WO2021044145A1

WO2021044145A1 - Energy storage apparatus

Info

Publication number: WO2021044145A1
Application number: PCT/GB2020/052106
Authority: WO
Inventors: Ian Mcdonald
Original assignee: Future Transport Systems Ltd
Priority date: 2019-09-03
Filing date: 2020-09-03
Publication date: 2021-03-11
Also published as: GB2584920A; GB201912648D0; GB2584920B

Abstract

A system for storing electrical energy in more than one battery unit, each battery unit being a sealed unit of known kind including within it one or more battery cells and a control means adapted to transmit and receive data to and from a controller outside the battery unit via a data bus, said data being arranged according to a standard protocol adapted for use with one battery unit within a substantially closed CAN network, each battery unit being adapted to be addressed identically by such a controller, and the system being characterised in that it is adapted so that each battery unit is controlled by a single controller, and that the controller is adapted to transmit and receive data to and from each battery unit and adapted to control the more than one battery units on the said single data bus, so that addressing information from each battery unit is not required.

Description

Energy storage apparatus

Field of the invention

The present inventive concept relates to the storage of electrical energy.

Background to the invention

The challenges around storage of electrical energy are well established. Electrical energy cannot be stored as such, and therefore traditionally mains electricity has been generated "on demand". As the world seeks renewable energy supplies, often from solar or wind power sources, the need arises to time-shift electricity generated to periods of high demand.

One particularly active field of research and development in such storage means is based around battery storage.

It is further known that batteries used in electric vehicles are often retired from the respective vehicle before the batteries themselves have ceased to be useful for electrical storage. Repurposing electric vehicle batteries leads to the term "second life” batteries, a field in which such batteries are used for a second purpose rather than being dismantled for recycling or disposal.

Summary of Invention

The present inventive concept provides a system for storing electrical energy in more than one battery unit, each battery unit being a sealed unit of known kind including within it one or more battery cells and a control means adapted to transmit and receive data to and from a controller outside the battery unit via a data bus, said data being arranged according to a standard protocol adapted for use with one battery unit within a substantially closed CAN network, each battery unit being adapted to be addressed identically by such a controller, and the system being characterised in that it is adapted so that each battery unit is controlled by a single controller, and that the controller is adapted to transmit and receive data to and from each battery unit and adapted to control the more than one battery units on the said single data bus, so that addressing information from each battery unit is not required.

Batteries designed for electric vehicles tend to be supplied as a sealed unit including a battery as such and a control means. Such battery units tend to be adapted to communicate with other vehicle systems using a Controller Area Network (CAN) data bus protocol, or similar. Because such battery units are generally designed to operate as a single unit within a substantially closed network environment (the vehicle itself) they are generally not adapted to operate within wider networks. This can be problematic when repurposing such battery units for "second life” applications. Especially, bringing such battery units into a wider network addressing scheme can be problematic.

In their original intended use, automotive battery packs (referred to herein as battery units) are only ever used individually, and therefore there is never the possibility of ambiguity of the origin of a CAN message from a battery unit. However, when controlling multiple battery units with a single controller, the CAN signals must be processed and organised in such a way that there is no ambiguity regarding the source of the CAN messages. Suitably addressing a battery unit is vital for such repurposing without the need to dismantle the battery unit.

Previous disclosures have suggested placing an intermediary CAN interface between each battery unit and a wider network. Thus, a CAN interface would present a suitable address to the wider network and communicate directly with a single battery unit. This is a resource-intensive proposal because each battery unit requires a dedicated CAN interface.

Thus, the present inventive concept enables a controller to interface with more than one battery unit without an intermediary CAN interface.

The controller may be a CAN to CAN module. Multiple battery units may feed information simultaneously into the CAN to CAN module, which can pool data from the battery units, identify each data stream and its origin, and can simultaneously stream the aggregated data out on a single CAN bus. This reduces the need for specific CAN interfaces to each battery unit.

Two or more battery units may be connected in series to form a string. Two or more strings can be connected to a common bi-directional inverter via a set of controllable DC switches, such as contactors. This can provide for the ability for the system to control the flow of power from the grid to each string, or vice versa.

More than two strings may be connected to a common bi-directional inverter. The said connection of more than two strings to an inverter involves overcoming certain complexities. With more than two strings, additional electrical protection and control hardware (such as contactors) will be required, resulting in more control and feedback signals. Thus, the controller may be adapted to optimise the switching of the strings, aiming to maximise the capacity of the system while minimising battery degradation. Thus, the controller may be further adapted to ensure that each battery unit remains within operational limits (e.g. cell temperature, cell voltage, etc). This process is more complex when there is more than a binary option of two strings.

The said bi-directional inverter has the function of converting AC power to DC power and vice versa, thus enabling the transfer of energy between the local mains grid and the battery units. The inverter is preferably provided with DC and AC protection. Such protection may comprise protective devices such as isolators and circuit breakers, to ensure the safety of the system under fault conditions. A combination of AC protection, bi-directional inverter and DC protection can be referred to as a power conversion system (PCS).

Modular configuration of switchable battery units and a PCS can be referred to as a channel. A plurality of channels may be connected to the grid in parallel, thus increasing the power and capacity of the overall system.

The controller may be adapted to provide switching of a calibratable value dictated by the operation of the system and the control mode. For example, a threshold may be set in a control strategy that requests a switch of strings if the difference in state of change (SoC) between strings exceeds a certain value.

The system may be adapted so that each channel is adapted to provide an independent ability to switch between its strings.

Each battery unit has an internal control means adapted for both receiving commands and transmitting information. The internal control means is sometimes referred to as a battery management system (BMS). Information which can be transmitted by the control means includes SoC for the battery unit, cell temperature, cell voltage, power available and the like.

In the present arrangement, the control means of each battery unit communicates with a CAN to CAN module.

The CAN to CAN module may comprise a plurality of opto-isolators. These enable the CAN to CAN module to transfer signals between a battery unit and the wider system indirectly. In other words, the or each battery unit is not directly electrically connected to the controller. Each opto-isolator may be connected to a battery unit. Such a connection between opto-isolator and battery unit may be described as a CAN line. The CAN to CAN module may be adapted to receive data from battery units by way of multiplex scanning of CAN lines. As an example, a CAN to CAN module may be adapted to receive data from three battery units by way of multiplex scanning of CAN lines. Further CAN to CAN modules may be provided to scale up the system.

The CAN to CAN module may be adapted to transmit data to a CAN server. Thus, data received from battery units by the CAN to CAN module can be transmitted to a CAN server.

The CAN server is a programmable controller that acts as a link between the or each CAN to CAN module and a power control module (PCM). The PCM acts as a high level control means, processing requests and managing commands to and from the or each PCS and each battery unit via the CAN server. Thus, the CAN server and CAN to CAN module(s) process and manage bi-directional data flows between each battery unit and the PCM. In turn, the PCM may be connected to a human machine interface (HMI) so that a user can interact with the system.

The CAN server may in turn be connected to a wider network. The CAN server comprises an input/output (I/O) interface.

The CAN server may be adapted to have intrinsic processing capability and to manage system sub-routines as well as monitor/respond to discrepancies/errors within the connected controller area network(s). The CAN server may be adapted to communicate with the PCM using a MODBUS TCP protocol. The CAN server may be adapted to communicate with the CAN to CAN modules via a CAN protocol. Thus, the CAN server can facilitate communication between the PCM and battery units, by converting messages suitably in either direction.

Furthermore, the CAN server may be adapted to provide an additional safety check by monitoring communication between the PCM and battery units. The CAN server may further be adapted to shut down the system under pre-determined conditions. For example, if the PCM does not respond to pre-determined abnormal conditions, the CAN server can shut down the system.

The system may further comprise a Power Control Module (PCM). The CAN server may be in data communication with the PCM. The CAN server may be in data communication with the gateway module.

The CAN server may also be adapted to act as a buffer for the PCM. The CAN server may be adapted to perform the task of a safety watchdog. This safety watchdog task would have been undertaken by CAN traps in prior art arrangements. Such CAN traps are not required in the present inventive concept.

The CAN lines and connections related thereto so far described provide data transmission. Each battery unit may be further connected via a Direct Current (DC) line to an inverter/rectifier for transmission of substantive electrical energy.

One or more battery units may be arranged as a string, the string being connected to an inverter/rectifier by a DC line. Such a DC line may be selectably connected to or disconnected from a respective inverter/rectifier.

Thus, a string may be connected to or disconnected from an inverter/rectifier selectably.

More than one string may be provided. An inverter/rectifier may be selectably connected to or disconnected from an individual string. Thus, an inverter/ rectifier can in effect switch from being connected from one string to another. This enables maintenance of a stable input or output of electrical energy, substantially independently of the specific battery unit or units being used to provide an input or output.

For example, during a storage mode of operation, the present system may receive electrical energy from the wider electricity grid at a stable and predetermined rate with the management of the charging of specific batteries being managed "behind the scenes" in a way that does not disrupt the rate of input of electrical energy. Likewise, during a release mode of operation, the present system may output electrical energy to the wider electricity grid at a stable and predetermined rate with the management of the discharge of specific batteries being managed "behind the scenes" in a way that does not disrupt the rate of output of electrical energy.

The or each inverter/rectifier may in turn be in communication with the CAN server. Such communication between an inverter/rectifier may provide for a safety supervisor signal communication. DC power input and output to the battery units may alternatively or additionally be via a DC power distribution unit.

The or each inverter/ rectifier may be in communication with a gateway module. Optionally, such communication may be via a CAN line. The gateway module may in turn be connected to a wider network.

The gateway module may be adapted to process power demands broadcast via the data network and selectably connect or disconnect a string to or from an inverter/rectifier or vary the power to or from the attached string.

The system may comprise pairs of inverters/rectifiers with common Alternating Current (AC) and Direct Current (DC) connections.

The system may further comprise a data transmission network. The data transmission network may apply a Transmission Control Protocol (TCP) to transmit data between components of the system.

Thus, the PCM, the gateway module and the CAN server may be in data communication with one another.

The PCM may be adapted to monitor data streams from all batteries within the data network and connect or disconnect all or any string from any inverter/rectifier. The PCM thus may maintain the battery parameters to comply with their design parameters, efficiency and maximise life expectancy.

The system may further comprise a router. The router may be in data communication with other components of the system. The router may be common to more than one system. Thus, a router may provide a data connection between systems.

The system may further comprise a Human Machine Interface (HMI).

The HMI may be in data communication with other components of the system.

The present system may be used in conjunction with further systems.

Systems may be in data communication with each other. Similar systems may apply a transmission control protocol to communicate with each other. The PCM may be adapted to operate selectably in a "master" mode or a “slave" mode.

When two or more systems are used in conjunction with one another, a single "master" is needed. All other systems must operate in “slave" mode.

In "master" mode, a PCM sets addressing and other relevant data communication schema for any other system which is in “slave" mode.

A HMI of a system may be adapted to nominate which PCM is the "master". All other PCMs may be set automatically into “slave" mode, consequently.

Thus, the present inventive concept provides for a scalable apparatus comprising more than one system of the type described.

The or each system may be adapted to connect to an AC low voltage (for example, of the order of 400V nominal) synchronised (V,l,Cos0, KVAr and Frequency) 3 phase, 3 or 4 wire power bus. In turn, such a power bus may be connected to further system.

Detailed description of the invention

Exemplary embodiments of a system of the present inventive concept will now be described, with reference to the accompanying drawings which show schematic representations.

In Figure 1, solid lines show substantive, i.e. power transmitting, electrical connections within the system; broken lines show data communication connections except in the case of the labelled 400 VAC supply.

Battery units 60 and 61, 70 and 71, and 80 and 81 are arranged in pairs to form strings. Battery units 60 and 61 form a string; battery units 70 and 71 form a string; and battery units 80 and 81 form a string. For each string the constituent battery units are connected together electrically. Each string is in turn selectably connected to an inverter/ rectifier (shown for strings 60, 61 and 70, 71). Pairs of inverters/rectifiers 35, 36 are in communication with a gateway module 300, which is in turn connected to other components of the system by way of a data network, managed by a TCP ("MODBUS"). Each battery unit 60, 61, 70, 71, 80, 81 is in data communication with an opto-isolator via a CAN line. Opto-isolators are grouped in sets of three to form a CAN to CAN module 230, 235 so that three battery units are connected to a CAN to CAN module 230, 235.

The CAN to CAN modules 230, 235 are in turn in data communication with a CAN server 250. The CAN server 250 is in turn connected to other components of the system by way of the data network. The CAN server has intrinsic processing capability and can manage system sub-routines as well as monitor/respond to discrepancies/errors within the connected controller area network(s).

A PCM 50 connects to other components by way of the data network.

A router 10 connects to other components by way of the data network. A HMI 40 connects to other components by way of the data network.

In use, the CAN to CAN modules multiplex scan the CAN lines to which they are respectively connected, thereby receiving relevant data from the respective battery units 60, 61, 70, 71, 80, 81. The CAN to CAN modules pass relevant data to the CAN server, in turn.

The CAN server is - as mentioned above - connected to other components by way of the data network. Especially, the CAN server is connected to the PCM 50 and gateway module 300.

Data received from the respective battery units 60, 61, 70, 71, 80, 81 thus informs the PCM 50 and enables the control of the flow of electrical energy to and from the strings 60 and 61, 70 and 71, 80 and 81. The PCM 50 is adapted to monitor data streams from all batteries within the data network and connects or disconnect all or any string from any inverter/rectifier. The PCM maintains the battery parameters to comply with their design parameters, efficiency and maximise life expectancy.

The gateway module 300 processes power demands broadcast via the data network and selectably connect or disconnect a string to or from an inverter/rectifier or varies the power to or from the attached string.

Figure 2 shows a high-level schematic illustrating the path of energy transfer between the grid and the battery units in an embodiment of the system and illustrating the nodal switching concept. The dashed boxes surrounding the battery units indicate their individual BMS units. Two or more battery units are connected in series to form a string. Two or more strings are connected to a common bi-directional inverter via a set of controllable DC contactors (controllable switches), which provide the ability for the system to control the flow of power from the grid to each string. In Figure 2, two selectable strings are shown but the modular concept of the present inventive concept allows the possible connection of more strings to a common bi-directional inverter. The bi-directional inverter has the function of converting AC power to DC power and vice versa, enabling the transfer of energy between the local grid and the battery units. The DC and AC protection consists of several protective devices such as isolators and circuit breakers that act to ensure the safety of the system under fault conditions. The combination of the AC protection, bi-directional inverter and DC protection is known as the power conversion system (PCS). The modular configuration of switchable battery units and PCS is known as a channel. As shown in Figure 2, several channels can be connected to the grid in parallel to increase the power and capacity of the overall system. The dashed boxes shown enclosing each battery unit indicate that each unit requires its own communication connection between its internal BMS (battery management system) and the controller, for both receiving commands and also transmitting feedback data to other elements such as a CAN server. Feedback data may be, for example, unit state of charge (SoC), cell temperature, cell voltage, power available, among many others.

Figure 3 shows a schematic illustrating the communication system transferring data and commands between the battery units and the PCM (power control module) and HMI (human machine interface). Dashed lines represent CAN communication and solid lines indicate MODBUS TCP communication. The dashed boxes surrounding the battery units indicate their individual BMS units and respective lines indicate their connection to specific CAN2CAN modules.

The high-level schematic in Figure 3 illustrates the communication network between the respective controller (labelled as CAN2CAN MODULE) and the battery units. The HMI (human machine interface) acts as the interface between the system and the user and passes power requests to the PCM (power control module) via MODBUS TCP. The PCM acts as a higher level system controller (distinct from the controller which addresses each battery unit), processing the requests and managing the distribution of commands to the PCS and battery units, incorporating feedback signals from each part of the system. The function of the CAN server and CAN2CAN (referred to elsewhere as CAN to CAN) modules is to process and manage the bi-directional flow of data between the battery units and the PCM.

The dashed lines shown in Figure 3 represent the CAN communication required for each battery unit. In their original application, automotive battery units are only ever used individually, and therefore there is never the possibility of ambiguity of the origin of a CAN message from a battery unit. However, when controlling multiple battery units with a single controller, the CAN signals must be processed and organised in such a way that there is no ambiguity regarding the source of the CAN messages; the CAN2CAN modules and CAN server provide this function.

The CAN server is a programmable unit that acts as the link between the PCM unit and the battery units and offers additional functionality in terms of input/output pins for control and monitoring. It processes the CAN messages from all battery units, organises them and sends them to the PCM using MODBUS TCP protocol. It also acts in the other direction, converting the MODBUS TCP messages from the PCM to CAN and distributing them to the battery units. It provides an additional safety check by monitoring the communication between the PCM and the battery units and has the ability of shutting down the system if the PCM does not react to abnormal conditions within a certain timeframe.

Several battery units are connected to each CAN2CAN module, which is then connected to the CAN server. The CAN2CAN modules are CAN bus switches, which act to multiplex the CAN signals from several battery units (an example of three is shown in Figure 3) onto a common CAN bus to the CAN Server. The CAN messages for each individual battery unit are processed in such a way that they remain identifiable for each battery unit although they are multiplexed on a single bus. An additional function of the CAN2CAN modules is to physically isolate the high voltage battery system from the controls system using opto-isolators.

In use, as illustrated by Figure 2, multiple battery units connected in series (strings) are connected to the PCS via switchable contactors to increase the capacity of the system. In this way, when one string is exhausted, a channel can switch to the other string which still holds available energy, allowing the channel to continue operating. The plots shown in Figure 4 illustrate this process for a single channel consisting of two strings (A and B).

Figure 4 shows at (a) a schematic highlighting the initial connection of string A to the PCS, with string B idle; at (b) simplified example plots illustrating the power delivered (top) and state of charge (bottom) for each string during a full discharge of the battery units; and at (c) a schematic demonstrating the switch of the PCS connection from string A to string B after the battery units of string A are exhausted.

In Figure 4(b), the upper plot presents the discharging power of each string above representative plots of state of charge (SoC), which is a well-known indicator of the amount of energy available in the string. Initially, string A is discharging power (transferring power to the grid from the battery units) and string B is disconnected and idle. The SoC for string A decreases with time as the battery units discharge, eventually becoming exhausted. At this point, the control system requests a switch of strings, resulting in a disconnection of string A. String B is then connected to the PCS, and the output power is restored as shown in the decreasing SoC of string B. The schematics (a) and (c) illustrate the corresponding connection of the strings to the PCS system. This process is demonstrated for discharging, but an identical process can be applied to charging (opposite direction of power flow).

Furthermore, this example shows that the strings are switched when string A is exhausted, but this does not necessarily have to be the case; the control system (PCM) has been developed in such a way that the point of switching is a calibratable value dictated by the operation of the system and the control mode. For example, a threshold may be set in the control strategy that requests a switch of strings if the difference in SOC between strings exceeds a certain value.

Each channel has the independent ability to switch between its strings; however, this must be coordinated by the control system to maintain constant power delivered by the system. During a switch, it is not possible to import or export power from the switching channel as the necessary safety checks are carried out during connection and disconnection of the DC contactors. This is illustrated in Figure 5. Figure 5 shows a further representation of the transitions shown in in Figure 4. For the system to maintain constant power while a single channel is switching, the other channels must increase the power that is imported or exported in order to compensate for the reduction in power due to the switching channel (a representation of which is shown in Figure 6). The proportional increase of power required to compensate for the switching channel is dependent on the number of channels available in the system (e.g. if there are 6 channels in a system, the 5 non-switching channels must each produce 20% more power to compensate for the switching channel).

The plots shown in Figure 7 demonstrate this process of compensation during a switch. Figure 7 shows example plots showing the power delivered by a switching channel demonstrating the temporary loss of power during the switch (upper part) and the power delivered by the other non-switching channels (lower part) that must increase the power delivered during a switch to compensate for the switching channel. The power output from the switching channel is shown in the upper plot of Figure 5. In the lower plot, the power output from the non-switching channels is shown. As described, the power output from the non-switching channels must increase during the process of switching in order to compensate for the loss of the switching channel.

Figure 8 shows a high-level flowchart indicating the process of switching in terms of the system control. Power requests are sent to the control system (PCM), which incorporates existing feedback from the system to provide closed loop control. A request for a switch of strings is dependent on many variables including the status of the battery units in each string and the adopted switching strategy. If no switch is required by any channel, then the control system distributes the power commands to each channel. If a switch is requested, the control system simultaneously acts to stop the flow power through that channel and increases the power output from the remaining non-switching channels. The DC contactors of the switching channel are then operated in such a way to disconnect the original string and connect the other string to the bi-directional inverter. Feedback from the DC contactors is required to ensure that the connection of the string is secure before power is permitted to flow to and from that string. Additional to software checks, there are also hardware checks in the form of electrical interlocks to prevent incorrect operation of the DC contactors during switching, ensuring the safety of the system. Once the connection is confirmed, power is permitted to flow through the switched string and the power output from the non-switching channels is reduced simultaneously. Commands from the PCM are distributed every 100 milliseconds to ensure fine control of the system output.

On a system level, with multiple channels operating, requests for string switches typically occur at similar times for each channel as the power flow from each channel is distributed equally. Therefore, a queuing system is used on a ‘first come, first serve' basis to implement the switches sequentially for each channel. If the power request from the user then changes from charge to discharge, or vice versa, the queue is refreshed.

It should be noted that the control system is a flexible platform that has been developed in a ‘battery-agnostic’ way so that it can function with different types of second life (e.g. EV) battery units and bi-directional inverters, as long as their electrical characteristics and communication parameters are fully specified.

Claims

1. A system for storing electrical energy in more than one battery unit, each battery unit being a sealed unit of known kind including within it one or more battery cells and a control means adapted to transmit and receive data to and from a controller outside the battery unit via a data bus, said data being arranged according to a standard protocol adapted for use with one battery unit within a substantially closed CAN network, each battery unit being adapted to be addressed identically by such a controller, and the system being characterised in that it is adapted so that each battery unit is controlled by a single controller, and that the controller is adapted to transmit and receive data to and from each battery unit and adapted to control the more than one battery units on the said single data bus, so that addressing information from each battery unit is not required..

2. A system according to claim 1, wherein the controller is a CAN to CAN module.

3. A system according to claim 2, wherein multiple battery units feed information simultaneously into the CAN to CAN module, to pool data from the battery units, identify each data stream and its origin, and simultaneously stream the aggregated data out on a single CAN bus.

4. A system according to claim 2 or claim 3, wherein the CAN to CAN module comprises a plurality of opto-isolators.

5. A system according to claim 4, wherein each opto-isolator is connected to a battery unit.

6. A system according to any of claims 2 to 5, wherein the CAN to CAN module is adapted to receive data from battery units by way of multiplex scanning of CAN lines.

7. A system according to any of claims 2 to 6, wherein the system further comprises a CAN server and the CAN to CAN module is adapted to transmit data to the CAN server.

8. A system according to claim 7, wherein the CAN server is adapted to have intrinsic processing capability and to manage system sub-routines as well as monitor/respond to discrepancies/errors within the connected controller area network(s).

9. A system according to any preceding claim, wherein each battery unit is further connected via a Direct Current (DC) line to an inverter/rectifier for transmission of substantive electrical energy.

10. A system according to claim 9, wherein a plurality of battery units are arranged as a string, the string being connected to an inverter/rectifier by a DC line.

11. A system according to claim 10, wherein a DC line of a string may be selectably connected to or disconnected from a respective inverter/rectifier.

12. A system according to claim 10 or 11, having more than one string.

13. A system according to any of claims 9 to 12 when read appendant to claim 7, wherein the or each inverter/ rectifier is in communication with the CAN server.

14. A system according any of claims 10 to 13, wherein the or each inverter/rectifier is in communication with a gateway module.

15. A system according to claim 14, wherein the gateway module is adapted to process power demands broadcast via the data network and selectably connect or disconnect a string to or from an inverter/rectifier or vary the power to or from the attached string.

16. A system according to any preceding claim, comprising pairs of inverters/rectifiers with common Alternating Current (AC) and Direct Current (DC) connections.

17. A system according to any preceding claim, further comprising a Power Control Module (PCM).

18. A system according to claim 17 when read appendant to claim 7, wherein the CAN server is adapted to act as a buffer for the PCM.

19. A system according to claim 18, wherein the CAN server is adapted to perform the task of a safety watchdog.

20. A system according to any of claims 17 to 19, wherein the PCM is adapted to operate selectably in a "master" mode or a “slave" mode.

21. A system according to any preceding claim, further comprising a data transmission network.

22. A system according to any of claims 17 to 20 when read appendant to claim 21, wherein the PCM is adapted to monitor data streams from all batteries within the data network and connect or disconnect all or any string from any inverter/rectifier.

23. A system according to any preceding claim, further comprising a router adapted to be in data communication with other components of the system.

24. A system according to any preceding claim, further comprising a Human

Machine Interface (HMI) adapted to be in data communication with other components of the system.