Power conversion device and control method

Abstract

A power conversion device (1) comprises: a resonator (30) that has a transformer (T) and a capacitor (Cr); a primary-side full-bridge circuit (10) that has a first switch (Q1), a second switch (Q2), a third switch (Q3), and a fourth switch (Q4); a secondary-side full-bridge circuit (20) that has a fifth switch (Q5), a sixth switch (Q6), a seventh switch (Q7), and an eighth switch (Q8); and a controller (40), wherein during phase shift control, the controller (40) turns on the fifth switch (Q5), the sixth switch (Q6), the seventh switch (Q7), and the eighth switch (Q8) with drive signals in a period corresponding to a phase difference between switching of the first switch and the second switch and switching of the third switch (Q3) and the fourth switch (Q4), and controls the on times of the drive signals in the period corresponding to the phase difference.

Description

Power conversion device and control method

[0001] The present disclosure relates to a power conversion device and a control method for a power conversion device.

[0002] Toward the realization of a carbon-neutral society, there is a demand for charging circuits that can efficiently charge home storage batteries or automotive batteries. Such charging circuits require isolated DC-DC converters, and resonant converters are commonly used for their compact size and high efficiency. Among resonant converters, LLC converters have attracted particular attention because they can achieve high efficiency with a simple circuit configuration.

[0003] LLC converters generally use frequency control to control output power. The loads to which power is supplied from LLC converters range from light loads to heavy loads, and to accommodate these, the frequency control range becomes wide, requiring measures to accommodate all operating conditions (e.g., EMC (Electromagnetic Compatibility) measures, etc.).

[0004] In response to this, Patent Document 1 describes an LLC type DC-DC converter that controls output power by making the transformer current have an asymmetric waveform between positive and negative by duty control.

[0005] Japanese Patent Application Laid-Open No. 2022-17179

[0006] However, in the DC-DC converter disclosed in Patent Document 1, the transformer current has an asymmetric waveform between positive and negative, which causes effects such as an increase in common mode noise.

[0007] Therefore, the present disclosure provides a power conversion device and the like that can effectively control output power while suppressing the frequency control range width.

[0008] A power conversion device according to the present disclosure includes a resonator having a transformer and a resonance capacitor, a primary-side full bridge circuit connected to a primary side of the resonator, a secondary-side full bridge circuit connected to a secondary side of the resonator, and a controller that controls the primary-side full bridge circuit and the secondary-side full bridge circuit, wherein the primary-side full bridge circuit has a first switch element provided on a high side of a first leg, a second switch element provided on a low side of the first leg, a third switch element provided on the high side of a second leg, and a fourth switch element provided on the low side of the second leg, and the secondary-side full bridge circuit has a fifth switch element provided on a high side of a third leg, a sixth switch element provided on the low side of the third leg, and a seventh switch element provided on the high side of a fourth leg. the controller operates the first switch element, the second switch element, the third switch element, and the fourth switch element so that the switching phases of the third switch element and the fourth switch element are delayed with respect to the switching phases of the first switch element and the second switch element, calculates a period corresponding to a phase difference between the switching of the first switch element and the second switch element and the switching of the third switch element and the fourth switch element, turns on the fifth switch element, the sixth switch element, the seventh switch element, and the eighth switch element by a drive signal in the period corresponding to the phase difference, and controls an on time of the drive signal in the period corresponding to the phase difference.

[0009] A control method according to the present disclosure is a control method for controlling a power conversion device, the power conversion device including a resonator having a transformer and a resonance capacitor, a primary-side full bridge circuit connected to a primary side of the resonator, and a secondary-side full bridge circuit connected to a secondary side of the resonator, the primary-side full bridge circuit including a first switch element provided on a high side of a first leg, a second switch element provided on a low side of the first leg, a third switch element provided on the high side of a second leg, and a fourth switch element provided on the low side of the second leg, the secondary-side full bridge circuit including a fifth switch element provided on the high side of a third leg, a sixth switch element provided on the low side of the third leg, a seventh switch element provided on the high side of a fourth leg, and and an eighth switch element provided on a low side of a fourth leg, wherein the control method operates the first switch element, the second switch element, the third switch element, and the fourth switch element so that a switching phase of the third switch element and the fourth switch element is delayed with respect to a switching phase of the first switch element and the second switch element, calculates a period corresponding to a phase difference between switching of the first switch element and the second switch element and switching of the third switch element and the fourth switch element, turns on the fifth switch element, the sixth switch element, the seventh switch element, and the eighth switch element by a drive signal in the period corresponding to the phase difference, and controls an on time of the drive signal in the period corresponding to the phase difference.

[0010] These comprehensive or specific aspects may be realized as a system, a method, an integrated circuit, a computer program, or a computer-readable recording medium such as a CD-ROM, or may be realized as any combination of a system, a method, an integrated circuit, a computer program, and a recording medium.

[0011] According to a power conversion device according to an aspect of the present disclosure, it is possible to effectively control output power while suppressing the frequency control range width.

[0012] FIG. 1 is a circuit configuration diagram showing an example of a power conversion device according to embodiment 1. FIG. 2 is a diagram for explaining the operation of the power conversion device according to embodiment 1. FIG. 3 is a diagram showing the effect of the operation of the power conversion device according to embodiment 1. FIG. 4 is a diagram for explaining losses occurring in a secondary-side switching element. FIG. 5 is a circuit configuration diagram showing an example of a power conversion device according to embodiment 2. FIG. 6 is a diagram for explaining the operation and effect of the power conversion device according to embodiment 2. FIG. 7 is a flowchart showing an example of a control method according to another embodiment.

[0013] Hereinafter, the embodiments will be specifically described with reference to the drawings.

[0014] The embodiments described below are all comprehensive or specific examples, and the numerical values, shapes, materials, components, arrangement and connection of the components, steps, and order of steps shown in the following embodiments are merely examples and are not intended to limit the present disclosure.

[0015] (First embodiment) Hereinafter, a power conversion device according to a first embodiment will be described.

[0016] FIG. 1 is a circuit configuration diagram showing an example of a power conversion device 1 according to an embodiment.

[0017] The power conversion device 1 is an isolated DC-DC converter that boosts or bucks an input voltage to a predetermined voltage and outputs it. The power conversion device 1 is capable of unidirectional or bidirectional power conversion. For example, the power conversion device 1 is an LLC converter. An LLC converter is a circuit that utilizes LLC resonance due to the leakage inductance, excitation inductance, and resonant capacitor of a transformer. In an LLC converter, frequency control, which changes the switching frequency, changes the input / output voltage ratio (Gain), thereby enabling the desired power output. Furthermore, in an LLC converter, phase shift control, which increases the phase difference between the switching phases of the two primary legs, increases the period during which the voltage applied to the transformer is zero. This reduces the power transmitted to the secondary side, significantly reducing the gain of the LLC converter and enabling even greater changes in the input / output voltage ratio. Below, we describe a power conversion device 1 that can control output power without frequency control.

[0018] The power conversion device 1 has terminals t1, t2, t3, and t4. The terminal t1 is an input terminal. The terminal t2 is a ground terminal. The terminal t3 is an output terminal. The terminal t4 is a ground terminal. Note that, since the power conversion device 1 is an isolated DC-DC converter, the terminals t2 and t4 are electrically isolated.

[0019] The power conversion device 1 includes a primary side full bridge circuit 10, a secondary side full bridge circuit 20, a resonator 30, capacitors Cin and Cout, and a controller 40. The capacitors Cin and Cout do not necessarily have to be components of the power conversion device 1.

[0020] The capacitor Cin is an input capacitor connected between the terminal t1 and the terminal t2, and the capacitor Cout is an output capacitor (smoothing capacitor) connected between the terminal t3 and the terminal t4.

[0021] The primary-side full-bridge circuit 10 is connected to the primary side of the resonator 30. The primary-side full-bridge circuit 10 has a first switch element provided on the high side of a first leg connecting the terminals t1 and t2, a second switch element provided on the low side of the first leg, a third switch element provided on the high side of a second leg connecting the terminals t1 and t2, and a fourth switch element provided on the low side of the second leg. The first leg and the second leg are connected in parallel.

[0022] The primary-side full-bridge circuit 10 has switches Q1, Q2, Q3, and Q4, where the switch Q1 is an example of a first switch element, the switch Q2 is an example of a second switch element, the switch Q3 is an example of a third switch element, and the switch Q4 is an example of a fourth switch element.

[0023] The switch Q1 is, for example, an N-channel metal oxide semiconductor field effect transistor (MOSFET). The drain of the switch Q1 is connected to the terminal t1, and the source of the switch Q1 is connected to the drain of the switch Q2.

[0024] The switch Q2 is, for example, an N-channel MOSFET. The drain of the switch Q2 is connected to the source of the switch Q1, and the source of the switch Q2 is connected to the terminal t2.

[0025] The switch Q3 is, for example, an N-channel MOSFET. The drain of the switch Q3 is connected to the terminal t1, and the source of the switch Q3 is connected to the drain of the switch Q4.

[0026] The switch Q4 is, for example, an N-channel MOSFET. The drain of the switch Q4 is connected to the source of the switch Q3, and the source of the switch Q4 is connected to the terminal t2.

[0027] The secondary-side full-bridge circuit 20 is connected to the secondary side of the resonator 30. The secondary-side full-bridge circuit 20 includes a fifth switch element provided on the high side of a third leg connecting the terminals t3 and t4, a sixth switch element provided on the low side of the third leg, a seventh switch element provided on the high side of a fourth leg connecting the terminals t3 and t4, and an eighth switch element provided on the low side of the fourth leg. The third leg and the fourth leg are connected in parallel. The secondary-side full-bridge circuit 20 also functions as a rectifier circuit capable of full-wave rectification.

[0028] The secondary-side full-bridge circuit 20 has switches Q5, Q6, Q7, and Q8, where the switch Q5 is an example of a fifth switch element, the switch Q6 is an example of a sixth switch element, the switch Q7 is an example of a seventh switch element, and the switch Q8 is an example of an eighth switch element.

[0029] The switch Q5 is, for example, an N-channel MOSFET. The drain of the switch Q5 is connected to the terminal t3, and the source of the switch Q5 is connected to the drain of the switch Q6.

[0030] The switch Q6 is, for example, an N-channel MOSFET. The drain of the switch Q6 is connected to the source of the switch Q5, and the source of the switch Q6 is connected to the terminal t4.

[0031] The switch Q7 is, for example, an N-channel MOSFET. The drain of the switch Q7 is connected to the terminal t3, and the source of the switch Q7 is connected to the drain of the switch Q8.

[0032] The switch Q8 is, for example, an N-channel MOSFET. The drain of the switch Q8 is connected to the source of the switch Q7, and the source of the switch Q8 is connected to the terminal t4.

[0033] The resonator 30 includes a transformer T and a capacitor Cr.

[0034] The capacitor Cr is an example of a resonant capacitor and is connected to a node between the switch Q1 and the switch Q2 in the first leg.

[0035] The transformer T is an isolated transformer having a primary winding and a secondary winding that are insulated from each other. One end of the primary winding of the transformer T is connected via a capacitor Cr to a node between the switches Q1 and Q2 in the first leg, and the other end of the primary winding of the transformer T is connected to a node between the switches Q3 and Q4 in the second leg. One end of the secondary winding of the transformer T is connected to a node between the switches Q5 and Q6 in the third leg, and the other end of the secondary winding of the transformer T is connected to a node between the switches Q7 and Q8 in the fourth leg.

[0036] The capacitor Cr may be connected to a node between the switches Q3 and Q4 in the second leg. In this case, one end of the primary winding of the transformer T is connected to a node between the switches Q1 and Q2 in the first leg, and the other end of the primary winding of the transformer T is connected to a node between the switches Q3 and Q4 in the second leg via the capacitor Cr.

[0037] The controller 40 controls the primary-side full-bridge circuit 10 and the secondary-side full-bridge circuit 20. Specifically, the controller 40 is a circuit for controlling the switching (on and off) of switches (e.g., switches Q1, Q2, Q3, Q4, Q5, Q6, Q7, and Q8) included in the power conversion device 1. For example, the controller 40 controls the switching of the switches Q1, Q2, Q3, Q4, Q5, Q6, Q7, and Q8 by controlling a gate drive circuit (not shown) connected to the gates of the switches Q1, Q2, Q3, Q4, Q5, Q6, Q7, and Q8 via a PWM generator (not shown) or the like.

[0038] The controller 40 is, for example, a computer including a processor (microprocessor) and a memory. The memory may be a read-only memory (ROM) or a random access memory (RAM), and can store programs to be executed by the processor. For example, the controller 40 is a microcontroller.

[0039] The controller 40 operates the switches Q1, Q2, Q3, and Q4 so that the switching phase of the switches Q3 and Q4 is delayed relative to the switching phase of the switches Q1 and Q2. In other words, the controller 40 performs phase shift control by setting the first leg (switches Q1 and Q2) as a reference leg and the second leg (switches Q3 and Q4) as a lagging leg, thereby increasing the phase difference between the switching of the first leg and the switching of the second leg.

[0040] The controller 40 also calculates a period corresponding to the phase difference between the switching of the switches Q1 and Q2 and the switching of the switches Q3 and Q4, and turns on the switches Q5, Q6, Q7, and Q8 using a drive signal during the period corresponding to the phase difference. At this time, the controller 40 controls the on time of the drive signal during the period corresponding to the phase difference.

[0041] Here, the operation of the power conversion device 1 will be described in detail with reference to FIG.

[0042] Fig. 2 is a diagram for explaining the operation of the power conversion device 1 according to embodiment 1. Fig. 2 shows, from the top to the bottom, timing charts of the gate signals of the switches Q1, Q4, Q5, and Q8, the gate signals of the switches Q2, Q3, Q6, and Q7, the voltage generated in the secondary winding of the transformer T (transformer secondary voltage), the current flowing in the primary winding of the transformer T (transformer primary current), and the current flowing in the secondary winding of the transformer T (transformer secondary current).

[0043] 2, it can be seen that, due to the phase shift control, the switching phase of the switch Q4 is delayed with respect to the switching phase of the switch Q1, and the switching phase of the switch Q3 is delayed with respect to the switching phase of the switch Q2. The phase shift period caused by the phase shift control is a period during which no current is passed through the loads connected to the terminals t3 and t4, and this period is also called a no-current period.

[0044] 2, the controller 40 turns on the switches Q5 and Q8 in the period from when the switch Q1 is turned on to when the switch Q4 is turned on, and turns on the switches Q6 and Q7 in the period from when the switch Q2 is turned on to when the switch Q3 is turned on, in response to a drive signal. The period corresponding to the phase difference, i.e., the non-conducting period, is the period from when the switch Q1 is turned on to when the switch Q4 is turned on, and the period from when the switch Q2 is turned on to when the switch Q3 is turned on.

[0045] The power conversion device 1, which is an LLC converter, is a circuit that can obtain a gain of 1 or more (i.e., increase the output power) by setting the switching frequency lower than the resonant frequency of the resonator 30 (the resonant frequency due to the capacitance of the capacitor Cr and the leakage inductance of the transformer T, etc.). Setting the switching frequency lower than the resonant frequency of the resonator 30 is equivalent to leading the phase of the resonant current relative to the phase of the input voltage (transformer input voltage) of the resonator 30. In other words, by leading the phase of the resonant current relative to the phase of the transformer input voltage, the output power can be increased. The controller 40 controls the switching of the switches Q1, Q2, Q3, Q4, Q5, Q6, Q7, and Q8 while fixing the switching frequency, so that the phase of the resonant current leads relatively to the phase of the input voltage of the resonant circuit.

[0046] Specifically, as described above, the controller 40 turns on the switches Q5 and Q8 during the period from when the switch Q1 is turned on until the switch Q4 is turned on, and turns on the switches Q6 and Q7 during the period from when the switch Q2 is turned on until the switch Q3 is turned on. Turning on the switches Q5 and Q8 delays the phase at which the transformer secondary voltage reverses polarity from positive to negative. Turning on the switches Q6 and Q7 also delays the phase at which the transformer secondary voltage reverses polarity from negative to positive. Controlling the transformer secondary voltage in this manner results in a corresponding waveform for the transformer primary voltage, i.e., the transformer input voltage. This increases the on-duty of the transformer T, which is determined by the phase shift amount achieved by the phase shift control. This advances the phase of the resonant current relative to the phase of the transformer input voltage, thereby increasing the output power. Further extending the on-time of the switches Q5, Q6, Q7, and Q8 during the non-energized period further advances the phase of the resonant current, thereby further increasing the output power.

[0047] Although not shown, the controller 40 may turn on switches Q6 and Q7 in the period from when switch Q1 is turned on until switch Q4 is turned on, and may turn on switches Q5 and Q8 in the period from when switch Q2 is turned on until switch Q3 is turned on, depending on the drive signal. Turning on switches Q6 and Q7 advances the phase at which the transformer secondary voltage reverses polarity from positive to negative. Turning on switches Q5 and Q8 also advances the phase at which the transformer secondary voltage reverses polarity from negative to positive. In this case, the on-duty of the transformer T, which is determined by the amount of phase shift by phase shift control, is increased, but the phase lead of the resonant current relative to the phase of the transformer input voltage is reduced, which can also reduce the output power. By further extending the on-time of switches Q5, Q6, Q7, and Q8 during the non-energized period, the relative phase lead of the resonant current is further reduced, thereby further reducing the output power.

[0048] In this way, the controller 40 can control the switching of the switches Q1, Q2, Q3, Q4, Q5, Q6, Q7, and Q8 so that the phase of the resonant current advances relative to the phase of the input voltage of the resonant circuit, i.e., the output power increases, while the switching frequency is fixed, and can also control the switching of the switches Q1, Q2, Q3, Q4, Q5, Q6, Q7, and Q8 so that the phase advance of the resonant current decreases relative to the phase of the input voltage of the resonant circuit, i.e., the output power decreases. This allows the power conversion device 1 to increase or decrease its output power while the switching frequency is fixed.

[0049] 3 is a diagram showing the effect of the operation of the power conversion device 1 according to embodiment 1. FIG. 3 shows the relationship between the clamp width (on time) of the secondary-side switch element and the output power. As shown in FIG. 3, it can be seen that the output power increases as the on time of the secondary-side switch element increases.

[0050] As described above, the period corresponding to the phase difference between the switching of the switches Q1 and Q2 and the switching of the switches Q3 and Q4, which occurs during phase shift control, is a non-energized period during which no current is passed through the load. By turning on the switches Q5, Q6, Q7, and Q8 for a certain period during this non-energized period, the timing at which the polarity of the voltage generated in the secondary winding of the transformer T (the transformer secondary voltage) is reversed can be adjusted. When the polarity of the transformer secondary voltage is reversed, the polarity of the excitation voltage of the transformer T is also reversed in accordance with the reversal of the polarity of the transformer secondary voltage. In other words, the timing at which the polarity of the excitation voltage of the transformer T is reversed (in other words, the phase at which the polarity of the excitation voltage of the transformer T is reversed) can be adjusted.

[0051] When the phase of polarity reversal of the excitation voltage of the transformer T is delayed, the phase of the resonant current is relatively advanced, thereby increasing the output power of the power conversion device 1. In other words, it is also possible to increase the input / output voltage ratio during phase shift control. Therefore, by controlling the on-time of the drive signals to the switches Q5, Q6, Q7, and Q8 during the non-energized period, the output power can be controlled without frequency control, and the output power can be effectively controlled while restricting the frequency control range.

[0052] In the first embodiment, the switches Q5, Q6, Q7, and Q8 of the secondary-side full-bridge circuit 20 are turned on at any timing during the non-energized period. However, depending on the timing at which the switches Q5, Q6, Q7, and Q8 are turned on during the non-energized period, losses may occur in the switches Q5, Q6, Q7, and Q8. This will be described with reference to FIG. 4.

[0053] 4 is a diagram for explaining losses occurring in the secondary-side switch elements (switches Q5, Q6, Q7, and Q8). From the top, Fig. 4 shows timing charts of the voltage occurring across the secondary winding of transformer T (transformer secondary voltage), the voltage occurring across secondary-side full bridge circuit 20 (secondary full bridge voltage), the gate voltages of switches Q5, Q6, Q7, and Q8, the drain-source voltage and drain current of switch Q8, the drain-source voltage and drain current of switch Q5, the voltage occurring across the primary winding of transformer T (transformer primary voltage) and the voltage occurring across primary-side full bridge circuit 10 (primary full bridge voltage), the gate voltages of switches Q1, Q2, Q3, and Q4, the drain-source voltage and drain current of switch Q4, and the drain-source voltage and drain current of switch Q1.

[0054] For example, if the switches Q5 and Q6 are turned on in synchronization with the drive signals for the switches Q1 and Q2, as shown in FIG. 4 , a phase difference occurs between the switching of the switch Q5 and the switching of the switch Q8 when the switch Q5 is turned on (specifically, the phase of the switching of the switch Q8 leads the phase of the switching of the switch Q5), as shown in FIG. 4 . As shown in FIG. 4 , the switch Q5 is turned on when a drain current flows through the switch Q5, and an off-state loss occurs when the switch Q5 is turned off (when the clamp is released). As such, there is a risk that the zero-current switching (ZCS) of the switches Q5, Q6, Q7, and Q8 will fail, causing loss in the secondary-side elements.

[0055] A power conversion device capable of suppressing losses occurring in the secondary side switching elements will be described below with reference to FIGS. 5 and 6. FIG.

[0056] FIG. 5 is a circuit configuration diagram showing an example of a power conversion device 2 according to the second embodiment.

[0057] The power conversion device 2 differs from the power conversion device 1 in the first embodiment in that it includes a current detector 50 and in the control content of the controller 40. Since the other points are basically the same as those of the power conversion device 1 in the first embodiment, a description thereof will be omitted, and the following description will focus on the points of difference.

[0058] The current detector 50 detects the transformer current flowing through the transformer T. For example, the current detector 50 is provided between the primary winding of the transformer T and a node between the switches Q3 and Q4 in the second leg. The current detector 50 is configured using a sensor element such as a current transformer, a Hall element, or a shunt resistor. Note that if the power conversion device 2 is provided with current detection means for preventing out-of-resonance, the current detection means may be used as the current detector 50.

[0059] The controller 40 calculates a period corresponding to half the switching period of the switches Q1 and Q2. In the second embodiment, the drive signal is a signal for a period corresponding to half the switching period of the switches Q1 and Q2, including a period corresponding to the phase difference. The controller 40 uses the drive signal for the period corresponding to the half period to turn on the switches Q5, Q6, Q7, and Q8 in synchronization with a zero-crossing detection signal of the transformer current. The zero-crossing detection signal indicates the timing at which the polarity of the transformer current reverses (the timing at which the transformer current changes from negative to positive or from positive to negative), and is detected by the current detector 50. The controller 40 controls the on-time of the drive signal for the period corresponding to the half period. For example, the controller 40 controls the on-time of the drive signal so that the length of the period corresponding to the half period is the upper limit.

[0060] Fig. 6 is a diagram for explaining the operation and effect of the power conversion device 2 according to embodiment 2. Fig. 6 shows, from the top to the bottom, a timing chart of the current flowing in the primary winding of the transformer T (transformer primary current), the drain-source voltage and drain current of the switch Q6, the voltage generated in the secondary winding of the transformer T (transformer secondary voltage), the gate voltages of the switches Q5, Q6, Q7, and Q8, the drain-source voltage and drain current of the switch Q8, the drain-source voltage and drain current of the switch Q5, the resonant voltage of the transformer T, the voltage generated in the primary winding of the transformer T (transformer primary voltage) and the voltage generated in the primary-side full bridge circuit 10 (primary full bridge voltage), the gate voltages of the switches Q1, Q2, Q3, and Q4, the drain-source voltage and drain current of the switch Q4, and the drain-source voltage and drain current of the switch Q1.

[0061] 6, the controller 40 uses the drive signal to turn on the switches Q5 and Q8 in synchronization with the detection signal of the negative-to-positive zero-crossing of the transformer current during the period from when the switch Q1 is turned on until when the switch Q4 is turned on. The controller 40 also uses the drive signal to turn on the switches Q6 and Q7 in synchronization with the detection signal of the positive-to-negative zero-crossing of the transformer current during the period from when the switch Q2 is turned on until when the switch Q3 is turned on.

[0062] During the period from when switch Q1 is turned on to when switch Q4 is turned on, which is the period corresponding to the phase difference, the polarity of the transformer current is reversed from negative to positive. Therefore, during this period, by turning on switches Q5 and Q8 in synchronization with the zero-cross detection signal indicating that the transformer current has changed from negative to positive, ZCS of switches Q5 and Q8 is established, thereby making it possible to suppress the occurrence of losses in switches Q5 and Q8.

[0063] During the period from when switch Q2 is turned on to when switch Q3 is turned on, which is the period corresponding to the phase difference, the polarity of the transformer current is reversed from positive to negative. Therefore, during this period, by turning on switches Q6 and Q7 in synchronization with the zero-crossing detection signal indicating that the transformer current has changed from positive to negative, ZCS of switches Q6 and Q7 is established, thereby making it possible to suppress the occurrence of losses in switches Q6 and Q7.

[0064] 6 , the controller 40 may use the drive signal to turn on the switches Q5 and Q8 in synchronization with the negative-to-positive zero-cross detection signal of the transformer current during the period from when the switch Q1 is turned on to when the switch Q4 is turned on, and maintain the on state during the period from when the switch Q4 is turned on to when the switch Q2 is turned on. The controller 40 may maintain the on state during the period from when the switch Q4 is turned on to when the switch Q2 is turned on, or may maintain the on state for any period from when the switch Q4 is turned on to when the switch Q2 is turned on. The controller 40 may also turn on the switches Q6 and Q7 in synchronization with the positive-to-negative zero-cross detection signal of the transformer current during the period from when the switch Q2 is turned on to when the switch Q3 is turned on, and maintain the on state during the period from when the switch Q3 is turned on to when the switch Q1 is turned on. The controller 40 may maintain the on state for the period from when the switch Q3 is turned on until when the switch Q1 is turned on, or for any period from when the switch Q3 is turned on until when the switch Q1 is turned on.

[0065] For example, if the switches Q5 and Q8 are turned on during the period from when the switch Q1 is turned on until the switch Q4 is turned on and then turned off during that period, the switches Q5 and Q8 will operate as diodes to pass current, resulting in increased conduction loss due to the forward voltage of the body diodes. Furthermore, if the switches Q6 and Q7 are turned on during the period from when the switch Q2 is turned on until the switch Q3 is turned on and then turned off during that period, the switches Q6 and Q7 will operate as diodes to pass current, resulting in increased conduction loss due to the forward voltage of the body diodes. Note that diode operation refers to the operation in which current flows from the source to the drain when the switch is in the off state, i.e., when the switch blocks current from the drain to the source. For example, this corresponds to the operation in which a forward current flows through the body diode when a Si or SiC MOSFET is turned off.

[0066] Therefore, by turning on switches Q5 and Q8 and maintaining the on state from the time when switch Q4 is turned on until switch Q2 is turned on, synchronous rectification can be performed and conduction loss generated in switches Q5 and Q8 can be suppressed. Also, by turning on switches Q6 and Q7 and maintaining the on state from the time when switch Q3 is turned on until switch Q1 is turned on, synchronous rectification can be performed and conduction loss generated in switches Q6 and Q7 can be suppressed.

[0067] The controller 40 of the power conversion device 2 shown in FIG. 5 may use a drive signal to turn on the switches Q6 and Q7 in synchronization with the detection signal of the zero-crossing of the transformer current from negative to positive during the period from when the switch Q1 is turned on until when the switch Q4 is turned on, and may turn on the switches Q5 and Q8 in synchronization with the detection signal of the zero-crossing of the transformer current from positive to negative during the period from when the switch Q2 is turned on until when the switch Q3 is turned on.

[0068] During the period from when switch Q1 is turned on to when switch Q4 is turned on, which is the period corresponding to the phase difference, the polarity of the transformer current is reversed from negative to positive. Therefore, during this period, by turning on switches Q6 and Q7 in synchronization with the zero-crossing detection signal indicating that the transformer current has changed from negative to positive, ZCS of switches Q6 and Q7 is established, thereby making it possible to suppress the occurrence of losses in switches Q6 and Q7.

[0069] During the period from when switch Q2 is turned on to when switch Q3 is turned on, which is the period corresponding to the phase difference, the polarity of the transformer current is reversed from positive to negative. Therefore, during this period, by turning on switches Q5 and Q8 in synchronization with the zero-cross detection signal indicating that the transformer current has changed from positive to negative, ZCS of switches Q5 and Q8 is established, thereby making it possible to suppress losses in switches Q5 and Q8.

[0070] As described above, the secondary current of the transformer T, whose polarity reverses over time, flows through the switches Q5, Q6, Q7, and Q8, and a current also flows through the switches Q5, Q6, Q7, and Q8 during the period corresponding to the phase difference. Therefore, if the switches Q5, Q6, Q7, and Q8 are turned on when a current is flowing through them, ZCS is not established and loss occurs. In contrast, by detecting the transformer current flowing through the transformer T, it is possible to detect the timing when the polarity of the transformer current reverses, i.e., the timing when the current flowing through the switches Q5, Q6, Q7, and Q8 becomes zero. Therefore, by turning on the switches Q5, Q6, Q7, and Q8 in synchronization with the zero-crossing detection signal indicating the timing when the polarity of the transformer current reverses during the period corresponding to the phase difference, ZCS of the switches Q5, Q6, Q7, and Q8 is established, and loss in the switches Q5, Q6, Q7, and Q8 can be suppressed.

[0071] In the first embodiment, as in the second embodiment, the controller 40 may calculate a period equivalent to half the switching period of the switches Q1 and Q2 and control the on-time of the drive signal during the period equivalent to the half cycle. In other words, the controller 40 may control the on-time of the drive signal with the length of the period equivalent to the half cycle as the upper limit.

[0072] (Other Embodiments) As described above, the embodiments have been described as examples of the technology according to the present disclosure. However, the technology according to the present disclosure is not limited to these, and can be applied to embodiments in which modifications, substitutions, additions, omissions, etc. are made as appropriate. For example, the following modifications are also included in one embodiment of the present disclosure.

[0073] For example, in the above embodiment, an example of an LLC converter consisting of the excitation inductance and leakage inductance of the transformer T and a resonance capacitor has been described, but the power conversion device may also be provided with a separate inductor equivalent to the leakage inductance.

[0074] For example, although the power conversion device is an LLC converter in the above embodiment, the present invention is not limited to this. For example, the power conversion device may be a resonant converter including a resonator configured with a series-parallel LC, such as an LCC converter or a CLLC converter.

[0075] For example, although the description of the embodiments as examples of the technology according to the present disclosure does not refer to minute periods of time such as dead times, the controller 40 may control the on-times of the switches Q5, Q6, Q7, and Q8 by taking into account minute periods of time such as dead times or voltage transition times (dV / dt).

[0076] For example, the present disclosure can be realized not only as a power conversion device, but also as a control method for controlling a power conversion device (specifically, a control method including steps (processing) performed by components that constitute the power conversion device (specifically, controller 40)).

[0077] FIG. 7 is a flowchart showing an example of a control method according to another embodiment.

[0078] The control method is a control method for controlling a power conversion device, the power conversion device including a resonator having a transformer and a resonance capacitor, a primary-side full bridge circuit connected to the primary side of the resonator, and a secondary-side full bridge circuit connected to the secondary side of the resonator, the primary-side full bridge circuit having a first switch element provided on the high side of a first leg, a second switch element provided on the low side of the first leg, a third switch element provided on the high side of the second leg, and a fourth switch element provided on the low side of the second leg, and the secondary-side full bridge circuit having a fifth switch element provided on the high side of a third leg, a sixth switch element provided on the low side of the third leg, a seventh switch element provided on the high side of the fourth leg, and a eighth switch element provided on the low side of the fourth leg. and an eighth switch element connected to the fifth switch element and an eighth switch element connected to the seventh switch element. In the control method, as shown in FIG. 7 , the first switch element, the second switch element, the third switch element, and the fourth switch element are operated so that the switching phase of the third switch element and the fourth switch element is delayed with respect to the switching phase of the first switch element and the second switch element (step S11), a period corresponding to a phase difference between the switching of the first switch element and the second switch element and the switching of the third switch element and the fourth switch element is calculated (step S12), the fifth switch element, the sixth switch element, the seventh switch element, and the eighth switch element are turned on by a drive signal in the period corresponding to the phase difference (step S13), and the on time of the drive signal in the period corresponding to the phase difference is controlled (step S14).

[0079] For example, the present disclosure can be realized as a program for causing a computer (processor) to execute steps included in the control method. Furthermore, the present disclosure can be realized as a non-transitory computer-readable recording medium, such as a CD-ROM, on which the program is recorded.

[0080] For example, when the present disclosure is realized as a program (software), each step is performed by running the program using hardware resources such as a computer's CPU, memory, input / output circuits, etc. In other words, each step is performed by the CPU acquiring data from memory or input / output circuits, etc., performing calculations, and outputting the calculation results to memory or input / output circuits, etc.

[0081] In the above-described embodiments, each component included in the power conversion device may be configured with dedicated hardware, or may be realized by executing a software program suitable for each component. Each component may be realized by a program execution unit such as a CPU or processor reading and executing a software program recorded on a recording medium such as a hard disk or semiconductor memory.

[0082] Some or all of the functions of the power conversion device according to the above-described embodiments are typically realized as an LSI, which is an integrated circuit. These may be individually integrated into a single chip, or some or all of them may be integrated into a single chip. Furthermore, the integrated circuit is not limited to an LSI, and may be realized using a dedicated circuit or a general-purpose processor. An FPGA (Field Programmable Gate Array) that can be programmed after LSI manufacturing, or a reconfigurable processor that can reconfigure the connections and settings of circuit cells within the LSI, may also be used.

[0083] Furthermore, if an integrated circuit technology that can replace LSI emerges due to advances in semiconductor technology or other derivative technologies, that technology may naturally be used to integrate the components included in the power conversion device.

[0084] In addition, this disclosure also includes forms obtained by making various modifications to the embodiments that a person skilled in the art would think of, and forms realized by arbitrarily combining the components and functions in each embodiment within the scope of the present disclosure.

[0085] (Additional Notes) The above description of the embodiments discloses the following techniques.

[0086] (Technology 1) A power supply includes a resonator having a transformer and a resonance capacitor, a primary-side full bridge circuit connected to a primary side of the resonator, a secondary-side full bridge circuit connected to a secondary side of the resonator, and a controller that controls the primary-side full bridge circuit and the secondary-side full bridge circuit, wherein the primary-side full bridge circuit has a first switch element provided on a high side of a first leg, a second switch element provided on a low side of the first leg, a third switch element provided on the high side of a second leg, and a fourth switch element provided on the low side of the second leg, and the secondary-side full bridge circuit has a fifth switch element provided on a high side of a third leg, a sixth switch element provided on the low side of the third leg, a seventh switch element provided on the high side of a fourth leg, and and an eighth switch element provided on a low side of four legs, wherein the controller operates the first switch element, the second switch element, the third switch element, and the fourth switch element so that a switching phase of the third switch element and the fourth switch element is delayed with respect to a switching phase of the first switch element and the second switch element, calculates a period corresponding to a phase difference between switching of the first switch element and the second switch element and switching of the third switch element and the fourth switch element, turns on the fifth switch element, the sixth switch element, the seventh switch element, and the eighth switch element by a drive signal in the period corresponding to the phase difference, and controls an on time of the drive signal in the period corresponding to the phase difference.

[0087] A period corresponding to the phase difference between the switching of the first switch element and the second switch element and the switching of the third switch element and the fourth switch element, which is generated when phase shift control is performed, is a non-conducting period in which no current is passed through the load. By turning on the fifth switch element, the sixth switch element, the seventh switch element, and the eighth switch element for a certain period during the non-conducting period, it is possible to adjust the timing at which the polarity of the voltage generated in the secondary winding of the transformer (the transformer secondary voltage) reverses. When the polarity of the transformer secondary voltage reverses, the polarity of the transformer excitation voltage also reverses in accordance with the polarity reversal of the transformer secondary voltage. In other words, it is possible to adjust the timing at which the polarity of the transformer excitation voltage reverses (in other words, the phase of polarity reversal of the transformer excitation voltage).

[0088] When the phase of polarity reversal of the transformer excitation voltage is delayed, the phase of the resonant current is relatively advanced, thereby increasing the output power of the power conversion device. In other words, it is also possible to increase the input / output voltage ratio during phase shift control. Therefore, by controlling the on-time of the drive signals for the fifth switch element, the sixth switch element, the seventh switch element, and the eighth switch element during the non-energized period, the output power can be controlled without frequency control, and therefore the output power can be effectively controlled while suppressing the frequency control range width.

[0089] (Technology 2) The power conversion device according to Technology 1, wherein the controller turns on the fifth switch element and the eighth switch element in a period from when the first switch element is turned on to when the fourth switch element is turned on, and turns on the sixth switch element and the seventh switch element in a period from when the second switch element is turned on to when the third switch element is turned on, by the drive signal.

[0090] In this way, by controlling the fifth switch element, the sixth switch element, the seventh switch element, and the eighth switch element by the drive signal in the period corresponding to the phase difference, it is possible to increase the output power of the power conversion device.

[0091] (Technology 3) In the power conversion device according to Technology 1, the controller turns on the sixth switch element and the seventh switch element in a period from when the first switch element is turned on to when the fourth switch element is turned on, and turns on the fifth switch element and the eighth switch element in a period from when the second switch element is turned on to when the third switch element is turned on, in response to the drive signal.

[0092] In this way, by controlling the fifth switch element, the sixth switch element, the seventh switch element, and the eighth switch element with the drive signal in the period corresponding to the phase difference, it is also possible to reduce the output power of the power conversion device.

[0093] (Technology 4) The power conversion device according to Technology 1, further including a current detector that detects a transformer current flowing through the transformer, wherein the controller calculates a period corresponding to half a switching period of the first switch element and the second switch element, the drive signal is a signal for the period corresponding to the half period including a period corresponding to the phase difference, and the controller turns on the fifth switch element, the sixth switch element, the seventh switch element, and the eighth switch element in synchronization with a zero-crossing detection signal of the transformer current by the drive signal for the period corresponding to the half period, and controls an on time of the drive signal for the period corresponding to the half period.

[0094] A secondary current of the transformer whose polarity reverses over time flows through the fifth switch element, the sixth switch element, the seventh switch element, and the eighth switch element, and current also flows through the fifth switch element, the sixth switch element, the seventh switch element, and the eighth switch element during a period corresponding to the phase difference. Therefore, if the fifth switch element, the sixth switch element, the seventh switch element, and the eighth switch element are turned on at a timing when current is flowing through the fifth switch element, the sixth switch element, the seventh switch element, and the eighth switch element, ZCS is not established and loss occurs. In contrast, by detecting the transformer current flowing through the transformer, it is possible to detect the timing when the polarity of the transformer current reverses, i.e., the timing when the current flowing through the fifth switch element, the sixth switch element, the seventh switch element, and the eighth switch element becomes zero. Therefore, by turning on the fifth switch element, the sixth switch element, the seventh switch element, and the eighth switch element in synchronization with the zero-crossing detection signal indicating the timing at which the polarity of the transformer current is reversed during the period corresponding to the phase difference, ZCS of the fifth switch element, the sixth switch element, the seventh switch element, and the eighth switch element is established, and it is possible to suppress the occurrence of loss in the fifth switch element, the sixth switch element, the seventh switch element, and the eighth switch element.

[0095] (Technology 5) In the power conversion device according to Technology 4, the controller turns on the fifth switch element and the eighth switch element in synchronization with the zero-crossing detection signal of the transformer current changing from negative to positive during a period from when the first switch element is turned on to when the fourth switch element is turned on, and turns on the sixth switch element and the seventh switch element in synchronization with the zero-crossing detection signal of the transformer current changing from positive to negative during a period from when the second switch element is turned on to when the third switch element is turned on, using the drive signal.

[0096] During the period from when the first switch element is turned on until the fourth switch element is turned on, which is a period corresponding to the phase difference, the polarity of the transformer current reverses from negative to positive, so that by turning on the fifth switch element and the eighth switch element in synchronization with a zero-crossing detection signal indicating that the transformer current has changed from negative to positive during this period, the ZCS of the fifth switch element and the eighth switch element can be established, thereby suppressing the occurrence of loss in the fifth switch element and the eighth switch element. During the period from when the second switch element is turned on until the third switch element is turned on, which is a period corresponding to the phase difference, the polarity of the transformer current reverses from positive to negative during this period, so that by turning on the sixth switch element and the seventh switch element in synchronization with a zero-crossing detection signal indicating that the transformer current has changed from positive to negative during this period, the ZCS of the sixth switch element and the seventh switch element can be established, thereby suppressing the occurrence of loss in the sixth switch element and the seventh switch element.

[0097] (Technology 6) In the power conversion device according to Technology 5, the controller, by the drive signal, turns on the fifth switch element and the eighth switch element in synchronization with the zero-crossing detection signal of the transformer current changing from negative to positive during a period from when the first switch element is turned on to when the fourth switch element is turned on, and maintains the on state during a period from when the fourth switch element is turned on to when the second switch element is turned on; and turns on the sixth switch element and the seventh switch element in synchronization with the zero-crossing detection signal of the transformer current changing from positive to negative during a period from when the second switch element is turned on to when the third switch element is turned on, and maintains the on state during a period from when the third switch element is turned on to when the first switch element is turned on.

[0098] For example, if the fifth switch element and the eighth switch element are turned on during the period from when the first switch element is turned on to when the fourth switch element is turned on and then turned off during that period, the fifth switch element and the eighth switch element will operate as diodes to pass current, and conduction loss due to the forward voltage of their body diodes will increase. Therefore, by turning on the fifth switch element and the eighth switch element and maintaining the on state during the period from when the fourth switch element is turned on to when the second switch element is turned on, synchronous rectification can be performed and conduction loss occurring in the fifth switch element and the eighth switch element can be suppressed. Furthermore, if the sixth switch element and the seventh switch element are turned on during the period from when the second switch element is turned on to when the third switch element is turned on and then turned off during that period, the sixth switch element and the seventh switch element will operate as diodes to pass current, and conduction loss due to the forward voltage of their body diodes will increase. Therefore, after the sixth switch element and the seventh switch element are turned on, the on state is maintained for the period from when the third switch element is turned on until when the first switch element is turned on, thereby enabling synchronous rectification and suppressing the conduction loss occurring in the sixth switch element and the seventh switch element.

[0099] (Technology 7) In the power conversion device according to Technology 4, the controller turns on the sixth switch element and the seventh switch element in synchronization with the zero-crossing detection signal of the transformer current changing from negative to positive during a period from when the first switch element is turned on to when the fourth switch element is turned on, and turns on the fifth switch element and the eighth switch element in synchronization with the zero-crossing detection signal of the transformer current changing from positive to negative during a period from when the second switch element is turned on to when the third switch element is turned on, using the drive signal.

[0100] During the period from when the first switch element is turned on until the fourth switch element is turned on, which is a period corresponding to the phase difference, the polarity of the transformer current reverses from negative to positive, so that by turning on the sixth switch element and the seventh switch element in synchronization with a zero-crossing detection signal indicating that the transformer current has changed from negative to positive during this period, the ZCS of the sixth switch element and the seventh switch element can be established, thereby suppressing the occurrence of loss in the sixth switch element and the seventh switch element. During the period from when the second switch element is turned on until the third switch element is turned on, which is a period corresponding to the phase difference, the polarity of the transformer current reverses from positive to negative during this period, so that by turning on the fifth switch element and the eighth switch element in synchronization with a zero-crossing detection signal indicating that the transformer current has changed from positive to negative during this period, the ZCS of the fifth switch element and the eighth switch element can be established, thereby suppressing the occurrence of loss in the fifth switch element and the eighth switch element.

[0101] (Technology 8) A control method for controlling a power conversion device, the power conversion device including a resonator having a transformer and a resonance capacitor, a primary-side full bridge circuit connected to a primary side of the resonator, and a secondary-side full bridge circuit connected to a secondary side of the resonator, the primary-side full bridge circuit including a first switch element provided on a high side of a first leg, a second switch element provided on a low side of the first leg, a third switch element provided on the high side of a second leg, and a fourth switch element provided on the low side of the second leg, the secondary-side full bridge circuit including a fifth switch element provided on a high side of a third leg, a sixth switch element provided on the low side of the third leg, a seventh switch element provided on the high side of a fourth leg, and a seventh switch element provided on the high side of the fourth leg. and an eighth switch element provided on a low side, wherein the control method operates the first switch element, the second switch element, the third switch element, and the fourth switch element so that a switching phase of the third switch element and the fourth switch element is delayed with respect to a switching phase of the first switch element and the second switch element, calculates a period corresponding to a phase difference between switching of the first switch element and the second switch element and switching of the third switch element and the fourth switch element, turns on the fifth switch element, the sixth switch element, the seventh switch element, and the eighth switch element by a drive signal in the period corresponding to the phase difference, and controls an on time of the drive signal in the period corresponding to the phase difference.

[0102] This makes it possible to provide a control method for a power conversion device that can effectively control output power while suppressing the frequency control range width.

[0103] The present disclosure can be applied to an isolated DC-DC converter or the like.

[0104] 1, 2 Power conversion device 10 Primary side full bridge circuit 20 Secondary side full bridge circuit 30 Resonator 40 Controller 50 Current detector Cin, Cout, Cr Capacitors Q1, Q2, Q3, Q4, Q5, Q6, Q7, Q8 Switch T Transformer t1, t2, t3, t4 Terminals

Claims

1. A power supply comprising: a resonator having a transformer and a resonant capacitor; a primary-side full-bridge circuit connected to the primary side of the resonator; a secondary-side full-bridge circuit connected to the secondary side of the resonator; and a controller for controlling the primary-side full-bridge circuit and the secondary-side full-bridge circuit, wherein the primary-side full-bridge circuit has a first switch element provided on the high side of a first leg, a second switch element provided on the low side of the first leg, a third switch element provided on the high side of a second leg, and a fourth switch element provided on the low side of the second leg; the secondary-side full-bridge circuit has a fifth switch element provided on the high side of a third leg, a sixth switch element provided on the low side of the third leg, a seventh switch element provided on the high side of a fourth leg, and an eighth switch element provided on the low side of the fourth leg; and the controller a power conversion device that operates the first switch element, the second switch element, the third switch element, and the fourth switch element so that a switching phase of the third switch element and the fourth switch element is delayed with respect to a switching phase of the first switch element and the second switch element; calculates a period corresponding to a phase difference between switching of the first switch element and the second switch element and switching of the third switch element and the fourth switch element; turns on the fifth switch element, the sixth switch element, the seventh switch element, and the eighth switch element by a drive signal in the period corresponding to the phase difference; and controls an on time of the drive signal in the period corresponding to the phase difference.

2. The power conversion device according to claim 1, wherein the controller turns on the fifth switch element and the eighth switch element in a period from when the first switch element is turned on to when the fourth switch element is turned on, and turns on the sixth switch element and the seventh switch element in a period from when the second switch element is turned on to when the third switch element is turned on, in response to the drive signal.

3. The power conversion device according to claim 1, wherein the controller turns on the sixth switch element and the seventh switch element in a period from when the first switch element is turned on until when the fourth switch element is turned on, and turns on the fifth switch element and the eighth switch element in a period from when the second switch element is turned on until when the third switch element is turned on, in response to the drive signal.

4. The power conversion device according to claim 1, further comprising a current detector that detects a transformer current flowing through the transformer; wherein the controller calculates a period equivalent to half a switching period of the first switch element and the second switch element; the drive signal is a signal for a period equivalent to the half period including a period equivalent to the phase difference; and the controller turns on the fifth switch element, the sixth switch element, the seventh switch element and the eighth switch element in synchronization with a zero-crossing detection signal of the transformer current by the drive signal for the period equivalent to the half period, and controls an on time of the drive signal for the period equivalent to the half period.

5. The power conversion device according to claim 4, wherein the controller, by the drive signal, turns on the fifth switch element and the eighth switch element in synchronization with the zero-cross detection signal of the transformer current changing from negative to positive during a period from when the first switch element is turned on to when the fourth switch element is turned on, and turns on the sixth switch element and the seventh switch element in synchronization with the zero-cross detection signal of the transformer current changing from positive to negative during a period from when the second switch element is turned on to when the third switch element is turned on.

6. The power conversion device according to claim 5, wherein the controller, by the drive signal, turns on the fifth switch element and the eighth switch element in synchronization with the zero-crossing detection signal of the transformer current changing from negative to positive during a period from when the first switch element is turned on to when the fourth switch element is turned on, and maintains the on state during a period from when the fourth switch element is turned on to when the second switch element is turned on; and turns on the sixth switch element and the seventh switch element in synchronization with the zero-crossing detection signal of the transformer current changing from positive to negative during a period from when the second switch element is turned on to when the third switch element is turned on, and maintains the on state during a period from when the third switch element is turned on to when the first switch element is turned on.

7. The power conversion device according to claim 4, wherein the controller, by the drive signal, turns on the sixth switch element and the seventh switch element in synchronization with the zero-cross detection signal of the transformer current changing from negative to positive during a period from when the first switch element is turned on to when the fourth switch element is turned on, and turns on the fifth switch element and the eighth switch element in synchronization with the zero-cross detection signal of the transformer current changing from positive to negative during a period from when the second switch element is turned on to when the third switch element is turned on.

8. A control method for controlling a power conversion device, wherein the power conversion device comprises: a resonator having a transformer and a resonance capacitor; a primary-side full-bridge circuit connected to the primary side of the resonator; and a secondary-side full-bridge circuit connected to the secondary side of the resonator, wherein the primary-side full-bridge circuit has a first switch element provided on the high side of a first leg, a second switch element provided on the low side of the first leg, a third switch element provided on the high side of a second leg, and a fourth switch element provided on the low side of the second leg, and the secondary-side full-bridge circuit has a fifth switch element provided on the high side of a third leg, a sixth switch element provided on the low side of the third leg, a seventh switch element provided on the high side of a fourth leg, and an eighth switch element provided on the low side of the fourth leg, and the control method comprises: a control method comprising: operating the first switch element, the second switch element, the third switch element, and the fourth switch element so that a switching phase of the third switch element and the fourth switch element is delayed with respect to a switching phase of the first switch element and the second switch element; calculating a period corresponding to a phase difference between switching of the first switch element and the second switch element and switching of the third switch element and the fourth switch element; turning on the fifth switch element, the sixth switch element, the seventh switch element, and the eighth switch element by a drive signal in the period corresponding to the phase difference; and controlling an on time of the drive signal in the period corresponding to the phase difference.

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