Auxiliary circuits for selection and enhancement of multi-frequency wireless power transfer to multiple loads

Abstract

This invention is related to a novel method and apparatus that provides selective and enhanced power flow in wireless power transfer systems with multiple receivers. Auxiliary circuits are introduced in the receiver circuits (and relay circuits if applicable) so as to ensure proper frequency-selective wireless power flow to the appropriate targeted receivers, with the pickup power by the non-targeted receivers substantially reduced even if the chosen tuned frequencies for different receivers are not widely apart.

Claims

1. A wireless power transfer system for transferring power at more than one frequency, comprising: a transmitter capable of transmitting power wirelessly at more than one frequency; a first targeted receiver tuned to resonate and receive power at a first frequency from the transmitter and passing it to a load of the first targeted receiver; a second non-targeted receiver tuned to resonate and receive power at a second frequency, but not passing to a load power at the first frequency from the transmitter; an auxiliary circuit in said second non-targeted receiver in the form of a filter with reactive components to pass or block power at the first frequency to cause a part of the second non-targeted receiver to act as a resonator for the first frequency so as to relay power from the second non-targeted receiver to the first targeted receiver at the first frequency, so as to ensure proper frequency-selective wireless power flow from said second non-targeted receiver to the first targeted receiver, with pickup power retained by the second non-targeted receiver substantially reduced, even if the first and second frequencies are not widely separated.

2. The power transfer system of claim 1 wherein the auxiliary circuit acts as one of a bandpass filter to shunt power at the first frequency to ground before a load of the second receiver and a bandstop filter to prevent the flow of the power at the first frequency to the load of the second receiver.

3. The power transfer system of claim 2 wherein the second non-targeted receiver comprises a resonant inductor, a resonant capacitor and a load, wherein the load is either connected in series with the resonant inductor and capacitor, or in parallel with the resonant capacitor.

4. The power transfer system of claim 3, wherein the resonant capacitor is in the form of two capacitors connected in series with one capacitor connected to one side of the load, and wherein the auxiliary circuit is a band-pass filter that includes the resonant capacitor, an auxiliary inductor and an auxiliary capacitor, the auxiliary capacitor and inductor are connected in series between the two capacitors of the resonant capacitor and the other side of the load.

5. The power transfer system of claim 3, wherein the resonant capacitor is in the form of two capacitors connected in series with one capacitor connected in parallel with the load and the other capacitor connected in series with the load and the resonant inductor, wherein the auxiliary circuit is a band-pass filter that includes the resonant capacitor, an auxiliary inductor and an auxiliary capacitor, and wherein the auxiliary inductor and auxiliary capacitor are connected in series to form a combination and the combination is connected in parallel with the one part of the resonant capacitor and the load.

6. The power transfer system of claim 3, wherein the resonant capacitor is in the form of two capacitors with one capacitor connected in series with one side of the load, and wherein the auxiliary circuit is a band-stop filter that includes an auxiliary inductor and an auxiliary capacitor connected in parallel with each other and connected in series with the resonant inductor at a junction and the one capacitor of the resonant capacitor, said auxiliary circuit further including the other capacitor of the resonant capacitor, which is connected between the junction of the auxiliary capacitor and inductor with the resonant inductor and the other side of the load.

7. The power transfer system of claim 3, wherein the resonant capacitor is in the form of two capacitors with one capacitor connected in parallel with the load, and the auxiliary circuit is a band stop filter that includes an auxiliary inductor and an auxiliary capacitor connected in parallel with each other and connected in series with the resonant inductor at a junction and with the load, said auxiliary circuit further including the one capacitor of the resonant capacitor and the other capacitor of the resonant capacitor, which is connected between junction of the auxiliary capacitor and inductor with the resonant inductor and the other side of the load.

8. The power transfer system of claim 1 wherein the second non-targeted receiver is merely a relay circuit.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The foregoing and other features of the present invention will e more readily apparent from the following detailed description and drawings of an illustrative embodiment of the invention in which:

(2) FIG. 1 is a schematic layout of a multi-frequency wireless power transfer system;

(3) FIG. 2 is a lumped circuit model of the two-receiver system with series compensation shown in FIG. 1;

(4) FIG. 3 shows the current variations according to the operating frequency f and the quality factor QA1 of the circuit of FIG. 2;

(5) FIG. 4 shows a schematic view of a transmission path from transmitter T to resonator A and from resonator A to resonator B;

(6) FIG. 5 is a schematic circuit of a multi-frequency wireless power transfer system utilizing auxiliary circuits according to the present invention;

(7) FIGS. 6A-6D show four types of auxiliary circuits which block power flow of a non-targeted frequency for series-connected and parallel-connected loads in the receivers;

(8) FIG. 7 shows the two equivalent circuits of FIG. 4 for the targeted and non-targeted frequencies;

(9) FIG. 8A shows an example of a relay resonator which can operate with two tuned frequencies, and FIG. 8B shows the two equivalent circuits for the resonator portions for the two frequencies;

(10) FIG. 9 is a circuit diagram of the arrangement of FIG. 4 utilizing an auxiliary circuit;

(11) FIG. 10 shows the waveform of the input voltage of the system of FIG. 9 and its Fast Fourier Transform; and

(12) FIG. 11 shows a wireless charging table in which two receivers are designed for respective targeted frequencies.

(13) FIG. 12 shows a comparison between the interferences of the straight wireless power transfer (WPT) system with auxiliary circuit and without auxiliary circuit and with power P.sub.A=P.sub.B=2.5 W.

(14) FIG. 13 shows comparison between the interferences of the straight wireless power transfer (WPT) system with auxiliary circuit and without auxiliary circuit and with power P.sub.A=2.5 W; P.sub.B=0.25 W.

(15) FIG. 14 shows comparison between the interferences of the straight wireless power transfer (WPT) system with auxiliary circuit and without auxiliary circuit and with power P.sub.A=0.25 W; P.sub.B=2.5 W.

DESCRIPTION OF AN ILLUSTRATIVE EMBODIMENT OF THE INVENTION

(16) According to the present invention, in order to utilize indirect power paths, new auxiliary circuits are provided as shown in FIG. 5. Assuming the tuned resonant frequencies of Resonator-A and Resonator-B are f.sub.1 and f.sub.2 respectively, the functions of the auxiliary circuit for the receivers are explained by means of the diagrams shown in FIG. 6.

(17) FIGS. 6A-6D show four types of auxiliary circuits to cover the use of shunt resonant branches to bypass, and parallel resonant branches to block, the power flow of the non-targeted frequency, for series-connected and parallel-connected loads in the receivers. In the traditional approach, a receiver consists of a resonant inductor (L), a resonant capacitor (C) and a load R connected in series with the L and C or in parallel with C.

(18) FIG. 6A shows an exemplary circuit that includes a shunt resonant branch to bypass current at the non-targeted frequency for a series-connected load. This circuit includes an auxiliary circuit (enclosed in the dotted box) for the coil of Receiver-A. The coil inductance is L.sub.A and the coil resistance is R.sub.PA. For Receiver-A, f.sub.1 is its targeted frequency and f.sub.2 is its non-targeted frequency. In the auxiliary circuit for Receiver-A, the resonant branch comprising L.sub.2 and C.sub.2 is designed to resonate at the frequency f.sub.2 so that it acts as a shunt circuit to short-circuit (bypass) the current caused by power transmission at frequency f.sub.2. In this way, the current of the non-targeted frequency will circulate within a closed loop. This special phenomenon offers two advantageous functions. First, if the transmitter is transmitting power at f.sub.2, this current loop of f.sub.2 will act as a relay loop resonator to enhance the magnetic coupling and power transfer between the transmitter and Receiver-B (which has a targeted frequency of f.sub.2). Consequently, it provides an extra power flow path from the transmitter to Receiver-B. Second, the circulating current of frequency f.sub.2 in the closed loop R.sub.PA-L.sub.A-C.sub.A2-L.sub.2-C.sub.2 will not affect the load R.sub.LA (which has its targeted frequency of f.sub.1).

(19) Note that the two capacitors CA1 and CA2 are used to form parts of the resonant circuit for the resonant frequency f.sub.1 for the Receiver-A and that the shunt resonant circuit is connected between the ground and the junction of CA1 and CA2.

(20) In order to design the circuit of FIG. 6A as Receiver-A, it is necessary for its resonant frequency to be tuned at or near the targeted frequency f.sub.1. With the help of the equivalent circuit in FIG. 7, the designs of the resonant inductors and capacitors can be achieved. FIG. 7 shows the two equivalent circuits of FIG. 4—the one on the left for frequency f.sub.1 and the one on the right for frequency f.sub.2.

(21) At an operating frequency f.sub.1, it is necessary to design the equivalent circuit of Receiver-A in FIG. 7 so that it receives power at the targeted frequency of f.sub.1. At f.sub.1, the total impedance of the auxiliary circuit connected with the load R.sub.LA will be equivalent to that of a capacitance C.sub.A1 in series with an equivalent load resistance R.sub.LA. The total impedance of Receiver-A can be expressed as

(22) $\begin{array}{cc}{Z}_A=R_{\mathrm{PA}}+\frac{X_2^2{R}_{\mathrm{LA}}}{R_{\mathrm{LA}}^2+{\left(X_2-\frac{1}{{\omega }_1{C}_{A1}}\right)}^2}+j\left({\omega }_1{L}_A+\frac{X_2\left(R_{\mathrm{LA}}^2+\frac{1}{{\omega }_1^2{C}_{A1}^2}-\frac{X_2}{{\omega }_1{C}_{A1}}\right)}{R_{\mathrm{LA}}^2+{\left(X_2-\frac{1}{{\omega }_1{C}_{A1}}\right)}^2}-\frac{1}{{\omega }_1{C}_{A2}}\right)& \left(11\right)\end{array}$
where

(23) $X_2={\omega }_1{L}_2-\frac{1}{{\omega }_1{C}_2}.$
therefore, the expressions for the equivalent load resistance and capacitance are:

(24) $\begin{array}{cc}{R}_{\mathrm{LA}}^{\prime }=\frac{X_2^2{R}_{\mathrm{LA}}}{R_{\mathrm{LA}}^2+{\left(X_2-\frac{1}{{\omega }_1{C}_{A1}}\right)}^2}& \left(12\right)\\ -\frac{1}{{\omega }_1{C}_{A1}^{\prime }}=\frac{X_2\left(R_{\mathrm{LA}}^2+\frac{1}{{\omega }_1^2{C}_{A1}^2}-\frac{X_2}{{\omega }_1{C}_{A1}}\right)}{R_{\mathrm{LA}}^2+{\left(X_2-\frac{1}{{\omega }_1{C}_{A1}}\right)}^2}-\frac{1}{{\omega }_1{C}_{A2}}& \left(13\right)\end{array}$

(25) From equation (13), the equivalent capacitor C′.sub.A1 can be calculated. Then the inductance L.sub.A and C′.sub.A1 can be designed so that the L.sub.A-C′.sub.A1 branch forms a resonant tank at or near its targeted resonant frequency of f.sub.1, where

(26) 0$\begin{array}{cc}{f}_1\approx \frac{1}{2\pi \sqrt{L_A{C}_{A1}^{\prime }}}& \left(14\right)\end{array}$

(27) At f.sub.2, L.sub.2 and C.sub.2 will bypass the current of f.sub.2, therefore Resonator-A is equivalent to a repeater resonator with C.sub.A2 as its compensating capacitor as shown in the equivalent circuit on the right of FIG. 7.

(28) The design principle applied to FIG. 6A can be applied to FIG. 6B. The only difference is that in FIG. 6B, the load R.sub.LA is connected across the capacitor C.sub.A1. Again, L.sub.2 and C.sub.2 are designed to form a bypass resonant tank for the non-targeted frequency f.sub.2. Then the circuit of FIG. 6B can be transformed into the equivalent form shown in FIG. 7. Afterwards, the equations of the equivalent load R′.sub.LA and the equivalent capacitor C′.sub.A1 specific for the circuit of FIG. 6B can be derived. From these equations, C′.sub.A1 can be chosen with L.sub.A to form a resonant tank at a frequency at or near its targeted frequency according to equation (14).

(29) Unlike the auxiliary circuits of FIG. 6A and FIG. 6B that use the series-connected L.sub.2 and C.sub.2 as a band-pass filter to short the current of the non-targeted frequency, those in FIG. 6C and FIG. 6D use the parallel-connected L.sub.2 and C.sub.2 as a band-stop filter to block the current of the non-targeted frequency f.sub.2 from Receiver-A. FIG. 6C has the load R.sub.LA connected in series with the capacitor C.sub.A1, while FIG. 6D has the load R.sub.LA connected in parallel with C.sub.A1. Regardless of the series or parallel connection of the load, the design methodology for the auxiliary circuits of FIG. 6C and FIG. 6D follow similar principles as previously described. The auxiliary circuits can be transformed into the equivalent forms of FIG. 7. Then the equivalent load R′.sub.LA and equivalent capacitance C′.sub.A1 equations can be derived. L.sub.A and C′.sub.A1 can be designed together to satisfy equation (14).

(30) The design methodology for Receiver-B is the same as that for Receiver-A, except that the targeted-frequency is f.sub.2 instead of f.sub.1.

(31) Basically, by replacing the loads in the proposed auxiliary circuits in FIG. 6 with a short circuit, the auxiliary circuits can be applied to a relay resonator. Such a resonator should be tuned to the multiple frequencies if they are used generally as relay resonators. FIG. 8A shows an example of a relay resonator which can operate with more than one tuned frequencies. In this example, it is tuned to work at frequencies f.sub.1 and f.sub.2. The two equivalent circuits for f.sub.1 and f.sub.2 are shown in FIG. 8B. At f.sub.1, the whole auxiliary circuit indicated in the block has a capacitive impedance which can compensate L.sub.R and form a L-C resonance at f.sub.1. At f.sub.2, L.sub.2 and C.sub.2 will be resonant and form a short circuit to bypass C.sub.R1, thereby causing L.sub.R and C.sub.R2 to form an L-C resonance at f.sub.2.

(32) In order to demonstrate the principle of the invention, a 3-coil wireless power transfer system was set up as shown in FIG. 4. The Transmitter, Receiver-A and Receiver-B were placed in a straight line in this example. For the straight system shown in FIG. 4, the indirect path T-A-B for Resonator-B is much more significant than the direct path T-B in terms of the power transfer efficiency. Therefore, this indirect path should be utilized. However, the indirect path T-B-A for Resonator-A has negligible effect since the direct path T-A is highly efficient. Generally, if the indirect path for one of the receivers, say B, is important, it implies the coupling between T-A (part of the path T-A-B) should be stronger than that between T-B (direct path). For Resonator-A, the indirect path T-B-A is weaker because the coupling between T-B (part of T-B-A) is already weaker than that between T-A (direct path). Therefore, the indirect path T-B-A has much less contribution for power transfer than the direct path T-A.

(33) Based on the system in FIG. 4, one auxiliary circuit is used in Resonator-A. The parameters and the load resistance values are shown in the circuit diagram of the system in FIG. 9. The excitation voltage consisting of two frequencies (namely 500 kHz and 600 kHz) is used to drive the transmitter coil.

(34) TABLE I lists the calculated and experimental results with and without the auxiliary circuit. From these results, the cross interference of the system with the proposed auxiliary circuit is much reduced when compared with those without the auxiliary circuit. With the rated output power, the power transfer efficiency (PTE) improvement is about 13% by applying the proposed auxiliary circuit.

(35) TABLE-US-00001 TABLE I COMPARISON BETWEEN CALCULATED AND EXPERIMENTAL RESULTS OF THE STRAIGHT WPT SYSTEM WITH AUXILIARY CIRCUIT AND WITHOUT AUXILIARY CIRCUIT P.sub.A at P.sub.B at With Auxiliary Circuit Without Auxiliary Circuit 600 kHz 500 kHz δ.sub.A δ.sub.B η δ.sub.A δ.sub.B η Calculated  2.5 W  2.5 W  0.1%  0.4% 66.0%   1%   1% 50.1% 0.25 W  2.5 W  1.1% 0.04% 59.9%   10%  0.1% 43.3%  2.5 W 0.25 W 0.01%  3.8% 73.4%  0.1%   10% 59.5% Experiment  2.5 W  2.5 W 0.47% 0.23% 59.7% 1.87% 0.97% 46.7% 0.25 W  2.5 W  7.2% 0.04% 44.6% 17.7% 0.09% 37.1%  2.5 W 0.25 W 0.17%  4.2% 72.6% 0.16%  8.8% 57.9%

(36) FIG. 10 shows the waveform of the input voltage of the system and its Fast Fourier Transform (FFT). It is clear that the input voltage mainly includes two components 500 kHz and 600 kHz. FIGS. 12-14 show the output voltage waveform comparisons between the systems with and without the proposed auxiliary circuit.

(37) Based on these practical measurements, it can be concluded that the auxiliary circuits are suitable for wireless power transfer systems with multi-frequency operation. The auxiliary circuits reduce the cross-interference from the power of the non-targeted frequency. At the same time, they improve the overall system energy efficiency.

(38) One application example is to use the invention in the design of wireless charging platform on which two or more types of loads are charged. If different types of loads are assigned with different targeted frequencies, then the Non-Target Receiver can still improve the coupling and power flow transfer between the Transmitter and the Targeted Receiver. Take the wireless system of FIG. 11 as an example in which the two receivers are designed for respective targeted frequencies of f.sub.1 and f.sub.2. This example can be realized in the form of a wireless charging table on which multiple loads may be placed and charged simultaneously. When multi-frequency power excitation is provided by the Transmitter, both Receivers will receive power according to their respective targeted frequencies. With the auxiliary circuit, Receiver A will act as a relay coil for enhancing the power transfer for Receiver B. In this way the efficient power transfer range of the charger is substantially extended.

(39) While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.