CONTROL METHOD OF A MINIMUM POWER INPUT

Abstract

A control method of a minimum power input applicable to a wireless power transfer system including a power transmission unit and at least one power receiving unit is provided. The power transmission unit is electrically connected with a control voltage signal and an input voltage signal and accordingly generates the minimum power input. The power transmission unit transmits the minimum power input wirelessly through a wireless transmission to the at least one power receiving unit for receiving. By adjusting the input voltage signal, the duty ratio and resonant frequency of the control voltage signal, the present invention ensures an optimal power transmission efficiency of the wireless power transmission system. Moreover, parameters of a charge pump reservoir and gate driving circuit can be further designed in view of the trend feedback of its gate drive waveforms so as to optimize the effect of the proposed invention.

Claims

1. A control method of a minimum power input, applicable to a wireless power transfer system including a power transmission unit and at least one power receiving unit, wherein the power transmission unit is electrically connected with a control voltage signal and an input voltage signal and accordingly generates the minimum power input, and wherein the power transmission unit transmits the minimum power input wirelessly to the at least one power receiving unit for receiving, the control method comprising: obtaining a distance, which is between the power transmission unit and the at least one power receiving unit; determining the input voltage signal based on the distance and a number of the at least one power receiving unit; computing a power input curve based on the input voltage signal and determining a minimum value of the power input curve, wherein the minimum value correlates with a specific resonant frequency and a specific duty ratio of the control voltage signal; retrieving the specific duty ratio and the specific resonant frequency sequentially which are corresponding to the minimum value; and inputting the control voltage signal having the specific duty ratio and the specific resonant frequency into the power transmission unit, such that the power transmission unit accordingly generates the minimum power input which is received sufficiently by the at least one power receiving unit.

2. The control method of the minimum power input of claim 1, wherein the wireless power transfer system includes a plurality of the at least one power receiving unit, and the minimum power input is transmitted wirelessly to the plurality of the at least one power receiving unit for being received and used sufficiently by the plurality of the at least one power receiving unit.

3. The control method of the minimum power input of claim 1, wherein the power transmission unit comprises a gate driving circuit, a pair of tuning resistor, a charge pump reservoir, a switching component and an amplifier circuit, the gate driving circuit receives the control voltage signal, the pair of tuning resistor is connected between the gate driving circuit and the charge pump reservoir, the switching component is connected with the charge pump reservoir and the amplifier circuit, and wherein when the gate driving circuit receives the control voltage signal having the specific duty ratio and the specific resonant frequency, and the amplifier circuit receives the input voltage signal, the minimum power input is accordingly generated at an output terminal of the amplifier circuit through turning on and turning off of the switching component.

4. The control method of the minimum power input of claim 3, wherein the switching component is a GaN high electron mobility transistor (GaN HEMT).

5. The control method of the minimum power input of claim 3, wherein the amplifier circuit is a class E amplifier circuit.

6. The control method of the minimum power input of claim 5, wherein the class E amplifier circuit comprises a capacitor, a first inductor, a second inductor and a load resistor, a node is configured between the switching component, the first inductor and the capacitor, another end of the first inductor which is opposite to the node is connected with the input voltage signal, another end of the capacitor which is opposite to the node is connected with the second inductor, and the second inductor is further connected to the load resistor, such that the minimum power input is accordingly generated at the output terminal which is located between the second inductor and the load resistor.

7. The control method of the minimum power input of claim 6, wherein the switching component is a metal-oxide-semiconductor field-effect transistor (MOSFET), a drain electrode of the MOSFET is connected to the node, a gate electrode of the MOSFET is connected to the charge pump reservoir and a source electrode of the MOSFET is connected to ground.

8. The control method of the minimum power input of claim 1, when determining the minimum value, further comprising: providing a plurality of transmission power successively to the at least one power receiving unit for receiving; and finding out a minimum of the plurality of transmission power which is sufficient for the at least one power receiving unit to receive and considering the minimum as the minimum value.

9. The control method of the minimum power input of claim 3, wherein the pair of tuning resistor comprises a first resistor and a second resistor which are connected in parallel, and the control method further comprises designing the charge pump reservoir in view of parameters of the first resistor and the second resistor so as to accordingly generate the minimum power input.

10. The control method of the minimum power input of claim 9, wherein the gate driving circuit at least comprises a PMOS and an NMOS which are connected in series, the first resistor is connected between a drain electrode of the PMOS and the charge pump reservoir, and the second resistor is connected between a drain electrode of the NMOS and the charge pump reservoir.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The accompanying drawings are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. In the drawings:

[0031] FIG. 1 shows a schematic diagram of a wireless power transfer (WPT) system in accordance with one embodiment of the present invention.

[0032] FIG. 2 shows a detailed circuit diagram of the power transmission unit in accordance with the embodiment of the present invention.

[0033] FIG. 3 shows a flow chart of the control method of the minimum power input in accordance with the embodiment of the present invention.

[0034] FIG. 4 shows a schematic diagram of a wireless power transfer (WPT) system which includes a plurality of power receiving unit in accordance with another embodiment of the present invention.

[0035] FIG. 5 shows a schematic diagram of the correlation between the power input and the duty ratio of the control voltage signal in accordance with the embodiment of the present invention.

[0036] FIG. 6 shows a schematic diagram of the correlation between the duty ratio and the resonant frequency of the control voltage signal in accordance with the embodiment of the present invention.

[0037] FIG. 7 shows a schematic diagram of various power input caused by different resonant frequency and duty ratio of the control voltage signal under VDD=108V.

[0038] FIG. 8 shows a schematic waveform of the gate-source voltage under the 6.78 MHz switch in accordance with the embodiment of the present invention.

[0039] FIG. 9 shows schematic waveform diagrams under VDD=262V and a 40 W class E amplifier circuit in accordance with a preferred embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0040] Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts.

[0041] The embodiments described below are illustrated to demonstrate the technical contents and characteristics of the present invention and to enable the persons skilled in the art to understand, make, and use the present invention. However, it shall be noticed that, it is not intended to limit the scope of the present invention. Therefore, any equivalent modification or variation according to the spirit of the present invention is to be also included within the scope of the present invention.

[0042] As known, performances of a class E amplifier circuit are mostly affected by its various load change and non-ideal factors. Although the existing prior arts have provided several analysis methods in considering of the non-ideal factors, including inductors, resistors, parasitic capacitance inductance, on-resistance, leakage current, and so on, for theoretically reducing the difference between its calculated result and the actual one, nevertheless, such conventional control and compensation methods are still considered to be much more complicated. In addition, the parameters of its gate driver are also difficult to drive and comply with power devices such as depletion-mode gallium nitride devices, etc. Therefore, in order to improve the circuit performance effectively and meanwhile extend transmission distance in a wireless power transmission system, the present invention discloses a control method of a minimum power input which is applicable to a wireless power transfer (WPT) system. Regarding the proposed embodiments of the present invention which will be disclosed in the following paragraphs, it is intended to clarify that these embodiments are disclosed for illustrating the main technical contents and technical characteristics of the present invention, and to enable those skilled in the art to understand, manufacture, and use the present invention. However, it should be noted that these embodiments are not intended to limit the scope of the present invention. And therefore, it is believed that any equivalent modifications or variations thereof based on the spirits of the present invention should also be included in the scope of the present invention.

[0043] The proposed control method of the present invention is applicable to a wireless power transfer system. Please refer to FIG. 1, which shows a schematic diagram of a wireless power transfer (WPT) system in accordance with one embodiment of the present invention, in which the WPT system includes a power transmission unit 11 and at least one power receiving unit 21. The power transmission unit 11 is electrically connected with a control voltage signal V.sub.S and an input voltage signal VDD and accordingly generates a minimum power input by employing its internal circuits. And, the minimum power input will be transmitted wirelessly through a wireless transmission 31 to the at least one power receiving unit 21 for receiving. Please refer to FIG. 2 at the same time. FIG. 2 shows a detailed circuit diagram of the power transmission unit in accordance with the embodiment of the present invention. As shown, the power transmission unit 11 includes a gate driving circuit 102, a pair of tuning resistor 104, a charge pump reservoir 106, a switching component 108 and an amplifier circuit 110. The gate driving circuit 102 at least includes an undervoltage lockout (UVLO) unit 22, a P-type metal-oxide-semiconductor field-effect transistor (PMOS) M.sub.p and an N-type metal-oxide-semiconductor field-effect transistor (NMOS) M.sub.n, wherein the PMOS M.sub.p and the NMOS M.sub.n are connected in series. The pair of tuning resistor 104 includes a first resistor R.sub.G,p and a second resistor R.sub.G,n which are connected in parallel, and the pair of tuning resistor 104 is connected between the gate driving circuit 102 and the charge pump reservoir 106.

[0044] A drain electrode of the PMOS M.sub.p is connected with the first resistor R.sub.G,p. A source electrode of the PMOS M.sub.p is connected with a high voltage level V.sub.GH. A drain electrode of the NMOS M.sub.n is connected with the second resistor R.sub.G,n. A source electrode of the NMOS M.sub.n is connected with a low voltage level V.sub.GL. The gate driving circuit 102 receives the foregoing control voltage signal V.sub.S.

[0045] The charge pump reservoir 106 includes a charge pump capacitor C.sub.C and a diode D.sub.C. The first resistor R.sub.G,p and the second resistor R.sub.G,n which are connected in parallel, are commonly connected to the charge pump capacitor C.sub.C. The switching component 108 is connected between the charge pump capacitor C.sub.C, the diode D.sub.C and the amplifier circuit 110. According to one embodiment of the present invention, the switching component 108, for instance can be a metal-oxide-semiconductor field-effect transistor (MOSFET). A drain electrode of the MOSFET is connected to a node V.sub.X and further in connection with the amplifier circuit 110. A gate electrode of the MOSFET is connected to the charge pump capacitor C.sub.C and the diode D.sub.C of the charge pump reservoir 106, and a source electrode of the MOSFET is connected to ground Vss. In a preferred embodiment of the present invention, the above-mentioned switching component 108 can be a depletion-mode (D-mode) GaN high electron mobility transistor (GaN HEMT).

[0046] Therefore, when the control voltage signal V.sub.S is input to the gate driving circuit 102 and the amplifier circuit 110 receives the input voltage signal VDD, through turning on and turning off of the switching component 108 (preferably a GaN HEMT), a corresponding power can be accordingly generated at an output terminal Vo of the amplifier circuit 110. The present invention is aimed to provide a novel control method for minimizing the correspondingly generated power, so as to obtain the minimum power input P.sub.in,min through our proposed control method. Please find Table 1 as follows for electrical characteristics of the D-mode GaN HEMT to be used in the embodiment of the present invention.

TABLE-US-00001 TABLE 1 parameter value unit V.sub.GS, ON turn-on voltage −7 V C.sub.DS drain-source parasitic capacitance 100 pF C.sub.GD gate-drain parasitic capacitance 80 pF C.sub.GS gate-source parasitic capacitance 420 pF V.sub.GS, max maximum gate-source voltage 8 V V.sub.DS, BD drain-source breakdown voltage 1000 V i.sub.d, max maximum drain current 35 A

[0047] In one embodiment, the amplifier circuit 110 of the present invention is described as a class E amplifier circuit for an illustrative example. Please refer to Table 2 below for effective parameters of the class E amplifier circuit to be used in the embodiment of the present invention.

TABLE-US-00002 TABLE 2 unit value R.sub.L kΩ 5 C.sub.DS pF 100 C.sub.2 pF 75 L.sub.1 μH 47 L.sub.2 μH 8

[0048] According to the embodiment of the present invention, the class E amplifier circuit includes a capacitor C.sub.2, a first inductor L.sub.1, a second inductor L.sub.2 and a load resistor R.sub.L. The node V.sub.X is configured between the switching component 108, the first inductor L.sub.1 and the capacitor C.sub.2. Another end of the first inductor L.sub.1 which is opposite to the node V.sub.X is connected with the input voltage signal VDD and receiving the input voltage signal VDD. Another end of the capacitor C.sub.2 which is opposite to the node V.sub.X is connected with the second inductor L.sub.2, and the second inductor L.sub.2 is further connected to the load resistor R.sub.L, such that the correspondingly generated power is provided at the output terminal Vo which is located between the second inductor L.sub.2 and the load resistor R.sub.L. Please refer to FIG. 3, which shows a flow chart of the control method of the minimum power input in accordance with the embodiment of the present invention. By employing the control method as disclosed in FIG. 3, including the steps of S302, S304, S306, S308 and S310, the present invention is aimed to minimize the correspondingly generated power (provided at the output terminal Vo), so as to obtain the minimum power input which can be received and used sufficiently by the at least one power receiving unit.

[0049] Specifically, as shown in the step S302 in FIG. 3, the control method of the present invention obtains a distance first. The distance D, as referring to FIG. 1, is configured between the power transmission unit 11 and the power receiving unit 21. Later, as shown in the step S304, the present invention determines the input voltage signal VDD based on the distance D and a number of the power receiving unit 21. According to the embodiments of the present invention, the number of the power receiving unit 21 is not limited to one. In other words, the WPT system may also alternatively include a plurality of the power receiving unit, as indicated in FIG. 4 of the present invention. In such an embodiment, the correspondingly generated minimum power input P.sub.in,min can be transmitted wirelessly through the wireless transmission 31 to the plurality of power receiving unit 21a, 21b . . . 21n, and received and used sufficiently by the plurality of power receiving unit 21a, 21b . . . 21n.

[0050] Generally speaking, in the WPT system applications, the farther the power transmission distance is, i.e. the distance D between the power transmission unit 11 and the power receiving units 21, 21a, 21b . . . 21n, the higher the input voltage signal VDD will be required. Meanwhile, under the circumstance that a plurality of power receiving units 21, 21a, 21b . . . 21n are disposed, it is necessary to accordingly increase the input voltage signal VDD for providing sufficient power to the plurality of power receiving units 21, 21a, 21b . . . 21n.

[0051] After the input voltage signal VDD is determined, as shown in the step S306, then the present invention is able to compute a power input curve based on empirical data of the input voltage signal VDD. Please refer to FIG. 5, in which each power input curve is computed according to different input voltage signal VDD. For example, in FIG. 5, three power input curves labelled as triangles, X symbols, and circles, are computed based on VDD=36V, 72V, 108V, respectively. And, each power input curve shows how the power input P.sub.in correlates with a duty ratio δ of the control voltage signal V.sub.S. In such the step, the present invention provides a plurality of transmission power successively to the power receiving unit or the plurality of power receiving units for receiving. And then, the present invention is aimed to find out a minimum of the plurality of transmission power to be transmitted, which is sufficient for the power receiving unit or the plurality of power receiving units to receive. And therefore, it considers the minimum as a minimum value of the power input curve. For example, in one embodiment of the present invention when D=100 cm, the WPT system includes only one power receiving unit and VDD=108V, a minimum value of the power input curve is determined as 3.2 W. At this time, as referring to (P.sub.in vs. δ) correlations illustrated in FIG. 5, it can be found out that the duty ratio δ of the control voltage signal V.sub.S is 30%.

[0052] Afterwards, the step S308 is performed, and please refer to FIG. 6 at the same time. It is obvious that FIG. 6 shows how the duty ratio δ of the control voltage signal V.sub.S correlates with a resonant frequency f.sub.0 of the control voltage signal V.sub.S. Following the above-mentioned embodiment when δ=30%, it is believed that the resonant frequency f.sub.0 of the control voltage signal V.sub.S can be found out as referring to the (δ vs. f.sub.0) correlations illustrated in FIG. 6, and f.sub.0=4.12 MHz. Therefore, it is apparent that by employing the steps of S306 and S308 of the present invention, once the minimum value of the power input curve is determined and the correlations in FIG. 5 and FIG. 6 are referred, showing that the minimum value correlates with a specific resonant frequency f.sub.0 and a specific duty ratio δ of the control voltage signal V.sub.S. The present invention is thus able to successfully retrieve the specific duty ratio δ and the specific resonant frequency f.sub.0 of the control voltage signal V.sub.S sequentially, which are corresponding to the minimum value, based on the applicants' fine empirical data.

[0053] At last, as shown in the step S310, the control voltage signal V.sub.S having the specific duty ratio δ and the specific resonant frequency f.sub.0 can be inputted into the power transmission unit 11, and through internal circuits thereof, including the gate driving circuit, the pair of tuning resistor, the charge pump reservoir, the switching component (GaN HEMT) and the amplifier circuit (class E amplifier circuit), the class E amplifier circuit is able to accordingly generate the minimum power input P.sub.in,min which is sufficient for the power receiving unit or the plurality of power receiving units to receive and use.

[0054] To be more practical, the Applicants of the present invention further provide a large number of 70 experimental data and perform statistics and interpolation on the experimental results. In such experiments, given that VDD=108V, f.sub.0=4.12 MHz and δ=30%, the minimum power input is computed. Please refer to FIG. 7, in which the data illustrated in FIG. 7 shows a schematic diagram of various power input Pm caused by different resonant frequency f.sub.0 and duty ratio δ under VDD=108V. Each the minimum power input is represented by a point in the figure and corresponds to a lowest power loss from the switching component to the ground. And according to other embodiments of the present invention, the experimental data can also be applied widely to a variety of input voltage signals VDD.

[0055] On the other hand, the control method of the minimum power input P.sub.in,min of the present invention may further comprise designing the charge pump reservoir in view of parameters of the first resistor R.sub.G,p and the second resistor R.sub.G,n so as to accordingly generate the minimum power input and to make the generated minimum power input optimized. Please find the following Table 3 for effective parameters of the charge pump reservoir to be used in the embodiment of the present invention.

TABLE-US-00003 TABLE 3 parameter value unit R.sub.G, p first resistor 12 Ω R.sub.G, n second resistor 30 Ω C.sub.C charge pump capacitor 5 nF C.sub.DC diode capacitance 40 pF I.sub.R diode reverse saturation current 50 μA

[0056] In details, please refer to FIG. 8, which shows a schematic waveform of the gate-source voltage under the 6.78 MHz switch. In the figure, the dashed line and the solid line respectively show a non-ideal and an ideal waveform of the gate-source voltage. VDS is the voltage level of the node V.sub.X in FIG. 2, which is the drain-source voltage level of the switching component 108. From the waveform diagrams, it can be observed that, when VDS is raised to a high voltage level and the gate of the switching component 108 is turned off, the charge pump reservoir 106 will require certain negative charges in a short time due to its gate-drain parasitic capacitance C.sub.GD (also known as a Miller capacitor). As for the gate of the switching component 108 being turned on, the charge pump reservoir 106 will need to withdraw the same amount of negative charges. Therefore, in view of its dynamic behaviors, the resulting effect is, when the gate is turned on, the Miller Plain of its waveform shows a low-voltage surge. However, when the gate flips, the Miller Plain of its waveform behaves to show a longer plateau region. If the resistance of the first resistor R.sub.G,p is too high (as shown by the dashed line in FIG. 8), then the negative charges will be quickly returned to the first resistor R.sub.G,p due to the gate-drain parasitic capacitance C.sub.GD and the charge pump capacitor C.sub.C. Therefore, the negative voltage surge will be formed, referring as the two areas E1, E2 characterized by the dotted line in FIG. 8. Under a circumstance like this, the negative voltage may drop down below −V.sub.GS,max and induce severe gate-source breakdown. As a result, to avoid a situation like this, according to an embodiment of the present invention, it is necessary to adjust and decrease the resistance of the first resistor R.sub.G,p so as to prevent the high voltage drop on V.sub.GH when the gate is turned on. In the similar design manners when regarding the second resistor R.sub.G,n, it is definitely also necessary to design the resistance of the second resistor R.sub.G,n and its gate drive design parameters with references made to the ideal gate-source voltage such that an ideal waveform, as shown by the solid line in FIG. 8, can be achieved.

[0057] As a result, the control method of the minimum power input disclosed in the present invention may further comprise designing the charge pump reservoir and its gate driving circuits in view of the gate drive waveforms of the switching component, so as to accomplish the implementation of D-mode GaN HEMT in wireless power transmission systems, and to guarantee an optimal power transmission efficiency at the same time. Please refer to FIG. 9, which shows schematic waveform diagrams under VDD=262V and a 40 W class E amplifier circuit in accordance with a preferred embodiment of the present invention, wherein V.sub.GS is shown as an experimental gate-source voltage waveform. It can be seen that by employing the control method of the present invention, it achieves to meet V.sub.GS: 0˜−25V, I.sub.d: ±1 A, and VDS: 0˜660V. V.sub.GS represents the gate-source voltage level, I.sub.d represents the current flowing through the second inductor L.sub.2 of the class E amplifier circuit, and VDS represents the drain-source voltage level.

[0058] Therefore, to sum above, it is apparent that the present invention proposes an extremely novel control method of a minimum power input and accomplishes the implementation of D-mode GaN HEMT in class E amplifier circuits. According to the control method disclosed in the present invention, by employing the control strategy of adjusting the input voltage signal VDD, duty ratio δ, and resonant frequency f.sub.0, the present invention is able to ensure an optimal power transmission efficiency of the wireless power transmission system. In addition, the operating requirements in 6.78 MHz resonant wireless power transmission applications can also be easily conformed by using a relatively simple look-up method. Furthermore, according to the present invention, parameters of the charge pump reservoir and the gate driving circuit can be further designed in view of the trend feedback of the gate drive waveforms, so as to realize a variety of applications of the depletion-mode GaN HEMT in wireless power transmission systems. And thus, based on the design of the depletion-mode GaN HEMT parameters, it further helps to provide an optimized influence on the system reliability and application realization of the resonant wireless power transmission (WPT) system as well.

[0059] It is worth reminding that the present invention is certainly not limited to the plurality of internal circuit layouts as disclosed above in the earlier paragraphs. In other words, those skilled in the art are able to make modifications and variations according to the actual circuit specifications, with equality based on the contents and spirits of the invention, and yet, still fall into the scope of the invention.

[0060] In view of the above, it is believed that, compared with the prior arts, the embodiments of the present invention and the control method being proposed are able to effectively solve the issues and deficiencies existing in the prior arts. Also, the present invention achieves not only to generate rapid and instant response and optimize the efficiency of a class E amplifier circuit based on electrical characteristics of the GaN HEMT and parameters of the depletion-mode GaN HEMT which is compatible with the charge pump reservoir and the gate driving circuit, but also to be able being widely applied in a variety of wireless charging or power converter devices in the semiconductor industry, integrated circuit industry, or power electronics industry and so on. As a result, the Applicants assert that the present invention is instinct, effective and highly competitive for incoming technologies, industries and researches developed in the future. Meanwhile, the Applicants also provide a variety of experimental data, empirical data, and so on to verify that the technical features, means and effects achieved by the present invention are significantly different from the current solutions, and can not be accomplished easily by those who are familiar with the industry. As a result, it is believed that the present invention is indeed characterized by patentability and shall be patentable soon in a near future.

[0061] It will be apparent to those skilled in the art that various modifications and variations can be made to the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the invention and its equivalent.