Abstract:
A wireless power transfer system includes a coil assembly including a pair of spaced apart inductive coils positioned on a same side of a ferrite pad, and a switching network. The switching network, in response to an indication of a corresponding inductive coil assembly configuration, selectively operates the coils in a two-pole mode or a three-pole mode.

Description:
TECHNICAL FIELD 
       [0001]    Described herein are wireless power transfer systems. 
       BACKGROUND 
       [0002]    Inductive wireless power transfer (WPT) utilizes magnetic coupling between two magnetic field coupling units (a primary coil and a secondary coil). WPT systems may be used to charge electric vehicles (EV), as well as mobile devices, medical devices, etc. In some examples, the secondary, or receiving coil, may employ a solenoidal winding topology. In other examples, the secondary coil may employ a circular winding topology. 
       SUMMARY 
       [0003]    A wireless power transfer method includes, in response to an indication that a secondary coil assembly has a two-pole configuration, controlling current flow in each of a pair of primary coils that are spaced apart and positioned on a same side of a ferrite pad such that directions of the current flow in the primary coils are opposite, and in response to an indication that the secondary coil assembly has a three-pole configuration, controlling current flow in each of the primary coils such that directions of the current flow in the primary coils are the same. 
         [0004]    A wireless power transfer system has a coil assembly including a pair of spaced apart inductive coils positioned on a same side of a ferrite pad, and a switching network configured to, in response to an indication of a corresponding inductive coil assembly configuration, selectively operate the coils in a two-pole mode or a three-pole mode. 
         [0005]    A vehicle includes a traction battery and a secondary coil assembly operatively arranged with the traction battery and configured to receive power from a corresponding primary coil assembly. The secondary coil assembly includes a ferrite pad and a pair of secondary inductive coils spaced apart and positioned on the pad. The vehicle further includes a controller configured to send data to the corresponding primary coil assembly indicating a two-pole configuration or a three-pole configuration for the secondary coil assembly. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  is schematic view of a wireless power transfer system; 
           [0007]      FIGS. 2, 3, 5, 9, 11 and 16  are schematic perspective views of primary coil assemblies; 
           [0008]      FIGS. 4 and 6  are side views, in cross-section, of primary and secondary coil assemblies for two-pole and three-pole configurations respectively; 
           [0009]      FIGS. 7, 8, 12 and 14  are perspective views of primary and secondary coil assemblies; 
           [0010]      FIG. 10  is a side view, in cross section, of the primary coil assembly of  FIG. 9 ; 
           [0011]      FIGS. 13 and 15  are side views, in cross-section, of primary and secondary coil assemblies for two-pole and three-pole configurations respectively; 
           [0012]      FIG. 17  is a side view, in cross section, of portions of the primary coil assembly of  FIGS. 12 and 14 ; 
           [0013]      FIG. 18  is a block diagram of a wireless power transfer system; 
           [0014]      FIGS. 19, 20 and 22  are block diagrams of coil combining networks for a wireless power transfer system; and 
           [0015]      FIGS. 21 a  through 21 f    are schematic diagrams of coil arrangements for the system of  FIG. 18 . 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention that may be embodied in various and alternative forms. The figures are not necessarily to scale; some features may be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention. 
         [0017]    WPT for electric vehicles may be implemented in public charging stations. These charging stations may be installed in parking lots, public garages, etc., to enable frequent charging of electric cars to improve their driving range and usability. Main components of the magnetic field coupling units in WPT systems are single or multiple windings of current carrying wire, ferrite blocks, a non-magnetic highly conductive shielding metal plate, and plastic packaging. The winding and core topology design along with current excitation determine the magnetic field distribution generated by the coupling unit. Current wireless power transfer systems may be composed of couplers with the same winding topologies but with different size to accommodate packaging restrictions into the vehicle. In some examples, the coils may employ a winding topology that creates a pair of poles distributed on opposite sides of the coupler (linear two-pole flux distribution). An example for this type of two-pole topology is a solenoidal winding topology. In other examples, the coils may create one central pole and one distributed pole around the coupler periphery (circular two-pole flux distribution) such as a circular winding topology or frame coupler. Since the pole locations of these coil topologies are different, a vehicle with a circular receiving coil cannot effectively charge over a coil that generates a linear two-pole flux distribution. Disclosed herein are winding topologies that can generate both linear two-pole and linear three-pole flux distributions. The two-pole flux generating operation of the proposed coil may support solenoidal coils (and also other similar coil topologies), whereas the three-pole flux generating operation of the proposed coil can support circular coils (and other three-pole flux distribution generating coils). The proposed coils can be used either as a primary or a secondary coil. 
         [0018]    In the automotive field, different automotive manufacturers may implement different systems within their vehicles. For example, some systems may implement a circular secondary coil which uses a centered pole for wireless power transfer. Others may implement a solenoidal secondary coil having no pole on the vehicle axis of symmetry. Such differences in the secondary coil assembly may make interoperability of the charging stations difficult, and/or require an offset condition between the vehicle and primary pad, which may be problematic for parking. 
         [0019]    Described herein are wireless power transfer systems that may allow a charging station to effectively and efficiently wirelessly charge a vehicle having either a two-pole or three-pole configuration. These wireless power transfer systems may be configured to wirelessly transmit power from a primary coil assembly to a secondary coil assembly. The coil assembly may include two coils defining a center space there between. The center space may be optimized for efficient power transfer when the secondary coil assembly is either a two pole configuration or a three pole configuration. 
         [0020]      FIG. 1  is an exemplary wireless power transfer system  100  showing a primary coil assembly  105  and a secondary coil assembly  110  within a vehicle  115 . The primary coil assembly  105  may be connected to an external power source  120 . The vehicle  115  may include a rechargeable battery  125  and a charge controller  135  in communication therewith. The charge controller  135  may be connected to a rectifier  130 . The rectifier  130  may convert the alternating current (AC) of the secondary coil assembly  110  to direct current (DC). The rectifier  130  may then transmit the electrical current from the secondary coil assembly  110  to the battery  125  in order to charge the battery  125 . The primary and secondary coil assemblies  105 ,  110  are described in more detail below. Each may include at least one coil. The coils of the primary coil assembly  105  may be coupled to secondary coils of the secondary coil assembly  110 . As current flows through the primary coils, the energy emitted from the primary coils may be received at the secondary coils, which is in turn used to charge the battery. 
         [0021]      FIG. 2  is an exemplary primary coil assembly  105 . The primary coil assembly  105  may include a backing plate  140 , a ferrite pad  145  and spiral windings  150 . The backing plate  140  may be constructed of aluminum or some other non-magnetic highly conductive material to create a shield for the magnetic field and to aid in directing the magnetic field towards the opposite coil. The ferrite pad  145  may include a plurality of ferrite pads. The ferrite pad  145  along with a backing plate  140  may help guide the magnetic flux to enhance coupling by directing the magnetic field towards the secondary coil assembly  110 . 
         [0022]    The spiral coils  150  may include a copper winding coil arranged on top of the ferrite pad  145 . The coils  150  may form a continuous ring-like shape defining a coil opening  155  in the center of each. The coils  150  may form a circular shape, or may have straight sides forming a quadrilateral shape, as shown in  FIG. 2 . The coils  150 ,  170  may be comprised of copper wire, typically Litz wire. As current is supplied to the coils  150 ,  170 , a magnetic field may be created between the primary coil assembly  105  and the secondary coil assembly  110 . 
         [0023]      FIG. 3  shows an exemplary current flow through the coils  150 . In this example, current is flowing in opposite directions in the coils  150  (clockwise in one, counter-clockwise in the other). As current is flowing through the coils  150  at the primary coil assembly  105 , energy may be transmitted to the secondary coil assembly  110  via a magnetic field. If the secondary coil assembly  110  supports a two-pole configuration, then current may likewise flow in opposite directions in coils of the secondary coil assembly  110 . 
         [0024]      FIG. 4  shows the corresponding flux distribution for a two-pole configuration when current is flowing in opposite directions as described above. As shown, a two-pole flux distribution is achieved in this example. 
         [0025]      FIG. 5  illustrates another implementation of the primary coil assembly  105  of  FIG. 2  in which current in the coils  150  is flowing in the same direction (both clockwise in this example). Current flow, in other examples however, may be counter-clockwise. This configuration may create a three-pole flux distribution. 
         [0026]      FIG. 6  illustrates the corresponding flux distribution for a three-pole configuration in which the flux is distributed at a central pole and two edge poles between the primary and secondary coil assemblies  105 ,  110 . 
         [0027]      FIG. 7  illustrates an exemplary secondary coil assembly  110  over the exemplary primary coil assembly  105  of  FIG. 2 . The secondary coil assembly  110  may include a secondary ferrite pad  180  with a secondary solenoidal coil  185  wrapped there around. Although not shown, the secondary coil assembly  110  may also include a backing plate. 
         [0028]      FIG. 8  illustrates another exemplary secondary coil assembly  110  having a circular coil  190  over the exemplary primary coil assembly  105  of  FIG. 2 . In this example, the secondary coil assembly  110  may include a secondary circular coil  190 . The coil  190  may be arranged on a ferrite pad  180 . Although not shown, the secondary coil assembly  110  may also include a backing plate. 
         [0029]      FIG. 9  shows the primary coil assembly  105  of  FIG. 2  with additional dimensions for the length L and width W.  FIG. 10  shows a cross-sectional view of the primary coil assembly  105  including the two circular coils  150 , each having an inner portion  205  and an outer portion  210 . The coil opening  155  between the inner and outer portions  205 ,  210  may have an opening width A. The inner portion  205  may have an inner portion width B, and the space between the two parallel coils  150  may be indicated as center space C. 
         [0030]    The dimensions of A, B, C, L and W may be relevant to the interoperability of the WPT system  100 . For example, the dimensions may be optimized so that the primary coil assembly  105  may operate as a coupler for both two-pole and three-pole systems. Optimum performance in a linear two-pole configuration may require a small value for center space C. Optimum performance in a linear three-pole configuration may require a large value for center space C. Optimization for each configuration may result in a compromise between the ideal values of C. For example, C may be approximately 10% of the length L of the ferrite pad  145 . This optimization may permit both the two-pole and three-pole configurations. 
         [0031]      FIG. 11  is another exemplary primary coil assembly  105  having two solenoidal coils  170 . The coils  170  may be copper windings, but unlike the windings of  FIG. 2 , the coils  170  may form a solenoidal structure having a continuous winding wrapped around the ferrite pad  145  instead of a spiral winding arranged on top of the pad  145 . The coils  170  may extend around and transverse to the pad  145 . The two coils  150 ,  170 , as shown in  FIGS. 2 and 3 , may be separated by a center space C. 
         [0032]      FIG. 12  illustrates a primary coil assembly  105  similar to  FIG. 11  and a solenoidal secondary coil assembly  110 .  FIG. 12  shows an exemplary current flow through the coils  170 . In this example, current is flowing in the same direction with respect to the center space C. As current is transmitted through the coils  170  at the primary coil assembly  105 , energy may be transmitted to the secondary coil assembly  110  via a magnetic field. If the secondary coil assembly  110  includes a two pole configuration, then the current may flow in the same direction with respect to the center space C. That is, both currents may extend parallel to each other, as shown in  FIG. 12 . An exemplary flux distribution for this configuration is shown in  FIG. 13 . 
         [0033]      FIG. 14  illustrates a primary coil assembly  105  similar to  FIG. 11  and a circular secondary coil assembly  110 . In this example, current is flowing in opposite directions in each of the coils  170 . This configuration may create a three-pole flux distribution, as shown in  FIG. 15 . 
         [0034]      FIG. 16  shows the primary coil assembly  105  of  FIG. 11  with additional dimensions for the length L and width W.  FIG. 17  shows a cross sectional view of the primary coil assembly  105  including the two solenoidal coils  170 , each having a width B separated by center space C. As explained above, the dimensions of A, B, C, L and W may be relevant to the interoperability of the WPT system  100 . Optimum performance in a linear three-pole configuration may require a large value for center space C. Optimization for each configuration may result in a compromise between the ideal values of C. For example, C may be approximately 10% of L. This optimization may permit both the two-pole and three-pole configurations for the solenoidal coils  170  of the primary coil assembly  105 . 
         [0035]    The primary coil assembly  105  may receive a command from the secondary coil assembly  110 . The command may include an indication of the configuration of the secondary coil assembly  110  (e.g., two-pole or three-pole configuration.) The primary coil assembly  105  may respond to the command by instructing current to flow through each of the coils in the appropriate direction. This is described below with respect to the coil combining network  260  of  FIG. 19 . 
         [0036]    By switching the direction of the current flow in one of the primary coils  150 ,  170  the primary coil assembly  105  may be configured to effectively transmit power to a secondary coil assembly  110  in either of the two-pole or three-pole configurations. Thus, the primary coil assembly  105  is interoperable between two- and three-pole configurations. Likewise, a secondary coil assembly  110  may be configured to effectively operate in a two- or three-pole configuration for coupling to a primary coil assembly  105  having various pole configurations. 
         [0037]    As explained herein, while specific reference was made to the coil assemblies  105  in  FIG. 2  and  FIG. 3  as the primary coil assemblies, the coil assemblies in  FIG. 2  and  FIG. 3  may also operate as the secondary coil assembly  110 . As described below with respect to  FIG. 19 , coil combining networks  260  may be used at the primary coil assembly when coil assemblies in  FIG. 2  and  FIG. 3  are used as the primary coil assembly. Similarly as shown in  FIG. 20 , coil combining networks  305  may be used at the secondary coil assembly  110  when coil assemblies in  FIG. 2  and  FIG. 3  are used as the secondary coil assembly  110 . While specific reference may be made to the primary assembly  105  and the secondary assembly  110 , each assembly may operate as the other. Additionally or alternatively, a DC combining network shown in  FIG. 22  may be used at the secondary assembly  110 . 
         [0038]      FIG. 18  illustrates a block diagram of the WPT system  100  having a power source  120 , a primary power unit  225 , a primary controller unit  235 , a secondary power unit  230 , a secondary controller unit  240  and a battery  125 . In this example, the primary and the secondary controller units  235 ,  240  may include processors and a memory for carrying out instructions as well as supplying instructions to the primary and secondary coil combining networks, as shown in  FIGS. 19 and 20 . These instructions may be configured to control the coil current flow and the configuration of the coils in the primary and secondary power units  225 ,  230  to support two-pole or three-pole flux distributions depending on the misalignment, and the combination of the primary and secondary coupler assemblies  105  and  110 . 
         [0039]    The primary coil assembly  105  and the secondary coil assembly  110  may communicate with one another. In one example, the communication may be facilitated over radio frequencies, or other wireless communications protocols. The primary coil assembly  105  may transmit a message to the secondary coil assembly  110  indicating the type of coil configuration of the primary coil assembly  105 . That is, the primary coil assembly  105  may indicate whether the primary assembly  105  has a two-pole configuration or a three-pole configuration (a solenoidal arrangement or circular arrangement). Depending on the configuration of the primary coil assembly  105 , the coil combining network  305  of the secondary may configure the secondary coils  150 ,  170  so that the secondary coil arrangement matches the primary coil arrangement. In another example, the secondary coil assembly  110  may transmit the message indicating the type of coil configuration to the primary coil assembly  105 , etc. As an alternative to communication between the primary and the secondary coil assemblies  105 ,  110 , the secondary or primary units  225 ,  230  may sweep between two-pole or three-pole modes at low power to find the best suited mode of operation. 
         [0040]      FIG. 19  illustrates the details of the coil combining network  260  in the primary power unit  225 . The power electronics block  250  connected to the power source  120  may include power electronics circuitry to convert the low frequency AC power to higher frequency AC power. The tuning network  255  may include passive electric components to create a resonance with the primary coils  150 ,  170 . The tuning network  255  may also be a part of the coil combining network  260 . The coil combining network  260  may be implemented using active power electronics and/or other passive elements. In this case, the combining network  260  may implement any desired set of S-port network properties defining the relationships between voltages and currents at the one input port and two output ports. 
         [0041]    The details of the coil combining network in the secondary power unit are shown in  FIG. 20 . The tuning network  310  may include passive electric components to create a resonance with the secondary coils  150 , 170 . The tuning network  310  may also be a part of the coil combining network  305  or may precede the coil combining network  305 . The coil combining network  305  may be implemented using active power electronics and/or other passive elements. In this case, the combining network  305  may implement any desired set of 3-port network properties defining the relationships between voltages and currents at the two input ports and one output port. The tuning network  310  in  FIG. 20  may be followed with a rectifier  315  to convert the high frequency AC power to DC power to charge the battery. 
         [0042]      FIGS. 21 and 22  illustrate detailed implementations of the passive coil combining networks.  FIGS. 21 a  through 21 f    show various coil arrangements for combining the coils in the AC circuitry. The coils may be configured in various arrangements including parallel in phase, parallel opposing phase, series in phase, and series opposite phase (see  FIGS. 21 a  through 21 d   , respectively). Implementing coils in series or parallel configuration may depend on the compensation and control method selected for the operation of the power electronics block. One configuration (e.g. series or parallel) may be selected over another configuration depending on the power electronics and tuning methods for the WPT system  100 . However, in-phase and out-of-phase configurations may be selected adaptively during operation at the start of the charging event to excite the two-pole or three-pole flux patterns. In an event in which a large misalignment is recognized between the primary and secondary assemblies  105 ,  110 , one coil may be shorted. Examples of these arrangements are shown in  FIGS. 21 e  through 21 f   . AC combining network may be used both for primary or secondary power units  225 ,  235 . 
         [0043]      FIG. 22  illustrates another exemplary coil combining network system  400  for combining the coils in the DC circuitry for the WPT system  100 . In this example, the system  400  may include a rectifier  415  and tuning network  410  for each coil. The system  400  may also include a switch  425  at each coil. The switch  425  may be used to short the respective coils in the event that a large misalignment is recognized. The optional switches may be before or after the tuning network  410  and/or incorporated with it. In this example, the currents on the coils are rectified separately and combined after rectification. Since this method requires rectification, this configuration may be applicable to the secondary power units. 
         [0044]    Computing devices described herein generally include computer-executable instructions in which the instructions may be executable by one or more computing devices such as those listed above. Computer-executable instructions may be compiled or interpreted from computer programs created using a variety of programming languages and/or technologies, including, without limitation, and either alone or in combination, Java™, C, C++, Visual Basic, Java Script, Perl, etc. In general, a processor (e.g., a microprocessor) receives instructions from a memory, a computer-readable medium, etc., and executes these instructions, thereby performing one or more processes, including one or more of the processes described herein. Such instructions and other data may be stored and transmitted using a variety of computer-readable media. 
         [0045]    With regard to the processes, systems, methods, heuristics, etc., described herein, it should be understood that, although the steps of such processes, etc., have been described as occurring according to a certain ordered sequence, such processes could be practiced with the described steps performed in an order other than the order described herein. It further should be understood that certain steps could be performed simultaneously, that other steps could be added, or that certain steps described herein could be omitted. In other words, the descriptions of processes herein are provided for the purpose of illustrating certain embodiments, and should in no way be construed so as to limit the claims. 
         [0046]    While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention. Additionally, the features of various implementing embodiments may be combined to form further embodiments of the invention.