GB2586652A

GB2586652A - Electric vehicle charging system and methods

Info

Publication number: GB2586652A
Application number: GB1912577.2A
Authority: GB
Inventors: Freeling-Wilkinson Olivier
Original assignee: Urban Electric Networks Ltd
Current assignee: Urban Electric Networks Ltd
Priority date: 2019-09-02
Filing date: 2019-09-02
Publication date: 2021-03-03
Also published as: GB201912577D0

Abstract

A wireless vehicle charging system 10 comprises a base 14 for installation on or in the ground, a housing 22 defining a chamber, a wireless power transmitter 20 and a positioning means 18 within the chamber, and a controller, the controller being configured to control the positioning means to move the transmitter into alignment with a receiver on a vehicle to optimise battery charging. The wireless power transmitter may be moved in two dimensions in a horizontal plane above the base and/or in a vertical axis perpendicular to the base. The optimal position may be detected using an impedance or position sensor, and the positioning means may be motorised. The charging point may be in a parking area. Also disclosed is a method of charging a plurality of electric vehicles comprising a plurality of charging points (10, figure 4) arranged in a line and spaced apart by more than a vehicle length, each vehicle being positioned above a charging point, the positions of which are adjusted to optimise battery charging. When a vehicle leaves the remaining vehicles move forward, possibly autonomously, to a new charging point in the line, which may be a taxi rank or delivery depot.

Description

ELECTRIC VEHICLE CHARGING SYSTEM AND METHODS

The present invention relates to an electric vehicle charging system, and to methods of charging an electric vehicle or series of electric vehicles positioned over a vehicle charging system.

BACKGROUND TO THE INVENTION

Conventional road-going vehicles are powered by petrol and diesel. In recent years, electrically-powered vehicles have become more prevalent as part of a drive to reduce pollution and combat climate change. This includes hybrid vehicles which include a battery and conventional petrol or dies& engine to recharge the battery, as well as wholly electric vehicles which rely solely on battery power.

For an electric or hybrid car, a charging port may be provided at the side, where petrol or diesel would be received in a conventional car. Alternatively, the charging port may be provided at the front or rear of the car, concealed behind a vehicle badge or logo, for example. For an electric or hybrid bus, a pantograph-style charging means may be mounted to its roof, for example. The battery is usually located low down in the vehicle.

This is because it adds significant weight to the vehicle, and positioning the battery as low as possible improves vehicle handling.

To charge an electric vehicle, the user often needs to manually plug in a charging cable connected to a high power source. There are relatively few dedicated electric vehicle charging stations at present, so it is often necessary to charge an electric vehicle at home. Charging at home can take a lot of time if charging from a low power outlet. Since most commuters can charge their vehicles overnight, this does not tend to cause significant difficulty.

Charging fleets of electric vehicles in a commercial operation is more problematic.

Commercial operations may run 24 hours a day, 7 days a week, which means that it is vital to ensure the vehicles are kept charged as much as possible. However, electric vehicle charging stations are expensive to install, and it can take a considerable amount of time for an electric vehicle to reach full charge. Since an electric vehicle still has a relatively small range compared to a conventional vehicle, it is often preferable to charge the battery as fully as possible before the vehicle is dispatched for a delivery, for example, to maximise its range, at the expense of increased charging time. The user must remember to plug in the vehicle as soon as it has been returned to a depot to maximise charging time.

Wireless charging systems address some of these issues. However, wireless charging is less efficient than wired charging, and requires precise alignment of the vehicle with the charging unit. If the vehicle is not carefully positioned in precise alignment with the charging unit, the rate of charging is low and, when a driver next comes to use the vehicle, it will have been insufficiently recharged since its last trip. Even small misalignments cause large drops in charging efficiency.

Where the charging means is located under the vehicle, the driver must also guess whether it is aligned properly on the first attempt. It takes time to check on the alignment and if necessary re-position the vehicle to ensure effective recharging. The check is done by eye which can only lead to a rough assessment of the accuracy of the alignment. In some cases, a mobile phone app can be used to aid the driver in positioning the vehicle. Furthermore, if a neighbouring vehicle has been badly parked, this can have a knock-on effect on how precisely the driver can park over their charging unit.

Wireless charging systems are also susceptible to damage if a vehicle drives over them. For example, a rear wheel may run over the charger if the vehicle turns early when driving away from the charger, or when pulling in or reversing into position over the charger.

It is an object of the present invention to reduce or substantially obviate the aforementioned problems.

STATEMENT OF INVENTION

According to a first aspect of the present invention, there is provided a vehicle charging system for wirelessly charging an electric vehicle including a battery and a wireless power receiver, the system comprising a base for installation on or in the ground, a housing or cover which defines a chamber above the base, a moveable wireless power transmitter disposed in the chamber for charging the battery, positioning means configured to move the wireless power transmitter relative to the base within the chamber, and a controller configured to control the positioning means and in use align the wireless power transmitter with the wireless power receiver, for optimising battery charging.

Optional features are provided in the dependent claims.

This provides a charging system where the driver of an electric vehicle can pull into a bay and park without needing to spend time precisely aligning the vehicle with its charging pad. Instead the system detects that a vehicle has been parked overhead, with the wireless charge receiver coarsely aligned with the wireless power transmitter in the charging pad. The controller can then move the wireless power transmitter into precise alignment with the receiver, to optimise power transfer to the receiver and battery. This reduces charging time as well as the time and effort required to properly wirelessly charge an electric vehicle.

An electric vehicle is considered to be a vehicle which includes a battery for powering movement of the vehicle. The system may be suitable for charging a hybrid vehicle, particularly a plug-in hybrid electric vehicle (PHEV).

A wireless power transmitter and wireless power receiver are considered to be devices for respectively transmitting or receiving power or energy without the use of wires between those devices. It will of course be appreciated that power may be provided to each of the devices through wires, but transmission between the devices is wireless.

The transmitter may be considered to be self-aligning with respect to the receiver.

Coarse alignment may be considered as a first stage of inaccurate alignment of the receiver over the transmitter. This may include partial vertical overlap of the transmitter and receiver. Coarse alignment may include the situation where the transmitter and receiver are aligned well enough for power transfer to the battery, but at a significantly sub-optimal transfer rate or with significantly sub-optimal transfer efficiency.

Precise (or fine) alignment may be considered to be a second stage of more accurate alignment following initial coarse alignment. This may include substantially complete vertical overlap of the transmitter and receiver. Precise alignment may be considered to apply to any arrangement of transmitter and receiver which leads to better power transfer than from the initial coarse alignment In some cases, precise alignment may include the situation where the transmitter and receiver are aligned well enough for power transfer to the battery at an optimal or near-optimal transfer rate or with optimal or near-optimal transfer efficiency.

Known inductive charging apparatus may be used to provide some or all of the wireless power transfer arrangement, including the wireless power transmitter and/or receiver. For example, the transmitter and receiver may each include coils. The vehicle or receiver may include one or more rectifiers. A Hevo power transmitter may be used,

for example.

The transmitter may be arranged in a plane substantially parallel to the base.

The controller may be configured to detect or measure any one of: impedance between the transmitter and the wireless power receiver in the vehicle; rate of battery charging; and/or charging efficiency.

The controller may be configured to move the wireless power transmitter from its starting position to another position within the chamber in which there is one or more of: reduced impedance; a greater rate of charging; and/or a greater magnitude of charging efficiency.

At least one sensor may be connected to the controller for detecting relative positions of the wireless power transmitter and receiver. The sensor (or a second sensor) may be configured to detect or monitor one or more of: impedance between the wireless power transmitter and receiver; the rate of power transfer between the wireless power transmitter and receiver; a battery charge value; the rate of battery charging; whether a vehicle is positioned over the transmitter. The sensor may allow detection of the position of the wireless power receiver. The sensor may allow detection of the vehicle.

The positioning means may include a support for the wireless power transmitter. The support may include a motor or other drive means for moving the support. The support may include a frame. The support may include a motorised dual-axis platform or arrangement for the wireless power transmitter.

The positioning means may be configured to move the wireless power transmitter in at least two dimensions relative to the base. The positioning means may be configured to move the wireless power transmitter in at least a horizontal plane above the base.

The positioning means may be configured to move the wireless power transmitter along a vertical axis which is substantially perpendicular to the base. In use, this allows the vertical distance between the transmitter and receiver to be reduced to improve wireless charging. For example, the transmitter may be moved to (or towards) the underside of the top of the housing. A motorised arm or hydraulic piston may be used to effect motion along the z axis, for example.

A seal may be provided between the housing and the base. The housing and base may provide a waterproof enclosure around at least the wireless power transmitter and the positioning means.

The housing may be made of a toughened and/or composite material. This mitigates the likelihood of damage in the event that the housing is impacted, for example in the event that a vehicle drives over it.

One or more, or all, of the side walls of the housing may be sloped or slanted. This makes it easier for a vehicle wheel to roll over the housing, in the event of an impact. In some embodiments, an upper part of the housing may be substantially frustopyramidal in shape. Edges of the housing (or frustopyramidal portion) may be rounded. In particular, upward-facing edges of the housing may be rounded.

The housing may be removable and/or have an access hatch or opening in the top for allowing maintenance after installation. The hatch or opening may be sealable against the ingress of water.

The top of the housing may be a maximum of about 120 mm above the base. The top of the housing may be substantially planar. At that height, most vehicles should have sufficient ground clearance to drive over the housing.

The width of the housing may be less than a distance between an innermost pair of wheels of the vehicle. That is, less than the distance across the axle between a pair of wheels.

The length of the housing may be the same as the width of the housing. The housing may be longer than it is wide. The length of the housing may be up to about the same length as the vehicle. This means that a vehicle with a receiver at the front or rear underside can be parked either way round over the transmitter and the transmitter can still be moved into alignment with the receiver.

A power supply cable or wire may be connected to and extend from one side of the base. A guard or a protective sheath or strip may be provided over the cable.

Where multiple charging systems or pads are provided, for example in a depot, the power supply cables may be connected to a central supply point. This minimises the number of above-ground wires. Some or all of the bays or parking spaces in a depot may each include a charging system or pad.

The controller may be adapted to detect a wireless tag or other identifier in or on the vehicle. The controller may be adapted to tailor battery charging in accordance with information detected in that tag or identifier. For example, the charge capacity of a battery in one vehicle may differ from another vehicle. The characteristics of battery charging such as target charge value or (anticipated) charge time may need to be tailored accordingly. Charging may be restricted or prevented if a vehicle is parked in the wrong

area, for example.

One or more foreign object detection sensors / apparatus may be included in the system.

At least one inverter may be included within the housing. If the inverter is within the housing, the inverter may be mounted in a position below the transmitter. Alternatively, the inverter may be disposed in a region adjacent to the charging system. For example, the inverter(s) may be provided in a pavement or pillar adjacent to a piece of a road containing the charging system.

The inverter is preferably sealed within the housing. Where an inverter is included, the housing may need to be deeper than for an equivalent system where an inverter is not provided within the housing. The inverter may be mounted centrally. A pair of inverters may be mounted at or towards sides of the housing or base.

The charging system may installed on the surface of the ground, or may be installed as a subsurface charging system. If subsurface, then a marker or series of markers, such as one or more lines or bumps, may be provided above ground to indicate where the charging system is located (or where multiple systems are located).

According to a second aspect of the present invention, there is provided a parking area or depot for a plurality of electric vehicles, the parking area or depot comprising a plurality of electric vehicle charging systems each as presented in the first aspect of the 20 invention.

The parking area may include a plurality of vehicle parking bays (which may or may not be demarcated by lines). Each parking bay may include an electric vehicle charging system.

The charging systems may be connected to a common power supply, e.g. the mains.

According to a third aspect of the present invention, there is provided a method of wirelessly charging an electric vehicle including a battery and a wireless power receiver, using a vehicle charging system which includes a wireless power transmitter for charging the battery, positioning means configured to move the wireless power transmitter, and a controller configured to control the positioning means, the method comprising the steps of: a) providing the electric vehicle above the wireless power transmitter in a stationary position relative to the wireless power transmitter, such that the wireless power receiver is coarsely aligned with the wireless power transmitter; b) moving the wireless power transmitter into a different position for charging, such that the wireless power transmitter is precisely aligned with the wireless power receiver, the charging position having been determined or predicted by the controller to provide optimal charging.

The advantages are substantially similar to those for the first aspect of the invention.

Step (b) may involve comparing charging efficiency in at least two positions, and then positioning wireless power transmitter in the position which provides optimal or near-optimal charging efficiency. An iterative process may be used to arrive at an optimal position of the wireless power transmitter for charging. Impedance or other charging characteristics may be measured at a series of positions and the transmitter then moved to an optimal detected position or optimal calculated position.

The controller may be adapted to detect or measure impedance between the wireless power transmitter and the wireless power receiver.

The wireless power transmitter may be moved from an initial position in step (a) to a subsequent position of relatively lower impedance in step (b).

Step (b) may include measuring impedance in the initial position, comparing the measured impedance to a set of calibration values, and then moving the wireless power transmitter to another position based on the expected impedance value at that position. This may reduce the time taken to iteratively arrive at an optimal charging position (or avoid the need for iterations altogether).

According to a fourth aspect of the present invention, there is provided a method of wirelessly charging a plurality of electric vehicles using one or more electric vehicle charging systems, each electric vehicle including a battery and a wireless power receiver, and the vehicle charging system including a plurality of wireless power transmitters for charging the batteries, at least one positioning means configured to move the wireless power transmitters, and at least one controller configured to control the positioning means, the method comprising the steps of: a) providing the wireless power transmitters arranged substantially in a line, each wireless power transmitter being spaced from each neighbouring wireless power transmitters by substantially at least the length of one of the electric vehicles; b) providing the electric vehicles in charging positions in a queue above the wireless power transmitters, and aligning each wireless power transmitter with the corresponding wireless power receiver via the positioning means, to optimise charging; c) when one of the electric vehicles (preferably at one end of the line) vacates its wireless power transmitter, moving one, some or all of the remaining electric vehicles into new charging positions over a different one of the wireless power transmitters to continue charging, to vacate the wireless power transmitter at the end of the line for receiving a new electric vehicle.

Queuing vehicles can therefore charge effectively whilst periodically moving towards the front of the queue as vehicles at the front move away. For example, this could be used at a taxi rank, a bus station, a car rental agency, or a depot, or any other area in which traffic must queue or wait stationary for a period of time.

Note that the vehicle charging system may comprise a plurality of charging systems each as described for the first aspect of the invention; or the vehicle charging system may include a plurality of wireless power transmitters, with positioning means to move each transmitter, and a controller which controls the positioning means of each transmitter. That is, where the system is scaled up, it may not be necessary to use multiple controllers, or even multiple positioning means, in some cases.

Step (b) may include moving each wireless power transmitter into a different position for charging, such that each wireless power transmitter is precisely aligned with the corresponding wireless power receiver. The charging position may have been determined or predicted by the controller to provide optimal charging.

The vehicle charging system may be provided in or as part of a taxi rank. This allows a queue of taxis to charge most effectively, as taxis leave and join the queue.

The controller may be adapted to automatically initiate movement of one or more of the electric vehicles to new wireless power transmitter in step (c), after the end transmitter has been vacated. For example, if any of the electric vehicles are automated or self-driving, then the vehicles can automatically roll forward when a lead vehicle has pulled away from the frontmost charging pad.

The system may be adapted to signal to the lead vehicle when it is fully charged. This allows the vehicle to vacate space for a new vehicle to begin charging.

The method may be performed using a series of electric vehicle charging systems each as presented in the first aspect of the invention.

Any feature or features presented with respect to one aspect of the present invention may be provided in any other aspect of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention, and to show more clearly how it may be carried into effect, reference will now be made by way of example only to the accompanying drawings, in which: Figure 1 shows a perspective view of an embodiment of an electric vehicle charging system in the form of a charging pad, and an electric vehicle parked in a charging position over the pad; Figure 2 shows an exploded perspective view of the electric vehicle charging system of Figure 1; Figure 3 shows an overhead view of the electric vehicle charging system of Figure 1, without a cover, and with a wireless power transmitter in first and second positions; Figure 4 shows a plan view schematic of a first embodiment of an installation of the electric vehicle charging system of Figure 1; and Figure 5 shows a plan view schematic of a second embodiment of an installation of the electric vehicle charging system of Figure 1.

DESCRIPTION OF PREFERRED EMBODIMENTS

An electric vehicle charging system (or pad), for wirelessly charging or recharging an electric vehicle, is indicated generally at 10 in Figure 1. A power supply cable 12 is connected to the pad. The pad 10 is installed on the ground in this embodiment. The pad 10 is approximately 100mm in height in this embodiment, although it is envisaged that the pad may be higher or lower in other embodiments.

An electric vehicle is indicated generally at 100, parked over the pad 10. The electric vehicle includes a battery or other electric power storage unit (not shown) for storing electrical energy for at least moving the vehicle. The vehicle 100 includes a wireless power receiver (not shown). The receiver is located on an underside of the vehicle 100. The receiver is positioned under the front end region of the vehicle 100 in this embodiment. The pad 10 fits between wheels on the same axle of the vehicle 100.

It will be appreciated that the receiver may be provided under a centre region or rear end region of the vehicle in other embodiments. The vehicle 100 would be positioned differently so that the receiver overlaid the pad 10 for charging.

The wireless charging pad 10 is shown in more detail in Figures 2 and 3. The pad 10 includes a planar base 14. The power supply cable 12 connects to the pad 10 at or above the base 14. Corners of the base 14 are rounded. The base 14 is about 1500mm long and about 1300mm wide in this embodiment, although alternate dimensions for length and/or width are contemplated for other embodiments.

A frame 16 is provided on the base 14. The frame 16 is sized to fit within the perimeter of the base 14. The frame 16 includes four upright walls 14a arranged to define a rectangular-shaped or square-shaped region within the base 14. A peripheral flange 14b is provided around the walls 14a.

Means for moving the wireless charging transmitter 20 is indicated generally at 18. The arrangement 18 fits within the frame 16.

The arrangement 18 for moving the transmitter includes parallel rods or rails 18a, 18b disposed towards opposing internal sides of the frame 16. Further parallel rods or rails 18c, 18d are connected to and arranged orthogonal to the first and second parallel rods 18a, 18b.

The further parallel rods 18c, 18d extend across the frame 16, between the first and second parallel rods 18a, 18b. The further parallel rods 18c, 18d are moveable or slidable along the first and second parallel rods 18a, 18b in a first direction (x axis).

A transmitter support 18e is connected to the further parallel rods 18c, 18d. The support 18e is moveable or slidable along the further parallel rods 18c, 18d in a second direction which is orthogonal to the first direction (y axis).

A flexible wire 18f is arranged to move with the support 18e. The wire 18f is part of the power supply arrangement for the transmitter 20. A motor (not shown) enables movement of the transmitter 20 along each of the x and y axes in either direction. It will be appreciated that other drive means may be provided in other embodiments.

The wireless charging transmitter 20 is a Flew) transmitter in this embodiment. The transmitter 20 is substantially planar. The transmitter 20 is mounted on top of the support 18e. The transmitter 20 is positioned substantially centrally on the support 18e.

The transmitter 20 is approximately in the shape of a square in this embodiment, with its length, width and height being similarly proportioned to that of the pad 10 as a whole.

In some embodiments, a controller (not shown) is provided in the vehicle 100 to control the transmitter positioning means 18 and transmitter 20. In such embodiments, the controller wirelessly provides signals or instructions for moving the transmitter 20 based on the detected charging efficiency or equivalent means for detecting relative overlap or alignment of the transmitter 20 and receiver.

A feedback system or mechanism allows the controller to determine the best position of the transmitter for charging the vehicle battery, and to move the transmitter to that position via the positioning means 18. In other embodiments, the controller can be provided in the pad 10 or near the pad rather than the vehicle, for example.

Figure 3 shows the transmitter in first and second positions 20', 20" at opposing corners of the pad 10, within the frame 16. Double-headed arrow A indicates movement either way along a first axis. Double-headed arrow B indicates movement either way along a second axis.

A cover or housing 22 is provided over the base 14, defining a chamber in which the transmitter 20 and transmitter positioning means 18 are provided. The cover 22 is adapted to fit the base. When the cover 22 is fitted to the base, the charging pad is waterproof by virtue of a seal between the cover 22 and base 14.

The cover 22 is made of a toughened composite in this embodiment. The cover 22 is substantially frustopyramidal in shape in this embodiment. In other words, it is shaped like a truncated pyramid. Upper edges and corners of the cover 22 are rounded. The top of the housing 22 is substantially planar. Sides of the cover 22 are sloped at about 45 degrees relative to the top of the housing 22.

In use, the electric vehicle 100 is parked over the pad 10 such that its wireless power receiver is roughly aligned with the transmitter 20 in its initial position. That is, the receiver is above the top of the cover 22. The controller can detect or determine when the receiver is above the transmitter 20.

In this embodiment, the controller is programmed to determine impedance between the transmitter 20 and receiver in the initial position. The controller then moves the transmitter to a different position within the pad 10 and determines impedance in that second position. This process is repeated or iterated to move the transmitter 20 relative to the receiver into a final position in the x-y plane in which impedance is lowest and thus wireless charging is optimised.

In some embodiments, measuring impedance in two or several locations may be sufficient to predict the location where lowest impedance will subsist. In some embodiments, vertical movement means may be provided for moving the transmitter 20 or pad 10 closer to the underside of the vehicle 100. When charging is complete, the transmitter or pad would be retracted prior to the vehicle vacating the pad.

Figure 4 shows two vehicle charging systems 10 installed in or on a road R. The spacing between the systems 10 is at least about 4-5 metres. The spacing is greater than the expected length of the vehicles intended to be using the pads 10. The systems 10 may be part of a taxi rank, for example. The pads 10 may be installed flush to the surface of the road R in some embodiments.

In some embodiments, additional charging pads may be provided in a line for a queue of vehicles. In use, if a vehicle in a queue of vehicles vacates a pad, the vehicles positioned over pads 10 to the rear of the vehicle that left may roll forward (ideally automatically) to vacate the rearmost charging pad in the line. This allows taxis in a taxi rank to charge their batteries with little interruption as a given lead taxi departs and the taxis drive forward to fill the vacant space.

Raised strips or bumps, or visual alignment means (e.g. one or more painted lines), are indicated generally at 50. These may be used by a driver to judge when their electric vehicle 100 is suitably positioned over a given pad 10 for charging the vehicle battery.

In Figure 4, a pillar or other power distribution unit indicated generally at 54 is installed in or on pavement P next to the road R. The pillar 54 contains the inverter or inverters (not shown) for the charging systems 10. Power cables 52 connect each pad 10 to the pillar 54. The cables 52 are installed in the ground.

Alternatively, with reference to Figure 5, a similar set of vehicle charging systems 10 is provided but inverters (indicated generally at 56) are installed in the pavement separately to a pillar or power distribution unit indicated generally at 54'. The inverters 56 may be installed flush to the surface of the pavement P for easier access and maintenance. The inverters 56 may extend below the pavement by around 300mm.

The embodiments described above are provided by way of example only, and various changes and modifications will be apparent to persons skilled in the art without departing from the scope of the present invention as defined by the appended claims. is

Claims

CLAIMS 1. 2. 3. 4. 5. 6.An electric vehicle charging system for charging an electric vehicle including a battery and a wireless power receiver, the system comprising a base for installation on or in the ground, a housing or cover which defines a chamber above the base, a moveable wireless power transmitter disposed in the chamber for charging the battery, positioning means configured to move the wireless power transmitter relative to the base within the chamber, and a controller configured to control the positioning means and in use align the wireless power transmitter with the wireless power receiver, for optimising battery charging.
An electric vehicle charging system as claimed in claim 1, in which the controller is adapted to detect or measure impedance between the wireless power transmitter and the wireless power receiver in the vehicle, and configured to move the wireless power transmitter from its starting position to another position within the chamber in which there is reduced impedance.
An electric vehicle charging system as claimed in claim I or claim 2, in which at least one sensor is connected to the controller for detecting impedance and/or relative positions of the wireless power transmitter and receiver.
An electric vehicle charging system as claimed in claim 3, in which the at least one sensor is configured to detect or monitor one or more of impedance between the wireless power transmitter and receiver; the rate of power transfer between the wireless power transmitter and receiver; a battery charge value; the rate of battery charging; whether a vehicle is positioned over the transmitter.
An electric vehicle charging system as claimed in any preceding claim, in which the positioning means includes a motorised support for the wireless power transmitter.
An electric vehicle charging system as claimed in any preceding claim, in which the positioning means is configured to move the wireless power transmitter in at least two dimensions relative to the base.
7. An electric vehicle charging system as claimed in any preceding claim, in which the positioning means is configured to move the wireless power transmitter in at least a horizontal plane above the base.
8. An electric vehicle charging system as claimed in any preceding claim, in which the positioning means is configured to move the wireless power transmitter along a vertical axis which is substantially perpendicular to the base.
9. An electric vehicle charging system as claimed in any preceding claim, in which a seal is provided between the housing and the base to provide a waterproof enclosure around at least the wireless power transmitter and the positioning means.
10. An electric vehicle charging system as claimed in any preceding claim, in which the housing is a made of a toughened and/or composite material.
11. An electric vehicle charging system as claimed in any preceding claim, in which some or all of the side faces of the housing are sloped or slanted.
12. An electric vehicle charging system as claimed in any preceding claim, in which at least part of the cover is substantially frustopyramidal in shape.
13. An electric vehicle charging system as claimed in any preceding claim, in which the top of the housing is a maximum of about 120 mm above the base.
14. An electric vehicle charging system as claimed in any preceding claim, in which a power supply cable or wire is connected to and extends from one side of the base.
15. An electric vehicle charging system as claimed in any preceding claim, in which the vehicle is provided with a wireless tag or other identifier, and the controller is adapted to detect the wireless tag or other identifier and tailor battery charging accordingly.
16. A parking area or depot for one or more electric vehicles, the parking area or depot comprising one or more electric vehicle charging systems each as claimed in any preceding claim.
17. A method of charging an electric vehicle which includes a battery and a wireless power receiver, using a vehicle charging system which includes a wireless power transmitter for charging the battery, positioning means configured to move the wireless power transmitter, and a controller configured to control the positioning means, the method comprising the steps of: a) providing the electric vehicle in a position above at least part of the vehicle charging system, such that the wireless power receiver is coarsely aligned with the wireless power transmitter; b) moving the wireless power transmitter into a different position for charging, such that the wireless power transmitter is precisely aligned with the wireless power receiver, the charging position having been determined or predicted by the controller to provide optimal charging.
18. A method of charging a vehicle as claimed in claim 17, in which step (b) involves comparing charging efficiency in a plurality of positions, and then positioning wireless power transmitter in the position which provides optimal or near-optimal charging efficiency.
19. A method of charging an electric vehicle as claimed in claim 17 or 18, in which the controller is adapted to detect or measure impedance between the wireless power transmitter and the wireless power receiver, and the wireless power transmitter is moved from an initial position in step (a) to a subsequent position of relatively lower impedance in step (b).
20. A method of charging a vehicle as claimed in claim 19, in which step (b) includes measuring impedance in the initial position, comparing the measured impedance to a set of calibration values, and moving the wireless power transmitter to another position based on the expected impedance value at that position.
21. A method of charging a plurality of electric vehicles using a vehicle charging system, each electric vehicle including a battery and a wireless power receiver, and the vehicle charging system including a plurality of wireless power transmitters for charging the batteries, positioning means configured to move the wireless power transmitters, and at least one controller configured to control the positioning means, the method comprising the steps of a) providing the wireless power transmitters arranged substantially in a line, each wireless power transmitter being spaced from each neighbouring wireless power transmitters by substantially at least the length of one of the electric vehicles; b) providing the electric vehicles in charging positions substantially in a line above the wireless power transmitters, and aligning each wireless power transmitter with each corresponding wireless power receiver via the positioning means, for optimising charging; c) when at least one of the electric vehicles vacates its wireless power transmitter, moving some or all of the remaining electric vehicles each into a new charging position over a different one of the wireless power transmitters to continue charging, to vacate at least one of the wireless power transmitters at the end of the line.
22. A method of charging a plurality of electric vehicles as claimed in claim 21, in which step (b) includes moving each wireless power transmitter into a different position for charging, such that each wireless power transmitter is precisely aligned with the corresponding wireless power receiver.
23. A method of charging a plurality of electric vehicles as claimed in claim 21 or 22, in which the vehicle charging system is provided in one of: a taxi rank; a bus station; a car rental area; a depot.
24. A method of charging a plurality of electric vehicles as claimed in any of claims 21 to 23, in which the controller is adapted to automatically initiate movement of one or more of the electric vehicles to new wireless power transmitter in step (c)
25. A method of charging an electric vehicle or a plurality of electric vehicles as claimed in any of claims 17 to 24, using one or more vehicle charging systems as claimed in any of claims 1 to 16.