Power conversion device and control method

Abstract

A power conversion device (1) comprises: a resonator (30) having a transformer (T) and a capacitor (Cr); a primary-side full-bridge circuit (10) having a first switch (Q1), a second switch (Q2), a third switch (Q3), and a fourth switch (Q4); a secondary-side full-bridge circuit (20) having a fifth diode (D5), a sixth switch (Q6), a seventh diode (D7), and an eighth switch (Q8); and a controller (40). During phase shift control, the controller (40) turns on the sixth switch (Q6) and the eighth switch (Q8) by a drive signal in a period corresponding to the phase difference between switching of the first switch (Q1) and the second switch (Q2) and switching of the third switch (Q3) and the fourth switch (Q4).

Description

Power conversion device and control method

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

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

[0003] LLC converters have the problem that high-frequency ringing occurs in the secondary circuit of the LLC converter, increasing circuit loss. Furthermore, when the drive frequency is increased, the occurrence of high-frequency ringing causes a major problem of high-frequency loss due to the influence of the harmonic components of the high-frequency ringing.

[0004] In response to this, Patent Document 1 discloses a technique for suppressing high-frequency ringing. Specifically, in an LLC DC-DC converter, all switch elements are turned off at a timing when the resonant current Ioff reaches a current value that cancels out the resonant current generated by the excitation current Ip, thereby solving the problem of high-frequency ringing occurring during dead time periods due to resonance between the resonant inductor and the parasitic capacitance present in parallel with the switch elements.

[0005] Japanese Patent Application Laid-Open No. 2014-217196

[0006] However, the DC-DC converter disclosed in Patent Document 1 cannot suppress high-frequency ringing due to parasitic capacitance under certain conditions. For example, in LLC DC-DC converters used in chargers, phase shift control is sometimes used in addition to frequency control, which controls the switching frequency, to accommodate a wide voltage range of the storage battery. Phase shift control increases the phase difference between the switching of the two legs on the primary side, thereby extending the period during which the voltage applied to the transformer is zero. This reduces the power transmitted to the secondary side, allowing the gain of the LLC converter to be significantly reduced, enabling it to accommodate a wide voltage range.

[0007] However, with phase shift control, high-frequency ringing due to parasitic capacitance can occur not only during the dead time but also during the phase shift period, so adjusting the timing of the dead time alone may not be enough to suppress high-frequency ringing. Furthermore, the calculation of the threshold for adjusting the timing of the dead time must take into account not only the parasitic capacitance of the switch element but also various parasitic components, such as the parasitic capacitance that occurs when the switch element is implemented, along with their variations, making it difficult to control the switch element.

[0008] Therefore, the present disclosure provides a power conversion device and the like that can suppress high-frequency ringing that occurs during phase shift control.

[0009] A power conversion device according to the present disclosure includes a resonator having a transformer and a resonance capacitor, a primary-side full bridge circuit connected to a primary side of the resonator, a secondary-side full bridge circuit connected to a secondary side of the resonator, and a controller that controls the primary-side full bridge circuit and the secondary-side full bridge circuit, wherein the primary-side full bridge circuit has a first 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 the high side of a second leg, and a fourth element provided on the low side of the second leg, and the secondary-side full bridge circuit has a fifth element provided on a high side of a third leg, a sixth element provided on the low side of the third leg, and a fourth element provided on the high side of the fourth leg. the first element, the second element, the third element, and the fourth element are each switch elements, and at least two elements among the fifth element, the sixth element, the seventh element, and the eighth element are each switch elements, and the controller operates the first element, the second element, the third element, and the fourth element so that the switching phase of the third element and the fourth element is delayed with respect to the switching phase of the first element and the second element, and turns on the at least two elements with a drive signal in a period corresponding to a phase difference between the switching of the first element and the second element and the switching of the third element and the fourth element.

[0010] A control method according to the present disclosure is a control method for controlling a power conversion device, the power conversion device including a resonator having a transformer and a resonance capacitor, a primary-side full bridge circuit connected to a primary side of the resonator, and a secondary-side full bridge circuit connected to a secondary side of the resonator, the primary-side full bridge circuit including a first 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 the high side of a second leg, and a fourth element provided on the low side of the second leg, the secondary-side full bridge circuit including a fifth element provided on the high side of a third leg, a sixth element provided on the low side of the third leg, and a seventh element provided on the high side of a fourth leg, and an eighth element provided on the low side of the fourth leg, wherein the first element, the second element, the third element, and the fourth element are each switch elements, and at least two elements among the fifth element, the sixth element, the seventh element, and the eighth element are each switch elements, and the control method operates the first element, the second element, the third element, and the fourth element so that the switching phase of the third element and the fourth element is delayed with respect to the switching phase of the first element and the second element, and turns on the at least two elements by a drive signal during a period corresponding to a phase difference between the switching of the first element and the second element and the switching of the third element and the fourth element.

[0011] These comprehensive or specific aspects may be realized as a system, a method, an integrated circuit, a computer program, or a computer-readable recording medium such as a CD-ROM, or may be realized as any combination of a system, a method, an integrated circuit, a computer program, and a recording medium.

[0012] According to the power conversion device and the like according to one aspect of the present disclosure, high-frequency ringing that occurs during phase shift control can be suppressed.

[0013] FIG. 1 is a circuit configuration diagram showing an example of a power conversion device according to a first embodiment. FIG. 2 is a diagram for explaining high-frequency ringing that occurs in phase shift control. FIG. 3 is a diagram for explaining an example of the operation and effect of the power conversion device according to the first embodiment. FIG. 4 is a diagram for explaining an example of the relationship between the phase difference and the output power in phase shift control when high-frequency ringing occurs. FIG. 5 is a diagram for explaining an example of the relationship between the phase difference and the output power in phase shift control when high-frequency ringing is suppressed. FIG. 6 is a circuit configuration diagram showing an example of a power conversion device according to a second embodiment. FIG. 7 is a diagram for explaining an example of the operation and effect of the power conversion device according to the second embodiment. FIG. 8 is a circuit configuration diagram showing an example of a power conversion device according to a third embodiment. FIG. 9 is a diagram for explaining a first example of the operation and effect of the power conversion device according to the third embodiment. FIG. 10 is a diagram for explaining a second example of the operation and effect of the power conversion device according to the third embodiment. FIG. 11 is a diagram for explaining a third example of the operation and effect of the power conversion device according to the third embodiment. FIG. 12 is a diagram for explaining a fourth example of the operation and effect of the power conversion device according to the third embodiment. FIG. 13 is a diagram for explaining losses that occur in elements on the secondary side. FIG. 14 is a circuit configuration diagram showing an example of a power conversion device according to a fourth embodiment. FIG. 15 is a diagram for explaining an example of the operation and effect of the power conversion device according to the fourth embodiment. FIG. 16 is a flowchart showing an example of a control method according to another embodiment.

[0014] Hereinafter, the embodiments will be specifically described with reference to the drawings.

[0015] The embodiments described below are all comprehensive or specific examples, and the numerical values, shapes, materials, components, arrangement and connection of the components, steps, and order of steps shown in the following embodiments are merely examples and are not intended to limit the present disclosure.

[0016] (First embodiment) Hereinafter, a power conversion device according to a first embodiment will be described.

[0017] FIG. 1 is a circuit configuration diagram showing an example of a power conversion device 1 according to the first embodiment.

[0018] The power conversion device 1 is an isolated DC-DC converter that boosts or bucks an input voltage to a predetermined voltage and outputs it. The power conversion device 1 is capable of unidirectional power conversion. For example, the power conversion device 1 may be an LLC converter. An LLC converter is a circuit that utilizes LLC resonance due to the leakage inductance, excitation inductance, and resonant capacitor of a transformer. The LLC converter changes the input / output voltage ratio (Gain) by changing the switching frequency, thereby enabling the desired power output. Furthermore, the LLC converter uses phase shift control to increase the phase difference between the switching of the two legs on the primary side, thereby increasing the period during which the voltage applied to the transformer is zero. This reduces the power transmitted to the secondary side, significantly reducing the gain of the LLC converter and enabling even greater changes in the input / output voltage ratio.

[0019] The power conversion device 1 has terminals t1, t2, t3, and t4. The terminal t1 is an input terminal. The terminal t2 is a ground terminal. The terminal t3 is an output terminal. The terminal t4 is a ground terminal. Note that, since the power conversion device 1 is an isolated DC-DC converter, the terminals t2 and t4 are electrically isolated.

[0020] The power conversion device 1 includes a primary side full bridge circuit 10, a secondary side full bridge circuit 20, a resonator 30, capacitors Cin and Cout, and a controller 40. The capacitors Cin and Cout do not necessarily have to be components of the power conversion device 1.

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

[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 provided on the high side of a first leg connecting terminals t1 and t2, a second element provided on the low side of the first leg, a third element provided on the high side of a second leg connecting terminals t1 and t2, and a fourth element provided on the low side of the second leg. The first leg and second leg are connected in parallel. The first element, second element, third element, and fourth element are each a switch element.

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

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

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

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

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

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

[0029] In the first embodiment, the secondary-side full-bridge circuit 20 has diodes D5 and D7 and switches Q6 and Q8, where the diode D5 is an example of a fifth element, the switch Q6 is an example of a sixth element, the diode D7 is an example of a seventh element, and the switch Q8 is an example of an eighth element. That is, in the first embodiment, the at least two elements that are switch elements are the sixth element (switch Q6) and the eighth element (switch Q8).

[0030] The anode of the diode D5 is connected to the drain of the switch Q6, and the cathode is connected to the terminal t3.

[0031] The switch Q6 is, for example, an N-channel MOSFET. The drain of the switch Q6 is connected to the anode of the diode D5, and the source of the switch Q6 is connected to the terminal t4.

[0032] The anode of the diode D7 is connected to the drain of the switch Q8, and the cathode is connected to the terminal t3.

[0033] The switch Q8 is, for example, an N-channel MOSFET. The drain of the switch Q8 is connected to the anode of the diode D7, and the source of the switch Q8 is connected to the terminal t4.

[0034] The resonator 30 includes a transformer T and a capacitor Cr.

[0035] The capacitor Cr is an example of a resonant capacitor and is connected to a node between the switch Q1 and the switch Q2 in the first leg.

[0036] The transformer T is an isolated transformer having a primary winding and a secondary winding that are isolated from each other. One end of the primary winding of the transformer T is connected via a capacitor Cr to a node between the switches Q1 and Q2 in the first leg, and the other end of the primary winding of the transformer T is connected to a node between the switches Q3 and Q4 in the second leg. One end of the secondary winding of the transformer T is connected to a node between the diode D5 and the switch Q6 in the third leg, and the other end of the secondary winding of the transformer T is connected to a node between the diode D7 and the switch Q8 in the fourth leg.

[0037] The capacitor Cr may be connected to a node between the switches Q3 and Q4 in the second leg. In this case, one end of the primary winding of the transformer T is connected to a node between the switches Q1 and Q2 in the first leg, and the other end of the primary winding of the transformer T is connected to a node between the switches Q3 and Q4 in the second leg via the capacitor Cr.

[0038] The controller 40 is a circuit for controlling the switching (on and off) of switches (e.g., switches Q1, Q2, Q3, Q4, Q6, and Q8) included in the power conversion device 1. For example, the controller 40 controls the switching of the switches Q1, Q2, Q3, Q4, Q6, and Q8 by controlling a gate drive circuit (not shown) connected to the gates of the switches Q1, Q2, Q3, Q4, Q6, and Q8 via a PWM generator (not shown) or the like.

[0039] The controller 40 is, for example, a computer including a processor (microprocessor) and a memory. The memory may be a read-only memory (ROM) or a random access memory (RAM), and can store programs to be executed by the processor. For example, the controller 40 is a microcontroller.

[0040] The controller 40 operates the switches Q1, Q2, Q3, and Q4 so that the switching phase of the switches Q3 and Q4 is delayed relative to the switching phase of the switches Q1 and Q2. That is, the controller 40 performs phase shift control, with the first leg (switches Q1 and Q2) as the reference leg and the second leg (switches Q3 and Q4) as the lagging leg, to increase the phase difference between the switching of the first leg and the switching of the second leg. However, with phase shift control, high-frequency ringing can occur during a phase shift period, which is a period corresponding to the phase difference.

[0041] 2 is a diagram for explaining high-frequency ringing that occurs during phase shift control. Fig. 2 shows, from top to bottom, a timing chart of the current flowing through the secondary winding of the transformer T (transformer secondary current), the gate signals of the switches Q1 and Q4, the gate signals of the switches Q2 and Q3, the voltage generated in the secondary winding of the transformer T (transformer secondary voltage), and the voltage generated in the primary winding of the transformer T (transformer primary voltage).

[0042] As shown in FIG. 2, phase shift control causes the switching phase of switch Q4 to lag behind that of switch Q1, and the switching phase of switch Q3 to lag behind that of switch Q2. The phase shift period caused by phase shift control is a period during which no current is passed to the load connected to terminals t3 and t4. This period is also referred to as a non-conduction period. During this non-conduction period, the charge accumulated in the parasitic capacitance of the devices on the secondary side of transformer T (e.g., diodes D5 and D7 and switches Q6 and Q8) cannot be extracted to the load, and high-frequency ringing may occur due to free resonance between the leakage inductance of transformer T and the parasitic capacitance of the devices on the secondary side. As shown in FIG. 2, high-frequency ringing occurs in the transformer secondary voltage and in the transformer secondary current during this non-conduction period.

[0043] Therefore, the controller 40 turns on the switches Q6 and Q8 using a drive signal during a non-energized period, which is a period corresponding to the phase difference between the switching of the switches Q1 and Q2 and the switching of the switches Q3 and Q4. In the first embodiment, the drive signal is a signal that turns on and off the switches Q6 and Q8 during the non-energized period. For example, the controller 40 turns on the switches Q6 and Q8 using the drive signal in synchronization with the control signals for the switches Q1 and Q2.

[0044] Next, the operation of the power conversion device 1 and the effects achieved by this operation will be described with reference to FIG.

[0045] Fig. 3 is a diagram for explaining an example of the operation and effect of the power conversion device 1 according to embodiment 1. Fig. 3 shows, from the top to the bottom, timing charts of the gate signals of the switches Q1, Q4, and Q8, the gate signals of the switches Q2, Q3, and Q6, the voltage generated in the secondary winding of the transformer T (transformer secondary voltage), the current flowing in the primary winding of the transformer T (transformer primary current), and the current flowing in the secondary winding of the transformer T (transformer secondary current).

[0046] As shown in FIG. 3 , the controller 40, in response to a drive signal, turns on switches Q6 and Q8 when switch Q1 changes from an off state to an on state, and when switch Q2 changes from an off state to an on state. The non-conducting periods are the period from when switch Q1 turns on to when switch Q4 turns on, and the period from when switch Q2 turns on to when switch Q3 turns on. By turning on switches Q6 and Q8 during these periods, both ends of the secondary winding of the transformer T can be connected to the negative terminal t4 of the load via switches Q6 and Q8, allowing the charge of the secondary-side device to be extracted to the load. This suppresses high-frequency ringing. As shown in FIG. 3 , it can be seen that high-frequency ringing in the transformer secondary voltage and in the transformer secondary current are suppressed.

[0047] The timing at which switches Q6 and Q8 are turned on does not have to be simultaneous with the timing at which switch Q1 is turned on, but may be a timing between when switch Q1 is turned on and when switch Q4 is turned on. Furthermore, the timing at which switches Q6 and Q8 are turned off does not have to be simultaneous with the timing at which switch Q4 is turned on, but may be a timing between when switches Q6 and Q8 are turned on and when switch Q4 is turned on. Similarly, the timing at which switches Q6 and Q8 are turned on does not have to be simultaneous with the timing at which switch Q2 is turned on, but may be a timing between when switch Q2 is turned on and when switch Q3 is turned on. Furthermore, the timing at which switches Q6 and Q8 are turned off does not have to be simultaneous with the timing at which switch Q3 is turned on, but may be a timing between when switches Q6 and Q8 are turned on and when switch Q3 is turned on.

[0048] Next, the effect achieved by suppressing high frequency ringing will be described with reference to FIGS. 4A and 4B. FIG.

[0049] 4A and 4B are diagrams illustrating an example of the relationship between the phase difference and the output power in the phase shift control when high-frequency ringing occurs and when high-frequency ringing is suppressed, respectively.

[0050] When high-frequency ringing occurs, the power change with respect to the phase shift amount may not be monotonically variable, as shown in FIG. 4A . During the period when high-frequency ringing occurs, the voltage difference between the transformer primary voltage and the transformer secondary voltage may fluctuate significantly depending on the phase shift amount when the switch Q3 or Q4 of the second leg (the lagging leg) is turned on due to the high-frequency ringing. Furthermore, since the potential difference between the transformer primary voltage and the transformer secondary voltage contributes to the output power, this causes the power change to not be monotonically variable, as shown in FIG. 4A . If the power change with respect to the phase shift amount is not monotonically variable, stable power control becomes extremely difficult. On the other hand, by suppressing high-frequency ringing, the power change with respect to the phase shift amount can be made monotonically variable, as shown in FIG. 4B . This is because the ringing is suppressed when the switch Q3 or Q4 of the second leg (the lagging leg) is turned on, and the voltage difference between the transformer primary voltage and the transformer secondary voltage can be considered constant regardless of the phase shift amount.

[0051] As described above, the period corresponding to the phase difference between the switching of switches Q1 and Q2 and the switching of switches Q3 and Q4, which occurs during phase shift control, is a non-energized period during which no current is applied to the load. If no control is performed on the devices on the secondary side of the transformer T (specifically, switches Q6 and Q8) during this period, the charge accumulated in the parasitic capacitance of the devices on the secondary side of the transformer T cannot be extracted to the load. Therefore, during this period, high-frequency ringing can occur due to free resonance between the leakage inductance of the transformer T and the parasitic capacitance of the devices on the secondary side. Therefore, by turning on switches Q6 and Q8 during this period, both ends of the secondary winding of the transformer T can be connected to the negative terminal t4 of the load (in other words, the potential across the transformer secondary winding can be fixed to the negative potential of the load), allowing the charge accumulated in the parasitic capacitance of the devices on the secondary side to be extracted to the load. Therefore, high-frequency ringing that occurs during phase shift control can be suppressed. This results in improved efficiency due to reduced high-frequency loss and improved EMC performance in the MHz band. Furthermore, since ringing suppression means such as a snubber circuit or an active clamp circuit are not required, miniaturization and cost reduction are possible. Furthermore, suppression of high-frequency ringing allows the power change relative to the phase shift amount in phase shift control to be a monotonic change. This enables stable power control with a simple control method.

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

[0053] FIG. 5 is a circuit configuration diagram showing an example of a power conversion device 2 according to the second embodiment.

[0054] The power conversion device 2 differs from the power conversion device 1 in the first embodiment in the components of the secondary-side full-bridge circuit 20 and the control content of the controller 40. Since the other points are basically the same as those of the power conversion device 1 in the first embodiment, a description thereof will be omitted, and the following description will focus on the points of difference.

[0055] In the second embodiment, the secondary-side full-bridge circuit 20 has switches Q5 and Q7 and diodes D6 and D8, where the switch Q5 is an example of a fifth element, the diode D6 is an example of a sixth element, the switch Q7 is an example of a seventh element, and the diode D8 is an example of an eighth element. That is, in the second embodiment, the at least two elements that are switch elements are the fifth element (switch Q5) and the seventh element (switch Q7).

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

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

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

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

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

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

[0062] The controller 40 turns on the switches Q5 and Q7 using a drive signal during a non-energized period, which is a period corresponding to the phase difference between the switching of the switches Q1 and Q2 and the switching of the switches Q3 and Q4. In the second embodiment, the drive signal is a signal that turns on and off the switches Q5 and Q7 during the non-energized period. For example, the controller 40 turns on the switches Q5 and Q7 using the drive signal in synchronization with the control signals for the switches Q1 and Q2.

[0063] Next, the operation of the power conversion device 2 and the effects achieved by this operation will be described with reference to FIG.

[0064] Fig. 6 is a diagram for explaining an example of the operation and effect of the power conversion device 2 according to embodiment 2. Fig. 6 shows, from the top, timing charts of the gate signals of the switches Q1, Q4, and Q5, the gate signals of the switches Q2, Q3, and Q7, the voltage generated in the secondary winding of the transformer T (transformer secondary voltage), the current flowing in the primary winding of the transformer T (transformer primary current), and the current flowing in the secondary winding of the transformer T (transformer secondary current).

[0065] As shown in FIG. 6 , the controller 40, in response to a drive signal, turns on switches Q5 and Q7 when switch Q1 changes from an off state to an on state, and when switch Q2 changes from an off state to an on state. The non-conducting periods are the period from when switch Q1 turns on to when switch Q4 turns on, and the period from when switch Q2 turns on to when switch Q3 turns on. By turning on switches Q5 and Q7 during these periods, both ends of the secondary winding of the transformer T can be connected to the positive terminal t3 of the load via switches Q5 and Q7, allowing the charge of the secondary-side device to be extracted to the load. This suppresses high-frequency ringing. As shown in FIG. 6 , it can be seen that high-frequency ringing in the transformer secondary voltage and in the transformer secondary current are suppressed.

[0066] The timing at which switches Q5 and Q7 are turned on does not have to be simultaneous with the timing at which switch Q1 is turned on, but may be a timing between when switch Q1 is turned on and when switch Q4 is turned on. Furthermore, the timing at which switches Q5 and Q7 are turned off does not have to be simultaneous with the timing at which switch Q4 is turned on, but may be a timing between when switches Q5 and Q7 are turned on and when switch Q4 is turned on. Similarly, the timing at which switches Q5 and Q7 are turned on does not have to be simultaneous with the timing at which switch Q2 is turned on, but may be a timing between when switch Q2 is turned on and when switch Q3 is turned on. Furthermore, the timing at which switches Q5 and Q7 are turned off does not have to be simultaneous with the timing at which switch Q3 is turned on, but may be a timing between when switches Q5 and Q7 are turned on and when switch Q3 is turned on.

[0067] As described above, by turning on switches Q5 and Q7 during the non-energized period, both ends of the secondary winding of the transformer T can be connected to the positive terminal t3 of the load (in other words, the potential across the secondary winding of the transformer can be fixed to the positive potential of the load), and the charge accumulated in the parasitic capacitance of the secondary-side device can be extracted to the load side. Therefore, high-frequency ringing that occurs during phase shift control can be suppressed.

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

[0069] FIG. 7 is a circuit configuration diagram showing an example of a power conversion device 3 according to the third embodiment.

[0070] The power conversion device 3 differs from the power conversion device 1 in embodiment 1 in the components of the secondary-side full bridge circuit 20 and the control details of the controller 40. As other points are basically the same as the power conversion device 1 in embodiment 1, a description thereof will be omitted, and the following description will focus on the differences. Note that while the power conversion device 1 in embodiment 1 is capable of unidirectional power conversion, the power conversion device 3 is capable of bidirectional power conversion as well as unidirectional power conversion.

[0071] In the third embodiment, the secondary-side full-bridge circuit 20 has switches Q5, Q6, Q7, and Q8, where the switch Q5 is an example of a fifth element, the switch Q6 is an example of a sixth element, the switch Q7 is an example of a seventh element, and the switch Q8 is an example of an eighth element. That is, in the third embodiment, the at least two elements that are switch elements are the fifth element (switch Q5), the sixth element (switch Q6), the seventh element (switch Q7), and the eighth element (switch Q8).

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

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

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

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

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

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

[0078] The controller 40 turns on the switches Q5, Q6, Q7, and Q8 using a drive signal during a non-energized period, which is a period corresponding to the phase difference between the switching of the switches Q1 and Q2 and the switching of the switches Q3 and Q4. In the third embodiment, the drive signal is a signal that turns on and off the switches Q5, Q6, Q7, and Q8 during the non-energized period. For example, the controller 40 turns on the switches Q5, Q6, Q7, and Q8 using the drive signal in synchronization with the control signals for the switches Q1 and Q2.

[0079] In the third embodiment, first to fourth examples of a method for controlling the switches Q5, Q6, Q7, and Q8 by the controller 40 will be described.

[0080] Fig. 8 is a diagram for explaining a first example of the operation and effect of the power conversion device 3 according to embodiment 3. Fig. 8 shows, from the top to the bottom, timing charts 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 the transformer T (transformer secondary voltage), the current flowing in the primary winding of the transformer T (transformer primary current), and the current flowing in the secondary winding of the transformer T (transformer secondary current). The same applies to Figs. 9 to 11, which will be described later.

[0081] In the first example, the drive signal for switches Q6 and Q8 is a signal that turns on switches Q6 and Q8 during the period from when switch Q1 is turned on to when switch Q4 is turned on, and the drive signal for switches Q5 and Q7 is a signal that turns on switches Q5 and Q7 during the period from when switch Q2 is turned on to when switch Q3 is turned on.

[0082] As shown in Figure 8, the controller 40 uses a drive signal to turn on switches Q6 and Q8 when switch Q1 is switched on from its off state. The non-energized period is the period from when switch Q1 is turned on until switch Q4 is turned on. By turning on switches Q6 and Q8 during this period, both ends of the secondary winding of transformer T can be connected to terminal t4 on the negative side of the load via switches Q6 and Q8, and the charge of the secondary-side device can be extracted to the load side. This suppresses high-frequency ringing.

[0083] As shown in Figure 8, the controller 40 uses a drive signal to turn on switches Q5 and Q7 when switch Q2 is switched on from its off state. The non-energized period is the period from when switch Q2 is turned on until switch Q3 is turned on. By turning on switches Q5 and Q7 during this period, 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, and the charge of the secondary-side device can be extracted to the load side. This suppresses high-frequency ringing.

[0084] As shown in FIG. 8, it can be seen that high frequency ringing in the transformer secondary voltage is suppressed, and also high frequency ringing in the transformer secondary current is suppressed.

[0085] The timing at which switches Q6 and Q8 are turned on does not have to be simultaneous with the timing at which switch Q1 is turned on, but may be a timing between when switch Q1 is turned on and when switch Q4 is turned on. The timing at which switches Q6 and Q8 are turned off does not have to be simultaneous with the timing at which switch Q4 is turned on, but may be a timing between when switches Q6 and Q8 are turned on and when switch Q4 is turned on. The timing at which switches Q5 and Q7 are turned on does not have to be simultaneous with the timing at which switch Q2 is turned on, but may be a timing between when switch Q2 is turned on and when switch Q3 is turned on. The timing at which switches Q5 and Q7 are turned off does not have to be simultaneous with the timing at which switch Q3 is turned on, but may be a timing between when switches Q5 and Q7 are turned on and when switch Q3 is turned on.

[0086] FIG. 9 is a diagram for explaining a second example of the operation and effect of the power conversion device 3 according to the third embodiment.

[0087] In the second example, the drive signal for switches Q5 and Q7 is a signal that turns on switches Q5 and Q7 during the period from when switch Q1 is turned on to when switch Q4 is turned on, and the drive signal for switches Q6 and Q8 is a signal that turns on switches Q6 and Q8 during the period from when switch Q2 is turned on to when switch Q3 is turned on.

[0088] As shown in Figure 9, the controller 40 uses a drive signal to turn on switches Q5 and Q7 when switch Q1 is switched on from its off state. The non-energized period is the period from when switch Q1 is turned on until switch Q4 is turned on. By turning on switches Q5 and Q7 during this period, 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, and the charge of the secondary-side device can be extracted to the load side. This suppresses high-frequency ringing.

[0089] As shown in Figure 9, the controller 40 uses a drive signal to turn on switches Q6 and Q8 when switch Q2 is switched on from its off state. The non-energized period is the period from when switch Q2 is turned on until switch Q3 is turned on. By turning on switches Q6 and Q8 during this period, both ends of the secondary winding of transformer T can be connected to terminal t4 on the negative side of the load via switches Q6 and Q8, and the charge of the secondary-side device can be extracted to the load side. This suppresses high-frequency ringing.

[0090] As shown in FIG. 9, it can be seen that high frequency ringing in the transformer secondary voltage is suppressed, and also high frequency ringing in the transformer secondary current is suppressed.

[0091] The timing at which switches Q5 and Q7 are turned on does not have to be simultaneous with the timing at which switch Q1 is turned on, but may be a timing between when switch Q1 is turned on and when switch Q4 is turned on. The timing at which switches Q5 and Q7 are turned off does not have to be simultaneous with the timing at which switch Q4 is turned on, but may be a timing between when switches Q5 and Q7 are turned on and when switch Q4 is turned on. The timing at which switches Q6 and Q8 are turned on does not have to be simultaneous with the timing at which switch Q2 is turned on, but may be a timing between when switch Q2 is turned on and when switch Q3 is turned on. The timing at which switches Q6 and Q8 are turned off does not have to be simultaneous with the timing at which switch Q3 is turned on, but may be a timing between when switches Q6 and Q8 are turned on and when switch Q3 is turned on.

[0092] FIG. 10 is a diagram for explaining a third example of the operation and effect of the power conversion device 3 according to the third embodiment.

[0093] In the third example, the drive signal for switches Q6 and Q7 is a signal that turns on switches Q6 and Q7 during the period from when switch Q1 is turned on to when switch Q4 is turned on, and the drive signal for switches Q5 and Q8 is a signal that turns on switches Q5 and Q8 during the period from when switch Q2 is turned on to when switch Q3 is turned on.

[0094] As shown in Figure 10, the controller 40 uses a drive signal to turn on switches Q6 and Q7 when switch Q1 is switched on from its off state. The non-energized period is the period from when switch Q1 is turned on until switch Q4 is turned on. By turning on switches Q6 and Q7 during this period, one end of the secondary winding of transformer T can be connected to the negative terminal t4 of the load via switch Q6, and the other end of the secondary winding of transformer T can be connected to the positive terminal t3 of the load via switch Q7, allowing the charge of the secondary-side device to be extracted to the load side. This suppresses high-frequency ringing.

[0095] As shown in Figure 10, the controller 40 uses a drive signal to turn on switches Q5 and Q8 when switch Q2 is switched on from its off state. The non-energized period is the period from when switch Q2 is turned on until switch Q3 is turned on. By turning on switches Q5 and Q8 during this period, one end of the secondary winding of transformer T can be connected to the positive terminal t3 of the load via switch Q5, and the other end of the secondary winding of transformer T can be connected to the negative terminal t4 of the load via switch Q8, allowing the charge of the secondary-side device to be extracted to the load side. This suppresses high-frequency ringing.

[0096] As shown in FIG. 10, it can be seen that high frequency ringing in the transformer secondary voltage is suppressed to some extent, and that high frequency ringing in the transformer secondary current is also suppressed to some extent.

[0097] The timing at which switches Q6 and Q7 are turned on does not have to be simultaneous with the timing at which switch Q1 is turned on, but may be a timing between when switch Q1 is turned on and when switch Q4 is turned on. The timing at which switches Q6 and Q7 are turned off does not have to be simultaneous with the timing at which switch Q4 is turned on, but may be a timing between when switches Q6 and Q7 are turned on and when switch Q4 is turned on. The timing at which switches Q5 and Q8 are turned on does not have to be simultaneous with the timing at which switch Q2 is turned on, but may be a timing between when switch Q2 is turned on and when switch Q3 is turned on. The timing at which switches Q5 and Q8 are turned off does not have to be simultaneous with the timing at which switch Q3 is turned on, but may be a timing between when switches Q5 and Q8 are turned on and when switch Q3 is turned on.

[0098] FIG. 11 is a diagram for explaining a fourth example of the operation and effect of the power conversion device 3 according to the third embodiment.

[0099] In the fourth example, the drive signal for switches Q5 and Q8 is a signal that turns on switches Q5 and Q8 during the period from when switch Q1 is turned on to when switch Q4 is turned on, and the drive signal for switches Q6 and Q7 is a signal that turns on switches Q6 and Q7 during the period from when switch Q2 is turned on to when switch Q3 is turned on.

[0100] As shown in Figure 11, the controller 40 uses a drive signal to turn on switches Q5 and Q8 when switch Q1 is switched on from its off state. The non-energized period is the period from when switch Q1 is turned on until switch Q4 is turned on. By turning on switches Q5 and Q8 during this period, one end of the secondary winding of transformer T can be connected to the positive terminal t3 of the load via switch Q5, and the other end of the secondary winding of transformer T can be connected to the negative terminal t4 of the load via switch Q8, allowing the charge of the secondary-side device to be extracted to the load side. This suppresses high-frequency ringing.

[0101] As shown in Figure 11, the controller 40 uses a drive signal to turn on switches Q6 and Q7 when switch Q2 is switched on from its off state. The non-energized period is the period from when switch Q2 is turned on until switch Q3 is turned on. By turning on switches Q6 and Q7 during this period, one end of the secondary winding of transformer T can be connected to terminal t4 on the negative side of the load via switch Q6, and the other end of the secondary winding of transformer T can be connected to terminal t3 on the positive side of the load via switch Q7, allowing the charge of the secondary-side device to be extracted to the load side. This suppresses high-frequency ringing.

[0102] As shown in FIG. 11, it can be seen that high frequency ringing in the transformer secondary voltage is suppressed, and also high frequency ringing in the transformer secondary current is suppressed.

[0103] The timing at which switches Q5 and Q8 are turned on does not have to be simultaneous with the timing at which switch Q1 is turned on, but may be a timing between when switch Q1 is turned on and when switch Q4 is turned on. The timing at which switches Q5 and Q8 are turned off does not have to be simultaneous with the timing at which switch Q4 is turned on, but may be a timing between when switches Q5 and Q8 are turned on and when switch Q4 is turned on. The timing at which switches Q6 and Q7 are turned on does not have to be simultaneous with the timing at which switch Q2 is turned on, but may be a timing between when switch Q2 is turned on and when switch Q3 is turned on. The timing at which switches Q6 and Q7 are turned off does not have to be simultaneous with the timing at which switch Q3 is turned on, but may be a timing between when switches Q6 and Q7 are turned on and when switch Q3 is turned on.

[0104] As described above, by turning on switches Q5, Q6, Q7, and Q8 during the non-energized period, both ends of the secondary winding of the transformer T can be connected to the positive terminal t3 or the negative terminal t4 of the load (in other words, the potential across the secondary winding of the transformer can be fixed to the positive or negative potential of the load), and the charge accumulated in the parasitic capacitance of the secondary-side device can be extracted to the load side. Therefore, high-frequency ringing that occurs during phase shift control can be suppressed.

[0105] The power conversion device 3 is capable of bidirectional power conversion, and the terminal t3 can be used as an input terminal and the terminal t1 as an output terminal. In this case, the control performed on the primary-side full-bridge circuit 10 in the above description is performed on the secondary-side full-bridge circuit 20, and the control performed on the secondary-side full-bridge circuit 20 in the above description is performed on the primary-side full-bridge circuit 10. In this case, the capacitor Cout serves as an input capacitor, and the capacitor Cin serves as an output capacitor.

[0106] In the first to third embodiments, examples have been described in which at least two elements of the secondary-side full-bridge circuit 20 are turned on at any timing during a non-energized period (for example, when the switches Q1 and Q2 are turned on). However, depending on the timing during which the at least two elements are turned on during a non-energized period, losses may occur in the at least two elements. This will be described with reference to FIG. 12 .

[0107] 12 is a diagram for explaining losses occurring in secondary-side elements. Fig. 12 shows, from top to bottom, timing charts of the voltage occurring across the secondary winding of transformer T (transformer secondary voltage), the voltage occurring across secondary-side full bridge circuit 20 (secondary full bridge voltage), the gate voltages of switches Q5, Q6, Q7, and Q8, the drain-source voltage and drain current of switch Q8, the drain-source voltage and drain current of switch Q5, the voltage occurring across the primary winding of transformer T (transformer primary voltage), the voltage occurring across primary-side full bridge circuit 10 (primary full bridge voltage), the gate voltages of switches Q1, Q2, Q3, and Q4, the drain-source voltage and drain current of switch Q4, and the drain-source voltage and drain current of switch Q1.

[0108] For example, if switches Q5 and Q6 are turned on in synchronization with the control signals for switches Q1 and Q2, as shown in Fig. 12, a phase difference occurs between the switching of switch Q5 and the switching of switch Q8 when switch Q5 is turned on (specifically, the phase of the switching of switch Q8 leads the phase of the switching of switch Q5). As shown in Fig. 12, switch Q5 turns on when a drain current flows through it, and off-state loss occurs when switch Q5 turns off (when the clamp is released). In this way, there is a risk that zero current switching (ZCS) of the secondary-side elements will fail, resulting in loss in the secondary-side elements.

[0109] A power conversion device capable of suppressing losses occurring in elements on the secondary side will be described below with reference to FIGS. 13 and 14. FIG.

[0110] FIG. 13 is a circuit configuration diagram showing an example of a power conversion device 4 according to the fourth embodiment.

[0111] The power conversion device 4 differs from the power conversion device 3 in the third embodiment in that it includes a current detector 50 and in the control content of the controller 40. Since the other points are basically the same as those of the power conversion device 3 in the third embodiment, a description thereof will be omitted, and the following description will focus on the points of difference.

[0112] The current detector 50 detects the transformer current flowing through the transformer T. For example, the current detector 50 is provided between the primary winding of the transformer T and a node between the switches Q3 and Q4 in the second leg. The current detector 50 is configured using a sensor element such as a current transformer, a Hall element, or a shunt resistor. Note that if the power conversion device 4 is provided with current detection means for preventing out-of-resonance operation, the current detection means may be used as the current detector 50.

[0113] The controller 40 turns on the switches Q5, Q6, Q7, and Q8 in synchronization with the zero-cross detection signal of the transformer current by a drive signal during a non-energized period, which corresponds to the phase difference between the switching of the switches Q1 and Q2 and the switching of the switches Q3 and Q4. The zero-cross detection signal indicates the timing at which the polarity of the transformer current reverses (the timing at which the transformer current changes from negative to positive or from positive to negative), and is detected by the current detector 50.

[0114] 14 is a diagram for explaining the operation and effect of the power conversion device 4 according to embodiment 4. Fig. 14 shows, from the top to the bottom, a timing chart of the current flowing in the primary winding of the transformer T (transformer primary current), the drain-source voltage and drain current of the switch Q6, the voltage generated in the secondary winding of the transformer T (transformer secondary voltage), the gate voltages of the switches Q5, Q6, Q7, and Q8, the drain-source voltage and drain current of the switch Q8, the drain-source voltage and drain current of the switch Q5, the resonant voltage of the transformer T, the voltage generated in the primary winding (transformer primary voltage) and the voltage generated in the primary-side full bridge circuit 10 (primary full bridge voltage), the gate voltages of the switches Q1, Q2, Q3, and Q4, the drain-source voltage and drain current of the switch Q4, and the drain-source voltage and drain current of the switch Q1.

[0115] 14, the controller 40 uses the drive signal to turn on the switches Q5 and Q8 in synchronization with the detection signal of the negative-to-positive zero-crossing of the transformer current during the period from when the switch Q1 turns on to when the switch Q4 turns on. The controller 40 also uses the drive signal to turn on the switches Q6 and Q7 in synchronization with the detection signal of the positive-to-negative zero-crossing of the transformer current during the period from when the switch Q2 turns on to when the switch Q3 turns on.

[0116] Since the polarity of the transformer current reverses from negative to positive during the period from when the switch Q1 is turned on to when the switch Q4 is turned on, which is a period corresponding to the phase difference, during this period, by turning on the switches Q5 and Q8 in synchronization with a zero-crossing detection signal indicating that the transformer current has changed from negative to positive, ZCS of the switches Q5 and Q8 is established, thereby suppressing the occurrence of losses in the switches Q5 and Q8. Furthermore, one end of the secondary winding of the transformer T can be connected to the positive terminal t3 of the load via the switch Q5, and the other end of the secondary winding of the transformer T can be connected to the negative terminal t4 of the load via the switch Q8, thereby suppressing high-frequency ringing.

[0117] Since the polarity of the transformer current reverses from positive to negative during the period from when switch Q2 is turned on to when switch Q3 is turned on, which is a period corresponding to the phase difference, during this period, by turning on switches Q6 and Q7 in synchronization with a zero-crossing detection signal indicating that the transformer current has changed from positive to negative, ZCS of switches Q6 and Q7 is established, thereby suppressing loss in switches Q6 and Q7. Furthermore, one end of the secondary winding of transformer T can be connected to terminal t4 on the negative side of the load via switch Q6, and the other end of the secondary winding of transformer T can be connected to terminal t3 on the positive side of the load via switch Q7, thereby suppressing high-frequency ringing.

[0118] The drive signal may be a signal for a period corresponding to half the switching period of the switches Q1 and Q2, including a period corresponding to the phase difference. In this case, as shown in FIG. 14 , the controller 40 may use the drive signal to turn on the switches Q5 and Q8 in synchronization with the negative-to-positive zero-crossing detection signal of the transformer current during the period from when the switch Q1 is turned on to when the switch Q4 is turned on, and maintain the on state during the period from when the switch Q4 is turned on to when the switch Q2 is turned on. The controller 40 may maintain the on state during the period from when the switch Q4 is turned on to when the switch Q2 is turned on, or for any period from when the switch Q4 is turned on to when the switch Q2 is turned on. The controller 40 may also turn on the switches Q6 and Q7 in synchronization with the positive-to-negative zero-crossing detection signal of the transformer current during the period from when the switch Q2 is turned on to when the switch Q3 is turned on, and maintain the on state during the period from when the switch Q3 is turned on to when the switch Q1 is turned on. The controller 40 may maintain the on state for the period from when the switch Q3 is turned on until when the switch Q1 is turned on, or for any period from when the switch Q3 is turned on until when the switch Q1 is turned on.

[0119] For example, if the switches Q5 and Q8 are turned on during the period from when the switch Q1 is turned on until the switch Q4 is turned on and then turned off during that period, the switches Q5 and Q8 will operate as diodes to pass current, resulting in increased conduction loss due to the forward voltage of the body diodes. Furthermore, if the switches Q6 and Q7 are turned on during the period from when the switch Q2 is turned on until the switch Q3 is turned on and then turned off during that period, the switches Q6 and Q7 will operate as diodes to pass current, resulting in increased conduction loss due to the forward voltage of the body diodes. Note that diode operation refers to the operation in which current flows from the source to the drain when the switch is in the off state, i.e., when the switch blocks current from the drain to the source. For example, this corresponds to the operation in which a forward current flows through the body diode when a Si or SiC MOSFET is turned off.

[0120] Therefore, by turning on switches Q5 and Q8 and maintaining the on state from the time when switch Q4 is turned on until switch Q2 is turned on, synchronous rectification can be performed and conduction loss generated in switches Q5 and Q8 can be suppressed. Also, by turning on switches Q6 and Q7 and maintaining the on state from the time when switch Q3 is turned on until switch Q1 is turned on, synchronous rectification can be performed and conduction loss generated in switches Q6 and Q7 can be suppressed.

[0121] The controller 40 of the power conversion device 4 shown in FIG. 13 may use a drive signal to turn on the switches Q6 and Q8 in synchronization with the detection signal of the zero-crossing of the transformer current from negative to positive during the period from when the switch Q1 is turned on until when the switch Q4 is turned on, and may turn on the switches Q5 and Q7 in synchronization with the detection signal of the zero-crossing of the transformer current from positive to negative during the period from when the switch Q2 is turned on until when the switch Q3 is turned on.

[0122] During the period from when switch Q1 turns on to when switch Q4 turns on, which is the period corresponding to the phase difference, the polarity of the transformer current reverses from negative to positive, so that during this period, by turning on switches Q6 and Q8 in synchronization with a zero-crossing detection signal indicating that the transformer current has changed from negative to positive, ZCS of switches Q6 and Q8 is established, thereby suppressing losses in switches Q6 and Q8. Furthermore, both ends of the secondary winding of transformer T can be connected to terminal t4 on the negative side of the load via switches Q6 and Q8, thereby suppressing high-frequency ringing.

[0123] During the period from when switch Q2 turns on to when switch Q3 turns on, which is the period corresponding to the phase difference, the polarity of the transformer current reverses from positive to negative, so that during this period, by turning on switches Q5 and Q7 in synchronization with a zero-crossing detection signal indicating that the transformer current has changed from positive to negative, ZCS of switches Q5 and Q7 is established, thereby suppressing losses in switches Q5 and Q7. Furthermore, both ends of the secondary winding of transformer T can be connected to terminal t3 on the positive side of the load via switches Q5 and Q7, thereby suppressing high-frequency ringing.

[0124] The controller 40 of the power conversion device 4 shown in FIG. 13 may use a drive signal to turn on the switches Q5 and Q7 in synchronization with the negative-to-positive zero-cross detection signal of the transformer current during the period from when the switch Q1 is turned on until when the switch Q4 is turned on, and may turn on the switches Q6 and Q8 in synchronization with the positive-to-negative zero-cross detection signal of the transformer current during the period from when the switch Q2 is turned on until when the switch Q3 is turned on.

[0125] During the period from when switch Q1 turns on to when switch Q4 turns on, which is the period corresponding to the phase difference, the polarity of the transformer current reverses from negative to positive, so that during this period, by turning on switches Q5 and Q7 in synchronization with a zero-crossing detection signal indicating that the transformer current has changed from negative to positive, ZCS of switches Q5 and Q7 is established, thereby suppressing losses in switches Q5 and Q7. Furthermore, both ends of the secondary winding of transformer T can be connected to terminal t3 on the positive side of the load via switches Q5 and Q7, thereby suppressing high-frequency ringing.

[0126] During the period from when switch Q2 turns on to when switch Q3 turns on, which is the period corresponding to the phase difference, the polarity of the transformer current reverses from positive to negative, so that during this period, by turning on switches Q6 and Q8 in synchronization with a zero-crossing detection signal indicating that the transformer current has changed from positive to negative, ZCS of switches Q6 and Q8 is established, thereby suppressing losses in switches Q6 and Q8. Furthermore, both ends of the secondary winding of transformer T can be connected to terminal t4 on the negative side of the load via switches Q6 and Q8, thereby suppressing high-frequency ringing.

[0127] The controller 40 of the power conversion device 4 shown in FIG. 13 may use a drive signal to turn on the switches Q6 and Q7 in synchronization with the negative-to-positive zero-cross detection signal of the transformer current during the period from when the switch Q1 is turned on until when the switch Q4 is turned on, and may turn on the switches Q5 and Q8 in synchronization with the positive-to-negative zero-cross detection signal of the transformer current during the period from when the switch Q2 is turned on until when the switch Q3 is turned on.

[0128] Since the polarity of the transformer current reverses from negative to positive during the period from when the switch Q1 is turned on to when the switch Q4 is turned on, which is a period corresponding to the phase difference, during this period, by turning on the switches Q6 and Q7 in synchronization with a zero-crossing detection signal indicating that the transformer current has changed from negative to positive, ZCS of the switches Q6 and Q7 is established, thereby suppressing the occurrence of losses in the switches Q6 and Q7. Furthermore, one end of the secondary winding of the transformer T can be connected to the negative terminal t4 of the load via the switch Q6, and the other end of the secondary winding of the transformer T can be connected to the positive terminal t3 of the load via the switch Q7, thereby suppressing high-frequency ringing.

[0129] Since the polarity of the transformer current reverses from positive to negative during the period from when switch Q2 is turned on to when switch Q3 is turned on, which is a period corresponding to the phase difference, by turning on switches Q5 and Q8 in synchronization with a zero-crossing detection signal indicating that the transformer current has changed from positive to negative during this period, ZCS of switches Q5 and Q8 is established, thereby suppressing losses in switches Q5 and Q8. Furthermore, one end of the secondary winding of transformer T can be connected to terminal t3 on the positive side of the load via switch Q5, and the other end of the secondary winding of transformer T can be connected to terminal t4 on the negative side of the load via switch Q8, thereby suppressing high-frequency ringing.

[0130] The power conversion device 1 according to the first embodiment may include a current detector 50. In this case, the controller 40 of the power conversion device 1 may use the drive signal to turn on the switches Q6 and Q8 in synchronization with a negative-to-positive zero-cross detection signal of the transformer current during the period from when the switch Q1 is turned on until when the switch Q4 is turned on, and may turn on the switches Q6 and Q8 in synchronization with a positive-to-negative zero-cross detection signal of the transformer current during the period from when the switch Q2 is turned on until when the switch Q3 is turned on.

[0131] During the period corresponding to the phase difference, from when switch Q1 turns on to when switch Q4 turns on, the polarity of the transformer current reverses from negative to positive. Therefore, during this period, by turning on switches Q6 and Q8 in synchronization with a zero-crossing detection signal indicating that the transformer current has changed from negative to positive, ZCS of switches Q6 and Q8 is established, thereby suppressing losses in switches Q6 and Q8. During the period corresponding to the phase difference, from when switch Q2 turns on to when switch Q3 turns on, the polarity of the transformer current reverses from positive to negative. Therefore, during this period, by turning on switches Q6 and Q8 in synchronization with a zero-crossing detection signal indicating that the transformer current has changed from positive to negative, ZCS of switches Q6 and Q8 is established, thereby suppressing losses in switches Q6 and Q8. Furthermore, both ends of the secondary winding of transformer T can be connected to terminal t4 on the negative side of the load via switches Q6 and Q8, thereby suppressing high-frequency ringing.

[0132] The power conversion device 2 according to the second embodiment may include a current detector 50. In this case, the controller 40 of the power conversion device 2 may use the drive signal to turn on the switches Q5 and Q7 in synchronization with a negative-to-positive zero-cross detection signal of the transformer current during the period from when the switch Q1 is turned on until when the switch Q4 is turned on, and may turn on the switches Q5 and Q7 in synchronization with a positive-to-negative zero-cross detection signal of the transformer current during the period from when the switch Q2 is turned on until when the switch Q3 is turned on.

[0133] During the period corresponding to the phase difference, from when switch Q1 turns on to when switch Q4 turns on, the polarity of the transformer current reverses from negative to positive. Therefore, during this period, by turning on switches Q5 and Q7 in synchronization with a zero-crossing detection signal indicating that the transformer current has changed from negative to positive, ZCS of switches Q5 and Q7 is established, thereby suppressing losses in switches Q5 and Q7. During the period corresponding to the phase difference, from when switch Q2 turns on to when switch Q3 turns on, the polarity of the transformer current reverses from positive to negative. Therefore, during this period, by turning on switches Q5 and Q7 in synchronization with a zero-crossing detection signal indicating that the transformer current has changed from positive to negative, ZCS of switches Q5 and Q7 is established, thereby suppressing losses in switches Q5 and Q7. Furthermore, both ends of the secondary winding of transformer T can be connected to terminal t3 on the positive side of the load via switches Q5 and Q7, thereby suppressing high-frequency ringing.

[0134] As described above, the secondary current of the transformer T, whose polarity reverses over time, flows through at least two elements on the secondary side. Even during the period corresponding to the phase difference, current flows through at least two elements. Therefore, if at least two elements are turned on when current flows through them, ZCS is not established and losses occur. In contrast, by detecting the transformer current flowing through the transformer T, it is possible to detect the timing when the polarity of the transformer current reverses, i.e., the timing when the current flowing through at least two elements becomes zero. Therefore, by turning on at least two elements in synchronization with the zero-crossing detection signal indicating the timing when the polarity of the transformer current reverses during the period corresponding to the phase difference, ZCS is established for at least two elements, thereby suppressing losses in at least two elements. Furthermore, both ends of the secondary winding of the transformer T can be connected to the positive terminal t3 or the negative terminal t4 of the load, thereby suppressing high-frequency ringing.

[0135] (Other Embodiments) As described above, the embodiments have been described as examples of the technology according to the present disclosure. However, the technology according to the present disclosure is not limited to these, and can be applied to embodiments in which modifications, substitutions, additions, omissions, etc. are made as appropriate. For example, the following modifications are also included in one embodiment of the present disclosure.

[0136] For example, the diodes included in the secondary-side full-bridge circuit 20 in the first and second embodiments may be replaced with switches (for example, N-channel MOSFETs) that function as diodes.

[0137] For example, in the above embodiment, an example of an LLC converter consisting of the excitation inductance and leakage inductance of the transformer T and a resonance capacitor has been described, but the power conversion device may also be provided with a separate inductor equivalent to the leakage inductance.

[0138] For example, although the power conversion device is an LLC converter in the above embodiment, the present invention is not limited to this. For example, the power conversion device may be a resonant converter including a resonator configured with a series-parallel LC, such as an LCC converter or a CLLC converter.

[0139] For example, in the description of the embodiments as an example of the technology according to the present disclosure, an example has been described in which the secondary-side switches are synchronized with the timing at which the primary-side switches are turned on, such as the period from when switch Q1 is turned on to when switch Q4 is turned on. However, this is not limited to this. For example, the secondary-side switches may be synchronized with the timing at which the primary-side switches are turned off. In other words, the period from when switch Q1 is turned on to when switch Q4 is turned on may be defined as the period from when switch Q2 is turned off to when switch Q3 is turned off. In this case, the synchronization signal may be delayed by the dead time. In this way, a small time such as dead time or voltage transition time (dV / dt) may be taken into account in the primary-side signal in which at least two elements of the secondary-side full-bridge circuit are synchronized.

[0140] For example, the present disclosure can be realized not only as a power conversion device, but also as a control method for controlling a power conversion device (specifically, a control method including steps (processing) performed by components that constitute the power conversion device (specifically, controller 40)).

[0141] FIG. 15 is a flowchart showing an example of a control method according to another embodiment.

[0142] The control method is a control method for controlling a power conversion device, the power conversion device including a resonator having a transformer and a resonance capacitor, a primary-side full bridge circuit connected to the primary side of the resonator, and a secondary-side full bridge circuit connected to the secondary side of the resonator, the primary-side full bridge circuit having a first element provided on the high side of a first leg, a second element provided on the low side of the first leg, a third element provided on the high side of the second leg, and a fourth element provided on the low side of the second leg, the secondary-side full bridge circuit having a fifth element provided on the high side of the third leg, a sixth element provided on the low side of the third leg, a seventh element provided on the high side of the fourth leg, and a fourth element provided on the low side of the fourth leg. and an eighth element provided on the low side of the block, wherein the first element, the second element, the third element, and the fourth element are each a switching element, and at least two of the fifth element, the sixth element, the seventh element, and the eighth element are each a switching element, and the control method, as shown in FIG. 15 , operates the first element, the second element, the third element, and the fourth element so that the switching phase of the third element and the fourth element is delayed with respect to the switching phase of the first element and the second element (step S11), and turns on at least two elements by a drive signal in a period corresponding to the phase difference between the switching of the first element and the second element and the switching of the third element and the fourth element (step S12).

[0143] For example, the present disclosure can be realized as a program for causing a computer (processor) to execute steps included in the control method. Furthermore, the present disclosure can be realized as a non-transitory computer-readable recording medium, such as a CD-ROM, on which the program is recorded.

[0144] For example, when the present disclosure is realized as a program (software), each step is performed by running the program using hardware resources such as a computer's CPU, memory, input / output circuits, etc. In other words, each step is performed by the CPU acquiring data from memory or input / output circuits, etc., performing calculations, and outputting the calculation results to memory or input / output circuits, etc.

[0145] In the above-described embodiments, each component included in the power conversion device may be configured with dedicated hardware, or may be realized by executing a software program suitable for each component. Each component may be realized by a program execution unit such as a CPU or processor reading and executing a software program recorded on a recording medium such as a hard disk or semiconductor memory.

[0146] Some or all of the functions of the power conversion device according to the above-described embodiments are typically realized as an LSI, which is an integrated circuit. These may be individually integrated into a single chip, or some or all of them may be integrated into a single chip. Furthermore, the integrated circuit is not limited to an LSI, and may be realized using a dedicated circuit or a general-purpose processor. An FPGA (Field Programmable Gate Array) that can be programmed after LSI manufacturing, or a reconfigurable processor that can reconfigure the connections and settings of circuit cells within the LSI, may also be used.

[0147] Furthermore, if an integrated circuit technology that can replace LSI emerges due to advances in semiconductor technology or other derivative technologies, that technology may naturally be used to integrate the components included in the power conversion device.

[0148] In addition, this disclosure also includes forms obtained by making various modifications to the embodiments that a person skilled in the art would think of, and forms realized by arbitrarily combining the components and functions in each embodiment within the scope of the present disclosure.

[0149] (Additional Notes) The above description of the embodiments discloses the following techniques.

[0150] (Technology 1) A power supply comprising: a resonator having a transformer and a resonance capacitor; a primary-side full bridge circuit connected to a primary side of the resonator; a secondary-side full bridge circuit connected to a secondary side of the resonator; and a controller that controls the primary-side full bridge circuit and the secondary-side full bridge circuit, wherein the primary-side full bridge circuit has a first 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 the low side of the second leg; and the secondary-side full bridge circuit has a fifth element provided on a high side of a third leg, a sixth element provided on the low side of the third leg, a seventh element provided on the high side of the fourth leg, and an eighth element provided on a low side of a fourth leg, wherein the first element, the second element, the third element, and the fourth element are each switch elements, and at least two elements among the fifth element, the sixth element, the seventh element, and the eighth element are each switch elements, and the controller operates the first element, the second element, the third element, and the fourth element so that a switching phase of the third element and the fourth element is delayed with respect to a switching phase of the first element and the second element, and turns on the at least two elements by a drive signal in a period corresponding to a phase difference between the switching of the first element and the second element and the switching of the third element and the fourth element.

[0151] The period corresponding to the phase difference between the switching of the first and second elements and the switching of the third and fourth elements, which occurs during phase shift control, is a non-energized period during which no current is passed to the load. If no control is performed on the devices (specifically, at least two elements) on the secondary side of the transformer during this period, the charge accumulated in the parasitic capacitance of the devices on the secondary side of the transformer cannot be extracted to the load. Therefore, during this period, high-frequency ringing may occur due to free resonance between the transformer's leakage inductance and the parasitic capacitance of the devices on the secondary side. Therefore, by turning on at least two elements during this period, both ends of the transformer's secondary winding can be connected to the positive or negative terminal of the load (in other words, the potential across the transformer's secondary winding can be fixed to the positive or negative potential of the load), allowing the charge accumulated in the parasitic capacitance of the devices on the secondary side to be extracted to the load. Therefore, high-frequency ringing that occurs during phase shift control can be suppressed. This results in improved efficiency due to reduced high-frequency loss and improved EMC performance in the MHz band. Furthermore, since ringing suppression means such as a snubber circuit or an active clamp circuit are not required, miniaturization and cost reduction are possible. Furthermore, suppression of high-frequency ringing allows the power change relative to the phase shift amount in phase shift control to be a monotonic change. This enables stable power control with a simple control method.

[0152] (Technology 2) The power conversion device according to Technology 1, wherein the controller turns on the at least two elements in synchronization with control signals for the first element and the second element using the drive signal.

[0153] According to this, by turning on at least two elements in synchronization with the control signals for the first element and the second element during the period corresponding to the above phase difference, both ends of the secondary winding of the transformer can be connected to the positive terminal or the negative terminal of the load, thereby suppressing high-frequency ringing.

[0154] (Technology 3) The power conversion device according to Technology 1 or 2, wherein the at least two elements are the sixth element and the eighth element.

[0155] This allows both ends of the secondary winding of the transformer to be connected to the negative terminal of the load via the sixth element and the eighth element, thereby suppressing high frequency ringing.

[0156] (Technology 4) The power conversion device described in Technology 3, wherein the controller turns on the sixth element and the eighth element when the first element changes from an off state to an on state, and turns on the sixth element and the eighth element when the second element changes from an off state to an on state, by the drive signal.

[0157] According to this, when the first element changes from an off state to an on state, in other words, when the period corresponding to the phase difference starts, the sixth and eighth elements are turned on, thereby connecting both ends of the secondary winding of the transformer to the negative terminal of the load via the sixth and eighth elements, thereby suppressing high-frequency ringing. Similarly, when the second element changes from an off state to an on state, in other words, when the period corresponding to the phase difference starts, the sixth and eighth elements are turned on, thereby connecting both ends of the secondary winding of the transformer to the negative terminal of the load via the sixth and eighth elements, thereby suppressing high-frequency ringing.

[0158] (Technology 5) The power conversion device according to Technology 1 or 2, wherein the at least two elements are the fifth element and the seventh element.

[0159] This allows both ends of the secondary winding of the transformer to be connected to the positive terminal of the load via the fifth element and the seventh element, thereby suppressing high frequency ringing.

[0160] (Technology 6) The power conversion device described in Technology 5, wherein the controller turns on the fifth element and the seventh element when the first element changes from an off state to an on state, and turns on the second element when the second element changes from an off state to an on state, by the drive signal.

[0161] According to this, when the first element changes from an off state to an on state, in other words, when the period corresponding to the phase difference starts, the fifth and seventh elements are turned on, thereby connecting both ends of the secondary winding of the transformer to the positive terminal of the load via the fifth and seventh elements, thereby suppressing high-frequency ringing. Similarly, when the second element changes from an off state to an on state, in other words, when the period corresponding to the phase difference starts, the fifth and seventh elements are turned on, thereby connecting both ends of the secondary winding of the transformer to the positive terminal of the load via the fifth and seventh elements, thereby suppressing high-frequency ringing.

[0162] (Technology 7) The power conversion device according to Technology 1 or 2, wherein the at least two elements are the fifth element, the sixth element, the seventh element, and the eighth element.

[0163] This allows both ends of the secondary winding of the transformer to be connected to the positive terminal or negative terminal of the load via the fifth, sixth, seventh, and eighth elements, thereby suppressing high-frequency ringing.

[0164] (Technology 8) A power conversion device according to Technology 7, wherein the controller turns on the sixth element and the eighth element when the first element is changed from an off state to an on state by the drive signal, and turns on the fifth element and the seventh element when the second element is changed from an off state to an on state.

[0165] According to this, when the first element changes from an off state to an on state, in other words, when the period corresponding to the phase difference starts, the sixth and eighth elements are turned on, thereby connecting both ends of the secondary winding of the transformer to the negative terminal of the load via the sixth and eighth elements, thereby suppressing high-frequency ringing. Also, when the second element changes from an off state to an on state, in other words, when the period corresponding to the phase difference starts, the fifth and seventh elements are turned on, thereby connecting both ends of the secondary winding of the transformer to the positive terminal of the load via the fifth and seventh elements, thereby suppressing high-frequency ringing.

[0166] (Technology 9) A power conversion device according to Technology 7, wherein the controller turns on the fifth element and the seventh element when the first element is changed from an off state to an on state by the drive signal, and turns on the sixth element and the eighth element when the second element is changed from an off state to an on state.

[0167] According to this, when the first element changes from an off state to an on state, in other words, when the period corresponding to the phase difference starts, the fifth and seventh elements are turned on, thereby connecting both ends of the secondary winding of the transformer to the positive terminal of the load via the fifth and seventh elements, thereby suppressing high-frequency ringing. Also, when the second element changes from an off state to an on state, in other words, when the period corresponding to the phase difference starts, the sixth and eighth elements are turned on, thereby connecting both ends of the secondary winding of the transformer to the negative terminal of the load via the sixth and eighth elements, thereby suppressing high-frequency ringing.

[0168] (Technology 10) A power conversion device according to Technology 7, wherein the controller turns on the sixth element and the seventh element when the first element is changed from an off state to an on state by the drive signal, and turns on the fifth element and the eighth element when the second element is changed from an off state to an on state.

[0169] According to this, when the first element changes from an off state to an on state, in other words, when the period corresponding to the phase difference starts, the sixth and seventh elements are turned on, thereby connecting one end of the secondary winding of the transformer to the negative terminal of the load via the sixth element and the other end of the secondary winding of the transformer to the positive terminal of the load via the seventh element, thereby suppressing high-frequency ringing. Also, when the second element changes from an off state to an on state, in other words, when the period corresponding to the phase difference starts, the fifth and eighth elements are turned on, thereby connecting one end of the secondary winding of the transformer to the positive terminal of the load via the fifth element and the other end of the secondary winding of the transformer to the negative terminal of the load via the eighth element, thereby suppressing high-frequency ringing.

[0170] (Technology 11) A power conversion device as described in Technology 7, wherein the controller turns on the fifth element and the eighth element when the first element is changed from an off state to an on state by the drive signal, and turns on the sixth element and the seventh element when the second element is changed from an off state to an on state.

[0171] According to this, when the first element is turned on from an off state, in other words, when the period corresponding to the phase difference starts, the fifth and eighth elements are turned on, thereby connecting one end of the secondary winding of the transformer to the positive terminal of the load via the fifth element and the other end of the secondary winding of the transformer to the negative terminal of the load via the eighth element, thereby suppressing high-frequency ringing. Also, when the second element is turned on from an off state, in other words, when the period corresponding to the phase difference starts, the sixth and seventh elements are turned on, thereby connecting one end of the secondary winding of the transformer to the negative terminal of the load via the sixth element and the other end of the secondary winding of the transformer to the positive terminal of the load via the seventh element, thereby suppressing high-frequency ringing.

[0172] (Technology 12) The power conversion device according to Technology 1, further comprising a current detector that detects a transformer current flowing through the transformer, and the controller uses the drive signal to turn on the at least two elements in synchronization with a zero-cross detection signal of the transformer current.

[0173] A secondary current of the transformer, whose polarity reverses over time, flows through at least two elements, and current also flows through at least two elements during the period corresponding to the phase difference. Therefore, if at least two elements are turned on when current flows through them, ZCS is not established and losses occur. In response to this, by detecting the transformer current flowing through the transformer, it is possible to detect the timing when the polarity of the transformer current reverses, i.e., the timing when the current flowing through at least two elements becomes zero. Therefore, by turning on at least two elements in synchronization with a zero-crossing detection signal indicating the timing when the polarity of the transformer current reverses during the period corresponding to the phase difference, ZCS is established for at least two elements, thereby suppressing losses in at least two elements. Furthermore, both ends of the transformer secondary winding can be connected to the positive or negative terminal of the load, thereby suppressing high-frequency ringing.

[0174] (Technology 13) The power conversion device according to Technology 12, wherein the at least two elements are the sixth element and the eighth element.

[0175] This allows the sixth and eighth elements to achieve ZCS, thereby suppressing losses in the sixth and eighth elements. Furthermore, 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, thereby suppressing high-frequency ringing.

[0176] (Technology 14) The power conversion device described in Technology 13, wherein the controller, using the drive signal, turns on the sixth element and the eighth element in synchronization with the zero-cross detection signal of the transformer current changing from negative to positive during the period from when the first element is turned on to when the fourth element is turned on, and turns on the sixth element and the eighth element in synchronization with the zero-cross detection signal of the transformer current changing from positive to negative during the period from when the second element is turned on to when the third element is turned on.

[0177] During the period corresponding to the phase difference, from when the first element is turned on until the fourth element is turned on, the polarity of the transformer current reverses from negative to positive. Therefore, during this period, by turning on the sixth and eighth elements in synchronization with a zero-crossing detection signal indicating that the transformer current has changed from negative to positive, ZCS of the sixth and eighth elements is established, thereby suppressing loss in the sixth and eighth elements. During the period corresponding to the phase difference, from when the second element is turned on until the third element is turned on, the polarity of the transformer current reverses from positive to negative. Therefore, during this period, by turning on the sixth and eighth elements in synchronization with a zero-crossing detection signal indicating that the transformer current has changed from positive to negative, ZCS of the sixth and eighth elements is established, thereby suppressing loss in the sixth and eighth elements. Furthermore, 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, thereby suppressing high-frequency ringing.

[0178] (Technology 15) The power conversion device according to Technology 12, wherein the at least two elements are the fifth element and the seventh element.

[0179] This allows the fifth and seventh elements to achieve ZCS, thereby suppressing losses in the fifth and seventh elements. Furthermore, 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, thereby suppressing high-frequency ringing.

[0180] (Technology 16) The power conversion device described in Technology 15, wherein the controller, using the drive signal, turns on the fifth element and the seventh element in synchronization with the zero-cross detection signal of the transformer current changing from negative to positive during a period from when the first element is turned on to when the fourth element is turned on, and turns on the fifth element and the seventh element in synchronization with the zero-cross detection signal of the transformer current changing from positive to negative during a period from when the second element is turned on to when the third element is turned on.

[0181] During the period corresponding to the phase difference, from when the first element turns on until the fourth element turns on, the polarity of the transformer current reverses from negative to positive. Therefore, during this period, the fifth and seventh elements are turned on in synchronization with a zero-crossing detection signal indicating that the transformer current has changed from negative to positive. This establishes ZCS for the fifth and seventh elements, thereby suppressing losses in the fifth and seventh elements. During the period corresponding to the phase difference, from when the second element turns on until the third element turns on, the polarity of the transformer current reverses from positive to negative. Therefore, during this period, the fifth and seventh elements are turned on in synchronization with a zero-crossing detection signal indicating that the transformer current has changed from positive to negative. This establishes ZCS for the fifth and seventh elements, thereby suppressing losses in the fifth and seventh elements. Furthermore, both ends of the transformer secondary winding can be connected to the positive terminal of the load via the fifth and seventh elements, thereby suppressing high-frequency ringing.

[0182] (Technology 17) The power conversion device according to Technology 12, wherein the at least two elements are the fifth element, the sixth element, the seventh element, and the eighth element.

[0183] This enables ZCS of the fifth, sixth, seventh, and eighth elements to be established, thereby suppressing losses in the fifth, sixth, seventh, and eighth elements. Also, both ends of the secondary winding of the transformer can be connected to the positive terminal or negative terminal of the load via the fifth, sixth, seventh, and eighth elements, thereby suppressing high-frequency ringing.

[0184] (Technology 18) The power conversion device described in Technology 17, wherein the controller, by the drive signal, turns on the sixth element and the eighth element in synchronization with the zero-cross detection signal of the transformer current changing from negative to positive during the period from when the first element is turned on to when the fourth element is turned on, and turns on the fifth element and the seventh element in synchronization with the zero-cross detection signal of the transformer current changing from positive to negative during the period from when the second element is turned on to when the third element is turned on.

[0185] During the period corresponding to the phase difference, from when the first element turns on until the fourth element turns on, the polarity of the transformer current reverses from negative to positive. Therefore, during this period, the sixth and eighth elements are turned on in synchronization with a zero-crossing detection signal indicating that the transformer current has changed from negative to positive. This establishes ZCS for the sixth and eighth elements, thereby suppressing losses in the sixth and eighth elements. Furthermore, both ends of the transformer secondary winding can be connected to the negative terminal of the load via the sixth and eighth elements, thereby suppressing high-frequency ringing. During the period corresponding to the phase difference, from when the second element turns on until the third element turns on, the polarity of the transformer current reverses from positive to negative. During this period, the fifth and seventh elements are turned on in synchronization with a zero-crossing detection signal indicating that the transformer current has changed from positive to negative. This establishes ZCS for the fifth and seventh elements, thereby suppressing losses in the fifth and seventh elements. Furthermore, 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, thereby suppressing high frequency ringing.

[0186] (Technology 19) The power conversion device described in Technology 17, wherein the controller, by the drive signal, turns on the fifth element and the seventh element in synchronization with the zero-cross detection signal of the transformer current changing from negative to positive during the period from when the first element is turned on to when the fourth element is turned on, and turns on the sixth element and the eighth element in synchronization with the zero-cross detection signal of the transformer current changing from positive to negative during the period from when the second element is turned on to when the third element is turned on.

[0187] During the period corresponding to the phase difference, from when the first element turns on until the fourth element turns on, the polarity of the transformer current reverses from negative to positive. Therefore, during this period, the fifth and seventh elements are turned on in synchronization with a zero-crossing detection signal indicating that the transformer current has changed from negative to positive. This establishes ZCS for the fifth and seventh elements, thereby suppressing losses in the fifth and seventh elements. Furthermore, both ends of the transformer secondary winding can be connected to the positive terminal of the load via the fifth and seventh elements, thereby suppressing high-frequency ringing. During the period corresponding to the phase difference, from when the second element turns on until the third element turns on, the polarity of the transformer current reverses from positive to negative. During this period, the sixth and eighth elements are turned on in synchronization with a zero-crossing detection signal indicating that the transformer current has changed from positive to negative. This establishes ZCS for the sixth and eighth elements, thereby suppressing losses in the sixth and eighth elements. Furthermore, both ends of the secondary winding of the transformer can be connected to the negative terminal of the load via the sixth element and the eighth element, thereby suppressing high frequency ringing.

[0188] (Technology 20) The power conversion device described in Technology 17, wherein the controller, by the drive signal, turns on the sixth element and the seventh element in synchronization with the zero-cross detection signal of the transformer current changing from negative to positive during the period from when the first element is turned on to when the fourth element is turned on, and turns on the fifth element and the eighth element in synchronization with the zero-cross detection signal of the transformer current changing from positive to negative during the period from when the second element is turned on to when the third element is turned on.

[0189] During the period corresponding to the phase difference, from when the first element turns on until the fourth element turns on, the polarity of the transformer current reverses from negative to positive. Therefore, during this period, the sixth and seventh elements are turned on in synchronization with a zero-crossing detection signal indicating that the transformer current has changed from negative to positive. This establishes ZCS for the sixth and seventh elements, thereby suppressing losses in the sixth and seventh elements. Furthermore, 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, thereby suppressing high-frequency ringing. During the period corresponding to the phase difference, from when the second element turns on until the third element turns on, the polarity of the transformer current reverses from positive to negative. During this period, the fifth and eighth elements are turned on in synchronization with a zero-crossing detection signal indicating that the transformer current has changed from positive to negative. This establishes ZCS for the fifth and eighth elements, thereby suppressing losses in the fifth and eighth elements. In addition, one end of the secondary winding of the transformer can be connected to the positive terminal of the load via the fifth element, and the other end of the secondary winding of the transformer can be connected to the negative terminal of the load via the eighth element, thereby suppressing high-frequency ringing.

[0190] (Technology 21) The power conversion device described in Technology 17, wherein the controller, by the drive signal, turns on the fifth element and the eighth element in synchronization with the zero-cross detection signal of the transformer current changing from negative to positive during a period from when the first element is turned on to when the fourth element is turned on, and turns on the sixth element and the seventh element in synchronization with the zero-cross detection signal of the transformer current changing from positive to negative during a period from when the second element is turned on to when the third element is turned on.

[0191] During the period corresponding to the phase difference, from when the first element turns on until the fourth element turns on, the polarity of the transformer current reverses from negative to positive. Therefore, during this period, the fifth and eighth elements are turned on in synchronization with a zero-crossing detection signal indicating that the transformer current has changed from negative to positive. This establishes ZCS for the fifth and eighth elements, thereby suppressing losses in the fifth and eighth elements. Furthermore, 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, thereby suppressing high-frequency ringing. During the period corresponding to the phase difference, from when the second element turns on until the third element turns on, the polarity of the transformer current reverses from positive to negative. During this period, the sixth and seventh elements are turned on in synchronization with a zero-crossing detection signal indicating that the transformer current has changed from positive to negative. This establishes ZCS for the sixth and seventh elements, thereby suppressing losses in the sixth and seventh elements. In addition, one end of the secondary winding of the transformer can be connected to the negative terminal of the load via the sixth element, and the other end of the secondary winding of the transformer can be connected to the positive terminal of the load via the seventh element, thereby suppressing high-frequency ringing.

[0192] (Technology 22) The power conversion device according to Technology 21, wherein the drive signal is a signal for a period corresponding to half a switching period of the first element and the second element, including a period corresponding to the phase difference, and the controller, using the drive signal, turns on the fifth element and the eighth element in synchronization with the zero-crossing detection signal of the transformer current changing from negative to positive during a period from when the first element is turned on to when the fourth element is turned on, and maintains the on state during a period from when the fourth element is turned on to when the second element is turned on, and turns on the sixth element and the seventh element in synchronization with the zero-crossing detection signal of the transformer current changing from positive to negative during a period from when the second element is turned on to when the third element is turned on, and maintains the on state during a period from when the third element is turned on to when the first element is turned on.

[0193] For example, if the fifth and eighth elements are turned on during the period from when the first element is turned on until the fourth element is turned on and then turned off during that period, the fifth and eighth elements will operate as diodes to conduct current, resulting in increased conduction loss due to the forward voltage of their body diodes. Therefore, by turning on the fifth and eighth elements and maintaining their on state during the period from when the fourth element is turned on until the second element is turned on, synchronous rectification can be performed, thereby reducing conduction loss in the fifth and eighth elements. Furthermore, if the sixth and seventh elements are turned on during the period from when the second element is turned on until the third element is turned on and then turned off during that period, the sixth and seventh elements will operate as diodes to conduct current, resulting in increased conduction loss due to the forward voltage of their body diodes. Therefore, by turning on the sixth and seventh elements and maintaining their on state during the period from when the third element is turned on until the first element is turned on, synchronous rectification can be performed, thereby reducing conduction loss in the sixth and seventh elements.

[0194] (Technology 23) A control method for controlling a power conversion device, the power conversion device including a resonator having a transformer and a resonance capacitor, a primary-side full bridge circuit connected to a primary side of the resonator, and a secondary-side full bridge circuit connected to a secondary side of the resonator, the primary-side full bridge circuit having 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 the high side of a second leg, and a fourth element provided on the low side of the second leg, the secondary-side full bridge circuit having a fifth element provided on a high side of a third leg, a sixth element provided on the low side of the third leg, a seventh element provided on the high side of a fourth leg, and a fifth element provided on the low side of the fourth leg. and an eighth element provided on a low side of a switching element, wherein the first element, the second element, the third element, and the fourth element are each switch elements, and at least two elements among the fifth element, the sixth element, the seventh element, and the eighth element are each switch elements, and the control method operates the first element, the second element, the third element, and the fourth element so that a switching phase of the third element and the fourth element is delayed with respect to a switching phase of the first element and the second element, and turns on the at least two elements by a drive signal in a period corresponding to a phase difference between the switching of the first element and the second element and the switching of the third element and the fourth element.

[0195] This makes it possible to provide a control method for a power conversion device that can suppress high-frequency ringing that occurs during phase shift control.

[0196] The present disclosure can be applied to an isolated DC-DC converter or the like.

[0197] 1, 2, 3, 4 Power conversion device 10 Primary side full bridge circuit 20 Secondary side full bridge circuit 30 Resonator 40 Controller 50 Current detector Cin, Cout, Cr Capacitors D5, D6, D7, D8 Diodes Q1, Q2, Q3, Q4, Q5, Q6, Q7, Q8 Switch T Transformer t1, t2, t3, t4 Terminals

Claims

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

2. The power conversion device according to claim 1, wherein the controller uses the drive signal to turn on the at least two elements in synchronization with control signals for the first element and the second element.

3. The power conversion device according to claim 1 or 2, wherein the at least two elements are the sixth element and the eighth element.

4. The power conversion device according to claim 3, wherein the controller turns on the sixth element and the eighth element when the first element changes from an off state to an on state, and turns on the sixth element and the eighth element when the second element changes from an off state to an on state, in response to the drive signal.

5. The power conversion device according to claim 1 or 2, wherein the at least two elements are the fifth element and the seventh element.

6. The power conversion device according to claim 5, wherein the controller turns on the fifth element and the seventh element when the first element changes from an off state to an on state, and turns on the second element when the second element changes from an off state to an on state, in response to the drive signal.

7. The power conversion device according to claim 1 or 2, wherein the at least two elements are the fifth element, the sixth element, the seventh element, and the eighth element.

8. The power conversion device according to claim 7, wherein the controller turns on the sixth element and the eighth element when the first element is changed from an off state to an on state, and turns on the fifth element and the seventh element when the second element is changed from an off state to an on state, in response to the drive signal.

9. The power conversion device according to claim 7, wherein the controller turns on the fifth element and the seventh element when the first element is changed from an off state to an on state, and turns on the sixth element and the eighth element when the second element is changed from an off state to an on state, in response to the drive signal.

10. The power conversion device according to claim 7, wherein the controller turns on the sixth element and the seventh element when the first element is changed from an off state to an on state, and turns on the fifth element and the eighth element when the second element is changed from an off state to an on state, in response to the drive signal.

11. The power conversion device according to claim 7, wherein the controller, in response to the drive signal, turns on the fifth element and the eighth element when the first element is changed from an off state to an on state, and turns on the sixth element and the seventh element when the second element is changed from an off state to an on state.

12. The power conversion device according to claim 1, further comprising a current detector that detects a transformer current flowing through the transformer, and the controller uses the drive signal to turn on the at least two elements in synchronization with a zero-cross detection signal of the transformer current.

13. The power conversion device according to claim 12, wherein the at least two elements are the sixth element and the eighth element.

14. The power conversion device of claim 13, wherein the controller uses the drive signal to turn on the sixth element and the eighth element in synchronization with the zero-cross detection signal of the transformer current changing from negative to positive during a period from when the first element is turned on until when the fourth element is turned on, and to turn on the sixth element and the eighth element in synchronization with the zero-cross detection signal of the transformer current changing from positive to negative during a period from when the second element is turned on until when the third element is turned on.

15. The power conversion device according to claim 12, wherein the at least two elements are the fifth element and the seventh element.

16. The power conversion device according to claim 15, wherein the controller, using the drive signal, turns on the fifth element and the seventh element in synchronization with the zero-cross detection signal of the transformer current changing from negative to positive during a period from when the first element is turned on until when the fourth element is turned on, and turns on the fifth element and the seventh element in synchronization with the zero-cross detection signal of the transformer current changing from positive to negative during a period from when the second element is turned on until when the third element is turned on.

17. The power conversion device according to claim 12, wherein the at least two elements are the fifth element, the sixth element, the seventh element, and the eighth element.

18. The power conversion device according to claim 17, wherein the controller, by the drive signal, turns on the sixth element and the eighth element in synchronization with the zero-cross detection signal of the transformer current changing from negative to positive during a period from when the first element is turned on until when the fourth element is turned on, and turns on the fifth element and the seventh element in synchronization with the zero-cross detection signal of the transformer current changing from positive to negative during a period from when the second element is turned on until when the third element is turned on.

19. The power conversion device of claim 17, wherein the controller, using the drive signal, turns on the fifth element and the seventh element in synchronization with the zero-cross detection signal of the transformer current changing from negative to positive during a period from when the first element is turned on until when the fourth element is turned on, and turns on the sixth element and the eighth element in synchronization with the zero-cross detection signal of the transformer current changing from positive to negative during a period from when the second element is turned on until when the third element is turned on.

20. The power conversion device of claim 17, wherein the controller, using the drive signal, turns on the sixth element and the seventh element in synchronization with the zero-cross detection signal of the transformer current changing from negative to positive during a period from when the first element is turned on until when the fourth element is turned on, and turns on the fifth element and the eighth element in synchronization with the zero-cross detection signal of the transformer current changing from positive to negative during a period from when the second element is turned on until when the third element is turned on.

21. The power conversion device of claim 17, wherein the controller, using the drive signal, turns on the fifth element and the eighth element in synchronization with the zero-cross detection signal of the transformer current changing from negative to positive during a period from when the first element is turned on until when the fourth element is turned on, and turns on the sixth element and the seventh element in synchronization with the zero-cross detection signal of the transformer current changing from positive to negative during a period from when the second element is turned on until when the third element is turned on.

22. The power conversion device of claim 21, wherein the drive signal is a signal for a period corresponding to half a switching period of the first element and the second element, including a period corresponding to the phase difference; and the controller, using the drive signal, turns on the fifth element and the eighth element in synchronization with the zero-cross detection signal of the transformer current changing from negative to positive during the period from when the first element is turned on to when the fourth element is turned on, and maintains the on state during the period from when the fourth element is turned on to when the second element is turned on; and turns on the sixth element and the seventh element in synchronization with the zero-cross detection signal of the transformer current changing from positive to negative during the period from when the second element is turned on to when the third element is turned on, and maintains the on state during the period from when the third element is turned on to when the first element is turned on.

23. A control method for controlling a power conversion device, the power conversion device comprising: a resonator having a transformer and a resonance capacitor; a primary-side full-bridge circuit connected to the primary side of the resonator; and a secondary-side full-bridge circuit connected to the secondary side of the resonator; the primary-side full-bridge circuit having a first element provided on the high side of a first leg, a second element provided on the low side of the first leg, a third element provided on the high side of a second leg, and a fourth element provided on the low side of the second leg; the secondary-side full-bridge circuit having a fifth element provided on the high side of a third leg, a sixth element provided on the low side of the third leg, a seventh element provided on the high side of a fourth leg, and an eighth element provided on the low side of the fourth leg; the first element, the second element, the third element, and the fourth element are each switch elements; At least two of the fifth element, the sixth element, the seventh element, and the eighth element are each a switching element, and the control method comprises: operating the first element, the second element, the third element, and the fourth element so that the switching phase of the third element and the fourth element is delayed relative to the switching phase of the first element and the second element; and turning on the at least two elements by a drive signal during a period corresponding to a phase difference between the switching of the first element and the second element and the switching of the third element and the fourth element.

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