Power conversion device and control method

Abstract

A current conversion device (1) comprises: a resonator (30) with a transformer (T) and a capacitor (Cr); a primary-side full bridge circuit (10) comprising a first switch (Q1), a second switch (Q2), a third switch (Q3) and a fourth switch (Q4); and a secondary-side full bridge circuit (20) comprising a fifth diode (D5), a sixth switch (Q6), a seventh diode (D7) and an eighth switch (Q8). The sixth switch (Q6) and the eighth switch (Q8) operate synchronously with control signals for the first switch (Q1), the second switch (Q2), the third switch (Q3) and the fourth switch (Q4) by applying control signals in a time interval that excludes a resonance period of the resonator (30) from a switching cycle of the first switch (Q1), the second switch (Q2), the third switch (Q3) and the fourth switch (Q4).

Description

[Technical field]

[0001] The present disclosure relates to a current conversion device that enables unidirectional or bidirectional current conversion, and to a control method for the current conversion device. [State of the art]

[0002] With the increasing importance of achieving a climate-neutral society, the demand is growing for charging circuits capable of efficiently charging home storage batteries and electric vehicle batteries. Such charging circuits require an isolated DC-DC converter, with resonant converters frequently used to achieve a compact size and higher efficiency. Among resonant converters, LLC-DC-DC converters, in particular, have attracted attention due to their ability to achieve high efficiency with simple circuitry.

[0003] However, LLC converters have the problem that high-frequency ringing on the secondary side leads to increased power losses in the circuit. When operating at higher drive frequencies, high-frequency ringing poses a significant problem due to the high-frequency losses caused by the harmonic components of the ringing.

[0004] In response to this problem, patent literature (PTL) 1 discloses a technique for suppressing high-frequency ringing. More specifically, in LLC-DC-DC converters, high-frequency ringing occurs during dead-time periods due to resonance between the resonant inductance and the parasitic capacitance parallel to the switching elements. This problem is solved by timing the switch-off of all switching elements to coincide precisely with the moment when the resonant current Ioff reaches a value that opposes the resonant current generated by the excitation current Ip. [Citation list][Patent literature]

[0005] [PTL 1] Japanese unpublished patent application no. 2014-217196 [Summary of the invention][Technical problem]

[0006] However, in the DC-DC converter disclosed in PTL 1, there are certain conditions under which it is not possible to suppress the high-frequency ringing caused by parasitic capacitance. For example, in LLC-DC-DC converters used in chargers and the like, the LLC boost operating mode is actively employed to handle the wide voltage range of storage batteries. In LLC boost mode, the LLC-DC-DC converter operates at a switching frequency lower than the resonant frequency determined by the resonant inductance and capacitor to achieve boost operation. However, in this operating mode, high-frequency ringing occurs not only during the dead-time periods but also throughout the entire portion of the switching cycle outside the resonant period. Consequently, simply adjusting the dead-time timing may be insufficient to effectively suppress the high-frequency ringing.Controlling switching elements is a challenge because various parasitic components must be taken into account when calculating the threshold for adjusting the dead-time timing, such as the parasitic capacitance caused by the mounting of the switching elements and its fluctuations, and not just the parasitic capacitance inherent in the switching elements themselves.

[0007] Against this background, the present disclosure provides a current conversion device and the like, which can effectively suppress high-frequency ringing. [Solution to the problem]

[0008] A current conversion device according to the present disclosure comprises: a resonator with a transformer and a resonant 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 comprises a first element located on a high side of a first leg, a second element located on a low side of the first leg, a third element located on a high side of a second leg, and a fourth element located on a low side of the second leg.The secondary-side full-bridge circuit has a fifth element located on the high side of a third leg, a sixth element located on the low side of the third leg, a seventh element located on the high side of a fourth leg, and an eighth element located on the low side of the fourth leg. The first, second, third, and fourth elements each constitute a switching element. At least two elements below the fifth, sixth, seventh, and eighth elements each constitute a switching element.The at least two elements are operated synchronously with control signals for the first element, the second element, the third element and the fourth element by means of control signals that are applied in a time span that excludes a resonance period of the resonator from a switching cycle of the first element, the second element, the third element and the fourth element.

[0009] A current conversion device according to the present disclosure comprises: a resonator with a transformer and a resonant capacitor; a primary-side half-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 half-bridge circuit comprises a first element provided on a high side and a second element provided on a low side. The secondary-side full-bridge circuit comprises a fifth element provided on a high side of a third leg, a sixth element provided on a low side of the third leg, a seventh element provided on a high side of a fourth leg, and an eighth element provided on a low side of the fourth leg. The first and second elements are each switching elements.At least two elements below the fifth, sixth, seventh, and eighth elements each constitute a switching element. These at least two elements are operated synchronously with control signals for the first and second elements by means of control signals applied within a time interval that excludes a resonator resonance period from a switching cycle of the first and second elements.

[0010] A control method according to the present disclosure serves to control a current conversion device. The current conversion device comprises: a resonator with a transformer and a resonant 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 comprises a first element located on a high side of a first leg, a second element located on a low side of the first leg, a third element located on a high side of a second leg, and a fourth element located on a low side of the second leg.The secondary-side full-bridge circuit has a fifth element located on the high side of a third leg, a sixth element located on the low side of the third leg, a seventh element located on the high side of a fourth leg, and an eighth element located on the low side of the fourth leg. The first, second, third, and fourth elements each constitute a switching element. At least two elements below the fifth, sixth, seventh, and eighth elements each constitute a switching element.The control method comprises: calculating a period that excludes a resonator resonance period from a switching cycle of the first element, the second element, the third element and the fourth element; and synchronizing the at least two elements with control signals for the first element, the second element, the third element and the fourth element by means of control signals applied in the period.

[0011] A control method according to the present disclosure serves to control a current conversion device. The current conversion device comprises: a resonator with a transformer and a resonant capacitor; a primary-side half-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 half-bridge circuit comprises a first element provided on a high side and a second element provided on a low side. The secondary-side full-bridge circuit comprises a fifth element provided on a high side of a third leg, a sixth element provided on a low side of the third leg, a seventh element provided on a high side of a fourth leg, and an eighth element provided on a low side of the fourth leg.The first and second elements are each a switching element. At least two elements below the fifth, sixth, seventh, and eighth elements are each a switching element. The control method comprises: calculating a period that excludes a resonator resonance period from a switching cycle of the first and second elements; and synchronizing the at least two elements with control signals for the first and second elements by means of control signals applied within the period.

[0012] General or specific aspects of the present disclosure may be realized as a system, method, integrated circuit, computer program or computer-readable recording medium such as CD-ROM or any combination thereof. [Advantageous effects of the invention]

[0013] The current conversion device and the like according to one aspect of the present disclosure are capable of effectively suppressing high-frequency ringing. [Brief description of the drawings] [ Fig. 1] Fig. Figure 1 is a circuit diagram showing an example of a current conversion device according to embodiment 1. [ Fig. 2] Fig. Figure 2 is a diagram illustrating the operating processes of a control system according to embodiment 1. [ Fig. 3] Fig. Figure 3 is a diagram illustrating an example of the operating process and effects of the current conversion device according to embodiment 1. [ Fig. 4] Fig. Figure 4 is a circuit diagram showing an example of a current conversion device according to embodiment 2. [ Fig. 5] Fig. Figure 5 is a diagram illustrating an example of the operating process and effects of the current conversion device according to embodiment 2. [ Fig. 6] Fig. Figure 6 is a circuit diagram showing an example of a current conversion device according to embodiment 3. [ Fig. 7] Fig. Figure 7 is a diagram illustrating a first example of the operating process and effects of the current conversion device according to embodiment 3. [ Fig. 8] Fig. Figure 8 is a diagram illustrating a second example of the operating process and effects of the current conversion device according to embodiment 3. [ Fig. 9] Fig. Figure 9 is a diagram illustrating a third example of the operating process and effects of the current conversion device according to embodiment 3. [ Fig. 10] Fig. Figure 10 is a diagram illustrating a fourth example of the operating process and effects of the current conversion device according to embodiment 3. [ Fig. 11] Fig. Figure 11 is a circuit diagram showing an example of a current conversion device according to embodiment 4. [ Fig. 12] Fig. Figure 12 is a diagram illustrating an example of the operating process and effects of the current conversion device according to embodiment 4. [ Fig. 13] Fig. Figure 13 is a circuit diagram showing an example of a current conversion device according to embodiment 5. [ Fig. 14] Fig. Figure 14 is a diagram illustrating an example of the operating process and effects of the current conversion device according to embodiment 5. [ Fig. 15] Fig. Figure 15 is a flowchart showing an example of a control procedure according to a further embodiment. [ Fig. 16] Fig. Figure 16 is a flowchart showing an example of a control procedure according to a further embodiment. [Description of the embodiments]

[0014] In the following, embodiments of the present disclosure are described in detail with reference to the drawings.

[0015] The embodiments described below each represent a general or specific example. The numerical values, shapes, materials, elements, arrangement and connection of the elements, steps, sequence of steps, etc., shown in the following embodiments are merely examples and therefore do not limit the scope of this disclosure. [Version 1]

[0016] The following describes a power conversion device according to embodiment 1.

[0017] Fig. Figure 1 is a circuit diagram showing an example of a current conversion device 1 according to embodiment 1.

[0018] Power conversion device 1 is, for example, an isolated DC-DC converter that increases or decreases an input voltage to a predetermined voltage and outputs the voltage. Power conversion device 1 is capable of unidirectional power conversion. For example, power conversion device 1 is an LLC converter. An LLC converter is a circuit that utilizes LLC resonance through the leakage inductance of a transformer, the magnetizing inductance, and a capacitor. In an LLC converter, changing the switching frequency alters the ratio between the input and output voltage (gain), thereby producing the desired power output.

[0019] The power conversion device 1 has terminals t1, t2, t3, and t4. Terminal t1 is an input terminal. Terminal t2 is a ground terminal. Terminal t3 is an output terminal. Terminal t4 is a ground terminal. Since the power conversion device 1 is an isolated DC-DC converter, terminal t2 and terminal t4 are electrically isolated from each other.

[0020] The current conversion device 1 comprises a primary-side full bridge circuit 10, a secondary-side full bridge circuit 20, a resonator 30, capacitors Cin and Cout, and a control circuit 40. It should be noted that the capacitors Cin and Cout need not be components of the current conversion device 1.

[0021] The capacitor Cin is an input capacitor connected between terminal t1 and terminal t2, and the capacitor Cout is an output capacitor (smoothing capacitor) connected between terminal t3 and terminal t4.

[0022] 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 element located on the high side of a first leg, a second element located on the low side of the first leg, a third element located on the high side of a second leg, and a fourth element located on the low side of the second leg. The first, second, third, and fourth elements are each switching elements.

[0023] The primary-side full bridge circuit 10 has switches Q1, Q2, Q3, and Q4. Switch Q1 is an example of the first element, switch Q2 is an example of the second element, switch Q3 is an example of the third element, and switch Q4 is an example of the fourth element.

[0024] Switch Q1, for example, is an N-channel metal-oxide-semiconductor field-effect transistor (MOSFET). The drain of switch Q1 is connected to terminal t1, and the source of switch Q1 is connected to the drain of switch Q2.

[0025] For example, switch Q2 is an N-channel MOSFET. The drain of switch Q2 is connected to the source of switch Q1, and the source of switch Q2 is connected to terminal t2.

[0026] For example, switch Q3 is an N-channel MOSFET. The drain of switch Q3 is connected to terminal t1, and the source of switch Q3 is connected to the drain of switch Q4.

[0027] For example, switch Q4 is an N-channel MOSFET. The drain of switch Q4 is connected to the source of switch Q3, and the source of switch Q4 is connected to terminal t2.

[0028] The secondary-side full-bridge circuit 20 is connected to the secondary side of the resonator 30. The secondary-side full-bridge circuit 20 has a fifth element located on the high side of a third leg, a sixth element located on the low side of the third leg, a seventh element located on the high side of a fourth leg, and an eighth element located on the low side of the fourth leg. At least two elements below the fifth, sixth, seventh, and eighth elements each constitute a switching element. The secondary-side full-bridge circuit 20 also functions as a rectifier circuit capable of full-wave rectification.

[0029] As will be described in detail later, the at least two elements are operated synchronously with the control signals for the first element, the second element, the third element and the fourth element by applying control signals in a time span that excludes a resonance period of the resonator 30 from the switching cycle of the first element, the second element, the third element and the fourth element.

[0030] In embodiment 1, the secondary-side full-bridge circuit 20 comprises diodes D5 and D7 and switches Q6 and Q8. Diode D5 is an example of the fifth element, switch Q6 is an example of the sixth element, diode D7 is an example of the seventh element, and switch Q8 is an example of the eighth element. In other words, in embodiment 1, the at least two elements that are switching elements are the sixth element (switch Q6) and the eighth element (switch Q8).

[0031] The anode of diode D5 is connected to the drain of switch Q6, and the cathode of diode D5 is connected to terminal t3.

[0032] For example, switch Q6 is an N-channel MOSFET. The drain of switch Q6 is connected to the anode of diode D5, and the source of switch Q6 is connected to terminal t4.

[0033] The anode of diode D7 is connected to the drain of switch Q8, and the cathode of diode D7 is connected to terminal t3.

[0034] For example, switch Q8 is an N-channel MOSFET. The drain of switch Q8 is connected to the anode of diode D7, and the source of switch Q8 is connected to terminal t4.

[0035] The resonator 30 includes the transformer T and the capacitor Cr.

[0036] Capacitor Cr is an example of a resonant capacitor. Capacitor Cr is connected to a node between switch Q1 and switch Q2 in the first leg.

[0037] Transformer T is an insulated transformer with a primary winding and a secondary winding that are electrically isolated from each other. One end of the primary winding of transformer T is connected via capacitor Cr to a junction between switch Q1 and switch Q2 in the first leg, and the other end of the primary winding of transformer T is connected to a junction between switch Q3 and switch Q4 in the second leg. One end of the secondary winding of transformer T is connected to a junction between diode D5 and switch Q6 in the third leg, and the other end of the secondary winding of transformer T is connected to a junction between diode D7 and switch Q8 in the fourth leg.

[0038] It should be noted that the capacitor Cr can be connected to a node between switch Q3 and switch Q4 in the second leg. In such cases, one end of the primary winding of transformer T is connected to a node between switch Q1 and switch Q2 in the first leg, and the other end of the primary winding of transformer T is connected via the capacitor Cr to a node between switch Q3 and switch Q4 in the second leg.

[0039] The controller 40 is a circuit for controlling the switching (on and off) of switches (for example, switches Q1, Q2, Q3, Q4, Q6, and Q8) contained in the current conversion device 1. For example, the controller 40 controls the switching of switches Q1, Q2, Q3, Q4, Q6, and Q8 by controlling a gate drive circuit (not shown in the drawings) which is connected to the gates of switches Q1, Q2, Q3, Q4, Q6, and Q8 via a PWM generator (not shown in the drawings) or the like.

[0040] The Controller 40, for example, is a computer that has a processor (microprocessor) and memory. The memory can be, for example, read-only memory (ROM) and random-access memory (RAM) and can store programs executed by the processor. The Controller 40 is, for example, a microcontroller.

[0041] The control unit 40 calculates a period that excludes a resonance period of the resonator 30 (a period of resonance due to the capacitance of the capacitor Cr and the leakage inductance of the transformer T) from the switching cycle of the switches Q1, Q2, Q3 and Q4, and operates the switches Q6 and Q8 synchronously with the control signals for the switches Q1, Q2, Q3 and Q4 by means of control signals applied during this time period.

[0042] Here, the operating process of control unit 40 is described with reference to Fig. 2 described in more detail.

[0043] Fig. Figure 2 is a diagram to illustrate the operating processes of the control unit 40 according to embodiment 1.

[0044] As in Fig. As shown in Figure 2, controller 40 controls the switching of switches Q1 and Q4 in the same phase and controls the switching of switches Q2 and Q3 in the same phase. It should be noted that controller 40 controls switches Q1, Q2, Q3, and Q4 such that the phase difference between the switching of switches Q1 and Q4 and the switching of switches Q2 and Q3 is 180 degrees. Accordingly, the control signals for switches Q1, Q2, Q3, and Q4 are, for example, as shown in Figure 2. Fig. Figure 2 shows that switches Q1 and Q4 repeatedly switch on and off with a duty cycle of 50%, switches Q2 and Q3 repeatedly switch on and off with a duty cycle of 50%, switches Q2 and Q3 are in an off state when switches Q1 and Q4 are in an on state, and switches Q1 and Q4 are in an off state when switches Q2 and Q3 are in an on state.

[0045] When, under the control of control unit 40, switches Q1 and Q4 are switched on and switches Q2 and Q3 are switched off, or when switches Q2 and Q3 are switched on and switches Q1 and Q4 are switched off, current (primary current) flows through the primary winding of transformer T. The primary current oscillates with a resonant period of resonator 30. When current flows through the primary winding of transformer T, current (secondary current) also flows through the secondary winding of transformer T. The secondary current likewise oscillates with a resonant period of resonator 30. Accordingly, the primary and secondary currents are as described in Fig. 2 shown.

[0046] The controller 40 calculates a time interval that corresponds to a resonance period of the resonator 30 (for example, the one in Fig. 2 shown resonance half-cycle) from a switching cycle of switches Q1, Q2, Q3 and Q4 (for example, the one shown in Fig. The switching half-cycle shown in Figure 2, in which the switches are in the on state with a duty cycle of 50%, is excluded. During this period, no current flows to the load connected to terminals t3 and t4. This period is also called the non-excitation period. During the non-excitation period, the charge accumulated in the parasitic capacitance of devices on the secondary side of transformer T (e.g., diodes D5 and D7 and switches Q6 and Q8) cannot be dissipated to the load side, and high-frequency ringing can occur due to free resonance caused by the leakage inductance of transformer T and the parasitic capacitance of the secondary-side devices.Against this background, the controller 40 can divert the charge of the secondary-side components to the load side by operating switches Q6 and Q8 synchronously with the control signals for switches Q1, Q2, Q3, and Q4 via drive signals applied during the non-excitation period. The drive signals for switches Q6 and Q8 are signals that turn on switches Q6 and Q8 during the non-excitation period in the second half of the turn-on period of switches Q1 and Q4, and during the non-excitation period in the second half of the turn-on period of switches Q2 and Q3. It should be noted that, as in . Fig. Figure 2 shows that the control signals for switches Q1, Q2, Q3, and Q4 and the drive signals for switches Q6 and Q8 are synchronized. It should be noted that the synchronization of a control signal and a drive signal means that there is a fixed relationship between the activation time of the control signal and the activation time of the drive signal. In this description, the activation of the drive signal after a fixed time interval following the activation of the control signal is described as the synchronization of the control signal and the drive signal.

[0047] Next, the operating processes of the power conversion device 1 and the effects achieved by these operating processes will be described with reference to Fig. 3 described.

[0048] Fig. Figure 3 is a diagram illustrating an example of the operating processes and effects of the current conversion device 1 according to embodiment 1. Fig. Figure 3 shows, from top to bottom, timing diagrams of the gate signals of switches Q1, Q4 and Q8, the gate signals of switches Q2, Q3 and Q6, the voltage generated in the secondary winding of transformer T (transformer secondary voltage), the current flowing through the primary winding of transformer T (transformer primary current) and the current flowing through the secondary winding of transformer T (transformer secondary current).

[0049] As in Fig. As shown in Figure 3, switches Q6 and Q8 turn on in response to the control signals before switches Q1 and Q4 turn off from an on state, and turn on before switches Q2 and Q3 turn off from an on state. In other words, using the control signals, the controller 40 turns on switches Q6 and Q8 before switches Q1 and Q4 turn off from an on state, and turns on switches Q6 and Q8 before switches Q2 and Q3 turn off from an on state.The non-excitation period is the time interval before switches Q1 and Q4 switch off from the on state (a time interval occurring in the second half of the time interval in which switches Q1 and Q4 are on), and the time interval before switches Q2 and Q3 switch off from the on state (a time interval occurring in the second half of the time interval in which switches Q2 and Q3 are on). By switching on switches Q6 and Q8 during these time intervals, both ends of the secondary winding of transformer T can be connected to the negative terminal t4 of the load via switches Q6 and Q8, thus preventing high-frequency ringing. As in . Fig. As shown in Figure 3, it is evident that high-frequency ringing in the secondary voltage of the transformer is prevented and high-frequency ringing in the secondary current of the transformer is prevented.

[0050] It should be noted that the upper limit for the length of the time interval before switches Q1 and Q4 switch off from the on state, and the length of the time interval before switches Q2 and Q3 switch off from the on state, is the length of the non-excitation period. In other words, the end of the time interval before switches Q1 and Q4 switch off from the on state is the time at which switches Q1 and Q4 switch off, and the start of the time interval occurs at a time that precedes the time at which switches Q1 and Q4 switch off by a duration that does not exceed the length of the non-excitation period.The end of the time period before switches Q2 and Q3 turn off from the on state is the time at which switches Q2 and Q3 turn off, and the beginning of the time period occurs at a time that precedes the time at which switches Q2 and Q3 turn off by a duration that does not exceed the length of the non-excitation period.

[0051] As described above, a period of time corresponding to one resonance period of resonator 30 from the switching cycle of switches Q1, Q2, Q3, and Q4 is a non-excitation period during which no current flows to the load. If devices on the secondary side of transformer T (in particular switches Q6 and Q8) are not controlled, the charge accumulated in the parasitic capacitance of the secondary-side devices of transformer T cannot be discharged to the load side. Therefore, during this period, a high-frequency ringing can occur due to free resonance caused by the leakage inductance of transformer T and the parasitic capacitance of the secondary-side devices.Given this, during this period, by synchronously operating switches Q6 and Q8 with the control signals for switches Q1, Q2, Q3, and Q4, both ends of the secondary winding of transformer T can be connected to the negative terminal t4 of the load (in other words, the potentials at both ends of the secondary winding of transformer T can be set to the potential on the negative side of the load), and the charge accumulated in the parasitic capacitance of the secondary-side devices can be dissipated to the load side. Accordingly, high-frequency ringing can be effectively suppressed. This allows for effects such as improved efficiency due to reduced high-frequency losses and improved EMC performance in the MHz band.Furthermore, since no means of suppressing vibrations, such as a snubber circuit or an active clamping circuit, are required, miniaturization and cost reduction can be achieved. [Version 2]

[0052] Next, a power conversion device according to embodiment 2 will be described.

[0053] Fig. Figure 4 is a circuit diagram showing an example of a current conversion device 2 according to embodiment 2.

[0054] The current conversion device 2 differs from the current conversion device 1 in embodiment 1 with regard to the elements comprising the secondary-side full bridge circuit 20 and the control content of the control unit 40. Since the other aspects are essentially the same as those of the current conversion device 1 according to embodiment 1, their description is omitted and the differences are discussed below.

[0055] In embodiment 2, the secondary-side full-bridge circuit 20 comprises switches Q5 and Q7 and diodes D6 and D8. Switch Q5 is an example of the fifth element, diode D6 is an example of the sixth element, switch Q7 is an example of the seventh element, and diode D8 is an example of the eighth element. In other words, in embodiment 2, the at least two elements that are switching elements are the fifth element (switch Q5) and the seventh element (switch Q7).

[0056] For example, switch Q5 is an N-channel MOSFET. The drain of switch Q5 is connected to terminal t3, and the source of switch Q5 is connected to the cathode of diode D6.

[0057] The anode of diode D6 is connected to terminal t4, and the cathode of diode D6 is connected to the source of switch Q5.

[0058] For example, switch Q7 is an N-channel MOSFET. The drain of switch Q7 is connected to terminal t3, and the source of switch Q7 is connected to the cathode of diode D8.

[0059] The anode of diode D8 is connected to terminal t4, and the cathode of diode D8 is connected to the source of switch Q7.

[0060] One end of the secondary winding of transformer T is connected to a node between switch Q5 and diode D6 in the third leg, and the other end of the secondary winding of transformer T is connected to a node between switch Q7 and diode D8 in the fourth leg.

[0061] For example, the controller 40 controls the switching of switches Q1, Q2, Q3, Q4, Q5 and Q7 by controlling a gate drive circuit (not shown in the drawings) connected to the gates of switches Q1, Q2, Q3, Q4, Q5 and Q7 via a PWM generator (not shown in the drawings) or the like.

[0062] The controller 40 calculates a time interval that excludes a resonance period of the resonator 30 from the switching cycle of switches Q1, Q2, Q3 and Q4, and operates switches Q5 and Q7 synchronously with the control signals for switches Q1, Q2, Q3 and Q4 by means of control signals applied during this time interval.

[0063] The controller 40 calculates a time interval that excludes a resonance period of the resonator 30 (for example, a resonance half-cycle) from a switching cycle of switches Q1, Q2, Q3, and Q4 (for example, a switching half-cycle in which the switches are in the on state at a duty cycle of 50%). During this time interval, no current flows to the load connected to terminals t3 and t4. This time interval is also referred to as the non-excitation period. During the non-excitation period, the charge accumulated in the parasitic capacitance of devices on the secondary side of the transformer T (e.g., diodes D6 and D8 and switches Q5 and Q7) cannot be dissipated to the load side, and high-frequency ringing can occur due to free resonance caused by the leakage inductance of the transformer T and the parasitic capacitance of the secondary-side devices.Against this background, the controller 40 can dissipate the charge accumulated in the parasitic capacitance of the secondary-side components to the load side by operating switches Q5 and Q7 synchronously with the control signals for switches Q1, Q2, Q3, and Q4 via drive signals applied during the non-excitation period. The drive signals for switches Q5 and Q7 are signals that switch on switches Q5 and Q7 during the non-excitation period in the second half of the on-time of switches Q1 and Q4, and during the non-excitation period in the second half of the on-time of switches Q2 and Q3.

[0064] Next, the operating processes of the power conversion device 2 and the effects achieved by these operating processes will be described with reference to Fig. 5 described.

[0065] Fig. Figure 5 is a diagram illustrating an example of the operating process and effects of the current conversion device 2 according to embodiment 2. Fig. Figure 5 shows, from top to bottom, timing diagrams of the gate signals of switches Q1, Q4 and Q7, the gate signals of switches Q2, Q3 and Q5, the voltage generated in the secondary winding of transformer T (transformer secondary voltage), the current flowing through the primary winding of transformer T (transformer primary current) and the current flowing through the secondary winding of transformer T (transformer secondary current).

[0066] As in Fig. As shown in Figure 5, switches Q5 and Q7 turn on in response to the control signals before switches Q1 and Q4 turn off from an on state, and turn on before switches Q2 and Q3 turn off from an on state. In other words, using the control signals, the controller 40 turns on switches Q5 and Q7 before switches Q1 and Q4 turn off from an on state, and turns on switches Q5 and Q7 before switches Q2 and Q3 turn off from an on state. By turning on switches Q5 and Q7 during these periods, both ends of the secondary winding of transformer T can be connected to the positive terminal t3 of the load via switches Q5 and Q7, thus preventing high-frequency ringing. As shown in Figure 5, the controller 40 turns on switches Q5 and Q7 before switches Q1 and Q4 turn off from an on state. Fig. As shown in Figure 5, it is evident that high-frequency ringing in the secondary voltage of the transformer is prevented and high-frequency ringing in the secondary current of the transformer is prevented.

[0067] As described above, during the non-excitation period, by synchronously operating switches Q5 and Q7 with the control signals for switches Q1, Q2, Q3, and Q4, both ends of the secondary winding of transformer T can be connected to the positive terminal t3 of the load (in other words, the potentials at both ends of the secondary winding of transformer T can be set to the potential on the positive side of the load), and the charge accumulated in the parasitic capacitance of the secondary-side devices can be discharged to the load side. Accordingly, high-frequency ringing can be effectively suppressed. [Version 3]

[0068] Next, a power conversion device according to embodiment 3 will be described.

[0069] Fig. Figure 6 is a circuit diagram showing an example of a current conversion device 3 according to embodiment 3.

[0070] The current conversion device 3 differs from the current conversion device 1 in embodiment 1 with regard to the elements comprising the secondary-side full bridge circuit 20 and the control content of the controller 40. Since the other aspects are essentially the same as those of the current conversion device 1 in embodiment 1, their description is omitted, and the differences are discussed below. It should be noted that the current conversion device 1 in embodiment 1 is capable of unidirectional current conversion, while the current conversion device 3 is capable of both unidirectional and bidirectional current conversion.

[0071] In embodiment 3, the secondary-side full-bridge circuit 20 comprises switches Q5, Q6, Q7, and Q8. Switch Q5 is an example of the fifth element, switch Q6 is an example of the sixth element, switch Q7 is an example of the seventh element, and switch Q8 is an example of the eighth element. In other words, in embodiment 3, the at least two elements that are switching elements are the fifth element (switch Q5), the sixth element (switch Q6), the seventh element (switch Q7), and the eighth element (switch Q8).

[0072] For example, switch Q5 is an N-channel MOSFET. The drain of switch Q5 is connected to terminal t3, and the source of switch Q5 is connected to the drain of switch Q6.

[0073] For example, switch Q6 is an N-channel MOSFET. The drain of switch Q6 is connected to the source of switch Q5, and the source of switch Q6 is connected to terminal t4.

[0074] For example, switch Q7 is an N-channel MOSFET. The drain of switch Q7 is connected to terminal t3, and the source of switch Q7 is connected to the drain of switch Q8.

[0075] Switch Q8, for example, is an N-channel MOSFET. The drain of switch Q8 is connected to the source of switch Q7, and the source of switch Q8 is connected to terminal t4.

[0076] One end of the secondary winding of transformer T is connected to a node between switch Q5 and switch Q6 in the third leg, and the other end of the secondary winding of transformer T is connected to a node between switch Q7 and switch Q8 in the fourth leg.

[0077] For example, the controller 40 controls the switching of switches Q1, Q2, Q3, Q4, Q5, Q6, Q7 and Q8 by controlling a gate drive circuit (not shown in the drawings) which is connected to the gates of switches Q1, Q2, Q3, Q4, Q5, Q6, Q7 and Q8 via a PWM generator (not shown in the drawings) or the like.

[0078] The controller 40 calculates a time interval that excludes a resonance period of the resonator 30 from the switching cycle of switches Q1, Q2, Q3 and Q4, and operates switches Q5, Q6, Q7 and Q8 synchronously with the control signals for switches Q1, Q2, Q3 and Q4 by means of control signals applied during this time interval.

[0079] The controller 40 calculates a time interval that excludes a resonance period of the resonator 30 (for example, a resonance half-cycle) from a switching cycle of switches Q1, Q2, Q3, and Q4 (for example, a switching half-cycle in which the switches are in the on state with a duty cycle of 50%). During this period, no current flows to the load connected to terminals t3 and t4. This time interval is also referred to as the non-excitation period. During the non-excitation period, the charge accumulated in the parasitic capacitance of devices on the secondary side of the transformer T (e.g., switches Q5, Q6, Q7, and Q8) cannot be discharged to the load side, and high-frequency ringing can occur due to free resonance caused by the leakage inductance of the transformer T and the parasitic capacitance of the secondary-side devices.In view of this, the controller 40 can divert the charge accumulated in the parasitic capacitance of the secondary-side components to the load side by operating the switches Q5, Q6, Q7 and Q8 synchronously with the control signals for the switches Q1, Q2, Q3 and Q4 by means of drive signals applied during the non-excitation period.

[0080] In embodiment 3, four examples, referred to as the first to fourth example, are given to show control methods by which the controller 40 controls the switches Q5, Q6, Q7 and Q8.

[0081] Fig. Figure 7 is a diagram illustrating a first example of the operating process and effects of the current conversion device 3 according to embodiment 3. Fig. Figure 7 shows, from top to bottom, timing diagrams of the gate signals of switches Q1, Q4, Q5, and Q8; the gate signals of switches Q2, Q3, Q6, and Q7; the voltage generated in the secondary winding of transformer T (transformer secondary voltage); the current flowing through the primary winding of transformer T (transformer primary current); and the current flowing through the secondary winding of transformer T (transformer secondary current). The same applies to the Fig. 8, Fig. 9 to Fig. 10, which will be described later.

[0082] In the first example, the control signals for switches Q6 and Q8 are signals that turn on switches Q6 and Q8 during the non-excitation period in the second half of the on-period of switches Q1 and Q4, and the control signals for switches Q5 and Q7 are signals that turn on switches Q5 and Q7 during the non-excitation period in the second half of the on-period of switches Q2 and Q3.

[0083] As in Fig. As shown in Figure 7, switches Q6 and Q8 turn on in response to the control signals before switches Q1 and Q4 turn off from an on state. In other words, using the control signals, the controller 40 turns on switches Q6 and Q8 before switches Q1 and Q4 turn off from an on state. By turning on switches Q6 and Q8 during this time interval, both ends of the secondary winding of transformer T can be connected to the negative terminal t4 of the load via switches Q6 and Q8, thus preventing high-frequency ringing.

[0084] As in Fig. As shown in Figure 7, switches Q5 and Q7 turn on before switches Q2 and Q3 turn off from the on state. In other words, using the control signals, the controller 40 turns on switches Q5 and Q7 before switches Q2 and Q3 turn off from the on state. By turning on switches Q5 and Q7 during this time interval, both ends of the secondary winding of transformer T can be connected to the positive terminal t3 of the load via switches Q5 and Q7, thus preventing high-frequency ringing.

[0085] As in Fig. As shown in Figure 7, it is evident that high-frequency ringing is suppressed in the secondary voltage of the transformer and high-frequency ringing is suppressed in the secondary current of the transformer.

[0086] Fig. Figure 8 is a diagram illustrating a second example of the operating process and effects of the current conversion device 3 according to embodiment 3.

[0087] In the second example, the control signals for switches Q5 and Q7 are signals that turn on switches Q5 and Q7 during the non-excitation period in the second half of the on-period of switches Q1 and Q4, and the control signals for switches Q6 and Q8 are signals that turn on switches Q6 and Q8 during the non-excitation period in the second half of the on-period of switches Q2 and Q3.

[0088] As in Fig. As shown in Figure 8, switches Q5 and Q7 turn on in response to the control signals before switches Q1 and Q4 turn off from an on state. In other words, using the control signals, the controller 40 turns on switches Q5 and Q7 before switches Q1 and Q4 turn off from an on state. By turning on switches Q5 and Q7 during this time interval, both ends of the secondary winding of transformer T can be connected to the positive terminal t3 of the load via switches Q5 and Q7, thus preventing high-frequency ringing.

[0089] As in Fig. As shown in Figure 8, switches Q6 and Q8 are turned on before switches Q2 and Q3 turn off from an on state.

[0090] In other words, using the control signals, the controller 40 switches on switches Q6 and Q8 before switches Q2 and Q3 switch off from an on state. By switching on switches Q6 and Q8 during this time period, both ends of the secondary winding of transformer T can be connected to the negative terminal t4 of the load via switches Q6 and Q8, thus preventing high-frequency ringing.

[0091] As in Fig. As shown in Figure 8, it is evident that high-frequency ringing is suppressed in the secondary voltage of the transformer and high-frequency ringing is suppressed in the secondary current of the transformer.

[0092] Fig. Figure 9 is a diagram illustrating a third example of the operating process and effects of the current conversion device 3 according to embodiment 3.

[0093] In the third example, the control signals for switches Q6 and Q7 are signals that turn on switches Q6 and Q7 during the non-excitation period in the second half of the on-period of switches Q1 and Q4, and the control signals for switches Q5 and Q8 are signals that turn on switches Q5 and Q8 during the non-excitation period in the second half of the on-period of switches Q2 and Q3.

[0094] As in Fig. As shown in Figure 9, switches Q6 and Q7 turn on in response to the control signals before switches Q1 and Q4 turn off from an on state. In other words, using the control signals, the controller 40 turns on switches Q6 and Q7 before switches Q1 and Q4 turn off from an on state. By turning on switches Q6 and Q7 during this time interval, one end of the secondary winding of transformer T can be connected via switch Q6 to the negative terminal t4 of the load, and the other end of the secondary winding of transformer T can be connected via switch Q7 to the positive terminal t3 of the load, thus suppressing high-frequency ringing.

[0095] As in Fig. As shown in Figure 9, switches Q5 and Q8 are turned on before switches Q2 and Q3 turn off from the on state. In other words, using the control signals, the controller 40 turns on switches Q5 and Q8 before switches Q2 and Q3 turn off from the on state. By turning on switches Q5 and Q8 during this time interval, one end of the secondary winding of transformer T can be connected to the positive terminal t3 of the load via switch Q5, the other end of the secondary winding of transformer T can be connected to the negative terminal t4 of the load via switch Q8, and high-frequency ringing can be suppressed.

[0096] As in Fig. As shown in Figure 9, it is evident that high-frequency ringing is suppressed in the secondary voltage of the transformer and high-frequency ringing is suppressed in the secondary current of the transformer.

[0097] Fig. Figure 10 is a diagram illustrating a fourth example of the operating process and effects of the current conversion device 3 according to embodiment 3.

[0098] In the fourth example, the control signals for switches Q5 and Q8 are signals that turn on switches Q5 and Q8 during the non-excitation period in the second half of the on-period of switches Q1 and Q4, and the control signals for switches Q6 and Q7 are signals that turn on switches Q6 and Q7 during the non-excitation period in the second half of the on-period of switches Q2 and Q3.

[0099] As in Fig. As shown in Figure 10, switches Q5 and Q8 turn on in response to the control signals before switches Q1 and Q4 turn off from an on state. In other words, using the control signals, the controller 40 turns on switches Q5 and Q8 before switches Q1 and Q4 turn off from an on state. By turning on switches Q5 and Q8 during this time interval, one end of the secondary winding of transformer T can be connected to the positive terminal t3 of the load via switch Q5, the other end of the secondary winding of transformer T can be connected to the negative terminal t4 of the load via switch Q8, and high-frequency ringing can be suppressed.

[0100] As in Fig. As shown in Figure 10, switches Q6 and Q7 are turned on before switches Q2 and Q3 turn off from the on state. In other words, using the control signals, the controller 40 turns on switches Q6 and Q7 before switches Q2 and Q3 turn off from the on state. By turning on switches Q6 and Q7 during this time interval, one end of the secondary winding of transformer T can be connected via switch Q6 to the negative terminal t4 of the load, and the other end of the secondary winding of transformer T can be connected via switch Q7 to the positive terminal t3 of the load, thus suppressing high-frequency ringing.

[0101] As in Fig. As shown in Figure 10, it is evident that the high-frequency ringing is suppressed in the secondary voltage of the transformer and the high-frequency ringing is suppressed in the secondary current of the transformer.

[0102] As described above, during the non-excitation period, by synchronously operating switches Q5, Q6, Q7, and Q8 with the control signals for switches Q1, Q2, Q3, and Q4, both ends of the secondary winding of transformer T can be connected to the positive terminal t3 or the negative terminal t4 of the load (in other words, the potentials at both ends of the secondary winding of transformer T can be set to the potential on the positive side or the potential on the negative side of the load), and the charge accumulated in the parasitic capacitance of the secondary-side devices can be dissipated to the load side. Accordingly, high-frequency ringing can be effectively suppressed.

[0103] It should be noted that the current conversion device 3 is capable of bidirectional current conversion and that terminal t3 can serve as the input terminal, while terminal t1 can serve as the output terminal. In such cases, the control described above for the primary-side full bridge circuit 10 is performed for the secondary-side full bridge circuit 20, and vice versa. In such cases, capacitor Cout serves as the input capacitor and capacitor Cin as the output capacitor. [Version 4]

[0104] Next, a power conversion device according to embodiment 4 is described.

[0105] Fig. Figure 11 is a circuit diagram showing an example of a current conversion device 4 according to embodiment 4.

[0106] The current conversion device 4 differs from the current conversion device 1 in embodiment 1 with regard to the elements comprising the secondary-side full bridge circuit 20 and the control content of the control unit 40. Since the other aspects are essentially the same as those of the current conversion device 1 in embodiment 1, their description is omitted and the differences are discussed below.

[0107] In embodiment 4, the secondary-side full-bridge circuit 20 comprises switches Q6 and Q7 and diodes D5 and D8. Diode D5 is an example of the fifth element, switch Q6 is an example of the sixth element, switch Q7 is an example of the seventh element, and diode D8 is an example of the eighth element. In other words, in embodiment 4, the at least two elements that are switching elements are the sixth element (switch Q6) and the seventh element (switch Q7).

[0108] The anode of diode D5 is connected to the drain of switch Q6, and the cathode of diode D5 is connected to terminal t3.

[0109] For example, switch Q6 is an N-channel MOSFET. The drain of switch Q6 is connected to the anode of diode D5, and the source of switch Q6 is connected to terminal t4.

[0110] For example, switch Q7 is an N-channel MOSFET. The drain of switch Q7 is connected to terminal t3, and the source of switch Q7 is connected to the cathode of diode D8.

[0111] The anode of diode D8 is connected to terminal t4, and the cathode of diode D8 is connected to the source of switch Q7.

[0112] One end of the secondary winding of transformer T is connected to a node between diode D5 and switch Q6 in the third leg, and the other end of the secondary winding of transformer T is connected to a node between switch Q7 and diode D8 in the fourth leg.

[0113] For example, the controller 40 controls the switching of switches Q1, Q2, Q3, Q4, Q6 and Q7 by controlling a gate drive circuit (not shown in the drawings) which is connected to the gates of switches Q1, Q2, Q3, Q4, Q6 and Q7 via a PWM generator (not shown in the drawings) or the like.

[0114] The controller 40 calculates a time interval that excludes a resonance period of the resonator 30 from the switching cycle of switches Q1, Q2, Q3 and Q4, and operates switches Q6 and Q7 synchronously with the control signals for switches Q1, Q2, Q3 and Q4 by means of control signals applied during this time interval.

[0115] For example, the controller 40 calculates a time interval that excludes a resonance period of the resonator 30 (e.g., a resonance half-cycle) from a switching cycle of switches Q1, Q2, Q3, and Q4 (e.g., a switching half-cycle in which the switches are in the on state at a duty cycle of 50%). During this time interval, no current flows to the load connected to terminals t3 and t4. This time interval is also called the non-excitation period. During the non-excitation period, the charge accumulated in the parasitic capacitance of devices on the secondary side of the transformer T (e.g., diodes D5 and D8 and switches Q6 and Q7) cannot be discharged to the load side, and high-frequency ringing can occur due to free resonance caused by the leakage inductance of the transformer T and the parasitic capacitance of the secondary-side devices.Against this background, the controller 40 can transfer the charge accumulated in the parasitic capacitance of the secondary-side components to the load side by operating switches Q6 and Q7 synchronously with the control signals for switches Q1, Q2, Q3, and Q4 via drive signals applied during the non-excitation period. The drive signals for switches Q6 and Q7 are signals that switch on switches Q6 and Q7 during the non-excitation period in the second half of the on-time of switches Q1 and Q4, and during the non-excitation period in the second half of the on-time of switches Q2 and Q3.

[0116] Next, the operating processes of the power conversion device 4 and the effects achieved by these operating processes will be described with reference to Fig. 12 described.

[0117] Fig. Figure 12 is a diagram illustrating an example of the operating processes and effects of the current conversion device 4 according to embodiment 4. Fig. Figure 12 shows, from top to bottom, timing diagrams of the gate signals of switches Q1 and Q4, the gate signals of switches Q2, Q3, Q6 and Q7, the voltage generated in the secondary winding of transformer T (transformer secondary voltage), the current flowing through the primary winding of transformer T (transformer primary current) and the current flowing through the secondary winding of transformer T (transformer secondary current).

[0118] As in Fig. As shown in Figure 12, switches Q6 and Q7 turn on in response to the control signals before switches Q1 and Q4 turn off from an on state, and turn on before switches Q2 and Q3 turn off from an on state. In other words, using the control signals, the controller 40 turns on switches Q6 and Q7 before switches Q1 and Q4 turn off from an on state, and turns on switches Q6 and Q7 before switches Q2 and Q3 turn off from an on state. By turning on switch Q6 during these time intervals, one end of the secondary winding of transformer T can be connected via switch Q6 to the negative terminal t4 of the load, thereby suppressing high-frequency ringing to some extent.By switching on switch Q7 during these time periods, the other end of the secondary winding of transformer T can be connected to the positive terminal t3 of the load via switch Q7, thereby suppressing high-frequency ringing to some extent. As in . Fig. As shown in Figure 12, it is evident that high-frequency ringing in the secondary voltage of the transformer can be suppressed to a certain degree and high-frequency ringing in the secondary current of the transformer can be suppressed to a certain degree.

[0119] It should be noted that the secondary-side full-bridge circuit 20 may have switches Q5 and Q8 instead of diodes D5 and D8, and diodes D6 and D7 instead of switches Q6 and Q7. In such cases, the controller 40 calculates a time interval that excludes a resonance period of the resonator 30 from the switching cycle of switches Q1, Q2, Q3, and Q4, and operates switches Q5 and Q8 synchronously with the control signals for switches Q1, Q2, Q3, and Q4 by means of drive signals applied during this time interval.

[0120] In such cases, switches Q5 and Q8 turn on in response to the control signals before switches Q1 and Q4 turn off from an on state, and turn on before switches Q2 and Q3 turn off from an on state. In other words, using the control signals, the controller 40 turns on switches Q5 and Q8 before switches Q1 and Q4 turn off from an on state, and turns on switches Q5 and Q8 before switches Q2 and Q3 turn off from an on state. By turning on switch Q5 during these time intervals, one end of the secondary winding of transformer T can be connected to the positive terminal t3 of the load via switch Q5, thus suppressing high-frequency ringing to some extent.By switching on switch Q8 during these time periods, the other end of the secondary winding of the transformer T can be connected to the negative terminal t4 of the load via switch Q8, thereby suppressing high-frequency ringing to some extent.

[0121] As described above, during the non-excitation period, by synchronously operating switches Q6 and Q7 or switches Q5 and Q8 with the control signals for switches Q1, Q2, Q3, and Q4, both ends of the secondary winding of transformer T can be connected to the positive terminal t3 or the negative terminal t4 of the load (in other words, the potentials at both ends of the secondary winding of transformer T can be set to the potential on the positive side or the potential on the negative side of the load), and the charge of the secondary-side devices can be drawn towards the load side. Accordingly, high-frequency ringing can be suppressed to a certain extent. [Version 5]

[0122] Next, a power conversion device according to embodiment 5 is described.

[0123] Fig. Figure 13 is a circuit diagram showing an example of a current conversion device 5 according to embodiment 5.

[0124] The current conversion device 5 differs from the current conversion device 1 in embodiment 1 in that it has a primary-side half-bridge circuit 50 instead of the primary-side full-bridge circuit 10 and differs in the control content of the controller 40. Since the other aspects are essentially the same as those of the current conversion device 1 in embodiment 1, their description is omitted and the differences are discussed below.

[0125] The primary-side half-bridge circuit 50 is connected to the primary side of the resonator 30. The primary-side half-bridge circuit 50 has a first element located on a high side and a second element located on a low side. The first element and the second element are each switching elements.

[0126] The primary-side half-bridge circuit 50 comprises switches Q1 and Q2. Switch Q1 is an example of the first element, and switch Q2 is an example of the second element. Since switches Q1 and Q2 are identical to those in embodiment 1, their description is omitted.

[0127] As will be described in detail later, the at least two elements, which are switching elements and are shown in the secondary-side full bridge circuit 20, are operated synchronously with the control signals for the first element and the second element by applying control signals in a period of time that excludes a resonance period of the resonator 30 from the switching cycle of the first element and the second element.

[0128] In embodiment 5, the secondary-side full-bridge circuit 20, as in embodiment 1, comprises diodes D5 and D7 and switches Q6 and Q8. Diode D5 is an example of the fifth element, switch Q6 is an example of the sixth element, diode D7 is an example of the seventh element, and switch Q8 is an example of the eighth element. In other words, in embodiment 5, the at least two elements that are switching elements are the sixth element (switch Q6) and the eighth element (switch Q8).

[0129] Capacitor Cr is an example of a resonant capacitor. Capacitor Cr is connected via a junction between switch Q1 and switch Q2.

[0130] Transformer T is an insulated transformer and has a primary winding and a secondary winding that are electrically isolated from each other. One end of the primary winding of transformer T is connected via capacitor Cr to a junction between switch Q1 and switch Q2, and the other end of the primary winding of transformer T is connected to the source of switch Q2.

[0131] It should be noted that the capacitor Cr can also be connected to the other end of the primary winding of transformer T. In such cases, one end of the primary winding of transformer T is connected to a junction between switch Q1 and switch Q2, and the other end of the primary winding of transformer T is connected to the power supply of switch Q2 via the capacitor Cr.

[0132] The controller 40 is a circuit for controlling the switching (on and off) of switches (for example, switches Q1, Q2, Q6, and Q8) that is included in the current conversion device 1. For example, the controller 40 controls the switching of switches Q1, Q2, Q6, and Q8 by controlling a gate drive circuit (not shown in the drawings) connected to the gates of switches Q1, Q2, Q6, and Q8 via a PWM generator (not shown in the drawings) or the like.

[0133] The control unit 40 calculates a time interval that excludes a resonance period of the resonator 30 from the switching cycle of switches Q1 and Q2, and operates switches Q6 and Q8 synchronously with the control signals for switches Q1 and Q2 by means of control signals applied during this time interval.

[0134] The controller 40 calculates a time interval that excludes a resonance period of the resonator 30 (for example, a resonance half-cycle) from a switching cycle of switches Q1 and Q2 (for example, a switching half-cycle in which the switches are in the on state with a duty cycle of 50%). During this time interval, no current flows to the load connected to terminals t3 and t4. This time interval is also referred to as the non-excitation period. During the non-excitation period, the charge stored in the parasitic capacitance of components on the secondary side of the transformer T (e.g., diodes D5 and D7 and switches Q6 and Q8) cannot be dissipated to the load side, and a high-frequency ringing can occur due to free resonance caused by the leakage inductance of the transformer T and the parasitic capacitance of the secondary-side components.Against this background, the controller 40 can transfer the charge accumulated in the parasitic capacitance of the secondary-side components to the load side by operating switches Q6 and Q8 synchronously with the control signals for switches Q1 and Q2 by means of drive signals applied during the non-excitation period. The drive signals for switches Q6 and Q8 are signals that switch on switches Q6 and Q8 during the non-excitation period in the second half of the on-time of switch Q1 and during the non-excitation period in the second half of the on-time of switch Q2.

[0135] Next, the operating processes of the power conversion device 5 and the effects achieved by these operating processes will be described with reference to Fig. 14 described.

[0136] Fig. Figure 14 is a diagram illustrating an example of the operating processes and effects of the current conversion device 5 according to embodiment 5. Fig. Figure 14 shows, from top to bottom, timing diagrams of the gate signals of switches Q1 and Q8, the gate signals of switches Q2 and Q6, the voltage generated in the secondary winding of transformer T (transformer secondary voltage), the current flowing through the primary winding of transformer T (transformer primary current), and the current flowing through the secondary winding of transformer T (transformer secondary current).

[0137] As in Fig. As shown in Figure 14, switches Q6 and Q8 turn on in response to the drive signals before switch Q1 turns off from an on state, and turn on before switch Q2 turns off from an on state. In other words, using the drive signals, the controller 40 turns on switches Q6 and Q8 before switch Q1 turns off from an on state, and turns on switches Q6 and Q8 before switch Q2 turns off from an on state. The non-excitation period is the time interval before switch Q1 turns off from an on state, and the time interval before switch Q2 turns off from an on state. By turning on switches Q6 and Q8 during these intervals, both ends of the secondary winding of transformer T can be connected to the negative terminal t4 of the load via switches Q6 and Q8, thus preventing high-frequency ringing. As shown in Figure 14, the controller 40 turns on switches Q6 and Q8 before switch Q1 turns off from an on state. Fig. As shown in Figure 14, it is evident that high-frequency ringing in the secondary voltage of the transformer is prevented and high-frequency ringing in the secondary current of the transformer is prevented.

[0138] It should be noted that the upper limit for the length of the time interval before switch Q1 switches off from the on state, and the length of the time interval before switch Q2 switches off from the on state, is the length of the non-excitation period. In other words, the end of the time interval before switch Q1 switches off from the on state is the time at which switch Q1 switches off, and the start of the time interval occurs at a time that precedes the time at which switch Q1 switches off by a duration that does not exceed the length of the non-excitation period. The end of the time interval before switch Q2 switches off from the on state is the time at which switch Q2 switches off, and the start of the time interval occurs at a time that precedes the time at which switch Q2 switches off by a duration that does not exceed the length of the non-excitation period.

[0139] As described above, a period of time that excludes a resonance period of resonator 30 from the switching cycle of switches Q1 and Q2 is a non-excitation period during which no current flows to the load. When devices on the secondary side of transformer T (in particular switches Q6 and Q8) are not controlled, the charge accumulated in the parasitic capacitance of the secondary-side devices of transformer T cannot be discharged to the load side. Therefore, during this period, a high-frequency ringing can occur due to the free resonance caused by the leakage inductance of transformer T and the parasitic capacitance of the secondary-side devices.In light of this, during this period, by synchronously operating switches Q6 and Q8 with the control signals for switches Q1 and Q2, both ends of the secondary winding of transformer T can be connected to the negative terminal t4 of the load (in other words, the potentials at both ends of the secondary winding of transformer T can be set to the potential on the negative side of the load), and the charge of the secondary-side devices can be drawn towards the load side. Accordingly, high-frequency ringing can be effectively suppressed.

[0140] It should be noted that embodiment 5 is configured such that the primary-side full-bridge circuit 10 in embodiment 1 is replaced by the primary-side half-bridge circuit 50; however, the primary-side full-bridge circuit 10 in embodiments 2 to 4 can also be replaced by the primary-side half-bridge circuit 50. In this case as well, although a detailed explanation is omitted, high-frequency ringing can be suppressed in the same way as in embodiments 2 to 4. (Other embodiments)

[0141] Above, one or more embodiments have been described as one or more examples of the techniques according to the present disclosure. However, the techniques according to the present disclosure are not limited to these examples; various modifications, substitutions, additions, omissions, etc., can be applied to the embodiments. For example, the following also exhibit variations in an embodiment of the present disclosure.

[0142] For example, the diode in the secondary-side full bridge circuit 20 in the above embodiment can be replaced by a switch (for example, an N-channel MOSFET) and designed to function as a diode.

[0143] In the embodiment described above, for example, the current conversion device is an LLC converter. However, the disclosure is not limited thereto, and the current conversion device can be a resonant converter comprising a resonator having series and / or parallel LC circuits, such as an LCC converter or a CLLC converter.

[0144] In the embodiment described above, for example, the LLC converter includes the magnetizing inductance and leakage inductance of the transformer, as well as a resonant capacitor. However, instead of the leakage inductance, a separate inductor corresponding to the leakage inductance can also be provided.

[0145] The present disclosure can be realized, for example, not only as a current conversion device, but also as a control method for controlling the current conversion device (in particular as a control method with steps (processes) that are carried out by elements (in particular the control 40) included in the current conversion device).

[0146] Fig. 15 and Fig. Figure 16 are flowcharts showing an example of a control procedure according to a further embodiment.

[0147] The control method is used, for example, to control a current conversion device. The current conversion device comprises: a resonator with a transformer and a resonant 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 has a first element located on the high side of a first leg, a second element located on the low side of the first leg, a third element located on the high side of a second leg, and a fourth element located on the low side of the second leg.The secondary-side full-bridge circuit has a fifth element located on the high side of a third leg, a sixth element located on the low side of the third leg, a seventh element located on the high side of a fourth leg, and an eighth element located on the low side of the fourth leg. The first, second, third, and fourth elements are each switching elements. At least two elements below the fifth, sixth, seventh, and eighth elements are each switching elements. The control method, as shown in [reference], [further details would be inserted here]. Fig. 15 shown, on: calculating a time interval that excludes a resonance period of the resonator from a switching cycle of the first element, the second element, the third element and the fourth element (step S11); and operating the at least two elements synchronously with control signals for the first element, the second element, the third element and the fourth element by means of control signals applied in the time interval (step S12) to operate synchronously (step S12).

[0148] The control method is used, for example, to control a current conversion device. The current conversion device comprises: a resonator with a transformer and a resonant capacitor; a primary-side half-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 half-bridge circuit has a first element located on a high side and a second element located on a low side. The secondary-side full-bridge circuit has a fifth element located on a high side of a third leg, a sixth element located on a low side of the third leg, a seventh element located on a high side of a fourth leg, and an eighth element located on a low side of the fourth leg.The first and second elements are each a switching element. At least two elements below the fifth, sixth, seventh, and eighth elements are each a switching element. The control method, as shown in [reference], [further details would be inserted here]. Fig. 16 shown, on: calculating a time interval that excludes a resonance period of the resonator from a switching cycle of the first element and the second element (step S21); and operating the at least two elements synchronously with control signals for the first element and the second element by means of control signals applied in the time interval (step S22).

[0149] For example, the present disclosure can be implemented as a program that causes a computer (processor) to execute the steps described in the control procedure. Furthermore, the present disclosure can be implemented as a non-transitory, computer-readable recording medium, such as a CD-ROM, on which the program is recorded.

[0150] If, for example, the present disclosure is implemented as a program (software), each step is performed while the program is running using hardware resources such as a computer's CPU, memory, and input / output circuits. In other words, each step is performed while the CPU retrieves data from memory or the input / output circuits, performs calculations, and outputs the results of the calculations to memory or the input / output circuits.

[0151] In the above embodiment, each element comprising the power conversion device can be configured using dedicated hardware or implemented by executing a software program suitable for that element. Each element can be implemented by a program execution unit such as a CPU or processor, which reads and executes a software program recorded on a recording medium such as a hard disk or semiconductor memory.

[0152] Some or all of the functions of the power conversion device according to the above embodiment are typically implemented as LSI circuits, which are integrated circuits. These elements can be integrated onto individual chips, or some or all of the elements can be integrated onto a single chip. Circuit integration is not limited to LSI; the elements can be implemented using dedicated circuitry or a general-purpose processor. A field-programmable gate array (FPGA) can be used, allowing programming after the LSI circuits have been fabricated, or a reconfigurable processor can be used, allowing reconfiguration of the connections and settings of circuit cells within the LSI circuits.

[0153] Furthermore, it goes without saying that the circuit integration of each element contained in the power conversion device can be carried out using this technology if, due to advances in semiconductor technology or other derived technologies, a new technology for circuit integration emerges that replaces LSI.

[0154] Embodiments obtained by a person skilled in the art through various modifications to one of the embodiments, or embodiments realized by arbitrary combinations of elements and functions in the embodiments that do not deviate from the essence of the present disclosure, are also listed in the present disclosure. (Additional notes)

[0155] Based on the foregoing description of the embodiments, the following technologies are disclosed.

[0156] (Technology 1) A current conversion device comprises: a resonator with a transformer and a resonant 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 has a first element located on a high side of a first leg, a second element located on a low side of the first leg, a third element located on a high side of a second leg, and a fourth element located on a low side of the second leg.The secondary-side full-bridge circuit has a fifth element located on the high side of a third leg, a sixth element located on the low side of the third leg, a seventh element located on the high side of a fourth leg, and an eighth element located on the low side of the fourth leg. The first, second, third, and fourth elements each constitute a switching element. At least two elements below the fifth, sixth, seventh, and eighth elements each constitute a switching element.The at least two elements are operated synchronously with control signals for the first element, the second element, the third element and the fourth element by means of control signals that are applied in a time span that excludes a resonance period of the resonator from a switching cycle of the first element, the second element, the third element and the fourth element.

[0157] This means that a period excluding a resonator resonance period from the switching cycle of the first, second, third, and fourth elements is a non-excitation period during which no current flows to the load. Furthermore, if devices on the secondary side of the transformer (especially at least two elements) are not controlled, the charge accumulated in the parasitic capacitance of the secondary-side devices of the transformer cannot be discharged to the load side. Therefore, during this period, high-frequency ringing can occur due to free resonance caused by the leakage inductance of the transformer and the parasitic capacitance of the secondary-side devices.Given this, during this period, by synchronously operating at least two elements with the control signals for the first, second, third, and fourth elements, both ends of the transformer's secondary winding can be connected to the positive or negative terminal of the load (in other words, the potentials at both ends of the transformer's secondary winding can be set to the positive or negative potential of the load), and the charge accumulated in the secondary-side capacitance can be dissipated to the load side. Accordingly, high-frequency ringing can be effectively suppressed. Consequently, effects such as improved efficiency due to reduced high-frequency losses and improved EMC performance in the MHz band can be achieved.Furthermore, since no means of suppressing vibrations, such as a snubber circuit or an active clamping circuit, are required, miniaturization and cost reduction can be achieved.

[0158] (Technology 2) The current conversion device according to Technology 1, wherein the at least two elements are the sixth element and the eighth element.

[0159] This allows both ends of the transformer's secondary winding to be connected to the negative terminal of the load via the sixth and eighth elements, and high-frequency ringing can be suppressed.

[0160] (Technology 3) The current conversion device according to Technology 2, wherein the sixth element and the eighth element, in response to the control signals: switch on before the first element and the fourth element switch off from a switched-on state; and switch on before the second element and the third element switch off from a switched-on state.

[0161] A time interval that excludes the resonator's resonant period from the switching cycle of the first, second, third, and fourth elements is the time interval before the first and fourth elements switch off from an on state, and the time interval before the second and third elements switch off from an on state. Therefore, by switching on the sixth and eighth elements during these time intervals, both ends of the transformer's secondary winding can be connected to the negative terminal of the load via the sixth and eighth elements, thus preventing high-frequency ringing.

[0162] (Technology 4) The current conversion device according to Technology 1, wherein the at least two elements are the fifth element and the seventh element.

[0163] This allows both ends of the transformer's secondary winding to be connected to the positive terminal of the load via the fifth and seventh elements, thus preventing high-frequency ringing.

[0164] (Technology 5) The current conversion device according to Technology 4, wherein the fifth element and the seventh element switch on in response to the control signals before the first element and the fourth element switch off from a switched-on state, and switch on before the second element and the third element switch off from a switched-on state.

[0165] A time interval that excludes the resonator's resonant period from the switching cycle of the first, second, third, and fourth elements is the time interval before the first and fourth elements switch off from an on state, and the time interval before the second and third elements switch off from an on state. Therefore, by switching on the fifth and seventh elements during these time intervals, both ends of the transformer's secondary winding can be connected to the positive terminal of the load via the fifth and seventh elements.

[0166] (Technology 6) The current conversion device according to Technology 1, wherein the at least two elements are the fifth element, the sixth element, the seventh element and the eighth element.

[0167] This allows both ends of the transformer's secondary winding to be connected to the positive or negative terminal of the load via the fifth, sixth, seventh and eighth elements, thus preventing high-frequency ringing.

[0168] (Technology 7) The current conversion device according to Technology 6, wherein the sixth element and the eighth element switch on in response to the control signals before the first element and the fourth element switch off from a switched-on state, and the fifth element and the seventh element switch on in response to the control signals before the second element and the third element switch off from a switched-on state.

[0169] A time interval that excludes the resonator's resonant period from the switching cycle of the first, second, third, and fourth elements is the time interval before the first and fourth elements switch off from an on state, and the time interval before the second and third elements switch off from an on state. Therefore, by switching on the sixth and eighth elements during a time interval before the first and fourth elements switch off from the on state, both ends of the transformer's secondary winding can be connected to the negative terminal of the load via the sixth and eighth elements, and high-frequency ringing can be suppressed.By switching on the fifth and seventh elements during a period of time before the second and third elements switch off from the switched-on state, both ends of the secondary winding of the transformer can be connected to the positive terminal of the load via the fifth and seventh elements, thus preventing high-frequency ringing.

[0170] (Technology 8) The current conversion device according to Technology 6, wherein the fifth element and the seventh element switch on in response to the control signals before the first element and the fourth element switch off from a switched-on state, and the sixth element and the eighth element switch on in response to the control signals before the second element and the third element switch off from a switched-on state.

[0171] A time interval that excludes the resonator's resonant period from the switching cycle of the first, second, third, and fourth elements is the time interval before the first and fourth elements switch off from an on state, and the time interval before the second and third elements switch off from an on state. Therefore, by switching on the fifth and seventh elements during a time interval before the first and fourth elements switch off from the on state, both ends of the transformer's secondary winding can be connected to the positive terminal of the load via the fifth and seventh elements, thus preventing high-frequency ringing.By switching on the sixth and eighth elements during a period of time before the second and third elements switch off from the switched-on state, both ends of the secondary winding of the transformer can be connected to the negative terminal of the load via the sixth and eighth elements, thus preventing high-frequency ringing.

[0172] (Technology 9) The current conversion device according to Technology 6, wherein the sixth element and the seventh element switch on in response to the control signals before the first element and the fourth element switch off from a switched-on state, and the fifth element and the eighth element switch on in response to the control signals before the second element and the third element switch off from a switched-on state.

[0173] A time interval that excludes the resonator's resonant period from the switching cycle of the first, second, third, and fourth elements is the time interval before the first and fourth elements switch off from an on state, and the time interval before the second and third elements switch off from an on state. Therefore, by switching on the sixth and seventh elements during a time interval before the first and fourth elements switch off, one end of the transformer's secondary winding can be connected to the negative terminal of the load via the sixth element, and the other end of the transformer's secondary winding can be connected to the positive terminal of the load via the seventh element, thus preventing high-frequency ringing.By switching on the fifth and eighth elements during a period of time before the second and third elements switch off from the switched-on state, one end of the secondary winding of the transformer can be connected to the positive terminal of the load via the fifth element, the other end of the secondary winding of the transformer can be connected to the negative terminal of the load via the eighth element, and high-frequency ringing can be suppressed.

[0174] (Technology 10) The current conversion device according to Technology 6, wherein the fifth element and the eighth element switch on in response to the control signals before the first element and the fourth element switch off from a switched-on state, and the sixth element and the seventh element switch on in response to the control signals before the second element and the third element switch off from a switched-on state.

[0175] A time interval that excludes the resonator's resonant period from the switching cycle of the first, second, third, and fourth elements is the time interval before the first and fourth elements switch off from an on state, and the time interval before the second and third elements switch off from an on state. Therefore, by switching on the fifth and eighth elements during a time interval before the first and fourth elements switch off from the on state, one end of the transformer's secondary winding can be connected to the positive terminal of the load via the fifth element, and the other end of the transformer's secondary winding can be connected to the negative terminal of the load via the eighth element, thus preventing high-frequency ringing.By switching on the sixth and seventh elements during a period of time before the second and third elements switch off from the switched-on state, one end of the secondary winding of the transformer can be connected to the negative terminal of the load via the sixth element, the other end of the secondary winding of the transformer can be connected to the positive terminal of the load via the seventh element, and high-frequency ringing can be prevented.

[0176] (Technology 11) A current conversion device comprises: a resonator with a transformer and a resonant capacitor; a primary-side half-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 half-bridge circuit comprises a first element located on a high side and a second element located on a low side. The secondary-side full-bridge circuit comprises a fifth element located on a high side of a third leg, a sixth element located on a low side of the third leg, a seventh element located on a high side of a fourth leg, and an eighth element located on a low side of the fourth leg. The first and second elements are each switching elements.At least two elements below the fifth, sixth, seventh, and eighth elements each constitute a switching element. These at least two elements are operated synchronously with control signals for the first and second elements by means of control signals applied within a time interval that excludes a resonator resonance period from a switching cycle of the first and second elements.

[0177] This means that a period of time excluding a resonator resonance period from the switching cycle of the first and second elements is a non-excitation period during which no current flows to the load. Furthermore, if devices on the secondary side of the transformer (especially at least two elements) are not controlled, the charge accumulated in the parasitic capacitance of the secondary-side devices of the transformer cannot be discharged to the load side. Therefore, during this period, high-frequency ringing can occur due to free resonance caused by the leakage inductance of the transformer and the parasitic capacitance of the secondary-side devices.Given this, during this time, by synchronously operating at least two elements with the control signals for the first and second elements, both ends of the transformer's secondary winding can be connected to the positive or negative terminal of the load (in other words, the potentials at both ends of the transformer's secondary winding can be set to the potential on the positive side or the potential on the negative side of the load), and the charge accumulated in the parasitic capacitance of the secondary-side devices can be dissipated to the load side. Accordingly, high-frequency ringing can be effectively suppressed.

[0178] (Technology 12) A control method for controlling a current conversion device. The current conversion device comprises: a resonator with a transformer and a resonant 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 has a first element located on a high side of a first leg, a second element located on a low side of the first leg, a third element located on a high side of a second leg, and a fourth element located on a low side of the second leg.The secondary-side full-bridge circuit has a fifth element located on the high side of a third leg, a sixth element located on the low side of the third leg, a seventh element located on the high side of a fourth leg, and an eighth element located on the low side of the fourth leg. The first, second, third, and fourth elements each constitute a switching element. At least two elements below the fifth, sixth, seventh, and eighth elements each constitute a switching element.The control method involves: calculating a time interval that excludes a resonance period of the resonator from a switching cycle of the first element, the second element, the third element and the fourth element; and operating the at least two elements synchronously with control signals for the first element, the second element, the third element and the fourth element by means of control signals applied during the time interval.

[0179] This allows a control method to be provided that is capable of effectively suppressing high-frequency ringing.

[0180] (Technology 13) A control method for controlling a current conversion device. The current conversion device comprises: a resonator with a transformer and a resonant capacitor; a primary-side half-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 half-bridge circuit comprises a first element located on a high side and a second element located on a low side. The secondary-side full-bridge circuit comprises a fifth element located on a high side of a third leg, a sixth element located on a low side of the third leg, a seventh element located on a high side of a fourth leg, and an eighth element located on a low side of the fourth leg.The first and second elements are each a switching element. At least two elements below the fifth, sixth, seventh, and eighth elements are each a switching element. The control method comprises: calculating a time interval that excludes a resonator resonance period from a switching cycle of the first and second elements; and operating the at least two elements synchronously with control signals for the first and second elements by means of control signals applied within this time interval.

[0181] This allows a control method to be provided that is capable of effectively suppressing high-frequency ringing. [Industrial applicability]

[0182] The present disclosure is applicable to isolated DC-DC converters and the like. [List of reference symbols] 1, 2, 3, 4, 5 Power conversion device 10 primary-side full bridge circuit 20 secondary-side full bridge circuit 30 Resonator 40 Control 50 primary-side half-bridge circuit Cin, Cout, Cr capacitor D5, D6, D7, D8 Diode Q1, Q2, Q3, Q4, Q5, Q6, Q7, Q8 switches T transformer t1, t2, t3, t4 connection QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] JP 2014-217196

[0005]

Claims

[1] A power conversion device comprising: a resonator comprising a transformer and a resonant 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, wherein the primary-side full bridge circuit has a first element provided on a high side of a first leg, a second element provided on a low side of the first leg, a third element provided on a high side of a second leg, and a fourth element provided on a low side of the second leg. the secondary-side full bridge circuit has a fifth element provided on a high side of a third leg, a sixth element provided on a low side of the third leg, a seventh element provided on a high side of a fourth leg, and an eighth element provided on a low side of the fourth leg, the first element, the second element, the third element and the fourth element are each a switching element, at least two elements below the fifth element, the sixth element, the seventh element and the eighth element are each a switching element, and the at least two elements operate synchronously with control signals for the first element, the second element, the third element and the fourth element by applying control signals in a time span that excludes a resonance period of the resonator from a switching cycle of the first element, the second element, the third element and the fourth element. [2] The power conversion device according to claim 1, wherein the at least two elements are the sixth element and the eighth element. [3] The current conversion device according to claim 2, wherein in response to the control signals the sixth element and the eighth element: turn on before the first and fourth elements turn off from a turned-on state; and turn on before the second element and the third element turn off from a turned-on state. [4] The power conversion device according to claim 1, wherein the at least two elements are the fifth element and the seventh element. [5] The current conversion device according to claim 4, wherein in response to the control signals the fifth element and the seventh element: turn on before the first and fourth elements turn off from a turned-on state; and turn on before the second element and the third element turn off from a turned-on state. [6] The power conversion device according to claim 1, wherein the at least two elements are the fifth element, the sixth element, the seventh element and the eighth element. [7] The power conversion device according to claim 6, wherein The sixth and eighth elements switch on in response to the control signals before the first and fourth elements switch off from an on state, and The fifth and seventh elements switch on in response to the control signals before the second and third elements switch off from a switched-on state. [8] The power conversion device according to claim 6, wherein The fifth and seventh elements switch on in response to the control signals before the first and fourth elements switch off from an on state. and The sixth and eighth elements switch on in response to the control signals before the second and third elements switch off from a switched-on state. [9] The power conversion device according to claim 6, wherein The sixth and seventh elements switch on in response to the control signals before the first and fourth elements switch off from an on state, and The fifth and eighth elements switch on in response to the control signals before the second and third elements switch off from an on state. [10] The power conversion device according to claim 6, wherein switch on the fifth and eighth elements in response to the control signals before to turn off the first and fourth elements from an on state, and switch on the sixth and seventh elements in response to the control signals, before the second and third elements switch off from an on state. [11] A power conversion device comprising: a resonator comprising a transformer and a resonant capacitor; a primary-side half-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, wherein the primary-side half-bridge circuit has a first element provided on a high side and a second element provided on a low side; the secondary-side full-bridge circuit has a fifth element provided on a high side of a third leg, a sixth element provided on a low side of the third leg, a seventh element provided on a high side of a fourth leg, and an eighth element provided on a low side of the fourth leg. the first element and the second element are each a switching element, at least two elements below the fifth element, the sixth element, the seventh element and the eighth element are each a switching element, and the at least two elements operate synchronously with control signals for the first element and the second element by means of control signals that are applied in a time span that excludes a resonance period of the resonator from a switching cycle of the first element and the second element. [12] A control method for controlling a power conversion device, the power conversion device comprising: a resonator comprising a transformer and a resonant 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 has a first element provided on a high side of a first leg, a second element provided on a low side of the first leg, a third element provided on a high side of a second leg, and a fourth element provided on a low side of the second leg. the secondary-side full bridge circuit has a fifth element provided on a high side of a third leg, a sixth element provided on a low side of the third leg, a seventh element provided on a high side of a fourth leg, and an eighth element provided on a low side of the fourth leg, the first element, the second element, the third element and the fourth element are each a switching element, at least two elements below the fifth element, the sixth element, the seventh element and the eighth element are each a switching element, the control procedure comprehensively: Calculating a time interval that excludes a resonance period of the resonator from a switching cycle of the first element, the second element, the third element, and the fourth element; and Operating at least two elements synchronously with control signals for the first element, the second element, the third element and the fourth element by means of control signals applied during the time period. [13] A control method for controlling a power conversion device, comprising the power conversion device: a resonator comprising a transformer and a resonant capacitor; a primary-side half-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 half-bridge circuit has a first element located on a high side and a second element located on a low side, the secondary-side full bridge circuit has a fifth element provided on a high side of a third leg, a sixth element provided on a low side of the third leg, a seventh element provided on a high side of a fourth leg, and an eighth element provided on a low side of the fourth leg, the first element and the second element are each a switching element, at least two elements below the fifth element, the sixth element, the seventh element and the eighth element are each a switching element, the control procedure comprehensively: Calculating a time interval that excludes a resonance period of the resonator from a switching cycle of the first element and the second element; and Operating at least two elements synchronously with control signals for the first element and the second element by means of control signals applied during the time period.

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