WO2024261463A2

WO2024261463A2 - Independent battery apparatus

Info

Publication number: WO2024261463A2
Application number: PCT/GB2024/051551
Authority: WO
Inventors: Lorenzo BERGAMASCHI; Jack Levy; Jonathan CARRIER; Jacob HOPKINS
Original assignee: Allye Energy Limited
Priority date: 2023-06-19
Filing date: 2024-06-19
Publication date: 2024-12-26
Also published as: WO2024261463A3; GB2631103A

Abstract

An energy storage and release apparatus, or battery apparatus, 100, 200 comprises a plurality of batteries 102 and a controller 135 configured to control the current to and from each battery individually. The apparatus 100 may comprise a plurality of bidirectional AC-DC power conversion modules 104, and an AC electrical link 140 configured to allow power flow between the power conversion modules and to allow electrical connection of the apparatus to an external load 145. Each battery may have a dedicated power conversion module between that battery and the AC electrical link. The apparatus 100 may be arranged such that power flow between the plurality of batteries 102 is permitted only via the AC electrical link 140. The apparatus 100 may comprise at least one temperature sensor, and the controller 135 may be arranged to control the current to two or more batteries 102 in a dynamically-varying way to provide Joule heating to warm the batteries.

Description

Independent Battery Apparatus

Field of the Invention

The present invention relates to the field of apparatuses for energy storage and release. Specifically, the present invention relates to an energy storage and release apparatus, or battery apparatus, comprising a plurality of batteries and a controller configured to independently control the current to and from each battery, and to thermal management for a system with individually-controllable batteries.

Background of the Invention

As the grid is decarbonised, the supply of energy becomes more volatile and sensitive to imbalance between supply and demand. Consequently, the grid needs greater flexibility to balance the electricity network and avoid capacity constraints.

Energy storage systems often include a single battery connected to a single power conversion module. To scale up these systems, modular batteries are made comprising multiple batteries connected in parallel or in series to a single power conversion module. This creates a problem as batteries in such modular systems need to be carefully paired with very similar characteristics. Capacities of batteries must match, chemistries of batteries must match, and states of health of batteries must at least be similar.

A common saying amongst battery engineers is: "a battery is as strong as its weakest cell" - when batteries are mismatched in terms of aging, one battery will be weaker at providing power, hence causing the other batteries to work harder to compensate. Also, when connected in parallel, the output voltage will be common for all batteries and using a weak/aged battery means that not all energy can be discharged whilst remaining within safe voltage limits. The same principle applies for chemistry. Different battery chemistries have different safe voltage constraints - battery management systems are designed and parametrised to keep the cells within their safe windows. Thus, using batteries of different chemistries within the same apparatus has equivalent challenges to using batteries with different states of health, with the additional concern that different battery chemistries have different optimal thermal limits and power constraints, so again requiring different controls for optimal use. For example, NMC batteries (NMC=lithium-Nickel-Manganese-Cobalt- oxide) are typically more energy dense, and have a higher maximum cell voltage, but have limited cycle life. By contrast, LFP batteries (LFP= Lithium iron phosphate) are less energy dense, and work less well at lower temperatures than NMC batteries, but may operate in a wider temperature range and generally have a greater cycle life and less susceptibility to thermal runaway. LFP batteries generally suffer less degradation than NMC batteries at higher temperatures and faster charging / discharging rates.

This incompatibility between batteries with different characteristics significantly inhibits the production of modular batteries from repurposed batteries, also known as second-life batteries (e.g. re-used electric vehicle battery packs), as even batteries of the same type and from the same manufacturer will have a different state of health (state of health, SOH, is generally defined by looking at capacity - e.g. 80% SOH means 80% of its original rated capacity). Furthermore, each manufacturer may choose a different chemistry cell, a different voltage range, and/or a different capacity. It is often the case that combining second-life batteries from different manufacturers with a single power conversion stage and a common direct current bus is not a commercially viable option.

WO 2021/044145 Al provides an apparatus for storing electrical energy in more than one battery unit wherein a controller can interface with more than one battery unit without an intermediary Controller Area Network (CAN) interface. Second-use batteries are combined in series into individual “strings” and two or more strings are connected to a common bidirectional power conversion module. The controller switches the strings in electrical communication with the power conversion module to maximise the capacity of the apparatus while minimising battery degradation. This approach means that only a single string can be charging or discharging at any one time.

In addition, battery projects such as Gemini™ (https ://one.ai/batteries/gemini) use DC-DC converters to manage cells of different chemistries within the same battery, linking the batteries together to effectively provide range extension.

Batteries, especially lithium-ion of chemistry including but not limited to Lithium-Nickel- Manganese-Cobalt-Oxide (NMC), Lithium Nickel-Cobalt-Aluminium Oxide (NCA), lithium-titanium-oxide (LTO), lithium iron phosphate (LFP) chemistries, are electrochemical devices and their operation is highly temperature dependent. The internal temperature of a cell within a battery affects the performance in terms of how much power can be delivered and efficiency of energy conversion, and the battery lifetime, usually measured in how many discharge/recharge cycles the battery will last in operation before power output and charge capacity are reduced below useful levels.

In automotive and energy storage applications, where multiple batteries are connected in series and in parallel to create larger modules and packs, the temperature gradient between the individual cells within the batteries also affects how long the pack as a whole will last and perform.

As a general rule used for illustration only, batteries should be kept cool at or below 15°C when they are not being used, and operated at 30°C (it will be appreciated that the optimal temperature ranges may vary for different battery chemistries and layouts). This requires active thermal management to achieve the desired average temperature and temperature homogeneity within a modular battery apparatus. In particular, batteries need to be heated from their storage temperature to their optimum operational temperature, and their optimum operational temperature is often above a temperature of the environment in which they are being used.

It is common to use an indirect liquid cooling approach to thermally condition batteries with resistive heating elements or heat pumps to achieve the heating effect. Dedicated power supplies for heating are often provided. However, this requires additional costly components that add size and weight to an apparatus and energy inefficient methods. Thermal management of apparatus comprising different battery chemistries adds another level of complexity as different chemistries have different thermal requirements.

US5362942A discloses a method that uses the internal resistance of the battery as the battery heating element wherein an internal load is connected across a first and second battery terminals of a battery. A dedicated power source is provided for heating. The method is designed for maintenance of a battery that is not in currently in use, and does not allow for thermal control of a battery in an apparatus that is supplying current to an external load.

There remains a need for an energy storage and release apparatus comprising modular batteries, that allows direct control over the individual batteries, that can accommodate batteries of different types. There is also a need for an apparatus and method that allow thermal management of individual batteries within the apparatus whilst also allowing the apparatus to provide power to an external load, or to maintain charge levels within the battery.

Summary of the Invention

In a first aspect, the present invention provides an energy storage and release apparatus comprising: a plurality of batteries; a plurality of bidirectional AC-DC power conversion modules; an AC electrical link configured to allow power flow between the power conversion modules and to allow electrical connection of the apparatus to an external load (i.e. to allow power flow to the external load from the apparatus, and vice versa - it will be appreciated that this connection to an external load may be cut off, e.g. by unplugging the apparatus, and then re-made), and wherein each battery of the plurality of batteries has a dedicated power conversion module of the plurality of power conversion modules connected between that battery and the AC electrical link; and a controller configured to control the power conversion modules individually, such that the current to and from each battery of the plurality of batteries is determined individually by the controller.

The apparatus may therefore comprise the same number of batteries as of bidirectional AC-DC power conversion modules.

The energy storage and release apparatus may alternatively be referred to as a battery apparatus. The apparatus is arranged such that power flow between the plurality of batteries, and between any battery of the plurality of batteries and the external load, is permitted only via the AC electrical link. The apparatus is arranged such that power flow between the plurality of batteries is permitted only via their respective power conversion modules. Each battery may therefore be agnostic as to whether power it receives is provided by another battery of the apparatus, or by something else connected to the AC link (e.g. a grid connection). Each battery may therefore be agnostic as to whether power it provides is sent to another battery of the apparatus, or to an external load (e.g. a grid connection).

This apparatus of the first aspect may allow transfer of energy between different batteries for the purposes of balancing state-of-charge, independent control of battery degradation of different batteries, and thermal management derating of batteries as they approach their thermal limits, without compromising on performance of the apparatus as a whole.

The apparatus of the first aspect also allows for the batteries to be used independently by the apparatus, allowing batteries with different performance characteristics to be used in combination. For example, each battery may provide power at a different current and/or a different voltage from one or more other batteries, and may provide more or less power at any given time than one or more other batteries, or only a selected subset of batteries may be used at a given time. As a result, batteries with different chemistries can be operated at their best suited temperature, current, and/or states of charge, as part of a single apparatus and contributing to total power provided by the apparatus. The apparatus also allows batteries of lower states-of-health to be used in conjunction with fresher batteries by limiting their power window.

It will be appreciated that whilst the system allows for the batteries to be controlled completely independently of each other, in general the potential output of all batteries is considered together and each battery controlled individually so as to provide a desired overall output. Whilst the batteries may be described as being “independently” controlled, it will therefore be appreciated that decisions on the control of one battery are likely to influence decisions on control of another battery - hence the batteries are described as being “individually controlled”.

The apparatus of the first aspect may be an energy storage apparatus suitable for combining repurposed battery packs without constraints on matching batteries of similar make, chemistry, state-of- health or capacity. The controller of the apparatus may be referred to as a “central” controller as it controls all batteries, effectively providing a control centre for the apparatus, irrespective of its physical location with respect to the batteries. The controller of the apparatus may comprise a memory configured to store information on each battery of the plurality of batteries. Optionally, the information stored includes the chemistry of each battery, or equivalently preferred operation windows which may be based on battery chemistry (e.g. temperature windows and/or state of charge windows). The controller may store a type identifier for each battery, where subsets of batteries have different types (e.g. due to their different chemistries). The type identifier may have operational constraints associated therewith (e.g. minimum temperature for a specified current draw, current range, operational temperature range).

The batteries of the plurality of batteries may each provide power to, or receive power from, that battery’s associated power conversion module via an electrical link. Each battery of the plurality of batteries may therefore be linked to its respective dedicated power conversion module via a dedicated electrical link, which may be a DC electrical link. There is therefore a one-to-one mapping of batteries to links, and of links to power conversion modules, in such embodiments.

The voltage of the link between at least one battery of the plurality of batteries and the power conversion module for that battery may be different from the voltage of the link between at least one further battery of the plurality of batteries and that further battery’s power conversion module. Likewise, currents carried by the link may differ between batteries, both in terms of current magnitude and in terms of changes in current magnitude with time. As such, the current supplied by a battery of the plurality of batteries to its dedicated power conversion module may be different from the current supplied by at least one further battery of the plurality of batteries to that further battery’s dedicated power conversion module.

The controller may be configured to control the current to and from the plurality of batteries such the currents of two or more of the batteries vary with time. Optionally the current may be controlled so as to vary with time according to a sinusoidal current profile. A battery having a current set to vary with time may be described as a battery having a dynamic current profile. The time-varying/dynamic current profiles may be selected such that total power provided by the plurality of batteries meets the external load on the apparatus. It will be appreciated that the power provided by the plurality of batteries may be set to slightly exceed the power demanded by the load in order to meet that load, as some losses will occur in transmission (e.g. in the power conversion modules and along cables) - these losses should generally be small and predictable, and are not discussed further herein.

The total power provided by the plurality of batteries may be arranged to meet the power required by the load on the apparatus - for a constant external load, at least some of the dynamic current profiles of different batteries may be out of phase with each other, and optionally in anti-phase, so that the overall power provided is constant despite variations in power output from each battery individually.

The apparatus may comprise one or more protection devices between the power conversion modules and a connection to a load, and optionally also between each power conversion module and its respective battery. Optionally, the protection device is a passive protection device or an active protection device. A protection device may be selected from a model case circuit breaker (MCCB), a residual current device (RCD), a G99 protection relay (G99), or a fuse.

The controller may be configured to receive information from the power conversion modules.

The controller may be configured to receive information from the batteries.

Each battery of the plurality of batteries may comprise communication electronics. The controller may be configured to receive information from each battery of the plurality of batteries. The controller may be configured to receive information from each battery directly, and/or via the power conversion module. Information received from a battery directly may be used to verify information received from the power conversion module, and/or compared against information received from the power conversion module so as to identify any issues between the battery and the power conversion module.

The apparatus may be configured such that the controller communicates with other components of the apparatus, optionally using a Controller Area Network bus (CAN bus) or an ethernet link. The controller may be arranged to communicate with each battery and each power conversion module directly, optionally using a CAN bus.

At least one battery of the plurality of batteries may differ from further batteries of the plurality of batteries according to one or more characteristics selected from chemistry, voltage, capacity, age, and state of health. States of charge may also vary between batteries, both at start-up and during operation.

The chemistry of at least one battery of the plurality of batteries may be of a first chemistry and the chemistry of at least one other battery of the plurality of batteries may be of a second chemistry, wherein the first and second chemistries may be different. The chemistries may be selected from lead-acid, aluminium ion, lithium-ion lithium cobalt oxide, lithium-silicon, lithium-ion manganese iron phosphate, lithium-ion manganese-oxide, lithium-ion polymer, lithium-nickel-manganese-cobalt oxide, lithium-nickel-cobalt- aluminium oxide, lithium-sulfur, lithium-titanate, thin-film lithium ion, lithium-ceramic (or the sodium-ion equivalents).

In various embodiments, the batteries may be selected from any lithium-ion or sodium-ion battery chemistry (e.g. NMC, NCA, LFP, LTO, etc.), including solid-state Li-ion battery chemistries. Lithiumpolymer, Lithium-metal, Lithium-sulfur, and/or Lithium-air batteries may be used.

The batteries may be lithium-ion batteries, and more specifically may be NMC, NCA, and/or LFP batteries. Lithium-titanate (LTO) batteries may also be used in some embodiments.

The apparatus may further comprise a thermal management system configured to control the temperature of one or more components of the system (e.g. the temperature(s) of the batteries). The thermal management system may be arranged to distribute heat between the plurality of batteries. The thermal management system may be one or more of an indirect liquid thermal management system and a forced air convection thermal management system.

The apparatus may further comprise one or more sensors configured to communicate with the controller. The sensors may be selected from one or more of temperature sensors, battery safety gas sensors, voltage sensors, current sensors, isolation sensors, humidity sensors, pressure sensors, acceleration sensors, or any combination thereof.

The apparatus may comprise a current sensor, such as a current clamp, configured to monitor the current between the load and the apparatus and to communicate this information to the controller. The apparatus may comprise a current sensor configured to monitor the current between each battery and its respective power conversion module, and/or between each power conversion module and the AC link, and to communicate this information to the controller. The controller may use this information to trigger or inform decisions on current profile changes, and/or to trigger implementation of safety cut-offs where appropriate. For example, closed-loop control of the power converters may be implemented, and battery terminal contactors may be used to isolate one or more batteries from the rest of the apparatus if any safety thresholds are met or exceeded.

The apparatus may comprise at least one temperature sensor. When a temperature sensor is present, the controller may be configured to receive data from the at least one temperature sensor and, if the temperature is below a set threshold, to independently / individually control current to and from each battery of the plurality of batteries such that two or more of the batteries have currents that vary with time and which are not in phase. The currents may be controlled such a total power provided by the plurality of batteries meets the power required by the load. The currents may be controlled such that the currents provided by the power conversion modules to the AC link match up to meet the total current demand of the load, with all power conversion modules operating on the same voltage AC link. The external load can therefore be met by the combined outputs from the apparatus.

Alternatively or additionally, the controller may use the temperature data to trigger a different heating or cooling system (e.g. a separate resistive heater), and/or to trigger implementing safety cut-offs where appropriate.

The at least one temperature sensor may be provided by one or more batteries of the apparatus. Each battery may comprise a temperature sensor, optionally as part of the battery’s internal battery management system. The controller may be configured to receive temperature data from each battery, and to choose which batteries to control, or how to control the batteries, based on information including which batteries report the lowest temperatures and optionally also chemistry or safe operating temperature window information for the batteries. For example, the batteries with the lowest temperatures may be given dynamic current profiles with low magnitudes, and/or nearby batteries may be given dynamic current profiles and/or higher loads so as to warm the identified battery /batteries near to them.

The controller may therefore be arranged to determine battery current profiles based on information including one or more of: temperature data received from the batteries’ internal temperature sensors; temperature data received from other sensors of the apparatus; which batteries report the lowest or highest temperatures; chemistry information, or, correspondingly, preferred windows of operation temperature, for each battery; battery lay-out / arrangement of batteries within the apparatus; and the load on the apparatus.

The currents may be controlled by the controller such that a level of heat determined based on the received temperature data is output by the batteries - for example, larger currents may be used if the temperature is lower, so as to increase levels of Joule heating from the batteries’ internal resistances (and optionally also from other system components), and vice versa.

The controller may be arranged to control currents such that the current of at least one battery varies with time between greater than 0 amps and less than 0 amps. The battery may therefore be charged and discharged as part of the process; providing power some of the time, and taking power some of the time.

The average (mean) current of at least one battery with a varying current profile may be zero, such that the battery provides no power overall and has the same state of charge at the start of operation as at the end of operation (at least for a particular phase of operation - e.g. a warm-up phase).

The current to and from each battery may be controlled to vary according to a sinusoidal current profile. The use of smoothly -varying currents (such as, but not limited to, sinusoidally -varying currents) rather than step-changes in currents may facilitate keeping overall power levels within accepted tolerances even if synchronisation of changes is imperfect between batteries.

In a second aspect, the present invention provides a method of providing electrical power comprising connecting the apparatus of the first aspect to a load, wherein the apparatus (and more specifically, the controller of the apparatus) controls the current output from each battery of the plurality of batteries separately in order to meet the total power demand of the load. The use of a bidirectional AC link connecting the batteries in the first and second aspects allows the batteries to be operated at different voltages, to draw (or provide) different currents, and to be run at different states of charge, whilst still contributing to the same load. As such, flexibility is greatly increased as compared to prior art systems in which a common DC link is used between batteries, limiting all batteries to the same voltage provision. The bidirectionality allows current flow battery to load, battery to grid (in implementations with a grid connection), and battery to battery whilst also allowing optimal use to be made of each battery based on its chemistry, state of health, current temperature, and/or other properties.

Being able to vary current profiles between batteries in a single system provides a key advantage in repurposing used or surplus battery packs, e.g. electric vehicle battery packs, which may have significantly differing properties. The ability to use individually-controllable batteries so as to thermally manage the apparatus is an optional advantage of individually-controllable batteries explored further in the subsequent aspects.

In a third aspect, there is provided a battery apparatus with internal thermal management, the apparatus being arranged to supply power to meet a load and comprising: a plurality of batteries; an electrical link between the batteries of the plurality of batteries; at least one temperature sensor; and a controller.

The controller is configured to receive data from the at least one temperature sensor and, if the sensed temperature is below a set threshold, to individually control current to and from each battery of the plurality of batteries such that two or more of the batteries have currents that vary with time and which are not in phase, the currents being controlled such that a total power provided by all of the batteries of the apparatus meets the power required by the load.

The operation of any battery generates heat due to the I²R losses as current (I) flows through the internal resistance (R) of the battery - this occurs whether the battery is being charged or discharged, and is known as Joule heating. Joule heating may therefore be used - both during normal operation meeting a non-zero external load and in a pre-heating phase with an external load of zero - to provide heat in situ where it is needed to warm the batteries. The varying current profiles allow flexibility in providing Joule heating where it is needed whilst optionally still meeting an external load, as described below.

Advantageously, Joule heating using the internal resistances of the batteries provides heat where it is needed, so reducing or avoiding the need for circulating a heat transfer fluid/coolant (as heat may otherwise need to be moved to the batteries from a remote heater), so reducing the number or size of components needed, and/or reducing use of less efficient heating mechanisms. When the electrical link between the batteries is an AC link (rather than DC), the power conversion from DC to AC has losses which generate heat - this heat can be captured to support heating of the system, so being used for the Joule heating management. By transferring energy from one battery to the next at a controllable rate (including two conversions - DC - AC then AC - DC) it is therefore possible to generate a controllable amount of heat without requiring a dedicated heating component.

Joule heating can be used to heat the battery producing the heat, but also can be used to heat other batteries in the systems that can be static (i.e. no current flow) or operating (i.e. non-zero current flow, be that charging or discharging). Heat may be transferred between batteries passively (e.g. relying on convection of air around the batteries and/or heat conduction through materials of the apparatus) or actively (e.g. using a fan or pump to move a heat transfer fluid).

An active heat transfer system - e.g. pumped liquid flow - may still be used with this internal battery Joule heating, to distribute heat between batteries, or indeed between cells of a given battery.

Currents may be negative for at least parts of the dynamic current profile - one battery of the apparatus may effectively charge another in those regions, transferring power between batteries to provide Joule heating in both batteries as currents flow through the internal resistance of those batteries.

The controller may be arranged to determine a level of heat to be supplied based on the received temperature data, and to control battery currents such that the required level of heat is output by the batteries. For example, more batteries may be given dynamic load profiles, and/or batteries may be given higher- current profiles, if the sensed temperature is lower, so as to provide more heat. By contrast, if the sensed temperature is only just below a desired threshold, the controller may determine that only a relatively small amount of heat input is required and may make use of fewer batteries, and/or lower-magnitude current profiles, to provide heating.

The battery apparatus may comprise a case, and the plurality of batteries may be located within the case. The temperature sensor may also be located within the case. The case may be thermally-insulating, so facilitating distribution of battery heat between batteries without excessive loss to the environment in cold conditions.

In various embodiments, one or more of the batteries (and optionally each battery) may have an integral temperature sensor, for example as part of a battery management system of the battery. The battery’s temperature sensor may be the (or a) temperature sensor providing data to the controller.

The controller may be arranged to control currents based on the temperature sensor data, for example such that a level of heat determined based on the received temperature data is output by the batteries.

The battery apparatus may comprise a heat transfer medium arranged to distribute heat between the plurality of batteries. The heat transfer medium may be a liquid heat transfer medium or a gaseous heat transfer medium. For example, the heat transfer medium may simply be air around the batteries, or may be a liquid coolant in pipes. In some embodiments, the heat transfer may be passive (e.g. relying on natural air movements and convection currents), whilst in other embodiments the heat transfer may be active (e.g. with a fan to move air, and/or a pump to move a fluid). The apparatus may therefore comprise a pump, fan, or other device arranged to move the heat transfer medium within the case so as to distribute heat amongst the plurality of batteries.

In a fourth aspect, the invention provides a method for thermal management of batteries in an apparatus comprising a plurality of batteries wherein the current to and from each battery is individually controlled, wherein the method comprises varying the currents of two or more of the batteries with time whilst ensuring that the total power provided by the plurality of batteries meets the power required by the load on the apparatus.

The method of the fourth aspect may be implemented using the apparatus of the first and/or third aspect.

The apparatus of the third aspect and the method of the fourth aspect utilise the internal resistance of a battery to generate heat within the battery itself. That heat may then be used solely to heat that battery, or may be distributed to one or more other batteries of the apparatus. Some battery chemistries are exothermic when discharging, whilst some are endothermic whilst discharging. This property of the battery chemistry can also be used to generate heat within the battery or to cool a battery as required by the apparatus. Given that batteries are not perfectly reversible systems, they will always tend to be net exothermic, with Joule heating dominating over any endothermic cooling (Joule heating may not dominate for some endothermic reactions at very low currents, but in practice has generally been found to dominate for current battery chemistries). However, more heat is generated by some chemistries than others, and whether more heat is generated by charging or by discharging also depends on battery chemistry. The chemistry of each battery can therefore be used by the apparatus or in the method for thermal management by varying the current delivered to and from each battery in the apparatus according to its chemistry.

Heating, and potentially some cooling (or at least a reduction in heating level as compared to using a different chemistry battery), therefore occurs directly within the battery where the thermal control is needed. By varying the current delivered by at least two batteries, batteries can be heated (or potentially cooled) whilst the current required by the load is delivered. This allows thermal management of the batteries whilst they provide the necessary power to the load.

In the apparatus of the third aspect or the method of the fourth aspect, the current of at least one battery may vary with time between greater than 0 amps and less than 0 amps. In particular, the controller may be configured to control current flow such that the current of at least one battery varies with time between greater than 0 amps and less than 0 amps. The battery may therefore be charged for some of the time and discharged for some of the time, optionally in a regular, repeating, pattern.

In the apparatus of the third aspect or the method of the fourth aspect, the average (mean) current of at least one battery with a varying current profile may be zero, such that the battery provides no overall power to the apparatus. In particular, the controller may be configured to control current flow such that the mean current of at least one battery being operated with a varying current is zero, such that the battery provides no overall power to the apparatus. A battery can therefore be warmed by its own internal Joule heating, whilst not changing its state of charge overall (at least not significantly).

Keeping loads relatively low whilst a battery is cool / in a battery -warming phase, may protect that battery (i.e. reduce degradation) - current magnitudes may therefore be kept relatively low for one or more batteries being heated, in addition to, or instead of, maintaining a state of charge overall. For example, the controller may be configured to control current flow to and/or from a battery to be heated to no more than 1%, 2%, 5%, or 10% of the current of the battery in the apparatus which is providing the most power to an external load. Alternatively or additionally, the controller may be configured to control current flow to and/or from a battery to be heated to no more than 0.1 A, 0.5 A, 1 A or 2 A. In various embodiments, the current flow may instead be controlled based on C-rate value to normalise against battery capacity (C-rate is the unit used in the field of battery technology to measure the speed at which a battery is fully charged or discharged. For example, charging at a C-rate of 1 means that the battery is charged from 0-100% in one hour). The controller may be configured to control current flow to and/or from a battery at no more than C/100 (i.e. 100 times lower current flow than its rated maximum), C/10, C/8, C/5.

In some embodiments, the load may be zero - this may be referred to as a pre-heating or warm-up stage of operation, prior to the apparatus providing power, or may be used as an apparatus protection step in cold climates, to maintain an acceptable minimum battery temperature when not in use. The controller may be configured to control current flow such that the overall power output of the plurality of batteries is zero at any point in time whilst the load is zero. Power may therefore be transferred between batteries to use the current flow to heat the batteries.

In the apparatus of the third aspect or the method of the fourth aspect, the current to and from each battery may vary according to a sinusoidal current profile. In particular, the controller may be configured to control current flow such that the current to and from each battery varies according to a sinusoidal current profile.

It will be appreciated that the features described for any one aspect may be applied to any other aspect, mutatis mutandis.

Summary of the Figures

Embodiments of the present invention will now be described by way of example with reference to the accompanying drawings, in which:

Figure 1 is a schematic view of a first energy storage and release apparatus according to the present invention;

Figure 2 is a schematic view of a second energy storage and release apparatus according to the present invention;

Figure 3 is a view of a first thermal management current or power profile of two batteries meeting the load on an apparatus according to the present invention; and

Figure 4 is a view of a second thermal management power profile of two batteries meeting the load on an apparatus according to the present invention.

In the Figures, like or corresponding reference numerals are used for like or corresponding features.

Detailed Description of the Invention

A battery comprises a container comprising one or more cells, in which chemical energy is converted into electricity and used as a source of power. The state of charge (SoC) of the battery is the difference between a fully charged battery and the same battery in use, or the quantity of electrical power available in the cell. It is defined as the percentage of the remaining charge in the battery divided by the maximum charge that can be delivered by the battery, expressed by the formula:

SoC = 100 x (Q_o + Q)/Q max, where Qo is the initial charge of the battery in mAh, Q is the quantity of electricity supplied to the battery in mAh (with a negative value used for electricity delivered by the battery), and Q_max is the maximum charge that can be stored in the battery in mAh.

The state of health (SoH) of the battery is defined as the percentage of the maximum battery charge to its rated capacity described by the formula:

SoH = 100 X Q_max/Cr, where Q_max is the maximum that can be stored in the battery in mAh and C_r is the rated capacity of the battery, also in mAh.

The present invention provides an energy storage and release apparatus (100, 200), examples of which are shown in Figures 1 and 2. The apparatus (100, 200), which may also be referred to as a battery apparatus, comprises a plurality of batteries (102a-n, 202a, b), a plurality of bidirectional power conversion modules (104a-n, 204a, b), an electrical link (140) configured to allow power flow between the power conversion modules and to allow electrical connection of the apparatus to an external load (which may be or comprise a grid connection (145) in some implementations). The apparatus further comprises a central controller (135) configured to control the power conversion modules individually, such that the current to and from each battery of the plurality of batteries, and optionally the voltage, is determined individually by the central controller (135). In the apparatus (100, 200) each battery of the plurality of batteries is connected to, and provides power to or is supplied power by, a different power conversion module (104, 204) from further batteries of the plurality of batteries. Each battery (102, 202) can only transfer power to or from further batteries of the plurality of batteries via its respective power conversion module.

Each battery therefore has a dedicated power conversion module dedicated thereto - all power flow to or from that battery is controlled via its associated power conversion module. Each battery of the plurality is associated with a separate power conversion module, such that there is a one-to-one ratio between the batteries and the power conversion modules, and no battery shares a power conversion module with a different battery. Power flowing from one battery to another therefore has to do so via two power conversion modules - one for each battery.

The power conversion modules (104, 204) control the flow of current to and from a battery. The power conversion modules are bidirectional DC-AC power conversion modules in the examples shown in Figures 1 and 2, although DC-DC converters may be used instead in embodiments with a DC link between batteries as discussed below.

Bidirectional power conversion modules (104, 204) convert direct current (DC) power to alternating current (AC) power, and vice versa. This allows the batteries in the apparatus, which provide DC power, to both be discharged to a load requiring AC power and also be recharged from supplied AC power. Each battery can therefore only transfer power to or from further batteries of the plurality of batteries via transforming that power from DC to AC and back again. Whilst this may increase system size and/or weight as compared to using a direct DC link between batteries, it improves system versatility as described below.

The central controller (135) is configured to control the power conversion modules (104a-n, 204a, b) so as to control the current to and from each battery (102a-n, 202a, b) individually. The apparatus (100, 200) therefore provides direct and individual control over the current passing to and from each battery within the apparatus. The batteries may therefore be described as being independently controlled.

Power flow between each battery and its associated power conversion module may be via an electrical link (106a-n, 206a, b). The electrical link (106, 206) may be described as a DC link as it connects the battery (102, 202) to the power conversion module (104, 204) without having any DC-AC converter therebetween to change the battery’s output to AC. However, in various implementations as described below, the battery (102, 202) may be sequentially charged and discharged in a regular repeated pattern so effectively providing an alternating current along the electrical link (106, 206) - the current may therefore have a standard sinusoidal AC profile with time in some implementations, but it will be appreciated that the voltage profile with time for the battery generally will not follow the standard sinusoidal AC profile as it would in a true AC link. The voltage may be approximately constant over the time period of a set current oscillation (ignoring longer-term effects such as voltage drop as the battery is depleted), with the power conversion module (104, 204) effectively altering the resistance so as to draw or provide the desired current level, in accordance with Ohm’s law. Further, the alternating current waveform on the DC link generally does not see a negative voltage (whilst by contrast in 230 V AC the voltage does go negative), so the amplitude varies within tight voltage ranges e.g. 320 to 380 V (depending on the load). The frequency of current oscillations is also likely to be much lower on the DC link, for example 0.1-2 Hz as compared to the 50-60 Hz of standard AC power. The voltage of the electrical link (106a, 206a) between at least one battery (102a, 202a) of the plurality of batteries and its dedicated power conversion module (104a, 204a) may be different from the voltage of the link (106b, 206b) between at least one further battery (102b, 202b) of the plurality of batteries and its dedicated power conversion module (104b, 204b). The power conversion modules (104, 204) adjust the power as appropriate for supply to the load (145), the adjustment generally including a conversion to AC.

The other electrical link (140), which is a bidirectional AC link in both examples shown in the figures, is configured to allow electrical connection / power flow between the power conversion modules and to allow electrical connection of the apparatus to an external load (145). This load could be a national or local electricity grid (145), and/or it may be a powered tool such as those used in construction, an electric vehicle, or any other device, or may comprise both. The apparatus (100, 200) may therefore be used to charge an electric vehicle, for example.

The electrical link (140) may comprise one or more protection devices between the power conversion modules (104a-n, 204a, b) and a connection to an external load (145). The one or more protection devices may be passive or active, for example one or protection devices may be selected from a model case circuit breaker (MCCB), a residual current device (RCD), G99 protection relay (G99), or fuse. Whilst an active device is something that can be actuated and which is triggered by a signal e.g. A pyrotechnic fuse, relay, contactor, or switch, a passive component acts independently, e.g. a fuse, a breaker MCB, or an RCD.

The apparatus (100, 200) may allow transfer of energy between different batteries (102, 202) for the purposes of balancing state-of-charge, so allowing the apparatus to control battery degradation of different batteries independently, and/or to provide thermal management derating of batteries as they approach their thermal limits, without compromising on the performance of the apparatus.

The central controller (135) controls the power conversion modules (104, 204) individually, such that for each battery the contribution to, and demand on, the total apparatus power is determined individually by the central controller.

The central controller may be configured to receive information from the power conversion modules, as indicated by dotted lines (155) in Figure 1. In various embodiments, including that of Figure 1, the power conversion modules are configured to contain or collect information and transmit this information to the central controller. For example, the power conversion modules may comprise one or more sensors (e.g. temperature, voltage, current), and may be arranged to provide sensor data to the controller on request, according to a schedule, and/or in response to certain triggers (e.g. a set threshold being exceeded).

In various embodiments, including that of Figure 1, the batteries (102, 202) themselves are configured to contain or collect information and transmit this information to the central controller (135). For example, as for the power conversion modules, the batteries may comprise one or more sensors (e.g. temperature, voltage, current), and may be arranged to provide sensor data to the controller on request, according to a schedule, and/or in response to certain triggers (e.g. a set threshold being exceeded). In addition, the batteries may store information of their type (e.g. a part number, and/or information on the manufacturer and/or cell chemistry) and may provide that data to the controller, e.g. on installation into the apparatus, and/or on start-up of the system.

This information may be sent to the controller directly, as indicated by the grey lines (150) in Figure 1, or may be sent via the associated power conversion module of that battery. In various embodiments, including that of Figure 1, the only link between each battery and its associated power conversion module is a power transfer link (the DC link 106a-n), and no data are communicated directly between the battery and its associated power conversion module.

In some embodiments the central controller (135) comprises a memory configured to store information on each battery of the plurality of batteries. The information stored may include one or more of the age, chemistry, voltage, capacity (in mAH), state of health, state of charge, temperature, and other information of the battery.

The information stored may include the chemistry of each battery. By chemistry of the battery, it is meant the chemical makeup of the battery that stores the electrical energy, e.g. Li-ion or Na-ion batteries, and optionally more specifically e.g. Lithium Iron Phosphate (LFP), Lithium-Nickel-Manganese-Cobalt- Oxide (Li-NMC, or NMC), Lithium Nickel-Cobalt-Aluminium Oxide (Li-NCA, or NCA), lithium ion manganese oxide (LMO), or lithium titanate (LTO), all of which are examples of Li-ion batteries, or Nickel- Cadmium (NiCad), Nickel-Metal Hydride (NiMH), Lead-Acid, etc. More specifically, battery chemistry indicates the chemical reactions that occur on charging and discharging of the battery.

Information on each battery may be provided to the central controller (135) by the user or manufacturer when batteries are added to the apparatus. This may be by way of inputting a serial number through a user interface, and the central controller may be configured to look up the serial number in a database, stored on the central controller or remotely, which also contains the battery information associated with this serial number. It may also or alternatively be by way of selecting a battery type from a drop-down list via a user interface to associate the battery added to the apparatus with information stored locally or remotely for that battery option, by communicating with the controller to provide information from a remote device electronically, or the battery itself may provide the information automatically.

Each battery (102a-n, 202a, b) of the plurality of batteries may comprise communication electronics. The central controller (135) may be configured to receive information from each battery of the plurality of batteries via these communication electronics. In the embodiment of Figure 1, each battery communicates information to the central controller (135) directly. Each battery communicates a serial number corresponding to that battery to the central controller in the specific example being described, and the controller is configured to then look up the characteristics of the battery in a database. In some embodiments, each battery provides updated information regarding that battery to the central controller constantly or regularly, such as every second, every five seconds or every minute or five minutes, or over a period defined by the load on the apparatus or when otherwise triggered, such as every time the temperature of the battery raises by 0.1°C, 0.5°C, 1°C, 2°C or 5°C or every time the state of charge of the battery changes by 0.1%, 0.5%, 1%, 2% or 5% of total capacity. It will be appreciated that frequency of data updates may depend on data types - for example, battery state of charge will change in use whereas battery chemistry is constant for a given battery.

Some characteristics of the battery and/or of power drawn from or supplied to the battery, and/or of power demand from the load/grid (145), are communicated to the central controller by the power conversion module constantly, or regularly as defined above, or at intervals defined by system or load changes (e.g. on crossing a threshold, as discussed above).

The plurality or batteries (102a-n, 202a, b) and the plurality of power conversion modules (104a-n, 204a, b) may be configured to both communicate with the central controller (135).

Information communicated to the central controller (135) may comprise characteristics that do not change, such as battery chemistry, manufacturer, capacity of battery when new, voltage of battery when new, or combinations thereof, and parameters that do change, such as temperature, state of charge, state of health, capacity or combinations thereof. The type and frequency of communication may vary accordingly. For example, data which remains constant for a given battery pack may be provided to the central controller only once - for example when a battery pack is first installed - or may be verified at regular intervals or on start-up. The data may be provided automatically by an integral battery management system of the battery, optionally in response to a request from the central controller. Alternatively, such information may be entered directly by a user, for example using a graphical user interface in communication with the central controller, or being sent to the central controller from a remote device. By contrast, “live” data may be provided from sensors and similar regularly throughout operation, at a frequency which may vary depending on sensor type and/or other settings or conditions. Each power conversion module (104a-n, 204a, b) may provide its values periodically or on request, as well as receiving and responding to commands from the central controller (135). It will be appreciated that various components may therefore communicate differently, and/or with different regularities, depending on data types and system requirements.

The apparatus (100, 200) may be configured such that the central controller (135) wirelessly communicates with the other components of the apparatus (e.g. the batteries and/or power conversion modules), optionally using a CAN bus, Modbus, or an ethernet link. TCP/IP protocol may be used for communications in some embodiments. Wireless methods are preferable for simplicity, but any suitable communication method known in the art could be used.

The central controller (135) may use this information to adjust the operation of the apparatus (100, 200) to provide the requested power output whilst ensuring that the operating conditions do not unduly reduce the lifespan of the batteries.

In an example where the apparatus (100, 200) is supplying current to a load (145), the central controller (135) may identify a battery (e.g. 102a) having a low state of charge (e.g., 5 %) and instruct the power conversion module (e.g. 104a) associated with that battery to draw current from the AC link / from the other batteries of the apparatus so that the battery (102a) can recharge. The central controller then instructs the power conversion modules associated with further batteries of the plurality of batteries to provide additional power to the AC link 140 to account for the power lost to the charging battery (102a) whilst continuing to meet the requirements of the load on the apparatus (100, 200).

Sample scenarios of how a central controller (135) may adapt to information received from the batteries and/or power conversion modules are provided below by way of non-limiting example:

Scenario (1):

The central controller receives sensor data from the batteries (102) and determines that one battery (102a) is still too cold. The definition of “too cold” may vary from battery to battery, depending, for example, on that battery’s chemistry and on the load on the battery. The central controller then calculates a new profile of current share between the batteries to match the load demand whilst providing additional heating to the identified cold battery, and adjusts the current setpoints of two or more of the power modules accordingly. For example, the cold battery (102a) may have its average current reduced and be set to follow a dynamic current profile centred around a current at or near 0 A, so not loading the battery significantly (avoiding stressing the battery outside of its optimum performance temperature range) whilst providing Joule heating from the current flow, and its net output may be increased as it warms up. A second battery may be set to have a higher average current, and to have a dynamic current profile in antiphase with the first, so offsetting the drops in power and meeting a constant external load (145). Alternatively or additionally, heat from one or more other batteries may be directed to the battery registered as being too cold - for example, one or more batteries located adjacent to the cold battery may have their currents increased so as to provide increased Joule heating, and/or an active thermal management system (as described below) may be used to distribute a fluid warmed with heat from other batteries to the cold battery.

Scenario (2):

Load demand changes, and the new load (145) is expected to last for a set period of time. The batteries (102) have different remaining capacities. The central controller (135) adjusts the current sharing between the batteries to drain them at different rates such that they will reach their minimum allowed state of charge (which may be 0%, or may be at least e.g. 5%, 10%, or 20% to protect the battery) at the same time. Batteries with a lower state of charge may therefore be drained more slowly than batteries with a higher state of charge, assuming equivalent total capacities of the batteries. Current setpoints are adjusted in the power modules (104a-n, 204a, b), in response to instructions from the central controller.

Scenario (3):

The unit (100, 200) is starting up from cold. One battery (102a, 202a) of the plurality of batteries of the unit has a chemistry more suited to provide the full demand load at lower temperatures than the other(s). The controller (135) applies a current profile to obtain most (if not all) of the load from this battery (102a, 202a) - which may be referred to as the “working” battery - whilst pre-heating the other battery /batteries - which may be referred to as “heating” batteries - with a dynamic current profile. The one or more batteries being heated may have current profiles centred around a low current, and optionally centred around a current of zero, so that their state of charge varies little, if at all. Variation in the dynamic profile of the main “working” battery may be set to offset variations in the power output of the “heating” battery or batteries such that a constant power is provided to the load. If multiple batteries are being heated, they may have out of phase current profiles such that they offset each other, and the working battery (or batteries) may effectively provide the full load, and may operate with a non-dynamic current profile (constant output). When the battery or batteries more sensitive to lower temperatures are up to a more reasonable operating temperature, the current profiles may be adapted and made more uniform between batteries - this may be described as finishing a warm-up phase of operation.

In various embodiments, the power conversion modules (104, 204) may be rated to operate across a wide voltage range (e.g. 200-1000 V DC).

In one example (200) of the apparatus, the apparatus may comprise a first battery (202a) in electrical communication with a first bidirectional power conversion module (204a) and a second battery (202b) in electrical communication with a second bidirectional power conversion module (204b) - this apparatus comprises a total of two batteries and two power conversion modules. A central controller (135) is configured to control each of the first and second power conversion modules separately, such that for each battery the contribution to and demand on the total apparatus power is individually controlled. The apparatus (200) comprises an alternating current link (140) between the first power conversion module and second power conversion module, the AC link being configured to allow aggregation of power from each battery and to allow electrical connection to a load. In other examples, more batteries may be provided.

The apparatus (100, 200) of various embodiments comprises one or more sensors configured to communicate with the central controller (135), the sensors selected from one or more of temperature sensors, battery safety gas sensors, voltage sensors, current sensors, isolation sensors or any combination thereof. In some embodiments, one or more such sensors may be integral with a battery of the plurality of batteries - a monitoring system of the battery (optionally provided as part of an internal battery management system, as is generally provided in electric vehicle battery packs, for example) may be used to provide sensor data to the apparatus.

The sensors gather information from the apparatus (100, 200) that allows the central controller (135) to take action to maintain the health of the apparatus. For example, should a battery safety gas sensor detect an unsafe release of gas from the batteries, the central controller could instruct the power conversion modules to prevent any power being drawn from, or fed to, any battery from the plurality of batteries. Alternatively, if several battery safety gas sensors are present in the apparatus and one detects an unsafe release of gas the central controller could instruct the power conversion modules to prevent any power being drawn from, or fed to, any battery in the vicinity of that sensor whilst allowing power to be drawn from other batteries from the plurality of batteries. Thus, safety is maintained whilst the apparatus continues to provide power; a safety protocol enabled by individual control of the current to and from each battery.

The temperature of each battery (102, 202) may be individually monitored with a temperature sensor and the central controller (135) may instruct the power conversion modules (204) to modulate current supplied to or from batteries of the plurality of batteries to avoid overheating, or unduly low temperatures, of individual batteries, several batteries, or all of the plurality of batteries.

The apparatus may comprise a current sensor, such as a current clamp, configured to monitor the current between the load (145) and the apparatus (100, 200) and to communicate this information to the central controller (135). The central controller may be configured to instruct the power conversion modules (104, 204) to reduce the current delivered by, or to, individual batteries to prevent the apparatus operating outside of operational limits in response to the current sensor communicating that a current in excess of a set threshold is being passed along the DC link (106a-n, 206a, b). A cut-out/ circuit-breaker or fuse may also be provided to cut power if the current drawn by the load exceeds that which can be safely delivered by the apparatus as a whole. This may prevent damage to the apparatus and improve safety, and may also be used to provide an alert in the case of a short circuit or other fault.

The energy storage and release apparatus (100, 200) is suitable for combining repurposed battery packs. Independent control of each battery of the plurality of batteries allows batteries of different chemistries, ages, states of health, capacities, and operational parameters such as temperature to be combined in one apparatus. This provides benefits including allowing the combination of different chemistries to allow specific current delivery profiles or for the combination repurposed battery packs without constraints on matching the characteristics of the batteries. The individual control may allow the apparatus to tune usage of each battery based on its chemistry, and/or other properties, so as to get the best out of each battery.

Therefore, at least one battery of the plurality of batteries may differ from further batteries of the plurality of batteries according to one or more characteristics selected from chemistry, voltage, capacity, age, and state of health.

In many embodiments, the chemistry of at least one battery of the plurality of batteries is therefore of a first chemistry and the chemistry of at least one battery of the plurality of batteries is of a second chemistry, wherein the first and second chemistries are different. Many battery chemistries are available, and many more are being developed constantly. Due to the independent control of each battery of the plurality of batteries, the apparatus may be able to accommodate any battery chemistry in combination with any other battery chemistry. Specific battery chemistries include lead-acid, aluminium ion, lithium-ion lithium cobalt oxide, lithium-silicon-lithium-ion manganese iron phosphate, lithium-ion manganese-oxide, lithium-ion polymer, lithium-nickel-manganese-cobalt oxide, Lithium-nickel-cobalt-aluminium oxide, lithium-sulfur, lithium-titanate, thin-film lithium ion, lithium-ceramic or combinations thereof.

Referring now to Figure 1 of the accompanying drawings in particular, this shows a schematic view of an energy storage and release apparatus (100) according to the present invention. The apparatus comprises a first battery (102a) electrically connected via a direct current link (106a) to a first bidirectional power conversion module (104a) and a second battery (106b) electrically connected via a direct current link (106b) to a second bidirectional power conversion module (104b). The apparatus (100) further comprises further batteries (... 102n), each electrically connected via individual direct current links (... 106n) with individual bidirectional power conversion modules (... 104n). The dots shown between the second battery (102b) and the nth battery (102n) are provided to illustrate that the number of batteries, n, and therefore also the number of sets of components associated with each battery, may vary - for example being between 2 and 100, and optionally between 2 and 10.

The apparatus (100) also comprises a central controller (135) configured to receive information from the power conversion modules (104) and the batteries (102) via a CAN bus (communications are indicated by lines 150 and 155). The power conversion modules (104, 204) may be controlled / communicate using the same communication bus as the batteries (102, 104), or a different bus. It will be appreciated that other communication approaches may be used in other embodiments, and that different communication methods may be used for the batteries from those used for the power converters in some implementations.

The central controller (135) is arranged to control each power conversion module (104) separately, such that for each battery (102) the contribution to and demand on the total apparatus power is individually controlled. An AC link (140) between the power conversion modules (104) is configured to allow aggregation of power from each battery (102), transfer of energy between batteries (102), and electrical connection to a load (145), which may be the grid. The apparatus may further comprise a connector (e.g. a plug or socket) arranged to allow the apparatus to be connected to, or disconnected from, an external load (145) and/or the grid, via the AC link.

The apparatus (100) may be used in a method of providing electrical power, the method comprising electrically connecting the energy storage and release apparatus (100) to a load (145), via the AC link (140), and using the apparatus to control the current output from each battery (102) separately in order to meet the total power demand of the load.

In the apparatus (100) shown in Figure 1, no active heat transfer system is shown for clarity of the communication lines shown. However, a heat transfer system such as that (260, 265) described below with respect to Figure 2 may be provided in some embodiments. Likewise, no case (210) is shown in Figure 1, but may be present.

Referring to Figure 2 of the accompanying drawings in particular, this shows a schematic view of an energy storage and release apparatus (200) similar to that shown in Figure 1. The following discussion emphasises the differences rather than the similarities to avoid excessive repetition. The apparatus (200) comprises a plurality of batteries (202) - in this embodiment, a total of just two batteries (202a, 202b) is present. The apparatus (200) has a central controller, although this is not shown for clarity. Each battery (202a, 202b) is electrically connected via a DC link (206a, 206b) to a respective power conversion module (204a, 204b). The power conversion modules (204) are electrically connected to one another, and to the load (145). In the example shown, this connection between the power conversion modules and the load is an AC link (140), although a DC link may be used in some embodiments. The controller (135) is not shown in

Figure 2 for clarity, but a controller is used.

The apparatus (200) comprises a case (210) surrounding and containing the other components of the apparatus. The case (210) may comprise one or more plugs, sockets, or other connectors for connection to the external load (145).

The apparatus (200) comprises a heat transfer system (260, 265) configured to distribute heat generated within the batteries between the batteries. Losses in the form of heat from inverters or other power electronics (e.g. in the power conversion modules (104, 204)) can also be “recycled”, redistributing that heat to one or more batteries to be warmed.

In the embodiment shown, the heat transfer system comprises a pump 260, and a heat transfer fluid (e.g. water, an ethylene glycol and water mixture, or any known suitable coolant, e.g. engine coolant) in a closed-loop pipe system. Any suitable thermal conditioning apparatus may be used in placed of, or in addition to, this in other embodiments.

Battery heating by Joule heating using internal resistances of the batteries themselves is used in the embodiments described with respect to Figure 2 - batteries are used to warm themselves, and the pipe system is used to transfer heat between the batteries. In some embodiments, a source of cooling may be provided (e.g. a coolant reservoir from which fluid is drawn to be circulated around the batteries, the reservoir providing a heat sink), but this is not discussed in detail herein.

The apparatus (100, 200) as shown in Figure 1 or Figure 2 may comprise a thermal management system configured to control the temperature of one or more components of the apparatus, and in particular of one or more of the batteries (102, 202). The controller (135) may act as a part of the thermal management system, or a separate thermal management controller may be provided, in communication with the central controller (135).

Thermal control of batteries is important in ensuring a battery is operating effectively in terms of power output and delivery efficiency. Operating batteries within the correct temperature range is important in terms of maintaining the effective life span of the battery. In an apparatus comprising mixed battery types, the optimum operating temperature might vary between batteries, therefore the thermal management system may be configured to control the temperature of each battery individually.

The apparatus (100, 200) may comprise a case (210) enclosing the batteries (102, 202) and power conversion modules (104, 204), and optionally also the controller (135).

The apparatus (100, 200) may comprise at least one temperature sensor, optionally as part of a, or each, battery. At least some of the temperature sensors are located within the case; a temperature sensor to provide an indication of external/environmental temperature may also be used in some embodiments. The central controller (135) may be configured to receive data from the at least one temperature sensor and to control the thermal management system accordingly.

For example, a fan or pump (260) may be turned on when a temperature rises past a threshold so as to cool one or more batteries (102, 202), e.g. bringing in outside air from the environment via one or more ventilation holes in a case (210) of the apparatus.

Equivalently, a fan or pump (260) may be turned on when a temperature drops below a threshold so as to warm one or more batteries (102, 202), e.g. transferring heat from a warmer region within the case (210) to a cooler region. Multiple temperature sensors may be provided within the case (210).

The fan or pump (260), and any associated pies or other components, may be referred to as a heat transfer system, as they move heat around within the apparatus (100, 200) but do not themselves generate any significant amount of heat. The thermal management system of various embodiments goes beyond this by generating heat on demand, and optionally in situ where it is needed although a heat transfer system may be used to distribute the generated heat in some embodiments.

The heat transfer system of various implementations may comprise one or more of an indirect liquid thermal management system and a forced air convection thermal management system. In embodiments using both an indirect liquid thermal management system and a forced air convection thermal management system, the two may be linked via an automotive high-performance radiator to obtain high efficiencies and performance.

In various embodiments, the controller (135) is arranged to control battery currents so as to make use of Joule heating from the batteries’ own internal resistances to provide heat.

In such embodiments, the apparatus (100, 200) comprises at least one temperature sensor, and the central controller is configured to receive data from the temperature sensor and to adjust current profiles of one or more batteries (102) independently based on the received temperature data.

In particular, the controller (135) independently controls current to and from at least two of the batteries (102, 202) such that those batteries have currents that vary with time and are not in phase. If only two batteries (102, 202) are controlled to have time-varying (i.e. dynamic) current profiles, those two current profiles may be set to be in anti-phase such that the variations in output power cancel each other out, allowing the apparatus (100, 200) as a whole to provide a constant output. If more than two batteries (102, 202) are controlled to have dynamic current profiles, the offsets in phase may again be selected such that a constant power output is provided overall. It will be appreciated that the external load may not be constant in some implementations, and that the dynamic current profiles may be set as appropriate to meet the external load when aggregated, whilst also providing Joule heating.

The controller (135) may be programmed to initiate use of two or more dynamic current profiles in response to temperature sensor data giving a reading below a set temperature threshold. In simplistic implementations, the same dynamic current profiles may be implemented, optionally for the same batteries (e.g. all batteries, or all batteries of certain chemistries), whenever a temperature reading is below the set threshold. In other implementations, more specific use is made of the temperature data by the controller so as to decide what current profiles to implement, and in which batteries.

In various such embodiments, the temperature data are associated with a sensor or battery location, and batteries (102, 202) in or near the location of a low temperature reading may therefore be selected to implement the dynamic current profiles. In alternative or additional such embodiments, the controller (135) determines a level of heat input needed based on the received temperature data, and adjusts the magnitude of the currents and/or current profiles accordingly. For example, a large r-magnitude current may be used in the region of a battery identified as being cold so as to generate more heat (Joule heating being proportional to current squared), or only batteries of certain chemistries (i.e. those more tolerant to lower-temperature operation) may have high loads put on them until temperatures have increased, with the batteries of other chemistries being assigned dynamic current profiles at relatively low currents to allow gradual heating without over-taxing the batteries.

The current of at least one battery (102, 202) may be set to vary with time between greater than 0 amps and less than 0 amps, such that the battery is charged for portions of its dynamic profile and discharged for other portions of its dynamic profile. This may be particularly beneficial for battery chemistries in which charging is an exothermic reaction (and in particular for chemistries in which charging is more exothermic than discharging), so providing additional heat from the chemical reactions themselves as well as from Joule heating. A dynamic current profile that includes charging the battery may therefore be preferentially selected for certain battery chemistries. The average power output over the dynamic profile may still be above zero, so allowing the battery to contribute to the external load whilst still getting the benefit of the exothermic reactions. Figures 3 and 4 of the accompanying drawings show possible dynamic charging/discharging profiles for use in such a scenario.

Current applied to a battery for use in heating that battery can be provided by a second battery of the apparatus, so also heating that battery. A highly efficient heating process at low power levels may therefore be provided.

Figure 3 provides a graphical representation of the current or power (305, 310) provided by a first battery (305) and second battery (310) according to such an implementation. The powers of the first battery (305) and the second battery (310) each vary with time according to a sinusoidal current profile. The sinusoidal profile of the second battery (310) is offset from the sinusoidal profile of the first battery (305) by 180° - i.e. they are out of phase, and more specifically in anti-phase, with the peaks in one aligning with the troughs of the other. The superimposed power amplitudes may be selected to match the power (315) required by the load (145) to generate a flat, constant, power profile for the combined output of the two batteries. It will be appreciated that the battery currents generally follow the same profile as the power, so the profiles shown also represent the current profiles of the batteries. The current profiles change with time and can therefore be described as dynamic current profiles. Whilst the mean current is above zero, both current profiles dip below zero amps around their minima, so charging each battery for a portion of its cycle, and so potentially getting some additional thermal benefit from exothermic charging reactions.

The power (305, 310) - and similarly the current - drawn from the battery, via the DC link (106, 206), may vary with a frequency in the range from 0.1 Hz to 2 Hz, for example with a time period of one complete cycle being around 1 to 5 seconds.

In other implementations, the mean current of at least one battery with a dynamic current profile may be zero, such that the battery provides no overall power to the apparatus, and is equally charged and discharged over the profile such that its state of charge is the same at the end of this period of operation as it was at the start, as shown in Figure 4. This battery (410) contributes a small amount to the external load over its peaks, but adds to the load on the rest of the apparatus in its troughs. One or more other batteries (405) therefore supply more than the external load at points to make up for the draw by the first battery (410).

Figure 4 of the accompanying drawings provides a graphical representation of a dynamic power profile (and therefore also the corresponding current profile) provided by a LFP battery (410) and by an NMC battery (405). The currents of the LFP battery (410) and the NMC battery (405) vary with time according to sinusoidal current profiles. The sinusoidal current profile of the NMC battery (405) is offset from the sinusoidal current profile of the LFP battery (410) by 180° (i.e. they are in anti-phase, as mentioned above). The superimposed power amplitudes together match the power required by the load (415) to generate a flat, constant, power profile from the apparatus as a whole.

A first battery (405) may therefore be discharged to provide the current required by a load using a varying current profile with an average power matching that of the load, whilst at the same time the variation in the current or power of the first battery (405) provides space for the second battery (410) to first contribute to, and then draw on, the current/power provided by the first battery. This flow of current into and out of the second battery (410) may be set to have an average current and power of zero, so causing the second battery to heat up without any overall change in the state of charge of the second battery. This method may be used to bring the second battery (410) to the temperature at which optimum performance is provided, and, once that temperature is reached, the load on the second battery may be increased. By generating heating (and indeed cooling when endothermic reactions allow it) within the batteries themselves, bulky and inefficient cooling systems external to the batteries are avoided or reduced.

In the example of Figure 4, the current provided by the two batteries is different. This arrangement allows the LFP battery (410) to generate heat within the battery (410) by alternatively discharging and recharging such that it can heat up to its optimum operating temperature without an overall change in the state of charge, whilst the NMC battery (405) - which has stronger performance at lower temperatures - provides the current required by the load (145).

In other examples, the overall current of provided by the apparatus (100, 200) may be 0 amps (i.e. the external load may be zero), and the currents delivered by two of more batteries of the plurality of batteries vary between greater than and less than 0 amps but with an average of 0 amps, such that the overall state of charge of the batteries does not change substantially, allowing for electrical energy to be converted into heat as it flows between batteries. This may be used as a pre-heating phase prior to use in supplying a load to an external device or the grid, allowing the apparatus, and more specifically at least some of the batteries in the apparatus, to be brought to the temperature range in which optimum performance is achieved before use, and without a significant change in the state of charge. The dynamic current profiles allow simultaneous charging of some batteries and discharging of others, so transferring power around the apparatus to generate warming even if all batteries are at or near their maximum capacities.

The current to and from each battery varies according to a sinusoidal current profile in the examples of both Figures 3 and 4. This smooth variation may assist in providing a constant output power, within apparatus tolerances, even if the dynamic profiles are imperfectly synchronised, as compared to stepchanges, or more rapid changes, in current. More generally, the currents of two or more of the batteries may vary with time according to any repeating pattern, such as a repeating stepwise current profile (square wave), a zig-zag shaped profile (triangle wave), or a sinusoidal current profile. The variation of the current flowing to and from each battery in the apparatus may be offset from the variation of at least one other battery in the apparatus such that the total power output by the apparatus (summed across the individual batteries) remains constant / follows the needs of the load, which is unlikely to be time-varying on a similar scale. This offset may be used to ensure that there are no peaks and troughs in the total current or power output by the apparatus. A sinusoidal, or other gradually-curved, profile may be preferred to a stepped profile in some embodiments, for example to ensure a more even power output even if two batteries’ profiles are not perfectly synchronised. For example, a first battery (202a) in an apparatus (200) may provide a current of 6 amps for one second followed by a step change to deliver 4 amps for 1 second, followed by multiple repetitions of this pattern delivering an average current of 5 amps over one minute. A second battery (202b) in the apparatus may deliver 4 amps for a second whilst the first battery delivers 6 amps, before a step change to deliver 6 amps whilst the first battery delivers 4 amps. The second battery therefore also delivers an average current of 5 amps over one minute and the apparatus (200) as a whole also delivers a constant current of 5 amps. By delivering power according to this varying pattern, both batteries may generate more heating than if they both delivered a constant current (depending on specifics of battery type and chemistry), and the temperature of both batteries may be raised or reduced more quickly than otherwise. Alternatively, the currents of two or more of the batteries of the plurality of batteries may vary according to a sinusoidal current profile. The sinusoidal pattern of each battery may be offset from the other, such that the total current is constant. Where two batteries are involved in the method, the sinusoidal current profile of the second may be offset from the sinusoidal current profile of the first by 180°, such that the profiles are in anti-phase. Use of a sinusoidal pattern assists in ensuring that any error in offsetting the variation of the two currents only results in a small over or under current that does not damage the apparatus or the load.

The thermal management system may be configured to directly sense the temperature of one or more components, to check if this temperature is outside of a predetermined temperature range, and to increase or decrease the temperature of the component so that it is moved towards or within the predetermined temperature range if so.

The heat transfer system may be configured to respond to an instruction from the central controller (135) to raise or lower the temperature of a component, e.g. by activating a pump 260. The heat transfer system may be configured to both directly sense the temperature of one or more component and respond accordingly (e.g. by activating a fan if a temperature exceeds a threshold) and also to respond to an instruction from the central controller (135).

Various implementations therefore provide a battery apparatus (100, 200) with internal thermal management, the apparatus being arranged to supply power to meet a load (145).

A method for thermal management of batteries using Joule heating within the batteries themselves may be performed in such an apparatus (100, 200), the method comprising controlling the current to and from each battery independently such that the currents of two or more of the batteries vary with time whilst still providing the overall power output needed to meet the load on the apparatus, even if that load is constant.

The methods and apparatuses as described herein may be especially useful for combining different battery chemistries. One example would be an apparatus combining different battery chemistries having one lithium iron phosphate (LFP) battery and a lithium nickel manganese cobalt oxide (NMC) battery, wherein the current to and from each battery is independently controlled (as for the example of Figure 4, above). In one scenario, the two batteries are at 10°C and need to provide a power of 10 kW to a load. NMC chemistry is better-suited for operation at lower temperatures, whilst LFP provides poorer power delivery performance at lower temperatures. The apparatus is therefore arranged to operate the NMC battery with a sinusoidal profile providing an average output power of lOkW and the LFP battery with an average current of zero but with a dynamic heating profile centred around zero. The LFP battery is thereby heated without a (significant) change in its state of charge until it is in the optimal operation temperature range. The load on the LFP battery may then be increased, and the load on the NMC battery decreased accordingly, spreading the load.

If operated at lower temperatures, LFP batteries generally degrade more quickly and suffer from higher internal resistance which in turn limits their power delivery. Pre-heating these batteries from low temperatures before drawing large loads from them therefore has advantages in terms of power delivery, safety, and lifetime.

Therefore, the plurality of batteries (102, 202) may comprise batteries of two or more different chemistries, and the controller (135) may be arranged to control the batteries individually based on their different chemistries. In some embodiments, these chemistries are selected from the lists provided above. The method for thermal management may raise the temperature of a first battery of the plurality of batteries towards or above the temperature of a second battery of the plurality of batteries.

The plurality of batteries may be or compromise a first and second battery, wherein the batteries are independently controlled by the central controller. The currents of the first and second batteries may be set to vary with time and the current provided by the first battery and the second battery may aggregate such that the total current magnitude meets the current required by the load on the apparatus. The current to and from the first or second battery or both may vary with time between greater than 0 amps and less than 0 amps. The mean current of one or more, or all, of the batteries of the plurality of batteries may be 0 amps in various implementations.

The method / the use by the apparatus of dynamic current profiles for heating may continue until one or more batteries of the plurality of batteries reaches a suitable operation temperature. The operation temperature may be the optimum operating temperature of the battery of the plurality of batteries, or a lower end of a favoured range, which may be predetermined by the manufacturer of the battery.

The method may comprise a heat management step occurring whilst heat is generated, or after heat has been generated in one or more batteries of the plurality of batteries, distributing heat to where it is needed. Such methods utilises a heat transfer medium to distribute heat between the plurality of batteries / to move heat from one location to another, e.g. to move heat from the battery in which it was generated to another battery, or to all batteries - this may be passive (e.g. relying on conduction and/or convection) or active (e.g. activating a fan or pump).

The method may comprise an initial step of sensing the temperature of one or more batteries and comparing this temperature to a predetermined temperature stored locally or remotely, optionally in the memory of the central controller (135) configured to independently control the current to and from each battery. The method then comprises a step of determining whether thermal management of one or more batteries is required, before proceeding to vary the currents with time if thermal management is required.

It will be appreciated that whilst the thermal management method described herein with reference to an apparatus with an AC link (140) between batteries (102, 202), it is separable from this feature and may be implemented in an apparatus with different power conversion electronics to aggregate power from the plurality of batteries, and optionally with a DC link replacing the AC link, in other implementations. Indeed, in some cases (e.g. in which a load is a DC load), no conversion may be needed, however an AC link may be used to improve flexibility in other embodiments. Similarly, it will be appreciated that methods of independent battery management as described herein may be implemented without implementing thermal management steps as described herein (for example, in warm environments battery pre-heating may not be needed, or a dedicated battery pre-heating system may be used instead of internal battery Joule heating). The scope of this application is therefore limited only by the appended claims.

Claims

1. An energy storage and release apparatus comprising: a plurality of batteries; a plurality of bidirectional AC-DC power conversion modules; an AC electrical link configured to allow power flow between the power conversion modules and to allow electrical connection of the apparatus to an external load, and wherein each battery of the plurality of batteries has a dedicated power conversion module of the plurality of power conversion modules between that battery and the AC electrical link; and a controller configured to control the power conversion modules individually, such that the current to and from each battery of the plurality of batteries is determined individually by the controller, and wherein the apparatus is arranged such that power flow between the plurality of batteries is permitted only via the AC electrical link.

2. The energy storage and release apparatus of claim 1, wherein the controller comprises a memory configured to store information on each battery of the plurality of batteries, and wherein optionally the information stored includes information relating to a chemistry of each battery.

3. The energy storage and release apparatus of any one of claims 1 or 2, wherein the batteries of the plurality of batteries are each linked to the respective dedicated power conversion module via a dedicated electrical link.

4. The energy storage and release apparatus of claim 3, wherein the voltage of the electrical link between one battery of the plurality of batteries and the power conversion module dedicated to that battery is different from the voltage of the electrical link between at least one further battery of the plurality of batteries and the power conversion module dedicated to that at least one further battery.

5. The energy storage and release apparatus of any preceding claim, wherein the current supplied by one battery of the plurality of batteries to its dedicated power conversion module is different from the current supplied by at least one further battery of the plurality of batteries to that further battery’s dedicated power conversion module.

6. The energy storage and release apparatus of any preceding claim, wherein the controller is configured to control the current to and from the plurality of batteries such the currents of two or more of the batteries vary with time, optionally according to a sinusoidal current profile, and wherein the varying current profiles are selected such that total power provided by the plurality of batteries meets the external load on the apparatus.

7. The energy storage and release apparatus of any preceding claim, further comprising at least one temperature sensor; and wherein the controller is configured to receive data from the at least one temperature sensor and, if the sensed temperature is below a set threshold, to individually control current to and from at least two batteries of the plurality of batteries such that two or more of the batteries have currents that vary with time and which are not in phase, the currents being controlled such that a total power provided by the plurality of batteries meets the power required by the load.

8. The energy storage and release apparatus of claim 7, wherein each battery comprises a temperature sensor and the controller is configured to receive temperature data from each battery, and to determine battery current profiles based on information including which batteries report the lowest temperatures.

9. The energy storage and release apparatus of any preceding claim, wherein the controller is configured to receive information from the power conversion modules.

10. The energy storage and release apparatus of any preceding claim, wherein each battery of the plurality of batteries comprises communication electronics and the controller is configured to receive information from each battery of the plurality of batteries.

11. The energy storage and release apparatus of any preceding claim, wherein the apparatus is configured such that the controller communicates with each battery and each power conversion module directly, optionally using a CAN bus.

12. The energy storage and release apparatus of any preceding claim, wherein at least one battery of the plurality of batteries differs from further batteries of the plurality of batteries according to one or more characteristics selected from chemistry, voltage, capacity, age, state of charge, and state of health.

13. The energy storage and release apparatus of any preceding claim, wherein the chemistry of at least one battery of the plurality of batteries is of a first chemistry and the chemistry of at least one battery of the plurality of batteries is of a second chemistry, wherein the first and second chemistries are different, and wherein optionally the chemistries are selected from lead-acid, aluminium ion, lithium-ion lithium cobalt oxide, lithium-silicon-lithium-ion manganese iron phosphate, lithium-ion manganese-oxide, lithium-ion polymer, lithium-nickel-manganese-cobalt oxide, Lithium-nickel-cobalt-aluminium oxide, lithium-sulfur, lithium-titanate, thin-film lithium ion, lithium-ceramic.

14. The energy storage and release apparatus of any preceding claim, wherein the apparatus further comprises a thermal management system configured to control the temperature of one or more components of the system, and optionally of one or more batteries of the plurality of batteries.

15. The energy storage and release apparatus of claim 14, wherein the thermal management system is arranged to distribute heat between the plurality of batteries, and optionally comprises one or more of an indirect liquid heat transfer system and a forced air convection heat transfer system.

16. The energy storage and release apparatus of any preceding claim, wherein the apparatus further comprises one or more sensors configured to communicate with the controller, the sensors selected from one or more of temperature sensors, battery safety gas sensors, voltage sensors, current sensors, isolation sensors.

17. The energy storage and release apparatus of claim 16, wherein the apparatus comprises a current sensor configured to monitor the current between the load and the apparatus and to communicate this information to the controller.

18. A battery apparatus with internal thermal management, the apparatus being arranged to supply power to meet a load and comprising: a plurality of batteries; an electrical link between the batteries of the plurality of batteries; at least one temperature sensor; and a controller configured to receive data from the at least one temperature sensor and, if the sensed temperature is below a set threshold, to individually control current to and from each battery of the plurality of batteries such that two or more of the batteries have currents that vary with time and which are not in phase, the currents being controlled such that a total power provided by the plurality of batteries meets the power required by the load.

19. The apparatus of claim 18, wherein the apparatus further comprises a heat transfer medium arranged to distribute heat generated by Joule heating between the plurality of batteries, and wherein optionally the apparatus comprises a pump arranged to move the heat transfer medium within the case so as to distribute heat amongst the plurality of batteries.

20. The apparatus of claim 18 or claim 19, wherein the controller is configured to control current flow such that the current of at least one battery varies with time between greater than 0 amps and less than 0 amps.

21. The apparatus of any one of claims 18 to 20, wherein the controller is configured to control current flow such that the mean current of at least one battery being operated with a varying current is zero, and that battery provides no overall power to the apparatus.

22. The apparatus of any one of claims 18 to 21, wherein the load is zero and the controller is configured to control current flow such that the overall power output of the plurality of batteries is zero at any point in time whilst the load is zero.

23. The apparatus of any one of claims 18 to 22, wherein the controller is configured to control current flow such that the current to and from each battery varies according to a sinusoidal current profile.

24. The apparatus of any one of claims 18 to 23, wherein the controller is arranged to determine a level of heat to be supplied based on the received temperature data, and to control battery currents such that the required level of heat is output by the batteries.

25. The apparatus of any one of claims 18 to 24, further comprising a case, and wherein the plurality of batteries and the temperature sensor are located within the case.