Magnetic resonance power supply device

Abstract

To provide a magnetic field resonance power supply device capable of suppressing reduction in transmission efficiency at a low load.SOLUTION: A magnetic field resonance power supply device includes: a first power supply unit 110 having a first transmission coil L1, a first resonance capacitor C1, a first switching element Q1, and a first diode D1; a second power supply unit 120 having a second transmission coil L2, a second resonance capacitor C2, a second switching element Q2, and a second diode D2; a phase shift control circuit (142, 144, 145) for controlling a first phase shift time that is time difference between turn-off of the first switching element Q1 and turn-off of the second switching element Q2 according to a power value of transmission power; and an on-time control circuit (132, 133) for controlling turn-off of the first switching element Q1 so as to shorten an on-time of the first switching element Q1 when the power value of the transmission power decreases.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a magnetic resonance power supply device that performs power transmission using magnetic resonance.

Background Art

[0002] As a magnetic resonance power supply device that performs power transmission using magnetic resonance, for example, in the case of a wireless charger having a non-contact transmission coil, it is possible to supply non-contact transmission power of about several kilowatts to an electric vehicle. In this magnetic resonance power supply device, it has been proposed to configure the power supply unit on the power transmission side and the power supply unit on the power reception side with single-ended converters each operating with a single switching element, and to control the transmission power by phase shift control (see, for example, Patent Document 1).

[0003] By performing phase shift control, it becomes unnecessary to perform voltage control at the front stage of the power supply unit on the power transmission side and at the rear stage of the power supply unit on the power reception side. As a result, since a DC / DC converter (for example, a buck-boost chopper circuit) provided at the front stage of the power supply unit on the power transmission side and at the rear stage of the power supply unit on the power reception side becomes unnecessary, the cost of the entire power supply device can be reduced.

[0004] However, by performing phase shift control, there is a problem that the transmission efficiency of the transmission power greatly decreases at low loads. For example, for a rated load of 6 [kW], as the load decreases to 3 [kW] and 1.5 [kW], the transmission efficiency decreases to 81% and 50%, respectively.

[0005] In the magnetic resonance power supply device described in Patent Document 1, a very large resonance current flows as an idle current between the resonance capacitor and the transmission coil of the power transmission side power supply unit and between the resonance capacitor and the transmission coil of the power reception side power supply unit, regardless of the transmitted power. When this resonance current flows through the resonance circuit composed of the resonance capacitor and the transmission coil, loss occurs as heat due to the resistance component of the resonance circuit. For example, if the resonance current is 80 [A] and the resistance of the resonance circuit is 50 [mΩ], a loss of 320 [W] occurs, and when the transmitted power is 6 [kW], the loss is about 5%. When the output voltage is 350 [V], the effective current when the transmitted power is 6 [kW] is 17 [A], so the resonance current, which is the idle current, is about five times the effective current.

[0006] Moreover, since the magnitude of the resonance current is independent of the magnitude of the load, the influence of the loss of the resonance current becomes greater at low load when the transmitted power is small. For example, when the transmitted power is 1.5 [kW], the loss is about 21%. At this time, the effective current is 3 [A], so the resonance current, which is the idle current, is about 27 times the effective current. Thus, there is a problem that the influence of the loss of the resonance current becomes greater at low load, and the transmission efficiency greatly decreases. In addition, when the resonance current flows through the transmission coil, abnormal heat generation occurs in the transmission coil due to the influence of the proximity effect, and there is also a problem that cost is required for countermeasures.

[0007] Note that in Patent Document 2, a method of improving the transmission efficiency of transmitted power by controlling the frequency so as to increase the effective current on the primary side has been proposed. However, when phase shift control is performed as in the above magnetic resonance power supply device, even if the frequency is changed by the method described in Patent Document 2 to increase the effective current, the magnitude of the resonance current does not change, so the decrease in transmission efficiency at low load cannot be suppressed.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

[0009] The present invention has been made in view of the above circumstances, and an object thereof is to provide a magnetic resonance power supply device capable of suppressing a decrease in transmission efficiency during low load operation. MEANS FOR SOLVING THE PROBLEMS

[0010] In order to solve the above problems, a magnetic resonance power supply device according to an embodiment of the present invention includes: a first power supply unit including a first transmission coil, a first resonance capacitor, a first switching element, and a first diode connected in parallel to the first switching element; a second power supply unit including a second transmission coil, a second resonance capacitor, a second switching element, and a second diode connected in parallel to the second switching element; a control unit, and is a magnetic resonance power supply device that supplies transmission power from the first power supply unit to the second power supply unit by magnetic resonance, wherein the control unit includes a phase shift control circuit that controls a first phase shift time, which is a time difference between the turn-off of the first switching element and the turn-off of the second switching element, according to the power value of the transmission power; and an on-time control circuit that controls the on-time of the first switching element by controlling the turn-off of the first switching element according to the power value of the transmission power. It is characterized by comprising the above.

[0011] According to this configuration, by controlling the turn-off of the first switching element according to the power value of the transmitted power, the on-time of the first switching element is controlled. Therefore, when the transmitted power decreases, the resonance current can be reduced by shortening the on-time of the first switching element. As a result, it is possible to suppress an increase in loss due to the influence of the resonance current during low load when the transmitted power is small, and it is possible to suppress a significant decrease in transmission efficiency.

[0012] In addition, in order to solve the above problems, a magnetic resonance power supply device according to another embodiment of the present invention includes a first power supply unit including a first transmission coil, a first resonance capacitor, a first switching element, and a first diode connected in parallel to the first switching element, a second power supply unit including a second transmission coil, a second resonance capacitor, and a second diode, a control unit, a magnetic resonance power supply device that supplies transmitted power from the first power supply unit to the second power supply unit by magnetic resonance, the second diode is turned off after the elapse of a first phase shift time, which is a predetermined time difference, after the first switching element is turned off by magnetic resonance, the control unit is characterized by including an on-time control circuit that controls the on-time of the first switching element by controlling the turn-off of the first switching element according to the power value of the transmitted power.

[0013] According to this configuration, by controlling the turn-off of the first switching element according to the power value of the transmitted power, the on-time of the first switching element is controlled. Therefore, when the transmitted power decreases, the resonance current can be reduced by shortening the on-time of the first switching element. As a result, it is possible to suppress an increase in loss due to the influence of the resonance current during low load when the transmitted power is small, and it is possible to suppress a significant decrease in transmission efficiency.

[0014] In the above magnetic resonance power supply device, the on-time control circuit A first arithmetic process for calculating a phase margin time, which is the difference between the maximum phase shift time, which is the time difference at the maximum transmission power at which the transmission power is maximum, and the first phase shift time; A second arithmetic process for calculating a first on-time, which is the difference between the maximum on-time, which is the on-time of the first switching element at the maximum transmission power, and the phase margin time, is performed; The first switching element can be configured to be turned off after the first on-time has elapsed since the first switching element was turned on.

[0015] In the magnetic resonance power supply device described above, The control unit An electric current detection circuit for detecting the value of the current flowing through the second transmission coil; A zero-cross detection circuit that outputs a zero-cross signal at the timing when a zero-cross point is detected when the current value changes from negative to positive; is further provided with The on-time control circuit can be configured to turn off the first switching element at the timing when the zero-cross signal is input.

[0016] In the magnetic resonance power supply device described above, The on-time control circuit has data indicating the relationship between the transmission power and the on-time of the first switching element, and can be configured to determine the turn-off timing of the first switching element based on the data.

[0017] In the magnetic resonance power supply device described above, The data may indicate a relationship in which, when the transmission power is from the maximum value to a predetermined first threshold value, the on-time of the first switching element becomes shorter as the transmission power becomes smaller, while when the transmission power is smaller than the first threshold value, the on-time of the first switching element becomes a constant value.

[0018] In the magnetic resonance power supply device described above, When the transmission power is equal to or greater than a predetermined second threshold value, the on-time control circuit controls the turn-off of the first switching element such that the on-time of the first switching element becomes shorter as the transmission power becomes smaller. On the other hand, when the transmission power is smaller than the second threshold value, the on-time control circuit can be configured to control the turn-off of the first switching element such that the on-time of the first switching element becomes a constant value.

Advantages of the Invention

[0019] According to the present invention, it is possible to provide a magnetic resonance power supply device capable of suppressing a decrease in transmission efficiency during low load.

Brief Description of the Drawings

[0020]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

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Figure 8

Figure 9

Figure 10

Figure 11

Embodiments for Carrying Out the Invention

[0021] Hereinafter, embodiments of the magnetic resonance power supply device according to the present invention will be described with reference to the accompanying drawings.

[0022] [First Embodiment] FIG. 1 shows a magnetic resonance power supply device 100A according to a first embodiment of the present invention. The magnetic resonance power supply device 100A includes a first power supply unit E 1 a first power feeding unit 110 connected to, and a second power feeding unit 120 connected to a second power supply unit E 2 and a first control unit 130 and a second control unit 140. The first control unit 130 and the second control unit 140 correspond to the "control unit" of the present invention.

[0023] The first power feeding unit 110 and the first control unit 130 are installed, for example, in a home. The second power feeding unit 120 and the second control unit 140 are mounted, for example, on an electric vehicle such as an electric car or a plug-in hybrid vehicle. The magnetic resonance power supply device 100A supplies transmitted power from the first power feeding unit 110 to the second power feeding unit 120 by magnetic resonance (synonymous with magnetic field resonance, magnetic resonance, magnetic resonance).

[0024] The first power supply unit E 1 is a DC power supply, and the first power supply unit E 1 is, for example, the DC output of an AC / DC converter (AC / DC conversion power supply) connected to the power grid or the DC output of a DC / DC converter connected to a storage battery installed at home. An LC filter circuit composed of a coil and a capacitor may be provided between the first power supply unit E 1 and the first power feeding unit 110.

[0025] The second power supply unit E 2 is, for example, a storage battery or a load mounted on an electric vehicle. The second power supply unit E 2An LC filter circuit composed of a coil and a capacitor may be provided between the first power supply unit 110 and the second power supply unit 120.

[0026] The first power supply unit 110 is a single-ended converter (one-stone converter) including a first transmission coil L 1 a first resonant capacitor C 1 and a first switch SW 1 The first switch SW 1 includes a first switching element Q 1 and a first diode D 1 connected in parallel in the reverse direction to the first switching element Q 1

[0027] One end of the first transmission coil L 1 is connected to the high potential side of the first power supply unit E 1 and the other end is connected to the low potential side of the first power supply unit E 1 through the current path of the first switching element Q 1 The first resonant capacitor C 1 is connected in parallel to at least one of the first transmission coil L 1 and the first switch SW 1 (in this embodiment, the first transmission coil L 1 ).

[0028] The first switching element Q 1 uses an IGBT (insulated gate bipolar transistor), but a power semiconductor switching element such as a MOSFET (metal oxide semiconductor field effect transistor), a bipolar transistor, or a SiC (silicon carbide) semiconductor may also be used. The first diode D 1 is an internal (parasitic) diode of the first switching element Q 1 or an external diode independent of the first switching element Q 1 Note that the connection relationship between the first switching element Q 1 and the first diode D 1 can be appropriately changed according to the capabilities of each element and the transmitted power.

[0029] ​The second power supply unit 120 includes a second transmission coil L 2 and a second resonance capacitor C 2 and a second switch SW 2 and is a single-ended converter (one-stone converter). The second switch SW 2 includes a second switching element Q 2 and a second diode D 2 connected in parallel in the reverse direction to the second switching element Q 2 . Since the configuration of the second power supply unit 120 is the same as that of the first power supply unit 110, a detailed description of the configuration is omitted.

[0030] The first control unit 130 includes a first resonance voltage detection circuit 131, a first synchronization circuit 132, a turn-off control circuit 133, and a first communication circuit 134. In the present embodiment, the first synchronization circuit 132 and the turn-off control circuit 133 correspond to the "on-time control circuit" of the present invention.

[0031] The second control unit 140 includes a second resonance voltage detection circuit 141, a second synchronization circuit 142, a power detection circuit 143, a comparison circuit 144, a phase difference control circuit 145, and a second communication circuit 146. In the present embodiment, the second synchronization circuit 142, the comparison circuit 144, and the phase difference control circuit 145 correspond to the "phase shift control circuit" of the present invention.

[0032] The first resonance voltage detection circuit 131 measures the voltage V 1 (across the first resonance capacitor C 1 ) at both ends of the first transmission coil L R1 to obtain the voltage value of the first resonance voltage by the first transmission coil L 1 and the first resonance capacitor C 1 . The first resonance voltage detection circuit 131 outputs a detection signal corresponding to the voltage value of the first resonance voltage to the first synchronization circuit 132.

[0033] The first synchronization circuit 132 controls the turn-on / turn-off of the first switching element Q 1 . The first synchronization circuit 132 controls the turn-on / turn-off of the first switching element Q 1The turn-on of the first switching element Q is controlled in synchronization with the first resonance voltage so as to perform zero-voltage switching operation. Also, the first synchronization circuit 132 controls the turn-off of the first switching element Q based on the on-time control signal from the turn-off control circuit 133. 1 The turn-off of the first switching element Q is controlled by the first synchronization circuit 132 based on the on-time control signal from the turn-off control circuit 133. 1

[0034] When the power value of the transmitted power becomes small according to the information on the phase shift time notified from the second control unit 140 described later, the turn-off control circuit 133 shortens the on-time of the first switching element Q so as to control the turn-off of the first switching element Q. Specifically, the turn-off control circuit 133 performs a first arithmetic process for calculating the phase margin time and a second arithmetic process for calculating the first on-time, and generates an on-time control signal. 1 The turn-off of the first switching element Q is controlled by the turn-off control circuit 133 so that the on-time of the first switching element Q becomes short. 1 Specifically, the turn-off control circuit 133 performs a first arithmetic process for calculating the phase margin time and a second arithmetic process for calculating the first on-time, and generates an on-time control signal.

[0035] In the first arithmetic process, the turn-off control circuit 133 calculates the difference (= phase margin time) between the "first phase shift time", which is the time difference between the turn-off of the first switching element Q and the turn-off of the second switching element Q, and the "maximum phase shift time", which is the time difference at the maximum transmitted power when the transmitted power is maximum. That is, the phase margin time is expressed as the absolute value of the difference between the maximum phase shift time and the first phase shift time, 1 The turn-off of the first switching element Q and the turn-off of the second switching element Q 2 Phase margin time = |Maximum phase shift time - First phase shift time| And can be represented as

[0036] The turn-off control circuit 133 acquires a signal related to the first phase shift time from the second control unit 140. Also, the turn-off control circuit 133 stores the maximum phase shift time in advance. The maximum transmitted power and the maximum phase shift time are determined by, for example, the specifications of the magnetic resonance power supply device 100A.

[0037] In the second arithmetic process, the turn-off control circuit 133 determines the first switching element Q at the maximum transmitted power. 1 ​​Calculate a first on-time, which is the difference between the "maximum on-time", which is the on-time of [[ID=]], and the "phase margin time", and generate an on-time control signal related to the first on-time. The turn-off control circuit 133 stores the maximum on-time in advance. The maximum on-time is determined by, for example, the specifications of the magnetic resonance power supply device 100A and is the time that can ensure the maximum phase shift time.

[0038] The turn-off control circuit 133 outputs the generated on-time control signal to the first synchronization circuit 132. Based on the on-time control signal, the first synchronization circuit 132 turns off the first switching element Q 1 at the timing when the first on-time has elapsed since the turn-on of [[ID=]]. Also, the first synchronization circuit 132 transmits a first timing signal related to the timing of turning off the first switching element Q 1 to the second control unit 140 via the first communication circuit 134. 1

[0039] The first communication circuit 134 is configured to transmit and receive a predetermined signal to and from the second communication circuit 146 by light or radio wave. The first communication circuit 134 can be composed of, for example, a light-emitting diode for transmission and a phototransistor for reception.

[0040] The second resonance voltage detection circuit 141 measures the voltage V 2 across both ends of the second transmission coil L 2 (second resonance capacitor C R2 ) to obtain the voltage value of the second resonance voltage by the second transmission coil L 2 and the second resonance capacitor C 2 . The second resonance voltage detection circuit 141 outputs a detection signal corresponding to the voltage value of the second resonance voltage to the second synchronization circuit 142.

[0041] The second synchronization circuit 142 controls the turn-on / turn-off of the second switching element Q 2 . The second synchronization circuit 142 synchronizes with the second resonance voltage so that the second switching element Q 2 performs a zero-voltage switching operation, and turns off the second switching element Q 2controls the turn-on. Also, the second synchronization circuit 142 controls the turn-off of the second switching element Q 2 based on the second timing signal from the phase difference control circuit 145.

[0042] The power detection circuit 143 measures the current and voltage flowing between the second power supply unit 120 and the second power source E 2 to obtain the power value of the transmission power supplied from the first power supply unit 110 to the second power supply unit 120, and outputs a signal (for example, a voltage signal) corresponding to the power value to the comparison circuit 144. The transmission power supplied from the first power supply unit 110 to the second power supply unit 120 has a predetermined relationship with the current and voltage flowing between the second power supply unit 120 and the second power source E 2 and.

[0043] The comparison circuit 144 compares the power value of the transmission power obtained by the power detection circuit 143 with a predetermined target value, and outputs a difference signal corresponding to the difference between the power value and the target value to the phase difference control circuit 145. In the present embodiment, the comparison circuit 144 is composed of a differential amplifier. A reference voltage signal Vref corresponding to the target value of the transmission power is input to the inverting input terminal of the differential amplifier, a signal from the power detection circuit 143 is input to the non-inverting input terminal of the differential amplifier, and a difference signal is output from the output terminal of the differential amplifier.

[0044] Based on the difference signal input from the comparison circuit 144, the phase difference control circuit 145 calculates the first phase shift time, which is the time difference between the turn-off of the first switching element Q 1 and the turn-off of the second switching element Q 2 so that the power value of the transmission power approaches the target value. The phase difference control circuit 145 transmits a signal regarding the first phase shift time to the turn-off control circuit 133 via the second communication circuit 146 and the first communication circuit 134. Note that the relationship between the power value of the transmission power and the first phase shift time can be clarified in advance by measurement or the like, and the target value can be calculated by storing the relationship.

[0045] Further, the phase difference control circuit 145 is based on the first timing signal regarding the timing to turn off the first switching element Q received from the first synchronization circuit 132 via the first communication circuit 134 and the second communication circuit 146, and the above-described first phase shift time, and determines the second timing to turn off the second switching element Q 1 and outputs the second timing signal to the second synchronization circuit 142. The second synchronization circuit 142 turns off the second switching element Q based on the second timing signal. 2 2

[0046] The second communication circuit 146 is configured to transmit and receive a predetermined signal by light or radio wave to and from the first communication circuit 134. The second communication circuit 146 can be composed of, for example, a light-emitting diode for transmission and a phototransistor for reception.

[0047] Next, with reference to FIGS. 2 to 5, the operation of the magnetic resonance power supply device 100A will be described. However, FIGS. 2 to 4 relate to a magnetic resonance power supply device (hereinafter referred to as "comparative example") according to a comparative example for explaining the conventional operation.

[0048] The comparative example has the configuration described in Patent Document 1, and is different in that the turn-off control circuit 133 is not provided in the magnetic resonance power supply device 100A according to the present embodiment. The first synchronization circuit 132 of the comparative example turns on the first switching element Q 1 and then turns off the first switching element Q on1 after a preset on-time T 1 has elapsed. Therefore, in the comparative example, the on-time T 1 of the first switching element Q on1 is constant regardless of the power value of the transmitted power. Other operations of the comparative example are common to the operations of the magnetic resonance power supply device 100A according to the present embodiment.

[0049] In FIG. 2, (A) is the waveform of the voltage V 1 across both ends of the first switch SW SW1 , and (B) is the current I 1 flowing through the first switch SWSW1 The waveform of (C) is the voltage V across the first transmission coil L 1 R1 The waveform of (D) is the gate voltage V of the first switching element Q 1 g1 The waveform of (E) is the gate voltage V of the second switching element Q 2 g2 The waveform of (F) is the voltage V across the second transmission coil L 2 R2 The waveform of (G) is the current I flowing through the second switch SW 2 SW2 The waveform of (H) is the voltage V across the second switch SW 2 SW2 The waveform of (I) is the current I flowing through the first transmission coil L 1 L1 The waveform of (J) is the current I flowing through the second transmission coil L 2 L2 is the waveform.

[0050] The first switch SW 1 During the off period T OFF1 of, across the first transmission coil L 1 at both ends, there is a first resonance voltage (voltage V 1 ) generated by the first transmission coil L and the first resonance capacitor C 1 . When the first resonance voltage detection circuit 131 detects the zero crossing point t R1 where the voltage V R1 crosses zero, the first synchronization circuit 132 synchronizes with the zero crossing point t 0 and at the time t 0 synchronized with the zero crossing point t 0 after a predetermined synchronization time has elapsed from the zero crossing point t 2 , switches the gate voltage V 1 of the first switching element Q g1 from low level to high level, and turns on the first switching element Q 1 in zero voltage switching operation.

[0051] During the period T OFF1 of, the voltage V 1 across both ends of the first switch SW SW1 draws a resonance arc, rises gently, then falls gently and reaches zero. At time t​​​​​​​​1 When the voltage V SW1 reaches zero, the first diode D 1 automatically turns on, and the first switch SW 1 enters the on state (conducting state).

[0052] During the period T 1 when the first switch SW is on ON1 the DC voltage of the first power supply E 1 is applied to the first transmission coil L 1 , so the current I 1 flowing through the first switch SW SW1 increases linearly. When the current I SW1 changes from negative to positive, the current flowing through the first diode D 1 smoothly flows into the first switching element Q 1 , and the on state of the first switch SW 1 continues.

[0053] The first synchronization circuit 132 switches the gate voltage V 2 of the first switching element Q from high level to low level at the time t on1 when a preset fixed period of on-time T 6 has elapsed since time t 1 , turning off the first switching element Q g1 . As a result, the first switch SW 1 enters the off state (blocking state), and the current stored in the first transmission coil L 1 flows into the first resonance capacitor C 1 , entering a resonance state. Note that the on-time T 1 is set to a time (maximum on-time) that can ensure the maximum phase shift time T on1 . ΦM

[0054] During the period T 2 when the second switch SW is off OFF2 the second resonance voltage (voltage V 2 across both ends of the second transmission coil L 2 is generated by the second transmission coil L 2 and the second resonance capacitor C​R2 ) occurs. Voltage V R2 crosses zero at the zero-crossing point t 3 When the second resonant voltage detection circuit 141 detects the zero-crossing point t 3 , the second synchronization circuit 142 synchronizes with the zero-crossing point t 3 and at the time t 5 when a predetermined synchronization time has elapsed from the zero-crossing point t 2 , the gate voltage V g2 of the second switching element Q 2 is switched from the low level to the high level to turn on the second switching element Q

[0055] During the period T OFF2 , the voltage V 2 across both ends of the second switch SW SW2 draws a resonance arc, rises gently, and then falls gently to reach zero. At the time t 4 when the voltage V SW2 reaches zero, the second diode D 2 automatically turns on and the second switch SW 2 enters the on state (conducting state).

[0056] During the period T 2 when the second switch SW ON2 is on, the energy stored in the second transmission coil L 2 is supplied to the second power supply unit E 2 through the second switch SW 2 . Therefore, the current I 2 flowing through the second switch SW SW2 increases linearly. When the current I SW2 reverses from negative to positive, the current flowing through the second diode D 2 smoothly flows to the second switching element Q 2 and the on state of the second switch SW 2 continues.

[0057] At the time t 6 , the first switching element Q 1When the first synchronization circuit 132 is turned off, the first timing signal is sent from the first synchronization circuit 132 to the phase difference control circuit 145. The phase difference control circuit 145 controls the first phase shift time T Φ and calculates the time t 6 to the first phase shift time T Φ Time t delayed by 7 The second synchronization circuit 142 outputs a second timing signal to the second synchronization circuit 142 at time t 6 to the first phase shift time T Φ Time t delayed by 7 In the second switching element Q 2 Gate voltage V g2 is switched from high level to low level, and the second switching element Q 2 This turns off the second switch SW 2 is turned off (disconnected), and the second transmission coil L 2 The current stored in the second resonant capacitor C 2 This current flows into the circuit, creating a resonant state.

[0058] Through the above operations, the first switching element Q 1 and the second switching element Q 2 While maintaining zero voltage switching with small switching loss, the second switching element Q 2 The turn-off phase of the first switching element Q 1 The time T Φ (phase angle Φ=2πT Φ / To (To: operation cycle) can be shifted.

[0059] 3 and 4 are the same as those in FIG. 2 at time t 1 ~t 4 The period between t 4 ~t 6 The period between t 6 ~t 7 The period between t 7 ~t 8FIG. is a diagram schematically showing currents flowing through the first power supply unit 110 and the second power supply unit 120 in each mode period when the interval is the mode 4 period. However, FIG. 3(B) shows the period (time t L1 to t L2 when current I 51 is positive and current I 52 is negative) during the mode 2 period. FIG. 4(B) shows the period during the mode 4 period when current I L1 is negative and current I L2 is positive.

[0060] At time t 1 , when voltage V SW1 reaches zero, the mode 1 period starts. In the first power supply unit 110 during the mode 1 period shown in FIG. 3(A), the first diode D 1 turns on and the first switch SW 1 becomes in the on state, and the negative current flowing through the first transmission coil L 1 flows through the first switch SW 1 and refluxes to the first power supply unit E 1 . At time t 2 , the first switching element Q 1 turns on, and the DC voltage of the first power supply unit E 1 is applied to the first transmission coil L 1 . Therefore, current I SW1 and current I L1 increase linearly. In the second power supply unit 120 during the mode 1 period, since the second switch SW 2 turns off and enters the resonance state, current I SW2 does not flow, and current I L2 reaches the negative peak and then increases gently.

[0061] At time t 4 , when voltage V SW2 reaches zero, the mode 2 period starts. In the first power supply unit 110 during the mode 2 period, similar to the mode 1 period, current I SW1 and current I L1 increase linearly. In the second power supply unit 120 during the mode 2 period, the second diode D 2 turns on and the second switch SW 2is turned on, and the energy stored in the second transmission coil L 2 is supplied to the second power supply unit E 2 through the second switch SW 2 . Therefore, the current I SW2 and the current I L2 increase linearly. The length of the period (from time t 51 to t 52 ) that contributes to the power transmission shown in Fig. 3(B) during the mode 2 period is the same as the length of the first phase shift time T Φ .

[0062] At time t 6 , when the first switching element Q 1 is turned off, the mode 3 period starts. As shown in Fig. 4(A), in the first power supply unit 110 during the mode 3 period, the first switch SW 1 is turned off, and the current stored in the first transmission coil L 1 flows into the first resonance capacitor C 1 to enter a resonance state. The current I L1 is a resonance current, and after reaching the positive peak, it gradually decreases. In the second power supply unit 120 during the mode 3 period, similar to the mode 2 period, the current I SW2 and the current I L2 increase linearly.

[0063] At time t 7 , when the second switching element Q 2 is turned off, the mode 4 period starts. As shown in Fig. 4(B), in the second power supply unit 120 during the mode 4 period, the second switch SW 2 is turned off, and the current stored in the second transmission coil L 2 flows into the second resonance capacitor C 2 to enter a resonance state. Therefore, the current I SW2 does not flow, and the current I L2 reaches the positive peak and then gradually decreases. In the first power supply unit 110 during the mode 4 period, since the first switch SW 1 is turned off and remains in the resonance state, the current I SW1 does not flow, and the current I L1After reaching the negative peak, it increases gently. At time t 8 when the voltage V SW1 reaches zero, the mode 4 period ends and the mode 1 period starts again.

[0064] Thus, the peak value of the current I L1 is not determined by the transmission power, i.e., the first phase shift time T Φ but is determined by the maximum transmission power, i.e., the maximum phase shift time T ΦM In other words, it is determined by the on-time T ΦM which is the time that can ensure the maximum phase shift time T on1 For this reason, in the comparative example, for example, at the low load when the second power supply unit E 2 is at a low load, the current I L1 which is the resonance current, becomes a large reactive current that is not necessary for the second power supply unit E 2 Also, regarding the peak value of the current I L2 similarly depends on the on-time T on1 so the current I L2 which is the resonance current, becomes a large reactive current that is not necessary at low loads.

[0065] FIG. 5 is a timing chart of each part of the magnetic resonance power supply device 100A according to the present embodiment. The signals (A) to (J) of each part in FIG. 5 are the same as the signals (A) to (J) of each part in FIG. 2. Also, the modes 1 to 4 in FIG. 5 are the same as the modes 1 to 4 in FIG. 2. Therefore, the description of the parts common to the comparative example in the operation of the magnetic resonance power supply device 100A is omitted.

[0066] In the magnetic resonance power supply device 100A, at the low load when the power value of the transmission power becomes small, the turn-off control circuit 133 generates an on-time control signal for controlling the on-time of the first switching element Q 1 so that the on-time of the first switching element Q 1 becomes shorter according to the power value.

[0067] Specifically, the turn-off control circuit 133 is the maximum phase shift time T ΦMand the first phase shift time T Φ Calculate the phase margin time as the absolute value of the difference from the first phase shift time T (first arithmetic processing), and the maximum on-time T on1 Calculate the first on-time T on1 ’ which is the difference between the maximum on-time T on1 ’ and the phase margin time, and generate an on-time control signal for the first on-time T

[0068] Based on the on-time control signal, the first synchronization circuit 132 turns off the first switching element Q 2 at the time t on1 when the first on-time T 61 ’ has elapsed. Therefore, the first on-time T 1 ’ is shorter than the on-time T on1 ’ of the comparative example on1 (= the maximum on-time T on1 ).

[0069] At the time t 61 when the first switching element Q 1 turns off, a first timing signal is sent from the first synchronization circuit 132 to the phase difference control circuit 145. The phase difference control circuit 145 outputs a second timing signal generated based on the first timing signal and the first phase shift time T Φ to the second synchronization circuit 142. The second synchronization circuit 142 turns off the second switching element Q 61 at the time t Φ when the first phase shift time T 71 has elapsed after the time t 2 . Therefore, the second on-time T 2 ’ which is the on-time of the second switching element Q on2 ’ is shorter than the on-time T on2 of the comparative example.

[0070] When the first on-time T on1 ’ and the second on-time T on2 ’ become shorter, the peak values of the current I SW1 and the current I SW2 become smaller, and the current I L1 and the current IL2 The peak value also becomes smaller.

[0071] That is, in the case of FIG. 5, the magnetic resonance power supply device 100A has a phase shift time (the first phase shift time T Φ ) being the same as that of the comparative example, so the power value of the transmitted power is the same as that of the comparative example. However, since the peak values of the resonance currents (current I L1 and current I L2 ) are smaller than those of the comparative example, the losses due to the resistance of the first transmission coil L 1 and the first resonance capacitor C 1 and the second transmission coil L 2 and the second resonance capacitor C 2 become smaller than those of the comparative example.

[0072] Therefore, the magnetic resonance power supply device 100A can suppress the increase in the loss due to the resistance component of the resonance circuit due to the influence of the resonance current when the transmitted power is small, and can suppress the significant decrease in the transmission efficiency. Also, the magnetic resonance power supply device 100A can reduce the heat generation of the first transmission coil L L1 and current I L2 and the first resonance capacitor C 1 and the second transmission coil L 1 and the second resonance capacitor C 2 due to the resonance current (current I 2 ), and can reduce the cost for heat generation countermeasures.

[0073] [Second Embodiment] FIG. 6 shows a magnetic resonance power supply device 100B according to the second embodiment of the present invention. The magnetic resonance power supply device 100B includes a first power supply unit 110, a second power supply unit 120, and a first control unit 130B and a second control unit 140B corresponding to the "control unit" of the present invention.

[0074] The first power supply unit 110 and the second power supply unit 120 have the same configuration as that of the first embodiment. The first control unit 130B has the same configuration as that of the first embodiment except for the turn-off control circuit 133B. The second control unit 140B has the same configuration as that of the first embodiment except that it further includes a current detection circuit 147B and a zero-cross detection circuit 148B.

[0075] The current detection circuit 147B measures the current I 2 flowing through the second transmission coil L L2 and outputs a signal (for example, a voltage signal) corresponding to the measured current value of the measured current I L2 to the zero-cross detection circuit 148B.

[0076] The zero-cross detection circuit 148B monitors the signal of the current detection circuit 147B and detects the zero-cross point when the current value of the current I L2 changes from negative to positive. The zero-cross detection circuit 148B transmits a zero-cross signal to the turn-off control circuit 133B via the second communication circuit 146 and the first communication circuit 134 at the timing when the zero-cross point is detected.

[0077] The turn-off control circuit 133B outputs a turn-off control signal for turning off the first switching element Q 1 to the first synchronization circuit 132 at the timing when the zero-cross signal is received. The first synchronization circuit 132 turns off the first switching element Q 1 based on the turn-off control signal.

[0078] FIG. 7 is a timing chart of each part of the magnetic resonance power supply device 100B according to the present embodiment. The signals (A) to (J) of each part in FIG. 7 are the same as the signals (A) to (J) of each part in FIG. 5 (first embodiment). Also, the modes 1 to 4 in FIG. 7 are the same as the modes 1 to 4 in FIG. 5.

[0079] As shown in FIG. 7(J), at time t 52 , the zero-cross detection circuit 148B detects the current I L2When the zero - cross point is detected, the zero - cross detection circuit 148B transmits the zero - cross signal to the turn - off control circuit 133B via the second communication circuit 146 and the first communication circuit 134. The turn - off control circuit 133B that has received the zero - cross signal outputs a turn - off control signal to the first synchronization circuit 132. At time t 62 In, the first synchronization circuit 132 turns off the first switching element Q 1 . Note that time t 62 corresponds to the same timing as time t 61 in the first embodiment.

[0080] During the period contributing to power transmission in the mode 2 period (between time t 51 and t 52 ), the length is the same as the length of the first phase - shift time T Φ , and at low loads less than the maximum transmission power, it becomes shorter than at least the maximum phase - shift time T ΦM . Therefore, similar to the first embodiment, the first on - time T on1 ’ is shorter than the on - time T on1 (= the maximum on - time T on1 ) of the comparative example, and the second on - time T on2 ’ is also shorter than the on - time T on2 of the comparative example.

[0081] When the first on - time T on1 ’ and the second on - time T on2 ’ become shorter, the peak values of the current I SW1 and the current I SW2 become smaller, and the peak value of the resonance current (the current I L1 and the current I L2 ) also becomes smaller.

[0082] Therefore, the magnetic - field resonance power supply device 100B can suppress the increase in losses due to the influence of the resonance current at low loads where the transmission power is small, and can suppress the significant decrease in transmission efficiency. Also, the magnetic - field resonance power supply device 100B is affected by the resonance current (the current I L1 and the current I L2 ) on the first transmission coil L 1 and the first resonance capacitor C 1and the second transmission coil L 2 and the second resonance capacitor C 2 The heat generation can be reduced, and the cost for heat generation countermeasures can be reduced.

[0083] [Third Embodiment] FIG. 8 shows a magnetic resonance power supply device 100C according to the third embodiment of the present invention. The magnetic resonance power supply device 100C includes a first power supply unit 110, a second power supply unit 120C, and a first control unit 130 and a second control unit 140C corresponding to the "control unit" of the present invention.

[0084] The first power supply unit 110 and the first control unit 130 have the same configuration as those in the first embodiment. The second power supply unit 120C has the same configuration as that in the first embodiment except that the second switch SW 2 consists only of the second diode D 2 . The second control unit 140C has the same configuration as that in the first embodiment except that it does not include the second resonance voltage detection circuit 141 and the second synchronization circuit 142 and includes a phase difference control circuit 145C.

[0085] Based on the differential signal input from the comparison circuit 144, the phase difference control circuit 145C calculates a first phase shift time T 1 , which is the time difference between the turn-off of the first switching element Q 2 (the second diode D 2 ) and the turn-off of the second switch SW Φ such that the power value of the transmitted power approaches the target value. The phase difference control circuit 145C transmits a signal related to the first phase shift time T Φ to the turn-off control circuit 133 via the second communication circuit 146 and the first communication circuit 134.

[0086] Different from the first embodiment, the phase difference control circuit 145C does not receive a first timing signal related to the timing for turning off the first switching element Q 1 , nor does it generate a second timing signal related to the timing for turning off the second switching element Q 2 .

[0087] The turn-off control circuit 133 calculates the phase margin time as the absolute value of the difference between the maximum phase shift time T ΦM and the first phase shift time T Φ (first arithmetic process), and calculates the first on-time T on1 ' which is the difference between the maximum on-time T on1 and the phase margin time, and generates an on-time control signal for the first on-time T on1 ' (second arithmetic process).

[0088] Based on the on-time control signal, the first synchronization circuit 132 turns on the first switching element Q 1 and turns off the first switching element Q on1 when the first on-time T 1 ' has elapsed. Therefore, the first on-time T on1 ' is shorter than the maximum on-time T on1 .

[0089] FIG. 9 is a timing chart of each part of the magnetic resonance power supply device 100C according to the present embodiment. The signals (A) to (D), (G) of each part in FIG. 9 are the same as the signals (A) to (D), (I) of each part in FIG. 5 (first embodiment).

[0090] FIG. 9(E) is a waveform of the current I 2 flowing through the second switch SW 2 (second diode D SW2 ). In the first embodiment, the second switching element Q R2 of the second switch SW 2 is turned on by the zero-cross signal of the voltage V 2 , but in the present embodiment, since the second switch SW 2 consists only of the second diode D 2 , the second diode D 2 is not controlled (automatically turns on and off). The second diode D 2 is in the on state during the periods of mode 2 and mode 3, and is in the off state during the periods of mode 4 and mode 1.

[0091] Figure 9(F) shows the second switch SW 2 (the second diode D 2 ) and the voltage V across both ends SW2 of it. In this embodiment, when current I 1 flows through the first transmission coil L L1 , a voltage V 2 across both ends is induced in the second switch SW SW2 .

[0092] Figure 9(H) shows the waveform of the current I 2 flowing through the second transmission coil L L2 . The current I L2 has a phase difference (the first phase shift time T L1 Φ ) corresponding to the transmitted power with respect to the current I. Also, power transmission from the first power supply unit 110 to the second power supply unit 120C is performed during the period when the current I L1 is positive and the current I L2 is negative in the mode 2 period.

[0093] In this embodiment, control is performed to turn off the first switching element Q 1 when the first on-time T on1 ’ has elapsed after turning on the first switching element Q 61 (for example, at time t 1 ). The second switch SW 2 (the second diode D 2 ) is not controlled and automatically turns off when the first phase shift time T 1 has elapsed after turning off the first switching element Q Φ (for example, at time t 71 ).

[0094] Therefore, similar to the first embodiment, the first on-time T on1 ’ is shorter than the on-time T on1 (= the maximum on-time T on1 ) of the comparative example, and the second on-time T on2 ’ is also shorter than the on-time T on2 of the comparative example. The first on-time T on1 ’ and the second on-time T on2When ’ becomes short, current I SW1 and current I SW2 have smaller peak values, and the peak values of the resonance current (current I L1 and current I L2 ) also become smaller.

[0095] Therefore, similar to the first embodiment, the magnetic resonance power supply device 100C can suppress an increase in loss due to the influence of the resonance current during low load when the transmission power is small, and can suppress a significant decrease in transmission efficiency. Further, the magnetic resonance power supply device 100C can reduce the heat generation of the first transmission coil L L1 and current I L2 and the first resonance capacitor C 1 and the second transmission coil L 1 and the second resonance capacitor C 2 and the second resonance capacitor C 2 due to the resonance current (current I

[0096] [Fourth Embodiment] FIG. 10 shows a magnetic resonance power supply device 100D according to a fourth embodiment of the present invention. The magnetic resonance power supply device 100D includes a first power supply unit 110, a second power supply unit 120, and a first control unit 130D and a second control unit 140D corresponding to the "control unit" of the present invention.

[0097] The first power supply unit 110 and the second power supply unit 120 have the same configuration as in the first embodiment. The first control unit 130D has the same configuration as in the first embodiment except for the turn-off control circuit 133D. The second control unit 140D has the same configuration as in the first embodiment except that the reference voltage signal Vref is input to the comparison circuit 144 and is transmitted from the second communication circuit 146. The reference voltage signal Vref is transmitted to the turn-off control circuit 133D via the second communication circuit 146 and the first communication circuit 134.

[0098] The turn-off control circuit 133D controls the transmission power (in this embodiment, the voltage value of the reference voltage signal Vref) and the on-time of the first switching element Q 1 (in this embodiment, the first on-time T on1’) and has data indicating the relationship therewith. The turn-off control circuit 133D obtains, without obtaining a signal regarding the first phase shift time T Φ from the second control unit 140D, and determines the turn-off timing of the first switching element Q 1 based on the reference voltage signal Vref and the above data, and generates an on-time control signal.

[0099] FIG. 11 shows an example of the relationship between the reference voltage signal Vref included in the above data and the first on-time T on1 ’. In FIG. 11, the signal value (voltage value) of the reference voltage signal Vref at the maximum transmission power is set as Xmax, and the maximum value of the first on-time T on1 ’ (the maximum on-time T on1 ) is set as Ymax.

[0100] In the data shown in FIG. 11, when the reference voltage signal Vref is Xmax, the first on-time T on1 ’ becomes Ymax. When the signal value of the reference voltage signal Vref is less than a predetermined first threshold X 1 (where X 1 < Xmax) to Xmax, the smaller the signal value of the reference voltage signal Vref (i.e., the smaller the transmission power), the shorter the first on-time T on1 ’. On the other hand, when the signal value of the reference voltage signal Vref is less than the first threshold X 1 , the first on-time T on1 ’ is a constant value Y 1 (where Y 1 < Ymax).

[0101] The first threshold X 1 is set, for example, to the signal value (voltage value) of the reference voltage signal Vref corresponding to the transmission power when the load is about 1 / 3 of the rated load. The constant value Y 1 is set, for example, to the time that can ensure the resonance current necessary to supply the above transmission power.

[0102] Similar to other embodiments, the magnetic resonance power supply device 100D can suppress an increase in loss due to the influence of the resonance current during a low load condition where the transmitted power is small, and can suppress a significant decrease in transmission efficiency. Further, the magnetic resonance power supply device 100D can reduce the heat generation of the first transmission coil L L1 and the current I L2 due to the resonance current (current I 1 and the first resonance capacitor C 1 as well as the heat generation of the second transmission coil L 2 and the second resonance capacitor C 2 , and can reduce the cost for heat dissipation countermeasures.

[0103] Furthermore, when the reference voltage signal Vref is smaller than the first threshold value X 1 , the magnetic resonance power supply device 100D controls the first on-time T on1 ' to be a constant value Y 1 , thereby avoiding an excessive decrease in the resonance current and instability of the operation. That is, the magnetic resonance power supply device 100D can operate stably even in a very low load condition of about 1 / 3 or less of the rated load.

[0104] [Modification Example] As described above, embodiments of the magnetic resonance power supply device according to the present invention have been described, but the present invention is not limited to the above-described embodiments.

[0105] If a magnetic resonance power supply device according to an embodiment of the present invention includes a first power supply unit including a first transmission coil, a first resonance capacitor, a first switching element, and a first diode connected in parallel to the first switching element, a second power supply unit including a second transmission coil, a second resonance capacitor, a second switching element, and a second diode connected in parallel to the second switching element, a phase shift control circuit that controls a first phase shift time, which is a time difference between the turn-off of the first switching element and the turn-off of the second switching element, according to the power value of the transmitted power, and an on-time control circuit that controls the on-time of the first switching element by controlling the turn-off of the first switching element according to the power value of the transmitted power, the configuration can be changed as appropriate.

[0106] A magnetic resonance power supply device according to another embodiment of the present invention includes a first power supply unit including a first transmission coil, a first resonance capacitor, a first switching element, and a first diode connected in parallel to the first switching element, a second power supply unit including a second transmission coil, a second resonance capacitor, and a second diode, and a control unit. The second diode turns off after a first phase shift time, which is a predetermined time difference after the first switching element turns off. If the control unit includes an on-time control circuit that controls the on-time of the first switching element by controlling the turn-off of the first switching element according to the power value of the transmitted power, the configuration can be changed as appropriate.

[0107] For example, in the first embodiment, the description was made assuming that the phase difference in the phase shift control is controlled in the range from 0° to 90° centered on 0°, but the present invention is not limited to this, and it may be controlled in the range from -180° to -90°. In that case, since the maximum phase shift time T ΦM becomes the minimum, subtracting the first phase shift time T Φ from the maximum phase shift time T ΦM results in the phase margin time.

[0108] In the third embodiment, the second switch SW 2 is configured to include only the second diode D 2 , but the second switch SW 2 may include a second switching element Q 2 and a second diode D 2 connected in parallel to the second switching element Q 2 in the reverse direction, and the second switching element Q 2 may be kept in the off state at all times.

[0109] In the first and second embodiments, for the sake of simplicity of explanation, the configuration in which power is transmitted in one direction from the first power supply unit 110 to the second power supply unit 120 was shown and described. However, by appropriately making the control circuit (the first control unit and the second control unit) bidirectional, it can also be applied to the configuration in which power is transmitted bidirectionally.

[0110] In the first and second embodiments, when performing power transmission from the first power supply unit 110 to the second power supply unit 120, the second switching element Q 2 is turned off, and power transmission may be performed using diode rectification by the second diode D 2 .

[0111] In the first to fourth embodiments, the first communication circuit 134 and the second communication circuit 146 are used as non-contact communication means, but in an environment where a wired connection is possible, communication means by a wired connection may be used instead.

[0112] In the fourth embodiment, when the reference voltage signal Vref is smaller than the first threshold value X 1 , the turn-off of the first switching element Q on1 is controlled so that the first on-time T 1 ' becomes a constant value Y 1 . However, also in the first to third embodiments, when the transmission power is smaller than a predetermined second threshold value X 2 at a low load, for example, in the case of a very low load where the load is less than 1 / 3 of the rated value, it is preferable to control the turn-off of the first switching element Q on1 so that the first on-time T 1 ' becomes a constant value (for example, Y 1 ). Further, when the transmission power is equal to or greater than the second threshold value X 2 , the turn-off of the first switching element Q on1 may be controlled so that the first on-time T 1 ' becomes shorter as the transmission power becomes smaller.

[0113] In the first embodiment, the first power supply unit 110, the second power supply unit 120, the first control unit 130, and the second control unit 140 can be configured as one device, and for example, can be installed in a home. When configured as one device, the first communication circuit 134 and the second communication circuit 146 can also be simplified or omitted as communication circuits within the device.

[0114] In the first embodiment, the first switching element Q 1Although the mutual phase detection control method for notifying the turn-off timing to the phase difference control circuit 145 on the power receiving side has been described, it is also applicable to the self-phase detection control method in which the phase difference (first phase shift time) is detected by detecting the power transmission power on the power transmission side or the power receiving side. In the case of the self-phase detection control method, phase information is transmitted to the power receiving side or the power transmission side, and control may be performed to shorten the on-time of the first switching element Q 1 by the phase margin time.

Explanation of Signs

[0115] 100A, 100B, 100C, 100D Magnetic resonance power supply 110 First power supply unit 120, 120C Second power supply unit 130, 130B, 130D First control unit 131 First resonance voltage detection circuit 132 First synchronization circuit 133, 133B, 133D Turn-off control circuit 134 First communication circuit 140, 140B, 140C, 140D Second control unit 141 Second resonance voltage detection circuit 142 Second synchronization circuit 143 Power detection circuit 144 Comparison circuit 145, 145C Phase difference control circuit 146 Second communication circuit 147B Current detection circuit 148B Zero-cross detection circuit

Claims

1. a first power supply unit including a first transmission coil, a first resonant capacitor, a first switching element, and a first diode connected in parallel to the first switching element; a second power supply unit including a second transmission coil, a second resonant capacitor, a second switching element, and a second diode connected in parallel to the second switching element; A control unit, A magnetic resonance power supply device that supplies transmission power from the first power supply unit to the second power supply unit by magnetic resonance, The control unit is a phase shift control circuit that controls a first phase shift time, which is a time difference between turning off the first switching element and turning off the second switching element, in response to a power value of the transmission power; an on-time control circuit that controls turn-off of the first switching element in response to the power value of the transmission power, thereby controlling an on-time of the first switching element; Equipped with the on-time control circuit has data indicating a relationship between the transmission power and an on-time of the first switching element, and determines a timing for turning off the first switching element based on the data; The data indicates a relationship in which, as the transmission power decreases from a predetermined first threshold to a maximum value, the on-time of the first switching element becomes shorter, while when the transmission power is smaller than the first threshold, the on-time of the first switching element is a constant value.

2. a first power supply unit including a first transmission coil, a first resonant capacitor, a first switching element, and a first diode connected in parallel to the first switching element; a second power supply including a second transmission coil, a second resonant capacitor, and a second diode; A control unit, A magnetic resonance power supply device that supplies transmission power from the first power supply unit to the second power supply unit by magnetic resonance, the second diode is turned off after a first phase shift time, which is a predetermined time difference, has elapsed since the first switching element was turned off; The control unit is an on-time control circuit that controls turn-off of the first switching element in response to a power value of the transmission power, thereby controlling an on-time of the first switching element; the on-time control circuit has data indicating a relationship between the transmission power and an on-time of the first switching element, and determines a timing for turning off the first switching element based on the data; The data indicates a relationship in which, as the transmission power decreases from a predetermined first threshold to a maximum value, the on-time of the first switching element becomes shorter, while when the transmission power is smaller than the first threshold, the on-time of the first switching element is a constant value.

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