Flying capacitor three-level Buck / Boost converter and pre-charging method

Abstract

The invention discloses a flying capacitor three-level Buck / Boost converter and a pre-charging method, and relates to the field of DC conversion, and the converter comprises a first power supply, a second power supply, a first capacitor connected in parallel with the two ends of the first power supply, and a second capacitor connected in parallel with the two ends of the second power supply. The first switch tube, the second switch tube, the third switch tube and the fourth switch tube are sequentially connected in series and then connected with the first power supply in parallel; one end of the second capacitor is electrically connected with the series connection end of the second switch tube and the third switch tube through an inductor, the other end of the second capacitor is electrically connected with the other end of the fourth switch tube, and the pre-charging circuit is connected with the first power supply in parallel and comprises a first switch, a first resistor, a flying capacitor, a second resistor and a second switch which are sequentially connected in series; the first switch and the second switch are used for controlling the first power supply or the second power supply to pre-charge the flying capacitor. The problem that the power device is easy to damage when the converter is normally started can be avoided.

Description

Technical Field

[0001] The present application relates to the field of direct current conversion, and in particular to a flying capacitor three-level Buck / Boost converter and a pre-charging method. Background Art

[0002] Non-isolated DC converters are suitable for photovoltaic DC energy storage systems with a wide voltage range due to their features of fewer components, low cost, and high voltage gain. Among them, the flying capacitor three-level Buck / Boost converter has the advantages of low switch tube voltage stress and small output filter inductor size, making it widely used in high-power energy storage systems.

[0003] When analyzing and studying transcapacitor three-level Buck / Boost converters, most literature assumes that the flying capacitor has been established at a suitable voltage before the circuit works. In fact, before the circuit works, the initial value of the flying capacitor voltage is zero. If the converter is started at this time, the power device will bear the entire bus voltage and is easily damaged. Summary of the invention

[0004] The present application aims to at least solve the problem in the prior art that the switching tube in the flying capacitor three-level Buck / Boost converter is easily damaged when charging. To this end, the example of the present application provides a flying capacitor three-level Buck / Boost converter and a charging method, which solves the problem that the power device voltage stress of the flying capacitor three-level Buck / Boost converter is too high and easily damaged during normal startup by switching two switches.

[0005] The solution of this application example is implemented through the following contents.

[0006] In a first aspect, the present application provides a flying capacitor three-level Buck / Boost converter, comprising: A first power supply, a second power supply, a first capacitor connected in parallel at both ends of the first power supply, and a second capacitor connected in parallel at both ends of the second power supply; a first switch tube, a second switch tube, a third switch tube and a fourth switch tube which are sequentially connected in series and connected in parallel with the first power source; One end of the second capacitor is electrically connected to the series end of the second switch tube and the third switch tube through an inductor, and the other end of the second capacitor is electrically connected to the other end of the fourth switch tube. a pre-charging circuit connected in parallel with the first power supply, the pre-charging circuit comprising a first switch, a first resistor, a flying capacitor, a second resistor and a second switch connected in series in sequence; Among them, the series end of the flying capacitor and the first resistor is electrically connected to the series end of the first switch tube and the second switch tube, and the series end of the flying capacitor and the second resistor is electrically connected to the series end of the third switch tube and the fourth switch tube; the first switch and the second switch are used to control the first power supply or the second power supply to pre-charge the flying capacitor.

[0007] As described above, the flying capacitor three-level Buck / Boost converter, optionally, the voltage of the first power supply is greater than the voltage of the second power supply, and the first power supply and the second power supply pre-charge the flying capacitor respectively so that the converter operates in Buck mode and Boost mode.

[0008] As described above, the flying capacitor three-level Buck / Boost converter, optionally, the first switch is closed and the second switch is opened, and the first power supply pre-charges the flying capacitor to make the converter operate in Buck mode.

[0009] As described above, in the flying capacitor three-level Buck / Boost converter, optionally, the first switch is opened and the second switch is closed, and the second power supply pre-charges the flying capacitor so that the converter operates in a Boost mode.

[0010] In the flying capacitor three-level Buck / Boost converter as described above, optionally, the preset charging voltage of the flying capacitor is half of the voltage of the first power supply.

[0011] As for the flying capacitor three-level Buck / Boost converter as described above, optionally, the conduction direction of the first switch tube, the second switch tube, the third switch tube and the fourth switch tube is from the negative electrode of the first power supply to the positive electrode of the first power supply. In the flying capacitor three-level Buck / Boost converter as described above, optionally, the first switch and the second switch include one or more of a relay, a semiconductor switch, and a power device.

[0012] In the flying capacitor three-level Buck / Boost converter as described above, optionally, the first switch tube, the second switch tube, the third switch tube and the fourth switch tube include one or more of a gallium nitride field effect transistor, a metal oxide semiconductor tube and a bipolar junction transistor.

[0013] A second aspect of the present application provides a method for charging a flying capacitor three-level Buck / Boost converter, which is used to charge a flying capacitor using the flying capacitor three-level Buck / Boost converter according to any one of the first aspects above, and the method comprises: The first switch is closed and the second switch is opened, so that the positive electrode of the first power supply outputs a first current; The first current sequentially passes through the first switch, the first resistor, the flying capacitor, the third switch tube, the inductor, the second capacitor, and the negative electrode of the first power supply to form a first loop to pre-charge the flying capacitor; When the voltage of the flying capacitor reaches half of the voltage of the first power supply, the first switch is turned on to complete pre-charging.

[0014] A third aspect of the present application provides a method for charging a flying capacitor three-level Buck / Boost converter, which is used to charge a flying capacitor using the flying capacitor three-level Buck / Boost converter according to any one of the first aspect, and the method comprises: The second switch is closed and the first switch is opened, so that the positive electrode of the second power supply outputs a second current; The second current sequentially passes through the inductor, the second switch tube, the flying capacitor, the second resistor, the second switch, and the negative electrode of the second power supply to form a second loop to pre-charge the flying capacitor; When the voltage of the flying capacitor reaches half of the voltage of the first power supply, the second switch is turned on to complete pre-charging.

[0015] This application has the following beneficial effects: The pre-charging circuit in this embodiment can quickly pre-charge the flying capacitor through the control of the first switch and the second switch before the converter works normally, charge the voltage of the flying capacitor to a preset value, and then close the first switch and the second switch to soft-start the converter, thereby avoiding the problem of excessive voltage stress on the power device causing damage to the power device during normal startup of the three-level Buck / Boost converter of the flying capacitor. In addition, setting the first resistor and the second resistor in the pre-charging circuit can limit the charging current output by the first power supply and the second power supply, thereby preventing overcurrent from damaging the power device. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] By reading the detailed description below with reference to the accompanying drawings, the above and other purposes, features and advantages of the exemplary embodiments of the present application will become easy to understand. In the accompanying drawings, several embodiments of the present application are shown in an exemplary and non-limiting manner, and the same or corresponding reference numerals represent the same or corresponding parts, wherein: Figure 1 A circuit diagram of a flying capacitor three-level Buck / Boost converter according to an embodiment of the present application; Figure 2A schematic flow chart of a pre-charging method for a flying capacitor three-level Buck / Boost converter according to an embodiment of the present application; Figure 3 A circuit diagram of a current loop of a pre-charging method according to an embodiment of the present application; Figure 4 A schematic flow chart of another method for precharging a flying capacitor three-level Buck / Boost converter according to an embodiment of the present application; Figure 5 A circuit diagram of a current loop of another pre-charging method according to an embodiment of the present application.

[0017] Description of reference numerals: First Power-U H ; Second power supply - V bus ; First capacitor - C H ; Second capacitor - C bus ; First switch tube-Q1; Second switch tube-Q2; Third switch tube-Q3; Fourth switch tube-Q4; Flying capacitor-C fly ; first switch-S1; second switch-S2; first resistor-R1; second resistor-R2; inductor-L. DETAILED DESCRIPTION

[0018] The following will be combined with the drawings in the embodiments of the present disclosure to clearly and completely describe the technical solutions in the embodiments of the present disclosure. Obviously, the described embodiments are part of the embodiments of the present disclosure, rather than all of the embodiments. Based on the embodiments in the present disclosure, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present disclosure.

[0019] For a transcapacitor three-level converter, in order to avoid the overvoltage problem of the power device when the flying capacitor is charged, the flying capacitor is generally pre-charged through soft start, and the converter is started when the flying capacitor is pre-charged to a set voltage value. This embodiment provides a combination of opening and closing of a dual switch to realize pre-charging of the flying capacitor, so that the converter can perform different working modes.

[0020] like Figure 1 The circuit diagram of the flying capacitor three-level Buck / Boost converter shown in FIG. 1 includes a main circuit and a pre-charging circuit. Specifically, the main circuit includes a first power supply U H and the second power supply V bus , the first power supply U H The first capacitor C is connected in parallel at both ends of H and the second power supply V bus The second capacitor C is connected in parallel across both ends of bus , and then connected in series with the first power supply UH The first switch tube Q1, the second switch tube Q2, the third switch tube Q3 and the fourth switch tube Q4 connected in parallel, and the inductor L; wherein the second capacitor C bus One end of the second capacitor Q2 is electrically connected to the series connection of the second switch tube Q2 and the third switch tube Q3 through the inductor L, and the other end of the second capacitor Q2 is electrically connected to the other end of the fourth switch tube Q4. The converter can realize two working modes, Buck / Boost, through two power supplies.

[0021] When specifically connected, the other end of the first switch tube Q1 is connected in parallel to the first power supply U H The other end of the fourth switch tube Q4 is connected in parallel to the first power supply U H The negative electrode and the second power supply V bus When the transformer is working, the first switch tube Q1 is the first active tube, the second switch tube Q2 is the second active tube, the third switch tube Q3 is the first synchronous rectifier tube, and the fourth switch tube Q4 is the second synchronous rectifier tube.

[0022] In addition, the pre-charging circuit and the first power supply U H The pre-charging circuit includes a first switch S1, a first resistor R1, and a flying capacitor C in series. fly , a second resistor R2 and a second switch S2; wherein the flying capacitor C fly The series end of the first resistor R1 is electrically connected to the series end of the first switch tube Q1 and the series end of the second switch tube Q2, and the flying capacitor C fly The series end of the third switch tube Q3 and the series end of the fourth switch tube Q4 are electrically connected to the series end of the second resistor R2; the first switch S1 and the second switch S2 are used to control the first power supply U H Or the second power supply V bus For flying capacitor C fly Perform pre-charge.

[0023] The first resistor R1 is connected in series with the first switch S1 and the flying capacitor C fly The second resistor R2 is connected in series between the second switch S2 and the flying capacitor C fly between the first power supply U H The output current and the second power supply V bus The output current is limited to prevent the current from being too large and damaging the power device. The resistance values ​​of the first resistor R1 and the second resistor R2 are selected according to the specific working scenario, and will not be described in detail in this embodiment.

[0024] The pre-charging circuit in this embodiment can quickly pre-charge the flying capacitor through the control of the first switch and the second switch before the converter works normally, charge the voltage of the flying capacitor to a preset value, and then close the first switch and the second switch to soft-start the converter, thereby avoiding the problem of power device damage caused by excessive voltage stress of the flying capacitor three-level converter during normal startup. In addition, setting the first resistor and the second resistor in the pre-charging circuit can limit the charging current output by the first power supply and the second power supply to prevent overcurrent from damaging the power device.

[0025] In this embodiment, the first power source U H The voltage is greater than the second power supply V bus The voltage of the first power supply U H As the high-voltage side power supply, the first capacitor C H Using high voltage bus capacitor, the second power supply V bus As a low-voltage side power supply, the second capacitor C bus Use low voltage bus capacitor. The first power supply U H和 Second power supply V bus They are respectively the flying capacitor C fly Pre-charge to make the converter work in Buck mode and Boost mode. H For flying capacitor C fly After pre-charging, the converter is soft-started and enters Buck mode; the second power supply V bus For flying capacitor C fly After pre-charging, the converter is soft-started and enters Boost mode.

[0026] Specifically, the first switch S1 is closed and the second switch S2 is opened. At this time, the first power supply U H is the flying capacitor C fly Precharge and fly capacitor C fly After pre-charging, the first switch S1 is also opened to make the converter work in Buck mode; the first switch S1 is opened and the second switch S2 is closed. bus is the flying capacitor C fly Precharge and fly capacitor C fly After pre-charging, the second switch S2 is also turned on to make the converter work in the Boost mode.

[0027] The first switch S1 and the second switch S2 are coordinated to control the first power supply U H Or the second power supply V bus For flying capacitor C fly During pre-charging, the flying capacitor C fly The preset charging voltage of the first power supply U Hhalf of the voltage.

[0028] In addition, the conduction directions of the first switch tube Q1, the second switch tube Q2, the third switch tube Q3 and the fourth switch tube Q4, which are connected in series in sequence, are all the same as the first power supply U H The negative pole of the first power supply U H positive direction. In this embodiment, the first switch S1 and the second switch S2 include one or more of a relay, a semiconductor switch, and a power device; the first switch tube Q1, the second switch tube Q2, the third switch tube Q3, and the fourth switch tube Q4 include one or more of a gallium nitride field effect transistor, a metal oxide semiconductor tube, a bipolar junction transistor, or any other appropriate type of transistor or combination of transistors.

[0029] like Figure 2 This embodiment also provides a method for charging a flying capacitor three-level Buck / Boost converter, which is used to charge a flying capacitor using any of the above-mentioned flying capacitor three-level Buck / Boost converters. The method includes the following steps: In the charging step, the current flows to Figure 3 As shown by the dashed line and arrow.

[0030] Start pre-charging, close the first switch S1 and open the second switch S2, the first power supply U H The positive electrode outputs the first current; the first current passes through the first switch S1, the first resistor R1, the flying capacitor C fly , the third switch tube Q31, the inductor L, the second capacitor C bus , first power supply U H The negative electrode forms the first loop, which is connected to the flying capacitor C fly Precharge is performed and the current is limited by the first resistor R1 in series; the flying capacitor C fly The voltage of the first power supply U H When the voltage is half of the voltage, the first switch S1 is turned on to complete the pre-charging. H The output current can be applied to the flying capacitor C fly Pre-charge until the first power supply U H This method is used to measure the flying capacitor C fly After pre-charging, the converter is started to enter the Buck working mode.

[0031] like Figure 4 This embodiment also provides a method for charging a flying capacitor three-level Buck / Boost converter, which is used to charge a flying capacitor using any of the above-mentioned flying capacitor three-level Buck / Boost converters. The method includes the following steps: In the charging step, the current flows to Figure 5As shown by the dashed line and arrow.

[0032] Start pre-charging, close the second switch S2 and open the first switch S1, the second power supply V bus The positive electrode outputs the second current; the second current passes through the inductor L, the second switch tube Q2, the flying capacitor C fly , a second resistor R2, a second switch S2, a second power supply V bus The negative electrode forms a second loop, which is connected to the flying capacitor V bus Precharge is performed and the current is limited by the second resistor R2 in series; the flying capacitor C fly The voltage of the first power supply U H When the voltage reaches half of the pre-charge voltage, the second switch S2 is turned on to complete the pre-charge. bus The output current can be applied to the flying capacitor C fly Pre-charge until the first power supply U H This method is used to measure the flying capacitor C fly After pre-charging, the converter is started to enter the Boost working mode.

[0033] In the above description of the present application, unless otherwise clearly specified and limited, the terms "fixed", "installed", "connected" or "connected" and the like should be understood in a broad sense. For example, with regard to the term "connection", it can be a fixed connection, a detachable connection, or an integral one; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, or it can be the internal connection of two elements or the interaction relationship between two elements. Therefore, unless otherwise clearly defined in the present application, those skilled in the art can understand the specific meanings of the above terms in the present application according to the specific circumstances.

[0034] According to the above description of the present application, those skilled in the art may also understand that the terms used below, such as "upper", "lower", "length", "width", "top", "bottom", "inside", "outside", "axial", "longitudinal", "horizontal", "clockwise" or "counterclockwise", etc., which indicate the orientation or position relationship, are based on the orientation or position relationship shown in the drawings of the present application. It is only for the purpose of facilitating the explanation of the scheme of the present application and simplifying the description, rather than explicitly or implicitly indicating that the device or element involved must have the specific orientation, be constructed and operate in a specific orientation, so the above-mentioned orientation or position relationship terms cannot be understood or interpreted as limiting the scheme of the present application.

[0035] In addition, the terms "first" or "second" used in this application to refer to numbers or ordinals are only used for convenience of description and cannot be understood as explicitly or implicitly indicating relative importance or implicitly indicating the number of technical features indicated. At the same time, a feature defined as "first" or "second" may explicitly or implicitly include at least one such feature. In the description of this application, the meaning of "plurality" is at least two, such as two, three or more, etc., unless otherwise clearly and specifically defined.

[0036] Although multiple embodiments of the present application have been shown and described herein, it will be appreciated by those skilled in the art that such embodiments are provided only by way of example. Those skilled in the art may think of many changes, modifications and alternatives without departing from the thought and spirit of the present application. It should be understood that in the process of practicing the present application, various alternatives to the embodiments of the present application described herein may be adopted. The attached claims are intended to define the scope of protection of the present application, and therefore cover equivalents or alternatives within the scope of these claims.

Claims

1. A flying capacitor three-level Buck / Boost converter, characterized in that: include: A first power supply, a second power supply, a first capacitor connected in parallel at both ends of the first power supply, and a second capacitor connected in parallel at both ends of the second power supply; a first switch tube, a second switch tube, a third switch tube and a fourth switch tube which are sequentially connected in series and connected in parallel with the first power source; One end of the second capacitor is electrically connected to the series end of the second switch tube and the third switch tube through an inductor, and the other end of the second capacitor is electrically connected to the other end of the fourth switch tube. a pre-charging circuit connected in parallel with the first power supply, the pre-charging circuit comprising a first switch, a first resistor, a flying capacitor, a second resistor and a second switch connected in series in sequence; Among them, the series end of the flying capacitor and the first resistor is electrically connected to the series end of the first switch tube and the second switch tube, and the series end of the flying capacitor and the second resistor is electrically connected to the series end of the third switch tube and the fourth switch tube; the first switch and the second switch are used to control the first power supply or the second power supply to pre-charge the flying capacitor.

2. The flying capacitor three-level Buck / Boost converter according to claim 1, characterized in that: The voltage of the first power supply is greater than the voltage of the second power supply, and the first power supply and the second power supply are used to pre-charge the flying capacitor respectively, so that the converter operates in Buck mode and Boost mode.

3. The flying capacitor three-level Buck / Boost converter according to claim 2, characterized in that: The first switch is closed and the second switch is opened, and the first power supply pre-charges the flying capacitor to enable the converter to operate in Buck mode.

4. The flying capacitor three-level Buck / Boost converter according to claim 2, characterized in that: The first switch is opened and the second switch is closed, and the second power source pre-charges the flying capacitor so that the converter operates in a Boost mode.

5. The flying capacitor three-level Buck / Boost converter according to claim 1, characterized in that: The preset charging voltage of the flying capacitor is half of the voltage of the first power supply.

6. The flying capacitor three-level Buck / Boost converter according to claim 1, characterized in that: The conduction direction of the first switch tube, the second switch tube, the third switch tube and the fourth switch tube is from the negative electrode of the first power supply to the positive electrode of the first power supply.

7. The flying capacitor three-level Buck / Boost converter according to claim 1, characterized in that: The first switch and the second switch include one or more of a relay, a semiconductor switch, and a power device.

8. The flying capacitor three-level Buck / Boost converter according to claim 1, characterized in that: The first switch tube, the second switch tube, the third switch tube and the fourth switch tube include one or more of a gallium nitride field effect transistor, a metal oxide semiconductor tube and a bipolar junction transistor.

9. A pre-charging method for a flying capacitor three-level Buck / Boost converter, characterized in that: The method is used to pre-charge a flying capacitor using the flying capacitor three-level Buck / Boost converter according to any one of claims 1 to 8, the method comprising: The first switch is closed and the second switch is opened, so that the positive electrode of the first power supply outputs a first current; The first current sequentially passes through the first switch, the first resistor, the flying capacitor, the third switch tube, the inductor, the second capacitor, and the negative electrode of the first power supply to form a first loop to pre-charge the flying capacitor; When the voltage of the flying capacitor reaches half of the voltage of the first power supply, the first switch is turned on to complete pre-charging.

10. A pre-charging method for a flying capacitor three-level Buck / Boost converter, characterized in that: The method is used to pre-charge a flying capacitor using the flying capacitor three-level Buck / Boost converter according to any one of claims 1 to 8, the method comprising: The second switch is closed and the first switch is opened, so that the positive electrode of the second power supply outputs a second current; The second current sequentially passes through the inductor, the second switch tube, the flying capacitor, the second resistor, the second switch, and the negative electrode of the second power supply to form a second loop to pre-charge the flying capacitor; When the voltage of the flying capacitor reaches half of the voltage of the first power supply, the second switch is turned on to complete pre-charging.

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