FIELD OF INVENTION

The present invention relates broadly to a wireless power transfer (WPT) system, a battery unit for a WPT system, a receiver unit for a WPT system and a method of WPT, in particular to a fully-enclosed battery without external electrically conducting output terminals that transfers power via resonant coupled wireless power transfer with regulated voltage through a wireless feedback control system.

BACKGROUND

Any mention and/or discussion of prior art throughout the specification should not be considered, in any way, as an admission that this prior art is well known or forms part of common general knowledge in the field.

Batteries are being used as power supplies for increasingly larger loads such as electric vehicles, mobile robots, and high-power tools or appliances. They require a suitable connection, such as a wire or pin, between external terminals of the battery and the terminals of the device or appliance.

There seems to be a lack of portable batteries that can efficiently power rapidly varying direct current (DC) electrical loads without an electrically conducting medium to carry current from the source to the load. Furthermore, the physical connection between the source and the load is susceptible to various problems, such as short circuits, arcing when the connection is broken while a large current is flowing, or degradation of the external electrical contacts over time. Such problems make it challenging to implement quick swapping of depleted batteries with charged ones to supply loads such as electrical motor drive trains.

Also, it remains a challenge to power a changing load, such as a variable motor drive with a constant voltage without human intervention.

Embodiments of the present invention seek to address at least one of the above problems.

SUMMARY

In accordance with a first aspect of the present invention, there is provided a wireless power transfer (WPT) system comprising: a battery unit configured to convert a first direct current (DC) voltage into a first alternating current (AC) voltage for transmission via a first transmitter coil; a receiver unit configured to wirelessly couple a first receiver coil to the first transmitter coil such that a second AC voltage is inducible in the first receiver coil and to convert the second AC voltage into a second DC voltage for powering a load; and a wireless feedback control system for tuning the frequency of the first AC voltage responsive to changes in the second DC voltage across the load for maintaining the second DC voltage within a selected range under varying current drawn by the load.

In accordance with a second aspect of the present invention, there is provided a battery unit for a WPT system, configured to convert a DC voltage into a first alternating current (AC) voltage for transmission via a first transmitter coil to an external receiver unit for powering a load, and comprising a wireless feedback control system for tuning the frequency of the first AC voltage responsive to changes in an output voltage of the external receiver unit across the load for maintaining the output voltage within a selected range under varying current drawn by the load.

In accordance with a third aspect of the present invention, there is provided receiver unit for a WPT system, configured to wirelessly couple a receiver coil of the receiver unit to a transmitter coil of an external battery unit such that an AC voltage is inducible in the receiver coil and to convert the AC voltage into an output DC voltage for powering a load, and comprising a wireless feedback control element for generating a feedback signal to the external battery unit to tune an operating frequency of the transmitter coil responsive to changes in the output DC voltage across the load for maintaining the output DC voltage within a selected range under varying current drawn by the load.

In accordance with a fourth aspect of the present invention, there is provided a method of wireless power transfer (WPT), the method comprising the steps of: converting a first direct current (DC) voltage from a battery into a first alternating current (AC) voltage for transmission via a first transmitter coil; coupling a first receiver coil wirelessly the first transmitter coil such that a second AC voltage is induced in the first receiver coil; converting the second AC voltage into a second DC voltage for powering a load; and using a wireless feedback control system for tuning the frequency of the first AC voltage responsive to changes in an output voltage across the load for maintaining the output voltage within a selected range under varying current drawn by the load.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will be better understood and readily apparent to one of ordinary skill in the art from the following written description, by way of example only, and in conjunction with the drawings, in which: Figure 1 is a schematic drawing illustrating the strength of the magnetic field at a certain radius away from a current carrying wire is proportional to the current flowing in the wire.

Figure 2 is a schematic drawing illustrating a changing magnetic field through an electrically conductive coil induces a voltage across the two ends of the coil that is proportional to the rate of change of the magnetic field.

Figure 3 is a schematic drawing illustrating a WPT system.

Figure 4 is a schematic drawing illustrating a resonant WPT system.

Figure 5 is a schematic drawing illustrating an exploded view of a fully enclosed battery (FEB) according to an example embodiment.

Figure 6 is a schematic drawings illustrating an exploded view of a receiver according to an example embodiment.

Figure 7 is a schematic drawing illustrating an exploded view of a charger of a WPT system according to an example embodiment.

Figure 8 shows a schematic circuit diagram of a transmitter module and a receiver module according to example embodiments.

Figure 9 shows a schematic circuit diagram of details of the transmitter module and the receiver module according to example embodiments.

Figure 10 shows a circuit diagram of an inverter in a transmitter module according to an example embodiment.

Figure 11 shows a circuit diagram of a rectifier in a receiver module according to an example embodiment.

Figure 12 is a schematic drawings illustrating maximizing coil coupling efficiency, according to an example embodiment.

Figure 13 shows a graph illustrating voltage gain (and hence output voltage) increases with increasing frequency up to the resonant frequency, before decreasing as frequency increases.

Figure 14 shows a photo of a disassembled FEB battery according to an example embodiment.

Figure 15 shows a photo of the disassembled FEB and a receiver module according to an example embodiment, as well as of a test set up used.

Figure 16 shows a flowchart illustrating a method of wireless power transfer (WPT), according to an example embodiment.

DETAILED DESCRIPTION Working Principles of Electromagnetic Induction

Ampere’s Law states that: § _C B ■ dl = ₀ /

: Closed line integral around the closed curve C

B: Magnetic Flux Density dl: A differential of the curve C j ₀ : Permeability of free space

I: Current enclosed by the closed curve C

In simpler terms and with reference to Figure 1, the strength of the magnetic field at a certain radius away from a current carrying wire is proportional to the current flowing in the wire.

Faraday’s Law of Induction states that: 8 = — N ~

8: Electromotive Force (EMF)

N: Number of coils of the wire t>: Magnetic flux enclosed within the coil t: Time

In simpler terms and with reference to Figure 2, a changing magnetic field through an electrically conductive coil induces a voltage across the two ends of the coil that is proportional to the rate of change of the magnetic field.

Based on Ampere’s Law and Faraday’s Law of Induction, if a changing magnetic field is produced by a changing current in a coil of wire, it can be placed close enough to a second coil of wire such that the magnetic field produced by the first coil induces a voltage in the second coil. This enables a transfer of electrical power from a source to a load without a conducting connection.

Working Principles of Resonant Coupled Wireless Power Transfer (WPT)

With reference to Figure 3, in a WPT system, there is a transmitter (TX) coil 302 that generates a changing magnetic field due to the changing current supplied to it from AC source 301. When coupled with the TX coil 302 with a coupling coefficient of k. The changing magnetic field produced by the TX coil 302 induces an EMF on the RX coil 303 by electromagnetic induction, causing a current to flow in the RX coil 303. The RX coil 303 is connected in series to an electrical load 304, which is powered by the EMF generated in the RX coil 303.

However, inductively coupled WPT systems have limited power transfer capability and efficiency due to the high reactance of the coils. As such, with reference to Figure 4, compensating capacitors 402, 405 are connected in series with the TX and RX coils 403, 404 to compensate for their high reactance, thus having resonance in both the source and load circuits. This resonant coupled WPT system improves the efficiency and transfer capability of the power source to the load 406. Note that the compensating capacitors 402, 405 can also be connected in parallel or in both series and parallel to the TX and RX coils.

To enable resonant coupled WPT, the equivalent reactance of the compensating capacitors 402, 405 should be almost the same magnitude as the reactance of the inductive coil, such that the overall reactance of the inductor and the compensating capacitors (whether parallel or in series) is almost zero. Note that reactance is dependent on the inductance or capacitance, as well as the frequency of the system.

Take for example a WPT system with the following parameters:

Coil inductance (L) is 10 j H

System frequency (f) is 100kHz; and

Compensating capacitors with variable capacitance (C) are in series configuration.

The overall reactance (X) of the LC circuit is given by the following formula:

1 1

X = 2nfL - ~ 6.3 -

^J 2nfC 630000C

For the circuit to operate at resonance (X = 0), C must be 252nF. Thus, a good capacitance to have would be between 100-500nF if the desired frequency is around 100kHz.

Description of an example embodiment of the present invention

An example embodiment of the present invention provides a Fully Enclosed Battery (FEB) without electrically conducting external output terminals. The design, according to an example embodiment, is a portable battery that can power dynamic loads without an electrically conductive connection to the load. The FEB according to an example embodiment is designed to power a wide range of loads, from low power appliances such as smartphones and cameras to high power motors such as mobile robots and electric vehicles with power ratings above lOkW. The FEB according to an example embodiment comprises a transmitter module and a receiver module that can transport power to and from a battery without the use of external currentcarrying conductors.

The FEB according to an example embodiment forms part of a resonant coupled WPT system according to an example embodiment and it can transfer power from the transmitter module to a receiver at the load to be powered within short distances ranging up to a few centimeters. In current lab environment testing, continuous WPT of up to 250W for one hour with a peak efficiency of 90% has been achieved for an example embodiment. Theoretically, the system according to an example embodiment can support higher power systems such as but not limited to light electric vehicles and industrial machinery.

Most dynamic loads operate on a large range of currents; thus, the output voltage of its power source must stay relatively constant under a varying current draw. In an example embodiment, a wireless feedback control system enables the WPT system to maintain the output voltage at a specified level regardless of the current drawn by the load, so long as this current is within the rated limits of the WPT system. This system, according to an example embodiment, is implemented by way of the receiver module (at the load) transmitting output voltage measurements wirelessly to the transmitter module of the FEB, where a feedback control system tunes the frequency of the AC voltage supply to the transmitter coil such that the output voltage is maintained within a defined range. The wireless communication can be, but is not limited to, Bluetooth or Wi-Fi.

Heat generated by the FEB is transported out of the battery casing through thermal conducting hardware, such as but not limited to heat pipes, according to an example embodiment. A pressure relief valve is included in an example embodiment. This is to e.g. allow heated gases to vent out in the case of battery malfunction (e.g. thermal runaway) to reduce the chances of explosion.

Construction of the FEB, Receiver and WPT system according to example embodiments

An FEB 500 according to an example embodiment comprises, with reference to Figure 5, the battery casing 501 and the components within the battery casing 501. The battery casing 501 protects the inner components from mechanical damage or external elements such as, but not limited, to water and dust. A battery 502 such as but not limited to a lithium-ion battery is positioned within the battery casing 501 and connected to a transmitter module 503 and receiver module 504 so that energy can be transferred in and out of the battery 502. The transmitter module 503 and receiver module 504 are connected to a WPT coil 505, which is made of a low resistance conductive coil that can, but not necessarily, be mounted on a ferrite plate. The WPT coil 505 acts as both the transmitter and receiver coil, depending on the whether the FEB 500 is in charging or discharging mode. To protect the electronic circuits in the transmitter module 503, it is preferably placed above the battery 502 so that the transmitter module 503 will not have to take the weight of the battery. The WPT coil 505 can be placed 702 (see Figures 6 and 7). It is noted that the face or portion of the casing 501 that will be sandwiched between the WPT coils 505 and 602 or 702 is made from an electrically insulating material to allow magnetic flux to pass through and prevent heating from eddy currents. The battery casing 501 also has a pressure relief valve 506. The battery casing 501 is sealed with a cover 507 that has a handle for easy carrying of the assembled FEB 500. To prevent excessive heat from building up within the battery casing 501, thermally conductive material such as but not limited to copper heat pipes 508 are placed in contact with the components and the battery casing 501 so that heat can be transferred out of the battery casing 501. For optimal heat dissipation, the majority of the battery casing 501 can be made up of thermally conducting material such as but not limited to aluminium.

To switch between charging and discharging modes, a multiplexing switch 509 is placed between the WPT coil 505 and the transmitter and receiver modules 503, 504. The switch 509 will selectively connect the coil to the transmitter and receiver modules 503, 504 depending on the operation mode. This switch 509 can be a digital or mechanical switch that takes an input signal, such as but not limited to a digital input, so that it can connect the coil to the transmitter or receiver module.

A receiver 600 according to an example embodiment, with reference to Figure 6, can convert the magnetic field generated by the transmitter module 503 (Figure 5) of the FEB 500 (Figure 5) to a DC supply that can power an electrical load. The receiver 600 has an outer casing 601 in which the face (or at least a portion) of the casing 601 that will be sandwiched between the WPT coils 505 (see Figure 5) and 602 is be made from an electrically insulating material to allow magnetic flux to pass through and prevent heating from eddy currents. The WPT coil 602 is made of a low resistance conductive coil that can, but not necessarily, be mounted on a ferrite plate. The WPT coil 602 is connected to a receiver module 603 that contains electronics which convert the AC generated by electromagnetic induction in the WPT coil 602 into a DC output to an electrical load. The receiver 600 supplies power to an external electrical load via the output terminals 604.

Another part of a WPT system according to an example embodiment is, with reference to Figure 7, a charger 700 which can generate a magnetic field that can be converted into electrical energy via the receiver module 505 (Figure 5) of the FEB 500 (Figure 5). It has an outer casing

701 in which the face (or at least a portion) of the casing 701 that will be sandwiched between the WPT coils 702 and 505 (see Figure 5) is made from an electrically insulating material to allow magnetic flux to pass through and prevent heating from eddy currents. The WPT coil

702 is made of a low resistance conductive coil that can, but not necessarily, be mounted on a ferrite plate. The WPT coil 702 is connected to a transmitter module 703 that has electronics which convert external DC power into an AC power for generating a changing magnetic field via the coil WPT 702. The charger 700 receives power from an external electrical source via the input terminals 704.

Detailed Description of WPT System according to an example embodiment As shown from a block diagram in Figure 8, in a transmitter module 800 (compare transmitter module 503 in Figure 5) according to an example embodiment, the battery pack terminals 801 are connected to the main TX circuit 802, which is in turn connected to the TX coil 803 (compare WPT coil 505 in Figure 5). A DC-DC converter 804 is connected in parallel to the battery pack terminals 801 and used to power the microcontroller 805. The microcontroller 805 controls the frequency of the AC in the coil by sending a PWM signal to the main TX circuit 802. The frequency is determined by a wireless feedback control system 806 based on the output voltage of the receiver module 810 (at the load) sent by the receiver microcontroller 815. An additional DC-DC converter 807 can, but not necessarily, be connected in parallel to the battery pack terminals 801 and can be used to power components in the main TX circuit 801.

In the receiver module 810 (compare receiver module 603 in Figure 6) according to an example embodiment, the outputs of the RX coil 811 (compare WPT coil 602 in Figure 6) are connected to the main RX circuit 812, which is in turn connected to the output terminals 813 of the receiver module. DC-DC converter 814 is connected in parallel to the output terminals 813 and used to power the microcontroller 815. The microcontroller 815 measures the output voltage of the receiver module 810 with a voltage sensor 816 and sends the reading to the transmitter microcontroller 805 as part of the wireless feedback control system. This maintains the receiver module 810 output voltage within a defined range.

Electrical Design of main TX and RX circuits according to an example embodiment

With reference to Figure 9, the WPT system according to an example embodiment transfers power from a DC source to a DC load via WPT. It has a transmitter module 900 (compare transmitter module 800 in Figure 8) that takes in a DC voltage, and a receiver module 910 (compare receiver module 810 in Figure 8) that outputs a DC voltage.

In the transmitter module 900, an AC voltage that generates a changing magnetic field is created from the DC supply from the battery 901 into a square wave by an inverter 902, which is then converted into a pseudo-sinusoidal wave after passing through the capacitor 903 (compare capacitor 403 in Figure 4). This pseudo-sinusoidal wave that flows through the TX coil 904 (compare TX coil 803 in Figure 8) generates the changing magnetic field.

The voltage induced in the RX coil 911 (compare RX coil 811 in Figure 8) and consequently the current that flows out of the RX coil 911 is also sinusoidal, thus it is converted into a square wave after passing through capacitor 912 (compare capacitor 405 in Figure 4) and then rectified into a DC voltage via the rectifier 913 that supplies the load 914.

With reference to Figure 10 and as an example, not limitation, inverter 902 comprises digitally controlled switches 1001, 1002, 1003, 1004 connected as shown in Figure 10 according to an example embodiment. The switches 1001, 1002, 1003 take turns to open and close as a pair, with switches 1001 and 1003 closing when the first input PWM 1006 from a microcontroller (comnare MCU 805 in Figure 8) is at logic high, while the switches 1002 and 1004 are closing whenever a second PWM 1006 from the microcontroller that is antiphase to the first is at logic high. By doing so, the DC input 1007 switches polarity at the same frequency as the PWM signals 1005, 1006, causing it to be a square wave at the output 1008. The above is just one implementation of the inverter 902 according to an example embodiment; any electrical circuit that can convert a DC into a square wave AC can be used as the inverter 902 in different example embodiments.

With reference to Figure 11 and as an example, not limitation, rectifier 913 according to an example embodiment comprises 4 switches or diodes 1101, 1102, 1103, 1104 that only allow current to flow in the specified direction. When the EMF across the input terminals 1105, 1106 causes a current to flow into terminal 1105, only 1101 and 1103 allow current to flow across it, while 1102 and 1104 only allow flowing current the current flows into 1106. This allows the output current at terminals 1107 to be a DC supply from a single direction. The above is just one implementation of the rectifier 913 according to an example embodiment; any system that can convert an AC voltage into a DC voltage can be used in different example embodiments.

Maximizing Efficiency in Magnetic Flux Coupling according to an example embodiment

With reference to Figure 12, to maximize efficiency, it is preferable that the coil coupling factor is high. This is achieved in two ways in an example embodiment: placing ferrite plates 1201, 1202 on the outer surfaces of the coils 1203, 1204 to limit the flux leakage on the surfaces that are facing outwards; and placing the coils 1203, 1204 close to each other with less than 1cm gap between them.

The above two methods are preferable but not necessary for the WPS system according to an example embodiment to work.

Active Frequency Tuning according to an example embodiment

Depending on (a) coil inductance, (b) series or parallel capacitance, (c) circuit impedances, (d) coil separation, and (e) other parameters such as but not limited to the power source characteristics and the circuit temperature, the output voltage at the receiver module will vary for a given load.

Therefore, based on the desired output voltage, the frequency of the AC in the transmitter module is tuned for the specific voltage, according to an example embodiment. Keeping all other factors equal, the relationship between the voltage and the frequency should look similar to the graph in Figure 13, where voltage gain (and hence output voltage) increases with increasing frequency up to the resonant frequency, before decreasing as frequency increases. The exact shape of the graph, however, depends on the circuit parameters. Using this relationship between the voltage gain and the frequency, the output voltage can be tuned to the desired value. By way of example, not limitation, the operating frequency may be around 100 - 200 kHz in an example embodiment.

The above tuning is applicable to fixed loads; active frequency control is used for dynamic loads such as but not limited to DC motors, according to an example embodiment. For a fixed frequency, the output voltage decreases as the current drawn increases. Thus, the frequency is adjusted according to an example embodiment to maintain a fixed output voltage at the receiver module.

One method of maintaining the output voltage (according to an example embodiment, not by limitation) is described as follows. Since the output voltage always decreases with frequency when above the resonant frequency, the WPT system according to an example embodiment is selected to operate above the resonant frequency. From there, a control system that aims to reduce the error between the output voltage and the desired voltage can be implemented, for example but not limited to a proportional-integral-derivative (PID) controller.

The feedback of the output voltage from the receiver module (at the load) can be sent to the transmitter module via a wireless communication system 806 (Figure 8, e.g. Bluetooth Low Energy) in an example embodiment.

Testing and Experimentation of an example embodiment

To validate the feasibility of the electrical aspect of the WPT system according to an example embodiment, the WPT system according to an example embodiment has been tested in a laboratory environment by implementing it on a 250W rated electric bike. A photo of a disassembled FEB battery 1400 according to an example embodiment in Figure 14. Figure 15 shows a photo of the disassembled FEB 1400, a receiver module 1500 (at the load) according to an example embodiment, as well as the test set up used.

Testing Methodology:

With reference to Figure 15, an example embodiment (was tested with an electric -bike 1502 with a 250W rated motor. A relative distance of 4mm gap between the two WPT coils (together indicated at numeral 1504) was achieved with plastic spacers. The electric-bicycle 1502 drive train was powered solely by the FEB 1400. No auxiliary battery or energy source is used. Static tests were done by setting the Motor to run at varying power levels by depressing brake levers at different forces. The Motor is set at constant linear speed of 25km/hr, as determined by drivetrain display. When brakes lever is depressed, motor will draw higher current to achieve constant defined speed.

Static Test results: 1. Constant output voltage to the electric bike for varying current drawn across its full operating range.

The WPT system according to an example embodiment output a voltage between 34.5V - 35.5V for a varying current drawn of 0.1 A to 7A.

2. Fast response to voltage fluctuations due to change in current drawn

The WPT system according to an example embodiment exhibited a response < 0.5 seconds for largest possible fluctuation of 0.1 A to 7A, and from 7A back to 0.1 A.

3. Power output up to 250W with a peak efficiency of 90%

The WPT system according to an example embodiment exhibited an efficiency of 80% at 50W and up to 90% at 200W, with fixed losses reducing the efficiency at low power levels.

4. The WPT system can continuously operate at 200W and above for 1 hour.

With the WPT system according to an example embodiment, the electric bike ran continuously for an hour at near maximum speed with brakes depressed operating at over 200W.

5. All components were working as expected and within their rated limits

For the WPT system according to an example embodiment, the voltage, current and temperature of the components were measured throughout the test, and all components were performing their intended function and operating within their rated limits.

In one embodiment, a wireless power transfer (WPT) system is provided comprising: a battery unit configured to convert a first direct current (DC) voltage into a first alternating current (AC) voltage for transmission via a first transmitter coil; a receiver unit configured to wirelessly couple a first receiver coil to the first transmitter coil such that a second AC voltage is inducible in the first receiver coil and to convert the second AC voltage into a second DC voltage for powering a load; and a wireless feedback control system for tuning the frequency of the first AC voltage responsive to changes in the second DC voltage across the load for maintaining the second DC voltage within a selected range under varying current drawn by the load. a battery; and a first electrical circuit comprising: a first inverter circuit coupled to the battery for converting the first DC voltage from the battery into the first AC voltage; the first transmitter coil coupled to the first inverter circuit; and a first primary compensating capacitor circuit coupled to the first transmitter coil; wherein the receiver unit comprises: a second electrical circuit comprising: the first receiver coil for wireless coupling to the first transmitter coil such that the second AC voltage is inducible in the first receiver coil; a first secondary compensating capacitor circuit coupled to the first receiver coil; and a first rectifier circuit for converting the second AC voltage into the second DC voltage for powering the load

A tuning range of the frequency may be chosen such that operating frequencies of the first and second resonant circuits remain higher than the resonance frequencies of the first and second electrical circuits, respectively.

The wireless feedback control system may comprise a feedback signal receiver of the battery unit, a transmitter microcontroller of the battery unit, a feedback signal transmitter of the receiver unit, and a receiver microcontroller of the receiver unit.

The battery unit may comprise a battery casing enclosing the battery unit. The battery casing may be fully-enclosed.

The receiver unit may comprise a receiver casing enclosing the second resonant circuit.

The first transmitter coil and the first receiver coil may each comprise a ferrite plate configured such that the first transmitter coil and the first receiver coil are sandwiched between the ferrite plates and separated by their respective casing walls in a near-field coupling configuration.

The battery unit may comprise: a second receiver coil for wireless coupling to an external transmitter unit such that a third AC voltage is inducible in the second receiver coil; a second secondary compensating capacitor circuit coupled to the second receiver coil; and a second rectifier circuit coupled to the second receiver coil for converting the third AC voltage into a third DC voltage for charging the battery unit.

The second receiver coil and the first transmitter coil may be provided as a single transceiver coil. The battery unit may comprise a switch for selectively coupling the transceiver coil for transmission of the first AC voltage to power the load or for converting the third AC voltage into the third DC voltage for charging the battery unit.

The system may comprise the transmitter unit for charging of the battery from an AC supply. The transmitter unit may comprise a second transmitter coil for coupling to the AC supply; and a second primary compensating capacitor circuit coupled to the first transmitter coil.

In one embodiment, a battery unit for a WPT system is provided, configured to convert a DC voltage into a first alternating current (AC) voltage for transmission via a first transmitter coil to an external receiver unit for powering a load, and comprising a wireless feedback control system for tuning the frequency of the first AC voltage responsive to changes in an output voltage of the external receiver unit across the load for maintaining the output voltage within a selected range under varying current drawn by the load.

The battery unit may comprise: a battery; and an electrical circuit comprising: an inverter circuit coupled to the battery for converting the first direct current (DC) voltage from the battery into the first alternating current (AC) voltage; the transmitter coil coupled to the inverter circuit and configured for wireless coupling to the external receiver unit such that a second AC voltage is inducible in the receiver unit for powering the load; and a primary compensating capacitor circuit coupled to the transmitter coil.

A tuning range of the frequency may be chosen such that an operating frequency of the first resonant circuit remains higher than the resonance frequency of the first electrical circuit.

The wireless feedback control element may comprise a feedback signal receiver and a microcontroller.

The battery unit may comprise a battery casing. The battery casing may be fully-enclosed.

The battery unit may comprise a ferrite plate, wherein the transmitter coil is sandwiched between the ferrite plate and a casing wall.

The battery unit may comprise: a receiver coil for wireless coupling to an external transmitter unit such that a third AC vol tape i inducible in the receiver coil - a secondary compensating capacitor circuit coupled to the receiver coil; and a rectifier circuit coupled to the receiver coil for converting the third AC voltage into a second DC voltage for charging the battery unit.

The second receiver coil and the first transmitter coil may be provided as a single transceiver coil. The battery unit may comprise a switch for selectively coupling the transceiver coil for transmission of the first AC voltage to power the load or for converting the third AC voltage into the third DC voltage for charging the battery unit.

In one embodiment, a receiver unit for a WPT system is provided, configured to wirelessly couple a receiver coil of the receiver unit to a transmitter coil of an external battery unit such that an AC voltage is inducible in the receiver coil and to convert the AC voltage into an output DC voltage for powering a load, and comprising a wireless feedback control element for generating a feedback signal to the external battery unit to tune an operating frequency of the transmitter coil responsive to changes in the output DC voltage across the load for maintaining the output DC voltage within a selected range under varying current drawn by the load.

The receiver unit may comprise: an electrical circuit comprising: the receiver coil for wireless coupling to a transmitter module of the external battery unit such that the AC voltage is inducible in the receiver coil; a secondary compensating capacitor circuit coupled to the receiver coil; and a rectifier circuit for converting the AC voltage into the output DC voltage for powering a load.

A tuning range of the frequency may be chosen such that an operating frequency of the electrical circuit remains higher than the resonance frequency of the electrical circuit.

The wireless feedback control element may comprise a feedback signal transmitter and a microcontroller.

The receiver unit may comprise a receiver casing.

The receiver unit may comprise a ferrite plate, wherein the transmitter coil is sandwiched between the ferrite plate and a casing wall.

Figure 16 shows a flowchart 1600 illustrating a method of wireless power transfer (WPT), according to an example embodiment. At step 1602, a first direct current (DC) voltage from a battery is converted into a first alternating current (AC) voltage for transmission via a first transmitter coil. At step 1604, a first receiver coil is coupled wirelessly to the first transmitter coil such that a second AC voltage is induced in the first receiver coil. At step 1606, the second AC voltage is converted into a second DC voltage for powering a load. At step 1608, a wireless feedback control system is used for tuning the frequency of the first AC voltage responsive to changes in an output voltage across the load for maintaining the output voltage within a selected range under varying current drawn by the load.

A tuning range of the frequency may be chosen such that operating frequencies of the first and second resonant circuits remain higher than the resonance frequencies of the first and second electrical circuits, respectively.

The method may comprise using a ferrite plate configured such that the first transmitter coil and the first receiver coil are sandwiched between the ferrite plates and separated by their respective casing walls in a near-field coupling configuration.

The method may comprise charging of the battery from an AC supply.

Embodiments of the present invention can have one or more of the following features and associated benefits/adv antages:

The industrial applications of embodiments of the present invention include but are not limited to: Portable energy for all types of electrical vehicle, machinery, electronics, including, but not limited to, Light Electric Vehicles, Marine Vehicles and Machinery, Robotics, and Off Grid Energy Storage.

Aspects of the systems and methods described herein, such as the transmitter modules and the receiver modules, may be implemented as functionality programmed into any of a variety of circuitry, including programmable logic devices (PLDs), such as field programmable gate _ /T7r>/^ _ _ _ _ _ /n 4 memory devices and standard cell-based devices, as well as application specific integrated circuits (ASICs). Some other possibilities for implementing aspects of the system include: microcontrollers with memory (such as electronically erasable programmable read only memory (EEPROM)), embedded microprocessors, firmware, software, etc. Furthermore, aspects of the system may be embodied in microprocessors having software-based circuit emulation, discrete logic (sequential and combinatorial), custom devices, fuzzy (neural) logic, quantum devices, and hybrids of any of the above device types. Of course the underlying device technologies may be provided in a variety of component types, e.g., metal-oxide semiconductor field-effect transistor (MOSFET) technologies like complementary metal-oxide semiconductor (CMOS), bipolar technologies like emitter-coupled logic (ECL), polymer technologies (e.g., silicon-conjugated polymer and metal-conjugated polymer-metal structures), mixed analog and digital, etc.

The various functions or processes disclosed herein may be described as data and/or instructions embodied in various computer-readable media, in terms of their behavioral, register transfer, logic component, transistor, layout geometries, and/or other characteristics. Computer-readable media in which such formatted data and/or instructions may be embodied include, but are not limited to, non-volatile storage media in various forms (e.g., optical, magnetic or semiconductor storage media) and carrier waves that may be used to transfer such formatted data and/or instructions through wireless, optical, or wired signaling media or any combination thereof. When received into any of a variety of circuitry (e.g. a computer), such data and/or instruction may be processed by a processing entity (e.g., one or more processors).

The above description of illustrated embodiments of the systems and methods is not intended to be exhaustive or to limit the systems and methods to the precise forms disclosed. While specific embodiments of, and examples for, the systems components and methods are described herein for illustrative purposes, various equivalent modifications are possible within the scope of the systems, components and methods, as those skilled in the relevant art will recognize. The teachings of the systems and methods provided herein can be applied to other processing systems and methods, not only for the systems and methods described above.

It will be appreciated by a person skilled in the art that numerous variations and/or modifications may be made to the present invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects to be illustrative and not restrictive. Also, the invention includes any combination of features described for different embodiments, including in the summary section, even if the feature or combination of features is not explicitly specified in the claims or the detailed description of the present embodiments.

In general, in the following claims, the terms used should not be construed to limit the systems and methods to the specific embodiments disclosed in the specification and the claims, but should be construed to include all processing systems that operate under the claims. Accordingly, the systems and methods are not limited by the disclosure, but instead the scope of the systems and methods is to be determined entirely by the claims. Unless the context clearly requires otherwise, throughout the description and the claims, the words "comprise," "comprising," and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in a sense of "including, but not limited to." Words using the singular or plural number also include the plural or singular number respectively. Additionally, the words "herein," "hereunder," "above," "below," and words of similar import refer to this application as a whole and not to any particular portions of this application. When the word "or" is used in reference to a list of two or more items, that word covers all of the following interpretations of the word: any of the items in the list, all of the items in the list and any combination of the items in the list.