Battery management system

Abstract

A battery management system (2) configured to supply or receive power in accordance with an external power demand. The battery management system (2) includes a plurality of power regulating devices (4a-d) connected in series. Each of the plurality of power regulating devices (4a-d) includes an interface connectable (8a-d) to an energy storage unit (6a-d) for exchange of power therewith. Each of the plurality of power regulating devices (4a-d) is configured to control power through its interface (8a-d). The battery management system (2) is configured to control at least one of the plurality of power regulating devices (4a-d) to operate in a maintenance mode while others of the plurality of power regulating devices (4a-d) contribute to meeting the external power demand.

Description

[0001] Battery Management System

[0002] Technical Field

[0003] This disclosure relates to a battery management system configured to supply or receive power. In particular, the disclosure relates to a battery management system having a plurality of power regulating devices configured to operate in a maintenance mode.

[0004] Background Art

[0005] Large batteries are often made up of many small cells integrated with many other systems such as electronics, HVAC systems, communication and control software, etc. As is the case for all large systems, the performance slowly changes over time. For batteries specifically, this can be due to degradation of individual components (cells or others), environmental changes (e.g. heatwaves), changes in the use case (e.g. participating in different power markets), inaccuracies in software or hardware which slowly add up over time (e.g. offsets in sensors causing errors in the state estimation), replacement of broken components, or other unexpected events and faults.

[0006] It is therefore desirable to perform certain maintenance processes on battery systems to ensure that the battery performs optimally and to prolong battery life. These maintenance processes are usually performed as part of a service on the battery which is carried out periodically. During the maintenance, the battery must be offline, or in other words the customer cannot use the battery. The maintenance can be split into many short periods (e.g. a few minutes of passive balancing at the end of every charge), or grouped into one big maintenance (e.g. an annual deep cycle to measure the capacity of the battery). This creates an inconvenience, as well as loss of revenue for the battery owners and operators. Not only do they need to arrange contractors to monitor the battery and perform maintenance if needed, but their asset is unavailable to them while maintenance is carried out.

[0007] Summary of the Disclosure According to a first aspect of the present disclosure, there is provided a battery management system configured to supply or receive power in accordance with an external power demand; wherein the battery management system comprises a plurality of power regulating devices, each having an interface connectable to an energy storage unit for exchange of power therewith; wherein each of the power regulating devices is configured to control power through its interface; and wherein the battery management system is configured to control at least one of the plurality of power regulating devices to operate in a maintenance mode while others of the plurality of power regulating devices contribute to meeting the external power demand.

[0008] According to a second aspect of the present disclosure, there is provided a battery management system configured to supply or receive power in accordance with an external power demand; wherein the battery management system comprises a plurality of power regulating devices connected in series; wherein each of the plurality of power regulating devices comprises an interface connectable to an energy storage unit for exchange of power therewith; wherein each of the plurality of power regulating devices is configured to control power through its interface; and wherein the battery management system is configured to control at least one of the plurality of power regulating devices to operate in a maintenance mode while others of the plurality of power regulating devices contribute to meeting the external power demand.

[0009] The external power demand may be from any source, e.g. it may be from an external entity that requires power and / or supplies power. By way of example, the external power demand may be from an electrical grid (for example, a national electrical grid system). Such batteries are often referred to as “grid energy storage” and are used to store energy from intermittent power sources such as renewables when supply exceeds demand. In other examples, the external power demand may be from an electrically powered vehicle (e.g. an electric car). The battery from an electric vehicle needs to supply power upon demand for acceleration and also to store power from regenerative braking.

[0010] The power regulating devices may be any type or design that control the amount of power through its interface. Any number of power regulating devices may be used in the battery management system. In some examples, the battery management system comprises at least 10 power regulating devices, optionally at least 25 power regulating devices, optionally at least 50 power regulating devices, optionally at least 100 power regulating devices, optionally at least 200 power regulating devices. It will be appreciated that larger batteries may have a larger number of power regulating devices. The number of power regulating devices may be selected according to the intended use of the battery. Each power regulating device defines one controllable unit of the system as each power regulating device is able to control the power flow to / from its attached energy storage unit.

[0011] In some examples, the power regulating devices are individually controllable by the battery management system. For example, each of the power regulating devices may be configured to receive a separate control signal from the battery management system. However, it will be understood that in some examples the power regulating devices may operate in a distributed control arrangement. It will also be appreciated that the battery management system may be configured to control the power regulating devices as one or more groups (e.g. by sending the same control signal to a plurality of the power regulating devices and / or sending a control signal to a connection that is shared by a plurality of the power regulating devices). Where different groups are provided, these may of course be controlled differently.

[0012] The power regulating devices may be connected in series with one another. In some examples, the current flowing through each of the power regulating devices may be substantially the same. Therefore, the power provided by each of the power regulating devices may be altered by adjusting its output voltage.

[0013] In some examples, each of the power regulating devices is connected to an adjacent power regulating device via at least one terminal. In some examples, an input terminal of one power regulating devices is connected to an output terminal of an adjacent power regulating device. In this manner, the plurality of power regulating devices may form a continuous current path.

[0014] Controlling one power regulating device in a series chain to operate in a maintenance mode is generally more complex and difficult than operating one device of a parallel arrangement in maintenance mode. In a parallel arrangement, all units are tied together such that they have the same voltage across them. Therefore removing one unit from the parallel arrangement simply causes more current to be drawn through the remaining parallel devices.

[0015] In a series chain, all devices have the same current through them and the voltage of the series chain is the sum of the voltages provided by each of the devices. To perform a maintenance procedure on a single unit, there may be a requirement for a specific (and chosen) current to run through the unit. Hence, it is desirable to be able to adapt the path of the current in order to produce the specific (and chosen) current in the unit undergoing maintenance.

[0016] Furthermore, taking one device out of operation (e.g. for a maintenance operation) will reduce the voltage across the series chain and in many practical arrangements, several series chains are also connected together in parallel such that the voltages across the chains are also tied together. If the voltage of one string decreases because one of its units is disconnected, this may result in very high currents running between the units (e.g. on the DC busbars) which can damage the batteries. Therefore, it is desirable to ensure that the total string voltage is not affected when one or more of the units is operated in maintenance mode.

[0017] To enable each device to be operated in maintenance mode, it is generally desired that each device comprises controllable power electronics. When a device in a chain fails (unpredictably) then the other devices must compensate very rapidly. However, when one or more devices are deliberately placed in maintenance mode (predictably) then the other devices in the series chain can be simultaneously controlled so that compensation happens seamlessly. In other words, where the effect that the maintenance mode has on the series chain is known, the effect can be anticipated and compensated simultaneously by appropriate control of the other devices in the chain.

[0018] The interface of the power regulating device may be any type that permits power exchange with an attached energy storage device. In one simple form the interface may simply comprise terminals to which an energy storage device can be attached. For example, the interface may comprise a positive terminal and a negative terminal for connection to the corresponding terminals of an energy storage unit. As will be discussed further below, the interface may also permit data exchange with an attached energy storage unit, e.g. to provide data to the unit or to receive data from the unit. The interface may comprise one or more additional terminals or one or more data ports (e.g. a USB port, wired network port, etc.) or a wireless transceiver device (e.g. a WiFi or Bluetooth device), In some examples, the interface may permit DC power transfer. In some examples, the interface may permit AC power transfer, for example single-phase or multi-phase (e.g. three- phase) AC power transfer. The energy storage unit may be directly or indirectly connected to the interface of the power regulating device (i.e. there may or may not be other intervening devices between the interface and the energy storage unit).

[0019] The interface may be configured to control current through the interface (e.g. to control electrical charge or current with the energy storage device) and / or the interface may be configured to control the voltage at the interface (which in turn may determine current flow across the interface). For example, the power regulating device may control the current and / or voltage at the interface in order to control the power through the interface. The power regulating device may be configured to receive power from and / or supply power to an attached energy storage unit via the interface. In some examples, the power regulating device may be configured to control its interface such that no power is exchanged with the energy storage unit at the interface.

[0020] By controlling at least one of the plurality of power regulating devices to operate in a maintenance mode while others of the plurality of power regulating devices contribute to meeting the external power demand, the battery management system can continue to meet the external power demand while at least one of the power regulating device is operating in a maintenance mode. In other words maintenance can be performed while the battery management system is in use (i.e. the battery remains online during the maintenance). Maintenance can thus be performed more frequently and / or with less delay (e.g. compared to waiting until the battery management system is not required to meet an external power demand and can be taken offline). With such arrangements there is less disruption to the user and less down time of the battery, thereby increasing its cost effectiveness.

[0021] The number of power regulating devices that are operated in maintenance mode at any given time can be varied and is not restricted to a single device at any one time. The number of devices that can be operated in maintenance mode simultaneously may be determined according to a particular implementation, e.g. according to the size of the overall battery and the expected loads that need to be met. When a power regulating device is operating in maintenance mode, any suitable maintenance process may be carried out. For example, various test or evaluation processes may be carried out or corrective action may be taken such as software updates or cell balancing procedures. In some examples, the maintenance process affects the ability of the power regulating device to contribute to meeting the external power demand. This may include drawing or supplying less power than would be drawn or supplied if it were in normal mode, or drawing or supplying more power than would be drawn or supplied if it were in normal mode, or it may include drawing power when it would normally be required to supply power or vice versa.

[0022] In some examples, the maintenance process may require power to be supplied at the interface of the power regulating device to the attached energy storage unit. If the battery management system is required to supply power to meet the external power demand, the power regulating device that is in maintenance mode is then unable to contribute to meeting the external power demand. In this example, the external power demand is still met by the other power regulating devices, i.e. those other power regulating devices in combination increase the power supply from their respective energy storage units to meet the demand. On the other hand, if the battery management system is instead required to receive power to meet the external power demand (i.e. the external demand is to charge the attached energy storage units) then the power regulating device that is operating in maintenance mode may contribute to meeting the external power demand by using the received power as part of the maintenance process. Likewise, in some examples, the maintenance process may produce power at the interface of the power regulating device from the attached energy storage unit. If the battery management system is required to receive power to meet the external power demand (i.e. the external demand is to charge the attached energy storage units) then the power regulating device that is in maintenance mode is unable to contribute to meeting that external power demand. In this example, the external power demand continues to be met during the maintenance process by the other power regulating devices, i.e. those other power regulating devices in combination increase the power drawn to their respective energy storage units to meet the demand. On the other hand, if the battery management system is required to supply power to meet the external power demand, the power regulating device that is in maintenance mode may contribute to meeting the external power demand by using the power produced from its attached energy storage unit as part of the maintenance process.

[0023] In some examples, in the maintenance mode the power through the interface is controlled according to a maintenance process of the maintenance mode. Power may be supplied or received at the interface.

[0024] The power through the interface may be determined in many different ways. In some examples, the battery management system may determine the power demand according to a selected maintenance process of the maintenance mode. For example, the battery management system may comprise a memory configured to store information about the power demand of certain maintenance processes. The battery management system may then look up the power associated with a selected maintenance process and control the power through the interface according to this information. In some examples, the battery management system (e.g. via the power regulating devices) may calculate or detect (e.g. in real time) the power demand of a maintenance process and adapt the power at the interface accordingly.

[0025] While at least one of the plurality of power regulating devices is operating in a maintenance mode, others of the plurality of power regulating devices contribute to meeting the external power demand. In some examples, the battery management system is arranged such that, when the at least one power regulating device operates in the maintenance mode, the others of the power regulating devices operate in a normal mode in which power through the interface is determined at least in part to contribute to meeting the external power demand.

[0026] Any number of the available power regulating devices may contribute to meeting the external power demand. In some examples, a single power regulating device may meet the external power demand. In other examples, any or all of the power regulating devices that are operating in normal mode may supply or receive power to meet the external demand.

[0027] The amount of power that each of the power regulating devices contributes may be determined in various ways. For example, the power regulating devices (that are operating in normal mode) may each be configured to supply or receive substantially the same amount of power. In other examples, the amount of power supplied or received by each power regulating device may be determined based on properties of the power regulating device and / or of the attached energy storage unit, e.g. the amount of power that the power regulating device can control, the amount of energy storage that is available in the storage unit, the state of charge, state of health, type of storage unit (battery, supercapacitor, cell chemistry, etc.), temperature of the energy storage unit or other conditions of the energy storage unit.

[0028] In some examples, in the normal mode the power through the interface is determined at least in part according to the power demand of the at least one power regulating device operating in the maintenance mode.

[0029] The power regulating devices operating in maintenance mode may produce a power demand, in that the maintenance process requires power or produces power. As discussed above, in order for the external power demand to be met, the other power regulating devices may need to adjust their power output or the amount of power received. In some examples, in the normal mode the power through the interface is determined at least in part to compensate for the at least one power regulating device in maintenance mode. For example, if the maintenance process of the power regulating device in maintenance mode requires power (e.g. to charge its attached energy storage unit), the power regulating devices that are operating in normal mode may increase their power output (from their attached energy storage units) to compensate for the additional power requirement while also still supplying the external load. Part of the power output of the devices in normal mode is supplied to the meet the external power demand and part of the power output of the devices in normal mode is supplied to the meet the power demand of the power regulating devices in maintenance mode. It will be appreciated that a similar scenario applies when the external demand is a supply of power.

[0030] Similarly, if the maintenance process of the power regulating device operating in maintenance mode produces power, the power regulating devices operating in normal mode may decrease their power output to compensate. The power output of the devices in both normal mode and maintenance mode are used to meet the external power demand.

[0031] In some examples, in the maintenance mode, one or more of the following maintenance processes is carried out: preventing power from passing through the interface; reducing the power drawn from or supplied to an energy storage unit through the interface; applying a predetermined current, voltage and / or power through the interface; applying power through the interface for a predetermined period of time; applying a predetermined current, voltage and / or power through the interface for a predetermined period of time; applying a predetermined pattern or sequence of current, voltage and / or power through the interface; applying power through the interface until the energy storage unit is fully charged; fully or partially discharging the energy storage unit; fully or partially charging the energy storage unit; instructing a local battery management system of the energy storage unit to perform an operation on the energy storage unit; and / or acquiring information from the energy storage unit.

[0032] Each of these processes will now be discussed.

[0033] In some examples, the maintenance process comprises preventing power from passing through the interface. When the power regulating device is connected to an energy storage unit, this maintenance process may be used to prevent the energy storage unit from supplying or receiving power. This may be useful if it is determined that there is a problem with the energy storage unit and / or the power regulating device. This may help to ensure that the energy storage unit and / or the power regulating device are not used until the problem is resolved. This may be useful if the energy storage unit is faulty and / or needs to be replaced. Preventing power from passing through the interface may help to ensure that no power is supplied or received until a working energy storage unit is attached and available for use. This maintenance process may also be used if the energy storage unit is receiving an update (e.g. to its software). This may be the case where the energy storage unit is itself a battery with multiple cells that are controlled by a local battery controller (e.g. its own battery management system) of the energy storage unit.

[0034] In some examples, power may be prevented from passing through the interface in order to allow the energy storage unit to reach a state of relaxation. After the energy storage unit has been relaxed, it may reach an equilibrium. This may be useful for determining an accurate open-circuit voltage. When done after a full discharge, this can also provide an accurate measure of a zero (or minimum) state of charge.

[0035] In some examples, the maintenance process comprises reducing the power drawn from or supplied to an energy storage unit through the interface. When the power regulating device is connected to an energy storage unit, this maintenance process may be used to reduce the strain on the energy storage unit. This may be used if it is determined that there is a problem with the energy storage unit and / or the power regulating device, but where it is not necessary to complete disable or bypass the energy storage unit. This may help to ensure that the energy storage unit and / or the power regulating device are not used to their full capacity, which may help to avoid exacerbating the identified problem. By way of example, if an elevated temperature is detected in an energy storage device, reducing the amount of power drawn from or supplied to the energy storage device may allow it to cool down and return to normal operation, but still allows it to contribute to the overall external power demand rather than being fully isolated. Further data can be gathered from the energy storage unit during this time for further analysis of the situation. An energy storage device may be operated in such a reduced power state for a significant period of time (e.g. until the energy storage unit can be replaced) or it may be operated in such a reduced power state only for a short period of time (e.g. until it is determined to be safe to return to normal operation).

[0036] In some examples, the maintenance process comprises applying a predetermined current, voltage and / or power through the interface. A predetermined fixed current, voltage and / or power may be useful for certain tests, e.g. to measure a particular response of the energy storage device to the fixed input. A predetermined varying current, voltage and / or power may also be useful for similar reasons, e.g. to measure a particular response of the energy storage device over a range of input values. In some examples, the maintenance process comprises applying power through the interface for a predetermined period of time. In some examples, the maintenance process comprises applying a predetermined current, voltage and / or power through the interface for a predetermined period of time. For example, a current, voltage or power may be applied to the energy storage unit for a short period of time (e.g. a pulse). This may be followed by a relaxation of the energy storage unit, for example as part of a “pulse test”, also called a “hybrid pulse power characterisation (or HPPC) test”, as part of a “relaxation” test, or as part of an OCV measurement, also called a “Galvanostatic intermittent titration technique, or GITT” test. This maintenance process may be used to determine one or more parameters of the energy storage unit. In particular, this may be used to determine the dynamic response of the energy storage unit. In other examples, a longer predetermined period of time may be used. For example, applying a predetermined current (or current profile) for a predetermined time defines an amount of charge sent to (or received from) the energy storage unit which can be useful for analysing the current state of health of the energy storage unit. In some examples, the maintenance process comprises applying a predetermined pattern or sequence of current, voltage and / or power through the interface, often referred to as a “drive cycle” or “load profile” test. For example, a pattern or sequence simulating the external power demand during a particular power scenario may be used to test the performance of the energy storage unit for that scenario. By way of example, one such scenario might be a particular drive condition of an electric vehicle, such as high acceleration or hard regenerative braking. In some examples, the current, voltage and / or power may be varied (e.g. increasing or decreasing in steps) to compare the response of the energy storage unit to different power demands. These tests may help to determine the dynamic response of the energy storage unit and / or build up a profile of the energy storage unit.

[0037] In some examples, the maintenance process comprises applying power through the interface until the energy storage unit is fully charged, for instance to perform a “capacity checkup” or a “pseudo-open-circuit voltage measurement”. This maintenance process may be used to check or measure the capacity of the energy storage unit (i.e. how much power the energy storage unit can store and / or supply) or its properties when in a full state of charge. When fully charged following a full discharge, the present state of health of the energy storage unit can be measured. This information may be useful in determining the ability of the energy storage unit to meet the external power demand.

[0038] In some examples, the maintenance process comprises fully or partially discharging the energy storage unit, for instance to perform a “capacity checkup” or a “pseudo- open-circuit voltage measurement”. Fully or partially discharging the energy storage unit may be used to determine one or more of: the capacity of the energy storage unit; the efficiency of the energy storage unit; the thermal performance of the energy storage unit (e.g. by cycling at high current or high power) and / or to record the open circuit voltage of the energy storage unit at full discharge (or minimum charge) or to record the open circuit voltage of the energy storage unit as a function of state of charge by discharging at a low current or low power. In some examples, the energy storage unit may be fully discharged and an estimated stored value of the state-of charge reset to zero in the battery management system. Note that this estimate may be stored / reset in either or both of the overall battery management system and a local battery management system for the particular energy storage unit.

[0039] In some examples, the maintenance process comprises fully or partially charging the energy storage unit, for instance to perform a “capacity checkup” or a “pseudo- open-circuit voltage measurement”. Fully or partially charging the energy storage unit may be used to determine one or more of: the capacity of the energy storage unit; the efficiency of the energy storage unit; the thermal performance of the energy storage unit (e.g. by cycling at high current or high power) and / or to record the open circuit voltage of the energy storage unit at full charge (or maximum charge) or to record the open circuit voltage of the energy storage unit as a function of state of charge by charging at a low current or low power. In some examples, the energy storage unit may be fully charged and an estimated stored value of the state-of charge reset to 100% in the battery management system. Note that this estimate may be stored / reset in either or both of the overall battery management system and a local battery management system for the particular energy storage unit.

[0040] In some examples, the maintenance process comprises instructing a local battery management system of the energy storage unit to perform an operation on the energy storage unit. In some examples, the energy storage unit may comprise a local battery management system. In particular, an energy storage unit that comprises a plurality of cells may comprise a local battery management system (e.g. to monitor the cells, balance the cells, and / or manage the power supplied by or to each of the plurality of cells in the energy storage unit). In some examples, the operation comprises active or passive balancing of the cells of the energy storage unit. During active or passive balancing, the power at the interface may be zero, but power may be received or exchanged by the cells in the energy storage unit. For example, power may be exchanged between the cells in the energy storage unit and / or power may be dissipated by a resistor in the energy storage unit. Performing operations within an energy storage unit (e.g. performing maintenance operations on one or more cells within an energy storage unit) may be advantageous because the performance of the energy storage unit may be limited by the cell with weakest performance. Therefore, improving the performance of individual cells within the energy storage unit may help to improve the overall performance of the energy storage unit.

[0041] In some examples, the maintenance process comprises acquiring information from the energy storage unit. The information may be any suitable or available type. For example, the information may comprise one or more of: a voltage of the energy storage unit; a current of the energy storage unit; a resistance of the energy storage unit; a capacitance of the energy storage unit; an impedance of the energy storage unit; a capacity of the energy storage unit; a state of health of the energy storage unit; a temperature of the energy storage unit and / or a state of charge of the energy storage unit.

[0042] In some examples, when the one or more maintenance processes have been completed, the power regulating device is operated in the normal mode.

[0043] When the power regulating device is connected to an energy storage unit, one or more of the above maintenance processes (or other maintenance processes not listed above) may be carried out without the energy storage unit being disconnected from the power regulating device. This may help to ensure that maintenance processes can be carried out without the need for a person (e.g. a maintenance technician) to remove the energy storage unit. This may help to simplify maintenance of the battery and ensure that maintenance can be undertaken with little or no adverse impact on meeting the external power demand.

[0044] In some examples, the interface of each of the plurality of power regulating devices is connectable to an energy storage unit for exchange of information therewith. In some examples, each of the plurality of power regulating devices is connected to a different energy storage unit. That is, there is a one-to-one mapping between the power regulating devices and the energy storage units. In some examples, each of the energy storage units is individually controllable (e.g. by the associated power regulating device).

[0045] The energy storage units may comprise any means for storing energy. For example, the or each of the energy storage units may comprise: a cell; a group of cells connected in parallel (a supercell); a group of cells or supercells connected in series (a module); a group of modules connected in series (a string or a rack) and / or a group of racks connected in series and / or in parallel (a battery container). In some examples, any number (e.g. each) of the energy storage units may be a different type of energy storage unit. In some examples, all of the energy storage units are the same type. Non-limiting examples of energy storage units include rechargeable batteries such as lead-acid, nickel-cadmium, nickel-metal-hydride, lithium-ion, lithium iron phosphate, lithium-ion polymer, sodium-ion, lithium metal, solid state, and flow batteries and supercapacitors.

[0046] Information may be sent to and / or received from the energy storage unit. The information exchanged at the interface may be any suitable and available type. The information may be exchanged by any means (e.g. via a wired or wireless connection).

[0047] In some examples, the information exchanged at the interface comprises sending instructions for operation of the energy storage unit. For example, the power regulating device may send an instruction to the energy storage unit to perform a maintenance operation on the energy storage device (such as cell balancing). In some examples, an instruction for operation comprises an instruction to send information about the energy storage device to the power regulating device. For example, the information may comprise an instruction to send data from one or more sensors (e.g. temperature sensor) of the energy storage unit to the power regulating device. In other examples, the information may comprise present estimated state of charge, state of health, usage history, or the like.

[0048] In some examples, the information exchanged at the interface comprises receiving information about the energy storage unit. For example, the energy storage unit may provide information about one or more of: a voltage of the energy storage unit; a current of the energy storage unit; a resistance of the energy storage unit; a capacitance of the energy storage unit; an impedance of the energy storage unit; a capacity of the energy storage unit; a temperature of the energy storage unit and / or a state of charge of the energy storage unit.

[0049] The power regulating devices may be controlled via a distributed control arrangement, e.g. by having local controllers at each power regulating device all in communication with each other such that they can effect overall control of the battery management system together. However, in other examples, the battery management system comprises a central controller configured to control each of the power regulating devices. The central controller may be any suitable type of computing device. In some examples, the central controller may comprise: a microprocessor, a general purpose computer, a server, a mobile computing device and / or a cloud computer. In some examples, the central controller may be located locally or remotely from the rest of the battery management system.

[0050] The central controller may be configured to communicate with the power regulating devices in various ways. For example, the central controller may be connected to the power regulating devices via a wired or a wireless connection. The central controller may be configured to control each of the power regulating devices individually. However, in some examples the central controller may control at least some of the power regulating devices as a group. The central controller may control more than one group, each group comprising one or more power regulating devices.

[0051] In some examples, each of the power regulating devices is configured to communicate the information exchanged at the interface to a central controller of the battery management system. The power regulating device may communicate with the central controller in any suitable manner (e.g. via a wired or wireless connection). In some examples, the power regulating device may perform some local processing on the information before communicating said information to the central controller. In some examples, the information exchanged at the interface and communicated to the central controller may be used by the controller to help determine operation of the battery management system. For example, the information may be used to help determine which of the plurality of power regulating devices should be operated in a maintenance mode and / or which of the plurality of power regulating devices should be operated in a normal mode.

[0052] In some examples, the central controller is configured to determine which of the plurality of power regulating devices is to be operated in maintenance mode. In some examples, the central controller is configured to determine which of the plurality of power regulating devices is to be operated in maintenance mode and / or which maintenance processes are carried out according to one or more of: a predetermined pattern or sequence; information received from one or more of the plurality of energy storage devices; the outcome of previous maintenance processes; the time elapsed since one or more of the plurality of power regulating devices was previously operated in maintenance mode; meeting the external power demand; information from one or more external entities; information received from one or more monitoring devices; and / or information received from one or more monitoring processes.

[0053] In some examples, the central controller makes its determination based on more than one of the factors above. In particular, the requirement to meet the external power demand may be considered alongside any goals or requirements of the battery management system itself.

[0054] In some examples, the central controller makes its determination according to a predetermined pattern or sequence. A predetermined pattern or sequence may be one in which the operations are decided in advance. For example, the central controller may be pre-programmed to send certain control signals (e.g. in a certain order and / or according to a certain timing sequence).

[0055] A predetermined pattern or sequence may include an order in which the plurality of power regulating devices is to be operated in maintenance mode. For example, the power regulating devices may be operated in maintenance mode according to the order in which they are connected together or according to the order of allocated identifiers for the power regulating devices, or according to any other arbitrary predetermined order. For example, when the power regulating devices are connected in series, a power regulating device may be placed into the maintenance mode when the adjacent power regulating device is returned to the normal mode. Working through all power regulating devices in some order ensures that each power regulating device undergoes appropriate maintenance operations on a regular basis and no power regulating devices are unintentionally skipped.

[0056] As well as determining a pattern or sequence for putting the power regulating devices into maintenance mode, it is also possible to determine a pattern or sequence in which various maintenance processes are carried out on the power regulating devices. For example, a maintenance program may include multiple tests or procedures, each of which (or a subset of which) is to be carried out on each power regulating device. These patterns can have different hierarchies. For example, a first sequence may determine the order of power regulating devices. Then, for each power regulating device, a set of maintenance processes may be carried out in a second sequence before moving on to the next power regulating device in the first sequence. Alternatively, a first sequence may determine an order of maintenance processes and for each maintenance process, that process is carried out on each power regulating device in a second sequence before moving on to the next maintenance process in the first sequence. There may be good reasons for both approaches. For example, it may be necessary to perform an emergency test on all attached storage units as quickly as possible. It would then be better to run this test across all devices before moving on to a new test. In other cases, when analysing cells for optimisation, some tests may take a while and be optimally done in a certain sequence (e.g. some before, some during and some after a full charge or a full discharge operation). It will be most efficient to carry out all such maintenance processes on storage unit before putting it back into normal operation, thereby reducing overall maintenance time for a full maintenance cycle. In some examples, the maintenance processes may include a number of tests and the tests may be carried out in order of their importance. The importance of the tests may be determined by the severity of the problems which they are configured to diagnose or resolve and / or by the severity of any potential consequences of the test. For example, a test that could result in the power regulating device preventing power from passing through the interface may be carried out before a test that could result in the power regulating device reducing the power drawn from or supplied to an energy storage unit through the interface.

[0057] In some examples, the central controller makes its determination according to information received from one or more of the plurality of energy storage devices. For example, the central controller may make its determination according to one or more of: a voltage of the energy storage unit; a current of the energy storage unit; a resistance of the energy storage unit; a capacitance of the energy storage unit; an impedance of the energy storage unit; a capacity of the energy storage unit; a temperature of the energy storage unit; a state of charge of the energy storage unit; a state of health of the energy storage unit; or other information acquired from the energy storage unit.

[0058] In some examples, the central controller makes its determination according to the outcome of previous maintenance processes. For example, when determining which of the plurality of power regulating devices is to be operated in maintenance mode, the central controller may use the results of previous maintenance processes. For example, if problems were identified in one of the power regulating devices during a previous maintenance process, the central controller may place that power regulating device into maintenance mode sooner (e.g. than one in which no problems were identified). This may help to ensure that any problems are resolved sooner.

[0059] In some examples, the order of maintenance processes may be determined by a present operational state of the system. By way of example, if a high external demand is expected at a particular time, the system may avoid tests which increase the power draw at that time. In another example, if multiple power regulating devices are operating in maintenance mode simultaneously, the system may order the tests to avoid two such devices simultaneously carrying out tests that draw power. It may be possible to match such devices so that one performs a power drawing process while another performs a power supplying process (e.g. one undergoing a charging test while the other undergoes a discharging test) so as to reduce the overall strain on the system and / or the overall effect on the capability to meet the external load.

[0060] In some examples, when determining which maintenance processes are to be carried out, the central controller may use the results of previous maintenance processes. For example, the central controller may determine which maintenance process to apply next based on whether any problems were identified in a previous maintenance process. For example, if a previous maintenance process identified a problem with the capacity of an energy storage device to which the power regulating device is connected, the central controller may determine that the next maintenance process should be to reduce the power drawn from or supplied to that energy storage unit through the interface. Using the results from previous maintenance processes to determine which maintenance process should be applied may help to ensure that any actions performed by the power regulating device are appropriate for the current state of the system. For example, in the case of a problem with the capacity of an energy storage unit, this may help to ensure that the energy storage unit is not over-charged or over-depleted, which could damage the energy storage unit.

[0061] In some examples, the central controller makes its determination according to the time elapsed since one or more of the plurality of power regulating devices was previously operated in maintenance mode. The central controller may prioritise those devices for which a greater amount of time has elapsed. This may help to ensure that the power regulating devices are all operated in maintenance mode regularly. In some examples, the power regulating devices may be operated in maintenance mode in a predetermined order, such that the device for which the longest time has elapsed will be placed into maintenance mode next. In some examples, the central controller may ensure that all of the power regulating devices are operated in maintenance mode once per cycle (e.g. once in a predetermined time period).

[0062] In some examples, the central controller makes its determination according to meeting the external power demand. In some examples, the central controller may be configured to calculate and / or obtain information about the power demand of one or more maintenance processes. The central controller may be configured to use this information to ensure that the external power demand can be met before controlling one or more of the power regulating devices to operate in maintenance mode and / or to carry out one or more maintenance processes. If the external power demand cannot be met, the central controller may determine not to place the one or more power regulating devices in maintenance mode and / or not to carry out one or more maintenance processes. This may help to ensure that the external power demand can be met. In some examples, the central controller makes its determination according to information from one or more external entities. In some examples, the external entity may be a person (e.g. a manager or user of the system). The information may comprise a command or instruction (e.g. to start a maintenance operation or to avoid maintenance operations).

[0063] In some examples, the central controller makes its determination based on information received from one or more monitoring devices. In some examples, the monitoring device may include at least one sensor configured to measure a parameter of a power regulating device and / or an energy storage unit. For example, the monitoring device may comprise a temperature sensor configured to measure the temperature of a power regulating device and / or an energy storage unit. If the temperature increases suddenly and / or passes a threshold value, that power regulating device may be operated in maintenance mode. In another example, the monitoring device may comprise a voltage, a current and / or a power sensor. If the power regulating device does not deliver the voltage, current and / or power that is expected of it (e.g. based on a command from a controller), then that power regulating device may be operated in maintenance mode.

[0064] In some examples, the central controller makes its determination based on information received from one or more monitoring processes. In some examples, the monitoring processes may be performed by one or more of: a power regulating device; a central controller and / or a local controller.

[0065] For example, the power regulating device may be configured to perform checks on its own operation. For example, the power regulating device may determine that its estimated state-of-charge is inaccurate or that its cells are not balanced. The power regulating device may be configured to output an error code or a request for maintenance if a fault is detected. A controller of the battery management system may be configured to receive this error code or request and operate that power regulating device in maintenance mode.

[0066] In some examples, a controller of the battery management system may be configured to compare the operation of the plurality of power regulating devices and operate a power regulating device in maintenance mode if that device is performing differently from the others. For example, a controller may receive data from each of the different modules (e.g. about their state of charge, state of health and / or temperature). If one of the power regulating devices differs significantly from the others (e.g. having much lower state of charge or state of health, or much higher or lower temperature), then that power regulating device may be operated in maintenance mode.

[0067] In some examples, the information received from the power regulating devices of the battery management system may be sent to an external entity (e.g. a cloud computing device). The maintenance processes may comprise analysis performed by an external entity to determine whether the power regulating devices are operating as expected. If it is determined that one or more power regulating devices are not operating as expected, these power regulating devices may be operated in maintenance mode.

[0068] More generally, the local controller, central controller or cloud computing device may detect any event (predetermined or unexpected) in the battery management system and, based on the detected event, may operate one or more power regulating devices in maintenance mode.

[0069] In some examples, the battery management system comprises a plurality of local controllers; wherein each of the plurality of local controllers is configured to control one or more of the plurality of power regulating devices.

[0070] The plurality of local controllers may be any type of device. In some examples, the plurality of local controllers may (e.g. each) comprise a microcontroller.

[0071] The plurality of local controllers may be configured to communicate with the plurality of power regulating devices in any suitable way. For example, the plurality of local controllers may be connected to the plurality of power regulating devices via a wired or a wireless connection. Each of the plurality of local controllers may be configured to control one of the plurality of power regulating devices individually. In some examples each of the plurality of local controllers may control at least some of the power regulating devices as a group. In some examples, each of the plurality of power regulating devices is in communication with and controllable by one local controller. That is, there is a one- to-one mapping between the power regulating devices and the local controllers. In some examples, the local controller may form part of the power regulating device.

[0072] In some examples, each of the local controllers is in communication with at least one of the other local controllers. For example, the local controllers may be configured to send information about the operation of the power regulating devices and / or the energy storage units. This may help to ensure that the operation of the plurality of power regulating devices is consistent between the local controllers and / or leads to the desired outcome in the operation of the power regulating devices.

[0073] The power regulating devices may take any of a number of forms depending on the energy storage units to be attached and the intended use of the battery management system. For example, each of the power regulating devices may comprise a DC-DC converter. The DC-DC converter may be any type, e.g. a buck converter, a boost converter, a buck-boost converter, a flyback converter, etc. Thus the power regulating device may be a step-up converter arranged to produce a higher voltage than the voltage of the energy storage device or it may be a stepdown converter arranged to produce a lower voltage than the voltage of the energy storage device, or it may be capable of both step-up and step-down conversion so as to provide a desired voltage according to instructions from a controller. The power regulating device may also be arranged to control (e.g. limit) the current flowing through it.

[0074] In other examples, each of the power regulating devices may comprise a DC to AC converter arranged to convert the DC voltage of the energy storage device into an AC voltage, e.g. for supplying an AC external load. The power regulating devices comprise an inverter. The inverter may be any type. For example it may provide a square wave output, modified sinewave output or pure sinewave output, it may be a half bridge or full bridge inverter, it may be a single phase or multiphase inverter, etc. In some examples, each of the power regulating devices may comprise both a DC- DC converter and a DC-AC converter. For example, the DC-DC converter may be connected to an energy storage unit and arranged to convert a first DC voltage (e.g. the DC voltage of the energy storage device) into a second DC voltage (e.g. a higher or lower DC voltage). The DC-AC converter may then convert the second DC voltage to AC.

[0075] In some examples, each of the plurality of power regulating devices comprises the same components (e.g. the same number and type of converters and / or switches) optionally having the same topology. In some examples, one or more of the plurality of power regulating devices may comprise different components (e.g. a different number or type of converters and / or switches), optionally having different topology. For example, it is not necessary that all power regulating devices have the same type of DC-DC converter.

[0076] In some examples, each of the power regulating devices comprises a switch configured to move from a first position in which the switch prevents power from passing through the interface to a second position in which the switch allows power to pass through the interface. When the power regulating device is connected to an energy storage unit and the switch is in the first position, no power is supplied by or received from that energy storage unit. Therefore, the switch may be used to isolate said energy storage unit from the external load. This may be useful if there is a problem with the energy storage unit, in particular one where it is desirable to prevent the energy storage unit from helping to meet the external power demand. Therefore, in some examples, the switch is configured to move from the second position to the first position when a problem is identified with the power regulating device and / or the energy storage unit.

[0077] In some examples, the switch is configured to move from the first position to the second position when it is determined that the problem with the power regulating device and / or the energy storage unit has been resolved. In this manner, the power regulating device and / or the energy storage unit may be returned to normal operation (i.e. a state in which the power regulating device is configured to help meet the external power demand). In some examples, an external entity may cause the switch to move from the first position to the second position. For example, a user may operate the switch or instruct the switch to move back to the second position when the problem with the power regulating device and / or the energy storage unit has been resolved.

[0078] In some examples, one or more of the plurality of power regulating devices may comprise a bypass switch. Each of the bypass switches may be arranged such that the power regulating device is bypassed completely (i.e. ensuring that current does not flow through the rest of the power regulating device as well as its attached energy storage device). Such a switch may be used if a problem with the power regulating device has been identified and allows the whole unit to be bypassed until maintenance can be carried out while the remaining power regulating devices continue to service the external load.

[0079] In some examples, each of the power regulating devices comprises a bypass switch. Using a bypass switch may help to ensure that the circuit is not broken (open circuit) if a power regulating device fails. Therefore, using a means to bypass one or more power regulating devices completely may be particularly advantageous in examples whereby the power regulating devices are connected in series.

[0080] In some examples, one or more of the power regulating devices comprises a switch and / or a bypass switch in addition to one or more of a DC-DC converter and / or a DC-AC converter. In some examples, any number of the plurality of power regulating devices in the battery management system comprises a different combination of switches and / or converters.

[0081] In examples where one or more of the power regulating devices comprises a bypass switch in addition to one or more of a DC-DC converter and / or a DC-AC converter, the bypass switch may be configured such that the one or more of DC- DC converter(s) and / or DC-AC converter(s) may be bypassed completely. That is, the bypass switch may be configured to ensure that current does not flow through the one or more of DC-DC converter(s) and / or DC-AC converter(s) as well as any attached energy storage device.

[0082] In some examples, the battery management system is connected to a load by a DC bus; and the plurality of power regulating devices are connected across the DC bus in series or in parallel or in a combination of series and parallel.

[0083] In some examples, the battery management system is connected to the load by an AC bus; and the plurality of power regulating devices are connected across the AC bus in series or in parallel or in a combination of series and parallel.

[0084] Particularly in some larger batteries, maintenance can be a near continuous process. For example, in large grid energy storage units which may comprise hundreds of individual energy storage units (and thus hundreds of power regulating devices), the time taken to carry out maintenance procedures on each energy storage unit in turn may be long enough that earliest maintained units are due another maintenance check. Thus, the cycle of maintenance may be ongoing. The systems described here thus allow the maintenance to be spread out in time and to be carried out while the battery is operational. This reduces down time and improves overall battery health as units can be maintained more regularly. Thus in some examples, while power is being supplied to the load, at least one of the plurality of power regulating devices is in maintenance mode at least 60% of the time, optionally at least 70% of the time, optionally at least 80% of the time, optionally at least 90% of the time, optionally 100% of the time. That is, the majority of the time that power is being supplied to the load, the battery management system is also instructing one or more of the plurality of power regulating devices to operate in a maintenance mode. In some examples, each of the power regulating devices is operated in maintenance mode for a small proportion of the time that power is being supplied to the load. However, overall the time that at least one of the power regulating devices is in maintenance mode is more than not (i.e. greater than 50%). Performing maintenance processes a majority of the time helps to ensure that the energy storage devices are effectively maintained. This may help to improve the performance of the energy storage devices as they no longer need to wait for a periodic overall service (in which the battery is offline) before they can be updated and optimised. It will of course also be appreciated that some batteries (particularly smaller ones or those with greater demands) may have units in maintenance mode less often than the figures above, while still gaining large benefits from the online maintenance described here. For example, smaller batteries may be able to do a maintenance cycle in a short period of time (while the batter is online) and then be able to run at full strength for a significant period of time before further maintenance becomes beneficial. In some use cases (e.g. in electric vehicles, it may also be desirable to avoid periods of maintenance during certain periods when battery performance needs to be optimal (e.g. while driving). Thus maintenance may be restricted to certain periods, such as charging periods.

[0085] In some examples, the battery management system comprises a memory configured to store information about one or more of: information received from one or more of the plurality of energy storage devices; the outcome of previous maintenance processes; the time elapsed since one or more of the plurality of power regulating devices was previously operated in maintenance mode; a number of times that one or more of the plurality of power regulating devices has been operated in maintenance mode; a frequency with which one or more of the plurality of power regulating devices has been operated in maintenance mode; information from one or more external entities; information received from one or more monitoring devices; and / or information received from one or more monitoring processes.

[0086] The memory of the battery management system may be any suitable and desired type and the information may be stored in any way. In some examples, the memory may be local to at least a part of the battery management system, or the memory may be remote (e.g. forming part of a cloud computing system).

[0087] In some examples, the stored information may be used to determine which of the plurality of power regulating devices is to be operated in maintenance mode and / or which maintenance processes are carried out.

[0088] According to a third aspect of the present disclosure, there is provided a controller configured to control a battery management system configured to supply or receive power in accordance with an external power demand, wherein the controller is configured to; control at least one of a plurality of power regulating devices of the battery management system to operate in a maintenance mode while others of the plurality of power regulating devices contribute to meeting the external power demand; and determine which of the plurality of power regulating devices is to be operated in maintenance mode and / or which maintenance processes are carried out according to one or more of: a predetermined pattern or sequence; information received from one or more of the plurality of energy storage devices; the outcome of previous maintenance processes; the time elapsed since one or more of the plurality of power regulating devices was previously operated in maintenance mode; a number of times that one or more of the plurality of power regulating devices has been operated in maintenance mode; and / or a frequency with which one or more of the plurality of power regulating devices has been operated in maintenance mode.

[0089] It will be appreciated that the preferred and optional features that are described above in relation to the first and second aspects are equally applicable to the third aspect and will be understood to be preferred and optional features of that apparatus.

[0090] According to a fourth aspect of the present disclosure, there is provided a battery system, comprising: a battery management system having any of the features described above; and an energy storage unit connected to each of the plurality of power regulating devices. In some examples, each of the power regulating devices is connected to one energy storage unit. The power regulating device may be connected to its respective energy storage unit in any suitable way. In some examples, the power regulating device may be connected to its respective energy storage unit in a plurality of ways. For example, the power regulating device may be connected to the energy storage unit via one or more wired connections for the transfer of power and one or more wired or wireless connections for the exchange of information. It will be appreciated that the preferred and optional features that are described above in relation to the first, second and third aspects are equally applicable to the fourth aspect and will be understood to be preferred and optional features of that apparatus.

[0091] In some examples, each of the energy storage units is a battery comprising: one or more cells; and a local battery management system configured to: receive instructions from the power regulating device; and / or send information about the energy storage unit to the power regulating device.

[0092] The or each of the energy storage units may comprise: a cell; a group of cells connected in parallel (a supercell); a group of cells or supercells connected in series (a module); a group of modules connected in series (a string or a rack) and / or a group of racks connected in series and / or in parallel (a battery container). In some examples, any number (e.g. each) of the energy storage units may be a different type of energy storage unit. In some examples, all of the energy storage units are the same type (e.g. batteries having the same cell chemistry).

[0093] The local battery management system may be any type (e.g. ranging from basic systems of sensors to complicated arrangements of sensors with passive and active cell balancing). Information may be sent to and / or received from the energy storage unit. The information exchanged at the interface may be any type (e.g. analogue or digital). The information may be exchanged by any means (e.g. via a wired or wireless connection).

[0094] According to a fifth aspect of the present invention, there is provided a method of controlling a battery management system configured to supply or receive power in accordance with an external power demand, comprising; controlling at least one of a plurality of power regulating devices of the battery management system to operate in a maintenance mode while others of the plurality of power regulating devices contribute to meeting the external power demand. It will be appreciated that the method according to the fifth aspect encompasses the carrying out of operations as described above in relation to the first, second, third and fourth aspects. Accordingly, the preferred and optional features that are described above in relation to the first, second, third and fourth aspects are equally applicable to the fifth aspect and will be understood to be preferred and optional features of that method.

[0095] According to a sixth aspect of the present invention, there is provided a method of controlling a battery management system configured to supply or receive power in accordance with an external power demand, comprising; controlling at least one of a plurality of power regulating devices of the battery management system to operate in a maintenance mode while others of the plurality of power regulating devices contribute to meeting the external power demand; wherein the battery management system comprises a plurality of power regulating devices connected in series.

[0096] It will be appreciated that the method according to the sixth aspect encompasses the carrying out of operations as described above in relation to the first, second, third, fourth and fifth aspects. Accordingly, the preferred and optional features that are described above in relation to the first, second, third, fourth and fifth aspects are equally applicable to the sixth aspect and will be understood to be preferred and optional features of that method.

[0097] According to a seventh aspect of the present invention, there is provided a method of controlling a battery management system configured to supply or receive power in accordance with an external power demand, comprising; controlling at least one of a plurality of power regulating devices of the battery management system to operate in a maintenance mode while others of the plurality of power regulating devices contribute to meeting the external power demand; and determining which of the plurality of power regulating devices is to be operated in maintenance mode and / or which maintenance processes are carried out according to one or more of: a predetermined pattern or sequence; information received from one or more of the plurality of energy storage devices; the outcome of previous maintenance processes; the time elapsed since one or more of the plurality of power regulating devices was previously operated in maintenance mode; a number of times that one or more of the plurality of power regulating devices has been operated in maintenance mode; and / or a frequency with which one or more of the plurality of power regulating devices has been operated in maintenance mode.

[0098] It will be appreciated that the method according to the seventh aspect encompasses the carrying out of operations as described above in relation to the first, second, third, fourth, fifth and sixth aspects. Accordingly, the preferred and optional features that are described above in relation to the first, second, third, fourth, fifth and sixth aspects are equally applicable to the seventh aspect and will be understood to be preferred and optional features of that method.

[0099] For example, the battery management system may use the time elapsed since one or more of the plurality of power regulating devices was previously operated in maintenance mode to determine which of the plurality of power regulating devices is to be operated in maintenance mode next. In some examples, the power regulating device having the longest elapsed time may be operated in maintenance mode next. This may result in maintenance operations being performed on each of the power regulating devices in an (e.g. continuous) repeating cycle.

[0100] In some examples, one or more of the power regulating devices may have different requirements for how often it is desirable to operate them in maintenance mode. For example, when a power regulating device is connected to an older energy storage unit, it may be desirable to operate this power regulating device in maintenance mode more frequently than a power regulating device that is connected to a newer energy storage unit. Therefore, when assessing the time elapsed since each of the power regulating devices was last operated in maintenance mode, the battery management system may compare the time elapsed to a threshold time period or a target time period for each of the power regulating devices. In some examples, the threshold time period or the target time period may be different for each of the power regulating devices. In some examples, the threshold time period or the target time period for each of the power regulating devices may be the same for one or more of the power regulating devices.

[0101] In some examples, the battery management system may use the outcome of previous maintenance processes to determine which of the plurality of power regulating devices is to be operated in maintenance mode next. For example, if an issue with a power regulating device was identified during a previous maintenance process, then that power regulating device may be operated in maintenance mode again sooner.

[0102] In some examples, the outcome of previous maintenance processes may comprise the number of times that (e.g. each of) the power regulating devices has been operated in maintenance mode. For example, if it is determined that a power regulating device has been operated in maintenance mode a greater number of times than others of the plurality of power regulating devices, then it may be determined that this power regulating device should be operated in maintenance mode more or less frequently and / or that different maintenance operations should be performed.

[0103] In some examples, the method further comprises: returning at least one power regulating device from maintenance mode to normal mode.

[0104] In some examples, the method further comprises: reporting the results of maintenance mode to a central controller.

[0105] In some examples, the results of maintenance mode may be stored for determining subsequent operation of the battery management system. For example, the results of maintenance mode may be used to determine which of the plurality of power regulating devices is to be operated in maintenance mode and / or which maintenance processes are to be carried out.

[0106] In some examples, the method comprises: controlling all of the plurality of power regulating devices to operate in maintenance mode at least once in a predetermined period.

[0107] The predetermined period may be any suitable and desired length of time. In some examples, the predetermined period may be more than a week, optionally more than a month, optionally more than one year, optionally more than two years.

[0108] In some examples, the plurality of power regulating devices may be operated in maintenance mode in a continuous cycle (e.g. such that at least one of the plurality of power regulating devices is operating at maintenance mode substantially all of the time). This may help to ensure that all of the power regulating devices can be operated in maintenance mode within the predetermined time period.

[0109] Brief Description of the Drawings

[0110] Certain examples of the present disclosure will now be described with reference to the accompanying drawings in which:

[0111] Figure 1 is a schematic diagram of a battery management system in accordance with an example of the present disclosure connected to a plurality of energy storage units;

[0112] Figure 2 is a schematic diagram of a battery management system in accordance with an example of the present disclosure connected to a plurality of energy storage units;

[0113] Figure 3 is a block diagram of a battery management system in accordance with an example of the present disclosure comprising a central controller;

[0114] Figure 4 is a block diagram of a battery management system in accordance with an example of the present disclosure comprising a plurality of local controllers;

[0115] Figures 5a-d are diagrams of power regulating devices;

[0116] Figure 6 is a flow chart showing a method of controlling a battery management system in accordance with an example of the present disclosure; and

[0117] Figure 7 illustrates the performance of a battery system over time under different maintenance schemes.

[0118] Detailed Description Figure 1 is a schematic diagram of a battery management system 2 according to an example of the present disclosure connected to a plurality of energy storage units 6a-d which may for example be rechargeable batteries. Each energy storage unit 6a-d may be a battery that itself comprises many individual cells connected together in series and / or parallel. Each energy storage unit 6a-6d may have its own built in management system for monitoring its own cells, carrying out cell balancing procedures and / or storing information about the battery’s usage history (e.g. keeping track of its state of health over time).

[0119] The battery management system includes a plurality of power regulating devices 4a-d. The power regulating devices 4a-d may be any device that regulates or controls the power supplied to or drawn from an attached energy storage unit. In this example, the power regulating devices 4a-d each comprise a DC-DC converter. The DC-DC converter can step up or step down the voltage from the energy storage device to a required level and can control the current drawn from the energy storage device 6a-d so as to control the power drawn from it. The DC-DC converter in this example is a bidirectional DC-DC converter such that it can operate in both directions. Thus the DC-DC converter can also step up or step down the voltage from an external source to a suitable voltage for charging the attached energy storage device 6a-d and can again control the current supplied to the energy storage device 6a-d so as to control the power supplied to it.

[0120] Each of the power regulating devices 4a-d has a first interface 8a-d and a second interface 12a-d. In this example, each of the first interfaces 8a-d includes two connections which provide a connection for attaching an energy storage unit. The first interface may for example comprise a positive interface terminal for connection to a positive battery terminal and a negative interface terminal for connection to a negative battery terminal..

[0121] In this example, each of the power regulating devices 4a-d is connected via its first interface 8a-d to an energy storage unit 6a-d. Each of the power regulating devices 4a-d exchanges power with the respective energy storage unit 6a-d via the first interface 8a-d. Power may be supplied to or received from the energy storage unit 6a-d through the first interface 8a-d according to an external power demand and / or a maintenance process. The battery management system 2 is configured to supply or receive power in accordance with an external power demand. In this example, the battery management system is connectable to a load (not shown) through load terminals 10a, 10b. The load may receive energy from the battery management system 2 and / or supply energy to the battery management system 2. For example, the battery management system 2 may supply power to the meet the power demands of a load system attached to load terminals 10a, 10b. The battery management system 2 may also receive power from the load system via load terminals 10a, 10b when the load system is generating power.

[0122] For example, if the load is an energy grid (such as a national electrical grid), the load may receive energy from the battery management system 2 when there is a power demand on the energy grid. If there is excess power available in the energy grid, the load may supply energy to the battery management system 2 (e.g. for storage on the energy storage units 6a-d.

[0123] In some examples, each of the power regulating devices 4a-d may be configured as a step-up converter and / or a step-down converter. The voltage at the first interface 8a-d of each of the power regulating devices 4a-d may be stepped up or stepped down by the DC-DC converter of the power regulating device 4a-d, such that the voltage at the second interface 12a-d is higher or lower than that at the first interface 8a-d. In this example, the second interfaces 12a-d of the power regulating devices 4a-c each comprise two connections, e.g. a positive terminal and a negative terminal.

[0124] In some examples, each of the power regulating devices 4a-d may be configured as an inverter. The voltage at the first interface 8a-d of each of the power regulating devices 4a-d may be inverted by the inverter of the power regulating device 4a-d, such that the voltage at the first interface 8a-d is a DC voltage and the voltage at the second interface 12a-d is an AC voltage. In this example, the second interfaces 12a-d of the power regulating devices 4a-d each comprise two connections, e.g. a positive terminal and a negative terminal. In some examples where the power regulating devices 4a-d are configured as an inverter, the string of power regulating devices 4a-d form a single arm of a modular multilevel converter. In this example, the power regulating devices 4a-d are connected in series between the load terminals 10a, 10b. Each of the power regulating devices 4a-d is connected to the adjacent power regulating devices 4a-d via their second interfaces 12a-d. The power regulating devices 4a-d may exchange power at their second interfaces 12a-d. In some examples, power is transferred between the power regulating devices 4a-d without any power being consumed. That is, the power regulating devices 4a-d simply pass power to the load via their connections at their second interfaces 12a-d. In some examples, one or more of the power regulating devices 4a-d may consume at least a portion of the power that is provided at its second interface 12a-d. This will be discussed in more detail below.

[0125] Each of the power regulating devices 4a-d is configured to control power through its first interface 8a-d. The power regulating device 4a-d may control the amount of power, the current and / or the voltage at the interface. In particular, the power regulating device 4a-d may control the amount of power or current that is exchanged with the energy storage unit 6a-d.

[0126] The battery management system 2 is configured to control at least one of the plurality of power regulating devices 4a-d to operate in a maintenance mode while others of the plurality of power regulating devices 4a-d contribute to meeting the power demand of the load. Any number of the power regulating devices 4a-d may operate in maintenance mode and any number of the power regulating devices 4a- d may contribute to meeting the power demand of the load.

[0127] In the following examples, power regulating devices 4a and 4b are in the maintenance mode (performing one or more maintenance processes), while power regulating devices 4c and 4d are in normal mode (contributing to meeting the power demand of the load).

[0128] In a first example, power regulating devices 4a and 4b are both performing maintenance operations that consume 20 W of power. Therefore, power regulating devices 4a and 4b are unable to contribute to meeting the external power demand of the load. If there is also an external power demand of 100 W from the load, the remaining power regulating devices 4c and 4d are required to meet a total power demand of 140 W. In this example, the total power demand is split equally between power regulating devices 4c and 4d, such that they each provide 70 W of power. 40 W of this power is provided to the other power regulating devices 4a and 4b and 100 W of this power is provided to the load.

[0129] In a second example, power regulating device 4a is performing a maintenance operation that consumes 50 W of power, while power regulating device 4b is performing a maintenance operation that produces an excess of 30 W of power. If there is also an external power demand of 100 W from the load, the remaining power regulating devices 4c and 4d are required to meet a total power demand of 120 W (100 W + 50 W- 30 W). In this example, the total power demand is split such that power regulating device 4c provides 80 W of power and power regulating device 4c provides 40 W of power (e.g. because power regulating device 4c has twice the capacity of power regulating device 4d). 20 W of power is provided to power regulating device 4a and 100 W of power is provided to the load.

[0130] It will be appreciated that the numbers in these examples are purely for the purposes of illustration. Other scenarios may have very different power consumptions both for the load and for the maintenance processes. It will also be appreciated that the examples here show four power regulating devices 4a-d and four energy storage units 6a-6d, but this is also purely by way of example. Other implementations may have many more power regulating devices and energy storage units such that any additional load due to compensating the maintenance processes may be shared among a much larger set of regulating devices I storage units.

[0131] In both of the above examples, the power regulating devices 4c, 4d operating in the normal mode compensate for the power regulating devices 4a, 4b operating in the maintenance mode, such that the external power demand (from the load) is still met. This allows maintenance processes to be carried out while the battery management system 2 meets the external power demand. Therefore, it is not required to take the battery management system 2 offline in order to perform maintenance. Figure 2 is a schematic diagram of a battery management system 2 according to an example of the present disclosure connected to a plurality of energy storage units 6a-c and an external load. The system of Figure 2 has many of the same features and functions as the system of Figure 1. However, in this example the power regulating devices 4a-c are connected in parallel across the load terminals 10a, 10b. Each of the power regulating devices 4a-c is connected to an energy storage unit 6a-c at its first interface 8a-c. The second interfaces 12a-c in this example are connected to a DC bus between the load terminals 10a, 10b.

[0132] Figure 3 is a block diagram of a battery management system 2 according to an example of the present disclosure comprising a central controller 14. The power regulating devices 4a-c, the energy storage units 6a-c and the central controller 14 are shown schematically, with arrows showing how information may be exchanged between them.

[0133] Information may be exchanged by various means. In some examples, the way that information is exchanged between the power regulating devices 4a-c and the controller 14 may be different from the way that information is exchanged between the power regulating devices 4a-c and the energy storage units 6a-c. For example, if the controller 14 is located remotely from the power regulating devices 4a-c, information may be exchanged wirelessly and / or over a wide area network such as the internet. However, as the power regulating devices 4a-c are typically located close to the energy storage units 6a-c, information may be exchanged via a wired connection, e.g. a direct wired connection such as a serial link. Furthermore, it will be understood that although the arrows show how information may be exchanged, information is not necessarily exchanged over all routes at all times.

[0134] The central controller 14 may send information to and receive information from each of the power regulating devices 4a-c. In some examples, the central controller 14 sends one or more control signals to the power regulating devices 4a-c. The control signal(s) may be different for each power regulating device 4a-c, or at least some of the power regulating devices 4a-c may be sent the same control signal. The control signal may include information such as: an instruction to operate in maintenance mode or an instruction to operate in normal mode; an instruction to control the power through the first interface 8a-c of the power regulating device 4a- c, e.g. to supply or draw a certain power; an instruction to perform a maintenance process; an instruction to send a control signal to an attached energy storage device 6a-c and / or an instruction to provide information from an attached energy storage device 6a-c.

[0135] Each of the power regulating devices 4a-c may send information to and receive information from an attached energy storage unit 6a-c. In some examples, the power regulating devices 4a-c send one or more control signals to the energy storage unit 6a-c. In some examples, the control signal may include an instruction to a local battery management system 18 a-c in the energy storage unit 6a-c to perform a maintenance process on the energy storage unit 6a-c. For example, this may include a process such as passive or active balancing of the cells within the energy storage unit 6a-c. In some examples, the control signal may include an instruction to send information. For example, the energy storage unit 6a-c may comprise one or more sensors that measure a parameter of the energy storage unit 6a-c and provide the measurement to the power regulating device 4a-c. For example, the energy storage unit 6a-c may be able to provide present temperature, current, voltage, estimated state of charge, estimated state of health, device usage history, etc.

[0136] Each of the power regulating devices 4a-c may send information to the central controller 14. In some examples, the information includes the information that has been sent from the energy storage device 6a-c to the power regulating device 4a-c (e.g. a measurement of a parameter of the energy storage device 4a-c). In some examples, the information includes an indication that an instruction has been carried out. The central controller 14 may use the information that it receives from the power regulating devices 4a-c to make a determination about operation of the battery management system 2. For example, the central controller 14 may use information about a parameter of the energy storage units 6a-c to determine which of the power regulating devices 4a-c should be operated in maintenance mode. For example, if readings from a certain energy storage unit 6a-c are indicative of unusual or unexpected operation, the control may decide to run additional tests, to reduce the strain on that energy storage unit, carry out maintenance procedures on that energy storage unit, or bypass that energy storage unit altogether. Figure 4 is a block diagram of a battery management system 2 according to an example of the present disclosure comprising a plurality of local controllers 16a-c. The power regulating devices 4a-c, the energy storage units 6a-c, the local battery management systems 18a-c and the local controllers 16a-c are shown schematically, with arrows showing how information may be exchanged between them.

[0137] As discussed in relation to Figure 3, information may be exchanged by any means. It will be understood that although the arrows show how information may be exchanged, information need not necessarily be exchanged over all routes at all times.

[0138] Each of the local controllers 16a-c may send information to and receive information from a power regulating device 4a-c. The local controller 16a-c may indeed be a part of the power regulating device 4a-c (although it is shown separate here for a more general representation). In some examples, each of the local controllers 16a-c sends one or more control signals to the corresponding power regulating device 4a- c. The control signal(s) may be different for each power regulating device 4a-c, or at least some of the power regulating devices 4a-c may be sent the same control signal. The control signal may include information such as: an instruction to operate in maintenance mode or an instruction to operate in normal mode; an instruction to control the power through the first interface 8a-c of the power regulating device 4a- c; an instruction to perform a maintenance process; an instruction to send a control signal to an attached energy storage device 6a-c and / or an instruction to provide information from an attached energy storage device 6a-c.

[0139] Furthermore, each of the local controller 16a-c may send information to and receive information from the other local controllers 16a-c. In some examples, the local controllers 16a-c may communicate to help ensure that the operation of the battery management system 2 is coordinated between the local controllers 16a-c. In some examples, the local controllers 16a-c may communicate to jointly determine how the battery management system 2 should be operated. For example, the local controllers 16a-c may jointly determine which of the power regulating devices 4a-c should be operated in maintenance mode and / or which maintenance processes should be carried out. Thus the local controllers 16a-c together provide distributed control of the battery management system 2. In such examples, there is no need for a central controller.

[0140] Each of the power regulating devices 4a-c may send information to and receive information from an energy storage unit 6a-c, in the same manner as discussed in relation to Figure 3.

[0141] Each of the power regulating devices 4a-c may send information to the corresponding local controller 16a-c. In some examples, the information includes the information that has been sent from the energy storage device 6a-c to the power regulating device 4a-c (e.g. a measurement of a parameter of the energy storage device 4a-c). In some examples, the information includes an indication that an instruction has been carried out. The local controllers 16a-c may use the information from the power regulating devices 4a-c to make a determination about operation of the battery management system 2.

[0142] In some examples, the local controllers 16a-c may each make a separate determination about operation of the corresponding power regulating device 4a-c. For example, if a serious problem is found with the operation of the corresponding power regulating device 4a-c and / or the corresponding energy storage unit 6a-c, the local controller 16a-c may determine that no power should pass through the first interface 8a-c of that power regulating device 4a-c, without any input from the other local controllers 16a-c.

[0143] However, as discussed above, the local controllers 16a-c are also configured to communicate with one another. Therefore, in some examples, the local controllers 16a-c may communicate to jointly determine how the battery management system 2 should be operated.

[0144] Figures 5a-d are diagrams of the structure of a power regulating device 4.

[0145] Figure 5a shows an example of a power regulating device 4 comprising a DC to AC converter. The first interface 8 may be connectable to an energy storage device (not shown) and the second interface 12 may be connectable to an external load (not shown). The DC to AC converter may be arranged to convert the DC voltage of the energy storage device into an AC voltage, e.g. for supplying an AC external load. The converter may also be arranged to convert an AC voltage (e.g. from the external load) into a DC voltage (e.g. for supplying to the energy storage unit).

[0146] In this example, the power regulating device 4 comprises a switch 20 configured to move from a first position in which the switch 20 prevents power from passing through the first interface 8 to a second position in which the switch 20 allows power to pass through the first interface 8. When the power regulating device 4 is connected to an energy storage unit and the switch 20 is in the first position, no power is supplied by or received from that energy storage unit. Therefore, the switch 20 may be used to isolate said energy storage unit from an external load. In this example, the switch 20 is a selector switch with two connections. When the switch 20 is in the first position it bypasses the energy storage device and connects the positive and negative terminals of the first interface 8. In other examples, the switch 20 may simply break the connection to the energy storage device.

[0147] In this example, the power regulating device 4 also comprises a bypass switch 22 configured to move from a first position in which the bypass switch 22 prevents power from passing through the second interface 12 to a second position in which the bypass switch 22 allows power to pass through the second interface 12. In the first position, the bypass switch 22 may be arranged to bypass the power regulating device 4 completely (i.e. bypassing the power regulating device 4 as well as its attached energy storage device if present). The bypass switch may be used if a problem with the power regulating device 4 has been identified.

[0148] Figure 5b shows an example of a power regulating device 4 comprising a full-bridge DC to AC converter. The first interface 8 may be connectable to an energy storage device (not shown) and the second interface 12 may be connectable to an external load (not shown). The DC to AC converter may be arranged to convert the DC voltage of the energy storage device into an AC voltage, e.g. for supplying an AC external load. The converter is bidirectional and thus may also be arranged to convert an AC voltage (e.g. from the external load) into a DC voltage (e.g. for supplying to the energy storage unit). In some examples, the functionality of a switch and / or a bypass switch may be implemented as part of a power regulating device 4. For example, in Fig. 5b, if QH1 and QH2 are ON, and QL1 and QL2 are both OFF, current may flow through the power regulating device 5b without passing through the energy storage device to which it is connected, thereby bypassing the energy storage device.

[0149] Figure 5c shows an example of a power regulating device 4 comprising a DC-DC converter. The first interface 8 may be connectable to an energy storage device (not shown) and the second interface 12 may be connectable to an external load (not shown). The DC-DC converter may be arranged to convert a first DC voltage (e.g. of an energy storage device) into a second DC voltage (e.g. for supplying a DC external load). The DC-DC converter may also be bidirectional and thus arranged to convert a DC voltage at the second interface 12 (e.g. from the external load) into a DC voltage at the first interface 8 (e.g. for suppling to the energy storage device). The DC-DC converter may be a step-up and / or a step-down converter or capable of both step-up and step-down conversion.

[0150] The power regulating device 4 of Figure 5c comprises a switch 20 and a bypass switch 22, which may be configured to operate in a similar manner to those described above in relation to Figure 5a.

[0151] Figure 5d shows an example of a power regulating device 4 comprising a bidirectional buck (or boost) converter. The first interface 8 may be connectable to an energy storage device (not shown) and the second interface 12 may be connectable to an external load (not shown). The power regulating device 4 may be arranged to convert a lower DC voltage (e.g. of an energy storage device) into a higher DC voltage (e.g. for supplying a DC external load). The power regulating device 4 may also be arranged to convert a higher DC voltage (e.g. of an external load) into a lower DC voltage (e.g. for storage on an energy storage device).

[0152] The power regulating devices 4 of Figures 5a-d each comprise a communication and control channel 24. The communication and control channel 24 may be configured to receive instructions (e.g. relating to the operation of the power regulating device, e.g. switch control instructions) from a controller (e.g. a local or central controller of the battery management system). The communication and control channel 24 may additionally or alternatively be configured to send information (e.g. relating to the performance of the power regulating device) to one or more components of the battery management system (e.g. a local or central controller).

[0153] Figure 6 is a flow chart showing a method of controlling a battery management system 2 according to an example of the present disclosure.

[0154] In this method, the battery management system 2 places each of the power regulating devices (PRD) into maintenance mode sequentially (e.g. based on the order in which they are connected to one another). Each power regulating device is assigned a value x, which may be considered as an identifier denoting its order in the maintenance cycle. For example, the first power regulating device is denoted x=1, the second power regulating device is denoted x=2 and so on. The total number of power regulating devices is denoted as n1.

[0155] When the power regulating device is in maintenance mode, the battery management system 2 performs a number of maintenance processes. Each maintenance process is assigned a value y, denoting its order in the maintenance cycle. For example, the first maintenance process is denoted y=1, the second maintenance process is denoted y=2 and so on. The total number of maintenance processes performed on each of the power regulating devices is denoted as n2.

[0156] The method starts at step 102. Initially, the value of x is set to 1 (step 104). Before starting any maintenance operations, it is determined whether the battery management system has enough capacity to meet the external power demand if that power regulating device is changed to operate in maintenance mode (step 106).

[0157] If the battery management system does not have enough capacity to meet the external power demand without device x, then the value of x is incremented by 1 (step 108). It is then determined whether this value of x is greater than the total number n1 of power regulating devices (i.e. whether x corresponds to one of the power regulating units) (step 110). If the value of x is less than n1 (i.e. it corresponds to a power regulating unit), then the battery management system returns to step 106. If at any point after incrementing the value of x, the current value of x is greater than n1 (i.e. it does not correspond to a power regulating device), the current process ends (step 112). In some examples, ending the current process may comprise operating the battery management system in a mode whereby no maintenance processes are carried out. In some examples, ending the current process may comprise starting the process of Figure 6 again.

[0158] If, however, the battery management system does have enough capacity to meet the external power demand without power regulating device x, then the method proceeds to step 114, whereby the power regulating device denoted by the current value of x is placed into maintenance mode.

[0159] Initially, when a power regulating device is placed into maintenance mode, the value of y is set to 1 (step 116). The maintenance process denoted by y is then carried out (step 118).

[0160] It is then determined whether the maintenance process y identified any problems with the operation of the power regulating device and / or the energy storage unit to which it is connected, where present (step 120). This may be checked, for example, as feedback from one or more sensors of the energy storage unit, where present.

[0161] If it is determined that there are no problems with the power regulating device and / or the energy storage unit to which it is connected at this stage, the method proceeds to step 122, whereby the value of y is incremented by 1. This indicates that the current maintenance process has been completed for this particular power regulating device (denoted by x) and the energy storage unit to which it is connected, where present.

[0162] If it is determined that there is a problem with the power regulating device and / or the energy storage unit (ESU), the method proceeds to step 124, whereby the battery management system checks whether the power regulating device and the energy storage unit are operational. This step may involve any type of measurement or analysis. In some examples, the power regulating device may be considered to be operational if it can safely supply or receive power. In some examples, the power regulating device may be considered to be operational if the problem can be solved by performing a corrective maintenance process.

[0163] If the power regulating device and the energy storage unit are operational, then the method proceeds to the optional step of performing a corrective maintenance operation (step 126). The corrective maintenance process may be any process capable of resolving the issue. For example, cell balancing may be carried out to resolve capacity issues. After the corrective maintenance process has been completed, the method proceeds to step 122, as discussed above.

[0164] If at step 124 it is determined that the power regulating device and / or the energy storage unit are not operational and a corrective maintenance operation would not resolve the problem, then the method proceeds to step 128, which comprises preventing power from passing through the first and / or second interface of the power regulating device. If it is determined that there is a problem with the energy storage unit only, it may only be necessary to prevent power from passing through the first interface. This ensures that no power is received from or supplied to the corresponding energy storage unit, if present. If it is determined that there is a problem with the power regulating device, it may be necessary to prevent power from passing through the second interface. This ensures that no power is received from or supplied to the power regulating device.

[0165] This step will generally only be carried out if it is determined that a serious problem exists with the power regulating device and / or the energy storage unit (e.g. one that cannot be solved with a corrective maintenance process). After step 128 has been completed, the method proceeds to step 132, which is discussed further below.

[0166] Returning to step 122, whereby the value of y is incremented by 1 , the method then proceeds to step 130. At step 130, it is determined whether this value of y corresponds to is greater than n2 (i.e. if it corresponds to one of the maintenance processes). If the value of y corresponds to one of the maintenance processes (i.e. if y is less than or equal to n2), then the battery management system returns to step 118 to perform the next maintenance process on the same power regulating device. If the value of y does not correspond to a power regulating device (i.e. if y is greater than n2), then this indicates that all maintenance processes have been carried out on the current power regulating device and the method proceeds to step 132. At step 132, the value of x is incremented by 1. If the value of x is less than n1 (i.e. if x corresponds to one of the power regulating devices), then the battery management system returns to step 106 to begin performing maintenance processes on the next power regulating device.

[0167] If the value of x is greater than n1 (i.e. if x does not correspond to one of the power regulating devices), then this indicates that all of the power regulating devices have undergone maintenance in the present maintenance cycle. Therefore, the current process ends (step 136). In some examples, ending the current process may comprise operating the battery management system in a mode whereby no maintenance processes are carried out. In some examples, ending the current process may comprise starting the method of Figure 6 again. In this manner, maintenance may be performed continuously on the battery management system. Importantly, while maintenance is being carried out, the external demand is still being met (as determined at step 106) such that the battery is not taken offline, but rather the maintenance is carried out while the battery remains online.

[0168] Figure 7 is a schematic line chart showing the performance of a battery management system over time. The horizontal axis of the chart is time and the vertical axis of the chart is performance. In particular, performance may be any metric relating to the energy storage units. For example, the performance may be related to one or more of: the capacity of the energy storage units; an open-circuit voltage of the energy storage units at full charge; the resistance of the energy storage units; the charge / discharge efficiency of the energy storage units and / or the self-discharge rate of the energy storage units.

[0169] Line A shows an example of the performance of a system that does not include the features of the present invention. In particular, line A shows the performance of a system that receives maintenance while the system is offline. For example, a typical system may be taken offline once per year in order to be serviced. Over time, the performance degrades as represented by the downward slope A1. Each time that maintenance is performed on the system, the performance improves as represented by the upward slope A2.

[0170] Line B shows an example of the performance of a battery management system in accordance with the present application. The performance of the battery management system degrades over time as represented by the downward slope B1 and each time that a maintenance process is performed, the performance of the battery management system improves as shown by the upward slope B2. It can be seen that the more regular maintenance operations for scenario B (the invention) mean that performance does not drop as much as it does for scenario A. The more regular maintenance operations in scenario B (the invention) also return the performance to a high level much more frequently than scenario A.

[0171] The present invention presents two advantages over the system of line A.

[0172] First, the average performance of the battery management system is higher for line B due to the fact that the performance does not drop as low as it does for line A. According to the present invention, the battery management system is able to perform maintenance without taking the battery management system offline. As the battery management system is still able to meet the external power demand, the battery management system is able to carry out maintenance more frequently than the system of line A. As the battery management system does not have as much time to degrade between the maintenance cycles of the present invention, the reduction in performance is smaller between each maintenance cycle. Therefore, the performance of the system is higher on average than that of line A.

[0173] Furthermore, the range in performance of the battery management system is smaller. As the battery management system does not have as much time to degrade between the maintenance cycles of the present invention, the reduction in performance is smaller between each maintenance cycle. This means that operation of the system is better optimised. For example, as the individual energy storage units are maintained (and thus optimised) more regularly, they are operated in a more optimal manner for the majority of the time. For example, it is less likely that the energy storage units will be overcharged or overdischarged which results in less internal damage in the cells. This means that over time, the system of line B is less damaged as it is better maintained, which prolongs its life compared to line A. This can be seen by comparing line B3 (which represents the decline in maximum performance over time for the system of line B) with line A3 (which represents the decline in maximum performance over time for the system of line A). In this example, it can actually be seen that the performance in line B is higher than the performance of line A at any given point in time. This highlights one of the advantages of regular maintenance.

[0174] What is not represented in Fig. 7 is the down time of the system of line A when the battery is taken offline for its annual service. This is effectively a period of zero performance that negatively impacts the financial return on the battery as it cannot be used during that maintenance period. By contrast, the system of line B has no such zero performance periods as it does not need to be taken offline.

Claims

Claims1. A battery management system configured to supply or receive power in accordance with an external power demand; wherein the battery management system comprises a plurality of power regulating devices connected in series; wherein each of the plurality of power regulating devices comprises an interface connectable to an energy storage unit for exchange of power therewith; wherein each of the plurality of power regulating devices is configured to control power through its interface; and wherein the battery management system is configured to control at least one of the plurality of power regulating devices to operate in a maintenance mode while others of the plurality of power regulating devices contribute to meeting the external power demand.

2. A battery management system as claimed in claim 1, wherein in the maintenance mode the power through the interface is controlled according to a maintenance process of the maintenance mode.

3. A battery management system as claimed in claim 1 or 2, arranged such that, when the at least one power regulating device operates in the maintenance mode, the others of the power regulating devices operate in a normal mode in which power through the interface is determined at least in part to contribute to meeting the external power demand.

4. A battery management system as claimed in claim 3, wherein in the normal mode the power through the interface is determined at least in part according to the power demand of the at least one power regulating device operating in the maintenance mode.

5. A battery management system as claimed in any preceding claim, wherein in the maintenance mode, one or more of the following maintenance processes is carried out: preventing power from passing through the interface;reducing the power drawn from or supplied to an energy storage unit through the interface; applying a predetermined current, voltage and / or power through the interface; applying power through the interface for a predetermined period of time; applying a predetermined current, voltage and / or power through the interface for a predetermined period of time; applying a predetermined pattern or sequence of current, voltage and / or power through the interface; applying power through the interface until the energy storage unit is fully charged; fully or partially discharging the energy storage unit; fully or partially charging the energy storage unit; instructing a local battery management system of the energy storage unit to perform an operation on the energy storage unit; and / or acquiring information from the energy storage unit.

6. A battery management system as claimed in any preceding claim, wherein the interface of each of the plurality of power regulating devices is connectable to an energy storage unit for exchange of information therewith.

7. A battery management system as claimed in claim 6, wherein the information exchanged at the interface comprises sending instructions for operation of the energy storage unit.

8. A battery management system as claimed in claim 6 or 7, wherein the information exchanged at the interface comprises receiving information about the energy storage unit.

9. A battery management system as claimed in any preceding claim, wherein the battery management system comprises a central controller configured to control each of the power regulating devices.

10. A battery management system as claimed in any of claims 6-9, wherein each of the power regulating devices is configured to communicate the informationexchanged at the interface to a central controller of the battery management system.

11. A battery management system as claimed in claim 9 or 10, wherein the central controller is configured to determine which of the plurality of power regulating devices is to be operated in maintenance mode.

12. A battery management system as claimed in claim 11, wherein the central controller is configured to determine which of the plurality of power regulating devices is to be operated in maintenance mode and / or which maintenance processes are carried out according to one or more of: a predetermined pattern or sequence; information received from one or more of the plurality of energy storage devices; the outcome of previous maintenance processes; the time elapsed since one or more of the plurality of power regulating devices was previously operated in maintenance mode; meeting the external power demand; a number of times that one or more of the plurality of power regulating devices has been operated in maintenance mode; a frequency with which one or more of the plurality of power regulating devices has been operated in maintenance mode; information from one or more external entities; information received from one or more monitoring devices; and / or information received from one or more monitoring processes.

13. A battery management system as claimed in any preceding claims, wherein the battery management system comprises a plurality of local controllers; wherein each of the plurality of local controllers is configured to control one or more of the plurality of power regulating devices.

14. A battery management system as claimed in any preceding claim, wherein each of the power regulating devices comprises a DC-DC converter.

15. A battery management system as claimed in any of claims 1-13, wherein each of the power regulating devices comprises an inverter.

16. A battery management system as claimed in any preceding claim, wherein each of the power regulating devices comprises a switch configured to move from a first position in which the switch prevents power from passing through the interface to a second position in which the switch allows power to pass through the interface.

17. A battery management system as claimed in any preceding claim, wherein the battery management system is connected to a load by a DC bus; and the plurality of power regulating devices are connected across the DC bus in series.

18. A battery management system as claimed in any preceding claim, wherein, while power is being supplied to the load, at least one of the plurality of power regulating devices is in maintenance mode at least 60% of the time, optionally at least 70% of the time, optionally at least 80% of the time, optionally at least 90% of the time, optionally 100% of the time.

19. A battery management system as claimed in any preceding claim, wherein the battery management system comprises a memory configured to store information about one or more of: information received from one or more of the plurality of energy storage devices; the outcome of previous maintenance processes; the time elapsed since one or more of the plurality of power regulating devices was previously operated in maintenance mode; a number of times that one or more of the plurality of power regulating devices has been operated in maintenance mode; a frequency with which one or more of the plurality of power regulating devices has been operated in maintenance mode; information from one or more external entities; information received from one or more monitoring devices; and / or information received from one or more monitoring processes.

20. A controller configured to control a battery management system configured to supply or receive power in accordance with an external power demand, wherein the controller is configured to; control at least one of a plurality of power regulating devices of the battery management system to operate in a maintenance mode while others of the plurality of power regulating devices contribute to meeting the external power demand; and determine which of the plurality of power regulating devices is to be operated in maintenance mode and / or which maintenance processes are carried out according to one or more of: a predetermined pattern or sequence; information received from one or more of the plurality of energy storage devices; the outcome of previous maintenance processes; the time elapsed since one or more of the plurality of power regulating devices was previously operated in maintenance mode; a number of times that one or more of the plurality of power regulating devices has been operated in maintenance mode; and / or a frequency with which one or more of the plurality of power regulating devices has been operated in maintenance mode.

21. A battery system, comprising: a battery management system as claimed in any preceding claim; and an energy storage unit connected to each of the plurality of power regulating devices.

22. A battery management system as claimed in claim 21 , wherein each of the energy storage units is a battery comprising: one or more cells; and a local battery management system configured to: receive instructions from the power regulating device; and / or send information about the energy storage unit to the power regulating device.

23. A method of controlling a battery management system configured to supply or receive power in accordance with an external power demand, comprising;controlling at least one of a plurality of power regulating devices of the battery management system to operate in a maintenance mode while others of the plurality of power regulating devices contribute to meeting the external power demand; wherein the battery management system comprises a plurality of power regulating devices connected in series.

24. A method of controlling a battery management system configured to supply or receive power in accordance with an external power demand, comprising; controlling at least one of a plurality of power regulating devices of the battery management system to operate in a maintenance mode while others of the plurality of power regulating devices contribute to meeting the external power demand; and determining which of the plurality of power regulating devices is to be operated in maintenance mode and / or which maintenance processes are carried out according to one or more of: a predetermined pattern or sequence; information received from one or more of the plurality of energy storage devices; the outcome of previous maintenance processes; the time elapsed since one or more of the plurality of power regulating devices was previously operated in maintenance mode; a number of times that one or more of the plurality of power regulating devices has been operated in maintenance mode; and / or a frequency with which one or more of the plurality of power regulating devices has been operated in maintenance mode.

25. A method of controlling a battery management system as claimed in claim24, further comprising: returning at least one power regulating device from maintenance mode to normal mode.

26. A method of controlling a battery management system as claimed in claim25, further comprising: reporting the results of the maintenance mode to a central controller.

27. A method of controlling a battery management system as claimed in claim24, 25 or 26, comprising: controlling all of the plurality of power regulating devices to operate in maintenance mode at least once in a predetermined period.

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