Patent Publication Number: US-2012025758-A1

Title: Contactless power transfer system

Description:
BACKGROUND 
     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. 
     BRIEF DESCRIPTION 
     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. 
    
    
     
       DRAWINGS 
       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: 
         FIG. 1  illustrates an exploded view of a contactless charging system according to an embodiment of the invention; 
         FIG. 2  illustrates a charging receptacle according to an embodiment of the invention; 
         FIG. 3  illustrates a charging handle according to an embodiment of the invention; 
         FIG. 4  illustrates a contactless charging system according to an embodiment of the invention; 
         FIG. 5  illustrates a block diagram of a contactless charging system according to an embodiment of the invention; 
         FIG. 6  illustrates a block diagram of an intelligent charging system according to an embodiment of the invention; 
         FIG. 7  illustrates an alternate embodiment of a contactless charging system according to an embodiment of the invention; 
         FIG. 8  illustrates a Swiss-roll resonator according to an embodiment of the invention; and 
         FIG. 9  illustrates charging receptacle according to an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     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. 
       FIG. 1  illustrates an exploded view of a contactless charging system according to an embodiment of the invention. A charging receptacle  14  is disposed on a vehicle (not shown) and illustrated as an inlet for purposes of example. In one embodiment, the charging receptacle  14  includes a cavity  20  for hosting a dielectric region  22 , a projection  18  for hosting a secondary coil  24 , and a field-focusing element  26 . In one embodiment, the charging receptacle  14  comprises a housing  28  made of ferromagnetic material for example. In another embodiment, the charging receptacle housing  28  and projection  18  both comprise ferromagnetic material. Ferromagnetic material helps to minimize penetration of magnetic fields generated by the primary coil and field-focusing element into surrounding metal frames and additionally helps to minimize the electromagnetic interference with adjacent electronic systems. In one embodiment, as shown in  FIG. 1 , the dielectric region  22  encompasses the field-focusing element  26 . Non-limiting examples of dielectric region materials include calcium copper titanate compositions and barium strontium titanate compositions. Using a dielectric enclosure around the field-focusing element  26  improves the permittivity and thus results in enhanced field focusing from the field-focusing element  26 . The charging receptacle  14  may further include a lid  34  disposed on the outside on the vehicle and optionally coupled by a hinge  33  to the housing  28  of the cavity  20 . Reference numeral  11  illustrates another view of the charging receptacle  14 . In one embodiment, a projection  35  on the lid  34  is configured to accommodate a charging handle (not shown in  FIG. 1 ) during a charging operation. 
     The field-focusing element  26  is used to focus a magnetic field from a primary coil  16  (as referenced in  FIG. 3 ) on to the secondary coil  24 . In one embodiment, the field-focusing element  26  includes a single loop coil. In another embodiment, the field-focusing element includes multiple turns such as in a split ring structure, a spiral structure, a Swiss-roll structure, or a helical coil. Selection of a structure for a particular application is determined by the power handling capability, self resonating frequency, and ability to focus the electromagnetic field in an axial direction to facilitate the contactless charging system. For example, passenger electric vehicles may have storage systems with energy ratings of about 8 kWh to about 40 kWh. Such storage systems are configured for at least three levels of charging depending on the time required for charging. For example, a level one charging requires charging power of about 1.5 kW to about 7 kW, a level two charging requires charging power of about 10 kW to 15 kW, and a level three charging requires charging power of about 15 kW up to about 150 kW (with a level three charging requiring less charging time than level one and two chargings). Similarly for high power vehicles such as mining trucks, power requirements may be in the range of 200 kW or more. Such high power requirements need operating frequency to be less than a few MHz up to about 500 kHz. 
     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. 
       FIG. 2  illustrates the charging receptacle according to an embodiment of the invention. The top view  14  illustrates the lid  34  hinged to the outer surface  28  of the cavity. The leads of the secondary coil  24  may be coupled to the electric motor or the storage system within the vehicle. A cut sectional view as referenced by the numeral  27  illustrates the projection  18  hosting the secondary coil  24  at the far end  25  within the cavity  20 . The cut sectional view  27  also illustrates the field-focusing element  26  disposed proximate the dielectric region  22 . For example, the dielectric region  22  may encompass the helical resonator  26  as illustrated by the cut section view  27 . In another embodiment, the dielectric region  106 - 110  may be disposed between or wrapped around the coil regions  98 - 104  of a Swiss-roll resonator as illustrated by reference numeral  97  in  FIG. 8 . As discussed earlier, the projection  35  on the lid  34  is to accommodate a charging handle. During a charging operation, the lid hosts the charging handle and is in a closed position wherein the projection  35  along with the charging handle is accommodated within the cavity  20 . After the charging, the lid  34  is replaced into the cavity  20  without the charging handle. 
       FIG. 3  illustrates a charging handle  13  according to an embodiment of the invention. A primary coil  16  is disposed within a housing  12  and configured to be disposed on the projection  35  of the lid  34  as referenced in  FIG. 2 . The housing  12  may comprise a non-conducting and non-magnetic material such as plastic, for example. The primary coil  16  is further coupled to a charging station, which in turn is coupled to a power source (not shown) such as an AC power outlet of a domestic home or an industrial three-phase power outlet via the leads  17 . The charging station converts frequency of the power received from the power source or utility from power frequency of 50/60 Hz to a resonance frequency of the field-focusing element to enable the efficient power transfer. 
       FIG. 4  illustrates a contactless charging system  30  according to an embodiment of the invention. In an exemplary embodiment, the charging handle housing  12  is mated into the projection  35  during a charging operation. The contactless charging system  30  includes a charging station  32  that may be coupled to a utility grid. The charging station  32  is adapted to supply power to a vehicle  36  that is capable of receiving power, for example, recharging the storage devices within the vehicle. Charging handle  13  is electrically coupled to the charging station  32 . A charging receptacle  14  disposed on the vehicle  36  includes a cavity  20  having field-focusing element  26  and secondary coil  24  disposed within the cavity  20 . As discussed above, secondary coil  24  may be coupled to an energy storage module within the vehicle that is powered by an electric motor. The energy storage module is configured to supply power to the electric motor to propel the vehicle. Reference numeral  31  illustrates another view of the contactless charging system  30 . 
       FIG. 5  illustrates a block diagram of a contactless charging system according to an embodiment of the invention. The contactless charging system  40  includes a power source  42  that is coupled to a grid. The power source  42  is configured to supply single phase or three phase AC power. A rectifier/inverter module  44  coupled to the power source  42  comprises a rectifier which converts the AC power to DC power and an inverter which then converts the rectified DC power to high frequency AC power. A controller  48  coupled to the rectifier/inverter module  44  controls the on and off states of switches of the rectifier/inverter module. An electrical outlet  46  is coupled to the rectifier/inverter module  44 . 
     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  FIG. 4 ). A battery management system  56  is coupled to the storage module  54  and configured to monitor the amount of charging required for the storage module  54 . Furthermore, battery management system  56  may be configured to provide signals for use in controlling on and off states of switches of the rectifier/inverter module  44  such that the power flow into the storage module  54  is controlled. Such a feedback mechanism, in an exemplary embodiment, is implemented via data transfer  60  in a contactless manner between the inlet  50  and the electrical outlet  46 . For example, during a charging operation, the battery management system  56  may generate a signal when the storage module  54  is fully charged and does not require any more charging. Such signal may be transmitted to the controller  48  in a contactless manner via the inlet  50  and electrical outlet  46 . Similarly, battery management system  56  may communicate via appropriate signals, the status of the storage module  54  at any stage during the charging operation. 
     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. 
       FIG. 6  illustrates a block diagram of an intelligent charging system according to an embodiment of the invention. The intelligent charging system  66  includes at least two sets of coils  74 ,  80 , a field-focusing element  78  and is configured for providing multi-channel bi-directional power transfer between a power source  72  and a storage module  82  on a vehicle (not shown in  FIG. 5 ). An inverter  73  coupled to the power source may be configured to convert power to high frequency AC power suitable for contactless power transmission. A battery management system  84  is coupled to the storage module  82  and configured to control a power flow to and from the storage module  82 . A processor  76  is coupled to the power source and configured to communicate with an external control station  70 . The external control station  70  may include, for example, a utility based power distribution unit or a distributed power generation unit. Several examples of distributed power generation units include photovoltaic modules, wind farms, and micro generation units. Several examples of utility distribution unit include substations and receiving stations coupled to a transmission grid. 
     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.” 
       FIG. 7  illustrates an alternate embodiment of a contactless charging system according to an embodiment of the invention. The contactless charging system  90  includes a charging receptacle  93  that includes a cavity  20  to accommodate the dielectric region  22  and a field-focusing element  26 . A projection  95  within the cavity  20  is configured to host a secondary coil  24 . A charging handle  91  includes a projection  19  that is hosted within the cavity  20  during a charging operation. Alignment key  94  on the projection  19  may be used to align a fit into the hole  94  on the projection  95  within the charging receptacle  93  during a charging operation. The charging handle  91  further hosts a primary coil  16  coupled to the utility grid via a charging station. In an alternate embodiment, the charging receptacle  93  is further configured to receive liquid fuel via multiple perforations such as  124  as referenced in  FIG. 9 . It may be noted that such an arrangement is advantageous in plug-in hybrid electrical vehicles that can operate using fuel or electricity. In one embodiment, a housing for cavity  20 , projection  95 , and projection  19  each comprise ferromagnetic material. 
     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.