Control system for controlling charging of an energy storage device

Abstract

a control system 200 for controlling the charging of at least one energy storage device 130 of a vehicle using a power source 110 of the vehicle, the control system configured to receive an energy sto

Description

TECHNICAL FIELD The present disclosure relates to a control system for controlling charging of an energy storage device. Aspects of the invention relate to a control system for controlling the charging of at least one energy storage device of a vehicle using a power source of the vehicle, to a power system of a vehicle and to a method for controlling the charging of at least one energy storage device of a vehicle using a power source of the vehicle. BACKGROUND It is known to provide one or more loads in a vehicle, such as a battery electric vehicle (BEV), plug-in hybrid electrical vehicle (PHEV) or combustion vehicle. These loads may require high current draws at certain times. For example, the power assisted steering system of a vehicle requires high currents for short periods of time. Providing these currents from a primary or high voltage battery of the vehicle may be difficult, requiring up-rated conductors or safety systems. Instead, energy storage devices, such as capacitors, may be located close to the load. Charged in advance, these energy storage devices are capable of supplying high transient currents. To charge the energy storage device on vehicle startup, energy storage devices may be coupled to a power source of the vehicle, such as a battery or DC-DC converter. However, as the voltage across the energy storage device is initially low or zero, the energy storage device may draw a large current that exceeds one or more current ratings of the vehicle. In some situations, the current draw may be higher than the fused rating of a fusebox or trip current of an electronic power distribution system. It is an aim of the present invention to address one or more of the disadvantages associated with the prior art. SUMMARY OF THE INVENTION Aspects and embodiments of the invention relate to a control system for controlling the charging of at least one energy storage device of a vehicle using a power source of the vehicle, to a power system of a vehicle and to a method for controlling the charging of at least one energy storage device of a vehicle using a power source of the vehicle. According to an aspect of the invention there is provided a control system for controlling the charging of at least one energy storage device of a vehicle using a power source of the vehicle, the control system configured to: receive an energy storage device voltage signal indicative of a voltage across the at least one energy storage device; determine, in dependence on the energy storage device voltage signal, whether the voltage across the at least one energy storage device is at a steady state; output a switch control signal to at least one switch to connect the power source to the at least one energy storage device in accordance with a duty cycle, the duty cycle selected in dependence on whether the voltage across the at least one energy storage device has reached a steady state. According to an aspect of the invention there is provided a control system for controlling the charging of at least one energy storage device of a vehicle using a power source of the vehicle, the control system configured to: receive an energy storage device voltage signal indicative of a voltage across the at least one energy storage device; determine, in dependence on the energy storage device voltage signal, whether the voltage across the at least one energy storage device is at a steady state; determine, in dependence on whether the voltage across the at least one energy storage device is at the steady state, a duty cycle of a switch control signal supplied to at least one switch, the at least one switch coupling the at least one energy storage device to the power source; output the switch control signal to the at least one switch to connect the power source to the at least one energy storage device in accordance with the duty cycle. When charging an energy storage device, a surge current may be drawn. Coupling a power source to the energy storage device allows the charging of the energy storage device to be carefully controlled to ensure that the peak current drawn does not exceed safety ratings of the system or a current limit set by an electronic power distribution system. When the voltage across an energy storage device is low or zero a large peak current may be drawn. When the voltage across the energy storage device is high, reaches a steady state, or is substantially constant, the current drawn is low as the energy storage device is substantially fully charged. By changing the duty cycle of the switch control signal supplied to the at least one switch, in dependence on whether the voltage across the at least one energy storage device has reached a steady state, the system may operate in different modes in dependence on the possible current draw of the energy storage device. The duty cycle supplied to the switch controls the amount of time of each cycle that the power source is coupled to the energy storage device. This allows the control system to control and reduce the peak current drawn and charge the energy storage device without exceeding safety limits of the vehicle. The control system may comprise one or more processors collectively configured to perform the steps outlined. The one or more processors may comprise CPUs, microcontrollers, application specific integrated circuits (ASICs), or field programmable gate arrays (FPGAs). The control system may comprise analog circuitry, for example latches and comparators, configured to perform the outlined steps. The control system may comprise Boolean logic configured to perform the outlined steps. A steady state voltage may comprise a substantially constant voltage, or a voltage that only changes within a calibratable threshold range. For example, a steady state voltage may change only within a small percentage such as 0-10%, for example 10%, 5%, 2% or 1%, over a period of 1 ms-10ms, for example 2ms, 3ms, or 5ms. The duty cycle may vary in dependence on the voltage across the energy storage device. The duty cycle of the switch control signal may be lower when the voltage across the energy storage device has not reached a steady state, for example the duty cycle may be less than 90%, for example 75%, 60%, or 50%. The duty cycle may be selected so that the current drawn by the at least one energy storage device is below a current limit or trip limit of an electronic power distribution unit or fuseboard of the vehicle. The duty cycle of the switch control signal when the voltage across the at least one energy storage device has reached a steady state may be higher, for example substantially 100%. For example, a duty cycle of more than 90%, for example, 95%, 99% or 100%. As such, the switch control signal may be a DC signal or substantially constant when the voltage has reached a steady state. The duty cycle may be adaptively changed to optimise the total charging time of the energy storage device. For example, as the voltage across the at least one energy storage device increases, the control system may increase the duty cycle of the switch control signal. The duty cycle may increase such that the peak current drawn by the energy storage device does not exceed the current limit of an electronic power distribution unit or fusebox of the vehicle. This may be determined based on the characteristics of the system, such as the properties of the energy storage device, the conductors of the system, the electronic power distribution unit, and the power source amongst others. This allows the charging time of the energy storage device to be optimised. The energy storage device may be any suitable energy storage device. For example, the energy storage device may be a capacitor or battery configured to supply charge to any system within the vehicle which has a high current draw (with a high di / dt) that cannot be supplied by the primary battery of the vehicle. For example, the energy storage device may form part of an electric power assisted steering system. Alternatively, it may form part of an anti-lock braking (ABS) system or steering actuator such as a rear-wheel steering actuator. The one or more energy storage device may comprise a single energy storage device or a plurality of energy storage device coupled in parallel or series. The number of energy storage device and how they are coupled may be selected so that they are capable of providing a required amount of charge to an external system coupled to the energy storage device. The one or more energy storage device may also be referred to as an array or bank of energy storage devices, for example a capacitor array or capacitor bank. The power source may comprise a battery of the vehicle, for example the main or high voltage battery system of a battery electric or hybrid electric vehicle or a low voltage battery of a combustion vehicle. Alternatively, the power source may comprise a DC-DC converter or any other suitable power source. The switch acts to couple the power source to the one or more energy storage devices. The switch may be any suitable switching device, such as a transistor and in particular a field effect transistor. The switching device may be a MOSFET. The one or more switches may comprise one switch or a plurality of switches coupled in series or parallel depending on the current and voltage requirements of the system. When the voltage across the at least one energy storage device is at the steady state, the control system may be configured to select the duty cycle of the switch control signal to be substantially 100%. When the voltage across the energy storage device has reached the steady state, the current that will be drawn by the energy storage device from the power source will be significantly lower than when the voltage across the energy storage device is increasing. As such, the one or more switches may be turned on permanently, such that the control signal to the switches is a DC or constant signal. The switch control signal may have a 100% duty cycle, or have a duty cycle that is close to 100%, such as 99%, 98%, 95% etc. When the voltage across the at least one energy storage device is not at the steady state, the control system may be configured to select the duty cycle of the switch control signal to be less than 100%. Setting the duty cycle to be less than 100% reduces the peak current and average current drawn by the at least one energy storage device. This reduces the chances that the current drawn will increase beyond the level of a current limit of a fuse within the vehicle or electronic protection or distribution system of the vehicle. Once the steady state has been reached, the control system may monitor the voltage across the energy storage device. If the voltage across the at least one energy storage device falls, the method may be repeated by lowering the duty cycle and charging the at least one energy storage device until the steady state voltage has been reached. The method may be repeated when the energy storage device voltage signal has changed compared to the steady state voltage (at which the voltage across the energy storage device became substantially constant) by a hysteresis threshold, this prevents the method being repeated for minor changes in voltage that would not result in a large current being drawn by the energy storage device. When the voltage across the at least one storage capacitor is not at the steady state, the duty cycle of the switch control signal may be selected so that a peak current drawn by the at least one energy storage device from the power source is limited to a first current limit. The duty cycle may be set in dependence on a current limit of the system. The duty cycle of the switch control signal is related to the peak current drawn. The lower the duty cycle the lower the peak current drawn. As such, setting the duty cycle in dependence on the current limit ensures that the system does not exceed the peak current limit. The peak current limit may be a current limit or current that will trip an electronic protection system of the vehicle. The control system may be further configured to compare the voltage across the at least one energy storage device to a previous voltage across the at least one energy storage device, wherein if the voltage across the at least one energy storage device and the previous voltage across the at least one energy storage device are within a first margin of one another, then the voltage across the at least one energy storage device is at the steady state. Comparing the voltage across the at least one energy storage device to a previously received voltage across the at least one energy storage device allows the control system to determine whether there is a large difference in voltage. If there is not a large difference, such that the voltages are within a first margin of one another, then the voltage across the energy storage device may be considered to be at a steady state. Determining that the voltages are within a first margin of one another may comprise determining whether the voltages are substantially the same. The margin may be a fixed margin (for example in the case of a voltage difference) or a variable margin (for example a percentage margin). The margin may be any suitable voltage difference or percentage difference, for example 0.001v, 0.01 v, 0.1v or 1v. The previous voltage across the at least one storage capacitor may be an energy storage device voltage signal received prior to the currently received energy storage device voltage signal. For example, it may be a voltage signal received 1ms, 2ms, 3ms, 4ms or 5ms prior to the currently received capacitor voltage signal. The margin may be a percentage margin, e.g. 10%, 5%, 2%, 1%, or within a measurement accuracy of the voltage measurement equipment used to measure the voltage. The control system may be further configured to receive a power source voltage signal indicative of a voltage of the power source; and compare the power source voltage signal to the voltage across the at least one energy storage device, wherein if the voltage across the at least one energy storage device and the voltage of the power source are within a second margin of one another, then the voltage across the at least one energy storage device is at the steady state. As the energy storage device is charged by the power source, when the voltages are within a second margin of one another then the voltage across the energy storage device may be considered to be in a steady state, at least because the voltage across the energy storage device should not increase beyond that of the power source. Determining that the voltages are within a second margin of one another may comprise determining whether the voltages are substantially the same. The margin may be a fixed margin (for example in the case of a voltage difference) or a variable or calibratable margin (for example a percentage margin). The margin may be any suitable voltage difference or percentage difference, for example 0.001v, 0.01 v, 0.1v or 1v. The margin may be a percentage margin, e.g. 10%, 5%, 2%, 1%, or within a measurement accuracy of the voltage measurement equipment used to measure the voltage. Determining the steady state in this manner does not require the use of a previous power source voltage signal. Further, as the power source voltage may be measured for other operations (such as to determine power source state of charge or power source state of health), reusing the power source voltage signal may not require further measurement operations. The control system may be further configured to: periodically receive the energy storage device voltage signal; and periodically determine whether the voltage across the least one energy storage device is at the steady state. As the voltage across the at least one energy storage device rises over time, a periodic determination as to whether it has reached the steady state may be used. The periodic determination may take place every 1-10ms, for example, 2, 3 or 5ms. Alternatively, a continuous determination may be used. The control system may be configured to perform the periodic determination after every ten pulses of the switch control signal. The switch control signal controls the charging of the one or more energy storage device. By considering whether the voltage has reached a steady state after 10 pulses of the switch control signal have occurred, the system can periodically determine the voltage. If the determination was made more frequently, for example after only 1 -3 pulses, the voltage would not be provided with sufficient time or charge to rise significantly, whilst increasing the power usage of the control system. A pulse may be a rising or falling edge of the switch control signal or may be considered to refer to a period of the control signal. The control system may further be configured to continuously receive the energy storage device voltage signal; and continuously determine whether the voltage across the least one energy storage device is at the steady state. As the voltage across the at least one energy storage device rises over time, there may be a continuous determination as to whether it has reached the steady state. This ensures that the determination will be made as soon as possible after the steady state has been reached. The control system may be further configured to receive a second energy storage device voltage signal indicative of a voltage across at least one second energy storage device; determine, in dependence on the second energy storage device voltage signal, whether the voltage across the at least one second energy storage device is at the steady state; determine, in dependence on whether the voltage across the least one second energy storage device is at the steady state, a duty cycle of a second switch control signal supplied to at least one second switch, the at least one second switch coupling the at least one second energy storage device to the power source; output the second switch control signal to the at least one second switch to connect the power source to the at least one second energy storage device in accordance with the duty cycle to thereby charge the at least one second energy storage device. Systems with high current draw, such as power steering and anti-lock braking systems which utilise energy storage devices such as capacitor banks at their inputs may include redundant systems. As such, there may be more than one energy storage device with each coupled to a separate, identical, system. The second energy storage device may be charged after the first energy storage device has been charged to reduce total current draw. According to an aspect of the present invention, there is provided a power system of a vehicle, the power system comprising the control system; a power source; at least one energy storage device; at least one switch coupling the power source to the at least one energy storage device. The power system may further comprise an electric power assisted steering system, wherein a power input of the electric power assisted steering system is coupled to the at least one energy storage device. Instead of or in addition to the electric power assisted steering system any suitable system may be coupled to the at least one energy storage device, for example an ABS system or rear wheel steer actuator may be coupled to the at least one energy storage device. The power system may further comprise at least one second energy storage device; at least one second switch coupling the power source to the at least one second energy storage device; a redundant system, wherein a power input of the redundant system is coupled to the at least one second energy storage device. According to an aspect of the present invention, there is provided a vehicle comprising the control system or the power system. According to an aspect of the present invention, there is provided a method for controlling the charging of at least one energy storage device of a vehicle using a power source of the vehicle, the method comprising: receiving an energy storage device voltage signal indicative of a voltage across the at least one energy storage device; determining, in dependence on the energy storage device voltage signal, whether the voltage across the at least one energy storage device is at a steady state; determining, in dependence on whether the voltage across the at least one energy storage device is at the steady state, a duty cycle of a switch control signal supplied to at least one switch, the at least one switch coupling the at least one energy storage device to the power source; outputting a switch control signal to the switch to connect the power source to the at least one energy storage device in accordance with the duty cycle to thereby charge the at least one energy storage device. Computer readable instructions may be provided which, when executed by a computer, are arranged to perform the method. Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and / or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and / or features of any embodiment can be combined in any way and / or combination, unless such features are incompatible. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and / or incorporate any feature of any other claim although not originally claimed in that manner. BRIEF DESCRIPTION OF THE DRAWINGS One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows a schematic representation of a power system of a vehicle according to an embodiment of the present invention; Figure 2 shows a schematic representation of a power system of a vehicle according to an embodiment of the present invention, including a switchable connection between a power source energy storage device; Figure 3 shows a control system of a vehicle according to an embodiment of the present invention; Figure 4 shows a first flow chart showing operations performed by the control system of Figure 3 according to an embodiment of the present invention; Figure 5 shows a graph illustrating an embodiment of the present invention; Figure 6 shows a second flow chart showing operations performed by the control system of Figure 3 according to an embodiment of the present invention; Figure 7 shows a third flow chart showing operations performed by the control system of Figure 3 according to an embodiment of the present invention; Figure 8 shows a schematic representation of a power system of a vehicle according to an embodiment of the present invention, including the measurement of a power source voltage; Figure 9 shows a schematic representation of a power system of a vehicle according to an embodiment of the present invention, including a redundant system; Figure 10 shows a fourth flow chart showing operations performed by the control system of Figure 3 according to an embodiment of the present invention; Figure 11 shows an analog control system of a vehicle according to an embodiment of the present invention, including a memory means; Figure 12 shows an analog control system of a vehicle according to an embodiment of the present invention, including the measurement of a battery voltage; Figure 13 shows a fifth flow chart showing operations performed by the control system of Figure 3 to restart charging of the energy storage device; Figure 14 shows a vehicle according to an embodiment of the present invention. DETAILED DESCRIPTION The present disclosure relates to the charging of one or more energy storage devices using a power source of a vehicle, and to control schemes thereof. Vehicles may comprise one or more electrical loads which require high current draws at certain times. These current requirements may be transient current demands that last a limited time period. For example, a power assisted steering system of a vehicle may demand high current draw at start-up or when the steering wheel is turned. In some situations, the current demand of the power assisted steering system (or any other load within the vehicle) may exceed the capabilities of a power source or power supply, such as a high or low voltage battery, within the vehicle. As such, one or more energy storage devices may be located close to the load and configured to supply the transient current as required. The energy storage devices are charged in advance, such as on startup of the vehicle (and continuously as charge levels vary throughout vehicle operation). These energy storage devices may be capacitors, and thus may be referred to as energy storage capacitors (in that they store charge that may then be used later), however it should be understood that any suitable energy storage device may be used, such as a battery. The current drawn by the energy storage devices whilst charging is dependent on the voltage across the energy storage devices. When the voltage across the energy storage devices is low or zero, the current draw is very high when connected to a power source. As the voltage across the energy storage devices increases, the current drawn to charge it decreases. As such, on vehicle startup when the energy storage devices are discharged, a high current is drawn known as in-rush current when a power source is connected to the energy storage device or capacitor. So as to ensure that currents within the vehicle do not increase beyond certain limits, fuses may be used with set current ratings. In place of a fuse box, an electronic power distribution system comprising current monitoring circuitry and switches may instead be used. Similar to a fuse, an electronic power distribution system acts to monitor current draws and could disconnect their load supply when they exceed certain current levels or limits. As the initial current draw on startup to charge the one or more energy storage devices may exceed the current limit of the fuse or electronic power distribution system, the vehicle may never be able to charge the energy storage devices. This may prevent certain loads from operating correctly. Currents drawn to maintain the energy storage devices charge following startup are significantly lower than those on startup (as the voltage across the energy storage devices is unlikely to fall to zero, or the energy storage devices are unlikely to fully discharge). As such, it is desirable to maintain the lower current limit of the electronic power distribution system or fuse, whilst still allowing the charging of the energy storage devices and operation of high current draw loads. 7 Figure 1 shows a power system 100 of a vehicle. The power system comprises a power source 110. The power source 110 may be a battery, for example the main or high voltage battery system of a battery electric or hybrid electric vehicle or a low voltage battery of a combustion vehicle. Alternatively, the power source 110 may comprise a DC-DC converter or any other suitable power source. The power source 110 is coupled to an electronic power distribution system 120 or fuse box, which acts to determine whether the currents drawn by downstream loads from the battery 110 are below set current limits. If the currents exceed the limits, the electronic power distribution system 120 acts to trip, disconnect or cut off the connection between the power source 110 and the one or more downstream loads that draw the excessive currents. The electronic power distribution system 120 is coupled to at least one energy storage device 130 and is configured to charge the one or more energy storage devices 130. The one or more energy storage devices 130 may comprise any suitable energy storage device. For example, the one or more energy storage devices may comprise one or more energy storage capacitors configured to supply charge to any system within the vehicle which has a high current draw (with a high di / dt) that cannot be supplied solely by the power source 110 of the vehicle. The one or more energy storage devices 130 may comprise a single energy storage device or a plurality of energy storage devices coupled in parallel or series. The number of energy storage devices 130 and how they are coupled may be selected so that they are capable of providing a required amount of charge to a system or load coupled to the energy storage devices 130. The one or more energy storage devices 130 may also be referred to as a capacitor array or capacitor bank. Alternatively, the energy storage devices 130 may comprise one or more energy storage batteries, such as low voltage batteries of a vehicle. The one or more energy storage devices are coupled to a load 140. The load may be a power assisted steering system or any other load within the vehicle. The one or more energy storage devices 130 are configured to supply at least part of the current demand of the load 140. As noted, the current demand during startup charging of the one or more energy storage devices 130 may exceed the current limit of the electronic power distribution system 120, causing the energy storage devices 130 to never charge to an acceptable level. Figure 2 shows a power system 200 of a vehicle including a switchable connection between the power source 110 and the one or more energy storage devices 130. The power system 200 of Figure 2 includes a power source 110, electronic power distribution system 120, one or more energy storage devices 130 and a load 140 that are the same as those depicted and described with respect to Figure 1. The power system of Figure 2 further comprises at least one switch 220 coupled between the power source 110 and the one or more energy storage devices 130. The at least one switch 220 is controllable or configurable to selectively connect and disconnect the power source 110 and the one or more energy storage devices 130. The one or more switches 220 maybe any suitable switching device, such as a transistor and in particular a field effect transistor. For example, the switching device may be a MOSFET. The one or more switches 220 may comprise one switch or a plurality of switches coupled in series or parallel depending on the current and voltage requirements of the system. The at least one switch 220 is controlled by a control system 300. The control system is configured to receive an energy storage device voltage signal 365 indicative or representative of a voltage across the at least one energy storage device 130. The control system is configured to determine a switch control signal in dependence on the energy storage device voltage signal and output the switch control signal to the at least one switch to selectively connect and disconnect the power source 110 to the at least one energy storage device130. A control system 300 in accordance with an embodiment of the present invention is described herein with reference to the accompanying Figure 3. As shown in Figure 14, the control system is installed in a vehicle 1400. With reference to Figure 3, there is illustrated a control system 300 for a vehicle. The control system 300 comprises one or more controllers 310. The control system 300 is configured to receive energy storage device voltage signals 365 indicative of the voltage across the one or more energy storage devices 130 from a voltage sensor 360 and determine whether the voltage across the at least one energy storage device has reached a steady state. The control system 310 may then output a switch control signal 355 with a duty cycle determined in dependence on whether the at least one energy storage device 130 is at the steady state to control the charging of the at least one energy storage device 130. As will be described further, a steady state voltage may be a substantially constant voltage, or a voltage that only changes within a calibratable threshold range. The control system 300 as illustrated in Figure 3 comprises one controller 310, although it will be appreciated that this is merely illustrative and one or more controllers may be used. The controller 310 comprises processing means 320 and memory means 330. The processing means 320 may be one or more electronic processing devices 320 which operably execute computer-readable instructions. The memory means 330 may be one or more memory devices 330. The memory means 330 is electrically coupled to the processing means 320. The memory means 330 is configured to store instructions, and the processing means 320 is configured to access the memory means 330 and execute the instructions stored thereon. The controller 310 comprises an input means 340 and an output means 350. The input means 340 may comprise an electrical input 340 of the controller 310. The output means 350 may comprise an electrical output 350 of the controller 310. The input 340 is arranged to receive the energy storage device voltage signal 365 indicative of a voltage across one or more energy storage devices 130 from a voltage sensor or other suitable device 360. The energy storage device voltage signal 365 is an electrical signal. The output 350 is arranged to output a switch control signal 355 with a certain duty cycle for controlling the switching of the at least one switch 220. The input means 340 may additionally optionally receive a power source voltage signal 810 indicative of a voltage of the power source 110. Figure 4 illustrates a method 400 according to an embodiment of the present invention. The method 400 of Figure 4 may be performed by the control system 300 of Figure 3. The method 400 comprises receiving the energy storage device voltage signal 365 indicative of a voltage across the at least one energy storage device 130. Once the energy storage device voltage signal has been received, the method comprises determining 420, in dependence on the energy storage device voltage signal, whether the voltage across the at least one energy storage device is at a steady state. At step 430, the method comprises determining, in dependence on whether the voltage across the at least one energy storage device 130 is at the steady state, a duty cycle of a switch control signal 355 supplied to at least one switch 220, the at least one switch 220 coupling the at least one energy storage device 130 to the power source 110. Once the duty cycle of the switch control signal is determined, the method comprises outputting 440 the switch control signal to the at least one switch 220 to connect the power source 110 to the at least one energy storage device 130 in accordance with the duty cycle. The switch control signal 355 is supplied to a control terminal of the at least one switch 220. For example, where the at least one switch 220 comprises a field effect transistor, the switch control signal 355 is provided to the gate of the field effect transistor. The duty cycle of the switch control signal is the ratio of the time that the signal is at a first level compared to the time the signal is at a second level. For example, where the system is referenced to ground, the duty cycle may be the proportion of one period in which the switch control signal 355 is at a high voltage level relative to ground. The first and second voltage levels may vary depending on the type of switch used and the reference level of the system. Varying the duty cycle of the switch control signal 355 varies the proportion of each period in which the at least one switch 220 is turned on or turned off. A duty cycle of 0% represents a situation in which the at least one switch 220 is off for the whole period. A duty cycle of 100% represents a situation in which the at least one switch 220 is on for the whole period. As such, varying the duty cycle of the switch control signal between 0% and 100% results in a change in the proportion of each period in which the power source 110 is coupled to the at least one energy storage device 130. By varying the duty cycle of the switch control signal 355, the charging of the at least one energy storage device 130 is controlled. When the duty cycle is less than 100%, the total current drawn by the at least one energy storage device 130 is reduced compared to when the duty cycle is 100%. As such, by controlling the duty cycle to be less than 100%, the peak current drawn by the at least one energy storage device 130 is reduced. When the voltage across the at least energy storage device has reached a steady state, the current drawn by the at least one energy storage device 130 will be low relative to the current drawn when the voltage across the at least one energy storage device 130 is low or zero, as such the duty cycle maybe changed as the current limit of the electronic power distribution system 120 will not be exceeded. This allows the at least one energy storage devices 130 to be adaptively charged in a system with a current limit. As such, when the voltage across the at least one energy storage device 130 is at the steady state, the control system 300 is configured to select the duty cycle of the switch control signal to be substantially 100%. Put another way, the at least one switch 220 may be turned on permanently, such that the switch control signal 355 provided to the switches is a DC or constant signal. When the voltage across the at least one energy storage device 130 is not at the steady state, the control system 300 is configured to select the duty cycle of the switch control signal to be less than 100%. Setting a duty cycle of less than 100% reduces the chances that the current drawn by the at least one energy storage device 130 will increase beyond the level of a current limit of a fuse within the vehicle or electronic power protection or distribution system 120 of the vehicle. Controlling the duty cycle of the switch control signal allows the peak current draw to be reduced, allowing the system to operate with the electronic power distribution system, whilst allowing the at least one energy storage device 130 to be charged. Figure 5 shows a graph indicating the voltage 510 across the at least one energy storage device 130 and the voltage 520 of the switch control signal. The Y-axis 530 represents voltage and the X-axis 540 represents time. At a first time 550, the voltage 510 across the at least one energy storage device 130 is zero or low. The switch control signal 520 is selected to have a duty cycle less than 100%, whilst the voltage across the at least one energy storage device 130 increases. As the voltage 510 across the at least one energy storage device 130 increases, it reaches a steady state at time 560. The steady state voltage is indicative of a small or zero voltage difference or potential difference between the energy storage device 130 and the power source 110. As the potential difference is low, the drawn current is minimal. The adaptive duty cycle of the switch control signal 530 may then be modified such that the switch control signal has a higher duty cycle or a duty cycle of 100%. The duty cycle of switch control signal 355 when the voltage across the at least one energy storage device 130 is not at the steady state may be selected in dependence on a current limit of the electronic power protection or distribution system 120 of the vehicle, such that a peak current drawn by the at least one energy storage device 130 from the power source 110 is limited to a first current limit of the electronic power protection or distribution system 120 of the vehicle. As the voltage across the at least one energy storage device 130 increases, the potential difference between the power source 110 and the energy storage device 130 decreases. As such, the current drawn for the same duty cycle will decrease. This results in a current drawn to charge the energy storage device 130 between the turn on of the system and the steady state voltage being reached being an exponentially decreasing value for the same duty cycle. As such, the control system can adaptively change the duty cycle or pulse width modulation of the switch control signal 355 to optimise the total charging time of the energy storage devices 130. For example, as the voltage across the at least one energy storage device 130 increases, the control system may increase the duty cycle of the switch control signal 355. The duty cycle of the switch control signal 355 when the voltage across the energy storage device 130 has not reached a steady state may start at a set or initial level, for example 50% duty cycle. As the voltage across the energy storage device 130 increases, the duty cycle may be an adaptive duty cycle and increase. The duty cycle may increase such that the peak current drawn does not exceed the current limit of the electronic power distribution unit 120. This may be determined based on the characteristics of the system, such as the properties of the energy storage device 130, the conductors of the system, the electronic power distribution unit 120, amongst others. This allows the charging time of the energy storage device 130 to be optimised. The duty cycle may follow a pre-calibrated pattern or set routine stored in a memory 330 of the control system 300. Alternatively, the duty cycle may be changed in dependence on a current measurement of the current that is charging the energy storage device 130. The adaptive duty cycle of the switch control signal 355 when the voltage across the energy storage device 130 has not reached a steady state may further be chosen or adapt based on environmental conditions, such as the ambient temperature in which the vehicle is operating. Further, the adaptive duty may be modified in dependence on a health monitoring or other property of the power source 110, such that when the power source 110 is reaching the end of life, the duty cycle may be decreased to decrease the current drawn from the power source 110. The determination that the voltage across the at least one energy storage device 130 has reached a steady state may be performed in a number of different ways. A steady state voltage may be a substantially constant voltage or a constant voltage. A substantially constant voltage is a voltage that is substantially the same over multiple samples of the voltage or over a time period. The steady state may be determined within a measurement accuracy of a measurement device, such that the voltage is considered to have reached a steady state when the voltage does not change beyond the measurement accuracy of the measurement device. As there may be a ripple introduced into the system by, for example, the power source 110, the voltage across the at least one energy storage device may comprise a ripple or oscillation. The steady state voltage may comprise a calibratable threshold, such that the voltage across the at least one energy storage device 130 may ripple within the calibratable threshold and still be considered to be at a steady state. The calibratable threshold may be a set voltage, for example 0.1, 0.5,1 Volt or set at manufacture based on the tolerance of components within the system and the current that the power source 110 is capable of supplying. To determine whether the voltage has reached a steady state, a value of the voltage across the at least one energy storage device 130 may be compared to a previous voltage across the at least one energy storage device 130. Figure 6 shows a method 600 according to an embodiment of the present invention. The method 600 of Figure 6 may be performed by the control system 300 of Figure 3. The method involves a number of steps that are the same as those shown in the method 400 of Figure 4, including receiving a first energy storage device voltage signal in step 410. In addition, a second energy storage device voltage signal is received in step 610 indicative of a voltage across the at least one energy storage device 130 at a second time later than when the first energy storage device voltage signal is received in step 410. Determining in step 420 whether the voltage across the at least one energy storage device 130 is at a steady state may comprise determining whether the voltages are within a first margin or calibratable threshold of one another. If the voltages are within the first margin or calibratable threshold, then the voltage across the at least one energy storage device is considered to be at the steady state. The margin or calibratable threshold may be a fixed margin (for example in the case of a voltage difference) or a variable margin (for example a percentage margin). The margin may be any suitable voltage, for example 0.001 v, 0.01 v, 0.1v or 1 Volt. The margin may be a percentage margin, e.g. 10%, 5%, 2%, 1%, or within a measurement accuracy of the voltage measurement equipment used to measure the voltage. Determining that the voltages are within a first margin or calibratable threshold of one another may comprise determining whether the voltages are substantially the same. As the voltage measurements will be accurate to the measurement accuracy of a voltage sensor, the first energy storage device voltage signal and second energy storage device voltage signal may be compared. If the voltages are the same when taking into account measurement accuracy, then the voltage across the at least one energy storage device 130 is considered to be at the steady state. As described with respect to method 400, the duty cycle of the switch control signal may then be determined in step 430 and output to the at least one switch in step 440. As shown in Figure 5, the voltage across the at least one energy storage device increases over time. As such, the receipt of an energy storage device voltage signal and determination as to whether the voltage across the at least one energy storage device is at a steady state may occur periodically or continuously. In particular, the control system may periodically or continuously receive the energy storage device voltage signal and periodically or continuously determine whether the voltage across the least one energy storage device 130 is at the steady state by comparing the energy storage device voltage signal to a previous energy storage device voltage signal. After the switch control signal has been output to the at least one switch 220, the method may return 620 to step 610, receiving an updated energy storage device voltage signal and repeating the determination as to whether the voltage across the at least one energy storage device 130 has reached the steady state 420. The switch control signal that is output in step 440 has a period T. The receipt of the energy storage device voltage signal and / or determination whether the voltage across the least one energy storage device 130 is at a steady state may occur periodically after a number of periods T or pulses of the switch control signal. For example, the control system may be configured to perform the periodic determination after every ten pulses or periods of the switch control signal. As the switch control signal directly controls the charging of the at least one energy storage device, relating the periodic determination to a number of pulses of the switch control signal allows the at least one energy storage device 130 to charge, and thus the voltage to rise or settle, between determinations. The control system of Figure 3 may store previous values of the energy storage device voltage signal in memory means 330, allowing previous and present values of the energy storage device voltage signal to be compared. The control system of Figure 3 is a digital system, however an analog or logic-based control system may be used instead. Figure 11 is a control system 1100 including analog control means. The energy storage device voltage signal 365 may be received at input means 340 and provided to a comparator 1120. A previous value of the energy storage device voltage signal may be stored in memory means 1110, for example a sample and hold system or device. The comparator 1120 may act to determine whether the voltage across the one or more energy storage devices is at a steady state by determining whether the present energy storage device voltage signal and the stored previous energy storage device voltage signal are within the first margin or calibratable threshold of one another. In dependence on the determination, the output means 350 may determine the duty cycle of the switch control signal 355. A value of the voltage across the at least one energy storage device 130 may be compared to a power source voltage of the power source 110 of the vehicle. Figure 7 shows a method 700 according to an embodiment of the present invention. The method 700 of Figure 7 may be performed by the control system 300 of Figure 3. The method involves a number of steps that are the same as those shown in the method 400 of Figure 4, including receiving a first energy storage device voltage signal in step 410. In addition, at step 710, the method comprises receiving a power source voltage signal indicative or representative of a voltage across the power source 110. For example, where the power source is a battery, the power source voltage signal is indicative or representative of a voltage across the battery 110. Where the power source is a DC-DC converter, the power source voltage signal is indicative or representative of a voltage across the output of the DC-DC converter 110. As shown in Figure 8, the control system 300 may receive the power source voltage signal 810 directly from the power source 110 or from a voltage sensor (not shown) that is coupled to the output of the power source 110. Determining whether the voltage across the at least one energy storage device 130 is at a steady state comprises comparing (at step 720) the power source voltage signal to the voltage across the at least one energy storage device 130, wherein if the voltage across the at least one energy storage device 130 and the power source 110 voltage are substantially the same or are within a second margin or calibratable threshold of one another, then the voltage across the at least one energy storage device 130 is at the steady state. As the energy storage device 130 is charged by the power source 110, when the voltages are within a second margin of one another then the voltage across the energy storage device may be considered to be in a steady state, at least because the voltage across the energy storage device should not increase beyond that of the power source. As with the previously described first margin, the second margin may be a fixed margin (for example in the case of a voltage difference), a variable margin (for example a percentage margin) or a calibratable threshold. As such, there may be some variation in the voltages / the margin may be any suitable voltage difference, for example 0.001 v, 0.01v, 0.1vor 1 Volt The margin may be a percentage margin, e.g. 10%, 5%, 2%, 1%, or within a measurement accuracy of the voltage measurement equipment used to measure the voltage of the power source 110. The system may periodically or continuously determine whether the voltage across the at least one energy storage device 130 has reached the steady state, after the switch control signal is output in step 440, by periodically or continuously 730 receiving the energy storage device voltage signal in step 410 and power source voltage signal in step 710. In the same manner as when the steady state is determined by comparing the energy storage device voltage signal over time, the receipt of an energy storage device voltage signal and power source voltage signal and determination as to whether the voltage across the at least one energy storage device is at a steady state may occur periodically or continuously. The control system of Figure 3 may receive values of the power source voltage signal, allowing the energy storage device voltage signal to be compared to the power source voltage signal. The control system of Figure 3 is a digital system, however an analog or logic-based control system may be used instead. Figure 12 is a control system 1200 including analog control means. The energy storage device voltage signal 365 may be received at input means 340 and provided to a comparator 1120. A power source voltage signal may be received from the power source 110 and provided to the comparator 1120. The comparator 1120 may act to determine whether the voltage across the one or more energy storage devices 130 are at a steady state by determining whether the energy storage device voltage signal and the power source voltage signal are within the second margin of one another. In dependence on the determination, the output means 350 may determine the duty cycle of the switch control signal 355. Critical systems in a vehicle may include redundancy, such that two or more loads may be included in the vehicle, with each load performing the same function. Figure 9 is a schematic diagram showing the power system according to Figure 3 further supplemented with a redundant system, including redundant load 940. A single power source 110 and electronic power distribution system 120 are used to supply power to two systems - a first load 140 and a second load 940. The control system 300 acts to charge the at least one energy storage device 130 by controlling the switching of the at least one switch 220. At least one additional or second switch 920 and at least one additional or second energy storage device 930 are included, configured to act to provide transient currents to the second 13 load 940. Following charging of the at least one energy storage device 130, when the at least one energy storage device 130 has reached a steady state voltage, the second energy storage device 930 is charged. The control system 300 receives a second energy storage device voltage signal 965 indicative of a voltage across the second energy storage device 930 and outputs a second switch control signal 955 to the at least one second switch. Following the determination that the voltage across the at least one energy storage device 130 has reached a steady state, the control system 300 may proceed to perform the same operation by controlling the charging of the second energy storage device 920. Figure 10 is a flowchart of a method that may be performed by the control system 300. At step 1010, the method comprises determining whether the voltage across the at least one energy storage device 130 has reached a steady state. If the voltage across the at least one energy storage device 130 has reached a steady state, the method proceeds to step 1020, in which a second energy storage device voltage signal 965 indicative of a voltage across at least one second energy storage device 930 is received. In step 1030 the method comprises determining, in dependence on the second energy storage device voltage signal 965, whether the voltage across the at least one second energy storage device 930 is at the steady state. At step 1040 the method comprises determining, in dependence on whether the voltage across the least one second energy storage device 930 is at the steady state, a duty cycle of a second switch control signal 955 supplied to at least one second switch 920. At step 1050, the method comprises outputting the second switch control signal 955 to the at least one second switch 920 to connect the power source 110 to the at least one second energy storage device 930 in accordance with the duty cycle to thereby charge the at least one second energy storage device 930. Following the determination that the voltage across the at least one energy storage device 130 has reached a steady state, following any of methods 400, 600, 700 or 1000, the energy storage device 130 may act to supply charge to the coupled load 140. Supplying charge to the coupled load 140 may result in a discharge of the energy storage device 130. In some instances, recharging the energy storage device 130 may involve only a small current being drawn from the power source 110 that would not trip the electronic power distribution system 120. However, in some cases, the energy storage device may discharge to such an extent that the current drawn to recharge is above the trip or maximum limit of the electronic power distribution system 120. As such, following the charging of the at least one energy storage device, the control system 300 may monitor the voltage across the at least one energy storage device and modify the duty cycle of the switch control signal if the voltage drops below a hysteresis threshold compared to the steady state voltage. Figure 13 shows a method 1300 according to an embodiment of the present invention. The method 1300 of Figure 13 may be performed by the control system 300 of Figure 3. In step 1310 the method comprises receiving the energy storage device voltage signal 365 indicative of a voltage across the at least one energy storage device 130. Once the energy storage device voltage signal has been received, the method comprises determining in step 1320 whether the energy storage device voltage signal 365 has changed compared to the steady state voltage (at which the voltage across the energy storage device 130 became substantially constant) by a hysteresis threshold. The hysteresis threshold may be a set voltage threshold, for example 0.5v, 1 v, 2v, 2.5v, or 5Volts less than the steady state voltage or a percentage of the steady state voltage, such as 5%, 10%, 15%, 20%, or 25% of the steady state voltage. Alternatively, the hysteresis threshold may be calculated in dependence on the current drawn by the energy storage device, such that the hysteresis threshold is set at a level that would not cause a current to be drawn that would trip the electronic power distribution system 120. If the voltage across the energy storage device 130 is above the hysteresis threshold, the method may repeat steps 1310 and 1320 periodically or continuously. If the voltage across the energy storage device 130 is below the hysteresis threshold, the method moves to step 1330, and the system may repeat any of methods 400, 600, 700 or 1000 until the voltage across the energy storage device 130 reaches the steady state. Figure 14 illustrates a vehicle 1400 according to an embodiment of the present invention. The vehicle 1400 comprises a control system 300, 1100 or 1200 operable to control the charging of at least one energy storage device of a vehicle using a power source of the vehicle. The vehicle 1400 further comprises the power system 200. 5 The vehicle 1400 may be a mild hybrid electric vehicle (MHEV). An MHEV may be characterised by having the electric battery 110 that may be charged only by the internal combustion engine and regenerative braking. The vehicle 1400 may be a plug-in hybrid electric vehicle (PHEV). A PHEV may be characterised by being arranged to receive electrical energy from an external source, such as via a connection to mains electricity. A PHEV may therefore comprise an external electrical connection for charging the battery 110 in addition to a combustion engine. The vehicle 1400 may be a battery electric vehicle (BEV) in which the vehicle is driven solely by 10 electric motors and a battery 110, with no combustion engine. Vehicle 1400 may be an EGO vehicle, i.e., a vehicle that is equipped with autonomous or semi-autonomous driving technology and is capable of sensing and navigating its environment without direct input from a human driver. Vehicle 1400 may also be any vehicle having an Electronic Power Distribution System. It will be appreciated that various changes and modifications can be made to the present invention without departing from the scope 15 of the present application.

Claims

1. A control system for controlling the charging of at least one energy storage device of a vehicle using a power sourceof the vehicle, the control system configured to:receive an energy storage device voltage signal indicative of a voltage across the at least one energy storage device; determine, in dependence on the energy storage device voltage signal, whether the voltage across the at least one energy storage device is at a steady state;determine, in dependence on whether the voltage across the at least one energy storage device is at the steady state, a duty cycle of a switch control signal supplied to at least one switch, the at least one switch coupling the at least one energy storage device to the power source; andoutput the switch control signal to the at least one switch to connect the power source to the at least one energy storage device in accordance with the duty cycle.

2. The control system according to claim 1, wherein when the voltage across the at least one energy storage device isat the steady state, the control system is configured to select the duty cycle of the switch control signal to be substantially 100%.

3. The control system according to any preceding claim, wherein when the voltage across the at least one energy storagedevice is not at the steady state, the control system is configured to select the duty cycle of the switch control signal to be less than 100%.

4. The control system according to any preceding claim, wherein when the voltage across the at least one energy storagedevice is not at the steady state, the duty cycle of the switch control signal is selected so that a peak current drawn by the at least one energy storage device from the power source is limited to a first current limit.

5. The control system according to any of claims 1-4, wherein the control system is further configured to:compare the voltage across the at least one energy storage device to a previous voltage across the at least one energy storage device, wherein if the voltage across the at least one energy storage device and the previous voltage across the at least one energy storage device are within a first margin of one another, then the voltage across the at least one energy storage device is at the steady state.

6. The control system according to any of claims 1-4, wherein the control system is further configured to:receive a power source voltage signal indicative of a voltage of the power source; and compare the power source voltage signal to the voltage across the at least one energy storage device, wherein if the voltage across the at least one energy storage device and the voltage of the power source are within a second margin of one another, then the voltage across the at least one energy storage device is at the steady state.

7. The control system according to any of claims 1-4, wherein the control system is further configured to:periodically receive the energy storage device voltage signal; and periodically determine whether the voltage across the least one energy storage device is at the steady state.

8. The control system according to claim 7, wherein the control system is configured to perform the periodicdetermination after every ten pulses of the switch control signal.9.The control system according to any of claims 1-4, wherein the control system is further configured to: continuously receive the energy storage device voltage signal; and continuously determine whether the voltage across the least one energy storage device is at the steady state.

10. The control system according to any preceding claims, the control system is further configured to:receive a second energy storage device voltage signal indicative of a voltage across at least one second energy storage device;determine, in dependence on the second energy storage device voltage signal, whether the voltage across the at least one second energy storage device is at the steady state;determine, in dependence on whether the voltage across the least one second energy storage device is at the steady state, a duty cycle of a second switch control signal supplied to at least one second switch, the at least one second switch coupling the at least one second energy storage device to the power source; andoutput the second switch control signal to the at least one second switch to connect the power source to the at least one second energy storage device in accordance with the duty cycle to thereby charge the at least one second energy storage device.

11. A power system of a vehicle, the power system comprising:the control system according to any preceding claim;a power source;at least one energy storage device; andat least one switch coupling the power source to the at least one energy storage device.

12. The power system according to claim 11, further comprising:an electric power assisted steering system, wherein a power input of the electric power assisted steering system is coupled to the at least one energy storage device.

13. The power system according to claim 11 or claim 12, further comprising:at least one second energy storage device;at least one second switch coupling the power source to the at least one second energy storage device; anda redundant system, wherein a power input of the redundant system is coupled to the at least one second energy storage device.

14. A vehicle, the vehicle comprising the control system according to any of claims 1-10, or the power system accordingto any of claims 11-13.

15. A method for controlling the charging of at least one energy storage device of a vehicle using a power source of thevehicle, the method comprising:receiving an energy storage device voltage signal indicative of a voltage across the at least one energy storage device;determining, in dependence on the energy storage device voltage signal, whether the voltage across the at least one energy storage device is at a steady state;determining, in dependence on whether the voltage across the at least one energy storage device is at the steady state, a duty cycle of a switch control signal supplied to at least one switch, the at least one switch coupling the at least one energy storage device to the power source; andoutputting the switch control signal to the switch to connect the power source to the at least one energy storage device 5 in accordance with the duty cycle to thereby charge the at least one energy storage device.s

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