Patent Application
20210335535
Aspects disclosed herein may generally relate to an apparatus for a low-profile wireless charger. This aspect and others will be discussed in more detail below.
U.S. Publication No. 2018/0211766 to Ansari et al. provides an assembly that includes a metallic housing, an electromagnetic (EM) device, and a bobbin in which the EM device is supported. The bobbin has a non-metallic, inner bobbin body, a non-metallic, outer bobbin body, and a metallic shield sandwiched between the inner and outer bobbin bodies. The EM device and the bobbin are mounted in the housing with the bobbin being between the EM device and the housing for heat from the EM device to thermally conduct through the inner and outer bobbin bodies and the shield to the housing while the shield shields noise of the EM device from the housing.
In at least one embodiment, a transformer assembly including a bobbin, a first winding and a second winding is provided. The bobbin defines a first chamber, a second chamber, and a gap. The first winding is positioned in the first chamber. The second winding is positioned in the second chamber. The gap separates the first chamber from the second chamber to cause the first winding and the second winding to generate a leakage inductance such that the leakage inductance and a capacitance of a capacitor that is operably coupled to the transformer assembly generate a resonant frequency to enable inductive mode charging with a vehicle pad.
In at least another embodiment, a transformer assembly including a bobbin, a first winding and a second winding is provided. The bobbin defines a gap. The first winding is positioned on the bobbin. The second winding is positioned on the bobbin. The gap separates the first chamber from the second chamber to cause the first winding and the second winding to generate a leakage inductance such that the leakage inductance and a capacitance of a capacitor that is operably coupled to the transformer assembly generate a resonant frequency to enable inductive mode charging with a vehicle pad.
In at least another embodiment, a transformer assembly including a bobbin, a first winding and a second winding is provided. The bobbin defines a gap. The first winding is positioned on the bobbin. The second winding is positioned on the bobbin. The gap separates the first winding from the second winding to cause the first winding and the second winding to generate a leakage inductance. The leakage inductance and a capacitance of a capacitor that is operably coupled to the transformer assembly generate a resonant frequency to enable a base pad to wirelessly transfer power at the resonant frequency to a vehicle pad.
The embodiments of the present disclosure are pointed out with particularity in the appended claims. However, other features of the various embodiments will become more apparent and will be best understood by referring to the following detailed description in conjunction with the accompany drawings in which:
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.
It is recognized that directional terms that may be noted herein (e.g., “upper”, “lower”, “inner”, “outer”, “top”, “bottom”, etc.) simply refer to the orientation of various components of a transformer assembly in connection with the wireless charger as illustrated in the accompanying figures. Such terms are provided for context and understanding of the embodiments disclosed herein.
Wireless chargers may be implemented for 3.7 kW, 7 kW, 11 kW, and 20 kW for various Original Equipment Manufacturers (OEMs). One design challenge may involve providing a design isolation transformer between a direct current (DC)/DC converter and a power transferring unit that provides power to a base pad via various customer requirements. An inverter may be used to invert DC energy into AC energy during a wireless charging operation. In some instances, the inverter may be generally enclosed in an enclosure that is not accessible to users (but for servicing by experienced and trained personnel) from safety point of view. The housing design for the inverter may be different from a normal power supply housing. For example, such a housing may include a window to facilitate air flow to cool electronics for power supply housing. However, the wireless charger itself may not enable the flow of air flow to adequately cool the charger and hence a transformer that forms a portion of the wireless charger. Thus, high power transformer thermal designs may not use air flow as a mechanism to reduce temperature. Thus, one potential thermal dispensation path is the use of a magnetic core that forms the transformer core that is coupled to a metallic housing.
Generally, to reduce cost for a wireless charger housing, the wireless charger may be designed as small as possible. However, this aspect may not allow for the packaging of an independent resonant circuit inductor which is generally required in a resonant inverter design. Thus, this aspect yields a transformer and a resonant inductor with a tight height and horizontal dimension limitation. One way to meet the housing design requirements is to provide an integrated transformer which combines a transformer and a resonant inductor into one transformer. Further, it is possible to utilize a transformer's leakage inductance as the resonant inverter's resonant inductor. Various considerations for such a transformer implementation are to locate a simple solution to balance transformer cost, dimension, turn ratio, magnetizing inductance, leakage inductance and thermal performance.
With a transformer design, the most effective way to higher transformer leakage may include (i) providing more turns in primary and secondary windings under a same turn ratio (ii) with a loose winding, particularly with a larger gap between primary and secondary windings. maintaining turns and a core winding window that is kept unchanged, and (iii) adding a magnetic sheet between the primary and secondary winding to boost the leakage inductance. However, in various desired wireless charger transformer designs, particularly those that are constrained by a housing design with a tight height limitation (i.e., a transformer height constraint), it may not be possible to provide a transformer with more turns or a larger gap between primary and secondary windings of the transformer. In these cases, a low-profile transformer is generally required with a limited winding window.
The winding material used for primary and secondary windings in planar transformer design may be copper foil or a printed circuit board (PCB) board trace winding, both of these winding methods may involve interleaved primary and secondary windings to reduce winding proximity loss. In this case, the primary and secondary winding may have a tight coupling. Such a tight coupling may adversely affect leakage inductance from the transformer's leakage which may otherwise be desirable to use as resonant inductance. The normal solution to boost leakage inductance of a planar transformer may include inserting a magnetic material sheet in between primary and secondary windings. One aspect that requires consideration for the wireless charger is that such a charger may not be able to support air cooling. In general. a high-power transformer magnetic field flux swing may generate an increase in eddy currents based on the inserted magnetic material sheet. The eddy current may generate loss on this sheet. Without air flow cooling, the heat associated with inserted sheet may cause the transformer malfunction.
In order to solve these transformer design considerations, a hybrid transformer design as disclosed herein generally utilizes a low profile-planar E core to replace a copper foil or printed circuit board (PCB) trace winding with a transformer winding Litz wire. This aspect may dramatically reduce winding proximity loss to package the primary and secondary windings together. With no core saturation, it is possible to select less turns for the winding in order to fit into a window area for the lower profile core. Meanwhile, a constant gap between the primary and secondary winding may be held via a transformer bobbin to control the transformer leakage inductance to meet OEM requirements.
In reference back to the assembly 100, the assembly 100 generally includes a bobbin 110, a primary winding (or first winding) 112, and a secondary winding (or second winding) 114. The primary winding 112 is positioned on a first side of the bobbin 110 and the secondary winding 114 is positioned on second side of the bobbin 110 opposite to the first side. A gap 116 is formed on the bobbin 110 between the primary winding 112 and the secondary winding 114 to separate the windings 112 and 114 from one another. The bobbin 110 is generally formed of Nylon based materials and supports the primary winding 112 and the secondary winding 114. In one example, the bobbin 110 may be formed of SLS Glass Filled Nylon.
The primary winding 112 may be implemented as a Litz wire. Similarly, the secondary winding 114 may be implemented as a Litz wire. As shown, the primary winding 112 may be implemented as turns, n1 around the bobbin 110. Similarly, the secondary winding 114 may be implemented as turns, n2 around the bobbin 110. The secondary winding 114 may include more or fewer turns than that of the primary winding 112. In one example, the number of turns employed for the primary winding 112 may be 15 turns and the number of turns employed for the secondary winding 114 may be 12 turns. In another example, the number of turns employed for the primary winding 112 may be 12 turns, and the number of turns employed for the second winding 114 may be 15 turns. In general, the number of turns, n1 for the primary winding 112 may be different than the number of turns, n1 for the second winding 114. The number of turns employed for the primary winding 112 and the secondary winding 114 aid in meeting power transfer requirements in addition to safety requirements. The utilization of the primary winding 112 and the secondary winding 114 negates the need to cool the transformer 101 since the transformer 101 does not employ a copper foil or PCB solution for purposes of inductive coupling. The Litz wire generally does not generate as much heat as a copper foil and therefore does not require additional cooling mechanisms to reduce the overall temperature of the transformer 101. Additionally, a potted transformer and/or in-directional cooling mechanism may be used to reduce the overall temperature of the transformer 101. The Litz wire may also reduce winding proximity losses.
The transformer 101 includes at least one magnetic core (or ferrite core) 120 that is supported by the bobbin 110.
The gap 116 as formed on the bobbin 110 and positioned between the primary winding 112 and the secondary winding 114 controls the amount of leakage inductance generated between the windings 112, 114. The gap 116 may extend to a length of 12 mm or less. The particular length selected for the gap 116 to obtain the desired leakage inductance may vary based on power requirements and the type of electrical requirements for a country (or territory) in which the transformer 101 is implemented in. In one example, the gap 116 along with the number of turns, n1 for the primary winding 112 and the number of turns, n2 for the secondary winding 114 may generate a leakage inductance in the amount of 25 μH. Such a leakage inductance when in series with a capacitor may provide a resonance frequency for a resonant inverter. In general, the leakage inductance and the capacitor form a resonant network that transfers AC energy at a resonant frequency from the base pad 103 to the vehicle pad 105 for inductive mode charging. The resonant frequency is defined by defined by Fr=½*n*√(L*C)), where L corresponds to the leakage inductance and C corresponds to the capacitance of the capacitor in series with the leakage inductance. In order to maintain a stable resonance frequency, the overall tolerance of the leakage inductance may be in the amount of 1 to 2 μH.
Generally, with transformer designs, it may be preferable to minimize the gap between the primary and secondary sides (or windings 112, 114) of the transformer 101. However, by providing (or increasing the gap) as illustrated in
For example,
The utilization of the leakage inductance from the transformer 101 as opposed to utilizing a resonant inductor as traditionally implemented may provide various advantages. For example, by avoiding the use of a resonant inductor, such a condition provides a smaller package size for the transformer 101 and also reduces overall cost. Further, resonant inductors generally include a +/−30% tolerance with respect to the overall inductance value. Such a large variation with respect to the overall inductance may adversely impact charging (i.e., overall charging efficiency) between the base pad 103 and the vehicle pad 105. The utilization of the leakage inductance from the gap 116 of the bobbin 110 provides a more stable and predictable inductance value by way of the leakage inductance to ensure proper resonant frequency.
Referring back to
It is shown the primary winding 112 is positioned in the primary chamber 250 and that the secondary winding 114 is positioned in the secondary chamber 252. As shown, a first plurality of magnetic cores 120 are positioned on the second side 202 of the bobbin 110. A second plurality of magnetic cores 120 are positioned on the first side 200 of the bobbin 110. In the embodiment illustrated in
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.
