KR20170135950A - A wireless battery charging system that varies the magnetic field frequency to maintain a desired voltage-current phase relationship - Google Patents

Abstract

An electrical charging system (12) configured to wirelessly charge an energy storage device (14), such as a battery (14). The charging system 12 includes an off-transducer 18 in electrical communication with an alternating current power source 48 and electromagnetically coupled to an on-vehicle transducer 20 connected to the energy storage device 14 do. The controller 53 changes the frequency of the electric power sourced by adjusting the variable frequency oscillator 71 in the power transmitter 16. [ The charging system 12 includes a phase detection circuit 72 that is configured to communicate with the controller 53 and the off-transducer 18 and to determine the phase difference between the alternating current and the alternating current supplied by the power source 48 ). The controller 53 is configured to adjust the variable frequency oscillator 71 based on the phase difference so that the frequency of the sourced electric power maintains a phase difference within a desired range.

Description

A wireless battery charging system that varies the magnetic field frequency to maintain a desired voltage-current phase relationship

Cross-reference to related application

This application claims the benefit of priority under Article 8 of the Patent Cooperation Treaty of U.S. Patent Application No. 14 / 708,526, filed May 11, 2015, the entire disclosure of which is incorporated herein by reference.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a charging system used to charge a battery of a vehicle wirelessly, and more particularly to a wireless battery charging system configured to vary a magnetic field frequency to maintain a desired voltage-current phase relationship.

Wireless charging systems with off-transducers and on-vehicle transducers that are magnetically coupled and deliver electrical energy wirelessly across physical intervals are well known. Due to various loads, the tolerances of the components, the temperature, and the resonant frequency for optimal magnetic coupling between the off-transducer and the on-vehicle transducer can vary. In order to maintain the highest level of efficiency, there is a need to have a way to operate the charging system to maintain the optimal magnetic coupling of the system. In addition, the interoperability of wireless charging systems with on-vehicle transducers built by different vendors with different resonant frequencies requires that each vendor's on-vehicle transducer be used only with its vendor's wireless charging system There is a need to be taken into account.

According to an embodiment of the present invention, an electrical charging system is provided. The electrical charging system is configured to wirelessly charge the energy storage device. An electrical charging system includes an electrical power transmitter including a variable frequency oscillator configured to source electrical power having alternating current, alternating voltage, and frequency, an electrical power transmitter operable to condition the variable frequency oscillator, A transducer configured to be electromagnetically coupled to an on-vehicle transducer in electrical communication with the energy storage device, the transducer being in electrical communication with the energy storage device, An off-transducer to derive a vehicle transducer, and a phase detector circuit configured to communicate with the controller and the off-transducer and to determine a phase difference between the ac voltage and the ac current. The controller is configured to adjust the variable frequency oscillator based on the phase difference such that the frequency of the electric power sourced maintains the phase difference within a desired range.

The controller may be configured to adjust the variable frequency oscillator to sweep the frequency of the sourced electrical power within a frequency range of 10 kilohertz (kHz) to 450 kHz.

The electrical charging system may further comprise a wireless transmitter in electrical communication with the controller. In this case, the on-vehicle transducer is in electrical communication with a power detection circuit configured to determine the value of the captured electric power. The power detection circuit is in electrical communication with a wireless receiver configured to wirelessly transmit the value of the electric power captured through the wireless transmitter to the controller and the controller compares the value of the captured electric power with the value of the sourced electric power, . The controller is configured to adjust the variable frequency oscillator based on power efficiency such that the frequency of the sourced electrical power maximizes power efficiency.

The on-vehicle transducer and the energy storage device may be located within the vehicle. The off-transducer and the electric power transmitter may be located outside the vehicle. Alternatively, the off-transducer and the electric power transmitter may be located in the vehicle.

According to another embodiment of the present invention, an electrical charging system is provided. The electrical charging system is configured to wirelessly charge the energy storage device. An electrical charging system includes an electrical power transmitter including a variable frequency oscillator configured to source electrical power having alternating current, alternating voltage, and frequency, a variable frequency oscillator operable to adjust the frequency of the sourced electrical power Vehicle transducer in electrical communication with a controller, an electrical power transmitter, and is configured to be electromagnetically coupled to an on-vehicle transducer in electrical communication with the energy storage device to provide an on-vehicle transducer An off-transducer for directing the signal, and a wireless transmitter in electrical communication with the controller. The on-vehicle transducer is in electrical communication with a power detection circuit configured to determine the value of the captured electric power. The power detection circuit is in electrical communication with a wireless receiver configured to wirelessly transmit the value of the captured electric power to the controller via the wireless transmitter. The controller is configured to determine the power efficiency by comparing the value of the captured electric power with the value of the sourced electric power. The controller is configured to adjust the variable frequency oscillator based on power efficiency such that the frequency of the sourced electrical power maximizes power efficiency.

The subject matter of the invention discussed in the Background section should not be assumed to be prior art simply as a result of its mentioning in the Background section. Likewise, it should not be assumed that the problems mentioned in the background section or associated with the subject matter of the invention of the background section have been previously recognized in the prior art. The subject matter of the invention in the Background section only represents different approaches, and these different approaches can also be inventions by themselves.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be further described with reference to the accompanying drawings,
1 is a pictorial side view of an electrical charging system including a variable frequency oscillator (VFO) circuit in accordance with the present invention;
Figure 2 is a schematic diagram of the charging system of Figure 1 disposed between a battery and an on-vehicle transducer;
Figure 3 shows a schematic diagram of the VFO circuit of Figure 1;
Figure 4 shows the angular phase difference relationship between voltage and current monitored by the VFO circuit of Figure 3;
5 shows a schematic diagram of a VFO circuit of a charging system according to an alternative embodiment of the present invention.

The resonant frequency of the wireless electrical charging system can vary due to variations in load, variations in electrical component performance due to tolerance stack up, variations in temperature, variations in component placement and orientation. If off-transducers are used with different on-vehicle transducers that are frequency-tuned for one particular on-vehicle transducer and then are not tuned to the same frequency or range of frequencies, then mismatch at the resonant frequency may also result have. Variations of these types can undesirably reduce the power transmission efficiency of the wireless charging system. It has been found that the power transmission efficiency can be effectively managed and controlled with respect to the above-mentioned variations by adjusting the output frequency of the off-transducer.

The output frequency of the power transmitter that supplies the electrical power to the off-transducer is determined by a variable frequency oscillator (VFO) circuit disposed in the power transmitter. The VFO circuit in the charging system advantageously provides regulation of the frequency of the magnetic energy generated by the off-transducer to more closely match the resonant frequency of the on-vehicle transducer. The VFO circuitry advantageously allows the resonant frequencies of the off-on-vehicle transducers to be adjusted to accommodate manufacturing tolerances, environmental conditions, and misalignment of off-transducers and on-vehicle transducers. The VFO circuit also accommodates differences in resonance frequency between off-on-on-vehicle transducers built by different manufactures for different specifications.

A non-limiting example of a wireless charging system 12 that implements the features of the present invention is shown in Figures 1 and 2. The wireless charging system 12 shown here is configured to electrically charge a battery 14 that is disposed within the vehicle 40. The vehicle 40 may be a hybrid vehicle or a hybrid electric vehicle and the battery 14 may be configured to drive a propulsion system (not shown) of the vehicle. The wireless charging system 12 includes an AC power transmitter 16, an off-transducer 18, and an on-vehicle transducer 20. The power transmitter 16 further includes a variable frequency oscillator (VFO) circuit 24. The power transmitter 16 is disposed outside the vehicle 40. The off-transducer 18 is in electrical communication with the VFO circuitry 24. Preferably, the off-transducer 18 is configured to be secured to a ground surface 22, such as a garage floor or a parking lot surface. The on-vehicle transducer 20 is attached to the vehicle 40. The on-vehicle transducer 20 may be located on an undercarriage 26 of the vehicle 40. The on-

The off-transducer 18 wirelessly transmits the magnetic energy 44 to the on-vehicle transducer 20 when excited by electrical energy having alternating voltage and alternating current supplied by the power transmitter 16 And a source coil (not shown) for generating a magnetic field. The on-vehicle transducer 20 is spaced from the off-transducer 18 and thus is located within the off-transducer 18 by a distance from the on-vehicle transducer 20, . The alternating magnetic field generated by the off-transducer 18 induces an alternating current having an alternating voltage at the capture coil (not shown). This captured electrical energy is used to charge the battery 14 of the vehicle 40. [

The energy transfer efficiency of the energy between the off-transducer 18 and the on-vehicle transducer 20 is such that these transducers 18, 20 ). ≪ / RTI > This alignment of the transducers 18, 20 can be realized when at least a portion of the on-vehicle transducer 20 is placed on the off-transducer 18. Referring to FIG. 2, at least a portion of the on-vehicle transducer 20 is placed on the off-transducer 18. Alternatively, the on-vehicle transducer 20 may not be placed on the off-transducer 18, but may still be close to the on-vehicle transducer 20 for wireless energy transmission to occur.

The power transmitter 16 is in electrical communication with the power source 48. The power source 48 may supply a voltage of 120 VAC or 240 VAC, which is typically associated with the utility main. The voltage of the power source 48 may typically have an alternating frequency of 60 Hertz (Hz) or 50 Hz, depending on the utilization standard for the particular geographic location. Alternatively, the power source 48 may have an operating voltage that is different from 120 VAC or 240 VAC or an operating frequency that is different from 50 Hz or 60 Hz.

The wireless charging system 12 further includes a controller / converter 53 disposed within the vehicle 40 and coupled with the power transmitter 16, off-transducer 18, and on-vehicle transducer 20 Thereby providing a current useful for electrically charging the battery 14. [ The converter portion of the controller / converter 53 includes electrical components that form a rectifier circuit (not shown). The rectifier circuit is in electrical communication with the on-vehicle transducer 20 to convert the HV HF AC signal output by the on-vehicle transducer 20 into a more efficient HV DC signal for electrically charging the battery 14. [ As used herein, the HV HF AC signal is generated by the VFO circuit 24 and input to the off-transducer 18 and is applied to the magnetic transducer 18, 20 between the off- High-frequency alternating current (AC) electrical signal output from the on-vehicle transducer 20 due to coupling. In the illustrated example, the voltage of the HV HF AC signal exceeds 120 VAC and the frequency of the HV HF AC signal exceeds 60 Hertz (Hz). The frequency may range from 10 kHz to 450 kHz. For example, this range is typically used for loosely coupled resonators typically in the 50 to 450 kHz range and frequencies typically used for tightly coupled resonators typically in the range of 10 to 70 kHz As shown in FIG. As also used herein, an HV DC signal is a high voltage, direct current (DC) electrical signal whose voltage and current are not time variant.

The controller portion of controller / converter 53 may be a microprocessor, an application specific integrated circuit (ASIC), or a central processing unit (not shown) that may be constructed from discrete logic and timing circuits Not shown). Software instructions for programming the controller portion may be stored in a non-volatile (NV) memory device (not shown). The NV memory device may be contained within a microprocessor or ASIC, or it may be a separate device. Non-limiting examples of types of NV memory that may be used include electrically erasable programmable read only memory (EEPROM), masked read only memory (ROM), and flash memory . The controller portion also includes a wired transceiver (not shown), such as a controller area network (CAN) transceiver, that allows the controller portion to establish electrical communication with other devices in the vehicle 40.

As illustrated in Figure 2, the charging system 12 establishes a radio link 65 from a transmitter (not shown) disposed in the controller / converter 53 and a controller / converter 53 to the power transmitter 16 And a receiver (not shown) disposed within the power transmitter 16. Transmitters and receivers may be configured as transceivers to establish a return wireless link 66 from the power transmitter 16 to the controller / converter 53.

The controller section measures voltage, current, and power. The controller portion of the controller / converter 53 is configured to provide the measured voltage, current, and current to enable the power transmitter 16 to further regulate the amount of power supplied to the off-transducer 18 to ensure optimum charging system power efficiency. And power data to the power transmitter 16 over the wireless link 65. Preferably, the optimum charging system power efficiency exceeds 85%. Similarly, the power transmitter 16 may further wirelessly transmit the supplied power data to the controller portion of the controller / converter 53 via the feedback wireless link 66. The instant controller / configuration described herein with other configurations is further described in U. S. Patent Application Publication No. 2013/0015812, entitled " ELECTRICAL CHARGING SYSTEM HAVING ENERGY COUPLING ARRANGEMENT FOR WIRELESS ENERGY TRANSMISSION THEREBETWEEN & Which is incorporated herein by reference in its entirety.

Referring to Figure 3, a block diagram of the VFO circuit 24 is shown. The VFO circuit 24 includes a voltage controlled oscillator (VCO) 71, an amplifier 70, a voltage monitor circuit 73, a current monitor circuit 74, and a phase detection circuit 72 . The VCO 71 is in electrical communication with the input of the amplifier 70. A feedback loop is provided between the off-transducer 18 and the VCO 71. The feedback loop includes a voltage monitor circuit 73 and a current monitor circuit 74 in electrical communication with the phase detection circuit 72. The voltage monitor circuit 73 measures the voltage input to the off-transducer 18 and the current monitor circuit 74 measures the current flow input to the off-transducer 18. The phase detection circuit 72 is configured to measure the phase difference between the voltage and the current at the input to the off- The phase detection circuit 72 is electrically coupled to the VCO 71 which controls the frequency of the current supplied to the output 67a.

The phase detection circuit 72 is configured to determine whether the voltage and current are within a predetermined phase difference range. If the phase difference is not within the desired range, the voltage output of the phase detection circuit 72 will vary and thus increase the frequency of the VFO circuit 24 along the frequency of the VCO 71 until the phase difference falls within the desired range Or decrease. The monitoring of the output voltage and current is continuously performed during operation of the charging system 12 and the frequency adjustment is applied as required based on the phase difference. The power transmitter 16 then adjusts the frequency of the power supplied to the off-transducer 18 to ensure that the charging system power efficiency is maintained at the desired level. In one embodiment, the preferred charging system power efficiency is at least 85%. Preferably, the operating frequency range of the VFO circuit 24 is from about 15 kHz to 200 kHz.

Referring now to FIG. 4, a graph 69 illustrates AC current flow measurement results 77 and AC voltage measurement results 78 as a function of time at the outputs 67a and 67b of the VFO circuit 24 of the power transmitter 16 As shown in Fig. AC current flow measurement results 77 and AC voltage measurement results 78 are sine waves that are out of phase by an amount represented by an angular phase difference or phase difference? Designated by reference numeral 79 in this specification. In the case of resonance between the off-transducer 18 and the on-vehicle transducer 20, i.e., loosely magnetically coupled energy transfer, the phase difference is preferably in the range of about 10 degrees to about 15 degrees And in the case of inductive, i.e., tightly coupled, energy transfer, the phase difference is about 0 to 2 degrees to ensure the optimum charging system power efficiency performance of the charging system 12. The phase difference accounts for partial tolerances, temperature, and alignment of the off-transducer 18 and the on-vehicle transducer 20.

Thus, the design of the charging system 12, including the VFO circuitry 24, determines whether the voltage and current waveforms are within a predetermined phase difference range that ensures that the charging system power efficiency delivered to the battery 14 is at an optimal level do. The phase difference is controlled by the charging system 12, more specifically by the controller in the VFO circuit 24 so that the optimum level of charging system power efficiency is maintained. After analysis of the voltage and current waveforms input to the off-transducer 18, the controller outputs a voltage operable to regulate the frequency in the VCO 71 and thus the voltage of the power transmitter 16 to the off- The output signal maintains the desired charging system power efficiency. This is because the voltage and current phase difference is about 15 degrees when the off-transducer 18 and the on-vehicle transducer 20 are loosely coupled and the off-transducer 18 and the on- But also to be maintained at zero when tightly coupled. Thus, the charging system 12 uses the angular phase difference value to determine whether the transducers 18,20 are loosely coupled or tightly coupled.

The charging system 12 is configured to receive power from the controller / converter 53 via the wireless link 65 to compare the power input to the off-transducer 18 with the power output by the on- Additional voltage and current data can be used. The frequency of the VFO circuit 24 may be further adjusted to maximize system power efficiency in addition to or in lieu of adjusting the frequency to maintain the desired phase angle difference.

It will be appreciated that the angular phase difference values may be pre-determined as being in a predetermined value range (i.e., tightly coupled or loosely coupled) corresponding to a range of predetermined frequencies associated with the radio transmission mechanisms as previously described herein It should be noted that it is determined. The charging system 12 sweeps the output frequency of the VFO circuit 24 over a wide range of frequencies, for example from about 15 kHz to 200 kHz, and then the system power efficiency and phase difference To determine whether the transducers 18,20 are tightly coupled or loosely coupled. Based on the system efficiency and phase difference measurement results, the charging system 12 can determine whether the transducers 18,20 are tightly coupled or loosely coupled and determine the operating frequency range and the desired phase difference range It can be set accordingly.

Referring now to FIG. 5, an alternative VFO circuit 225 is illustrated. Elements similar to those shown in the VFO circuit 24 of FIG. 3 have different reference numerals by 200. Similar to the VFO circuit 24 as previously described, the VCO circuit 225 includes a voltage controlled oscillator (VCO) 271, an amplifier 270, a voltage monitor circuit 273, a current monitor circuit 274, And a phase detection circuit 272 are employed. The phase detection circuit 272 includes a flip-flop circuit 287 and a controller 288. The flip-flop circuit 287 provides the controller 288 with a count number that allows the controller 288 to determine the voltage provided on the output 299 to control the frequency of the VCO 271. Resistors 281-284 and 289 allow electrical signals to be biased to the correct voltage level. The current monitor circuit 274 is electrically connected to the sense coil 285 that provides the result of the current measurement from the output of the amplifier 270. VCO 271 is in electrical communication with the inputs of amplifier 270. Voltage signals are carried on signal paths 292 and 293 and received by voltage monitor circuit 273. Current signals are carried on signal paths 290 and 291 and received by current monitor circuit 274. The flip-flop circuit 287 receives the output 296 from the voltage monitor circuit 273 and the output 297 from the current monitor circuit 274. The output 298 of the flip-flop circuit 287 is received by the controller 288. The VCO 271 receives an output 299 from the controller 288. For example, if electrical pulses of zero are output from the flip-flop to the controller 288, no adjustment at the frequency of the VCO 271 is needed. If the number of pulses on the output of the flip-flop is greater than the pulse of zero due to feedback of the voltage monitor circuit 273 and the current monitor circuit 274, then voltage regulation for the VFO may occur in relation to the amount of feedback signal received .

Alternatively, the phase detection circuit 72 of the VFO circuit 24 may comprise an embedded controller. Such a circuit implementation may, for example, simplify the circuit design and remove other electrical blocks / electrical components in the VFO circuit 24 to provide a lower cost. 3, the use of the embedded controller allows integrated functions such that the voltage monitor circuit 73, current monitor circuit 74, phase detection circuit 72, and VCO 71 may not be needed have. 5, voltage monitor circuit 273, current monitor circuit 274, flip-flop circuit 287, controller 288, and VCO 271 may not be needed when the embedded controller is used have.

Turning now to FIG. 2, there is shown an improved charging system 12a that further includes an integrated charger 60 and a transfer switch 57. As shown in FIG. The integrated charger 60 and the transfer switch 57 are disposed within the vehicle 40 and cooperate with the power transmitter 16, off-transducer 18 and on-vehicle transducer 20 to power the battery 14 Providing an electrical charging current. The controller / converter 53, the integrated charger 60, and the transfer switch 57 comprise electrical components forming the electrical signal shaping device 45.

A secondary charging system 62 (i.e., a backup charging system) is connected to an integrated charger (not shown) disposed within the vehicle 40 to provide current to charge the battery 14 when access to the wireless charging system 12 is not available. 60). ≪ / RTI > The secondary charging system 62 advantageously provides a replacement mode for charging the battery 14 for enhanced convenience.

The transfer switch 57 is operatively controlled by the controller portion of the controller / converter 53 via the signal line 55 for switching between the secondary charging system 62 and the wireless charging system 12. An output 52 carries the electrical signal generated by the on-vehicle transducer 20, which is received by the converter portion of the controller / converter 53. The output 56 carries an electrical signal from the converter portion of the controller / converter 53 that is received by the transfer switch 57. The output 58 carries the electrical signal from the transfer switch 57 to the battery 14. The communication data bus 54, such as a controller area network (CAN) bus, receives vehicle data information for the advanced charging system 12a or charging system data for other electrical devices disposed within the vehicle 40 To the controller portion of the controller / converter (53).

The wheels 51a, 51b, 51c and 51d of the vehicle 40 are used to support the alignment of the on-vehicle transducer 20 and the off-transducer 18. [ The alignment means 99, such as the strut 63, may additionally support this alignment of the off-transducer 18 and the on-vehicle transducer 20. The alignment device 64 may also support positioning the vehicle 40 so that the off-transducer 18 and the on-vehicle transducer 20 are properly aligned. The alignment of the off-on-vehicle transducers 18, 20 is required to optimize the energy transmission from the off-transducer 18 to the on-vehicle transducer 20. 2, the alignment of the off-transducer 18 and the on-vehicle transducer 20 is such that at least a portion of the on-vehicle transducer 20, as best illustrated in FIG. 2, Off-transducer 18 of the present invention. Alternatively, the alignment of the off-transducer 18 and the on-vehicle transducer 20 may occur when the off-transducer 18 and the on-vehicle transducer 20 are sufficiently spaced apart, 40 may allow wireless transmission of energy to occur between them so that battery 14 of battery 40 is electrically charged.

The secondary charging system 62 generates an output 61 that carries the electrical signal received by the integrated charger 60 which is coupled to an output < RTI ID = 0.0 > (59).

Accordingly, a robust charging system 12 is provided that adjusts the operating frequency of the charging system 12 to provide optimal charging system power efficiency. In addition, the charging system 12 is configured to transmit magnetic energy wirelessly across the distance between the tightly coupled or loosely coupled off-transducer 18 and the pair of on-vehicle transducers 20 . The VFO circuit 24 is used to effectively manage the frequency of the electrical signal so that the phase difference between the voltage and current supplied to the off-transducer 18 is maintained to provide optimum charging system power efficiency.

BACKGROUND OF THE INVENTION [0002] Charging systems consist of electrical components, such as resistors, capacitors, relays, etc., that are commonly available in the electrical arts. The VCO 71 may be purchased as a commonly available component at the frequencies of interest. The phase detection circuit 272 may be readily configured with a flip-flop circuit 287 and a controller 288.

The charging system 12 further determines the system power efficiency between the off-transducer 18 and the on-vehicle transducer 20 and makes further adjustments to the operating frequency to provide the optimum charging system power efficiency .

While the invention has been described in terms of its preferred embodiments, it is not intended to be so limited, but rather is intended to be limited only to the extent that it is recited in the claims that follow. Moreover, the use of terms such as first, second, etc. do not denote any order of importance, but rather the terms first, second, etc. are used to distinguish one element from another. Moreover, the use of terms corresponding to English indefinite articles does not imply a limitation of quantity, but rather refers to the presence of at least one of the referenced items.

Claims (11)

An electrical charging system (12) configured to wirelessly charge an energy storage device (14), the system (12) comprising:
An electrical power transmitter (16) comprising a variable frequency oscillator (71) configured to source electrical power having alternating current, ac voltage, and frequency;
A controller (53) operable to adjust the variable frequency oscillator (71) to change the frequency of the electric power sourced;
Is configured to be electromagnetically coupled to an on-vehicle transducer (20) in electrical communication with the electrical power transmitter (16) and in electrical communication with the energy storage device (14) to charge the energy storage device An off-transducer (18) that directs the on-vehicle transducer (20) to capture electrical power to be delivered; And
And a phase detection circuit (72) configured to communicate with the controller (53) and the off-transducer (18) and to determine a phase difference between the alternating voltage and the alternating current, the controller (53) And adjust the variable frequency oscillator (71) based on the difference so that the frequency of the sourced electric power maintains a phase difference within a desired range. 7. The system of claim 1, wherein the controller (53) is configured to adjust the variable frequency oscillator (71) to sweep the frequency of the electric power sourced within a frequency range of 10 kilohertz System (12). The system of claim 1, further comprising a wireless transmitter (65) in electrical communication with the controller (53), the on-vehicle transducer (20) comprising a power detection circuit configured to determine a value of the captured electric power And wherein said power detection circuitry is operable to communicate with a wireless receiver (65) configured to wirelessly transmit the value of the captured electrical power to said controller (53) via said wireless transmitter (65) And the controller (53) is configured to determine power efficiency by comparing the value of the captured electric power with the value of the sourced electric power. 4. The system of claim 3, wherein the controller (53) is configured to adjust the variable frequency oscillator (71) based on power efficiency such that the frequency of the sourced electric power maximizes power efficiency. . 2. The electrical charging system (12) of claim 1, wherein the preferred range of phase differences is between 10 and 21 degrees. 6. The electrical charging system (12) of claim 5, wherein the preferred range of phase differences is between 10 and 15 degrees. 7. The electrical charging system (12) of claim 6, wherein the preferred range of phase differences is between 0 and 10 degrees. 8. The electrical charging system (12) of claim 7, wherein the phase difference is about zero degrees. The electrical charging system (12) of claim 1, wherein the on-vehicle transducer (20) and the energy storage device (14) are located within a vehicle (40). 10. The electrical charging system (12) of claim 9, wherein the off-transducer (18) and the electric power transmitter (16) are located outside the vehicle (40). An electrical charging system (12) configured to wirelessly charge an energy storage device (14), the system (12) comprising:
An electrical power transmitter (16) comprising a variable frequency oscillator (71) configured to source electrical power having alternating current, ac voltage, and frequency;
A controller (53) operable to adjust the variable frequency oscillator (71) to change the frequency of the sourced electric power;
Is configured to be electromagnetically coupled to an on-vehicle transducer (20) in electrical communication with the electrical power transmitter (16) and in electrical communication with the energy storage device (14) to charge the energy storage device An off-transducer (18) that directs the on-vehicle transducer (20) to capture electrical power to be delivered; And
And a wireless transmitter (65) in electrical communication with the controller (53)
The on-vehicle transducer (20) is in electrical communication with a power detection circuit (24) configured to determine a value of the captured electric power, the power detection circuit (24) The controller 53 is in electrical communication with a radio receiver 65 that is configured to transmit wirelessly to the controller 53 via the controller 65. The controller 53 compares the value of the captured electric power with the value of the sourced electric power, And the controller (53) is configured to adjust the variable frequency oscillator (71) based on the power efficiency such that the frequency of the sourced electric power maximizes power efficiency. ).

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