Self-aligned wireless power transfer system that transfers power current into aligned electromagnets

Abstract

A wireless power transmitter having an electromagnet and a transmitter coil mounted on a moving plate. Current in a main DC circuit is transferred to the electromagnet by a transistor, which controls the magnitude and direction of the current through the electromagnet to control the strength and polarity of the electromagnetic field generated by the electromagnet. A controller initially applies a high gate voltage to the transistor to cause the electromagnet on the transmitter to generate maximum attraction with the magnet on the receiver, thereby causing the moving plate to move the transmitter coil into a closer alignment with the receiver coil. Power factor is measured on the receiver and transmitter to estimate wireless power transfer efficiency. The controller will then gradually reduce the gate voltage and measure the power factor again to estimate power transfer efficiency. The gate voltage is continuously adjusted and the power transfer efficiency is optimized until a maximum value is reached.

Description

Technical Field

[0001] The present invention relates to wireless power transfer systems, and more particularly to self-alignment of power transfer systems. Background Art

[0002] Traditionally, bulky cables and wires are used to deliver power to devices. In recent years, wireless power transmission has been used to charge battery-powered devices. For example, a cell phone can be placed on a stand for charging, which aligns the receiver in the phone with the wireless power transmitter. Magnets can be used to improve the alignment between the power transmitter and receiver. The power transmitter and receiver can transfer power without wires through time-varying electromagnetic fields.

[0003] Figure 1 An existing wireless power transmission system is shown. A power source 102 delivers power to a transmitter 104 via a cable or wire connection. The transmitter 104 generates a time-varying current, which acts on a transmitter coil 110 to generate a time-varying electromagnetic field, which induces a current in a receiver coil 112. The receiver 106 converts the induced current from the receiver coil 112 into a current that powers a load 108.

[0004] The transmitter coil 110 and the receiver coil 112 must be aligned with each other to enable efficient wireless power transfer. As the distance between the transmitter coil 110 and the receiver coil 112 increases, the electromagnetic field strength near the receiver coil 112 decreases, as does the induced current and power transferred.

[0005] The central axis of the transmitter coil 110 should be aligned with the central axis of the receiver coil 112. When the receiver coil 112 moves laterally relative to the transmitter coil 110, their central axes are no longer aligned and the transmitted induced current and power will also decrease.

[0006] Adding a capacitor in series to the coil circuit creates an LC resonant circuit. Power is wirelessly transmitted by matching the resonant frequencies of the transmitter and receiver circuits. Electromagnetic resonance allows wireless power transmission over longer distances than would be possible with a non-resonant circuit using electromagnetic induction.

[0007] 2A-2B show the change of electromagnetic resonance wireless power transmission efficiency with offset. In FIG2A, as the center axis offset of the transmitter coil 110 and the receiver coil 112 increases along the X direction, the power transmission efficiency gradually decreases. Figure 1 As the receiver coil 112 moves in the Y direction and away from the transmitter coil, the offset will also increase.

[0008] For wireless power transmission using electromagnetic induction, the efficiency increases monotonically as the distance between the transmitter and the receiver decreases. However, for wireless power transmission using electromagnetic resonance, the efficiency decreases when the transmitter and the receiver are too close. In FIG. 2B , for a particular wireless power transmission system using electromagnetic resonance, the transmission efficiency is maximized when the distance between the transmitter coil 110 and the receiver coil 112 is approximately 16 cm. As the Z distance or gap between the transmitter coil 110 and the receiver coil 112 (in Figure 1 When the distance between the transmitter coil 110 and the receiver coil 112 increases to more than the maximum transmission efficiency value, the power transmission efficiency decreases. When the transmitter coil 110 and the receiver coil 112 are too close, for example, less than 16 cm, the power transmission efficiency also decreases.

[0009] Depending on the size and shape of the coils and the characteristics of the alternating current provided by the transmitter, when the transmitter coil 110 and the receiver coil 112 are too close, the coupling electromagnetic field or mutual induction magnetic flux generated between the transmitter coil 110 and the receiver coil 112 may be reduced due to anti-resonance. This excessive coupling may cause magnetic flux leakage, thereby reducing power transmission efficiency.

[0010] For electromagnetic resonance systems, simply bringing the receiver as close as possible to the transmitter does not necessarily achieve maximum power transfer efficiency. When they are too close, the power transfer efficiency decreases and more energy is converted into heat. The transmitter and receiver may overheat due to inefficient power transfer in Figure 2B.

[0011] The design of the transmitter and receiver may introduce a physical separation that prevents the transmitter coil 110 and the receiver coil 112 from being too close together. However, the Z distance for maximum efficiency is not a fixed value and may change with conditions such as temperature, input power, output power, etc. Additionally, this separation may be impractical in a robotic or transportation system.

[0012] What is desired is a wireless power transfer system with continuously optimized alignment to optimize efficiency. What is desired is active alignment of the transmitter coil and the receiver coil to improve power transfer efficiency. What is desired is a self-aligning system embedded in the transmitter. In particular, in an electromagnetic resonant wireless power transfer system, what is desired is an adaptive self-aligning system that can adjust the in-plane X, Y distance and out-of-plane Z distance to achieve maximum power transfer efficiency. Summary of the invention

[0013] In one aspect, the present invention provides a self-aligning wireless power transmitter, comprising: a movable part; an electromagnet, the electromagnet being fixed to the movable part; a transmitter coil, the transmitter coil being fixed to the movable part, the transmitter coil generating a power transmission electromagnetic field, and when the transmitter coil and a receiver coil located on a receiver are aligned, the power transmission electromagnetic field transmits power to the receiver coil; a transistor, the transistor transferring a first current into the electromagnet in response to a gate voltage applied to the transistor; a controller, the controller generating the gate voltage to adjust the strength of the alignment electromagnetic field generated by the electromagnet to adjust the force applied to the movable part by the alignment electromagnetic field generated by the electromagnet to move the movable part to adjust the alignment between the transmitter coil and the receiver coil; and an AC / DC converter, the AC / DC converter receiving AC power from an AC power source and generating a DC output including the first current as DC and a first bypass current; a power converter, the power converter receiving the first current and bypassing the first current a first bypass current of an electromagnet, the power converter generating a second current from the first current and the first bypass current; wherein the second current is applied to the transmitter coil and passes through the transmitter coil to generate the power transmission electromagnetic field; wherein the first current passes through the electromagnet to generate the alignment electromagnetic field, wherein the first current powers the electromagnet and at least partially powers the power converter to power the transmitter coil to transfer power to the receiver, whereby the electromagnet is integrated into a power circuit that powers the power converter to power the transmitter coil; wherein the electromagnet and the transistor constitute a switchable element group, the switchable element group comprising: a first switchable element and a second switchable element, the first switchable element and the second switchable element are connected in series on a positive power line between the AC / DC converter and the power converter; and a third switchable element and a fourth switchable element, the third switchable element and the fourth switchable element are connected in series on a power return line between the AC / DC converter and the power converter.

[0014] On the other hand, the present invention provides a resonant wireless power transmitter with an integrated aligner, comprising: a transmitter coil, the transmitter coil being used to generate a first electromagnetic field to wirelessly transfer power to a receiver coil in a receiver; a capacitor, the capacitor being connected in series with the transmitter coil, the capacitor being used to adjust the resonant frequency of the resonant wireless power transmitter determined by the transmitter coil; a movable support, the movable support being used to support the transmitter coil and move the transmitter coil relative to a fixed portion of the transmitter; an electromagnet, the electromagnet being fixed to the movable support, the electromagnet being pre-aligned with a receiver magnet on the receiver and being more accurately aligned with the receiver magnet when the electromagnet is energized; wherein the electromagnet moves the movable support from a pre-aligned position to an aligned position when the electromagnet is energized; wherein the transmitter coil has a higher wireless power transfer efficiency to the receiver coil on the receiver when the movable support is in the aligned position than when it is in the pre-aligned position; a first power device, the first power device supplying a first power current on a positive power line; a second power device, the first power device supplying a first power current on a positive power line; Two power devices drive an alternating current into the transmitter coil, the second power device having a second power input for powering the second power device to generate the alternating current; a first switch element, the first switch element is connected between the positive power line and the second power input, the first switch element transfers at least a portion of the first power current into the electromagnet in response to a first gate control signal; and a controller, the controller is used to generate the first gate control signal, the controller adjusts the voltage of the first gate control signal to adjust the current passing through the electromagnet to adjust the magnetic force between the electromagnet and the receiver magnet; wherein the electromagnet and the first switch element constitute a switchable element group, the switchable element group includes: a first switchable element and a second switchable element, the first switchable element and the second switchable element are connected in series on the positive power line between the first power device and the second power device; and a third switchable element and a fourth switchable element, the third switchable element and the fourth switchable element are connected in series on the power return line between the first power device and the second power device.

[0015] In yet another aspect, the present invention provides a wireless power transmitter comprising: a transmitter coil that wirelessly transmits power to a receiver coil in a receiver when aligned; a first electromagnet that is fixedly attached to the transmitter coil by a movable bracket; a rigid frame of the wireless power transmitter; a flexible link between the rigid frame and the movable bracket that generates a magnetic force on a receiver magnet on the receiver when the first electromagnet is energized, the flexible link allowing the movable bracket with the transmitter coil to move relative to the rigid frame; a first power device that generates a first power current on a positive power line and receives a return current on a power return line; a second power device that converts the first power current received on a second power input into an alternating current through the transmitter coil, the second power device having a second return terminal for providing the return current; and a first element that is coupled between the first power device and the second power device, the first element receiving a first control signal that controls a first input current that is input into the first electromagnet, wherein the first input current is a portion of the first power current. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a wireless power transmission system.

[0017] 2A-2B show the electromagnetic resonance wireless power transfer efficiency as it changes with offset.

[0018] Figure 3 Demonstrating the mechanical design of a self-aligning wireless power transmitter.

[0019] Figure 4 Schematic diagram of a wireless power transfer circuit integrating a self-aligning electromagnet.

[0020] Figure 5 is a flow chart of the initialization process of the self-aligning wireless power transfer transmitter and receiver.

[0021] Figure 6 is a graph of wireless power transfer efficiency as a function of in-plane offset.

[0022] Figure 7 is a graph of wireless power transfer efficiency as a function of out-of-plane offset.

[0023] Figure 8 is a flow chart of the gate voltage adjustment process.

[0024] Fig. 9 Demonstrating an alternative mechanical design for a self-aligning wireless power transmitter.

[0025] Fig.10 Demonstrating an alternative mechanical design for a self-aligning wireless power transmitter using a coil spring.

[0026] Fig.11 Demonstrating an alternative circuit design for a self-aligned wireless power transmitter using a dual-winding electromagnet. DETAILED DESCRIPTION

[0027] The present invention relates to improvements in self-aligned wireless power transmission systems. The following description enables a person of ordinary skill in the art to make and use the invention provided below in a specific application and its requirements. Various modifications to the preferred embodiments will be apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments. Therefore, the present invention is not limited to the specific embodiments shown and described, but should be given the broadest scope consistent with the principles and innovative features disclosed herein.

[0028] Figure 3 The mechanical design of the self-aligned wireless power transmitter is shown. The transmitter coil 110 is molded on or fixed to the central moving plate 135. The spring 120 connects the central moving plate 135 to the rigid frame 130, allowing the transmitter coil 110 and the central moving plate 135 to move relative to the rigid frame 130, which is fixed to the rest of the transmitter. Flexible wires (not shown) can attach the transmitter coil 110 to the drive circuit of the transmitter, which are fixed to the rigid frame 130. These flexible wires are long enough to allow the transmitter coil 110 and the central moving plate 135 to move within the rigid frame 130.

[0029] The electromagnets 20, 30, 40, 50 are mounted in fixed positions on the four corners of the central moving plate 135. The electromagnets 20, 30, 40, 50 may also be connected to flexible wires (not shown) to allow them to be powered by a controller in the transmitter attached to the rigid frame 130. When the central moving plate 135 moves during the self-alignment process, the electromagnets 20, 30, 40, 50 and the transmitter coil 110 move together while being fixed to the central moving plate 135. However, the rigid frame 130 does not move and remains in a fixed position relative to the rest of the transmitter.

[0030] when Figure 3 After the transmitter is placed in a position roughly aligned with a receiver having a similar layout but with a receiver coil 112 and four magnets, the electromagnets 20, 30, 40, 50 are powered to attract the four magnets in the receiver. This magnetic attraction causes the electromagnets 20, 30, 40, 50 to pull the central moving plate 135 with the transmitter coil 110 closer to the receiver and aligned with it, and the spring 120 bends, compresses, extends or otherwise elastically deforms as needed.

[0031] Figure 4 Schematic diagram of a wireless power transmission circuit integrating a self-aligned electromagnet. An alternating current (AC) power source 60 drives an AC / DC converter 114 to generate direct current (DC) on lines P and N. The current on lines P and N passes through a switch network and drives a DC / AC inverter 116, which powers the transmitter coil 110. The DC current on lines P and N can enter the electromagnets 20, 30, 40, 50 through switches before powering the transmitter coil 110 through the DC / AC inverter 116.

[0032] Each of the electromagnets 20, 30, 40, 50 is surrounded by four transistors. These four transistors allow the magnitude and direction of the current through the electromagnet to be adjusted. These transistors may be metal oxide semiconductor field effect transistors (MOSFETs).

[0033] For example, electromagnet 20 is surrounded by transistors 22, 24, 26, 28. When the gates of transistors 22, 28 are driven high and the gates of transistors 24, 26 are driven low, DC current flows through electromagnet 20 in a downward direction from node P through transistor 22, electromagnet 20 and transistor 28 to node X, causing electromagnet 20 to generate an electromagnetic field with the north pole (N pole) pointing downward.

[0034] On the other hand, when the gates of transistors 22, 28 are driven low and the gates of transistors 24, 26 are driven high, DC current flows through electromagnet 20 in an upward direction from node P through transistor 26, electromagnet 20 and transistor 24 to node X, causing electromagnet 20 to generate an electromagnetic field with its N pole pointing upward.

[0035] When the gates of transistors 22, 24 are both high and the gates of transistors 26, 28 are both low, current is bypassed around electromagnet 20 from node P to node X, causing electromagnet 20 to be turned off and not generate an effective electromagnetic field. On the other hand, when the gates of transistors 26, 28 are both high and the gates of transistors 22, 24 are both low, current is also bypassed around electromagnet 20 from node P to node X, causing electromagnet 20 to be turned off and not generate a significant electromagnetic field.

[0036] Controller 100 generates gate control signals EM1_CTL[0:3] for application to the gates of transistors 22, 24, 26, 28. Controller 100 also generates gate control signals EM2_CTL[0:3] for application to the gates of transistors 42, 44, 46, 48 surrounding electromagnet 40, gate control signals EM3_CTL[0:3] for application to the gates of transistors 32, 34, 36, 38 surrounding electromagnet 30, and gate control signals EM4_CTL[0:3] for application to the gates of transistors 52, 54, 56, 58 surrounding electromagnet 50.

[0037] These gate control signals can be analog voltage signals rather than binary on / off signals. The low gate voltage can still be non-zero and above the transistor threshold voltage, allowing some current to pass through the "off" transistor and more current to pass through the "on" transistor. The current is divided into one current branch through the electromagnet and another current branch that bypasses the electromagnet. The DC current can therefore be adjusted by controlling the transistor. The current through the electromagnet is adjusted to adjust the strength and direction of the electromagnetic field generated.

[0038] When adjusting the strength of the electromagnetic field generated by the electromagnets 20, 30, 40, 50, it is not necessary to change the total current through the DC / AC inverter 116 and the transmitter coil 110. Adjustment of the gate voltage causes more or less current to flow through the electromagnets, with the remainder flowing through the bypass around the electromagnets, so that the total current in the main DC circuit remains constant. The total current is the sum of the current flowing through the electromagnets and the current flowing through the bypass.

[0039] Figure 5 Flowchart of the initialization process for a self-aligning wireless power transfer transmitter and receiver. The transmitter and receiver require rough pre-alignment, such as driving an electric vehicle over a charging pad. The pre-alignment needs to be accurate enough so that power can be wirelessly transferred from the transmitter to the receiver, although not necessarily with high efficiency.

[0040] Pre-alignment places the electromagnets 20, 30, 40, 50 in proper positions close to the four corresponding magnets in the receiver. The four magnets in the receiver can be all N-poles pointing towards the transmitter, or all S-poles facing the transmitter, or alternately with two N-poles facing the transmitter, two S-poles facing the transmitter, or any other pre-set layout. The exact layout configuration of the receiver magnets should be known, as it is determined by the design of the receiver. When pre-aligned, the magnetic pole direction of the electromagnets 20, 30, 40, 50 of the transmitter should be determined by the overall system design.

[0041] When the electromagnet 20 is placed near a receiver magnet with its S pole facing the transmitter, the electromagnet 20 should be powered to generate an electromagnetic field with its N pole facing the receiver magnet. In this example, the gates of transistors 22, 28 are driven high, and the gates of transistors 24, 26 are driven low, so that a DC current flows through the electromagnet 20 in a downward direction, causing the electromagnet 20 to generate an electromagnetic field with its N pole pointing toward the receiver, which will attract the S pole of the corresponding receiver magnet. The gate voltages of the transistors around the electromagnet 20 are set to a voltage value that generates the maximum attraction with the corresponding receiver magnet.

[0042] Likewise, the electromagnet 30 may be placed near a receiver magnet with the N pole facing the electromagnet 30. The controller 100 generates a high voltage applied to the gates of the transistors 34, 36, and a low voltage to the gates of the transistors 32, 38 to pass current through the electromagnet 30 in an upward direction, causing the electromagnet 30 to generate an electromagnetic field with the S pole pointing toward the receiver, which will attract the N pole of the corresponding receiver magnet.

[0043] Similarly, other transistors are selected and turned on with a high gate voltage or turned off with a low gate voltage to create a maximum attraction between the transmitter electromagnet 20, 30, 40, 50 and its corresponding magnet on the receiver, step 302. This maximum attraction will pull the electromagnet 20, 30, 40, 50 in the horizontal and vertical directions to bring it closest to the receiver magnet. The spring 120 ( Figure 3 ) allows the movement of the central moving plate 135 to which the electromagnets 20, 30, 40, 50 and the transmitter coil 110 are fixed. This movement can be along the X, Y directions in the plane, i.e. parallel to the plane of the central moving plate 135, and also along the Z direction out of the plane, i.e. perpendicular to the plane of the central moving plate 135.

[0044] The attractive force generated by the electromagnets 20, 30, 40, 50 pulls the central moving plate 135 to a better alignment position with the receiver. This better alignment position improves the efficiency of wireless power transmission because the transmitter coil 110 and the receiver coil 112 can be better aligned.

[0045] Measure the wireless power transfer efficiency (E%), step 306. The power transfer efficiency can be determined by comparing the power received by the receiver with the power transmitted at the transmitter. Depending on the system requirements, the transmitted power can be obtained by measuring the current flowing through the transmitter coil 110 or by measuring the current in other parts of the transmitter (such as the current flowing through line P). The voltage of line P is also measured or estimated to obtain the power of the transmitter according to P=I*V. Similar measurements are made on the current and voltage at the receiver coil 112 or another point in the receiver. The receiver can send the power measurement value to the transmitter via a wireless connection, such as an independent Bluetooth or Wifi connection between the transmitter and the receiver. The transmitter then uses the ratio of the received power to the transmitted power as the power transfer efficiency E%.

[0046] When the estimated wireless power transmission efficiency E% is greater than the efficiency threshold TH, step 310, the self-alignment performed by the electromagnets 20, 30, 40, 50 has optimized the wireless power transmission state and the efficiency has entered an acceptable range. The existing gate voltage is maintained for a period of time T, step 312, and the power transmission efficiency is checked again, step 306.

[0047] When the measured power transfer efficiency E% is less than the efficiency threshold TH, in step 310, the self-alignment performed by the electromagnets 20, 30, 40, 50 has not yet fully optimized the efficiency. Using the gate voltage adjustment process 330 ( Figure 8 ) to adjust the gate voltage and re-measure the power transfer efficiency, step 306, to check whether further adjustment optimizes the transfer efficiency to exceed a threshold, step 310.

[0048] Figure 6 is a graph of wireless power transfer efficiency as a function of in-plane offset. When powered, the electromagnets 20, 30, 40, 50 move the center moving plate 135 in three dimensions to better align with the magnets on the receiver. The three-dimensional movement can be decomposed into in-plane X, Y direction movement and out-of-plane Z direction movement. Movement within the plane of the center moving plate 135 is called in-plane movement or X, Y movement.

[0049] The axes of the transmitter coil 110 and the receiver coil 112 are perfectly aligned at X=0 and Y=0. When the normalized offset is within about 0.5, the misalignment will cause a small decrease in the wireless power transfer efficiency of this particular system. However, when the normalized offset is greater than 0.5, the power transfer efficiency will be severely reduced, such as Figure 6 shown.

[0050] Figure 7is a graph of wireless power transfer efficiency as a function of out-of-plane offset. When powered, the electromagnets 20, 30, 40, 50 move the center moving plate 135 in three dimensions to better align with the magnets on the receiver. Movement perpendicular to the plane of the center moving plate 135 is called out-of-plane movement or Z movement.

[0051] Different from Figure 6 The X and Y curves in Figure 7 The Z curve in reaches maximum efficiency at non-zero distances. For this particular wireless power transfer system, the maximum efficiency occurs at an offset position of about 0.4 after normalization instead of at 0. When the transmitter and receiver move closer from a farther pre-aligned position, the power transfer efficiency initially improves, but then decreases rapidly after exceeding the maximum efficiency value. In the specific case when the transmitter and receiver are in contact with each other, the Z distance is 0 and the power transfer efficiency drops significantly. Even if perfectly aligned in the X and Y directions, the two coils being too close in the Z direction may cause a significant drop in wireless power transfer efficiency due to excessive coupling of electromagnetic resonance.

[0052] When the maximum attractive electromagnetic force ( Figure 5 ), this maximum attraction may bring the transmitter and receiver too close together, resulting in reduced power transfer efficiency. For example, the maximum attraction may move the transmitter to a position with a standardized distance of 0.2 from the receiver, at which point the efficiency is only 60%.

[0053] The inventors have realized that after applying the maximum attractive electromagnetic force, the electromagnetic force can be appropriately reduced to move the transmitter to a larger Z distance to obtain higher power transfer efficiency. For example, the electromagnetic force can be reduced so that the normalized distance increases from 0.2 to 0.4, which will significantly increase the power transfer efficiency from 60% to 80%.

[0054] Depending on the physical and electrical characteristics of the transmitter and receiver, the power transfer efficiency may be very sensitive to the Z distance. Especially at short distances, the power transfer efficiency is more sensitive to the Z distance than the X, Y distance.

[0055] Figure 8 is a flow chart of the gate voltage adjustment process. When the maximum attraction force ( Figure 5 ) but when the power transmission efficiency is lower than the efficiency threshold, the gate voltage adjustment process 330 is activated.

[0056] The high gate voltage is slightly reduced, and the low gate voltage is slightly increased, step 332. This gate voltage adjustment causes less current to flow through the electromagnet, thereby reducing the attractive force and thus increasing the distance between the transmitter and the receiver. The power transfer efficiency is measured again, step 334. The newly measured power transfer efficiency NE% is compared to the previous power transfer efficiency E%, step 336. When NE% is greater than E%, the efficiency has improved and the adjustment direction is correct. The gate voltage adjustment is repeated, step 332, and NE% becomes E% and is compared to the newer measured value of power transfer efficiency NE%, step 334.

[0057] Step 332 is repeated, adjusting the high gate voltage downward and the low gate voltage upward, until the new power transfer efficiency is no longer greater than the previous power transfer efficiency, step 336. The last gate voltage adjustment made in the previous round of step 332 is then undone, step 338, to restore the previous maximum power transfer efficiency. The maximum power transfer efficiency is thus obtained by gradually adjusting the gate voltage until the power transfer efficiency no longer continues to increase.

[0058] In some cases, the gate voltage adjustment process 330 may reverse the magnetic polarity of the electromagnets 20, 30, 40, 50. When the high gate voltage is reduced and the low gate voltage is increased, the high gate voltage may eventually be lower than the low gate voltage, and the direction of the current through the electromagnets 20, 30, 40, 50 may be reversed, resulting in a repulsive electromagnetic force instead of the attractive electromagnetic force at the beginning of the gate voltage adjustment process 330.

[0059] When the transmitter and receiver are too close in the Z direction, gradually reducing the attractive electromagnetic force can increase the Z distance and improve the power transfer efficiency. However, reducing the attractive force also leads to a larger offset in the X and Y directions in the plane, which may reduce the power transfer efficiency. Due to the loss of power transfer efficiency caused by the offset in the X and Y directions, the maximum value of the overall power transfer efficiency may be less than Figure 7 The gate voltage adjustment process 330 measures the overall power transmission efficiency, so the maximum value of the power transmission efficiency found has taken into account the effects of the offsets in the X, Y and Z directions.

[0060] Fig. 9 An alternative mechanical design of a self-aligning wireless power transmitter is shown. The transmitter coil 110 is either free-standing or connected to a central moving plate 135 (not shown). The flexible rod 126 can be elastic or soft, for example made of rubber or other elastic memory material. The flexible rod 126 acts as a spring 120 to connect the transmitter coil 110 to the rigid frame 130, thereby allowing the transmitter coil 110 to move relative to the rigid frame 130 fixed to the rest of the transmitter.

[0061] The electromagnets 20 , 30 , 40 , 50 are mounted at fixed positions at the ends of the flexible rod 126 , close to where the flexible rod 126 is connected to the transmitter coil 110 , and away from the other end of the flexible rod 126 connected to the rigid frame 130 .

[0062] Flexible wires (not shown) may connect the electromagnets 20, 30, 40, 50 and the transmitter coil 110 to a transmitter drive circuit fixed to the rigid frame 130. These flexible wires are long enough to allow the electromagnets 20, 30, 40, 50 and the transmitter coil 110 to move within the rigid frame 130.

[0063] Fig.10 An alternative mechanical design of a self-aligning wireless power transmitter using helical springs is shown.The transmitter coil 110 is attached to a central moving plate 135 which also has electromagnets 20, 30, 40, 50 mounted on the four corners.

[0064] Coil springs 128 are connected to the bottom of the central moving plate 135 and the top of the rigid plate 132. Coil springs 128 allow the central moving plate 135, on which the electromagnets 20, 30, 40, 50 and the transmitter coil 110 are mounted, to move relative to the rigid plate 132 fixed to the rest of the transmitter.

[0065] Flexible wires (not shown) may connect the electromagnets 20, 30, 40, 50 and the transmitter coil 110 to a transmitter drive circuit fixed to the rigid board 132. These flexible wires are long enough to allow the electromagnets 20, 30, 40, 50 and the transmitter coil 110 to move relative to the rigid board 132.

[0066] Fig.11 An alternative circuit design for a self-aligned resonant wireless power transmitter using a dual-winding electromagnet is shown. A capacitor 90 is connected in series with the transmitter coil 110, thereby forming an LC resonant circuit having a resonant frequency, which is determined at least in part by the inductance value of the transmitter coil 110 and the capacitance value of the capacitor 90. When the frequency of the AC current generated by the DC / AC inverter 116 and applied to the transmitter coil 110 is at or near the resonant frequency, the wireless power transfer efficiency is maximized for the current physical configuration. When the applied AC frequency deviates from this resonant frequency, for example by more than 30%, the power transfer efficiency drops significantly.

[0067] Capacitor 92 is a filter capacitor for providing filtering for the power supply. Capacitor 92 or other capacitors may also be placed between nodes P and N.

[0068] Instead of having a single winding, the electromagnets 70, 80 each have two insulated, independent windings as two separate coils. The two windings are wound around the same central axis.

[0069] When controller 100 drives the gate of transistor 72 low and the gate of transistor 74 high, current flows to the right through the upper winding of electromagnet 70 and no current flows to the left through the lower winding of electromagnet 70, thereby generating a maximum electromagnetic field with the N pole pointing to the right.

[0070] When the controller 100 drives the gate of transistor 72 high and the gate of transistor 74 low, current is bypassed around the upper winding of the electromagnet 70, and current flows to the left through the lower winding of the electromagnet 70, thereby generating a maximum electromagnetic field with the N pole pointing to the left. If both transistors 72, 74 are driven with the same gate voltage, the electromagnet 70 will generate two electromagnetic fields that cancel each other, resulting in a zero total net electromagnetic field.

[0071] The electromagnet 80 is configured to generate an N-pole rightward electromagnetic field by the controller 100 driving a low gate voltage to the transistor 76 and a high gate voltage to the transistor 78. When the electromagnet 80 requires an N-pole leftward electromagnetic field, the controller 100 may drive a high gate voltage to the transistor 76 and a low gate voltage to the transistor 78.

[0072] When a high gate voltage is applied to transistors 74, 78 to bypass the lower winding, while a low gate voltage is applied to transistors 72, 76 to control current through the upper winding, the electromagnets 70, 80 are both configured for positive polarity.

[0073] and Figure 4 Each electromagnet requires four transistors, compared to Fig.11 Each dual-winding electromagnet in the circuit requires only two transistors. However, dual-winding electromagnets are more expensive and more complex than single-winding electromagnets.

[0074] The AC / DC converter 114 ( Figure 4 ). The gates of transistors 62, 64, 66, 68 can switch the power provided from AC power source 60 in a certain sequence of pulses. Transistors 62, 64, 66, 68 can be gallium nitride (GaN) transistors or conventional metal oxide semiconductor field effect transistors (MOSFETs).

[0075] Alternative Embodiments

[0076] The inventors contemplate several other embodiments. Although a self-aligning wireless power transmitter is described above, a self-aligning receiver can also be constructed in the same manner. Both or one of the transmitter and receiver are equipped with an electromagnet and controller 100 for self-alignment. When the transmitter coil 110 is replaced with a receiver coil 112 and the AC / DC converter 114 is replaced with a DC / DC converter, Figure 3, 9 The design of 10 can also be applied to the receiver instead of the transmitter.

[0077] The self-aligning system can be applied to wireless power transmission systems using induction or using electromagnetic resonance. For electromagnetic resonance wireless power transmission systems, capacitor 90 can be part of DC / AC inverter 116, and other components inside DC / AC inverter 116 can also change the resonant frequency. For inductive power transmission systems, capacitor 90 can be removed.

[0078] The AC / DC converter 114 can convert standard AC power such as 110v / 220v, 50Hz / 60Hz into DC power. The DC / AC inverter 116 can convert DC power into AC power at or near a resonant frequency such as 6.78MHz. The resonant frequency can be adjusted by at least adjusting the capacitance value of the capacitor connected in series with the transmitter coil 110.

[0079] although Figure 4 The transistors 22, ... 58 are n-channel metal oxide semiconductor field effect transistors (MOSFETs), but can also be replaced by p-channel transistors and a controller 100 that generates a reverse gate voltage. Other types of transistors can also be used as replacements, such as depletion or enhancement, gallium nitride (GaN), gallium arsenide (GaAs), bipolar, etc. Other types of components with switching functions or that can provide enablement or bypass of parallel electromagnets can also be used as replacements. Various estimation and approximation methods can be used to generate the wireless power transfer efficiency E%.

[0080] The receiver can send power or current and voltage measurements to the transmitter via a standard wireless connection (e.g., a separate Bluetooth or Wifi connection between the transmitter and the receiver). The transmitter can also modulate the signal from the transmitter coil 110 to send data to the receiver, and the receiver can modulate the signal from the receiver coil 112 to send its power measurements back to the transmitter. Current sensors and voltage sensors can be added to the DC / AC inverter 116 to determine the transmitted power of the transmitter coil 110. Current, voltage measurement, and wireless communication can be integrated with the controller 100 to make the DC / AC inverter 116 a standard module.

[0081] The polarity of a magnet can be considered arbitrary, depending on the reference point. When two magnets point toward each other with opposite poles (e.g. N and S or S and N), an attractive force is created. When two magnets point toward each other with the same poles (e.g. N and N or S and S), a repulsive force is created. Magnet polarity can be associated with either N or S, depending on the definition used.

[0082] The magnet in the receiver can be a permanent magnet or a fixed magnet, or an electromagnet or some combination. The polarity of the transmitter electromagnet should be opposite to the polarity of the receiver magnet it is pointing to. For example, when the S pole of the receiver magnet or electromagnet is facing the gap, the electromagnet 20 in the transmitter should be energized so that its N pole is pointing to the receiver to ensure attraction.

[0083] When electromagnets are used, the receiver electromagnets should be powered with current so that the transmitter and receiver poles pointing toward the middle gap have opposite polarity. For example, when the transmitter electromagnet 20 is powered to produce an N pole toward the gap, the corresponding receiver electromagnet should be powered to produce an S pole pointing toward the gap. If the transmitter electromagnets 20, 30, 40, 50 have N, S, N, S poles, respectively, their corresponding receiver magnets should have S, N, S, N poles, respectively, to produce an attractive force. If the gate voltage adjustment process 330 causes the magnet polarity to reverse and produce a repulsive force to increase the Z distance, the transmitter and receiver magnet polarities will also match after the transmitter electromagnet polarity is reversed.

[0084] Depending on the application scenario or external conditions such as temperature, the maximum current and the high and low gate voltages for achieving maximum attraction can be preset to different values. The maximum current can be set to a value that prevents damage to the electromagnet or other circuits. The setting of the maximum current can be determined based on laboratory tests or system trials, such as a high enough value that can still pull the transmitter and receiver together under typical pre-alignment or worst-case pre-alignment. A system with good pre-alignment may require a lower maximum gate voltage than a system with poor pre-alignment. In addition to initially applying the maximum attraction, a smaller force can also be applied initially and subsequently adjusted through a control program. There can also be many variations in the control program.

[0085] Some systems may not have Figure 7 The power transfer efficiency is shown to be strongly dependent on the Z distance. Some systems, such as non-resonant inductively coupled wireless power transfer systems, have a maximum efficiency near Z=0 and therefore do not have the curve shown. These systems may not need to use the gate voltage adjustment process 330.

[0086] Depending on the system and application, the efficiency threshold TH( Figure 5 Step 310) is set to a different value. Systems with steeper wireless power transfer efficiency curves, better self-alignment, greater attraction, or higher power transfer requirements may allow for higher efficiency thresholds. The step size of the voltage regulation can be increased ( Figure 8 , step 332) to achieve faster convergence, or the step size can be reduced for more precise adjustment to reach the efficiency maximum. The step size can be initially large and then reduced when approaching the efficiency maximum.

[0087] The power transfer efficiency can be approximated or estimated. For example, the ratio of power factors of current can be used to estimate the power transfer efficiency. Figure 5 and Figure 8 The flowchart in can be replaced by a more complex process, or the steps can be added or rearranged. Figure 5 The efficiency threshold TH used in step 310, or other thresholds used in other steps for other control purposes, can be replaced with different values. There may be many variations in the control process. The controller 100, the gate voltage adjustment process 330 and other processes can be implemented by hardware, logic gates, programmable logic controllers, microcontrollers, firmware, software, processors or various combinations. The controller 100 may include gate voltage generation and adjustment circuits such as voltage dividers and more complex DACs, and sequence controllers such as processors or state machines. The AC / DC converter 114 and the DC / AC inverter 116 can have many embodiments and circuits. If a DC power supply replaces the AC power supply 60, the AC / DC converter 114 can be removed. Other components such as filters, capacitors, resistors, clamps, protection devices, etc. can be added to various nodes of the circuit. The transmitter coil 110 and the receiver coil 112 can have different physical forms, winding arrangements and patterns. The receiving coil 112 can have more than one winding. Each winding can have a different number of turns to provide different voltages to the receiver.

[0088] Although Fig.11 Only two electromagnets 70, 80 are shown, but there can be four or more electromagnets by adding more transistors in series with transistors 72, 76 and transistors 74, 78 and controlling the current of another two-winding electromagnet. The four two-winding electromagnets 70, ... 80 will replace Figure 3 , 9 , 10. Although four electromagnets 20, 30, 40, 50 are shown, other numbers and arrangements of electromagnets are possible, such as 1, 2, 3, 6, 8, etc. Some electromagnets may be larger or more powerful than others. The electromagnets do not have to have the same shape or be made of the same material.

[0089] Although transistors of the same size, such as transistors 72, 74, 76, 78, are used, they do not have to be the same size. Transistors of different kinds, types, layouts or sizes can be used to allow greater or less current for a particular gate voltage. The transistors can all be matched or proportional to each other. Controller 100 can generate different gate voltages as needed. However, using matched transistors can simplify the design.

[0090] Other switching networks may be used instead to divert current into the electromagnet or to bypass the electromagnet. The current diverted into the electromagnet is part of the current that powers the DC / AC inverter 116 to drive the transmitter coil 110. Therefore, the electromagnet does not have to have a separate circuit. The electromagnet is tightly integrated into the main DC circuit.

[0091] In addition to using a variable gate voltage to adjust the magnetic force, a signal that is pulse-width modulated (PWM) between high and low voltages can be used as the gate voltage. The gate voltage is adjusted by varying the pulse on time.

[0092] The shortest distance between the transmitter coil 110 and the receiver coil 112 when aligned is along the Z direction separating the two coils. The in-plane X, Y directions are planes that intersect the axes of the electromagnetic fields generated by the coils. Other nomenclatures may be used instead.

[0093] Although the space between the transmitter coil 110 and the receiver coil 112 is described as a gap, the space therein may be filled with water when underwater, or may be a vacuum in space, or the space therein may be filled with a housing, plastic or other packaging of the transmitter coil 110 or receiver coil 112, or a body or wall of the transmitter or receiver system, or combinations and stacks of various materials.

[0094] Different physical configurations and embodiments are possible. The central moving plate 135 need not be rectangular, but can be circular or have other shapes suitable for the rigid frame 130. The rigid frame 130 can have more complex shapes and can surround the central moving plate 135 ( Figure 3 ) or at a position below the central moving plate 135 ( Fig.10 ), or otherwise provide fixation for the spring 120 or other flexible support for the central moving plate 135. The rigid frame 130 may lack a side and may not completely surround the central moving plate 135. The central moving plate 135 may not be in the center, but still be able to move relative to the rigid frame 130. The central moving plate 135 may be any type of movable member or frame, support or assembly. The central moving plate 135 may be implemented by a transmitter coil 110 with a bracket or other connector to support or connect the electromagnet 20, 30, 40, 50 or 70, 80 to the coil.

[0095] Different types of springs or spring-like or flexible connectors can be used to support the central moving plate 135 and allow relative movement with respect to the rigid frame and the receiver. Guide rails or sliding systems can be used to allow relative movement. Some parts of the receiver can be mounted on the central moving plate 135, while other parts of the receiver are on the rigid frame 130 or other rigid components.

[0096] Although physical mechanisms such as magnetic fields, currents, and operation have been described, these descriptions are theoretical and may be incomplete or even incorrect. Terms such as up, down, above, below, horizontal, vertical, inside, outside, X, Y, Z, etc. are relative and depend on the reference point and are not meant to limit the invention to a particular viewing angle. Current can be considered positive or negative and flows in either direction. The device can be rotated so that vertical becomes horizontal and horizontal becomes vertical, so these terms depend on the viewing angle of the observer.

[0097] The background section may contain background information about the problem or environment of the invention rather than describing prior art by others. Therefore, the content contained in the background section is not an admission by the applicant that the prior art is available.

[0098] Any method or process described herein is machine-implemented or computer-implemented and is intended to be performed by a machine, computer or other device, and is not intended to be performed solely by humans without the assistance of such machines. Tangible results produced may include reports or other displays produced by the machine and appearing on display devices, such as computer monitors, projection devices, audio production devices, and related media devices, and may include paper printouts that are also produced by the machine. Computer control of other machines is another tangible result.

[0099] Any advantages and benefits described may not apply to all embodiments of the present invention. When the word "component" is recited in a claim, the applicant wishes to place the claim element under the protection of 35 USC Chapter 112, paragraph 6. There is usually a mark with one or more words before the word "component". The words before the word "component" are intended to facilitate the reference to the claim and are not intended to represent structural limitations. Such component-plus-function claims are intended to cover not only the structures and structural equivalents thereof described herein for performing the functions, but also equivalent structures. For example, although nails and screws have different structures, they are equivalent structures because they both perform fastening functions. Claims that do not use the word "component" are not intended to be protected under 35 USC Chapter 112, paragraph 6. Signals are typically electronic signals, but can also be optical signals, such as those that can be transmitted over optical fiber lines.

[0100] For the purpose of illustration and description, the foregoing description has presented embodiments of the present invention. This is not intended to be exhaustive or to limit the present invention to the disclosed forms. Based on the above description, many modifications and variations are possible. It is hoped that the scope of the present invention is not limited by this detailed description, but by the appended claims.

Claims

1. A self-aligning wireless power transmitter, comprising: movable parts; an electromagnet fixed to the movable member; a transmitter coil affixed to the movable member, the transmitter coil generating a power transfer electromagnetic field that transfers power to a receiver coil located on a receiver when the transmitter coil and the receiver coil are aligned; a transistor that diverts a first current into the electromagnet in response to a gate voltage applied to the transistor; a controller that generates the gate voltage to adjust the strength of the alignment electromagnetic field generated by the electromagnet to adjust the force applied by the alignment electromagnetic field generated by the electromagnet to the movable member to move the movable member to adjust the alignment between the transmitter coil and the receiver coil; as well as an AC / DC converter that receives AC power from an AC power source and generates a DC output including the first current and a first bypass current as DC; a power converter receiving the first current and a first bypass current that bypasses the electromagnet, the power converter generating a second current from the first current and the first bypass current; wherein the second current is applied to the transmitter coil and passes through the transmitter coil to generate the power transmission electromagnetic field; wherein the first current passes through the electromagnet to generate the alignment electromagnetic field, wherein the first current powers the electromagnet and at least partially powers the power converter to power the transmitter coil to transfer power to the receiver, whereby the electromagnet is integrated into a power circuit which powers the power converter to power the transmitter coil; The electromagnet and the transistor constitute a switchable element group, and the switchable element group includes: a first switchable element and a second switchable element, the first switchable element and the second switchable element being connected in series on a positive power line between the AC / DC converter and the power converter; as well as A third switchable element and a fourth switchable element are connected in series on a power return line between the AC / DC converter and the power converter.

2. The self-aligned wireless power transmitter of claim 1, wherein the power converter is a direct current (DC) / alternating current (AC) inverter; wherein the first current passing through the electromagnet is a DC current; wherein the second current passing through the transmitter coil is an AC current; Wherein the electromagnet is powered by DC and the transmitter coil is powered by AC.

3. The self-aligning wireless power transmitter according to claim 2, in: Alignment between the transmitter coil and the receiver coil is performed by passing a DC current through the electromagnet; as well as Wireless power transfer to the receiver is performed by passing an AC current through the transmitter coil.

4. The self-aligning wireless power transmitter of claim 3, further comprising the receiver having the receiver coil; wherein the electromagnet comprises at least four electromagnets, each of the at least four electromagnets being fixed to a different position on the movable member; at least four receiver magnets affixed to different locations on the receiver, wherein when the receiver is aligned to the transmitter, the at least four receiver magnets are positioned to align with the at least four electromagnets on the transmitter; wherein the transistors include at least four transistors, each transistor being configured to control a first current through one of the at least four electromagnets in response to a gate voltage from the controller; The controller generates a plurality of gate voltage signals for controlling the at least four transistors.

5. The self-aligned wireless power transmitter of claim 3, wherein the transistor is connected between a first terminal and a second terminal of the electromagnet, wherein the first bypass current flows through the transistor and the first current flows through the electromagnet, wherein the transistor adjusts a ratio of the first current to the first bypass current in response to the gate voltage from the controller.

6. The self-aligned wireless power transmitter of claim 3, wherein each switchable element comprises: Component input; Component output; an element electromagnet having a first terminal connected to the first element node and a second terminal connected to the second element node; a first element transistor between the element input and the first element node, the first element transistor having a gate that receives a first gate voltage from the controller to control current through the first element transistor; a second element transistor between the element input and the second element node, the second element transistor having a gate that receives a second gate voltage from the controller to control current through the second element transistor; a third element transistor between the first element node and the element output, the third element transistor having a gate that receives a third gate voltage from the controller to control current through the third element transistor; A fourth element transistor between the second element node and the element output, the fourth element transistor having a gate that receives a fourth gate voltage from the controller to control current through the fourth element transistor.

7. The self-aligning wireless power transmitter of claim 1 , further comprising: a capacitor connected in series with the transmitter coil, the capacitor being used to adjust a resonant frequency of a transmitter including the transmitter coil, wherein the transmitter coil can transfer power more efficiently when operating at the resonant frequency than when operating at a first non-resonant frequency at least 30% higher than the resonant frequency or at a second non-resonant frequency at least 30% lower than the resonant frequency; wherein the controller initially generates an initial gate voltage to be applied to the transistor to cause the electromagnet to generate an initial alignment electromagnetic field, the initial alignment electromagnetic field causing the movable member to move the transmitter coil from a pre-alignment position to an initial alignment position; Wherein the controller subsequently adjusts the gate voltage to adjust the alignment electromagnetic field to move the movable member to a new alignment position.

8. The self-aligning wireless power transmitter of claim 7, wherein the controller compares a previous power transfer efficiency of a previous alignment position with a new power transfer efficiency of the new alignment position; wherein when the new power transmission efficiency is greater than the previous power transmission efficiency, the controller continues to adjust the gate voltage by adjusting the gate voltage; When the new power transmission efficiency is less than the previous power transmission efficiency, the controller removes the previous adjustment of the gate voltage, and the power transmission efficiency reaches a maximum value.

9. The self-aligned wireless power transmitter of claim 8, wherein power transfer efficiency is estimated by a ratio of a receiver measurement of a power factor of power received by the receiver coil to a transmitter measurement of a power factor of power transmitted by the transmitter coil.

10. The self-aligning wireless power transmitter of claim 9, wherein the transmitter measurement of the power factor is the second current through the transmitter coil; Wherein the receiver measurement of the power factor is an induced current flowing through the receiver coil generated by magnetic resonance induction of the power transfer electromagnetic field generated by the transmitter coil.

11. A resonant wireless power transmitter with an integrated aligner, comprising: a transmitter coil for generating a first electromagnetic field to wirelessly transfer power to a receiver coil in the receiver; a capacitor, the capacitor being connected in series with the transmitter coil, the capacitor being used to adjust the resonant frequency of the resonant wireless power transmitter determined by the transmitter coil; a movable support for supporting the transmitter coil and moving the transmitter coil relative to a fixed portion of the transmitter; an electromagnet secured to the movable support, the electromagnet being pre-aligned with a receiver magnet on a receiver and being more precisely aligned with the receiver magnet when the electromagnet is energized; wherein the electromagnet moves the movable support from the pre-alignment position to the alignment position when the electromagnet is energized; wherein the transmitter coil has a higher wireless power transfer efficiency to a receiver coil on the receiver when the movable support is in the aligned position than when in the pre-aligned position; a first power device that supplies a first power current on the positive power line; a second power device driving an alternating current into the transmitter coil, the second power device having a second power input for powering the second power device to generate the alternating current; a first switching element connected between the positive power line and the second power input, the first switching element diverting at least a portion of the first power current into the electromagnet in response to a first gate control signal; as well as a controller configured to generate the first gate control signal, the controller adjusting a voltage of the first gate control signal to adjust a current through the electromagnet to adjust a magnetic force between the electromagnet and the receiver magnet; The electromagnet and the first switch element constitute a switchable element group, and the switchable element group includes: a first switchable element and a second switchable element, the first switchable element and the second switchable element being connected in series on a positive power line between the first power device and the second power device; as well as A third switchable element and a fourth switchable element are connected in series on a power return line between the first power device and the second power device.

12. The resonant wireless power transmitter with the integrated aligner according to claim 11, further comprising: a power transmission efficiency optimization process, the power transmission efficiency optimization process being at least partially executed by the controller, for receiving the power transmission efficiency of the power applied to the transmitter coil and the power induced in the receiver by the transmitter coil, the power transmission efficiency optimization process causing the controller to adjust the voltage of the first gate control signal, the power transmission efficiency optimization process comparing the power transmission efficiency before and after adjusting the voltage of the first gate control signal to further adjust and maximize the power transmission efficiency, Power transmission efficiency is thereby maximized by adjusting the voltage of the first gate control signal and examining a change in the power transmission efficiency.

13. The resonant wireless power transmitter with the integrated aligner of claim 12, wherein the controller initially applies a maximum voltage to the first gate control signal to move the movable support from the pre-aligned position to the aligned position; The controller gradually reduces the voltage of the first gate control signal from the maximum voltage and checks the power transmission efficiency until a maximum power transmission efficiency is reached at a maximum efficiency voltage less than the maximum voltage.

14. The resonant wireless power transmitter with the integrated aligner of claim 13, wherein the movable support moves between the transmitter coil and the receiver coil in three dimensions including the Z direction; wherein when the controller applies the maximum voltage, the initial Z distance between the transmitter coil and the receiver reaches a minimum; wherein the maximum efficiency Z distance is reached when the controller applies the maximum efficiency voltage; wherein the maximum efficiency Z distance is greater than the initial Z distance; The controller adjusts the voltage of the first gate control signal to increase the Z distance between the transmitter coil and the receiver coil to improve power transmission efficiency.

15. A wireless power transmitter, comprising: a transmitter coil that, when aligned, wirelessly transmits power to a receiver coil in the receiver; a first electromagnet fixedly attached to the transmitter coil via a movable mount; a rigid frame of the wireless power transmitter; a flexible link between the rigid frame and the movable support, which generates a magnetic force on a receiver magnet on the receiver when the first electromagnet is energized, the flexible link allowing the movable support having the transmitter coil to move relative to the rigid frame; a first power device for generating a first power current on a positive power line and receiving a return current on a power return line; a second power device for converting a first power current received on a second power input into an alternating current through the transmitter coil, the second power device having a second return terminal for providing the return current; as well as a first element coupled between the first power device and the second power device, the first element receiving a first control signal, the first control signal controlling a first input current input into the first electromagnet, wherein the first input current is a portion of the first power current; The first electromagnet and the first element constitute a switchable element group, and the switchable element group includes: a first switchable element and a second switchable element, the first switchable element and the second switchable element being connected in series on a positive power line between the first power device and the second power device; A third switchable element and a fourth switchable element are connected in series on a power return line between the first power device and the second power device.

16. The wireless power transmitter of claim 15, further comprising: a controller that generates the first control signal, the controller initially applying a maximum voltage to the first control signal to cause the first electromagnet to generate a maximum electromagnetic field, the maximum electromagnetic field generating a maximum attractive magnetic force to initially align the transmitter coil and the receiver coil; wherein the controller receives an estimate of power transfer efficiency from the transmitter coil to the receiver coil; When the power transmission efficiency estimate is lower than a threshold, the controller reduces the voltage of the first control signal and observes a change in the power transmission efficiency estimate, and when the power transmission efficiency estimate increases, continues to reduce the voltage of the first control signal until the power transmission efficiency estimate at the maximum efficiency voltage of the first control signal reaches a maximum value; Wherein after finding the maximum value of the power transmission efficiency estimate, the controller applies the maximum efficiency voltage to the first control signal.

17. The wireless power transmitter of claim 16, further comprising: a second electromagnet fixedly connected to the transmitter coil via the movable support; A second element is coupled in series with the first element between the first power device and the second power device, the second element receiving a second control signal, the second control signal controlling a second input current that is input into the second electromagnet, wherein the second input current is a portion of the first power current.

18. The wireless power transmitter of claim 16, further comprising: a capacitor connected in series with the transmitter coil, the capacitor being used to adjust a resonant frequency of the wireless power transmitter determined at least in part by the transmitter coil, wherein the transmitter coil can transfer power at a higher efficiency when operating at the resonant frequency than when operating at a first non-resonant frequency at least 30% higher than the resonant frequency or at a second non-resonant frequency at least 30% lower than the resonant frequency; wherein the first power device is an alternating current (AC) / direct current (DC) converter; wherein the second power device is a DC / AC inverter; The first electromagnet is powered by DC and the transmitter coil is powered by AC.

19. A self-aligning wireless power transmitter comprising: movable parts; an electromagnet fixed to the movable member; a transmitter coil affixed to the movable member, the transmitter coil generating a power transfer electromagnetic field that transfers power to a receiver coil located on a receiver when the transmitter coil and the receiver coil are aligned; a transistor that diverts a first current into the electromagnet in response to a gate voltage applied to the transistor; a controller that generates the gate voltage to adjust the strength of the alignment electromagnetic field generated by the electromagnet to adjust the force applied by the alignment electromagnetic field generated by the electromagnet to the movable member to move the movable member to adjust the alignment between the transmitter coil and the receiver coil; as well as an AC / DC converter that receives AC power from an AC power source and generates a DC output including the first current and a first bypass current as DC; a DC / AC inverter receiving the first current and a first bypass current that bypasses the electromagnet, the DC / AC inverter generating a second current from the first current and the first bypass current; wherein the second current is applied to the transmitter coil and passes through the transmitter coil to generate the power transmission electromagnetic field; wherein the first current passes through the electromagnet to generate the alignment electromagnetic field, wherein the first current powers the electromagnet and at least partially powers the DC / AC inverter to power the transmitter coil to transfer power to the receiver, whereby the electromagnet is integrated into a power circuit which powers the DC / AC inverter to power the transmitter coil; wherein the electromagnet and the transistor comprise: a first two-winding electromagnet having a first winding having a first terminal connected to the positive power line of the AC / DC converter and a second terminal connected to an intermediate positive node and a second winding having a first terminal connected to the negative power line of the AC / DC converter and a second terminal connected to an intermediate negative node; a first positive line transistor between the positive power line of the AC / DC converter and the intermediate positive node, the first positive line transistor having a gate that receives a first gate voltage from the controller for controlling current through the first positive line transistor; a first negative line transistor between the negative power line of the AC / DC converter and the intermediate negative node, the first negative line transistor having a gate that receives a second gate voltage from the controller for controlling current through the first negative line transistor; a second dual-winding electromagnet having a first winding having a first terminal connected to the intermediate positive node and a second terminal connected to a positive power line of the DC / AC inverter and a second winding having a first terminal connected to the intermediate negative node and a second terminal connected to a negative power line of the DC / AC inverter; a second positive line transistor between the intermediate positive node and the positive power line of the DC / AC inverter, the second positive line transistor having a gate that receives a third gate voltage from the controller for controlling current through the second positive line transistor; and A second negative line transistor between the intermediate negative node and the negative power line of the DC / AC inverter, the second negative line transistor having a gate receiving a fourth gate voltage from the controller for controlling current through the second negative line transistor.

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