Wireless Power Transmission System

Abstract

To realize high efficiency, space saving, and low cost in a wireless power transmission system.SOLUTION: A power transmission device has a first switching element having a first terminal and a second terminal, a first capacitor having a third terminal connected to the first terminal and a fourth terminal connected to the second terminal, a power transmission inductor connected to the first switching element and transmitting AC power wirelessly, and a second capacitor connected in series between the first switching element and the power transmission inductor. A power reception device has a power reception inductor configured to receive the AC power wirelessly, a third capacitor connected to the power reception inductor in series, and an AC / DC conversion circuit converting the AC power received by the power reception inductor into DC power. An impedance Zc of the second capacitor in a switching frequency f of the first switching element is smaller than an impedance ZL of the transmission inductor in the switching frequency f.SELECTED DRAWING: Figure 7

Description

[Technical field]

[0001] The present invention relates to a wireless power transmission system. [Background technology]

[0002] In recent years, with the increasing speed of power switching devices, wireless power transmission technology in high frequency bands with operating frequencies of several MHz or more has been researched and developed.

[0003] Patent Document 1 discloses a power transmission system having a power transmitting device side resonant capacitor which constitutes a power transmitting device side resonant circuit together with a power transmitting coil, and a switch circuit which is electrically connected to the power transmitting coil and is composed of a parallel connection circuit of a switch element, a diode and a capacitor, and which has a power receiving device side resonant circuit together with a power receiving coil which is coupled to the power transmitting coil by magnetic field resonance. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 5787027 Summary of the Invention [Problem to be solved by the invention]

[0005] As conventional power transmission systems that were previously wired are converted to wireless power transmission systems using wireless power transmission technology, there is an increasing demand for higher efficiency, smaller space, and lower costs.

[0006] An object of the present invention is to solve at least one of the above problems in a wireless power transmission system. [Means for solving the problem]

[0007] The wireless power transmission system of the present invention is a wireless power transmission system having a power transmitting device and a power receiving device, wherein the power transmitting device has a first switching element having a first terminal and a second terminal, a first capacitor having a third terminal connected to the first terminal and a fourth terminal connected to the second terminal, a power transmitting inductor connected to the first switching element and transmitting AC power wirelessly, and a second capacitor connected in series between the first switching element and the power transmitting inductor, and the power receiving device has a power receiving inductor configured to receive AC power wirelessly, a third capacitor connected in series with the power receiving inductor, and an AC-DC conversion circuit that converts the AC power received by the power receiving inductor into DC power, and an impedance Zc of the second capacitor at a switching frequency f of the first switching element is smaller than an impedance ZL of the power transmitting inductor at the switching frequency f. Effect of the Invention

[0008] According to the present invention, it is possible to achieve high efficiency, space saving, and cost reduction in a wireless power transmission system. [Brief description of the drawings]

[0009] [Figure 1] 1 is a block diagram showing a configuration example of a wireless power transmission system. [Diagram 2] FIG. 1 is a diagram illustrating an example of the configuration of an E-class power supply. [Diagram 3] 1 is a circuit diagram showing a configuration example of a wireless power transmission system using an E-class power supply. [Figure 4] 1 is a graph showing the efficiency of a wireless power transmission system. [Diagram 5] 1 is an equivalent circuit diagram of a wireless power transmission system. [Figure 6] FIG. 1 is a diagram illustrating a configuration example of a wireless power transmission system. [Figure 7] 1 is a circuit diagram showing a configuration example of a wireless power transmission system. [Figure 8] 1 is a circuit diagram showing a configuration example of a wireless power transmission system. [Figure 9] 1 is a circuit diagram showing a configuration example of a wireless power transmission system. [Figure 10] 1 is a circuit diagram showing a configuration example of a wireless power transmission system. [Figure 11] FIG. 13 is a diagram showing a switching control signal waveform and a Vds waveform. [Figure 12] FIG. 1 illustrates a wireless power transmission system. [Figure 13] FIG. 2 is a diagram showing a power transmitting antenna and a power receiving antenna. [Figure 14] FIG. 1 is a diagram showing the adjacency coefficient and skin depth of a conductor. [Figure 15] FIG. 13 is a diagram showing values ​​set for each variable. [Figure 16] FIG. 1 is a diagram showing self-inductance versus the number of turns of a solenoid coil. [Figure 17] 13 is a flowchart for determining the relationship between the overall system efficiency and α. [Figure 18] FIG. 13 illustrates overall system efficiency. [Figure 19] FIG. 13 illustrates overall system efficiency. [Figure 20] FIG. 13 illustrates overall system efficiency. [Figure 21] FIG. 13 illustrates overall system efficiency. [Figure 22] FIG. 13 illustrates overall system efficiency. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] 1 is a block diagram showing an example of the configuration of a wireless power transmission system 100 according to the present embodiment. The wireless power transmission system 100 includes a power transmitting device 107 and a power receiving device 108. The power transmitting device 107 includes a DC power supply 101, a DC-AC conversion circuit (DC-AC conversion circuit) 102, and a power transmitting antenna 103. The DC power supply 101 supplies a DC voltage (DC power). The DC-AC conversion circuit 102 converts the DC voltage supplied by the DC power supply 101 into an AC voltage. The power transmitting antenna 103 wirelessly transmits the AC voltage (AC power) converted by the DC-AC conversion circuit 102 to the power receiving device 108.

[0011] The power receiving device 108 has a power receiving antenna 104, an AC-DC conversion circuit (AC-DC conversion circuit) 105, and a load 106. The power receiving antenna 104 receives AC power from the power transmitting antenna 103, and an AC voltage is induced in the power receiving antenna 104. The AC-DC conversion circuit 105 converts the AC voltage induced in the power receiving antenna 104 into a DC voltage, and supplies the DC voltage to the load 106. Note that the AC-DC conversion circuit 105 can be omitted. In that case, the power receiving antenna 104 supplies the induced AC voltage to the load 106.

[0012] For example, the DC-AC conversion circuit 102 converts DC power supplied from a DC power supply 101 into AC power by a switching element that performs a high-speed switching operation, and supplies the AC power to a power transmitting antenna 103. In order to improve the conversion efficiency, a wireless power transmission system 100 using a class E power supply will be described.

[0013] The class E power supply is a power supply method that enables highly efficient high-frequency switching by reducing the conduction loss and switching loss in the switching element. The operating principle of the class E power supply is explained below. The class E power supply is defined as a power supply in which, assuming that the terminal voltage of the switching element is Vs, the switching element transitions from the off state to the on state when Vs=0 [V] and dVs / dt=0. Hereinafter, this switching operation is referred to as ZVS (Zero Voltage Switching) operation. The DC-AC conversion circuit 102 converts DC power to AC power through ZVS operation, thereby reducing switching loss and achieving highly efficient power conversion.

[0014] 2(a) is a circuit diagram showing an example of the configuration of the class E power supply 200, and FIG. 2(b) is a block diagram showing an example of the functional configuration of the class E power supply 200. The class E power supply 200 has a DC power supply 201, a choke coil 202, a switching circuit 203, a phase shift circuit 204, a filter circuit 205, and a load 206.

[0015] The DC power supply 201 includes a DC power supply 211. The choke coil 202 includes an inductor L c The switching circuit 203 includes a switch control signal source 212 and a switching element 213. The phase shift circuit 204 includes a capacitor C1 and an inductor L x The filter circuit 205 includes an inductor L o and a capacitor C2. The load 206 has a resistance RL.

[0016] The negative terminals of the DC power supply 211 and the switch control signal source 212 are connected to a reference potential node (ground potential node). The switching element 213 is, for example, a field effect transistor (FET). An inductor L cis connected between the positive terminal of the DC power supply 211 and the drain terminal of the switching element 213. The positive terminal of the switch control signal source 212 is connected to the gate terminal of the switching element 213 and supplies a switch control signal (pulse signal) to the switching element 213. The source terminal of the switching element 213 is connected to a reference potential node. The capacitor C1 is connected between the drain terminal and the source terminal of the switching element 213. The inductor L x and inductor L o The series connection circuit of the capacitor C2 and the resistor RL is connected in parallel to the capacitor C1.

[0017] The DC power supply 201 supplies a DC voltage to the power transmitting device 107. The choke coil 202 converts the DC voltage supplied from the DC power supply 201 into a DC current and smoothes the current. The switching circuit 203 switches the DC current supplied from the DC power supply 201 via the choke coil 202 using a switching element 213, and converts the DC power into AC power. The switching element 213 is, for example, a FET capable of high-speed operation and small conduction loss. The phase shift circuit 204 has a role of changing the phase of the current and voltage in order to perform ZVS operation of the switching circuit 203. Mainly, the inductor L x This role is played by the inductor L x However, a necessary condition for the class E power supply to perform ZVS operation is that it has sufficient impedance for the switching frequency. The filter circuit 205 filters the AC power supplied from the switching circuit 203 via the phase shift circuit 204, and limits the band of the AC voltage supplied to the load 206. The Q (Quality Factor) value Q, which indicates the narrowness of the passband of the filter circuit, L is given by [Equation 1], where r Lo is the inductor L o represents the DC resistance of Lx is the inductor L x Represents the DC resistance value of

[0018]

number

[0019]

number

[0020] Here, ω is the angular frequency of the switching frequency of the switching circuit 203. The constant 1.1525 is a constant determined by the duty ratio Dt of the switch control signal of the switch control signal source 212. Here, the duty ratio Dt is set to 0.5. As is clear from [Equation 2], L x is a limited inductance value calculated from the multidimensional parameters of the load resistance RL, switching frequency, and switching duty ratio in the E-class power supply. x Only when the L is properly designed, the drain-source voltage waveform of the FET (hereinafter referred to as the Vds waveform) satisfies the E class operating conditions. xis appropriately designed and satisfies the class E operating conditions are shown in Fig. 11. It can be seen that the Vds waveform 208 satisfies the class E operating conditions, with Vds = 0V and dVds / dt = 0 at the timing when the switching control signal waveform 207 transitions from the off state (0V) to the on state (5V).

[0021] Fig. 3 is a circuit diagram showing a configuration example of a wireless power transmission system 100 using an E-class power supply. The wireless power transmission system 100 uses the E-class power supply 200 of Fig. 2(a) for the power transmitting device 107 of Fig. 1. The wireless power transmission system 100 of Fig. 3 is obtained by deleting the AC-DC conversion circuit 105 from the wireless power transmission system 100 of Fig. 1.

[0022] DC power supply 211 and inductor L c The connections of the switch control signal source 212, the switching element 213, and the capacitor C1 are the same as those in FIG. 2(a). L1 The series connection circuit is connected in parallel to the capacitor C1.

[0023] The inductor L2 is coupled to the inductor L1 with a coupling coefficient k. One terminal of the inductor L2 is connected to the reference potential node. The other terminal of the inductor L2 is connected to a resistor r L2 and capacitor C r and a resistor RL connected in series to the reference potential node.

[0024] The DC power supply 211 corresponds to the DC power supply 101 in Fig. 1. The switch control signal source 212 and the switching element 213 correspond to the DC-AC conversion circuit 102 in Fig. 1. The inductor L1 corresponds to the power transmitting antenna 103 in Fig. 1 and is the inductor L x and L o The inductance of inductor L1 is the sum of the inductor L x and L o is the sum of the inductances of

[0025] The inductor L2 corresponds to the power receiving antenna 104 in FIG. 1. The inductors L1 and L2 are coupled to each other with a coupling coefficient k. The resistance r L1 is the real resistance component of the inductor (transmitting antenna) L1. Resistance r L2 is the real resistance component of the inductor (power receiving antenna) L2. The capacitor Cr is a resonant capacitor, and has a capacitance that resonates with the inductance of the inductor L2 at the power transmission frequency. The resistor RL corresponds to the load 106 in FIG. 1. The theoretical limit η of the power transmission efficiency of the wireless power transmission system 100 MAX is calculated using the following formula:

[0026]

number

[0027] Figure 4 shows the resistance r L1 1 is a graph showing the results of a numerical analysis of the influence of on the power transmission efficiency of the wireless power transmission system 100. The horizontal axis represents resistance RL, and the vertical axis represents the power transmission efficiency of the wireless power transmission system 100.

[0028] The inductance of the inductors L1 and L2 is 2 μH. The coupling coefficient k is 0.8. The angular frequency ω is 2πf=2π×3×10 6 Resistance r L2 is 0.4 Ω.

[0029] Wire 401 has resistance r L1 The line 402 shows the power transfer efficiency versus resistance RL when the resistance r L1 The line 403 shows the power transfer efficiency versus resistance RL when the resistance r L1 The power transfer efficiency for resistance RL when r is 3Ω is shown. L1 It can be seen that when the resistance r increases, the power transmission efficiency deteriorates, especially in a region where the resistance RL is large. L1By reducing the load resistance RL, high power transmission efficiency can be obtained even if the load resistance RL varies.

[0030] When the power receiving device 108 of the wireless power transmission system 100 is in a resonant state at the power transmission frequency, the impedance R of the power receiving device 108 seen from the power transmitting device 107 is eq is expressed by the following formula:

[0031]

number

[0032] Fig. 5 is an equivalent circuit diagram of the wireless power transmission system 100 of Fig. 3. The wireless power transmission system 100 of Fig. 5 is different from the wireless power transmission system 100 of Fig. 3 in that an inductor L2 and a resistor r L2 and capacitor C r and resistor RL are deleted, and resistor r L1 A series circuit of the capacitor C2, the inductor L1, and the resistor 501 is connected in parallel to the capacitor C1. The resistor 501 is the same as the resistor r L1 The value of and the impedance R eq The impedance is the sum of

[0033] 6 is a diagram showing a configuration example of the wireless power transmission system 100 in which the components of the wireless power transmission system 100 in FIG. 5 are decomposed into functions of the E-class power supply 200 in FIG. 2(a) and (b). The wireless power transmission system 100 in FIG. 6 differs from the wireless power transmission system 100 in FIG. 5 in that an inductor L x ,L o and capacitor C2 and resistor r Lx ,r Lo A connection circuit is provided between the inductor L x and inductor L o and capacitor C2 and resistor r Lx and resistance r LoThe series circuit of the capacitor C1 and resistor 601 is connected in parallel to the capacitor C1. The resistor 601 is connected in series to the capacitor C1. eq Resistance r Lx is the inductor L x Resistance r Lo is the inductor L o is the real resistance component.

[0034] As shown in Figure 4, the resistor r L1 When the power conversion efficiency η of the power transmitting device 107 of the wireless power transmission system 100 increases, the power transmission efficiency decreases. The reason for this will be described below with reference to FIG. TX is expressed by the following formula:

[0035]

number

[0036] resistance r L1 is the resistance r Lx and resistance r Lo As is clear from the above formula, the power conversion efficiency η TX In order to improve the resistance r L1 Therefore, the resistance r L1 The resistance r L1 Minimizing is equivalent to minimizing the inductance of the inductor (transmitting antenna) L1. x Since the inductance of is limited, the inductor L used in the filter circuit is o If it is acceptable for the voltage waveform supplied to the load 206 to contain harmonics, the inductor L o Therefore, the maximum efficiency of the class E power supply is given by [Equation 6].

[0037]

number

[0038]

number

[0039] Therefore, in the wireless power transmission system 100, the inductance of the inductor (power transmitting antenna) L1 is calculated by the above formula: x If the inductance is close to that of the power transmitting device 107, the power conversion efficiency η TX It is possible to maximize the

[0040] Inductor L functions as a filter circuit o (r Lo It has been mentioned that the power conversion efficiency of the power transmission circuit can be maximized by minimizing . Here, the capacitor C2 used in the filter circuit will be explained. The capacitance C2 of the filter circuit 205 is calculated by [Mathematical Expression 8].

[0041]

number

[0042]

number

[0043] FIG. 7 shows a wireless power transmission system 100 in which C2 is eliminated by the above principle and the inductor (power transmission antenna) L1 and the switching element 213 are connected in a DC manner, either directly or via a conductor. The potential difference Vs between the drain terminal and the source terminal of the switching element 213 of the E-class power supply has a peak value that is 3 to 5 times the DC power supply voltage, so the withstand voltage performance of each component is required to be equal to or higher than that peak voltage. Since capacitors with good high-frequency characteristics and high withstand voltage are generally expensive and large, being able to eliminate C2 as shown in FIG. 7 is a great advantage in terms of low cost and space saving. In addition, since the mounting space for C2 is not required, the switching node (the wiring pattern connected to the drain of the FET) can be minimized, which is advantageous in terms of noise radiation.

[0044] However, the wireless power transmission system 100 may physically include a capacitor C2 with a sufficiently small reactance. In this case, the number of components increases, but the wireless power transmission system 100 can achieve the same power transmission performance as the configuration shown in FIG. o The relationship between the inductor L1 and the capacitance C2 has been described. Now, the relationship between the inductor L1 and the capacitor C2 will be described. o If the inductance ratio of the inductors is 1:α, then the inductor L o The inductance is expressed by [Number 10].

[0045]

number

[0046] When the relationship of [Equation 8] holds, the capacitance C2 of the filter circuit 205 is given by [Equation 11].

[0047]

number

[0048] That is, the reactance Z of the capacitance C2 of the filter circuit 205 c2becomes [Number 12].

[0049]

number

[0050] Here, Z L1 is the reactance of inductor L1. When α is sufficiently smaller than 1, the capacitance of capacitor C2 increases, and its reactance Z c2 In other words, [Equation 9] can be expressed as [Equation 13] using α.

[0051]

number

[0052] When the condition of [Equation 13] is satisfied, the capacitor C2 and the inductor L o In the present embodiment, the function as a filter is almost lost. In other words, the power conversion efficiency η TX When priority is given to improving the efficiency, the design according to [Equation 13] is most desirable.

[0053] In an application that satisfies the condition of [Equation 13] and does not cause any problem even if the function of the filter circuit 205 is sacrificed, a coupling capacitor C2 may be inserted for the purpose of AC coupling at a position that is electrically equivalent to the capacitor C2. Note that the insertion of the capacitor C2 that satisfies the condition described in [Equation 13] reduces the power conversion efficiency η TX This does not in any way hinder the improvement of the

[0054] Fig. 7 is a circuit diagram showing an example of the configuration of a wireless power transmission system 100 according to this embodiment. The wireless power transmission system 100 in Fig. 7 is obtained by deleting the capacitor C2 from the wireless power transmission system 100 in Fig. 3 and adding the AC-DC conversion circuit 105 in Fig. 1. The AC-DC conversion circuit 105 has diodes 701-704 and a capacitor 705, and converts AC power into DC power.

[0055] The efficiency of the wireless power transmission system 100 can be expressed as the product of the efficiency between the transmitting antenna 103 and the receiving antenna 104 and the DC-AC conversion efficiency (AC-DC conversion efficiency). The wireless power transmission system 100 can optimize the overall efficiency by optimizing each efficiency. The wireless power transmission system 100 determines parameters (inductances of inductors L1 and L2, switching frequency, circuit constants) that optimize the above two efficiencies under constraints such as the size of inductors L1 and L2, output power, input voltage, and ZVS operation guarantee.

[0056] The switching frequency of the switching element 213 is, for example, 100 kHz to 15 MHz. At that switching frequency, the wireless power transmission system 100 in Fig. 7 can eliminate the capacitor C2 in Fig. 3 and reduce the size and cost. Below, differences between the wireless power transmission system 100 in Fig. 7 and the wireless power transmission system 100 in Fig. 3 will be described.

[0057] In Figure 7, the resistor r L1 and r L2 Although the notation of resistor r in FIG. 3 is omitted, the wireless power transmission system 100 in FIG. 7 actually has a resistor r L1 andr L2 A DC power supply 211 and an inductor L c is connected in series between the drain terminal and the source terminal of the switching element 213.

[0058] The wireless power transmission system 100 includes a power transmitting device 107 and a power receiving device 108 shown in FIG. 1. The power transmitting device 107 includes a DC power supply 211, a switch control signal source 212, a switching element 213, and an inductor L cThe power receiving device 108 includes an inductor L2, a capacitor C1, and an inductor L1. r The circuit includes diodes 701 to 704, a capacitor 705, and a resistor RL.

[0059] The inductor L1 has a first terminal and a second terminal, and is a power transmission inductor that wirelessly transmits AC power. The first terminal and the second terminal of the inductor L1 are connected to the drain terminal and the source terminal of the switching element 213, respectively. The drain terminal and the source terminal of the switching element 213 are connected to the first terminal and the second terminal of the inductor L1, respectively, in a direct current manner. That is, the drain terminal and the source terminal of the switching element 213 are connected to the first terminal and the second terminal of the inductor L1, respectively, directly or via a conductor. The capacitor C1 is connected between the drain terminal and the source terminal of the switching element 213.

[0060] The inductor L2 has a first terminal and a second terminal, and is a power receiving inductor that wirelessly receives AC power. r is connected between a first terminal of the inductor L2 and the node N1. A second terminal of the inductor L2 is connected to the node N2.

[0061] The diode 701 has an anode connected to the node N1 and a cathode connected to the node N3. The diode 702 has an anode connected to the reference potential node and a cathode connected to the node N1. The diode 703 has an anode connected to the reference potential node and a cathode connected to the node N2. The diode 704 has an anode connected to the node N2 and a cathode connected to the node N3.

[0062] Diodes 701 to 704 are a full-wave rectifier circuit that rectifies AC power (AC voltage) at nodes N1 and N2 and outputs DC power (DC voltage) to node N3 and the reference potential node. Capacitor 705 is connected between node N3 and the reference potential node and smoothes the DC power. Resistor RL is load 106 in FIG. 1 and is connected between node N3 and the reference potential node. DC power is supplied to resistor RL.

[0063] In the wireless power transmission system 100, similarly to the class E power supply, when the switching element 213 transitions from the off state to the on state, the potential difference Vs between the drain terminal and the source terminal of the switching element 213 is approximately zero. Furthermore, when the switching element 213 transitions from the off state to the on state, the change (dVs / dt) in the potential difference between the drain terminal and the source terminal of the switching element 213 is approximately zero.

[0064] 7 may be configured to eliminate the AC-DC conversion circuit 105 (diodes 701 to 704 and capacitor 705) in the same manner as in FIG. 3. In that case, the first terminal of the inductor L2 is connected to the capacitor C r A second terminal of the inductor L2 is connected to a node N3 via a resistor R. A second terminal of the inductor L2 is connected to a reference potential node. A resistor R.sub.L is connected between the node N3 and the reference potential node.

[0065] As described above, the size and cost of the wireless power transmission system 100 can be reduced by eliminating the capacitor C2 in FIG.

[0066] Fig. 12(a) shows a circuit example in which specific circuit constants are set for the wireless power transmission system 100 in Fig. 7. Here, the inductor L1 and the inductor L2 are coupled with a coupling coefficient of 0.3. The switching frequency of the switching element 213 is set to 1 MHz.

[0067] FIG. 12(b) shows the result of a circuit simulation of the wireless power transmission system 100 of FIG. 12(a). In the wireless power transmission system 100 of FIG. 12(b), the load resistance RL consumes power of about 13 W (8 V·1.6 A). A waveform 801 is a switching signal of the switching element 213 output by the switch control signal source 212. A waveform 802 is a voltage Vs between the drain terminal and the source terminal of the switching element 213. In the waveform 802, at the timing when the switching element 213 transitions from the OFF state to the ON state, the potential difference Vs between the drain terminal and the source terminal of the switching element 213 is approximately zero. Furthermore, at the timing when the switching element 213 transitions from the OFF state to the ON state, the change (dVs / dt) in the potential difference between the drain terminal and the source terminal of the switching element 213 is approximately zero. Therefore, this simulation showed the feasibility of a highly efficient E-class power supply that achieves ZVS operation for the wireless power transmission system 100 without the capacitor C2. By using the methods described above, we can optimize L1 (r L1 By minimizing the power transmission efficiency, the power transmitting section of the wireless power transmission system 100 can be made as highly efficient as possible.

[0068] Up to this point, the description has been given from the viewpoint of maximizing the efficiency of the power transmission unit of the wireless power transmission system 100. However, the overall system efficiency η ALL If one wishes to achieve maximization of the power receiving antenna 104, the loss due to the power receiving antenna 104 cannot be ignored.

[0069] Overall system efficiency η of the wireless power transmission system 100 ALL Let us consider the relationship between r and α. Here, as a representative example of the power transmitting antenna 103 and the power receiving antenna 104, we assume a solenoid coil of the form shown in FIG. 13. Here, N is the number of turns of the solenoid coil. R is the radius of the solenoid coil. h is the height (thickness) of the solenoid coil. The number of turns N and radius r of the solenoid coil RIn order to calculate the equivalent series resistance and self-inductance for the change in , we introduce a commonly known representative analytical formula. The self-inductance of a solenoid coil is expressed by [Equation 14].

[0070]

number

[0071] Here, K N is the Nagaoka coefficient and μ0 is the magnetic permeability of a vacuum. N is expressed as [Equation 15].

[0072]

number

[0073] where k N is given by [Equation 16].

[0074]

number

[0075] Also, the function K(k N ) and function E(k N ) are k N are given by [Equation 17] and [Equation 18], respectively.

[0076]

number

[0077]

number

[0078] Next, we introduce an analytical formula for calculating the equivalent series resistance of a solenoid coil. It is known that as the frequency f of the current flowing through a solenoid coil increases, the equivalent series resistance increases due to the proximity effect between the conductors and the skin effect. The rate of increase in this equivalent series resistance is defined as F R , DC resistance of the solenoid coil is R wdc Then, the equivalent series resistance of the solenoid coil is given by [Equation 19].

[0079]

number

[0080] Equivalent series resistance increase rate F R Dowell's equation is used as the analytical formula to express the above. Dowell's equation is expressed as [Number 20].

[0081]

number

[0082] Here, N l is the number of laminations of the radial winding of the solenoid coil. A is given by [Equation 21].

[0083]

number

[0084] d is the diameter of the conductor. p is the adjacency coefficient of the conductor. δ w is the skin depth corresponding to the frequency f of the current flowing through the conductor, and is given by [Equation 22]. Note that the adjacent coefficient p of the conductor and the skin depth δ w The physical image of the above is shown in FIG.

[0085]

number

[0086] ρ wis the resistivity of the conductor. Let l be the winding length of the conductor. w Then, the DC resistance of the solenoid coil is R wdc is given by [equation 23].

[0087]

number

[0088] We will set specific values ​​for [Equation 14] to [Equation 23] and proceed with the discussion. The values ​​set for each variable are shown in Figure 15. Here, we set 50 mm as a practical antenna radius. We also set 0.5 MHz, 1.0 MHz, 2.5 MHz, and 6.78 MHz as the switching frequency f (= the frequency of the current flowing through the conductor).

[0089] Fig. 16(a) shows the self-inductance versus the number of turns N of the solenoid coil, calculated using [Equation 14]. Fig. 16(b) shows the equivalent series resistance versus the number of turns N of the solenoid coil, calculated using [Equation 19] with switching frequency f as a parameter.

[0090] The self-resonant frequency of the power transmitting antenna 103 and the power receiving antenna 104 of the wireless power transmission system 100 needs to be sufficiently higher than the switching frequency f. In this embodiment, the maximum switching frequency f is 6.78 MHz. As a condition for operating the wireless power transmission system 100 at a switching frequency f of 6.78 MHz, the lower limit of the self-resonant frequency of the power transmitting antenna 103 and the power receiving antenna 104 is defined as 10 MHz. If the parasitic capacitance that can actually occur in the solenoid coil is about 25 pF, the self-inductance of the solenoid coil that has a self-resonant frequency of 10 MHz can be calculated to be about 10 uH from [Mathematical Expression 24].

[0091]

number

[0092] From the results in Figure 16(a), we can see that the solenoid coil designed under the conditions in [Table 1] has an inductance of about 10 uH when it has about 7 turns. Therefore, in the following discussion, the upper limit Nmax of the number of turns is limited to 7 turns.

[0093] 17 is an analysis flowchart for determining the relationship between the overall system efficiency and α of the wireless power transmission system 100. The load 106 of the wireless power transmission system 100 is a 10 Ω resistor. The coupling coefficient between the power transmitting antenna 103 and the power receiving antenna 104 is 0.5.

[0094] Fig. 18(a) shows an example of an analysis performed by winding the power transmitting antenna 7 times and fixing the switching frequency f to 2.5 MHz according to the analysis flow in Fig. 17. In Fig. 18(a) and Fig. 18(b), the number of turns Nrx of the power receiving antenna 104 increases in the direction moving leftward in the figure.

[0095] From the result of FIG. 18(a), the power conversion efficiency η TX increases monotonically with the decrease of α. On the other hand, the power conversion efficiency η RX decreases monotonically with the decrease of α. ALL is the power conversion efficiency η of the power receiving device 108 RX and the power conversion efficiency η of the power transmitting device 107 TX Therefore, at a certain α, the overall system efficiency η of the wireless power transmission system 100 is expressed as ALL The total system efficiency η of the wireless power transmission system 100 is ALL is calculated using [Equation 3].

[0096] 19(a) shows the results of an analysis of the relationship between the overall system efficiency of the wireless power transmission system 100 and α when the switching frequency f is set to 0.5 MHz and the number of turns of the power transmitting antenna 103 and the power receiving antenna 104 is changed from 1 to 7 turns. ALL19B shows the overall system efficiency η ALL and the narrowness of the passband of the filter circuit 205, Q L From these results, the wireless power transmission system 100 with a switching frequency f of 0.5 MHz satisfies α<0.13(Q L <1.33), the overall system efficiency η ALL can be made the maximum.

[0097] FIG. 20(a) shows the overall system efficiency η of the wireless power transmission system 100 when the switching frequency f is set to 1.0 MHz and the number of turns of the power transmitting antenna 103 and the power receiving antenna 104 is changed from 1 to 7 turns. ALL 20(b) shows the result of analyzing the relationship between the total system efficiency η of the wireless power transmission system 100 under the above-mentioned conditions. ALL and the narrowness of the passband of the filter circuit 205, Q L From these results, the wireless power transmission system 100 with a switching frequency f of 1.0 MHz satisfies α<0.32(Q L <1.69), the overall system efficiency η ALL can be made the maximum.

[0098] 21(a) shows the results of an analysis of the relationship between the overall system efficiency of the wireless power transmission system 100 and α when the switching frequency f is set to 2.5 MHz and the number of turns of the power transmitting antenna 103 and the power receiving antenna 104 is changed from 1 to 7 turns. ALL 21(b) shows the overall system efficiency η ALL and the narrowness of the passband of the filter circuit 205, Q LFrom these results, the wireless power transmission system 100 with a switching frequency f of 2.5 MHz has a relationship of α<0.49(Q L <2.24), the overall system efficiency η ALL can be made the maximum.

[0099] FIG. 22(a) shows the overall system efficiency η of the wireless power transmission system 100 when the switching frequency f is set to 6.78 MHz and the number of turns of the power transmitting antenna 103 and the power receiving antenna 104 is changed from 1 to 7 turns. ALL The figure shows the result of analyzing the relationship between the overall system efficiency η ALL Similarly, FIG. 22(b) shows the overall system efficiency η ALL and the narrowness of the passband of the filter circuit 205, Q L From these results, the wireless power transmission system 100 with a switching frequency f of 6.78 MHz has a relationship of α<0.62(Q L <3.03), the overall system efficiency η ALL can be made the maximum.

[0100] 8 is a circuit diagram showing a configuration example of a wireless power transmission system 100 according to another embodiment. The wireless power transmission system 100 in FIG. 8 differs from the wireless power transmission system 100 in FIG. c Instead of the inductor L ca and L cb8 is provided with switch control signal sources 212a and 212b instead of the switch control signal source 212 compared to the wireless power transmission system 100 in FIG. 7. Moreover, the wireless power transmission system 100 in FIG. 8 is provided with switching elements 213a and 213b instead of the switching element 213 compared to the wireless power transmission system 100 in FIG. 7. Moreover, the wireless power transmission system 100 in FIG. 8 is provided with a capacitor C 1a and C 1b This embodiment is generally called a push-pull circuit configuration. The wireless power transmission system 100 in FIG. 8 is capable of outputting four times the power at the same DC input voltage and load as the wireless power transmission system 100 in FIG. 7. In addition, an effect of suppressing even-order harmonic distortion is also obtained. Below, the points where the wireless power transmission system 100 in FIG. 8 differs from the wireless power transmission system 100 in FIG. 7 will be described.

[0101] The negative terminal of the DC power supply 211 is connected to the reference potential node. The negative terminals of the switch control signal sources 212a and 212b are connected to the reference potential node. The switching elements 213a and 213b are, for example, FETs.

[0102] Inductor L ca is connected between the positive terminal of the DC power supply 211 and the drain terminal of the switching element 213a. The switch control signal source 212a is connected to the gate terminal of the switching element 213a and supplies a switch control signal (pulse signal) to the switching element 213a. The source terminal of the switching element 213a is connected to the reference potential node. The capacitor C 1a is connected between the drain terminal and the source terminal of the switching element 213a. A first terminal of the inductor L1 is DC connected to the drain terminal of the switching element 213a.

[0103] Inductor L cbis connected between the positive terminal of the DC power supply 211 and the drain terminal of the switching element 213b. The switch control signal source 212b is connected to the gate terminal of the switching element 213b and supplies a switch control signal (pulse signal) to the switching element 213b. The switch control signal supplied by the switch control signal source 212b is out of phase with the switch control signal supplied by the switch control signal source 212a. The source terminal of the switching element 213b is connected to the reference potential node. The capacitor C 1b is connected between the drain terminal and the source terminal of the switching element 213b. A second terminal of the inductor L1 is DC connected to the drain terminal of the switching element 213b.

[0104] The switching elements 213a and 123b are alternately turned on to convert DC power into AC power and supply the AC power to the inductor L1.

[0105] A drain terminal of the switching element 213a is DC connected to a first terminal of the inductor L1. A drain terminal of the switching element 213b is DC connected to a second terminal of the inductor L1. The size and cost of the wireless power transmission system 100 can be reduced by eliminating the capacitor C2 in FIG. 3.

[0106] 9 is a circuit diagram showing a configuration example of a wireless power transmission system 100 according to still another embodiment. The wireless power transmission system 100 in FIG. 9 differs from the wireless power transmission system 100 in FIG. 8 in that an inductor L ca The drain terminal of the switching element 213a is connected to the inductor L ca The DC power supply 211 and the inductor L cb is connected in series to the drain terminal of the switching element 213b. The wireless power transmission system 100 in Fig. 9 performs the same operation and provides the same effects as the wireless power transmission system 100 in Fig. 8.

[0107] 10 is a circuit diagram showing a configuration example of a wireless power transmission system 100 according to still another embodiment. The wireless power transmission system 100 in FIG. 10 differs from the wireless power transmission system 100 in FIG. 8 in that an inductor L ca ,L cb Instead of the inductor L c The following describes the differences between the wireless power transmission system 100 in Fig. 10 and the wireless power transmission system 100 in Fig. 8.

[0108] The inductor L1 has a first terminal, a center tap, and a second terminal. The first terminal of the inductor L1 is connected to the drain terminal of the switching element 213a. The second terminal of the inductor L1 is connected to the drain terminal of the switching element 213b. The center tap of the inductor L1 is connected to the positive terminal of the DC power supply 211 via the inductor Lc. c and a DC power supply 211 are connected in series to the center tap of the inductor L1. The negative terminal of the DC power supply 211 is connected to the reference potential node. The wireless power transmission system 100 in Fig. 10 performs the same operation and can obtain the same effects as the wireless power transmission system 100 in Fig. 8.

[0109] Inductor L used in the wireless power transmission system 100 shown in FIG. ca ,L cb are generally large components, and being able to unify them into one is extremely advantageous in terms of miniaturization.

[0110] The wireless power transmission system 100 described in this embodiment may be mounted on a non-contact part of a rotating movable part of a robot arm. The wireless power transmission system 100 described in this embodiment may be mounted on a non-contact part of a rotating movable part of a network camera. The wireless power transmission system 100 described in this embodiment may be mounted on a non-contact part of a translation part of an actuator. The wireless power transmission system 100 described in this embodiment may be mounted on a non-contact part of a reticle movable part of a semiconductor exposure apparatus. The wireless power transmission system 100 described in this embodiment may be mounted on a non-contact part between a vehicle device and a charging device. The wireless power transmission system 100 described in this embodiment may be mounted on a non-contact part between a drone and a ground power source.

[0111] It should be noted that the above-mentioned embodiments are merely examples of the implementation of the present invention, and the technical scope of the present invention should not be interpreted as being limited by these. In other words, the present invention can be implemented in various forms without departing from its technical concept or main features. [Explanation of symbols]

[0112] 100 wireless power transmission system, 107 power transmitting device, 108 power receiving device, 211 DC power source, 212 switch control signal source, 213 switching element

Claims

1. A power transmission device; A wireless power transmission system having a power receiving device, The power transmitting device is a first switching element having a first terminal and a second terminal; a first capacitor having a third terminal connected to the first terminal and a fourth terminal connected to the second terminal; a power transmitting inductor connected to the first switching element and configured to wirelessly transmit AC power; a second capacitor connected in series between the first switching element and the power transmitting inductor; The power receiving device includes a power receiving inductor configured to wirelessly receive AC power; a third capacitor connected in series with the receiving inductor; an AC / DC conversion circuit that converts the AC power received by the power receiving inductor into DC power; A wireless power transmission system, characterized in that an impedance Zc of the second capacitor at a switching frequency f of the first switching element is smaller than an impedance ZL of the power transmitting inductor at the switching frequency f.

2. 2. The wireless power transmission system of claim 1, wherein the ratio of Zc / ZL between the impedance Zc of the second capacitor at the switching frequency f and the impedance ZL of the power transmitting inductor at the switching frequency f is Zc / ZL<0.

62.

3. The wireless power transmission system according to claim 1 , wherein the third capacitor resonates with the power receiving inductor at the switching frequency f.

4. The wireless power transmission system according to claim 1 , wherein the power transmitting inductor and the second capacitor are directly connected to each other through a wiring pattern.

5. 2. The wireless power transmission system according to claim 1, wherein the AC / DC conversion circuit is a rectifier circuit.

6. 6. The wireless power transmission system according to claim 5, wherein the rectifier circuit is a full-wave rectifier circuit composed of four diodes.

7. 2. The wireless power transmission system according to claim 1, wherein the switching frequency f of the first switching element is equal to or higher than 0.5 MHz and equal to or lower than 6.78 MHz.

8. 2. The wireless power transmission system according to claim 1, wherein the wireless power transmission system is mounted on at least one of a rotating movable part of a robot arm, a network camera, a parallel moving part of an actuator, and a reticle movable part of a semiconductor exposure apparatus.

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