thus, there is a need for a more flexible, scalable and adaptable energy storage, which is easier to relocate. SUMMARY An object of the present disclosure is to provide a battery system which seeks to mitigate, alleviate, or eliminate one or more of the above-identified deficiencies in the art and disadvantages singly or in any combination and to provide a battery pack and a controller configured to be used with one or more battery packs in the battery system.

This object is obtained by a controller for an energy storage system comprising an external grid input/output connection, a load output, an AC/DC inverter, a control circuitry (PLC), a common DC bus and a communication interface. The controller is configured to communicate with a plurality of battery packs to receive information related to charge status for each battery pack, balance the plurality of battery packs based on the received charge status for each pack to reduce a difference in charge status between the battery packs below a predetermined level and transmit instructions to connect the plurality of battery packs to the common DC bus when the difference is below the predetermined level..

Confidential 2 The charge status may be open circuit voltage, OCV, over each battery pack and/or state of charge, SOC, for each battery pack. There are a few options available to balance the battery packs in order to reduce the difference between the battery packs to the predetermined level.

An advantage with the controller is that battery packs may easily be removed or added based on the need ofthe application to which power is supplied.

According to an aspect, a battery pack comprising at least one battery string and battery monitoring system, BMS is provided. The battery pack is configured to communicate with a controller, as defined in independent claim 1, to provide information related to charge status, receive control signals from the controller to balance the battery pack to a predetermined charge level and make power accessible to the controller via a common DC bus, when instructions to connect the battery string to the common DC bus is received.

An advantage with the battery pack is that it is safe to connect to an existing energy storage system.

According to a further aspect, a modular energy storage system comprising a controller as defined in independent claim 1 and one or more battery packs as defined in independent claim 12 is provided.

An advantage with the modular energy storage system is that it is flexible and may be adapted to suit the need ofthe application to which power is supplied.

Further aspects and advantages may be obtained by a skilled person from the detailed description. BRIEF DESCRIPTION OF THE DRAWINGS The foregoing will be apparent from the following more particular description of the example embodiments, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the example embodiments. Figure 1 is a perspective view of an energy storage solution according to prior art; Figure 2 is a block diagram of an example embodiment of an energy storage system; Confidential 3 Figure 3 is a perspective view of an energy storage system comprising a controller, HUB, and five battery packs; Figure 4 illustrates an example process for supplying power to loads in Island mode; Figure 5 illustrates an example process for supplying power to loads while peak shaving; and Figure 6 is a flow chart illustrating a process for integrating a battery pack into an energy system. Figures 7a- 7c illustrate different scenarios when introducing a battery pack in an ESS. DETAILED DESCRIPTION Aspects of the present disclosure will be described more fully hereinafter with reference to the accompanying drawings. The apparatus disclosed herein can, however, be realized in many different forms and should not be construed as being limited to the aspects set forth herein.

Like numbers in the drawings refer to like elements throughout.

The terminology used herein is for the purpose of describing particular aspects of the disclosure only, and is not intended to limit the invention. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

Some of the example embodiments presented herein are directed towards a controller and battery packs. The battery pack comprises strings of battery cells, which may be prismatic cells, often referred to as ”secondary cells", (in particular lithium-ion cells) and the example embodiments of the battery pack and controller may be used for a modular energy storage systems.

The energy storage system is divided into units that are interconnected by cabling to provide a flexible solution. The units comprises a controller, also called HUB, and one or more battery packs. The core unit is the HUB, which has three main interfaces: ~ to an external grid 0 toloads Confidential ~ to one or more battery packs The HUB is configured to monitor grid fluctuations, and based on these provide different functionality, such as island mode, peak shaving, grid boost, etc. The HUB also channels energy from the connected battery packs to the loads during island mode or when performing peak shaving and to the external grid during a grid boost.

The HUB provides a 400V AC pluggable input and output allowing the energy storage to interface to standard distribution equipment and plug-and-play functionality. ln a preferred embodiment, up to five battery packs can be connected to a HUB, providing the innovative modular scalability of the product.

Each battery pack comprises one or more battery strings, each having a nominal voltage (e.g. 750 V) and a nominal capacity to provide the possibility to store energy accessible to the HUB. As an example, each battery pack may contain energy capacity equivalent to 245 kWh and up to five battery packs may be connected to the HUB. The battery strings may be connected via High Voltage wiring to a common DC bus within the HUB and each battery pack is configured to communicate with the HUB via a Low Voltage wiring.

The energy storage system is configured to allow battery packs to be connected/disconnected from the DC bus in a plug and play functionality. This means that one of the basic functionality of the modular design is to handle battery packs with different state of charge being connected to the DC bus. The HUB is configured to receive information regarding the state-of-charge, SOC, when a battery pack is connected to the DC bus, and discharge the battery pack with the highest SOC in order to prevent unintentional current spikes due to different SOC of battery packs connected to the DC bus. The purpose is to balance the battery packs before they are connected together via the DC bus.

The ESS, together with increased renewable penetration in the European electricity grid to the market will lead to a significant reduction in GHG-emissions and air pollutants through: ~ Enabling large-scale adoption of renewable energy sources in the energy grid ~ Direct replacement of diesel-based power generation Confidential The ESS in the present disclosure does not only offer a substitute to conventional temporary power for applications in e.g. construction and events, it serves the rest of energy sectors as well. The flexibility and modularity of the ESS, is an enabler of renewable energy transition through synergy and symbiosis with other industries and actors in the de -carbonization transition. The ESS is also able to provide services for distribution grid flexibility and enable electric mobility through supporting EV charging stations.

As an example, the ESS is a Lithium-ion battery energy storage system that delivers power up to 225 kVA, with a scalable energy capacity from 255 to 1275 kWh of available energy. The ESS consists of two separable units: the battery pack and the HUB. The battery pack may be an individual self-contained, liquid-cooled, industrial-grade, high energy-dense lithium-ion battery pack with a capacity ofe.g. 255 kWh per unit. The HUB is the central power unit, through which the system access energy capacity from the battery packs and provides the external power interface to the system.

The ESS units are designed as standardized building blocks as opposed to geared towards specific project solutions and requirements (as is the case for existing industrial/commercial storage solutions). This gives the ESS in the present disclosure the advantage of being possible to efficiently mass produce on a standardized production line while enabling customization of the system through the ESS's modular nature, providing customers with a high degree of flexibility in use cases and requirements. The battery pack is the energy storage unit which is connected to the power conversion unit in the HUB. Together these units form the building blocks of the ESS. Through combination of up to five battery packs with one HUB, a capacity of up to 1275 kWh may be achieved.

The units may be connected to and communicate with a cloud service to provide communication with external resources, such as logistics centers and clients, to collect manufacturing, field use and recycling data, allowing the customers to receive real -time asset insights and direct product control. The cloud service allows for a safe remote control and monitoring of all the assets and functionalities to predict future product performance and prescribe preventive actions.

The HUB contains all the necessary power and control equipment to facilitate the distribution and conversion of power to the battery units. As an example, the HUB may contain liquid-cooled Confidential 6 power electronic modules for power Conversion, integrated controllers for battery system and energy management, a transformer for galvanic isolation and necessary protection and monitoring systems. Furthermore, the HUB may comprise a 400VAC/400A output for providing standard distribution output from the batteries and a 400VAC / 32-125A supply input for charging the battery packs.

The flexibility ofthe ESS, allows it to serve multiple use cases. This means the asset owner will always have multiple potential sources of revenue depending on the use case. There are four main operating modes of the ESS: island, rapid peak shave (RPS), grid deployment and microgrid. Island mode: create a standalone grid through the inverter's voltage source mode RPS mode: Grid connection is available but not strong enough to support short bursts in power demand (i.e. for minutes/hours) and seamless transition to island mode in case of grid failure. Grid deployment mode: respond to external setpoints of active and reactive power I\/|icrogrid mode: battery storage to enable microgrid functionality, storing locally produced solar/wind power, etc.

Thus, the ESS in the present disclosure offers the same simplicity of deployment as diesel generators, eliminates hurdle of deployment compared to prior art ESS due to the mobility of the ESS.

The plug & play functionality for adding/removing battery packs to the ESS leads to quicker and cheaper site deployments which results in simpler operations.

The modularity aspect of the present ESS will enable the most cost effective configuration to be deployed at each site, and also provides a sustainable alternative to a refueling concept.

The flexibility of the ESS, which is designed for a multitude of use cases, allows for a wider range of potential revenue streams for the same equipment and a quicker payback time.

From a sustainability point of view, the ESS allows for switching to a less carbon intensive technology, by delivering temporary power with the smallest carbon footprint available.

Confidential 7 Figure 1 is a perspective view ofan energy storage solution 10 according to prior art, comprising a predetermined amount of battery cells arranged in battery strings and interconnected by fixed cabling. This type of arrangement requires long installation time, special equipment for handling the container, and staff with special competence to transport and install such a system. Furthermore, it is difficult to upgrade a system already deployed into the field if more battery cells are needed to perform the desired functionality.

Figure 2 is a block diagram of an example embodiment of an energy storage system (ESS) 20 comprising a controller 21 and a plurality of battery packs 22a - 22e, each comprising one or more sub packs 23. ln this example up to five battery packs may be included in the ESS. The controller comprises an external grid input/output connection 24, a load output 25, an AC/DC inverter 26, a control circuitry PLC 27, a common DC bus 28 and a communication interface 29. The external grid input/output connection 24 is connected to an external grid from which external power may be supplied to the controller, or power may be outputted to the external grid to boost the grid depending on the purpose of the ESS 20. The load output 25 is connected to one or more loads depending on the application, and the externa grid and the loads are connected to the AC/DC converter 26 via switches that are controlled by the PLC 27. The thick lines interconnecting the loads, external grid and AC/DC converter indicate 3 phase wiring.

The controller is further provided with a Thermal Management System, TI\/|S, to monitor and control the system in case a thermal issue is detected in the battery packs connected to the DC bus 28. The AC/DC converter 26 is connected to the common DC bus 28 which in this example is provided with five quick connects 28a to electrically connect one or more battery packs 22.

Each battery pack 22 comprises at least one battery string 23, or sub packs, and a battery monitoring system, BI\/|S, configured to communicate with the controller 21 via the communication interface 29 (as indicated by the dotted lines in Figure 2). The battery strings 23 are connected via an internal DC bus, a battery connection 23a using a quick connect 28a to the common DC bus 28 in the controller, and a local TMS is provided to monitor the battery pack in case a thermal issue is detected. The BMS is further configured to control switches interconnecting the local DC bus with the battery connection 23a based on instructions received from the controller via the communication interface 29.

Confidential 8 The BMS is further configured to provide information related to charge status in the battery pack to the controller, receive control signals from the controller to balance the battery pack to a predetermined charge level, and make power accessible to the controller 21 via a common DC bus 28, when instructions to connect the battery strings 23 to the common DC bus 28 is received.

Figure 3 is a perspective view of an energy storage system 30 comprising a controller 31, also called HUB, and five battery packs 32a-32e, commonly denoted 32. The HUB 31 is a basic part and is required in the energy storage system, ESS, 30, while each battery pack 32, which are provided as separate units, may be interconnected with the HUB depending on the requirements needed for the ESS in the selected application.

Each battery pack is connected to the HUB via a power cable (connecting the local DC bus of the battery pack with the common DC bus in the controller 31) and a communication cable (connecting the BMS of the battery pack with the PLC of the HUB 31). This is illustrated in figure 3, where the protective panel of battery pack 33c is open and the power cable 33 is connected to the common DC bus of the HUB 31, and a communication cable 34 is provided from the battery pack 33c to the communication interface ofthe controller 31 in order for the HUB 31 to be able to communicate with the battery pack 33c.

Each unit 31, 32 are easy to transport on a truck without any special arrangements, and when the units arrive at the installation site, a qualified technician needs to connect power cables and communication cables and ensure that the system is powered up.

Figure 4 illustrates an example process 40 for supplying power to loads in Island mode. ln island mode the ESS is placed at site with no grid connection available, used until the energy storage is depleted and then removed from site. This allows the ESS to provide power to sites which have no electrical connection. Typically, these are locations which are currently serviced by diesel generators. lf more than one battery pack is connected to the HUB, an individual battery pack may be removed for charging while the remaining battery packs continue providing power, ensuring uninterrupted service. ln this example, an ESS with a HUB and a first battery pack has previously been installed at a desired location. A logistics center has been informed that the charge status of the first battery Confidential 9 pack in the ESS is approaching a preset charge level when the first battery pack needs to be replaced since the ESS has no access to an external grid.

Thus, a second battery pack is charged 41 from the power grid and provided to the logistics center for handling. The second battery pack is distributed and connected 42 to the ESS, which includes transporting the second battery pack to ESS and power-up. An example for a procedure to power-up is described below. When the second battery pack is installed, the ESS continuous its operations 43 to discharge to the application in Island mode, i.e. supply power to off-grid loads, providing power from the first battery pack having the lowest charge status. When the charge status of the first battery pack is too low, the EES replaces the first battery pack 44 by swapping battery packs since more energy is needed than can be supplied from the first battery pack. The first battery pack will be returned for charging 45, and is disconnected and shipped back to the logistics center and the process is repeated by charging the battery pack in waiting to be distributed again.

This procedure is illustrated in Figure 7a, where the first battery pack ”A” approaches a preset level 71. A charged second battery pack ”B” is distributed and connected to the ESS and the HUB retrieves information regarding charge status when the power cable and communication cable are connected to the HUB. However, since there still remains energy in the first battery pack ”A”, the energy in the second battery pack ”B” is not accessible to the HUB since the local switches in the battery pack are open waiting for instructions from the PLC in the HUB.

When the charge status is too low, e.g. below the preset level 71, the battery packs are swapped and energy is provided from the second battery pack ”B” to the off-grid loads, while the first battery pack ”A” will be returned to the logistics center for recharging.

Figure 5 illustrates an example process 50 for supplying power to loads while peak shaving, also known as rapid peak shave, RPS, mode. RPS mode is an operating mode that allows the ESS to expand an existing grid connection. lt may be used where the existing grid connection is too small in power capacity to support the desired loads, either due to a temporary scale up in loads (i.e. an event) or a restriction in the available network supply (grid congestion). This use case is highly relevant to EV-adoption where the roll-out of EV-chargers is required but the lead time for infrastructure deployment is long. The operating modes work by connecting the ESS via Confidential standard electrical plug (common to any commercial or industrial building) to the site's electrical grid. ln this example, a logistics center has been informed that an ESS, with a HUB and at least one battery pack, is required to perform peak shaving at a desired location. Information regarding the size of the energy storage in order to provide the desired functionality will be needed for configuration ofthe ESS by the logistics center. ln this example, deployment 51 will be made of a configured ESS with a HUB and a first battery pack ”A” and a second battery pack ”B” which will be transported to the location. At the location, the ESS is connected 52 to the loads and the power grid before powered-up. The ESS will in this example provide peak shaving, i.e. provide power at high peak demands 53, due to limited grid connection. The performance ofthe ESS will be evaluated in order to identify if the ESS needs to be modified 54 by add/remove battery packs or move system if peak shaving is not required anymore. lf more battery packs are required, it may be shipped from the logistics center, and connected to the ESS. lf a battery pack should be removed, it may be disconnected and transported back to the logistics center, similar to what is described in Fig. 4. lf the ESS is not needed anymore, the complete system is powered down and transported back for new deployment. ln Figure 7b, an example is illustrated when a third battery pack ”C” is added to the ESS. The charge status of battery packs ”A” and ”B” is the same 72, e.g. 80% SOC, since they have been used by the ESS to provide peak shaving. However, there is a need to increase the energy buffer by adding a third battery pack ”C” which have 100% SOC when delivered to the location. ln order to balance the battery pack two options are available depending on the state of operations: 1) lf peak shaving is performed, it is beneficial to connect battery pack ”C” while disconnecting battery packs ”A” and ”B” until the difference between the battery packs are below a predetermined level, e.g. within a couple of percent ofthe average charge status of the battery packs, which predetermined level may be temperature dependent. The reason for this is to avoid current spikes when connecting the battery packs to the common DC bus, and as an example the difference in charge status between battery packs should be less than, or equal to, an OCV of 10VDC and/or a SOC of 5%.

Confidential 11 lf the predetermined value is temperature dependent, and the OCV is used as indication of charge status, the predetermined level may bedifferent values at different temperatures, e.g. 10 VDC @ 20°C or 20VDC @ 30°C. The same applies for the SOC when is used as indication of charge status. The predetermined level may in that case be different percentage of SOC at different temperatures, e.g. 5% @ 20°C or 10% @ 30°C. A combination of OCV and SOC may be used as indication of charge status.

Also, there may also be a defined allowed temperature window, e.g. 20°C - 42°C, within which the battery pack is allowed to be connected to the common DC bus in the HUB. 2) lf no peak shaving is performed and grid power is available, battery packs ”A” and ”B” should be charged from the grid until they reach 100% SOC, or at least to the point where the difference in charge status is below the predetermined level (as explained above). When the battery packs are balanced, they are connected to the common DC bus. ln Figure 7c, an alternative scenario is illustrated wherein battery pack ”C” is connected to the ESS while the charge status of battery pack ”A” and ”B” are not the same, ”A” at 60% SOC and ”B” at 80% SOC. lf peak shaving is performed (compare with option 1 above), the discharge of battery pack ”C” down to level 72 needs to be performed before battery pack ”B” also is connected to the common DC bus to be used together by the ESS for peak shaving. lf possible, battery pack ”A” may thereafter be charged to the same charge status as battery packs ”B” and ”C” by disconnecting battery packs ”B” and ”C” from the common DC bus, before the battery packs have the same charge status and may be connected to the common DC bus. Alternatively battery packs ”B” and ”C” are further discharged to the next level 73 before connecting all battery packs to the common DC bus. lt is of course possible to only connect battery pack ”A” to the common DC bus for charging if no peak shaving is performed, and when battery pack ”A” reaches the same charge status at 72 as battery pack ”B”, then both battery packs may be connected to the common DC bus. Balancing of the battery packs may hereafter be performed as illustrated in connection with figure 7b.

Figure 6 is a flow chart illustrating a process 60 for integrating a battery pack into an energy storage system. The flow starts in 61, and the ESS provides power to an application 62. During Confidential 12 operation, the system monitors if there is a request for modifying the configuration of the ESS 63. lf nor request has been received, the flow is looped back to step 62. However, if there is a request, the process continues to 64 where a battery pack is either connected or disconnected from the ESS.

The process is different depending on the number of battery packs connected to the ESS, as is investigated in 65. lf only one battery pack is connected to the HUB within the SS, the process continues to 66 where the system is powered-up and continuous to supply power to the application as indicated by 62. On the other hand, if multiple battery packs are connected to the HUB in the ESS, the HUB will retrieve charge state, such as SOC level and/or OCV level, from all battery packs 67 to determine difference in charge status between battery packs.

The process then commences with balancing the battery packs 68, e.g. by discharging the battery pack/packs with the highest charge status 68a and evaluating if the difference in charge status between all battery packs is less than a predetermined level 68b. lf not, step 68a is repeated until the criteria is met and the difference between the battery packs is below the predetermined level. Thereafter, all battery packs may be connected to the common DC bus in the HUB and the ESS may use them for providing power to the application 62.

As an alternative, balancing 68 may also be achieved by charging the battery pack/packs with the lowest charge status 68a and evaluating if the difference in charge status between all battery packs is less than the predetermined level 68b. lf not, charging or discharging of a selected number of battery packs may be performed to balance the battery packs in step 68a.

This disclosure relates to a controller 21 for an energy storage system, ESS, 20 comprising an external grid input/output connection, a load output, an AC/DC inverter, a control circuitry (PLC), a common DC bus and a communication interface. The controller is configured to communicate with a plurality of battery packs 22a-e to receive information related to charge status for each battery pack, balance the plurality of battery packs based on the received charge status for each pack to reduce a difference in charge status between the battery packs below a predetermined level, and transmit instructions to connect the plurality of battery packs to the common DC bus when the difference in charge status is below the predetermined level.

Confidential 13 According to some embodiments, the predetermined level is temperature dependent, and the controller is further configured to receive information regarding temperature of each battery pack to determine the predetermined level. According to some embodiments, the charge status is state of charge, SOC, and/or open circuit voltage, OCV, over each battery pack. Thus, this may result in different charge status for each battery pack attached to the controller.

When OCV is used as indication of charge status, the predetermined level may be an absolute voltage value, e.g. 10 VDC When SOC is used as indication of charge status, the predetermined level may be a percentage of SOC, e.g. 5% A combination of OCV and SOC may be used as indication of charge status. ln addition, there may also be a defined allowed temperature window, e.g. 20°C - 42°C, within which the battery pack is allowed to be connected to the common DC bus in the HUB.There are a few options available to balance the battery packs in order to reduce the difference between the battery packs to the predetermined level.

According to some embodiments, the controller is further configured to discharge a first set of the plurality of battery packs, which is connected to the common DC bus, to a first charge level, to balance the plurality of battery packs. ln this embodiment, the first charge level may be a fixed value or a dynamic value associated with the charge status of the other battery packs in the ESS.

According to some embodiments, the first set of the plurality of battery packs has a higher charge status than the rest of the battery packs connected to the common DC bus. This may occur when a fully charged battery pack is introduced into an ESS where the charge status of the previously connected battery packs has a lower charge status. This is typical when the ESS is used for island mode.

According to some embodiment, the first charge level is a fixed value, e.g. a SOC value and/or a OCV value, or a dynamic value corresponding to a battery pack of the plurality of battery packs with the lowest charge status. As an example, the fixed value may be 60% of SOC and/or 80% of nominal voltage, over each battery pack.

According to some embodiment, when the first set of the plurality of battery packs has been discharged to the first charge level, the controller is further configured to discharge a second set of the plurality of battery packs, if a difference in charge status between the plurality of Confidential 14 battery packs is above the predetermined level, to balance the plurality of battery packs. This may occur when there several battery packs with different charge status is introduced to an ESS at the same time, e.g. when increasing the energy storage buffer within the ESS.

According to some embodiment, the controller is further configured to charge a third set ofthe plurality of battery packs, which is connected to the common DC bus, to a second charge level, to balance the plurality of battery packs. The second charge level may be a fixed value or a dynamic value corresponding to the charge status of the rest of the battery packs connected to the controller.

According to some embodiment, the third set ofthe plurality of battery packs has a lower charge status than the rest of the battery packs connected to the common DC bus.

According to some embodiments, the second charge level is a fixed value related to a SOC value and/or OCV value, or a dynamic value corresponding to a battery pack of the plurality of battery packs with the highest charge status. As an example, the fixed value may be 100% SOC and/or 110% of nominal voltage.

According to some embodiments, when the third set of the plurality of battery packs has been charged to the second charge level, the controller is further configured to charge a fourth set of the plurality of battery packs, if a difference in charge status between the plurality of battery packs is above the predetermined level, to balance the plurality of battery packs.

This disclosure also relates to a battery pack comprising at least one battery string and battery monitoring system, BI\/|S, wherein the battery pack is configured to communicate with a controller as defined above to provide information related to charge status, receive control signals from the controller to balance the battery pack to a predetermined charge level; and make power accessible to the controller via a common DC bus, when instructions to connect the battery string to the common DC bus is received. Information regarding charge status may also include temperature of the battery pack in order for the controller to determine the predetermined charge level.

This disclosure also relates to a modular energy storage system comprising a controller as defined above and one or more battery packs as defined above.

Confidential The description of the example embodiments provided herein have been presented for purposes of illustration. The description is not intended to be exhaustive or to limit example embodiments to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of various alternatives to the provided embodiments. The examples discussed herein were chosen and described in order to explain the principles and the nature of various example embodiments and its practical application to enable one skilled in the art to utilize the example embodiments in various manners and with various modifications as are suited to the particular use contemplated. The features of the embodiments described herein may be combined in all possible combinations of apparatus, modules and systems. lt should be appreciated that the example embodiments presented herein may be practiced in any combination with each other. lt should be noted that the word ”comprising” does not necessarily exclude the presence of other elements or steps than those listed and the words ”a” or ”an” preceding an element do not exclude the presence of a plurality of such elements. lt should further be noted that any |ll reference signs do not limit the scope of the claims, and that severa means", ”units” or ”devices” may be represented by the same item of hardware. ln the drawings and specification, there have been disclosed exemplary embodiments. However, many variations and modifications can be made to these embodiments. Accordingly, although specific terms are employed, they are used in a generic and descriptive sense only and not for purposes of limitation, the scope of the embodiments being defined by the following claims.

Claims

1. A controller (21) for an energy storage system, ESS, (20) comprising an external grid input/output connection, a load output, an AC/DC inverter, a control circuitry (PLC), a common DC bus and a communication interface, wherein the controller is configured to: - communicate with a plurality of battery packs (22a-e) to receive information related to charge status for each battery pack; - balance the plurality of battery packs based on the received charge status for each pack to reduce a difference in charge status between the battery packs below a predetermined level; and - transmit instructions to connect the plurality of battery packs to the common DC bus.

2. The controller according to claim 1, wherein the predetermined level is temperature dependent, and the controller is further configured to receive information regarding temperature of each battery pack to determine the predetermined level.

3. The controller according to claim 1 and 2, wherein the charge status is state of Charge, SOC, and/or open circuit voltage, OCV, over each battery pack.

4. The controller according to any ofclaims 1-3, wherein the controller is further configured to discharge a first set of the plurality of battery packs, which is connected to the common DC bus, to a first charge level, to balance the plurality of battery packs.

5. The controller according to claim 4, wherein the first set ofthe plurality of battery packs has a higher charge status than the rest ofthe battery packs connected to the common DC bus.

6. The controller according to any of claims 4-5, wherein the first charge level is a fixed value or a dynamic value corresponding to a battery pack of the plurality of battery packs with the lowest charge status.

7. The controller according to any ofclaims 4-6,wherein the controlleris further configured to discharge a second set of the plurality of battery packs, if a difference in charge status between the plurality of battery packs is above the predetermined level, to balance the plurality of battery packs.

8. Confidential 17 8. The controller according to any ofclaims 1-3, wherein the controller is further configured to charge a third set of the plurality of battery packs, which is connected to the common DC bus, to a second charge level, to balance the plurality of battery packs.

9. The controller according to claim 8, wherein the third set ofthe plurality of battery packs has a lower charge status than the rest of the battery packs connected to the common DC bus.

10. The controller according to any of claims 8-9, wherein the second charge level is a fixed value or a dynamic value corresponding to a battery pack of the plurality of battery packs with the highest charge status.

11. The controller according to any of claims 8-10, wherein the controller is further configured to charge a fourth set ofthe plurality of battery packs, ifa difference in charge status between the plurality of battery packs is above the predetermined level, to balance the plurality of battery packs.

12. A battery pack comprising at least one battery string and battery monitoring system, BI\/IS, wherein the battery pack is configured to: - communicate with a controller according to any of claims 1-11 to provide information related to charge status; - receive control signals from the controller to balance the battery pack to a predetermined charge level; and - make power accessible to the controller via a common DC bus, when instructions to connect the battery string to the common DC bus is received.

13. A modular energy storage system comprising a controller according to any of claims 1- 11 and one or more battery packs according to claim 12.