Flying capacitor high-voltage end pre-charging circuit for flying capacitor three-level DC / DC

Abstract

The utility model relates to the technical field of DC / DC converters, in particular to a flying capacitor high-voltage end pre-charging circuit for flying capacitor three-level DC / DC, which comprises a bus HV end, a bus LV input end and a switch module string formed by connecting 2N switch modules in series, the head end and the tail end of the switch module string are respectively connected to the bus HV end; the middle interface of the switch module string is connected with an inductor L1, and the inductor L1 and the tail end of the switch module string form an LV input end; two ends of any N continuous switch modules are connected in parallel with a flying capacitor C3; and the flying capacitor C3 is connected in parallel with a controlled constant current source for pre-charging the flying capacitor C3 and / or a pre-charging circuit connected with a bus HV end. According to the invention, the pre-charging of the flying capacitor C3 can be realized only by adopting resistor voltage division, the function is simple, the cost is low, the performance is stable, the reliable pre-charging of the flying capacitor is ensured, and the technical problem that the pre-charging of the flying capacitor needs to be realized by switching tube PWM duty ratio soft start and diode auxiliary clamping and cannot be applied to application occasions needing to be subjected to soft start from a high-voltage end is solved.

Description

Technical Field

[0001] The present application relates to the technical field of DC / DC converters, and in particular to a flying capacitor high-voltage end precharging circuit for a flying capacitor three-level DC / DC. Background Art

[0002] In the field of battery testing, a DC / DC converter is required to convert electrical energy, converting DC power to DC power of different voltages. A flying capacitor three-level DC / DC converter is a DC-DC converter with three voltage levels that uses a flying capacitor to achieve voltage conversion. It typically includes a flying capacitor three-level power conversion bridge set between the two poles on the high-voltage side. One end of the flying capacitor is connected to the positive electrode of the high-voltage side through the upper tube diode in the upper half bridge, and the other end is connected to the negative electrode of the high-voltage side through the lower tube diode in the lower half bridge. The output voltage consists of three levels: 0, less than half of the output voltage, and full output voltage.

[0003] By controlling the duty cycle of the switching transistors, the flying capacitor voltage of the three-level DC / DC converter can be automatically stabilized at k parts of a V. Its voltage stress is the difference between the voltages of two adjacent flying capacitors. Because the output equivalent switching frequency is twice that of a two-level bidirectional DC converter, the inductor size can be effectively reduced while maintaining the same output current ripple, thereby improving the converter's dynamic performance and efficiency. The AC component of the output voltage is also reduced, further improving the converter's dynamic performance and efficiency.

[0004] Figure 1 This is the circuit diagram of a flying capacitor three-level DC / DC converter. Its switching device stress is half the bus voltage, and the current ripple frequency of inductor L1 is twice the switching frequency. These characteristics significantly reduce switching device stress, switching losses, and the size of inductors and capacitors, making it ideal for high-voltage, high-frequency DC / DC conversion applications. These include charging and discharging energy storage battery clusters, photovoltaic-storage-direct-flexible systems, and energy recovery from the DC bus of high-voltage trains. The flying capacitor three-level DC / DC converter with the above topology requires precharging the flying capacitor C3 voltage to within half the HV bus voltage before operation. Otherwise, switches S1-S4 will be subjected to the entire HV bus voltage at the moment of turn-on, causing damage.

[0005] Existing flying capacitor precharging is mostly achieved from the LV side, using a soft-start circuit using the S1-S4 PWM duty cycle and a diode-assisted clamp. The LV input is typically a battery or DC voltage source. This approach is not suitable for applications requiring a soft-start from the high-voltage (HV) side, such as when the preceding stage is a high-voltage DC bus. Utility Model Content

[0006] The purpose of the present application is to provide a flying capacitor high-voltage end pre-charging circuit for a flying capacitor three-level DC / DC. The technical solution provided by the present application solves the technical problem that the flying capacitor pre-charging of the flying capacitor three-level DC / DC converter requires a switching tube PWM duty cycle soft start plus a diode auxiliary clamp to achieve, and cannot be applied to applications that require soft start from the high-voltage end.

[0007] In order to achieve the above-mentioned objectives, the present application provides a flying capacitor high-voltage end pre-charging circuit for a flying capacitor three-level DC / DC, comprising: a busbar HV end and an LV input end, and a switch module string formed by 2N switch modules connected in series; the head and tail ends of the switch module string are respectively connected to the busbar HV end; the middle interface of the switch module string is connected to an inductor L1, and constitutes the LV input end together with the end of the switch module string; a flying capacitor C3 is connected in parallel at both ends of any N consecutive switch modules; a controlled constant current source for pre-charging the flying capacitor C3 and / or a pre-charging circuit connected to the busbar HV end is connected in parallel to the flying capacitor C3.

[0008] By adopting the above technical solution, a controlled constant current source and / or precharging circuit for precharging the flying capacitor C3 is connected in parallel to the flying capacitor C3. The flying capacitor can be precharged without the need for PWM duty cycle soft start of the switch tube and diode auxiliary clamping. This can be applied to technical problems in applications that require soft start from the high voltage end.

[0009] As a preferred embodiment, a DC relay is connected in series with the charging circuit formed by the controlled constant current source and the flying capacitor C3. When the flying capacitor C3 needs to be charged, the DC relay is closed and the high-voltage constant current source is started. When the voltage of the flying capacitor C3 is detected to reach half the voltage of the bus HV terminal, the high-voltage constant current source is turned off and the DC relay is disconnected. This embodiment can achieve pre-charging of the flying capacitor without the need for PWM duty cycle soft starting of the switch tube and diode auxiliary clamping, and can be applied to technical problems in applications requiring soft starting from the high voltage end.

[0010] As another embodiment, the pre-charging circuit includes 2M resistors R connected in series to the busbar HV end, and both ends of any M consecutive resistors R are connected in parallel to the flying capacitor C3.

[0011] The pre-charging circuit adopts the above structure, and the flying capacitor C3 can be pre-charged only by using a resistor voltage divider. It has simple functions, low cost, and stable performance. It can not only ensure the reliable pre-charging of the flying capacitor, but also ensure that the operating voltage of the switch module string during the pre-charging process is within half of the voltage at the HV end of the bus, thereby improving system reliability. At the same time, the pre-charging circuit has high adaptability to the bus at the HV end, and is compatible with both the bus formed by the upper and lower groups of power supplies connected in series and the single DC bus.

[0012] Preferably, a relay K1 may be connected in series with the LV input terminal. During the pre-charging process of the flying capacitor C3, the relay K1 remains disconnected. This can prevent the instantaneous short-circuit characteristics of the flying capacitor C3 from causing the first switch tube module to withstand the full voltage of the bus HV terminal, resulting in breakdown and damage to the entire three-level DC / DC. After the pre-charging of the flying capacitor C3 is completed, the relay K1 is closed again, and the switch module string enters the PWM constant voltage soft-start state for the output capacitor C4, thereby ending the pre-charging process of the flying capacitor.

[0013] As a preferred embodiment, a relay K2 is connected in series with the resistor R connected to the busbar HV terminal. The relay K2 can control the start time of pre-charging and close the pre-charging circuit after the pre-charging is completed, thereby reducing power consumption.

[0014] As a preferred embodiment, the switch module includes a transistor and a diode connected in series to the emitter and collector of the transistor.

[0015] As a preferred embodiment, an RC filtering circuit is connected in parallel to the HV end of the busbar and / or the LV input end. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the description of the embodiments. Obviously, the drawings described below are some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0017] Figure 1 This is the circuit diagram of a flying capacitor three-level DC / DC converter;

[0018] Figure 2 This is a circuit diagram of a DC / DC converter using a controlled constant current source as a pre-charge module in an embodiment of the present application;

[0019] Figure 3 The embodiment of the present application uses a pre-charge circuit as a DC / DC converter circuit of the pre-charge module Figure 1 ;

[0020] Figure 4 The embodiment of the present application uses a pre-charge circuit as a DC / DC converter circuit of the pre-charge module Figure 2 . DETAILED DESCRIPTION

[0021] The following will be combined with the accompanying drawings to clearly and completely describe the technical solutions in this application. Obviously, the embodiments described are part of the embodiments of this application, not all of them. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0022] A flying capacitor three-level DC / DC converter is a DC-DC converter with three voltage levels. It uses a flying capacitor to achieve voltage conversion, with the output voltage consisting of three levels: 0, less than half the output voltage, and full output voltage. Before the flying capacitor three-level DC / DC converter officially operates, the flying capacitor C3 voltage must be precharged to less than half the high-voltage bus voltage. Otherwise, the switching transistors S1-S4 will be subjected to the entire high-voltage bus voltage at the moment of turn-on, causing damage. Existing flying capacitor precharging is mostly achieved from the low-voltage side, using a PWM duty cycle soft start of S1-S4 and a diode auxiliary clamp. The low-voltage input is typically a battery or a DC voltage source. This is not suitable for applications requiring a soft start from the high-voltage high-voltage side, such as when the preceding stage is a high-voltage DC bus.

[0023] It's important to note that the busbar (HV) side refers to the high-voltage side of a flying capacitor three-level DC / DC converter. This is the higher-voltage port within the converter and is used to connect to a high-voltage power source or load. Depending on the application, it can be either the input (e.g., connecting to a high-voltage DC bus) or the output (e.g., supplying power to high-voltage equipment). The LV side refers to the low-voltage side of a flying capacitor three-level DC / DC converter. This is the lower-voltage port within the converter and is used to connect to a low-voltage power source (e.g., a battery, low-voltage DC bus) or load (e.g., auxiliary equipment).

[0024] In order to solve the above technical problems, this embodiment provides a flying capacitor high-voltage end pre-charging circuit for a flying capacitor three-level DC / DC. The technical solution provided by this embodiment can pre-charge the flying capacitor through the high-voltage end, solving the technical problem that the flying capacitor pre-charging of the flying capacitor three-level DC / DC converter requires a PWM duty cycle soft start of the switch tube and a diode auxiliary clamp to be implemented, which cannot be applied to applications that require soft start from the high-voltage end.

[0025] To achieve the above objectives, the flying capacitor high-voltage pre-charging circuit of this embodiment includes: a busbar HV terminal and an LV input terminal. The HV busbar can be flexibly configured to accommodate both a busbar formed by two series-connected power supplies and a single DC busbar, making the pre-charging circuit highly adaptable to the HV busbar. The LV input is typically a battery or a DC voltage source, a conventional technical approach for three-level DC / DC converters and will not be further elaborated here.

[0026] like Figure 2As shown, a switch module string is formed by 2N switch modules connected in series. The first and last ends of the switch module string are connected to the busbar HV terminal, and the middle interface of the switch module string is connected to an inductor L1, which forms the LV input terminal with the end of the switch module string. Here, N represents the number and is a positive integer. It should be noted that in this embodiment, the middle interface of the switch module string is connected to the inductor L1. The stress of the switch module string is half the busbar voltage, and the current ripple frequency of the inductor L1 is twice the switch module string frequency. These characteristics significantly reduce the stress of the switch components, switching losses, and the size of the inductor and capacitor. It is very suitable for high-voltage and high-frequency DC / DC conversion applications such as energy storage battery cluster charging and discharging, photovoltaic storage and direct current flexible systems, and high-voltage train DC bus energy recovery. To this end, the number of switch modules in the switch module string must be an even number, which can be 2, 4, 6, or more. Preferably, four switch modules S1-S4 are used. In this embodiment, four switch modules S1-S4 are used as a specific embodiment for explanation.

[0027] like Figure 2 As shown, an RC filter circuit can also be connected in parallel to the HV end of the busbar and / or the LV input end to achieve filtering. The RC filter circuit connected to the HV end of the busbar consists of resistors R1-R2 and capacitors C1-C2; the RC filter circuit connected to the LV input end consists of resistor R7 and capacitor C4.

[0028] In order to realize the basic function of the flying capacitor three-level DC / DC converter, in this embodiment, a flying capacitor C3 is connected in parallel at both ends of any N consecutive switch modules. If four switch modules are used, the flying capacitor C3 is connected in parallel at both ends of two consecutive switch modules; if six switch modules are used, the flying capacitor C3 is connected in parallel at both ends of three consecutive switch modules; and so on. Since this embodiment uses four switch modules R1-R4, the flying capacitor C3 is connected in parallel at both ends of two consecutive switch modules R2-R3. It should be noted that the selection of any consecutive switch modules here, that is, the parallel connection of the flying capacitor C3, must be on both sides of the connection between the inductor L1 and the switch module string in order to realize the function of the flying capacitor C3. Therefore, no matter how the switch module is selected, it will not deviate from the premise that the parallel connection of the flying capacitor C3 must be on both sides of the connection between the inductor L1 and the switch module string.

[0029] The switch modules R1-R4 include a transistor and a diode connected in series to the emitter and collector of the transistor.

[0030] In order to realize the pre-charging of the flying capacitor C3, the present embodiment is connected in parallel to the flying capacitor C3 with a controlled constant current source for pre-charging the flying capacitor C3 and / or a pre-charging circuit connected to the busbar HV end. The controlled constant current source and / or the pre-charging circuit constitute the pre-charging module of the flying capacitor C3. The pre-charging module is used to pre-charge the flying capacitor C3, and the pre-charging of the flying capacitor can be realized without the need for soft-starting of the PWM duty cycle of the switching tube and the auxiliary clamping of the diode, which can be applied to technical problems in applications that require soft-starting from the high-voltage end. It should be noted that the controlled constant current source and the pre-charging circuit can be adopted selectively or together.

[0031] like Figure 2 As shown, when the pre-charge module adopts a controlled constant current source I1, the controlled constant current source I1 adopts a high-voltage constant current source. A DC relay K1-K2 is connected in series in the charging circuit formed by the controlled constant current source I1 and the flying capacitor C3. When it is necessary to charge the flying capacitor C3, the DC relay K1-K2 is closed and the high-voltage constant current source I1 is started. When it is detected that the voltage value of the flying capacitor C3 reaches half of the voltage value of the bus HV end, the high-voltage constant current source I1 is turned off and the DC relay K1-K2 is disconnected. This embodiment can realize the pre-charging of the flying capacitor without the need for soft-starting of the PWM duty cycle of the switch tube and the auxiliary clamping of the diode, and can be applied to the technical problems of applications that require soft-starting from the high-voltage end.

[0032] like Figure 3 As shown, when the pre-charge module adopts the pre-charge circuit, the pre-charge circuit includes 2M resistors R connected in series to the busbar HV end, and any two ends of M continuous resistors R are connected in parallel to the flying capacitor C3. Here, M represents the quantity, which is a positive integer. Similarly to the number of switch modules, the number of resistors R is also set in an even number, and 2, 4, 6 and more can be used. In this embodiment, 4 resistors R3-R6 are used as a specific embodiment to explain.

[0033] In the parallel connection between resistors R3-R6 and flying capacitor C3, since this embodiment uses four resistors R3-R6, a flying capacitor C3 is connected in parallel across two consecutive resistors R4-R5. It should be noted that this embodiment only uses resistor R for voltage division to achieve pre-charging of flying capacitor C3. Therefore, the selection of resistor R does not need to follow the selection rules of the switch module. In the parallel connection between flying capacitor C3 and resistor R, it is only necessary to arbitrarily select M resistors, that is, two resistors R connected in series and then connected to flying capacitor C3.

[0034] The pre-charging circuit adopts the above structure, and the flying capacitor C3 can be pre-charged only by using a resistor voltage divider. It has simple functions, low cost, and stable performance. It can not only ensure the reliable pre-charging of the flying capacitor C3, but also ensure that the operating voltage of the switch module string during the pre-charging process is within half of the voltage of the bus HV end, thereby improving the system reliability. At the same time, the pre-charging circuit has high adaptability to the bus at the HV end, and is compatible with both the bus formed by the upper and lower groups of power supplies connected in series and the single DC bus.

[0035] like Figure 4 As shown, it's possible. Relay K1 is connected in series with the LV input. During the pre-charging process of flying capacitor C3, relay K1 remains open. This prevents the instantaneous short-circuit characteristics of flying capacitor C3 from causing the first switching module to withstand the full voltage of the bus HV terminal, leading to breakdown and damage to the entire three-level DC / DC converter. After the pre-charging of flying capacitor C3 is completed, relay K1 is closed again, and the switching module string enters the PWM constant voltage soft-start state for output capacitor C4, thus ending the pre-charging process of the flying capacitor.

[0036] A relay K2 can also be connected in series with the resistors R3-R6 connected to the HV end of the busbar. Relay K2 can control the start time of pre-charging and close the pre-charging circuit after pre-charging is completed, thereby reducing power consumption.

[0037] To sum up, by adopting the technical solution provided in this embodiment, the flying capacitor C3 can be pre-charged by using resistance voltage division, which has simple functions, low cost and stable performance. It can not only ensure the reliable pre-charging of the flying capacitor, but also ensure that the operating voltage of the switch module string during the pre-charging process is within half of the voltage of the bus HV end, thereby improving the system reliability. At the same time, the pre-charging circuit has high adaptability to the bus at the HV end, and is compatible with both the bus formed by the upper and lower groups of power supplies connected in series and the single DC bus.

[0038] Those skilled in the art will appreciate that the devices and algorithm steps of each example described in conjunction with the embodiments disclosed in this application can be implemented in electronic hardware, computer software, or a combination of the two. In order to clearly illustrate the interchangeability of hardware and software, the composition and steps of each example have been generally described in terms of function in the above description. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professional and technical personnel can use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of this application.

[0039] Those skilled in the art will clearly understand that, for the convenience and brevity of description, the specific working process of the device described above can refer to the corresponding process in the aforementioned method embodiment and will not be repeated here.

[0040] In the several embodiments provided in this application, it should be understood that the disclosed devices and methods can be implemented in other ways. For example, the components and steps of each example are described. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professionals and technicians can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application.

[0041] The embodiments of the methods or devices described above are merely illustrative. In addition, the mutual coupling or direct coupling or communication connection shown or discussed may be an indirect coupling or communication connection through some interfaces, devices or units, or may be an electrical, mechanical or other form of connection.

[0042] Based on this understanding, the technical solution of this application, or the portion that contributes to the prior art, or all or part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes a number of instructions for causing a computer device (which can be a personal computer, server, or network device, etc.) to execute all or part of the steps of the method described in each embodiment of this application. The aforementioned storage medium includes: a USB flash drive, a mobile hard drive, a read-only memory (ROM), a random access memory (RAM), a magnetic disk, or an optical disk, etc., various media that can store program code.

[0043] The above description is merely a specific embodiment of the present application, but the scope of protection of the present application is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in the present application, and such modifications or substitutions should be included in the scope of protection of the present application. Therefore, the scope of protection of the present application should be based on the scope of protection of the claims.

Claims

1. A flying capacitor high-voltage end pre-charging circuit for a flying capacitor three-level DC / DC, characterized in that: include: The busbar HV end and LV input end, as well as a switch module string formed by 2N switch modules connected in series; The head and tail ends of the switch module string are respectively connected to the bus HV end; the middle interface of the switch module string is connected to an inductor L1, and constitutes the LV input end together with the end of the switch module string; a flying capacitor C3 is connected in parallel at both ends of any N consecutive switch modules; a controlled constant current source for pre-charging the flying capacitor C3 and / or a pre-charging circuit connected to the bus HV end is connected in parallel to the flying capacitor C3.

2. The flying capacitor high voltage end precharge circuit according to claim 1, wherein: A DC relay is connected in series to the charging circuit formed by the controlled constant current source and the flying capacitor C3.

3. The flying capacitor high voltage end precharge circuit according to claim 1, wherein: The pre-charging circuit includes 2M resistors R connected in series to the HV end of the busbar, and both ends of any M consecutive resistors R are connected in parallel to the flying capacitor C3.

4. The flying capacitor high-voltage end precharge circuit according to claim 3, wherein: A relay K1 is connected in series to the LV input terminal.

5. The flying capacitor high voltage end precharge circuit according to claim 4, wherein: A relay K2 is also connected in series to the resistor R connected to the HV end of the busbar.

6. The flying capacitor high-voltage end precharge circuit according to any one of claims 1 to 5, wherein: The switch module includes a transistor and a diode connected in series to the emitter and collector of the transistor.

7. The flying capacitor high-voltage end precharge circuit according to claim 6, wherein: An RC filtering circuit is connected in parallel to the busbar HV end and / or the LV input end.

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