Midpoint voltage self-balancing anpc-dab hybrid topology and method

Abstract

The application discloses a midpoint voltage self-balancing ANPC-DAB hybrid topology, comprising a direct-current input module, a primary ANPC bridge module, a DAB isolation conversion module, a secondary ANPC bridge module and a direct-current output module which are electrically connected in sequence. The application further discloses a midpoint voltage self-balancing method. The midpoint voltage self-balancing ANPC-DAB hybrid topology and method disclosed by the application solve the problem of excessively large charging and discharging current when a single flying capacitor is balanced in the prior art.

Description

Technical Field

[0001] This invention belongs to the field of power electronic conversion circuit technology, specifically relating to a midpoint voltage self-balancing ANPC-DAB hybrid topology, and also to a midpoint voltage self-balancing method for this hybrid topology. Background Technology

[0002] In medium- and high-voltage high-power power electronic conversion systems, DC-DC conversion is the core component for efficient energy transfer, and its performance directly determines the stability, conversion efficiency, and power density of the entire system. The dual active bridge (DAB) topology, with its outstanding advantages such as electrical isolation, bidirectional power flow, symmetrical structure, and ease of soft switching, has become one of the mainstream preferred topologies for medium- and high-voltage high-power DC-DC conversion scenarios. However, in medium- and high-voltage applications, the switching devices of the traditional two-level DAB topology must withstand voltage stress equal to the DC bus voltage, necessitating the use of high-voltage switching devices. This not only significantly increases device procurement costs but also limits the high-frequency design of the system, thus restricting power density improvement. Furthermore, switching losses increase significantly at high frequencies, affecting system conversion efficiency.

[0003] To address the voltage stress issue in traditional two-level DAB topologies, the integration of multi-level and DAB topologies has become a hot research topic in the industry. Active Neutral Point Clamping (ANPC) topology, as a typical three-level topology, can reduce the voltage stress on switching devices to half that of the DC bus voltage, effectively reducing the selection difficulty and cost of high-voltage devices, while improving the system's voltage level adaptability to meet the needs of medium- and high-voltage scenarios. However, traditional ANPC-DAB hybrid topologies have an inherent defect of unbalanced neutral point voltage. Neutral point voltage deviation leads to uneven voltage stress distribution on switching devices, output waveform distortion, and increased system losses. In severe cases, it can damage switching devices, significantly reducing system stability and reliability, becoming a core bottleneck for its widespread application in medium- and high-voltage, high-power scenarios. Currently, solutions for neutral point voltage balancing in ANPC topologies mainly fall into two categories: software control and hardware topology improvements. Software control methods, such as those based on space vector pulse width modulation (SVM) and zero-sequence component injection, require no additional hardware and are relatively low-cost. However, they suffer from complex control logic, slow dynamic response, and poor balancing performance under complex operating conditions such as load abrupt changes, DC bus voltage fluctuations, and bidirectional power flow switching, making them unsuitable for the real-time control requirements of high-power systems. Hardware topology improvement methods, which achieve midpoint voltage balancing by adding additional balancing circuits such as independent balancing power supplies, balancing resistor networks, and dedicated balancing chips, can improve balancing stability but significantly increase circuit complexity, system size, and hardware cost. They may also introduce additional power losses, hindering the improvement of system power density and reducing overall system reliability.

[0004] The flying capacitor type multilevel topology can flexibly expand the number of levels by connecting flying capacitors in parallel between the midpoints of the bridge arms, and has the advantages of simple structure, good voltage balance, fast dynamic response, and no need for complex control. However, in a single flying capacitor structure, the charging and discharging current is too large when the midpoint voltage changes abruptly, which can easily lead to accelerated capacitor loss, shortened lifespan, and limited balance accuracy. Summary of the Invention

[0005] The first objective of this invention is to provide a midpoint voltage self-balancing ANPC-DAB hybrid topology to solve the problem of excessive charging and discharging current when a single flying capacitor is balanced in the prior art.

[0006] A second objective of this invention is to provide a method for self-balancing the midpoint voltage of the topology.

[0007] The first technical solution adopted in this invention is a midpoint voltage self-balancing ANPC-DAB hybrid topology, which includes a DC input module, a primary ANPC bridge module, a DAB isolation conversion module, a secondary ANPC bridge module, and a DC output module connected in sequence. The DC input module includes a DC power supply Vdc1, a first voltage divider capacitor C1, and a second voltage divider capacitor C2. The connection point of the first voltage divider capacitor C1 and the second voltage divider capacitor C2 is the midpoint O of the topology.

[0008] The first technical solution of this invention is also characterized in that, The DC power supply Vdc1 has a positive DC bus Vdc+ and a negative DC bus Vdc- at its two ends respectively; the first voltage divider capacitor C1 and the second voltage divider capacitor C2 are connected in series, and the first voltage divider capacitor C1 is connected to Vdc+, and the second voltage divider capacitor C2 is connected to the negative DC bus Vdc-; the primary side ANPC bridge module is connected between the positive DC bus Vdc+ and the negative DC bus Vdc-.

[0009] The primary-side ANPC bridge module includes switching devices S1, S2, S3, and S4, clamping switching devices S5 and S6, flying capacitor Cf1, and current-limiting resistor Rf1; the output terminals of the primary-side ANPC bridge module are A and B, and both output terminals A and B are connected to the DAB isolation conversion module. The collector of switching device S1 is connected to the positive DC bus Vdc+ of the DC input module, the emitter of switching device S1 is connected to the collector of switching device S2, the emitter of switching device S2 is connected to the collector of switching device S3, the emitter of switching device S3 is connected to the collector of switching device S4, and the emitter of switching device S4 is connected to the negative DC bus Vdc- of the DC input module. Switching devices S1, S2, S3 and S4 are connected in series. The collector of clamping switch S5 is connected to the collector of switch S2, and the emitter of clamping switch S5 is connected to the topology midpoint O of the DC input module; the collector of clamping switch S6 is connected to the topology midpoint O of the DC input module, and the emitter of clamping switch S6 is connected to the emitter of switch S3; clamping switches S5 and S6 are connected in series; flying capacitor Cf1 and current-limiting resistor Rf1 are connected in series to form a composite balanced branch; the other end of flying capacitor Cf1 is connected to the connection point of switch S1 and S2, and the other end of current-limiting resistor Rf1 is connected to the connection point of switch S3 and S4.

[0010] The secondary-side ANPC bridge module includes switching devices S7, S8, S9, and S10, clamping switching devices S11 and S12, flying capacitor Cf2, and current-limiting resistor Rf2; the secondary-side ANPC bridge module includes input terminals C and D, both of which are connected to the DAB isolation converter module. The collector of switching device S7 is connected to the DC output module, the emitter of switching device S7 is connected to the collector of switching device S8, the emitter of switching device S8 is connected to the collector of switching device S9, the emitter of switching device S9 is connected to the collector of switching device S10, and the emitter of switching device S10 is connected to the DC output module. Switching devices S7, S8, S9, and S10 are connected in series. The collector of clamping switch S11 is connected to the emitter of switch S7, and the emitter of clamping switch S11 is connected to the DC output module; the collector of clamping switch S12 is connected to the DC output module, and the emitter of clamping switch S12 is connected to the emitter of switch S9; clamping switches S11 and S12 are connected in series; flying capacitor Cf2 and current-limiting resistor Rf2 are connected in series to form a composite balanced branch; the other end of current-limiting resistor Rf2 is connected to the connection point of switch S8 and clamping switch S11, and the other end of flying capacitor Cf2 is connected to the connection point of switch S9 and clamping switch S12.

[0011] Both the switching device and the clamping switch device use IGBT, MOSFET or wide bandgap semiconductor devices. Each switching device and clamping switch device is connected to an anti-parallel diode, which is either the device's built-in body diode or an external fast recovery diode.

[0012] The first voltage divider capacitor C1, the second voltage divider capacitor C2, and the flying capacitors Cf1 and Cf2 are all high-frequency film capacitors; the first output capacitor C3 and the second output capacitor C4 are both film capacitors, electrolytic capacitors, or supercapacitors; and the current limiting resistors Rf1 and Rf2 are power resistors.

[0013] The DAB isolation conversion module includes an isolation transformer T1 and a primary power transmission inductor L1; one end of the primary winding of the isolation transformer T1 is connected to the output terminal A through the primary power transmission inductor L1, and the other end of the primary winding of the isolation transformer T1 is directly connected to the output terminal B; one end of the secondary winding of the isolation transformer T1 is connected to the input terminal C of the secondary ANPC bridge module, and the other end of the secondary winding of the isolation transformer T1 is directly connected to the input terminal D of the secondary ANPC bridge module.

[0014] The DC output module includes a power supply Vdc2, a first output capacitor C3 and a second output capacitor C4. The connection point of the first output capacitor C3 and the second output capacitor C4 is the topological midpoint O. The first output capacitor C3 and the second output capacitor C4 are connected in series. The power supply Vdc2 leads out a positive bus BUS+ and a negative bus BUS-. And the first output capacitor C3 is connected to the positive bus BUS+, and the second output capacitor C4 is connected to the negative bus BUS-. The collector of the switching device S7 is connected to the positive bus BUS+, and the emitter of the switching device S10 is connected to the negative bus BUS-. The emitter of the clamping switching device S11 is connected to the topological midpoint O of the DC output module. The collector of the clamping switching device S12 is connected to the topological midpoint O of the DC output module.

[0015] The second technical solution adopted by the present invention is a midpoint voltage self-balancing method. Using the above-mentioned midpoint voltage self-balancing ANPC-DAB hybrid topology, it includes the following steps: self-balance the voltage Vmid of the topological midpoint O of the DC input module: through Cf1 and Rf1, cooperate with the on and off of the clamping switching devices S5, S6 and the switching devices S1~S4 to adjust Vmid to be stable at half of the input DC bus voltage Vdc1; at the same time, self-balance the voltage Vmid of the topological midpoint O of the DC output module: through Cf2 and Rf2, cooperate with the on and off of the clamping switching devices S11, S12 and the switching devices S7~S10 to adjust Vmid to be stable at half of the output DC bus voltage Vdc2.

[0016] The characteristics of the second technical solution of the present invention also lie in that The control logic for self-balancing the topological midpoint O of the DC input module is: When Vmid<Vdc1 / 2 on the input side, turn on the clamping switching device S5, and at the same time turn on the switching device S2 or S1, so that the flying capacitor Cf1 releases charge to the topological midpoint O of the DC input module through the current-limiting resistor Rf1 and the clamping switching device S5. After the input side Vmid rises to Vdc1 / 2, turn off the corresponding switching device; When the input - side Vmid > Vdc1 / 2, turn on the clamping switch device S6, and at the same time turn on the switch device S3 or S4, so that the topological mid - point O of the DC - input module charges the flying capacitor Cf1 through the clamping switch device S6 and the current - limiting resistor Rf1. After the input - side Vmid drops to Vdc1 / 2, turn off the corresponding switch device; The control logic for self - balancing the topological mid - point O of the DC - output module is as follows: When the output - side Vmid < Vdc2 / 2, turn on the clamping switch device S11, and at the same time turn on the switch device S8 or S7, so that the flying capacitor Cf2 discharges charge to the topological mid - point O of the DC - output module through the current - limiting resistor Rf2 and the clamping switch device S11. After the output - side Vmid gradually rises to Vdc2 / 2, turn off the corresponding switch device; When the output - side Vmid > Vdc2 / 2, turn on the clamping switch device S12, and at the same time turn on the switch device S9 or S10, so that the topological mid - point O of the DC - output module charges the flying capacitor Cf2 through the clamping switch device S12 and the current - limiting resistor Rf2. After the output - side Vmid drops to Vdc2 / 2, turn off the corresponding switch device.

[0017] The beneficial effects of the present invention are as follows: (1) The mid - point voltage self - balancing ANPC - DAB hybrid topology and method provided by the present invention adopt a composite structure of "flying capacitor combined with resistor" and cooperate with the clamping switch device, without complex control strategies and additional balancing circuits, to achieve automatic balancing of the topological mid - point voltage; the current - limiting resistor effectively limits the charging and discharging current of the flying capacitor, avoids current impact damage to the device, and at the same time improves the balancing accuracy. Under complex working conditions such as load mutation, power bidirectional switching, and DC - bus voltage fluctuation, the fluctuation range of the mid - point voltage is smaller, the dynamic response speed is fast, effectively avoiding problems such as uneven voltage stress of switch devices and output waveform distortion caused by mid - point voltage offset, and significantly improving the stability and reliability of the system.

[0018] (2) The mid - point voltage self - balancing ANPC - DAB hybrid topology and method provided by the present invention reduce the voltage stress of the primary - side switch devices S1 - S6 to half of the DC - bus voltage Vdc1, and reduce the voltage stress of the secondary - side switch devices S7 - S12 to half of the secondary - side output voltage. Switch devices with a lower voltage rating can be selected, significantly reducing the device procurement cost; at the same time, wide - bandgap semiconductor devices (SiC, GaN) with a lower voltage rating have better adaptability, which is conducive to the high - frequency design of the system and further improves the power density.

[0019] (3) The midpoint voltage self-balancing ANPC-DAB hybrid topology and method provided by the present invention retains the core structure of the DAB isolation conversion module and combines the phase shift control strategy to realize bidirectional power transmission, which can be flexibly adapted to scenarios such as energy storage systems and electric vehicle charging that require bidirectional energy flow; at the same time, it realizes zero voltage turn-on (ZVS) and zero current turn-off (ZCS) of the switching devices, which greatly reduces the switching losses. The current limiting resistor is selected with a reasonable resistance value, which will not introduce too much additional loss.

[0020] (4) The midpoint voltage self-balancing ANPC-DAB hybrid topology and method provided by the present invention are suitable for medium and high voltage, high power DC-DC conversion scenarios. They can be widely used in new energy power generation, energy storage systems, electric vehicle DC fast charging piles, industrial high frequency power supplies, smart grid energy conversion and other fields, and have good practicality and promotion value. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the midpoint voltage self-balancing ANPC-DAB hybrid topology of the present invention; Figure 2 This is a schematic diagram of the DC positive bus voltage regulation process of the midpoint voltage self-balancing control of the present invention under the condition of Vmid < Vdc1 / 2.

[0022] Figure 3 This is a schematic diagram of the DC negative bus voltage regulation process under the condition of Vmid < Vdc1 / 2, which is the midpoint voltage self-balancing control of the present invention.

[0023] Figure 4 This is a schematic diagram of the DC positive bus voltage regulation process of the midpoint voltage self-balancing control of the present invention under the condition that Vdc1 / 2 < Vmid.

[0024] Figure 5 This is a schematic diagram of the DC negative bus voltage regulation process under the midpoint voltage self-balancing control of the present invention when Vdc1 / 2 < Vmid. Detailed Implementation

[0025] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0026] This invention provides a midpoint voltage self-balancing ANPC-DAB hybrid topology, such as... Figure 1As shown, the system comprises a DC input module, a primary-side ANPC bridge module, a DAB isolation converter module, a secondary-side ANPC bridge module, and a DC output module, all electrically connected in sequence, forming a complete DC-DC energy conversion link. The DC input module includes a DC power supply Vdc1, a first voltage-dividing capacitor C1, and a second voltage-dividing capacitor C2. The connection point of the first and second voltage-dividing capacitors C1 and C2 is the topology midpoint O, and the voltage at midpoint O is Vmid. Under normal operating conditions, Vmid is stable at Vdc1 / 2, providing symmetrical voltage support for the ANPC full-bridge module. The DC power supply Vdc1 has a positive DC bus Vdc+ and a negative DC bus Vdc- connected to its two ends. The first and second voltage-dividing capacitors C1 and C2 are connected in series, with C1 connected to Vdc+ and C2 connected to the negative DC bus Vdc-. The primary-side ANPC bridge module is connected between the positive DC bus Vdc+ and the negative DC bus Vdc-.

[0027] The primary-side ANPC bridge module includes switching devices S1, S2, S3, and S4; clamping switching devices S5 and S6; a flying capacitor Cf1; and a current-limiting resistor Rf1. The ANPC bridge module has outputs A and B, both of which are connected to the DAB isolation converter module. The collector of switching device S1 is connected to the positive DC bus Vdc+ of the DC input module; the emitter of switching device S1 is connected to the collector of switching device S2; the emitter of switching device S2 is connected to the collector of switching device S3; the emitter of switching device S3 is connected to the collector of switching device S4; and the emitter of switching device S4 is connected to the negative DC bus Vdc- of the DC input module. Switches S1, S2, S3, and S4 are connected in series. The collector of clamping switching device S5 is connected to the collector of switching device S2. The collector of clamping switch S5 is connected to the midpoint O of the DC input module topology; the collector of clamping switch S6 is connected to the midpoint O of the DC input module topology, and the emitter of clamping switch S6 is connected to the emitter of switch S3. Clamping switches S5 and S6 are connected in series to achieve voltage clamping between the topology midpoint O and the midpoint of the bridge arm; flying capacitor Cf1 and current-limiting resistor Rf1 are connected in series to form a composite balanced branch. The other end of flying capacitor Cf1 is connected to the connection point of switch S1 and S2, and the other end of current-limiting resistor Rf1 is connected to the connection point of switch S3 and S4. Current-limiting resistor Rf1 is used to limit the charging and discharging current of flying capacitor Cf1. Flying capacitor Cf1 is used to achieve voltage equalization and midpoint voltage self-regulation. The two work together to achieve high-precision balance of midpoint voltage.

[0028] The secondary-side ANPC bridge module includes switching devices S7, S8, S9, and S10, clamping switching devices S11 and S12, flying capacitor Cf2, and current-limiting resistor Rf2. The secondary-side ANPC bridge module includes input terminals C and D, both of which are connected to the DAB isolation converter module. The collector of switching device S7 is connected to the DC output module, the emitter of switching device S7 is connected to the collector of switching device S8, the emitter of switching device S8 is connected to the collector of switching device S9, the emitter of switching device S9 is connected to the collector of switching device S10, and the emitter of switching device S10 is connected to the DC output module. Switches S7 and S8... S8, S9, and S10 are connected in series. The collector of clamping switch S11 is connected to the emitter of switch S7, and the emitter of clamping switch S11 is connected to the DC output module. The collector of clamping switch S12 is connected to the DC output module, and the emitter of clamping switch S12 is connected to the emitter of switch S9. Clamping switches S11 and S12 are connected in series. Flying capacitor Cf2 and current-limiting resistor Rf2 are connected in series to form a composite balanced branch. The other end of current-limiting resistor Rf2 is connected to the connection point of switch S8 and clamping switch S11, and the other end of flying capacitor Cf2 is connected to the connection point of switch S9 and clamping switch S12. The current-limiting resistor Rf2 and flying capacitor Cf2 work together with the composite balanced branch of the primary ANPC bridge module to achieve self-balancing of the topology midpoint voltage.

[0029] The switching devices and clamping switching devices all employ insulated-gate bipolar transistors (IGBTs), metal-oxide-semiconductor field-effect transistors (MOSFETs), or wide-bandgap semiconductor devices (SiC-MOSFETs, GaN). The anti-parallel diodes of the switching devices can be the built-in body diodes or external fast recovery diodes, adapting to the high-frequency operating requirements of the system, effectively reducing switching losses and improving system conversion efficiency. The first voltage divider capacitor C1, the second voltage divider capacitor C2, and the flying capacitors Cf1 and Cf2 are all high-frequency film capacitors, characterized by low high-frequency losses, good voltage withstand performance, and long lifespan, ensuring the stability, reliability, and voltage ripple control effect of the topology under high-frequency operating conditions. The first output capacitor C3 and the second output capacitor C4 are both film capacitors, electrolytic capacitors, or supercapacitors, balancing voltage stability and ripple suppression. The current-limiting resistors Rf1 and Rf2 are power resistors, flexibly selected according to the flying capacitor capacity and system operating current, effectively limiting the charging and discharging current without introducing excessive additional losses. The primary-side power transfer inductor L1 uses a high-frequency magnetic core inductor with low-loss magnetic core material to optimize power transfer characteristics and reduce the impact on system performance; the isolation transformer T1 uses a high-frequency isolation transformer, whose turns ratio can be flexibly designed according to the input and output voltage requirements to achieve precise matching between input and output voltage.

[0030] The DAB isolation converter module, comprising an isolation transformer T1 and a primary-side power transfer inductor L1, is the core module for achieving energy transfer, electrical isolation, and voltage ratio regulation. The isolation transformer T1 provides electrical isolation between the primary and secondary sides, while also regulating the input and output voltage ratio. One end of the primary winding of the isolation transformer T1 is connected to output terminal A via the primary-side power transfer inductor L1, and the other end is directly connected to output terminal B. One end of the secondary winding of the isolation transformer T1 is connected to input terminal C of the secondary ANPC bridge module, and the other end is directly connected to input terminal D of the secondary ANPC bridge module.

[0031] Among them, the DAB isolation converter module adopts a phase-shift control strategy. By adjusting the phase shift angle of the switching devices of the primary ANPC bridge module and the secondary ANPC bridge module, it realizes bidirectional power transmission and soft-switching control, which can realize zero-voltage turn-on (ZVS) and zero-current turn-off (ZCS) of the switching devices, significantly reducing switching losses and further improving the system conversion efficiency.

[0032] The DC output module includes a power supply Vdc2, a first output capacitor C3, and a second output capacitor C4, mainly used to stabilize the output voltage and suppress voltage ripple. The connection point of the first output capacitor C3 and the second output capacitor C4 is the topology midpoint O. The first output capacitor C3 and the second output capacitor C4 are connected in series. The power supply Vdc2 has a positive bus BUS+ and a negative bus BUS-. The first output capacitor C3 is connected to the positive bus BUS+, and the second output capacitor C4 is connected to the negative bus BUS-. The collector of the switching device S7 is connected to the positive bus BUS+, and the emitter of the switching device S10 is connected to the negative bus BUS-. The emitter of the clamping switching device S11 is connected to the topology midpoint O of the DC output module. The collector of the clamping switching device S12 is connected to the topology midpoint O of the DC output module. It also includes a load module, which includes a load R, used to consume or store the DC power output by the DC output module. The load R is connected in parallel to the output terminal of the DC output module. Depending on the actual application scenario, resistive load, inductive load or hybrid load can be selected, or it can be directly adapted to energy storage units (such as lithium battery packs and supercapacitors) to realize bidirectional power transmission and meet the needs of energy storage system charging and discharging, energy recovery and other scenarios.

[0033] The working principle of the topology structure of this invention is as follows: Taking the primary-side ANPC bridge module as an example, the DC input module divides the DC power supply Vdc1 into two equal voltages (Vdc1 / 2) evenly through the first voltage divider capacitor C1 and the second voltage divider capacitor C2. The voltage Vmid at the midpoint O of the DC input module topology is Vdc1 / 2, providing a symmetrical voltage foundation for the entire topology. The primary-side ANPC bridge module, serving as the primary bridge of the DAB isolation converter module, generates a multi-level output voltage through the switching combinations of devices S1-S6, effectively reducing voltage harmonics compared to the traditional two-level output. The secondary-side ANPC bridge module, through the switching combinations of devices S7-S12 and in conjunction with a phase-shift control strategy, works in tandem with the primary-side bridge. The isolation transformer T1 achieves electrical isolation between the primary and secondary sides and voltage ratio regulation, while the primary-side power transmission inductor L1 ensures stable power transmission. The DC output module stabilizes the output voltage through the first output capacitor C3 and the second output capacitor C4, supplying power to the load module. When the load is an energy storage unit, adjusting the phase shift angle enables feedback power transmission from the energy storage unit to the DC input side, achieving energy recovery and bidirectional power flow.

[0034] The mechanism for achieving midpoint voltage self-balancing: Flying capacitors Cf1 and Cf2 are connected in series with current-limiting resistors Rf1 and Rf2 to form a composite balance branch. During the switching process, flying capacitors Cf1 and Cf2 automatically absorb or release charge, and current-limiting resistors Rf1 and Rf2 limit the charging and discharging current in real time to avoid excessive current leading to increased capacitor loss and device damage. With the clamping effect of clamping switches S5, S6, S11, and S12, the voltage at the midpoint O of the topology is adjusted in real time to achieve high-precision self-balancing of the midpoint voltage.

[0035] This invention also provides a midpoint voltage self-balancing method, comprising the following steps: self-balancing the voltage Vmid at the midpoint O of the DC input module topology: by using Cf1 and Rf1, in conjunction with the on / off states of clamping switches S5 and S6 and switches S1-S4, Vmid is adjusted to stabilize at half the input DC bus voltage Vdc1; simultaneously, self-balancing the voltage Vmid at the midpoint O of the DC output module topology: by using Cf2 and Rf2, in conjunction with the on / off states of clamping switches S11 and S12 and switches S7-S10, Vmid is adjusted to stabilize at half the output DC bus voltage Vdc2. In this invention, the voltage Vmid at the midpoint O of the DC input module topology is uniformly referred to as the input-side Vmid, and the voltage Vmid at the midpoint O of the DC output module topology is uniformly referred to as the output-side Vmid.

[0036] The control logic for self - balancing the topological mid - point O of the DC input module is as follows: when the input - side Vmid < Vdc1 / 2, turn on the clamping switch device S5, and at the same time turn on the switch device S2 or S1, so that the flying capacitor Cf1 releases charge to the topological mid - point O of the DC input module through the current - limiting resistor Rf1 and the clamping switch device S5. After the input - side Vmid rises to Vdc1 / 2, turn off the corresponding switch device; when the input - side Vmid > Vdc1 / 2, turn on the clamping switch device S6, and at the same time turn on the switch device S3 or S4, so that the topological mid - point O of the DC input module charges the flying capacitor Cf1 through the clamping switch device S6 and the current - limiting resistor Rf1. After the input - side Vmid drops to Vdc1 / 2, turn off the corresponding switch device; The control logic for self - balancing the topological mid - point O of the DC output module is as follows: when the output - side Vmid < Vdc2 / 2, turn on the clamping switch device S11, and at the same time turn on the switch device S8 or S7, so that the flying capacitor Cf2 releases charge to the topological mid - point O of the DC output module through the current - limiting resistor Rf2 and the clamping switch device S11. After the output - side Vmid gradually rises to Vdc2 / 2, turn off the corresponding switch device; when the output - side Vmid > Vdc2 / 2, turn on the clamping switch device S12, and at the same time turn on the switch device S9 or S10, so that the topological mid - point O of the DC output module charges the flying capacitor Cf2 through the clamping switch device S12 and the current - limiting resistor Rf2. After the output - side Vmid drops to Vdc2 / 2, turn off the corresponding switch device.

[0037] Through the above - mentioned adjustment process, without additional control strategies and balancing circuits, the stable balance of the mid - point voltage can be achieved, ensuring that Vmid on the input - side and the output - side always remains around Vdc / 2, guaranteeing the uniform distribution of the voltage stress of the switch devices, avoiding device damage and system performance degradation caused by the mid - point voltage deviation, and at the same time extending the service life of the flying capacitor.

[0038] Embodiment 1 This embodiment provides a mid - point voltage self - balancing ANPC - DAB hybrid topology, as Figure 1 shown, which includes a DC input module, a primary - side ANPC bridge module, a DAB isolation transformation module, a secondary - side ANPC bridge module, and a DC output module connected in series electrically. The DC input module includes a DC power supply Vdc1, a first voltage - dividing capacitor C1, and a second voltage - dividing capacitor C2. The connection point of the first voltage - dividing capacitor C1 and the second voltage - dividing capacitor C2 is the topological mid - point O of the DC input module.

[0039] This embodiment defines the basic hierarchical structure of the topology, retains the isolation and bidirectional power transmission capabilities of DAB, and organically integrates the ANPC multilevel structure with DAB isolation transformation, providing a basic framework for reducing the voltage stress of switch devices.

[0040] Embodiment 2 Based on Example 1, the DC power supply Vdc1 has a positive DC bus Vdc+ and a negative DC bus Vdc- respectively led out from its two ends; the first voltage divider capacitor C1 and the second voltage divider capacitor C2 are connected in series, and the first voltage divider capacitor C1 is connected to Vdc+, and the second voltage divider capacitor C2 is connected to the negative DC bus Vdc-; the primary side ANPC bridge module is connected between the positive DC bus Vdc+ and the negative DC bus Vdc-.

[0041] This embodiment further refines the design by drawing positive bus Vdc+ and negative bus Vdc- from the DC power supply Vdc1. A first voltage-dividing capacitor C1 is connected between Vdc+ and the topology midpoint O, and a second voltage-dividing capacitor C2 is connected between the topology midpoint O and Vdc-. The primary-side ANPC bridge module is directly connected between Vdc+ and Vdc-. This stabilizes the topology midpoint O of the DC input module at Vdc1 / 2, providing a symmetrical potential reference for the charging and discharging of the flying capacitors.

[0042] Example 3 Based on the above embodiments, the primary-side ANPC bridge module includes switching devices S1, S2, S3, and S4, clamping switching devices S5 and S6, a flying capacitor Cf1, and a current-limiting resistor Rf1. The output terminals of the primary-side ANPC bridge module are A and B, both of which are connected to the DAB isolation converter module. The collector of switching device S1 is connected to the positive DC bus Vdc+ of the DC input module, the emitter of switching device S1 is connected to the collector of switching device S2, the emitter of switching device S2 is connected to the collector of switching device S3, the emitter of switching device S3 is connected to the collector of switching device S4, and the emitter of switching device S4 is connected to the negative DC bus of the DC input module. Bus Vdc-, switching devices S1, S2, S3 and S4 are connected in series; the collector of clamping switch S5 is connected to the collector of switching device S2, and the emitter of clamping switch S5 is connected to the topology midpoint O of the DC input module; the collector of clamping switch S6 is connected to the topology midpoint O of the DC input module, and the emitter of clamping switch S6 is connected to the emitter of switching device S3, and clamping switches S5 and S6 are connected in series; flying capacitor Cf1 and current-limiting resistor Rf1 are connected in series to form a composite balanced branch, the other end of flying capacitor Cf1 is connected to the connection point of switching devices S1 and S2, and the other end of current-limiting resistor Rf1 is connected to the connection point of switching devices S3 and S4.

[0043] This embodiment presents a composite balanced branch formed by a flying capacitor Cf1 and a current-limiting resistor Rf1 connected in series, which is connected between the connection points of switching devices S1 and S2 and the connection points of switching devices S3 and S4. Unlike a traditional single flying capacitor, the current-limiting resistor Rf1 limits the current when Cf1 is charging and discharging, preventing excessive charging and discharging current from damaging the capacitor or causing voltage overshoot.

[0044] Example 4 Based on the above embodiments, the secondary-side ANPC bridge module includes switching devices S7, S8, S9, and S10, clamping switching devices S11 and S12, a flying capacitor Cf2, and a current-limiting resistor Rf2; the secondary-side ANPC bridge module includes input terminals C and D, both of which are connected to the DAB isolation converter module; the collector of switching device S7 is connected to the DC output module, the emitter of switching device S7 is connected to the collector of switching device S8, the emitter of switching device S8 is connected to the collector of switching device S9, the emitter of switching device S9 is connected to the collector of switching device S10, and the emitter of switching device S10 is connected to the DC output module. 7. S8, S9, and S10 are connected in series. The collector of clamping switch S11 is connected to the emitter of switch S7, and the emitter of clamping switch S11 is connected to the DC output module. The collector of clamping switch S12 is connected to the DC output module, and the emitter of clamping switch S12 is connected to the emitter of switch S9. Clamping switches S11 and S12 are connected in series. Flying capacitor Cf2 and current-limiting resistor Rf2 are connected in series to form a composite balanced branch. The other end of current-limiting resistor Rf2 is connected to the connection point of switch S8 and clamping switch S11, and the other end of flying capacitor Cf2 is connected to the connection point of switch S9 and clamping switch S12.

[0045] The switching and clamping devices both utilize IGBTs. Each switching and clamping device is connected to an anti-parallel diode, which can be either an integrated body diode or an external fast recovery diode. The first voltage divider capacitor C1, the second voltage divider capacitor C2, and the flying capacitors Cf1 and Cf2 are all high-frequency film capacitors. The first output capacitor C3 and the second output capacitor C4 are film capacitors, electrolytic capacitors, or supercapacitors. The current-limiting resistors Rf1 and Rf2 are power resistors.

[0046] Example 5 Based on the above embodiments, both the switching device and the clamping switching device adopt MOSFETs. The DAB isolation converter module includes an isolation transformer T1 and a primary power transfer inductor L1. One end of the primary winding of the isolation transformer T1 is connected to the output terminal A through the primary power transfer inductor L1, and the other end of the primary winding of the isolation transformer T1 is directly connected to the output terminal B. One end of the secondary winding of the isolation transformer T1 is connected to the input terminal C of the secondary ANPC bridge module, and the other end of the secondary winding of the isolation transformer T1 is directly connected to the input terminal D of the secondary ANPC bridge module.

[0047] Example 6 Based on the above embodiments, both the switching device and the clamping switching device adopt wide bandgap semiconductor devices. The DC output module includes a power supply Vdc2, a first output capacitor C3, and a second output capacitor C4. The connection point of the first output capacitor C3 and the second output capacitor C4 is the topology midpoint O of the DC output module. The first output capacitor C3 and the second output capacitor C4 are connected in series. The power supply Vdc2 has a positive bus BUS+ and a negative bus BUS-. The first output capacitor C3 is connected to the positive bus BUS+, and the second output capacitor C4 is connected to the negative bus BUS-. The collector of the switching device S7 is connected to the positive bus BUS+, and the emitter of the switching device S10 is connected to the negative bus BUS-. The emitter of the clamping switching device S11 is connected to the topology midpoint O of the DC output module. The collector of the clamping switching device S12 is connected to the topology midpoint O of the DC output module.

[0048] In this embodiment, the composite balanced branch consisting of the flying capacitor Cf2 and the current-limiting resistor Rf2 connected in series can quickly respond to the deviation of the output side Vmid. By controlling the conduction and cutoff of clamping switches S11 and S12 and switches S7 to S10, the charging and discharging regulation of the output side midpoint O is completed, realizing the self-balancing of the midpoint voltage. At the same time, the voltage stress of each switch is clamped to half of the voltage Vdc2, reducing the difficulty of device selection and conduction loss.

[0049] The specific process of this embodiment is as follows: Start-up phase: After the DC power supply Vdc1 is connected, the first voltage divider capacitor C1 and the second voltage divider capacitor C2 are slowly charged to Vdc1 / 2, and the initial voltage of the topology midpoint O is Vdc1 / 2; the flying capacitors Cf1 and Cf2 are initially charged through the parasitic diodes of the switching devices and the current limiting resistors Rf1 and Rf2, and the voltage quickly stabilizes at around Vdc1 / 2. Rf1 and Rf2 limit the charging current within the set range to avoid damage to the capacitors; the first output capacitor C3 and the second output capacitor C4 are initially charged to the target output voltage, and the entire topology completes the start-up preparation.

[0050] During normal power transmission: A phase-shift control strategy is adopted to control the devices of the primary-side ANPC bridge module and the secondary-side ANPC bridge module to switch on and off according to preset logic, and adjust the phase shift angle (0-180°) to achieve stable power transmission from the DC input side to the load side; the isolation transformer T1 achieves electrical isolation between the primary and secondary sides to ensure system safety; the switching devices S1-S12 achieve zero-voltage switching (ZVS), which greatly reduces switching losses and ensures efficient system operation.

[0051] Power bi-directional transmission stage: When the load is replaced by an energy storage battery, adjust the phase-shift angle direction to make the secondary side bridge the energy input terminal and the primary side bridge the energy output terminal, realizing the feedback transmission of power from the energy storage battery to the DC input side, completing energy recovery, adapting to the charging and discharging requirements of the energy storage system, and the transmitted power can be flexibly adjusted according to the phase-shift angle. When the load changes suddenly, the power bi-directionally switches, or the midpoint voltage Vmid deviates from Vdc1 / 2 due to the fluctuation of the DC bus voltage, the self-balancing mechanism starts.

[0052] Embodiment 7 This embodiment provides a midpoint voltage self-balancing method, which adopts the midpoint voltage self-balancing ANPC-DAB hybrid topology provided in the above embodiment, and includes the following steps: Self-balance the voltage Vmid of the topological midpoint O of the DC input module: Through Cf1 and Rf1, cooperate with the conduction and turn-off of the clamping switch devices S5, S6 and the switch devices S1~S4 to adjust Vmid to be stable at half of the input DC bus voltage Vdc1; At the same time, self-balance the voltage Vmid of the topological midpoint O of the DC output module: Through Cf2 and Rf2, cooperate with the conduction and turn-off of the clamping switch devices S11, S12 and the switch devices S7~S10 to adjust Vmid to be stable at half of the output DC bus voltage Vdc2.

[0053] Among them, the control logic for self-balancing the topological midpoint O of the DC input module is: When Vmid<Vdc1 / 2 on the input side, turn on the clamping switch device S5, and at the same time turn on the switch device S2 or S1, the flying capacitor Cf1 starts to charge and discharge through the current-limiting resistor Rf1. Rf1 limits the charging and discharging current, so that the flying capacitor Cf1 releases charge to the topological midpoint O of the DC input module through the current-limiting resistor Rf1 and the clamping switch device S5. After the input side Vmid rises to Vdc1 / 2, turn off the corresponding switch device; The voltage equalization adjustment circuit of the positive and negative busbars is as Figure 2 、 Figure 3 shown, and the voltage equalization function is realized by relying on this circuit.

[0054] When Vmid>Vdc1 / 2 on the input side, turn on the clamping switch device S6, and at the same time turn on the switch device S3 or S4, the flying capacitor Cf1 starts to charge and discharge through the current-limiting resistor Rf1. The current-limiting resistor Rf1 limits the charging and discharging current within a certain range to avoid excessive current from damaging the flying capacitor Cf1, so that the topological midpoint O of the DC input module charges the flying capacitor Cf1 through the clamping switch device S6 and the current-limiting resistor Rf1. After the input side Vmid drops to Vdc1 / 2, turn off the corresponding switch device; The voltage equalization adjustment circuit of the positive and negative busbars is as Figure 4 、 Figure 5 shown, and the voltage equalization function is realized by relying on this circuit.

[0055] The control logic for self-balancing the topological midpoint O of the DC output module is as follows: When Vmid on the output side is less than Vdc2 / 2, turn on the clamping switch device S11 and simultaneously turn on the switch device S8 or S7, so that the flying capacitor Cf2 releases charge to the topological midpoint O of the DC output module through the current-limiting resistor Rf2 and the clamping switch device S11. After Vmid on the output side gradually rises to Vdc2 / 2, turn off the corresponding switch device; When Vmid on the output side is greater than Vdc2 / 2, turn on the clamping switch device S12 and simultaneously turn on the switch device S9 or S10, so that the topological midpoint O of the DC output module charges the flying capacitor Cf2 through the clamping switch device S12 and the current-limiting resistor Rf2. After Vmid on the output side drops to Vdc2 / 2, turn off the corresponding switch device.

Claims

1. A hybrid ANPC-DAB topology with self-balancing midpoint voltage, characterized in that, It includes a DC input module, a primary-side ANPC bridge module, a DAB isolation conversion module, a secondary-side ANPC bridge module, and a DC output module that are connected in sequence. The DC input module includes a DC power supply Vdc1, a first voltage divider capacitor C1, and a second voltage divider capacitor C2. The connection point of the first voltage divider capacitor C1 and the second voltage divider capacitor C2 is the topology midpoint O.

2. The midpoint voltage self-balancing ANPC-DAB hybrid topology according to claim 1, characterized in that, The DC power supply Vdc1 has a positive DC bus Vdc+ and a negative DC bus Vdc- at its two ends, respectively; the first voltage divider capacitor C1 and the second voltage divider capacitor C2 are connected in series, with the first voltage divider capacitor C1 connected to Vdc+ and the second voltage divider capacitor C2 connected to the negative DC bus Vdc-; the primary-side ANPC bridge module is connected between the positive DC bus Vdc+ and the negative DC bus Vdc-.

3. The midpoint voltage self-balancing ANPC-DAB hybrid topology according to claim 2, characterized in that, The primary-side ANPC bridge module includes switching devices S1, S2, S3, and S4, clamping switching devices S5 and S6, flying capacitor Cf1, and current-limiting resistor Rf1; the output terminals of the primary-side ANPC bridge module are A and B, and both output terminals A and B are connected to the DAB isolation conversion module. The collector of the switching device S1 is connected to the positive DC bus Vdc+ of the DC input module, the emitter of the switching device S1 is connected to the collector of the switching device S2, the emitter of the switching device S2 is connected to the collector of the switching device S3, the emitter of the switching device S3 is connected to the collector of the switching device S4, and the emitter of the switching device S4 is connected to the negative DC bus Vdc- of the DC input module. The switching devices S1, S2, S3 and S4 are connected in series. The collector of clamping switch S5 is connected to the collector of switch S2, and the emitter of clamping switch S5 is connected to the topology midpoint O of the DC input module; the collector of clamping switch S6 is connected to the topology midpoint O of the DC input module, and the emitter of clamping switch S6 is connected to the emitter of switch S3; clamping switches S5 and S6 are connected in series; flying capacitor Cf1 and current-limiting resistor Rf1 are connected in series to form a composite balanced branch; the other end of flying capacitor Cf1 is connected to the connection point of switch S1 and S2, and the other end of current-limiting resistor Rf1 is connected to the connection point of switch S3 and S4.

4. The midpoint voltage self-balancing ANPC-DAB hybrid topology according to claim 3, characterized in that, The secondary-side ANPC bridge module includes switching devices S7, S8, S9, and S10, clamping switching devices S11 and S12, flying capacitor Cf2, and current-limiting resistor Rf2; the secondary-side ANPC bridge module includes input terminals C and D, both of which are connected to the DAB isolation converter module. The collector of the switching device S7 is connected to the DC output module, the emitter of the switching device S7 is connected to the collector of the switching device S8, the emitter of the switching device S8 is connected to the collector of the switching device S9, the emitter of the switching device S9 is connected to the collector of the switching device S10, and the emitter of the switching device S10 is connected to the DC output module. The switching devices S7, S8, S9, and S10 are connected in series. The collector of clamping switch S11 is connected to the emitter of switch S7, and the emitter of clamping switch S11 is connected to the DC output module; the collector of clamping switch S12 is connected to the DC output module, and the emitter of clamping switch S12 is connected to the emitter of switch S9; clamping switches S11 and S12 are connected in series; flying capacitor Cf2 and current-limiting resistor Rf2 are connected in series to form a composite balanced branch; the other end of current-limiting resistor Rf2 is connected to the connection point of switch S8 and clamping switch S11, and the other end of flying capacitor Cf2 is connected to the connection point of switch S9 and clamping switch S12.

5. The midpoint voltage self-balancing ANPC-DAB hybrid topology according to claim 4, characterized in that, Both the switching device and the clamping switch device use IGBT, MOSFET or wide bandgap semiconductor devices. Each switching device and clamping switch device is connected to an anti-parallel diode, which is either the device's built-in body diode or an external fast recovery diode.

6. The midpoint voltage self-balancing ANPC-DAB hybrid topology according to claim 5, characterized in that, The DAB isolation converter module includes an isolation transformer T1 and a primary power transfer inductor L1. One end of the primary winding of the isolation transformer T1 is connected to the output terminal A through the primary power transfer inductor L1, and the other end of the primary winding of the isolation transformer T1 is directly connected to the output terminal B. One end of the secondary winding of the isolation transformer T1 is connected to the input terminal C of the secondary ANPC bridge module, and the other end of the secondary winding of the isolation transformer T1 is directly connected to the input terminal D of the secondary ANPC bridge module.

7. The midpoint voltage self-balancing ANPC-DAB hybrid topology according to claim 6, characterized in that, The DC output module includes a power supply Vdc2, a first output capacitor C3, and a second output capacitor C4. The connection point of the first output capacitor C3 and the second output capacitor C4 is the topology midpoint O. The first output capacitor C3 and the second output capacitor C4 are connected in series. The power supply Vdc2 has a positive bus BUS+ and a negative bus BUS-. The first output capacitor C3 is connected to the positive bus BUS+, and the second output capacitor C4 is connected to the negative bus BUS-. The collector of the switching device S7 is connected to the positive bus BUS+, and the emitter of the switching device S10 is connected to the negative bus BUS-. The emitter of the clamping switching device S11 is connected to the topology midpoint O of the DC output module. The collector of the clamping switching device S12 is connected to the topology midpoint O of the DC output module.

8. The midpoint voltage self-balancing ANPC-DAB hybrid topology according to claim 7, characterized in that, The first voltage divider capacitor C1, the second voltage divider capacitor C2, and the flying capacitors Cf1 and Cf2 are all high-frequency film capacitors; the first output capacitor C3 and the second output capacitor C4 are film capacitors, electrolytic capacitors, or supercapacitors; and the current limiting resistors Rf1 and Rf2 are power resistors.

9. A method for self-balancing midpoint voltage, characterized in that, Using the midpoint voltage self-balancing ANPC-DAB hybrid topology as described in claim 8, the following steps are included: self-balancing the voltage Vmid at the midpoint O of the DC input module topology: by using Cf1 and Rf1, in conjunction with the conduction and cutoff of clamping switch devices S5, S6 and switch devices S1~S4, Vmid is adjusted to stabilize at half of the input DC bus voltage Vdc1. At the same time, self-balance the voltage Vmid of the topological midpoint O of the DC output module: through Cf2 and Rf2, in cooperation with the on-off of the clamping switch devices S11, S12 and the switch devices S7 to S10, adjust Vmid to stabilize it at half of the output DC bus voltage Vdc2.

10. The midpoint voltage self-balancing method according to claim 9, characterized in that, The control logic for self-balancing the topological midpoint O of the DC input module is as follows: When the input-side Vmid < Vdc1 / 2, turn on the clamping switch device S5, and at the same time turn on the switch device S2 or S1, so that the flying capacitor Cf1 releases charge to the topological midpoint O of the DC input module through the current-limiting resistor Rf1 and the clamping switch device S5. After the input-side Vmid rises to Vdc1 / 2, turn off the corresponding switch device; When the input-side Vmid > Vdc1 / 2, turn on the clamping switch device S6, and at the same time turn on the switch device S3 or S4, so that the topological midpoint O of the DC input module charges the flying capacitor Cf1 through the clamping switch device S6 and the current-limiting resistor Rf1. After the input-side Vmid drops to Vdc1 / 2, turn off the corresponding switch device; The control logic for self-balancing the topological midpoint O of the DC output module is as follows: When the output-side Vmid < Vdc2 / 2, turn on the clamping switch device S11, and at the same time turn on the switch device S8 or S7, so that the flying capacitor Cf2 releases charge to the topological midpoint O of the DC output module through the current-limiting resistor Rf2 and the clamping switch device S11. After the output-side Vmid gradually rises to Vdc2 / 2, turn off the corresponding switch device; When the output-side Vmid > Vdc2 / 2, turn on the clamping switch device S12, and at the same time turn on the switch device S9 or S10, so that the topological midpoint O of the DC output module charges the flying capacitor Cf2 through the clamping switch device S12 and the current-limiting resistor Rf2. After the output-side Vmid drops to Vdc2 / 2, turn off the corresponding switch device.

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