Flying capacitor three-level BOOST conversion device, control method and storage medium

Abstract

The invention discloses a flying capacitor three-level BOOST conversion device, a control method and a storage medium, the device comprises a first diode D1, a second diode D2, a first switch tube T1, a second switch tube T2, a third diode D11, a fourth diode D12 and a flying capacitor voltage sampling resistor Rf, the first diode D1 and the second diode D2 are connected with the positive electrode of a flying capacitor Cf, and the second diode D2 is connected with the negative electrode of the flying capacitor Cf; the first switch tube T1 and the second switch tube T2 are connected with the negative electrode of the flying capacitor Cf; and one end of the charging relay K1 is connected with the third diode D11, and the other end of the charging relay K1 is connected with the midpoint of the direct-current bus. The control method is implemented based on the system. The storage medium is used for storing a computer program for executing the method. The device has the advantages of simple structure, low cost, wide application range, high safety and the like.

Description

Technical Field

[0001] The present invention mainly relates to the field of power electronic device design, and in particular to a flying capacitor three-level BOOST conversion device, a control method and a storage medium. Background Art

[0002] With the development of the new energy power generation and energy storage market, the system voltage level is gradually increasing and the system capacity is tending to be larger. Therefore, the semiconductor power conversion device of the energy conversion device is also developing towards multi-level and multi-stage conversion.

[0003] When the system requires multiple front-stage DC / DC boost converters to be connected in parallel, the front-stage DC / DC boost converter circuit usually adopts the following advantages due to the advantages of simple system, small voltage stress of switching devices and low cost. Figure 1 The flying capacitor three-level boost power conversion circuit topology shown in FIG. In this technical solution, the boost conversion circuit includes an input inductor L, a conversion bridge composed of two switch tubes T1 and T2 connected in series and two freewheeling diodes D1 and D2, a flying capacitor Cf, and an output filter capacitor Cout. Through the ON / OFF action of the switch tube of the boost conversion bridge, not only can the input current be controlled to the desired value, the input power can be converted and output to the output DC bus with a higher voltage, but the flying capacitor voltage can also be controlled to the desired value. Because the flying capacitor voltage is directly related to the voltage borne by the switching device, it must be maintained within a reasonable range. Therefore, it is usually controlled at half of the output bus voltage so that the voltage borne by each switching device is balanced.

[0004] In static state, the flying capacitor three-level BOOST converter topology needs to precharge the flying capacitor to prevent IGBT overvoltage damage caused by the flying capacitor not being charged at the beginning of control. For the flying capacitor connected to the power supply, it will be precharged through the following path: Cin->L->D2->Cf->D12->Cout2. In the topology of multiple DC / DC boost converters in parallel, for the flying capacitor not connected to the power supply, it will be precharged through the following path: Cout2->D11->Cf->TD1->L->Cin.

[0005] However, if the above existing technical solutions are adopted, there will be two technical problems in charging: 1. When there is a large difference in the output voltage of each battery panel, or the input voltage of the battery panel is around 1 / 2 of the bus voltage, the static charging voltage of the flying capacitor will be too low, making it impossible for the boost converter to start normally.

[0006] 2. In practical applications, since it is necessary to sample the voltage of the flying capacitor and participate in the control, the presence of the sampling circuit will lead to an additional pre-charging circuit for the flying capacitor, which often makes the pre-charging voltage of the flying capacitor too high under special power supply conditions. The usual practice is to add a discharge resistor at both ends of the flying capacitor to suppress the flying capacitor voltage from being too high under static conditions. However, adding a flying capacitor discharge circuit not only increases the hardware circuit cost, but also when the BOOST converter is in a long-term standby state, the voltage of the flying capacitor will gradually decrease after passing through the discharge circuit, which may cause the first diode D1 and the second switch tube T2 to have an overvoltage risk.

[0007] At the same time, if a new control module is added based on the flying capacitor pre-charging topology, the control logic of the entire converter will become more complicated. Summary of the invention

[0008] The technical problem to be solved by the present invention is: in view of the technical problems existing in the prior art, the present invention provides a flying capacitor three-level BOOST conversion device, a control method and a storage medium with simple structure, low cost, wide application range and high safety.

[0009] In order to solve the above technical problems, the present invention adopts the following technical solutions: A flying capacitor three-level BOOST conversion device comprises: a first diode D1, a second diode D2, a first switch tube T1, a second switch tube T2, a third diode D11, a fourth diode D12 and a flying capacitor voltage sampling resistor Rf, wherein the first diode D1 and the second diode D2 are connected to the positive electrode of the flying capacitor Cf, and the first switch tube T1 and the second switch tube T2 are connected to the negative electrode of the flying capacitor Cf; and further comprises a charging relay K1, wherein one end of the charging relay K1 is connected to the third diode D11, and the other end is connected to the midpoint of a DC bus.

[0010] As a further improvement of the device of the present invention: the anode of the third diode D11 is connected to the positive electrode of the flying capacitor Cf, and the cathode of the third diode D11 is connected in series with the charging relay K1.

[0011] As a further improvement of the device of the present invention: the anode of the fourth diode D12 is connected to the midpoint of the DC bus, and the cathode of the fourth diode D12 is connected to the negative electrode of the flying capacitor Cf.

[0012] As a further improvement of the device of the present invention: the flying capacitor voltage sampling resistor Rf is directly connected in parallel across the flying capacitor, or is connected to an operational amplifier after passing through a sampling resistor.

[0013] As a further improvement of the device of the present invention: a current limiting resistor R1 is provided between the charging relay K1 and the midpoint of the output busbar to limit the excessive charging current to protect the devices in the circuit.

[0014] As a further improvement of the device of the present invention: the cathode of the first diode D1 is connected to the positive electrode of the flying capacitor Cf in the boost conversion bridge; the anode of the second diode D2 is connected to the positive electrode of the flying capacitor Cf.

[0015] As a further improvement of the device of the present invention: the emitter of the first switch tube T1 is connected to the negative electrode of the flying capacitor Cf; the collector of the second switch tube T2 is connected to the negative electrode of the flying capacitor Cf.

[0016] A control method for a flying capacitor three-level BOOST converter based on any one of the above, comprising: When the flying capacitor voltage is lower than the first preset value, the boost converter does not operate; When the flying capacitor voltage is higher than the first preset value but lower than the second preset value, the flying capacitor Cf is charged by turning on the second switch tube T2 at a low frequency while keeping the first switch tube T1 disconnected until the flying capacitor voltage is higher than the second preset value; After charging is stopped, when the flying capacitor voltage drops to the third preset value, the second switch tube T2 is turned on at a low frequency while the first switch tube T1 is kept disconnected to charge the flying capacitor Cf until the flying capacitor voltage is higher than the second preset value and the third preset value is slightly lower than the second preset value.

[0017] As a further improvement of the method of the present invention: the first preset value should be greater than the difference between the DC bus voltage and the withstand voltage of the first diode D1, so as to ensure that the voltage borne by the first diode D1 is below the withstand voltage after starting the BOOST boost circuit.

[0018] As a further improvement of the method of the present invention: the second preset value is lower than the voltage of the second voltage-dividing capacitor.

[0019] The present invention further provides a storage medium, which can be read by a computer or a processor, and stores a computer program for executing any one of the above methods.

[0020] Compared with the prior art, the advantages of the present invention are: 1. The flying capacitor three-level BOOST converter, control method and storage medium of the present invention have simple structure, low cost, wide application range and high safety. The method of the present invention can maintain the flying capacitor voltage fluctuation caused by the sampling circuit and the flying capacitor itself after the flying capacitor three-level BOOST converter is pre-charged within a safe range, and ensure that the boost circuit can be started at any time, thereby improving the safety and availability of the converter system.

[0021] 2. The flying capacitor three-level BOOST conversion device, control method and storage medium of the present invention detect the flying capacitor voltage through a sampling circuit. When the flying capacitor voltage is less than a preset value, the flying capacitor voltage is charged to a hot standby state by controlling the conduction of the T2 tube and disconnecting the T1 tube. When the flying capacitor voltage is greater than the preset value, the flying capacitor voltage is discharged by controlling the conduction of the T1 tube and disconnecting the T2 tube until the voltages borne by the flying capacitor, the switch tube T1, the switch tube T2, the diode D1 and the diode D2 are all within a safe range.

[0022] 3. The flying capacitor three-level BOOST conversion device, control method and storage medium of the present invention, after the pre-charging is completed and the BOOST is in the standby state, the flying capacitor voltage is maintained within a reasonable range by reasonably controlling the on-off of the relay K1 and the action pulses of the switching tubes T1 and T2. The present invention can maintain the flying capacitor voltage within a reasonable range without adding additional hardware circuits, thereby ensuring the safety of the devices in the BOOST topology and improving the reliability and safety of the power conversion device. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The diagram is a schematic diagram of the topological structure principle of a flying capacitor three-level boost circuit in the prior art.

[0024] Figure 2 It is a schematic diagram of the topological structure principle of a specific embodiment of the present invention.

[0025] Figure 3 This is a schematic diagram of the control logic in a specific embodiment of the present invention. Figure 1 . Figure 4 This is a schematic diagram of the control logic flow in a specific embodiment of the present invention. Figure 1 .

[0026] Figure 5 This is a schematic diagram of the control logic in a specific embodiment of the present invention. Figure 2 . Figure 6 This is a schematic diagram of the control logic flow in a specific embodiment of the present invention. Figure 2 .

[0027] Figure 7It is a schematic diagram of the topological structure principle in another specific embodiment of the present invention. DETAILED DESCRIPTION

[0028] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0029] In the description of the present application, it should be understood that the terms "length", "width", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present application.

[0030] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of this application, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0031] In this application, unless otherwise clearly specified and limited, the terms "assemble", "connect", "connect", "fix" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0032] like Figure 2-Figure 6 As shown, the present invention discloses a flying capacitor three-level BOOST conversion device, including: a first diode D1, a second diode D2, a first switch tube T1, a second switch tube T2, a third diode D11, a fourth diode D12, a flying capacitor voltage sampling resistor Rf and a charging relay K1; wherein: The cathode of the first diode D1 is connected to the positive electrode of the flying capacitor Cf in the boost conversion bridge; The anode of the second diode D2 is connected to the positive electrode of the flying capacitor Cf; The emitter of the first switch tube T1 is connected to the negative electrode of the flying capacitor Cf; The collector of the second switch tube T2 is connected to the negative electrode of the flying capacitor Cf; The flying capacitor voltage sampling resistor Rf is connected in parallel to both ends of the flying capacitor Cf; The anode of the third diode D11 is connected to the positive electrode of the flying capacitor Cf, and the cathode thereof is connected in series with the charging relay K1; One end of the charging relay K1 is connected to the third diode D11, and the other end is connected to the midpoint of the DC bus; The anode of the fourth diode D12 is connected to the midpoint of the DC bus, and the cathode of the fourth diode D12 is connected to the negative electrode of the flying capacitor Cf.

[0033] In a specific application example, the flying capacitor voltage sampling resistor Rf can be directly connected in parallel across the flying capacitor, or can be connected to an operational amplifier after passing through a sampling resistor.

[0034] After adopting the above scheme of the present invention, when the input voltage of the BOOST boost converter is greater than the starting voltage, after the pre-charging of the flying capacitor is completed through the aforementioned pre-charging path, the charging relay K1 is disconnected to avoid the generation of impact current on the charging relay K1 when the second switch tube T2 is turned on. At this time, the BOOST boost converter is in standby mode. However, in a topology where multiple DC / DC boost converters are connected in parallel, when the input voltage of a certain DC / DC boost converter is about half of the output bus voltage, due to the simultaneous action of the input voltage and the output bus midpoint voltage, the flying capacitor voltage cannot be charged normally, which ultimately manifests as the flying capacitor voltage being too low.

[0035] See also Figure 3-Figure 6 When the flying capacitor voltage is lower than the first preset value, the boost converter does not operate. The first preset value should be slightly larger than the difference between the DC bus voltage and the withstand voltage of the first diode D1, so as to ensure that the voltage borne by the first diode D1 is below the withstand voltage after starting the BOOST boost circuit.

[0036] When the flying capacitor voltage is higher than the first preset value but lower than the second preset value, the second switch tube T2 is turned on at a low frequency while the first switch tube T1 is kept disconnected. The BOOST voltage-boosting device will charge the flying capacitor Cf through the following path: Cin->L->D2->Cf->T2. Until the flying capacitor voltage is higher than the second preset value. The second preset value is generally slightly lower than the voltage of the second voltage-dividing capacitor.

[0037] After charging stops, when the flying capacitor voltage drops to the third preset value, the second switch tube T2 is turned on at a low frequency while the first switch tube T1 is kept disconnected. The BOOST voltage conversion device will continue to charge the flying capacitor Cf through the following path: Cin->L->D2->Cf->T2. Until the flying capacitor voltage is higher than the second preset value and the third preset value is slightly lower than the second preset value, the second switch tube T2 is prevented from operating too frequently.

[0038] Through the above control, it can be ensured that the machine can be started normally at any time when the initial state of the flying voltage is higher than the first preset value, thereby preventing the flying voltage from dropping to a value that cannot be started under special working conditions.

[0039] According to the above-mentioned BOOST flying capacitor voltage balance control method of the present invention, when the BOOST boost converter is in standby mode, the flying capacitor voltage is higher than the preset value to be controlled and the sum of the input voltage and the flying voltage is greater than the bus voltage, by controlling the logic of turning on the first switch tube T1 and turning off the second switch tube T2, the flying capacitor will be discharged through the discharge path of the inductor L, the first switch tube T1, the flying capacitor Cf, the first diode D1, and the output capacitors Cout1 and Cout2 until the voltages borne by the flying capacitor, the first switch tube T1, the second switch tube T2, the first diode D1 and the second diode D2 are all within a safe range.

[0040] In another specific embodiment, Figure 7 As shown, the present invention further adds a current limiting resistor R1 between the charging relay K1 and the midpoint of the output bus, which can limit the excessive charging current generated in the following flying pre-charging path, thereby protecting the devices on the loop, Cout2->R1->K1->D11->Cf->TD1->L->Cin.

[0041] The present invention further provides a storage medium, which can be read by a computer or a processor and stores a computer program for executing the above method.

[0042] Those skilled in the art should understand that the above-mentioned embodiments of the present application can be provided as methods, systems, or computer program products. Therefore, the present application can take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, the present application can take the form of a computer program product implemented on one or more computer-readable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code. The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the process Figure 1 A process or multiple processes and / or boxes Figure 1 These computer program instructions can also be stored in a computer-readable memory that can guide a computer or other programmable data processing device to work in a specific way, so that the instructions stored in the computer-readable memory produce a product including an instruction device, which implements the functions specified in the process. Figure 1 A process or multiple processes and / or boxes Figure 1 These computer program instructions can also be loaded onto a computer or other programmable data processing device, so that a series of operation steps are executed on the computer or other programmable device to produce a computer-implemented process, so that the instructions executed on the computer or other programmable device provide for implementing the process in the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0043] The above are only preferred embodiments of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, some improvements and modifications without departing from the principle of the present invention should be regarded as the protection scope of the present invention.

Claims

1. A flying capacitor three-level BOOST conversion device, comprising: A first diode D1, a second diode D2, a first switch tube T1, a second switch tube T2, a third diode D11, a fourth diode D12 and a flying capacitor voltage sampling resistor Rf, wherein the first diode D1 and the second diode D2 are connected to the positive electrode of the flying capacitor Cf, and the first switch tube T1 and the second switch tube T2 are connected to the negative electrode of the flying capacitor Cf, and the charging relay K1 is also included, wherein one end of the charging relay K1 is connected to the third diode D11, and the other end is connected to the midpoint of the DC bus.

2. The flying capacitor three-level BOOST converter according to claim 1, characterized in that: The anode of the third diode D11 is connected to the positive electrode of the flying capacitor Cf, and the cathode of the third diode D11 is connected in series with the charging relay K1.

3. The flying capacitor three-level BOOST converter according to claim 1, characterized in that: The anode of the fourth diode D12 is connected to the midpoint of the DC bus, and the cathode of the fourth diode D12 is connected to the negative electrode of the flying capacitor Cf.

4. The flying capacitor three-level BOOST converter according to claim 1, characterized in that: The flying capacitor voltage sampling resistor Rf is directly connected in parallel to both ends of the flying capacitor, or is connected to an operational amplifier after passing through a sampling resistor.

5. The flying capacitor three-level BOOST converter according to any one of claims 1 to 4, characterized in that: A current limiting resistor R1 is provided between the charging relay K1 and the midpoint of the output busbar, for limiting the excessive charging current to protect the devices in the circuit.

6. The flying capacitor three-level BOOST converter according to any one of claims 1 to 4, characterized in that: The cathode of the first diode D1 is connected to the positive electrode of the flying capacitor Cf in the boost conversion bridge; the anode of the second diode D2 is connected to the positive electrode of the flying capacitor Cf.

7. The flying capacitor three-level BOOST converter according to any one of claims 1 to 4, characterized in that: The emitter of the first switch tube T1 is connected to the negative electrode of the flying capacitor Cf; the collector of the second switch tube T2 is connected to the negative electrode of the flying capacitor Cf.

8. A control method for a flying capacitor three-level BOOST converter according to any one of claims 1 to 7, characterized in that: include: When the flying capacitor voltage is lower than the first preset value, the boost converter does not operate; When the flying capacitor voltage is higher than the first preset value but lower than the second preset value, the flying capacitor Cf is charged by turning on the second switch tube T2 at a low frequency while keeping the first switch tube T1 disconnected until the flying capacitor voltage is higher than the second preset value; After charging is stopped, when the flying capacitor voltage drops to the third preset value, the second switch tube T2 is turned on at a low frequency while the first switch tube T1 is kept disconnected to charge the flying capacitor Cf until the flying capacitor voltage is higher than the second preset value and the third preset value is slightly lower than the second preset value.

9. The control method according to claim 8, characterized in that: The first preset value should be greater than the difference between the DC bus voltage and the withstand voltage of the first diode D1, so as to ensure that the voltage borne by the first diode D1 is below the withstand voltage after starting the BOOST boost circuit.

10. The control method according to claim 8, characterized in that: The second preset value is lower than the voltage of the second voltage-dividing capacitor.

11. A storage medium, which can be read by a computer or a processor, characterized in that: The storage medium stores a computer program for executing any one of the methods in claims 8-10.

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