Bidirectional DC / DC converter, operation method thereof, and bidirectional obc including same

Abstract

A bidirectional DC / DC converter according to an embodiment of the present invention comprises: a transformer; a primary-side circuit connected to one side of the transformer and including a full-bridge circuit composed of first to fourth switches, a first resonant inductor, a magnetizing inductor, and a first resonant capacitor; and a secondary-side circuit connected to the other side of the transformer and including a full-bridge circuit composed of fifth to eighth switches, a second resonant inductor, a second resonant capacitor, and a third capacitor. In a mode in which power is supplied from the secondary-side circuit to the primary-side circuit among operation modes of the bidirectional DC / DC converter, the sixth switch is set to OFF, the eighth switch is set to ON, and the fifth switch and the seventh switch may be turned ON / OFF according to a first switching frequency.

Description

Bidirectional DC / DC converter, method of operation thereof, and bidirectional OBC including the same

[0001] The present invention relates to a bidirectional DC / DC converter, a method of operation thereof, and a bidirectional OBC including the same, and more specifically, to a bidirectional DC / DC converter capable of operating at a low switching frequency, a method of operation thereof, and a bidirectional OBC including the same.

[0002] Electrical energy is widely used because it is easy to convert and transmit. To utilize this electrical energy efficiently, an Energy Storage System (ESS) is used. An Energy Storage System receives power, charges batteries, and supplies power by discharging the stored power from the batteries when power is needed. Through this, the Energy Storage System can supply power flexibly.

[0003] For example, if a power supply system includes an energy storage system, it operates as follows. When the load or grid is overloaded, the energy storage system discharges electrical energy stored in the battery, and when the load or grid is light load, the energy storage system receives power from a power generator or grid and charges the battery.

[0004] As another example, in the case where an energy storage system exists independently of a power supply system, the energy storage system receives idle power from an external power source to charge the battery, and when the grid or load is overloaded, the energy storage system discharges the power charged in the battery to supply power. Therefore, an electric vehicle can also be considered to have an energy storage system independent of a power supply system.

[0005] The technical problem that the present invention aims to solve is to provide a bidirectional DC / DC converter, a method of operation thereof, and a bidirectional OBC including the same.

[0006] The technical problem to be solved by the present invention is to provide a bidirectional DC / DC converter capable of lowering the switching frequency in discharge mode compared to conventional technology without changing the circuit configuration, a method of operation thereof, and a bidirectional OBC including the same.

[0007] The technical problem to be solved by the present invention is to provide a bidirectional DC / DC converter with increased charging efficiency, a method of operation thereof, and a bidirectional OBC including the same.

[0008] Furthermore, the technical problem that the present invention aims to solve is not limited to the purposes mentioned above, and other unmentioned purposes will be clearly understood by a person skilled in the art from the description below.

[0009] A bidirectional DC / DC converter according to an embodiment of the present invention comprises a transformer, a first switch, a second switch, a third switch, a fourth switch, a first resonant inductor, a magnetizing inductor, and a first resonant capacitor, and a primary circuit connected to one side of the transformer, and a secondary circuit connected to the other side of the transformer, comprising a fifth switch, a sixth switch, a seventh switch, an eighth switch, a second resonant inductor, a second resonant capacitor, and a third capacitor, and a secondary circuit connected to the other side of the transformer, wherein in the primary circuit, the first switch and the third switch are connected in series, the second switch and the fourth switch are also connected in series, the first switch and the third switch and the second switch and the fourth switch are connected in parallel, the node between the first switch and the third switch is connected to the first resonant inductor, the first resonant inductor is connected to the magnetizing inductor, and the node between the second switch and the fourth switch is connected to the first resonant capacitor, and the In the secondary circuit, the fifth switch and the seventh switch are connected in series, the sixth switch and the sixth switch are also connected in series, the fifth switch and the seventh switch, the sixth switch and the eighth switch and the third capacitor are connected in parallel, the node between the fifth switch and the seventh switch is connected to the second resonant inductor, and the node between the sixth switch and the eighth switch is connected to the second resonant capacitor, and in the mode in which power is supplied from the secondary circuit to the primary circuit among the operating modes of the bidirectional DC / DC converter, the sixth switch is set to off, the eighth switch is set to on, and the fifth switch and the seventh switch can be turned on / off according to the set first switching frequency.

[0010] In a bidirectional DC / DC converter according to an embodiment of the present invention, the first switching frequency set may be determined according to the magnitude of the power supplied from the secondary circuit to the primary circuit.

[0011] In a bidirectional DC / DC converter according to an embodiment of the present invention, the fifth switch and the seventh switch may be set to alternately turn on or off.

[0012] In the bidirectional DC / DC converter according to an embodiment of the present invention, in the mode in which power is supplied from the primary side circuit to the secondary side circuit among the operating modes of the DC / DC converter, the fifth switch to the eighth switch may be turned on / off according to a set second switching frequency.

[0013] In a bidirectional DC / DC converter according to an embodiment of the present invention, the set second switching frequency can be determined according to the magnitude of the power supplied from the primary circuit to the secondary circuit.

[0014] In a bidirectional DC / DC converter according to an embodiment of the present invention, the set second switching frequency may be the same as the set first switching frequency.

[0015] In a bidirectional DC / DC converter according to an embodiment of the present invention, each of the first to eighth switches may have a MOSFET, a diode, and a capacitor connected in parallel.

[0016] A bidirectional OBC (on-board charger) according to an embodiment of the present invention may include any one of the bidirectional DC / DC converters described above and an AC / DC converter connected to the primary side circuit of the bidirectional DC / DC converter.

[0017] A transformer according to an embodiment of the present invention comprises a first switch, a second switch, a third switch, a fourth switch, a first resonant inductor, a magnetizing inductor, and a first resonant capacitor, and a primary circuit connected to one side of the transformer, and a secondary circuit connected to the other side of the transformer, comprising a fifth switch, a sixth switch, a seventh switch, an eighth switch, a second resonant inductor, a second resonant capacitor, and a third capacitor. In the primary circuit, the first switch and the third switch are connected in series, the second switch and the fourth switch are also connected in series, the first switch and the third switch and the second switch and the fourth switch are connected in parallel, the node between the first switch and the third switch is connected to the first resonant inductor, the first resonant inductor is connected to the magnetizing inductor, and the node between the second switch and the fourth switch is connected to the first resonant capacitor. In the secondary circuit, the A method of operation of a bidirectional DC / DC converter in which the fifth switch and the seventh switch are connected in series, the sixth switch and the sixth switch are also connected in series, the fifth switch and the seventh switch, the sixth switch and the eighth switch, and the third capacitor are connected in parallel, the node between the fifth switch and the seventh switch is connected to the second resonant inductor, and the node between the sixth switch and the eighth switch is connected to the second resonant capacitor, wherein when the mode is changed to supply power from the secondary side circuit to the primary side circuit, the method includes the steps of setting the sixth switch to off and the eighth switch to on, setting a first switching frequency according to the magnitude of the power supplied from the secondary side circuit to the primary side circuit, and turning the fifth switch and the seventh switch on / off according to the set first switching frequency, and the fifth switch and the seventh switch may be turned on or off alternately.

[0018] The method of operation of a bidirectional DC / DC converter according to an embodiment of the present invention may further include the step of setting a second switching frequency according to the magnitude of the power supplied from the primary circuit to the secondary circuit when the mode of supplying power from the primary circuit to the secondary circuit is changed, and the step of turning on / off the fifth to eighth switches according to the set second switching frequency.

[0019] In the operation method of a bidirectional DC / DC converter according to an embodiment of the present invention, the set second switching frequency may be the same as the set first switching frequency.

[0020] In the operation method of a bidirectional DC / DC converter according to an embodiment of the present invention, each of the first to eighth switches may have a MOSFET, a diode, and a capacitor connected in parallel.

[0021] According to the present invention, a bidirectional DC / DC converter, a method of operation thereof, and a bidirectional OBC including the same can be provided.

[0022] According to the present invention, a bidirectional DC / DC converter with increased charging efficiency, a method of operation thereof, and a bidirectional OBC including the same can be provided.

[0023] According to the present invention, a bidirectional DC / DC converter capable of lowering the switching frequency in discharge mode compared to the prior art without changing the circuit configuration, a method of operation thereof, and a bidirectional OBC including the same can be provided.

[0024] In addition to these, the effects obtainable from the present invention are not limited to those mentioned above, and other unmentioned effects will be clearly understood by those skilled in the art to which the present invention belongs from the description below.

[0025] Figure 1 is an example of a schematic diagram of a charging module for bidirectional charging.

[0026] FIG. 2 is a circuit diagram of a DC / DC converter in a charging module for bidirectional charging according to one embodiment of the present invention.

[0027] Figures 3a and 3b are graphs showing the gains in the charging and discharging modes of the DC / DC converter of Figure 2.

[0028] FIG. 4 is a circuit diagram in the discharge mode of a DC / DC converter according to one embodiment of the present invention.

[0029] Figure 5 is a graph showing the gain in the discharge mode of the DC / DC converter according to Figure 4.

[0030] FIGS. 6a to 6g are graphs showing the current flowing through or the voltage applied to each component in the circuit in the discharge mode of a DC / DC converter according to one embodiment of the present invention.

[0031] FIGS. 7a to 7f show the operating state of each component within a DC / DC converter over time.

[0032] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the attached drawings.

[0033] However, the technical concept of the present invention is not limited to some of the described embodiments but can be implemented in various different forms, and within the scope of the technical concept of the present invention, one or more of the components among the embodiments may be selectively combined or substituted.

[0034] In addition, terms used in the embodiments of the present invention (including technical and scientific terms) may be interpreted in a sense that is generally understood by those skilled in the art to which the present invention belongs, unless explicitly and specifically defined otherwise. Terms that are commonly used, such as terms defined in advance, may be interpreted in consideration of their meaning in the context of the relevant technology.

[0035] Furthermore, the terms used in the embodiments of the present invention are for the purpose of describing the embodiments and are not intended to limit the present invention.

[0036] In this specification, the singular form may include the plural form unless specifically stated otherwise in the text, and when described as "at least one of A and B and C (or more than one)," it may include one or more of all combinations that can be formed from A, B, and C.

[0037] In addition, terms such as first, second, A, B, (a), (b), etc. may be used when describing the components of the embodiments of the present invention.

[0038] These terms are intended merely to distinguish a component from other components and are not limited by the nature, order, sequence, etc., of the said component.

[0039] And, where it is stated that a component is 'connected', 'combined', or 'joined' to another component, this may include not only cases where the component is directly connected, combined, or joined to the other component, but also cases where it is 'connected', 'combined', or 'joined' due to another component located between the component and the other component.

[0040] Furthermore, when described as being formed or placed "above or below" each component, "above" or "below" includes not only cases where two components are in direct contact with each other, but also cases where one or more other components are formed or placed between the two components. Additionally, when expressed as "above or below," it may include the meaning of a downward direction as well as an upward direction relative to a single component.

[0041] Figure 1 is an example of a schematic diagram of a charging module for bidirectional charging.

[0042] Referring to FIG. 1, a charging module (100) for bidirectional charging may include an EMI (Electro Magnetic Interference) filter (110), an AC / DC converter (120), and a DC / DC converter (130). The charging module (100) for bidirectional charging may convert AC power supplied from an AC power supply (140) into DC power to charge a battery (150), or convert DC power charged in the battery (150) into AC power to supply power to the AC power supply (140). According to one embodiment, the AC power supply (140) may represent a grid, and the AC power of the AC power supply (140) may be single-phase or three-phase.

[0043] According to one embodiment, the charging module (100) for bidirectional charging must be able to transmit power in both directions, and the components included in the charging module (100) for bidirectional charging must also be able to operate in both directions.

[0044] More specifically, the EMI filter (110) is used to reduce or block electromagnetic interference caused by AC power supplied from the AC power supply (140) or AC power supplied to the AC power supply (140). An EMI filter (110) may be required if the AC power supplied from the AC power supply (140) or AC power supplied to the AC power supply (140) has high voltage and / or current values ​​that affect surrounding circuits. Additionally, an EMI filter (110) may be required to reduce or block EMI, as EMI may occur during high-frequency switching in the operation of the AC / DC converter (120) or DC / DC converter (130). That is, the use of the EMI filter (110) can resolve electromagnetic interference issues and ensure the reliability of the AC / DC converter (120) and / or DC / DC converter (130). However, the EMI filter (110) may be omitted if separate shielding means are included to prepare for EMI generation.

[0045] The AC / DC converter (120) can convert AC power into DC power and DC power into AC power. That is, when AC power is supplied from the AC power supply (140), the AC / DC converter (120) can convert the AC power into DC power and transmit it to the DC / DC converter (130), and when DC power is supplied from the battery (150), it can convert the DC power into AC power and transmit it to the EMI filter (110). According to one embodiment, a totem pole PFC (Power Factor Correction) converter capable of power factor improvement and bidirectional operation may be used as the AC / DC converter (120).

[0046] A DC / DC converter (130) can convert DC power into DC power. Since the power converted by the AC / DC converter (120) may not be suitable for charging the battery (150), a DC / DC converter (130) may be used to resolve this. Similarly, since the battery (150) may not be suitable for supplying power to the AC / DC converter (120), a DC / DC converter (130) may be used. Therefore, the DC / DC converter (130) may also be capable of bidirectional conversion. As an example, a CLLC (Capacitor-Inductor-Inductor-Capacitor) converter, which has a simple structure and excellent efficiency, may be used as the DC / DC converter (130). A CLLC converter may be capable of soft switching in the full load region. Additionally, a CLLC converter may be suitable for meeting high power density and insulation requirements as one of the resonant power converters.

[0047] In FIG. 1, the EMI filter (110), AC / DC converter (120), and DC / DC converter (130) are shown as a single configuration for a charging module (100) for bidirectional charging, but the AC / DC converter (120) and DC / DC converter (130) may be configured separately and referred to as a bidirectional OBC (on-board charger).

[0048] FIG. 2 is a circuit diagram of a DC / DC converter in a charging module for bidirectional charging according to one embodiment of the present invention.

[0049] Referring to FIG. 2, the DC / DC converter (200) may be configured as a CLLC converter. The DC / DC converter (200) may include a transformer (210), a primary circuit (220) to the left of the transformer, and a secondary circuit (230) to the right. According to one embodiment, an AC / DC converter may be connected to the primary circuit (220), and a battery may be connected to the secondary circuit (230). The voltage (V) connected to the primary circuit (220)link ) can be 410V, and the voltage (V) connected to the secondary circuit (230) battery The voltage may be 250 to 450V. Additionally, the DC / DC converter (200) may further include a controller (not shown) for converting modes or controlling switches.

[0050] Specifically, the primary side circuit (220) may include a first switch (S1), a second switch (S2), a third switch (S3), and a fourth switch (S4). The first switch (S1) and the third switch (S3) are connected in series, and the second switch (S2) and the fourth switch (S4) are also connected in series. The first switch (S1) and the third switch (S3), and the second switch (S2) and the fourth switch (S4) are connected in parallel.

[0051] The node between the first switch (S1) and the third switch (S3) is connected to the first resonant inductor (Lrp), and the first resonant inductor (Lrp) is a magnetizing inductor (L M It is connected to ). The node between the second switch (S2) and the fourth switch (S4) is connected to the first resonant capacitor (Crp). A primary side current (ip) flows through the first resonant inductor (Lrp), and the magnetizing inductor (L M A magnetization current (iLm) flows through it.

[0052] Additionally, the secondary circuit (230) may include a fifth switch (S5), a sixth switch (S6), a seventh switch (S7), and an eighth switch (S8). The fifth switch (S5) and the seventh switch (S7) are connected in series, and the sixth switch (S6) and the eighth switch (S8) are also connected in series. The fifth switch (S5) and the seventh switch (S7), the sixth switch (S6) and the eighth switch (S8), and the third capacitor (Co) are connected in parallel with each other.

[0053] The node between the 5th switch (S5) and the 7th switch (S7) is connected to the 2nd resonant inductor (Lrs), and the node between the 6th switch (S6) and the 8th switch (S8) is connected to the 2nd resonant capacitor (Crs). A secondary current (is) flows through the 2nd resonant inductor (Lrs).

[0054] According to one embodiment, a controller (not shown) can control the on / off of a plurality of switches included in the primary circuit (220) and the secondary circuit (230). The controller can control the on / off of the plurality of switches according to a charging mode and a discharging mode. The charging mode and the discharging mode are named based on the power source, i.e., the battery, connected to the secondary circuit (230). The charging mode refers to a mode in which power is applied from the primary circuit (220) to the secondary circuit (230), and the discharging mode refers to a mode in which power is applied from the secondary circuit (230) to the primary circuit (220).

[0055] Figures 3a and 3b are graphs showing the gains in the charging and discharging modes of the DC / DC converter of Figure 2.

[0056] The gain of each mode in the DC / DC converter of Fig. 2 can be expressed by the following formula.

[0057] [Mathematical Formula 1]

[0058]

[0059] [Mathematical Formula 2]

[0060]

[0061] Specifically, [Equation 1] represents the gain in charging mode, and [Equation 2] represents the gain in discharging mode.

[0062] In this regard, referring to FIGS. 3a and 3b, the voltage (V) connected to the secondary circuit (230) in charging mode battery Since ) is 250 ~ 450V, the switching frequency is 6*10 4 ~ 105 It must be (310), and the voltage (V) input connected to the primary side circuit (220) in discharge mode must be link Since ) is 410V, the switching frequency is 2.8*10 5 ~ 3.8*10 5 It must be (320). That is, in discharge mode, the switching frequency must be higher than in charging mode to match the voltage.

[0063] However, operation at high frequencies presents difficulties in designing circuit components. Furthermore, operating at high frequencies increases losses, which can reduce the efficiency of the charging module itself. Accordingly, the present invention proposes an operation method that can lower the switching frequency in discharge mode without changing the circuit configuration.

[0064] FIG. 4 is a circuit diagram of a DC / DC converter in a discharge mode according to an embodiment of the present invention, and FIG. 5 is a graph showing the gain in the discharge mode of the DC / DC converter according to FIG. 4.

[0065] Referring to FIG. 4, the DC / DC converter of FIG. 2 can be configured in discharge mode by fixing the 6th switch (S6) to off and the 8th switch (S8) to on. Accordingly, the secondary circuit of the DC / DC converter in discharge mode can be converted from a Full Bridge structure to a Half Bridge structure. When converted from a Full Bridge structure to a Half Bridge structure, the gain is reduced by half. Therefore, the graph of FIG. 3b can be changed as shown in the graph of FIG. 5, and the switching frequency required to discharge the same voltage can be lowered. Accordingly, the switching frequency can be selected considering the voltage to be discharged, and the 5th switch (S5) and the 7th switch (S7) can be operated alternately.

[0066] According to one embodiment, when the switching frequency in the charging mode and the switching frequency in the discharging mode are the same, if the size of the power to be supplied and the size of the power to be discharged are within a certain range, the switching frequency in the charging mode and the switching frequency in the discharging mode may be set to be the same.

[0067] According to one embodiment, each switch may be configured in a form in which a MOSFET, a diode, and a capacitor are connected in parallel.

[0068] FIGS. 6a to 6g are graphs showing the current flowing through or the voltage applied to each component in the circuit in the discharge mode of a DC / DC converter according to one embodiment of the present invention.

[0069] Specifically, FIG. 6a is a graph showing the operation of the fifth switch and the seventh switch over time. The switching frequency of the fifth switch and the seventh switch can be determined according to the magnitude of the power supplied from the secondary circuit to the primary circuit. The on / off operation of the fifth switch and the seventh switch can be alternate. That is, when the fifth switch is turned on, the seventh switch can be set to turn off, and when the fifth switch is turned off, the seventh switch can be set to turn on. As the on / off state of the fifth switch and the seventh switch changes based on the set switching frequency, the current and voltage flowing through each component within the DC / DC converter may change. FIG. 6b to 6g show the current and voltage flowing through each component within the DC / DC converter.

[0070] Specifically, FIG. 6b shows the voltage across the fifth switch and the seventh switch, FIG. 6c shows the current flowing through the seventh switch, FIG. 6d shows the current flowing through the second switch and the third switch, FIG. 6e shows the current flowing through the fifth switch, FIG. 6f shows the current flowing through the first switch and the fourth switch, and FIG. 6g shows the current flowing through the magnetizing inductor and the second resonant inductor.

[0071] Hereinafter, the operation of each component within the DC / DC converter over time will be described with reference to FIGS. 6a to 6g.

[0072] FIGS. 7a to 7f show the operating state of each component within a DC / DC converter over time.

[0073] Specifically, FIG. 7a shows the operating state of each component in the DC / DC converter from t0 to t1. During t0 to t1, the seventh switch is gradually switched off, while the fifth switch is still on. Therefore, current flows through the fifth switch, and the voltage across the fifth switch is 0V. At this time, the voltage supplied externally from the primary circuit can be the voltage across the magnetizing inductor.

[0074] FIG. 7b shows the operating state of each component within the DC / DC converter from t1 to t2. From t1 to t2 is the period in which the seventh switch is switched off and the fifth switch is gradually switched on. During this period, the direction of the current in the secondary circuit changes. Although the direction of the current changes, it flows through the fifth switch because the fifth switch is on, and the voltage across the fifth switch is 0V. At this time, resonance begins between the second resonant capacitor (Crs) and the second resonant inductor (Lrs), and charging begins in the second resonant capacitor (Crs). As with FIG. 7a, the voltage supplied externally from the primary circuit can be the voltage across the magnetizing inductor. The externally supplied current decreases to 0 at t2 due to the resonance between the second resonant capacitor (Crs) and the second resonant inductor (Lrs). When the current flowing through the second resonant inductor (iLrs) and the current flowing through the magnetizing inductor (iLm) become equal, the state of the circuit can be changed as shown in FIG. 7c.

[0075] FIG. 7c shows the operating state of each component in the DC / DC converter at t2 to t3. Referring to FIG. 7c, only the current (iLm) flowing through the magnetizing inductor can flow in the secondary circuit. The fifth switch is switched off, and the current (iLm) flowing through the magnetizing inductor can charge the capacitor in the fifth switch and discharge the capacitor in the seventh switch. When the capacitor in the seventh switch is completely discharged, the diode in the seventh switch can be turned on.

[0076] FIG. 7d shows the operating state of each component in the DC / DC converter at t3 to t4. Referring to FIG. 7d, the current in the secondary circuit can flow through the seventh switch. More specifically, it can flow through the diode in the seventh switch. At this time, the voltage across the seventh switch can be 0V. As with FIG. 7a, the voltage supplied externally from the primary circuit can be the voltage across the magnetizing inductor.

[0077] FIG. 7e shows the operating state of each component in the DC / DC converter at t4 to t5. Referring to FIG. 7e, the current in the secondary circuit can be discharged from the second resonant capacitor (Crs) and flow through the seventh switch. As in FIG. 7a, the voltage supplied externally from the primary circuit can be the voltage across the magnetizing inductor. The externally supplied current decreases to zero at t5 due to the resonance between the second resonant capacitor (Crs) and the second resonant inductor (Lrs). When the current flowing through the second resonant inductor (iLrs) and the current flowing through the magnetizing inductor (iLm) become equal, the state of the circuit can be changed as shown in FIG. 7f.

[0078] FIG. 7f shows the operating state of each component in the DC / DC converter at t5 to t6. Referring to FIG. 7f, only the current (iLm) flowing through the magnetizing inductor can flow in the secondary circuit. The seventh switch is turned off, and the current (iLm) flowing through the magnetizing inductor charges the capacitor contained within the seventh switch and discharges the energy stored in the capacitor contained within the fifth switch. When all the energy in the capacitor contained within the fifth switch is discharged, the diode contained within the fifth switch is turned on.

[0079] According to one embodiment, t6 is in the same state as t0, and the DC / DC converter can operate again from FIG. 7a.

[0080] In the above, an example of setting the switching frequency by fixing only some switches of the secondary circuit was described, but similarly, the switching frequency can also be set by fixing only some switches of the primary circuit. When fixing only some switches of the primary circuit, the fourth switch can be set to ON and the second switch can be set to OFF. In addition, the switching frequency can be set by fixing some switches of both the primary and secondary circuits. In this case, the fourth switch can be set to ON, the second switch to OFF, the eighth switch to ON, and the sixth switch to OFF. As previously explained, the switching frequency can be set by considering the voltage to be charged or / and the voltage to be discharged.

[0081] Although the invention has been described above with reference to embodiments, this is merely illustrative and does not limit the invention. Those skilled in the art will understand that various modifications and applications not exemplified above are possible within the scope of the essential characteristics of the embodiments. For example, each component specifically shown in the embodiments may be modified and implemented. Furthermore, differences related to such modifications and applications should be interpreted as being included within the scope of the invention as defined in the appended claims.

Claims

1. Transformer; A primary circuit including a first switch, a second switch, a third switch, a fourth switch, a first resonant inductor, a magnetizing inductor, and a first resonant capacitor, and connected to one side of the transformer; and It includes a fifth switch, a sixth switch, a seventh switch, an eighth switch, a second resonant inductor, a second resonant capacitor, and a third capacitor, and includes a secondary circuit connected to the other side of the transformer, In the above primary circuit, The first switch and the third switch are connected in series, the second switch and the fourth switch are also connected in series, the first switch and the third switch and the second switch and the fourth switch are connected in parallel, the node between the first switch and the third switch is connected to the first resonant inductor, the first resonant inductor is connected to the magnetizing inductor, and the node between the second switch and the fourth switch is connected to the first resonant capacitor, and In the above secondary circuit The fifth switch and the seventh switch are connected in series, the sixth switch and the sixth switch are also connected in series, the fifth switch and the seventh switch, the sixth switch and the eighth switch and the third capacitor are connected in parallel, the node between the fifth switch and the seventh switch is connected to the second resonant inductor, and the node between the sixth switch and the eighth switch is connected to the second resonant capacitor. In the mode of operation of the bidirectional DC / DC converter in which power is supplied from the secondary circuit to the primary circuit, The above 6th switch is set to off, and the above 8th switch is set to on, and The above-mentioned fifth switch and the above-mentioned seventh switch are a bidirectional DC / DC converter that is turned on / off according to a set first switching frequency.

2. In Paragraph 1, A bidirectional DC / DC converter in which the first switching frequency set above is determined according to the magnitude of the power supplied from the secondary circuit to the primary circuit.

3. In Paragraph 1, A bidirectional DC / DC converter in which the fifth switch and the seventh switch are set to alternately turn on or off.

4. In Paragraph 1, In the mode of operation of the above DC / DC converter in which power is supplied from the primary circuit to the secondary circuit, The above-mentioned fifth to eighth switches are a bidirectional DC / DC converter that is turned on / off according to a set second switching frequency.

5. In Paragraph 4, A bidirectional DC / DC converter in which the second switching frequency set above is determined according to the magnitude of the power supplied from the primary circuit to the secondary circuit.

6. In Paragraph 4, A bidirectional DC / DC converter in which the second switching frequency set above is the same as the first switching frequency set above.

7. In Paragraph 1, Each of the first to eighth switches is a bidirectional DC / DC converter in which a MOSFET, a diode, and a capacitor are connected in parallel.

8. A bidirectional DC / DC converter according to any one of paragraphs 1 to 7; and A bidirectional OBC (on-board charger) comprising an AC / DC converter connected to the primary circuit of the above-mentioned bidirectional DC / DC converter.

9. Transformer; A primary circuit including a first switch, a second switch, a third switch, a fourth switch, a first resonant inductor, a magnetizing inductor, and a first resonant capacitor, and connected to one side of the transformer; and It includes a fifth switch, a sixth switch, a seventh switch, an eighth switch, a second resonant inductor, a second resonant capacitor, and a third capacitor, and includes a secondary circuit connected to the other side of the transformer, In the above primary circuit, The first switch and the third switch are connected in series, the second switch and the fourth switch are also connected in series, the first switch and the third switch and the second switch and the fourth switch are connected in parallel, the node between the first switch and the third switch is connected to the first resonant inductor, the first resonant inductor is connected to the magnetizing inductor, and the node between the second switch and the fourth switch is connected to the first resonant capacitor, and In the above secondary circuit, In a method of operation of a bidirectional DC / DC converter in which the fifth switch and the seventh switch are connected in series, the sixth switch and the sixth switch are also connected in series, the fifth switch and the seventh switch, the sixth switch and the eighth switch and the third capacitor are connected in parallel, the node between the fifth switch and the seventh switch is connected to the second resonant inductor, and the node between the sixth switch and the eighth switch is connected to the second resonant capacitor, the When the mode is changed from the above secondary circuit to supplying power to the above primary circuit, A step of setting the 6th switch to off and the 8th switch to on; A step of setting a first switching frequency according to the magnitude of the power supplied from the secondary circuit to the primary circuit; and The above-mentioned fifth switch and the above-mentioned seventh switch include a step of turning on / off according to the above-mentioned first switching frequency, and A method of operation of a bidirectional DC / DC converter in which the fifth switch and the seventh switch are alternately turned on or off.

10. In Paragraph 9, When the mode is changed from the above primary circuit to supplying power to the above secondary circuit, A step of setting a second switching frequency according to the magnitude of the power supplied from the primary circuit to the secondary circuit; and A method of operating a bidirectional DC / DC converter, further comprising the step of turning on / off the fifth to eighth switches according to the set second switching frequency.

11. In Paragraph 10, A method of operation of a bidirectional DC / DC converter in which the second switching frequency set above is the same as the first switching frequency set above.

12. In Paragraph 10, A method of operation of a bidirectional DC / DC converter in which the second switching frequency set above is the same as the first switching frequency set above.

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