JP2015035868A - Non-contact power transmission device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To resolve a problem that, in a non-contact power transmission device, in a case where a power transmission part of the non-contact power transmission device supplies an AC power to a power transmission resonator by using a circuit consisting of a semiconductor switching element, when a power transmission frequency of a high-frequency power that the power transmission part transmits to the power transmission resonator is accorded to a resonance frequency of the power transmission resonator, a power loss at the switching element of the power transmission part becomes large.SOLUTION: A power transmission frequency of a power transmission part of a non-contact power transmission device is set to be higher than such a frequency that resonance of a power transmission resonator becomes maximum. Due to this configuration, a power loss at a switching element of the power transmission part can be reduced while keeping a resonance state of the power transmission resonance circuit high. Thus, a non-contact power transmission device that can transmit a power with a small temperature rise at the switching element and with a high efficiency can be provided.

Description

  The present invention relates to a non-contact power transmission device that performs non-contact (wireless) power transmission via a power transmission coil provided in a power transmission device and a power reception coil provided in the power reception device.

  As a method of transmitting power in a non-contact manner, an electromagnetic induction type by electromagnetic induction (several hundreds of kHz), an electric field / magnetic field resonance type by transmission between LC resonances via electric field or magnetic field resonance, a microwave power transmission type by radio waves (several GHz), Alternatively, a laser power transmission type using electromagnetic waves (light) in the visible light region is known. Among them, the electromagnetic induction type has already been put into practical use. This has the advantage that it can be realized with a simple circuit (transformer system), but there is also a problem that the transmission distance is short.

  Therefore, recently, electric field / magnetic field resonance type power transmission capable of short-distance transmission (up to 2 m) has attracted attention. Among these, in the case of the electric field resonance type, when a hand or the like is put in the transmission path, the human body is a dielectric, so that energy is absorbed as heat and dielectric loss occurs. On the other hand, in the case of the magnetic resonance type, the human body hardly absorbs energy, and dielectric loss can be avoided. From this point of view, attention to the magnetic resonance type has been increasing.

  Generally, the magnetic field resonance type includes a power transmission device and a power reception device, and the power transmission device includes a power transmission resonator including at least a power transmission coil and a resonance capacitor, and a power transmission unit that supplies power to the power transmission resonator. On the other hand, the power receiving device includes a power receiving resonator including at least a power receiving coil and a resonant capacitor. Patent Document 1 discloses that when the power transmission resonator of the power transmission device and the power reception resonator of the power reception device resonate at the drive frequency of the power transmission unit of the power transmission device, power can be transmitted from the power transmission device to the power reception device with high efficiency. ing.

JP 2010-130878 A

  The power transmission unit of the power transmission device supplies relatively large AC power to the power transmission resonator. Therefore, a power circuit using a semiconductor switching element is often used for the power transmission unit. However, when a semiconductor switching element is used for the power transmission unit, if the resonance frequency of the power transmission resonator matches the power transmission frequency of the AC power supplied to the power transmission resonator as in the past, the power in the semiconductor switching element is It was found that the loss increased, resulting in a decrease in transmission efficiency. The details are described below.

  FIG. 2 shows a general half-bridge circuit using two semiconductor switching elements. By alternately conducting the upper and lower switching elements 21 and 22 to generate an AC voltage V0, an AC current I0 can be passed through the coil 23.

  10 to 12 show an operation when the half-bridge circuit of FIG. 2 is used as a power transmission unit of a power transmission device and a power transmission resonator including a power transmission coil and a resonance capacitor is connected as a load. When the transmission frequency equal to the switching frequency of the half-bridge circuit is Fsw and the resonance frequency of the transmission resonator is Fres, FIG. 10 shows Fsw = Fres, FIG. 11 shows Fsw <Fres, and FIG. 12 shows Fsw> Fres. Show the case.

  10 to 12, (1) is a steady state in which the switching element 21 is on and the switching element 22 is off, and (2) is a state in which the switching element 21 is switched from on to off and the switching element 22 is switched from off to on. The transient state immediately before, (3) is the transient state immediately after the switching element 21 is switched from on to off and the switching element 22 is switched from off to on, and (4) is the switching element 21 is off and the switching element 22 is switched off. Indicates a steady state of ON.

  In the case of resonance at Fsw = Fres shown in FIG. 10, the current I0 and the voltage V0 are in phase. In this case, the operation of the circuit is as follows.

  In the steady state of FIG. 10 (1), a large current I 0 flows from the power source to the coil 23 through the switching element 21. At this time, I0> 0.

  In the transient state of FIG. 10 (2), I0 becomes smaller with I0> 0 and resonates with Fsw = Fres, so that the switching element 21 is switched from on to off and the switching element 22 is switched from off to on. In this case, I0 = 0.

  In the transient state of FIG. 10 (3), a small current I 0 flows from the power source to the coil 23 through the switching element 22. At this time, I0 <0.

  In the steady state of FIG. 10 (4), a large current I 0 flows from the power source to the coil 23 through the switching element 22. At this time, I0 <0.

  Therefore, when Fsw = Fres, the power loss due to the switching element does not matter and can be said to be an ideal state.

  In the case of resonance at Fsw <Fres shown in FIG. 11, the phase of the current I0 advances with respect to the phase of the voltage V0. In this case, the operation of the circuit is as follows.

  In the steady state of FIG. 11 (1), a large current I 0 flows from the power source to the coil 23 through the switching element 21. At this time, I0> 0.

  In the transient state of FIG. 11 (2), the phase of the current I0 is advanced with respect to the phase of the voltage V0, so that the current I0 flows from the coil 23 to the power supply through the parasitic diode of the switching element 21. Therefore, V0> power supply voltage, and the potential of V0 increases. At this time, I0 <0.

  In the transient state of FIG. 11 (3), since the switching element 21 is switched from on to off and immediately after the switching element 22 is switched from off to on, the current I0 flows from the coil 23 to the ground through the switching element 22. At this time, V0 rapidly changes from a state higher than the power supply voltage to the ground, and a large current flows through the switching element 22. Therefore, the switching element 22 generates heat, and power loss occurs in the switching element 22. At this time, I0 <0.

  In the steady state of FIG. 11 (4), a large current I 0 flows from the power source to the coil 23 through the switching element 22. At this time, I0 <0.

  Therefore, in the case of Fsw <Fres, power loss at the time of switching by the switching element becomes large, which becomes a problem.

  In the case of resonance at Fsw> Fres shown in FIG. 12, the phase of the current I0 is delayed with respect to the phase of the voltage V0. In this case, the operation of the circuit is as follows.

  In the steady state of FIG. 12 (1), a large current I 0 flows from the power source to the coil 23 through the switching element 21. At this time, I0> 0.

  In the transient state of FIG. 12 (2), a current I 0 flows from the power source to the coil 23 through the switching element 21. At this time, I0> 0.

  In the transient state of FIG. 12 (3), since the switching element 21 is switched from on to off and immediately after the switching element 22 is switched from off to on, the current I0 flows to the coil 23 through the parasitic diode of the switching element 22. . At this time, I0> 0.

  In the steady state of FIG. 12 (4), the current changes from I0> 0 to I0 = 0, and then the direction of the current is opposite to I0 <0. The current I0 flows from the coil 23 to the ground through the switching element 22.

  In the case of Fsw> Fres, unlike the case of Fsw <Fres, a rapid change in the voltage in the switching element 21 and the switching element 22 does not occur. As a result, unlike the case of Fsw <Fres, a large current does not flow through the switching elements 21 and 22, so that the power loss is small.

  By the way, as shown in Patent Document 1, it has been conventionally preferable to set Fsw = Fres in order to realize high-efficiency power transmission. That is, it has been preferable to operate as shown in FIG.

  However, even if the operation in the actual circuit is designed so that, for example, Fsw = Fres, due to disturbance factors such as environmental temperature change, aging of parts, and the proximity of an object near the power transmission circuit and power reception circuit, There are cases where the condition of Fsw = Fres is not satisfied. In particular, when Fsw <Fres as shown in FIG. 11 due to the disturbance factor, a large power loss occurs in the switching element, and there is a problem that highly efficient non-contact power transmission cannot be realized.

  In order to solve the above problems, a contactless power transmission device according to the present invention includes a power transmission resonance of a power transmission device of a contactless power transmission device having a power transmission unit and a power transmission resonator, and the power transmission unit includes a semiconductor switching element. In the case where AC power is supplied to the device, the power transmission frequency of the power transmission unit is set to a frequency higher than the frequency at which resonance is maximized.

  According to the present invention, it is possible to reduce the power loss in the switching element of the power transmission unit while keeping the resonance state of the power transmission resonance circuit in a high state. A possible contactless power transmission device can be provided.

The block diagram which shows the structure of the non-contact electric power transmission apparatus in Embodiment 1. The circuit diagram which shows the outline of the power transmission part in Embodiment 1 The flowchart which shows operation | movement of the power transmission control part in Embodiment 1. Table for obtaining a desired power transmission frequency from the frequency that maximizes the voltage of the power transmission coil in the first embodiment The figure which shows the relationship between the voltage of the power transmission coil in Embodiment 1, and power transmission frequency The figure which shows the effect of this invention in Embodiment 1 The flowchart which shows operation | movement of the power transmission control part in Embodiment 2. The figure which shows the relationship between the voltage of the power transmission coil in Embodiment 2, and power transmission frequency The flowchart which shows operation | movement of the power transmission control part in Embodiment 3. The figure explaining operation of a switching circuit Another figure explaining operation of switching circuit Yet another diagram illustrating the operation of the switching circuit

  FIG. 1 shows a configuration of a non-contact power transmission apparatus according to the present invention. The non-contact power transmission device includes a power transmission device 1 and a power reception device 2. The power transmission device 1 includes a power transmission coil 4 for non-contact transmission of high-frequency power. The power receiving device 2 includes a power receiving coil 8 for receiving high-frequency power supplied from the power transmitting coil 4. The non-contact power transmission apparatus having the configuration shown in FIG. 1 can be configured to transmit power from the power transmission apparatus 1 to the power reception apparatus 2 via magnetic field resonance between the power transmission coil 4 and the power reception coil 8, for example. Note that the coupling form of the power transmission coil 4 and the power reception coil 8 can be appropriately adopted such as electromagnetic induction, radio wave, electric field or magnetic field sharing.

  In the power transmission device 1, the power transmission coil 4 and the resonance capacitor 5 constitute a power transmission resonator, and the power transmission unit 3 supplies high-frequency power to the power transmission resonator.

  The power transmission unit 3 of the power transmission device 1 supplies relatively large AC power to the power transmission resonator. Therefore, a power circuit using a semiconductor switching element is used for the power transmission unit 3. As the power circuit, a half bridge circuit or a full bridge circuit is widely used. FIG. 2 shows a half-bridge circuit using two FETs as switching elements. Below, the case where the half bridge circuit shown in FIG. 2 comprises the power transmission part 3 is demonstrated. The power transmission unit 3 may be configured by a full bridge circuit using four FETs as switching elements.

  By the way, in order to realize high-efficiency power transmission, the resonance frequency Fres of the power transmission resonator by the power transmission coil 4 and the resonance capacitor 5 and the power transmission frequency Fsw of the high-frequency power supplied to the power transmission resonator by the power transmission unit 3 are approximately the same. It has been preferred to do so.

  However, even if the operation in the actual circuit is designed so that, for example, Fsw = Fres, due to disturbance factors such as environmental temperature change, aging of parts, and the proximity of an object near the power transmission circuit and power reception circuit, The condition of Fsw = Fres may not be satisfied. In particular, when a power circuit using a semiconductor switching element is used for the power transmission unit 3, if Fsw <Fres as shown in FIG. 10 due to the disturbance factor, a large power loss occurs in the switching element, There is a problem that efficient non-contact power transmission cannot be realized.

  Therefore, the power transmission control unit 7 of the present invention optimizes the resonance state of the power transmission resonator so that Fsw> Fres, assuming that the above-described disturbance occurs. Then, even if a disturbance occurs, Fsw <Fres is not satisfied, and a large power loss does not occur in the switching element.

  When the resonance state of the power transmission resonator is optimal, the voltage across the power transmission coil 4 is maximized. Therefore, the resonance state of the power transmission resonator can be detected by measuring the voltage across the power transmission coil 4. The power transmission coil voltage detection unit 6 measures the voltage across the power transmission coil 4, and the power transmission control unit 7 controls the power transmission unit 3 based on the resonance state information detected by the power transmission coil voltage detection unit 6. This resonance state control is a feature of the present invention and will be described in detail later. In addition, although it is preferable to comprise the power transmission control part 7 with a microcomputer, it can also be comprised by FPGA and an electronic circuit.

  The power receiving device 2 includes a power receiving coil 8 that receives power transmitted from the power transmitting coil 4 of the power transmitting device 1. A power converter 10 is connected to a power receiving resonator constituted by the power receiving coil 8 and the resonance capacitor 9. The power conversion unit 10 detects and smoothes the high-frequency power received by the power receiving coil 8, converts it to a required power format, and outputs it from the power output terminal 11.

  The above is the outline of the power transmission operation in the non-contact power transmission apparatus of the present invention.

The present invention is characterized by controlling the resonance state in the power transmission device 1 of the non-contact power transmission device. Hereinafter, the control of the resonance state will be described in detail for each embodiment.
<Embodiment 1>
The power transmission control unit 7 controls the transmission frequency of the high frequency power output from the power transmission unit 3. In the present invention, since a half bridge circuit is used for the power transmission unit 3, the switching frequency Fsw of the half bridge circuit is set so that the power transmission resonator is in an optimal resonance state.

  In order to find the optimum switching frequency Fsw, the value of Fsw is changed from the initial start frequency to a predetermined end frequency. While changing the value of Fsw, the power transmission coil voltage is detected, and the power transmission frequency at which the power transmission side resonance frequency becomes maximum is set as Fsw.

  FIG. 3 shows a flowchart of resonance state control in Embodiment 1 of the present invention.

  When the power transmission device 1 starts operating, the power transmission control unit 7 sets the transmission frequency of the high-frequency power output from the power transmission unit 3. The initial value of the power transmission frequency is set to a predetermined start frequency, and the value is substituted into the variable fmax, and 0 is substituted into the variable Vmax that stores the maximum value of the power transmission coil voltage (step S101).

  Power transmission is started with this power transmission frequency being the start frequency (step S102).

  The power transmission coil voltage detection part 6 measures the both-ends voltage of the power transmission coil 4 (step S103).

  The measured both-end voltage of the power transmission coil 4 and the value of the variable Vmax are compared. When the measured both-end voltage of the power transmission coil 4 is smaller than Vmax, the process proceeds to step S106, and otherwise, the process proceeds to step S105 (step S104). .

  When the measured voltage across power transmission coil 4 is equal to or higher than Vmax, the measured value is substituted into variable Vmax, and the power transmission frequency at this time is substituted into variable fmax (step S105).

  In step S106, the power transmission frequency is decreased. The amount of decrease in the transmission frequency may be determined appropriately by the system.

  When the power transmission frequency is equal to or higher than the predetermined end frequency, the process returns to step S103 and the same operation is repeated. On the other hand, when the power transmission frequency becomes lower than the end frequency, the process proceeds to step S108 (step S107).

  Through the above steps, the maximum value Vmax of the voltage across the power transmission coil 4 and the resonant power transmission frequency fmax that maximizes the voltage across the power transmission coil 4 can be detected.

  The present invention is characterized in that, when a semiconductor switching element is used for the power transmission unit, Fsw> Fres when the switching frequency is Fsw and the resonance frequency of the power transmission resonator is Fres. In step S108, the optimum power transmission frequency fsend is obtained from the resonance power transmission frequency fmax.

  FIG. 4 is a table showing a relationship in which the relationship between the resonant power transmission frequency fmax and the optimum power transmission frequency fsend is determined in advance. The fsend can be determined based on the table of FIG. 4 and the obtained fmax.

  FIG. 5 is a graph showing the measurement results of the transmission frequency and the voltage across the transmission coil 4. The inductance of the power transmission coil 4 is 425 μH, and the capacitance of the resonance capacitor 5 is 4950 pF. When these values of the power transmission coil and the resonant capacitor are connected in series, the calculated resonant frequency is about 110 kHz. However, the determined fmax was 105 kHz. The difference from the calculated value is due to the positional relationship between the power transmission device 1 and the power reception device 2, the surrounding environment of the power transmission device 1 and the power reception device 2, and other influences.

  Based on the table of FIG. 4, since fmax was 105 kHz, fsend was set to 107 kHz (step S108).

  Next, the power transmission frequency control unit 7 sets the desired power transmission frequency fsend obtained for the power transmission unit 3 as the power transmission frequency Fsw (step S109). Since the resonance frequency Fres of the power transmission resonator is fmax, the relationship of Fsw> Fres is satisfied.

FIG. 6 shows the switching of the power transmission unit 3 when contactless power transmission is performed with the transmission frequency Fsw set to fmax (105 kHz) and when contactless power transmission is performed with Fsw set to fsend (107 kHz). It is the graph which showed the time change of the temperature of FET which is an element. Compared to when Fsw = fmax (105 kHz), when Fsw = fsend (107 kHz), the power loss in the FET is suppressed, so that the temperature rise in the FET is suppressed.
<Embodiment 2>
In the power transmission device 1 of the present invention, the power transmission coil 4 and the resonance capacitor 5 constitute a power transmission resonator. This power transmission resonator is a so-called series resonance circuit in which the power transmission coil 4 and the resonance capacitor 5 are connected in series. Here, assuming that the power transmission coil 4 and the resonance capacitor 5 are an ideal coil and an ideal capacitor having no resistance component, when the power transmission resonator as the series resonance circuit resonates, the power transmission coil 4 and the resonance capacitance The voltage applied to 5 becomes infinite. Actually, the power transmission coil 4 and the resonance capacitor 5 also have a resistance component, and there is also a resistance component of the circuit itself due to the resistance of the lead wire, so that the voltage applied to the power transmission coil 4 and the resonance capacitor 5 is infinite. There is no going up. However, when the power transmission resonator resonates, a very high voltage is applied. In particular, when the breakdown voltage of the capacitor having the resonance capacitance 5 is exceeded, the capacitor is broken. Therefore, it is possible to prevent the components from being destroyed by operating the power transmission resonator in a range exceeding the upper limit voltage of the capacitor or the upper limit voltage of the coil.

  FIG. 7 shows a flowchart of resonance state control in the second embodiment of the present invention. As shown in FIG. 8, when the voltage upper limit value of the power transmission coil 4 is Vlimit, the measured voltage of the power transmission coil 4 is compared with Vlimit according to the flowchart of FIG. Advances to step S104 (step S204). Since other steps are the same as those in the first embodiment, detailed description thereof will be omitted.

In the first and second embodiments described above, it is desirable from the obtained fmax using the table of FIG. 4 in which the relationship between fmax that maximizes the voltage across power transmission coil 4 and the optimum power transmission frequency fsend is determined in advance. The power transmission frequency fsend was calculated. On the other hand, fsend may be calculated by performing a certain calculation based on fmax. For example, fsend can be obtained by adding a constant numerical value to fmax or multiplying by a constant numerical value, or by obtaining a period of fmax and subtracting a constant numerical value from the period, or by dividing a constant numerical value. fsend can also be obtained.
<Embodiment 3>
When the power transmission operation of the present invention is continuously performed, a change such as an environmental temperature change, a secular change of parts, and an object approaching the periphery of the power transmission circuit or the power reception circuit may occur during the operation. In Embodiment 3 of the present invention, the power transmission frequency control unit detects a constant environmental temperature change or a constant voltage change across the power transmission coil after setting the power transmission frequency of the power transmission unit, or a constant If the time has elapsed, reset the power transmission frequency of the power transmission unit. Thereby, even when the disturbance and the time change occur, the optimum power transmission can be realized.

  FIG. 9 shows a flowchart of control in Embodiment 3 of the present invention.

  Also in the present embodiment, the same frequency setting operation as steps S101 to S109 in the first embodiment or steps S101 to S108 and S204 in the second embodiment is performed (step S301). Since this operation is the same as that of the first embodiment or the second embodiment, detailed description thereof is omitted.

  When a change in the environmental temperature exceeding the predetermined change amount, or a change in the voltage across the power transmission coil exceeding the predetermined change amount is detected, or when a predetermined time has elapsed, the process returns to step S301. Perform the frequency setting operation again. In other cases, step S302 is executed again. The environmental temperature is obtained by measuring the temperature of the switching element, the resonant capacitance, the resonant coil, etc. (step S302).

  As described above, the non-contact power transmission apparatus of the present invention sets the power transmission frequency Fsw of the power transmission unit to a frequency Fres that is higher than the frequency at which resonance is maximized. Thereby, even when a disturbance factor such as an environmental temperature change, component secular change, or an object approaches the periphery of the power transmission circuit or the power reception circuit, the state of Fsw <Fres can be prevented. Therefore, the power loss of the switching element can be reduced, and highly efficient contactless power transmission can be performed.

  The contactless power transmission device of the present invention enables efficient power transmission even when a switching element such as an FET is used for the power transmission device.

DESCRIPTION OF SYMBOLS 1 Power transmission apparatus 2 Power reception apparatus 3 Power transmission part 4 Power transmission coil 5 Resonance capacity 6 Power transmission coil voltage detection part 7 Power transmission control part 8 Power reception coil 9 Resonance capacity 10 Power conversion part 11 Power output terminal 21 Switching element 22 Switching element 23 Coil

Claims (4)

A power transmission device having a power transmission resonator composed of a power transmission coil and a resonant capacitor;
A power receiving device having a power receiving resonator composed of a power receiving coil and a resonant capacitor;
In a non-contact power transmission device that transmits power from the power transmission device to the power reception device via magnetic resonance between the power transmission coil and the power reception coil,
The power transmission device further includes:
A power transmission unit that applies high-frequency power to the power transmission resonator in a power transmission circuit using a switching element;
A voltage detector for measuring the voltage across the power transmission coil;
A power transmission frequency control unit for controlling a power transmission frequency of the power transmission unit,
The power transmission frequency control unit obtains a resonant power transmission frequency that maximizes the voltage across the power transmission coil based on the voltage across the power transmission coil measured by the voltage detection unit, and determines the power transmission frequency of the power transmission unit as the resonance power transmission frequency. A non-contact power transmission device, characterized in that it is set to a higher frequency.   The contactless power transmission device according to claim 1, wherein the power transmission frequency control unit sets a power transmission frequency of the power transmission unit within a range in which a voltage across the power transmission coil does not exceed a predetermined upper limit value. .   The power transmission frequency control unit, after setting the power transmission frequency of the power transmission unit, when detecting a constant change in environmental temperature, or a change in the voltage across the constant power transmission coil, or when a certain time has elapsed, The non-contact power transmission apparatus according to claim 1, wherein a power transmission frequency of the power transmission unit is reset.   The power transmission circuit using the switching element is a half bridge circuit using two FETs as switching elements or a full bridge circuit using four FETs as switching elements. The non-contact power transmission device according to any one of the above.

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