Power conversion device and power conversion system

Abstract

To obtain a power converter capable of performing precharge operation with a simple configuration.SOLUTION: A power converter comprises: a first power terminal; a switching unit including a first switching element provided on a path connecting a first power node with a first node, a second switching element provided on a path connecting the first node with a second power node, a third switching element provided on a path connecting the first power node with a second node, and a fourth switching element provided on a path connecting the second node with the second power node; a transformer having a first winding connected to the switching unit and a second winding; a rectification unit; a second power terminal; and a control unit. The control unit controls operation of the switching unit and the rectification unit so that power is supplied from the second power terminal to the first power terminal in a predetermined period differing from a period in which power is supplied from the first power terminal to the second power terminal.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a power conversion device and a power conversion system for converting electric power. [Background technology]

[0002] A power conversion device that converts the power of a primary battery and supplies it to a secondary battery has a so-called Precharge For example, Patent Document 1 discloses a technique for detecting the current value of a choke coil on the secondary side during this precharge operation, and controlling the operation of a switching element on the secondary side based on the detection result. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2017-034862 Summary of the Invention [Problem to be solved by the invention]

[0004] Generally, a simple configuration is desired for a power conversion device, and a simple configuration with few additional components is also desired for a power conversion device that performs a precharge operation.

[0005] It is desirable to provide a power conversion device and a power conversion system that can perform a precharge operation with a simple configuration that has few additional components. [Means for solving the problem]

[0006] According to one embodiment of the present invention 1st The power conversion device includes a first power terminal, a switching unit, a transformer, and a rectifier unit. A smooth portion;The inverter includes a second power terminal and a control unit. The first power terminal has a first connection terminal and a second connection terminal. The switching unit has a first switching element provided in a path connecting a first power node connected to the first connection terminal and the first node, a second switching element provided in a path connecting the first node and a second power node connected to the second connection terminal, a third switching element provided in a path connecting the first power node and the second node, and a fourth switching element provided in a path connecting the second node and the second power node. The transformer has a first winding having a first terminal connected to the first node and a second terminal connected to the second node, and a second winding. The rectifier unit is connected to the second winding and has a plurality of switching elements. The smoothing section is connected to the rectifying section and includes a choke coil. The second power terminal is smooth The control unit is configured to control the operation of the first switching element, the second switching element, the third switching element, the fourth switching element, and the plurality of switching elements. The control unit controls the operation of the first switching element, the second switching element, the third switching element, the fourth switching element, and the plurality of switching elements. The period before The power supply is configured to control the operation of the switching unit and the rectifier unit so as to supply power from the second power terminal to the first power terminal during a predetermined period. The control unit operates the switching unit at a first duty ratio and the rectifier unit at a second duty ratio during the predetermined period. The first duty ratio is greater than 0 and equal to or less than the second duty ratio. The second power terminal has a third connection terminal and a fourth connection terminal. The second winding has a first terminal connected to a fourth node and a second terminal connected to a fifth node. The multiple switching elements of the rectifier unit include a fifth switching element provided in a path connecting a third power node led to the third connection terminal and the fourth node, a sixth switching element provided in a path connecting the fourth node and the fourth power node led to the fourth connection terminal, a seventh switching element provided in a path connecting the third power node and the fifth node, and an eighth switching element provided in a path connecting the fifth node and the fourth power node. The control unit repeatedly performs the first control, second control, third control, fourth control, fifth control, and sixth control in this order during a predetermined period. In the first control, the control unit turns on the third switching element, the fifth switching element, and the eighth switching element, and turns off the first switching element, the second switching element, the fourth switching element, the sixth switching element, and the seventh switching element. In the second control, the control unit turns on the fifth switching element and the eighth switching element, and turns off the first switching element, the second switching element, the third switching element, the fourth switching element, the sixth switching element, and the seventh switching element. In the third control, the control unit turns off the first switching element, the second switching element, the third switching element, the fourth switching element, the fifth switching element, the sixth switching element, the seventh switching element, and the eighth switching element. In the fourth control, the control unit turns on the fourth switching element, the sixth switching element, and the seventh switching element, and turns off the first switching element, the second switching element, the third switching element, the fifth switching element, and the eighth switching element.In the fifth control, the control unit turns on the sixth switching element and the seventh switching element, and turns off the first switching element, the second switching element, the third switching element, the fourth switching element, the fifth switching element, the sixth switching element, the seventh switching element, and the eighth switching element. In the sixth control, the control unit turns off the first switching element, the second switching element, the third switching element, the fourth switching element, the fifth switching element, the sixth switching element, the seventh switching element, and the eighth switching element. A second power conversion device according to one embodiment of the present invention includes a first power terminal, a switching unit, a transformer, a rectifier, a smoothing unit, a second power terminal, and a control unit. The first power terminal is configured to have a first connection terminal and a second connection terminal. The switching unit is configured to have a first switching element provided in a path connecting a first power node connected to the first connection terminal and the first node, a second switching element provided in a path connecting the first node and a second power node connected to the second connection terminal, a third switching element provided in a path connecting the first power node and the second node, and a fourth switching element provided in a path connecting the second node and the second power node. The transformer is configured to have a first winding having a first terminal connected to the first node and a second terminal connected to the second node, and a second winding. The rectifier is connected to the second winding and is configured to have a plurality of switching elements. The smoothing unit is connected to the rectifier unit and has a choke coil. The second power terminal is configured to be connected to the smoothing unit. The control unit is configured to control the operation of the first switching element, the second switching element, the third switching element, the fourth switching element, and the plurality of switching elements. The control unit is configured to control the operation of the switching unit and the rectifier unit to supply power from the second power terminal to the first power terminal during a predetermined period that is a period before the period during which power is supplied from the first power terminal to the second power terminal. During the predetermined period, the control unit operates the switching unit with a first duty ratio and the rectifier unit with a second duty ratio. The first duty ratio is greater than 0 and less than or equal to the second duty ratio. The second power terminal has a third connection terminal and a fourth connection terminal. The transformer further has a third winding. The second winding has a first terminal connected to a third power node connected to the third connection terminal and a second terminal connected to a sixth node. A third winding has a first terminal connected to the third power node and a second terminal connected to the seventh node.The multiple switching elements of the rectifier unit include a ninth switching element provided on a path connecting the sixth node and a fourth power node led to the fourth connection terminal, and a tenth switching element provided on a path connecting the seventh node and the fourth power node. The control unit repeatedly performs first control, second control, third control, fourth control, fifth control, and sixth control in this order during a predetermined period. In the first control, the control unit turns the third switching element and the ninth switching element on and turns the first switching element, second switching element, fourth switching element, and tenth switching element off. In the second control, the control unit turns the ninth switching element on and turns the first switching element, second switching element, third switching element, fourth switching element, and tenth switching element off. In the third control, the control unit turns off the first switching element, the second switching element, the third switching element, the fourth switching element, the ninth switching element, and the tenth switching element. In the fourth control, the control unit turns on the fourth switching element and the tenth switching element, and turns off the first switching element, the second switching element, the third switching element, and the ninth switching element. In the fifth control, the control unit turns on the tenth switching element, and turns off the first switching element, the second switching element, the third switching element, the fourth switching element, the ninth switching element, and the tenth switching element. In the sixth control, the control unit turns off the first switching element, the second switching element, the third switching element, the fourth switching element, the ninth switching element, and the tenth switching element.

[0007] According to one embodiment of the present invention 1stThe power conversion system includes a first battery, a capacitor, a first switch, a second switch, a power conversion device, and a second battery. The first battery is configured to have a first terminal and a second terminal. The capacitor is configured to have a first terminal and a second terminal. The first switch is provided in a path connecting the first terminal of the first battery and the first terminal of the capacitor. The second switch is provided in a path connecting the second terminal of the first battery and the second terminal of the capacitor. The power conversion device includes a first power terminal, a switching unit, a transformer, a rectifying unit, and A smooth portion; The inverter includes a second power terminal and a control unit. The first power terminal has a first connection terminal connected to a first terminal of the capacitor and a second connection terminal connected to a second terminal of the capacitor. The switching unit includes a first switching element provided in a path connecting a first power node connected to the first connection terminal and the first node, a second switching element provided in a path connecting the first node and a second power node connected to the second connection terminal, a third switching element provided in a path connecting the first power node and the second node, and a fourth switching element provided in a path connecting the second node and the second power node. The transformer includes a first winding having a first terminal connected to the first node and a second terminal connected to the second node, and a second winding. The rectifier unit is connected to the second winding and includes multiple switching elements. The smoothing section is connected to the rectifying section and includes a choke coil. The second power terminal is smooth The control unit is configured to control the operation of the first switching element, the second switching element, the third switching element, the fourth switching element, and the plurality of switching elements. The control unit controls the operation of the first switching element, the second switching element, the third switching element, the fourth switching element, and the plurality of switching elements. The period beforeThe power supply is configured to control the operation of the switching unit and the rectifier unit so as to supply power from the second power terminal to the first power terminal during a predetermined period. The control unit operates the switching unit at a first duty ratio and the rectifier unit at a second duty ratio during the predetermined period. The first duty ratio is greater than 0 and equal to or less than the second duty ratio. The second power terminal has a third connection terminal and a fourth connection terminal. The second winding has a first terminal connected to a fourth node and a second terminal connected to a fifth node. The multiple switching elements of the rectifier unit include a fifth switching element provided in a path connecting a third power node led to the third connection terminal and the fourth node, a sixth switching element provided in a path connecting the fourth node and the fourth power node led to the fourth connection terminal, a seventh switching element provided in a path connecting the third power node and the fifth node, and an eighth switching element provided in a path connecting the fifth node and the fourth power node. The control unit repeatedly performs the first control, second control, third control, fourth control, fifth control, and sixth control in this order during a predetermined period. In the first control, the control unit turns on the third switching element, the fifth switching element, and the eighth switching element, and turns off the first switching element, the second switching element, the fourth switching element, the sixth switching element, and the seventh switching element. In the second control, the control unit turns on the fifth switching element and the eighth switching element, and turns off the first switching element, the second switching element, the third switching element, the fourth switching element, the sixth switching element, and the seventh switching element. In the third control, the control unit turns off the first switching element, the second switching element, the third switching element, the fourth switching element, the fifth switching element, the sixth switching element, the seventh switching element, and the eighth switching element. In the fourth control, the control unit turns on the fourth switching element, the sixth switching element, and the seventh switching element, and turns off the first switching element, the second switching element, the third switching element, the fifth switching element, and the eighth switching element.In the fifth control, the control unit turns on the sixth switching element and the seventh switching element, and turns off the first switching element, the second switching element, the third switching element, the fourth switching element, the fifth switching element, the sixth switching element, the seventh switching element, and the eighth switching element. In the sixth control, the control unit turns off the first switching element, the second switching element, the third switching element, the fourth switching element, the fifth switching element, the sixth switching element, the seventh switching element, and the eighth switching element. A second power conversion system according to an embodiment of the present invention includes a first battery, a capacitor, a first switch, a second switch, a power conversion device, and a second battery. The first battery is configured to have a first terminal and a second terminal. The capacitor is configured to have a first terminal and a second terminal. The first switch is provided in a path connecting the first terminal of the first battery and the first terminal of the capacitor. The second switch is provided in a path connecting the second terminal of the first battery and the second terminal of the capacitor. The power conversion device includes a first power terminal, a switching unit, a transformer, a rectifier, a smoothing unit, a second power terminal, and a control unit. The first power terminal is configured to have a first connection terminal connected to the first terminal of the capacitor and a second connection terminal connected to the second terminal of the capacitor. The switching unit is configured to have a first switching element provided in a path connecting a first power node led to the first connection terminal and the first node, a second switching element provided in a path connecting the first node and a second power node led to the second connection terminal, a third switching element provided in a path connecting the first power node and the second node, and a fourth switching element provided in a path connecting the second node and the second power node. The transformer is configured to have a first winding having a first terminal connected to the first node and a second terminal connected to the second node, and a second winding. The rectifier is connected to the second winding and is configured to have multiple switching elements. The smoothing unit is connected to the rectifier and has a choke coil. The second power terminal is configured to be led to the smoothing unit and connected to a second battery. The control unit is configured to control the operation of the first switching element, the second switching element, the third switching element, the fourth switching element, and the multiple switching elements. The control unit is configured to control the operation of the switching unit and the rectification unit so as to supply power from the second power terminal to the first power terminal during a predetermined period that is a period before a period during which power is supplied from the first power terminal to the second power terminal.The control unit operates the switching unit at a first duty ratio and the rectification unit at a second duty ratio during a predetermined period. The first duty ratio is greater than 0 and equal to or less than the second duty ratio. The second power terminal has a third connection terminal and a fourth connection terminal. The transformer further has a third winding. The second winding has a first terminal connected to a third power node connected to the third connection terminal and a second terminal connected to a sixth node. The third winding has a first terminal connected to the third power node and a second terminal connected to a seventh node. The multiple switching elements of the rectification unit include a ninth switching element provided in a path connecting the sixth node and a fourth power node connected to the fourth connection terminal, and a tenth switching element provided in a path connecting the seventh node and the fourth power node. The control unit repeatedly performs first control, second control, third control, fourth control, fifth control, and sixth control in this order during a predetermined period. In the first control, the control unit turns on the third switching element and the ninth switching element, and turns off the first switching element, the second switching element, the fourth switching element, and the tenth switching element. In the second control, the control unit turns on the ninth switching element, and turns off the first switching element, the second switching element, the third switching element, the fourth switching element, and the tenth switching element. In the third control, the control unit turns off the first switching element, the second switching element, the third switching element, the fourth switching element, the ninth switching element, and the tenth switching element. In the fourth control, the control unit turns on the fourth switching element and the tenth switching element, and turns off the first switching element, the second switching element, the third switching element, and the ninth switching element. In the fifth control, the control unit turns on the tenth switching element, and turns off the first switching element, the second switching element, the third switching element, the fourth switching element, and the ninth switching element.In the sixth control, the control unit turns off the first switching element, the second switching element, the third switching element, the fourth switching element, the ninth switching element, and the tenth switching element. [Effects of the Invention]

[0008] According to one embodiment of the present invention 1st Power Conversion Device , a second power conversion device, a first power conversion system, and Second According to the power conversion system, the precharge operation can be performed with a simple configuration that requires few additional components. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a circuit diagram illustrating an example of a configuration of a power conversion system according to an embodiment of the present invention. [Figure 2] 2 is a block diagram illustrating an example of the configuration of a control unit illustrated in FIG. 1. FIG. [Figure 3] 2 is a timing chart illustrating an example of an operation of the power conversion system shown in FIG. [Figure 4] 2 is a timing waveform diagram illustrating an example of an operation of the power conversion system shown in FIG. 1. [Figure 5] 1. FIG. 4 is another timing waveform diagram illustrating an example of an operation of the power conversion system shown in FIG. [Figure 6] 1. FIG. 4 is another timing waveform diagram illustrating an example of an operation of the power conversion system shown in FIG. [Figure 7A] 2 is an explanatory diagram illustrating one operating state of the power conversion system shown in FIG. 1. FIG. [Figure 7B] 1. FIG. 4 is an explanatory diagram illustrating another operating state of the power conversion system shown in FIG. [Figure 7C] 1. FIG. 4 is an explanatory diagram illustrating another operating state of the power conversion system shown in FIG. [Figure 7D] 1. FIG. 4 is an explanatory diagram illustrating another operating state of the power conversion system shown in FIG. [Figure 7E] 1. FIG. 4 is an explanatory diagram illustrating another operating state of the power conversion system shown in FIG. [Figure 7F] 1. FIG. 4 is an explanatory diagram illustrating another operating state of the power conversion system shown in FIG. [Figure 7G] 1. FIG. 4 is an explanatory diagram illustrating another operating state of the power conversion system shown in FIG. [Figure 8] 2 is a flowchart illustrating an example of an operation of the power conversion system shown in FIG. [Figure 9] 10 is a flowchart illustrating an example of an operation of a power conversion system according to a modified example. [Figure 10] FIG. 10 is a timing chart illustrating an example of operation of a power conversion system according to another modified example. [Figure 11] FIG. 10 is a timing waveform diagram illustrating an example of an operation of a power conversion system according to another modified example. [Figure 12] 10 is a flowchart illustrating an example of an operation of a power conversion system according to another modified example. [Figure 13] FIG. 10 is a circuit diagram illustrating a configuration example of a power conversion system according to another modified example. [Figure 14] FIG. 10 is a circuit diagram illustrating a configuration example of a power conversion system according to another modified example. [Figure 15] FIG. 10 is a circuit diagram illustrating a configuration example of a power conversion system according to another modified example. [Figure 16] 16 is a block diagram illustrating an example of the configuration of a control unit illustrated in FIG. 15. FIG. [Figure 17] FIG. 10 is a block diagram illustrating an example of the configuration of a control unit according to another modified example. [Figure 18] FIG. 10 is a block diagram illustrating an example of the configuration of a control unit according to another modified example. [Figure 19] FIG. 10 is a block diagram illustrating an example of the configuration of a control unit according to another modified example. [Figure 20] FIG. 10 is a circuit diagram illustrating a configuration example of a power conversion system according to another modified example. [Figure 21]FIG. 10 is a circuit diagram illustrating an example of a configuration of an active clamp circuit according to another modified example. [Figure 22] FIG. 10 is a circuit diagram illustrating a configuration example of a power conversion system according to another modified example. [Figure 23] 23 is a timing waveform diagram illustrating an example of an operation of the power conversion system shown in FIG. 22. FIG. [Figure 24] 23 is another timing waveform diagram illustrating an example of an operation of the power conversion system shown in FIG. 22. FIG. [Figure 25] 23 is another timing waveform diagram illustrating an example of an operation of the power conversion system shown in FIG. 22. FIG. [Figure 26A] FIG. 23 is an explanatory diagram illustrating one operating state of the power conversion system shown in FIG. 22. [Figure 26B] 23 is an explanatory diagram illustrating another operating state of the power conversion system shown in FIG. 22. FIG. [Figure 26C] 23 is an explanatory diagram illustrating another operating state of the power conversion system shown in FIG. 22. FIG. [Figure 26D] 23 is an explanatory diagram illustrating another operating state of the power conversion system shown in FIG. 22. FIG. [Figure 26E] 23 is an explanatory diagram illustrating another operating state of the power conversion system shown in FIG. 22. FIG. [Figure 26F] 23 is an explanatory diagram illustrating another operating state of the power conversion system shown in FIG. 22. FIG. [Figure 26G] 23 is an explanatory diagram illustrating another operating state of the power conversion system shown in FIG. 22. FIG. [Figure 26H] 23 is an explanatory diagram illustrating another operating state of the power conversion system shown in FIG. 22. FIG. [Figure 27] FIG. 10 is a circuit diagram illustrating a configuration example of a power conversion system according to another modified example. [Figure 28] 28 is a flowchart illustrating an example of an operation of the power conversion system shown in FIG. 27. [Figure 29] FIG. 10 is a circuit diagram illustrating a configuration example of a power conversion system according to another modified example. [Figure 30] 30 is a timing waveform diagram illustrating an example of an operation of the power conversion system shown in FIG. 29. [Figure 31A] FIG. 30 is an explanatory diagram illustrating one operating state of the power conversion system shown in FIG. 29. [Figure 31B] FIG. 30 is an explanatory diagram illustrating one operating state of the power conversion system shown in FIG. 29. [Figure 31C] FIG. 30 is an explanatory diagram illustrating one operating state of the power conversion system shown in FIG. 29. [Figure 31D] FIG. 30 is an explanatory diagram illustrating one operating state of the power conversion system shown in FIG. 29. [Figure 31E] FIG. 30 is an explanatory diagram illustrating one operating state of the power conversion system shown in FIG. 29. [Figure 32] FIG. 10 is a circuit diagram illustrating a configuration example of a power conversion system according to another modified example. [Figure 33] FIG. 10 is a circuit diagram illustrating a configuration example of a power conversion system according to another modified example. [Figure 34] FIG. 10 is a circuit diagram illustrating a configuration example of a power conversion system according to another modified example. [Figure 35] FIG. 10 is a circuit diagram illustrating a configuration example of a power conversion system according to another modified example. [Figure 36] FIG. 10 is a circuit diagram illustrating a configuration example of a power conversion system according to another modified example. [Figure 37] FIG. 10 is a circuit diagram illustrating a configuration example of a power conversion system according to another modified example. [Figure 38] FIG. 10 is a circuit diagram illustrating a configuration example of a power conversion system according to another modified example. [Figure 39] FIG. 10 is a circuit diagram illustrating a configuration example of a power conversion system according to another modified example. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0011] <Embodiment> [Configuration example] 1 shows an example of the configuration of a power conversion system 1 including a power conversion device according to an embodiment of the present invention. The power conversion system 1 includes a high-voltage battery BH, switches SW1 and SW2, a capacitor 9, a power conversion device 10, and a low-voltage battery BL. The power conversion system 1 is configured to convert power supplied from the high-voltage battery BH and supply the converted power to the low-voltage battery BL.

[0012] The high-voltage battery BH is configured to store electric power and supplies the electric power to the power conversion device 10 via the switches SW1 and SW2.

[0013] The switches SW1 and SW2 are configured to supply power stored in the high-voltage battery BH to the power conversion device 10 when they are turned on. The switches SW1 and SW2 are configured using, for example, relays. When the switch SW1 is turned on, it connects the positive terminal of the high-voltage battery BH to the terminal T11 of the power conversion device 10. When the switch SW2 is turned on, it connects the negative terminal of the high-voltage battery BH to the terminal T12 of the power conversion device 10. The switches SW1 and SW2 are turned on and off based on instructions from a system control unit (not shown).

[0014] One end of the capacitor 9 is connected to the terminal T11 of the power conversion device 10 and the switch SW1, and the other end is connected to the terminal T12 of the power conversion device 10 and the switch SW2.

[0015] The power conversion device 10 is configured to convert power by stepping down the voltage supplied from the high-voltage battery BH and supply the converted power to the low-voltage battery BL. The power conversion device 10 has terminals T11 and T12, a voltage sensor 12, a switching unit 13, a transformer 14, a rectifier 15, a smoothing unit 41, a voltage sensor 18, a control unit 19, and terminals T21 and T22. The high-voltage battery BH, switches SW1 and SW2, capacitor 9, voltage sensor 12, and switching unit 13 form a primary circuit of the power conversion system 1, and the rectifier 15, smoothing unit 41, voltage sensor 18, and low-voltage battery BL form a secondary circuit of the power conversion system 1.

[0016] When the switches SW1 and SW2 are turned on, the terminals T11 and T12 are supplied with a voltage from the high-voltage battery BH. Within the power conversion device 10, the terminal T11 is connected to the voltage line L11, and the terminal T12 is connected to the reference voltage line L12.

[0017] The voltage sensor 12 is configured to detect the voltage on the voltage line L11. One end of the voltage sensor 12 is connected to the voltage line L11, and the other end is connected to a reference voltage line L12. The voltage sensor 12 detects the voltage on the voltage line L11 relative to the voltage on the reference voltage line L12 as a voltage VH. The voltage sensor 12 then supplies the detection result of the voltage VH to the control unit 19.

[0018] The switching unit 13 is configured to convert a DC voltage supplied from the high-voltage battery BH into an AC voltage. The switching unit 13 is a full-bridge circuit and includes transistors S1 to S4. The transistors S1 to S4 are switching elements that perform switching operations based on gate signals GA to GD, respectively. The transistors S1 to S4 are configured using, for example, N-type field effect transistors (FETs). The transistors S1 to S4 include body diodes D1 to D4, respectively. For example, the anode of the body diode D1 is connected to the source of the transistor S1, and the cathode is connected to the drain of the transistor S1. The same is true for the body diodes D2 to D4. Note that, although an N-type field effect transistor is used in this example, any switching element may be used.

[0019] The transistor S1 is provided in a path connecting the voltage line L11 and the node N1, and is configured to connect the node N1 to the voltage line L11 when turned on. The drain of the transistor S1 is connected to the voltage line L11, the gate is supplied with a gate signal GA, and the source is connected to the node N1. The transistor S2 is provided in a path connecting the node N1 and the reference voltage line L12, and is configured to connect the node N1 to the reference voltage line L12 when turned on. The drain of the transistor S2 is connected to the node N1, the gate is supplied with a gate signal GB, and the source is connected to the reference voltage line L12. The node N1 is the connection point between the source of the transistor S1 and the drain of the transistor S2.

[0020] The transistor S3 is provided in a path connecting the voltage line L11 and the node N2, and is configured to connect the node N2 to the voltage line L11 when turned on. The drain of the transistor S3 is connected to the voltage line L11, the gate is supplied with a gate signal GC, and the source is connected to the node N2. The transistor S4 is provided in a path connecting the node N2 and the reference voltage line L12, and is configured to connect the node N2 to the reference voltage line L12 when turned on. The drain of the transistor S4 is connected to the node N2, the gate is supplied with a gate signal GD, and the source is connected to the reference voltage line L12. The node N2 is the connection point between the source of the transistor S3 and the drain of the transistor S4.

[0021] Transformer 14 is configured to insulate the primary side circuit from the secondary side circuit in terms of DC current and connect them in terms of AC current, convert the AC voltage supplied from the primary side circuit at a transformation ratio N of transformer 14, and supply the converted AC voltage to the secondary side circuit. Transformer 14 has windings 14A and 14B. One end of winding 14A is connected to node N1 in switching unit 13, and the other end is connected to node N2 in switching unit 13. One end of winding 14B is connected to node N4 (described later) in rectifier unit 15, and the other end is connected to node N5 (described later) in rectifier unit 15.

[0022] The rectifier 15 is configured to generate an output voltage by rectifying the AC voltage output from the winding 14B of the transformer 14. The rectifier 15 is a full-bridge circuit and includes transistors S5 to S8. The transistors S5 to S8 are configured to perform switching operations based on gate signals GE and GF. Like the transistors S1 to S4 of the switching unit 13, the transistors S5 to S8 are configured using, for example, N-type field effect transistors. Like the transistors S1 to S4, the transistors S5 to S8 include body diodes D5 to D8, respectively.

[0023] The transistor S5 is provided in a path connecting the voltage line L21A and the node N4, and is configured to connect the node N4 to the voltage line L21A when turned on. The drain of the transistor S5 is connected to the voltage line L21A, the gate is supplied with a gate signal GF, and the source is connected to the node N4. The transistor S6 is provided in a path connecting the node N4 and the reference voltage line L22, and is configured to connect the node N4 to the reference voltage line L22 when turned on. The drain of the transistor S6 is connected to the node N4, the gate is supplied with a gate signal GE, and the source is connected to the reference voltage line L22. The node N4 is the connection point between the source of the transistor S5 and the drain of the transistor S6.

[0024] Transistor S7 is provided in a path connecting voltage line L21A and node N5, and is configured to connect node N5 to voltage line L21A when turned on. The drain of transistor S7 is connected to voltage line L21A, a gate signal GE is supplied to its gate, and a source is connected to node N5. Transistor S8 is provided in a path connecting node N5 and reference voltage line L22, and is configured to connect node N5 to reference voltage line L22 when turned on. The drain of transistor S8 is connected to node N5, a gate signal GF is supplied to its gate, and a source is connected to reference voltage line L22. Node N5 is the connection point between the source of transistor S7 and the drain of transistor S8.

[0025] The smoothing unit 41 is configured to smooth the output voltage of the rectifying unit 15. The smoothing unit 41 has a choke inductor 16 and a capacitor 17. One end of the choke inductor 16 is connected to the voltage line L21A, and the other end is connected to the voltage line L21B. One end of the capacitor 17 is connected to the voltage line L21B, and the other end is connected to the reference voltage line L22. Note that in this example, the choke inductor 16 is provided on the voltage lines L21A and L21B, but this is not limiting and instead, the choke inductor 16 may be provided on the reference voltage line L22, for example.

[0026] The voltage sensor 18 is configured to detect the voltage on the voltage line L21B. One end of the voltage sensor 18 is connected to the voltage line L21B, and the other end is connected to the reference voltage line L22. The voltage sensor 18 detects the voltage on the voltage line L21B relative to the voltage on the reference voltage line L22 as the voltage VL. The voltage sensor 18 then supplies the detection result of the voltage VL to the control unit 19.

[0027] The control unit 19 is configured to control the operation of the power conversion device 10 by controlling the operation of the switching unit 13 and the rectification unit 15 based on the voltage VH detected by the voltage sensor 12 and the voltage VL detected by the voltage sensor 18. Specifically, the control unit 19 generates gate signals GA to GF based on the voltages VH and VL, and controls the operation of the power conversion device 10 by performing PWM (Pulse Width Modulation) control using the gate signals GA to GF.

[0028] The terminals T21 and T22 are configured to supply the voltage generated by the power conversion device 10 to the low-voltage battery BL. Within the power conversion device 10, the terminal T21 is connected to the voltage line L21B, and the terminal T22 is connected to the reference voltage line L22. Furthermore, the terminal T21 is connected to the positive terminal of the low-voltage battery BL, and the terminal T22 is connected to the negative terminal of the low-voltage battery BL.

[0029] The low-voltage battery BL is configured to store the power supplied from the power conversion device 10.

[0030] With this configuration, the power conversion system 1 performs a power conversion operation of converting the power supplied from the high-voltage battery BH and supplying the converted power to the low-voltage battery BL.

[0031] Furthermore, the power conversion system 1 also has a function of performing a so-called precharge operation, which charges the capacitor 9 during a preparation period (precharge period P1) before starting such a power conversion operation. In this precharge operation, the switches SW1 and SW2 are turned off, and the control unit 19 controls the operation of the switching unit 13 and the rectifier unit 15, so that the power conversion system 1 supplies power from the low-voltage battery BL to the capacitor 9. This allows the power conversion device 10 to suppress inrush current flowing from the high-voltage battery BH to the capacitor 9 when the switches SW1 and SW2 are turned on to perform the power conversion operation.

[0032] 2 shows an example of the configuration of the control unit 19. The control unit 19 has a precharge control unit 21, a power conversion control unit 25, and gate signal generation units 26 and 27.

[0033] The precharge control unit 21 is configured to generate, based on the voltages VH and VL, a duty ratio DP for the switching operation in the switching unit 13 and a duty ratio DS for the switching operation in the rectification unit 15 during the precharge period P1. The precharge control unit 21 includes a target value determination unit 22 and duty ratio generation units 23 and 24.

[0034] The target value determination unit 22 is configured to determine whether the voltage VH has reached the target voltage VH_target during the precharge period P1. The target value determination unit 22 then supplies the determination result to the duty ratio generation units 23 and 24.

[0035] The duty ratio generation unit 23 is configured to calculate the duty ratio DP of the switching unit 13 based on the voltage VL during the precharge period P1. Specifically, the duty ratio generation unit 23 generates the duty ratio DP such that the duty ratio DP decreases as the voltage VL increases. The duty ratio generation unit 23 can generate the duty ratio DP based on the voltage VL using, for example, an equation such as "DP = X1 / VL," where "X1" is an arbitrary constant. Alternatively, the duty ratio generation unit 23 may generate the duty ratio DP based on the voltage VL using, for example, table data indicating the relationship between the duty ratio DP and the voltage VL. The duty ratio generation unit 23 generates the duty ratio DP such that the duty ratio DP gradually increases during the precharge period P1. This allows the power conversion system 1 to reduce current stress within the circuit. Furthermore, when the target value determination unit 22 determines that the voltage VH has reached the target voltage VH_target, the duty ratio generation unit 23 determines that the precharge period P1 has ended and terminates the generation of the duty ratio DP.

[0036] The duty ratio generation unit 24 is configured to generate a duty ratio DS for the rectifier unit 15 based on the voltage VL during the precharge period P1. Specifically, the duty ratio generation unit 24 generates the duty ratio DS such that the duty ratio DS decreases as the voltage VL increases. The duty ratio generation unit 24 can generate the duty ratio DS based on the voltage VL using, for example, an equation such as "DS=X2 / VL," where "X2" is an arbitrary constant. Alternatively, the duty ratio generation unit 24 may generate the duty ratio DS based on the voltage VL using, for example, table data indicating the relationship between the duty ratio DS and the voltage VL. The duty ratio generation unit 24 generates the duty ratio DS during the precharge period P1 such that the duty ratio DS gradually increases. This allows the power conversion system 1 to reduce current stress within the circuit. Furthermore, when the target value determination unit 22 determines that the voltage VH has reached the target voltage VH_target, the duty ratio generation unit 24 determines that the precharge period P1 has ended and terminates the generation of the duty ratio DS.

[0037] When generating the duty ratios DP and DS, the duty ratio generating units 23 and 24 generate the duty ratios DP and DS so as to satisfy the following equations EQ1 and EQ2. 0 < DS ≦ 0.5 …(EQ1) 0 < DP ≦ DS …(EQ2) That is, the duty ratio DS in the rectification unit 15 is controlled to be equal to or less than 0.5. Also, the duty ratio DP in the switching unit 13 is controlled to be equal to or less than the duty ratio DS in the rectification unit 15. The duty ratio generation units 23 and 24 are configured to generate such duty ratios DP and DS.

[0038] The power conversion control unit 25 is configured to generate a duty ratio DP for the switching operation in the switching unit 13 and a duty ratio DS for the switching operation in the rectification unit 15 based on the voltages VH and VL during a period in which the power conversion operation is performed (power conversion period P2).

[0039] The gate signal generation unit 26 is configured to generate gate signals GA to GD based on the duty ratio DP generated by the duty ratio generation unit 23 and the power conversion control unit 25. Specifically, in this example, during the precharge period P1, the gate signal generation unit 26 generates gate signals GC and GD based on the duty ratio DP generated by the duty ratio generation unit 23, and maintains the gate signals GA and GB at a low level. Furthermore, during the power conversion period P2, the gate signal generation unit 26 generates the gate signals GA to GD based on the duty ratio DP generated by the power conversion control unit 25.

[0040] The gate signal generation unit 27 is configured to generate gate signals GE and GF based on data of the duty ratio DS supplied from the duty ratio generation unit 24 and the power conversion control unit 25. Specifically, in this example, the gate signal generation unit 27 generates the gate signals GE and GF in the precharge period P1 based on the duty ratio DS generated by the duty ratio generation unit 23. Furthermore, in the power conversion period P2, the gate signal generation unit 27 generates the gate signals GE and GF based on the duty ratio DS generated by the power conversion control unit 25.

[0041] Here, terminals T11 and T12 correspond to a specific example of a "first power terminal" in the present disclosure. Terminal T11 corresponds to a specific example of a "first connection terminal" in the present disclosure. Terminal T12 corresponds to a specific example of a "second connection terminal" in the present disclosure. Switching unit 13 corresponds to a specific example of a "switching unit" in the present disclosure. Voltage line L11 corresponds to a specific example of a "first power node" in the present disclosure. Reference voltage line L12 corresponds to a specific example of a "second power node" in the present disclosure. Node N1 corresponds to a specific example of a "first node" in the present disclosure. Node N2 corresponds to a specific example of a "second node" in the present disclosure. Transistor S1 corresponds to a specific example of a "first switching element" in the present disclosure. Transistor S2 corresponds to a specific example of a "second switching element" in the present disclosure. Transistor S3 corresponds to a specific example of a "third switching element" in the present disclosure. Transistor S4 corresponds to a specific example of a "fourth switching element" in the present disclosure. Transformer 14 corresponds to a specific example of a "transformer" in the present disclosure. Winding 14A corresponds to a specific example of a "first winding" in the present disclosure. Winding 14B corresponds to a specific example of a "second winding" in the present disclosure. Rectifier 15 corresponds to a specific example of a "rectifier" in the present disclosure. Voltage line L21A corresponds to a specific example of a "third power node" in the present disclosure. Reference voltage line L22 corresponds to a specific example of a "fourth power node" in the present disclosure. Node N4 corresponds to a specific example of a "fourth node" in the present disclosure. Node N5 corresponds to a specific example of a "fifth node" in the present disclosure. Transistor S5 corresponds to a specific example of a "fifth switching element" in the present disclosure. Transistor S6 corresponds to a specific example of a "sixth switching element" in the present disclosure. Transistor S7 corresponds to a specific example of a "seventh switching element" in the present disclosure. Transistor S8 corresponds to a specific example of an "eighth switching element" in the present disclosure. Terminals T21 and T22 correspond to a specific example of a "second power terminal" in the present disclosure. Terminal T21 corresponds to a specific example of a "third connection terminal" in the present disclosure. Terminal T22 corresponds to a specific example of a "fourth connection terminal" in the present disclosure.The control unit 19 corresponds to a specific example of a "control unit" in the present disclosure. The duty ratio DP corresponds to a specific example of a "first duty ratio" in the present disclosure. The duty ratio DS corresponds to a specific example of a "second duty ratio" in the present disclosure. The precharge period P1 corresponds to a specific example of a "predetermined period" in the present disclosure.

[0042] [Actions and Actions] Next, the operation and function of the power conversion system 1 of this embodiment will be described.

[0043] (Overview of overall operation) First, an overview of the overall operation of the power conversion system 1 will be described with reference to Figures 1 and 2. During the precharge period P1, the switches SW1 and SW2 are turned off, and the control unit 19 generates gate signals GC to GF based on the voltages VH and VL, while maintaining the gate signals GA and GB at a low level. This activates the switching unit 13 and rectifier 15, and the power conversion device 10 supplies power from the low-voltage battery BL to the capacitor 9. As a result, the capacitor 9 is charged, and the voltage VH increases. When the voltage VH reaches the target voltage VH_target, the precharge operation ends, the switches SW1 and SW2 are turned on, and the control unit 19 generates the gate signals GA to GF based on the voltages VH and VL. This allows the power conversion device 10 to convert the power supplied from the high-voltage battery BH and supply the converted power to the low-voltage battery BL.

[0044] (Detailed operation) 3 shows an example of a precharge operation. In this example, the precharge control unit 21 generates duty ratios DP and DS so that they gradually increase during the period from timing t1 to t2 (precharge period P1). The precharge control unit 21 generates duty ratios DP and DS so that the duty ratio DS is 0.5 or less and the duty ratio DP is equal to or less than the duty ratio DS, as shown in equations EQ1 and EQ2. The gate signal generation unit 26 then generates gate signals GC and GD based on this duty ratio DP and maintains the gate signals GA and GB at a low level. The switching unit 13 performs switching operations based on these gate signals GA to GD. The gate signal generation unit 27 generates gate signals GE and GF based on this duty ratio DS. The rectification unit 15 performs switching operations based on these gate signals GE and GF. As a result, the voltage VH across the capacitor 9 gradually increases after timing t1, when the precharge period P1 begins.

[0045] 4 shows an example of simulated waveforms of the precharge operation, where (A) shows the waveforms of gate signals GE and GF, (B) shows the waveforms of gate signals GC and GD, (C) shows the waveform of the current (charge current ICHG) flowing into capacitor 9, (D) shows the waveform of excitation current IM of transformer 14, (E) shows the waveform of the current (inductor current IL) flowing from voltage line L21B to voltage line L21A in choke inductor 16, (F) shows the waveform of the voltage (transformer voltage VTR2) at node N4 in winding 14B of transformer 14 relative to node N5, and (G) shows the waveform of voltage VH. In FIG. 4, T indicates the period of the switching operation.

[0046] In the precharge operation, the control unit 19 generates gate signals GC and GD based on a duty ratio DP, and generates gate signals GE and GF based on a duty ratio DS. The duty ratio DP indicates the pulse width of each of the gate signals GC and GD when the period T (the time length from timings t11 to t13) is set to "1," and the duty ratio DS indicates the pulse width of each of the gate signals GE and GF when the period T is set to "1." As shown in FIGS. 4A and 4B, the control unit 19 changes the gate signals GC and GF from low to high at timing t11. Then, the control unit 19 changes the gate signal GC from high to low when a time corresponding to the duty ratio DP (duty ratio DP × period T) has elapsed since timing t11, and changes the gate signal GF from high to low when a time corresponding to the duty ratio DS (duty ratio DS × period T) has elapsed since timing t11. Next, at timing t12, the control unit 19 changes the gate signals GD and GE from low to high. Then, the control unit 19 changes the gate signal GD from high to low when a time corresponding to the duty ratio DP (duty ratio DP × period T) has elapsed since timing t12, and changes the gate signal GE from high to low when a time corresponding to the duty ratio DS (duty ratio DS × period T) has elapsed since timing t12. Although not shown, the control unit 19 maintains the gate signals GA and GB at low levels. The power conversion system 1 charges the capacitor 9 by repeating the operation from timing t11 to t13 while changing the duty ratios DP and DS. As a result, the voltage VH gradually increases, as shown in FIG. 4(G).

[0047] The following will explain in detail the operation based on the gate signals GC and GF during the period from timing t11 to t12 as an example, and the same applies to the operation based on the gate signals GD and GE during the period from timing t12 to t13.

[0048] 5 and 6 show the operation in more detail during the period from timing t11 to t12, where (A) shows the waveforms of gate signals GE and GF, (B) shows the waveforms of gate signals GC and GD, (C) shows the waveform of the current (charge current ICHG) flowing into capacitor 9, (D) shows the waveform of excitation current IM of transformer 14, (E) shows the waveform of the current (inductor current IL) flowing from voltage line L21B to voltage line L21A in choke inductor 16, (F) shows the waveform of the voltage (transformer voltage VTR1) at node N1 in winding 14A of transformer 14 relative to node N2, (G) shows the waveform of the voltage (transformer voltage VTR2) at node N4 in winding 14B of transformer 14 relative to node N5, and (H) shows the waveform of voltage VH. As shown in FIG. 5, power conversion system 1 can be in seven operating states ST1 to ST7 during the period from timing t11 to t12. The operating state ST of the power conversion system 1 changes in the order of operating state ST1, operating state ST2, operating state ST3, ..., and operating state ST7. Operating states ST3 and ST4 are operating states during a short period. Fig. 6 shows an enlarged view of the operation during the period corresponding to these operating states ST3 and ST4 and the period around them.

[0049] 7A to 7G show the operation of the power conversion system 1 in seven operating states ST1 to ST7. For ease of explanation, the power conversion system 1 is depicted in a more simplified manner in FIGS.

[0050] In the operating state ST1, the control unit 19 sets the gate signals GC and GF to a high level and the gate signals GA, GB, GD, and GE to a low level (FIGS. 5A and 5B). This turns on the transistors S3, S5, and S8, and turns off the transistors S1, S2, S4, S6, and S7 (FIG. 7A). In the secondary-side circuit, a current I2 flows through the positive terminal of the low-voltage battery BL, the choke inductor 16, the on-state transistor S5, the winding 14B, the on-state transistor S8, and the negative terminal of the low-voltage battery BL, storing energy in the choke inductor 16. In the primary-side circuit, the body diode D1 of the transistor S1 turns on, and a current I1 flows through one end of the winding 14A (node ​​N1), the body diode D1 of the transistor S1, the on-state transistor S3, and the other end of the winding 14A (node ​​N2), storing energy in the leakage inductor LLK of the transformer 14. At this time, the primary circuit is almost short-circuited when viewed from the secondary circuit, so the transformer voltages VTR1 and VTR2 are almost 0 V (Fig. 5(F) and (G)).

[0051] In the next operating state ST2, the control unit 19 changes the gate signal GC from high to low (FIG. 5(B)). This causes the transistor S3 to change from on to off (FIG. 7B). In the primary circuit, the body diode D4 of the transistor S4 turns on, and current I1 flows through one end of the winding 14A (node ​​N1), the body diode D1 of the transistor S1, the capacitor 9, the body diode D4 of the transistor S4, and the other end of the winding 14A (node ​​N2) in this order, resulting in a charge current ICHG (FIG. 5(C)). In other words, the energy stored in the leakage inductor LLK of the transformer 14 is released and stored in the capacitor 9. In this way, the voltage VH rises (FIG. 5(H)). In the secondary circuit, the transformer voltage VTR2 becomes positive (FIG. 5(G)), and the excitation current IM begins to flow through the transformer 14 (FIG. 5(D)). If the voltage VH has not yet risen sufficiently and satisfies the following equation EQ3, the power conversion system 1 performs a step-down operation, and if the voltage VH has risen sufficiently and satisfies the following equation EQ4, the power conversion system 1 performs a step-up operation. VH < N × VL …(EQ3) VH ≧ N × VL …(EQ4) Here, N is the transformation ratio of the transformer 14, and can be expressed by the following equation EQ5 using the number of turns Np of the winding 14A, which is the primary winding of the transformer 14, and the number of turns Ns of the winding 14B, which is the secondary winding. N = Np / Ns …(EQ5) In this operating state ST2, when the power conversion system 1 performs a step-down operation, the inductor current IL increases with a positive slope over time, and when the power conversion system 1 performs a step-up operation, the inductor current IL decreases with a negative slope over time. In this example, the power conversion system 1 is performing a step-up operation, so the inductor current IL decreases (FIG. 5(E)).

[0052] In the next short period of operation state ST3, the control unit 19 changes the gate signal GF from high to low (FIGS. 5(A) and 6(A)). This causes the transistors S5 and S8 to change from the on state to the off state (FIG. 7C). In the secondary circuit, a back electromotive force is generated in the choke inductor 16, increasing the drain-source voltage of each of the transistors S5 to S8, and reaching the breakdown voltage of the avalanche breakdown. As a result, an avalanche current flows in each of the transistors S5 to S8, and each of the transistors S5 to S8 enters the avalanche breakdown state AVA. The energy stored in the choke inductor 16 is then released, and the inductor current IL decreases (FIGS. 5(E) and 6(E)). As a result of each of the transistors S5 to S8 entering the avalanche breakdown state AVA, the transformer voltage VTR2 becomes approximately 0 V (FIGS. 5(G) and 6(G)). In the primary circuit, continuing from the previous operating state ST2, current I1 flows through one end of winding 14A (node ​​N1), body diode D1 of transistor S1, capacitor 9, body diode D4 of transistor S4, and the other end of winding 14A (node ​​N2) in this order. The back electromotive force of leakage inductor LLK of transformer 14 appears in transformer voltage VTR1.

[0053] In the next short period, during the operating state ST4, in the primary circuit, the energy stored in the leakage inductor LLK of the transformer 14 is released, and the body diode D1 of the transistor S1 and the body diode D4 of the transistor S4 are turned off (FIG. 7D). Thus, in the primary circuit, no current flows through the switching unit 13, so the charge current ICHG becomes 0 A (FIGS. 5(C) and 6(C)). In the secondary circuit, each of the transistors S5 to S8 maintains the avalanche breakdown state AVA. The avalanche current flowing through the transistor S5 is greater than the avalanche current flowing through the transistor S6 by the excitation current I M. Similarly, the avalanche current flowing through the transistor S8 is greater than the avalanche current flowing through the transistor S7 by the excitation current I M. Therefore, the avalanche current flowing through the transistors S6 and S7 approaches 0 A more quickly than the avalanche current flowing through the transistors S5 and S8.

[0054] In the next operating state ST5, the avalanche current flowing through transistors S6 and S7 reaches 0 A, and the avalanche breakdown state AVA of transistors S6 and S7 is eliminated (FIG. 7E). Transistors S5 and S8 maintain the avalanche breakdown state AVA. This causes transformer voltages VTR1 and VTR2 to become negative (FIGS. 5(F) and 5(G)). As a result, in the primary circuit, the body diodes D2 of transistor S2 and D3 of transistor S3 turn on, and current I1 flows through the other end of winding 14A (node ​​N2), the body diode D3 of transistor S3, capacitor 9, the body diode D2 of transistor S2, and one end of winding 14A (node ​​N1) in this order, resulting in a charge current ICHG (FIG. 5(C)). In other words, the energy stored in the magnetizing inductor LM of transformer 14 is released and stored in capacitor 9. In this way, voltage VH rises (FIG. 5(H)).

[0055] In the next operating state ST6, the release of energy stored in choke inductor 16 in the secondary circuit ends, and the avalanche breakdown state AVA of transistors S5 and S8 is eliminated (FIG. 7F). As a result, no current flows through rectifier 15 in the secondary circuit. In the primary circuit, continuing from the previous operating state ST5, current I1 flows in the following order: the other end of winding 14A (node ​​N2), body diode D3 of transistor S3, capacitor 9, body diode D2 of transistor S2, and one end of winding 14A (node ​​N1). In other words, the energy stored in magnetizing inductor LM of transformer 14 is released and stored in capacitor 9. In this way, voltage VH rises (FIG. 5(H)).

[0056] In the next operating state ST7, in the primary side circuit, the release of energy stored in the magnetizing inductor LM of the transformer 14 finishes, and the body diode D2 of the transistor S2 and the body diode D3 of the transistor S3 are turned off (FIG. 7G). As a result, in the primary side circuit, no current flows through the switching unit 13. That is, in this operating state ST7, no current flows in either the primary side circuit or the secondary side circuit.

[0057] In this way, during the period from timing t11 to t12, the capacitor 9 is charged and the voltage VH rises. The same applies to the period from timing t12 to t13. Note that the above-described operation is an example. For example, when the duty ratio DS rises and approaches "0.5", for example, the operating state ST7 of the operating states ST1 to ST7 may disappear. In the power conversion system 1, as shown in FIG. 4, by repeating such an operation from timing t11 to t13, the capacitor 9 is gradually charged and the voltage VH gradually rises.

[0058] Then, as shown in FIG. 3, when the voltage VH reaches the target voltage VH_target at timing t2, the precharge control unit 21 stops generating the duty ratios DP and DS. This ends the precharge operation. Then, after the switches SW1 and SW2 are turned on, the power conversion operation starts. Note that in this example, the power conversion system 1 starts the power conversion operation immediately after the precharge operation ends at timing t2, but this is not limited to this. For example, after the precharge operation ends, the power conversion system 1 may perform a voltage maintaining operation to maintain the voltage VH at a voltage near the target voltage VH_target by generating the duty ratios DP and DS, and then perform the power conversion operation.

[0059] The precharge operation described above is controlled by the precharge control unit 21 of the control unit 19. Next, an example of the operation of the precharge control unit 21 will be described.

[0060] 8 shows an example of the operation of the precharge control unit 21. When the switches SW1 and SW2 are set to the OFF state, the precharge control unit 21 performs the following operation.

[0061] First, the duty ratio generation units 23 and 24 of the precharge control unit 21 set the sequence of duty ratios DP and DS in the precharge period P1 based on the voltage VL (step S101). Specifically, as shown in FIG. 3, the duty ratio generation unit 23 generates the duty ratio DP so that the duty ratio DP gradually increases in the precharge period P1. As shown in FIG. 3, the duty ratio generation unit 24 generates the duty ratio DS so that the duty ratio DS gradually increases in the precharge period P1. As shown in equations EQ1 and EQ2, the duty ratio generation units 23 and 24 generate the duty ratios DP and DS so that the duty ratio DS is 0.5 or less and the duty ratio DP is equal to or less than the duty ratio DS.

[0062] Next, the control unit 19 starts PWM control based on the sequence set in step S101 (step S102). Specifically, the control unit 19 generates gate signals GC to GF based on the sequence set in step S101, and maintains gate signals GA and GB at a low level. As a result, in the power conversion system 1, PWM control is performed, the capacitor 9 is gradually charged, and the voltage VH gradually increases, as shown in FIGS. 4 to 6.

[0063] Next, the target value determination unit 22 determines whether the voltage VH has reached the target voltage VH_target (step S103). If the voltage VH has not reached the target voltage VH_target ("N" in step S103), the process of step S103 is repeated until the voltage VH reaches the target voltage VH_target.

[0064] If the voltage VH reaches the target voltage VH_target ("Y" in step S103), the control unit 19 ends the PWM control (step S104).

[0065] This ends the precharge operation. After that, the switches SW1 and SW2 are turned on, and the power conversion device 10 starts a power conversion operation in which it converts the power supplied from the high-voltage battery BH and supplies the converted power to the low-voltage battery BL.

[0066] As described above, in the power conversion system 1, during the precharge period P1, which is a preparation period before supplying power from the first power terminals (terminals T11 and T12) to the second power terminals (terminals T21 and T22), the operation of the switching unit 13 and the rectifier unit 15 is controlled to supply power from the second power terminals (terminals T21 and T22) to the first power terminals (terminals T11 and T12). This allows the precharge operation to be performed with a simple configuration. That is, for example, in the technology described in Patent Document 1, the switching operation of the secondary-side circuit is controlled based on the current value of the choke coil during the precharge operation. In this case, a current sensor is required to detect the current flowing through the choke coil. On the other hand, in the power conversion system 1 according to the present embodiment, the operation of the switching unit 13 and the rectifier unit 15 is controlled during the precharge period P1. For example, the operation of the switching unit 13 and the rectifier unit 15 can be controlled so that the duty ratio DS is 0.5 or less and the duty ratio DP is equal to or less than the duty ratio DS. This allows the power conversion system 1 to omit the current sensor, thereby enabling the precharge operation to be performed with a simple configuration.

[0067] [effect] As described above, in this embodiment, during the precharge period, which is the preparation period before power is supplied from the first power terminal to the second power terminal, the operation of the switching unit and the rectification unit is controlled so that power is supplied from the second power terminal to the first power terminal, thereby enabling the precharge operation to be performed with a simple configuration.

[0068] [Variation 1] In the above embodiment, during the precharge period P1, the operations of the transistors S3 and S4 of the four transistors S1 to S4 in the switching unit 13 are controlled, but this is not limiting. Instead, for example, the operations of the transistors S1 and S2, the operations of the transistors S1 and S3, or the operations of the transistors S2 and S4 may be controlled.

[0069] [Variation 2] In the above embodiment, as shown in Fig. 8, when the precharge operation is started, the sequence of the duty ratios DP and DS in the precharge period P1 is set in advance, but this is not limited to this. The power conversion system 1 according to this modification will be described in detail below.

[0070] FIG. 9 shows an example of the operation of the precharge control unit 21 according to this modification.

[0071] First, the duty ratio generating units 23 and 24 of the precharge control unit 21 set the sequence of the duty ratios DP and DS in the precharge period P1 based on the voltage VL (step S101).

[0072] Next, the control unit 19 starts PWM control based on the sequence set in step S101 (step S102). As a result, the power conversion system 1 performs PWM control, the capacitor 9 is gradually charged, and the voltage VH gradually increases.

[0073] Next, the target value determination unit 22 determines whether the voltage VH has reached the target voltage VH_target (step S103).

[0074] If the voltage VH has not reached the target voltage VH_target ("N" in step S103), the duty ratio generation units 23 and 24 check whether the voltage VL has changed by a predetermined amount or more from the initial voltage VL in step S101 (step S113). If the voltage VL has not changed by the predetermined amount or more ("N" in step S113), the process returns to step S103.

[0075] In step S113, if the voltage VL has changed by a predetermined amount or more ("Y" in step S113), the duty ratio generation units 23 and 24 reset the sequence of the subsequent duty ratios DP and DS based on the voltage VL (step S114). Then, the control unit 19 performs PWM control based on the sequence reset in step S114 (step S115). That is, if the voltage VL has changed significantly from the initial voltage VL, the sequence of the duty ratios DP and DS set based on the initial voltage VL in step S101 may not be appropriate. Therefore, if the voltage VL has changed by a predetermined amount or more, the duty ratio generation units 23 and 24 reset the sequence of the subsequent duty ratios DP and DS based on the latest voltage VL. Then, the process returns to step S103.

[0076] In step S103, if the voltage VH reaches the target voltage VH_target ("Y" in step S103), the control unit 19 ends the PWM control (step S104), thereby ending the precharge operation.

[0077] [Variation 3] In the above embodiment, as shown in FIG. 3, during the precharge period P1, the switching unit 13 is operated based on the duty ratio DP from timing t1 when the precharge operation starts. However, this is not limited to this. Alternatively, for example, as shown in FIG. 10, the switching unit 13 may be operated based on the duty ratio DP a short time after the precharge operation starts. In this example, the precharge control unit 21 generates the duty ratio DS so that the duty ratio DS gradually increases from timing t21 to t22. Then, when the voltage VH reaches the threshold Vth, the precharge control unit 21 generates the duty ratios DP and DS so that the duty ratios DP and DS gradually increase from timing t22 to t23. As a result, the rectifier unit 15 performs a switching operation from timing t21 to t22, and the switching unit 13 and the rectifier unit 15 perform a switching operation from timing t22 to t23, as in the above embodiment (FIG. 4). The threshold Vth is set to satisfy, for example, the following equation EQ6: Vth < N × VL …(EQ6) That is, as shown in equation EQ3, the threshold value Vth is set to a voltage within the range of the voltage VH at which the power conversion system 1 performs a step-down operation in the precharge operation.

[0078] Figure 11 shows an example of simulation waveforms of operation during the period from timing t21 to t22, where (A) shows the waveform of gate signals GE and GF, (B) shows the waveform of gate signals GC and GD, (C) shows the waveform of the current (charge current ICHG) flowing into capacitor 9, (D) shows the waveform of the excitation current IM of transformer 14, (E) shows the waveform of the current (inductor current IL) flowing from voltage line L21B to voltage line L21A in choke inductor 16, (F) shows the waveform of the voltage (transformer voltage VTR2) at node N4 in winding 14B of transformer 14 with node N5 as the reference, and (G) shows the waveform of voltage VH.

[0079] As shown in FIG. 11A, the control unit 19 changes the gate signal GF from low level to high level at timing t31. Then, the control unit 19 changes the gate signal GF from high level to low level when a time corresponding to the duty ratio DS has elapsed since timing t31. Next, the control unit 19 changes the gate signal GE from low level to high level at timing t32. Then, the control unit 19 changes the gate signal GE from high level to low level when a time corresponding to the duty ratio DS has elapsed since timing t32. The control unit 19 maintains the gate signals GA to GD at low level. In the power conversion system 1, the duty ratio DS is changed during this period from timing t21 to t22, and the operation from timing t31 to t33 is repeated to charge the capacitor 9. As a result, the voltage VH gradually increases as shown in FIG. 11G.

[0080] In this example, the power conversion system 1 can be in four operating states ST11 to ST14 during the period from timing t31 to t32. The operating state ST of the power conversion system 1 changes in the order of operating state ST11, operating state ST12, operating state ST13, and operating state ST14.

[0081] In the operating state ST11, the control unit 19 sets the gate signal GF to a high level and the gate signals GA to GE to a low level (FIGS. 11(A) and 11(B)). This turns on the transistors S5 and S8, and turns off the transistors S1 to S4, S6, and S7. In the secondary circuit, a current I2 flows in the order of the positive terminal of the low-voltage battery BL, the choke inductor 16, the transistor S5 in the on state, the winding 14B, the transistor S8 in the on state, and the negative terminal of the low-voltage battery BL, and energy is stored in the choke inductor 16. In the primary circuit, an excitation current IM flows through the transformer 14 (FIG. 11(D)).

[0082] In the next operating state ST12, the control unit 19 changes the gate signal GF from high to low (FIG. 11(A)). This causes transistors S5 and S8 to change from on to off. In the secondary circuit, a back electromotive force is generated in the choke inductor 16, increasing the drain-source voltages of the transistors S5 and S8, and reaching the avalanche breakdown voltage. As a result, an avalanche current flows in each of the transistors S5 and S8, causing each of the transistors S5 and S8 to enter the avalanche breakdown state AVA. This causes the transformer voltages VTR1 and VTR2 to become negative (FIG. 11(F)). In the primary circuit, the body diode D2 of transistor S2 and the body diode D3 of transistor S3 are turned on, and current I1 flows through the other end of winding 14A (node ​​N2), the body diode D3 of transistor S3, capacitor 9, the body diode D2 of transistor S2, and one end of winding 14A (node ​​N1) in this order, resulting in a charge current ICHG (FIG. 11(C)). In this way, voltage VH rises (FIG. 11(G)).

[0083] In the next operating state ST13, the release of energy stored in choke inductor 16 ends, and the avalanche breakdown state AVA of transistors S5 and S8 is eliminated. In the primary side circuit, continuing from the previous operating state ST12, current I1 flows in the following order: the other end of winding 14A (node ​​N2), body diode D3 of transistor S3, capacitor 9, body diode D2 of transistor S2, and one end of winding 14A (node ​​N1). In other words, the energy stored in magnetizing inductor LM of transformer 14 is released and stored in capacitor 9. In this way, voltage VH rises (FIG. 11(G)).

[0084] In the next operating state ST14, in the primary circuit, the release of energy stored in the magnetizing inductor LM of the transformer 14 finishes, and the body diode D2 of the transistor S2 and the body diode D3 of the transistor S3 are turned off, so that no current flows through the switching unit 13 in the primary circuit.

[0085] In this way, during the period from timing t31 to t32, the capacitor 9 is charged and the voltage VH rises. The same applies to the period from timing t32 to t33. Note that the above-described operation is an example. For example, when the duty ratio DS rises and approaches "0.5", for example, the operating state ST14 of the operating states ST11 to ST14 may disappear. In the power conversion system 1, as shown in FIG. 11, by repeating such an operation from timing t31 to t33, the capacitor 9 is gradually charged and the voltage VH gradually rises.

[0086] Then, as shown in Fig. 10, in the period from timing t22 to t23 after voltage VH reaches threshold value Vth, power conversion system 1 operates as shown in Figs. 4 to 6. As a result, voltage VH gradually increases as shown in Fig. 4(G).

[0087] 10, when the voltage VH reaches the target voltage VH_target at timing t23, the precharge control unit 21 stops generating the duty ratios DP and DS. This ends the precharge operation. Then, after the switches SW1 and SW2 are turned on, the power conversion operation starts.

[0088] FIG. 12 shows an example of the operation of the precharge control unit 21 according to this modification.

[0089] First, the duty ratio generating section of the precharge control section 21 23,The duty ratio generation unit 24 sets the sequence of duty ratios DP and DS in the precharge period P1 based on the voltage VL (step S121). Specifically, the duty ratio generation unit 23 generates the duty ratio DP so that the duty ratio DP gradually increases in the precharge period P1. The duty ratio generation unit 24 generates the duty ratio DS so that the duty ratio DS gradually increases in the precharge period P1. The duty ratio generation units 23 and 24 generate the duty ratios DP and DS so that the duty ratio DS is 0.5 or less and the duty ratio DP is equal to or less than the duty ratio DS, as shown in equations EQ1 and EQ2.

[0090] Next, the control unit 19 starts PWM control based on the sequence of the duty ratio DS set in step S121 (step S122). Specifically, the control unit 19 generates the gate signals GE and GF based on the sequence of the duty ratio DS set in step S121, and maintains the gate signals GA to GD at a low level. As a result, in the power conversion system 1, PWM control is performed, the capacitor 9 is gradually charged, and the voltage VH gradually increases, as shown in FIG.

[0091] Next, the target value determination unit 22 determines whether the voltage VH has reached the threshold value Vth (step S123). If the voltage VH has not reached the threshold value Vth ("N" in step S123), the process of step S123 is repeated until the voltage VH reaches the threshold value Vth.

[0092] If the voltage VH reaches the threshold value Vth ("Y" in step S123), the control unit 19 performs PWM control based on the sequence of the duty ratios DP and DS set in step S121 (step S124). Specifically, the control unit 19 generates gate signals GC to GF based on the sequence of the duty ratios DP and DS set in step S121, and maintains the gate signals GA and GB at a low level. As a result, in the power conversion system 1, as shown in FIGS. 4 to 6, PWM control is performed, the capacitor 9 is gradually charged, and the voltage VH gradually increases.

[0093] Next, the target value determination unit 22 determines whether the voltage VH has reached the target voltage VH_target (step S125). If the voltage VH has not reached the target voltage VH_target ("N" in step S125), this step is repeated until the voltage VH reaches the target voltage VH_target. S125 Repeat the process.

[0094] If the voltage VH reaches the target voltage VH_target ("Y" in step S125), the control unit 19 ends the PWM control (step S126).

[0095] This completes the precharge operation.

[0096] In this example, as shown in steps S123 and S124, when voltage VH reaches threshold value Vth, control unit 19 performs PWM control based on the set duty ratio DP, but this is not limiting. For example, control unit 19 may perform PWM control based on the set duty ratio DP after a predetermined time has elapsed since the start of the precharge operation.

[0097] [Variation 4] In the above embodiment, as shown in FIG. 1, the switching unit 13 and the transformer 14 are directly connected. However, this is not limiting. Instead, for example, as in a power conversion system 1A shown in FIG. 13, a resonant inductor Lr may be provided between the switching unit 13 and the transformer 14. The power conversion system 1A includes a power conversion device 10A. The power conversion device 10A has a resonant inductor Lr. One end of the resonant inductor Lr is connected to a node N2, and the other end is connected to a node N3. The other end of the winding 14A of the transformer 14 is connected to the node N3. Here, the resonant inductor Lr corresponds to a specific example of an "inductor" in the present disclosure. Note that in this example, one end of the resonant inductor Lr is connected to the node N2 and the other end is connected to the other end of the winding 14A. However, this is not limiting. Instead, for example, one end of the resonant inductor Lr may be connected to a node N1, and the other end may be connected to one end of the winding 14A.

[0098] [Variation 5] In the above embodiment, as shown in FIG. 1, the switching unit 13 is provided on the primary side. However, for example, as in a power conversion system 1B shown in FIG. 14, a resonant inductor Lr and diodes D11 and D12 may be further provided. This power conversion system 1B includes a power conversion device 10B. The power conversion device 10B has a resonant inductor Lr and diodes D11 and D12. One end of the resonant inductor Lr is connected to node N2, and the other end is connected to node N3. The other end of the winding 14A of the transformer 14 is connected to node N3. The anode of the diode D11 is connected to node N3, and the cathode is connected to the voltage line L11. The anode of the diode D12 is connected to the reference voltage line L12, and the cathode is connected to node N3. Here, the resonant inductor Lr corresponds to a specific example of an “inductor” in the present disclosure. The diode D11 corresponds to a specific example of a “first diode” in the present disclosure. The diode D12 corresponds to a specific example of a “second diode” in the present disclosure. With this configuration, in the power conversion system 1B, when performing a power conversion operation of converting power supplied from the high-voltage battery BH and supplying the converted power to the low-voltage battery BL, the diodes D11 and D12 function as so-called clamp diodes, thereby suppressing surge voltages generated in the secondary circuit. In the precharge operation, the power conversion system 1B operates transistors S3 and S4 of the four transistors S1 to S4 in the switching unit 13, as shown in FIGS. 4 to 6. As a result, in the precharge operation, when transistor S3 is on, for example, current flows through transistor S3 rather than diode D11, and when transistor S4 is on, for example, current flows through transistor S4 rather than diode D12. This reduces the current flowing through diodes D11 and D12 during the precharge operation, eliminating the need to increase the size of diodes D11 and D12.

[0099] [Variation 6] In the above embodiment, the control unit 19 generates a sequence of duty ratios DP, DS during the precharge period P1 based on the voltage VL, and controls the operations of the switching unit 13 and the rectifier unit 15 based on the generated sequence, but this is not limited to this. Instead, for example, the operations of the switching unit 13 and the rectifier unit 15 may be controlled by performing feedback control based on the current flowing through the capacitor 9. This modification will be described in detail below with some examples.

[0100] FIG. 15 shows an example of the configuration of a power conversion system 1C according to this modification. The power conversion system 1C includes a power conversion device 10C. The power conversion device 10C includes a current sensor 11C and a control unit 19C. The current sensor 11C is configured to detect a current flowing through a terminal T11. One end of the current sensor 11C is connected to the terminal T11, and the other end is connected to a voltage line L11. The current sensor 11C detects the current flowing from the voltage line L11 to the terminal T11 as a current IH. The current sensor 11C then supplies the detection result of the current IH to the control unit 19C. The control unit 19C is configured to control the operations of the switching unit 13 and the rectifier unit 15 based on the current IH detected by the current sensor 11C, the voltage VH detected by the voltage sensor 12, and the voltage VL detected by the voltage sensor 18.

[0101] 16 shows an example of the configuration of the control unit 19C. The control unit 19C has a precharge control unit 21C. The precharge control unit 21C has an average current calculation unit 25C, a reference level generation unit 26C, an error amplifier 27C, and a duty ratio generation unit 24C.

[0102] The average current calculation unit 25C is configured to calculate the average value of the current IH detected by the current sensor 11C. The reference level generation unit 26C is configured to generate a reference level REF for the average value of the current IH. The error amplifier 27C is configured to generate an error signal Serr by amplifying the difference between the reference level REF and the average value of the current IH. The duty ratio generation unit 24C is configured to generate a duty ratio DS based on the error signal Serr.

[0103] As a result, in the power conversion system 1C, feedback control is performed based on the current flowing through the capacitor 9 during the precharge operation, thereby making it possible to control the operation of the rectifier 15.

[0104] Next, a description will be given of another power conversion system 1D according to this modification. This power conversion system 1D includes a current sensor 11C and a control unit 19D, similar to the power conversion system 1C (FIG. 15).

[0105] 17 shows an example configuration of the control unit 19D. The control unit 19D has a precharge control unit 21D. The precharge control unit 21D has an average current calculation unit 25C, a reference level generation unit 26C, an error amplifier 27C, and a duty ratio generation unit 23D. The duty ratio generation unit 23D is configured to generate a duty ratio DP based on the error signal Serr.

[0106] As a result, in the power conversion system 1D, feedback control is performed based on the current flowing through the capacitor 9 during the precharge operation, thereby making it possible to control the operation of the switching unit 13.

[0107] Furthermore, without being limited to this, for example, these may be combined and the operations of both the switching unit 13 and the rectification unit 15 may be controlled by performing feedback control based on the current flowing through the capacitor 9 during the precharge operation.

[0108] 15, current sensor 11C is provided between terminal T11 and voltage line L11 in power conversion system 1C, but this is not limited thereto. Instead, current sensor 11C may be provided between terminal T12 and reference voltage line L12, between node N1 and one end of winding 14A, or between node N2 and the other end of winding 14A. In this example, current sensor 11C is provided in the primary-side circuit, but this is not limited thereto. Instead, current sensor 11C may be provided in the secondary-side circuit, for example.

[0109] [Variation 7] In the above embodiment, the control unit 19 generates a sequence of duty ratios DP and DS during the precharge period P1 based on the voltage VL, and controls the operations of the switching unit 13 and the rectification unit 15 based on the generated duty ratios DP and DS, but this is not limited to this. Instead, for example, the operations of the switching unit 13 and the rectification unit 15 may be controlled by performing feedback control based on the voltage VH. This modification will be described in detail below with some examples.

[0110] A power conversion system 1E according to this modification includes a control unit 19E.

[0111] 18 shows an example of the configuration of the control unit 19E. The control unit 19E has a precharge control unit 21E. The precharge control unit 21E has a reference level generation unit 26E, an error amplifier 27E, and a duty ratio generation unit 24E.

[0112] The reference level generating unit 26E is configured to generate a reference level REF for the voltage VH. The error amplifier 27E is configured to generate an error signal Serr by amplifying the difference between the reference level REF and the voltage VH. The duty ratio generating unit 24E is configured to generate a duty ratio DS based on the error signal Serr.

[0113] As a result, in the power conversion system 1E, the operation of the rectifier 15 can be controlled by performing feedback control based on the voltage VH during the precharge operation.

[0114] Next, a description will be given of another power conversion system 1F according to this modification. This power conversion system 1F includes a control unit 19F, similar to the power conversion system 1E.

[0115] 19 shows an example of the configuration of a control unit 19F. The control unit 19F has a precharge control unit 21F. The precharge control unit 21F has a reference level generation unit 26E, an error amplifier 27E, and a duty ratio generation unit 23F. The duty ratio generation unit 23F is configured to generate a duty ratio DP based on the error signal Serr.

[0116] As a result, in the power conversion system 1F, the operation of the switching unit 13 can be controlled by performing feedback control based on the voltage VH during the precharge operation.

[0117] Furthermore, the present invention is not limited to this, and for example, these may be combined to control the operations of both the switching unit 13 and the rectifying unit 15 by performing feedback control based on the voltage VH in the precharge operation.

[0118] [Variation 8] In the above embodiment, as shown in FIG. 1, four transistors S5 to S8 are provided between the voltage line L21A and the reference voltage line L22. However, as in a power conversion system 1G shown in FIG. 20, a Zener diode DZ may be further provided between the voltage line L21A and the reference voltage line L22. This power conversion system 1G includes a power conversion device 10G. The power conversion device 10G includes a rectifier 15G. The rectifier 15G includes a Zener diode DZ. The anode of the Zener diode DZ is connected to the reference voltage line L22, and the cathode is connected to the voltage line L21A. The Zener voltage of the Zener diode DZ is lower than the avalanche breakdown voltage of the transistors S5 to S8. This prevents the transistors S5 to S8 from entering the avalanche breakdown state AVA in the operating states ST3 to ST5 (FIGS. 7C to 7E) when a back electromotive force is generated in the choke inductor 16. Here, the Zener diode DZ corresponds to a specific example of a "Zener diode" in the present disclosure. In this example, the Zener diode DZ is provided between the voltage line L21A and the reference voltage line L22, but this is not limiting. Alternatively, a Zener diode may be provided between the drain and source of each of the transistors S5 to S8.

[0119] In this example, the Zener diode DZ is provided between the voltage line L21A and the reference voltage line L22, but this is not limiting. Alternatively, for example, an active clamp circuit 90 including the Zener diode DZ, as shown in FIG. 21, may be provided between the voltage line L21A and the reference voltage line L22. The active clamp circuit 90 includes the Zener diode DZ, a resistor R1, and a transistor TR. The anode of the Zener diode DZ is connected to one end of the resistor R1 and the gate of the transistor TR, and the cathode is connected to the voltage line L21A. One end of the resistor R1 is connected to the anode of the Zener diode DZ, and the other end is connected to the reference voltage line L22. The transistor TR is an N-type field-effect transistor, with its drain connected to the voltage line L21A, its gate connected to the anode of the Zener diode DZ and one end of the resistor R1, and its source connected to the reference voltage line L22. This increases the degree of freedom in setting the clamp voltage of the active clamp circuit 90, so that when a back electromotive force occurs in the choke inductor 16, the transistors S5 to S8 can be prevented from entering the avalanche breakdown state AVA.

[0120] [Variation 9] In the above-described embodiment, the choke inductor 16 is provided. However, this is not limiting. Instead, for example, a choke transformer 31 may be provided as in a power conversion system 1H shown in FIG. 22 . This power conversion system 1H includes a power conversion device 10H. The power conversion device 10H includes a smoothing unit 41H and a diode D13. The smoothing unit 41H includes a choke transformer 31. The choke transformer 31 includes windings 31A and 31B. One end of the winding 31A is connected to the voltage line L11, and the other end is connected to the cathode of the diode D13. One end of the winding 31B is connected to the voltage line L21A, and the other end is connected to the voltage line L21B. The anode of the diode D13 is connected to the reference voltage line L12, and the cathode is connected to the other end of the winding 31A. Here, the choke transformer 31 corresponds to a specific example of a “choke transformer” in the present disclosure. The diode D13 corresponds to a specific example of a “third diode” in the present disclosure.

[0121] Figure 23 shows an example of a simulation waveform of the precharge operation in the power conversion system 1H, where (A) shows the waveform of the gate signals GE and GF, (B) shows the waveform of the gate signals GC and GD, (C) shows the waveform of the current flowing into the capacitor 9 (charge current ICHG), (D) shows the waveform of the current flowing into the diode D13 (diode current ID), (E) shows the waveform of the excitation current IM of the transformer 14, (F) shows the waveform of the excitation current ILCH of the choke transformer 31, (G) shows the waveform of the voltage (transformer voltage VTR2) at node N4 in the winding 14B of the transformer 14 with respect to node N5, and (H) shows the waveform of the voltage VH.

[0122] As shown in FIGS. 23A and 23B, the control unit 19 changes the gate signals GC and GF from low to high at timing t41. Then, the control unit 19 changes the gate signal GC from high to low when a time corresponding to the duty ratio DP has elapsed since timing t41, and changes the gate signal GF from high to low when a time corresponding to the duty ratio DS has elapsed since timing t41. Next, the control unit 19 changes the gate signals GD and GE from low to high at timing t42. Then, the control unit 19 changes the gate signal GD from high to low when a time corresponding to the duty ratio DP has elapsed since timing t42, and changes the gate signal GE from high to low when a time corresponding to the duty ratio DS has elapsed since timing t42. The control unit 19 maintains the gate signals GA and GB at low levels. In the power conversion system 1H, the operation from timing t41 to t43 is repeated while changing the duty ratios DP and DS, thereby charging the capacitor 9. As a result, the voltage VH gradually increases as shown in FIG.

[0123] The following will explain in detail the operation based on the gate signals GC and GF during the period from timing t41 to t42 as an example, and the same applies to the operation based on the gate signals GD and GE during the period from timing t42 to t43.

[0124] 24 and 25 show the operation in more detail during the period from timing t41 to t42, in which (A) shows the waveforms of gate signals GC to GF, (B) shows the waveform of the current (charge current ICHG) flowing into capacitor 9, (C) shows the waveform of excitation current IM of transformer 14, (D) shows the waveform of the voltage (transformer voltage VTR1) at node N1 in winding 14A of transformer 14 with node N2 as the reference, and (E) shows the waveform of the voltage (transformer voltage VTR2) at node N4 in winding 14B of transformer 14 with node N5 as the reference. (F) shows the waveform of the excitation current ILCH of the choke transformer 31, (G) shows the waveform of the current ILLK flowing through the low-voltage battery BL, (H) shows the waveform of the current (diode current ID) flowing through the diode D13, (I) shows the waveform of the voltage (voltage VLCH2) on the voltage line L11 in the winding 31A of the choke transformer 31, with the cathode of the diode D13 as the reference, (J) shows the waveform of the voltage (voltage VLCH1) on the voltage line L21A in the winding 31B of the choke transformer 31, with the voltage line L21B as the reference, and (K) shows the waveform of the voltage VH. As shown in FIG. 24, the power conversion system 1H can take eight operating states ST21 to ST28 during the period from timing t41 to t42. The operating states ST of the power conversion system 1H change in the order of operating state ST21, operating state ST22, operating state ST23, ..., operating state ST28. Operating states ST23 to ST25 are operating states during short periods. Fig. 25 shows an enlarged view of the operation during periods corresponding to these operating states ST23 to ST25 and their surrounding periods.

[0125] 26A to 26H show the operation of the power conversion system 1H in eight operating states ST21 to ST28.

[0126] In operating state ST21, the control unit 19 sets gate signals GC and GF to a high level and gate signals GA, GB, GD, and GE to a low level (FIG. 24(A)). This turns on transistors S3, S5, and S8, and turns off transistors S1, S2, S4, S6, and S7 (FIG. 26A). In the secondary circuit, current I2 flows in the following order: the positive terminal of the low-voltage battery BL, winding 31B of the choke transformer 31, transistor S5 (which is on), winding 14B, transistor S8 (which is on), and the negative terminal of the low-voltage battery BL, and energy is stored in the exciting inductor LCH of the choke transformer 31. In the primary circuit, the body diode D1 of transistor S1 turns on, causing current I1 to flow through one end of winding 14A (node ​​N1), the body diode D1 of transistor S1, the on-state transistor S3, and the other end of winding 14A (node ​​N2), storing energy in the leakage inductor LLK of transformer 14. At this time, the primary circuit appears nearly short-circuited from the perspective of the secondary circuit. Therefore, transformer voltages VTR1 and VTR2 are nearly 0 V (Figures 24(D) and (E)).

[0127] In the next operating state ST22, the control unit 19 changes the gate signal GC from high to low (FIG. 24(A)). This causes the transistor S3 to change from on to off (FIG. 26B). In the primary circuit, the body diode D4 of the transistor S4 turns on, and a current I1 flows through one end of the winding 14A (node ​​N1), the body diode D1 of the transistor S1, the capacitor 9, the body diode D4 of the transistor S4, and the other end of the winding 14A (node ​​N2) in this order, resulting in a charge current ICHG (FIG. 24(B)). In other words, the energy stored in the leakage inductor LLK of the transformer 14 is released and stored in the capacitor 9. In this way, the voltage VH rises (FIG. 24(K)). In the secondary circuit, the transformer voltage VTR2 becomes positive (FIG. 24(E)), and the excitation current IM begins to flow through the transformer 14 (FIG. 24(C)). When the power conversion system 1H performs a step-down operation, the inductor current IL increases, and when the power conversion system 1H performs a step-up operation, the inductor current IL decreases (FIG. 24(F)).

[0128] In the next short period of operation state ST23, the control unit 19 changes the gate signal GF from high to low (FIGS. 24(A) and 25(A)). This causes transistors S5 and S8 to change from on to off (FIG. 26C). In the secondary circuit, a back electromotive force is generated in the choke transformer 31, and the drain-source voltages of the transistors S5 to S8 increase, reaching the breakdown voltage of the avalanche breakdown. As a result, an avalanche current flows in each of the transistors S5 to S8, and each of the transistors S5 to S8 enters the avalanche breakdown state AVA. As a result of each of the transistors S5 to S8 entering the avalanche breakdown state AVA, the transformer voltage VTR2 becomes approximately 0V (FIGS. 24(E) and 25(E)). In the primary circuit, continuing from the previous operating state ST22, current I1 flows in the following order from one end of winding 14A (node ​​N1), through body diode D1 of transistor S1, capacitor 9, body diode D4 of transistor S4, and the other end of winding 14A (node ​​N2). A back-EMF voltage of leakage inductor LLK of transformer 14 appears in transformer voltage VTR1. Furthermore, a voltage is generated in winding 31A of choke transformer 31 due to the back-EMF voltage of choke transformer 31 (Figures 24(I) and 25(I)). This turns on diode D13, and diode current ID begins to flow (Figures 24(H) and 25(H)).

[0129] In the next short period of operation state ST24, in the primary circuit, the release of energy stored in the leakage inductor LLK of the transformer 14 ends, and the body diode D1 of transistor S1 and the body diode D4 of transistor S4 are turned off (FIG. 26D). Thus, in the primary circuit, no current flows through the switching unit 13. In the secondary circuit, each of transistors S5 to S8 maintains an avalanche breakdown state AVA. The avalanche current flowing through transistor S5 is greater than the avalanche current flowing through transistor S6 by the excitation current I M. Similarly, the avalanche current flowing through transistor S8 is greater than the avalanche current flowing through transistor S7 by the excitation current I M. Therefore, the avalanche current flowing through transistors S6 and S7 approaches 0 A more quickly than the avalanche current flowing through transistors S5 and S8. Furthermore, diode D13 continues to be in the on state from the previous operating state ST23, and diode current ID flows (FIGS. 24(H), 25(H)). That is, the energy stored in the exciting inductor LCH of the choke transformer 31 is released and stored in capacitor 9. In this way, charge current ICHG flows (FIGS. 24(B), 25(B)), and voltage VH rises (FIG. 24(K)).

[0130] In the next short period, during operating state ST25, the avalanche current flowing through transistors S6 and S7 reaches 0 A, and the avalanche breakdown state AVA of transistors S6 and S7 is eliminated, as shown in FIG. 26E. Transistors S5 and S8 maintain the avalanche breakdown state AVA. This causes the transformer voltages VTR1 and VTR2 to become negative. As a result, in the primary circuit, the body diodes D2 of transistor S2 and D3 of transistor S3 turn on, and current I1 flows through the other end of winding 14A (node ​​N2), the body diode D3 of transistor S3, capacitor 9, the body diode D2 of transistor S2, and one end of winding 14A (node ​​N1) in this order. In other words, the energy stored in the magnetizing inductor LM of transformer 14 is released and stored in capacitor 9. Furthermore, diode D13 remains on, and a diode current ID flows (FIGS. 24(H) and 25(H)). That is, the energy stored in the magnetizing inductor LCH of the choke transformer 31 is released and stored in the capacitor 9. In this way, the charge current ICHG flows (FIGS. 24(B), 25(B)), and the voltage VH rises (FIG. 24(K)).

[0131] In the next operating state ST26, in the secondary circuit, the release of energy stored in the leakage inductor LLKCH of the choke transformer 31 is completed, and the avalanche breakdown state AVA of the transistors S5 and S8 is eliminated (FIG. 26F). As a result, in the secondary circuit, no current flows through the rectifier unit 15. In the primary circuit, continuing from the previous operating state ST25, the current I1 flows in the following order: the other end of the winding 14A (node ​​N2), the body diode D3 of the transistor S3, the capacitor 9, the body diode D2 of the transistor S2, and one end of the winding 14A (node ​​N1). That is, the energy stored in the excitation inductor LM of the transformer 14 is released and stored in the capacitor 9. Furthermore, the diode D13 remains on, and a diode current ID flows (FIG. 24(H)). That is, the energy stored in the excitation inductor LCH of the choke transformer 31 is released and stored in the capacitor 9. In this way, the charge current ICHG flows (FIG. 24(B)), and the voltage VH rises (FIG. 24(K)).

[0132] In the next operating state ST27, in the primary circuit, the release of energy stored in the magnetizing inductor LM of the transformer 14 ends, and the body diode D2 of the transistor S2 and the body diode D3 of the transistor S3 are turned off (FIG. 26G). As a result, no current flows through the switching unit 13 in the primary circuit. Furthermore, the diode D13 remains on, and a diode current ID flows (FIG. 24(H)). That is, the energy stored in the magnetizing inductor LCH of the choke transformer 31 is released and stored in the capacitor 9. In this way, a charge current ICHG flows (FIG. 24(B)), and the voltage VH rises (FIG. 24(K)).

[0133] In the next operating state ST28, in the primary circuit, the release of energy stored in the exciting inductor LCH of the choke transformer 31 ends, and the diode D13 turns off (FIG. 26H). As a result, no current flows in the primary circuit. That is, in this operating state ST28, no current flows in either the primary circuit or the secondary circuit.

[0134] In this way, the capacitor 9 is charged during the period from timing t41 to t42, and the voltage VH rises. The same applies to the period from timing t42 to t43. Note that the above-described operation is an example. For example, when the duty ratio DS rises and approaches "0.5", for example, the operating state ST28 of the operating states ST21 to ST28 may disappear. Power Conversion System 1H Then, as shown in FIG. 23, by repeating the operation from timing t41 to t43, capacitor 9 is gradually charged and voltage VH gradually increases.

[0135] In the power conversion system 1H according to this modification, a choke transformer 31 is provided instead of the choke inductor 16 (FIG. 1) according to the above embodiment. As a result, in the power conversion system 1H, for example, when the transistors S5 to S8 are in the avalanche breakdown state AVA, the energy consumed can be efficiently transmitted to the primary side circuit and regenerated. Also, in the power conversion system 1H, for example, the length of the period during which the transistors S5 to S8 are in the avalanche breakdown state AVA can be shortened.

[0136] In the example of FIG. 22, the diode D13 and the winding 31A of the choke transformer 31 are provided in the path connecting the reference voltage line L12 and the voltage line L11. However, this is not limiting. For example, as in the power conversion system 1I shown in FIG. 27, a switch SW may be further provided in this path. This power conversion system 1I includes a power conversion device 10I. The power conversion device 10I includes the switch SW and a control unit 19I. One end of the switch SW is connected to the reference voltage line L12, and the other end is connected to the anode of the diode D13. The switch SW operates based on an instruction from the control unit 19I, and when turned on, connects the anode of the diode D13 to the reference voltage line L12. Similar to the control unit 19 according to the above embodiment, the control unit 19I is configured to control the operation of the switching unit 13 and the rectifier unit 15, thereby controlling the operation of the power conversion device 10I, based on the voltage VH detected by the voltage sensor 12 and the voltage VL detected by the voltage sensor 18. The control unit 19I turns on the switch SW during the precharge operation and turns off the switch SW during the power conversion operation. Specifically, as shown in Fig. 28, when the voltage VH reaches the threshold Vth ("Y" in step S103), the control unit 19I ends the PWM control (step S104) and turns off the switch SW (step S135). Here, the switch SW corresponds to a specific but not limitative example of "switch" in the present disclosure.

[0137] FIG. 29 shows a configuration example of another power conversion system 1J according to this modification. In the power conversion system 1J, both ends of the winding 31A of the choke transformer 31 are connected to a secondary circuit. That is, in the power conversion system 1H shown in FIG. 22, both ends of the winding 31A of the choke transformer 31 are connected to a primary circuit closer to the high-voltage battery BH than the transformer 14, but in the power conversion system 1J according to this modification, both ends of the winding 31A of the choke transformer 31 are connected to a secondary circuit closer to the low-voltage battery BL than the transformer 14. This power conversion system 1J includes a power conversion device 10J. The power conversion device 10J includes a smoothing unit 41J and a diode D13. The smoothing unit 41J includes a choke transformer 31. The choke transformer 31 includes windings 31A and 31B. One end of the winding 31A is connected to the voltage line L21B, and the other end is connected to the cathode of the diode D13. One end of the winding 31B is connected to the voltage line L21A, and the other end is connected to the voltage line L21B. The anode of the diode D13 is connected to the reference voltage line L22, and the cathode is connected to the other end of the winding 31A. Here, the choke transformer 31 corresponds to a specific example of a "choke transformer" in the present disclosure. The diode D13 corresponds to a specific example of a "third diode" in the present disclosure.

[0138] Figure 30 shows an example of precharge operation in power conversion system 1J, where (A) shows the waveforms of gate signals GE and GF, (B) shows the waveforms of gate signals GC and GD, (C) shows the waveform of the current flowing into capacitor 9 (charge current ICHG), (D) shows the waveform of the current flowing into winding 14A of transformer 14 (transformer current IP), (E) shows the waveform of the current flowing into winding 31B of choke transformer 31 (coil current ILCH1), (F) shows the waveform of the current flowing into winding 31A of choke transformer 31 (coil current ILCH2), (G) shows the waveform of the voltage (transformer voltage VTR2) at node N4 in winding 14B of transformer 14, with node N5 as the reference, and (H) shows the waveform of voltage VH.

[0139] As shown in Figures 30(A) and (B), the control unit 19 changes the gate signals GC and GF from low level to high level at timing t51. Then, the control unit 19 changes the gate signal GC from high level to low level at a timing when a time corresponding to the duty ratio DP has elapsed from timing t51, and changes the gate signal GF from high level to low level at a timing when a time corresponding to the duty ratio DS has elapsed from timing t51. Next, the control unit 19 changes the gate signals GD and GE from low level to high level at timing t52. Then, the control unit 19 changes the gate signals GD and GE from low level to high level at this timing. t52 When a time corresponding to the duty ratio DP has elapsed since the start of the gate signal GD, the gate signal GD is changed from high to low. t52 When a time corresponding to the duty ratio DS has elapsed since the time t51, the gate signal GE is changed from high to low. The control unit 19 maintains the gate signals GA and GB at low levels. In the power conversion system 1J, the capacitor 9 is charged by repeating the operation from timing t51 to t53 while changing the duty ratios DP and DS. As a result, the voltage VH gradually increases, as shown in FIG. 30(H).

[0140] The operation based on the gate signals GC and GF during the period from timing t51 to t52 will be described in detail below as an example. The same applies to the operation based on the gate signals GD and GE during the period from timing t52 to t53. The power conversion system 1J can take five operating states ST31 to ST35 during the period from timing t51 to t52. Note that this description does not include a description of operating states during short periods such as the operating states ST23 to ST25 in FIG. 24. The operating state ST of the power conversion system 1J changes in the order of operating state ST31, operating state ST32, ..., operating state ST35.

[0141] 31A to 31E show the operation of the power conversion system 1J in five operating states ST31 to ST35.

[0142] In the operating state ST31, the control unit 19 sets the gate signals GC and GF to a high level and the gate signals GA, GB, GD, and GE to a low level ( Figure 31A ). This turns on transistors S3, S5, and S8, and turns off transistors S1, S2, S4, S6, and S7 (Figure 31A). In the secondary circuit, current I2 flows through the positive terminal of the low-voltage battery BL, winding 31B of choke transformer 31, transistor S5 (which is on), winding 14B, transistor S8 (which is on), and the negative terminal of the low-voltage battery BL, in this order, storing energy in the excitation inductor LCH of choke transformer 31. In the primary circuit, body diode D1 of transistor S1 turns on, and current I1 flows through one end of winding 14A (node ​​N1), body diode D1 of transistor S1, transistor S3 (which is on), and the other end of winding 14A (node ​​N2), storing energy in leakage inductor LLK of transformer 14. At this time, the primary circuit is essentially short-circuited when viewed from the secondary circuit. Therefore, the transformer voltage VTR2 is approximately 0 V (FIG. 30(G)).

[0143] In the next operating state ST32, the control unit 19 changes the gate signal GC from high to low (FIG. 30(B)). This causes the transistor S3 to change from on to off (FIG. 31B). In the primary circuit, the body diode D4 of the transistor S4 turns on, and a current I1 flows through one end of the winding 14A (node ​​N1), the body diode D1 of the transistor S1, the capacitor 9, the body diode D4 of the transistor S4, and the other end of the winding 14A (node ​​N2) in this order, resulting in a charge current ICHG (FIG. 30(C)). In other words, the energy stored in the leakage inductor LLK of the transformer 14 is released and stored in the capacitor 9. In this way, the voltage VH rises (FIG. 30(H)). In the secondary circuit, the transformer voltage VTR2 becomes a positive voltage (FIG. 30(G)). When the power conversion system 1J performs a step-down operation, the choke coil current ILCH1 increases, and when the power conversion system 1J performs a step-up operation, the choke coil current ILCH1 decreases (FIG. 30(E)).

[0144] In the next operating state ST33, the control unit 19 changes the gate signal GF from high to low (FIG. 30(A)). This causes transistors S5 and S8 to change from the on state to the off state (FIG. 31C). In the primary-side circuit, continuing from the previous operating state ST32, current I1 flows through one end of the winding 14A (node ​​N1), the body diode D1 of transistor S1, capacitor 9, the body diode D4 of transistor S4, and the other end of the winding 14A (node ​​N2) in this order. This causes voltage VH to continue to rise (FIG. 30(H)). In the secondary-side circuit, a back-EMF voltage is generated in the choke transformer 31, and this back-EMF voltage generates a voltage in the winding 31A of the choke transformer 31. This causes diode D13 to turn on, and current I2 flows through the winding 31A, the low-voltage battery BL, diode D13, and winding 31A in this order, resulting in choke coil current ILCH2 (FIG. 30(F)).

[0145] In the next operating state ST34, in the primary circuit, the release of the excitation energy of the transformer 14 ends, and the body diode D1 of the transistor S1 and the body diode D4 of the transistor S4 are turned off (FIG. 31D). Thus, in the primary circuit, no current flows through the switching unit 13. In the secondary circuit, the diode D13 remains in the state of the previous operating state. ST33 The ON state continues from the time of the power-on state, and the choke coil current ILCH2 flows (FIG. 30(F)).

[0146] In the next operating state ST35, Secondary side In the circuit, the release of energy stored in the exciting inductor LCH of the choke transformer 31 ends, and the diode D13 turns off (FIG. 31E). As a result, no current flows in the secondary circuit. That is, in this operating state ST35, no current flows in either the primary circuit or the secondary circuit.

[0147] In this way, the capacitor 9 is charged during the period from timing t51 to t52, and the voltage VH rises. The same applies to the period from timing t52 to t53.

[0148] In the example of FIG. 29, the diode D13 and the winding 31A of the choke transformer 31 are provided in the path connecting the reference voltage line L22 and the voltage line L21B. However, this is not limiting. For example, as in the power conversion system 1K shown in FIG. 32, a switch SW may be further provided in this path. This power conversion system 1K includes a power conversion device 10K. The power conversion device 10K includes the switch SW and a control unit 19K. One end of the switch SW is connected to the reference voltage line L22, and the other end is connected to the anode of the diode D13. The switch SW operates based on an instruction from the control unit 19K, and when turned on, connects the anode of the diode D13 to the reference voltage line L22. Similar to the control unit 19 according to the above embodiment, the control unit 19K is configured to control the operation of the switching unit 13 and the rectifier unit 15 based on the voltage VH detected by the voltage sensor 12 and the voltage VL detected by the voltage sensor 18, thereby controlling the operation of the power conversion device 10K. The control unit 19K turns on the switch SW during the precharge operation, and turns off the switch SW during the power conversion operation.

[0149] [Variation 10] In the above embodiment, the rectifier 15 is configured using a full-bridge circuit as shown in Fig. 1, but this is not limited to this. Instead, for example, a so-called center-tap type power conversion system may be used. This modification will be described in detail below.

[0150] 33 shows an example of the configuration of a power conversion system 2 according to this modification. The power conversion system 2 includes a power conversion device 30. The power conversion device 30 includes a transformer 34, a rectifier 35, and a control unit 39.

[0151] The transformer 34 has windings 34A, 34B, and 34C. One end of the winding 34A is connected to a node N1 in the switching unit 13, and the other end is connected to a node N2 in the switching unit 13. One end of the winding 34B is connected to a node N6, and the other end is connected to one end of the winding 34C and the voltage line L21A. One end of the winding 34C is connected to the other end of the winding 34B and the voltage line L21A, and the other end is connected to a node N7.

[0152] The rectification unit 35 has transistors S9 and S10. The transistors S9 and S10 are configured using, for example, N-type field effect transistors. The transistors S9 and S10 have body diodes D9 and D10, respectively. The transistor S9 is provided in a path connecting the node N6 and the reference voltage line L22, and is configured to connect the node N6 to the reference voltage line L22 when turned on. The drain of the transistor S9 is connected to the node N6, the gate is supplied with a gate signal GF, and the source is connected to the reference voltage line L22. The transistor S10 is provided in a path connecting the node N7 and the reference voltage line L22, and is configured to connect the node N7 to the reference voltage line L22 when turned on. Transistor S10 The drain of this transistor is connected to the node N7, the gate of which is supplied with a gate signal GE, and the source of which is connected to the reference voltage line L22.

[0153] The control unit 39 is configured to control the operation of the power conversion device 30 by controlling the operation of the switching unit 13 and the rectifier unit 35 based on the voltage VH detected by the voltage sensor 12 and the voltage VL detected by the voltage sensor 18. Specifically, the control unit 39 generates gate signals GA to GF based on the voltages VH and VL, and controls the operation of the power conversion device 30 by performing PWM (Pulse Width Modulation) control using the gate signals GA to GF.

[0154] Here, transformer 34 corresponds to a specific example of a "transformer" in the present disclosure. Winding 34A corresponds to a specific example of a "first winding" in the present disclosure. Winding 34B corresponds to a specific example of a "second winding" in the present disclosure. Winding 34C corresponds to a specific example of a "third winding" in the present disclosure. Rectifier 35 corresponds to a specific example of a "rectifier" in the present disclosure. Node N6 corresponds to a specific example of a "sixth node" in the present disclosure. Node N7 corresponds to a specific example of a "seventh node" in the present disclosure. Transistor S9 corresponds to a specific example of a "ninth switching element" in the present disclosure. Transistor S10 corresponds to a specific example of a "tenth switching element" in the present disclosure.

[0155] The above-described modified examples may be applied to this power conversion system 2. Below, several examples of power conversion systems to which the modified examples are applied will be described.

[0156] 34 shows an example of the configuration of a power conversion system 2A to which Modification 4 is applied. This power conversion system 2A includes a power conversion device 30A. The power conversion device 30A has a resonant inductor Lr. One end of the resonant inductor Lr is connected to a node N2, and the other end is connected to the other end of a winding 34A of a transformer 34.

[0157] FIG. 35 shows an example of the configuration of a power conversion system 2B to which Modification 5 is applied. This power conversion system 2B includes a power conversion device 30B. The power conversion device 30B has a resonant inductor Lr and diodes D11 and D12. One end of the resonant inductor Lr is connected to node N2, and the other end is connected to node N3. The other end of the winding 34A of the transformer 34 is connected to node N3. The anode of the diode D11 is connected to node N3, and the cathode is connected to the voltage line L11. The anode of the diode D12 is connected to the reference voltage line L12, and the cathode is connected to node N3.

[0158] FIG. 36 illustrates a configuration example of a power conversion system 2C to which Modification 6 is applied. The power conversion system 2C includes a power conversion device 30C. The power conversion device 30C includes a current sensor 11C and a control unit 39C. The current sensor 11C is configured to detect a current flowing through a terminal T11. One end of the current sensor 11C is connected to the terminal T11, and the other end is connected to the voltage line L11. The current sensor 11C detects, as a current IH, a current flowing from the voltage line L11 to the terminal T11. The control unit 39C is configured to control the operations of the switching unit 13 and the rectifier unit 35 based on the current IH detected by the current sensor 11C, the voltage VH detected by the voltage sensor 12, and the voltage VL detected by the voltage sensor 18. The control unit 39C may include, for example, the precharge control unit 21C illustrated in FIG. 16 or the precharge control unit 21D illustrated in FIG. 17.

[0159] FIG. 37 shows an example of a configuration of a power conversion system 2G to which Modification 8 is applied. This power conversion system 2G includes a power conversion device 30G. The power conversion device 30G includes a rectifier 35G. The rectifier 35G includes Zener diodes DZ1 and DZ2. The anode of the Zener diode DZ1 is connected to the reference voltage line L22, and the cathode is connected to a node N6. The anode of the Zener diode DZ2 is connected to the reference voltage line L22, and the cathode is connected to a node N7. Note that this example is not limiting, and the active clamp circuit 90 shown in FIG. 21 may also be used. Specifically, an active clamp circuit 90 (active clamp circuit 90A) may be provided between the node N6 and the reference voltage line L22, and another active clamp circuit 90 (active clamp circuit 90B) may be provided between the node N7 and the reference voltage line L22.

[0160] FIG. 38 shows an example of the configuration of a power conversion system 2H ​​to which Modification 9 is applied. This power conversion system 2H ​​includes a power conversion device 30H. The power conversion device 30H has a choke transformer 31 and a diode D13. The choke transformer 31 has windings 31A and 31B. One end of the winding 31A is connected to the voltage line L11, and the other end is connected to the cathode of the diode D13. One end of the winding 31B is connected to the voltage line L21A, and the other end is connected to the voltage line L21B. The anode of the diode D13 is connected to the reference voltage line L12, and the cathode is connected to the other end of the winding 31A. As with the example of FIG. 27, a switch SW may also be provided.

[0161] FIG. 39 shows a configuration example of another power conversion system 2J to which Modification 9 is applied. This power conversion system 2J includes a power conversion device 30J. The power conversion device 30J has a choke transformer 31 and a diode D13. The choke transformer 31 has windings 31A and 31B. One end of the winding 31A is connected to the voltage line L21B, and the other end is connected to the cathode of the diode D13. One end of the winding 31B is connected to the voltage line L21A, and the other end is connected to the voltage line L21B. The anode of the diode D13 is connected to the reference voltage line L22, and the cathode is connected to the other end of the winding 31A. As with the example of FIG. 32, a switch SW may also be provided.

[0162] [Other variations] Two or more of these variations may also be combined.

[0163] Although the present invention has been described above by way of embodiments and modifications, the present invention is not limited to these embodiments and can be modified in various ways.

[0164] For example, in the above embodiment, the voltage step-down operation is performed in the power conversion operation, but this is not limitative, and the voltage step-up operation may also be performed.

[0165] For example, in the above embodiment, the power conversion operation is a unidirectional conversion operation in which power is supplied from the high-voltage battery BH to the low-voltage battery BL, but this is not limited to this. For example, the power conversion operation may be bidirectional by providing a mode in which power is supplied from the high-voltage battery BH to the low-voltage battery BL and a mode in which power is supplied from the low-voltage battery BL to the high-voltage battery BH. Even in this case, the capacitor 9 can be charged based on the power supplied from the low-voltage battery BL during the preparation period before the power conversion operation is performed in the mode in which power is supplied from the high-voltage battery BH to the low-voltage battery BL.

[0166] For example, in the above embodiment, the control unit 19 generates the duty ratios DP and DS so as to satisfy the equations EQ1 and EQ2 in the precharge operation, but this is not limiting. Instead, for example, in a power conversion system that performs bidirectional conversion operation and has a mode in which power is supplied from the high-voltage battery BH to the low-voltage battery BL and a mode in which power is supplied from the low-voltage battery BL to the high-voltage battery BH, when performing power conversion operation in the mode in which power is supplied from the low-voltage battery BL to the high-voltage battery BH, the control unit 19 may generate the duty ratios DP and DS so as to satisfy the equations EQ1 and EQ2.

[0167] For example, when the body diode of a transistor turns on, the gate signal of the transistor may be set to high level at this timing to synchronize the transistor to the on state, thereby improving the conversion efficiency of the power conversion system. [Explanation of symbols]

[0168] 1, 1A, 1B, 1C, 1G, 1H, 1I, 1J, 1K, 2, 2A, 2B, 2C, 2G, 2H, 2J... Power conversion system, 9... Capacitor, 10, 10A, 10B, 10C, 10G, 10H, 10I, 10J, 10K, 30, 30A, 30B, 30C, 30G, 30H, 30J... Power conversion device, 11C... Current sensor, 12... Voltage sensor, 13... Switching unit, 14, 34... Transformer, 14A, 14B, 34A to 34C... Winding, 15 , 15G, 35, 35G... rectification unit, 16... choke inductor, 17... capacitor, 18... voltage sensor, 19, 19C, 19D, 19E, 19F, 19I, 19K, 39, 39C... control unit, 21, 21C, 21D, 21E, 21F... precharge control unit, 22... target value determination unit, 23, 23D, 23F, 24, 24C, 24E... duty ratio generation unit, 25... power conversion control unit, 25C... average current calculation unit, 26, 27... gate signal generation unit, 2 6C, 26E...Reference level generation section, 27C, 27E...Error amplifier, 31...Choke transformer, 31A, 31B...Winding, 41, 41H, 41J...Smoothing section, 90...Active clamp circuit, AVA...Avalanche breakdown state, BH...High voltage battery, BL...Low voltage battery, DP, DS...Duty ratio, DZ, DZ1, DZ2...Zener diode, D1 to D10...Body diode, D11, D12, D13...Diode, GA~ GF...gate signal, IH...current, L11, L21A, L21B...voltage line, L12, L22...reference voltage line, Lr...resonant inductor, N1 to N7...node, P1...precharge period, P2...power conversion period, R1...resistance element, SW...switch, SW1, SW2...switch, S1 to S10...transistor, TR...transistor, T11, T12, T21, T22...terminal, VH, VL...voltage, VH_target...target voltage, Vth...threshold value.

Claims

1. a first power terminal having a first connection terminal and a second connection terminal; a switching unit including a first switching element provided on a path connecting a first node and a first power node led to the first connection terminal, a second switching element provided on a path connecting the first node and a second power node led to the second connection terminal, a third switching element provided on a path connecting the first power node and a second node, and a fourth switching element provided on a path connecting the second node and the second power node; a transformer having a first winding having a first terminal connected to the first node and a second terminal connected to the second node, and a second winding; a rectifier unit connected to the second winding and having a plurality of switching elements; a smoothing unit connected to the rectifying unit and having a choke coil; a second power terminal connected to the smoothing portion; a control unit that controls operations of the first switching element, the second switching element, the third switching element, the fourth switching element, and the plurality of switching elements; Equipped with the control unit controls operations of the switching unit and the rectification unit so as to supply power from the second power terminal to the first power terminal during a predetermined period that is a period before a period during which power is supplied from the first power terminal to the second power terminal; the control unit operates the switching unit at a first duty ratio and the rectification unit at a second duty ratio during the predetermined period; the first duty ratio is greater than 0 and equal to or less than the second duty ratio, the second power terminal has a third connection terminal and a fourth connection terminal; the second winding has a first terminal connected to a fourth node and a second terminal connected to a fifth node; the plurality of switching elements of the rectification unit include a fifth switching element provided on a path connecting a third power node led to the third connection terminal and the fourth node, a sixth switching element provided on a path connecting the fourth node and a fourth power node led to the fourth connection terminal, a seventh switching element provided on a path connecting the third power node and the fifth node, and an eighth switching element provided on a path connecting the fifth node and the fourth power node, the control unit repeatedly performs a first control, a second control, a third control, a fourth control, a fifth control, and a sixth control in this order during the predetermined period; In the first control, the control unit turns on the third switching element, the fifth switching element, and the eighth switching element, and turns off the first switching element, the second switching element, the fourth switching element, the sixth switching element, and the seventh switching element, In the second control, the control unit turns the fifth switching element and the eighth switching element to an ON state, and turns the first switching element, the second switching element, the third switching element, the fourth switching element, the sixth switching element, and the seventh switching element to an OFF state, In the third control, the control unit turns off the first switching element, the second switching element, the third switching element, the fourth switching element, the fifth switching element, the sixth switching element, the seventh switching element, and the eighth switching element, In the fourth control, the control unit turns on the fourth switching element, the sixth switching element, and the seventh switching element, and turns off the first switching element, the second switching element, the third switching element, the fifth switching element, and the eighth switching element, In the fifth control, the control unit turns the sixth switching element and the seventh switching element to an ON state, and turns the first switching element, the second switching element, the third switching element, the fourth switching element, the fifth switching element, and the eighth switching element to an OFF state, In the sixth control, the control unit turns off the first switching element, the second switching element, the third switching element, the fourth switching element, the fifth switching element, the sixth switching element, the seventh switching element, and the eighth switching element. Power conversion device.

2. A first power terminal having a first connection terminal and a second connection terminal; a switching unit including a first switching element provided on a path connecting a first node and a first power node led to the first connection terminal, a second switching element provided on a path connecting the first node and a second power node led to the second connection terminal, a third switching element provided on a path connecting the first power node and a second node, and a fourth switching element provided on a path connecting the second node and the second power node; a transformer having a first winding having a first terminal connected to the first node and a second terminal connected to the second node, and a second winding; a rectifier unit connected to the second winding and having a plurality of switching elements; a smoothing unit connected to the rectifying unit and having a choke coil; a second power terminal connected to the smoothing portion; a control unit that controls operations of the first switching element, the second switching element, the third switching element, the fourth switching element, and the plurality of switching elements; Equipped with the control unit controls operations of the switching unit and the rectification unit so as to supply power from the second power terminal to the first power terminal during a predetermined period that is a period before a period during which power is supplied from the first power terminal to the second power terminal; the control unit operates the switching unit at a first duty ratio and the rectification unit at a second duty ratio during the predetermined period; the first duty ratio is greater than 0 and equal to or less than the second duty ratio, the second power terminal has a third connection terminal and a fourth connection terminal; the transformer further has a third winding; the second winding has a first terminal connected to a third power node leading to the third connection terminal and a second terminal connected to a sixth node; the third winding has a first terminal connected to the third power node and a second terminal connected to a seventh node; the plurality of switching elements of the rectification unit include a ninth switching element provided on a path connecting the sixth node and a fourth power node led to the fourth connection terminal, and a tenth switching element provided on a path connecting the seventh node and the fourth power node, the control unit repeatedly performs a first control, a second control, a third control, a fourth control, a fifth control, and a sixth control in this order during the predetermined period; In the first control, the control unit turns on the third switching element and the ninth switching element, and turns off the first switching element, the second switching element, the fourth switching element, and the tenth switching element, In the second control, the control unit turns the ninth switching element on and turns the first switching element, the second switching element, the third switching element, the fourth switching element, and the tenth switching element off, In the third control, the control unit turns off the first switching element, the second switching element, the third switching element, the fourth switching element, the ninth switching element, and the tenth switching element, In the fourth control, the control unit turns on the fourth switching element and the tenth switching element, and turns off the first switching element, the second switching element, the third switching element, and the ninth switching element, In the fifth control, the control unit turns the tenth switching element on and turns the first switching element, the second switching element, the third switching element, the fourth switching element, and the ninth switching element off, In the sixth control, the control unit turns off the first switching element, the second switching element, the third switching element, the fourth switching element, the ninth switching element, and the tenth switching element. Power conversion device.

3. The second duty ratio is greater than 0 and equal to or less than 0.

5. The power conversion device according to claim 1 or 2.

4. the predetermined period includes a first period and a second period that follows the first period; The control unit controls the operation of the rectification unit in the first period, and controls the operations of the switching unit and the rectification unit in the second period. The power conversion device according to any one of claims 1 to 3.

5. The control unit determines a sequence of the first duty ratio of the switching unit and a sequence of the second duty ratio of the rectifier unit during the predetermined period based on a voltage at the second power terminal, and controls operations of the switching unit and the rectifier unit based on the determination results. The power conversion device according to any one of claims 1 to 4.

6. The control unit controls the operation of one or both of the switching unit and the rectifying unit by performing feedback control based on a first current corresponding to the current flowing through the first power terminal. The power conversion device according to any one of claims 1 to 5.

7. The first current includes any one of a current flowing through the first power terminal, a current flowing through the switching unit, and a current flowing through the first winding. The power conversion device according to claim 6.

8. The control unit controls the operation of one or both of the switching unit and the rectifying unit by performing feedback control based on the voltage at the first power terminal. The power conversion device according to any one of claims 1 to 7.

9. The control unit terminates the control for the predetermined period when the voltage at the first power terminal reaches a predetermined voltage. The power conversion device according to any one of claims 1 to 8.

10. an inductor having a first terminal connected to the second node and a second terminal connected to a third node; The second terminal of the first winding is connected to the third node and to the second node via the inductor. The power conversion device according to any one of claims 1 to 9.

11. a first diode having a cathode connected to the first power node and an anode connected to the third node; a second diode having a cathode connected to the third node and an anode connected to the second power node; Furthermore, The control unit controls, during the predetermined period, the operations of the third switching element and the fourth switching element among the first switching element, the second switching element, the third switching element, and the fourth switching element in the switching unit. The power conversion device according to claim 10.

12. The rectification unit further includes a Zener diode provided in a path connecting the third power node and the fourth power node. The power conversion device according to claim 1 .

13. The rectifying unit is a first Zener diode provided in a path connecting the sixth node and the fourth power node; a second Zener diode provided in a path connecting the seventh node and the fourth power node; Further having The power conversion device according to claim 2 .

14. a choke transformer having a first winding and a second winding; a third diode; Equipped with the second winding of the choke transformer constitutes the choke coil; the first winding and the third diode of the choke transformer are provided in a path connecting the first power node and the second power node; The second winding of the choke transformer is provided in a path connecting the rectifier unit and the third connection terminal. The power conversion device according to any one of claims 1 to 11.

15. Further provided with a switch, the first winding of the choke transformer, the third diode, and the switch are provided in a path connecting the first power node and the second power node; The switch is in an on state during the predetermined period. The power converter according to claim 14.

16. a choke transformer having a first winding and a second winding; a third diode; and Equipped with the second winding of the choke transformer constitutes the choke coil; the first winding and the third diode of the choke transformer are provided in a path connecting the third connection terminal and the fourth connection terminal, The second winding of the choke transformer is provided in a path connecting the rectifier unit and the third connection terminal. The power conversion device according to any one of claims 1 to 11.

17. Further provided with a switch, the first winding of the choke transformer, the third diode, and the switch are provided on a path connecting the third connection terminal and the fourth connection terminal, The switch is in an on state during the predetermined period. The power converter according to claim 16.

18. A capacitor is connected to the first connection terminal and the second connection terminal. The power conversion device according to any one of claims 1 to 17.

19. a first battery having a first terminal and a second terminal; a capacitor having a first terminal and a second terminal; a first switch provided in a path connecting the first terminal of the first battery and the first terminal of the capacitor; a second switch provided in a path connecting the second terminal of the first battery and the second terminal of the capacitor; a power conversion device; a second battery; Equipped with The power conversion device is a first power terminal having a first connection terminal connected to the first terminal of the capacitor and a second connection terminal connected to the second terminal of the capacitor; a switching unit including a first switching element provided on a path connecting a first node and a first power node led to the first connection terminal, a second switching element provided on a path connecting the first node and a second power node led to the second connection terminal, a third switching element provided on a path connecting the first power node and a second node, and a fourth switching element provided on a path connecting the second node and the second power node; a transformer having a first winding having a first terminal connected to the first node and a second terminal connected to the second node, and a second winding; a rectifier unit connected to the second winding and having a plurality of switching elements; a smoothing unit connected to the rectifying unit and having a choke coil; a second power terminal led to the smoothing section and connected to the second battery; a control unit that controls operations of the first switching element, the second switching element, the third switching element, the fourth switching element, and the plurality of switching elements; and the control unit controls operations of the switching unit and the rectification unit so as to supply power from the second power terminal to the first power terminal during a predetermined period that is a period before a period during which power is supplied from the first power terminal to the second power terminal; the control unit operates the switching unit at a first duty ratio and the rectification unit at a second duty ratio during the predetermined period; the first duty ratio is greater than 0 and equal to or less than the second duty ratio, the second power terminal has a third connection terminal and a fourth connection terminal; the second winding has a first terminal connected to a fourth node and a second terminal connected to a fifth node; the plurality of switching elements of the rectification unit include a fifth switching element provided on a path connecting a third power node led to the third connection terminal and the fourth node, a sixth switching element provided on a path connecting the fourth node and a fourth power node led to the fourth connection terminal, a seventh switching element provided on a path connecting the third power node and the fifth node, and an eighth switching element provided on a path connecting the fifth node and the fourth power node, the control unit repeatedly performs a first control, a second control, a third control, a fourth control, a fifth control, and a sixth control in this order during the predetermined period; In the first control, the control unit turns on the third switching element, the fifth switching element, and the eighth switching element, and turns off the first switching element, the second switching element, the fourth switching element, the sixth switching element, and the seventh switching element, In the second control, the control unit turns the fifth switching element and the eighth switching element to an ON state, and turns the first switching element, the second switching element, the third switching element, the fourth switching element, the sixth switching element, and the seventh switching element to an OFF state, In the third control, the control unit turns off the first switching element, the second switching element, the third switching element, the fourth switching element, the fifth switching element, the sixth switching element, the seventh switching element, and the eighth switching element, In the fourth control, the control unit turns on the fourth switching element, the sixth switching element, and the seventh switching element, and turns off the first switching element, the second switching element, the third switching element, the fifth switching element, and the eighth switching element, In the fifth control, the control unit turns the sixth switching element and the seventh switching element to an ON state, and turns the first switching element, the second switching element, the third switching element, the fourth switching element, the fifth switching element, and the eighth switching element to an OFF state, In the sixth control, the control unit turns off the first switching element, the second switching element, the third switching element, the fourth switching element, the fifth switching element, the sixth switching element, the seventh switching element, and the eighth switching element. Power conversion systems.

20. A battery comprising: a first battery having a first terminal and a second terminal; a capacitor having a first terminal and a second terminal; a first switch provided in a path connecting the first terminal of the first battery and the first terminal of the capacitor; a second switch provided in a path connecting the second terminal of the first battery and the second terminal of the capacitor; a power conversion device; a second battery; Equipped with The power conversion device is a first power terminal having a first connection terminal connected to the first terminal of the capacitor and a second connection terminal connected to the second terminal of the capacitor; a switching unit including a first switching element provided on a path connecting a first node and a first power node led to the first connection terminal, a second switching element provided on a path connecting the first node and a second power node led to the second connection terminal, a third switching element provided on a path connecting the first power node and a second node, and a fourth switching element provided on a path connecting the second node and the second power node; a transformer having a first winding having a first terminal connected to the first node and a second terminal connected to the second node, and a second winding; a rectifier unit connected to the second winding and having a plurality of switching elements; a smoothing unit connected to the rectifying unit and having a choke coil; a second power terminal led to the smoothing section and connected to the second battery; a control unit that controls operations of the first switching element, the second switching element, the third switching element, the fourth switching element, and the plurality of switching elements; and the control unit controls operations of the switching unit and the rectification unit so as to supply power from the second power terminal to the first power terminal during a predetermined period that is a period before a period during which power is supplied from the first power terminal to the second power terminal; the control unit operates the switching unit at a first duty ratio and the rectification unit at a second duty ratio during the predetermined period; the first duty ratio is greater than 0 and equal to or less than the second duty ratio, the second power terminal has a third connection terminal and a fourth connection terminal; the transformer further has a third winding; the second winding has a first terminal connected to a third power node leading to the third connection terminal and a second terminal connected to a sixth node; the third winding has a first terminal connected to the third power node and a second terminal connected to a seventh node; the plurality of switching elements of the rectification unit include a ninth switching element provided on a path connecting the sixth node and a fourth power node led to the fourth connection terminal, and a tenth switching element provided on a path connecting the seventh node and the fourth power node, the control unit repeatedly performs a first control, a second control, a third control, a fourth control, a fifth control, and a sixth control in this order during the predetermined period; In the first control, the control unit turns on the third switching element and the ninth switching element, and turns off the first switching element, the second switching element, the fourth switching element, and the tenth switching element, In the second control, the control unit turns the ninth switching element on and turns the first switching element, the second switching element, the third switching element, the fourth switching element, and the tenth switching element off, In the third control, the control unit turns off the first switching element, the second switching element, the third switching element, the fourth switching element, the ninth switching element, and the tenth switching element, In the fourth control, the control unit turns on the fourth switching element and the tenth switching element, and turns off the first switching element, the second switching element, the third switching element, and the ninth switching element, In the fifth control, the control unit turns the tenth switching element on and turns the first switching element, the second switching element, the third switching element, the fourth switching element, and the ninth switching element off, In the sixth control, the control unit turns off the first switching element, the second switching element, the third switching element, the fourth switching element, the ninth switching element, and the tenth switching element. Power conversion systems.

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