Induction power transfer system with coupling and reactance selection

A power receiver is configured to supply current to a load and to be wirelessly operatively coupled to a power transmitter and includes a plurality of inductive elements. The power receiver further includes a circuit operatively coupled to the plurality of inductive elements and configured to be selectively switched among a plurality of coupling states. The circuit is further configured to be selectively switched such that each inductive element has a reactance state of a plurality of reactance states. The power receiver further includes a controller configured to select the coupling state and to select the reactance state of each inductive element based on one or more signals indicative of one or more operating parameters of at least one of the power receiver and the power transmitter.

FIELD

The present disclosure relates generally to wireless power transfer, and more specifically to devices, systems, and methods related to wireless power transfer to remote systems such as vehicles including batteries by controlling the coupling of a receiver with a transmitter and controlling a reactance of the receiver.

BACKGROUND

Remote systems, such as vehicles, have been introduced that include locomotion power derived from electricity received from an energy storage device such as a battery. For example, hybrid electric vehicles include on-board chargers that use power from vehicle braking and traditional motors to charge the vehicles. Vehicles that are solely electric generally receive the electricity for charging the batteries from other sources. Battery electric vehicles (electric vehicles) are often proposed to be charged through some type of wired alternating current (AC) such as household or commercial AC supply sources. The wired charging connections require cables or other similar connectors that are physically connected to a power supply. Cables and similar connectors may sometimes be inconvenient or cumbersome and have other drawbacks. Wireless charging systems that are capable of transferring power in free space (e.g., via a wireless field) to be used to charge electric vehicles may overcome some of the deficiencies of wired charging solutions. As such, wireless charging systems and methods that efficiently and safely transfer power for charging electric vehicles.

SUMMARY

One aspect of the disclosure provides a power receiver configured to supply current to a load and to be wirelessly operatively coupled to a power transmitter. The power receiver comprises a plurality of inductive elements configured to inductively generate current in response to a magnetic field generated by the power transmitter. The power receiver further comprises a coupling circuit operatively coupled to the plurality of inductive elements. The coupling circuit is configured to be selectively switched among a plurality of coupling states, each coupling state of the plurality of coupling states having a corresponding set of inductive elements of the plurality of inductive elements configured to provide current to the load. The coupling circuit is further configured to be selectively switched such that each inductive element of the set of inductive elements has a reactance state of a plurality of reactance states, each reactance state of the plurality of reactance states having a corresponding reactance. The power receiver further comprises a controller coupled to the coupling circuit and configured to select the coupling state from the plurality of coupling states and to select the reactance state of each inductive element of the set of inductive elements from the plurality of reactance states based on one or more signals indicative of one or more operating parameters of at least one of the power receiver or the power transmitter.

Another aspect of the disclosure provides a method for controlling a current supplied to a load by a power receiver wirelessly operatively coupled to a power transmitter. The power receiver comprises a plurality of inductive elements configured to inductively generate current in response to a magnetic field generated by the power transmitter. The method comprises adjusting a coupling state of the power receiver based on one or more operating parameters of at least one of the power receiver or the power transmitter. The coupling state is selected from a plurality of coupling states, each coupling state of the plurality of coupling states having a corresponding set of inductive elements of the plurality of inductive elements configured to provide current to the load. The method further comprises adjusting a reactance state for each inductive element of the set of inductive elements based on the one or more operating parameters of at least one of the power receiver or the power transmitter, the reactance state selected from a plurality of reactance states.

Another aspect of the disclosure provides a power receiver configured to supply current to a load and to be wirelessly operatively coupled to a power transmitter. The power receiver comprises means for inductively generating current in response to a magnetic field generated by the power transmitter. The power receiver further comprises first means for selectively switching among a plurality of coupling states. Each coupling state of the plurality of coupling states has a corresponding portion of the means for inductively generating current configured to provide current to the load. The power receiver further comprises second means for selectively switching the means for inductively generating current among a plurality of reactance states. The power receiver further comprises means for controlling the first means for selectively switching and for controlling the second means for selectively switching based on one or more signals indicative of one or more operating parameters of at least one of the power receiver or the power transmitter.

DETAILED DESCRIPTION

The detailed description set forth below in connection with the appended drawings is intended as a description of exemplary embodiments of the invention and is not intended to represent the only embodiments in which the invention may be practiced. The term “exemplary” used throughout this description means “serving as an example, instance, or illustration,” and should not necessarily be construed as preferred or advantageous over other exemplary embodiments. The detailed description includes specific details for the purpose of providing a thorough understanding of the exemplary embodiments of the invention. In some instances, some devices are shown in block diagram form.

Wirelessly transferring power may refer to transferring any form of energy associated with electric fields, magnetic fields, electromagnetic fields, or otherwise from a transmitter to a receiver without the use of physical electrical conductors (e.g., power may be transferred through free space). The power output into a wireless field (e.g., a magnetic field) may be received, captured by, or coupled by a “receiving coil” to achieve power transfer.

An electric vehicle is used herein to describe a remote system, an example of which is a vehicle that includes, as part of its locomotion capabilities, electrical power derived from a chargeable energy storage device (e.g., one or more rechargeable electrochemical cells or other type of battery). As non-limiting examples, some electric vehicles may be hybrid electric vehicles that include besides electric motors, a traditional combustion engine for direct locomotion or to charge the vehicle's battery. Other electric vehicles may draw all locomotion ability from electrical power. An electric vehicle is not limited to an automobile and may include motorcycles, carts, scooters, and the like. By way of example and not limitation, a remote system is described herein in the form of an electric vehicle (EV). Furthermore, other remote systems that may be at least partially powered using a chargeable energy storage device are also contemplated (e.g., electronic devices such as personal computing devices and the like).

FIG. 1is a diagram of an exemplary wireless power transfer system100for charging an electric vehicle112, in accordance with an exemplary embodiment of the invention. The wireless power transfer system100enables charging of an electric vehicle112while the electric vehicle112is parked near a base wireless charging system102a. Spaces for two electric vehicles are illustrated in a parking area to be parked over corresponding base wireless charging system102aand102b. In some embodiments, a local distribution center130may be connected to a power backbone132and configured to provide an alternating current (AC) or a direct current (DC) supply through a power link110to the base wireless charging system102a. The base wireless charging system102aalso includes a base system induction coil104afor wirelessly transferring or receiving power. An electric vehicle112may include a battery unit118, an electric vehicle induction coil116, and an electric vehicle wireless charging system114. The electric vehicle induction coil116may interact with the base system induction coil104afor example, via a region of the electromagnetic field generated by the base system induction coil104a.

In some exemplary embodiments, the electric vehicle induction coil116may receive power when the electric vehicle induction coil116is located in an energy field produced by the base system induction coil104a. The field corresponds to a region where energy output by the base system induction coil104amay be captured by an electric vehicle induction coil116. For example, the energy output by the base system induction coil104amay be at a level sufficient to charge or power the electric vehicle112. In some cases, the field may correspond to the “near field” of the base system induction coil104a. The near-field may correspond to a region in which there are strong reactive fields resulting from the currents and charges in the base system induction coil104athat do not radiate power away from the base system induction coil104a. In some cases the near-field may correspond to a region that is within about ½π of wavelength of the base system induction coil104a(and vice versa for the electric vehicle induction coil116) as will be further described below.

Local distribution1130may be configured to communicate with external sources (e.g., a power grid) via a communication backhaul134, and with the base wireless charging system102avia a communication link108.

In some embodiments the electric vehicle induction coil116may be aligned with the base system induction coil104aand, therefore, disposed within a near-field region simply by the driver positioning the electric vehicle112correctly relative to the base system induction coil104a. In other embodiments, the driver may be given visual feedback, auditory feedback, or combinations thereof to determine when the electric vehicle112is properly placed for wireless power transfer. In yet other embodiments, the electric vehicle112may be positioned by an autopilot system, which may move the electric vehicle112back and forth (e.g., in zig-zag movements) until an alignment error has reached a tolerable value. This may be performed automatically and autonomously by the electric vehicle112without or with only minimal driver intervention provided that the electric vehicle112is equipped with a servo steering wheel, ultrasonic sensors, and intelligence to adjust the vehicle. In still other embodiments, the electric vehicle induction coil116, the base system induction coil104a, or a combination thereof may have functionality for displacing and moving the induction coils116and104arelative to each other to more accurately orient them and develop more efficient coupling therebetween.

The base wireless charging system102amay be located in a variety of locations. As non-limiting examples, some suitable locations include a parking area at a home of the electric vehicle112owner, parking areas reserved for electric vehicle wireless charging modeled after conventional petroleum-based filling stations, and parking lots at other locations such as shopping centers and places of employment.

Charging electric vehicles wirelessly may provide numerous benefits. For example, charging may be performed automatically, virtually without driver intervention and manipulations thereby improving convenience to a user. There may also be no exposed electrical contacts and no mechanical wear out, thereby improving reliability of the wireless power transfer system100. Manipulations with cables and connectors may not be needed, and there may be no cables, plugs, or sockets that may be exposed to moisture and water in an outdoor environment, thereby improving safety. There may also be no sockets, cables, and plugs visible or accessible, thereby reducing potential vandalism of power charging devices. Further, since an electric vehicle112may be used as distributed storage devices to stabilize a power grid, a docking-to-grid solution may be used to increase availability of vehicles for Vehicle-to-Grid (V2G) operation.

A wireless power transfer system100as described with reference toFIG. 1may also provide aesthetical and non-impedimental advantages. For example, there may be no charge columns and cables that may be impedimental for vehicles and/or pedestrians.

As a further explanation of the vehicle-to-grid capability, the wireless power transmit and receive capabilities may be configured to be reciprocal such that the base wireless charging system102atransfers power to the electric vehicle112and the electric vehicle112transfers power to the base wireless charging system102ae.g., in times of energy shortfall. This capability may be useful to stabilize the power distribution grid by allowing electric vehicles to contribute power to the overall distribution system in times of energy shortfall caused by over demand or shortfall in renewable energy production (e.g., wind or solar).

FIG. 2is a schematic diagram of exemplary core components of the wireless power transfer system100ofFIG. 1. As shown inFIG. 2, the wireless power transfer system200may include a base system transmit circuit206including a base system induction coil204having an inductance L1. The wireless power transfer system200further includes an electric vehicle receive circuit222including an electric vehicle induction coil216having an inductance L2. Embodiments described herein may use capacitively loaded wire loops (i.e., multi-turn coils) forming a resonant structure that is capable of efficiently coupling energy from a primary structure (transmitter) to a secondary structure (receiver) via a magnetic or electromagnetic near field if both primary and secondary are tuned to a common resonant frequency. The coils may be used for the electric vehicle induction coil216and the base system induction coil204. Using resonant structures for coupling energy may be referred to “magnetic coupled resonance,” “electromagnetic coupled resonance,” and/or “resonant induction.” The operation of the wireless power transfer system200will be described based on power transfer from a base wireless power charging system202to an electric vehicle112, but is not limited thereto. For example, as discussed above, the electric vehicle112may transfer power to the base wireless charging system102a.

With reference toFIG. 2, a power supply208(e.g., AC or DC) supplies power PSDCto the base wireless power charging system202to transfer energy to an electric vehicle112. The base wireless power charging system202includes a base charging system power converter236. The base charging system power converter236may include circuitry such as an AC/DC converter configured to convert power from standard mains AC to DC power at a suitable voltage level, and a DC/low frequency (LF) converter configured to convert DC power to power at an operating frequency suitable for wireless high power transfer. The base charging system power converter236supplies power P1to the base system transmit circuit206including the capacitor C1in series with the base system induction coil204to emit an electromagnetic field at a desired frequency. The capacitor C1may be provided to form a resonant circuit with the base system induction coil204that resonates at a desired frequency. The base system induction coil204receives the power P1and wirelessly transmits power at a level sufficient to charge or power the electric vehicle112. For example, the power level provided wirelessly by the base system induction coil204may be on the order of kilowatts (kW) (e.g., anywhere from 1 kW to 110 kW or higher or lower).

The base system transmit circuit206including the base system induction coil204and electric vehicle receive circuit222including the electric vehicle induction coil216may be tuned to substantially the same frequencies and may be positioned within the near-field of an electromagnetic field transmitted by one of the base system induction coil204and the electric vehicle induction coil116. In this case, the base system induction coil204and electric vehicle induction coil116may become coupled to one another such that power may be transferred to the electric vehicle receive circuit222including capacitor C2and electric vehicle induction coil116. The capacitor C2may be provided to form a resonant circuit with the electric vehicle induction coil216that resonates at a desired frequency. Element k(d) represents the mutual coupling coefficient resulting at coil separation. Equivalent resistances Req,1and Req,2represent the losses that may be inherent to the induction coils204and216and the anti-reactance capacitors C1and C2. The electric vehicle receive circuit222including the electric vehicle induction coil316and capacitor C2receives power P2and provides the power P2to an electric vehicle power converter238of an electric vehicle charging system214.

The electric vehicle power converter238may include, among other things, a LF/DC converter configured to convert power at an operating frequency back to DC power at a voltage level matched to the voltage level of an electric vehicle battery unit218. The electric vehicle power converter238may provide the converted power PLDCto charge the electric vehicle battery unit218. The power supply208, base charging system power converter236, and base system induction coil204may be stationary and located at a variety of locations as discussed above. The battery unit218, electric vehicle power converter238, and electric vehicle induction coil216may be included in an electric vehicle charging system214that is part of electric vehicle112or part of the battery pack (not shown). The electric vehicle charging system214may also be configured to provide power wirelessly through the electric vehicle induction coil216to the base wireless power charging system202to feed power back to the grid. Each of the electric vehicle induction coil216and the base system induction coil204may act as transmit or receive induction coils based on the mode of operation.

While not shown, the wireless power transfer system200may include a load disconnect unit (LDU) to safely disconnect the electric vehicle battery unit218or the power supply208from the wireless power transfer system200. For example, in case of an emergency or system failure, the LDU may be triggered to disconnect the load from the wireless power transfer system200. The LDU may be provided in addition to a battery management system for managing charging to a battery, or it may be part of the battery management system.

Further, the electric vehicle charging system214may include switching circuitry (not shown) for selectively connecting and disconnecting the electric vehicle induction coil216to the electric vehicle power converter238. Disconnecting the electric vehicle induction coil216may suspend charging and also may adjust the “load” as “seen” by the base wireless charging system102a(acting as a transmitter), which may be used to “cloak” the electric vehicle charging system114(acting as the receiver) from the base wireless charging system102a. The load changes may be detected if the transmitter includes the load sensing circuit. Accordingly, the transmitter, such as a base wireless charging system202, may have a mechanism for determining when receivers, such as an electric vehicle charging system114, are present in the near-field of the base system induction coil204.

As described above, in operation, assuming energy transfer towards the vehicle or battery, input power is provided from the power supply208such that the base system induction coil204generates a field for providing the energy transfer. The electric vehicle induction coil216couples to the radiated field and generates output power for storage or consumption by the electric vehicle112. As described above, in some embodiments, the base system induction coil204and electric vehicle induction coil116are configured according to a mutual resonant relationship such that when the resonant frequency of the electric vehicle induction coil116and the resonant frequency of the base system induction coil204are very close or substantially the same. Transmission losses between the base wireless power charging system202and electric vehicle charging system214are minimal when the electric vehicle induction coil216is located in the near-field of the base system induction coil204.

As stated, an efficient energy transfer occurs by coupling a large portion of the energy in the near field of a transmitting induction coil to a receiving induction coil rather than propagating most of the energy in an electromagnetic wave to the far-field. When in the near field, a coupling mode may be established between the transmit induction coil and the receive induction coil. The area around the induction coils where this near field coupling may occur is referred to herein as a near field coupling mode region.

While not shown, the base charging system power converter236and the electric vehicle power converter238may both include an oscillator, a driver circuit such as a power amplifier, a filter, and a matching circuit for efficient coupling with the wireless power induction coil. The oscillator may be configured to generate a desired frequency, which may be adjusted in response to an adjustment signal. The oscillator signal may be amplified by a power amplifier with an amplification amount responsive to control signals. The filter and matching circuit may be included to filter out harmonics or other unwanted frequencies and match the impedance of the power conversion module to the wireless power induction coil. The power converters236and238may also include a rectifier and switching circuitry to generate a suitable power output to charge the battery.

The electric vehicle induction coil216and base system induction coil204as described throughout the disclosed embodiments may be referred to or configured as “loop” antennas, and more specifically, multi-turn loop antennas. The induction coils204and216may also be referred to herein or be configured as “magnetic” antennas. The term “coil” generally refers to a component that may wirelessly output or receive energy four coupling to another “coil.” The coil may also be referred to as an “antenna” of a type that is configured to wirelessly output or receive power. As used herein, coils204and216are examples of “power transfer components” of a type that are configured to wirelessly output, wirelessly receive, and/or wirelessly relay power. Loop (e.g., multi-turn loop) antennas may be configured to include an air core or a physical core such as a ferrite core. An air core loop antenna may allow the placement of other components within the core area. Physical core antennas including ferromagnetic or ferromagnetic materials may allow development of a stronger electromagnetic field and improved coupling.

As discussed above, efficient transfer of energy between a transmitter and receiver occurs during matched or nearly matched resonance between a transmitter and a receiver. However, even when resonance between a transmitter and receiver are not matched, energy may be transferred at a lower efficiency. Transfer of energy occurs by coupling energy from the near field of the transmitting induction coil to the receiving induction coil residing within a region (e.g., within a predetermined frequency range of the resonant frequency, or within a predetermined distance of the near-field region) where this near field is established rather than propagating the energy from the transmitting induction coil into free space.

A resonant frequency may be based on the inductance and capacitance of a transmit circuit including an induction coil (e.g., the base system induction coil204) as described above. As shown inFIG. 2, inductance may generally be the inductance of the induction coil, whereas, capacitance may be added to the induction coil to create a resonant structure at a desired resonant frequency. As a non-limiting example, as shown inFIG. 2, a capacitor may be added in series with the induction coil to create a resonant circuit (e.g., the base system transmit circuit206) that generates an electromagnetic field. Accordingly, for larger diameter induction coils, the value of capacitance needed to induce resonance may decrease as the diameter or inductance of the coil increases. Inductance may also depend on a number of turns of an induction coil. Furthermore, as the diameter of the induction coil increases, the efficient energy transfer area of the near field may increase. Other resonant circuits are possible. As another non limiting example, a capacitor may be placed in parallel between the two terminals of the induction coil (e.g., a parallel resonant circuit). Furthermore an induction coil may be designed to have a high quality (Q) factor to improve the resonance of the induction coil. For example, the Q factor may be 300 or greater.

As described above, according to some embodiments, coupling power between two induction coils that are in the near field of one another is disclosed. As described above, the near field may correspond to a region around the induction coil in which electromagnetic fields exist but may not propagate or radiate away from the induction coil. Near-field coupling-mode regions may correspond to a volume that is near the physical volume of the induction coil, typically within a small fraction of the wavelength. According to some embodiments, electromagnetic induction coils, such as single and multi-turn loop antennas, are used for both transmitting and receiving since magnetic near field amplitudes in practical embodiments tend to be higher for magnetic type coils in comparison to the electric near fields of an electric type antenna (e.g., a small dipole). This allows for potentially higher coupling between the pair. Furthermore, “electric” antennas (e.g., dipoles and monopoles) or a combination of magnetic and electric antennas may be used.

FIG. 3is another functional block diagram showing exemplary core and ancillary components of the wireless power transfer system300ofFIG. 1. The wireless power transfer system300illustrates a communication link376, a guidance link366, and alignment systems352,354for the base system induction coil304and electric vehicle induction coil316. As described above with reference toFIG. 2, and assuming energy flow towards the electric vehicle112, inFIG. 3a base charging system power interface354may be configured to provide power to a charging system power converter336from a power source, such as an AC or DC power supply126. The base charging system power converter336may receive AC or DC power from the base charging system power interface354to excite the base system induction coil304at or near its resonant frequency. The electric vehicle induction coil316, when in the near field coupling-mode region, may receive energy from the near field coupling mode region to oscillate at or near the resonant frequency. The electric vehicle power converter338converts the oscillating signal from the electric vehicle induction coil316to a power signal suitable for charging a battery via the electric vehicle power interface.

The base wireless charging system302includes a base charging system controller342(which can be referred to as a base controller unit or BCU) and the electric vehicle charging system314includes an electric vehicle controller344(which can be referred to as a vehicle controller unit or VCU). The base charging system controller342may include a base charging system communication interface162to other systems (not shown) such as, for example, a computer, and a power distribution center, or a smart power grid. The electric vehicle controller344may include an electric vehicle communication interface to other systems (not shown) such as, for example, an on-board computer on the vehicle, other battery charging controller, other electronic systems within the vehicles, and remote electronic systems.

The base charging system controller342and electric vehicle controller344may include subsystems or modules for specific application with separate communication channels. These communications channels may be separate physical channels or separate logical channels. As non-limiting examples, a base charging alignment system352may communicate with an electric vehicle alignment system354through a communication link376to provide a feedback mechanism for more closely aligning the base system induction coil304and electric vehicle induction coil316, either autonomously or with operator assistance. Similarly, a base charging guidance system362may communicate with an electric vehicle guidance system364through a guidance link to provide a feedback mechanism to guide an operator in aligning the base system induction coil304and electric vehicle induction coil316. In addition, there may be separate general-purpose communication links (e.g., channels) supported by base charging communication system372and electric vehicle communication system374for communicating other information between the base wireless power charging system302and the electric vehicle charging system314. This information may include information about electric vehicle characteristics, battery characteristics, charging status, and power capabilities of both the base wireless power charging system302and the electric vehicle charging system314, as well as maintenance and diagnostic data for the electric vehicle112. These communication channels may be separate physical communication channels such as, for example, Bluetooth, zigbee, cellular, etc.

Electric vehicle controller344may also include a battery management system (BMS) (not shown) that manages charge and discharge of the electric vehicle principal battery, a parking assistance system based on microwave or ultrasonic radar principles, a brake system configured to perform a semi-automatic parking operation, and a steering wheel servo system configured to assist with a largely automated parking ‘park by wire’ that may provide higher parking accuracy, thus reducing the need for mechanical horizontal induction coil alignment in any of the base wireless charging system102aand the electric vehicle charging system114. Further, electric vehicle controller344may be configured to communicate with electronics of the electric vehicle112. For example, electric vehicle controller344may be configured to communicate with visual output devices (e.g., a dashboard display), acoustic/audio output devices (e.g., buzzer, speakers), mechanical input devices (e.g., keyboard, touch screen, and pointing devices such as joystick, trackball, etc.), and audio input devices (e.g., microphone with electronic voice recognition).

Furthermore, the wireless power transfer system300may include detection and sensor systems. For example, the wireless power transfer system300may include sensors for use with systems to properly guide the driver or the vehicle to the charging spot, sensors to mutually align the induction coils with the required separation/coupling, sensors to detect objects that may obstruct the electric vehicle induction coil316from moving to a particular height and/or position to achieve coupling, and safety sensors for use with systems to perform a reliable, damage free, and safe operation of the system. For example, a safety sensor may include a sensor for detection of presence of animals or children approaching the wireless power induction coils104a,116beyond a safety radius, detection of metal objects near the base system induction coil304that may be heated up (induction heating), detection of hazardous events such as incandescent objects on the base system induction coil304, and temperature monitoring of the base wireless power charging system302and electric vehicle charging system314components.

The wireless power transfer system300may also support plug-in charging via a wired connection. A wired charge port may integrate the outputs of the two different chargers prior to transferring power to or from the electric vehicle112. Switching circuits may provide the functionality as needed to support both wireless charging and charging via a wired charge port.

To communicate between a base wireless charging system302and an electric vehicle charging system314, the wireless power transfer system300may use both in-band signaling and an RF data modem (e.g., Ethernet over radio in an unlicensed band). The out-of-band communication may provide sufficient bandwidth for the allocation of value-add services to the vehicle user/owner. A low depth amplitude or phase modulation of the wireless power carrier may serve as an in-band signaling system with minimal interference.

In addition, some communication may be performed via the wireless power link without using specific communications antennas. For example, the wireless power induction coils304and316may also be configured to act as wireless communication transmitters. Thus, some embodiments of the base wireless power charging system302may include a controller (not shown) for enabling keying type protocol on the wireless power path. By keying the transmit power level (amplitude shift keying) at predefined intervals with a predefined protocol, the receiver may detect a serial communication from the transmitter. The base charging system power converter336may include a load sensing circuit (not shown) for detecting the presence or absence of active electric vehicle receivers in the vicinity of the near field generated by the base system induction coil304. By way of example, a load sensing circuit monitors the current flowing to the power amplifier, which is affected by the presence or absence of active receivers in the vicinity of the near field generated by base system induction coil104a. Detection of changes to the loading on the power amplifier may be monitored by the base charging system controller342for use in determining whether to enable the oscillator for transmitting energy, to communicate with an active receiver, or a combination thereof.

To enable wireless high power transfer, some embodiments may be configured to transfer power at a frequency in the range from 10-60 kHz. This low frequency coupling may allow highly efficient power conversion that may be achieved using solid state devices. In addition, there may be less coexistence issues with radio systems compared to other bands.

The wireless power transfer system100described may be used with a variety of electric vehicles102including rechargeable or replaceable batteries.FIG. 4is a functional block diagram showing a replaceable contactless battery disposed in an electric vehicle412, in accordance with an exemplary embodiment of the invention. In this embodiment, the low battery position may be useful for an electric vehicle battery unit that integrates a wireless power interface (e.g., a charger-to-battery cordless interface426) and that may receive power from a charger (not shown) embedded in the ground. InFIG. 4, the electric vehicle battery unit may be a rechargeable battery unit, and may be accommodated in a battery compartment424. The electric vehicle battery unit also provides a wireless power interface426, which may integrate the entire electric vehicle wireless power subsystem including a resonant induction coil, power conversion circuitry, and other control and communications functions as needed for efficient and safe wireless energy transfer between a ground-based wireless charging unit and the electric vehicle battery unit.

It may be useful for the electric vehicle induction coil to be integrated flush with a bottom side of electric vehicle battery unit or the vehicle body so that there are no protrusive parts and so that the specified ground-to-vehicle body clearance may be maintained. This configuration may require some room in the electric vehicle battery unit dedicated to the electric vehicle wireless power subsystem. The electric vehicle battery unit422may also include a battery-to-EV cordless interface422, and a charger-to-battery cordless interface426that provides contactless power and communication between the electric vehicle412and a base wireless charging system102aas shown inFIG. 1.

In some embodiments, and with reference toFIG. 1, the base system induction coil104aand the electric vehicle induction coil116may be in a fixed position and the induction coils are brought within a near-field coupling region by overall placement of the electric vehicle induction coil116relative to the base wireless charging system102a. However, in order to perform energy transfer rapidly, efficiently, and safely, the distance between the base system induction coil104aand the electric vehicle induction coil116may need to be reduced to improve coupling. Thus, in some embodiments, the base system induction coil104aand/or the electric vehicle induction coil116may be deployable and/or moveable to bring them into better alignment.

FIGS. 5A, 5B, 5C, and 5Dare diagrams of exemplary configurations for the placement of an induction coil and ferrite material relative to a battery, in accordance with exemplary embodiments of the invention.FIG. 5Ashows a fully ferrite embedded induction coil536a. The wireless power induction coil may include a ferrite material538aand a coil536awound about the ferrite material538a. The coil536aitself may be made of stranded Litz wire. A conductive shield532amay be provided to protect passengers of the vehicle from excessive EMF transmission. Conductive shielding may be particularly useful in vehicles made of plastic or composites.

FIG. 5Bshows an optimally dimensioned ferrite plate (i.e., ferrite backing) to enhance coupling and to reduce eddy currents (heat dissipation) in the conductive shield532b. The coil536bmay be fully embedded in a non-conducting non-magnetic (e.g., plastic) material. For example, as illustrated inFIG. 5A-5D, the coil536bmay be embedded in a protective housing534b. There may be a separation between the coil536band the ferrite material538bas the result of a trade-off between magnetic coupling and ferrite hysteresis losses.

FIG. 5Cillustrates another embodiment where the coil536c(e.g., a copper Litz wire multi-turn coil) may be movable in a lateral (“X”) direction.FIG. 5Dillustrates another embodiment where the induction coil module is deployed in a downward direction. In some embodiments, the battery unit includes one of a deployable and non-deployable electric vehicle induction coil module540das part of the wireless power interface. To prevent magnetic fields from penetrating into the battery space530dand into the interior of the vehicle, there may be a conductive shield532d(e.g., a copper sheet) between the battery space530dand the vehicle. Furthermore, a non-conductive (e.g., plastic) protective layer533dmay be used to protect the conductive shield532d, the coil536d, and the ferrite material538dfrom environmental impacts (e.g., mechanical damage, oxidization, etc.). Furthermore, the coil536dmay be movable in lateral X and/or Y directions.FIG. 5Dillustrates an embodiment wherein the electric vehicle induction coil module540dis deployed in a downward Z direction relative to a battery unit body.

The design of this deployable electric vehicle induction coil module542bis similar to that ofFIG. 5Bexcept there is no conductive shielding at the electric vehicle induction coil module542d. The conductive shield532dstays with the battery unit body. The protective layer533d(e.g., plastic layer) is provided between the conductive shield432dand the electric vehicle induction coil module542dwhen the electric vehicle induction coil module542dis not in a deployed state. The physical separation of the electric vehicle induction coil module542from the battery unit body may have a positive effect on the induction coil's performance.

As discussed above, the electric vehicle induction coil module542dthat is deployed may contain only the coil536d(e.g., Litz wire) and ferrite material538d. Ferrite backing may be provided to enhance coupling and to prevent from excessive eddy current losses in a vehicle's underbody or in the conductive shield532d. Moreover, the electric vehicle induction coil module542dmay include a flexible wire connection to power conversion electronics and sensor electronics. This wire bundle may be integrated into the mechanical gear for deploying the electric vehicle induction coil module542d.

With reference toFIG. 1, the charging systems described above may be used in a variety of locations for charging an electric vehicle112, or transferring power back to a power grid. For example, the transfer of power may occur in a parking lot environment. It is noted that a “parking area” may also be referred to herein as a “parking space.” To enhance the efficiency of a vehicle wireless power transfer system100, an electric vehicle112may be aligned along an X direction and a Y direction to enable an electric vehicle induction coil116within the electric vehicle112to be adequately aligned with a base wireless charging system102awithin an associated parking area.

Furthermore, the disclosed embodiments are applicable to parking lots having one or more parking spaces or parking areas, wherein at least one parking space within a parking lot may comprise a base wireless charging system102a. Guidance systems (not shown) may be used to assist a vehicle operator in positioning an electric vehicle112in a parking area to align an electric vehicle induction coil116within the electric vehicle112with a base wireless charging system102a. Guidance systems may include electronic based approaches (e.g., radio positioning, direction finding principles, and/or optical, quasi-optical and/or ultrasonic sensing methods) or mechanical-based approaches (e.g., vehicle wheel guides, tracks or stops), or any combination thereof, for assisting an electric vehicle operator in positioning an electric vehicle112to enable an induction coil116within the electric vehicle112to be adequately aligned with a charging induction coil within a charging base (e.g., base wireless charging system102a).

As discussed above, the electric vehicle charging system114may be placed on the underside of the electric vehicle112for transmitting and receiving power from a base wireless charging system102a. For example, an electric vehicle induction coil116may be integrated into the vehicles underbody preferably near a center position providing maximum safety distance in regards to EM exposure and permitting forward and reverse parking of the electric vehicle.

FIG. 6is a chart of a frequency spectrum showing exemplary frequencies that may be used for wireless charging an electric vehicle, in accordance with an exemplary embodiment of the invention. As shown inFIG. 6, potential frequency ranges for wireless high power transfer to electric vehicles may include: VLF in a 3 kHz to 30 kHz band, lower LF in a 30 kHz to 150 kHz band (for ISM-like applications) with some exclusions, HF 6.78 MHz (ITU-R ISM-Band 6.765-6.795 MHz), HF 13.56 MHz (ITU-R ISM-Band 13.553-13.567), and HF 27.12 MHz (ITU-R ISM-Band 26.957-27.283).

FIG. 7is a chart showing exemplary frequencies and transmission distances that may be useful in wireless charging electric vehicles, in accordance with an exemplary embodiment of the invention. Some example transmission distances that may be useful for electric vehicle wireless charging are about 30 mm, about 75 mm, and about 150 mm. Some exemplary frequencies may be about 27 kHz in the VLF band and about 135 kHz in the LF band.

As described above, the wireless power transfer system100(e.g., an inductive power transfer system) in certain embodiments comprises a power transmitter (e.g., base wireless power charging system202) configured to be wirelessly operatively coupled to a power receiver (e.g., electric vehicle charging system214). In a typical inductive power transfer system, the base current (e.g., the current supplied to the power transmitter) is adjusted to provide a corresponding change in the output current provided by the power receiver to the load.

However, to effectively provide current to a load (e.g., to effectively charge a battery, such as the battery unit118of an electric vehicle112), the output generated by the power receiver can be advantageously controlled such that more than merely the output current is within a predetermined range of values. More effective use of the output from the power receiver can be achieved by maintaining other operating parameters of the output (e.g., output voltage, output power) to be within predetermined ranges compatible with effective use of the current. For example, when charging a battery using the output of the power receiver, the operating parameters can be selected to match a “battery charge curve” corresponding to effective charging of the battery.

Additional control of one or both of the output voltage and the output power is provided to by regulating the base current in response to measurements of the output voltage and the output current. In certain such embodiments, a state machine can prioritize the operating parameters and regulate the base current to a setpoint that achieves the desired performance.

FIG. 8shows two example plots of ranges of operating parameters (e.g., “operating zones”) for battery charging by the output of a power receiver compatible with certain embodiments described herein. In the top plot ofFIG. 8, a maximum operating zone is shown which is defined at least in part by a maximum output current (e.g., “absolute current limit”), a maximum output voltage (e.g., “absolute voltage limit”), and a maximum output power (e.g., “power limit line”). The maximum operating zone shown in the top plot ofFIG. 8is defined by a maximum output current of 13 amps, a maximum output voltage of 410 volts, and a maximum power of 3.3 kilowatts.

In the bottom plot ofFIG. 8, an example operating zone (e.g., a specific charge curve for a specific battery to be charged) is shown in which the maximum values of the output current, voltage, and power are further limited from their maximum values (shown in the top plot ofFIG. 8). For example, for an example lithium-ion battery, the operating zone (e.g., charge curve) can be defined by a current limit of 10 amps, a power limit of 2.4 kilowatts, and a voltage limit of 400 volts with a linear rampdown beginning at 380 volts (e.g., a 20-volt voltage delta).

FIGS. 9A-9Cschematically illustrate example proportional-integral (PI) controllers900for controlling the base current of the power transmitter in accordance with certain embodiments described herein. The PI controller900calculates an error function e(t) equal to a difference between the output current of the power receiver (e.g., the current provided to the load) and a predetermined current value (e.g., a setpoint selected by the controller). The error function can be calculated in a module905, as shown schematically inFIGS. 9A-9C. The PI controller900also calculates a process function D(t) equal to the sum of a first term proportional to the error function and a second term proportional to an integral of the error function over a time interval. The first term can be calculated in a module910, the second term can be calculated in a module920, and the sum of the first term and the second term can be calculated in a module930, as shown schematically inFIGS. 9A-9C. For example, the process function D(t) can take the following form:
D(t)=Kp(Ir(t−T)−Iout(t−T))+Ki∫0t(Iset(τ−T)−Iout(τ−T))dτ.Eq. 1

Using the calculated value of the process function (e.g., varying the base current so as to reduce the value or providing the value to the current source of the base controller unit or BCU), the PI controller900can control the output current by adjusting the base current. For example, the output current can be maintained at a predetermined current value (e.g., a setpoint less than or equal to a maximum output current). In certain embodiments, varying the base current is done iteratively (e.g., adjusting the base current towards a calculated setpoint, recalculating the value of the process function and/or the setpoint to determine a next adjustment of the base current towards the setpoint, and repeating until the base current equals the setpoint or approximates the setpoint within a predetermined range). The example PI controller900ofFIG. 9Bincludes a “Bluetooth delay” (e.g., about 5 milliseconds) which limits the bandwidth (e.g., to 250 Hz), and which can be applied by a module940. The example PI controller900ofFIG. 9Cincludes an additional control loop (e.g., having a 20 Hz bandwidth) that adjusts the DC bus voltage of the power transmitter in response to the value of the process function D(t) and using the conduction angle (e.g., bridge phase angle), which is discussed more fully below. In response, the controller900calculates a second error function eD(t) and uses its integral over a time period to set the DC bus voltage VDC(t). For example, as schematically shown inFIG. 9C, the second error function can be calculated by a module950and a term proportional to the second error function can be calculated by a module960.

The example PI controllers900ofFIGS. 9A-9Ceach receives at least one signal970indicative of the output current and adjusts the base current to control the output current to be within a predetermined range (e.g., at the setpoint). In certain other embodiments, the PI controller900is configured to adjust the base current to implement the different modes of operation compatible with the predetermined operating zone (e.g., the charge curves) of the load. For example, the at least one signal970received by the controller900from the power receiver can be further indicative of at least one of an output voltage of the power receiver or an output power of the power receiver, and the controller900can control the base current such that the power receiver is within the predetermined operating zone (e.g., the charge curves) defined at least by a maximum current, a maximum output voltage, or a maximum output power. Other operating parameters that can be used as control variables include, but are not limited to, power factor correction (PFC) DC voltage (PFC Vdc) of the power transmitter, the bridge phase angle or current, current generated by a selected one or more coils of the power receiver (e.g., quadrature Isc, DD Isc), phase angle of a selected one or more coils of the power receiver (e.g., quadrature phase, DD phase), thermal measurements of the power transmitter, input AC current or frequency, input power, efficiency, and operating frequency.

FIG. 10is an example flow diagram of a method1000compatible with certain such embodiments in which the controller900regulates the base current in response to signals that are further indicative of at least one of the output voltage or the output power of the power receiver. Knowledge of the values of two of these operating parameters can be used to calculate the third of these operating parameters (e.g., using the relation P=IV). For example, using signals indicative of the output current and the output voltage, the controller900can calculate the output power. In certain embodiments, the controller900is configured to calculate, in response to the signals received from the power receiver, a setpoint for the base current in which the operating parameters are all within the predetermined operating zone. This setpoint can be selected by the controller900to be the largest value of the base current that results in the operating parameters each being within the predetermined operating zone. The controller900further adjusts the base current towards the calculated setpoint. For example, if the signals received from the power receiver are indicative of the output current and output voltage resulting in an output power exceeding the power limit value, the controller900can regulate the base current to reduce the base current until the output power is below the power limit value.

As shown in the example flow diagram of the method1000ofFIG. 10, the controller900determines whether an output power limit of the power receiver has been reached (e.g., whether the output power is greater than a predetermined maximum output power of the operating zone) in an operational block1002. If the output power limit has been reached, the controller900calculates a first target current value corresponding to the maximum output power of the operating zone in an operational block1004. The controller900further determines whether an output voltage of the power receiver has been reached (e.g., whether the output voltage is greater than a predetermined maximum output voltage of the operating zone) in an operational block1006. If the output voltage limit has been reached, the controller900calculates a second target current value corresponding to the maximum output voltage of the operating zone in an operational block1008.

If neither the maximum output power nor the maximum output voltage has been reached (e.g., upon checking the output power in the operational block1002and the output voltage in an operational block1010), the controller900updates the charging state to a constant current state (e.g., adjusts the base current towards the setpoint current value) in an operational block1012. If the output power is greater than the maximum output power and the output voltage is not greater than the maximum output voltage, then the controller900updates the charging state to a constant power state (e.g., adjusts the base current towards the first target current value) in an operational block1014. If the output power is not greater than the maximum output power and the output voltage is greater than the maximum output voltage, then the controller900calculates the second target current value corresponding to the maximum output voltage of the operating zone in an operational block1016and updates the charging state to a constant voltage state (e.g., adjusts the base current towards the second target current value) in an operational block1018. If the output power is greater than the maximum output power and the output voltage is greater than the maximum output voltage, and the first target current is less than or equal to the second target current (e.g., upon checking in an operational block1020), then the controller900updates the charging state to a constant power state (e.g., adjusts the base current towards the first target current value) in the operational block1014. If the output power is greater than the maximum output power and the output voltage is greater than the maximum output voltage, and the first target current is greater than the second target current (e.g., upon checking in the operational block1020), then the controller900updates the charging state to a constant voltage state (e.g., adjusts the base current towards the second target current value) in the operational block1018.

The method1000ofFIG. 10that can be practiced by the controller900further regulates the base current in response to a signal that is indicative of a temperature of the power transmitter. The controller900determines whether temperature foldback (e.g., reduction) is required (e.g., whether the temperature is above a predetermined maximum temperature value) in an operational block1022. If the temperature is above the maximum temperature value, the controller900calculates a new setpoint value (e.g., reduced by a factor of two) in an operational block1024and updates the charging state to a temperature limited state (e.g., adjusts the base current to the new setpoint value) in an operational block1026. If the temperature is below or equal to the maximum temperature value, the controller900proceeds with controlling the base current. If the controller900determines that the temperature foldback is not required, the controller900determines whether an output current limit of the power receiver has been reached (e.g., whether the output current is greater than a predetermined maximum output current of the operating zone) in an operational block1028, calculates a target current value corresponding to the maximum output current of the operating zone in an operational block1030, and updates the charging state to a current limited state in the operational block1032.

FIG. 10also shows operational blocks for adjusting the base current once the charging state is determined that may be included in the method1000in certain embodiments. These operational blocks include, but are not limited to, incrementing the base current towards the target current with a ramp rate (e.g., changing the base current at a predetermined speed) in the operational block1034, calculating a power factor correction (PFC) voltage, power supply current, and AC switch PI controller parameters (e.g., using these operational parameters for further adjustment of the base current) in an operational block1036, updating a delay angle of a controllable rectifier in an operational block1038, and sending a “set current” command message to the base controller unit (BCU) (e.g., with a delay time of 10 milliseconds) in an operational block1040.

FIG. 11schematically illustrates a portion1102of the power transmitter (e.g., BCU) and a portion1104of the power receiver (e.g., vehicle controller unit or VCU) in accordance with certain embodiments described herein. The BCU comprises a PFC module1106which can be used to avoid excessive currents from the utility grid due to out of phase voltage and current, to avoid harmonic distortion due to other portions of the circuitry (e.g., switching action of a rectifier), and to filter the utility power at 50/60 Hz. The DC voltage from the PFC module1106can be supplied to an inverter module1108, the output of which can be referred to as a bridge current or base current. The magnitude of the fundamental of the output of the inverter module1108is dependent on the DC voltage received from the PFC module1106and the conduction angle θ (which can take any value from 0° to 180°) of the inverter bridge according to the following equation:

The conduction angle θ generally corresponds to a duty cycle. Higher conduction angles correspond to more time that power is being delivered. A lower conduction angle translates to lower voltage and higher current for the same power. Lower conduction angles require higher currents. In some implementations, the inverter module1108operates at conduction angles over 90°. Avoiding lower conduction angles and their associated higher currents can reduce component stress. If the inverter module1108is run at substantially 130°, then the total harmonic distortion (THD) of the output voltage may be reduced. As the inverter module1108increases the conduction angle from 120° to approximately 130°, third order harmonics increase as fifth order harmonics decrease. THD does not vary much between 120° and 130°, and increases slowly as it approaches 140°. Some implementations operate in the range of 115° to 140°.

As shown inFIG. 11, the output current from the power receiver is proportional to the DC bus voltage (Vdc), the conduction angle θ, and the coupling coefficient kbvbetween the power transmitter and the power receiver. In addition,FIG. 11shows that the reactance Xvof the power receiver is a factor in the output current, as will be discussed further below.

FIG. 12is a plot showing an example selected operating zone of the inductive power transfer (IPT) system in accordance with certain embodiments described herein. While the selected operating zone ofFIG. 12is labeled using the term “ideal,” as used herein, the term “ideal” is meant to signify that the “ideal” operating zone is one of many operating zones which provides satisfactory operation of the IPT system, but that the operation in the “ideal” operating zone is better in some way than in some other zones of operation. Use of the term “ideal” inFIG. 12does not imply that operation of the IPT system or the power receiver is necessarily optimized or maximized in the selected operating zone, but in certain embodiments, the operating zone may be selected to optimize or maximize operation of the IPT system or the power receiver (e.g., charging of the battery).

The example selected operating zone can be defined by a range of DC bus voltages and a range of H-bridge conduction angles, as shown inFIG. 12. For example, the selected operating zone can be defined to have the range of DC bus voltages (e.g., between the two values indicated by the horizontal dashed lines), and the range of conduction angles (e.g., between the two values indicated by the vertical dashed lines). As shown inFIG. 11, the output current is dependent upon the DC bus voltage, the conduction angle, and the coupling coefficient. It is desirable to select the values of DC bus voltage, conduction angle, and coupling coefficient to achieve a selected value of the output current while being in the selected operating zone. For example, for an example output current of 10 amps, there are various combinations of values of the DC bus voltage, conduction angle, and coupling coefficient that fall within the selected operating zone. However, for some values of the coupling coefficient, none of the values of the DC bus voltage and the conduction angle which result in an output current of 10 amps is within the selected operation zone. For example, for coupling coefficients of 0.15, 0.2, and 0.25, the DC bus voltage and conduction angle values that result in an output current of 10 amps intersect the selected operating zone, but for coupling coefficients of 0.1 or 0.3, there are no values of these operation parameters that result in an output current of 10 amps while intersecting the selected operating zone. Therefore, it can be desirable to vary the coupling coefficient between the power transmitter and the power receiver to be able to provide a selected output current while being in a selected operating zone.

In an IPT system, the level of coupling between the transmitter and receiver circuits may determine the output current for a given base current. The level of coupling is indicated by the coupling coefficient k, which may be determined at least in part by geometric factors such as the alignment of the inductors in the transmitter and receiver circuits and the distance between the inductors. These factors may vary between charging events, for example, depending on the positioning of the wireless power receiver. Therefore, the coupling coefficient k may also vary between charging events.

The power transmitter and the power receiver may be inductively coupled to one another by induction coils of various configurations (see, e.g.,FIGS. 5A-5C). The induction coils may be referred to or configured as “loop” antennas, and more specifically, multi-turn loop antennas. The induction coils may also be referred to herein or be configured as “magnetic” antennas. The coil may also be referred to as an “antenna” of a type that is configured to wirelessly output or receive power. As used herein, induction coils are examples of “power transfer components” of a type that are configured to wirelessly output, wirelessly receive, and/or wirelessly relay power. Loop (e.g., multi-turn loop) antennas may be configured to include an air core or a physical core such as a ferrite core. An air core loop antenna may allow the placement of other components within the core area. Physical core antennas including ferromagnetic or ferrimagnetic materials may allow development of a stronger electromagnetic field and improved coupling.

In this specification, the term “coil” is used in the sense of a localized winding arrangement having a number of turns of electrically conducting material that all wind around one or more central points. The term “coil arrangement” is used to mean any winding arrangement of conducting material, which may comprise a number of “coils.”

Efficient transfer of energy between a transmitter and receiver occurs during matched or nearly matched resonance between a transmitter and a receiver. However, even when resonance between a transmitter and receiver are not matched, energy may be transferred at a lower efficiency. Transfer of energy occurs by coupling energy from the near field of the transmitting induction coil to the receiving induction coil residing within a region (e.g., within a predetermined frequency range of the resonant frequency, or within a predetermined distance of the near-field region) where this near field is established rather than propagating the energy from the transmitting induction coil into free space.

According to some embodiments, the near field may correspond to a region around the induction coil in which electromagnetic fields exist. Near-field coupling-mode regions may correspond to a volume that is near the physical volume of the induction coil, typically within a small fraction of the wavelength. According to some embodiments, electromagnetic induction coils, such as single and multi-turn loop antennas, are used for both transmitting and receiving since magnetic near field amplitudes in practical embodiments tend to be higher for magnetic type coils in comparison to the electric near fields of an electric type antenna (e.g., a small dipole). This allows for potentially higher coupling between the pair. Furthermore, “electric” antennas (e.g., dipoles and monopoles) or a combination of magnetic and electric antennas may be used.

FIG. 13is a perspective view illustration of induction coils used in an IPT system1300in accordance with certain embodiments described herein. The IPT system1300comprises a base or transmitter which includes transmitter coil arrangement1301and a pick-up or receiver which includes receiver coil arrangement1302. Only the coils of the system1300are shown inFIG. 13for clarity purposes. The system1300may include one or more additional components as described herein. For the purposes of this specification, it may be assumed that the coils inFIG. 13are viewed in the longitudinal direction (e.g., relative to the electric vehicle).FIG. 13shows receiver coils1302positioned over transmitter coils1301, a position suitable for wireless power transfer between the transmitter and receiver coils1301and1302upon energizing the transmitter coils1301.

In the configuration ofFIG. 13, transmitter coils1301comprise two substantially co-planar transmitter coils1303aand1303bconnected to one or more power sources (not shown). In an embodiment, electric current flows in the same direction in the adjacent portions of the two coils1303aand1303band the current in these adjacent portions has substantially the same magnitude and phase.

Receiver coils1302comprise two substantially co-planar receiver coils1304aand1304b(e.g., which can be termed “DD coils”) and a third coil1305(e.g., which can be termed a “quadrature coil” or “QD coil”) positioned over the co-planar receiver coils1304aand1304b. The coils in coil arrangement1302may be connected to a battery (e.g., of an electric vehicle) to which they are configured to supply a charging current.

Both transmitter and receiver coil arrangements1301and302are associated with magnetically permeable members such as ferrite cores (not shown) positioned under the transmitter coils1301and above the receiver coils1302(see, e.g.,FIGS. 5A-5C). To transfer power using the coils1301and1302ofFIG. 13, an alternating electric current is passed through the transmitter coils1301. This creates a magnetic field in the form of a “flux pipe,” a zone of high flux concentration, looping above coil arrangement1301between the holes in transmitter coils1303aand1303b. In use, receiver coils1302are positioned such that the DD coils1304a,1304band the QD coil1305intersect the lines of magnetic flux, thus inducing electric current in the DD coils1304a,1304band the QD coil1305, which can be supplied to the battery of the electric vehicle.

The co-planar DD coils1304aand1304bextract power from the horizontal components of magnetic flux generated by the transmitter coils1301. The single QD coil1305extracts power from the vertical component of the magnetic flux generated by the transmitter coils. Thus, in combination, the coils of receiver coils1302enable energy transfer between the transmitter and receiver devices of the wireless power transfer system to a reasonably efficient degree.

FIG. 14Ais a plot of example short circuit currents for the DD coils and the QD coil for various lateral offsets of these receiver coils from a position directly above and centered on the transmitter coils. The measurement of the short circuit current across each inductive element (e.g., the QD coil and the DD coils) can be achieved by selectively closing both the switches in the sub-circuit nearest the inductive element, for example, closing switches S1and S2in the coupling circuit ofFIG. 15B, thereby shorting the coupling circuit. For a given base current in the primary inductor of the power transmitter, the short circuit current across the inductive element can be indicative of the level of coupling between the inductive element and the power transmitter. Any appropriate means of measuring the short circuit current may be used.

The current inductively generated by the QD coil is at a maximum when the receiver coils have zero lateral offset relative to the transmitter coils, and falls off with increasing lateral offset. The current inductively generated by the DD coils is at a minimum when the receiver coils have zero lateral offset relative to the transmitter coils, and increases with increasing lateral offset, to a maximum at approximately 160 mm, and then falls off with further increasing lateral offset. In other words, the coupling coefficients of the DD coils and of the QD coil are different from one another for most values of the lateral offset (the curves do intersect one another at a lateral offset value of about 90 mm). At a first range of lateral offsets (e.g., less than 90 mm), the QD coil can be denoted as “dominant” and the DD coils can be denoted as “recessive,” since the current generated by the QD coil is greater than that of the DD coils for the first range of lateral offsets. At a second range of lateral offsets (e.g., at 90 mm and above), the DD coils can be denoted as “dominant” and the QD coil can be denoted as “recessive,” since the current generated by the QD coil is less than that of the DD coils for the second range of lateral offsets.FIG. 14Bis the plot ofFIG. 14Awith an example demarcation line between the QD coil being dominant and the DD coils being dominant at a lateral offset value that is at the crossing point of the two curves. In certain embodiments, the power receiver comprises sensors configured to measure the short circuit current in each of the inductive elements and determine which of the inductive elements is dominant and which is recessive.

FIG. 14Cis a plot of the example currents for the DD coils and the QD coil ofFIG. 14A, along with their sum. By selecting whether the current generated by the QD coil, the DD coils, or both the QD coil and the DD coils are used to supply current to the load, the effective coupling coefficient of the system can be selected among three values for most values of the lateral offset. The configuration in which current only generated by the QD coil is used can be considered as a first coupling state, the configuration in which current only generated by the DD coils is used can be considered as a second coupling state, and the configuration in which current from both the QD coil and the DD coils is used can be considered to be a third coupling state. This method for selecting the coupling state can be used to provide a coupling coefficient for which the DC bus current and the conduction angle can be selected to be within the selected operation zone.

However, for many of these lateral offset values, the differences between these three effective coupling coefficients can be large, such that all three of the effective coupling coefficients miss the selected operation zone (see, e.g.,FIG. 12). Thus, it can be desirable to have further granularity in the selection of the effective coupling coefficient.

FIGS. 15A-15Eschematically illustrate an example coupling circuit1500of the power receiver in which a reactance of the power receiver can be varied in accordance with certain embodiments described herein.FIG. 15Ais a schematic diagram of a receiver coupling circuit1500in which, through inductive coupling between the power transmitter and the receiver circuit, a voltage Vocis induced in inductive element L2. This voltage is represented by voltage source VocinFIG. 15A. When an alternating current I1having a frequency ω is present in the base circuit of the power transmitter, the induced voltage in the coupling circuit ofFIG. 15Ais given by:
Voc=jωI1k√{square root over (L1L2)}  Eq. 3

The values of C1and C2may be chosen so that, with inductive element L2, a tuned resonant circuit is formed at the frequency of the alternating base circuit current I1. To achieve tuning in the coupling circuit shown inFIG. 15A, the values of C1, C2, and L2may be related:

The output current IRsupplied to the load R may be given by:
IR=VocωC1Eq. 5
It should be noted that the formulae used herein assume perfect tuning and ideal components as presented in the figures. In reality, there may be losses or minor residual effects that cause the true values to differ from the ideal case. However, the formulae provide values that approximate the real values and usefully illustrate relationships between variables.

The values of capacitances C1and C2may be varied in order to vary the output current for a given base current and a given level of coupling. However, varying C1and C2may further affect the tuning of the coupling circuit, which may reduce the efficiency of power transfer at the resonant frequency. It may therefore be desirable to vary the partial series or parallel capacitance while keeping the coupling circuit tuned.

In certain embodiments, the receiver coupling circuit1500can be configured to respond to control signals from a controller to selectively connect capacitive elements in the power receiver circuit to enable the reactance Xvof the coupling circuit, and hence the output current (see, e.g.,FIG. 11), to be varied for a given level of coupling, thus enabling the coupling circuit to selectively deliver the particular output current, while the resonant frequency at which inductive element L2is tuned remains substantially the same for different configurations of the capacitive elements.

FIG. 15Bis a schematic diagram of an example switchable coupling circuit1500in accordance with certain embodiments described herein. The coupling circuit1500includes an inductive element L2in which a voltage Vocis induced by means of resonant inductive coupling from an inductive element of a power transmitter (not shown). The induced voltage is shown as an equivalent voltage source. The coupling circuit1500further comprises capacitive elements in the form of capacitors C1, C2, and C3, respectively. The coupling circuit also includes switching elements S1and S2. An output current IRis drawn from across capacitor C1to supply a load R, which is representative of a battery unit, and is depicted as being a resistive load of resistance R. In other embodiments, current IRmay be supplied to directly power a load, or may be used to charge a battery unit and to power a load.

Capacitors C1, C2, and C3and switching elements S1and S2are connected such that switching elements S1and S2are connected in series and capacitors C1and C2are connected in series, with the two switching elements S1and S2being connected in parallel with the two capacitors C1and C2. Capacitor C3is connected to bridge from between the two switching elements S1and S2to between capacitors C1and C2.

Switches S1and S2can be opened and closed to configure the connection of capacitors C1, C2, and C3and the reactance presented to the inductor L2and thereby vary the output current IR.FIG. 15Cschematically illustrates a configuration in which switch S1ofFIG. 15Bis closed and switch S2is open, capacitors C2and C3are connected in parallel with each other and in series with capacitor C1. In this configuration, the output current may be given by:
IR=VocωC1Eq. 6

FIG. 15Dschematically illustrates another configuration in which switch S1ofFIG. 15Bis open and switch S2is closed. In this case, capacitors C1and C3are connected in parallel with each other and in series with capacitor C2. In this configuration, the output current may be given by:
IR=Vocω(C1+C3)  Eq. 7

In the configuration ofFIG. 15C, the series reactance of the tuning circuit is lower, and the output current is lower. In the configuration ofFIG. 15D, the series reactance is higher, and the output current is higher.

To maintain the tuning of the receive coupling circuit in both configurations discussed above, the reactance of both coupling circuits may be substantially equal. The reactance of the coupling circuit in which switch S1is closed and switch S2is open may be given by:

Xhigh⁢⁢k=(C1+C2+C3ω⁡(C2+C3)⁢C1)Eq.⁢8
The reactance of the coupling circuit in which switch606is open and switch607is closed may be given by:

Xlow⁢⁢k=(C1+C2+C3ω⁡(C1+C3)⁢C2)Eq.⁢9
For these values of reactance to be equal, the relationship between C1and C2may be given by:
C1=C2Eq. 10

In some embodiments, the capacitances of capacitors C1and C2may be substantially equal in order to be able to switch the coupling circuit between “high” and “low” current modes while maintaining the same reactance of the tuning circuit in both configurations. As a result, the coupling circuit may advantageously remain tuned and energy transfer may be improved.

FIG. 15Eschematically illustrates an example coupling circuit1500in which multiple sub-circuits each comprise two switching elements and three capacitors are connected in parallel with one another. In the coupling circuit ofFIG. 15E, the sub-circuit of switching elements and capacitors shown inFIG. 15Bhas been repeated n times, each connected in parallel to the other. As a result, the coupling circuit1500includes 2×n switching elements and 3×n capacitors. The capacitances of the capacitors may vary between the sub-circuits. The output current IRdrawn by the load R is the sum of the output currents of each of the sub-circuits. To maintain the tuning of the coupling circuit in one or more configurations of the 2×n switching elements, the capacitors connected in series in sub-circuits may have equal capacitances such that C1=C2, C4=C5, C(3n−2)=C(3n−1), etc. The number of different output currents that can be achieved by the coupling circuit ofFIG. 15Ethrough different combinations of open and closed switches for a given induced voltage Vocmay be given by 2n. Therefore, the coupling circuit1500can be configured to provide many different levels of output current IRfor a given induced voltage. In addition, the values of the capacitances in each of the sub-circuits can be selected to tailor spacings between each level of output current. For example, the capacitances can be selected to linearly space achievable output current levels, or more closely space the achievable output current levels where desirable. As another example, if efficiency is lost for small changes at certain levels, more capacitance configurations can be made to achieve output currents around that level. By using this level of configuration, an IPT system can select the configuration of capacitors that provides the output current giving an optimal efficiency for the parameters of the IPT system and circumstances of charging events, such as the alignment or distance between inductors which affects the coupling coefficient.

FIG. 16Ais a plot of the various short circuit currents generated by each of the QD coil and the DD coils in two possible reactance states (e.g., “low” and “high,” see e.g.,FIGS. 15C and 15D) in accordance with certain embodiments described herein.FIG. 16Bis a plot of the various short circuit currents generated by the three coupling states of the QD coil and the DD coils in their two possible reactance states each, in accordance with certain embodiments described herein. There are eight possible states (combinations of three coupling states and two reactance states), each having a different generated current as a function of the lateral offset.

In some embodiments, the power receiver comprises a plurality of inductive elements (e.g., the QD coil and the DD coils) configured to inductively generate current in response to a magnetic field generated by the power transmitter. The power receiver further comprises a coupling circuit operatively coupled to the plurality of inductive elements. The coupling circuit is configured to be selectively switched among a plurality of coupling states, with each coupling state having a corresponding set of inductive elements configured to provide current to the load. For example, the coupling circuit can be switched such that only the QD coil provides current to the load, only the DD coils provide current to the load, or both the QD coil and the DD coils provide current to the load. The coupling circuit is further configured to be selectively switched such that each inductive element of the set of inductive elements has a reactance state of a plurality of reactance states. For example, when only the QD coil provides current to the load, the coupling circuit can be switched such that the QD coil is either in the “high” reactance state or in the “low” reactance state. The power receiver further comprises a controller coupled to the coupling circuit and configured to respond to one or more signals indicative of one or more operating parameters of the power receiver, the power transmitter, or both, by selecting the coupling state and selecting the reactance state of each inductive element of the set of inductive elements.

The coupling state can be selected by the controller by opening and closing switching elements (e.g., relays or other electrically operated switches) of the coupling circuit of the power receiver that connect or disconnect the various inductive elements of the power receiver to the load. The reactance state can be selected by the controller by opening and closing the switching elements S1and S2(e.g., relays or other electrically operated switches) for the inductive elements connected to the load (see, e.g.,FIG. 15B). The controller may use the exemplary logic described below to decide the appropriate switch configuration in different circumstances. The controller may comprise appropriate storage and processor means for determining a configuration of switching elements given measured system parameters. The controller may also close the switches corresponding to each inductive element to enable the short circuit current to be measured and subsequently switch the switches to the configuration for the selected coupling states and reactance states.

FIG. 17is a plot of an example selection of coupling states and reactance states to approximate a constant output current (e.g., 13 amps) for a range of lateral offset values in accordance with certain embodiments described herein. For the lowest values of lateral offset (e.g., from 0 to about 50 mm), the controller can select the coupling state in which current from only the QD coil is used and the reactance state of the QD coil being in the “low” reactance configuration. For the next higher values of lateral offset (e.g., from about 50 mm to about 90 mm), the controller can select the coupling state in which current from only the QD coil is used and the reactance state of the QD coil being in the “high” reactance configuration. For the next higher values of lateral offset (e.g., from about 90 mm to about 150 mm), the controller can select the coupling state in which current from only the DD coils is used and the reactance state of the DD coils being in the “high” reactance configuration. For the next higher values of lateral offset (e.g., from about 150 mm to about 180 mm), the controller can select the coupling state in which current from both the QD coil and the DD coils is used and the reactance state of the QD coil being in the “low” reactance configuration and the reactance state of the DD coils being in the “low” reactance configuration. For the next higher values of lateral offset (e.g., above about 180 mm), the controller can select the coupling state in which current from only the DD coils is used and the reactance state of the DD coils being in the “high” reactance configuration.

FIG. 18schematically illustrates a controller1800compatible with certain embodiments described herein. The controller1800includes the PI controller900schematically illustrated inFIG. 9C, with additional functionality. To determine whether the DC bus voltage is stable, the integral of the second error function eD(t) is calculated in the module1810and if the integral equals zero and if Vdcequals the maximum voltage or the minimum voltage (e.g., determined in the module1820), then the DC bus voltage is deemed stable in the module1830. The conduction angle (e.g., the duty cycle) is measured and determined whether it is within the desired range that corresponds to the selected operating zone (e.g., between 115° and 140°) in the module1840. If the conduction angle is outside the desired range, the reactance states of the various inductive elements may be switched to achieve the selected operating zone. For example, the state machine can be incremented only after the normal output current control and the DC bus voltage are stable.

If the conduction angle is within the desired range, the controller1800increments its state machine in the module1850to select which coupling and reactance states to use. If the coupling circuit is not in the selected coupling and reactance states, then the controller1800sends appropriate control signals to the various switching elements of the coupling circuit to achieve the selected coupling and reactance states.

However, in certain embodiments, the use of all eight possible permutations may not be needed, and only some of the possible permutations may be used. Certain such embodiments can advantageously avoid excessive switching among the various coupling states and reactance states.FIG. 19schematically illustrates an example state machine1900of the controller compatible with certain embodiments described herein. For example, the state machine1900ofFIG. 19uses only five of the eight possible permutations, which are shown inFIG. 19are increasing in output current from left to right: (i) “dominant low”: only the dominant inductive element providing current to the load while in its “low” reactance state; (ii) “dominant high”: only the dominant inductive element providing current to the load while in its “high” reactance state; (iii) “dominant low and recessive low”: both the dominant inductive element while in its “low” reactance state and the recessive inductive element while in its “low” reactance state providing current to the load; (iv) “dominant high and recessive low”: both the dominant inductive element while in its “high” reactance state and the recessive inductive element while in its “low” reactance state providing current to the load; and (v) “dominant high and recessive high”: both the dominant inductive element while in its “high” reactance state and the recessive inductive element while in its “high” reactance state providing current to the load. In certain such embodiments, the following permutations are not used: the dominant inductive element is in its “low” reactance state while the recessive inductive element is in its “high” reactance state; only the recessive inductive element is in its “low” reactance state; and only the recessive inductive element is in its “high” reactance state.

In deciding whether to switch among the coupling and reactance states, the state machine1900ofFIG. 19utilizes information regarding whether the duty cycle (“Dcycle”) is below the desired range of values (e.g., whether the conduction angle is below 115 degrees) or whether the duty cycle is above the desired range of values (e.g., whether the conduction angle is above 140 degrees). The state machine1900also utilizes information regarding whether the DC bus voltage is low (e.g., less than 328 volts) or whether the DC bus voltage is high (e.g., greater than 332 volts). The state machine1900also utilizes information regarding whether the dominant inductive element has enough current to meet the desired output current by itself (e.g., “dominant low coil good”). Such an evaluation can be based on couplings measured during a verification of the alignment, scaled for output voltage, of the inductive elements of the power receiver with those of the power transmitter.

The various operations of methods described above may be performed by any suitable means capable of performing the operations, such as various hardware and/or software component(s), circuits, and/or module(s). Generally, any operations illustrated in the Figures may be performed by corresponding functional means capable of performing the operations. For example, a power receiver configured to supply current to a load and to be wirelessly operatively coupled to a power transmitter can comprise means for inductively generating current (e.g., a plurality of inductive elements including at least a first inductive element or a second inductive element) in response to a magnetic field generated by the power transmitter. The power receiver can further comprise first means for selectively switching among a plurality of coupling states (e.g., a first sub-circuit having switching elements configured to selectively connect the inductive elements to the load). Each coupling state of the plurality of coupling states has a corresponding portion of the means for inductively generating current configured to provide current to the load. The power receiver can further comprise second means for selectively switching the means for inductively generating current among a plurality of reactance states (e.g., a plurality of second sub-circuits each having one or more switching elements configured to change the reactance of a corresponding inductive element connected to the load and one or more capacitive elements). The power receiver can further comprises means for controlling the first means for selectively switching and for controlling the second means for selectively switching in response to one or more signals indicative of one or more operating parameters of at least one of the power receiver or the power transmitter (e.g., a processor).

The steps of a method or algorithm and functions described in connection with the embodiments disclosed herein may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. If implemented in software, the functions may be stored on or transmitted over as one or more instructions or code on a tangible, non-transitory computer-readable medium. A software module may reside in Random Access Memory (RAM), flash memory, Read Only Memory (ROM), Electrically Programmable ROM (EPROM), Electrically Erasable Programmable ROM (EEPROM), registers, hard disk, a removable disk, a CD ROM, or any other form of storage medium known in the art. A storage medium is coupled to the processor such that the processor can read information from, and write information to, the storage medium. In the alternative, the storage medium may be integral to the processor. Disk and disc, as used herein, includes compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk and blu ray disc where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above should also be included within the scope of computer readable media. The processor and the storage medium may reside in an ASIC. The ASIC may reside in a user terminal. In the alternative, the processor and the storage medium may reside as discrete components in a user terminal.

Various modifications of the above described embodiments will be readily apparent, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.