Wireless high power transfer

Abstract

In a system for wirelessly transferring power from a primary side across an airgap to a secondary side, the secondary side includes two parallel resonating circuits (27) each including two parallel resonating paths with a series connection of a resonating inductor (28), and a resonating capacitor 29. A rectifier (21) is connected to the output of each resonating path for converting the AC output (12) of the resonating paths to a DC output (13). The outputs of the rectifiers (21) are connected in parallel to provide the AC output power (13) to a load such as a battery or the like. Each resonating path further includes a symmetry inductance connected in series to improve current sharing among the resonating paths and to reduce the higher harmonic portion in the resonating paths. For balancing the flux each resonating circuit 27 includes in a preferred embodiment of the invention a symmetry winding (30) wound on the same core as the resonating inductor 28 of that resonating path where all symmetry windings (3) are connected in parallel to ensure optimal flux sharing.

Claims

1. A wireless power transfer arrangement for wirelessly transferring power from a primary side across an airgap to a secondary side by inductive coupling, wherein a) the primary side includes an input stage for converting an input power to an AC primary output power and a primary resonator for receiving the AC primary output power and inducing a magnetic field, b) the secondary side includes a secondary resonator for converting the power received through the magnetic field to an AC secondary output power and an output stage for converting the AC secondary output power to a DC secondary output power, characterised in that the secondary resonator includes a secondary magnetic core structure and at least two secondary resonating circuits connected in parallel, wherein c) each secondary resonating circuit includes a resonating path with a resonating inductor and a resonating capacitor connected in series, d) the resonating inductor includes a winding wound on a section of the secondary magnetic core structure encompassing a magnetic flux of that secondary resonating circuit and e) each resonating path includes a symmetry inductance connected in series with the resonating inductor and the resonating capacitor of that resonating path.

2. The wireless power transfer arrangement according to claim 1, wherein each secondary resonating circuit includes two resonating paths arranged in parallel, wherein the resonating inductors of the two resonating paths of a secondary resonating circuit are wound on the same section of the secondary magnetic core structure.

3. The wireless power transfer arrangement according to claim 1, wherein the symmetry inductance of a resonating path is arranged between the resonating inductor and the resonating capacitor of that resonating path, wherein the resonating capacitor is preferably split into two split-capacitors each of them being arranged at a different output terminal of that resonating path.

4. The wireless power transfer arrangement according to claim 1, wherein the symmetry inductance is chosen such that an unwanted resonance frequency of the resonating paths of a secondary resonating circuit is positioned in a middle of two adjacent harmonics of a resonance frequency of the secondary resonator, preferably in the middle of a 2.sup.nd and a 3.sup.rd harmonic of the resonance frequency of the secondary resonator.

5. The wireless power transfer arrangement according to claim 4, wherein the secondary resonator includes three secondary resonating circuits each including two resonating paths and the symmetry inductance is chosen to be between 1.1*L2 and 1.5*L2, with L2 being a resulting inductance of the secondary resonator.

6. The wireless power transfer arrangement according to claim 1, wherein each secondary resonating circuit includes a symmetry winding wound on a section of the secondary magnetic core structure encompassing the same magnetic flux of that secondary resonating circuit and all symmetry windings are connected in parallel to balance the magnetic flux within the at least two secondary resonating circuits.

7. The wireless power transfer arrangement according to claim 6, wherein the symmetry winding of a secondary resonating circuit is wound on the section of the secondary magnetic core structure between the secondary windings of the resonating paths of that secondary resonating circuit.

8. The wireless power transfer arrangement according to claim 1, wherein the sections of the secondary magnetic core structure of the secondary resonating circuits are arranged in parallel and magnetically connected by a first yoke core element on one side and a second yoke core element on another side.

9. The wireless power transfer arrangement according to claim 1, wherein the output stage includes a rectifier for each resonating path, wherein each rectifier is connected to an output of a different resonating path.

10. The wireless power transfer arrangement according to claim 9, wherein a secondary of the rectifiers is connected in parallel to provide the DC secondary output power.

11. The wireless power transfer arrangement according to claim 1, wherein the primary resonator includes two primary resonating circuits connected in parallel, wherein each primary resonating circuit includes a resonating inductor and a resonating capacitor connected in series.

12. The wireless power transfer arrangement according to claim 11, wherein the primary resonator includes a magnetic core structure, preferably a sheet-like, generally rectangular magnetic core structure, wherein the resonating inductor of each primary resonating circuit includes an O-shaped primary coil wherein all primary coils are arranged on a same side of the magnetic core structure.

13. The wireless power transfer arrangement according to claim 1, adapted for wireless charging of a battery, particularly the traction battery of a vehicle, particularly of an automotive vehicle.

14. A secondary side for the wireless power transfer arrangement according to claim 1, including said secondary resonator as well as said output stage.

15. A method for wirelessly transferring power from a primary side across an airgap to a secondary side, including the steps of f) converting an input power to an AC primary output power by means of an input stage, receiving the AC primary output power and inducing a magnetic field for wireless power transfer by means of a primary resonator, g) converting the power received through the magnetic field to an AC secondary output power by means of a secondary resonator and converting the AC secondary output power to a DC secondary output power by means of an output stage, characterised in that the steps of converting the power received through the magnetic field to an AC secondary output power and converting the AC secondary output power to a DC secondary output power include the steps of h) converting the power received through the magnetic field to a plurality of AC secondary output power parts by means of at least two secondary resonating circuits connected in parallel, i) converting the plurality of AC secondary output power parts to a plurality of DC secondary output power parts and j) combining the plurality of DC secondary output power parts to provide the DC secondary output power by connecting them in parallel, wherein k) converting the power received through the magnetic field by a secondary resonating circuit includes converting the power received through the magnetic field by a resonating path with a series connection of a resonating capacitor and a resonating inductor including a winding wound on a magnetic core element and l) balancing a current flow within the resonating path by providing the resonating path with a symmetry inductance connected in series with the resonating inductor and the resonating capacitor of that resonating path.

16. The method according to claim 15, including a step of balancing a magnetic flux among the secondary resonating circuits by providing each resonating secondary circuit with a symmetry winding wound on the same magnetic core element as the resonating inductor and connecting all symmetry windings in parallel.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The drawings used to explain the embodiments show:

(2) FIG. 1 A schematic of a first embodiment of a wireless power transfer arrangement according to the invention,

(3) FIG. 2 a schematic of another embodiment of a wireless power transfer arrangement according to the invention,

(4) FIG. 3 a schematic of a primary resonator for use in a wireless power transfer arrangement according to the invention,

(5) FIG. 4 a schematic of a further primary resonator for use in a wireless power transfer arrangement according to the invention,

(6) FIG. 5 a schematic of a primary core structure for use in a primary resonator of a wireless power transfer arrangement according to the invention,

(7) FIG. 6 a schematic of a secondary resonator for use in a wireless power transfer arrangement according to the invention,

(8) FIG. 7 a schematic of a secondary core structure for use in a secondary resonator of a wireless power transfer arrangement according to the invention in a top view,

(9) FIG. 8 the secondary core structure of FIG. 7 in a side view,

(10) FIG. 9 a schematic of another secondary core structure for use in a secondary resonator of a wireless power transfer arrangement according to the invention in a top view,

(11) FIG. 10 the secondary core structure of FIG. 9 in a side view,

(12) FIG. 11 a schematic of an application of a wireless power transfer arrangement according to the invention for charging the traction battery of a forklift,

(13) FIG. 12 a schematic of an implementation of a symmetry inductor and

(14) FIG. 13 a schematic of another embodiment of a secondary side of a wireless power transfer arrangement according to the invention.

(15) In the figures, the same components are given the same reference symbols.

PREFERRED EMBODIMENTS

(16) FIG. 1 shows a schematic representation of a first embodiment of a wireless power transfer arrangement 1 according to the invention. The wireless power transfer arrangement 1 includes a primary side 2, a secondary side 3 and a controller 15. The primary side 2 includes an input stage 5 for converting an input power 4 into an AC primary output power 7 which is fed to a primary resonator 6. The primary resonator 6 induces a magnetic field 9 to wirelessly transmit power across an airgap 8. The secondary side 3 includes a secondary resonator 10 which picks up the magnetic field 9 and converts the power received through the magnetic field 9 into an AC secondary output 12. An output stage 11 is connected to the secondary resonator 10 and converts the AC secondary output 12 to a DC secondary output 13 which is then provided at an output of the wireless power transfer arrangement 1 as an output power 14.

(17) The controller 15 controls the power transfer from the primary side 2 to the secondary side 3 over the airgap 8 such as to meet the requirements of a particular application. The controller 15 controls the primary side 2 for example to meet a certain output power 14 needed by a device connected to the output stage 11. Here, the controller receives some input signal 16 from the secondary side 3 and based on this input signal 16 generates control signals 17 to control the primary side 2 such as to induce a magnetic field 9 to meet the required power at the output of the wireless power transfer arrangement 1. The input signal 16 may for example be a signal representing the power difference between the power outputted by the output stage 11 and the set value for the output power of the output stage 11. The input signal 16 may however also be just a measured value such as for example the actual power, current or voltage at the output stage 11 where the controller 15 therefrom calculates the control signals 17. To do so, the controller 15 also knows the set value for the power, the current or the voltage or the set value is inputted to the controller 15.

(18) The input stage 5 for example includes a converter arrangement for converting an input power 4 to the AC primary output power 7. In the case of an AC input power 4, the converter arrangement for example includes an AC/DC stage, a DC link and a DC/AC inverter. In such a configuration, the control signals 17 for example include the signals to control the input stage 5 by providing the control signals 17 for switching the switches of the inverter.

(19) Whereas the controller 15 is shown to be a separate unit it may also be integrated into any of the units shown in FIG. 1. It may also be split into two or more controller units to control the frequency and the switches and possible also other functions of the wireless power transfer arrangement 1 or even the function of other devices.

(20) FIG. 2 shows a schematic of another embodiment of a wireless power transfer arrangement according to the invention.

(21) On the primary side the wireless power transfer arrangement includes an inverter 25 which is connected to a primary resonator that includes a capacitor 22 and an inductor 23 connected in series. To induce the magnetic field for power transfer across the airgap 8, the primary resonator further includes a primary core structure 24. The inductor 23 for example includes a winding wound on a section of the core structure 24 to produce a magnetic field that is directed towards the secondary side.

(22) The secondary side includes a secondary core structure 26 and two secondary resonating circuits 27 that are arranged in parallel. The secondary core structure 26 is part of both secondary resonating circuits 27. Each secondary resonating circuits 27 includes a resonating inductor 28 and a resonating capacitor 29 connected in series, where the resonating inductor 28 includes a winding wound on a section of the secondary core structure 26. The output of the secondary resonator provides an AC secondary output 12 that is fed to a rectifier 21. The entirety of the rectifiers forms the output stage of this wireless power transfer arrangement. Each rectifier 21 converts the AC secondary output 12 to a DC secondary output 13 which is then combined by connecting the rectifier outputs in parallel to form the overall DC secondary output 13 which forms the output of the output stage.

(23) Each secondary resonating circuits 27 further includes a symmetry windings 30 that is wound on the same section of the secondary core structure 26 as the winding of the resonating inductor 28 of that resonating circuit 27. And all symmetry windings 30 are connected in parallel to balance the magnetic flux induced within the secondary resonating circuits 27.

(24) FIG. 3 shows a schematic of a primary resonator 36 for use in a wireless power transfer arrangement according to the invention. The primary resonator 36 includes two primary resonating circuits 37 connected in parallel to an input stage (not shown). Each primary resonating circuits 37 includes a series circuit of a capacitance and an inductance where the capacitance is split into two capacitors 32 and the inductance includes a coil 33 that is connected between the two capacitors 32. The coils 33 include at least one winding wound on a primary core structure 34.

(25) FIG. 4 shows a schematic of a further primary resonator 46 for use in a wireless power transfer arrangement according to the invention. The primary resonator 46 includes two primary resonating circuits 47 connected in parallel to an input stage (not shown). Each primary resonating circuits 47 includes a series circuit of a capacitance and an inductance where the capacitance is split into four capacitors 42 and the inductance includes two coils 43. The capacitors 42 and the coils 43 of a primary resonating circuits 47 form two sub-circuits where each sub-circuit includes a coil 43 that is connected between two of the capacitors 42. Both sub-circuits are connected in series to form a primary resonating circuit 47. The coils 43 include at least one winding wound on a primary core structure 44.

(26) FIG. 5 shows a schematic of a primary core structure 54 for use in a primary resonator of a wireless power transfer arrangement according to the invention. The primary core structure 54 in this example includes a generally rectangular ferrite core sheet 56 and two primary coils 55 arranged on top of the core sheet 56. The coils 55 are wound such that they touch each other or are at least close to each other in a middle area of the core sheet 56 and such that the currents in the coils flow in the same direction in that middle area. In this way, the magnetic field lines are concentrated in that middle area and the resulting magnetic field induced by this primary core structure 54 is directed into a direction perpendicular to the core sheet 56. The coils 55 are for example O-shaped coils as previously described.

(27) The ferrite core sheet 56 is shown to project beyond the coils 55 in every direction. However, the ferrite core sheet 56 may be made smaller such that it does not project beyond the coils 55 in some or even all areas.

(28) FIG. 6 shows a schematic of a secondary resonator 60 for use in a wireless power transfer arrangement according to the invention. The secondary resonator 60 includes a secondary core structure 66 with a common yoke section 66 and three winding sections 66. Further, the secondary resonator 60 includes three secondary resonating circuits 67 that are arranged in parallel.

(29) Each secondary resonating circuit 67 includes two parallel resonating paths 72 where each resonating path 72 includes a series circuit of a resonating inductor 68, and a resonating capacitor that is split into two resonating split-capacitors 69 that are arranged at the two output terminals of each resonating path 72. The output of each resonating path is fed to a rectifier 61 that converts the AC output power of a resonating path into a DC output power. Since the output of all rectifiers is connected in parallel, the AC output powers of the single resonating paths is summed to produce the total DC output power 73.

(30) The secondary core structure 66 is part of all three secondary resonating circuits 67. Each resonating inductor 68 includes a winding wound on a winding section 66 of the secondary core structure 66, where the windings of the two resonating inductors 68 of the two resonating paths 72 of a secondary resonating circuit 67 are wound on the same winding section 66 and where the windings of the resonating inductors 68 of different secondary resonating circuits are wound on different windings sections 66.

(31) Each secondary resonating circuits 67 further includes a symmetry winding 70 where the symmetry winding of a particular resonating circuit 67 is wound on the same winding section 66 as the windings of the two resonating inductors 68 of that particular resonating circuit 67. All symmetry windings 70 are connected in parallel to balance the magnetic flux induced within the secondary resonating circuits 67. Each symmetry winding 70 in this example includes two turns wound around the corresponding windings section 66. The symmetry windings 70 may however include another number of turns as long as each symmetry winding 70 has the same number of turns as the other symmetry windings 70.

(32) FIG. 6 further shows the symmetry inductances 71 included in each of the resonating paths 72 in series with the resonating inductor 68 and the resonating capacitors 69 of each resonating path 72. In this example, symmetry inductance 71 of a particular resonating path 72 is arranged between the resonating inductor 68 and one of the two resonating split-capacitors 69 of that particular resonating path 72.

(33) It is to note that the entirety of the capacitors 69 at the outputs of the resonating paths is to be chosen such as to result in a total capacitance required in a particular application of the wireless power transfer arrangement. The required capacities may be achieved by providing any suitable combination of single capacitors arranged in parallel and/or series.

(34) FIGS. 7 and 8 shows a schematic of an exemplary embodiment of a secondary core structure 76 for use in a secondary resonator of a wireless power transfer arrangement according to the invention that has three secondary resonating circuits and two resonating paths per secondary resonating circuit. The secondary core structure 76 may for example be used in the secondary resonator 60 shown in FIG. 6. FIG. 7 shows the secondary core structure in a top view and FIG. 8 shows it in a side view.

(35) The secondary core structure 76 includes two parallel arranged yoke core elements 77 and three winding sections 78 that are arranged parallel to each other in a distance and that are arranged perpendicular to the yoke core elements 77. Each winding section 78 is shown to carry three windings. The two outer windings 79 are the windings of the resonating inductors 68 of the two resonating paths 72 of a secondary resonating circuit 67 and the middle winding 80 is the symmetry winding 70 of that secondary resonating circuit 67.

(36) As shown in FIG. 8, the two yoke core elements 77 and the three winding sections 78 do have a more or less square cross section where the front ends of the winding sections 78 are in contact with the inner side surfaces of the yoke core elements 77.

(37) FIGS. 9 and 10 shows a schematic of another exemplary embodiment of a secondary core structure 86 for use in a secondary resonator of a wireless power transfer arrangement according to the invention that has three secondary resonating circuits and two resonating paths per secondary resonating circuit. The secondary core structure 86 may for example be used in the secondary resonator 60 shown in FIG. 6. FIG. 9 shows the secondary core structure in a top view and FIG. 10 shows it in a side view.

(38) The secondary core structure 86 is rather similar to the secondary core structure 76 shown in FIGS. 7 and 8. The secondary core structure 86 also includes two parallel arranged yoke core elements 87 and three winding sections 88 that are arranged parallel to each other in a distance and that are arranged perpendicular to the yoke core elements 87. Each winding section 88 is shown to carry three windings. The two outer windings 89 are the windings of the resonating inductors 68 of the two resonating paths 72 of a secondary resonating circuit 67 and the middle winding 90 is the symmetry winding 70 of that secondary resonating circuit 67.

(39) The difference to the secondary core structure 78 shown in FIGS. 7 and 8 is that the core elements do have a different cross section and are in contact with each other in a different way. As shown in FIG. 10, the two yoke core elements 87 and the three winding sections 88 do have a rectangular, but rather flat cross section. Accordingly, the winding sections 78 are in contact with the flat, upper sides of the yoke core elements 87 by means of the end areas of their lower lateral surfaces. The terms upper and lower in this context are to be understood to have the meaning according to the representation in FIGS. 9 and 10.

(40) The windings 79, 80, 89, 90 may also be arranged in a different way than shown in FIGS. 7 to 10. The two outer windings 79, 89 of the resonating inductors may for example be wound on the winding sections 78, 88 such that they are positioned directly near each other and cover as much of the winding sections 78, 88 as possible. As less as possible shall be visible of each windings section 78, 88. Then, the middle winding 80, 90, i.e. the symmetry windings, are wound on top of the two outer windings 79, 89 such as to further cover the transition area between the two outer windings 79, 89. Such a coil arrangement reduces the field lines undesirably leaving the magnetic core between the windings or even between the single turns of a winding.

(41) FIG. 11 shows a schematic of an application of a wireless power transfer arrangement according to the invention for charging the traction battery of a forklift.

(42) The input stage of the charging arrangement is in this embodiment arranged in a wallbox 95 which is mounted on a wall of the premises 92 and connected to the power supply network 94 within the premises 92. The primary resonator 96 is mounted on another wall 91 of the premises 92, for example the wall 91 of a garage, a car port, a parking area or the like in or near the premises 92. The primary resonator 96 may also be mounted on the same wall as the wallbox 95 or it may be integrated partly or fully into the wall 91 such that it would require less or no extra space near the wall 91. The primary resonator 96 is connected to the wallbox 95 by means of a fixed cable 97.

(43) A forklift 100 includes the secondary side 93 of the charging arrangement. The forklift 100 further includes a battery 98 with a BMS 105 (battery management system) and two electric motors 102, 103 where the electric motor 102 is used for driving the forklift 100 and the electric motor 103 is used for driving the lift 104 of the forklift 100. The BMS 105 manages the energy flow into and usually also out of the battery 98.

(44) For providing the charging current to the battery 98 of the forklift 100, the secondary side 93 is connected to the battery 98 via the charging line 99 and the secondary side 93 is also connected to the batteries 98 BMS 105 by signal line 106. For charging the battery 98 the BMS 105 defines the charging current allowed or needed at a particular point in time and provides this set value to the secondary side 93 via the signal line 106. The secondary side 93 for example measures the actual current provided to the battery 98, compares the actual current with the set current and calculates therefrom an error signal that is transmitted to the wallbox 95 via a wireless communication link 107 established by the wireless transceivers 108 included in the secondary side 93 as well as in the wallbox 95. The wireless transceiver 108 of the primary side may however also be provided within the primary resonator 96. Based on this current set value the controller then controls the input stage such that the power transferred from the primary resonator 96 through the airgap 8 to the secondary side 93 results in a charging current provided to the battery 98 via the charging line 99 that matches the set value of the BMS 105.

(45) FIG. 12 shows a schematic of an implementation of a symmetry inductor. Shown is a magnetic core structure 110 for winding the coil 111 of a symmetry inductor. The magnetic core structure 110 includes an E-shaped core element 113 with a middle leg and two outer legs. A yoke core element 117 is further arranged such as to close the E-shaped core element 113 to form an 8-shaped core. The coil 111 now is provided on the middle leg of the E-shaped core element 113. The yoke core element 117 may either be a yoke core element of a secondary core structure as previously described or it may also be an additional core element. Accordingly, in a secondary resonator such as for example shown in FIG. 6 having three resonating circuits each including two resonating paths, six E-shaped core elements 113 are provided to implement the six symmetry inductors. Therefore, each of these symmetry inductors is an independent inductor such that there occurs no flux sharing between them.

(46) FIG. 13 shows a schematic of another embodiment of a secondary side of a wireless power transfer arrangement according to the invention. The secondary side includes a secondary resonating circuit 127 with two resonating paths 122. A rectifier 131 is connected to each resonating path 122. Each resonating path 122 includes a symmetry inductance 121, two split-capacitors 119 and two resonating inductors. However, in this embodiment, the resonating inductors of the resonating paths 122 are realised by a circular winding 118 arranged on a circular secondary core element 116. Each circular winding 118 is shown to include just one turn. It is however also possible that each circular winding 118 includes two or more turns. And the circular windings 118 are shown to be arranged on the circular secondary core element 116 near each other. It is however also possible that the circular windings 118 are provided on top of each other or in any other suitable way. The resonating inductors are preferably realised by winding the circular windings 118 and providing them on the secondary core element 116 such that their resulting inductances are equal to each other.

(47) In this embodiment, the circular secondary core element 116 has a ring-like shape, where the circular windings 118 are provided on the ring-shaped part of the circular secondary core element 116. The circular secondary core element 116 could also be implemented as a circular disc, i. e. without a hole in the centre. The circular secondary core element 116 is for example a flat ferrite ring or disc.

(48) In a wireless power transfer arrangement with two or more secondary resonating circuits, such a secondary side arrangement with a common circular secondary core element 116 has the advantage, that the resonating inductors realised by the circular windings 118 do also balance the flux among the secondary resonating circuits. Accordingly, these circular windings take over the flux balancing function of the symmetry windings wherefore no additional symmetry windings are needed in such an arrangement.

(49) In summary, it is to be noted that the invention enables the creation of a wireless power transfer arrangement, a corresponding secondary side and a corresponding method for wireless power transfer that allows an efficient transfer of high powers.