JP2014124020A - Wireless power transmission system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wireless power transmission system for performing power transmission in a non-contact manner between a power feeding side resonant circuit and power receiving side resonant circuit, where the system can perform efficient and stable power transmission while having a switching element which is freed from the fear of destruction even when using a bridge type high-frequency power supply as driving means for the system.SOLUTION: A wireless power transmission system 100 includes a full-bridge type circuit (high-frequency power supply 10) having an operation frequency f which satisfies an expression (1) X>0 and expression (2) δX/δf≥0; where δf is a variation in the operation frequency, X is an imaginary part of impedance of a wireless power transmission network 80 configured by a circuit including a power feeding side resonant circuit 40, a power reception side resonant circuit 50, and a load circuit 60 to which power is supplied by the power reception side resonant circuit 50 as seeing the power feeding side resonant circuit 40 from the full-bridge type circuit, and δX is a variation in the imaginary part to the operation frequency.

Description

  The present invention relates to a wireless power transmission system.

  Portable devices such as smartphones and notebook personal computers have built-in power supplies such as lithium-ion secondary batteries, so you can take them anywhere, indoors or outdoors. Since it can be used, it is extremely convenient. On the other hand, when the battery is exhausted, charging or the like is required, and performing charging using a cable or the like is a factor that hinders the convenience of these devices. Therefore, development of a wireless power transmission system capable of supplying power to these portable devices in a contactless manner is active. As this type, a part using an electromagnetic induction method has been put into practical use.

  On the other hand, in recent years, a magnetic field resonance type wireless power transmission system using a resonance phenomenon of a magnetic field formed by a resonance coil has been proposed. Compared to the electromagnetic induction method described above, this method can transmit large amounts of power between power receiving and receiving devices that are relatively distant from each other, so that it can be used in a wide range of applications, such as studies aimed at applying power to electric vehicles. Consideration is being made.

  In the electromagnetic induction type or magnetic field resonance type wireless power transmission system described above, the power supply side resonance means (power supply side resonance circuit) and the power reception side resonance means (power reception side resonance circuit) have substantially the same resonance frequency. By setting to, wireless power transmission with high efficiency is made possible.

However, in the wireless power transmission system in which the power supply side resonance circuit and the power reception side resonance circuit are electromagnetically coupled by, for example, the principle of electromagnetic induction or the principle of magnetic field resonance to constitute one resonance system as a whole, the power supply side resonance circuit and It is known that the resonance frequency of the transmission system changes depending on the distance and relative position between the power receiving side resonance circuit (the power feeding coil and the power receiving coil). Therefore, in the wireless power transmission system, it is necessary to set the drive frequency (operating frequency) of the system, that is, the frequency of the power supply side power supply so as to match the resonance frequency of the wireless power transmission system.

  In such a wireless power transmission system, a technique disclosed in Patent Document 1 is known as a method for setting the drive frequency. That is, the power supply side resonance means and the power reception side resonance means are coupled by magnetic field resonance, and the frequency dependence of the impedance viewed from the power supply side is detected, and the frequency at which the absolute value of the detected impedance is minimized or the phase of the impedance is The drive frequency of the system is set to a frequency that becomes zero. By setting the drive frequency in this way, it is said that high transmission efficiency can be maintained as a wireless power transmission system.

JP 2010-233442 A

  As a power source for driving the wireless power transmission system, for example, a full bridge type circuit using four switching elements is known. A full-bridge circuit converts DC power into high-frequency power that substantially matches the resonance frequency of the system. This full-bridge circuit is considered to be particularly useful for applications requiring high power. A normal full-bridge circuit is considered to generate a switching loss when the switching element is turned ON / OFF, but this switching loss can be suppressed by using a so-called phase shift method.

  By the way, in a wireless power transmission system including a power supply side resonance circuit and a power reception side resonance circuit, if the wireless power transmission system is driven by a high-frequency power source using a bridge circuit composed of a plurality of switching elements, the switching elements may be damaged. It has been found by experiments by the present inventors. In particular, the frequency at which the absolute value of the impedance when the resonance system is viewed from the high frequency power supply side is the minimum, or the frequency at which the phase of the impedance is zero, that is, the power supply side resonance circuit and the power reception side resonance circuit are electromagnetically coupled. It was found that when the wireless power transmission system is driven at the resonance frequency, the switching element in the high frequency power source is damaged. This phenomenon becomes prominent when the power supply voltage is increased to perform high power transmission, and when the bridge-type high-frequency power supply circuit is a full-bridge type and is operated in a phase shift system.

  Therefore, an object of the present invention is to perform switching even when a bridge type high frequency power supply is used as a driving means in a wireless power transmission system that performs power transmission in a contactless manner between a power supply side resonance circuit and a power reception side resonance circuit. It is an object of the present invention to provide a wireless power transmission system capable of high-efficiency and stable power transmission without causing damage to elements.

  As a result of various examinations by experiments in order to solve the above problem, in a high frequency power supply of a full bridge type circuit, a pulse is applied to the gate electrode of the switching element in the OFF state of two switching elements having a serial connection configuration. As a result, it was inferred that the two switching elements in the series connection configuration are both turned on, and a large current flows through the switching elements, leading to destruction. In particular, when the power supply side resonance circuit is viewed from a full-bridge circuit, the impedance of the circuit network including the power supply side resonance circuit, the power reception side resonance circuit, and the load circuit that is supplied with power from the power reception side resonance circuit It has been found that when the imaginary part (reactance) becomes capacitive (capacitive reactance), pulse-like noise frequently occurs on the gate electrode of the switching element. Conventionally, high-efficiency wireless power transmission is achieved by driving a wireless power transmission system at a frequency where the absolute value of the impedance when the resonance frequency, that is, the coupled resonance system is viewed, or the phase of the impedance is zero. It was supposed to be possible. However, the resonance frequency, that is, the frequency at which the impedance phase is close to zero is also a region where the reactance can suddenly become capacitive reactance, and this is considered to have caused the sudden breakage of the switching element.

The present invention has been made on the basis of the above-described experimental study, and is a full-bridge circuit having a plurality of switching elements, a power supply side resonance circuit including a power supply coil and a power supply side capacitor, a power reception coil, and a power reception side capacitor. In a wireless power transmission system comprising: a power-receiving-side resonance circuit comprising: a full-bridge circuit operating frequency f; a change in operating frequency δf; X is the imaginary part of the impedance of the wireless power transmission network composed of the side resonance circuit, the power reception side resonance circuit, and the circuit having the load circuit to which power is supplied from the power reception side resonance circuit, and δX Then, the operating frequency f satisfies the following formulas (1) and (2).
X> 0 Formula (1)
δX / δf ≧ 0 Formula (2)
By doing this, no pulse noise is added to the gate electrode of the switching element included in the full-bridge circuit, so there is no risk of damage to the switching element, and the wireless power transmission system is highly efficient and stable. It can be operated.

  Preferably, the full bridge circuit is driven by a phase shift method. Even with such a configuration of the high-frequency power supply, it is possible to avoid that switching elements connected in series are both turned on due to pulsed noise, so there is no risk of damage to the switching elements, and the wireless power transmission system is highly efficient. It can be operated stably.

  According to the present invention, in a wireless power transmission system that performs non-contact power transmission between a power supply side resonance circuit and a power reception side resonance circuit, even when a bridge type high frequency power source is used as the driving means, It is possible to provide a wireless power transmission system that is capable of high-efficiency and stable power transmission without fear of breakage.

1 is a diagram illustrating a wireless power transmission system according to a first embodiment of the present invention. It is a graph which shows the imaginary part of the impedance of the wireless power transmission network in 1st Embodiment, and power transmission efficiency. It is a figure which shows the wireless power transmission system by the 2nd Embodiment of this invention. It is a graph which shows the imaginary part of the impedance and power transmission efficiency of the wireless power transmission network in 2nd Embodiment. It is a figure which shows the bridge type circuit used as a high frequency power supply.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.

  First, a high-frequency power source 10 composed of a full-bridge circuit used in the embodiment of the present invention described below will be described with reference to FIG. In FIG. 5, the high frequency power supply 10 includes four switching elements Q1 to Q4. A DC voltage is applied to the circuit from the DC power supply 20, and the control circuit 30 controls ON / OFF of the switching elements Q1 to Q4. Thus, high frequency power is output from the output end. As the switching elements Q1 to Q4, MOSFET semiconductor switches can be used, and ON / OFF can be controlled by applying a voltage from the control circuit to the gate electrode (indicated by G in the figure) of the MOSFET. In FIG. 5, Q1 = Q4 = ON, Q2 = Q3 = OFF (first period), Q1 = Q2 = Q3 = Q4 = OFF (second period), Q2 = Q3 = ON, Q1 = Q4 = OFF (third Period), Q1 = Q2 = Q3 = Q4 = OFF (fourth period), and by repeating this cycle, high frequency power having a frequency corresponding to the cycle period can be output. In the phase shift method, Q1 and Q4 are not turned on at the same time at the start point of the cycle, and the time when Q4 is turned on is delayed from Q1 by a certain width (phase). In such an operation method, the period during which all of the four switching elements Q1 to Q4 are OFF is shortened.

  In FIG. 5, when looking at the part where Q1 and Q2 are connected in series, when Q1 is ON, Q2 is OFF, so that the current supplied from the DC power supply 20 is directed to the load connected to the output terminal. And flow. Here, if pulse-like noise is applied to the gate electrode of Q2 which is OFF, both Q1 and Q2 are turned on. A circuit in which Q1 and Q2 are connected in series is short-circuited. Therefore, a large current flows here, resulting in damage to the MOSFET element. The generation of the pulse noise depends on the impedance of the load connected to the output of the high frequency power supply 10, more specifically, the phase of the impedance.

[First Embodiment]
FIG. 1 is a diagram illustrating a wireless power transmission system 100 according to a first embodiment of the present invention. As shown in FIG. 1, the wireless power transmission system 100 according to the present embodiment is connected to the high-frequency power source 10, the DC power source 20, the control circuit 30 for the high-frequency power source, and the feeding coil L2 described in FIG. The power supply side resonance circuit 40 is composed of the capacitor C2, the power reception coil L3, and the power reception side resonance circuit 50 and the load circuit 60 are composed of the capacitor C3 connected in series therewith. The power supply coil L2 of the power supply side resonance circuit 40 and the power reception coil L3 of the power reception side resonance circuit 50 are electromagnetically coupled, and wireless power transmission is performed from the power supply coil L2 to the power reception coil L3. In the present embodiment, the reactor 70 is disposed between the output end of the high-frequency power supply 10 and the power supply side resonance circuit 40. However, even if this reactor is not provided, it can be operated as a wireless power transmission system. The power supply side resonance circuit 40, the power reception side resonance circuit 50, and the load circuit 60 including the reactor 70 are referred to as a wireless power transmission network 80. The wireless power transmission network 80 is a circuit connected to the output terminal of the high frequency power supply 10 including the case where the reactor 70 is not used.

FIG. 2 shows the imaginary part of the impedance Z (= R + jX) of the wireless power transmission network 80 as viewed from the output terminal of the high-frequency power supply 10, that is, the frequency characteristic (solid line) of reactance, and the power transmission efficiency at this time depends on the operating frequency. It is the graph which showed the property (broken line). Here, R represents the actual resistance of the wireless power transmission network 80, and X represents the imaginary part, that is, the reactance. J is an imaginary unit. Based on the frequency characteristic of the reactance, the operating frequency of the wireless power transmission system 100 is examined by dividing it into four regions. Region 1 is a frequency range in which the reactance is from the capacitive reactance to the resonance frequency, region 2 is an inductive reactance, and its slope (frequency differentiation) is zero or more, and region 3 is the reactance. Is an inductive reactance frequency range in which the slope is negative, and region 4 is a frequency range in which the reactance is inductive reactance as in region 2 and at the same time the slope is greater than or equal to zero. . In each of the above four areas, if wireless power transmission is performed with the operating frequency (driving frequency) within the range of each area, the switching elements in the areas 1 and 3 may be damaged during long-time operation. However, in the region 2 and the region 3, the switching element is not damaged even when operated for a long time, and stable wireless power transmission can be performed. That is, the operating frequency of the high-frequency power supply 10 is f, the change in the operating frequency is δf, the imaginary part (reactance) of the impedance of the wireless power transmission network 80 viewed from the output end of the high-frequency power supply 10 is X, and the imaginary part (reactance) Assuming that the change with respect to the operating frequency is δX, if the operating frequency f satisfies the following formulas (1) and (2), the switching element is not damaged, and stable wireless power transmission can be performed.
X> 0 Formula (1)
δX / δf ≧ 0 Formula (2)
From the viewpoint of power transmission efficiency, as apparent from FIG. 2, the operation in the region 2 is preferable to the region 4.

[Second Embodiment]
FIG. 3 is a diagram illustrating a wireless power transmission system 200 according to a second embodiment of the present invention. As shown in FIG. 3, the wireless power transmission system 200 according to the present embodiment is connected in series with the high-frequency power source 10, the DC power source 20, the control circuit 30 for the high-frequency power source described above with reference to FIG. The power supply side resonance circuit 40 including the capacitor C2 and the coil L1 electromagnetically coupled to the power supply coil L2 to supply power to the power supply side resonance circuit 40, the power reception coil L3 and the power reception side resonance including the capacitor C3 connected in series thereto. A circuit 50, a coil L4 that electromagnetically couples with the power receiving coil L3, and extracts power from the power receiving resonance circuit, and a load circuit 60. The power supply coil L2 of the power supply side resonance circuit 40 and the power reception coil L3 of the power reception side resonance circuit 50 are electromagnetically coupled, and wireless power transmission is performed from the power supply coil L2 to the power reception coil L3. In the present embodiment, L1, the power supply side resonance circuit 40, the power reception side resonance circuits 50 and L4, and the load circuit 60 are collectively referred to as a wireless power transmission network 90. That is, the circuit connected to the output terminal of the high frequency power supply 10 is the wireless power transmission network 90.

FIG. 4 shows the imaginary part of the impedance Z (= R + jX) of the wireless power transmission network 90 as seen from the output terminal of the high-frequency power supply 10, that is, the frequency characteristic (solid line) of reactance, and the power transmission efficiency at this time depends on the operating frequency. It is the graph which showed the property (broken line). Here, R represents the actual resistance of the wireless power transmission network 90, and X represents the imaginary part, that is, the reactance. J is an imaginary unit. Based on the frequency characteristic of the reactance, the operating frequency of the wireless power transmission system 200 is examined by dividing it into six regions. Region 1 is a frequency range in which the reactance is inductive reactance and the slope is zero or more, and region 2 is a frequency range in which the reactance is inductive reactance but the slope is negative. Region 3 is a frequency range in which the reactance sandwiched between the two resonance points is a capacitive reactance, and region 4 is a frequency range in which the reactance is an inductive reactance and the slope thereof is zero or more. Yes, region 5 is a frequency region in which the reactance is inductive reactance but its slope is negative, and region 6 is a frequency range in which the reactance is inductive reactance and the slope is zero or more. It is. In each of the above six areas, when wireless power transmission is performed with the operating frequency (driving frequency) within the range of each area, the switching elements in the areas 2, 3, and 5 are damaged during long-time operation. However, in the regions 1, 4 and 6, the switching element is not damaged even during long-time operation, and stable wireless power transmission can be performed. That is, the operating frequency of the high-frequency power supply 10 is f, the change in the operating frequency is δf, the imaginary part (reactance) of the impedance of the wireless power transmission network 90 viewed from the output end of the high-frequency power supply 10 is X, and the imaginary part (reactance) Assuming that the change with respect to the operating frequency is δX, if the operating frequency f satisfies the following formulas (1) and (2), the switching element is not damaged, and stable wireless power transmission can be performed.
X> 0 Formula (1)
δX / δf ≧ 0 Formula (2)
From the viewpoint of power transmission efficiency, as is apparent from FIG. 4, the operation in the region 4 is preferable to the regions 1 and 6.

  The present invention has been described based on the embodiments. It will be understood by those skilled in the art that the embodiments are illustrative, and that various modifications and changes are possible within the scope of the claims of the present invention, and that such modifications and changes are also within the scope of the claims of the present invention. By the way. Accordingly, the description and drawings herein are to be regarded as illustrative rather than restrictive.

  For example, any method can be applied as power transmission means from the power feeding coil to the power receiving coil. In other words, the power feeding coil may transmit power by electromagnetic induction, and the power receiving coil may receive power from the power feeding coil by electromagnetic induction. Alternatively, a method may be employed in which the power feeding coil transmits power by magnetic field resonance and the power receiving coil receives power from the power feeding coil by magnetic field resonance.

  According to the wireless power transmission system of the present invention, not only wireless charging of a portable terminal or the like but also wireless charging of an electric vehicle or the like that requires high voltage and large capacity can be stably performed.

DESCRIPTION OF SYMBOLS 10 High frequency power supply 20 DC power supply 30 Control circuit 40 Power supply side resonance circuit 50 Power reception side resonance circuit 60 Load circuit 70 Reactor 80, 90 Wireless power transmission network 100, 200 Wireless power transmission system

Claims (2)

A full-bridge circuit having a plurality of switching elements;
A power supply side resonance circuit comprising a power supply coil and a power supply side capacitor;
In a wireless power transmission system including a power receiving coil and a power receiving side resonance circuit including a power receiving side capacitor,
When the operating frequency of the full-bridge circuit is f, the change of the operating frequency is δf, and the power-feeding-side resonance circuit is viewed from the full-bridge circuit, the power-feeding-side resonance circuit, the power-receiving-side resonance circuit, and the When the imaginary part of the impedance of the wireless power transmission network composed of a circuit having a load circuit to which power is supplied from the power-receiving-side resonance circuit is X, and the change of the imaginary part with respect to the operating frequency is δX,
The operating frequency f is a wireless power transmission system that satisfies the following equations (1) and (2).
X> 0 Formula (1)
δX / δf ≧ 0 Formula (2)   The wireless power transmission system according to claim 1, wherein the full bridge circuit is driven by a phase shift method.

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