Three-level bidirectional buck-boost converter and control method thereof

Abstract

The embodiment of the invention provides a three-level bidirectional buck-boost converter and a control method thereof, and belongs to the technical field of power electronics. The three-level bidirectional buck-boost converter comprises a first bridge arm, a second bridge arm, a first energy storage capacitor, a second energy storage capacitor, a third energy storage capacitor and a first energy storage inductor; the first energy-storage capacitor and the second energy-storage capacitor are connected in series at two ends of a power supply; the third energy-storage capacitor is connected in parallel at two ends of the battery and the first energy-storage inductor; a first end of the first bridge arm is connected with a power supply anode, a second end of the first bridge arm is connected with a battery anode through the first energy storage inductor, and a third end of the first bridge arm is connected with a second end of the first energy storage capacitor; the first end of the second bridge arm is connected with the second end of the first energy storage capacitor, the second end of the second bridge arm is connected with the battery cathode through the first energy storage inductor, and the third end of the second bridge arm is connected with the power supply cathode. According to the scheme, a circuit topological structure is constructed, and the circuit is compatible with buck-boost bidirectional circuit control, so that device stress can be reduced, and lightweight design is realized.

Description

Technical Field

[0001] This application relates to the field of power electronics technology, and particularly to a three-level bidirectional buck-boost converter and its control method. Background Art

[0002] In rail transit systems, high voltage input and high power and large current output are generally required, which pose high requirements on the process, withstand voltage level, volume, power loss, system stability, and equipment lightweight of the devices used.

[0003] In an on-vehicle energy storage bidirectional power supply system, the DC bus voltage of the motor car is as high as 1800V or even higher. When using two-level control, when the upper and lower drive tubes are respectively turned on, the stress at both ends of the other tube is the voltage of the power supply, which significantly increases the stress requirements of the high-voltage switch tubes. Currently, the manufacturing process of high-voltage drive tubes is difficult, expensive, and extremely prone to damage when the bus is unstable, and the damage risk also increases in a high-stress environment, thus affecting the reliability and safety of the entire system.

[0004] At the same time, due to the large stress at both ends of the drive tube, the loss of the drive tube increases, the heat generation is serious, the heat dissipation requirement is high, the heat dissipation design cost is increased. Also affected by the switching loss, the operating frequency cannot be increased, the required inductor has a large volume and mass, and the overall volume and weight of the system are relatively high, making it difficult to meet the lightweight design requirements. Summary of the Invention

[0005] The main purpose of the embodiments of this application is to propose a three-level bidirectional buck-boost converter and its control method, aiming to reduce the stress of the devices and achieve lightweight design.

[0006] To achieve the above object, on the one hand, an embodiment of this application proposes a three-level bidirectional buck-boost converter, which includes a first bridge arm, a second bridge arm, a first energy storage capacitor, a second energy storage capacitor, a third energy storage capacitor, and a first energy storage inductor;

[0007] The first end of the first energy storage capacitor is connected to the positive pole of the power supply, the second end of the first energy storage capacitor is connected to the first end of the second energy storage capacitor, the second end of the second energy storage capacitor is connected to the negative pole of the power supply, the first end of the third energy storage capacitor is respectively connected to the first energy storage inductor and the positive pole of the battery, and the second end of the third energy storage capacitor is respectively connected to the first energy storage inductor and the negative pole of the battery;

[0008] The first end of the first bridge arm is connected to the positive pole of the power supply, the second end of the first bridge arm is connected to the positive pole of the battery through the first energy storage inductor, and the third end of the first bridge arm is connected to the second end of the first energy storage capacitor;

[0009] The first end of the second bridge arm is connected to the second end of the first energy storage capacitor. The second end of the second bridge arm is connected to the negative electrode of the battery through the first energy storage inductor. The third end of the second bridge arm is connected to the negative electrode of the power supply.

[0010] In some embodiments, the first bridge arm includes a first driving transistor, a second driving transistor, a first body diode, and a second body diode. The second bridge arm includes a third driving transistor, a fourth driving transistor, a third body diode, and a fourth body diode. Among them, the first driving transistor is connected in parallel with the first body diode, the second driving transistor is connected in parallel with the second body diode, the third driving transistor is connected in parallel with the third body diode, and the fourth driving transistor is connected in parallel with the fourth body diode.

[0011] The collector of the first driving transistor serves as the first end of the first bridge arm. The emitter of the first driving transistor is connected to the collector of the second driving transistor to serve as the second end of the first bridge arm. The emitter of the second driving transistor serves as the third end of the first bridge arm.

[0012] The collector of the third driving transistor serves as the first end of the second bridge arm. The emitter of the third driving transistor is connected to the collector of the fourth driving transistor to serve as the second end of the second bridge arm. The emitter of the fourth driving transistor serves as the third end of the second bridge arm.

[0013] In some embodiments, the three-level bidirectional buck-boost converter further includes a first filter capacitor and a second filter capacitor. Among them, the first filter capacitor is connected in parallel with the first bridge arm, and the second filter capacitor is connected in parallel with the second bridge arm.

[0014] In some embodiments, the three-level bidirectional buck-boost converter further includes a first resistor, a second resistor, and a third resistor. Among them, the first resistor is connected in parallel with the first energy storage capacitor, the second resistor is connected in parallel with the second energy storage capacitor, and the third resistor is connected in parallel with the third energy storage capacitor.

[0015] In some embodiments, the three-level bidirectional buck-boost converter further includes a third bridge arm and a fourth bridge arm.

[0016] The first end of the third bridge arm is connected to the positive electrode of the power supply. The second end of the third bridge arm is connected to the positive electrode of the battery through the first energy storage inductor. The third end of the third bridge arm is connected to the second end of the first energy storage capacitor.

[0017] The first end of the fourth bridge arm is connected to the second end of the first energy storage capacitor. The second end of the fourth bridge arm is connected to the negative electrode of the battery through the first energy storage inductor. The third end of the fourth bridge arm is connected to the negative electrode of the power supply.

[0018] In some embodiments, the third bridge arm includes a fifth driving transistor, a sixth driving transistor, a fifth body diode, and a sixth body diode, and the fourth bridge arm includes a seventh driving transistor, an eighth driving transistor, a seventh body diode, and an eighth body diode. Among them, the fifth driving transistor is connected in parallel with the fifth body diode, the sixth driving transistor is connected in parallel with the sixth body diode, the seventh driving transistor is connected in parallel with the seventh body diode, and the eighth driving transistor is connected in parallel with the eighth body diode;

[0019] The collector of the fifth driving transistor serves as the first end of the third bridge arm; the emitter of the fifth driving transistor is connected to the collector of the sixth driving transistor to serve as the second end of the third bridge arm; the emitter of the sixth driving transistor serves as the third end of the third bridge arm;

[0020] The collector of the seventh driving transistor serves as the first end of the fourth bridge arm; the emitter of the seventh driving transistor is connected to the collector of the eighth driving transistor to serve as the second end of the fourth bridge arm; the emitter of the eighth driving transistor serves as the third end of the fourth bridge arm.

[0021] In some embodiments, the three-level bidirectional buck-boost converter further includes a third filter capacitor and a fourth filter capacitor. Among them, the third filter capacitor is connected in parallel with the third bridge arm, and the fourth filter capacitor is connected in parallel with the fourth bridge arm.

[0022] To achieve the above object, another aspect of the embodiments of the present application provides a control method for a three-level bidirectional buck-boost converter, which is applied to the aforementioned three-level bidirectional buck-boost converter. The control method includes the following steps:

[0023] Determine the working mode of the three-level bidirectional buck-boost converter according to the energy flow direction, where the working mode includes a forward buck mode and a reverse boost mode;

[0024] Based on the working mode, adjust the duty cycle of the driving signals of each driving transistor according to the change amount of the load;

[0025] Determine the on-off state of the driving transistor according to the duty cycle of the driving signal;

[0026] Determine the working state of the three-level bidirectional buck-boost converter according to the on-off state of the driving transistor.

[0027] In some embodiments, when the working mode is the forward buck mode, determining the working state of the three-level bidirectional buck-boost converter according to the on-off state of the driving transistor includes the following steps:

[0028] When the first driving transistor and the fifth driving transistor are turned on, and the second driving transistor, the third driving transistor, the fourth driving transistor, the sixth driving transistor, the seventh driving transistor, and the eighth driving transistor are turned off, it is determined that the operating state of the three-level bidirectional buck-boost converter is the first state. In the first state, the power supply, the first energy storage capacitor, the first driving transistor, the fifth driving transistor, the first energy storage inductor, the seventh body diode, and the third body diode are connected in sequence to form a first loop, and the load is powered through the first loop. At the same time, the second energy storage capacitor is charged and stored with energy;

[0029] Alternatively, when the first driving transistor, the fourth driving transistor, the fifth driving transistor, and the eighth driving transistor are turned on, and the second driving transistor, the third driving transistor, the sixth driving transistor, and the seventh driving transistor are turned off, it is determined that the operating state of the three-level bidirectional buck-boost converter is the second state. In the second state, the power supply, the first driving transistor, the fifth driving transistor, the first energy storage inductor, the eighth driving transistor, and the fourth driving transistor are connected in sequence to form a second loop, and the load is powered through the second loop. At the same time, the first energy storage capacitor and the second energy storage capacitor are charged and stored with energy through the power supply;

[0030] Alternatively, when the fourth driving transistor and the eighth driving transistor are turned on, and the first driving transistor, the second driving transistor, the third driving transistor, the fifth driving transistor, the sixth driving transistor, and the seventh driving transistor are turned off, it is determined that the operating state of the three-level bidirectional buck-boost converter is the third state. In the third state, the power supply, the second energy storage capacitor, the second body diode, the sixth body diode, the first energy storage inductor, the eighth driving transistor, and the fourth driving transistor are connected in sequence to form a third loop, and the load is powered through the third loop. At the same time, the first energy storage capacitor is charged and stored with energy;

[0031] Alternatively, when the first driving transistor, the second driving transistor, the third driving transistor, the fourth driving transistor, the fifth driving transistor, the sixth driving transistor, the seventh driving transistor, and the eighth driving transistor are turned off, it is determined that the operating state of the three-level bidirectional buck-boost converter is the fourth state. In the fourth state, the second body diode, the sixth body diode, the first energy storage inductor, the seventh body diode, and the third body diode are connected in sequence to form a fourth loop, and the first energy storage capacitor and the second energy storage capacitor are charged and stored with energy through the power supply.

[0032] In some embodiments, when the operating mode is the reverse boost mode, determining the operating state of the three-level bidirectional buck-boost converter according to the on-off states of the driving transistors includes the following steps:

[0033] When the third driving transistor and the seventh driving transistor are turned on, and the first driving transistor, the second driving transistor, the fourth driving transistor, the fifth driving transistor, the sixth driving transistor and the eighth driving transistor are turned off, it is determined that the operating state of the three-level bidirectional buck-boost converter is the fifth state. In the fifth state, the battery, the third energy storage capacitor, the first energy storage inductor, the fifth body diode, the first body diode, the second energy storage capacitor, the fourth body diode, the eighth body diode, the third driving transistor and the seventh driving transistor are connected in sequence to form a fifth loop, and power is supplied to the load through the fifth loop; at the same time, the battery, the third energy storage capacitor, the first energy storage inductor, the fifth body diode, the first body diode, the third driving transistor and the seventh driving transistor are connected in sequence to form a sixth loop, and the first energy storage capacitor is charged and stored through the sixth loop;

[0034] Alternatively, when the second driving transistor, the third driving transistor, the sixth driving transistor and the seventh driving transistor are turned on, and the first driving transistor, the fourth driving transistor, the fifth driving transistor and the eighth driving transistor are turned off, it is determined that the operating state of the three-level bidirectional buck-boost converter is the sixth state. In the sixth state, the battery, the third energy storage capacitor, the first energy storage inductor, the sixth driving transistor, the second driving transistor, the third driving transistor and the seventh driving transistor are connected in sequence to form a seventh loop, and the first energy storage inductor is charged and stored through the seventh loop. At the same time, power is supplied to the load through the first energy storage capacitor and the second energy storage capacitor

[0035] Alternatively, when the second driving transistor and the sixth driving transistor are turned on, and the first driving transistor, the third driving transistor, the fourth driving transistor, the fifth driving transistor, the seventh driving transistor and the eighth driving transistor are turned off, it is determined that the operating state of the three-level bidirectional buck-boost converter is the seventh state. In the seventh state, the battery, the third energy storage capacitor, the first energy storage inductor, the fifth body diode, the first body diode, the first energy storage capacitor, the fourth body diode and the eighth body diode are connected in sequence to form an eighth loop, and power is supplied to the load through the eighth loop; at the same time, the battery, the third energy storage capacitor, the first energy storage inductor, the sixth driving transistor, the second driving transistor, the fourth body diode and the eighth body diode are connected in sequence to form a ninth loop, and the second energy storage capacitor is charged and stored through the ninth loop;

[0036] Alternatively, when the first driving transistor, the second driving transistor, the third driving transistor, the fourth driving transistor, the fifth driving transistor, the sixth driving transistor, the seventh driving transistor, and the eighth driving transistor are turned off, it is determined that the operating state of the three-level bidirectional buck-boost converter is the eighth state. In the eighth state, the battery, the third energy storage capacitor, the first energy storage inductor, the fifth body diode, the first body diode, the fourth body diode, and the eighth body diode are connected in sequence to form a tenth loop, and power is supplied to the load through the tenth loop. At the same time, the first energy storage capacitor and the second energy storage capacitor are charged and stored.

[0037] To achieve the above object, on the other hand, an embodiment of the present application provides an electronic device, which includes a memory and a processor. The memory stores a computer program, and when the processor executes the computer program, the above control method is implemented.

[0038] To achieve the above object, on the other hand, an embodiment of the present application provides a computer-readable storage medium, which stores a computer program, and when the computer program is executed by a processor, the above control method is implemented.

[0039] The embodiments of the present application at least include the following beneficial effects: The present application provides a three-level bidirectional buck-boost converter and its control method. The three-level bidirectional buck-boost converter includes a first bridge arm, a second bridge arm, a first energy storage capacitor, a second energy storage capacitor, a third energy storage capacitor, and a first energy storage inductor. The first end of the first energy storage capacitor is connected to the positive pole of the power supply, the second end of the first energy storage capacitor is connected to the first end of the second energy storage capacitor, and the second end of the second energy storage capacitor is connected to the negative pole of the power supply; the first end of the first bridge arm is connected to the positive pole of the power supply, the second end of the first bridge arm is connected to the positive pole of the battery through the first energy storage inductor, and the third end of the first bridge arm is connected to the second end of the first energy storage capacitor; the first end of the second bridge arm is connected to the second end of the first energy storage capacitor, the second end of the second bridge arm is connected to the negative pole of the battery through the first energy storage inductor, and the third end of the second bridge arm is connected to the negative pole of the power supply; the first end of the third energy storage capacitor is respectively connected to the first energy storage inductor and the positive pole of the battery, and the second end of the third energy storage capacitor is respectively connected to the first energy storage inductor and the negative pole of the battery. This solution can reduce device stress and achieve lightweight design by constructing a circuit topology structure and being compatible with buck-boost bidirectional circuit control. Description of the Drawings

[0040] Figure 1 is the circuit structure diagram of the two-level three-phase interleaved conversion circuit provided by the embodiment of the present application;

[0041] Figure 2 is the circuit structure diagram of the three-level bidirectional buck-boost converter provided by the embodiment of the present application;

[0042] Figure 3 is the circuit structure diagram of a three-level bidirectional buck-boost converter provided by another embodiment of the present application;

[0043] Figure 4 is the current flow diagram of the first state provided by the embodiment of the present application;

[0044] Figure 5 is the current flow diagram of the second state provided by the embodiment of the present application;

[0045] Figure 6 is the current flow diagram of the third state provided by the embodiment of the present application;

[0046] Figure 7 is the current flow diagram of the fourth state provided by the embodiment of the present application;

[0047] Figure 8 is the current flow diagram of the fifth state provided by the embodiment of the present application;

[0048] Figure 9 is the current flow diagram of the sixth state provided by the embodiment of the present application;

[0049] Figure 10 is the current flow diagram of the seventh state provided by the embodiment of the present application;

[0050] Figure 11 is the current flow diagram of the eighth state provided by the embodiment of the present application;

[0051] Figure 12 is the schematic diagram of the hardware structure of the electronic device provided by the embodiment of the present application.

[0052] Reference numerals: first bridge arm Q1, second bridge arm Q2, third bridge arm Q3, fourth bridge arm Q4, first resistor R1, second resistor R2, third resistor R3, first energy storage capacitor C1, second energy storage capacitor C2, third energy storage capacitor C7, first filter capacitor C3, second filter capacitor C4, third filter capacitor C5, fourth filter capacitor C6, first energy storage inductor L1, first driving transistor VT1, second driving transistor VT2, third driving transistor VT3, fourth driving transistor VT4, fifth driving transistor VT5, sixth driving transistor VT6, seventh driving transistor VT7, eighth driving transistor VT8, first body diode VD1, second body diode VD2, third body diode VD3, fourth body diode VD4, fifth body diode VD5, sixth body diode VD6, seventh body diode VD7, eighth body diode VD8. Detailed implementation manners

[0053] In order to make the objectives, technical solutions, and advantages of this application clearer and more understandable, the following further details this application in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely for explaining this application and are not used to limit this application. When the following description refers to the accompanying drawings, unless otherwise indicated, the same numerals in different drawings represent the same or similar elements. The implementation manners described in the following exemplary embodiments do not represent all implementation manners consistent with the embodiments of this application. They are merely examples of devices and methods that are consistent with some aspects of the embodiments of this application as detailed in the appended claims.

[0054] It can be understood that the terms "first", "second", etc. used in this application may be used herein to describe various concepts, but unless otherwise specified, these concepts are not limited by these terms. These terms are only used to distinguish one concept from another. For example, without departing from the scope of the embodiments of this application, the first information may also be referred to as the second information. Similarly, the second information may also be referred to as the first information. Depending on the context, the words "if", "when" as used herein may be interpreted as "when...", "while...", or "in response to determining".

[0055] The terms "at least one", "a plurality of", "each", "any one", etc. used in this application, at least one includes one, two, or more than two, a plurality of includes two or more than two, each refers to each of the corresponding plurality, and any one refers to any one of the plurality.

[0056] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which this application belongs. The terms used herein are only for the purpose of describing the embodiments of this application and are not intended to limit this application.

[0057] Before elaborating on the embodiments of this application in detail, some related technologies involved in the embodiments of this application are first described.

[0058] Refer to Figure 1, in the traditional on-vehicle energy storage bidirectional power supply system, the DC / DC conversion circuit adopts a dual-level three-phase interleaved chopper control. When the power supply charges the battery, the system adjusts the circuit into three parallel buck circuits by controlling the driving tubes, sets the three-phase driving signals to be offset by a phase of 2π / 3 in sequence, makes the upper-bridge driving tubes VT1, VT3, and VT5 conduct alternately, and the lower-bridge driving tubes VT2, VT4, and VT6 are always turned off. The freewheeling is realized through the reverse diodes connected in parallel with the lower-bridge driving tubes, and then the required voltage drop is adjusted by controlling the duty cycle of the three upper-bridge driving tubes, thereby realizing the buck output to charge the battery; when the power supply loses power, the battery can also supply power to the power supply in reverse. The circuit is adjusted into three parallel boost circuits by controlling the driving tubes, and the lower-bridge driving tubes VT2, VT4, and VT6 conduct alternately to charge and store energy in the inductor. The upper-bridge driving tubes VT1, VT3, and VT5 are always turned off. When the lower-bridge driving tubes are turned off, a loop is formed through the reverse diodes connected in parallel with the upper-bridge driving tubes to supply power to the power supply, and the duty cycle is adjusted according to the boost situation.

[0059] During the conduction processes of the upper and lower driving tubes respectively, the stress at both ends of the other driving tube is the voltage of the power supply, and the DC bus voltage of the motor car is 1800V or even higher. Therefore, strict requirements are put forward for the manufacturing process and withstand voltage level of the driving tubes. Currently, the manufacturing process of high-voltage driving tubes is difficult and expensive, and they are extremely easy to be damaged when the bus is unstable, increasing the manufacturing cost and damage risk.

[0060] At the same time, due to the large stress at both ends of the driving tubes, the loss of the driving tubes increases, the heating is serious, and the requirements for heat dissipation are high, increasing the heat dissipation design cost. Also affected by the switching loss, the working frequency cannot be increased, the required inductors are large in volume and mass and there are three of them, and the overall volume and weight of the system are relatively high, making it difficult to meet the lightweight design requirements.

[0061] Affected by factors such as inductor differences and bus structures, it will also cause the phase currents in the conversion circuit to be unbalanced, resulting in an increase in thermal stress and magnetic saturation in the corresponding phases, affecting the reliability of the system. Moreover, since the phase currents need to be obtained for control, the number of sensors required is large, and the accuracy of the sensors will also cause control deviation of the system, exacerbating the instability in control.

[0062] In view of this, the embodiment of the present application provides a three-level bidirectional buck-boost converter, and this solution proposes an application topology structure for the defects of the dual-level three-phase interleaved conversion circuit in rail transit applications.

[0063] Refer to Figure 2 , Figure 2It is the circuit structure diagram of the three-level bidirectional buck-boost converter provided by the embodiments of the present application. The three-level bidirectional buck-boost converter includes a first bridge arm Q1, a second bridge arm Q2, a first energy storage capacitor C1, a second energy storage capacitor C2, a third energy storage capacitor C7, and a first energy storage inductor L1.

[0064] The first end of the first energy storage capacitor is connected to the positive pole of the power supply, the second end of the first energy storage capacitor is connected to the first end of the second energy storage capacitor, the second end of the second energy storage capacitor is connected to the negative pole of the power supply, the first end of the third energy storage capacitor is respectively connected to the first energy storage inductor and the positive pole of the battery, and the second end of the third energy storage capacitor is respectively connected to the first energy storage inductor and the negative pole of the battery.

[0065] The first end of the first bridge arm is connected to the positive pole of the power supply, the second end of the first bridge arm is connected to the positive pole of the battery through the first energy storage inductor, and the third end of the first bridge arm is connected to the second end of the first energy storage capacitor.

[0066] The first end of the second bridge arm is connected to the second end of the first energy storage capacitor, the second end of the second bridge arm is connected to the negative pole of the battery through the first energy storage inductor, and the third end of the second bridge arm is connected to the negative pole of the power supply.

[0067] Specifically, when the application scenario is of low power, the three-level bidirectional buck-boost converter mainly consists of a first bridge arm, a second bridge arm, a first energy storage capacitor, a second energy storage capacitor, a third energy storage capacitor, and a first energy storage inductor.

[0068] The first energy storage capacitor, the second energy storage capacitor, and the third energy storage capacitor are bus capacitors, which are used for energy storage and filtering of the switching circuit, preventing bus voltage fluctuations, and improving the anti-interference ability of the system. Among them, the first energy storage capacitor and the second energy storage capacitor are connected in series at both ends of the power supply, and the third energy storage capacitor is connected in parallel at both ends of the battery and the first energy storage inductor. The first end of the first energy storage capacitor is connected to the positive pole of the power supply, the second end of the first energy storage capacitor is connected to the first end of the second energy storage capacitor, the second end of the second energy storage capacitor is connected to the negative pole of the power supply, the first end of the third energy storage capacitor is respectively connected to the first energy storage inductor and the positive pole of the battery, and the second end of the third energy storage capacitor is respectively connected to the first energy storage inductor and the negative pole of the battery.

[0069] The first energy storage inductor uses a double-wound inductor, which is used for energy storage in the buck and boost bidirectional circuits, can be applied to a high-frequency working environment, has a filtering effect, can effectively suppress high-frequency interference and electromagnetic radiation, and improves the system stability.

[0070] Optionally, the first bridge arm and the second bridge arm can be composed of two drive tubes connected in series or an integrated insulated gate bipolar transistor (IGBT) module. Among them, the first end of the first bridge arm is connected to the positive pole of the power supply, the second end of the first bridge arm is connected to the positive pole of the battery through the first energy storage inductor, and the third end of the first bridge arm is connected to the second end of the first energy storage capacitor.

[0071] The first end of the second bridge arm is connected to the second end of the first energy storage capacitor, the second end of the second bridge arm is connected to the negative electrode of the battery through the first energy storage inductor, and the third end of the second bridge arm is connected to the negative electrode of the power supply.

[0072] When the power supply is charging the battery, the upper tube of the first bridge arm and the lower tube of the second bridge arm are controlled to be turned on alternately, so as to achieve a step-down output and charge the battery.

[0073] Specifically, according to different duty cycles of the driving signal, the three-level bidirectional buck-boost converter can be divided into four working states: the upper tube of the first bridge arm is turned on and the lower tube of the second bridge arm is turned off, the upper tube of the first bridge arm is turned off and the lower tube of the second bridge arm is turned on, the upper tube of the first bridge arm is turned on and the lower tube of the second bridge arm is turned on, and the upper tube of the first bridge arm is turned off and the lower tube of the second bridge arm is turned off.

[0074] When the battery is used as power supply, the inductor is charged and energy is stored by controlling the lower tube of the first bridge arm and the upper tube of the second bridge arm to be turned on alternately.

[0075] Specifically, according to different duty cycles of the driving signal, the three-level bidirectional buck-boost converter can be divided into four working states: the lower tube of the first bridge arm is turned on and the upper tube of the second bridge arm is turned off, the lower tube of the first bridge arm is turned off and the upper tube of the second bridge arm is turned on, the lower tube of the first bridge arm is turned on and the upper tube of the second bridge arm is turned on, and the lower tube of the first bridge arm is turned off and the upper tube of the second bridge arm is turned off.

[0076] In this embodiment, compared with the two-level topology, the switch stress in the circuit topology of the three-level bidirectional buck-boost converter is only half of the power supply voltage, and the voltage resistance level of the capacitor is only half of the original. This means that when subjected to the same voltage, the working conditions are more relaxed, and devices with lower voltage resistance levels can be selected to replace customized high-voltage devices. The overall price of the system can be greatly reduced, and the safety and reliability are improved, and the devices are not easily damaged.

[0077] At the same time, the three-level bidirectional buck-boost converter has four working states in both boost and buck conditions. The switching frequency is doubled compared to the two-level topology, and the inductor operating frequency is also doubled, which can make the inductor smaller in size and weight in design, meeting the needs of lightweight design.

[0078] In some embodiments, the first bridge arm includes a first driving transistor VT1, a second driving transistor VT2, a first body diode VD1, and a second body diode VD2, and the second bridge arm includes a third driving transistor VT3, a fourth driving transistor VT4, a third body diode VD3, and a fourth body diode VD4. Among them, the first driving transistor is connected in parallel with the first body diode, the second driving transistor is connected in parallel with the second body diode, the third driving transistor is connected in parallel with the third body diode, and the fourth driving transistor is connected in parallel with the fourth body diode.

[0079] The collector of the first driving transistor serves as the first end of the first bridge arm; the emitter of the first driving transistor is connected to the collector of the second driving transistor and serves as the second end of the first bridge arm; the emitter of the second driving transistor serves as the third end of the first bridge arm.

[0080] The collector of the third driving transistor serves as the first end of the second bridge arm; the emitter of the third driving transistor is connected to the collector of the fourth driving transistor and serves as the second end of the second bridge arm; the emitter of the fourth driving transistor serves as the third end of the second bridge arm.

[0081] Specifically, each bridge arm is composed of two driving transistors and their built-in body diodes. By turning on and off different driving transistors and combining their built-in body diodes, it is compatible with the control of buck and boost bidirectional circuits.

[0082] The first bridge arm includes a first driving transistor, a second driving transistor, a first body diode, and a second body diode, and the second bridge arm includes a third driving transistor, a fourth driving transistor, a third body diode, and a fourth body diode. Among them, the first driving transistor is connected in parallel with the first body diode, the second driving transistor is connected in parallel with the second body diode, the third driving transistor is connected in parallel with the third body diode, and the fourth driving transistor is connected in parallel with the fourth body diode.

[0083] The collector of the first driving transistor serves as the first end of the first bridge arm; the emitter of the first driving transistor is connected to the collector of the second driving transistor and serves as the second end of the first bridge arm; the emitter of the second driving transistor serves as the third end of the first bridge arm.

[0084] It can be understood that the first bridge arm is connected to the positive pole of the power supply through the collector of the first driving transistor, and is connected to the second end of the first energy storage capacitor through the emitter of the second driving transistor. After the emitter of the first driving transistor is connected to the collector of the second driving transistor, they are jointly connected to the positive pole of the battery through the first energy storage inductor.

[0085] The collector of the third driving transistor serves as the first end of the second bridge arm; the emitter of the third driving transistor is connected to the collector of the fourth driving transistor and serves as the second end of the second bridge arm; the emitter of the fourth driving transistor serves as the third end of the second bridge arm.

[0086] It can be understood that the second arm is connected to the second end of the first energy storage capacitor through the collector of the third driving transistor, and is connected to the negative power supply through the emitter of the fourth driving transistor. After the emitter of the third driving transistor is connected to the collector of the fourth driving transistor, they are jointly connected to the negative terminal of the battery through the first energy storage inductor.

[0087] In some embodiments, the three-level bidirectional buck-boost converter further includes a first filter capacitor C3 and a second filter capacitor C4. Among them, the first filter capacitor is connected in parallel with the first arm, and the second filter capacitor is connected in parallel with the second arm.

[0088] Specifically, the three-level bidirectional buck-boost converter further includes a first filter capacitor and a second filter capacitor. The first filter capacitor and the second filter capacitor are both high-frequency suppression capacitors, which are used to suppress the ringing phenomenon generated on the arm during the switching process, improve the switching efficiency, and at the same time reduce the risk of module damage. Among them, the first filter capacitor is connected in parallel with the first arm to suppress the ringing phenomenon generated on the first arm during the switching process; the second filter capacitor is connected in parallel with the second arm to suppress the ringing phenomenon generated on the second arm during the switching process.

[0089] In some embodiments, the three-level bidirectional buck-boost converter further includes a first resistor R1, a second resistor R2, and a third resistor R3. Among them, the first resistor is connected in parallel with the first energy storage capacitor, the second resistor is connected in parallel with the second energy storage capacitor, and the third resistor is connected in parallel with the third energy storage capacitor.

[0090] Specifically, the three-level bidirectional buck-boost converter further includes a first resistor, a second resistor, and a third resistor. Resistors R1-R3 are all discharge resistors, which are used for discharging the capacitor when the power is off. Among them, the first resistor is connected in parallel with the first energy storage capacitor, the second resistor is connected in parallel with the second energy storage capacitor, and the third resistor is connected in parallel with the third energy storage capacitor. At the same time, the first resistor and the second resistor also play a role in equalizing the voltage of the first energy storage capacitor and the second energy storage capacitor to ensure the safe use of the system.

[0091] Refer to Figure 3 , in some embodiments, the three-level bidirectional buck-boost converter further includes a third arm Q3 and a fourth arm Q4.

[0092] The first end of the third arm is connected to the positive power supply, the second end of the third arm is connected to the positive terminal of the battery through the first energy storage inductor, and the third end of the third arm is connected to the second end of the first energy storage capacitor.

[0093] The first end of the fourth arm is connected to the second end of the first energy storage capacitor, the second end of the fourth arm is connected to the negative terminal of the battery through the first energy storage inductor, and the third end of the fourth arm is connected to the negative power supply.

[0094] Specifically, the three-level bidirectional buck-boost converter further includes a third bridge arm and a fourth bridge arm. The parallel mode of the bridge arms improves the over-current capacity of the loop, reduces the over-current capacity required for single-tube operation, enables conventional devices to be applied to high-power density occasions such as rail transit, and is suitable for high-power density scenarios.

[0095] Optionally, the third bridge arm is connected in parallel with the first bridge arm, and the fourth bridge arm is connected in parallel with the first bridge arm. Among them, the first end of the third bridge arm is connected to the positive pole of the power supply, the second end of the third bridge arm is connected to the positive pole of the battery through a first energy storage inductor, and the third end of the third bridge arm is connected to the second end of the first energy storage capacitor.

[0096] The first end of the fourth bridge arm is connected to the second end of the first energy storage capacitor, the second end of the fourth bridge arm is connected to the negative pole of the battery through a first energy storage inductor, and the third end of the fourth bridge arm is connected to the negative pole of the power supply.

[0097] It should be noted that the third bridge arm and the fourth bridge arm are in a parallel structure. When the usage scenario is low power, the parallel structure can also be removed to simplify the system architecture. When the usage scenario requires stronger loop over-current capacity, a fifth bridge arm and a sixth bridge arm can also be added as a parallel structure.

[0098] In some embodiments, the third bridge arm includes a fifth driving transistor VT5, a sixth driving transistor VT6, a fifth body diode VD5, and a sixth body diode VD6. The fourth bridge arm includes a seventh driving transistor VT7, an eighth driving transistor VT8, a seventh body diode VD7, and an eighth body diode VD8. Among them, the fifth driving transistor is connected in parallel with the fifth body diode, the sixth driving transistor is connected in parallel with the sixth body diode, the seventh driving transistor is connected in parallel with the seventh body diode, and the eighth driving transistor is connected in parallel with the eighth body diode.

[0099] The collector of the fifth driving transistor serves as the first end of the third bridge arm; the emitter of the fifth driving transistor is connected to the collector of the sixth driving transistor as the second end of the third bridge arm; the emitter of the sixth driving transistor serves as the third end of the third bridge arm.

[0100] The collector of the seventh driving transistor serves as the first end of the fourth bridge arm; the emitter of the seventh driving transistor is connected to the collector of the eighth driving transistor as the second end of the fourth bridge arm; the emitter of the eighth driving transistor serves as the third end of the fourth bridge arm.

[0101] Specifically, each bridge arm is also composed of two driving transistors and their built-in body diodes. The over-current capacity of the loop is improved by the series and parallel connection of different driving transistors.

[0102] The third bridge arm includes a fifth driving transistor, a sixth driving transistor, a fifth body diode, and a sixth body diode. The fourth bridge arm includes a seventh driving transistor, an eighth driving transistor, a seventh body diode, and an eighth body diode. Among them, the fifth driving transistor is connected in parallel with the fifth body diode, the sixth driving transistor is connected in parallel with the sixth body diode, the seventh driving transistor is connected in parallel with the seventh body diode, and the eighth driving transistor is connected in parallel with the eighth body diode.

[0103] The collector of the fifth driving transistor serves as the first end of the third bridge arm; the emitter of the fifth driving transistor is connected to the collector of the sixth driving transistor to serve as the second end of the third bridge arm; the emitter of the sixth driving transistor serves as the third end of the third bridge arm.

[0104] It can be understood that the third bridge arm is connected to the positive power supply through the collector of the fifth driving transistor, and is connected to the second end of the first energy storage capacitor through the emitter of the sixth driving transistor. After the emitter of the fifth driving transistor is connected to the collector of the sixth driving transistor, they are jointly connected to the positive pole of the battery through the first energy storage inductor.

[0105] The collector of the seventh driving transistor serves as the first end of the fourth bridge arm; the emitter of the seventh driving transistor is connected to the collector of the eighth driving transistor to serve as the second end of the fourth bridge arm; the emitter of the eighth driving transistor serves as the third end of the fourth bridge arm.

[0106] It can be understood that the fourth bridge arm is connected to the second end of the first energy storage capacitor through the collector of the seventh driving transistor, and is connected to the negative power supply through the emitter of the eighth driving transistor. After the emitter of the seventh driving transistor is connected to the collector of the eighth driving transistor, they are jointly connected to the negative pole of the battery through the first energy storage inductor.

[0107] In some embodiments, the three-level bidirectional buck-boost converter further includes a third filter capacitor C5 and a fourth filter capacitor C6. Among them, the third filter capacitor is connected in parallel with the third bridge arm, and the fourth filter capacitor is connected in parallel with the fourth bridge arm.

[0108] Specifically, the three-level bidirectional buck-boost converter further includes a third filter capacitor and a fourth filter capacitor. Both the third filter capacitor and the fourth filter capacitor are high-frequency suppression capacitors, which are used to suppress the ringing phenomenon generated on the bridge arm during the switching process, improve the switching efficiency, and at the same time reduce the risk of module damage. Among them, the third filter capacitor is connected in parallel with the third bridge arm to suppress the ringing phenomenon generated on the third bridge arm during the switching process; the fourth filter capacitor is connected in parallel with the fourth bridge arm to suppress the ringing phenomenon generated on the fourth bridge arm during the switching process.

[0109] The embodiment of the present application also provides a control method for a three-level bidirectional buck-boost converter, which is applied to the aforementioned three-level bidirectional buck-boost converter. The control method includes but is not limited to steps S101 to S104.

[0110] Step S101: Determine the operating mode of the three-level bidirectional buck-boost converter according to the energy flow direction, where the operating mode includes a forward buck mode and a reverse boost mode.

[0111] Step S102: Based on the operating mode, adjust the duty cycle of the driving signals of each driving transistor according to the change in the load.

[0112] Step S103: Determine the on / off state of the driving transistors according to the duty cycle of the driving signals.

[0113] Step S104: Determine the operating state of the three-level bidirectional buck-boost converter according to the on / off state of the driving transistors.

[0114] It should be noted that the working principles of the simplified structure and the parallel structure are basically the same. Taking the three-level bidirectional buck-boost converter shown below as an example, determine the operating mode of the three-level bidirectional buck-boost converter according to the energy flow direction, where the operating mode includes a forward buck mode and a reverse boost mode. When the energy flows from the power supply to the battery, it can be determined that the circuit is in the forward buck mode; when the energy flows from the battery to the power supply, it can be determined that the circuit is in the reverse boost mode. Figure 3 Adjust the duty cycle of the driving signals of each driving transistor according to the change in the load. Based on the determined operating mode, according to the operating mode, calculate the required output energy of the converter according to the change in the load, and match the current load demand by adjusting the ratio of the high-level time of the driving signals of each driving transistor to the total time in one cycle. The driving signals of each driving transistor are output staggered.

[0115] Determine the on / off state of the driving transistors according to the duty cycle of the driving signals. When the driving signal is at a high level, the corresponding driving transistor will conduct; when the driving signal is at a low level, the corresponding driving transistor will turn off. By adjusting the duty cycle of the driving signal, the conduction time of the driving transistor can be controlled, thereby controlling the on / off state of the driving transistor.

[0116] Determine the operating state of the three-level bidirectional buck-boost converter according to the on / off state of the driving transistors. The system cabinet controls the conduction and turning off of the driving transistors through driving signals with a specific timing sequence, thereby generating four operating states. In different operating states, the three-level bidirectional buck-boost converter transmits energy through different paths.

[0117] In some embodiments, when the operating mode is the forward buck mode, step S104 includes but is not limited to steps S201 to S204.

[0118]

[0119] ​Step S201: When the first driving transistor and the fifth driving transistor are turned on and the second driving transistor, the third driving transistor, the fourth driving transistor, the sixth driving transistor, the seventh driving transistor and the eighth driving transistor are turned off, it is determined that the operating state of the three-level bidirectional buck-boost converter is the first state. In the first state, the power supply, the first energy storage capacitor, the first driving transistor, the fifth driving transistor, the first energy storage inductor, the seventh body diode and the third body diode are connected in sequence to form a first loop, and the load is powered through the first loop. At the same time, the second energy storage capacitor is charged and stored.

[0120] Step S202: When the first driving transistor, the fourth driving transistor, the fifth driving transistor and the eighth driving transistor are turned on and the second driving transistor, the third driving transistor, the sixth driving transistor and the seventh driving transistor are turned off, it is determined that the operating state of the three-level bidirectional buck-boost converter is the second state. In the second state, the power supply, the first driving transistor, the fifth driving transistor, the first energy storage inductor, the eighth driving transistor and the fourth driving transistor are connected in sequence to form a second loop, and the load is powered through the second loop. At the same time, the first energy storage capacitor and the second energy storage capacitor are charged and stored through the power supply.

[0121] Step S203: When the fourth driving transistor and the eighth driving transistor are turned on and the first driving transistor, the second driving transistor, the third driving transistor, the fifth driving transistor, the sixth driving transistor and the seventh driving transistor are turned off, it is determined that the operating state of the three-level bidirectional buck-boost converter is the third state. In the third state, the power supply, the second energy storage capacitor, the second body diode, the sixth body diode, the first energy storage inductor, the eighth driving transistor and the fourth driving transistor are connected in sequence to form a third loop, and the load is powered through the third loop. At the same time, the first energy storage capacitor is charged and stored.

[0122] Step S204: When the first driving transistor, the second driving transistor, the third driving transistor, the fourth driving transistor, the fifth driving transistor, the sixth driving transistor, the seventh driving transistor and the eighth driving transistor are turned off, it is determined that the operating state of the three-level bidirectional buck-boost converter is the fourth state. In the fourth state, the second body diode, the sixth body diode, the first energy storage inductor, the seventh body diode and the third body diode are connected in sequence to form a fourth loop, and the first energy storage capacitor and the second energy storage capacitor are charged and stored through the power supply.

[0123] When the working mode is the forward buck mode, if the duty ratio of the driving signal is greater than 0.5, the three-level bidirectional buck-boost converter circulates among the first state, the second state and the third state.

[0124] Exemplarily, taking the duty ratio of the driving signal as 0.6 and the period as 1 s as an example, the driving signals of the driving transistors VT1 and VT5 output high level during 0 s to 0.6 s, and the driving signals of the driving transistors VT4 and VT8 output high level during 0.4 s to 1 s.

[0125] During the period from 0 s to 0.4 s, the first drive tube and the fifth drive tube are turned on, and the other drive tubes are turned off. When the first drive tube and the fifth drive tube are turned on and the second drive tube, the third drive tube, the fourth drive tube, the sixth drive tube, the seventh drive tube, and the eighth drive tube are turned off, it is determined that the operating state of the three-level bidirectional buck-boost converter is the first state.

[0126] Reference Figure 4 , in the first state, the power supply, the first energy storage capacitor, the first drive tube, the fifth drive tube, the first energy storage inductor, the seventh body diode, and the third body diode are connected in sequence to form a first loop, and the load is powered through the first loop. At the same time, the second energy storage capacitor is charged and stored.

[0127] During the period from 0.4 s to 0.6 s, the first drive tube, the fourth drive tube, the fifth drive tube, and the eighth drive tube are turned on, and the other drive tubes are turned off. When the first drive tube, the fourth drive tube, the fifth drive tube, and the eighth drive tube are turned on and the second drive tube, the third drive tube, the sixth drive tube, and the seventh drive tube are turned off, it is determined that the operating state of the three-level bidirectional buck-boost converter is the second state.

[0128] Reference Figure 5 , in the second state, the power supply, the first drive tube, the fifth drive tube, the first energy storage inductor, the eighth drive tube, and the fourth drive tube are connected in sequence to form a second loop, and the load is powered through the second loop. At the same time, the first energy storage capacitor and the second energy storage capacitor are charged and stored through the power supply.

[0129] During the period from 0.6 s to 1 s, the fourth drive tube and the eighth drive tube are turned on, and the other drive tubes are turned off. When the fourth drive tube and the eighth drive tube are turned on and the first drive tube, the second drive tube, the third drive tube, the fifth drive tube, the sixth drive tube, and the seventh drive tube are turned off, it is determined that the operating state of the three-level bidirectional buck-boost converter is the third state.

[0130] Reference Figure 6 , in the third state, the power supply, the second energy storage capacitor, the second body diode, the sixth body diode, the first energy storage inductor, the eighth drive tube, and the fourth drive tube are connected in sequence to form a third loop, and the load is powered through the third loop. At the same time, the first energy storage capacitor is charged and stored.

[0131] If the duty cycle of the drive signal is less than 0.5, the three-level bidirectional buck-boost converter cycles among the first state, the third state, and the fourth state.

[0132] Exemplarily, taking the duty cycle of the drive signal as 0.3 and the period as 1 s as an example, the drive signals of the drive tubes VT1 and VT5 output high level during the period from 0 s to 0.3 s, and the drive signals of the drive tubes VT4 and VT8 output high level during the period from 0.5 s to 0.8 s.

[0133] During the period from 0 s to 0.3 s, the first driving tube and the fifth driving tube are turned on, and the other driving tubes are turned off. According to the on / off states of the driving tubes, it can be determined that the three-level bidirectional buck-boost converter operates in the first state.

[0134] During the period from 0.3 s to 0.5 s, all the driving tubes are turned off. When the first driving tube, the second driving tube, the third driving tube, the fourth driving tube, the fifth driving tube, the sixth driving tube, the seventh driving tube, and the eighth driving tube are turned off, it is determined that the operating state of the three-level bidirectional buck-boost converter is the fourth state.

[0135] Reference Figure 7 , in the fourth state, the second body diode, the sixth body diode, the first energy storage inductor, the seventh body diode, and the third body diode are connected in sequence to form a fourth loop, and the first energy storage capacitor and the second energy storage capacitor are charged and stored through the power supply.

[0136] During the period from 0.5 s to 0.8 s, the fourth driving tube and the eighth driving tube are turned on, and the other driving tubes are turned off. According to the operating states of the driving tubes, it can be determined that the three-level bidirectional buck-boost converter operates in the third state.

[0137] During the period from 0.8 s to 1 s, all the driving tubes are turned off. According to the operating states of the driving tubes, it can be determined that the three-level bidirectional buck-boost converter operates in the fourth state.

[0138] In some embodiments, when the operating mode is the reverse boost mode, step S104 includes but is not limited to steps S301 to S304.

[0139] Step S301: When the third driving tube and the seventh driving tube are turned on, and the first driving tube, the second driving tube, the fourth driving tube, the fifth driving tube, the sixth driving tube, and the eighth driving tube are turned off, it is determined that the operating state of the three-level bidirectional buck-boost converter is the fifth state. In the fifth state, the battery, the third energy storage capacitor, the first energy storage inductor, the fifth body diode, the first body diode, the second energy storage capacitor, the fourth body diode, the eighth body diode, the third driving tube, and the seventh driving tube are connected in sequence to form a fifth loop, and the load is powered through the fifth loop; at the same time, the battery, the third energy storage capacitor, the first energy storage inductor, the fifth body diode, the first body diode, the third driving tube, and the seventh driving tube are connected in sequence to form a sixth loop, and the first energy storage capacitor is charged and stored through the sixth loop.

[0140] Step S302: When the second driving transistor, the third driving transistor, the sixth driving transistor, and the seventh driving transistor are turned on, and the first driving transistor, the fourth driving transistor, the fifth driving transistor, and the eighth driving transistor are turned off, it is determined that the operating state of the three-level bidirectional buck-boost converter is the sixth state. In the sixth state, the battery, the third energy storage capacitor, the first energy storage inductor, the sixth driving transistor, the second driving transistor, the third driving transistor, and the seventh driving transistor are connected in sequence to form a seventh loop, and the first energy storage inductor is charged and stored through the seventh loop. At the same time, the load is powered by the first energy storage capacitor and the second energy storage capacitor.

[0141] Step S303: When the second driving transistor and the sixth driving transistor are turned on, and the first driving transistor, the third driving transistor, the fourth driving transistor, the fifth driving transistor, the seventh driving transistor, and the eighth driving transistor are turned off, it is determined that the operating state of the three-level bidirectional buck-boost converter is the seventh state. In the seventh state, the battery, the third energy storage capacitor, the first energy storage inductor, the fifth body diode, the first body diode, the first energy storage capacitor, the fourth body diode, and the eighth body diode are connected in sequence to form an eighth loop, and the load is powered through the eighth loop; at the same time, the battery, the third energy storage capacitor, the first energy storage inductor, the sixth driving transistor, the second driving transistor, the fourth body diode, and the eighth body diode are connected in sequence to form a ninth loop, and the second energy storage capacitor is charged and stored through the ninth loop.

[0142] Step S304: When the first driving transistor, the second driving transistor, the third driving transistor, the fourth driving transistor, the fifth driving transistor, the sixth driving transistor, the seventh driving transistor, and the eighth driving transistor are turned off, it is determined that the operating state of the three-level bidirectional buck-boost converter is the eighth state. In the eighth state, the battery, the third energy storage capacitor, the first energy storage inductor, the fifth body diode, the first body diode, the fourth body diode, and the eighth body diode are connected in sequence to form a tenth loop, and the load is powered through the tenth loop. At the same time, the first energy storage capacitor and the second energy storage capacitor are charged and stored.

[0143] When the working mode is the reverse boost mode, if the duty ratio of the driving signal is greater than 0.5, the three-level bidirectional buck-boost converter cycles among the fifth state, the sixth state, and the seventh state.

[0144] Exemplarily, taking the duty ratio of the driving signal as 0.7 and the period as 1 s as an example, the driving signals of the driving transistors VT3 and VT7 output high levels during 0 s to 0.7 s, and the driving signals of the driving transistors VT2 and VT6 output high levels during 0.3 s to 1 s.

[0145] During 0 s to 0.3 s, the third driving transistor and the seventh driving transistor are turned on, and the other driving transistors are turned off. When the third driving transistor and the seventh driving transistor are turned on, and the first driving transistor, the second driving transistor, the fourth driving transistor, the fifth driving transistor, the sixth driving transistor, and the eighth driving transistor are turned off, it is determined that the operating state of the three-level bidirectional buck-boost converter is the fifth state.

[0146] Refer to Figure 8 In the fifth state, the battery, the third energy storage capacitor, the first energy storage inductor, the fifth body diode, the first body diode, the second energy storage capacitor, the fourth body diode, the eighth body diode, the third drive transistor, and the seventh drive transistor are connected in sequence to form a fifth loop, and the load is powered through the fifth loop.

[0147] Meanwhile, the battery, the third energy storage capacitor, the first energy storage inductor, the fifth body diode, the first body diode, the third drive transistor, and the seventh drive transistor are connected in sequence to form a sixth loop. The sixth loop serves as a charging loop, and the first energy storage capacitor is charged and stored through the sixth loop.

[0148] During the period from 0.3 s to 0.7 s, the second drive transistor, the third drive transistor, the sixth drive transistor, and the seventh drive transistor are turned on, and the other drive transistors are turned off. When the second drive transistor, the third drive transistor, the sixth drive transistor, and the seventh drive transistor are turned on, and the first drive transistor, the fourth drive transistor, the fifth drive transistor, and the eighth drive transistor are turned off, it is determined that the working state of the three-level bidirectional buck-boost converter is the sixth state.

[0149] Refer to Figure 9 In the sixth state, the battery, the third energy storage capacitor, the first energy storage inductor, the sixth drive transistor, the second drive transistor, the third drive transistor, and the seventh drive transistor are connected in sequence to form a seventh loop. The seventh loop serves as an energy storage loop, and the first energy storage inductor is charged and stored through the seventh loop. Meanwhile, the load is powered through the first energy storage capacitor and the second energy storage capacitor.

[0150] During the period from 0.7 s to 1 s, the second drive transistor and the sixth drive transistor are turned on, and the other drive transistors are turned off. When the second drive transistor and the sixth drive transistor are turned on, and the first drive transistor, the third drive transistor, the fourth drive transistor, the fifth drive transistor, the seventh drive transistor, and the eighth drive transistor are turned off, it is determined that the working state of the three-level bidirectional buck-boost converter is the seventh state.

[0151] Refer to Figure 10 In the seventh state, the battery, the third energy storage capacitor, the first energy storage inductor, the fifth body diode, the first body diode, the first energy storage capacitor, the fourth body diode, and the eighth body diode are connected in sequence to form an eighth loop, and the load is powered through the eighth loop.

[0152] Meanwhile, the battery, the third energy storage capacitor, the first energy storage inductor, the sixth drive transistor, the second drive transistor, the fourth body diode, and the eighth body diode are connected in sequence to form a ninth loop. The ninth loop serves as a charging loop, and the second energy storage capacitor is charged and stored through the ninth loop.

[0153] If the duty cycle of the drive signal is less than 0.5, the three-level bidirectional buck-boost converter circulates among the fifth state, the seventh state, and the eighth state.

[0154] Exemplarily, taking the duty cycle of the driving signal as 0.2 and the period as 1 s as an example, the driving signals of the driving transistors VT3 and VT7 output high level during 0 s to 0.2 s, and the driving signals of the driving transistors VT2 and VT6 output high level during 0.5 s to 0.7 s.

[0155] During 0 s to 0.2 s, the third driving transistor and the seventh driving transistor are turned on, and other driving transistors are turned off. According to the on-off states of the driving transistors, it can be determined that the three-level bidirectional buck-boost converter operates in the fifth state.

[0156] During 0.2 s to 0.5 s, all driving transistors are turned off. When the first driving transistor, the second driving transistor, the third driving transistor, the fourth driving transistor, the fifth driving transistor, the sixth driving transistor, the seventh driving transistor, and the eighth driving transistor are turned off, it is determined that the operating state of the three-level bidirectional buck-boost converter is the eighth state.

[0157] Reference Figure 11 , in the eighth state, the battery, the third energy storage capacitor, the first energy storage inductor, the fifth body diode, the first body diode, the fourth body diode, and the eighth body diode are connected in sequence to form a tenth loop. The tenth loop serves as a power supply loop to supply power to the load through the tenth loop. At the same time, the first energy storage capacitor and the second energy storage capacitor are charged and stored.

[0158] During 0.5 s to 0.7 s, the second driving transistor and the sixth driving transistor are turned on, and other driving transistors are turned off. According to the on-off states of the driving transistors, it can be determined that the three-level bidirectional buck-boost converter operates in the seventh state.

[0159] During 0.7 s to 1 s, all driving transistors are turned off. According to the on-off states of the driving transistors, it can be determined that the three-level bidirectional buck-boost converter operates in the eighth state.

[0160] Next, in combination with specific examples, the solutions of the embodiments of the present invention will be introduced and described in detail.

[0161] Refer to Figure 1 , when the driving transistors of the two-level topology architecture are turned on or off, they need to withstand the voltage of the entire power supply terminal. However, for the three-level bidirectional buck-boost converter provided in the embodiments of the present application, through the topology structure, the switching stress of the driving transistors is only half of the power supply voltage, and the withstand voltage level of the capacitor only needs to be half of the original. Moreover, by connecting the driving transistors in parallel, the overcurrent capacity required for single-tube operation is reduced, so that conventional devices can also be applied to high-power density occasions such as rail transit, avoiding the high premium and high risk of high-voltage high-power customized devices, reducing the overall cost of the system, and at the same time, the reliability is greatly improved.

[0162] Compared with the two-level topology structure which has only two working states, the three-level circuit topology structure has four working states. Relatively, the switching frequency is twice as fast as that of the two-level topology structure, and the inductor operating frequency is also doubled. According to the basic law of inductors, under the condition of the same DC output voltage, the output inductance value is inversely proportional to the output inductor operating frequency. The expression of the basic law of inductors is:

[0163] L=(U*D) / (f_l*di) (1)

[0164] In formula (1), L is the inductance value, U is the inductance change voltage, D is the duty cycle of the drive signal, f1 is the inductor operating frequency, and di is the changing current.

[0165] Therefore, the higher the inductor operating frequency, the lower the required inductance.

[0166] At the same time, according to the inductor core selection method, the product (Ap) value of the cross-sectional area and window area of the inductor is inversely proportional to the square of the inductor operating frequency. The expression of the inductor core selection method is:

[0167] Ap=(W_l*10^n) / (Bm*f_l*Ji*Kf*Ku) (2)

[0168] In formula (2), W_1 is the inductor transmission power, Bm is the maximum operating magnetic flux density, Ji is the current density, Kf is the waveform coefficient, and Ku is the window utilization coefficient.

[0169] The Ap value of the inductor directly depends on the size of the selected inductor core. The larger the core, the larger the Ap value. Therefore, when the inductor operating frequency is larger, the required inductor core is smaller.

[0170] According to Faraday's law, under the same output voltage condition, the winding turns N of the inductor is also inversely proportional to the inductor operating frequency. The expression of Faraday's law is:

[0171] U=(N*B*Ae*f_l) / D (3)

[0172] In formula (3), U is the inductor input voltage, B is the magnetic flux density of the core, and Ae is the cross-sectional area of the core winding.

[0173] Therefore, the higher the inductor operating frequency, the smaller the required inductor turns, that is, the fewer the required conductive coils.

[0174] In summary, when stepping up or stepping down, as the inductor operating frequency increases, the inductor only needs to select a smaller core and use fewer conductive coils, which can make the inductor smaller in volume and weight in design, thereby reducing the volume and weight of the three-level bidirectional buck-boost converter and meeting the lightweight design requirements.

[0175] In addition, the waveform of the three-level control is closer to a sine wave, the system has a low harmonic content and small interference, which can effectively improve the stability and reliability of the three-level bidirectional buck-boost converter and improve the power quality.

[0176] The embodiment of the present application also provides an electronic device, which includes a memory and a processor. The memory stores a computer program, and when the processor executes the computer program, it implements the control method of the above three-level bidirectional buck-boost converter. This electronic device can be any intelligent terminal including a tablet computer, an in-vehicle computer, etc.

[0177] It can be understood that the content in the above method embodiments is applicable to the device embodiments of the present application. The functions specifically implemented by the device embodiments of the present application are the same as those of the above method embodiments, and the beneficial effects achieved are also the same as those of the above method embodiments.

[0178] Please refer to Figure 12 , Figure 12 which schematically shows the hardware structure of an electronic device in another embodiment. The electronic device includes:

[0179] A processor 901, which can be implemented in ways such as a general-purpose CPU (Central Processing Unit), a microprocessor, an application-specific integrated circuit (ASIC), or one or more integrated circuits, and is used to execute relevant programs to implement the technical solutions provided by the embodiments of the present application.

[0180] A memory 902, which can be implemented in forms such as a read-only memory (ROM), a static storage device, a dynamic storage device, or a random access memory (RAM). The memory 902 can store an operating system and other application programs. When implementing the technical solutions provided by the embodiments of this specification through software or firmware, the relevant program codes are stored in the memory 902 and are called by the processor 901 to execute the control method of the three-level bidirectional buck-boost converter in the embodiments of the present application.

[0181] An input / output interface 903, which is used to implement information input and output.

[0182] A communication interface 904, which is used to implement communication interaction between this device and other devices, and can implement communication through wired means (such as USB, network cable, etc.) or wireless means (such as mobile network, WIFI, Bluetooth, etc.).

[0183] The bus 905 transmits information among various components of the device (such as the processor 901, the memory 902, the input / output interface 903, and the communication interface 904).

[0184] Among them, the processor 901, the memory 902, the input / output interface 903, and the communication interface 904 achieve communication connections with each other inside the device through the bus 905.

[0185] The embodiment of the present application also provides a computer-readable storage medium, which stores a computer program. When the computer program is executed by a processor, it implements the control method of the above three-level bidirectional buck-boost converter.

[0186] It can be understood that the content in the above method embodiments is applicable to the embodiments of this storage medium. The functions specifically implemented by the embodiments of this storage medium are the same as those of the above method embodiments, and the beneficial effects achieved are also the same as those of the above method embodiments.

[0187] As a non-transitory computer-readable storage medium, the memory can be used to store non-transitory software programs and non-transitory computer-executable programs. In addition, the memory may include high-speed random access memory, and may also include non-transitory memory, such as at least one magnetic disk storage device, a flash memory device, or other non-transitory solid-state storage devices. In some embodiments, the memory may optionally include a memory remotely provided with respect to the processor, and these remote memories can be connected to the processor through a network. Examples of the above network include but are not limited to the Internet, an enterprise intranet, a local area network, a mobile communication network, and their combinations.

[0188] The embodiments described in the embodiments of the present application are for more clearly illustrating the technical solutions of the embodiments of the present application, and do not constitute a limitation on the technical solutions provided by the embodiments of the present application. Those skilled in the art know that with the evolution of technology and the emergence of new application scenarios, the technical solutions provided by the embodiments of the present application are equally applicable to similar technical problems.

[0189] Those skilled in the art can understand that the technical solutions shown in the figures do not constitute a limitation on the embodiments of the present application, and may include more or fewer steps than those shown in the figures, or combine certain steps, or different steps.

[0190] The system embodiments described above are merely illustrative. The units described as separate components may or may not be physically separated, that is, they may be located in one place, or may be distributed to multiple network units. Some or all of the modules can be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0191] Those of ordinary skill in the art can understand that all or some of the steps in the methods disclosed above, and the functional modules / units in the systems and devices, can be implemented as software, firmware, hardware, and their appropriate combinations.

[0192] The terms "first", "second", "third", "fourth", etc. (if any) in the specification of this application and the above-mentioned drawings are used to distinguish similar objects, and do not necessarily have to be used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged under appropriate circumstances, so that the embodiments of the present application described here can be implemented in an order other than those illustrated or described here. In addition, the terms "comprising" and "having" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or device that includes a series of steps or units does not necessarily have to be limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or are inherent to these processes, methods, products, or devices.

[0193] The preferred embodiments of the embodiments of the present application have been described above with reference to the drawings, but this does not limit the scope of the rights of the embodiments of the present application. Any modifications, equivalent replacements, and improvements made by those skilled in the art without departing from the scope and essence of the embodiments of the present application shall be within the scope of the rights of the embodiments of the present application.

Claims

1. A three-level bidirectional buck-boost converter, characterized in that: The three-level bidirectional buck-boost converter comprises a first bridge arm, a second bridge arm, a first energy storage capacitor, a second energy storage capacitor, a third energy storage capacitor and a first energy storage inductor; The first end of the first energy storage capacitor is connected to the positive electrode of the power supply, the second end of the first energy storage capacitor is connected to the first end of the second energy storage capacitor, the second end of the second energy storage capacitor is connected to the negative electrode of the power supply, the first end of the third energy storage capacitor is connected to the first energy storage inductor and the positive electrode of the battery, respectively, and the second end of the third energy storage capacitor is connected to the first energy storage inductor and the negative electrode of the battery, respectively; The first end of the first bridge arm is connected to the positive electrode of the power supply, the second end of the first bridge arm is connected to the positive electrode of the battery through the first energy storage inductor, and the third end of the first bridge arm is connected to the second end of the first energy storage capacitor; The first end of the second bridge arm is connected to the second end of the first energy storage capacitor, the second end of the second bridge arm is connected to the negative electrode of the battery through the first energy storage inductor, and the third end of the second bridge arm is connected to the negative electrode of the power supply.

2. The three-level bidirectional buck-boost converter according to claim 1, characterized in that: The first bridge arm includes a first driving tube, a second driving tube, a first body diode and a second body diode, and the second bridge arm includes a third driving tube, a fourth driving tube, a third body diode and a fourth body diode, wherein the first driving tube is connected in parallel with the first body diode, the second driving tube is connected in parallel with the second body diode, the third driving tube is connected in parallel with the third body diode, and the fourth driving tube is connected in parallel with the fourth body diode; The collector of the first driving tube serves as the first end of the first bridge arm; the emitter of the first driving tube is connected to the collector of the second driving tube as the second end of the first bridge arm; the emitter of the second driving tube serves as the third end of the first bridge arm; The collector of the third driving tube serves as the first end of the second bridge arm; the emitter of the third driving tube is connected to the collector of the fourth driving tube as the second end of the second bridge arm; the emitter of the fourth driving tube serves as the third end of the second bridge arm.

3. The three-level bidirectional buck-boost converter according to claim 1, characterized in that: The three-level bidirectional buck-boost converter further includes a first filter capacitor and a second filter capacitor, wherein the first filter capacitor is connected in parallel with the first bridge arm, and the second filter capacitor is connected in parallel with the second bridge arm.

4. The three-level bidirectional buck-boost converter according to claim 1, characterized in that: The three-level bidirectional buck-boost converter also includes a first resistor, a second resistor and a third resistor, wherein the first resistor is connected in parallel with the first energy storage capacitor, the second resistor is connected in parallel with the second energy storage capacitor, and the third resistor is connected in parallel with the third energy storage capacitor.

5. The three-level bidirectional buck-boost converter according to claim 1, characterized in that: The three-level bidirectional buck-boost converter further includes a third bridge arm and a fourth bridge arm; The first end of the third bridge arm is connected to the positive electrode of the power supply, the second end of the third bridge arm is connected to the positive electrode of the battery through the first energy storage inductor, and the third end of the third bridge arm is connected to the second end of the first energy storage capacitor; The first end of the fourth bridge arm is connected to the second end of the first energy storage capacitor, the second end of the fourth bridge arm is connected to the negative electrode of the battery through the first energy storage inductor, and the third end of the fourth bridge arm is connected to the negative electrode of the power supply.

6. The three-level bidirectional buck-boost converter according to claim 5, characterized in that: The third bridge arm includes a fifth driving tube, a sixth driving tube, a fifth body diode, and a sixth body diode, and the fourth bridge arm includes a seventh driving tube, an eighth driving tube, a seventh body diode, and an eighth body diode, wherein the fifth driving tube is connected in parallel with the fifth body diode, the sixth driving tube is connected in parallel with the sixth body diode, the seventh driving tube is connected in parallel with the seventh body diode, and the eighth driving tube is connected in parallel with the eighth body diode; The collector of the fifth driving tube serves as the first end of the third bridge arm; the emitter of the fifth driving tube is connected to the collector of the sixth driving tube as the second end of the third bridge arm; the emitter of the sixth driving tube serves as the third end of the third bridge arm; The collector of the seventh driving tube serves as the first end of the fourth bridge arm; the emitter of the seventh driving tube is connected to the collector of the eighth driving tube as the second end of the fourth bridge arm; the emitter of the eighth driving tube serves as the third end of the fourth bridge arm.

7. The three-level bidirectional buck-boost converter according to claim 5, characterized in that: The three-level bidirectional buck-boost converter further includes a third filter capacitor and a fourth filter capacitor, wherein the third filter capacitor is connected in parallel with the third bridge arm, and the fourth filter capacitor is connected in parallel with the fourth bridge arm.

8. A control method for a three-level bidirectional buck-boost converter, characterized in that: Applied to the three-level bidirectional buck-boost converter according to claim 6, the control method comprises the following steps: Determining an operating mode of the three-level bidirectional buck-boost converter according to the direction of energy flow, wherein the operating mode includes a forward buck mode and a reverse boost mode; Based on the working mode, the duty cycle of the driving signal of each driving tube is adjusted according to the change of the load; Determining the on / off state of the driving tube according to the duty cycle of the driving signal; The working state of the three-level bidirectional buck-boost converter is determined according to the on-off state of the driving tube.

9. The control method according to claim 8, characterized in that: When the working mode is the forward buck mode, determining the working state of the three-level bidirectional buck-boost converter according to the on-off state of the driving tube comprises the following steps: When the first drive tube and the fifth drive tube are turned on, and the second drive tube, the third drive tube, the fourth drive tube, the sixth drive tube, the seventh drive tube and the eighth drive tube are turned off, it is determined that the working state of the three-level bidirectional buck-boost converter is a first state. In the first state, the power supply, the first energy storage capacitor, the first drive tube, the fifth drive tube, the first energy storage inductor, the seventh body diode and the third body diode are sequentially connected to form a first loop, and the load is powered by the first loop, and at the same time, the second energy storage capacitor is charged and stored; Alternatively, when the first drive tube, the fourth drive tube, the fifth drive tube and the eighth drive tube are turned on, and the second drive tube, the third drive tube, the sixth drive tube and the seventh drive tube are turned off, it is determined that the working state of the three-level bidirectional buck-boost converter is the second state. In the second state, the power supply, the first drive tube, the fifth drive tube, the first energy storage inductor, the eighth drive tube and the fourth drive tube are sequentially connected to form a second loop, and the load is powered by the second loop. At the same time, the first energy storage capacitor and the second energy storage capacitor are charged and stored by the power supply; Alternatively, when the fourth drive tube and the eighth drive tube are turned on, and the first drive tube, the second drive tube, the third drive tube, the fifth drive tube, the sixth drive tube and the seventh drive tube are turned off, it is determined that the working state of the three-level bidirectional buck-boost converter is a third state. In the third state, the power supply, the second energy storage capacitor, the second body diode, the sixth body diode, the first energy storage inductor, the eighth drive tube and the fourth drive tube are sequentially connected to form a third loop, and the load is powered by the third loop. At the same time, the first energy storage capacitor is charged and stored; Alternatively, when the first drive tube, the second drive tube, the third drive tube, the fourth drive tube, the fifth drive tube, the sixth drive tube, the seventh drive tube and the eighth drive tube are turned off, it is determined that the working state of the three-level bidirectional buck-boost converter is a fourth state. In the fourth state, the second body diode, the sixth body diode, the first energy storage inductor, the seventh body diode and the third body diode are connected in sequence to form a fourth loop, and the first energy storage capacitor and the second energy storage capacitor are charged and stored by the power supply.

10. The control method according to claim 8, characterized in that: When the working mode is the reverse boost mode, determining the working state of the three-level bidirectional buck-boost converter according to the on-off state of the driving tube comprises the following steps: When the third drive tube and the seventh drive tube are turned on, and the first drive tube, the second drive tube, the fourth drive tube, the fifth drive tube, the sixth drive tube and the eighth drive tube are turned off, it is determined that the working state of the three-level bidirectional buck-boost converter is the fifth state. In the fifth state, the battery, the third energy storage capacitor, the first energy storage inductor, the fifth body diode, the first body diode, the second energy storage capacitor, the fourth body diode, the eighth body diode, the third drive tube and the seventh drive tube are connected in sequence to form a fifth loop, and the load is powered by the fifth loop; at the same time, the battery, the third energy storage capacitor, the first energy storage inductor, the fifth body diode, the first body diode, the third drive tube and the seventh drive tube are connected in sequence to form a sixth loop, and the first energy storage capacitor is charged and stored by the sixth loop; Alternatively, when the second drive tube, the third drive tube, the sixth drive tube and the seventh drive tube are turned on, and the first drive tube, the fourth drive tube, the fifth drive tube and the eighth drive tube are turned off, it is determined that the working state of the three-level bidirectional buck-boost converter is a sixth state. In the sixth state, the battery, the third energy storage capacitor, the first energy storage inductor, the sixth drive tube, the second drive tube, the third drive tube and the seventh drive tube are sequentially connected to form a seventh loop, and the first energy storage inductor is charged and stored through the seventh loop. At the same time, the load is powered by the first energy storage capacitor and the second energy storage capacitor; Alternatively, when the second drive tube and the sixth drive tube are turned on, and the first drive tube, the third drive tube, the fourth drive tube, the fifth drive tube, the seventh drive tube and the eighth drive tube are turned off, it is determined that the working state of the three-level bidirectional buck-boost converter is the seventh state. In the seventh state, the battery, the third energy storage capacitor, the first energy storage inductor, the fifth body diode, the first body diode, the first energy storage capacitor, the fourth body diode and the eighth body diode are connected in sequence to form an eighth loop, and the load is powered by the eighth loop; at the same time, the battery, the third energy storage capacitor, the first energy storage inductor, the sixth drive tube, the second drive tube, the fourth body diode and the eighth body diode are connected in sequence to form a ninth loop, and the second energy storage capacitor is charged and stored by the ninth loop; Alternatively, when the first drive tube, the second drive tube, the third drive tube, the fourth drive tube, the fifth drive tube, the sixth drive tube, the seventh drive tube and the eighth drive tube are turned off, it is determined that the working state of the three-level bidirectional buck-boost converter is the eighth state. In the eighth state, the battery, the third energy storage capacitor, the first energy storage inductor, the fifth body diode, the first body diode, the fourth body diode and the eighth body diode are connected in sequence to form a tenth loop, and power is supplied to the load through the tenth loop. At the same time, the first energy storage capacitor and the second energy storage capacitor are charged and stored.

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