Method and system for optimizing wireless power transfer to on-road electric vehicles via adaptive frequency

Abstract

A system for controlling the frequency of a wireless power signal transmitted from a plurality of power transmission segments disposed along a roadway may include a plurality of base stations disposed along the roadway, each base station including, for each one of the segments: a power converter for converting alternating current at a power distribution frequency; a phase detection circuit configured to detect the voltage-to-current phase of the power signal in one of the powered segments; and a frequency control circuit configured to control the power transmission frequency of the power signal in the powered segment based on the voltage-to-current phase so as to reduce the absolute value of the voltage-to-current phase to a predetermined level as long as a power receiving coil of an electric vehicle passes through the powered power transmission segment.

Description

[Technical Field]

[0001] The present invention relates generally to wireless power transfer in electric vehicles. [Background technology]

[0002] Before describing the background of the present invention, definitions of the following terms are provided:

[0003] The term "electric vehicle" generally refers to a vehicle or the like that is powered solely or partially by electrical energy stored (e.g., chemically) in a battery or the like. As used herein, an "electric vehicle" also includes configuration for receiving wirelessly induced electromotive force (i.e., voltage) (e.g., in a coil located on the underside of the vehicle), which may be stored to recharge the battery or otherwise utilized. For an electromagnetically induced voltage to occur, the vehicle (i.e., "conductor") may be moving relative to, for example, a magnetic field projected onto the road along which the vehicle is traveling. Alternatively, the magnetic field may be periodically changed (e.g., using an alternating current), thereby inducing a voltage in the vehicle.

[0004] The term "road section" generally refers to a portion of, for example, a highway, motorway, or main road that has been modified to include a medium for wirelessly transmitting power (i.e., a "power transmitter"). This may mean that the road includes multiple coils embedded below the surface of the road section that are operable to emit a magnetic field. In a typical arrangement, the medium (coils) may be connected to an AC power source, for example, an electrical grid, to generate a changing magnetic field, thereby inducing a voltage in nearby conductors. One possible method of powering on-road electric vehicles via wireless power transmission is disclosed in EP 3089886, which is incorporated herein by reference.

[0005] FIG. 1 is a block diagram illustrating a prior art wireless power transfer system 100. The wireless power transfer system 100 may include a plurality of electric vehicles 150, each including a power receiver mounted, for example, on the underside of the vehicle. The plurality of electric vehicles may travel along a road section 101, further comprising one or more power transmitters 120, for example, disposed below the surface of the road section and powered by a power converter 122 connected to an electrical grid. In some embodiments, the power receivers and transmitters may each comprise one or more windings or loop-shaped coils coupled to an AC power source, for example. In some variations, these coils may be operable to emit a static or varying magnetic field around the coil, for example, around the road section or a portion thereof. As each electric vehicle travels along the road section 101, the magnetic field created by the power transmitters in the road section 101 induces a voltage in each power receiver, which is stored and / or converted by the electric vehicle, for example, into chemical energy in a battery. In an alternative embodiment, the induced energy may be used immediately by the electric vehicle's engine without being stored.

[0006] When an electric vehicle passes over the transmit coil, it changes the alignment of the receive coil with respect to the transmit coil, which can lower the resonant frequency of the receive array relative to the operating resonant frequency of the transmit array, resulting in less than optimal power transfer. Summary of the Invention

[0007] The present invention provides a system for controlling the power supply frequency of a wireless transmitter for an electric vehicle moving on the road. The transmitter side has a control unit that monitors the voltage vs. current phase and infers the offset between the receiver side coil and the corresponding transmitter side coil, and dynamically changes the frequency based on this offset to ensure operation at or near resonance.

[0008] According to some embodiments of the present invention, there is provided a system for controlling the frequency of wireless power signals transmitted from a plurality of power transmission segments disposed below a road surface along a road to power receiving coils disposed on electric vehicles moving along the road, each power transmission segment comprising two or more transmitting coils, the system comprising a plurality of base stations disposed along the road, each base station configured to selectively supply power to a plurality of consecutively disposed and separately wired segments, for each one of the segments powered by the base station, a power converter configured to convert an alternating current coming from a power grid at a distribution frequency and output a power signal at a power transmission frequency band; a phase detection circuit configured to detect a voltage-to-current phase of the power signal in one of the powered segments; and a frequency control circuit configured to control the power transmission frequency of the power signal in the powered segments based on the voltage-to-current phase so as to reduce an absolute value of the voltage-to-current phase to a predetermined level as long as the power receiving coil of the electric vehicle passes through the one of the power transmission segments.

[0009] These and other advantages of the present invention are discussed in detail in the following description. [Brief explanation of the drawings]

[0010] For a better understanding of the invention, and to show how it may be carried into effect, reference will now be made, purely by way of example, to the accompanying drawings in which like numerals represent corresponding elements and sections, in which: [Figure 1] 1 is a block diagram illustrating a wireless power transfer system for electric vehicles on roads according to the prior art. [Figure 2A] FIG. 1 illustrates the placement of receive coils in a transmit array and a receive array in some embodiments of the present invention. [Figure 2B] FIG. 1 illustrates the placement of receive coils in a transmit array and a receive array in some embodiments of the present invention. [Figure 3] FIG. 1 illustrates a system in accordance with some embodiments of the present invention. [Figure 4A] FIG. 10 is a diagram illustrating how power varies across various frequency bands of a generator in some embodiments of the present invention. [Figure 4B] FIG. 10 is a diagram illustrating how power should be varied based on the displacement band of a receiver side coil relative to a corresponding transmitter side coil in some embodiments of the present invention. [Figure 5] 1 is a flowchart illustrating a method in accordance with some embodiments of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] Referring now in detail and specifically to the drawings, it is emphasized that the specific details shown are for illustrative purposes only, for the purpose of discussing preferred embodiments of the invention, and are presented for the sole purpose of providing what is believed to be the most useful and readily understood explanation of the principles and conceptual aspects of the invention. In this regard, no attempt is made to show more detailed structural details than are necessary for a fundamental understanding of the invention. By taking the drawings into consideration, it will become apparent to those skilled in the art how certain aspects of the invention may be embodied in practice.

[0012] Before describing embodiments of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the drawings. The invention is applicable to other embodiments and can be practiced or carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein is for the purpose of description and should not be regarded as limiting.

[0013] 2A and 2B show an example arrangement of receiver coils 210 in a receiver array 200. The dimensions shown are exemplary only and are not intended to be limiting. The receive coils 210 may be positioned below an electric vehicle (not shown) parallel to a road having a road section on which the transmit coils 220 are positioned. The receive coils 210 may receive power transmitted by the transmit coils 220. The lower receive coils 212 may be positioned end-to-end, thereby defining a joint line 212a in the shared plane of the road section and the coils. Such a joint coil 212 is sometimes referred to as a "figure-eight" coil. The upper receive coil 214 may be positioned above the lower receive coil 212. The upper receive coil 214 may have different dimensions from the lower receive coil 212, or the upper receive coil 214 may have the same dimensions as the transmit coil 220.

[0014] The upper receive coil 214 may be positioned such that its geometric center 214a is located on the joining line 212a of the lower receive coil 212. The geometric center of an object is defined as the average position of all points on the object in all coordinate directions. The configuration of the upper and lower receive coils 210 may be repeated periodically along the underside of the electric vehicle. The shape of the receive coils 210 may be circular or rectangular, or variations thereof, such as elliptical or oblong. The receiver array 200 may include ferrite plates 205. When deployed, the ferrite plates 205 serve to shape and contain magnetic flux to prevent adverse effects caused by its transmission into the interior of the electric vehicle.

[0015] This top-bottom receiver coil 210 configuration has been found to provide optimal power transfer with fixed alignment for fixed frequency operation of the transmitter coil 220. However, relative motion between the transmitter coil 220 and receiver coil 210 due to the motion of the electric vehicle reduces the efficiency of power transfer due to changes in the coupling coefficient. One solution would be to power the transmitter coil 220 at average power, but this is inefficient.

[0016] Therefore, it would be useful to dynamically adjust the power transfer characteristics of the transmitter coil in response to information about the position of the receiver coil relative to the transmitter coil. Because power transfer occurs over a road section that is only, for example, 2 m wide, the positioning of the coils relative to each other is on a centimeter scale, and precision positioning systems with centimeter-scale errors are not suitable.

[0017] FIG. 3 shows a wireless power system 300 for an electric vehicle 350 on a road 030. The road 030 may have a road section 301 with a transmitter coil 320 located (potentially below the surface of the road 030). The road section 301 is powered by a power converter 322, which may itself be powered by an electrical grid (not shown). The power converter 322 may be connected to a base station (not shown). The base station may have access to a database of electric vehicles enrolled in electricity payment plans. The power converter 322 may be connected to a capacitor pack 326 via an access cable 324. The access cable 324 may transmit different types of electrical signals; for example, the access cable 324 may include at least one communication channel and at least one power delivery channel. The electric vehicle 350 may travel along the road 030 in a direction 302 toward the road section 301. The electric vehicle 350 may include a power receiver array comprising a plurality of receive coils 310 that may be located on the underside of the electric vehicle 350 .

[0018] Electric vehicle 350 may also include a communication loop 360. Communication loop 360 may transmit a communication signal 362. Communication signal 362 may be modulated with an identity (ID) code to uniquely associate with electric vehicle 350. For example, the ID code may include, but is not limited to, a vehicle registration number, a driver registration number, or a subscriber number. Communication signal 362 may be transmitted at a frequency higher than the frequency of the power transmitted by transmitter coil 320.

[0019] The communication signal 362 may be received by a communication antenna loop 365 associated with the road section 301. The communication antenna loop 365 may be connected to the capacitor pack 326. The communication antenna loop 365 may be configured to control the power transmission of the transmit coil 320. The communication antenna loop 365 may be configured to initialize the power transmission of the transmit coil 320 only in response to the communication signal 362 identifying the electric vehicle 350 as being associated with a valid subscription to an electricity payment plan. A determination of the validity of the communication signal 362 may be performed at a base station and relayed to the road section 301.

[0020] During operation, the power of the converter 322 of each powered segment 365 is monitored and adaptively changed to ensure resonance or near resonance. This is achieved without a control or measurement unit on the power receiving side, i.e., without the need to monitor anything on the electric vehicle, but only on the power transmitting side.

[0021] According to some embodiments of the present invention, the resonant frequency is set as the frequency at which the current to voltage phase of the converter 322 equals zero.

[0022] According to some embodiments of the present invention, the resonant frequency of a transmitter segment is measured without a power receiver (eg, an electric vehicle) thereon and is defined as the zero load resonance (ZLR).

[0023] As an electric vehicle travels along a road, its communication transmitter continuously transmits a communication signal requesting power to the road segment it is passing through. The power request signal contains an ID code modulated onto the frequency of the communication signal, allowing the segment and base station to recognize it and provide power accordingly. As soon as the electric vehicle's receiving unit approaches a given power transmission segment, the power transmission segment's dedicated communication receiver receives and detects the identification code, activating the transmitter segment's transducer at a minimum power level (allowing it to measure current, voltage, phase, etc.).

[0024] From this point on, as soon as the transmitter recognizes communication, it begins to power the primary coil with minimal current.When the electric vehicle receiver unit passes over the transmitter segment, the common resonant frequency drops, increasing coupling between the two and lowering the resonant frequency.

[0025] To address the drop in resonant frequency, in some embodiments of the present invention, the transducer associated with a particular transmitter segment is monitored to detect a phase difference between the voltage and current in the transmitter segment. In response to such phase detection, the frequency of the transducer is changed until the phase is again zero.

[0026] According to some embodiments of the present invention, to determine the operating frequency of the converter, a look-up table or similar mechanism can be used to map the measured voltage versus current phase and the required change in frequency.

[0027] A similar look-up table can be used to determine the displacement of the power receiver unit relative to the power transmitter segment, and thus the exact position of the electric vehicle relative to the road.

[0028] According to some embodiments of the present invention, there is provided a system for controlling the frequency of a wireless power signal transmitted from a plurality of power transmission segments disposed below a road surface along the road to a power receiving coil disposed in an electric vehicle moving along the road, each power transmission segment comprising two or more transmitting coils; a plurality of base stations disposed along the road, each configured to selectively supply power to a plurality of consecutively disposed and separately wired segments, and for each one of the segments powered by the base station, the system comprises: a power converter, the power converter being equipment for the respective one of the segments powered by the base station and configured to convert an AC current coming from a power grid at a certain power distribution frequency and output a power signal in a certain power transmission frequency band; a phase detection circuit configured to detect a voltage-to-current phase of the power signal in one of the powered segments; and a frequency control circuit configured to control the power transmission frequency of the power signal of the powered segment based on the voltage-to-current phase so as to reduce the absolute value of the voltage-to-current phase to a predetermined level as long as the power receiving coil of the electric vehicle passes through one of the powered power transmission segments.

[0029] According to some embodiments of the present invention, the power transmission segment comprises a communication receiver configured to receive a power request signal from an authorized electric vehicle, and the converter is switched on only if the power request signal is authorized.

[0030] According to some embodiments of the present invention, the power transmission frequency band is from 80 KHz to 90 Khz.

[0031] According to some embodiments of the present invention, modifying the frequency of the power transmission signal based on the voltage versus current phase may ensure operation at or near resonance between the power transmission coil and the power receiving coil while the power receiving coil passes through one of the power transmission segments.

[0032] According to some embodiments of the present invention, the frequency control circuit may be further configured to increase the power level of the power signal based on the voltage versus current phase.

[0033] According to some embodiments of the present invention, the frequency control circuit may be configured to modify the frequency of the power transmission signal using a switching circuit.

[0034] According to some embodiments of the present invention, the frequency control circuit may be further configured to increase the power level of the power signal based on the voltage versus current phase by controlling the duty cycle of the switching circuit for various bands.

[0035] According to some embodiments of the present invention, the voltage versus current phase represents one of a plurality of bands, each band representing a level of overlap between a power transmission coil of one of a plurality of power transmission segments and a power receiving coil of the electric vehicle as the electric vehicle passes through one of the plurality of power transmission segments.

[0036] According to some embodiments of the present invention, the base station may be configured to calculate a relative displacement of a receiving coil of the vehicle with respect to a power transfer coil of one of the plurality of power transfer segments based on voltage versus current phase.

[0037] According to some embodiments of the present invention, the voltage versus current phase represents one of a plurality of bands, each band representing a level of overlap between a power transfer coil of one of a plurality of power transfer segments and a power receiving coil of the electric vehicle as the electric vehicle passes through one of the plurality of power transfer segments.

[0038] According to some embodiments of the present invention, power at zero load is guaranteed to be off to ensure that no power supply occurs on a transmission segment when there are no vehicles on it. This is done for safety and power supply efficiency.

[0039] 4A and 4B are diagrams illustrating how power is varied across various frequency bands of a generator in some embodiments of the present invention, and how the power should be varied based on the displacement band of the receiver coil relative to the corresponding transmitter coil.

[0040] 5 is a flowchart illustrating a method according to some embodiments of the present invention. The method includes the steps of: converting an AC current coming from a power grid at a distribution frequency and outputting a power signal at a power transmission frequency band 510; controlling the power transmission frequency of the power signal based on the voltage-current phase of the power signal 520; switching on the power signal at a minimum power level sufficient to detect the voltage-current phase in response to detecting an authorized electric vehicle having a power receiving coil approaching one of the power transmission segments 530; switching on the power transmission level and detecting the voltage-current phase of the power signal in response to the authorized electric vehicle passing through one of the power transmission segments 540; and modifying the frequency of the power transmission signal based on the voltage-current phase so as to zero the voltage-current phase as long as the power receiving coil is passing through one of the power transmission segments 550.

[0041] The foregoing flowcharts and figures illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer program products according to various embodiments of the present invention. In this regard, each portion of a flowchart or sub-diagram may represent a module, segment, or portion of code, comprising one or more executable instructions for implementing one or more specified logical functions. It should also be noted that in some alternative implementations, the functions noted in the portions may occur out of the order noted in the figures. For example, two portions shown in succession may, in fact, be executed substantially concurrently, or the portions may sometimes be executed in the reverse order, depending on the functionality involved. It should also be noted that each portion of the sub-diagrams and / or flowchart diagrams, and combinations of portions of the sub-diagrams and / or flowchart diagrams, may be implemented by a special-purpose hardware-based system that performs the specified functions or acts, or by a combination of special-purpose hardware and computer instructions.

[0042] As will be appreciated by those skilled in the art, aspects of the present invention may be embodied as a system or device. Accordingly, aspects of the present invention may take the form of an entirely hardware embodiment or an embodiment combining software and hardware, generally referred to herein as a "circuit," "module," or "system."

[0043] The foregoing figures illustrate the architecture, functionality, and operation of possible implementations of systems and devices in various embodiments of the present invention. Where referred to in the above description, an embodiment is an example or implementation of the present invention. Various appearances of "one embodiment," "one embodiment," or "some embodiments" do not necessarily all refer to the same embodiment.

[0044] Although various features of the invention may be described in the context of a single embodiment, the features may also be provided separately or in any suitable combination. Conversely, although the invention may, for clarity, be described herein in the context of separate embodiments, the invention may also be implemented in a single embodiment.

[0045] References herein to "some embodiments," "one embodiment," "one embodiment," or "other embodiments" mean that a particular feature, structure, or characteristic described in connection with an embodiment is included in at least some embodiments of the invention, but not necessarily in all embodiments. Furthermore, it is recognized that aspects of the invention described herein above may be combined or otherwise coexist in embodiments of the invention.

[0046] It is understood that the phraseology and terminology employed herein is not to be construed as limiting and is for the purpose of description only.

[0047] The principles and applications of the teachings of the present invention may be better understood with reference to the accompanying description, figures and examples.

[0048] It is understood that the details set forth herein are not to be construed as limitations on the application of the present invention.

[0049] Furthermore, it is understood that the invention can be practiced or carried out in various ways and that the invention can be embodied in embodiments other than those outlined in the description above.

[0050] It is understood that the terms "comprises," "comprises," "consists," and grammatical variations thereof do not exclude the addition of one or more elements, features, steps, or integers or groups thereof, but rather the terms are to be interpreted as specifying elements, features, steps, or integers.

[0051] When the specification and claims refer to "an additional" element, this does not exclude the presence of a plurality of the additional element.

[0052] When a claim or the specification refers to "an" element, such a reference is not to be understood as meaning that there is only one of that element.

[0053] When a component, feature, structure, or characteristic is described herein as "may include," "might include," "can include," or "potentially include," it is understood that the particular component, feature, structure, or characteristic is not required to be included.

[0054] Where applicable, embodiments may be described using state diagrams, flow diagrams, or both, but the invention is not limited to these diagrams or the corresponding descriptions. For example, flow need not move through each illustrated box or state, or in the exact same order as illustrated and described.

[0055] Methods of the present invention can be implemented by performing or completing selected steps or tasks manually, automatically, or a combination thereof.

[0056] The term "method" may refer to, but is not limited to, any acts, means, techniques, and procedures for accomplishing a given task, and includes any acts, means, techniques, and procedures that are known or that can be readily developed from known acts, means, techniques, and procedures by one of ordinary skill in the art to which the invention pertains.

[0057] The descriptions, examples, and materials presented in the claims and specification should not be construed as limiting, but rather as illustrative only.

[0058] Unless otherwise defined, the meanings of technical and scientific terms used herein are commonly understood by one of ordinary skill in the art to which this invention belongs.

[0059] The present invention can be tested or practiced using materials equivalent or similar to those described herein.

[0060] While the present invention has been described with respect to a limited number of embodiments, these should not be construed as limiting the scope of the invention, but rather as illustrating some of the preferred embodiments. Other or equivalent variations, modifications, and applications are also within the scope of the present invention. Therefore, the scope of the present invention is not limited by what has been described above, but rather by the appended claims and their legal equivalents.

Claims

1. 1. A system for controlling a frequency of a wireless power signal transmitted from a plurality of power transmission segments disposed below a road surface along a road to a power receiving coil disposed in an electric vehicle moving along the road, the system comprising: Each power transfer segment comprises two or more transfer coils; The system comprises a plurality of base stations arranged along the road; each base station configured to selectively power a plurality of said segments arranged consecutively and separately wired; For each one of the segments powered by the base station, each base station: a power converter for each one of the segments powered by the base station, the power converter being configured to convert an alternating current coming from a power grid at a distribution frequency and output a power signal in a power transmission frequency band; a phase detection circuit configured to detect the voltage versus current phase of the power signal in one of the powered segments; a frequency control circuit configured to control the power transmission frequency of the power signal of one of the powered segments based on the voltage versus current phase so as to reduce the absolute value of the voltage versus current phase to a predetermined level as long as the power receiving coil of the electric vehicle passes through the one of the power transmission segments; Equipped with system.

2. the power transmission segment includes a communications receiver configured to receive a power request signal from an authorized electric vehicle; the converter is switched on only if the power request signal is granted; The system of claim 1 .

3. The power transmission frequency band is from 80 KHz to 90 KHz. The system of claim 1 .

4. modifying the frequency of the power transmission signal based on the voltage versus current phase ensures operation at or near resonance between the power transmission coil and the power receiving coil during passage of the power receiving coil through the one of the power transmission segments; The system of claim 1 .

5. the frequency control circuit is further configured to increase a power level of the power signal based on the voltage versus current phase. The system of claim 3 .

6. the frequency control circuit is configured to modify the frequency of the power transmission signal using a switching circuit; The system of claim 1 .

7. the frequency control circuit is further configured to increase a power level of the power signal based on the voltage versus current phase by controlling a duty cycle of the switching circuit for various bands. The system of claim 6.

8. the voltage versus current phase represents one of a plurality of bands; each band representing a level of overlap between the power transmission coil of the one of the plurality of power transmission segments and the power receiving coil of the electric vehicle when the electric vehicle passes through the one of the plurality of power transmission segments; The system of claim 1 .

9. the base station is configured to calculate a relative displacement of the receiving coil of the vehicle with respect to the power transfer coil of the one of the plurality of power transfer segments based on the voltage versus current phase. The system of claim 1 .

10. the voltage versus current phase represents one of a plurality of bands; each band representing a level of overlap between the power transmission coil of the one of the plurality of power transmission segments and the power receiving coil of the electric vehicle when the electric vehicle passes through the one of the plurality of power transmission segments; The system of claim 9.

11. 1. A method for controlling a frequency of a wireless power signal transmitted from a plurality of power transmission segments disposed below a road surface along a road to a power receiving coil disposed in an electric vehicle moving along the road, the method comprising: Each power transfer segment comprises two or more transfer coils; Selectively supplying power to a plurality of said consecutively arranged and separately wired segments via a plurality of base stations arranged along said road; for each segment powered by said base station, converting an AC current coming from a power grid at a distribution frequency and outputting a power signal at a power transmission frequency band; detecting a voltage versus current phase of the power signal in one of the powered segments; controlling the power transmission frequency of the power signal of the powered segment based on the voltage vs. current phase so as to reduce the absolute value of the voltage vs. current phase to a predetermined level as long as the power receiving coil of the electric vehicle passes through the one of the power transmission segments; A method having the following.

12. the power transmission segment includes a communications receiver configured to receive a power request signal from an authorized electric vehicle; the converter is switched on only if the power request signal is granted; The method of claim 11.

13. The power transmission frequency band is from 80 KHz to 90 KHz. The method of claim 11.

14. modifying the frequency of the power transmission signal based on the voltage versus current phase ensures operation at or near resonance between the power transmission coil and the power receiving coil during passage of the power receiving coil through the one of the power transmission segments; The method of claim 11.

15. controlling the power transmission frequency includes increasing a power level of the power signal based on the voltage versus current phase; The method of claim 13.

16. controlling the power transmission frequency includes modifying the frequency of the power transmission signal using a switching circuit; The method of claim 11.

17. controlling the power transmission frequency includes increasing a power level of the power signal based on the voltage versus current phase by controlling a duty cycle of the switching circuit for various bands.

17. The method of claim 16.

18. the voltage versus current phase represents one of a plurality of bands; each band representing a level of overlap between the power transmission coil of the one of the plurality of power transmission segments and the power receiving coil of the electric vehicle when the electric vehicle passes through the one of the plurality of power transmission segments; The method of claim 11.

19. calculating a relative displacement of the receiving coil of the vehicle relative to the power transfer coil of the one of the plurality of power transfer segments based on the voltage versus current phase; 12. The method of claim 11 further comprising:

20. the voltage versus current phase represents one of a plurality of bands; each band representing a level of overlap between the power transmission coil of the one of the plurality of power transmission segments and the power receiving coil of the electric vehicle when the electric vehicle passes through the one of the plurality of power transmission segments; 20. The method of claim 19.

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