Wireless power supply device

Abstract

A wireless power supply device (10) comprises: a power conversion circuit (11) configured to receive input of a voltage from a power supply (90); a control unit (53) configured to control the power conversion circuit (11); a power supply resonance circuit (31) configured to receive input of a voltage from the power conversion circuit (11); and a power reception resonance circuit (41) connected to a load (91). The power supply resonance circuit (31) is provided with a power supply coil (32) and a power supply capacitor (33) connected to the power supply coil (32). The power reception resonance circuit (41) is provided with a power reception coil (42) and a power reception capacitor (43) connected to the power reception coil (42). The control unit (53) is configured to control the power conversion circuit (11) to adjust, in accordance with the voltage from the power supply (90), a proportion of time during which the voltage is applied to the power supply resonance circuit (31) in one cycle.

Description

Wireless power supply

[0001] This disclosure relates to a wireless power supply device.

[0002] Patent Document 1 discloses a wireless power transfer device using magnetic resonance that utilizes PT (Parity-Time) symmetry. PT symmetry refers to a symmetry that combines parity symmetry and time reversal symmetry. The wireless power transfer device comprises a power supply resonant circuit and a power receiving resonant circuit. The power supply resonant circuit comprises a power supply coil and a power supply capacitor. The power receiving resonant circuit comprises a power receiving coil and a power receiving capacitor. In wireless power transfer utilizing PT symmetry, the power transmission efficiency is maintained at a constant level even if the distance between the power supply coil and the power receiving coil fluctuates.

[0003] Japanese Patent Publication No. 2022-121324

[0004] In wireless power transfer devices that utilize PT symmetry, fluctuations in the voltage input to the power supply resonant circuit cause fluctuations in the output voltage.

[0005] A wireless power supply device according to one aspect of the present disclosure includes a power conversion circuit configured to receive a voltage from a power source, a control unit configured to control the power conversion circuit, a power supply resonant circuit configured to receive a voltage from the power conversion circuit, and a power receiving resonant circuit connected to a load. The wireless power supply device is configured such that the PT symmetry between the power supply resonant circuit and the power receiving resonant circuit is preserved. The power supply resonant circuit includes a power supply coil and a power supply capacitor connected to the power supply coil. The power receiving resonant circuit includes a power receiving coil and a power receiving capacitor connected to the power receiving coil. The control unit is configured to control the power conversion circuit to adjust the proportion of time during which a voltage is applied to the power supply resonant circuit in one cycle, according to the voltage from the power source.

[0006] Figure 1 is a circuit diagram of a wireless power transmission device. Figure 2 is a diagram showing the relationship between the states of a first leg and a second leg provided in the wireless power transmission device of Figure 1 and an input voltage. Figure 3 is a flowchart showing control performed by a control unit provided in the wireless power transmission device of Figure 1. Figure 4 is a diagram showing an input voltage input to the power feeding resonance circuit of Figure 1. Figure 5 is a diagram showing a first phase shift period representing a switching delay time of the first leg of Figure 1 and a second phase shift period representing a switching delay time of the second leg of Figure 1. Figure 6 is a circuit diagram of the wireless power transmission device. Figure 7 is a circuit diagram of a power conversion circuit. Figure 8 is a circuit diagram of the wireless power transmission device.

[0007] An embodiment of a wireless power transmission device will be described. As shown in Figure 1, the wireless power transmission device 10 supplies power supplied from a power source 90 to a load 91. The power source 90 has a voltage V ｄｃ and outputs the voltage V. The power source 90 is, for example, a battery. The power source 90 may be a power supply circuit that converts an alternating voltage into a direct voltage and outputs the direct voltage. The load 91 is a device driven by power supplied from the wireless power transmission device 10. The load 91 may be an alternating current load driven by alternating current power, or may be a direct current load driven by direct current power. When the load 91 is a direct current load, the wireless power transmission device 10 includes a rectifier circuit that outputs direct current power to the direct current load.

[0008] The wireless power transmission device 10 includes a power conversion circuit 11, a resistance element 21, a power feeding resonance circuit 31, a power receiving resonance circuit 41, a voltage detection circuit 51, a zero-cross comparator 52, and a control unit 53.

[0009] The power conversion circuit 11 includes a first leg 12 and a second leg 16. The first leg 12 includes a first switching element 13 and a second switching element 14 connected in series to the first switching element 13. The second leg 16 includes a third switching element 17 and a fourth switching element 18 connected in series to the third switching element 17. The power conversion circuit 11 is a full-bridge circuit including four switching elements 13, 14, 17, 18. The switching elements 13, 14, 17, 18 are, for example, MOSFETs (Metal Oxide Semiconductor Field Effect Transistors). The first leg 12 and the second leg 16 are provided in parallel with each other. The first switching element 13 and the second switching element 14 are connected to the positive electrode of a power supply 90. A voltage V is supplied from the power supply 90 to the power conversion circuit 11 ｄｃ is input to the power conversion circuit 11.

[0010] The resistance element 21 is connected to a first connection point 15, which is a connection point between the first switching element 13 and the second switching element 14. The power feeding resonance circuit 31 includes a power feeding coil 32 and a power feeding capacitor 33. A first end of the power feeding coil 32 is connected to the resistance element 21. Accordingly, the first end of the power feeding coil 32 is connected to the first connection point 15 via the resistance element 21. A second end of the power feeding coil 32 is connected to a second connection point 19, which is a connection point between the third switching element 17 and the fourth switching element 18. Therefore, both ends of the power feeding coil 32 are electrically connected to the power conversion circuit 11.

[0011] The power feeding capacitor 33 is connected in parallel to the power feeding coil 32. A resistance component 34 exists between the power feeding coil 32 and the power feeding capacitor 33. This resistance component 34 is a winding resistance of the power feeding coil 32.

[0012] A voltage is input from the power conversion circuit 11 to the power feeding resonance circuit 31. This voltage is an input voltage V ｉｎ . The input voltage V ｉｎThis is the potential difference between the first connection point 15 and the second connection point 19. The resonant power receiving circuit 41 comprises a power receiving coil 42 and a power receiving capacitor 43. The power receiving coil 42 is connected to the load 91. The power receiving capacitor 43 is connected in parallel to the power receiving coil 42. A resistive component 44 exists between the power receiving coil 42 and the power receiving capacitor 43. This resistive component 44 is the winding resistance of the power receiving coil 42.

[0013] The circuit configuration of the wireless power supply device 10 is a PP (Parallel-Parallel) topology. In a PP topology, the power supply capacitor 33 is connected in parallel to the power supply coil 32, and the power receiving capacitor 43 is connected in parallel to the power receiving coil 42.

[0014] The voltage detection circuit 51 detects the resonant voltage of the power supply resonant circuit 31. The input voltage V ｉｎ When a signal is input, resonance occurs in the power supply resonant circuit 31 according to the inductance of the power supply coil 32 and the capacitance of the power supply capacitor 33. This generates a resonant voltage. The voltage detection circuit 51 detects, for example, the voltage across the power supply capacitor 33. The voltage detection circuit 51 outputs a signal indicating the resonant voltage to the zero-crossing comparator 52.

[0015] The zero-crossing comparator 52 is a comparator that compares the input signal with a reference signal. The zero-crossing comparator 52 compares the input signal with the reference signal and outputs a rectangular signal based on the comparison result. The zero-crossing comparator 52 outputs a high-level signal when the resonant voltage is higher than the reference voltage. The zero-crossing comparator 52 outputs a low-level signal when the resonant voltage is less than or equal to the reference voltage. The reference voltage is, for example, 0 [V]. The signal showing the resonant voltage is an example of a signal input to the zero-crossing comparator 52. The reference voltage is an example of a reference signal.

[0016] The control unit 53 controls the switching elements 13, 14, 17, and 18. The control unit 53, which is a processing circuit, may include one or more processors that perform various processes according to a computer program. The control unit 53 may also include one or more dedicated hardware circuits that perform at least some of the various processes. The hardware circuits are, for example, ASICs (Application Specific Integrated Circuits) or FPGAs (Field Programmable Gate Arrays).

[0017] The control unit 53 includes a drive circuit 54 that switches the switching elements 13, 14, 17, and 18 on and off. The drive circuit 54 performs phase shift control. Phase shift control is a control that adjusts the amount of phase shift ts between the switching of the first leg 12 and the switching of the second leg 16. Switching of the first leg 12 means switching between the first switching element 13 and the second switching element 14, that is, switching which of the first switching element 13 and the second switching element 14 is turned on. When the first switching element 13 is on, the second switching element 14 is off. When the second switching element 14 is on, the first switching element 13 is off. Switching of the second leg 16 means switching between the third switching element 17 and the fourth switching element 18, that is, switching which of the third switching element 17 and the fourth switching element 18 is turned on. When the third switching element 17 is on, the fourth switching element 18 is off. When the fourth switching element 18 is ON, the third switching element 17 is OFF.

[0018] As shown in Figure 2, the input voltage V depends on the state of the first leg 12 and the second leg 16. ｉｎ This changes. In this embodiment, turning on the first switching element 13 is equivalent to turning on the first leg 12, and turning on the third switching element 17 is equivalent to turning on the second leg 16.

[0019] When the first leg 12 is ON and the second leg 16 is OFF, the input voltage V ｉｎ is, +V ｄｃ. When the first leg 12 is off and the second leg 16 is on, the input voltage V ｉｎ is -V ｄｃ . When the first leg 12 is on and the second leg 16 is on, the input voltage V ｉｎ becomes 0. When the first leg 12 is off and the second leg 16 is off, the input voltage V ｉｎ becomes 0. That is, when both the first leg 12 and the second leg 16 are on, or both are off, no voltage is applied to the feeding resonance circuit 31. Therefore, the application time ratio D can be adjusted by adjusting the period in which both the first leg 12 and the second leg 16 are on, or both are off. The application time ratio D is the ratio of the time during which a voltage is applied to the feeding resonance circuit 31 in one cycle.

[0020] The control unit 53 adjusts the phase shift amount ts from the switching of the first leg 12 to the switching of the second leg 16 while keeping the duty ratio of the first leg 12 and the duty ratio of the second leg 16 constant. Thereby, the control unit 53 adjusts the application time ratio D according to the voltage V from the power supply 90 ｄｃ . The duty ratio of the first leg 12 is the ratio of the on-time of the first switching element 13 in one cycle. The duty ratio of the second leg 16 is the ratio of the on-time of the third switching element 17 in one cycle. For example, the duty ratio of the first leg 12 and the duty ratio of the second leg 16 are 50%.

[0021] As shown in FIG. 1, the control unit 53 includes a processing unit 55. The processing unit 55 is an arithmetic circuit that calculates parameters necessary for the driving circuit 54 to switch the switching elements 13, 14, 17, 18 between on and off. The control performed by the processing unit 55 will be described in detail.

[0022] As shown in FIG. 3, in step S1, the processing unit 55 sets the target output voltage V ｏ . The target output voltage V ｏ is a target value of the output voltage applied across the load 91. Next, in step S2, the processing unit 55 acquires the voltage V of the power supply 90 ｄｃ . The processing unit 55 acquires the voltage V of the power supply 90 ｄｃVoltage V measured from a voltage sensor ｄｃ The processing unit 55 may obtain the voltage V from a battery management system or the like that monitors the status of the power supply 90. ｄｃ You may obtain it.

[0023] Next, in step S3, the processing unit 55 sets the target output voltage V ｏ The application time ratio D required to output the signal is calculated. As shown in Figure 4, the input voltage V ｉｎ is, +V ｄｃ , -V ｄｃ The input voltage V is a square wave whose voltage changes between 0 and 0. ｉｎ When the input voltage V is input to the power supply resonant circuit 31, the power supply resonant circuit 31 reacts to the input voltage V ｉｎ Only the signal at the resonant frequency, i.e., the fundamental wave, is allowed to pass through. Let f(ωt) be a square wave, and the amplitude V of the fundamental wave contained in the square wave is... ｆ When the amplitude V is extracted, ｆ This can be expressed as shown in equation (1) below.

[0024]

[0025] In the wireless power transfer device 10 that utilizes PT (Parity-Time) symmetry, the amplitude V of the fundamental wave ｆ This becomes the output voltage. Therefore, the amplitude V of the fundamental wave ｆ = Target output voltage V ｏ It can be considered as follows. From equation (1), the application time ratio D can be expressed by the following equation (2).

[0026]

[0027] The processing unit 55 controls the voltage V of the power supply 90. ｄｃ , and target output voltage V ｏ The application time ratio D is calculated from this. As shown in Figures 3 and 5, in step S4, the processing unit 55 detects the zero-crossing point P1 from the signal output by the zero-crossing comparator 52. For example, the processing unit 55 detects the point in time when the signal of the zero-crossing comparator 52 rises to a high level as the zero-crossing point P1 from negative to positive. For example, the processing unit 55 detects the point in time when the signal of the zero-crossing comparator 52 falls to a low level as the zero-crossing point P1 from positive to negative.

[0028] Next, in step S5, the processing unit 55 calculates the period T of the resonant voltage. The processing unit 55 calculates the period T from the zero-crossing point P1. The period T may be calculated each time, or it may be the average value of the most recent multiple times.

[0029] Next, in step S6, the processing unit 55 performs the first phase shift period ts １ , and the second phase shift period ts ２ The following is calculated. Figure 5 shows the state of the first leg 12 and the second leg 16 with respect to the zero-crossing point P1, with the phase shift amount ts being 0, as indicated by dashed lines. First phase shift period ts １ This is the delay time for switching the first leg 12 when the phase shift amount ts is 0. Second phase shift period ts ２ This is the delay time for switching to the second leg 16 when the phase shift amount ts is 0. And the first phase shift period ts １ This delays the switching of the first leg 12 and also delays the second phase shift period ts ２ The phase shift amount ts is the phase difference between the switching of the first leg 12 and the second leg 16 that occurs when the switching of the second leg 16 is delayed by only a certain amount.

[0030] As can be seen from Figure 5, the application time ratio D, the period T, and the first phase shift period ts are shown. １ The following relationship (3) holds: From equation (3), the first phase shift period ts １ This can be expressed by equation (4).

[0031]

[0032] Second phase shift period ts ２ This can be expressed by equation (5).

[0033]

[0034] The processing unit 55 calculates the first phase shift period ts from equation (4) １ The processing unit 55 calculates the second phase shift period ts from equation (5). ２Next, in step S7, the processing unit 55 calculates the first phase shift period ts from the zero-crossing point P1. １ A command is sent to the drive circuit 54 to switch the first leg 12 on and off with a delay of only a few seconds. The drive circuit 54 operates from the zero-crossing point P1 for the first phase shift period ts １ The first leg 12 is switched on and off with only a slight delay.

[0035] Next, in step S8, the processing unit 55 performs a second phase shift period ts from the zero-crossing point P1. ２ A command is sent to the drive circuit 54 to switch the first leg 12 on and off with a delay of only a few seconds. The drive circuit 54 operates from the zero-crossing point P1 for the second phase shift period ts ２ The second leg 16 is switched on and off with a delay of only a short time. In this way, the control unit 53 controls the power conversion circuit 11 based on the zero-crossing point P1 of the resonant voltage detected by the voltage detection circuit 51.

[0036] The first leg 12 is in the first phase shift period ts １ The delay is limited to the second phase shift period ts. ２ By delaying by this amount, a phase shift amount ts is set that achieves the application time ratio D. This allows the target output voltage V to be achieved. ｏ Switching of switching elements 13, 14, 17, and 18 is performed to output the specified value.

[0037] After completing the process in step S8, the processing unit 55 returns to step S2. Then, the processing unit 55 repeatedly performs the processes from step S2 onward. This increases the voltage V of the power supply 90. ｄｃ Even if the target output voltage V changes, ｏ The application time ratio D is calculated so that the output can be achieved. Then, the switching elements 13, 14, 17, and 18 are switched so that the application time ratio D can be achieved.

[0038] The circuit, which includes the power conversion circuit 11, the power supply resonant circuit 31, the voltage detection circuit 51, the zero-crossing comparator 52, and the control unit 53, is configured to function as a negative resistance circuit that behaves as a negative resistance corresponding to the load 91. This preserves the PT symmetry between the power supply resonant circuit 31 and the power receiving resonant circuit 41.

[0039] [Operation of this embodiment] Voltage V input from power supply 90 to power conversion circuit 11 ｄｃ This can change. For example, if the power source 90 is a battery, the voltage V input to the power conversion circuit 11 will vary depending on the battery's charge level. ｄｃ The voltage V changes. ｄｃ While it's possible to stabilize the voltage using a DC-DC converter or similar device in response to these changes, this would require a large-scale circuit.

[0040] In this embodiment, the control unit 53 adjusts the application time ratio D by controlling the power conversion circuit 11. By adjusting the application time ratio D, the amplitude V of the fundamental wave is controlled. ｆ This can be adjusted. If PT symmetry is preserved, the amplitude V of the fundamental wave ｆ This becomes the output voltage. Therefore, the control unit 53 sets the target output voltage V ｏ The output voltage can be adjusted by adjusting the application time ratio D accordingly. In other words, the control unit 53 adjusts the voltage V by adjusting the application time ratio D. ｄｃ The AC power is adjusted to maintain PT symmetry while absorbing the changes.

[0041] [Effects of this embodiment] (1) The control unit 53 adjusts the application time ratio D. In the wireless power supply device 10 that utilizes PT symmetry, the amplitude V of the fundamental wave ｆ This becomes the output voltage. By adjusting the application time ratio D, the amplitude V of the fundamental wave can be changed. ｆ The voltage V input from the power supply 90 to the power conversion circuit 11 can be adjusted. ｄｃ Even if the voltage V of the power supply 90 changes, the wireless power supply device 10 can adjust the output voltage. ｄｃ Even if the output voltage changes, the wireless power supply device 10 can maintain its output voltage.

[0042] (2) The power supply capacitor 33 is connected in parallel with the power supply coil 32. As a result, the power supply resonant circuit 31 becomes a parallel resonant circuit, where the voltage is at its maximum and the current is at its minimum. Therefore, the period T can be easily calculated by calculating the period T from the zero-crossing point P1 of the resonant voltage detected by the voltage detection circuit 51.

[0043] (3) The control unit 53 controls the phase shift amount ts between the switching of the first switching element 13 and the second switching element 14 and the switching of the third switching element 17 and the fourth switching element 18. This allows the applied time ratio D to be adjusted.

[0044] [Examples of Modifications] The embodiment can be implemented with the following modifications. The embodiment and the following examples of modifications can be combined with each other to the extent that they do not contradict each other technically.

[0045] ○The control unit 53 may adjust the application time ratio D by adjusting the duty cycle of the first leg 12 and the duty cycle of the second leg 16. As described in the embodiment, when both the first leg 12 and the second leg 16 are on, or both are off, no voltage is applied to the power supply resonant circuit 31. For this reason, the application time ratio D can be adjusted by adjusting the duty cycle of the first leg 12 and the duty cycle of the second leg 16.

[0046] As shown in Figure 6, in addition to the configuration of the embodiment, the wireless power supply device 10 includes a triangular wave generation unit 56 that generates a triangular wave, which is an example of a carrier wave. The triangular wave generation unit 56 receives a signal from the zero-crossing comparator 52. The triangular wave generation unit 56 generates a triangular wave synchronized with the signal input from the zero-crossing comparator 52. Specifically, it generates a triangular wave with the same period as the period T calculated from the zero-crossing point P1.

[0047] Processing unit 55 controls the target output voltage V ｏ and power supply voltage V ｄｃ From the ratio, the target output voltage V ｏThe duty cycles of the first leg 12 and the second leg 16 are calculated so that a rectangular wave AC voltage as shown in Figure 4 can be output. Then, the processing unit 55 calculates a threshold voltage to be compared with a triangular wave so that the duty cycles of the first leg 12 and the second leg 16 can be achieved.

[0048] The drive circuit 54 includes a PWM circuit that generates a PWM signal by comparing a triangular wave with a threshold voltage. The PWM circuit may generate a PWM signal that is high level when the threshold voltage is higher than the triangular wave and low level when the threshold voltage is less than or equal to the triangular wave. The drive circuit 54 switches the switching elements 13, 14, 17, and 18 on and off using the PWM signal. This adjusts the duty cycle of the first leg 12 and the duty cycle of the second leg 16 so that the application time ratio D is achieved.

[0049] If the frequency is changed in order to establish PT symmetry, the amplitude of the triangular wave may fluctuate due to the change in frequency. The processing unit 55 may calculate a threshold voltage based on the upper and lower voltage limits of the triangular wave by knowing the upper and lower voltage limits.

[0050] Furthermore, due to dead time, the phase between the switching of the first leg 12 and the switching of the second leg 16 may be shifted. In this case, a phase compensation circuit may be used to adjust the phase so that it remains constant.

[0051] As shown in Figure 7, the power conversion circuit 60 may include a first switching element 61 connected to the power supply 90, a second switching element 62 connected in series with the first switching element 61, a third switching element 63, and a fourth switching element 64.

[0052] In this case, the wireless power supply device 10 includes a first capacitor 71 and a second capacitor 72. The first capacitor 71 and the second capacitor 72 are connected in series with each other. The first capacitor 71 is connected to the power supply 90.

[0053] The third switching element 63 and the fourth switching element 64 are connected in series between the connection point between the first switching element 61 and the second switching element 62 and the connection point between the first capacitor 71 and the second capacitor 72.

[0054] The connection point between the first switching element 61 and the second switching element 62, and the connection point between the first capacitor 71 and the second capacitor 72 are connected to the power supply resonant circuit 31. When the first switching element 61 is ON, the input voltage V ｉｎ ha + V ｄｃ It is / 2. When the second switching element 62 is ON, the input voltage V ｉｎ ha-V ｄｃ It is / 2. When the third switching element 63 and the fourth switching element 64 are ON, the input voltage V ｉｎ It is 0. In this case, +V in Figure 4 ｄｃ , -V ｄｃ + V ｄｃ / 2, -V ｄｃ By replacing it with / 2 and rearranging equations (1) and (2) accordingly, the application time ratio D can be calculated. Therefore, the application time ratio D can be adjusted by controlling the switching elements 61, 62, 63, and 64. This makes it possible to obtain the same effects as in the embodiment.

[0055] ○As shown in Figure 8, the power supply capacitor 33 may be connected in series with the power supply coil 32. In this case, the wireless power supply device 10 may be equipped with a current detection circuit 81 instead of a voltage detection circuit 51. The current detection circuit 81 detects the resonant current of the power supply resonant circuit 31. The resonant current is the current that flows into the power supply resonant circuit 31 due to the resonance of the power supply resonant circuit 31. In this case, the zero-crossing comparator 52 outputs a high-level signal when the resonant current is greater than the reference current. The zero-crossing comparator 52 outputs a low-level signal when the resonant current is less than or equal to the reference current. As a result, the processing unit 55 can detect the zero-crossing point P1.

[0056] When the power supply capacitor 33 is connected in series with the power supply coil 32, the power supply resonant circuit 31 becomes a series resonant circuit, where the current is maximized and the voltage is minimized. Therefore, the period T can be easily calculated by calculating the period T from the zero-crossing point P1 of the resonant current detected by the current detection circuit 81.

[0057] In the wireless power supply device 10 shown in Figure 8, the receiving capacitor 43 is connected in parallel with the receiving coil 42, but the receiving capacitor 43 may also be connected in series with the receiving coil 42. That is, the wireless power supply device 10 may have an SP (Series-Parallel) topology or an SS (Series-Series) topology.

[0058] ○The power receiving resonant circuit 41 may have a circuit configuration in which a power receiving capacitor 43 is connected in series with the power receiving coil 42. In other words, the wireless power supply device 10 may have a PS (Parallel-Series) topology.

[0059] ○The wireless power supply device 10 may include a rectifier circuit connected to the power receiving resonant circuit 41. That is, the load 91 may operate on a DC voltage or on an AC voltage.

Claims

1. A wireless power supply device comprising: a power conversion circuit configured to receive voltage from a power source; a control unit configured to control the power conversion circuit; a power supply resonant circuit configured to receive voltage from the power conversion circuit; and a power receiving resonant circuit connected to a load, wherein the PT symmetry between the power supply resonant circuit and the power receiving resonant circuit is preserved, the power supply resonant circuit comprising: a power supply coil; and a power supply capacitor connected to the power supply coil; the power receiving resonant circuit comprising: a power receiving coil; and a power receiving capacitor connected to the power receiving coil; and the control unit configured to control the power conversion circuit to adjust the ratio of time over which voltage is applied to the power supply resonant circuit in one cycle according to the voltage from the power source.

2. The wireless power supply device according to claim 1, wherein the power supply capacitor is connected in parallel with the power supply coil, the wireless power supply device includes a voltage detection circuit configured to detect the resonant voltage of the power supply resonant circuit, and the control unit is configured to control the power conversion circuit based on the zero-crossing point of the resonant voltage detected by the voltage detection circuit.

3. The wireless power supply device according to claim 1, wherein the power supply capacitor is connected in series with the power supply coil, the wireless power supply device includes a current detection circuit configured to detect the resonant current of the power supply resonant circuit, and the control unit is configured to control the power conversion circuit based on the zero-crossing point of the resonant current detected by the current detection circuit.

4. The wireless power supply device according to claim 1, wherein the power conversion circuit comprises a first leg and a second leg provided in parallel with the first leg, the first leg comprises a first switching element and a second switching element connected in series with the first switching element, the second leg comprises a third switching element and a fourth switching element connected in series with the third switching element, and the control unit is configured to control the amount of phase shift between the switching of the first switching element and the second switching element and the switching of the third switching element and the fourth switching element.

5. The wireless power supply device according to claim 1, wherein the power conversion circuit comprises a first leg and a second leg provided in parallel with the first leg, the first leg comprises a first switching element and a second switching element connected in series with the first switching element, the second leg comprises a third switching element and a fourth switching element connected in series with the third switching element, and the control unit is configured to control the duty cycle of the first leg and the duty cycle of the second leg.

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