GB2614718A

GB2614718A - Battery system for an electric vehicle

Info

Publication number: GB2614718A
Application number: GB2200378.4A
Authority: GB
Inventors: Fordonnell Aaron
Original assignee: Individual
Current assignee: Individual
Priority date: 2022-01-13
Filing date: 2022-01-13
Publication date: 2023-07-19

Abstract

A battery system 200 for an electric vehicle (EV) may be fully charged using a lower voltage charger. The battery system includes: plural battery cells 202; first, second and third terminals 120, 122, 110; a charging port 114 to receive a charging current; and a switching module 112 to selectively connect the charging port to two of the terminals. A first subset 204 of the battery cells is connected between the first and third terminals. A second subset 206 of the battery cells is connected between the third and second terminals. The first and second subsets of battery cells are electrically connected in series. A first discharge terminal 120 connected to the first terminal and a second discharge terminal 122 connected to the second terminal may convey a discharging current to a drive system of the EV. The switching module may include: a first state (fig 2a) where the first and third terminals are connected to the charging port; and a second state (fig 2b) where the second and third terminals are connected to the charging port. The charging port may connect to an external power source to charge the battery cells by controlling the switching module to alternate between the first and second states at regular time intervals.

Description

BATTERY SYSTEM FOR AN ELECTRIC VEHICLE

FIELD OF THE INVENTION

The present invention relates to a battery system for an electric vehicle, the battery system having two subsets of battery cells connected in series.

BACKGROUND

An electric vehicle is a vehicle that uses an electric motor for propulsion, with the electric motor being powered by one or more batteries in the vehicle. Some electric vehicles, known as hybrid electric vehicles, combine a conventional internal combustion engine with an electric motor. Typically, the batteries used for powering electric vehicles are rechargeable lithium-ion batteries, although other types of battery can also be used. In contrast to an internal combustion engine, operation of the electric motor in an electric vehicle does not produce any tailpipe emissions. Because of this, electric vehicles are promoted as a means for reducing greenhouse gas emissions caused by transportation. In particular, where renewable energy is used for recharging electric vehicle batteries, significant reductions in greenhouse gas emissions associated with transportation may be achieved.

As an electric vehicle is driven, the charge in its battery decreases. To recharge the battery, the electric vehicle is plugged into a charger (or charging station), which provides power to charge the battery. Typically, the battery can be charged up to a maximum voltage supplied by the charger. For example, a conventional charger available at a service station may supply a voltage of 400 V, meaning that the electric vehicle battery can be charged up to a voltage of 400 V. This may be suitable for electric vehicles that have a battery with a maximum voltage at or below 400 V. In some cases, it may be desirable to use a battery having a higher voltage, such as an 800 V battery, in vehicles requiring a larger amount of power. However, a conventional 400 V charger would usually be unable to charge such a battery. Indeed, an 800 V battery could generally not be charged to more than 400 V, if at all, using a 400 V charger without taking additional measures. One solution for addressing this problem is to incorporate transformers into the electric vehicle, to step up the voltage from the charger and enable full charging of the battery. However, the transformers are typically bulky and heavy, resulting in an increased size and mass of the vehicle. Another solution for addressing this problem is to use the vehicle's high voltage inverter(s) as a DC-DC converter to step up the voltage from a 400 V charger to 800 V. This may avoid having to add additional transformers to the vehicle. However, a drawback associated with this solution is that power conversion is inefficient, resulting in slow charging as well as large heating effects.

SUMMARY OF THE INVENTION

At its most general, the present invention provides a battery system for an electric vehicle, which enables full charging of a high voltage battery even when using a lower voltage charger, and without having to use additional transformers or otherwise sacrifice charging speed and efficiency. The battery system includes a plurality of battery cells which are arranged into a first subset and a second subset of battery cells, the first and second subsets of battery cells being connected in series. The battery system further includes a switching module configured to selectively connect the first subset or the second subset of the plurality of battery cells to a charging port of the system. In this manner, when a charger is connected to the charging port, the switching module may be operated to alternately connect the first subset and the second subset of the plurality of battery cells to the charging port, to enable alternate charging of the first and second subsets. In this manner, even if the charger has a voltage that is lower than a total maximum voltage across the plurality of battery cells, the charger may be capable of fully charging each subset of the plurality of battery cells individually. In other words, the plurality of battery cells may become fully charged by using the switching module to charge each of the first and second subsets of the plurality of battery cells individually. As a result, a high voltage battery may be fully charged using a lower voltage charger. For example, a maximum (i.e. fully charged) voltage across the plurality of battery cells may be 800 V. The first subset and the second subset may then each correspond to a respective half of the plurality of battery cells, such that they each have a maximum (i.e. fully charged) voltage of 400 V. Accordingly, each subset of the plurality of battery cells may be fully charged by a conventional 400 V charger, e.g. by controlling the switching module to alternate between coupling the charging port to the first subset and the second subset. Of course, the plurality of battery cells may be split into more than two subsets, depending on the total maximum voltage across the plurality of battery cells.

The battery system of the invention may thus enable an electric vehicle to incorporate a high voltage battery, without having to provide it with bulky transformers or other electronics for converting the voltage supplied by the charger. This may serve to reduce a mass and size of the electric vehicle, which in turn may improve its power efficiency and therefore its travel range.

Furthermore, the battery system of the invention may make the electric vehicle compatible with a wide array of conventional chargers, as the battery can be fully charged even using a charger having a lower voltage than the maximum voltage across the plurality of battery cells.

According to a first aspect of the invention, there is provided a battery system for an electric vehicle, the battery system comprising: a plurality of battery cells; a first terminal, a second terminal, and a third terminal, wherein a first subset of the plurality of battery cells is electrically connected between the first terminal and the third terminal, a second subset of the plurality of battery cells is electrically connected between the third terminal and the second terminal, and the first subset and the second subset of the plurality of battery cells are electrically connected in series; a charging port configured to receive a charging current; and a switching module configured to selectively connect the charging port to two of the first terminal, the second terminal, and the third terminal.

The battery system may be used in any type of electric vehicle. Herein, an electric vehicle may refer to a vehicle comprising an electrically powered drive system. In particular, the electric vehicle may comprise an electric motor, and the battery system may be configured to power the electric motor. The electric vehicle may be a road vehicle, e.g. a road car.

The plurality battery cells may form part of a battery unit. The battery cells may be any suitable type of rechargeable battery cell. For example, the plurality of battery cells may comprise lithium-ion battery cells, although other known types of battery cells may be used.

The first subset and the second subset of the plurality of battery cells may each comprise one or more battery cells. Preferably, the first subset and the second subset of the plurality of battery cells may each comprise two or more battery cells connected in series and/or in parallel. For example, the first subset of the plurality of battery cells may comprise two or more battery cells connected in series, and the second subset of the plurality of battery cells may comprise two or more battery cells connected in series. Additionally or alternatively, the first subset of the plurality of battery cells may comprise two or more battery cells connected in parallel, and/or the second subset of the plurality of battery cells may comprise two or more battery cells connected in parallel.

The first subset and the second subset of the plurality of battery cells are connected together in series, i.e. such that the voltages across the first subset and the second subset of the plurality of battery cells add up to provide a total voltage across the plurality of battery cells. Thus, a voltage between the first terminal and the second terminal corresponds to the total voltage across the plurality of battery cells.

In some cases, the first subset of the plurality of battery cells is implemented by a first battery module, and the second subset of the plurality of battery cells is implemented by a second battery module, the first battery module and the second battery module being connected in series. In other words, each battery module may include a respective subset of the plurality of battery cells. Arranging the plurality of battery cells into battery modules may facilitate assembling the battery system, as well as facilitate maintenance and repair of the battery system.

The battery unit may comprise a housing, in which the plurality of battery cells is contained. This may serve to protect the plurality of battery cells, as well as improve safety of the battery system.

The first terminal is electrically connected to the first subset of the plurality of battery cells, and the second terminal is electrically connected to the second subset of the plurality of battery cells. Thus, the first terminal may be connected to a first end of the plurality of battery cells, and the second terminal may be connected to a second end of the plurality of battery cells. In other words, the first and second terminals are electrically connected to opposite ends of the plurality of battery cells. Thus, for example, the first terminal may correspond to a positive terminal of the plurality of battery cells, and the second terminal may correspond to a negative terminal of the plurality of battery cells. A voltage between the first terminal and the second terminal therefore corresponds to a sum of the voltages across the first subset and the second subset of the plurality of battery cells.

The third terminal may be electrically connected to the plurality of battery cells, at a location between the first and second terminals. Thus, the third terminal may be electrically connected between two adjacent battery cells in the plurality of battery cells. For example, the third terminal may be electrically connected to a conductor that electrically connects the two adjacent cells. Alternatively, the third terminal may be directly connected to a terminal on one of the adjacent battery cells. A voltage at the third terminal may correspond to a voltage at a point in the plurality of battery cells between the adjacent battery cells, such that the voltage at the third terminal may be between a voltage at the first terminal and a voltage at the second terminal.

The third terminal may effectively split the plurality of battery cells into the first subset of the plurality of battery cells and the second subset of the plurality of battery cells. In this manner, a voltage between the third terminal and the first terminal may correspond to a voltage across the first subset of the plurality of battery cells, and a voltage between the second terminal and the third terminal may correspond to a voltage across the second subset of the plurality of battery cells. As an example, where the first subset of the plurality of battery cells comprises two or more battery cells in series, the voltage between the third terminal and the first terminal may correspond to a sum of the voltages of the two or more battery cells in the first subset. Likewise, where the second subset of the plurality of battery cells comprises two or more battery cells in series, the voltage between the second terminal and the third terminal may correspond to a sum of the voltages of the two or more battery cells in the second subset.

Where the plurality of battery cells is provided in a housing, the first terminal, second terminal and third terminal may be provided on the housing.

The charging port is configured to receive a charging current from an external source, in order to charge the plurality of battery cells. The charging port may comprise a positive terminal and a negative terminal, for receiving the charging current. The charging current may be provided, for example, by a charger or charging station for an electric vehicle. The charging port may be configured for connection to a charger, e.g. the charging port may comprise any suitable electrical connector for connecting the battery system to the charger. For example, the electrical connector may be in the form or a plug or a socket that is configured for connection with an electric vehicle charger.

The switching module serves to selectively connect the charging port to two of the first terminal, the second terminal and the third terminal. Thus, the switching module can be switched between three states: a first state in which the first terminal and the third terminal are electrically connected to the charging port, a second state in which the second terminal and the third terminal are electrically connected to the charging port, and a third state in which the first terminal and the second terminal are electrically connected to the charging port. Therefore, the switching module can be controlled to select which pair of terminals is connected to the charging port to receive the charging current from the charging port. As an example, in the first state, the positive terminal of the charging port may be connected to the first terminal, and the negative terminal of the charging port may be connected to the third terminal; in the second state, the positive terminal of the charging port may be connected to the third terminal and the negative terminal of the charging port may be connected to the second terminal; and in the third state the positive terminal of the charging port may be connected to the first terminal and the negative terminal of the charging port may be connected to the second terminal.

When the charging port is connected to the charger and the switching module is in the first state, the charging port is connected to the first and third terminals, such that the charging current charges (i.e. passes through) the first subset of the plurality of battery cells. As a result, the first subset of battery cells can be charged when the switching module is in the first state. When charging port is connected to the charger and the switching module is in the second state, the charging port is connected to the second and third terminals, such that the charging current charges (i.e. passes through) the second subset of the plurality of battery cells. As a result, the second subset of battery cells can be charged when the switching module is in the second state. When charging port is connected to the charger and the switching module is in the third state, the charging port is connected to the first and second terminals, such that the charging current charges (i.e. passes through) the first subset and the second subset of the plurality of battery cells. As a result, the plurality of battery cells can be charged when the switching module is in the third state.

In this manner, it is possible to select which subset of the plurality of battery cells is charged by the charging current. If the charger has a maximum voltage that is less than a maximum (i.e. fully charged) voltage across the plurality of battery cells, the switching module can be operated so that the first and second subsets of battery cells are charged separately.

This may increase the level of charge which can be achieved, compared to a case where the entire plurality of battery cells is charged at the same time. Indeed, where the plurality of battery cells is charged at the same time (i.e. when the switching module is in the third state), the maximum voltage across the plurality of battery cells which can be achieved is limited to the maximum voltage of the charger. In contrast, where the first and second subset of battery cells are charged separately, each subset can in principle be charged to the maximum voltage level of the charger, meaning that the total achievable voltage across the plurality of battery cells can be twice the maximum voltage of the charger.

The switching module may comprise two or more switches, which are configured to selectively connect the charging port to two of the first terminal, the second terminal, and the third terminal. The two or more switches may include any suitable type of electrical switches, such as a contactor switch, a relay switch or a solid state switch.

As an example, the switching module may comprise a first switch which is configured to selectively couple a first (e.g. positive) terminal of the charging port to the first terminal or the third terminal, and a second switch which is configured to selectively couple a second (e.g. negative) terminal of the charging port to the second terminal or the third terminal.

The two or more switches of the switching module may be located outside of the plurality of battery cells. In other words, there may be no switch connected in series between any two battery cells of the plurality of battery cells. Thus, the battery cells in the plurality of battery cells may be directly connected to one another, with no switches electrically connected between battery cells in the plurality of battery cells. This may serve to minimise heat generation within the plurality of battery cells, which may reduce energy losses and improve a range of the electric vehicle. This may also serve to increase a discharging current which can be drawn from the plurality of battery cells, as the discharging current need not pass through any switches of the switching module. By placing the two or more switches such that the discharging current does not pass through them, a size, mass and cost of the switches may be reduced (as the switches need not be rated to support the discharging current), in turn reducing a size, mass and cost of the battery system.

The switching module may be operated manually, e.g. so that a user can control which state the switching module is in. For example, the switching module may comprise an input interface (such as one or more buttons, switches or knobs) to enable a user to manually control the switching module. Additionally or alternatively, the battery system may comprise a controller which is configured to automatically control the switching module, as discussed in more detail below.

The third terminal may also be referred to as an intermediate terminal, due to its connection at an intermediate location between the first end and the second end of the plurality of solar cells. In some embodiments, there may be multiple intermediate terminals connected to the plurality of battery cells at locations between the first end and the second end of the plurality of battery cells. The further intermediate terminals may serve to divide the plurality of battery cells into additional subsets of cells, each of which can be charged separately by controlling the switching module. This may facilitate charging a plurality of battery cells which has a maximum voltage that is greater than the maximum voltage of the charger that is used.

Thus, in some embodiments, there may be one or more intermediate terminals (e.g. instead of just the third terminal discussed above) electrically connected to the plurality of battery cells, each of the one or more intermediate terminals being connected at a respective location between the first end and the second end of the plurality of battery cells. Then, the switching module may be configured to selectively connect the charging port to two terminals selected from the first terminal, the second terminal and the one or more intermediate terminals. The one or more intermediate terminals may be configured similarly to the third terminal discussed above. A respective subset of the plurality of battery cells may be connected between each adjacent pair of the terminals. Accordingly, the switching module can be switched between multiple states, such that in each state the charging port is connected to a respective one of the subsets of battery cells. In this manner, each subset of battery cells can be charged independently. In the below, discussions relating to switching between the first and second state are equally applicable to embodiments where the switching module can be switched between multiple (e.g. more than two) states.

The battery system may further comprise a first discharge terminal electrically connected to the first terminal and a second discharge terminal electrically connected to the second terminal, the first discharge terminal and the second discharge terminal being configured to convey a discharging current from the plurality of battery cells to a drive system of the electric vehicle, and the first discharge terminal and the second discharge terminal being arranged such that the discharging current does not pass through the switching module. In this manner, the discharging current which is used to power the drive system of the electric vehicle may not pass through the switching module, e.g. it may not pass through any switches in the switching module. Typically, the maximum discharging current which is used to power the drive system may be larger than the maximum charging current which is used to charge the plurality of battery cells. Thus, by avoiding passing the discharging current through the switching module, the switching module need only be rated to support the maximum charging current, and need not be rated to support the larger maximum discharging current. As a result, a switching module with smaller and more lightweight switches may be used. This arrangement may also avoid power losses which would otherwise occur if passing the discharging current through the switching module. Therefore, an efficiency of the power output of the battery system may be improved.

In order to avoid passing the discharging current through the switching module, the first discharge terminal may be directly connected to the first terminal, i.e. such that the connection between the first discharge terminal and the first terminal does not pass through the switching module. Likewise, the second discharge terminal may be directly connected to the second terminal, i.e. such that the connection between the second discharge terminal and the second terminal does not pass through the switching module. In some cases, the first terminal and the first discharge terminal may be formed as a single part, i.e. they may be formed as a single terminal. Similarly, the second terminal and the second discharge terminal may be formed as a single part, i.e. they may be formed as a single terminal.

The first discharge terminal and the second discharge terminal may be connectable (or connected) to a drive system of an electric vehicle, so that the drive system can be powered by the plurality of battery cells. For example, the first discharge terminal and the second discharge terminal may each comprise a respective connector and/or cable for connection to the drive system.

Herein, a discharging current may refer to a current which is drawn from the plurality of battery cells in order to provide power to a load, such as a drive system of an electric vehicle. When the discharging current is drawn from the plurality of battery cells, the charge in the plurality of battery cells decreases. In contrast, when the charging current is supplied to the plurality of battery cells, the charge in the plurality of battery cells is increased.

The drive system of the electric vehicle may correspond to an electrically powered system for driving the electric vehicle. The drive system may comprise an electric motor which is arranged to receive the discharging current to power the electric motor.

The switching module may be configured to switch between a first state in which the first terminal and the third terminal are electrically connected to the charging port, and a second state in which the second terminal and the third terminal are electrically connected to the charging port. Thus, as discussed above, when the switching module is in the first state, the charging current received from the charging port acts to charge the first subset of battery cells connected between the first terminal and the third terminal. Wien the switching module is in the second state, the charging current received from the charging port acts to charge the second subset of battery cells connected between the third terminal and the second terminal.

The battery system may further comprise a controller configured to control switching of the switching module between the first state and the second state. In this manner, the controller may control charging of the plurality of battery cells. In particular, by controlling switching between the first and second states, the controller can control when each of the first subset and the second subset of battery cells is charged with the charging current received from the charging port. Where the switching module can be switched to a third state, as discussed above, the controller may be configured to control switching of the switching module between the first, second and third states. Further, where there are multiple intermediate terminals, such that the switching module can be switched between multiple states, the controller may be configured to control switching of the switching module between each of the multiple states. Accordingly, in the below, features relating to switching between the first state and the second state may be equally applicable to switching between each of the multiple states.

When controlling the switching module to switch from the first state to the second state, the controller may be configured to control the switching module to first disconnect the first subset of battery cells from the charging port, before connecting the second subset of battery cells to the charging port. This may be achieved, for example, by operating the switching module to disconnect the first terminal and the third terminal from the charging port prior to connecting the second terminal and the third terminal to the charging port. Likewise, when controlling the switching module to switch from the second state to the first state, the controller may be configured to control the switching module to first disconnect the second subset of battery cells from the charging port, before connecting the first subset of battery cells to the charging port. This may be achieved, for example, by operating the switching module to disconnect the second terminal and the third terminal from the charging port prior to connecting the first terminal and the third terminal to the charging port. This procedure may serve to ensure safe switching between the first state and the second state, by avoiding a risk of different parts of the battery and/or terminals of the charging port being shorted together during the switching process.

The controller may be communicatively coupled to the switching module (e.g. via a wired or wireless connection), so that it can transmit one or more control signals to the switching module, to control switching of the switching module. In some cases, the controller may be connected to each of the switches in the switching module, so that the controller can transmit a respective control signal to each switch for controlling a state of that switch. In this manner, the controller may control the state of each switch in the switching module, to control which part of the plurality of battery cells is electrically coupled to the charging connector.

The controller may be implemented using any suitable device capable of controlling the switching module. As an example, the controller may be implemented by a computing device having suitable control software installed thereon. In some cases, the controller may be implemented by an existing on-board computer of the electric vehicle, which may also be configured to control other vehicle systems. For instance, the controller may be implemented by a main on-board computer of the vehicle, a battery management system (13MS) of the vehicle, or an electronic control unit (ECU) of the vehicle. Alternatively the controller of the battery system may be implemented as a dedicated device that is separate from other on-board computers of the electric vehicle.

When the charging port is connected to an external power source, the controller may be configured to control charging of the plurality of battery cells by controlling the switching module to alternate over time between the first state and the second state. In this manner, the first subset of battery cells and the second set of battery cells may be charged in alternation over time. Alternating between charging the first subset of battery cells and the second subset of battery cells may enable each of the subsets of battery cells to be progressively charged, whilst avoiding large differences in charge level between the two subsets. As a result, a full charge of the plurality of the battery cells may be achieved. Alternating between charging of the first and second subsets of battery cells may also serve to reduce heating of the battery cells in each subset compared to continuous charging of the battery cells. This may in turn improve charging efficiency, reduce a rate of degradation of the battery cells and reduce a risk of acute damage to the battery cells.

As an example, the controller may be configured to perform a sequence where the switching module is put in the first state for a period of time to charge the first subset of battery cells, and then the switching module is put in the second state for a period of time to charge the second subset of battery cells. This sequence may then be repeated until each of the first subset and the second subset of battery cells is fully charged.

The controller may be configured to control the switching module to alternate between the first state and the second state at regular time intervals. This may serve to minimise any imbalance in charge level between the first and second subsets of battery cells. In other words, this may enable a charge of the first subset of battery cells and a charge of the second subset of battery cells to be kept at similar levels throughout the charging process. This may serve to ensure that a charge level for the plurality of battery cells is maximised at the end of the charging process, thus maximising a travel range of the electric vehicle. For example, where the first subset of battery cells includes a first half of the plurality of battery cells, and the second subset of battery cells includes the second half of the plurality of battery cells, the controller may be configured to alternate between the first state and the second state at equal time intervals, i.e. so that the switching module spends equal intervals of time in each of the first and second states. In this manner, the first subset and the second subset may alternately be charged by equal amounts, so that they each have substantially the same charge level at the end of the charging process.

The controller may be configured to control the switching module to alternate between the first state and the second state such that the switching module does not remain in the first state or the second state for more than one minute at a time. Limiting the amount of time spent in each state may serve to ensure that neither the first subset nor the second subset of battery cells is continuously charged for an extended period of time, thus avoiding excessive heating of the battery cells. In particular, the inventors have found that, by limiting the time spent in each switching state to one minute (i.e. 60 seconds) or less, heating of the battery cells may be reduced compared to continuous charging of the battery cells. As a result, damage to the battery cells due to overheating may be avoided, degradation due to heat cycling may be reduced, and charging efficiency may be improved. This may also enable more rapid charging of the plurality of battery cells. This is because, as the battery cells experience less heating compared to continuous charging, they can withstand a larger charging current without exceeding their thermal limits, compared to a case where continuous charging is used.

Such a short time interval between switching states may further serve to minimise an imbalance in charge level between the first subset and the second subset of battery cells. In this manner, the voltage across the first subset of battery cells and the voltage across the second subset of battery cells may be kept at a similar level. This may facilitate alternating charging of the first and second subsets, as the charger may measure a similar voltage regardless of which subset of battery cells is currently connected to the charging port. As a result, the charger may not detect that it is charging different subsets of battery cells, and so can be operated as if it were charging a single subset of battery cells, i.e. as if it were charging a normal battery. Minimising the imbalance in charge level between the first subset and the second subset of battery cells may also be beneficial if the charging process is suddenly interrupted (e.g. by a user) before the plurality of battery cells is fully charged, as this may increase the charge level across the plurality of battery cells compared to a scenario where a longer amount of time is spent in each state. As a result, a range of the electric vehicle may be improved for a given charging time.

Preferably, the time spent in each switching state may be less than one minute, in order to minimise heating experienced by the battery cells, and minimise any charge imbalance between the subsets of battery cells. For example, the controller may be configured to control the switching module to alternate between the first state and the second state such that the switching module does not remain in the first state or the second state for more than 45 seconds, 30 seconds, 25 seconds, 20 seconds, 15 seconds, 10 seconds, or 5 seconds at a time.

The controller may be configured to control a duty cycle of the alternation between the first state and the second state based on a difference between a first voltage and a second voltage, the first voltage corresponding to a voltage between the first terminal and the third terminal, and the second voltage corresponding to a voltage between the third terminal and the second terminal. In this manner, the duty cycle may be controlled based on a difference between the first voltage (i.e. the voltage across the first subset of battery cells) and the second voltage (i.e. the voltage across the second subset of battery cells). This may facilitate maintaining the first subset and the second subset of battery cells at a similar charge level over the course of the charging sequence, and preventing a large imbalance in the charge levels of the subsets from developing. The duty cycle may correspond to a proportion of time spent by the switching module in the first state or the second state over one cycle of the alternation between the first state and the second state (where the switching module spends the remainder of the cycle in the other one of the first state and the second state). The first voltage may be indicative of a charge level of the first subset of the battery cells, e.g. by comparing the first voltage to a maximum (i.e. fully charged) voltage across the first subset of cells. Likewise, the second voltage may be indicative of a charge level of the second subset of battery cells, e.g. by comparing the second voltage to a maximum (i.e. fully charged) voltage across the second subset of cells.

The controller may be configured to monitor the first voltage and the second voltage. For example, the battery system may include a first voltmeter connected between the first terminal and the third terminal to measure the first voltage, and a second voltmeter connected between the third terminal and the second terminal to measure the second voltage. The controller may be communicatively coupled to the first voltmeter and the second voltmeter, in order to receive data indicative of the first voltage and the second voltage.

As another example, the first voltage and the second voltage may be monitored using a battery management system (BMS). The BMS may also be configured to monitor the voltage of each subset of battery cells, of each battery module in the battery system, and/or the voltage across the plurality of battery cells. The BMS may be configured to monitor these voltages directly, e.g. via electrical connections to the first, second and third terminals. Additionally or alternatively, the BMS may be configured to monitor the voltages of individual battery cells, and/or voltages across parallel strings of cells in the plurality of battery cells. Thus, if the voltages across the first subset and the second subset of battery cells are not monitored directly, the BMS can determine them based on the voltages across the individual cells and/or the voltages across parallel strings of cells in the plurality of battery cells. Where the BMS and the controller are separate entities, the BMS may then be configured to transmit the first voltage and the second voltage to the controller, to enable the control discussed above. In some cases, the electronic control unit (ECU) of the vehicle may be connected to or integrated with the BMS, such that the ECU is configured to transmit the first voltage and the second voltage to the controller.

In some implementations, if the first voltage is greater than the second voltage by a predetermined amount, the controller may be configured to adjust the duty cycle to decrease a proportion of time spent by the switching module in the first state and increase a proportion of time spent by the switching module in the second state; and if the second voltage is greater than the first voltage by the predetermined amount, the controller may be configured to adjust the duty cycle to increase the proportion of time spent by the switching module in the first state and decrease the proportion of time spent by the switching module in the second state. In this manner, the duty cycle may be dynamically updated based on the difference between the first voltage and the second voltage, to correct for voltage imbalances between the two subsets of battery cells. This may serve to keep the first voltage and the second voltage within the predetermined amount of one another over the course of the charging process. As a result, the first subset and the second subset of battery cells may be kept at a similar charge level over the course of the charging process, which may maximise the charge level that is achieved for the plurality of battery cells. Additionally, in line with the discussion above, keeping the first voltage and the second voltage close to one another may facilitate rapid switching between charging of the first subset and the second subset of battery cells.

The predetermined amount may be given as a percentage, e.g. such that a difference between the first voltage and the second voltage is kept to less than a predetermined percentage. Alternatively, the predetermined amount may correspond to a voltage, e.g. such that a difference between the first voltage and the second voltage is kept to less than a predetermined voltage.

In some cases, the duty cycle may be adjusted such that a voltage difference between a first battery cell in the first subset of battery cells and a second battery cell in the second subset of battery cells is less than a predetermined voltage (noting that the battery cells within a given subset may all have substantially the same voltage). Thus, if the voltage of the first battery cell exceeds the voltage of the second battery cell by (at least) the predetermined voltage, the controller may be configured to adjust the duty cycle to decrease the proportion of time spent by the switching module in the first state and increase a proportion of time spent by the switching module in the second state. If the voltage of the second battery cell exceeds the voltage of the first battery cell by (at least) the predetermined voltage, the controller may be configured to adjust the duty cycle to increase the proportion of time spent by the switching module in the first state and decrease the proportion of time spent by the switching module in the second state. For instance, the predetermined voltage may be 10 mV, preferably 1 mV.

In some cases, the duty cycle may be adjusted such that the voltage of the first battery cell in the first subset of battery cells and the voltage of the second battery cell in the second subset of battery cells are kept within a predetermined percentage of one another. Thus, if the voltage of the first battery cell exceeds the voltage of the second battery cell by (at least) the predetermined percentage, the controller may be configured to adjust the duty cycle to decrease the proportion of time spent by the switching module in the first state and increase a proportion of time spent by the switching module in the second state. If the voltage of the second battery cell exceeds the voltage of the first battery cell by (at least) the predetermined percentage, the controller may be configured to adjust the duty cycle to increase the proportion of time spent by the switching module in the first state and decrease the proportion of time spent by the switching module in the second state. For instance, the predetermined percentage may be in the range 0.24%-0.4%, and preferably in the range 0.024%-0.04%.

The controller may be configured to control a period of the alternation between the first state and the second state based on a temperature of the switching module. In other words, the controller may be configured to control a length (or period) of the duty cycle of the alternation between the first state and the second state. Thus, the controller may effectively control a rate at which the switching module alternates between the first state and the second state based on the temperature of the switching module. This may ensure that the switches are kept at a safe and efficient temperature. This is because switching between the first state and the second state may cause the switches in the switching module to heat up. Therefore, by controlling the period of the alternation between states, it is possible to control heat generation in the switches, e.g. by increasing an amount of time for them to cool down between switching events. For example, the controller may be configured to increase the length of the duty cycle if the temperature of the switches in the switching module exceeds a predetermined temperature, in order to reduce their temperature. Another mechanism which may contribute to heating of the switching module is the passing of charging current through switches in the switching module.

The charging current may flow through different switches (or different sets of switches) in the switching module in the first state and the second state. Thus, by switching between the first and second state, it is possible to ensure that the charging current does not continuously flow through the same switches, to avoid excessive heating of the switches.

The controller may be configured to control the period of the alternation, in addition to adjusting the duty cycle as discussed above. By controlling the period of the alternation, the controller can reduce heating in the switching module, whilst by adjusting the duty cycle (i.e. adjusting the proportion of time spent in each of the first state and the second state over the course of one alternation cycle) the controller may ensure that the first subset and the second subset of battery cells remain substantially balanced.

Herein, a period of the alternation between the first state and the second state may correspond to an amount of time taken up by one cycle of the periodic alternation between the first state and the second state.

The controller may monitor a temperature of the switches in the switching module, and control the switching rate between the first state and the second state to keep the temperature of the switches below a predetermined maximum temperature. The predetermined maximum temperature may depend on the type of switches used, and may for example correspond to a maximum operating temperature of the switches.

The switching module may include one or more temperature sensors, for detecting a temperature of the switches in the switching module. For example, there may be a respective temperature sensor for detecting a temperature of each switch in the switching module. The controller may be communicatively coupled to the one or more temperature sensors, to receive signal(s) indicative of the temperature of the switches in the switching module.

In some embodiments, the switching module may be configured to switch between the first state and the second state in less than one second. Such a rapid switching time may serve to minimise an amount of time spent switching between states, and therefore increase an amount of time spent charging the battery cells. As a result, a total charging time for the plurality of battery cells may be reduced. Additionally, a conventional charger is usually configured to interrupt charging when it detects that it has been disconnected from the battery. By using a rapid switching time (e.g. less than one second), the inventors have found that the charger may not detect that it has been disconnected from one subset of battery cells and connected to another subset of battery cells. In other words, the charger may effectively be blind to the fact that it is charging different subsets of battery cells. As a result, the charger may not interrupt charging when the switching module switches between states, such that the charger may operate continuously during the charging process. This may facilitate using a conventional charger with the battery system of the invention, and enable rapid charging of the plurality of battery cells. In particular, this may avoid having to manually restart charging each time the switching module switches states. In some cases, the switching time between states may be less than 0.8 seconds, 0.7 seconds, 0.6 seconds, 0.5 seconds, 0.4 seconds, 0.3 seconds, 0.2 seconds or 0.1 seconds. Depending on the types of switches used in the switching module, switching between states may be achieved extremely rapidly. For example, the switching module may be configured to switch between states in less than 100 nanoseconds, and in some cases less than 50 nanoseconds. Reducing the switching time may serve to further improve charging speed and facilitate use of the battery system with a conventional charger.

As discussed above, switching from the first state to the second state may comprise disconnecting the first subset of battery cells from the charging port, before connecting the second subset of battery cells to the charging port. Likewise, switching from the second state to the first state may comprise disconnecting the second subset of battery cells from the charging port, before connecting the first subset of battery cells to the charging port. Thus, when switching between states, the switching module may be configured to perform both the disconnecting and connecting steps in less than one second.

The switching module may comprise two or more switches, and the two or more switches may be solid state switches (also referred to as solid state relays). Using solid state switches in the switching module may facilitate achieving the rapid switching times mentioned above, as solid state switches typically have very fast switching times (e.g. ranging from 10 ms to 1 ns, depending on the solid state switch used). Solid state switches may also require less power to operate, e.g. compared to contactor switches or relay switches, and so may contribute to improved energy efficiency of the battery system.

The battery system may further comprise a first contactor switch connected between the first subset of battery cells and the first terminal, and a second contactor switch connected between the second subset of battery cells and the second terminal. In other words, the first contactor switch may be connected between the first end of the plurality of battery cells and the first terminal, whilst the second contactor switch may be connected between the second end of the plurality of battery cells and the second terminal. The first contactor switch may be closed to connect the first terminal to the first subset of battery cells, and opened to disconnect the first terminal from the first subset of battery cells. Likewise, the second contactor switch may be closed to connect the second terminal to the second subset of battery cells, and opened to disconnect the second terminal from the second subset of battery cells.

In some cases, a third contactor switch may be connected between the third terminal and the plurality of battery cells at the location between the first end and the second end of the plurality of battery cells, such that the third terminal can be connected to, or disconnected from, the plurality of battery cells by closing or opening the third contactor switch. The contactor switches may thus facilitate disconnecting the plurality of battery cells from the terminals, e.g to facilitate repair or maintenance of the battery system. This may also enable the plurality of battery cells to be easily disconnected from the terminals in case of a failure in the battery system. The contactor switches may be provided in addition to the switching module, to enable the plurality of battery cells to be disconnected from the terminals, regardless of the state of the switching module.

The contactor switches may be controlled by the controller, in a similar manner to the switching module. In particular, the controller may be connected to each of the contactor switches, and configured to transmit a respective control signal to each contactor switch to control a state (i.e. open or closed) of that contactor switch.

In some embodiments, when the plurality of battery cells is fully charged, a first voltage between the first terminal and the third terminal may be equal to a second voltage between the third terminal and the second terminal. For example, a first half of the plurality of battery cells may be connected between the first terminal and the third terminal, and a second half of the plurality of battery cells may be connected between the third terminal and the second terminal. In this manner, the first subset of battery cells and the second subset of battery cells may each contribute half of the total voltage across the plurality of battery cells. As a result, a charger having half the maximum voltage across plurality of battery cells can be used to fully charge the plurality of battery cells, by charging the first subset and the second subset separately. For example, when the plurality of battery cells is fully charged, the first voltage and the second voltage may both be equal to 400 V, such that the total voltage across the plurality of battery cells is 800 V. The plurality of battery cells may then be fully charged using a 400 V charger, by charging each subset of battery cells separately up to 400 V. Splitting the plurality of battery cells in half may also facilitate keeping the first voltage and the second voltage at similar levels during the charging process by alternating charging of the first and second subsets of battery cells, as discussed above. If the first voltage and the second voltage are kept at similar levels throughout the charging process, then the charger may not detect when it is disconnected from one subset of battery cells and connected to another, so that the charger can operate continuously.

In embodiments where there are multiple intermediate terminals, the intermediate terminals may be arranged such that, when the plurality of battery cells is fully charged, voltages across adjacent pairs of terminals (including the first terminal, the second terminal and the multiple intermediate terminals) may be equal. Thus, the intermediate terminals may be arranged to divide the plurality of battery cells into multiple adjacent subsets of battery cells, each subset having the same number of battery cells. Thus, similarly to the discussion above, the plurality of battery cells may be fully charged by independently charging each subset. As an example, there may be two intermediate terminals, such that the plurality of battery cells is divided into three subsets of battery cells. Wien the plurality of battery cells is charged, there may be a voltage of 400 V across each subset, meaning that the total voltage across the plurality of battery cells is 1200 V. Accordingly, the plurality of battery cells may be charged using a 400 V charger, by independently charging each subset of battery cells.

The battery system may further comprise a balancing circuit configured to equalise a first voltage between the first terminal and the third terminal and a second voltage between the third terminal and the second terminal. This may avoid imbalances in the voltages across the first and second subsets of battery cells from arising. This may facilitate charging of the plurality of battery cells, as well as maximise a usable charge of the plurality of battery cells to increase a travel range of the electric vehicle.

In one example, the balancing circuit may comprise a passive balancing circuit, which is configured to reduce the voltages of the battery cells in the subset having the highest voltage, by drawing energy from those battery cells and dissipating the energy, e.g. as heat via one or more resistors. As a result, the voltages of the most charged cells may be reduced, thus reducing any voltage difference between the first and second subsets of battery cells. In another example, the balancing circuit may comprise an active balancing circuit which is configured to draw energy stored in the battery cells of the subset with the higher voltage, and transfer the energy to the battery cells in the subset with the lower voltage. The active balancing circuit may comprise one or more capacitors, configured to temporarily store the energy drawn from the battery cells. Alternatively, the active balancing circuit may comprise a DC-DC converter that is configured to selectively couple battery cells together to transfer charge from battery cells having a higher voltage to battery cells having a lower voltage. Using an active balancing circuit may be improve an energy efficiency of the battery system, e.g. compared to using a passive balancing circuit.

The switching module may comprise a cooling mechanism for removing heat from switches (i.e. the two or more switches) in the switching module. This may serve to reduce a temperature of the switching module during the charging process, thus improving a charging efficiency for the battery system. The cooling mechanism may involve active and/or passive cooling. For example, the cooling mechanism may include one or more heatsinks that are thermally coupled to the switches for removing heat from the switches. Additionally or alternatively, the cooling mechanism may include one or more fans arranged to cool the switches in the switching module. In some cases, the switches in the switching module may be thermally coupled to a cooling circuit of the electric vehicle.

According to a second aspect of the invention, there is provided an electric vehicle comprising a battery system according to the first aspect of the invention, wherein the plurality of battery cells is electrically connected to a drive system of the vehicle to power the drive system. Any of the features described above in relation with the first aspect may be included in the vehicle of the second aspect.

The electric vehicle may refer to a vehicle comprising an electrically powered drive system. In particular, the electric vehicle may comprise an electric motor, with the plurality of battery cells being arranged to power the electric motor. In some cases the electric vehicle may include multiple electric motors, e.g. a first electric motor for driving the front wheels and a second electric motor for driving the rear wheels. In such a case, the plurality of battery cells may be arranged to power the multiple electric motors. The electric vehicle may be a hybrid electric vehicle, e.g. it may comprise an internal combustion engine and an electric motor which are arranged to power the vehicle. The electric vehicle may be a road vehicle, e.g. a road car. In other words, the vehicle may be designed to be driven on roads.

The battery system may comprise a first discharge terminal that is electrically connected to the first terminal, and a second discharge terminal electrically connected to the second terminal, the first discharge terminal and the second discharge terminal being connected to the drive system to convey a discharging current from the plurality of battery cells to the drive system for powering the drive system, wherein the first discharge terminal and the second discharge terminal are arranged such that the discharging current does not pass through the switching module.

According to a third aspect of the invention, there is provided a method of operating a battery system according to the first aspect of the invention, the method comprising: receiving, at the charging port, power from an external power source; and operating the switching module to alternate over time between a first state in which the first terminal and the third terminal are electrically connected to the charging port and a second state in which the second terminal and the third terminal are electrically connected to the charging port, such that the first subset of the plurality of battery cells is charged when the switching module is in the first state, and the second subset of the plurality of battery cells is charged when the switching module is in the second state.

The method of the third aspect of the invention may be applied to the battery system of the first aspect. Therefore, any features above discussed in relation to the first aspect may be included in the method of the third aspect.

Operating of the switching module may performed using a controller, as discussed above in relation to the first aspect of the invention. Additionally or alternatively, operating the switching module may be performed by a user, e.g. by manually controlling the switching module.

The method may comprise operating the switching module to alternate between the first state and the second state at regular time intervals.

The switching module may be alternated between the first state and the second state such that the switching module does not remain in the first state or the second state for more than one minute at a time.

The method may further comprise controlling a duty cycle of the alternation between the first state and the second state based on a difference between a first voltage and a second voltage, the first voltage corresponding to a voltage between the first terminal and the third terminal, and the second voltage corresponding to a voltage between the third terminal and the second terminal.

In some embodiments of the method, if the first voltage is greater than the second voltage by a predetermined amount, a proportion of the duty cycle corresponding to the first state may be decreased and a proportion of the duty cycle corresponding to the second state may be increased; and if the second voltage is greater than the first voltage by the predetermined amount, the proportion of the duty cycle corresponding to the first state may be increased and the proportion of the duty cycle corresponding to the second state may be decreased.

The method may further comprise controlling a period of the alternation between the first state and the second state based on a temperature of the switching module. In other words, the method may further comprise controlling a length of the duty cycle of the alternation between the first state and the second state, i.e. an amount of time between switching events for each switch of the switching module.

Herein, where two parts are referred to as being connected together, this may refer to an electrical connection between the two parts, unless context dictates otherwise.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention are discussed below with reference to the accompanying drawings, in which: Fig. 1 is a schematic diagram of an electric vehicle according to an embodiment of the invention, where the electric vehicle is connected to an external charger; Fig. 2a is a schematic circuit diagram of a battery system according to an embodiment of the invention, where a switching module of the battery system is in a first state; Fig. 2b is a schematic circuit diagram of the battery system of Fig. 2a, where the switching module of the battery system is in a second state; and Fig. 3 is a schematic circuit diagram of another battery system according to an embodiment of the invention.

DETAILED DESCRIPTION; FURTHER OPTIONAL FEATURES

Fig. 1 shows a schematic diagram of an electric vehicle 100 according to an embodiment of the invention. The electric vehicle 100 includes an electrically powered drive system 102. The drive system 102 may comprise one or more electric motors, which are arranged to drive wheels of the electric vehicle 100. The electric vehicle 100 further includes a battery system according to the invention, the battery system being arranged to power the drive system 102.

The battery system comprises a battery unit (or battery pack) 104, including a plurality of battery cells (not shown) divided into a first subset of battery cells and a second subset of battery cells, the first and second subsets of battery cells being connected in series. The battery unit 104 may include a housing in which the plurality of battery cells is contained. Three terminals are provided on the battery unit 104, which are electrically connected to the plurality of battery cells. In particular, a first terminal 106 is electrically connected to a first end (i.e. a first extremity) of the plurality of battery cells, and a second terminal 108 is connected at a second end (i.e. a second extremity) of the plurality of battery cells. Thus, the plurality of battery cells is electrically connected between the first terminal 106 and the second terminal 108.

A third terminal 110 is electrically connected to the plurality of battery cells at a location between the first end and the second end of the plurality of battery cells. So, for example, the third terminal 110 may be connected to the plurality of battery cells at a point between adjacent battery cells in the plurality of battery cells. The third terminal 110 may be connected to a conductor which connects the adjacent battery cells, and/or it may be connected to an electrode of one of the adjacent battery cells. The third terminal 110 splits the plurality of battery cells into the first subset of the battery cells, which is connected between the first terminal 106 and the third terminal 110, and the second subset of the battery cells, which is connected between the third terminal 110 and the second terminal 108. Preferably, the third terminal 110 may be arranged such that it splits the plurality of battery cells in half, i.e. such that a first half of the plurality of battery cells is connected between the first terminal 106 and the third terminal 110, and a second half of the plurality of battery cells is connected between the third terminal 110 and the second terminal 108. Thus, when all of the battery cells are fully charged, a first voltage between the first terminal 106 and the third terminal 110 and a second voltage between the third terminal 110 and the second terminal 108 may be equal. In one embodiment, the battery unit 104 may be an 800 V battery pack, meaning that a voltage across the plurality of battery cells in the battery unit 104 is 800 V when fully charged. Accordingly, the first voltage and the second voltage may each be equal to 400 V when the battery cells are fully charged. The first terminal 106, the second terminal 108 and the third terminal 110 may be provided on an outside of the housing of the battery unit 104.

The battery system further comprises a switching module 112 and a charging port 114, with the switching module 112 being connected between the charging port 114 and the terminals on the battery unit 104. The charging port 114 is connectable to an external charger (i.e. power source) to receive a charging current from the charger. Thus, the charging port 114 may comprise a connector and/or a cable for connecting it to an external charger. The switching module 112 is configured to selectively connect the charging port 114 to two of the first terminal 106, the second terminal 108, and the third terminal 110. In other words, the switching module 112 can be switched between three states: a first state in which the first terminal 106 and the third terminal 110 are electrically connected to the charging port 114, a second state in which the second terminal 108 and the third terminal 110 are electrically connected to the charging port 114, and a third state in which the first terminal 106 and the second terminal 108 are electrically connected to the charging port 114. Accordingly, when the switching module 112 is in the first state, the charging port 114 is electrically connected to the first subset of the plurality of battery cells, which is connected between the first terminal 106 and the third terminal 110.

So, in the first state, a charging current received by the charging port 114 from an external charger charges the first subset of the plurality of battery cells. VVhen the switching module 112 is in the second state, the charging port 114 is electrically connected to the second subset of the plurality of battery cells, which is connected between the third terminal 110 and the second terminal 108. So, in the second state, a charging current received by the charging port 114 from an external charger charges the second subset of the plurality of battery cells. When the switching module 112 is in the third state, the charging port 114 is electrically connected to the plurality of battery cells, which is connected between the first terminal 106 and the second terminal 108. So, in the third state, a charging current received by the charging port 114 from an external charger charges the plurality of battery cells. In this manner, by operating the switching module, it is possible to charge the first subset and the second subset of the plurality of battery cells independently, or to charge the plurality of battery cells together.

The switching module 112 may include any suitable arrangement of switches for selectively connecting the charging port 114 to two of the first, second and third terminals 106, 108, 110 on the battery unit 104. More detailed examples of possible switching module configurations are described below, in relation to Figs. 2a, 2b and 3. As shown in Fig. 1, the switching module 112 is electrically connected to each of the first terminal 106, the second terminal 108 and the third terminal 110 via a respective line (e.g. wire or cable). Additionally, a positive terminal and a negative terminal of the charging port 114 are each connected to the switching module 112 via a respective line (e.g. wire or cable). In the first state, the switching module 112 is configured to connect the positive and negative terminals of the charging port 114 to the first and third terminals 106, 110 such that the charging current charges the first subset of battery cells. In the second state, the switching module 112 is configured to connect the positive and negative terminals of the charging port 114 to the third and second terminals 110, 108 such that the charging current charges the second subset of battery cells. In the third state, the switching module 112 is configured to connect the positive and negative terminals of the charging port 114 to the first and second terminals 106, 108 such that the charging current charges the plurality of battery cells.

During charging of the plurality of battery cells, the charging current passes through switches in the switching module 112. As a result, the switches in the switching module may heat up during the charging process. In order to reduce heating of the switches during charging, the switches in the switching module 112 may comprise a cooling mechanism (not shown) for removing heat from the switches in the switching module 112. This may serve to avoid damage to the switches, as well as improve efficiency of power transmission through the switching module 112. The cooling mechanism may involve active and/or passive cooling. For example, the cooling mechanism may include one or more heatsinks that are thermally coupled to the switches for removing heat from the switches. Additionally or alternatively, the cooling mechanism may include one or more fans arranged to cool the switches in the switching module. In some cases, the switches in the switching module 112 may be thermally coupled to a cooling circuit of the electric vehicle 100.

Fig. 1 illustrates a configuration where the charging port 114 is connected an external charger 116 via a connecting cable 118. The charger 116 may supply power to the charging port 114, which is then conveyed to the battery cells in the battery unit 104 via the switching module 112 in order to charge the battery cells. In particular, the charger 116 may supply a charging current to the charging port 114, which is used to charge the battery cells as discussed above. Once charging of the battery cells has been completed, the cable 118 may be disconnected from the charging port 114 so that the electric vehicle 100 can drive away. The charger 116 may, for example, have an output voltage of 400 V. Then, with the example given above where the battery unit 104 is an 800 V battery pack, and the third terminal 110 is arranged such that the first subset and the second subset of battery cells each have a voltage of 400 V when fully charged, the battery unit 104 can be fully charged by charging each subset of battery cells independently (by controlling the switching module 112).

The battery unit 104 comprises a first discharge terminal 120 and a second discharge terminal 122. The first discharge terminal 120 is electrically connected to the first terminal 106 (e.g. via a first electrical connector in the battery unit 104), whilst the second discharge terminal 122 is electrically connected to the second terminal 108 (e.g. via a second electrical connector in the battery unit 104). Thus, the plurality of battery cells in the battery unit 104 is electrically connected between the first discharge terminal 120 and the second discharge terminal 122. In some embodiments, the first terminal 106 and the first discharge terminal 120 may be implemented as a single terminal. Likewise, in some embodiments, the second terminal 108 and the second discharge terminal 122 may be implemented as a single terminal. The first discharge terminal 120 and the second discharge terminal 122 are connected to the drive system 102, so that a discharging current from the plurality of battery cells in the battery unit 104 can be conveyed (e.g. transmitted) to the drive system 102 in order to power the drive system 102. The electrical connection between the drive system 102 and the first and second discharge terminals 120, 122 does not pass through the switching module 112. For example, as shown in Fig. 1, the drive system 102 may be directly connected to the first and second discharge terminals 120, 122 via a pair of electrical lines (e.g. wires or cables). In this manner, the discharging current conveyed from the plurality of battery cells in the battery unit 104 to the drive system 102 does not pass through any of the switches in the switching module 112. Accordingly, the switching module 112 need only be configured to support the maximum charging current, which may typically be smaller than the maximum discharging current which is used to power the drive system 102. This may enable smaller and more lightweight switches to be used in the switching module 112 (e.g. compared to a case where the discharging current is made to pass through the switching module 112).

The battery system further comprises a controller 124 which is configured to control operation of the switching module 112. The controller 124 is communicatively coupled (i.e. connected) to the switching module 112, so that the controller 124 can transmit one or more control signals to the switching module to control which state the switching module 112 is in. Thus, the controller 124 can control the switching module 112 to put the switching module in one of the first, second and third states. In this manner, the controller 124 can operate the switching module 112 to control which part of the plurality of battery cells (i.e. the first subset, the second subset, or the whole plurality of battery cells) is electrically connected to the charging port 114, to control which part of the plurality of battery cells is charged with a charging current from the charging port 114. The control signals transmitted from the controller 124 to the switching module 112 may, for example, include one or more signals for controlling positions of the switches in the switching module 112, so as to set the state of the switching module 112. In the example shown, the controller 124 is connected to the switching module 112 via a cable. However, in other examples, the controller 124 may communicate wirelessly with the switching module 112 or be integrated with the switching module 112 directly.

The controller 124 may also be configured to monitor the first voltage (between the first terminal 106 and the third terminal 110), the second voltage (between the third terminal 110 and the second terminal 108), and a third voltage (between the first terminal 106 and the second terminal 108). In this manner, the controller 124 can determine a charge level of the battery cells in the first subset and the second subset, as well as the overall charge level of the plurality of battery cells. For example, the controller 124 may be connected to each of the first, second and third terminals 106, 108, 110 so that it can measure the first, second and third voltages. Alternatively, the controller 124 may be coupled to a monitoring device of the vehicle which is arranged to detect the first, second and third voltages. In some cases, monitoring of the first voltage and the second voltage may be performed using a battery management system of the electric vehicle 100, which is arranged to detect voltages of individual battery cells and/or groups of battery cells.

The controller 124 may be implemented using any suitable electronic controller device. For example, the controller 124 may be implemented by a computing device having suitable control software installed thereon. In some cases, the controller 124 may be implemented by an existing on-board computer of the electric vehicle 100, which may also be configured to control other vehicle systems. For instance, the controller 124 may be implemented by a main on-board computer of the vehicle 100, a battery management system (BMS) of the vehicle 100, or an electronic control unit (ECU) of the vehicle. Alternatively, the controller 124 may be a dedicated device that is separate from other on-board computers of the vehicle 100.

When the charging port 114 is connected to a charger 116 to receive a charging current, the controller 124 may be configured to perform a control sequence whereby the first subset of battery cells and the second subset of battery cells are alternately charged over time. In particular, the controller 124 may be configured to control the switching module 112 to alternate between the first state and the second state over time, to alternate between charging of the first subset and the second subset of battery cells. In this manner the first subset and the second subset of battery cells can be progressively charged in alternation, until all of the battery cells are fully charged. Such alternation avoids continuously charging the first and second subsets of battery cells, which may reduce heat generation inside the battery unit 104 over the course of the charging process. Additionally, such alternation enables, for example, charging of a higher voltage (e.g. 800 V) battery unit using a lower voltage (e.g. 400 V) charger, as discussed above.

The controller 124 may be configured to control the switching module 112 to alternate between the first state and the second state at regular time intervals. In other words, the controller 124 may control the switching module 112 to perform a sequence where it is initially in the first state for an amount of time, and then switched to the second state for the same amount of time. The controller 124 may repeat this sequence, until the battery cells in the first subset and the second subset are fully charged. Charging the first subset and the second subset of battery cells for equal amounts of time may mean that they are charged by similar amounts over each iteration (or cycle) of the sequence. This may facilitate keeping the first and second subset of battery cells at similar charge levels, and avoid a large charge imbalance arising between the two subsets.

The amount of time spent in each state before switching to the next state may be set based on various factors, such as the type of battery cells used, type of charger used, the magnitude of the charging current, the state of charge of the battery cells, and switching speed of the switching module 112. In some implementations, the amount of time spent in each state may be relatively long, e.g. of the order of 1 to 10 minutes. This may enable a large amount of charge to be added to each subset of battery cells over each iteration of the charging sequence.

However, a drawback of using such a long time interval is that there may be a significant imbalance in the charge level between the first and second subsets over a significant portion of the charging sequence, as the first and second subsets are charged one at a time. As a result, if charging is interrupted before both subsets of battery cells are fully charged, there is likely to be an imbalance in the charge level between the two subsets. This may cause the discharging current supplied by the plurality of battery cells to be limited by the voltage of the subset having the lowest charge level. Additionally, due to the large difference between the first voltage and the second voltage which may arise over the course of the charging sequence (e.g. right before switching from the first state to the second state), when switching occurs the charger 116 may detect that it has been disconnected from the battery cells that is has been charging, and so interrupt charging. Therefore, a user may need to manually initiate charging at the charger 116 each time the switching module 112 switches between the first and second states. A further drawback of using long time intervals for the alternation between the first and second states is that the battery cells may age (e.g. degrade) more quickly, as they may effectively experience a larger number of charge cycles (including electrical and thermal cycling).

Accordingly, in one embodiment, the controller 124 may be configured to keep the switching module 112 in a given state for only a short amount of time before switching to the next state. The inventors have found that, by controlling the switching module 112 so that it does not remain in the same state for more than one minute at a time during charging, it may be possible to avoid the drawbacks mentioned above. In particular, this may serve to minimise any imbalance in charge levels between the first and second subsets that occurs over the course of the charging sequence. Thus, if charging is interrupted before both subsets of battery cells are fully charged, the two subsets will be at a similar charge level such that the discharging current may not be significantly limited by the subset having the (slightly) lower charge level.

Additionally, a difference between the first voltage and the second voltage may be kept small enough so that it does not cause the charger to interrupt charging when the switching module 112 switches between states. In this manner, the charging sequence may be fully automated, without a user having to supervise the charger. As an example, the switching module 112 may be controlled so that it does not remain in the same state for more than 10 seconds at a time.

Furthermore, when using a shorter time interval between switching events, the time interval may be less than a time constant of the battery cells, meaning the switching module may switch states before a thermal or electrical cycle is registered for the battery cells. For example, the switching module may switch from the first state to the second state before the battery cells in the first subset have time to significantly heat up (and vice versa). As a result, the battery cells may age more slowly compared to the scenario where longer intervals are used between switching events, such that a lifetime of the battery unit 104 may be improved.

In some cases, the controller 124 may be configured to correct for imbalances in charge level between the first subset and the second subset of battery cells, by adjusting a duty cycle of the alternation between the first state and the second state. In other words, the controller 124 may adjust a proportion of the amount of time spent in the first state and a proportion of the amount of time spent in the second state for the alternation between the first state and the second state. This serves to compensate for differences in the charge levels between the first subset and the second subset of battery cells. This may avoid large differences in charge levels between the first and second subsets of battery cells arising over the course of the charging process, as well as enable the controller 124 to compensate for differences in the charge levels. For example, the controller 124 may be configured to monitor the first voltage and the second voltage. Then, if a difference between the first voltage and the second voltage exceeds a predetermined amount (i.e. due to an imbalance in the charge levels between the first and second subsets of battery cells), the controller 124 may be configured to adjust the duty cycle of the alternation between the first state and the second state to reduce the difference between the first voltage and the second voltage. Specifically, if the first voltage is greater than the second voltage by a predetermined amount, the controller 124 may be configured to adjust the duty cycle to decrease a proportion of time spent by the switching module 112 in the first state and increase a proportion of time spent by the switching module 112 in the second state. For instance, the controller 124 may control the switching module 112 such that the amount of time spent in the second state before switching is greater than the amount of time spent in the first state before switching. On the other hand, if the second voltage is greater than the first voltage by the predetermined amount, the controller 124 may be configured to adjust the duty cycle to increase the proportion of time spent by the switching module 112 in the first state and decrease the proportion of time spent by the switching module 112 in the second state. For instance, the controller 124 may control the switching module 112 such that the amount of time spent in the first state before switching is greater than the amount of time spent in the second state before switching.

Adjustments to the duty cycle made by the controller 124 may be made within certain constraints. For example, as mentioned above, the controller 124 may be configured such that there is an upper limit on how long the switching module 112 can stay in a given state at a time (i.e. before switching to another state). Thus, the controller 124 may be configured to adjust the duty cycle to compensate for imbalances in the charge levels between the first and second subsets of battery cells, whilst ensuring that the switching module 112 does not stay in the same state for more than one minute at a time.

The switching module 112 may be configured to switch between the first state and the second state in less than one second. Such a rapid switching time may serve to improve an efficiency of the charging process, by minimising the amount of time spent switching between states. Additionally, such a rapid switching time may serve to avoid the charger 116 interrupting charging when the switching module 112 switches from one state to another. In particular, due to the rapid switching time, the charger 116 may not detect that it has been disconnected from one subset of battery cells and connected to another subset of battery cells, such that the charger 116 may operate continuously over the course of the charging sequence. This may facilitate automating the charging process, as it may avoid a user having to supervise the charger 116 and re-activate the charger 116 after the switching module 112 switches states.

In order to achieve a short switching time, the switching module 112 may include high-speed switches, such as solid state switches. Solid state switches typically have very short switching times (e.g. of the order of 10 ms to 1 ns), such that the switching module 112 may be capable of very fast switching between the first and second states. Such fast switching between the states may ensure that the charger 116 does not detect that switching has occurred, as well as improve charging efficiency by minimising the amount of time spent switching between states. By way of example, insulated-gate bipolar transistor (IGBT) switches and/or silicon metal-oxide-semiconductor field-effect transistor (MOSFET) switches may be used in the switching module 112. As solid state switches may not typically be rated to high currents, the switching module may employ multiple solid state switches connected in parallel, to ensure that the switching module 112 is capable of supporting a maximum charging current used for the battery unit 104. Typically, the maximum charging current may range from 50 A to 750 A, such that 2 to 20 solid state switches may need to be connected in parallel in order to support the maximum charging current (depending on the current rating of the solid state switches used).

As the switching module 112 switches between the first state and the second state, switches in the switching module 112 may heat up, due to heat generated in the switches when they are switched. Additionally, as mentioned above, switches in the switching module 112 may heat up during the charging process due to the charging current passing through the switching module 112. The controller 124 may be configured to operate the switching module 112 so as to avoid excessive heating of the switches. To do this, the controller 124 may be connected to one or more temperature sensors in the switching module 112, so that the controller 124 can monitor a temperature of the switches in the switching module 112. The controller 124 may then be configured to control switching of the switching module 112 to minimise a temperature of switches in the switching module 112. By way of example, the switching module 112 may include a respective temperature sensor for detecting a temperature of each switch in the switching module, so that the controller 124 can monitor the temperature of each switch. Alternatively, the one or more temperature sensors may serve to indicate an overall temperature of the switching module 112, without necessarily being associated with a particular switch.

The controller 124 may be configured to minimise the temperature of the switching module 112 during charging by adjusting the period of the switching module's alternation between the first state and the second state. Adjusting the period of the alternation effectively adjusts the amount of time between subsequent switching events of the switching module. Thus, by increasing the period of the alternation, an average time between switching events of the switching module 112 may be increased, thus allowing more time for switches in the switching module 112 to cool between switching events. Therefore, in one implementation, the controller 124 may be configured to increase the period of the switching module's alternation between the first state and the second state if the temperature of the switching module 112 increases above a first predetermined threshold. Further, if the temperature of the switching module 112 decreases below a second predetermined, the controller 124 may be configured to decrease the period of the switching module's alternation between the first state and the second state. This control of the period of the alternation may enable the switching module 112 to be kept within a suitable range of working temperatures.

It should be noted that Fig. 1 shows a schematic representation of the electric vehicle 100, and is intended to illustrate connections between some of the components included in the electric vehicle 100. However, the schematic representation of Fig. 1 is not intended to specify the physical layout of components of the electric vehicle 100, and these may be arranged in the electric vehicle 100 in any suitable manner.

Figs. 2a and 2b show schematic circuit diagrams of a battery system 200 according to an embodiment of the invention. The battery system 200 may, for example, correspond to the battery system of the electric vehicle 100 described above. For convenience, features of the battery system 200 corresponding to those of the battery system of vehicle 100 are labelled in Figs. 2a and 2b with the same reference numerals as in Fig. 1, and are not described again.

As can be seen in Figs. 2a and 2b, the battery unit 104 of the battery system 200 includes a plurality of battery cells 202, all of which are connected in series. The plurality of battery cells 202 is electrically connected between the first terminal 106 and the second terminal 108. Further, as shown, the first terminal 106 is electrically connected to the first discharge terminal 120, whilst the second terminal 108 is electrically connected to the second discharge terminal 122 of the battery system 200. The third terminal 110 of the battery system 200 is electrically connected to the plurality of battery cells 202 at a location half-way along the plurality of battery cells 202. In other words, a same number of battery cells 202 is connected between the first terminal 106 and the third terminal 110 as between the third terminal 110 and the second terminal 108. The part of the plurality of battery cells 202 connected between the first terminal 106 and the third terminal 110 may be referred to as a first subset 204, whilst the part of the plurality of battery cells 202 connected between the third terminal 110 and the second terminal 108 may be referred to as a second subset 206. As an example, the battery unit 104 of the battery system 200 may be an 800 V battery, such that a voltage between the first terminal 106 and the second terminal 108 (i.e. across the plurality of battery cells 202) is 800 V when the battery cells 202 are fully charged. Then, a first voltage across the first subset 204 may be 400 V when the battery cells 202 in the first subset 204 are fully charged, and a second voltage across the second subset 206 may be 400 V when the battery cells 202 in the second subset 206 are fully charged. Thus, when the battery cells 202 are all fully charged, a voltage at the first terminal 106 may be +400 V, a voltage at the third terminal 110 may be 0 V, and a voltage at the second terminal 108 may be -400 V. In the example shown, each of the first subset 204 and the second subset 206 includes eight battery cells 202. However, in other examples different numbers of battery cells 202 may be used. Likewise, the plurality of battery cells 202 may be arranged to have a different maximum voltage (e.g. other than 800 V), depending on the application. It should also be noted that, although all of the battery cells 202 in the plurality of battery cells 202 are connected in series, other arrangements of battery cells within the first subset 204 and the second subset 206 may also be used. For example, the first subset 204 may include two or more battery cells connected in parallel On addition, or alternatively to the series connected battery cells 202 shown in Figs. 2a and 2b). Likewise, the second subset 206 may include two or more battery cells connected in parallel On addition, or alternatively to the series connected battery cells 202 shown in Figs. 2a and 2b). However, in all cases, the first subset 204 and the second subset 206 of battery cells 202 are connected in series between the first terminal 106 and the second terminal 108, to enable selective charging of the first subset 204 and the second subset 206.

As shown in Figs. 2a and 2b, the switching module 112 of the battery system 200 includes a first switch 208 and a second switch 210. The first switch 208 is configured to selectively couple a positive terminal 212 of the charging port 114 to the first terminal 106 or the third terminal 110. The second switch 210 is configured to selectively couple a negative terminal 214 of the charging port 114 to the third terminal 110 or the second terminal 108. As a result of this switch arrangement, the switching module 112 can be operated to switch between a first state in which the first subset 204 of battery cells 202 is charged by a charging current received from the charging port 114, and a second state in which the second subset 206 of battery cells 202 is charged by a charging current received from the charging port 114. The first switch 208 and the second switch 210 may be implemented using high-speed switches, such as solid state switches, as discussed above. Other switch types such as relay switches or contactor switches may also be used.

In Fig. 2a, the switching module 112 is shown in the first state. In the first state, the positive terminal 212 of the charging port 114 is connected to the first terminal 106 via the first switch 208, and the negative terminal 214 of the charging port 114 is connected to the third terminal 110 via the second switch 210. In this manner, a charging current received at the charging port 114 from an external charger may be conveyed to the first subset 204 of battery cells 202 to charge the first subset 204. A path of the charging current when the switching module 112 is in the first state is indicated by the bold lines in Fig. 2a. In Fig. 2b, the switching module 112 is shown in the second state. In the second state, the positive terminal 212 of the charging port 114 is connected to the third terminal 110 via the first switch 208, and the negative terminal 214 of the charging port 114 is connected to the second terminal 108 via the second switch 210. In this manner, a charging current received at the charging port 114 from an external charger may be conveyed to the second subset 206 of battery cells 202 to charge the second subset 206. A path of the charging current when the switching module 112 is in the second state is indicated by the bold lines in Fig. 2b. Thus, the first subset 204 and the second subset 206 of battery cells can be charged independently of one another. The switching module 112 can further be switched to a third state (not shown), where the positive terminal 212 of the charging port 114 is connected to the first terminal 106 via the first switch 208, and the negative terminal 214 of the charging port 114 is connected to the second terminal 108 via the second switch 210. In the third state, the charging port 114 is therefore connected across the plurality of battery cells 202, such that the current received from the external charger can be used to charge all of the battery cells 202 in the battery unit 104 at once. The switching module 112 may be controlled as discussed above, e.g. using controller 124, in order to alternate charging of the first and second subsets 204, 206 over time.

The process of switching from the first state to the second state may involve first operating the second switch 210 to disconnect the negative terminal 214 of the charging port 114 from the third terminal 110, prior to operating the first switch 208 to connect the positive terminal 212 of the charging port 114 to the third terminal 110. Similarly, the process of switching from the second state to the first state may involve first operating the first switch 208 to disconnect the positive terminal 212 of the charging port 114 from the third terminal 110, prior to operating the second switch 210 to connect the negative terminal 214 of the charging port to the third terminal 110. Performing the switching process in this manner may improve a safety of the switching process, as it may avoid a risk of the positive and negative terminals 212, 214 of the charging port 114 of being short circuited via the third terminal 110.

As shown in Figs. 2a and 2b, all of the switches of the switching module 112 are located outside the plurality of battery cells 202. In particular, none of the switches is connected in series between two adjacent battery cells 202. Additionally, none of the switches of the switching module 112 are connected between the plurality of battery cells 202 and the first and second discharge terminals 120, 122. Locating the switches 208, 210 of the switching module 112 in this manner may serve to ensure that a discharging current supplied from the plurality of battery cells 202 to a drive system (e.g. drive system 102) via the first and second discharge terminals 120, 122 does not pass through any switches of the switching module 112. Therefore, the first and second switches 208, 210 need only be configured to withstand the maximum charging current received from the charging port 114, and do not need to be rated for the often much larger maximum discharging current which is used to power the drive system of the vehicle. Indeed, in practice, the discharging current which is used to power the drive system of the electric vehicle may have a magnitude several times (e.g. five times) greater than a magnitude of the charging current used to charge the battery cells 202.

Fig. 3 shows a schematic circuit diagram of a battery system 300 according to an embodiment of the invention. The battery system 300 may, for example, correspond to the battery system of the electric vehicle 100 described above. For convenience, features of the battery system 300 corresponding to those of the battery system of vehicle 100 are labelled in Fig. 3 with the same reference numerals as in Fig. 1, and are not described again.

As can be seen in Fig. 3, the battery unit 104 of the battery system 300 includes a plurality of battery cells 302 which are connected in series. The plurality of battery cells 302 is electrically connected between the first terminal 106 and the second terminal 108. Further, as shown, the first terminal 106 is electrically connected to the first discharge terminal 120, whilst the second terminal 108 is electrically connected to the second discharge terminal 122 of the battery system 300. The third terminal 110 of the battery system 300 is electrically connected to the plurality of battery cells 302 at a location half-way along the plurality of battery cells 302, between two adjacent battery cells 302 in the plurality of battery cells 302. Thus, the third terminal 110 splits the plurality of battery cells 302 into a first subset 304 connected between the first terminal 106 and the third terminal 110, and a second subset 306 connected between the third terminal 110 and the second terminal 108. Similarly to battery system 200 discussed above, the battery unit 104 of battery system 300 may be an 800 V battery pack, i.e. such that a maximum voltage across the first subset 304 and a maximum voltage across the second subset 306 is 400 V. However, in other examples, the plurality of battery cells may be arranged to have a different maximum voltage (e.g. other than 800 V), depending on the application.

In the embodiment shown, the first subset 304 and the second subset 306 each include two battery cells 302 connected in series. In other embodiments (not shown) the first subset 304 may additionally or alternatively include two or more battery cells connected in parallel.

Similarly, the second subset 306 may additionally or alternatively include two or more battery cells connected in parallel.

The battery unit 104 of the battery system 300 may further include a first contactor switch 308, a second contactor switch 312, and a third contactor switch 310. The first terminal 106 is connected to a first end of the plurality of battery cells 302 via the first contactor switch 308, whilst the second terminal 108 is connected to a second end of the plurality of battery cells 302 via the second contactor switch 312. The third terminal 110 is connected to the location half-way along the plurality of battery cells 302 via the third contactor switch 310. The contactor switches 308, 310, 312 can be opened in order to disconnect the first, second and third terminals 106, 108, 110 from the plurality of battery cells 302. This may facilitate disconnecting the battery unit 104 from the rest of the battery system 300, e.g. in order to repair and/or replace the battery unit 104 or other parts of the high voltage system. In some embodiments, the battery unit 104 may further comprise a pre-charge circuit which is connected in parallel with the first contactor switch 308. The pre-charge circuit may comprise a resistor 314 in series with a pre-charge contactor switch 316.

As shown in Fig. 3, the switching module 112 of the battery system 300 includes a first switch 318, second switch 320, third switch 322 and fourth switch 324. The first switch 318 is arranged such that, when closed it connects a positive terminal 326 of the charging port 114 to the first terminal 106, and when open it disconnects the positive terminal 326 of the charging port 114 from the first terminal 106. The second switch 320 is arranged such that, when closed it connects a negative terminal 328 of the charging port 114 to the third terminal 110, and when open it disconnects the negative terminal 328 of the charging port 114 from the third terminal 110. The third switch 322 is arranged such that, when closed it connects the positive terminal 326 of the charging port 114 to the third terminal 110, and when open it disconnects the positive terminal 326 of the charging port 114 from the third terminal 110. The fourth switch 324 is arranged such that, when closed it connects the negative terminal 328 of the charging port 114 to the second terminal 108, and when open it disconnects the negative terminal 328 of the charging port 114 from the second terminal 108. Similarly to the discussion above in relation to the battery system 200, the first and second discharge terminals 120 and 122 are arranged such that a discharging current from the plurality of battery cells 302 that is conveyed via the first and second discharge terminals 120 and 122 (e.g. for powering a drive system of the vehicle), does not pass through any of the switches in the switching module 112. The switches 318, 320, 322, 324 in the switching module 112 may be implemented by any suitable switches, such as relay switches, contactor switches, or solid state switches, depending on the switching speed to be achieved. Preferably, the switches 318, 320, 322, 324 may be implemented by high speed switches, such as solid state switches.

Table 1 below indicates the state of each of the switches 318, 320, 322, 324 of the switching module 112 for performing different charging operations. For embodiments having the contactor switches 308, 310, 312, Table 2 below indicates the state of each of the contactor switches 308, 310, 312 during various operations.

Switch 318 Switch 320 Switch 322 Switch 324 1. Charging first subset 304 X X 0 0 2. Charging second subset 306 0 0 X X 3. Charging all battery cells 302 X 0 0 X 4. No charging 0 0 0 0 Table 1: Switch positions for performing different charging operations Contactor switch 308 Contactor switch 310 Contactor switch 312 1. Charging first subset 304 X X 0 2. Charging second subset 306 0 X X 3. Charging all X 0 X battery cells 302 4. Vehicle operating X 0 X 5. Battery unit 104 0 0 0 disconnected Table 2: Contactor switch positions for performing various operations In the above tables, 'X' is used to indicate that the corresponding switch is closed, whilst '0' is used to indicate that the corresponding switch is open. Thus, from Table 1, it can be seen that the switching module can be switched between four states (numbered 1,2, 3,4 in Table 1), i.e. a first state in which the first subset 304 of battery cells 302 is connected to the charging port 114, a second state in which the second subset 306 of battery cells 302 is connected to the charging port 114, a third state in which the plurality of battery cells 302 is connected to the charging port 114, and a fourth state in which none of the plurality of battery cells 302 are connected to the charging port 114. Thus, by controlling the switches 318, 320, 322, 324 in the switching module 112, the first subset 304 and the second subset 306 of battery cells 302 can be charged independently. Table 2 shows the positions of the contactor switches 308, 310, 312 in each of the first three charging states. Additionally, Table 2 shows the positions of the contactor switches 308, 310, 312 when the vehicle is operating, i.e. when a discharging current is supplied from the plurality of battery cells 302 to power a drive system of the vehicle, and when the battery unit 104 is disconnected from the rest of the vehicle, which are occasions when the switching module would occupy the fourth state (no charging). The positions of the switches 318, 320, 322, 324 in the switching module 112 may be controlled in accordance with Table 1 by a controller, e.g. controller 124, to alternate charging of the first and second subsets 304, 306 of battery cells 302 as discussed above. The same controller may further be configured to control the positions of the contactor switches 308, 310, 312 in accordance with Table 2.

The pre-charge circuit is designed to limit in-rush currents during a start-up procedure of the electric vehicle, to avoid damage to electrical components. The pre-charge contactor switch 316, together the second contactor switch 312 may be closed for a short period (e.g. 5-10 seconds) during start-up of the vehicle. The pre-charge contactor switch 316 is open for normal (i.e. steady state) operation of the battery system 300, including charging and discharging of the battery unit 104.

The process of switching from the first state to the second state may involve first opening the first switch 318 and the second switch 320 prior to closing the third switch 322 and the fourth switch 324. Likewise, the process of switching from the second state to the first state may involve first opening the third switch 322 and the fourth switch 324 prior to closing the first switch 318 and the second switch 320. Operating the switching module 112 in this manner may serve to ensure that short circuits do not arise within the battery system during the switching processes.

In the above embodiments of Figs. 1, 2a, 2b and 3, the battery systems are disclosed as having a single terminal (i.e. the third terminal 110) which is connected to the plurality of battery cells at a location between the ends of the plurality of battery cells. However, these embodiments may be modified to include multiple terminals connected to the plurality of battery cells at locations between the first end and the second end of the plurality of battery cells. Thus, the intermediate terminals may split the plurality of battery cells into more than two subsets. In particular, a respective subset of the plurality of battery cells may be connected between each pair of adjacent terminals (including the first terminal 106, the second terminal 108 and the multiple intermediate terminals). The switching module 112 may then be configured so that the pair of terminals corresponding to each subset of battery cells can be selectively connected to the charging port 114, so that each subset of battery cells can be independently charged with a charging current from the charging port 114. For example, the arrangements of switches shown for battery systems 200 and 300 may be modified to enable charging of a larger number of subsets of battery cells. The controller 124 may be configured to alternate between charging of each of the subsets of battery cells, in a manner analogous to alternation between the first subset and the second subset discussed above. For example, the controller 124 may be configured to perform a charging sequence where it charges each of the multiple subsets of battery cells in turn for an amount of time, and to repeat the charging sequence until the plurality of battery cells is fully charged. Similarly to the discussion above, the controller 124 may be configured to control the switching module 112 so that the switching module does not stay in a given state for more than a predetermined amount of time (e.g. one minute). The controller 124 may adjust a duty cycle of the alternation between the multiple subsets (i.e. it may adjust a proportion of time spent in each of the states), e.g. to compensate for imbalances in charge levels between the subsets. Additionally, the controller 124 may adjust a period of the alternation between the multiple subsets (i.e. it may adjust a duration of a whole switching cycle), e.g. to minimise a temperature of the switches in the switching module.

Claims

CLAIMS1. A battery system for an electric vehicle, the battery system comprising: a plurality of battery cells; a first terminal, a second terminal, and a third terminal, wherein a first subset of the plurality of battery cells is electrically connected between the first terminal and the third terminal, a second subset of the plurality of battery cells is electrically connected between the third terminal and the second terminal, and the first subset and the second subset of the plurality of battery cells are electrically connected in series; a charging port configured to receive a charging current; and a switching module configured to selectively connect the charging port to two of the first terminal, the second terminal, and the third terminal.
2. A battery system according to claim 1, further comprising a first discharge terminal electrically connected to the first terminal and a second discharge terminal electrically connected to the second terminal, wherein the first discharge terminal and the second discharge terminal are configured to convey a discharging current from the plurality of battery cells to a drive system of the electric vehicle, and wherein the first discharge terminal and the second discharge terminal are arranged such that the discharging current does not pass through the switching module.
3. A battery system according to claim 1 or 2, wherein the switching module is configured to switch between a first state in which the first terminal and the third terminal are electrically connected to the charging port, and a second state in which the second terminal and the third terminal are electrically connected to the charging port.
4. A battery system according to claim 3, further comprising a controller configured to control switching of the switching module between the first state and the second state.
5. A battery system according to claim 4, wherein, when the charging port is connected to an external power source, the controller is configured to control charging of the plurality of battery cells by controlling the switching module to alternate over time between the first state and the second state.
6. A battery system according to claim 5, wherein the controller is configured to control the switching module to alternate between the first state and the second state at regular time intervals.
7. A battery system according to claim 5 or 6, wherein the controller is configured to control the switching module to alternate between the first state and the second state such that the switching module does not remain in the first state or the second state for more than one minute at a time.
8. A battery system according to one of claims 5 to 7, wherein the controller is configured to control a duty cycle of the alternation between the first state and the second state based on a difference between a first voltage and a second voltage, the first voltage corresponding to a voltage between the first terminal and the third terminal, and the second voltage corresponding to a voltage between the third terminal and the second terminal.
9. A battery system according to claim 8 wherein: if the first voltage is greater than the second voltage by a predetermined amount, the controller is configured to adjust the duty cycle to decrease a proportion of time spent by the switching module in the first state and increase a proportion of time spent by the switching module in the second state; and if the second voltage is greater than the first voltage by the predetermined amount, the controller is configured to adjust the duty cycle to increase the proportion of time spent by the switching module in the first state and decrease the proportion of time spent by the switching module in the second state.
10. A battery system according to one of claims 5 to 9, wherein the controller is configured to control a period of the alternation between the first state and the second state based on a temperature of the switching module.
11. A battery system according to one of claims 3 to 10, wherein the switching module is configured to switch between the first state and the second state in less than one second.
12. A battery system according to claim 11, wherein the switching module comprises two or more switches, the two or more switches being solid state switches.
13. A battery system according to any preceding claim, further comprising a first contactor switch connected between the first subset of battery cells and the first terminal, and a second contactor switch connected between the second subset of battery cells and the second terminal.
14. A battery system according to any preceding claim, wherein, when the plurality of battery cells is fully charged, a first voltage between the first terminal and the third terminal is equal to a second voltage between the third terminal and the second terminal.
15. A battery system according to any preceding claim, further comprising a balancing circuit configured to equalise a first voltage between the first terminal and the third terminal and a second voltage between the third terminal and the second terminal.
16. An electric vehicle comprising a battery system according to any preceding claim, wherein the plurality of battery cells is electrically connected to a drive system of the vehicle to power the drive system.
17. A method of operating a battery system according to one of claims 1 to 15, the method cornprising: receiving, at the charging port, power from an external power source; and operating the switching module to alternate over time between a first state in which the first terminal and the third terminal are electrically connected to the charging port and a second state in which the second terminal and the third terminal are electrically connected to the charging port, such that the first subset of the plurality of battery cells is charged when the switching module is in the first state, and the second subset of the plurality of battery cells is charged when the switching module is in the second state.
18. A method according to claim 17, comprising operating the switching module to alternate between the first state and the second state at regular time intervals.
19. A method according to claim 17 or 18, wherein the switching module is alternated between the first state and the second state such that the switching module does not remain in the first state or the second state for more than one minute at a time.
20. A method according to one of claims 17 to 19, further comprising controlling a duty cycle of the alternation between the first state and the second state based on a difference between a first voltage and a second voltage, the first voltage corresponding to a voltage between the first terminal and the third terminal, and the second voltage corresponding to a voltage between the third terminal and the second terminal.
21. A method according to claim 20, wherein: if the first voltage is greater than the second voltage by a predetermined amount, a proportion of the duty cycle corresponding to the first state is decreased and a proportion of the duty cycle corresponding to the second state is increased; and if the second voltage is greater than the first voltage by the predetermined amount, the proportion of the duty cycle corresponding to the first state is increased and the proportion of the duty cycle corresponding to the second state is decreased.
22. A method according to one of claims 17 to 21, further comprising controlling a period of the alternation between the first state and the second state based on a temperature of the switching module.