Power Conversion Equipment

Abstract

A bidirectional power conversion device according to one embodiment of the present invention includes a first switching unit including a plurality of switches connected to a first input / output terminal, a transformer having one side connected to the first switching unit, a second switching unit including a plurality of switches connected to the other side of the transformer, and a third switching unit connected to the other side of the transformer and a second input / output terminal, wherein the third switching unit includes a first switch having one end connected to the second input / output terminal and a first diode connected to the other end of the first switch.

Description

[Technical field]

[0001] The present invention relates to a power converter, and more particularly to a bidirectional power converter capable of being precharged. [Background technology]

[0002] A DC-DC converter is used to convert the battery power into a power supply suitable for the load. At this time, a bidirectional DC-DC converter can be used to enable both charging and discharging of the battery.

[0003] A bidirectional DC-DC converter is placed between the battery and the load and can operate in buck mode, which drops the voltage from the high voltage side to the low voltage side, or in boost mode, which increases the voltage from the low voltage side to the high voltage side. Summary of the Invention [Problem to be solved by the invention]

[0004] The technical problem to be solved by the present invention is to provide a bidirectional power conversion device capable of being precharged. [Means for solving the problem]

[0005] In order to solve the above technical problems, a bidirectional power conversion device according to one embodiment of the present invention includes a first switching unit including a plurality of switches connected to a first input / output terminal, a transformer having one side connected to the first switching unit, a second switching unit including a plurality of switches connected to the other side of the transformer, and a third switching unit connected to the other side of the transformer and a second input / output terminal, wherein the third switching unit includes a first switch having one end connected to the second input / output terminal, and a first diode connected to the other end of the first switch.

[0006] Furthermore, when a second power source is connected to the second input / output terminal, the first switch may operate in any one of a PWM operation mode, an on mode, and an off mode.

[0007] In addition, in a precharge mode including a first capacitor connected in parallel to the first input / output terminal and a second power source connected to the second input / output terminal to charge the first capacitor, the first switch may operate in any one of a PWM operation mode, an on mode, and an off mode depending on a first voltage which is a voltage of the first capacitor.

[0008] In addition, the first switch may operate in the PWM mode at the beginning of the precharge mode or when the first voltage is lower than a first reference voltage, operate in the on mode when the first voltage is equal to or greater than the first reference voltage and lower than a second reference voltage, and operate in the off mode when the first voltage is the second reference voltage.

[0009] The power supply may also include a first inductor connected between the transformer and the first switch, a current measuring unit that measures a first current flowing through the first inductor, and a control unit that controls the second switching unit and the first switch using the measured first current.

[0010] Furthermore, in the PWM mode, the control unit can PWM-control the second switching unit and the first switch so that the first current becomes a first reference current.

[0011] Furthermore, in the on mode, the control unit can maintain the first switch in an on state and perform PWM control on the second switching unit so that the first current becomes a second reference current.

[0012] Furthermore, in the off mode, the control unit can turn off the first switch.

[0013] Furthermore, before turning off the first switch in the off mode, the control unit may PWM control the second switching unit so that the first current becomes a third reference current.

[0014] In addition, the first switch may maintain an on state when a first power source is connected to the first input / output terminal and a load is connected to the second input / output terminal.

[0015] In addition, the first diode may have a cathode connected to the other end of the first switch and an anode connected to ground.

[0016] Also, a voltage of a first power source connected to the first input / output terminal may be higher than a voltage of a second power source connected to the second input / output terminal.

[0017] A vehicle battery system according to an embodiment of the present invention may include any one of the bidirectional power conversion devices. Effect of the Invention

[0018] According to the embodiment of the present invention, it is possible to control the LV inductor current in average current mode during boost mode pre-charge operation with only a simple circuit, and it is also possible to limit the inrush current and easily realize various functions by using the PWM operation method. [Brief description of the drawings]

[0019] [Figure 1] 1 is a block diagram of a bidirectional power converter according to an embodiment of the present invention; [Diagram 2] 1 is a block diagram of a bidirectional power converter according to an embodiment of the present invention; [Diagram 3] 1 is a circuit diagram of a bidirectional power converter according to an embodiment of the present invention. [Figure 4-10] 1 is a diagram for explaining a bidirectional power converter according to an embodiment of the present invention; [Figure 11] 1 is a block diagram of a vehicle battery system according to an embodiment of the present invention. [Figure 12-13] 2 is a flow diagram of a power conversion method according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0021] However, the technical concept of the present invention is not limited to the embodiments described, but can be implemented in various different forms, and one or more of the components of the embodiments can be selectively combined or substituted within the scope of the technical concept of the present invention.

[0022] Furthermore, terms (including technical and scientific terms) used in the embodiments of the present invention may be interpreted in the sense that they are commonly understood by a person having ordinary knowledge in the technical field to which the present invention belongs, unless otherwise clearly and specifically defined, and commonly used terms, such as terms defined in a dictionary, may be interpreted in the context of the relevant art.

[0023] Furthermore, the terms used in the embodiments of the present invention are intended to explain the embodiments and are not intended to limit the present invention.

[0024] In this specification, the singular form can include the plural form unless otherwise specified in the text, and when it is described as "A and (and) at least one (or more) of B and C," it can include one or more of all combinations of A, B, and C.

[0025] In addition, in describing components of the embodiments of the present invention, terms such as first, second, A, B, (a), (b), etc. are used to distinguish the components from other components, and the terms are not intended to limit the essence, order, or sequence of the components.

[0026] Furthermore, when a component is described as being "coupled," "coupled," or "connected" to another component, this includes not only cases where the component is directly "coupled," "coupled," or "connected" to the other component, but also cases where the component is "coupled," "coupled," or "connected" by another component between the component and the other component.

[0027] In addition, when described as being formed or disposed "above" or "below" each component, "above" or "below" includes not only the case where two components are in direct contact with each other, but also the case where one or more other components are formed or disposed between the two components. In addition, when expressed as "above" or "below", it can include not only the upward direction based on one component, but also the downward direction.

[0028] The modified example according to the present embodiment may include some configurations of each embodiment together with some configurations of other embodiments. That is, the modified example may include one embodiment of various embodiments, but some configurations may be omitted and some configurations of the corresponding other embodiment may be included. Or vice versa. The features, structures, effects, etc. described in the embodiments are included in at least one embodiment and are not necessarily limited to one embodiment. Furthermore, the features, structures, effects, etc. exemplified in each embodiment may be combined or modified in other embodiments by a person skilled in the art to which the embodiments belong. Therefore, the contents related to such combinations and modifications should be interpreted as being included in the scope of the embodiments.

[0029] FIG. 1 is a block diagram of a bidirectional power converter according to one embodiment of the present invention, FIG. 2 is a block diagram of a bidirectional power converter according to an embodiment of the present invention, FIG. 3 is a circuit diagram of a bidirectional power converter according to an embodiment of the present invention, and FIGS. 4 to 10 are diagrams for explaining a bidirectional power converter according to an embodiment of the present invention.

[0030] A bidirectional power conversion device according to one embodiment of the present invention includes a first input / output port 110, a second input / output port 160, a first switching unit 120, a second switching unit 140, a third switching unit 150, and a transformer 130, and may include a first capacitor 170, a first inductor 180, a control unit 190, a current measuring unit (not shown), etc., and may be realized as shown in the circuit diagram of FIG.

[0031] The bidirectional power converter according to an embodiment of the present invention may receive power from the first input / output port 110, convert the power, and output the power to the second input / output port 160, or may receive power at the second input / output port 160, convert the power, and output the power to the first input / output port 110. Here, the voltage of the first power source connected to the first input / output port 110 may be higher than the voltage of the second power source connected to the second input / output port 160. That is, the first input / output port 110 may be a high voltage side (High, HV) input / output port, and the second input / output port 160 may be a low voltage side (Low Voltage, LV) input / output port.

[0032] The first switching unit 120 includes a plurality of switches connected to the first input / output port 110. The first switching unit 120 may include a plurality of upper switches and a plurality of lower switches corresponding to the upper switches. In this case, the plurality of switches may form an H (half) bridge or an F (full) bridge. Also, the first switching unit 120 may include a pair of upper and lower diodes. Each switch of the first switching unit 120 may be a MOSFET and may include a body diode.

[0033] One side of the transformer 130 is connected to the first switching unit 120. The first switching unit 120 may be connected to a primary side of the transformer 130. The first switching unit 120 includes a first upper switch, a first lower switch, a second upper switch, a second lower switch, an upper diode, and a lower diode, and a node between the first upper switch and the first lower switch may be connected to one end of the primary side of the transformer 130, and a node between the second upper switch and the second lower switch may be connected to the other end of the primary side of the transformer 130. In this case, an inductor is connected between a node between the first upper switch and the first lower switch and one end of the primary side of the transformer 130, and a node between the upper diode and the lower diode may be connected to one end of the primary side of the transformer.

[0034] The second switching unit 140 includes a plurality of switches connected to the other side of the transformer 130. The first switching unit 120 may include a plurality of switches connected in parallel to each other. For example, two switches may be connected in parallel. Each switch of the first switching unit 120 may be a MOSFET and may include a body diode.

[0035] The second switching unit 140 may include two switches each connected to the secondary side of the transformer. The primary side of the transformer 130 may be composed of one coil, and the secondary side may be composed of two coils, and the two secondary coils may be connected to each switch of the second switching unit 140. In this case, one switch of the second switching unit 140 may have one end connected to one end of one of the secondary coils of the transformer 130 and the other end connected to the ground, and the other switch of the second switching unit 140 may have one end connected to the ground and the other end connected to the other end of one of the secondary coils of the transformer 130. That is, the polarities of the transformers connected to each switch of the second switching unit 140 may be opposite to each other.

[0036] The third switching unit 150 is connected to the other end of the transformer 130 and the second input / output port 160. The third switching unit 150 is disposed between the transformer 130 and the second input / output port 160. Here, the third switching unit 150 includes a first switch 151 connected in series to the second input / output port 160 and a first diode 152 connected to the other end of the first switch 151. The first switch 151 may be a MOSFET and may include a body diode. The first diode 152 may have a cathode connected to the other end of the first switch 151 and an anode connected to ground.

[0037] When power is applied to the first input / output port 110, which is the primary side, the transformer 130 converts the power to a preset transformation ratio and outputs the power to the second input / output port 160, which is the secondary side. When power is applied to the second input / output port 160, which is the secondary side, the transformer 130 converts the power to a preset transformation ratio and outputs the power to the first input / output port 110, which is the primary side. Here, the transformer 130 may be, but is not limited to, an isolated transformer.

[0038] Input and output inductors may be respectively connected to the primary and secondary sides of the transformer 130. The primary inductor may be connected between a node between the first upper switch and the first lower switch and one end of the primary side of the transformer, and the first inductor 180, which is a secondary inductor, may be connected between a node between the two coils and the first switch 151.

[0039] The first input / output port 110 and the second input / output port 160 may include input / output capacitors connected in parallel, respectively. A signal can be stably input / output through the input / output capacitors. A first capacitor 170 may be connected in parallel to the first switching unit 120 to the first input / output port 110. A capacitor connected in parallel to the first switch 151 may also be connected to the second input / output port 160.

[0040] A battery may be connected to the first input / output terminal 110, and a vehicle load may be connected to the second input / output terminal 160. Here, the battery voltage may be a high voltage of 400V or 800V, and the rated voltage of the load inside the vehicle may be a low voltage of 12V. The high voltage of the battery may be reduced to match the rated voltage of the load inside the vehicle and output. Conversely, in order to charge the battery, the power source applied to the second input / output terminal 160 may be boosted to charge the battery. Alternatively, before connecting the battery to the first input / output terminal 110, a pre-charge may be performed to charge the first capacitor 170 to the voltage of the battery, thereby improving safety when connecting the battery.

[0041] In this way, when stepping down or stepping up the voltage in both directions, the first switch 151 can operate to suit each situation.

[0042] When the first power source is connected to the first input / output terminal 110 and the load is connected to the second input / output terminal 160, the first switch 151 maintains an on state. When the first power source such as a battery is connected to the first input / output terminal 110 as the high voltage side and the load is connected to the second input / output terminal 160 as the low voltage side, the bidirectional power converter according to the embodiment of the present invention operates as a buck converter. The power source applied to the first input / output terminal 110 is output to the second input / output terminal 160 through the first switching unit 120, the transformer 130, and the second switching unit 140, and at this time, the first switch 151 of the third switching unit 150 maintains an on state to transfer the output output from the transformer 130 to the second input / output terminal 160 through the rectification of the second switching unit 140. When the first switch 151 maintains an on state, the voltage of the cathode terminal is higher than the anode terminal of the first diode 152, so that the first diode 152 is turned off. That is, during the buck operation, the third switching unit 150 does not seem to exist, and power conversion is performed in the same manner as in the existing phase-shifted full bridge (PSFB).

[0043] When a second power source is connected to the second input / output terminal 160, the first switch 151 operates in any one of a PWM operation mode, an on mode, and an off mode. When a first power source is connected to the second input / output terminal 160 as a low voltage side and a load is connected to the first input / output terminal 110 as a high voltage side, the bidirectional power conversion device according to an embodiment of the present invention can operate as a boost converter or an H-bridge. Here, the load may be a battery that needs to be charged. A boost operation is required to convert a low voltage to a high voltage.

[0044] As in the case of operating as a buck converter, when the first switch 151 maintains an on state, power is continuously applied from the second I / O port 160, and the second switching unit 140 operates as a boost converter. In this case, the first diode 152 is turned off, and during boost operation, the third switching unit 150 does not seem to exist, and power conversion is performed in the same manner as in an existing boost converter.

[0045] When the first switch 151 is PWM controlled, power is not continuously applied from the second I / O port 160, but is applied or cut off according to the duty. In addition, the bidirectional power converter according to the embodiment of the present invention operates as an H-bridge circuit according to the operation of the second switching unit 140. That is, it can operate like a buck-boost or flyback converter.

[0046] In addition, by using all of the PWM operation mode, on mode, and off mode that control the first switch 151, it is possible to pre-charge the first input / output terminal 110, i.e., the first capacitor 170 connected in parallel to the first input / output terminal 110, without connecting a load to the first input / output terminal 110.

[0047] If there is no control of the first switch 151, i.e., if the third switching unit 150 including the first switch 151 and the first diode 152 as shown in FIG. 4 is not included, or if the first switch 151 is always maintained in the on state to perform precharging, various problems may occur.

[0048] In order to perform precharging, all four switches (Q4 to Q7) of the primary side first switching unit 120 are turned off. At this time, all four switches include a body diode, and each operates only with its body diode. At this time, when i_Lo is applied with Q2 and Q3 all turned on, Q2 and Q3 are connected with opposite polarity to each other, so that the secondary side of the transformer 130 appears to be shorted, and i_Lo flowing through the first inductor 180 becomes large. After that, when either Q2 or Q3 is turned off, it is output from the secondary side to the primary side by the transformer, and i_p flows. i_p charges C_i, which is the first capacitor 170, through D2. After that, when Q2 and Q3 are turned on again according to the duty, the secondary side of the transformer is shorted again, and i_p becomes 0.

[0049] At this time, the transformer has a magnetizing inductance, which affects the precharge. In an ideal case where there is no magnetizing inductance, as shown in FIG. 6, it operates according to the duty, but when there is a magnetizing inductance, the duty is affected by the magnetizing inductance. When Q2 and Q3 are all on and only Q3 is turned on, i_p starts to flow. At this time, if the magnetizing inductance current i_m is built up, the voltage charged in the first capacitor 170 is applied to the magnetizing inductance, and the magnetizing inductance current i_m becomes larger due to the magnetizing inductance voltage v_m. Here, i_Lo=i_p+i_m across the transformer 130 secondary side to the primary side, but when the magnetizing inductance current i_m becomes large and becomes the same as i_Lo across the transformer 130 secondary side to the primary side, i_p=0 and i_p stops flowing. At this time, the magnetizing inductance and the first capacitor 170 resonate with i_m, and as a result, as shown in FIG. 5, v_m becomes small, and when it passes 0 (zero), the potential of the secondary transformer is reversed, so that the body diode of Q2 conducts even though Q2 is not turned on. As a result, Q2 and Q3 are all turned on, and as shown in FIG. 6, i_Lo becomes larger than the duty set to turn on all Q2 and Q3. That is, the duty becomes larger than the set value, making voltage control difficult, and there is a possibility that the voltage charged to the first capacitor 170 becomes larger than the voltage to be charged by pre-charge. At this time, if a period in which the first switch 151 is turned off is provided to prevent i_Lo from becoming excessively large, this problem can be solved.

[0050] Also, when precharging is performed using a boost converter, it can be expressed by an equivalent circuit as shown in Fig. 7, and in this case, the moment a duty is applied, an inrush current occurs in which the output side M immediately jumps up to 1. In this case, if the third switching unit 150 includes a first switch 151 and a first diode, it can operate as an H-bridge rather than a boost converter by controlling the first switch 151, and even if a duty is applied, M can be controlled from 0, thereby solving the inrush current problem.

[0051] That is, by controlling the first switch 151 to be on and off, control can be performed without inrush current at a desired duty. Thus, in a precharge mode in which a second power source is connected to the second I / O terminal 160 and the second power source is boosted to charge the first capacitor 170, the first switch 151 can operate in any one of a PWM operation mode, an on mode, and an off mode according to a first voltage, which is a voltage of the first capacitor 170. Here, the first voltage of the first capacitor 170 can be measured through a voltage measuring sensor or the like. The first switch 151 operates in the PWM mode at the beginning of the precharge mode or when the first voltage is lower than a first reference voltage, operates in the on mode when the first voltage is equal to or higher than the first reference voltage and lower than the second reference voltage, and operates in the off mode when the first voltage is the second reference voltage, thereby performing precharge.

[0052] At this time, a first current flowing through a first inductor 180 connected between the transformer 130 and the first switch 151 may be measured, and a control unit 190 may control the second switching unit and the first switch using the measured first current. The first current flowing through the first inductor 180 may be measured by a current measuring unit.

[0053] The current measurement unit can measure the current through a current measurement sensor such as a shunt resistor. The control unit 190 can perform precharging by controlling the current flowing through the first inductor 180, i.e., i_Lo, to be constant in average current control mode.

[0054] In the initial stage of the precharge mode, an inrush current may occur, and in order to prevent the inrush current from occurring until the first capacitor 170 is fully charged, the first switch 151 must be operated in an H-bridge. At this time, the first switch 151 is operated in a PWM mode, and when performing PWM control, the first current flowing through the first inductor 180 is measured as shown in FIG. 8 for average current control. The first current is compared with a reference current, and a duty is generated through PI control, which is a digital control, using the comparison result, and thus the first switch 151, Q1, and the second switching unit 140, Q2 and Q3, are PWM-controlled. When the first current is greater than the reference current, PI control is performed in a direction to reduce the first current, and when the first current is smaller than the reference current, PI control is performed in a direction to increase the first current. That is, it is possible to control in an average current mode in which the average of the first current becomes the reference current.

[0055] PWM control is performed until no inrush current occurs, that is, until M in Fig. 7 becomes a sufficient value. When the first voltage of the first capacitor is lower than the first reference voltage, the control unit 190 PWM controls the second switching unit 140 and the first switch 151 so that the first current becomes the first reference current. At this time, as shown in Fig. 9, Q1 which is the first switch 151 is turned on and off, and Q2 and Q3 can be controlled to be turned off alternately like Q1.

[0056] For example, as shown in Fig. 10, from the beginning of the precharge mode until the first voltage becomes 400V, the control is performed in PWM mode (Mode-1), but in order to minimize ripple and voltage ring, the first current can be controlled to 50A. At this time, I_ref, which is a reference current compared with the first current, is set to 50A, and Q1 to Q3 can be PWM controlled so that the first current becomes 50A.

[0057] When the first capacitor 170 is sufficiently charged so that no inrush current occurs, the inrush current is not an issue, and the first switch 151, Q1, is kept on to operate as a boost converter, quickly charging the first capacitor 170. In this case, the first current of the first inductor 180 is controlled to be constant, thereby preventing errors due to magnetizing inductance.

[0058] For example, as shown in Figure 10, when the first voltage becomes 400V, Q1 is kept on and controlled to the on mode (Mode-2) to perform boost operation, but the first current can be controlled to 250A to minimize ripple and voltage ring. At this time, 400V keeps Q1 on, but the reference current I_ref is set to 250A and Q2 and Q3 are PWM controlled so that the first current becomes 250A. As shown in Figure 9, PWM control can be performed by keeping Q1 on and turning both Q2 and Q3 on, and turning one of the two off.

[0059] When the first capacitor 170 is fully charged to the voltage to be precharged through charging in boost mode, the first switch 151, Q1, is turned off to control the off mode (Mode-3) so that the first capacitor 170 is not further charged. At this time, before turning off the first switch 151, the reference current I_ref is first reduced to the third reference current to PWM control Q2 and Q3 to minimize ringing, and then Q1 is turned off. This can improve reliability and safety.

[0060] It can also be used to check whether the voltage of the bus line of the first input / output terminal 110, which is a high voltage, is normal. That is, the bus line can be checked after controlling the first switch 151 and the second switching unit 140 in PWM mode. For example, the first current is controlled to 40A, and when the first voltage reaches 50V, the first switch 151 is turned off. At this time, it can be confirmed that the charging time is about 40 ms. As a result, it can be checked whether the bus line is being charged properly or the voltage is being maintained.

[0061] Also, after the bus-test, precharging can be performed after a certain waiting time. In this case, it can be confirmed that it takes about 600 ms in total, including the bus-test (40 ms) and waiting time (100 ms).

[0062] Fig. 12 is a block diagram of a vehicle battery system according to an embodiment of the present invention. A detailed description of the bidirectional power converter 210 corresponds to the detailed description of the bidirectional power converter in Figs. 1 to 11, so that the overlapping description will be omitted below. The vehicle battery system includes a battery 220 and a bidirectional power converter 210 which converts the power of the battery 220 and outputs it to a load 230, or is connected to a power source 230 and converts it to a power source for charging the battery 220 and outputs it to the battery 220. The bidirectional power converter 210 can perform pre-charging to charge the battery connection end when the battery 220 is not connected.

[0063] 12 and 13 are flow charts of a power conversion method according to an embodiment of the present invention. Detailed explanations of each step in Fig. 12 and Fig. 13 correspond to the detailed explanations of the bidirectional power converter in Figs. 1 to 11, so that duplicated explanations will be omitted below.

[0064] In a bidirectional power converter including a first switch and a first diode on a low-voltage side, in order to precharge a voltage of a high-voltage side first capacitor to match a battery voltage before connecting a battery to a high-voltage side, a first switching unit and a first switch are PWM-controlled so that a first current of a first inductor becomes a first reference current at the beginning of a pre-charge mode or until a first voltage of the first capacitor becomes a first reference voltage in step S11, where the first inductor is an inductor connected between the first switch and the low-voltage side switching unit.

[0065] When the first voltage becomes the first reference voltage, in step S12, the first switch is maintained in the on state until the first voltage becomes the second reference voltage, and the first switching unit is PWM-controlled so that the first current becomes the second reference current.

[0066] When the first voltage becomes the second reference voltage, the first switch is turned off in step S13. The first switch is turned off so that the first voltage is maintained at the second reference voltage. Then, the battery can be connected to the high-voltage side input / output terminal.

[0067] When the first voltage becomes the second reference voltage in step S13, the first switching unit can be PWM-controlled so that the first current becomes the third reference current in step S21 before turning off the first switch, thereby improving reliability and safety.

[0068] Meanwhile, the embodiments of the present invention may be realized as computer readable codes on a computer readable recording medium. The computer readable recording medium includes all kinds of recording devices in which data readable by a computer system is stored.

[0069] Examples of computer readable recording media include ROM, RAM, CD-ROM, magnetic tape, floppy disk, optical data storage device, etc. Also, the computer readable recording media can be distributed in computer systems connected to a network, and computer readable code can be stored and executed in a distributed manner. And, functional programs, codes and code segments for implementing the present invention can be easily construed by a programmer skilled in the art to which the present invention pertains.

[0070] Those skilled in the art in the art related to this embodiment will understand that the present invention can be implemented in modified forms without departing from the essential characteristics of the substrate described above. Therefore, the disclosed method should be considered from an explanatory perspective, not a limiting perspective. The scope of the present invention is shown in the claims, not the above description, and all differences within the equivalent range should be interpreted as being included in the present invention.

Claims

1. a first switching unit including a plurality of switches connected to the first input / output terminal; a transformer connected to the first switching unit at one side; a second switching unit including a plurality of switches connected to the other side of the transformer; a third switching unit connected to the other side of the transformer and the second input / output terminal; The third switching unit a first switch having one end connected to the second input / output port; a first diode connected to the other end of the first switch, The first switch is When a second power source is connected to the second input / output terminal, the power conversion device operates in one of a PWM operation mode, an on mode, and an off mode.

2. a first capacitor connected in parallel to the first input / output terminal; 2. The power conversion device of claim 1, wherein in a precharge mode in which the second power source is connected to the second input / output terminal to charge the first capacitor, the first switch operates in one of a PWM operation mode, an on mode, and an off mode in response to a first voltage that is a voltage of the first capacitor.

3. The first switch is At the beginning of the precharge mode or when the first voltage is lower than a first reference voltage, the PWM operation mode is operated; When the first voltage is equal to or greater than the first reference voltage and is smaller than the second reference voltage, the device operates in the on mode; The power conversion device according to claim 2 , wherein the power conversion device operates in the off mode if the first voltage is the second reference voltage.

4. a first inductor connected between the transformer and the first switch; a current measuring unit that measures a first current flowing through the first inductor; The power conversion device according to claim 3 , further comprising: a control unit that controls the second switching unit and the first switch by using the measured first current.

5. The control unit The power conversion device according to claim 4 , wherein in the PWM operation mode, the second switching unit and the first switch are PWM controlled so that the first current becomes a first reference current.

6. The control unit The power conversion device according to claim 4 , wherein in the on mode, the first switch is maintained in an on state, and the second switching unit is PWM-controlled so that the first current becomes a second reference current.

7. The control unit The power conversion device according to claim 4 , wherein the first switch is turned off in the off mode.

8. The control unit The power conversion device according to claim 7 , wherein before turning off the first switch in the off mode, the second switching unit is PWM-controlled so that the first current becomes a third reference current.

9. The first switch is The power conversion device according to claim 1 , wherein the power conversion device maintains an on state when a first power source is connected to the first input / output terminal and a load is connected to the second input / output terminal.

10. The first diode is The power conversion device according to any one of claims 1 to 8, wherein the other end of the first switch is connected to a cathode and the first switch is connected to a ground and an anode.

11. The power conversion device according to any one of claims 1 to 8, wherein a voltage of a first power source connected to the first input / output terminal is higher than a voltage of a second power source connected to the second input / output terminal.

12. Battery and a power converter that converts the power of the battery and outputs it to a load, or converts the power of a power supply and outputs it to the battery; The power conversion unit a first switching unit including a plurality of switches connected to a first input / output terminal connected to the battery; a transformer connected to the first switching unit at one side; a second switching unit including a plurality of switches connected to the other side of the transformer; a third switching unit connected to the other side of the transformer and the second input / output terminal; The third switching unit a first switch having one end connected to the second input / output port; a first diode connected to the other end of the first switch, The first switch is The battery system operates in one of a PWM operation mode, an on mode, and an off mode when the power supply unit is connected to the second input / output terminal.

13. The power conversion unit a first capacitor connected in parallel to the first input / output terminal; 13. The battery system of claim 12, wherein in a precharge mode in which the power source is connected to the second input / output terminal to charge the first capacitor, the first switch operates in one of a PWM operation mode, an on mode, and an off mode in response to a first voltage that is a voltage of the first capacitor.

14. The first switch is At the beginning of the precharge mode or when the first voltage is lower than a first reference voltage, the PWM operation mode is operated; When the first voltage is equal to or greater than the first reference voltage and is smaller than the second reference voltage, the device operates in the on mode; The battery system of claim 13 , wherein the battery system operates in the off mode when the first voltage is the second reference voltage.

15. The power conversion unit a first inductor connected between the transformer and the first switch; a current measuring unit that measures a first current flowing through the first inductor; The battery system of claim 14 , further comprising: a control unit that controls the second switching unit and the first switch using the measured first current.

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