Systems and methods for encrypted resonant inductive power transfer - Patents.com

Abstract

To provide systems and methods for ensuring that resonant inductive power transfer only reach authorized users using encryption.SOLUTION: Resonant inductive power transfer requires near-identical resonant frequencies in a transmitter and a receiver. The frequency of the power transfer signal changes on a schedule known only to the transmitter 1 and receiver 3 so that a "power eavesdropper" cannot track the frequency well enough to efficiently receive power. To make the frequency transitions energetically efficient, a capacitive or inductive element is switched to or from each circuit at moments of zero-crossing, i.e., zero charge on a capacitor or zero current in an inductor. To maintain phase alignment, either switching an inductor 2b on the transmit side is nearly simultaneous with switching a capacitor 8b on the receive side, or switching a capacitor 6 on the transmit side is nearly simultaneous with switching an inductor 4 on the receive side.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present disclosure relates generally to systems and methods for wireless power transmission, and more particularly to wireless power transmission by a resonant inductively coupled transmitter and receiver. [Background technology]

[0002] Resonant inductive coupling is the near-field wireless transfer of electrical energy between two coils tuned to resonate at the same frequency. Resonant transfer works by creating a primary coil ring with an oscillating current that creates an oscillating magnetic field. A secondary coil in close proximity to the primary coil can pick up energy from the oscillating magnetic field. When the primary and secondary coils resonate at a common frequency, large amounts of power can be transferred from the primary coil to the secondary coil over a range of several coil diameters with reasonable efficiency.

[0003] A common problem is to wirelessly transmit power from a transmitter to a receiver. A common approach for short-range transmission is resonant inductive power transfer. In this method, both the transmitter and the receiver have resonant circuits tuned to the same frequency. For example, resonant inductive power transfer can be used for wireless recharging of batteries on board aircraft, such as unmanned aerial vehicles. Resonant inductive power transfer is also used for consumer electronics and to recharge electric vehicles.

[0004] Ideally, all power sent from the transmitter follows a low-loss path to the authorized receiver. This does not happen if unauthorized receivers detect the resonant frequency and tune their receivers to the same frequency. In this case, unauthorized receivers steal power. This increases the cost to the sender and reduces the power available to authorized receivers. One solution is to impose physical security so that unauthorized receivers cannot get close enough to the transmitter to receive power. Such shortcomings increase the inconvenience, delays, and costs for authorized receivers.

[0005] Improved systems and methods for preventing unauthorized receivers from receiving power while allowing efficient transmission to authorized receivers would be advantageous. Summary of the Invention

[0006] The subject matter disclosed in some detail below is directed to a system and method for using encryption to ensure that resonant inductive power transfer occurs only to authorized users. Resonant inductive power transfer requires nearly identical resonant frequencies at the transmitter and receiver. According to the embodiments disclosed below, the frequency of the power transfer signal is changed on a schedule known only to the transmitter and receiver so that a "power eavesdropper" cannot successfully track the frequency and receive power efficiently. To make the frequency transitions energy efficient, capacitive or inductive elements are switched in and out of each circuit at the zero crossings: the instant of zero charge on the capacitor or zero current in the inductor. To maintain phase alignment, the switching of the inductor on the transmitter side is nearly simultaneous with the switching of the capacitor on the receiver side, or the switching of the capacitor on the transmitter side is nearly simultaneous with the switching of the inductor on the receiver side.

[0007] Various embodiments of systems and methods for encrypted resonant inductive power transfer are described in some detail herein below, one or more of which may be characterized by one or more of the following aspects.

[0008] One aspect of the subject matter disclosed in detail below is a method for transferring power from a resonant inductive power transmitter to a resonant inductive power receiver, the method including: (a) disposing a resonant inductive power receiver within electromagnetic coupling range of the resonant inductive power transmitter; (b) generating, using the resonant inductive power transmitter, a first oscillating electromagnetic field having a first frequency for a first time interval; (c) generating, during the first time interval, a first vibrating electromotive force in the resonant inductive power receiver having the first frequency by resonant electromagnetic induction; (d) generating, using the resonant inductive power transmitter, a second oscillating electromagnetic field having a second frequency different from the first frequency for a second time interval after the first time interval; and (e) generating, during the second time interval, by resonant electromagnetic induction, a second vibrating electromotive force in the resonant inductive power receiver having the second frequency.

[0009] According to some embodiments of the method described in the immediately preceding paragraph, the method further includes: (f) configuring the resonant inductive power transmitter to generate a first oscillating electromagnetic field by opening a first switch of the resonant inductive power transmitter before step (b); (g) configuring the resonant inductive power receiver to generate a first oscillating electromagnetic field by closing a second switch of the resonant inductive power receiver before step (c); (h) configuring the resonant inductive power transmitter to generate a second oscillating electromagnetic field by closing the first switch before step (d); and (i) configuring the resonant inductive power receiver to generate a second oscillating electromagnetic field by opening the second switch before step (e). The states of the first and second switches and the first and second time intervals are indicated by a frequency change switching sequence. The method further includes sending encrypted information including the frequency change switching sequence from the resonant inductive power transmitter to the resonant inductive power receiver.

[0010] Another aspect of the subject matter disclosed herein is a resonant inductive power transfer system including a resonant inductive power transmitter and a resonant inductive power receiver having synchronized switching states for enabling resonant inductive power transfer according to a frequency altering switching sequence. The resonant inductive power transmitter includes: a voltage source; a first inductor and a first capacitor connected to form a first resonant circuit powered by the voltage source; a first switch and a second inductor connected in parallel with the first inductor when the first switch is closed; and a transmit switch controller configured to control a state of the first switch according to the frequency altering switching sequence. The resonant inductive power receiver includes: a third inductor and a second capacitor connected to form a second resonant circuit; a second switch and a second capacitor connected in parallel with the first capacitor when the second switch is closed; and a receive switch controller configured to control a state of the second switch according to the frequency altering switching sequence. The resonant frequencies of the first and second resonant circuits are each equal to a first resonant frequency when the first switch is closed and the second switch is open, and are each equal to a second resonant frequency different from the first resonant frequency when the first switch is open and the second switch is closed.

[0011] A further aspect of the subject matter disclosed herein is a resonant inductive power transfer system in which the resonant inductive power transmitter includes: a voltage source, a first inductor and a first capacitor connected to form a first resonant circuit powered by the voltage source, a first switch and a second capacitor connected in parallel with the first capacitor when the first switch is closed, and a transmit switch controller configured to control a state of the first switch according to a frequency altering switching sequence. Conversely, the resonant inductive power receiver includes: a second inductor and a third capacitor connected to form a second resonant circuit, a second switch and a third inductor connected in parallel with the second inductor when the second switch is closed, and a receive switch controller configured to control a state of the second switch according to a frequency altering switching sequence.

[0012] Other aspects of systems and methods for encrypted resonant inductive power transfer are disclosed below.

[0013] The features, functions, and advantages discussed in the previous section may be realized individually in various embodiments or may be combined in other embodiments. To illustrate the above and other aspects, various embodiments are described below with reference to the drawings. None of the drawings briefly described in this section are drawn to scale. [Brief description of the drawings]

[0014] [Figure 1] FIG. 2 is a circuit diagram illustrating some components of a transmitter and a receiver of a resonant system. [Diagram 2] FIG. 1 is a circuit diagram showing some components of a transmitter and a receiver of a resonant system with a relay coil. [Diagram 3] This is a circuit diagram showing some components of the transmitter (left) and receiver (right), including a transmit switch for switching inductors and a receive switch for switching capacitors to match the resonant frequencies of the transmitter and receiver. [Figure 4] 4 is a graph showing the current through the transmit coil (shown in FIG. 3) during the time interval in which the state of the transmitter switch S1 changes from closed to open. [Diagram 5] 5 is a graph showing the induced electromotive force (EMF) generated by the receive coil of the receiver during the time interval in which the state of switch S1 changes from closed to open as shown in FIG. 4. [Figure 6] 5 is a graph showing the voltage across the receiver's capacitor C2 during the time interval in which the state of the transmitter's switch S1 changes from closed to open as shown in FIG. 4. [Figure 7] FIG. 1 is a flow diagram identifying steps of a method 100 for encrypted resonant inductive power transfer. [Figure 8]FIG. 1 is a block diagram identifying several components of an encrypted resonant inductive power transfer system according to one embodiment. [Figure 9] FIG. 1 is a circuit diagram showing some of the components of a common-base Colpitts oscillator consisting of an NPN bipolar junction transistor whose output is connected to the input in a feedback loop that includes a parallel resonant circuit (tuned circuit) that acts as a bandpass filter that sets the frequency of oscillation. [Figure 10] FIG. 1 is a circuit diagram illustrating some components of a common-base Colpitts oscillator modified to include a second inductor having an inductance L2 connected in parallel with a first inductor having an inductance L1, and a switch S1 for adding or removing the second inductor in parallel with the first inductor, according to one embodiment. [Figure 11] FIG. 1 is a circuit diagram identifying several components of a battery charging system, including a resonant inductive power receiver and a rectifier for generating a direct current for recharging the battery when an EMF is induced in a receiving coil of the resonant inductive power receiver. [Figure 12] FIG. 1 is a circuit diagram identifying several components of a battery charging system modified to include a second capacitor having a capacitance C3 connected in parallel with a first capacitor having a capacitance C2, and a switch S2 for adding or removing the second capacitor in parallel with the first capacitor, according to one embodiment. [Figure 13] This is a circuit diagram showing some components of the transmitter (left) and receiver (right), including a transmit switch for switching in a capacitor and a receive switch for switching inductors to match the resonant frequencies of the transmitter and receiver. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Reference will now be made to the drawings, in which like elements in different drawings are numbered the same.

[0016] For purposes of illustration, systems and methods for encrypted resonant inductive power transfer are described in detail below. However, not all features of an actual implementation are described herein. Those skilled in the art will appreciate that numerous implementation decisions must be made in the development of any such embodiment to achieve the developer's particular objectives, such as adhering to system-related and business-related constraints that vary from implementation to implementation. Moreover, it will be appreciated that such development efforts may be tedious and time-consuming, but would be routine for those skilled in the art having the benefit of this disclosure.

[0017] Resonant inductive coupling is the near-field wireless transfer of electrical energy between two coils tuned to resonate at the same frequency. Resonant transfer works by creating a primary coil (referred to above and below as the "transmitting coil") ring with an oscillating current that creates an oscillating magnetic field. A secondary coil (referred to above and below as the "receiving coil") in close proximity to the primary coil can pick up energy from the oscillating magnetic field. When the primary and secondary coils resonate at a common frequency, large amounts of power can be transferred from the primary coil to the secondary coil with reasonable efficiency within a range of approximately one-quarter of a wavelength, where the wavelength is the speed of light divided by the frequency of the oscillating current. Resonant inductive coupling requires both matching resonant frequencies and matching orientations between the transmitter and receiver (i.e., the transmitting and receiving resonant circuits) to transmit large amounts of power. Specifically, the transmitting and receiving coils are preferably oriented such that the magnetic dipole field from the transmitting coil through the receiving coil is oriented within about 45 degrees of parallel to the receiving coil.

[0018] FIG 1 is a circuit diagram showing a transmitter 1 and a resonant inductive power receiver 3 forming a resonant system when separated by a distance within a resonant inductive coupling range. Transmitter 1 includes a resonant circuit connected to an AC source 10 (hereafter referred to as "AC source 10"). (As used herein, "connected" means electrically connected.) AC source 10 outputs an alternating current having a voltage V0. The resonant circuit of transmitter 1 includes a transmitting coil 2 and a capacitor 6 that tunes transmitting coil 2 to generate a magnetic field B (represented by a circle in FIG 1) that oscillates at a resonant frequency. Transmitting coil 2 receives a current I from AC source 10. s and the current from capacitor 6, I c1 The current I total (That is, I s +I c1 =I total ) in the resonant inductive power receiver 3. The resonant inductive power receiver 3 includes a resonant circuit connected to a load 12 (e.g., a battery charger). The resonant circuit of the resonant inductive power receiver 3 includes a receiving coil 4 and a capacitor 8 that tunes the receiving coil 4 to a resonant frequency. During the resonant inductive coupling, the load 12 receives a current I induced in the receiving coil 4. total and the current I from capacitor 6 c2 The current I load (That is, I total +I c2 =I load ) is received.

[0019] According to some of the embodiments disclosed herein, "relay" coils can be used in the receive and transmit coils to amplify the amount of power transferred. FIG. 2 is a circuit diagram of a resonant system transmitter 1 and resonant inductive power receiver 3 with relay coils 14a and 14b. Relay coil 14a is resonantly inductively coupled to transmit coil 2; relay coil 14b is resonantly inductively coupled to relay coil 14a; and relay coil 14b is resonantly inductively coupled to receive coil 4. Although not shown in FIG. 2, each of relay coils 14a and 14b is connected to a respective capacitor (not shown) to form a respective resonant circuit. Relay coil 14a is preferably located in close proximity to and in parallel with transmit coil 2, and relay coil 14b is preferably located in close proximity to and in parallel with receive coil 4. (The term "parallel" as used herein in the context of coils means that the axes of the coils are parallel to each other.)

[0020] The addition of a relay coil contributes to a larger accumulation of current in the circuit. Specifically, an alternating current driven by a voltage V0 of an AC source 10 passes through a transmitting coil 2 and is supplied to a capacitor 6. When the capacitor 6 discharges, the current I c1 is the source current I s This process is repeated continuously until the total current I total The large current induces an equally large current in the relay coil 14a, which is also connected to a capacitor (not shown in FIG. 2). The current through the relay coil 14a charges its associated capacitor. When this capacitor discharges, its current adds to the current induced in the relay coil 14a. The current through the relay coil 14a is now I totaland the extra current from the capacitor to which relay coil 14a is electrically coupled. This total current induces a current in the capacitor connected to relay coil 14b on the receiver side. Through a similar process as described above, the current through relay coil 14b on the receiver side is increased by the additional capacitor current from the capacitor to which relay coil 16 is electrically coupled (not shown in FIG. 2). Finally, this current induces a current in receiving coil 4 that also increases over time through capacitor 8. Through the process described, the current induced in receiving coil 4 is much larger than when relay coils 14a and 14b are not used, and therefore the total power transferred is also larger (P=IV).

[0021] Systems and methods for encrypted resonant inductive power transfer are now described in some detail. In the embodiments disclosed below, the frequency is changed on a schedule known only to the transmitter and receiver. To make the frequency transition energy efficient, capacitive or inductive elements are switched in or out of each circuit at the instant of zero crossing: zero charge on the capacitor or zero current in the inductor. To maintain phase alignment, the switching of the inductor on the transmit side is approximately simultaneous with the switching of the capacitor on the receive side, or the switching of the capacitor on the transmit side is approximately simultaneous with the switching of the inductor on the receive side.

[0022] 3 is a circuit diagram showing some components of a transmitter (left) and a receiver (right), including a transmit switch for switching an inductor and a receive switch for switching a capacitor to match the resonant frequencies of the transmitter and receiver. The system includes a resonant inductive power transmitter 1 and a resonant inductive power receiver 3 configured to enable encrypted resonant inductive power transfer. In particular, the resonant inductive power transmitter 1 and the resonant inductive power receiver 3 include respective switches S1 and S2 for switching compensation elements to match the resonant frequencies of the transmitter and receiver.

[0023] According to the embodiment shown in Fig. 3, the resonant inductive power transmitter 1 includes a transmitting coil 2a having an inductance L1 and a capacitor 6 having a capacitance C1, connected to form a first resonant circuit. The resonant inductive power transmitter 1 further includes a coil 2b connected in parallel to the transmitting coil 2a and a switch 18 (hereinafter referred to as "switch S1") for adding or removing the coil 2b in parallel to the transmitting coil 2a. The coil 2b has an inductance L2 that may be equal or different to the inductance L1. The resonant inductive power transmitter 1 also includes a circuit, e.g. an amplifier (not shown in Fig. 3), configured to create an oscillator based on the resonant frequency of the first resonant circuit.

[0024] According to the embodiment shown in Fig. 3, the resonant inductive power receiver 3 includes a receiving coil 4 having an inductance L3 and a first capacitor 8a having a capacitance C2, connected to form a second resonant circuit. The resonant inductive power receiver 3 further includes a second capacitor 8b connected in parallel to the first capacitor 8a and a switch 20 (hereinafter "switch S2") for adding or removing the second capacitor 8b in parallel with the first capacitor 8a. The second capacitor 8b has a capacitance C3 that may be equal to or different from the capacitance C2. The resonant inductive power receiver 3 also includes a circuit, e.g., a rectifier (not shown in Fig. 3), configured to extract power from the resonant inductive power receiver 3 and deliver it to a useful load. The inductor and capacitor values ​​of the resonant inductive power receiver 3 are selected such that: (a) when switch S2 is closed, the resonant inductive power receiver 3 has the same first resonant frequency as the resonant inductive power transmitter 1 has when switch S1 is open; and (b) when switch S2 is open, the resonant inductive power receiver 3 has the same second resonant frequency (different from the first resonant frequency) as the resonant inductive power transmitter 1 has when switch S1 is closed. The resonant inductive power transmitter 1 and the resonant inductive power receiver 3 each have a respective switch controller (not shown in FIG. 3 ) that controls the state of the switch S1 and the switch S2, respectively. Each switch controller is a processor configured (e.g., programmed) to execute a common switch control program in the form of a digital copy of an agreed frequency change switching sequence stored in a non-transient tangible computer readable storage medium, or to execute an algorithm capable of determining a frequency change switching sequence. The state of the switches (open or closed) determines the resonant frequencies of the resonant inductive power transmitter 1 and the resonant inductive power receiver 3. As long as only the transmit and receive switch controllers of the resonant inductive power transmitter 1 and the resonant inductive power receiver 3 know the switching sequence, an unauthorized receiver cannot steal power from the system because it cannot effectively track the changing (switched) resonant frequency.

[0025] FIG. 3 illustrates in simplified form one embodiment of an encrypted resonant inductive power transfer system. The oscillator network (shown in FIG. 9 below) and the switch controller are not shown in FIG. 3. Only the inductive and capacitive elements that determine the resonant frequencies of the transmitter and receiver are shown. Closing switch S1 reduces the total inductance of the transmit circuit, which raises the resonant frequency. Opening switch S2 reduces the total capacitance of the receive circuit, which raises the resonant frequency. By appropriately selecting the inductance and capacitance values, the system designer can make the lower and upper resonant frequencies of the resonant inductive power transmitter 1 match (equal) the lower and upper resonant frequencies of the resonant inductive power receiver 3, respectively.

[0026] The term "inductor" as used herein includes but is not limited to coils. Resonant power transfer works by electromagnetic induction (also known as magnetic induction) from a transmitting coil to a receiving coil. Electromagnetic induction is the generation of an electromotive force (i.e., voltage) across an electrical conductor in a changing magnetic field dB / dt (where B is the magnitude of the magnetic field). The transmitting coil must generate an external magnetic field; the receiving coil must be sensitive to the external magnetic field. Some inductors, such as closed loops, do not generate an external field and do not react to external magnetic fields. They are not suitable for use as inductances L1 and L3. Inductance L2 can also contribute to the power transfer in the form of a coil; however, it is within the scope of the present invention for inductance L2 to be an inductor with no external field (i.e., not a coil), especially when inductance L2 is small compared to inductance L1. The functionality of the circuit network shown in FIG. 3 will now be described with reference to FIGS. 4-6.

[0027] FIG. 4 is a graph showing the current through the transmitting coil 2a (shown in FIG. 3) during the time interval when the state of the switch S1 of the resonant inductive power transmitter 1 changes from closed to open. FIG. 4 shows what happens to the current through the transmitting coil 2a with inductance L1 as the switch S1 transitions from closed to open. At time t0, the switch S1 is closed and the current is split between the transmitting coil 2a with inductance L1 and the coil 2b with inductance L2. Here, for simplicity (for purposes of illustration only), it is assumed that both coils have equal inductance values. At time t0, the current is zero; all charge is stored as a positive voltage on the capacitor 6 (shown in FIG. 3). In the first half cycle (a complete cycle is from time t0 to time t1), the current flows from the capacitor 6 (with capacitance C1) through the transmitting coil 2a and the coil until the capacitor 6 is fully negatively charged. In the second half cycle, the current flows in the opposite direction. Throughout the interval from time t0 to time t1, the resonant inductive power transmitter 1 has a current twice that shown in the graph of Figure 4 (again assuming L1 = L2) due to the current split by the two inductors. For simplicity, the inductance L2 does not generate an external magnetic field, the resonant inductive power transmitter 1 generates an external magnetic field proportional to the current shown.

[0028] At time t1, switch S1 is opened. The current flowing from capacitor 6 (see FIG. 3) flows only through the transmitting coil 2a. The energy E of the inductor is calculated by the equation E=1 / 2LI 2 where L is the inductance and I is the current. Since the energy in the transmit circuit at time t1 is the same as the energy in the transmit circuit at time t0 (assuming steady state power transfer), the peak current through the transmit coil 2a (see Figure 3) is now square root of two (√2) times higher than in the first cycle. Also, the inductance of the circuit is now twice as high. In addition, the angular frequency of the LC oscillator is given by the following equation: ω=(LC) -1 / 2 (1) (where L is the inductance and C is the capacitance such that the oscillator angular frequency is reduced by a factor of √2).

[0029] Figure 5 is a graph showing the induced electromotive force (EMF) generated by the receiving coil 4 (see Figure 3) of the resonant inductive power receiver 3 during the time interval t0 to t1. Figure 5 shows the effect that opening switch S1 has on the EMF induced in the receiving coil 4. The magnitude of the induced EMF is proportional to the magnetic flux Φ B is a function of the rate of change of Φ B The rate of change of is proportional to both the magnitude of the magnetic field and the angular frequency ω. The associated magnetic flux is generated by the current through the transmitting coil 2a (again, for simplicity, we assume that the second inductor generates no external field). The rate of change is proportional to the derivative of the graph in Figure 5 and therefore the phase of the EMF leads the current in the transmitting coil 2a to 90°.

[0030] After time t1, the frequency of the induced EMF drops by a factor of √2. The magnitude of the magnetic field cycle increases by the same factor as the drop in frequency, so dΦ B The magnitude of / dt, and therefore the magnitude of the EMF, does not change. This is advantageous: the amount of power transferred from transmitter to receiver at any instant is proportional to the product of the EMF and the current in the receiving coil 4. When switch S1 changes state, the EMF remains constant, and therefore the rate of power transfer remains constant. This minimises electromagnetic interference and keeps the cost of the transmitter and receiver circuits low.

[0031] FIG. 6 is a graph showing the voltage across the capacitor 8a (see FIG. 3) of the resonant inductive power receiver 3 during the time interval when the switch S1 shown in FIG. 4 is open. At time t0, the capacitor 8a is empty. To avoid "stranding" the energy of the capacitor 8b, the best time to open or close the switch S2 is when the capacitor is not charged and therefore the switch S2 is open at time t0. Since all the current through the receiving coil 4 flows into the capacitor 8a, it charges up quickly. After one cycle, the switch S2 is closed at time t1, the capacitor 8b is brought into the circuit and the resonant frequency is lowered by a factor of √2 (for simplicity, we assume that the capacitances C2 and C3 of the capacitors 8a and 8b are equal). The energy E of the capacitor is given by the equation E=½Cv 2 where C is capacitance and V is voltage, and since the energy in the receiving circuit at time t1 is the same as the energy at time t0 (assuming steady state power transfer), the peak voltage on capacitor 8a in the second cycle is √2 times lower than the peak voltage in the first cycle.

[0032] By switching the inductor in the transmitter and the capacitor in the receiver, the resonant inductive power transfer system can change the resonant frequencies of the transmitter and receiver simultaneously, and does so without the energy-wasting switching of non-zero current inductors or non-zero voltage capacitors.

[0033] 7 is a flow diagram identifying steps of a method 100 for encrypted resonant inductive power transfer, according to one embodiment. The process includes the steps of: (a) constructing a transmitter and receiver with switches and programming their respective switch controllers (step 102) such that the switching of the inductor on the transmit side is approximately simultaneous with the switching of the capacitor on the receive side, or vice versa; (b) exchanging information to determine a frequency change sequence, e.g., an encryption key (step 104); (c) increasing the power of the transmitter oscillator (step 106); and (d) the transmit switch controller initiating the transmitter frequency switching according to the frequency change sequence. (e) bringing the receiver within range of the transmitter (step 110); (f) the receive switch controller detecting the presence of the oscillating magnetic field of the transmitter (in some embodiments, the receive switch controller specifically looks for the agreed upon frequencies and switches between them at times consistent with the frequency change sequence) (step 112); (g) the receive switch controller initiating switching of the receiver frequencies according to the frequency change sequence (step 114); and (h) assuming that the receiver has an electrical load, the load begins receiving power after a few cycles (step 116).

[0034] 8 is a block diagram identifying several components of an encrypted resonant inductive power transfer system according to one embodiment. The system includes a resonant inductive power transmitter 1 and a resonant inductive power receiver 3. The resonant inductive power transmitter 1 includes a switch S1 and a transmit switch controller 70 configured to control the state of switch S1. The resonant inductive power receiver 3 includes a switch S2 and a receive switch controller 72 configured to control the state of switch S2.

[0035] The time intervals for commanding the switches to change state are determined by a secure method such as public key cryptography or one-time pad cryptography. The transmit switch controller 70 is further configured to send an encryption key to the transceiver 74, and the receive switch controller 72 is further configured to receive the encryption key from the transceiver 76 following successful transmission and receipt of the encryption key by the transceivers 74 and 76, respectively. The resonant inductive power receiver 3 further includes a detector 78 for detecting the presence of the transmitter's oscillating magnetic field. The receive switch controller 72 is further configured to receive a signal from the detector 78 indicative of the presence of the transmitter's oscillating magnetic field, and in response, the receive switch controller 72 initiates a receiver frequency switch according to a frequency change sequence.

[0036] The systems and methods for encrypted resonant inductive power transfer disclosed herein provide at least the following advantages: First, compared to overt transmission, encrypted resonant inductive power transfer provides reliable protection against energy loss, thereby improving the economics of resonant energy transfer. (The level of protection depends on the type of encryption chosen, as with digital information.) Second, compared to physical security such as guards or code-locked doors, the systems and methods disclosed herein are much easier and cheaper to use, thus improving the economics of resonant power transfer.

[0037] It is well known that a resonant circuit oscillates with an angular frequency given by equation (1). In the above description, a simple resonant circuit is shown for clarity of explanation. In practical use, the resonant circuit must be integrated into a harmonic oscillator on the transmitting side. On the receiving side, the resonant circuit must be coupled to a load, such as a rectifier, a battery charger, or other load.

[0038] FIG. 9 is a circuit diagram showing some components of a common-base Colpitts oscillator 28 (hereafter "oscillator 28") that uses a combination of an inductor and a capacitor to generate oscillations at a specific frequency. A unique feature of the Colpitts oscillator is that the feedback for the active device is taken from a voltage divider made of two capacitors connected in series across an inductor. The oscillator 28 includes an NPN bipolar junction transistor 22 (hereafter "bipolar junction transistor 22") whose output is connected to its input in a feedback loop that includes a parallel resonant circuit (tuned circuit), which acts as a bandpass filter to set the frequency of oscillation. Instead of a bipolar junction transistor, another active component, such as a field effect transistor, capable of generating gain at the desired frequency may be used.

[0039] An NPN transistor contains two semiconductor junctions that share a thin p-doped region. The regions of a bipolar junction transistor are called the emitter, base, and collector. As shown in Figure 9, the base of bipolar junction transistor 22 is connected to junction 34, the emitter of bipolar junction transistor 22 is connected to junction 42, and the collector of bipolar junction transistor 22 is connected to junction 46.

[0040] Oscillator 28 further includes resistor 52 having resistance R1, resistor 54 having resistance R2, and resistor 56 having resistance R3. One end of resistor 52 is connected to junction 44 and the other end of resistor 52 is connected to junction 40. One end of resistor 54 is connected to junction 34 and the other end of resistor 54 is connected to junction 38, which is connected to junction 40. One end of resistor 56 is connected to junction 34 and the other end of resistor 56 is connected to junction 32.

[0041] Oscillator 28 further includes capacitors 6a and 6b connected in series via junction 42, which is connected to junction 44. One side of capacitor 6b is connected to junction 42, and the other side of capacitor 6b is connected to junction 40. One side of capacitor 6a is connected to junction 42, and the other side of capacitor 6a is connected to junction 46. Oscillator 28 further includes capacitor 6c, having one side connected to junction 34 and the other side connected to junction 36, which is connected to junction 38.

[0042] The oscillator 28 also includes a transmitter coil 2a having an inductance L1. One end of the transmitter coil 2a is connected to junction 46 and the other end of the transmitter coil 2a is connected to junction 32.

[0043] The oscillator 28 generates a voltage V s One end of voltage source 48 is connected to junction 32; the other end of voltage source 48 is connected to junction 36.

[0044] According to one proposed implementation: (a) capacitors 6a, 6b, and 6c have capacitances of 100 pF, 100 pF, and 100 nF, respectively; (b) resistors 52, 54, and 56 have resistances R1=2.2 kΩ, R2=10 kΩ, and R3=10 kΩ, respectively; (c) transmit coil 2 has inductance L1=150 nH; (d) voltage source 48 has a voltage V s =6V. Using these values, the oscillation frequency ω is given by equation (1), where L is shown as L1 (150 nH) and C is the series capacitance of capacitors 6a and 6b (50 pF). (The connection from junction 42 between capacitors 6a and 6b provides feedback to amplifying bipolar junction transistor 22 but does not substantially affect the resonant frequency. Thus, capacitors 6a and 6b act in series and affect the circuit as a single capacitor.) The angular frequency ω in this example is approximately 365 s. -1 and the cycle frequency is about 58 MHz.

[0045] FIG. 10 is a circuit diagram depicting some components of an improved common-base Colpitts oscillator 30 (hereinafter "oscillator 30") according to one proposed implementation. In contrast to oscillator 28 shown in FIG. 9, oscillator 30 is improved to include a coil 2b having one end connected to junction 50. Junction 50 is connected to junction 46 and one side of capacitor 6a. In addition, oscillator 30 includes a switch S1 that switchably couples the other end of coil 2b to junction 58. Coil 2b has an inductance L2 and is connected in parallel with a transmitting coil 2a having an inductance L1. In a closed state, switch S1 adds coil 2b in parallel to transmitting coil 2a; in an open state, switch S1 disconnects coil 2b from junction 58, thereby removing coil 2b from parallel with transmitting coil 2a. Assume L1=L2=150 nH. When switch S1 is open, the resonant frequency is the same as that of oscillator 28 shown in FIG. 9, and is approximately 365 s -1 When switch S1 is closed, the total inductance drops by half to 75 nH, the resonant frequency increases by a factor of √2, and ω = 516 sec. -1 (For simplicity, in this disclosure, the inductors are treated as independent. In reality, both generate external fields that reach the receiver such that the inductors have some mutual inductance. Those skilled in the art of oscillator design know how to manage the mutual inductance and select the correct inductance value that gives the desired frequency shift.)

[0046] Given the embodiment shown in FIG. 10, one skilled in the art should be able to implement a suitable transmitter to enable encrypted resonant inductive power transfer using any of several types of LC oscillators: Hartley, Clapp, etc. One inventive aspect is to provide an inductor or capacitor in parallel with an existing inductor or capacitor, connected via a switch, such that the oscillator frequency changes between two known values ​​as the switch changes state.

[0047] FIG. 11 is a circuit diagram identifying several components of a battery charging system including a resonant inductive power receiver 3 and a rectifier 24 for generating a direct current for recharging a battery 62 when an EMF is induced in the receiving coil 4. The system was disclosed in U.S. Patent Application Publication No. 2019 / 0237999, published August 1, 2019. The battery charging system can be mounted on a vehicle (e.g., an aircraft) for wirelessly receiving power from a resonant inductive power transmitter (not shown in FIG. 11). The battery charging system shown in FIG. 11 includes a receiving coil 4 in which an alternating current is induced, and a capacitor 8 connected to the receiving coil 4 for tuning the receiving coil 4 to a resonant frequency. The system further includes a rectifier 24 connected to the receiving coil 4 and the capacitor 8 for converting the alternating current from the receiving coil 4 and the capacitor 8 to a direct current. A smoothing capacitor 26 is connected to receive the direct current from the rectifier 24. A battery charger 60 is connected to receive the direct current from the rectifier 24. The battery 62 has a positive terminal 64 and a negative terminal 66 connected to the battery charger 60. The battery charger 60 is configured to charge the battery 62 using a DC current generated from the AC current induced in the receive coil 4 and an AC current generated by the capacitor 8. More specifically, the battery charger 60 includes a voltage regulator to avoid overcharging the battery 62, a current limiter to ensure that charging does not occur too quickly, and a temperature sensor to indicate to the battery charger 60 when charging should be terminated because the battery 62 is overheating. As shown in Figure 11, after the battery 62 has been recharged, it can be used to provide a DC current to the load 12.

[0048] FIG. 12 is a circuit diagram identifying some components of a cryptographic battery charging system having a resonant inductive power receiver 3 modified to include a second capacitor with capacitance C3 connected in parallel with a first capacitor with capacitance C2 (see FIG. 3) and a switch S2 for adding or removing the second capacitor 8b in parallel with the first capacitor 8a, according to one embodiment. More specifically, when switch S2 is closed, the second capacitor 8b is in parallel with the first capacitor 8a. Assume C2=C3=100pF. When switch S1 is open, the resonant frequency is the same as in the resonant inductive power receiver 3 shown in FIG. 11. When the state of switch S2 changes from open to closed, the total capacitance doubles and the resonant angular frequency drops by √2 times.

[0049] Combining a resonant inductive power transmitter 1 in the form of oscillator 30 shown in Figure 10 and a resonant inductive power receiver 3 shown in Figure 12 into an operating system, whenever the transmit switch controller 70 (see Figure 8) closes switch S1 to raise the resonant frequency of the resonant inductive power transmitter 1, the receive switch controller 72 opens switch S2 to raise the resonant frequency of the resonant inductive power receiver 3. Conversely, whenever the transmit switch controller 70 opens switch S1, the receive switch controller 72 closes switch S2.

[0050] Transmitter and receiver switch controllers coordinate the frequency transitions. In some embodiments, a mutually known string of 1's and 0's signals a high or low frequency with the transition occurring at the end of each sine wave cycle. In some embodiments, a mutually known string of 1's and 0's signals either a change or no change at the end of each sine wave signal. In some embodiments, the string of 1's and 0's is generated by a mutually known random number generator seeded with a time-based value, e.g., a GPS time signal expressed in IRIG-B format, that provides a new seed value every second.

[0051] Although a parallel inductor at the transmitter side and a parallel capacitor at the receiver side are shown in Figure 3, it is also possible to add a parallel capacitor at the transmitter side and a parallel inductor at the receiver side and select the appropriate type of oscillator and receiver. For example, instead of the Colpitts type oscillator used in Figure 10, a Hartley oscillator can be used and an inductor can replace the capacitor, and vice versa. These alternative embodiments are within the scope of the present invention, providing two frequencies that can be switched by the transmitter and can be switched by the receiver when the same frequency pair is used.

[0052] 13 is a circuit diagram showing some components of the transmitter (left) and receiver (right), including a transmit switch for switching a capacitor and a receive switch for switching an inductor to match the resonant frequencies of the transmitter and receiver. The system includes a resonant inductive power transmitter 1 and a resonant inductive power receiver 3 configured to enable encrypted resonant inductive power transfer. In particular, the resonant inductive power transmitter 1 and the resonant inductive power receiver 3 include respective switches S1 and S2 for switching compensation elements to match the resonant frequencies of the transmitter and receiver.

[0053] According to the embodiment shown in Fig. 13, the resonant inductive power transmitter 1 includes a transmit coil 2 having an inductance L1 and a first capacitor 6a having a capacitance C1, connected to form a first resonant circuit. The resonant inductive power transmitter 1 further includes a second capacitor 6b connected in parallel to the capacitor 6a and a switch 18 (hereinafter "switch S1") for adding or removing the capacitor 6b in parallel with the capacitor 6a. The capacitor 6b has a capacitance C2 that may be equal to or different from the capacitance C1. The resonant inductive power transmitter 1 also includes a circuit, e.g., an amplifier (not shown in Fig. 13), configured to create an oscillator based on the resonant frequency of the first resonant circuit.

[0054] According to the embodiment shown in Fig. 13, the resonant inductive power receiver 3 includes a receiving coil 4a having an inductance L2 and a capacitor 8 having a capacitance C3, connected to form a second resonant circuit. The resonant inductive power receiver 3 further includes a coil 4b connected in parallel to the receiving coil 4a and a switch 20 (hereinafter "switch S2") for adding or removing the coil 4b in parallel with the transmitting coil 4a. The coil 4b has an inductance L3 that may be equal to or different from the inductance L2. The resonant inductive power receiver 3 also includes a circuit, e.g., a rectifier (not shown in Fig. 13), configured to extract power from the resonant inductive power receiver 3 and deliver it to a useful load. The inductor and capacitor values ​​of the resonant inductive power receiver 3 are selected such that: (a) when switch S2 is closed, the resonant inductive power receiver 3 has the same first resonant frequency as the resonant inductive power transmitter 1 has when switch S1 is open; and (b) when switch S2 is open, the resonant inductive power receiver 3 has the same second resonant frequency (different from the first resonant frequency) as the resonant inductive power transmitter 1 has when switch S1 is closed. As previously described with reference to Figure 3, the resonant inductive power transmitter 1 and the resonant inductive power receiver 3 each have a respective switch controller (not shown in Figure 13) that controls the state of the switches S1 and S2, respectively.

[0055] FIG. 13 illustrates in simplified form one embodiment of an encrypted resonant inductive power transfer system. The oscillator network and switch controller are not shown in FIG. 13. Only the inductive and capacitive elements that determine the resonant frequencies of the transmitter and receiver are shown. Opening switch S1 reduces the total capacitance of the transmit circuit, which raises the resonant frequency. Closing switch S2 reduces the total inductance of the receive circuit, which raises the resonant frequency. By appropriately selecting the inductance and capacitance values, the system designer can make the lower and upper resonant frequencies of the resonant inductive power transmitter 1 match (equal) the lower and upper resonant frequencies of the resonant inductive power receiver 3, respectively.

[0056] The encrypted resonant inductive power transfer system can be realized in many ways. According to one embodiment, the transmitter has an inductor and two capacitors and the receiver has a capacitor and two inductors (see FIG. 13). According to another embodiment, the transmitter has a capacitor and two inductors and the receiver has an inductor and two capacitors (see FIG. 3).

[0057] According to another embodiment, the transmit and receive coils may be electromagnetically coupled through one or more relay coils (see FIG. 2). The relay coils include an inductive coil and a capacitor tuned to resonate at the same frequency as the transmitter and receiver. The relay coils have no direct electrical connection to either, but are coupled to each by induction. Because they are electrically isolated, the relay coils can have an extremely high Q; therefore, their magnetic field can be very strong, thereby increasing the power transferred.

[0058] Alternative embodiments have more than two resonant frequencies. For example, a transmitter can have an inductor and three capacitors of different sizes that, when switched in various combinations, produce four resonant frequencies. A corresponding receiver would have a capacitor and three inductors of different sizes. The encryption then specifies the hopping pattern between the four frequencies.

[0059] The resonant circuit of the resonant inductive power transmitter 1 may be configured as part of an oscillator, where the oscillator is selected from the group including Armstrong, Clapp, Colpitts, Hartley, Lampkin, Seiler, and Vackar oscillators. The resonant circuit of the resonant inductive power receiver 3 is connected to the input of a rectifier, which is in turn connected to the input of a battery charger (see FIG. 12).

[0060] The encrypted resonant inductive power transfer system disclosed herein uses a varying resonant frequency that varies according to a pattern that is known to both the transmitter and receiver, but not easily guessed by others. In comparison to frequency hopping wireless technology, the technology disclosed herein: (A) transmits power rather than data; (b) operates in the near field rather than the electromagnetic far field; and (c) requires simultaneous switching of an inductor on one side (e.g., the transmitter) and a capacitor on the other side (e.g., the receiver). This is necessary because the transmitter and receiver are in the near field of each other, such that the energy in the inductor on one side is closely phase-aligned with the energy in the capacitor on the other side. Frequency hopping schemes in wireless technology are performed in the far field, such that tight phase alignment of switching times is not necessary (or is sometimes possible). In such a scheme, frequency changes in the receiver and transmitter can be achieved independently by any convenient means (switching inductors, switching capacitors, or switching to different crystal oscillators).

[0061] Although systems and methods for encrypted resonant inductive power transfer have been described with reference to various embodiments, those skilled in the art will recognize that various modifications may be made without departing from the teachings herein and that equivalents may be substituted for elements thereof. In addition, many modifications may be made to adapt the concepts and simplicity of practice disclosed herein to a particular situation. It is therefore intended that the subject matter covered by the claims not be limited to the disclosed embodiments.

[0062] The term "controller" as used in the claims should be interpreted broadly to include a system having at least one computer or processor, and a system may have multiple computers or processors. The terms "computer" and "processor" as used in the preceding sentences both refer to a device having a processing unit (e.g., a central processing unit) and some form of memory (i.e., a computer-readable medium) for storing a program readable by the processing unit. For example, the term "controller" includes, but is not limited to, a small computer on an integrated circuit that includes a processor core, memory, and programmable input / output peripherals.

[0063] NOTE: The following clauses describe further aspects of the present disclosure.

[0064] Clause 1. A resonant inductive power transfer system comprising a resonant inductive power transmitter (1), the resonant inductive power transmitter comprising: Voltage source (10); a first inductor (2) and a first capacitor (6a) connected together to form a first resonant circuit supplied with a voltage by the voltage source; a first switch (S1) and a second capacitor (6b), the first switch (S1) and the second capacitor (6b) being connected in parallel with the first capacitor when the first switch is closed; and a transmit switch controller (70) configured to control a state of the first switch in accordance with a frequency change switching sequence; Including, the system.

[0065] Clause 2. The system of clause 1, wherein the transmit switch controller commands the first switch to change state when a voltage on the second capacitor exceeds zero.

[0066] Clause 3. The method further comprises a resonant inductive power receiver (3), the resonant inductive power receiver comprising: a second inductor (4a) and a third capacitor (8) connected together to form a second resonant circuit; a second switch (S2) and a third inductor (4b) connected in parallel with the second inductor when the second switch is closed; and a receiving switch controller (72) configured to control a state of the second switch in accordance with a frequency change switching sequence; 2. The system of claim 1, comprising:

[0067] Clause 4. A system as described in Clause 3, wherein when the first switch is closed and the second switch is open, the resonant frequencies of the first and second resonant circuits are equal to a first resonant frequency, and when the first switch is open and the second switch is closed, the resonant frequencies are equal to a second resonant frequency different from the first resonant frequency.

[0068] Clause 5. The system of clause 3, wherein the receiving switch controller commands the second switch to change state when a current in the third inductor exceeds zero.

Claims

1. A resonant inductive power transfer system comprising a resonant inductive power transmitter (1) and a resonant inductive power receiver (3), the resonant inductive power transmitter comprising: Voltage source (10); a first inductor (2a) and a first capacitor (6) connected to form a first resonant circuit supplied with a voltage by the voltage source; a first switch (S1) and a second inductor (2b), the first switch (S1) and the second inductor (2b) being connected in parallel with the first inductor when the first switch is closed; and a transmit switch controller (70) configured to control the state of said first switch in accordance with a frequency change switching sequence; Including, The resonant inductive power receiver comprises: a third inductor (4) and a second capacitor (8a) connected to form a second resonant circuit; a second switch (S2) and a third capacitor (8b) connected in parallel with the second capacitor (8a) when the second switch (S2) is closed; and a receiving switch controller (72) configured to control a state of the second switch in accordance with the frequency change switching sequence; Including, The resonant inductive power transfer system comprises: a first transceiver (74) communicatively coupled to the transmit switch controller; and a second transceiver (76) communicatively coupled to the receiving switch controller; Further comprising:

11. A system, comprising: a transmitting switch controller configured to transmit the frequency change switching sequence to the first transceiver in an encrypted format; and a receiving switch controller configured to receive the frequency change switching sequence from the second transceiver in an encrypted format.

2. The system of claim 1 , wherein the first inductor is a transmit coil.

3. The system of claim 2 , wherein the second inductor is a coil.

4. The system of claim 2 , wherein the second inductor is of a type that does not generate an external electromagnetic field.

5. The system of claim 1 , wherein the transmit switch controller commands the first switch to change state when a current in the second inductor exceeds zero.

6. The system of claim 1 , wherein the third inductor is a receive coil.

7. 2. The system of claim 1, wherein a resonant frequency of each of the first resonant circuit and the second resonant circuit is equal to a first resonant frequency when the first switch is closed and the second switch is open, and is equal to a second resonant frequency different from the first resonant frequency when the first switch is open and the second switch is closed.

8. The system of claim 1 , wherein the receiving switch controller commands the second switch to change state when the voltage across the third inductor exceeds zero.

9. A method for transferring power from a resonant inductive power transmitter (1) to a resonant inductive power receiver (3), comprising: (a) disposing the resonant inductive power receiver within electromagnetic coupling range of the resonant inductive power transmitter; (b) generating a first oscillating electromagnetic field having a first frequency using the resonant inductive power transmitter during a first time interval; (c) generating a first vibration electromotive force in the resonant inductive power receiver having the first frequency by resonant electromagnetic induction during the first time interval; (d) generating, during a second time interval after the first time interval, a second oscillating electromagnetic field having a second frequency different from the first frequency using the resonant inductive power transmitter; (e) generating a second vibration electromotive force in the resonant inductive power receiver having the second frequency by resonant electromagnetic induction during the second time interval; (f) configuring the resonant inductive power transmitter to generate the first oscillating electromagnetic field by opening a first switch (S1) of the resonant inductive power transmitter prior to step (b); (g) configuring the resonant inductive power receiver to generate the first vibration electromotive force by closing a second switch (S2) of the resonant inductive power receiver before step (c); (h) configuring the resonant inductive power transmitter to generate the second oscillating electromagnetic field by closing the first switch prior to step (d); and (i) configuring the resonant inductive power receiver to generate the second vibration electromotive force by opening the second switch prior to step (e); Including, The resonant inductive power transmitter includes a transmit switch controller configured to control a state of the first switch according to a frequency change switching sequence; the resonant inductive power receiver includes a receiver switch controller configured to control a state of the second switch in accordance with the frequency change switching sequence; a first transceiver communicatively coupled to the transmit switch controller; a second transceiver communicatively coupled to the receive switch controller; the transmit switch controller is configured to send the frequency change switching sequence to the first transceiver in an encrypted format, and the receive switch controller is configured to receive the frequency change switching sequence from the second transceiver in an encrypted format; the first switch state and the second switch state and the first time interval and the second time interval are indicated according to the frequency change switching sequence, the method further comprising sending information in an encrypted form including the frequency change switching sequence from the resonant inductive power transmitter to the resonant inductive power receiver.

10. 10. The method of claim 9, further comprising detecting a presence of the first oscillating electromagnetic field within an electromagnetic coupling range of the resonant inductive power receiver, the resonant inductive power receiver initiating switching of the second switch according to the frequency alteration switching sequence in response to detecting the presence of the first oscillating electromagnetic field within the electromagnetic coupling range.

11. The method of claim 9 , wherein steps (f) through (i) are repeated according to the frequency change switching sequence.

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