Bidirectional dc-dc converter and charging pile

Abstract

This application provides a bidirectional DC-DC converter and a charging pile. The bidirectional DC-DC converter includes a first power conversion circuit, a second power conversion circuit, a three-phase transformer, a three-phase resonant circuit, a resonant switching circuit, and an inductor circuit. Each phase resonant circuit includes a first capacitor and a first inductor connected in series. One end of each phase resonant circuit is connected to the first power conversion circuit, and the other end of each phase resonant circuit is connected to the second power conversion circuit through the three-phase transformer. The resonant switching circuit is used to connect either end of each phase resonant circuit to the inductor circuit, so that each phase resonant circuit and the inductor circuit form an LLC resonant circuit. This application can improve the voltage regulation range and power conversion efficiency of the bidirectional DC-DC converter during bidirectional power transmission, thereby achieving wide voltage range and high-efficiency input or output.

Description

Technical Field

[0001] This application relates to the field of charging, and more specifically, to a bidirectional DC-DC converter and a charging pile. Background Technology

[0002] With the rapid development of electric vehicles, in addition to charging, they have also begun to possess discharging capabilities, such as vehicle-to-grid (V2G) discharge. Correspondingly, charging stations, as supporting infrastructure, are increasingly adopting bidirectional DC-DC converters capable of two-way power transmission. Specifically, when an electric vehicle is charging through a charging station, the bidirectional DC-DC converter operates in the forward direction; conversely, when the electric vehicle is discharging into the grid through the charging station, the bidirectional DC-DC converter operates in the reverse direction.

[0003] Currently, in order to meet the charging and discharging voltage requirements of different electric vehicles, the bidirectional DC-DC converter in charging piles needs to support bidirectional power transmission over a wide voltage range. However, the current bidirectional DC-DC converters used in charging piles have a narrow voltage regulation range when operating in reverse, which cannot adequately meet the requirement of bidirectional power transmission over a wide voltage range. Summary of the Invention

[0004] This application provides a bidirectional DC-DC converter and a charging pile, which can improve the voltage regulation range and power conversion efficiency of the bidirectional DC-DC converter during bidirectional power transmission, thereby achieving wide voltage range and high efficiency input or output.

[0005] In a first aspect, embodiments of this application provide a bidirectional DC-DC converter, comprising a first power conversion circuit, a second power conversion circuit, a three-phase transformer, and a three-phase resonant circuit. Each phase of the three-phase resonant circuit includes a first capacitor and a first inductor connected in series. One end of each phase resonant circuit is connected to the first power conversion circuit, and the other end of each phase resonant circuit is connected to the second power conversion circuit via the three-phase transformer. The bidirectional DC-DC converter further includes a resonant switching circuit and an inductor circuit. The resonant switching circuit is used to connect either end of each phase resonant circuit to the inductor circuit, thereby forming an inductor-inductor-capacitor LLC resonant circuit between each phase resonant circuit and the inductor circuit.

[0006] Based on the above design, when electrical energy is transmitted from the first power conversion circuit to the second power conversion circuit via a three-phase resonant circuit, or from the second power conversion circuit to the first power conversion circuit via a three-phase resonant circuit—that is, when electrical energy is transmitted in the bidirectional DC-DC converter in either the forward or reverse direction—the resonant switching circuit can be used to connect the circuit between the output end of each phase resonant circuit and the inductor circuit, so that each phase resonant circuit and the inductor circuit form an LLC resonant circuit. Since the voltage gain of the LLC resonant circuit can be less than or equal to 1 or greater than 1, the bidirectional DC-DC converter can achieve both step-down and step-up voltage conversion, thereby improving the voltage regulation range of the bidirectional DC-DC converter during bidirectional power transmission. Furthermore, the LLC resonant circuit has smaller input and output ripple currents and higher power density, and can achieve soft switching, thus further improving the power conversion efficiency of the bidirectional DC-DC converter during bidirectional power transmission. Consequently, the bidirectional DC-DC converter can achieve a wide voltage range and efficient input or output.

[0007] In one implementation, the resonant switching circuit is used to: connect the circuit between the other end of each phase resonant circuit and the inductor circuit when the first power conversion circuit is used to convert the received DC power to AC power and the second power conversion circuit is used to convert the AC power output from the first power conversion circuit to DC power and then output it; or, when the second power conversion circuit is used to convert the received DC power to AC power and the first power conversion circuit is used to convert the AC power output from the second power conversion circuit to DC power and then output it, connect the circuit between one end of each phase resonant circuit and the inductor circuit.

[0008] Based on the above design, when electrical energy is transmitted in the forward or reverse direction in the bidirectional DC-DC device, the circuit between the output end of each phase resonant circuit and the inductor circuit can be made conductive, thereby ensuring that the bidirectional DC-DC converter forms an LLC resonant circuit in both forward and reverse transmission of electrical energy.

[0009] In one implementation, the inductor circuit includes three second inductors, and the two ends of each phase resonant circuit are connected to one end of a second inductor through a resonant switching circuit.

[0010] Based on the above design, the first capacitor and the first inductor connected in series in each phase resonant circuit can be connected to a second inductor through a resonant switching circuit to form an LLC resonant circuit. Furthermore, compared to the current practice of integrating the magnetizing inductor with the three-phase transformer, which results in a large air gap size in the three-phase transformer core, the three second inductors in this embodiment can be used as three magnetizing inductors and are separated from the three-phase transformer. This can significantly reduce the air gap size of the three-phase transformer core, thereby further improving the efficiency and stability of the three-phase transformer.

[0011] In one implementation, the resonant switching circuit includes three resonant switches. The two ends of each phase resonant circuit are connected to one end of a second inductor via a resonant switch. Each phase resonant circuit is connected to one of the two stationary contacts of a resonant switch. One end of each second inductor is connected to the moving contact of a resonant switch, and the other ends of the three second inductors are connected together. Alternatively, the three second inductors are connected sequentially end-to-end, and the connection point between one second inductor and another is connected to the moving contact of a resonant switch.

[0012] Based on the above design, when electrical energy is transmitted in the bidirectional DC-DC converter in either the forward or reverse direction, by connecting the moving contact of each resonant switch to one of its two stationary contacts, the circuit between the output end of each phase resonant circuit and a second inductor can be activated. This allows the first inductor and first capacitor connected in series in each phase resonant circuit to form an LLC resonant circuit with the second inductor. Furthermore, the three second inductors can be connected in a star configuration to make the bidirectional DC-DC converter more suitable for applications requiring higher voltage and lower current. Alternatively, the three second inductors can be connected in a delta configuration to make the bidirectional DC-DC converter more suitable for applications requiring lower voltage and higher current.

[0013] In one implementation, the bidirectional DC-DC converter further includes multiple second capacitors, and the second power conversion circuit includes three power conversion bridge arms connected in parallel. The midpoint of each second power conversion bridge arm is connected to a three-phase transformer through a second capacitor.

[0014] Based on the above design, when electrical energy is transmitted from the second power conversion circuit to the first power conversion circuit, that is, when electrical energy is transmitted in reverse in the bidirectional DC-DC converter, the second capacitor can prevent the magnetic core of the three-phase transformer from becoming magnetized, thereby further improving the stability of the three-phase transformer during operation.

[0015] In one implementation, the three-phase transformer includes three-phase primary windings and three-phase secondary windings. The three-phase primary windings are connected one-to-one with the other end of a three-phase resonant circuit, and the three-phase secondary windings are connected one-to-one with the midpoints of the three power conversion bridge arms. The bidirectional DC-DC converter further includes at least one of a first turns-changing switch circuit and a second turns-changing switch circuit. The first turns-changing switch circuit is connected to the three-phase primary windings and is used to switch the number of turns of each phase of the primary winding connected to the circuit. The second turns-changing switch circuit is connected to the three-phase secondary windings and is used to switch the number of turns of each phase of the secondary winding connected to the circuit.

[0016] Based on the above design, when electrical energy is transmitted in the forward or reverse direction in the bidirectional DC-DC converter, the winding turns ratio of the three-phase transformer connected to the circuit can be adjusted by at least one of the first and second turns switching circuits to adjust the operating voltage range of the bidirectional DC-DC converter, thereby enabling the bidirectional DC-DC converter to achieve wide voltage range input or output.

[0017] In one implementation, when the bidirectional DC-DC converter includes a first turns-switching switch circuit, each phase primary winding includes a first primary winding and a second primary winding. One end of each of the three first primary windings is connected to the other end of a three-phase resonant circuit. The other end of the first primary winding of one phase is connected to one end of the second primary winding of another phase to form a first tap. The other ends of the three second primary windings are connected together. The first turns-switching switch circuit includes two first turns-switching switches, each connected to one of the other two phase primary windings (excluding the first phase primary winding) of the three-phase primary windings. Each first turns-switching switch is used to connect the circuit between the other end of the first primary winding of the corresponding phase and one end of the second primary winding of the corresponding phase. Alternatively, each first turns-switching switch is used to connect the circuit between the other end of the first primary winding of the corresponding phase and the first tap.

[0018] Based on the above design, when electrical energy is transmitted in the bidirectional DC-DC converter in either the forward or reverse direction, the number of turns connected to the circuit of each phase primary winding can be switched by connecting the moving contact of each first turns switching switch to one of its two stationary contacts. This allows the number of turns connected to the circuit to be either the number of turns of the first primary winding of each phase, or the sum of the number of turns of the first and second primary windings of each phase. Furthermore, the operating voltage range of the bidirectional DC-DC converter can be adjusted to achieve a wide voltage range for input or output.

[0019] In one implementation, when the bidirectional DC-DC converter includes a second turns switching circuit, each phase secondary winding includes a first secondary winding and a second secondary winding. One end of each of the three first secondary windings is connected to the midpoint of one of the three power conversion bridge arms. The other end of the first secondary winding of one phase secondary winding is connected to one end of the second secondary winding of another phase secondary winding to form a second tap, and the other ends of the three second secondary windings are connected together. The second turns switching circuit includes two second turns switching switches, each connected to one of the other two phase secondary windings (excluding one of the phase secondary windings). Each second turns switching switch is used to connect the circuit between the other end of the first secondary winding of the corresponding phase secondary winding and one end of the second secondary winding of the corresponding phase secondary winding. Alternatively, each second turns switching switch is used to connect the circuit between the other end of the first secondary winding of the corresponding phase secondary winding and the second tap.

[0020] Based on the above design, when electrical energy is transmitted in the bidirectional DC-DC converter in either the forward or reverse direction, the number of turns connected to the circuit of each phase secondary winding can be switched by connecting the moving contact of each second turns switching switch to one of its two stationary contacts. This allows the switch to either match the number of turns of the first secondary winding of each phase secondary winding, or the sum of the number of turns of the first and second secondary windings of each phase secondary winding. Furthermore, the operating voltage range of the bidirectional DC-DC converter can be adjusted, achieving a wide voltage range for input and output.

[0021] In one implementation, each phase secondary winding includes multiple sets of secondary windings, and the number of second power conversion circuits is also multiple. Each set of secondary windings is connected one-to-one with the midpoint of a bridge arm of each of the multiple second power conversion circuits. The bidirectional DC-DC converter also includes one or more connection switching circuits, where any two second power conversion circuits are connected via a connection switching circuit. Each connection switching circuit includes one series switch and two parallel switches. The series switch is used to connect any two second power conversion circuits in series, and the two parallel switches are used to connect any two second power conversion circuits in parallel.

[0022] Based on the above design, when electrical energy is transferred from the first power conversion circuit to the second power conversion circuit—that is, when electrical energy is transferred in the forward direction in the bidirectional DC-DC converter—multiple connection switching circuits can connect the multiple second power conversion circuits in series or parallel. This allows for adjustment of the voltage range output by the multiple second power conversion circuits, enabling the bidirectional DC-DC converter to achieve a wide voltage output range. Thus, when the multiple second power conversion circuits output the converted DC power to electric vehicles for charging, the charging power requirements of different electric vehicles can be better met.

[0023] Secondly, a charging station is provided, comprising an AC-DC converter and a bidirectional DC-DC converter as described in any of the first aspects above. One end of the AC-DC converter is connected to an AC power source, and the other end of the AC-DC converter is connected to a charging gun via the bidirectional DC-DC converter.

[0024] In one implementation, one end of the first power conversion circuit is connected to the other end of the AC-DC conversion device, and the other end of the first power conversion circuit is connected to one end of each phase resonant circuit.

[0025] It should be understood that one end of the first power conversion circuit can be understood as the DC connection terminal of the first power conversion circuit, and the other end of the first power conversion circuit can be understood as the three-phase AC connection terminal of the first power conversion circuit.

[0026] Based on the above design, when the charging pile outputs electrical energy to the electric vehicle through the charging gun, the electrical energy output by the AC-DC converter can flow through the first power conversion circuit, the three-phase transformer, and the second power conversion circuit in the bidirectional DC-DC converter before being output to the charging gun. In this way, the LLC resonance formed by the three-phase resonant circuit and the three second inductors in the bidirectional DC-DC converter can be located on the primary side of the three-phase transformer. Compared to the LLC resonance being located on the secondary side of the three-phase transformer, the LLC resonance on the primary side can better ensure soft switching, reduce switching losses, and thus improve the charging efficiency of the charging pile for electric vehicles.

[0027] For details regarding the beneficial effects not covered in the second aspect, please refer to the beneficial effects described in the first aspect above; they will not be repeated here. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of a charging pile charging an electric vehicle, provided in an embodiment of this application.

[0029] Figure 2 This is an example provided in the embodiments of this application. Figure 1 The diagram shows the circuit connection of the charging station.

[0030] Figure 3 This is a schematic diagram of the structure of a bidirectional DC-DC converter provided in an embodiment of this application.

[0031] Figure 4 and Figure 5 These are schematic diagrams of another bidirectional DC-DC converter provided in the embodiments of this application.

[0032] Figures 6 to 8 These are examples provided in the embodiments of this application. Figure 4 The diagram shows the specific structure of the bidirectional DC-DC converter.

[0033] Figure 9 This is a schematic diagram of the structure of a charging pile provided in an embodiment of this application. Detailed Implementation

[0034] To facilitate understanding of the embodiments of this application, the following points will be explained before introducing the embodiments of this application.

[0035] In the description of the embodiments of this application, "connection" can refer to an electrical connection. An electrical connection can be understood as the transmission of signals between two electrical components through a direct or indirect electrical connection. For example, an electrical connection between A and B can be understood as a direct electrical connection between A and B, or an indirect electrical connection between A and B through one or more other electrical components.

[0036] In the embodiments of this application, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, features defined as "first" or "second" may explicitly or implicitly include one or more features. Furthermore, in the description of the embodiments of this application, "multiple" refers to two or more, and "at least one" and "one or more" refer to one, two, or more than two.

[0037] In the description of the embodiments in this application, unless otherwise stated, "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone.

[0038] The technical solutions in this application will now be described with reference to the accompanying drawings.

[0039] First, to facilitate understanding of the technical solutions provided in the embodiments of this application, we will introduce the application scenarios applicable to the embodiments of this application.

[0040] Figure 1 This is a schematic diagram of a scenario where a charging pile 10 charges an electric vehicle 21, as provided in an embodiment of this application.

[0041] Combination Figure 1 In (a) and (b), the charging pile 10 is used to receive the AC power output from the power grid 22, convert the AC power into stable DC power and then deliver it to the electric vehicle 21 to charge the electric vehicle 21.

[0042] In some embodiments, such as Figure 1As shown in (a), the charging pile 10 is a split-type charging pile. Specifically, the charging pile 10 includes a charging host 11, one or more charging terminals 12, and one or more charging guns 13.

[0043] The charging host 11 includes multiple power conversion devices (not shown in the figure), which convert the AC power output from the power grid 22 into stable DC power before supplying it to the charging terminal 12. These power conversion devices may include, for example, multiple alternating current-to-direct current (AC-DC) converters and multiple DC-DC converters. Specific descriptions of the AC-DC and DC-DC converters will be provided below and will not be repeated here.

[0044] Each charging terminal 12 is connected to at least one of one or more charging guns 13, and each charging gun 13 is used to connect to an electric vehicle 21. Each charging terminal 12 is used to deliver DC power output from multiple power conversion devices to the electric vehicle 21 through the connected charging gun 13. In a specific implementation, an electric vehicle 21 may be connected to one or more charging guns 13.

[0045] It should be understood that, in the embodiments of this application, the charging terminal 12 may include a cabinet, a human-machine interface, a charging control unit, and a metering and billing unit, etc., for information interaction, energy transmission, and metering and billing with the electric vehicle 21.

[0046] It should also be understood that, in the embodiments of this application, electric vehicle 21 is a means of transportation driven by electric power. Electric vehicle 21 can be a pure electric vehicle (pure EV / battery EV), a hybrid electric vehicle (HEV), a range-extended electric vehicle (REEV), or a plug-in hybrid electric vehicle (PHEV), etc.

[0047] In other embodiments, as shown in Figure (1)(b), the charging pile 10 is an integrated charging pile. Specifically, the human-machine interface, charging control unit, and metering and billing unit in the charging pile 10 are directly installed in the charging host 11. Thus, the charging pile 10 may include the charging host 11 and the charging gun 13 connected to the charging host 11, but does not include the charging terminal 12. In a specific implementation, multiple power conversion devices in the charging host 11 convert the AC power output from the grid 22 into stable DC power, which is then directly transmitted to the electric vehicle 21 through the charging gun 13.

[0048] The following is based on Figure 1 Taking the split-type charging pile shown in (a) as an example, the structure of the multiple power conversion devices installed in the charging host 11 will be further introduced.

[0049] Figure 2 This is an example provided in the embodiments of this application. Figure 1 A schematic diagram of the specific structure of the charging pile 10 shown in (a) is shown in the figure.

[0050] See Figure 2 In the charging pile 10, the charging host 11 includes multiple AC-DC converters 111, multiple DC-DC converters 112, a DC bus 113, and a power distribution device 114. The input terminal of each AC-DC converter 111 is connected to the power grid 22, and the output terminal of each AC-DC converter 111 is connected to the input terminal of each DC-DC converter 112 via the DC bus 113. The output terminal of each DC-DC converter 112 is connected to each charging terminal 12 in the charging pile 10 via the power distribution device 114, and each charging terminal 12 is connected to a charging gun 13.

[0051] In practical implementation, each AC-DC converter 111 converts the alternating current output from the power grid 22 into direct current and outputs it to the DC bus 113. Each DC-DC converter 112 further converts the DC power obtained from the DC bus 113 into DC power suitable for the electric vehicle 21 and outputs it to the power distribution device 114. The power distribution device 114 dynamically distributes the DC power output from each DC-DC converter 112 according to the actual charging power required by the electric vehicle 21, and transmits the distributed power to the charging gun 13 through the charging terminal 12, so that the power output from the charging gun 13 to the electric vehicle 21 meets the charging needs of the electric vehicle 21.

[0052] As described in the background section above, in order to meet the needs of the electric vehicle 21 charging through the charging pile 10 and discharging into the power grid 22 through the charging pile 10, the AC-DC converter 111 and DC-DC converter 112 in the charging pile 10 are respectively bidirectional AC-DC converters and bidirectional DC-DC converters capable of bidirectional power transmission. Specifically, when the electric vehicle 21 is charging through the charging pile 10, the bidirectional AC-DC converter and bidirectional DC-DC converter operate in the forward direction. A detailed description of the forward operation of the bidirectional AC-DC converter and bidirectional DC-DC converter can be found above and will not be repeated here.

[0053] When the electric vehicle 21 discharges to the power grid 22 through the charging pile 10, the bidirectional AC-DC converter and the bidirectional DC-DC converter operate in opposite directions. The bidirectional DC-DC converter is used to convert the DC power output from the electric vehicle 21 and output it to the DC bus 113, while the bidirectional AC-DC converter is used to convert the DC power obtained from the DC bus 113 into AC power and output it to the power grid 22.

[0054] There are many types of electric vehicles on the market. Different types of electric vehicles 21 not only have significantly different voltages during charging, but also during discharging. Therefore, to meet the charging and discharging needs of different types of electric vehicles 21, the bidirectional DC-DC converter in the charging pile 10 needs to support bidirectional power transmission over a wide voltage range. However, the bidirectional DC-DC converters currently used in charging piles 10 mostly replace the diodes in the traditional three-phase inductor-inductor-capacitor (LC) resonant unidirectional charging circuit with switching transistors to form a bidirectional circuit topology. When this bidirectional circuit topology operates in reverse, i.e., when the electric vehicle 21 discharges to the grid through the charging pile 10, the circuit characteristics of the bidirectional circuit topology degenerate from LLC resonant characteristics to LC resonant characteristics. Since the maximum gain of the LC resonant voltage is 1, the bidirectional circuit topology cannot achieve boost output when operating in reverse, and the voltage regulation range of the bidirectional circuit topology is greatly narrowed, thus failing to adequately meet the requirements for bidirectional power transmission over a wide voltage range.

[0055] Based on the above, this application provides a bidirectional DC-DC converter and a charging pile including the bidirectional DC-DC converter, which can improve the voltage regulation range and power conversion efficiency of the bidirectional DC-DC converter during bidirectional power transmission, thereby achieving wide voltage range and high efficiency input or output.

[0056] The bidirectional DC-DC converter provided in this application will be described below with reference to the accompanying drawings. It should be noted that the bidirectional DC-DC converter provided in this application can be applied not only to charging piles, but also to power modules in charging stations, on-board chargers for electric vehicles, and charging modules in energy storage scenarios. For ease of description and understanding, the following embodiments use the application of the bidirectional DC-DC converter in a charging pile as an example.

[0057] Figure 3 This is a schematic diagram of the structure of a bidirectional DC-DC converter 30 provided in an embodiment of this application.

[0058] See Figure 3 The bidirectional DC-DC converter 30 includes a first power conversion circuit 31, a three-phase resonant circuit 32, a three-phase transformer 33, and a second power conversion circuit 34. Each phase of the three-phase resonant circuit 32 includes a first capacitor and a first inductor connected in series; that is, the three-phase resonant circuit 32 is a three-phase LC resonant circuit. One end of each phase resonant circuit is connected to the first power conversion circuit 31, and the other end of each phase resonant circuit is connected to the second power conversion circuit 34 through the three-phase transformer 33. Thus, the first power conversion circuit 31 can be connected to the second power conversion circuit 34 through the three-phase resonant circuit 32 and the three-phase transformer 33.

[0059] It should be understood that, in specific implementation, the first power conversion circuit 31 includes a DC connection terminal 311 and a three-phase AC connection terminal 312, and the second power conversion circuit 34 includes a DC connection terminal 341 and a three-phase AC connection terminal 342. The DC connection terminal 311 of the first power conversion circuit 31 and the DC connection terminal 341 of the second power conversion circuit 34 serve as two sets of connection terminals for the bidirectional DC-DC converter 30. One set of these connection terminals is used to connect to a DC power supply, and the other set is used to connect to a load. The DC power supply may be, for example, a DC power supply... Figure 2 The DC bus 113 shown can be loaded with, for example, a load of... Figure 2 The electric vehicle 21 shown.

[0060] It should be noted that, for ease of description and understanding, the embodiments of this application are described using the example of the DC connection terminal 311 of the first power conversion circuit 31 being used to connect to a DC power supply and the DC connection terminal 341 of the second power conversion circuit 34 being used to connect to a load.

[0061] For example, the three-phase resonant circuit 32 includes an A-phase resonant circuit, a B-phase resonant circuit, and a C-phase resonant circuit. The A-phase resonant circuit includes a first capacitor Cr1 and a first inductor Lr1 connected in series; the B-phase resonant circuit includes a first capacitor Cr2 and a first inductor Lr2 connected in series; and the C-phase resonant circuit includes a first capacitor Cr3 and a first inductor Lr3 connected in series. One end of each of the A-phase, B-phase, and C-phase resonant circuits is connected to the A-phase AC connection terminal Ua, B-phase AC connection terminal Ub, and C-phase AC connection terminal Uc of the three-phase AC connection terminal 312 of the first power conversion circuit 31, respectively. The other end of each of the A-phase, B-phase, and C-phase resonant circuits is connected to the A-phase AC connection terminal Ua, B-phase AC connection terminal Ub, and C-phase AC connection terminal Uc of the three-phase AC connection terminal 342 of the second power conversion circuit 34, respectively, through a three-phase transformer 33. This allows the first power conversion circuit 31 to transmit electrical energy to the second power conversion circuit 34 via the three-phase resonant circuit 32 and the three-phase transformer 33.

[0062] Based on the above design, when the load is charged by a DC power supply, the DC connection terminal 311 of the first power conversion circuit 31 serves as the input terminal of the bidirectional DC-DC converter 30, and the DC connection terminal 341 of the second power conversion circuit 34 serves as the output terminal of the bidirectional DC-DC converter 30. Specifically, the first power conversion circuit 31 converts the DC power output from the DC power supply into AC power, which is then output to the three-phase transformer 33 via the three-phase resonant circuit 32. The second power conversion circuit 34 converts the AC power output from the three-phase transformer 33 into DC power and outputs it to the load. That is, electrical energy flows from the first power conversion circuit 31 to the second power conversion circuit 34, with the first power conversion circuit 31 used for inversion and the second power conversion circuit 34 used for rectification.

[0063] Alternatively, when the load discharges to the DC power supply, the DC connection terminal 341 of the second power conversion circuit 34 serves as the input terminal of the bidirectional DC-DC converter 30, and the DC connection terminal 311 of the first power conversion circuit 31 serves as the output terminal of the bidirectional DC-DC converter 30. In this configuration, electrical energy flows from the second power conversion circuit 34 to the first power conversion circuit 31, with the second power conversion circuit 34 used for inversion and the first power conversion circuit 31 used for rectification.

[0064] It should be noted that, for ease of description and understanding, in this application embodiment, the flow of electrical energy from the first power conversion circuit 31 to the second power conversion circuit 34 is referred to as the forward transmission of electrical energy in the bidirectional DC-DC converter 30, and the flow of electrical energy from the second power conversion circuit 34 to the first power conversion circuit 31 is referred to as the reverse transmission of electrical energy in the bidirectional DC-DC converter 30.

[0065] Continue reading Figure 3The bidirectional DC-DC converter 30 also includes a resonant switching circuit 35 and an inductor circuit 36. Each phase of the three-phase resonant circuit 32 is connected to the inductor circuit 36 ​​via the resonant switching circuit 35. The resonant switching circuit 35 is used to activate the circuit between either end of each phase of the resonant circuit 32 and the inductor circuit 36, so that each phase of the resonant circuit 32 and the inductor circuit 36 ​​form an LLC resonant circuit.

[0066] It should be understood that, in the embodiments of this application, the inductor circuit 36 ​​may include a plurality of second inductors. Thus, when the resonant switching circuit 35 turns on the circuit between either end of each phase resonant circuit 32 and the inductor circuit 36, the first inductor and the first capacitor connected in series in each phase resonant circuit can form an LLC resonant circuit with the second inductors in the inductor circuit 36.

[0067] The specific structure of the LLC resonant circuit formed by the resonant switching circuit 35 and the second inductor in the inductor circuit 36 ​​for each phase resonant circuit will be described below and will not be repeated here.

[0068] Based on the above design, when electrical energy is transmitted from the first power conversion circuit 31 to the second power conversion circuit 34 through the three-phase resonant circuit 32, or when electrical energy is transmitted from the second power conversion circuit 34 to the first power conversion circuit 31 through the three-phase resonant circuit 32, i.e. when electrical energy is transmitted in the bidirectional DC-DC converter 30 in either the forward or reverse direction, the resonant switching circuit 35 can be used to connect the circuit between the output end of each phase resonant circuit and the inductor circuit 36, so that electrical energy flows to the inductor circuit 36 ​​through the series-connected first capacitor and first inductor, thereby forming an LLC resonant circuit between each phase resonant circuit and the inductor circuit. Since the voltage gain of the LLC resonant circuit can be less than or equal to 1 or greater than 1, the bidirectional DC-DC converter 30 can either reduce or boost voltage, thereby improving the voltage regulation range of the bidirectional DC-DC converter 30 during bidirectional power transmission. In addition, the LLC resonant circuit has a small input and output ripple current and a high power density, and can achieve soft switching, thus further improving the power conversion efficiency of the bidirectional DC-DC converter 30 during bidirectional power transmission. Furthermore, the bidirectional DC-DC converter 30 can achieve wide voltage range and efficient input or output.

[0069] The following describes the specific structure of the LLC resonant circuit formed by the resonant switching circuit 35 and the second inductor in the inductor circuit 36 ​​for each phase resonant circuit.

[0070] Figure 4 and Figure 5 This is a schematic diagram of another bidirectional DC-DC converter 30 provided in the embodiments of this application.

[0071] In some embodiments, combined with Figure 4 and Figure 5 The inductor circuit 36 ​​includes three second inductors. In the three-phase resonant circuit 32, the two ends of each phase resonant circuit are connected to one end of a second inductor via a resonant switching circuit 35. That is, the three-phase resonant circuit 32 is connected to the three second inductors in a one-to-one correspondence via the resonant switching circuit 35.

[0072] For example, such as Figure 3 As shown, the inductor circuit 36 ​​includes a second inductor Lm1, a second inductor Lm2, and a second inductor Lm3. In the three-phase resonant circuit 32, the two ends of phase A resonant circuit are connected to the second inductor Lm1 via a resonant switching circuit 35; the two ends of phase B resonant circuit are connected to the second inductor Lm2 via the resonant switching circuit 35; and the two ends of phase C resonant circuit are connected to the second inductor Lm3 via the resonant switching circuit 35.

[0073] It should be understood that in the embodiments of this application, the first capacitor and the first inductor can also be referred to as resonant capacitor and resonant inductor, and the second inductor can also be referred to as magnetizing inductor.

[0074] Based on the above design, the first capacitor and the first inductor connected in series in each phase resonant circuit can be connected to one end of a second inductor in the inductor circuit 36 ​​via the resonant switching circuit 35 to form an LLC resonant circuit. For example, when the resonant switching circuit 35 turns on the circuit between either end of the A-phase resonant circuit and one end of the second inductor Lm1, the first inductor Lr1 and the first capacitor Cr1 connected in series in the A-phase resonant circuit can be connected to the second inductor Lm1 to form an LLC resonant circuit. Furthermore, compared to the current practice of integrating the magnetizing inductor with the three-phase transformer 33, which results in a large air gap size in the core of the three-phase transformer 33, the three second inductors, i.e., the three magnetizing inductors, in this embodiment can be separated from the three-phase transformer 33. This can significantly reduce the air gap size in the core of the three-phase transformer 33, thereby further improving the efficiency and stability of the three-phase transformer 33.

[0075] It should be understood that, in order to achieve LLC resonance in both forward and reverse power transmission of the bidirectional DC-DC converter 30, some current designs employ LLC resonant circuits between the first power conversion circuit 31 and the three-phase transformer 33, and between the second power conversion circuit 34 and the three-phase transformer 33. Alternatively, some designs use an LLC resonant circuit between the first power conversion circuit 31 and the three-phase transformer 33 to achieve LLC resonance during forward power transmission, and then add a magnetizing inductor between the first power conversion circuit 31 and the three-phase transformer 33 to achieve LLC resonance during reverse power transmission. However, these designs use a large number of resonant elements, resulting in a complex and bulky resonant cavity structure in the bidirectional DC-DC converter 30.

[0076] In this embodiment, the resonant switching circuit 35 enables the bidirectional DC-DC converter 30 to form an LLC resonant circuit in both forward and reverse power transmission. Therefore, an additional LLC resonant circuit is not required between the three-phase transformer 33 and the second power conversion circuit 34, and an additional magnetizing inductor is not needed between the first power conversion circuit 31 and the three-phase transformer 33. This further reduces the structural complexity and volume of the resonant cavity in the bidirectional DC-DC converter 30.

[0077] In one embodiment, continue to combine Figure 4 and Figure 5 The resonant switching circuit 35 includes three resonant switching switches. The two ends of each phase resonant circuit in the three-phase resonant circuit 32 are connected to one end of a second inductor in the inductor circuit 36 ​​through a resonant switching switch.

[0078] Specifically, in one example, such as Figure 4 As shown, the two ends of each phase resonant circuit are connected one-to-one with the two stationary contacts of a resonant switching switch. One end of a second inductor is connected to the moving contact of that resonant switching switch, and the other ends of the three second inductors are connected together. That is, each resonant switching switch can be a single-pole double-throw switch.

[0079] For example, with Figure 4Taking the inductor circuit 36 ​​shown as an example, which includes second inductors Lm1, Lm2, and Lm3, the resonant switching circuit 35 includes resonant switching switches S1, S2, and S3. In the three-phase resonant circuit 32, the two ends of phase A resonant circuit are connected one-to-one with the two stationary contacts of resonant switching switch S1; the two ends of phase B resonant circuit and one end of second inductor Lm2 are connected to the two stationary contacts and one moving contact of resonant switching switch S2; and the two ends of phase C resonant circuit and one end of second inductor Lm3 are connected to the two stationary contacts and one moving contact of resonant switching switch S3. Furthermore, the other ends of second inductors Lm1, Lm2, and Lm3 are connected in a star configuration.

[0080] Based on the above design, when electrical energy is transmitted in the bidirectional DC-DC converter 30 in either the forward or reverse direction, by connecting the moving contact of each resonant switch to one of its two stationary contacts, the circuit between one end of each phase resonant circuit as an output and one end of the corresponding second inductor can be turned on. Furthermore, each phase resonant circuit in the three-phase resonant circuit 32 can form an LLC resonance with its corresponding second inductor. In addition, by connecting the three second inductors in a star configuration, the bidirectional DC-DC converter 30 can be more suitable for applications requiring higher voltage and lower current.

[0081] In another example, such as Figure 5 As shown, the two ends of each phase resonant circuit are connected one-to-one with the two stationary contacts of a resonant switching switch, and the three second inductors in the inductor circuit 36 ​​are connected end to end in sequence. The connection point between one second inductor and another second inductor can be used as one end of the second inductor and connected to the moving contact of the resonant switching switch.

[0082] For example, with Figure 5Taking the inductor circuit 36 ​​shown as including second inductors Lm1, Lm2, and Lm3 as an example, the resonant switching circuit 35 also includes resonant switching switches S1, S2, and S3. The two ends of the A-phase resonant circuit are connected to the two stationary contacts of resonant switching switch S1, the two ends of the B-phase resonant circuit are connected to the two stationary contacts of resonant switching switch S2, and the two ends of the C-phase resonant circuit are connected to the two stationary contacts of resonant switching switch S3, respectively. The second inductors Lm1, Lm2, and Lm3 are connected end-to-end in sequence. The connection point between the second inductors Lm1 and Lm3 serves as one end of the second inductor Lm1 connected to the moving contact of resonant switching switch S1. The connection point between the second inductors Lm1 and Lm2 serves as one end of the second inductor Lm2 connected to the moving contact of resonant switching switch S2. The connection point between the second inductors Lm2 and Lm3 serves as one end of the second inductor Lm3 connected to resonant switching switch S3. That is, the three second inductors are connected in a delta configuration.

[0083] Based on the above design, when electrical energy is transmitted in the bidirectional DC-DC converter 30 in either the forward or reverse direction, by connecting the moving contact of each resonant switch to one of its two stationary contacts, the circuit between one end of each phase resonant circuit as an output and one end of the corresponding second inductor can be turned on. Furthermore, each phase resonant circuit in the three-phase resonant circuit 32 can form an LLC resonance with its corresponding second inductor. In addition, by connecting the three second inductors in a delta configuration, the bidirectional DC-DC converter 30 can be made more suitable for applications requiring lower voltage and higher current.

[0084] It should be understood that the above-described resonant switching switch as a single-pole double-throw switch is merely an example. For instance, in some other embodiments, the resonant switching switch may also be a relay or a semiconductor switching device, or other devices capable of switching the circuit conduction between each phase resonant circuit and the corresponding second inductor.

[0085] It should also be understood that, in the embodiments of this application, the three first inductors in the three-phase resonant circuit 32, namely the first inductor Lr1, the first inductor Lr2, and the first inductor Lr3, are integrated. The three second inductors, namely the second inductor Lm1, the second inductor Lm2, and the second inductor Lm3, are integrated. Alternatively, the first inductor Lr1 and the second inductor Lm1 are integrated, the first inductor Lr2 and the second inductor Lm2 are integrated, and the first inductor Lr3 and the second inductor Lm3 are integrated.

[0086] In specific implementations, some embodiments combine Figures 3 to 5The resonant switching circuit 35 is used to: when the first power conversion circuit 31 is used to convert the received DC power into AC power, and the second power conversion circuit 34 is used to convert the AC power output from the first power conversion circuit 31 into DC power and output it, conduct the circuit between the other end of each phase resonant circuit connected to the three-phase transformer 33 and the inductor circuit 36.

[0087] Specifically, with Figure 4 and Figure 5 Taking the inductor circuit 36 ​​shown as including second inductors Lm1, Lm2, and Lm3 as an example, when electrical energy is transmitted from the first power conversion circuit 31 to the second power conversion circuit 34, the right end of the two ends of the A-phase resonant circuit, B-phase resonant circuit, and C-phase resonant circuit connected to the three-phase transformer 33 serves as the output end of each phase resonant circuit. In this case, the resonant switching switches S1, S2, and S3 in the resonant switching circuit 35 can be used to connect the circuit between the right end of the A-phase resonant circuit and the second inductor Lm1, the right end of the B-phase resonant circuit and the second inductor Lm2, and the right end of the C-phase resonant circuit and the second inductor Lm3, respectively. Thus, the electrical energy output from the A-phase resonant circuit, B-phase resonant circuit, and C-phase resonant circuit can flow to the corresponding connected second inductors and the three-phase transformer 33. Therefore, when electrical energy is transmitted in the forward direction in the bidirectional DC-DC converter 30, the first capacitor and the first inductor connected in series in each phase resonant circuit can form an LLC resonant circuit with the corresponding connected second inductor.

[0088] In other embodiments, the resonant switching circuit 35 is used to: when electrical energy is transmitted from the second power conversion circuit 34 to the first power conversion circuit 31, and when the second power conversion circuit 34 is used to convert the received DC power into AC power and the first power conversion circuit is used to convert the AC power output from the second power conversion circuit into DC power before outputting it, the circuit between the end of each phase resonant circuit connected to the first power conversion circuit 31 and the inductor circuit 36 ​​is turned on.

[0089] Specifically, still based on Figure 4 and Figure 5Taking the inductor circuit 36 ​​shown as including second inductors Lm1, Lm2, and Lm3 as an example, when electrical energy is transmitted from the second power conversion circuit 34 to the first power conversion circuit 31, the left end of the A-phase resonant circuit, B-phase resonant circuit, and C-phase resonant circuit connected to the first power conversion circuit 31 serves as the output terminal of each phase resonant circuit. In this case, the resonant switching switches S1, S2, and S3 in the resonant switching circuit 35 can be used to connect the circuit between the left end of the A-phase resonant circuit and the second inductor Lm1, the left end of the B-phase resonant circuit and the second inductor Lm2, and the left end of the C-phase resonant circuit and the second inductor Lm3, respectively. Thus, the electrical energy output from the A-phase resonant circuit, B-phase resonant circuit, and C-phase resonant circuit can flow to the corresponding connected second inductors and the first power conversion circuit 31. Therefore, when electrical energy is transmitted in reverse in the bidirectional DC-DC converter 30, the first capacitor and the first inductor connected in series in each phase resonant circuit can also form an LLC resonant circuit with the corresponding connected second inductor.

[0090] Based on the above design, when electrical energy is transmitted in the bidirectional DC-DC converter 30 in the forward or reverse direction, the circuit between the output end of each phase resonant circuit and the corresponding second inductor can be made conductive, thereby ensuring that the bidirectional DC-DC converter 30 forms an LLC resonant circuit in both the forward and reverse transmission of electrical energy.

[0091] The above describes the structure of the inductor circuit 36 ​​in the bidirectional DC-DC converter 30, and the resonant switching circuit 35 connected to the inductor circuit 36. The following section will describe... Figure 4 Taking the three second inductors shown in a star connection as an example, the other circuit structures in the bidirectional DC-DC converter 30 will be introduced.

[0092] Figure 6 This is an example provided in the embodiments of this application. Figure 3 The schematic diagram shows the specific circuit structure of the bidirectional DC-DC converter 30.

[0093] In some embodiments, see Figure 6 The first power conversion circuit 31 includes three first power conversion bridge arms connected in parallel, each first power conversion bridge arm including two switching transistors connected in series. The two ends of the three first power conversion bridge arms connected in parallel serve as the DC connection terminals 311 of the first power conversion circuit 31, the series connection point of the two switching transistors in each first power conversion bridge arm serves as the bridge arm midpoint of the first power conversion bridge arm, and the three bridge arm midpoints of the three first power conversion bridge arms serve as the three-phase AC connection terminals 312 of the first power conversion circuit 31 for connection with the three-phase resonant circuit 32.

[0094] For example, such as Figure 6 As shown, the three first power conversion bridge arms respectively include series-connected switches Q1 and Q2, series-connected switches Q3 and Q4, and series-connected switches Q5 and Q6. The midpoints P11, P12, and P13 of the three first power conversion bridge arms serve as the three-phase AC connection terminals 312 of the first power conversion circuit 31.

[0095] In one example, the first power conversion circuit 31 also includes a capacitor C1, which is connected in parallel with the three first power conversion bridge arms and is used to filter the DC power received at the DC connection terminal 311 of the first power conversion circuit 31.

[0096] In some embodiments, see further reference. Figure 6 Similar to the first power conversion circuit 31, the second power conversion circuit 34 includes three parallel second power conversion bridge arms, each including two switching transistors connected in series. The two ends of the three parallel second power conversion bridge arms serve as DC connection terminals 341 of the second power conversion circuit 34, and the midpoints of the three bridge arms serve as three-phase AC connection terminals 342 of the second power conversion circuit 34 for connection to the three-phase transformer 33.

[0097] For example, such as Figure 6 As shown, the three second power conversion bridge arms respectively include series-connected switches Q7 and Q8, series-connected switches Q9 and Q10, and series-connected switches Q11 and Q12. The midpoints P21, P22, and P23 of the three second power conversion bridge arms serve as the three-phase AC connection terminals 342 of the second power conversion circuit 34.

[0098] In one example, the second power conversion circuit 34 also includes a capacitor C2, which is connected in parallel with the three arms of the second power conversion bridge, and the capacitor C2 is used to filter the DC power output from the DC connection terminal 341 of the second power conversion circuit 34.

[0099] In some embodiments, see further reference. Figure 6 The bidirectional DC-DC converter 30 also includes multiple second capacitors, and the second power conversion circuit 34 includes three second power conversion bridge arms connected in parallel. The midpoint of each second power conversion bridge arm is connected to the three-phase transformer 33 via a second capacitor, and the second capacitor connected to the midpoint of each second power conversion bridge arm is different.

[0100] For example, such as Figure 6As shown, the bidirectional DC-DC converter 30 also includes a second capacitor Cs1, a second capacitor Cs2, and a second capacitor Cs3. The midpoints P21, P22, and P23 of the three second power conversion bridge arms are respectively connected to the three-phase transformer 33 through the second capacitors Cs1, Cs2, and Cs3.

[0101] Based on the above design, when electrical energy is transmitted in reverse in the bidirectional DC-DC converter 30, that is, when electrical energy is transmitted from the second power conversion circuit 34 to the first power conversion circuit 31, the second capacitor can prevent the magnetic core of the three-phase transformer 33 from becoming magnetized, thereby further improving the stability of the three-phase transformer 33 during operation.

[0102] In some embodiments, see further reference. Figure 6 The three-phase transformer 33 includes a three-phase primary winding 331 and a three-phase secondary winding 332. The three-phase primary winding 331 is connected to the other end of the three-phase resonant circuit 32 in a one-to-one correspondence, and the three-phase secondary winding 332 is connected to the midpoints of the three bridge arms in the second power conversion circuit 34 in a one-to-one correspondence. In this way, the three-phase resonant circuit 32 can transfer electrical energy between the three-phase transformer 33 and the second power conversion circuit 34.

[0103] It should be understood that, in practical implementation, when electrical energy is transmitted in the forward direction in the bidirectional DC-DC converter 30, the three-phase primary winding 331 of the three-phase transformer 33 and the first power conversion circuit 31 can be referred to as the primary side circuit of the three-phase transformer 33, and the three-phase secondary winding 332 and the second power conversion circuit 34 can be referred to as the secondary side circuit of the three-phase transformer 33. Conversely, when electrical energy is transmitted in the reverse direction in the bidirectional DC-DC converter 30, the three-phase primary winding 331 of the three-phase transformer 33 and the first power conversion circuit 31 can be referred to as the secondary side circuit of the three-phase transformer 33, and the three-phase secondary winding 332 and the second power conversion circuit 34 can be referred to as the primary side circuit of the three-phase transformer 33.

[0104] In some embodiments, the combination continues Figure 6 The bidirectional DC-DC converter 30 further includes at least one of a first turns-changing switch circuit 37 and a second turns-changing switch circuit 38. For example, Figure 5 An exemplary bidirectional DC-DC converter 30 is shown, which also includes a first turns switching circuit 37 and a second turns switching circuit 38.

[0105] The first turns switching circuit 37 is connected to the three-phase primary winding 331 and is used to switch the number of turns of each phase of the three-phase primary winding 331 connected to the circuit. The second turns switching circuit 38 is connected to the three-phase secondary winding 332 and is used to switch the number of turns of each phase of the three-phase secondary winding 332 connected to the circuit.

[0106] Based on the above design, when electrical energy is transmitted in the bidirectional DC-DC converter 30 in the forward or reverse direction, the winding turns ratio of the three-phase transformer 33 connected to the circuit can be adjusted by at least one of the first turns switching circuit 37 and the second turns switching circuit 38, so as to adjust the operating voltage range of the bidirectional DC-DC converter 30, thereby enabling the bidirectional DC-DC converter 30 to achieve a wide voltage range input or output.

[0107] For example, when an electric vehicle is connected to the DC connection terminal 341 of the second power conversion circuit 34, when the electric vehicle is charging, that is, when electrical energy is being transmitted in the forward direction in the bidirectional DC-DC converter 30, the winding turns ratio of the three-phase transformer 33 connected to the circuit can be adjusted by at least one of the first turns switching circuit 37 and the second turns switching circuit 38, so that the bidirectional DC-DC converter 30 can achieve a wide range of voltage output, thereby meeting the charging voltage requirements of different electric vehicles.

[0108] Furthermore, when the winding turns ratio of the three-phase transformer 33 connected to the circuit is switched by at least one of the first turns switching circuit 37 and the second turns switching circuit 38, if the magnetizing inductor and the three-phase transformer 33 are integrated, the inductance of the magnetizing inductor is easily affected by the turns ratio switching of the three-phase transformer 33, resulting in unstable operation of the bidirectional DC-DC converter 30. However, in this embodiment, since the three second inductors, i.e., the three magnetizing inductors, are separately configured from the three-phase transformer 33, the inductance of the three magnetizing inductors is unaffected by the turns ratio switching when the winding turns ratio of the three-phase transformer 33 connected to the circuit is switched by at least one of the first turns switching circuit 37 and the second turns switching circuit 38, thereby further ensuring the operation of the bidirectional DC-DC converter 30.

[0109] In some embodiments, see further reference. Figure 6The bidirectional DC-DC converter 30 includes a first turns switching circuit 37. Each phase of the three-phase primary winding 331 includes a first primary winding and a second primary winding. One end of each of the three first primary windings is connected to the other end of the three-phase resonant circuit 32. The other end of the first primary winding of one phase is connected to one end of the second primary winding of another phase to form a first tap. The other ends of the three second primary windings are connected together.

[0110] Furthermore, the first turns-changing switch circuit includes two first turns-changing switches, each connected one-to-one with the other two primary windings of the three-phase primary winding 331, excluding one of the primary windings. Each first turns-changing switch is used to connect the circuit between the other end of the first primary winding of the corresponding primary winding and one end of the second primary winding of the corresponding primary winding. Alternatively, each first turns-changing switch is used to connect the circuit between the other end of the first primary winding of the corresponding primary winding and the first tap.

[0111] For example, such as Figure 6 As shown, the three-phase transformer 33's three-phase primary winding 331 includes an A-phase primary winding, a B-phase primary winding, and a C-phase primary winding. The A-phase primary winding includes a first primary winding Np11 and a second primary winding Np12; the B-phase primary winding includes a first primary winding Np21 and a second primary winding Np22; and the C-phase primary winding includes a first primary winding Np31 and a second primary winding Np32. The first turns switching circuit 37 includes a first turns switching switch ST1 and a first turns switching switch ST2, both of which are single-pole double-throw switches.

[0112] In this circuit, one end of the first primary windings Np11, Np21, and Np31 is connected to the A-phase resonant circuit, B-phase resonant circuit, and C-phase resonant circuit in the three-phase resonant circuit 32, respectively. The other end of the first primary winding Np21 in the B-phase primary winding is connected to one end of the second primary winding Np22 to form the first tap P31. The other ends of the second primary windings Np12, Np22, and Np32 are connected together. The moving contact of the first turns-to-turn switch ST1 is connected to the other end of the first primary winding Np11, and the two stationary contacts of the first turns-to-turn switch ST1 are connected to one end of the second primary winding Np12 and the first tap P31, respectively. The moving contact of the second turns-to-turn switch ST2 is connected to the other end of the first primary winding Np31, and the two stationary contacts of the second turns-to-turn switch ST2 are connected to one end of the second primary winding Np32 and the first tap P31, respectively. That is, the three-phase primary winding 331 of the three-phase transformer 33 is connected in a Y-shape through two first turns switching switches.

[0113] Based on the above design, by connecting the moving contact of each first turns switching switch to one of its two stationary contacts, the number of turns of each phase primary winding of the three-phase transformer 33 connected to the circuit can be adjusted to be the sum of the number of turns of the first primary winding and the second primary winding, or the number of turns of the first primary winding. This allows the operating voltage range of the bidirectional DC-DC converter 30 to be adjusted so that the bidirectional DC-DC converter 30 can achieve a wide voltage range input or output.

[0114] In some embodiments, see further reference. Figure 6 The bidirectional DC-DC converter 30 includes a second turns switching circuit 38. Each phase of the three-phase secondary winding 332 includes a first secondary winding and a second secondary winding. One end of each of the three first secondary windings is connected to one of the midpoints P21, P22, and P23 of the three bridge arms in the second power conversion circuit 34. The other end of the first secondary winding of one phase is connected to one end of the second secondary winding of another phase to form a second tap. The other ends of the three second secondary windings are connected together.

[0115] Furthermore, the second turns switching circuit 38 includes two second turns switching switches, each connected one-to-one with the other two secondary windings of the three-phase secondary winding 332, excluding one of the secondary windings. Each second turns switching switch is used to connect the circuit between the other end of the first secondary winding of the corresponding secondary winding and one end of the second secondary winding of the corresponding secondary winding. Alternatively, each second turns switching switch is used to connect the circuit between the other end of the first secondary winding of the corresponding secondary winding and the second tap.

[0116] For example, such as Figure 6 As shown, the three-phase transformer 33's three-phase secondary winding 332 includes an A-phase secondary winding, a B-phase secondary winding, and a C-phase secondary winding. The A-phase primary winding includes a first secondary winding Ns11 and a second secondary winding Ns12; the B-phase secondary winding includes a first secondary winding Ns21 and a second secondary winding Ns22; and the C-phase secondary winding includes a first secondary winding Ns31 and a second secondary winding Ns32. One end of each of the first secondary windings Ns11, Ns21, and Ns31 is connected to the midpoints P21, P22, and P23 of the bridge arm in the second power conversion circuit 34. The other end of the first secondary winding Ns21 in the B-phase secondary winding is connected to one end of the second secondary winding Ns22 to form a second tap P41. Furthermore, the second turns switching circuit 38 includes a second turns switching switch SK1 and a second turns switching switch SK2.

[0117] It should be understood that the specific way in which the second turns switching switch SK1 and the second turns switching switch SK2 are connected to the three-phase secondary winding 332 is similar to the way in which the two first turns switching switches in the first turns switching switch circuit 37 are connected to the three-phase primary winding 331, and will not be described again here.

[0118] Based on the above design, by connecting the moving contact of each second turns switching switch to one of its two stationary contacts, the number of turns of each phase secondary winding of the three-phase transformer 33 connected to the circuit can be adjusted to be the sum of the number of turns of the first secondary winding and the second secondary winding, or the number of turns of each phase secondary winding of the three-phase transformer 33 connected to the circuit can be adjusted to be the number of turns of the first secondary winding. This allows the operating voltage range of the bidirectional DC-DC converter 30 to be adjusted so that the bidirectional DC-DC converter 30 can achieve a wide voltage range input or output.

[0119] Figure 7 This is another example provided in the embodiments of this application. Figure 3 The schematic diagram shows the specific circuit structure of the bidirectional DC-DC converter 30.

[0120] and Figure 6 The difference between the illustrated embodiment and the one shown is that, in Figure 7 In the illustrated embodiment, the bidirectional DC-DC converter 30 may include only the second turns switching circuit 38, without the first turns switching circuit 37. In this case, the three-phase primary windings 331 of the three-phase transformer 33 include phase A primary winding Np1, phase B primary winding Np2, and phase C primary winding Np3. One end of each of the phase A primary winding Np1, phase B primary winding Np2, and phase C primary winding Np3 is connected to the other end of the three-phase resonant circuit 32, and the other ends of each are connected together.

[0121] It should be understood that a detailed description of the second turns switching circuit 38 can be found in [reference needed]. Figure 6 The relevant descriptions of the embodiments shown will not be repeated here.

[0122] Based on the above design, when the electrical energy is transmitted in the bidirectional DC-DC converter 30 in the forward or reverse direction, the number of turns of the three-phase secondary winding 332 of the three-phase transformer 33 connected to the circuit can be adjusted by the second turns switching circuit 38, thereby adjusting the operating voltage range of the bidirectional DC-DC converter so that the bidirectional DC-DC converter can achieve a wide voltage range input or output.

[0123] Figure 8 This is yet another example provided in the embodiments of this application. Figure 3 The schematic diagram shows the specific circuit structure of the bidirectional DC-DC converter 30.

[0124] and Figure 6 The difference between the illustrated embodiment and the one shown is that, in Figure 8 In the illustrated embodiment, the bidirectional DC-DC converter 30 may include only the first turns-changing switch circuit 37, excluding the second turns-changing switch circuit 38. A detailed description of the first turns-changing switch circuit 37 can be found in [reference needed]. Figure 5 The relevant descriptions of the embodiments shown will not be repeated here.

[0125] In some embodiments, see Figure 8 Each phase of the three-phase secondary winding 332 may include multiple sets of secondary windings, and the number of second power conversion circuits 34 in the bidirectional DC-DC converter 30 may be multiple. Each set of secondary windings is connected one-to-one with the midpoint of one arm of each of the multiple second power conversion circuits 34.

[0126] For example, Figure 8 The example illustrates that each phase secondary winding includes two sets of secondary windings, and the bidirectional DC-DC converter 30 has two second power conversion circuits 34. Specifically, the three-phase transformer 33's three-phase secondary winding 332 includes an A-phase secondary winding, a B-phase secondary winding, and a C-phase secondary winding. The A-phase secondary winding includes a first set of secondary windings Ns11 and a second set of secondary windings Ns12. The B-phase secondary winding includes a first set of secondary windings Ns21 and a second set of secondary windings Ns22. The C-phase secondary winding includes a first set of secondary windings Ns31 and a second set of secondary windings Ns32. The bidirectional DC-DC converter 30 includes a second power conversion circuit 34a and a second power conversion circuit 34b.

[0127] Specifically, the first set of secondary windings Ns11 and Ns12 are connected one-to-one with the midpoints P21 and P24 of the bridge arms of the second power conversion circuit 34a and 34b, respectively. The first set of secondary windings Ns21 and Ns22 are connected one-to-one with the midpoints P22 and P25 of the bridge arms of the second power conversion circuit 34a and 34b, respectively. The first set of secondary windings Ns31 and Ns32 are connected one-to-one with the midpoints P23 and P26 of the bridge arms of the second power conversion circuit 34a and 34b, respectively. In this way, the three-phase transformer 33 can transmit electrical energy to the second power conversion circuits 34a and 34b, respectively.

[0128] In addition, please continue to refer to Figure 8The bidirectional DC-DC converter 30 also includes one or more connection switching circuits 39. Any two of the plurality of second power conversion circuits 34 are connected via a connection switching circuit 39. Each connection switching circuit 39 includes one series switch and two parallel switches. The series switch is used to connect any two second power conversion circuits 34 in series, and the two parallel switches are used to connect any two second power conversion circuits 34 in parallel.

[0129] For example, still using Figure 8 The bidirectional DC-DC converter 30 shown includes two second power conversion circuits 34, namely, second power conversion circuits 34a and 34b. Taking this as an example, the bidirectional DC-DC converter 30 also includes a connection switching circuit 39, which includes a series switch SC, a parallel switch SP1, and a parallel switch SP2. The two ends of the parallel connection of the three power conversion bridge arms in the second power conversion circuit 34a serve as the positive DC connection terminal DC+ and the negative DC connection terminal DC- of the second power conversion circuit 34a, respectively. Similarly, the two ends of the parallel connection of the three power conversion bridge arms in the second power conversion circuit 34b serve as the positive DC connection terminal DC+ and the negative DC connection terminal DC- of the second power conversion circuit 34b, respectively.

[0130] The series switch SC is connected between the positive DC+ terminal of the second power conversion circuit 34a and the negative DC- terminal of the second power conversion circuit 34b. The parallel switch SP1 is connected between the positive DC+ terminal of the second power conversion circuit 34a and the positive DC+ terminal of the second power conversion circuit 34b, and the parallel switch SP2 is connected between the negative DC- terminal of the second power conversion circuit 34a and the negative DC- terminal of the second power conversion circuit 34b.

[0131] Based on the above design, when electrical energy is transferred from the first power conversion circuit 31 to the second power conversion circuit 34, by closing the series switch SC and opening the parallel switches SP1 and SP2, the second power conversion circuit 34a and the second power conversion circuit 34b can be connected in series; or, by closing the parallel switches SP1 and SP2 and opening the series switch SC, the second power conversion circuit 34a and the second power conversion circuit 34b can be connected in parallel. Furthermore, the voltage range output by the second power conversion circuit 34a and the second power conversion circuit 34b can be adjusted to enable the bidirectional DC-DC converter 30 to achieve a wide range of voltage output. Thus, when the positive DC connection terminal DC+ of the second power conversion circuit 34a and the negative DC connection terminal DC- of the second power conversion circuit 34b are used as the output terminals of the bidirectional DC-DC converter 30 and connected to an electric vehicle, the charging voltage requirements of different electric vehicles can be better met.

[0132] For example, when the number of second power conversion circuits 34 in the bidirectional DC-DC converter 30 is three, the bidirectional DC-DC converter 30 also includes three connection switching circuits 39. Each pair of the three second power conversion circuits 34 is connected via a connection switching circuit 39. For a detailed description, please refer to the above description of the connection between the second power conversion circuits 34a and 34b via a connection switching circuit 38, which will not be repeated here.

[0133] Based on the above design, when electrical energy is transmitted from the first power conversion circuit 31 to the second power conversion circuit 34, that is, when electrical energy is transmitted in the forward direction in the bidirectional DC-DC converter 30, the three second power conversion circuits 34 can be connected in series and / or in parallel through the three connection switching circuits 39, thereby adjusting the voltage range output by the three second power conversion circuits 34.

[0134] The bidirectional DC-DC converter 30 provided in the embodiments of this application has been described above. The charging pile including the bidirectional DC-DC converter 30 provided in the embodiments of this application is described below with reference to the accompanying drawings.

[0135] Figure 9 This is a schematic diagram of the structure of a charging pile 40 provided in an embodiment of this application.

[0136] See Figure 9 The charging pile 40 includes an AC-DC converter 41, a bidirectional DC-DC converter 30 as described above, and a charging gun 42. One end of the AC-DC converter 41 is connected to an AC power source, such as the power grid. The other end of the AC-DC converter 41 is connected to the charging gun 42 via the bidirectional DC-DC converter 30, and the charging gun 42 is used to connect to an electric vehicle.

[0137] Based on the above design, the AC-DC converter 41 can be used to convert the AC power output from the AC power source into DC power and then output it to the bidirectional DC-DC converter 30. The bidirectional DC-DC converter 30 is used to further convert the received DC power and then output it to the charging gun 42 so as to charge the electric vehicle through the charging gun 42.

[0138] It should be understood that in this embodiment, the number of AC-DC converters 41 and DC-DC converters 30 can be multiple, with one end of each AC-DC converter 41 connected to one end of each DC-DC converter 30, and the other end of each DC-DC converter 30 connected to the charging gun 42. Alternatively, as... Figure 9As shown, the charging pile 40 also includes a DC bus 43. The other end of each AC-DC converter 41 is connected to one end of each bidirectional DC-DC converter 30 via the DC bus 43. The other end of each bidirectional DC-DC converter 30 is connected to the charging gun 42.

[0139] In some embodiments, see Figure 9 In the bidirectional DC-DC converter 30, the DC connection terminal 311 of the first power conversion circuit 31 is connected to the other end of the AC-DC converter 41. For example, the DC connection terminal 311 of the first power conversion circuit 31 can be connected to the DC bus 43 to connect to the other end of the AC-DC converter 41. The DC connection terminal 341 of the second power conversion circuit 34 is connected to the charging gun 42.

[0140] Based on the above design, when the charging pile 40 is charging an electric vehicle, the electrical energy output by the AC-DC conversion device 41 can be output to the electric vehicle through the first power conversion circuit 31, the three-phase transformer 33, and the second power conversion circuit 34. The LLC resonant circuit formed by the resonant circuit of each phase and the inductor circuit 36 ​​is located on the primary side of the three-phase transformer 33. Compared with the LLC resonant circuit located on the secondary side of the three-phase transformer 33, the LLC resonant circuit on the primary side can better ensure soft switching and reduce switching losses, thereby improving the charging efficiency of the charging pile 40 for charging electric vehicles.

[0141] In other embodiments, the DC connection terminal 341 of the second power conversion circuit 34 in the bidirectional DC-DC converter 30 is connected to the other end of the AC-DC converter 41. The DC connection terminal 341 of the second power conversion circuit 34 can be connected to the DC bus 43, for example, to connect to the other end of the AC-DC converter 41 via the DC bus 43. The DC connection terminal 311 of the first power conversion circuit 31 is connected to the charging gun 42.

[0142] Based on the above design, when the charging pile 40 is charging the electric vehicle, the electrical energy output by the AC-DC conversion device 41 can be output to the electric vehicle by the second power conversion circuit 34 through the three-phase transformer 33 and the first power conversion circuit 31. The LLC resonant circuit formed by each phase resonant circuit and the inductor circuit 36 ​​is located on the secondary side of the three-phase transformer 33.

[0143] It should be understood that in the embodiments of this application, the AC-DC conversion device 41 may be a unidirectional DC-DC conversion device or a bidirectional AC-DC conversion device.

[0144] In some embodiments, the AC-DC converter 41 can be a unidirectional AC-DC converter. That is, the AC-DC converter 41 can be used only to transmit electrical energy output from the grid to the bidirectional DC-DC converter 30, so as to charge electric vehicles through the bidirectional DC-DC converter 30 and the charging gun 42. In addition, when one end of the multiple bidirectional DC-DC converters 30 in the charging pile 40 is connected to the DC bus 43 and the other end of the multiple bidirectional DC-DC converters 30 is connected to multiple charging guns 42, multiple electric vehicles connected to the multiple charging guns 42 can transfer electrical energy to each other through the multiple bidirectional DC-DC converters 30.

[0145] For example, with Figure 8 Taking the charging pile 40 shown as an example, where the two bidirectional DC-DC converters 30 are connected to two charging guns 42 respectively, the electric vehicle connected to one of the charging guns 42 can output electrical energy to the electric vehicle connected to the other charging gun 42 through the two bidirectional DC-DC converters 30 and the DC bus 43.

[0146] Based on the above design, the charging pile 40 can meet the charging needs of electric vehicles, as well as the vehicle-to-vehicle (V2V) discharge needs of electric vehicles.

[0147] In other embodiments, the AC-DC converter 41 can be a bidirectional AC-DC converter. That is, in addition to transmitting electrical energy output from the grid to the bidirectional DC-DC converter 30, the AC-DC converter 41 can also transmit electrical energy output from the bidirectional DC-DC converter 30 to the grid.

[0148] Based on the above design, electric vehicles connected to the charging gun 42 can output electrical energy to the power grid through the bidirectional DC-DC converter 30 and AC-DC converter 41, so that the charging pile 40 can meet the charging needs of electric vehicles and the V2G discharge needs of electric vehicles at the same time.

[0149] It should also be understood that, in the embodiments of this application, each AC-DC converter 41 and each bidirectional DC-DC converter 30 in the charging pile 40 can be independently configured, that is, each AC-DC converter 41 and each bidirectional DC-DC converter 30 can be configured in different housings. Alternatively, an AC-DC converter 41 can be integrated with a bidirectional DC-DC converter 30, that is, an AC-DC converter 41 can be integrated with a bidirectional DC-DC converter 30 in the same housing.

[0150] For details regarding charging station 40, please refer to [link / reference]. Figure 1 and Figure 2 The relevant descriptions of the embodiments shown will not be repeated here.

[0151] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A bidirectional DC-to-DC converter, characterized in that, The bidirectional DC-DC converter includes a first power conversion circuit, a second power conversion circuit, a three-phase transformer, and a three-phase resonant circuit. Each phase of the three-phase resonant circuit includes a first capacitor and a first inductor connected in series. One end of each phase resonant circuit is connected to the first power conversion circuit, and the other end of each phase resonant circuit is connected to the second power conversion circuit through the three-phase transformer. The bidirectional DC-DC converter further includes a resonant switching circuit and an inductor circuit. The resonant switching circuit is used to connect the circuit between any one end of each phase resonant circuit and the inductor circuit, so that each phase resonant circuit and the inductor circuit form an inductor-inductor-capacitor LLC resonant circuit.

2. The bidirectional DC-DC converter according to claim 1, characterized in that, The resonant switching circuit is used for: When the first power conversion circuit is used to convert the received DC power into AC power, and the second power conversion circuit is used to convert the AC power output from the first power conversion circuit into DC power and then output it, the circuit between the other end of the resonant circuit of each phase and the inductor circuit is turned on; or, When the second power conversion circuit is used to convert the received DC power into AC power, and the first power conversion circuit is used to convert the AC power output from the second power conversion circuit into DC power and then output it, the circuit between one end of the resonant circuit of each phase and the inductor circuit is turned on.

3. The bidirectional DC-DC converter according to claim 1 or 2, characterized in that, The inductor circuit includes three second inductors, and the two ends of each phase resonant circuit are connected to one end of a second inductor through the resonant switching circuit.

4. The bidirectional DC-DC converter according to claim 3, characterized in that, The resonant switching circuit includes three resonant switches, and the two ends of each phase resonant circuit are connected to one end of the second inductor through one of the resonant switches; wherein, The two ends of each phase resonant circuit are connected one-to-one with the two stationary contacts of the resonant switching switch; One end of the second inductor is connected to the moving contact of the resonant switching switch, and the other ends of the three second inductors are connected together; or, the three second inductors are connected end to end in sequence, and the connection point of the second inductor and another second inductor is connected to the moving contact of the resonant switching switch.

5. The bidirectional DC-DC converter according to any one of claims 1 to 4, characterized in that, The bidirectional DC-DC converter also includes multiple second capacitors. The second power conversion circuit includes three power conversion bridge arms connected in parallel. The midpoint of each second power conversion bridge arm is connected to the three-phase transformer through a second capacitor.

6. The bidirectional DC-DC converter according to claim 5, characterized in that, The three-phase transformer includes a three-phase primary winding and a three-phase secondary winding. The three-phase primary winding is connected to the other end of the three-phase resonant circuit in a one-to-one correspondence. The three-phase secondary winding is connected to the midpoint of the three power conversion bridge arms in a one-to-one correspondence. The bidirectional DC-DC converter further includes at least one of a first turns-changing switch circuit and a second turns-changing switch circuit, wherein... The first turns switching circuit is connected to the three-phase primary winding, and the first turns switching circuit is used to switch the number of turns of each phase primary winding connected to the circuit in the three-phase primary winding. The second turns switching circuit is connected to the three-phase secondary winding, and the second turns switching circuit is used to switch the number of turns of each phase secondary winding connected to the circuit in the three-phase secondary winding.

7. The bidirectional DC-DC converter according to claim 6, characterized in that, The bidirectional DC-DC converter includes the first turns switching circuit, each phase primary winding includes a first primary winding and a second primary winding, one end of each of the three first primary windings is connected to the other end of the three-phase resonant circuit, wherein the other end of the first primary winding of one phase primary winding is connected to one end of the second primary winding of one phase primary winding to form a first tap, and the other ends of the three second primary windings are connected together. The first turns-changing switch circuit includes two first turns-changing switches, each connected one-to-one with a primary winding of the other two phases, excluding the primary winding of one phase. Each of the first turns switching switches is used to connect the circuit between the other end of the first primary winding of the corresponding primary phase and one end of the second primary winding of the corresponding primary phase, or, each of the first turns switching switches is used to connect the circuit between the other end of the first primary winding of the corresponding primary phase and the first tap.

8. The bidirectional DC-DC converter according to claim 6 or 7, characterized in that, The bidirectional DC-DC converter includes a second turns switching circuit. Each phase secondary winding includes a first secondary winding and a second secondary winding. One end of each of the three first secondary windings is connected to the midpoint of the three power conversion bridge arms in a one-to-one correspondence. The other end of the first secondary winding of one phase secondary winding is connected to one end of the second secondary winding of one phase secondary winding to form a second tap. The other ends of the three second secondary windings are connected together. The second turns switching circuit includes two second turns switching switches, each connected one-to-one with the other two secondary windings (excluding one of the secondary windings). Each of the second turns switching switches is used to connect the circuit between the other end of the first secondary winding of the corresponding secondary winding and one end of the second secondary winding of the corresponding secondary winding, or, each of the second turns switching switches is used to connect the circuit between the other end of the first secondary winding of the corresponding secondary winding and the second tap.

9. The bidirectional DC-DC converter according to claim 6 or 7, characterized in that, Each phase secondary winding includes multiple sets of secondary windings, and the number of the second power conversion circuits is multiple. The multiple sets of secondary windings are connected one-to-one with the midpoint of a bridge arm of each of the multiple second power conversion circuits. The bidirectional DC-DC converter further includes one or more connection switching circuits. Any two of the plurality of second power conversion circuits are connected through one of the connection switching circuits. Each connection switching circuit includes one series switch and two parallel switches. The series switch is used to connect any two second power conversion circuits in series, and the two parallel switches are used to connect any two second power conversion circuits in parallel.

10. A charging pile, characterized in that, The charging pile includes an AC-DC converter, a bidirectional DC-DC converter as described in any one of claims 1 to 9, and a charging gun. One end of the AC-DC converter is used to connect to an AC power source, and the other end of the AC-DC converter is connected to the charging gun through the bidirectional DC-DC converter.

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