AU2015100550B4

AU2015100550B4 - Power management for an electric drive system

Info

Publication number: AU2015100550B4
Application number: AU2015100550A
Authority: AU
Inventors: Abdol Reza Vatandoust
Original assignee: Power Management Tech Pty Ltd
Current assignee: POWER MANAGEMENT TECHNOLOGIES Pty Ltd
Priority date: 2014-11-28
Filing date: 2015-04-23
Publication date: 2015-06-25
Anticipated expiration: 2022-11-28
Also published as: AU2014268249B1; WO2016081988A1; AU2015100550A4

Description

POWER MANAGEMENT FOR AN ELECTRIC DRIVE SYSTEM Field of the Invention [001]The present invention relates to a power management system and in particular to a power management in the context of an electric vehicle. [002] The invention has been developed primarily for use with electric road vehicles and will be described hereinafter with reference to this application. However, it will be appreciated that the invention is not limited to this particular field of use. Background of the Invention [003] For reasons of cost-efficiency and environmental concerns, there is a constant desire to promote and adopt fully electrically powered vehicles. However, fully electrically powered vehicles have failed to prove commercially popular. The main issue centres around the limited range, in terms of distance, an electric vehicle can offer. [004] Electric vehicles use rechargeable batteries which power electric motors for propulsion. The practical issue is that, currently, most commercially viable rechargeable batteries can only store a limited amount of sufficient energy for powering the motor before requiring a recharge. [005] A number of modern commercially available electric vehicles are able to offer approximately 150-200km range on a fully charged battery. However, the recharging time can be 6-8 hours to fully recharge the battery. [006] Unfortunately, the infrastructure for providing convenient public recharging stations has yet to grow. Consequently, electric vehicle drivers tend to only rely on the fact that the capability for recharging is at home. This has brought so-called 'range anxiety' to electric car drivers that worry about how far they have travelled from home and whether there is sufficient charge for the return journey. [007] It is apparent that much of the concerns about electric vehicles would be overcome if the distance driving range between recharging could be improved.

[008] It is to be understood that, if any prior art information is referred to herein, such reference does not constitute an admission that the information forms part of the common general knowledge in the art, in Australia or any other country. Summary of the Invention [009] An object of the claimed invention is to provide a power system for an electric vehicle which will overcome or substantially ameliorate at least some of the deficiencies of the prior art, or to at least provide an alternative. [0010] According to a first aspect of the present invention there is provided a power system for an electric vehicle, comprising: [0011] an electric motor arranged to provide driving mechanical output for moving the vehicle; [0012] an electric generator arranged to convert mechanical energy, due to movement of the vehicle, into electrical energy; [0013] a first and a second rechargeable electrical power storage device, wherein said first and second rechargeable electrical power storage devices are electrically isolated from one another, wherein said first and second rechargeable electrical power storage devices are deep cycle battery devices; [0014] a third rechargeable electrical power storage device, wherein said third rechargeable electrical power storage device is electrically isolated from said first and second rechargeable electrical power storage devices, wherein said third rechargeable electrical power storage device is a high discharge battery device; [0015] a controller arranged to determine the load demand of the motor; wherein, when the load demand is less than a predetermined amount, the controller is arranged to selectively connect one of the first and second rechargeable electrical power storage device with the electric motor in order to power the motor, and selectively connect the other of the first and second electrical power storage device with the generator to receive charging; wherein when the load demand is equal to or greater than the predetermined amount, the controller is arranged to connect the third rechargeable electrical power storage device with the electric motor in order to power the motor.

[0016] Preferably, when the load demand is less than the predetermined amount, the controller connects the first rechargeable electrical power source device with the electric motor to power the motor, wherein, when the charge level of the first rechargeable electrical power source device is at or below a predetermined charge level, the controller disconnects the first rechargeable electrical power source from the motor, connects the first rechargeable electrical power source with the generator to receive charge and connects the second rechargeable power source with the electric motor to power the motor; wherein, when the charge level of the second rechargeable electrical power source device is at or below the predetermined charge level, the controller disconnects the second rechargeable electrical power source from the motor, disconnects the first rechargeable power source device from the generator, connects the second rechargeable electrical power source with the generator to receive charge and connects the first rechargeable power source with the electric motor to power the motor; wherein the controller continues to repeat the process of selectively connecting and disconnecting the first and second rechargeable power source devices between the motor and generator until the charge levels in both the first and second rechargeable electrical power source are at or below the predetermined charge level. [0017] Preferably, the controller is prevented from connecting a rechargeable electrical power source to the generator when the charge level in the rechargeable electrical power source is at maximum capacity. When the generator is not connected to a rechargeable electrical power source device, the controller can connect the generator to an alternative electrical load, such as a climate control system for the vehicle. [0018] Preferably, the deep cycle battery device can be a battery pack of multiple series connected batteries or a Lithium-Ion battery. [0019] Preferably, the controller may selectively connect the third rechargeable electrical power source device to the generator to receive charging when one of the first and second rechargeable electrical power source device is connected to the motor and the other of the first and second rechargeable electrical power source device is at maximum capacity charge level. [0020] Preferably, the electric motor is an in-wheel motor arranged with a first wheel of the vehicle and the electric generator is an in-wheel motor-generator arranged with a second wheel of the vehicle. The first wheel may have a larger diameter than said second wheel. A second in-wheel motor-generator may be arranged with a third wheel of the vehicle. [0021] Preferably, the system includes an additional generator for generating additional charging energy, such as a solar system. [0022] According to further aspects of the invention there is provided a controller and a method controlling the power system. [0023] Other aspects of the invention are also disclosed. Brief Description of the Drawings [0024] Notwithstanding any other forms which may fall within the scope of the present invention, a preferred embodiment / preferred embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which: Fig. 1 is a block diagram of a power system in accordance with a preferred embodiment of the present invention; Fig. 2 illustrates a controller and connections in accordance with another preferred embodiment of the present invention; Fig. 3 illustrates a logic diagram for use by the controller; and Fig. 4 shows an electric vehicle in accordance with a preferred embodiment of the present invention; Description of Embodiments [0025] It should be noted in the following description that like or the same reference numerals in different embodiments denote the same or similar features. [0026] The disclosure relates to a power system for an electric vehicle, see Figs 1 and 2. The electric vehicle illustrated is a three-wheel vehicle, see Fig. 4. The rear wheel 25 of the vehicle has an imbedded in-wheel motor 20, which in the present embodiment represents a dedicated drive motor for the vehicle. In other words, it is this drive motor 20 which is used to provide the mechanical energy to propel the vehicle.

[0027] Each of the front wheels 85 also have imbedded in-wheel motors 80. However, these motors 80 are configured to act as dedicated generators. In other words, these generators 80 convert the rotation of the respective wheel into electrical energy. Potentially, only one of the front wheels 85 could have an imbedded motor. Clearly, in alternative embodiments in which there is a two wheel vehicle, it would only be possible to have one in-wheel generator. [0028] Practical experiments have been conducted using the in-wheel motor taken from a Vmoto e-max 11 OS scooter, which is a 48V, 4kW permanent magnet 3-phase AC motor. [0029] Practical experiments have been conducted using the same, albeit modified, motor for the dedicated generators 80. The modifications employed a re-wiring of the motor to increase the windings in order to maximize generated electricity at low rpm. In should be noted that the front wheels 85 are of smaller diameter (about 75%) compared with the rear wheel 25, hence the rpm of the front wheels 85 are greater than the rpm of the rear wheel 25. This again, is intended to maximize generated output by maximizing rpm of the generating wheels for a given vehicle speed. [0030] The power system also includes two deep cycle rechargeable power storage devices 50, 60 which are isolated from one another. As will be described, these devices 50, 60 are predominantly employed to power the drive motor 20 under normal driving conditions, i.e. when current load requirements are below a certain threshold, such as less than 40A. Each device 50, 60 is a battery pack of series connected Lithium-ion batteries which offer 48V, 56AH. It will be appreciated that each device 50, 60 could be a single large Lithium-Ion battery or conceivably be a suitable supercapacitor. [0031] The power system further includes a high discharge rechargeable power source device 40, which is also isolated from the other devices 50, 60. As will be described, this device 40 is employed for when current load requirements are above the optimum threshold for the deep cycle devices 50, 60, such as greater than 40A. In practice, the driving motor 20 will require these excessive currents for short periods during vehicle take-off. [0032] In operation, the driving motor 20 receives input electrical power from only one of the devices 40, 50, 60 at any one time. The selection of which device powers the motor 20 at any given time is selected by a controller 10. It will be appreciated that the DC output of the selected device requires conversion into a 3-phase AC current for input into the motor 20 which is done by a suitable inverter 100. [0033] As the vehicle moves, the resultant rotation of the front wheels 85 causes the generators 80 to generate electricity. In practice, useful generation begins when the vehicle reaches speeds of approximately 10km/h and above. Relevant to the present invention, the generated electricity can be used to recharge any power storage device 40, 50, 60 which is not connected to the motor 20. It will be appreciated that, in order to do so, the 3-phase AC current generated output from the generators 80 needs to be converted into DC current, which is done by a suitable rectifier 90. [0034] An important aspect of the power system is the controlled and selective switching of the power storage devices 40, 50, 60 and the motor 20 and generators 80. A controller 10 operates switches, ideally in the form of contactors, under instruction from a processor which monitors various system parameters and determines suitable connections between system components in accordance with the parameters. [0035] The main parameters under consideration are the current load requirements requiring electrical power and the current charge levels of the various power storage devices 40, 50, 60. [0036] While the vehicle is operating under normal driving conditions, the driving motor's 20 electric power is provided by a first one of the deep cycle rechargeable power storage devices 50 while the second other deep cycle rechargeable power storage device 60 can be recharged by output from the generators 80. When the charge level of the first device 50 is depleted to a predetermined level, the controller 10 causes a switching between the devices so that the second device 60 powers the motor 20 while the first device 50 is recharged by the generators 80. When the charge level of the second device 60 is depleted to the predetermined level the controller 10 switches between the devices again. The switching between devices is able to continue until the charge level in both devices 50, 60 is at the predetermined level. [0037] In a preferred embodiment, the predetermined level is set at 70% of full charge capacity. It is understood that this represents an optimum level of depletion for Lithium-lon batteries before recharging, which will prolong the life cycle of the batteries. Using 70% discharge in Lithium ion deep cycle batteries in currently commercially available batteries achieves 8000 cycles rather then 1600 cycles only at full discharge.

It will be appreciated that a different predetermined level can be selected and, in fact, may be suitable for different types of power storage devices. In fact, the controller can be provided with a user input interface 110 which would allow a user to select and set the predetermined level. [0038] When both devices 50, 60 are depleted to the 70% charge level, the devices 50, 60 require recharging from an external power source, for example a charging station. [0039] It will be appreciated that by switching the motor powering responsibility between the devices 50, 60 and continually recharging the non-powering device, the time required between external charging is extended and, hence, the driving range of the vehicle is increased. [0040] In practice, it was found that the addition of in-wheel generators 80 did have a negative impact upon the top speed of the vehicle. The in-wheel motor employed normally provides a top speed of around 45km/h; however, with the generators 80 in the front wheels 85 the vehicle's top speed was found to be reduced to around 42km/h. Nevertheless, the driving range was found to be increased by almost four times. Consequently, the trade-off between increased range and reduced speed appear acceptable. [0041] An example logic diagram for the controller's switching is shown in Fig. 3. As shown, when the controller 10 determines that the current load requirements for the motor 20 exceed a selected threshold, the high discharge power source device 40 is employed to power the motor 20. When the current load requirements fall back down to this threshold, the controller 10 switches to one of the deep cycle power storage devices 50, 60 for powering the motor 20. [0042] While the high discharge device 40 is powering the motor 20, the logic dictates how the controller 10 causes the generator 80 output to be directed. As shown, the controller 10 normally directs generated power for recharging the deep cycle device 50, 60 having the lowest charge level. In the case that the charge levels are the same, the controller 10 is biased towards recharging one of the devices 50, 60 before the other. In the case that both devices 50, 60 are actually fully charged (which occurs, for example, when the vehicle initially operates after an external recharge) the generated power can be directed to an alternative electrical load 70. In preferred embodiments this alternative load could be a climate control system 70 for the vehicle, e.g. an air conditioner or heater. [0043] When the current load requirements fall below the threshold, the controller 10 switches to one of the deep cycle devices 50, 60 for powering the motor 20 until the charge level of the loaded device falls to 70% when the loaded device is switched to recharging and the other device is switched to load. As shown, the controller 10 normally directs generated power to the unloaded deep cycle device. However, if the unloaded deep cycle device is actually fully charged, then the controller can switch the high discharge device 40 to receive the charge. If both the unloaded deep cycle device and the high discharge device are fully charged then the generated power can be directed to the alternative electrical load 70. [0044] As shown a capacitor 30 should be connected with the motor 20 to maintain power to the motor 20 during switching transition. [0045] The power system can be enhanced by providing an additional generating source, such as a solar system 150 or wind turbine, thereby increasing the potential recharging capabilities. [0046] It will be appreciated that the controller can cause a switching of the three phase inputs to the motor 20 in order to cause the motor to operate in reverse and, hence, reverse the electric vehicle. [0047] Further improvements could be provided by allowing the controller 10 to switch the motor 20 into a generator during periods in which the vehicle is moving but no driving power is required, for example during braking, slowing down or driving downhill. It will be appreciated that the controller 10 would need to switch the generating output of the motor 20 via a suitable rectifier to convert to DC. [0048] Potentially, the controller 10 could facilitate the switching of the in-wheel generators 80 into additional driving motors to provide an all-wheel drive option for the vehicle in case of emergency power requirements or hard surfaces. Obviously, it would be undesirable to maintain this option for prolonged periods as it removes the recharging capability and would deplete the batteries quickly. [0049] It will be appreciated that in bigger vehicles, such as trucks or trains, a bigger power system would be required to handle potentially more in-wheel motors and generators and more batteries. To handle this, more than one controller would be required. Consequently, as shown, the controller can be provided with suitable dip switches 120 and communication ports 130, for example RJ45 connections, to link multiple controllers together to control expanded systems. [0050] The processes and logic flows described in this specification can be performed by one or more programmable processors executing one or more computer programs to perform functions by operating on input data and generating output thereby tying the process to a particular machine (e.g., a machine programmed to perform the processes described herein). The processes and logic flows can also be performed by, and apparatus can also be implemented as, special purpose logic circuitry, e.g., an FPGA (field programmable gate array) or an ASIC (application specific integrated circuit). [0051] Computer readable media suitable for storing computer program instructions and data include all forms of non-volatile memory, media and memory devices. The processor and the memory can be supplemented by, or incorporated in, special purpose logic circuitry. [0052] Although this disclosure makes reference to electric vehicles, which include but is not limited to, cars, motorcycles, tractor trailers, tractors of all sizes, trains, buses, boats, airplanes, and golfcarts, this disclosure is not intended to be limited to electric vehicles. Interpretation [0053] Processes: [0054] Unless specifically stated otherwise, as apparent from the following discussions, it is appreciated that throughout the specification discussions utilizing terms such as "processing", "computing", "calculating", "determining", "analysing" or the like, refer to the action and/or processes of a computer or computing system, or similar electronic computing device, that manipulate and/or transform data represented as physical, such as electronic, quantities into other data similarly represented as physical quantities. [0055] Processor: [0056] In a similar manner, the term "processor" may refer to any device or portion of a device that processes electronic data, e.g., from registers and/or memory to transform that electronic data into other electronic data that, e.g., may be stored in registers and/or memory. A "computer" or a "computing device" or a "computing machine" or a "computing platform" may include one or more processors. [0057] The methodologies described herein are, in one embodiment, performable by one or more processors that accept computer-readable (also called machine-readable) code containing a set of instructions that when executed by one or more of the processors carry out at least one of the methods described herein. Any processor capable of executing a set of instructions (sequential or otherwise) that specify actions to be taken are included. Thus, one example is a typical processing system that includes one or more processors. The processing system further may include a memory subsystem including main RAM and/or a static RAM, and/or ROM. [0058] Computer-Readable Medium: [0059] Furthermore, a compUter-readable carrier medium may form, or be included in a computer program product. A computer program product can be stored on a computer usable carrier medium, the computer program product comprising a computer readable program means for causing a processor to perform a method as described herein. [0060] Implementation: [0061] It will be understood that the steps of methods discussed are performed in one embodiment by an appropriate processor (or processors) of a processing (i.e., computer) system executing instructions (computer-readable code) stored in storage. It will also be understood that the invention is not limited to any particular implementation or programming technique and that the invention may be implemented using any appropriate techniques for implementing the functionality described herein. The invention is not limited to any particular programming language or operating system. [0062] Means For Carrying out a Method or Function [0063] Furthermore, some of the embodiments are described herein as a method or combination of elements of a method that can be implemented by a processor of a processor device, computer system, or by other means of carrying out the function.

Thus, a processor with the necessary instructions for carrying out such a method or element of a method forms a means for carrying out the method or element of a method. Furthermore, an element described herein of an apparatus embodiment is an example of a means for carrying out the function performed by the element for the purpose of carrying out the invention. [0064] Connected [0065] Similarly, it is to be noticed that the term connected, when used in the claims, should not be interpreted as being limitative to direct connections only. Thus, the scope of the expression a device A connected to a device B should not be limited to devices or systems wherein an output of device A is directly connected to an input of device B. It means that there exists a path between an output of A and an input of B which may be a path including other devices or means. "Connected" may mean that two or more elements are either in direct physical or electrical contact, or that two or more elements are not in direct contact with each other but yet still co-operate or interact with each other. Embodiments: [0066] Reference throughout this specification to "one embodiment" or "an embodiment" means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases "in one embodiment" or "in an embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment, but may. Furthermore, the particular features, structures or characteristics may be combined in any suitable manner, as would be apparent to one of ordinary skill in the art from this disclosure, in one or more embodiments. [0067] Similarly it should be appreciated that in the above description of example embodiments of the invention, various features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of one or more of the various inventive aspects. This method of disclosure, however, is not to be interpreted as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects lie in less than all features of a single foregoing disclosed embodiment. Thus, the claims following the Detailed Description of Specific Embodiments are hereby expressly incorporated into this Detailed Description of Specific Embodiments, with each claim standing on its own as a separate embodiment of this invention. [0068] Furthermore, while some embodiments described herein include some but not other features included in other embodiments, combinations of features of different embodiments are meant to be within the scope of the invention, and form different embodiments, as would be understood by those in the art. For example, in the following claims, any of the claimed embodiments can be used in any combination. Different Instances of Objects [0069] As used herein, unless otherwise specified the use of the ordinal adjectives "first", "second", "third", etc., to describe a common object, merely indicate that different instances of like objects are being referred to, and are not intended to imply that the objects so described must be in a given sequence, either temporally, spatially, in ranking, or in any other manner. Specific Details [0070] In the description provided herein, numerous specific details are set forth. However, it is understood that embodiments of the invention may be practiced without these specific details. In other instances, well-known methods, structures and techniques have not been shown in detail in order not to obscure an understanding of this description. Terminology [0071] In describing the preferred embodiment of the invention illustrated in the drawings, specific terminology will be resorted to for the sake of clarity. However, the invention is not intended to be limited to the specific terms so selected, and it is to be understood that each specific term includes all technical equivalents which operate in a similar manner to accomplish a similar technical purpose. Terms such as "forward", "rearward", "radially", "peripherally", "upwardly", "downwardly", and the like are used as words of convenience to provide reference points and are not to be construed as limiting terms. Comprising and Including [0072] In the claims which follow and in the preceding description of the invention, except where the context requires otherwise due to express language or necessary implication, the word "comprise" or variations such as "comprises" or "comprising" are used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention. [0073] Any one of the terms: including or which includes or that includes as used herein is also an open term that also means including at least the elements/features that follow the term, but not excluding others. Thus, including is synonymous with and means comprising. Scope of Invention [0074] Thus, while there has been described what are believed to be the preferred embodiments of the invention, those skilled in the art will recognize that other and further modifications may be made thereto without departing from the spirit of the invention, and it is intended to claim all such changes and modifications as fall within the scope of the invention. For example, any formulas given above are merely representative of procedures that may be used. Functionality may be added or deleted from the block diagrams and operations may be interchanged among functional blocks. Steps may be added or deleted to methods described within the scope of the present invention. [0075] Although the invention has been described with reference to specific examples, it will be appreciated by those skilled in the art that the invention may be embodied in many other forms. Industrial Applicability [0076] It is apparent from the above, that the arrangements described are applicable to the electric vehicle industries.

Claims

1. A power system for an electric vehicle, comprising: an electric motor arranged to provide driving mechanical output for moving the vehicle; an electric generator arranged to convert mechanical energy, due to movement of the vehicle, into electrical energy; a first and a second rechargeable electrical power storage device, wherein said first and second rechargeable electrical power storage devices are electrically isolated from one another, wherein said first and second rechargeable electrical power storage devices are deep cycle battery devices; a third rechargeable electrical power storage device, wherein said third rechargeable electrical power source device is electrically isolated from said first and second rechargeable electrical power source devices, wherein said third rechargeable electrical power source device is a high discharge battery device; a controller arranged to determine the load demand of the motor; wherein, when the load demand is less than a predetermined amount, the controller is arranged to selectively connect one of the first and second rechargeable electrical power storage device with the electric motor in order to power the motor, and selectively connect the other of the first and second electrical power storage device with the generator to receive charging; wherein when the load demand is equal to or greater than the predetermined amount, the controller is arranged to connect the third rechargeable electrical power storage device with the electric motor in order to power the motor.

2. A power system for an electric vehicle according to claim 1, wherein, when the load demand is less than the predetermined amount, said controller connects the first rechargeable electrical power source device with the electric motor to power the motor, wherein, when the charge level of the first rechargeable electrical power source device is at or below a predetermined charge level, the controller disconnects the first rechargeable electrical power source from the motor, connects the first rechargeable electrical power source with the generator to receive charge and connects the second rechargeable power source with the electric motor to power the motor; wherein, when the charge level of the second rechargeable electrical power source device is at or below the predetermined charge level, the controller disconnects the second rechargeable electrical power source from the motor, disconnects the first rechargeable power source device from the generator, connects the second rechargeable electrical power source with the generator to receive charge and connects the first rechargeable power source with the electric motor to power the motor; wherein the controller continues to repeat the process of selectively connecting and disconnecting the first and second rechargeable power source devices between the motor and generator until the charge levels in both the first and second rechargeable electrical power source are at or below the predetermined charge level.

3. A controller for controlling a power system for an electric vehicle, the power system including an electric motor arranged to provide driving mechanical output for moving the vehicle, an electric generator arranged to convert mechanical energy, due to movement of the vehicle, into electrical energy, and a first, a second and a third rechargeable electrical power storage device, wherein said first, second and third rechargeable electrical power storage devices are electrically isolated from one another, wherein said first and second rechargeable electrical power storage devices are deep cycle battery devices and said third rechargeable electrical power storage device is a high discharge battery device; wherein the controller is programmed and arranged to determine the load demand of the motor; wherein, when the load demand is less than a predetermined amount, the controller is programmed and arranged to selectively connect one of the first and second rechargeable electrical power storage device with the electric motor in order to power the motor, and selectively connect the other of the first and second electrical power storage device with the generator to receive charging; wherein when the load demand is equal to or greater than the predetermined amount, the controller is arranged to connect the third rechargeable electrical power storage device with the electric motor in order to power the motor.

4. A controller according to claim 3, wherein, when the load demand is less than the predetermined amount, said controller connects the first rechargeable electrical power source device with the electric motor to power the motor, wherein, when the charge level of the first rechargeable electrical power source device is at or below a predetermined charge level, the controller disconnects the first rechargeable electrical power source from the motor, connects the first rechargeable electrical power source with the generator to receive charge and connects the second rechargeable power source with the electric motor to power the motor; wherein, when the charge level of the second rechargeable electrical power source device is at or below the predetermined charge level, the controller disconnects the second rechargeable electrical power source from the motor, disconnects the first rechargeable power source device from the generator, connects the second rechargeable electrical power source with the generator to receive charge and connects the first rechargeable power source with the electric motor to power the motor; wherein the controller continues to repeat the process of selectively connecting and disconnecting the first and second rechargeable power source devices between the motor and generator until the charge levels in both the first and second rechargeable electrical power source are at or below the predetermined charge level.

5. A method of controlling a power system for an electric vehicle, the power system including an electric motor arranged to provide driving mechanical output for moving the vehicle, an electric generator arranged to convert mechanical energy, due to movement of the vehicle, into electrical energy, and a first, a second and a third rechargeable electrical power storage device, wherein said first, second and third rechargeable electrical power storage devices are electrically isolated from one another, wherein said first and second rechargeable electrical power storage devices are deep cycle battery devices and said third rechargeable electrical power storage device is a high discharge battery device; the method comprising monitoring the load demand of the motor; when the load demand is less than a predetermined amount, selectively connecting one of the first and second rechargeable electrical power storage device with the electric motor in order to power the motor, and selectively connecting the other of the first and second electrical power storage device with the generator to receive charging; when the load demand is equal to or greater than the predetermined amount, the controller is arranged to connect the third rechargeable electrical power storage device with the electric motor in order to power the motor.