Patent Application
20120025758
The invention relates generally to contactless power transfer systems and, in particular, to contactless power transfer for plug-in hybrid vehicles and electric vehicles.
A typical motor vehicle with an internal combustion engine has a battery that is used predominantly for providing power to crank the engine to start the vehicle. Charging the battery is usually done via an alternator driven by the engine. However, in a plug-in hybrid or all electric vehicle, the battery typically provides power to an electric motor coupled to a drive shaft to drive the vehicle. The power storage capacity of an electric vehicle battery typically has to be sufficient to deliver power in a range similar to that of a vehicle powered by a combustion engine. Such power requirements involve recharging over extended periods of time such as, for example, overnight or during the work day while the vehicle is parked.
To date, most electric vehicle charging systems includes contact based charging connectors having plug and socket connectors for contact based charging. Contact based charging connector systems have several disadvantages. For example, in outdoor applications, environmental impact may cause corrosion and damage of electrical contacts. The power cord and plug connectors may become damaged due to improper or excessive use by different people at the charging station.
It would therefore be advantageous to provide contactless vehicle charging.
It would further be advantageous to provide a contactless vehicle charging system that can allow the electrical contacts to be permanently concealed inside insulating casing. Further, it would be useful for the system to be capable of ensuring a correct charging rate and total charge delivered to the vehicle to prevent overcharging. Additionally, it would be useful for the system to provide smart grid compatibility to enable intelligent charging and effective utilization of electrical power from the utility.
Briefly, in accordance with one embodiment, a contactless charging system is presented. The contactless charging system includes an electrical outlet coupled to a power source and comprising a primary coil. An inlet on a vehicle comprising a dielectric region is disposed within a cavity. A secondary coil is disposed within the cavity and coupled to a storage module. A field focusing element is disposed proximate the dielectric region and configured to focus a magnetic field.
In another embodiment, an intelligent charging system is presented. The intelligent charging system includes a contactless power transfer system comprising at least two coils and a field focusing element. The intelligent charging system is configured for providing bi-directional power transfer between a power source and a storage module on a vehicle. A battery management system is coupled to the storage module and configured to control a power flow to and from the storage module. A processor is coupled to the power source and configured to communicate with an external control station.
In another embodiment, a vehicle having a charging receptacle is presented. The charging receptacle includes an inlet comprising a dielectric region disposed within a cavity. A secondary coil is disposed within the cavity and coupled to a storage module. A field focusing element is disposed proximate the dielectric region and configured to focus a magnetic field. The charging receptacle is configured for receiving a charging handle comprising a primary coil coupled to a power source.
These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:
As used herein, “contactless” means that a power cord, wire, or other tangible electrical conduit is absent for at least a portion of a power transfer circuit. Unless otherwise indicated by context or explicit language, “power,” as used herein, refers to electrical power or electricity. The word “vehicle” is intended to include any non-fixed item of equipment, and specifically includes at least self-propelled vehicles. Examples of such vehicles include passenger vehicles, mass transit vehicles, locomotives, and industrial equipment (such as forklifts and loaders). Examples of passenger vehicles include all-electric vehicles and plug-in hybrid electric vehicles. Other examples include mining equipment and semi-portable devices. The terms “primary coil” and “secondary coil” are provided with reference to the directional flow of power. In certain instances, power flow may be bi-directional, and the terms may be interchanged with each other. The phrases “connected to,” “coupled to,” and “in communication with” refer to any form of interaction between two or more entities, including mechanical, electrical, magnetic, electromagnetic, fluid, and thermal interaction. Two components may be coupled to each other even though they are not in direct contact with each other.
The field-focusing element 26 is used to focus a magnetic field from a primary coil 16 (as referenced in
A Swiss-roll coil may be implemented as the field-focusing element to provide a compact resonator that may be configured to operate at frequencies from about 100 kHz up to about a few MHz. Swiss-roll resonators includes spiral wrapped coils that may be embedded in high dielectric material (with a dielectric constant ranging from 10 to 100, for example) to achieve increased capacitance and inductance and hence a compact design. A single Swiss Roll resonator is expected to be capable of focusing a magnetic field up to few inches of distance.
Alternatively, a helical resonator may be embedded in dielectric region 22 and configured as a field focusing structure. This embodiment of helical structure may include a wire wound in the form of a helix and, when used as magnetic field-focusing element, may achieve high Q factor. In one embodiment, coating the surface of the conductor in the helical structure with high conductivity material helps minimize skin effects in the magnetic field-focusing element at high frequencies and hence enables the higher Q factor. A helical resonator is analogous to an array of dipoles and loops and designed for focusing magnetic field in an axial direction by optimizing the pitch and number of turns.
The field-focusing element 26 may further include multiple resonators. In one embodiment, the field-focusing element 26 comprises at least two sets of resonators having self-resonant frequencies that are unique (in other words, that differ from each other). In such a configuration, power may be transferred through a first resonance frequency and data on a second resonance frequency. If desired, bi-directional power or power and data may be transferred. In one example, power is transferred in one direction via the first resonance frequency and data is transferred in an opposite direction via the second resonance frequency simultaneously.
The secondary coil 24 disposed within the cavity may be coupled to an energy storage module (not shown) within an electric vehicle or a plug-in hybrid vehicle that is powered by an electric motor. The energy storage module may in turn be configured to supply power to the electric motor.
The electrical outlet 46, in one embodiment, includes a charging handle equipped with a primary coil for transmitting high frequency AC power from the rectifier/inverter module 44. An inlet 50 is disposed on a vehicle configured to receive power for charging purposes. The electrical outlet 46 and the inlet 50 are mechanically mated so that during charging operation, the inlet 50 accommodates electrical outlet 46 for receiving power. In one embodiment, the inlet 50 includes a field-focusing element enclosed within a dielectric region to focus a magnetic field and a secondary coil to receive power. In may be noted that, though electrical outlet 46 and inlet 50 are mechanically mated, the primary and secondary coils are not in physical contact. Power 58 is transferred in a contactless manner between the electrical outlet 46 and the inlet 50. The secondary coil may further be coupled to a rectifier 52 to convert high frequency AC power to a DC power suitable for charging a storage module 54. In one embodiment, the storage module 54 includes a battery or multiple batteries. The storage module 54 may be further coupled to an electric motor 57 configured to propel a vehicle (not shown in
In one embodiment, a power-flow measuring module 45 is coupled between the rectifier/inverter 44 and the primary coil in the electrical outlet 46. Power-flow measuring module 45 may be configured to measure the amount of power delivered from the electrical outlet. Such measurements may be used for utility billing purposes. Furthermore, such measurements help monitor abnormal operations that may occur, for example, during an incompatible charging handle being used for a vehicle or during a fault condition that may occur during a short circuit. During such abnormal conditions, an alarm device within the power-flow measuring module may be activated to warn the user to abort the operation.
In an exemplary embodiment, while the primary and secondary coils are coupled, the intelligent charging system 66 may be configured to include smart grid capabilities such as optimum load utilization and enable functionality such as the transfer of power from the storage module to the grid when it appears that such power will be needed by the grid prior to being needed by the vehicle. In one embodiment, load data such as the charging current and the power flow into the power source 72 may be monitored and communicated to the utility 70 via the processor 76. It may be noted that sharing such data with the utility is advantageous in several aspects. For example, when multiple such vehicles are coupled to the grid at the same time during the night, multiple such intelligent systems as disclosed herein may be coupled configured to share the demand for load thereby relieving an overload condition on the grid. Additionally, if a vehicle is fully charged, excess power from such a vehicle may be pumped back to the grid to relieve new demand for power on the grid. Many such load optimization techniques may be implemented within the intelligent charging system 66. Further details of contactless power transfer systems in general and data transfer in particular can be found in co-pending U.S. patent application Ser. No. 12/820,208, filed on Jun. 22, 2010, entitled “CONTACTLESS POWER TRANSFER SYSTEM.”
Advantageously, contactless charging systems as disclosed herein are more efficient compared to induction based charging systems. Further, high efficiencies may be achieved (such as about 90% or more for a 6.6 kW system) over a distance of few millimeters. The contactless charging system is further insensitive to any misalignment between the charging handle and the charging receptacle. Furthermore, such contactless charging systems are immune to load variations that occur at various stages of battery charging/discharging. Bi-directional power transfer enables simultaneous transfer of power and data. Power-flow monitor and alarm functions may be used to enable overall system protection during abnormal operations such as in-compatible devices or faulty device. Intelligent charging systems disclosed herein may be used to enable smart grid capabilities such as load optimization and resource sharing.
While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.
