Power conversion device

Abstract

To disclose a power conversion device that can prevent occurrence of resonance on a secondary side of an insulating DC / DC converter circuit.SOLUTION: A power conversion device of the present invention comprises: a DC / DC converter having a first full-bridge circuit including a first switching leg and a second switching leg connected in parallel with a first input / output terminal pair, a second full-bridge circuit including a third switching leg and a fourth switching leg connected in parallel with a second input / output terminal pair, and a transformer including one winding connected with the first full-bridge circuit and the other winding connected with the second full-bridge circuit; and a control unit controlling the DC / DC converter. The control unit always turns on any one of a plurality of switching elements included on a low side of the full-bridge circuit on a secondary side, of the first full-bridge circuit and the second full-bridge circuit.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a power conversion device. [Background technology]

[0002] As a power conversion device, for example, an isolated DC / DC converter having full-bridge circuits on both sides of a transformer has been proposed (see, for example, Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-48700 [Patent Document 2] Patent Publication No. 2021-48699 Summary of the Invention [Problem to be solved by the invention]

[0004] In an isolated DC / DC converter circuit, in a discontinuous section where the current flowing through the inductor temporarily becomes zero, resonance due to the excitation current caused by the operation of the secondary-side switching element may occur in the secondary-side circuit, causing the excitation current to be commutated to the load side. Therefore, this application discloses a power conversion device capable of preventing the occurrence of resonance on the secondary side of an isolated DC / DC converter circuit. [Means for solving the problem]

[0005] In order to solve the above problems, in the present invention, one of a plurality of switching elements on the low side of the full bridge circuit, which is the secondary side of the first full bridge circuit and the second full bridge circuit of the DC / DC converter, is kept ON at all times.

[0006] In detail, the present invention is a power conversion device comprising: a DC / DC converter having a first full bridge circuit including a first switching leg and a second switching leg connected in parallel to a first input / output terminal pair, a second full bridge circuit including a third switching leg and a fourth switching leg connected in parallel to a second input / output terminal pair, and a transformer including one winding connected to the first full bridge circuit and the other winding connected to the second full bridge circuit, and a control unit that controls the DC / DC converter, wherein the control unit constantly keeps ON one of a plurality of switching elements on the low side of the full bridge circuit that is the secondary side of the first full bridge circuit or the second full bridge circuit.

[0007] In the above power conversion device, one of the first and second full bridge circuits, which is the secondary side, has a plurality of switching elements on the low side that are always ON, so commutation of the excitation current to the load side on the secondary side is prevented, making it possible to prevent the generation of a current accompanied by resonance.

[0008] The control unit may have a discontinuous mode in which each switching element of the DC / DC converter is operated with a switching pattern that forms a discontinuous section in which no current flows through the inductor in the DC / DC converter, and the control unit may maintain the ON state of the switching element on the low side of the switching leg that was turned ON before the discontinuous section was entered until the switching element on the low side of the switching leg that is to be turned ON next is turned ON, thereby keeping one of the multiple switching elements on the low side of the full bridge circuit that is the secondary side always ON. According to this, since one of the multiple switching elements on the low side of the full bridge circuit that is the secondary side is always ON, Therefore, it is possible to prevent the occurrence of a current accompanied by resonance.

[0009] Moreover, the first switching leg has a first switching element and a third switching element, a source terminal of the first switching element and a drain terminal of the third switching element are connected in series at a first connection point, and a drain terminal of the first switching element and a source terminal of the third switching element are connected to the first input / output terminal pair; the second switching leg has a second switching element and a fourth switching element, a source terminal of the second switching element and a drain terminal of the fourth switching element are connected in series at a second connection point, and a drain terminal of the second switching element and a source terminal of the fourth switching element are connected to the first input / output terminal pair; the third switching leg has a fifth switching element and a seventh switching element, a source terminal of the fifth switching element and a drain terminal of the seventh switching element are connected in series at a third connection point, and , the drain terminal of the fifth switching element and the source terminal of the seventh switching element are connected to the second input / output terminal pair, the fourth switching leg has a sixth switching element and an eighth switching element, the source terminal of the sixth switching element and the drain terminal of the eighth switching element are connected in series at a fourth connection point, the drain terminal of the sixth switching element and the source terminal of the eighth switching element are connected to the second input / output terminal pair, one winding of the transformer is connected to the first connection point and the second connection point, and the other winding of the transformer is connected to the third connection point and the fourth connection point, and the control unit may be configured to always turn on either the seventh switching element or the eighth switching element when the second full bridge circuit is the secondary side, and to always turn on either the third switching element or the fourth switching element when the first full bridge circuit is the secondary side. According to this, one of the two switching elements on the low side of the full bridge circuit that is the secondary side is always turned on, making it possible to prevent the generation of a current accompanied by resonance.

[0010] Also, each of the first to eighth switching elements may have a diode connected in anti-parallel with the cathode connected to the drain terminal side and the anode connected to the source terminal side. In such a circuit, when any of the multiple switching elements on the low side of the full bridge circuit on the secondary side is always ON, commutation of the excitation current to the load side on the secondary side is prevented. This makes it possible to prevent the generation of a current accompanied by resonance. Effect of the Invention

[0011] The above power conversion device can prevent the occurrence of resonance on the secondary side of the isolated DC / DC converter circuit. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic configuration diagram of a power conversion device according to an embodiment. [Diagram 2] FIG. 2 is a diagram showing an application example and a comparative example of a timing chart of signals used when the DC / DC converter is operated as a step-down converter. [Diagram 3] FIG. 3 is a control block diagram realized by the control device. [Figure 4] FIG. 4 shows a timing chart according to a first example of signals used when the DC / DC converter according to the embodiment is operated as a step-down converter. [Diagram 5] FIG. 5 is a first schematic diagram showing a current path when the DC / DC converter is operated in accordance with the timing chart according to the first example. [Figure 6] FIG. 6 is a second schematic diagram showing a current path when the DC / DC converter is operated in accordance with the timing chart according to the first example. [Figure 7] FIG. 7 is an image diagram of a waveform of a load current transmitted by the timing chart according to the first example. [Figure 8]FIG. 8 shows a timing chart according to a second example of signals used when the DC / DC converter according to this embodiment is operated as a step-down converter. [Figure 9] FIG. 9 is a first schematic diagram showing a current path when the DC / DC converter is operated in accordance with the timing chart according to the second example. [Figure 10] FIG. 10 is a second schematic diagram showing a current path when the DC / DC converter is operated in accordance with the timing chart according to the second example. [Figure 11] FIG. 11 is an image diagram of a waveform of a load current transmitted by the timing chart according to the second example. [Figure 12] FIG. 12 shows a timing chart according to a third example of signals used when the DC / DC converter according to this embodiment is operated as a boost converter. [Figure 13] FIG. 13 is a first schematic diagram showing a current path when the DC / DC converter is operated in accordance with the timing chart according to the third example. [Figure 14] FIG. 14 is a second schematic diagram showing a current path when the DC / DC converter is operated in accordance with the timing chart according to the third example. [Figure 15] FIG. 15 is an image diagram of a waveform of a load current transmitted by the timing chart according to the third example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] <Application Examples> BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram showing an example of an application of the present invention; FIG.

[0014] The power conversion device 1 includes a DC / DC converter 10, a control device 20, and two pairs of input / output terminals 13 (13p, 13m) and 14 (14p, 14m). Capacitors C1 and C2 for smoothing the input voltages are connected between the input / output terminals 13m and 13p, and between the input / output terminals 14m and 14p, respectively.

[0015] The DC / DC converter 10 is an insulated bidirectional DC / DC converter whose main components are a transformer TR, two reactors Lr1 and Lr2, and two full-bridge circuits 11 and 12. The reactors Lr1 and Lr2 generate AC power under the control of the full-bridge circuits 11 and 12, and the capacitors C1 and C2 smooth the AC power into DC power. An insulating transformer can be used as the transformer TR, but a non-insulated reactor may also be used.

[0016] The full bridge circuit 11 of the DC / DC converter 10 includes a leg L1 having switching elements Q1 and Q3 connected in series, and a leg L2 having switching elements Q2 and Q4 connected in series. The full bridge circuit 12 of the DC / DC converter 10 includes a leg L3 having switching elements Q5 and Q7 connected in series, and a leg L4 having switching elements Q6 and Q8 connected in series.

[0017] Fig. 2 shows an application example and a comparative example of timing charts of signals used when operating DC / DC converter 10 as a step-down converter. The lower part of Fig. 2 shows a timing chart related to this application example, and the upper part of Fig. 2 shows a timing chart related to the comparative example. Fig. 3 shows waveforms of the load current flowing through DC / DC converter 10 for the application example and the comparative example.

[0018] When the switching elements of the DC / DC converter 10 are operated according to the timing chart shown in the comparative example of FIG. 2, the switching elements Q5 and Q8 are turned off simultaneously, as indicated by *1 in FIG. 2. In this case, the excitation current on the secondary side is commutated to the load side through the body diode of the switching element Q6. For this reason, a current accompanied by resonance may be generated on the load side due to interaction with the capacitor C2. On the other hand, in FIG. When operating according to the timing chart shown in the application example of 2, the switching pattern is such that at least one of switching element Q7 and switching element Q8 is always ON, as shown by *2 in Figure 2. Therefore, switching element Q8 does not turn OFF even when switching element Q5 is turned OFF. As a result, the excitation current circulates within the full bridge circuit on the secondary side, and no current accompanied by resonance is generated on the load side.

[0019] <Embodiment> Hereinafter, the power conversion device according to the embodiment of the present invention will be described in more detail with reference to the drawings.

[0020] <Configuration of power conversion device> FIG. 1 is a schematic diagram of a power conversion device according to an embodiment. The power conversion device 1 according to this embodiment is a device capable of bidirectional power conversion. As shown in the figure, the power conversion device 1 includes a DC / DC converter 10, a control device 20, and two pairs of input / output terminals 13 (13p, 13m) and an input / output terminal pair 14 (14p, 14m). In the input / output terminal pairs 13 and 14, the input / output terminals 13p and 14p are high-potential input / output terminals, and the input / output terminals 13m and 14m are low-potential input / output terminals. A capacitor C1 for smoothing the input / output voltage is connected between the input / output terminals 13m and 13p. Similarly, a capacitor C2 for smoothing the input / output voltage is connected between the input / output terminals 14m and 14p. Electrolytic capacitors can be used as the capacitors C1 and C2.

[0021] The DC / DC converter 10 is an insulated bidirectional DC / DC converter whose main components are a transformer TR, two reactors Lr1 and Lr2, and two full-bridge circuits 11 and 12. The reactors Lr1 and Lr2 may utilize leakage inductances of windings Wn1 and Wn2 of the transformer TR. The transformer TR of the DC / DC converter 10 does not need to have a turns ratio of 1:1. However, hereinafter, the configuration and operation of the power conversion device 1 will be described assuming that the turns ratio of the transformer TR is 1:1.

[0022] The full-bridge circuit 11 of the DC / DC converter 10 includes a leg L1 having a switching element Q1 and a switching element Q3 connected in series, and a leg L2 having a switching element Q2 and a switching element Q4 connected in series. As shown in the figure, a diode Dn (n=1 to 4) is connected in parallel between the terminals of the switching element Qn (n=1 to 4) of each leg. Each leg is connected to an input / output terminal pair 13, and a connection point p1 between the switching element Q1 and the switching element Q3 of the leg L1 is connected to one end of the winding Wn1 of the transformer TR via a reactor Lr1. A connection point p2 between the switching element Q2 and the switching element Q4 of the leg L2 is connected to the other end of the winding Wn1 of the transformer TR.

[0023] The full bridge circuit 12 of the DC / DC converter 10 includes a leg L3 having a switching element Q5 and a switching element Q7 connected in series, and a leg L4 having a switching element Q6 and a switching element Q8 connected in series. As shown in the figure, a diode Dn (n=5 to 8) is connected in parallel between the terminals of the switching element Qn (n=5 to 8) of each leg. In addition, both the leg L3 and the leg L4 are connected to an input / output terminal pair 14. In addition, a connection point p3 between the switching element Q5 and the switching element Q7 of the leg L3 is connected to one end of the winding Wn2 of the transformer TR via a reactor Lr2, and a connection point p4 between the switching element Q6 and the switching element Q8 of the leg L4 is connected to the other end of the winding Wn2 of the transformer TR.

[0024] The semiconductor materials for the switching elements Q1 to Q8 may be gallium nitride (GaN), silicon (Si), silicon carbide (SiC), or the like. The semiconductor switching elements are not limited to those described above. Metal Oxide Semiconductor Field Effect Transistors (MOSFETs), Insulated Gate Bipolar Transistors (IGBTs), etc. may be used as the semiconductor switching elements Q1 to Q8. Diodes D1 to D8 are connected in anti-parallel to these semiconductor switching elements used as the switching elements Q1 to Q8.

[0025] The DC / DC converter 10 is also equipped with various sensors (not shown) for measuring the magnitude of the input / output voltages and the input / output currents.

[0026] Control device 20 is a unit that controls DC / DC converter 10 (ON / OFF of each switching element in DC / DC converter 10) by changing the level of a control signal to each switching element in DC / DC converter 10.

[0027] The control device 20 includes a processor (in this embodiment, a microcontroller), a gate driver, and the like.

[0028] The control device 20 is configured (programmed) to determine whether the DC / DC converter 10 should operate as one of the following four types of converters based on the input data (current value, voltage value), and to control the DC / DC converter 10 so that it operates as the determined converter. Input / output terminal pair 13 is the primary side boost converter Input / output terminal pair 13 is the primary side of the step-down converter Input / output terminal pair 14 is the primary side boost converter Input / output terminal pair 14 is the primary side of the step-down converter

[0029] In addition, the control device 20 is configured (programmed) to instantly change the control content for the DC / DC converter 10 (such as changing from control that causes the DC / DC converter 10 to operate as a step-up converter with the input / output terminal pair 13 side as the primary side to control that causes the DC / DC converter 10 to operate as a step-down converter with the input / output terminal pair 14 side as the primary side).

[0030] Fig. 3 is a control block diagram realized by the control device 20. As shown in Fig. 3, in this embodiment, the DC / DC converter 10 is connected to an EV2 (electrically-driven automobile) and an inverter 30. The inverter 30 is a device that performs AC / DC conversion, and electrically connects the DC / DC converter 10, which is a direct current, to an AC power system. Examples of the EV2 include a BEV (Battery Electric Vehicle) that runs only on battery power, a PHV (Plug-in Hybrid Vehicle) that uses both a battery and an internal combustion engine, an FCV (Fuel Cell Vehicle) that runs on fuel cell power, and various other types of electrically-driven automobiles. However, the DC / DC converter The DC / DC converter 10 is not limited to being used with such an EV 2, and may be connected to, for example, a residential storage battery. The DC / DC converter 10 may also be used for controlling the running of an electric vehicle that runs on DC power, or for controlling various other electric devices.

[0031] The control device 20 controls the DC / DC converter 10 according to a command value sent from a higher-level device. The command value sent from the higher-level device to the control device 20 is a value determined based on the remaining charge of the EV2 and the power consumption of the load. The control device 20 includes a CPU (Central Processing Memory devices such as ROM (read only memory) and RAM (Random Access Memory) The control device 20 is equipped with an input / output interface, and the CPU executes a computer program stored in the storage device to realize each of the functional blocks shown below. The control device 20 uses each of the functional blocks shown below to generate a PWM signal according to a command value sent from a higher-level device, and sends the PWM signal to the DC / DC converter 10.

[0032] The control device 20 executes a computer program to implement a phase shift amount generating section 21 and a PWM generating section 22, as shown in Fig. 3. Each functional block in the control device 20 will be described below.

[0033] The phase shift amount generator 21 generates a phase shift amount, which is the phase difference between pulse-like control signals related to the ON / OFF of each switching element included in legs L1 to L4.

[0034] The PWM generating unit 22 generates a PWM signal based on the amount of phase shift. The PWM signal generated by the PWM generating unit 22 is sent to the DC / DC converter 10 and operates each of the switching elements Q1 to Q8.

[0035] <Operation of the power conversion device> The operation of the power conversion device 1 according to this embodiment will be described below.

[0036] Basically, the DC / DC converter 10 can switch between the step-up operation and the step-down operation by relatively changing the phase shift amount related to the ON / OFF of each switching element included in legs L1 to L4. That is, in the power conversion device 1 according to this embodiment, the control device 20 can switch between the step-up operation and the step-down operation of the DC / DC converter 10 by changing the phase shift amount as follows.

[0037] For example, when the operation of the DC / DC converter 10 is switched from the step-down operation to the step-up operation with the input / output terminal pair 13 side as the primary side and the input / output terminal pair 14 side as the secondary side, the phase shift amount of the switching element Q4 relative to the switching element Q1 or the phase shift amount of the switching element Q2 relative to the switching element Q3 is transitioned to a predetermined value. Then, the phase shift amount of the switching element Q7 relative to the switching elements Q1 and Q4 or the phase shift amount of the switching element Q8 relative to the switching elements Q3 and Q2 is adjusted to a predetermined phase value. Here, the phase shift amount of the step-down operation can be expressed as the time (TΦ) when the ON of the switching element Q1 and the switching element Q4 overlaps, or the time (TΦ) when the ON of the switching element Q3 and the switching element Q2 overlaps. In addition, the phase shift amount of the boost operation can be expressed as the time (TΦ) when the ON state of switching element Q1 and switching element Q7 overlaps with the ON state of switching element Q4, or the time (TΦ) when the ON state of switching element Q3 and switching element Q8 overlaps with the ON state of switching element Q2.

[0038] Furthermore, for example, when the operation of DC / DC converter 10 is switched from step-up operation to step-down operation with input / output terminal pair 13 as the primary side and input / output terminal pair 14 as the secondary side, the phase shift amount of switching element Q7 relative to switching element Q1 and switching element Q4, or the phase shift amount of switching element Q8 relative to switching element Q3 and switching element Q2, is transitioned to a predetermined value. Then, the phase shift amount of switching element Q4 relative to switching element Q1, or the phase shift amount of switching element Q2 relative to switching element Q3, is adjusted to the predetermined phase value.

[0039] In the following description, the terms "step-up operation" and "step-down operation" in DC / DC converter 10 refer to operations based on switching patterns relating to the ON / OFF of each switching element included in legs L1 to L4, and do not refer to the relationship between the input voltage and the output voltage relating to voltage conversion. In other words, in this embodiment, DC / DC converter 10 may operate with "input voltage > output voltage" in "step-up operation", and may also operate with "input voltage < output voltage" in "step-down operation". The The step-up operation is also called "step-up mode," and the step-down operation is also called "step-down mode."

[0040] In the power conversion device 1 of this embodiment, the control device 20 acquires information such as the input / output conditions of the DC / DC converter 10, and determines in which mode the DC / DC converter 10 will operate using information previously set in a table or the like, and outputs a switching pattern signal according to the determination result.

[0041] <An example of step-down operation> Fig. 4 shows a timing chart according to a first example of signals used when the DC / DC converter 10 according to this embodiment is operated as a step-down converter. Fig. 5 is a first schematic diagram showing a current path when the DC / DC converter 10 is operated according to the timing chart according to the first example. Fig. 6 is a second schematic diagram showing a current path when the DC / DC converter 10 is operated according to the timing chart according to the first example. The control device 20 realizes the current flow shown in Figs. 5 and 6 by operating each switching element of the DC / DC converter 10 with a switching pattern according to the timing chart shown in Fig. 4.

[0042] The correspondence between the current paths in each section from #11 to #16 shown in FIG. 4 and each diagram shown in FIG. 5 and FIG. 6 is as follows. In state #11, only switching elements Q1, Q4, and Q8 are ON, and other switching elements are OFF. At this time, the current path in DC / DC converter 10 is as shown in Fig. 5(A). That is, as shown by the solid arrows in Fig. 5(A), power transmission by switching elements Q1 and Q4 begins. In state #12, only switching elements Q1, Q4, Q5, and Q8 are ON, and the other switching elements are OFF. At this time, the current path in DC / DC converter 10 is as shown in Fig. 5(B). That is, as shown by the solid arrow in Fig. 5(B), synchronous rectification by switching element Q5 starts. In state #13, only switching elements Q4, Q5, and Q8 are ON, and the other switching elements are OFF. At this time, the current path in the DC / DC converter 10 is as shown in Fig. 5(C). That is, as shown by the dashed arrow in Fig. 5(C), the return flow of the excitation current starts on the primary side when switching element Q1 is turned OFF. In state #14, only switching elements Q3, Q4, Q5, and Q8 are ON, and the other switching elements are OFF. At this time, the current path in the DC / DC converter 10 is as shown in Fig. 6(A). That is, as shown by the dashed arrow in Fig. 6(A), the return flow of the excitation current continues on the primary side due to switching element Q3 being ON. In state #15, only switching elements Q3, Q4, and Q8 are ON, and the other switching elements are OFF. At this time, the current path in DC / DC converter 10 is as shown in Fig. 6(B). That is, as shown by the solid arrow in Fig. 6(B), the load current continues even after switching element Q5 is turned OFF, and the excitation current circulates on the primary side. In state #16, only switching elements Q3 and Q8 are ON, and the other switching elements are OFF. At this time, the current path in DC / DC converter 10 is as shown in Fig. 6(C). That is, as shown by the solid and dashed arrows in Fig. 6(C), when switching element Q4 is turned OFF, both the load current and the excitation current are regenerated and disappear.

[0043] Fig. 7 is an image diagram of the waveform of the load current transmitted by the timing chart according to the first example. The waveform shown by the solid line in the graph of Fig. 7 is the waveform of the load current transmitted by the timing chart according to the first example.

[0044] 7, the load current increases in the switching pattern between #11 and #12, and decreases in the switching pattern between #13 and #16.

[0045] <An example of step-down operation (discontinuous mode)> Fig. 8 shows a timing chart according to a second example of signals used when the DC / DC converter 10 according to this embodiment is operated as a step-down converter. Fig. 9 is a first schematic diagram showing a current path when the DC / DC converter 10 is operated according to the timing chart according to the second example. Fig. 10 is a second schematic diagram showing a current path when the DC / DC converter 10 is operated according to the timing chart according to the second example. The control device 20 operates each switching element of the DC / DC converter 10 with a switching pattern according to the timing chart shown in Fig. 8, thereby realizing the current flow shown in Figs. 9 and 10.

[0046] The correspondence between the current paths in each section from #21 to #26 shown in FIG. 8 and each diagram shown in FIG. 9 and FIG. 10 is as follows. In state #21, only switching elements Q1, Q4, and Q8 are ON, and the other switching elements are OFF. At this time, the current path in DC / DC converter 10 is as shown in Fig. 9(A). That is, as shown by the solid arrows in Fig. 9(A), power transmission by switching elements Q1 and Q4 begins. In state #22, only switching elements Q1, Q4, Q5, and Q8 are ON, and the other switching elements are OFF. At this time, the current path in DC / DC converter 10 is as shown in Fig. 9(B). That is, as shown by the solid arrow in Fig. 9(B), synchronous rectification by switching element Q5 starts. In state #23, only switching elements Q4, Q5, and Q8 are ON, and the other switching elements are OFF. At this time, the current path in DC / DC converter 10 is as shown in Fig. 9(C). That is, as shown by the dashed arrow in Fig. 9(C), the return flow of excitation current begins on the primary side due to switching element Q1 being turned OFF. In the state of #24, only switching elements Q3, Q4, Q5, and Q8 are ON, and the other switching elements are OFF. At this time, the current path in the DC / DC converter 10 is as shown in Fig. 10(A). That is, as shown by the dashed arrow in Fig. 10(A), the ON state of switching element Q3 causes the return flow of the excitation current on the primary side to continue. In the state of #25, only switching elements Q3, Q4, and Q8 are ON, and the other switching elements are OFF. At this time, the current path in the DC / DC converter 10 is as shown in FIG. 10(B). That is, when switching element Q5, which was performing synchronous rectification, turns OFF, the load current is lost, as shown in FIG. 10(B). Also, as shown by the dashed arrows in FIG. 10(B), the excitation current circulates in a proportional manner between the primary side and the secondary side. In state #26, only switching elements Q3 and Q8 are ON, and the other switching elements are OFF. At this time, the current path in DC / DC converter 10 is as shown in Fig. 10(C). That is, as shown by the dashed arrow in Fig. 10(C), the excitation current is regenerated and disappears due to switching element Q4 being turned OFF.

[0047] Fig. 11 is an image diagram of the waveform of the load current transmitted by the timing chart according to the second example. The waveform shown by the solid line in the graph of Fig. 11 is the waveform of the load current transmitted by the timing chart according to the second example.

[0048] As shown in the graph of Figure 11, in the switching pattern between #21 and #22, In the switching pattern between #23 and #24, the load current decreases.

[0049] Note that, although an example has been given here of a configuration in which switching element Q8 is not turned OFF when switching element Q5 is turned OFF, the same applies to the switching pattern, for example, 0.5 cycles before or after, in which switching element Q7 is not turned OFF when switching element Q6 is turned OFF.

[0050] <An example of boost operation> Fig. 12 shows a timing chart according to a third example of signals used when the DC / DC converter 10 according to this embodiment is operated as a boost converter. Fig. 13 is a first schematic diagram showing a current path when the DC / DC converter 10 is operated according to the timing chart according to the third example. Fig. 14 is a second schematic diagram showing a current path when the DC / DC converter 10 is operated according to the timing chart according to the third example. The control device 20 operates each switching element of the DC / DC converter 10 with a switching pattern according to the timing chart shown in Fig. 12, thereby realizing the current flow as shown in Figs. 13 and 14.

[0051] The correspondence between the current paths in each section from #31 to #35 shown in FIG. 12 and each diagram shown in FIG. 13 and FIG. 14 is as follows. In the state of #31, only switching elements Q1, Q4, Q7, and Q8 are ON, and the other switching elements are OFF. At this time, the current path in the DC / DC converter 10 is as shown in FIG. 13(A). That is, as shown by the solid arrows in FIG. 13(A), preparations for power transmission by the switching elements Q1 and Q4 begin. In the state of #32, only switching elements Q1, Q4, and Q8 are ON, and the other switching elements are OFF. At this time, the current path in the DC / DC converter 10 is as shown in FIG. 13(B). That is, as shown by the solid arrows in FIG. 13(B), power transmission begins with switching element Q7 being turned OFF. In state #33, only switching elements Q1, Q4, Q5, and Q8 are ON, and the other switching elements are OFF. At this time, the current path in DC / DC converter 10 is as shown in Fig. 13(C). That is, as shown by the solid arrow in Fig. 13(C), synchronous rectification is started by switching element Q5 ON. In state #34, only switching elements Q4 and Q8 are ON, and the other switching elements are OFF. At this time, the current path in DC / DC converter 10 is as shown in Fig. 14(A). That is, as shown by the dashed arrow in Fig. 14(A), the excitation current circulates on the primary side due to switching element Q1 being OFF. This causes the load current to continue as shown by the solid arrow in Fig. 14(A). In state #35, only switching elements Q3 and Q8 are ON, and the other switching elements are OFF. At this time, the current path in DC / DC converter 10 is as shown in Fig. 14(B). That is, as shown by the solid and dashed arrows in Fig. 14(B), when switching element Q4 is turned OFF, both the load current and the excitation current are regenerated and disappear.

[0052] Fig. 15 is an image diagram of the waveform of the load current transmitted by the timing chart according to the third example. The waveform shown by the solid line in the graph of Fig. 15 is the waveform of the load current transmitted by the timing chart according to the third example.

[0053] 15, the load current increases in the switching pattern #31, and decreases in the switching patterns #32 to #35.

[0054] <Other> The above embodiment is merely an example, and the disclosure of the present embodiment may be modified as appropriate without departing from the spirit of the present disclosure. The processes and means described in the present disclosure may be freely combined and implemented as long as no technical contradiction occurs.

[0055] Furthermore, a process described as being performed by one circuit or device may be shared and executed by multiple circuits or devices, or a process described as being performed by different circuits or devices may be executed by a single circuit or device.

[0056] In addition, this application includes the following additional matters. <Appendix 1> a DC / DC converter (10) including: a first full bridge circuit (11) including a first switching leg (L1) and a second switching leg (L2) connected in parallel to a first input / output terminal pair (13p, 13m); a second full bridge circuit (12) including a third switching leg (L3) and a fourth switching leg (L4) connected in parallel to a second input / output terminal pair (14p, 14m); and a transformer (TR) including one winding connected to the first full bridge circuit and the other winding connected to the second full bridge circuit; A control unit (20) that controls the DC / DC converter, the control unit constantly turns on any one of a plurality of switching elements included in a full bridge circuit serving as a secondary side of the first full bridge circuit and the second full bridge circuit on a low side. Power conversion equipment. [Explanation of symbols]

[0057] 1. Power conversion device 2··EV 10. DC / DC converter 20. Control device 30. Inverter 21 Phase shift amount generator 22...PWM generation section Q1~Q8 Switching elements

Claims

1. a DC / DC converter including: a first full bridge circuit including a first switching leg and a second switching leg connected in parallel to a first input / output terminal pair; a second full bridge circuit including a third switching leg and a fourth switching leg connected in parallel to a second input / output terminal pair; and a transformer including one winding connected to the first full bridge circuit and the other winding connected to the second full bridge circuit; A control unit that controls the DC / DC converter, the control unit constantly turns on any one of a plurality of switching elements included in a low-side full bridge circuit of the first full bridge circuit and the second full bridge circuit, the full bridge circuit being a secondary side; Power conversion equipment.

2. The control unit is The DC / DC converter has a discontinuous mode in which each switching element of the DC / DC converter is operated with a switching pattern that forms a discontinuous section in which no current flows through an inductor, The ON state of the switching element on the low side of the switching leg that was turned ON before entering the discontinuous section is maintained until the switching element on the low side of the switching leg to be turned ON next is turned ON, thereby keeping any one of the multiple switching elements on the low side of the full bridge circuit that serves as the secondary side always ON. The power conversion device according to claim 1 .

3. the first switching leg has a first switching element and a third switching element, a source terminal of the first switching element and a drain terminal of the third switching element are connected in series at a first connection point, and a drain terminal of the first switching element and a source terminal of the third switching element are connected to the first input / output terminal pair; the second switching leg has a second switching element and a fourth switching element, a source terminal of the second switching element and a drain terminal of the fourth switching element are connected in series at a second connection point, and a drain terminal of the second switching element and a source terminal of the fourth switching element are connected to the first input / output terminal pair, the third switching leg has a fifth switching element and a seventh switching element, a source terminal of the fifth switching element and a drain terminal of the seventh switching element are connected in series at a third connection point, and a drain terminal of the fifth switching element and a source terminal of the seventh switching element are connected to the second input / output terminal pair, the fourth switching leg has a sixth switching element and an eighth switching element, a source terminal of the sixth switching element and a drain terminal of the eighth switching element are connected in series at a fourth connection point, and a drain terminal of the sixth switching element and a source terminal of the eighth switching element are connected to the second input / output terminal pair, one winding of the transformer is connected to the first connection point and the second connection point, and the other winding of the transformer is connected to the third connection point and the fourth connection point; The control unit is When the second full-bridge circuit is on the secondary side, either the seventh switching element or the eighth switching element is always ON; When the first full-bridge circuit serves as a secondary side, either the third switching element or the fourth switching element is always turned on. The power conversion device according to claim 1 or 2.

4. Each of the first switching element to the eighth switching element In the figure, the cathode is connected to the drain terminal and the anode is connected to the source terminal, and the diodes are connected in inverse parallel. The power conversion device according to claim 3 .

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