Modular multilevel sub-module of integrated dual active bridge and solid state transformer

Abstract

The application belongs to the field of power electronic converters, and relates to a modular multilevel sub-module of an integrated dual active bridge and a solid-state transformer, the sub-module comprising: a modular multilevel converter function unit, an integrated magnetic element, a dual active bridge function unit and an integrated local controller connected in sequence; the modular multilevel converter function unit comprises a main power bridge arm and a direct-current support capacitor, is used for connecting a high-voltage direct-current or alternating-current bus, and realizes voltage synthesis and the like; the integrated magnetic element is a high-frequency transformer containing leakage inductance and magnetizing inductance, and is used for electrical isolation and voltage transformation; the dual active bridge function unit comprises a primary side high-frequency H bridge and a secondary side high-frequency H bridge, an input end of the primary side high-frequency H bridge is connected to two ends of the direct-current support capacitor C sm , and an output end is connected to a primary side of the high-frequency transformer; the application has the advantages of high integration, high power density and efficiency, strong intrinsic voltage self-balancing capability, cost and reliability advantages, simplified and modularized control and high application flexibility.

Description

Technical Field

[0001] This invention relates to the field of power electronic converter technology, and more particularly to a modular multilevel sub-module with integrated dual active bridges and a solid-state transformer. Background Technology

[0002] With the large-scale integration of renewable energy and the development of DC distribution networks, solid-state transformers (SSTs), as key interface devices for voltage transformation, electrical isolation, and bidirectional energy flow, are increasingly being researched and developed. Currently, mainstream SST topologies typically employ a cascaded structure of modular multilevel converters (MMCs) and dual active bridges (DABs).

[0003] In existing technologies, MMCs are typically composed of a large number of cascaded half-bridge or full-bridge submodules with identical structures. Each submodule contains power switching devices, DC support capacitors, and auxiliary circuitry to achieve high-voltage side voltage synthesis and waveform control. DABs, as high-performance isolated DC-DC converters, are widely used as intermediate isolation stages in SSTs due to their high power density, excellent soft-switching characteristics, and bidirectional power transfer capabilities.

[0004] However, existing technical solutions have the following main drawbacks: Large size and high cost: As independent physical units, MMC submodules and DAB converters require their own independent magnetic components, control circuits and heat dissipation systems, resulting in large system size, low power density and high material and manufacturing costs.

[0005] Efficiency bottleneck: There is an intermediate DC link between the two-stage energy conversion structure, and the energy needs to be converted twice, which increases the sum of conduction loss and switching loss.

[0006] Reliability challenges: The large number of MMC submodules and corresponding DAB units results in a large number of system components, an increase in potential failure points, and a complex system reliability design.

[0007] High control complexity: It requires coordination of voltage balancing of the MMC submodule and phase shift control of DAB, resulting in a complex control system architecture and high requirements for communication and synchronization.

[0008] Parasitic parameter effects: The connecting busbar or cable between the two stages can introduce parasitic inductance and capacitance, which may cause voltage spikes and electromagnetic interference problems during high-frequency switching.

[0009] To address the aforementioned issues, this invention proposes an integrated submodule topology that deeply integrates the MMC submodule with the DAB converter in terms of physical structure, and constructs a high-performance solid-state transformer based on this topology. Summary of the Invention

[0010] To address the aforementioned technical problems, this invention provides a modular multilevel submodule integrating dual active bridges, employing the following technical solution, including: The modular multilevel converter functional unit, integrated magnetic components, dual active bridge functional unit, and integrated local controller are connected sequentially via electrical connections. The modular multilevel converter functional unit includes a main power bridge arm and a DC support capacitor C. sm It is used to connect to high-voltage DC or AC busbars to achieve voltage synthesis and energy buffering; The integrated magnetic component includes a leakage inductance L. k and magnetizing inductor L m High-frequency transformers are used for electrical isolation and voltage transformation; The dual active bridge functional unit includes a primary-side high-frequency H-bridge and a secondary-side high-frequency H-bridge, with the input terminal of the primary-side high-frequency H-bridge connected to the DC support capacitor C. sm The output end is connected to the primary side of the high-frequency transformer; the input end of the secondary high-frequency H-bridge is connected to the secondary side of the high-frequency transformer, and the output end forms a low-voltage DC port. The integrated local controller connects to and controls the power switching transistors in the modular multilevel converter functional unit and the dual active bridge functional unit to achieve integrated control of power transmission and capacitor voltage self-balancing.

[0011] Preferably, the main power arm of the modular multilevel converter functional unit is a full-bridge structure, including the first to fourth power switches S1, S2, S3, S4 and their anti-parallel diodes, and the DC support capacitor C. sm The two terminals of the full-bridge structure are connected in parallel across the DC input terminals; the two series midpoints of the full-bridge structure respectively constitute the high-voltage DC positive port (HVDC) of the submodule. P and high voltage DC negative port HVDC N .

[0012] Preferably, the main power bridge arm in the modular multilevel converter functional unit is a half-bridge structure, including first and second power switches S1 and S2 and their anti-parallel diodes, and the DC support capacitor Csm is connected in parallel across the DC input terminals of the half-bridge structure; the series midpoint of the half-bridge structure constitutes the high-voltage output port of the submodule.

[0013] Preferably, the magnetizing inductor L mConnected in parallel across the primary winding of the high-frequency transformer, so that current flows through the magnetizing inductor L m The current can be controlled by the integrated local controller to supply the DC support capacitor C. sm It performs charging or discharging to achieve self-balancing of the capacitor voltage in the submodule.

[0014] Preferably, the integrated local controller generates drive signals through a dual phase-shift control algorithm, the dual phase-shift control algorithm comprising: According to power command P ref Calculate the basic phase shift angle φ0; According to the DC support capacitor C sm voltage V sm The deviation from the reference value is used to calculate the zero-voltage duty cycle D for voltage equalization. z And the correction amount Δφ for the phase shift angle; Calculate the phase shift angle φ = φ0 + Δφ and the zero-voltage duty cycle D acting on the dual active bridge functional unit. z .

[0015] To address the aforementioned technical problems, the present invention also provides a solid-state transformer, comprising: At least one bridge arm, the bridge arm comprising multiple modular multilevel sub-modules of integrated dual active bridge as described above, cascaded on the high-voltage side; the low-voltage DC ports of all the modular multilevel sub-modules of integrated dual active bridge are electrically connected in parallel to form a common low-voltage DC bus. A system-level controller is used to issue power commands to the integrated local controller of each of the modular multilevel submodules with integrated dual active bridges.

[0016] Preferably, the solid-state transformer further includes a DC load or energy storage system connected to the common low-voltage DC bus.

[0017] Preferably, the solid-state transformer further includes an inverter unit connected to the common low-voltage DC bus for converting DC power into AC power to supply AC loads.

[0018] Preferably, the high-voltage side port of the solid-state transformer is used to connect to a medium- or high-voltage AC power grid or a high-voltage DC power grid. By controlling the modular multilevel converter functional unit of the cascaded integrated dual active bridge modular multilevel submodule to operate in rectification or inversion mode, AC-DC conversion or DC voltage support is achieved.

[0019] Preferably, the capacitor voltage self-balancing process of each of the modular multilevel submodules with integrated dual active bridges is distributed and autonomous; self-balancing refers to adjusting the zero-voltage duty cycle D through an integrated local controller. z Reused magnetized inductor Lm The energy stored in the DC support capacitor C sm This is achieved through charging and discharging.

[0020] Compared with the prior art, the present invention has the following main advantages: (1) High integration and structural innovation: The MMC sub-module and DAB are deeply integrated at the level of power devices and magnetic components, and the independent DAB converter unit is completely eliminated, which is a fundamental innovation in topology.

[0021] (2) It has extremely high power density and efficiency: the number of energy conversion links and discrete components is reduced, and the utilization rate of magnetic cores and semiconductor devices is maximized. It is expected that the overall power density can be increased by more than 30%, and the peak efficiency can be increased by 1-2 percentage points.

[0022] (3) It has inherent voltage self-balancing capability: By adopting the magnetization energy reuse mechanism, the sub-module can achieve fast and efficient distributed capacitor voltage balancing without the need for externally added complex active balancing circuits, which significantly enhances the system stability and dynamic response speed.

[0023] (4) Significant cost and reliability advantages: The total number of components is greatly reduced (approximately 30%-40% reduction in switching transistors and magnetic components), lowering material costs, assembly costs, and thermal management costs. Fewer connection points and a simpler structure directly improve the inherent reliability of the system (increased MTBF).

[0024] (5) Control simplification and modularization: The complex system-level equalization control is decentralized to the local sub-module, realizing a plug-and-play modular design, which greatly simplifies the system-level control logic and facilitates capacity expansion and maintenance.

[0025] (6) High application flexibility: This integrated sub-module can be used as a general building module and can be flexibly combined to form a high-performance solid-state transformer for various application scenarios such as medium and high voltage DC grids, AC distribution networks, energy storage integration, and ship DC power systems, and has a wide range of application prospects. Attached Figure Description

[0026] To more clearly illustrate the solutions in this invention, the accompanying drawings used in the description of the embodiments of this invention will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0027] Figure 1 This is a schematic diagram of the modular multilevel sub-module with integrated dual active bridges of the present invention. Figure 2This is a circuit schematic of the modular multilevel submodule of the integrated dual active bridge of the present invention, taking the full-bridge type as an example; Figure 3 This is a circuit topology diagram of the modular multilevel submodule with integrated dual active bridges of the present invention, taking the full-bridge type as an example; Figure 4 This is a typical application topology diagram of a solid-state transformer (SST) constructed from the modular multilevel sub-module with integrated dual active bridges of the present invention. Detailed Implementation

[0028] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains; the terminology used herein in the specification is for the purpose of describing particular embodiments only and is not intended to limit the invention; the terms "comprising" and "having," and any variations thereof, in the specification, claims, and foregoing drawings are intended to cover non-exclusive inclusion. The terms "first," "second," etc., in the specification, claims, or foregoing drawings are used to distinguish different objects and not to describe a particular order.

[0029] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of the invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0030] To enable those skilled in the art to better understand the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings.

[0031] Example 1 Please refer to Figure 1 This diagram illustrates the structural components of the modular multilevel submodule with integrated dual active bridges according to the present invention. The modular multilevel submodule with integrated dual active bridges includes: The modular multilevel converter functional unit, integrated magnetic components, dual active bridge functional unit, and integrated local controller are connected sequentially via electrical connections. The modular multilevel converter functional unit includes the main power bridge arm and the DC support capacitor C. sm It is used to connect to high-voltage DC or AC busbars to achieve voltage synthesis and energy buffering; Integrated magnetic components include leakage inductance L k and magnetizing inductor L m High-frequency transformers are used for electrical isolation and voltage transformation; The dual active bridge functional unit includes a primary-side high-frequency H-bridge and a secondary-side high-frequency H-bridge. The input terminal of the primary-side high-frequency H-bridge is connected to a DC support capacitor C. sm The output end is connected to the primary side of the high-frequency transformer; the input end of the secondary high-frequency H-bridge is connected to the secondary side of the high-frequency transformer, and the output end forms a low-voltage DC port. The integrated local controller connects to and controls the power switches in the modular multilevel converter functional unit and the dual active bridge functional unit to achieve integrated control of power transmission and capacitor voltage self-balancing.

[0032] The modular multilevel converter functional unit, as the main bridge arm, can be composed of a full-bridge or half-bridge structure. Figure 2 This is a circuit diagram of the modular multilevel submodule of the integrated dual active bridge of the present invention, taking the full-bridge type as an example. Figure 3 This is a circuit topology diagram of the modular multilevel submodule with integrated dual active bridges of the present invention, taking the full-bridge type as an example. Figure 2 , Figure 3 As shown, taking the full-bridge type as an example, the main power bridge arm in the modular multilevel converter functional unit is a full-bridge structure, including the first to fourth power switches S1, S2, S3, S4 and their anti-parallel diodes, and the DC support capacitor C. sm The two terminals of the full-bridge structure are connected in parallel across the DC input terminals; the two series midpoints of the full-bridge structure respectively constitute the high-voltage DC positive port (HVDC) of the submodule. P and high voltage DC negative port HVDC N .

[0033] The first power switch S1 and the second power switch S2 are connected in series, and the connection point is defined as the positive port of the high voltage DC (HVDC). P The third power switch S3 and the fourth power switch S4 are connected in series, and the connection point is defined as the negative port of the high-voltage DC (HVDC). N DC support capacitor C sm It is connected in parallel across the DC input (i.e., HVDC) terminals of the full bridge formed by the first to fourth power switches S1-S4. P With HVDC N (DC bus between).

[0034] Taking the half-bridge type as an example, the main power bridge arm in the modular multilevel converter functional unit is a half-bridge structure, including the first and second power switching transistors S1 and S2 and their anti-parallel diodes. The DC support capacitor Csm is connected in parallel across the DC input terminals of the half-bridge structure. The series midpoint of the half-bridge structure constitutes the high-voltage output port of the submodule.

[0035] The modular multilevel converter (MMC) functional unit serves as the interface between the submodule and the high-voltage DC bus or AC grid, realizing the voltage synthesis, waveform generation, and DC fault blocking functions required by the MMC system. DC support capacitor C sm Used for storing and buffering energy at the submodule level to maintain its port voltage V. sm Stability.

[0036] The working principle of the modular multilevel converter functional unit is as follows: by controlling the switching state combination of the first to fourth power switches S1-S4, the submodule can output a positive voltage (+V). sm (First power switch S1 and fourth power switch S4 are turned on), negative voltage (-V) sm The second power switch S2 and the third power switch S3 are turned on) or at zero voltage (the first power switch S1 and the second power switch S2 are turned on or the third power switch S3 and the fourth power switch S4 are turned on or in a bypass state), thereby synthesizing the required multi-level AC voltage waveform in the MMC bridge arm.

[0037] The integrated magnetic component is a high-frequency transformer model, which is the core of the integrated DAB function. This transformer model includes three key electrical parameters: turns ratio n:1, leakage inductance L connected in series in the primary circuit. k And the magnetizing inductance L connected in parallel across the primary winding of the transformer. m .

[0038] Magnetizing inductor L m Connected in parallel across the primary winding of the high-frequency transformer, allowing current to flow through the magnetizing inductance L m The current can be controlled by the integrated local controller to control the DC support capacitor C. sm It performs charging or discharging to achieve self-balancing of the capacitor voltage in the submodule.

[0039] Integrated magnetic components (high-frequency transformers) are used to achieve electrical isolation and voltage transformation between the high-voltage and low-voltage sides. Their leakage inductance L... k As the main inductive reactance for traditional DAB power transmission, its magnetizing inductance L... m It is a key component for realizing the innovative mechanism of magnetization energy reuse in this invention.

[0040] The voltage equalization algorithm model for magnetization energy reuse is: equalization current based on magnetization inductor current reuse. The average value can be approximated as: .

[0041] in, In one switching cycle Internally, the submodule support capacitor flows in (or flows out). The average equalization current. A positive value indicates that... Charging increases its voltage; negative values ​​indicate... Discharge to reduce its voltage. : Switching frequency of the integrated DAB section. The magnetizing inductance of an integrated high-frequency transformer. It is a core component for storing and transferring energy, and its magnitude determines the slope of the current change. During the zero voltage period ( At the start of the time period, the current flows through the magnetized inductor. The current change (peak value). This value is mainly determined by the phase shift angle of the previous power transfer phase. Determined by the port voltage, approximately: . The duty cycle of the zero-voltage state inserted into the square wave output voltage of the H-bridge on the primary (or secondary) side. This is a direct control variable, adjusted by... The magnitude and polarity (i.e., which pair of switches is turned on to generate a zero state) can precisely control the equalization current. The direction and size.

[0042] Equalizing current The average value formula establishes the zero voltage duty cycle of the control variable. With the generated equalization current The quantitative relationship between them. Through closed-loop adjustment. It can precisely control the capacitors of the submodules. The charging and discharging current, thereby achieving its voltage. Rapid and precise adjustment.

[0043] The working principle of integrated magnetic components is: transformers transfer energy through electromagnetic induction. Leakage inductance L k The rate of change of current is limited during power transfer, and its energy is exchanged during switching. Magnetized inductor L m The energy required to establish the transformer's magnetic field is stored. In this embodiment, by controlling the switching timing, the energy stored in the magnetizing inductor L is... m The energy in the capacitor can be reused for the DC support capacitor C. sm It can charge or discharge to achieve voltage self-balancing.

[0044] The primary-side H-bridge includes two power switches: the fifth power switch S5 and the sixth power switch S6, along with their anti-parallel diodes. Its input DC bus is directly drawn from the DC support capacitor C. sm The two ends of the circuit are connected. Its output end is connected to the two ends of the primary winding of the integrated magnetic component (high-frequency transformer).

[0045] The secondary-side H-bridge includes two power switches: the seventh power switch S7 and the eighth power switch S8, along with their anti-parallel diodes. Its input terminals are connected to the secondary winding of an integrated magnetic component (high-frequency transformer). Its output, after filtering, forms a stable low-voltage DC port (LV). DC + and LV DC -).

[0046] The dual active bridge functional unit (high-frequency H-bridge) is used to realize the internal switching from the high-voltage DC port C of the submodule. sm to low voltage DC port LV DC Controllable, bidirectional, isolated power transmission between them.

[0047] The instantaneous power transfer model for the dual active bridge DAB section is as follows: Under single-phase shift control, the instantaneous power transferred through the integrated DAB is... It can be described by the following formula: .in, : Turns ratio of a high-frequency transformer (secondary side / primary side). DC support capacitor for submodule The voltage at both ends. : Voltage of the low-voltage side DC port (LV_DC). : The switching frequency of the integrated DAB section, i.e. the operating frequency of the high-frequency H-bridge (S5-S8). The leakage inductance of a high-frequency transformer is the main inductive reactance for power transmission. The phase shift angle between the primary-side H-bridge output voltage square wave and the secondary-side H-bridge output voltage square wave ( ). This indicates that power flows from the primary side (high voltage side) to the secondary side (low voltage side). This indicates reverse flow.

[0048] Instantaneous power The formula describes the transmission power under given circuit parameters. With phase angle The nonlinear relationship between them is the theoretical basis for designing controllers and achieving precise power control.

[0049] The working principle of the dual active bridge functional unit is as follows: the primary-side H-bridge (the fifth power switch S5 and the sixth power switch S6) connects the DC support capacitor C sm The DC voltage at both ends is inverted into a high-frequency square wave voltage and applied to the primary side of the transformer. The secondary H-bridge (seventh power switch S7, eighth power switch S8) rectifies the high-frequency voltage on the secondary side of the transformer into a DC voltage. By controlling the phase shift angle (φ) between the primary and secondary square wave voltages, the leakage inductance L through the transformer can be precisely controlled. k The magnitude and direction of the transmitted power.

[0050] The integrated local controller is used to uniformly control all power switches (S1-S8) within the submodule. It receives power commands from the upper-level system controller and local voltage and current sampling signals, executes a dual phase-shift control algorithm, and generates PWM signals to drive all power switches (S1-S8).

[0051] The integrated local controller generates drive signals through a dual phase-shift control algorithm, which includes: According to power command P ref Calculate the basic phase shift angle φ0; According to the DC support capacitor C sm voltage V sm The deviation from the reference value is used to calculate the zero-voltage duty cycle D for voltage equalization. z And the correction amount Δφ for the phase shift angle; Calculate the phase shift angle φ = φ0 + Δφ and the zero-voltage duty cycle D acting on the dual active bridge functional unit. z .

[0052] The integrated local controller acts as the "brain" of the submodule, coordinating the MMC and DAB functions to perform integrated control of power transfer and voltage self-balancing.

[0053] The working principle of the integrated local controller is: the controller is based on the received power command P ref and the submodule capacitor voltage V detected in real time sm The dual phase-shift control algorithm is executed. This algorithm comprehensively calculates the basic phase shift angle φ0 required to achieve power transmission, as well as the phase shift angle for correcting V. sm The zero voltage duty cycle D required for the deviation z And the correction amount Δφ for the phase shift angle, ultimately generating a unified value containing φ and D. z The PWM signal of the information drives the power switching transistors S1-S8, enabling power transmission and voltage fine-tuning to be completed simultaneously within one switching cycle.

[0054] In some optional implementations of this embodiment, a specific example of a full-bridge integrated submodule is as follows: MMC Functional Unit: IGBTs are selected as power switching transistors S1-S4, with rated voltage and current chosen based on the system's high voltage level (e.g., ±10kV) and the submodule's power level (e.g., 50kW). DC support capacitor C sm Thin-film capacitors are selected, and their capacitance values ​​are calculated and determined based on voltage ripple requirements and system dynamic response requirements, for example, 2mF.

[0055] Integrated magnetic components: Design a high-frequency transformer. The core can be made of nanocrystalline or ferrite materials to reduce high-frequency losses. The turns ratio n:1 is based on the high-voltage side capacitor voltage V. sm (e.g., 1.6kV) and low-voltage side bus voltage V low (e.g., 750V) Determined, for example, n=2:1. Leakage inductance L k Designed in the tens of microhenries to meet power transfer characteristics. Magnetized inductor L m The design of the value is crucial. It needs to meet the excitation requirements of the transformer while taking into account the response speed of voltage balance and current stress, and is usually in the range of several hundred microhenries.

[0056] DAB functional units: S5-S8 use high-frequency performance MOSFETs or SiC MOSFETs. The DC input of the primary-side H-bridge (S5, S6) is directly connected to the C busbar. sm The outputs are led out at both ends. The outputs of the secondary-side H-bridge (S7, S8) are connected to an LC filter to form an LV. DC port.

[0057] Local controller: Implemented using a high-performance FPGA or dual-core DSP chip. Its ADC module samples V. sm Low-voltage side voltage V low And the primary current of the transformer. Calculate φ and D. z It outputs 8 isolated drive signals through the PWM module.

[0058] The beneficial effects of implementing this embodiment are: (1) High integration and structural innovation: The MMC sub-module and DAB are deeply integrated at the level of power devices and magnetic components, and the independent DAB converter unit is completely eliminated, which is a fundamental innovation in topology.

[0059] (2) It has extremely high power density and efficiency: the number of energy conversion links and discrete components is reduced, and the utilization rate of magnetic cores and semiconductor devices is maximized. It is expected that the overall power density can be increased by more than 30%, and the peak efficiency can be increased by 1-2 percentage points.

[0060] (3) It has inherent voltage self-balancing capability: By adopting the magnetization energy reuse mechanism, the sub-module can achieve fast and efficient distributed capacitor voltage balancing without the need for externally added complex active balancing circuits, which significantly enhances the system stability and dynamic response speed.

[0061] (4) Significant cost and reliability advantages: The total number of components is greatly reduced (approximately 30%-40% reduction in switching transistors and magnetic components), lowering material costs, assembly costs, and thermal management costs. Fewer connection points and a simpler structure directly improve the inherent reliability of the system (increased MTBF).

[0062] (5) Control simplification and modularization: The complex system-level equalization control is decentralized to the local sub-module, realizing a plug-and-play modular design, which greatly simplifies the system-level control logic and facilitates capacity expansion and maintenance.

[0063] (6) High application flexibility: This integrated sub-module can be used as a general building module and can be flexibly combined to form a high-performance solid-state transformer for various application scenarios such as medium and high voltage DC grids, AC distribution networks, energy storage integration, and ship DC power systems, and has a wide range of application prospects.

[0064] This invention can be used in a wide variety of general-purpose or special-purpose computer system environments or configurations. Examples include: personal computers, server computers, handheld or portable devices, tablet devices, multiprocessor systems, microprocessor-based systems, set-top boxes, programmable consumer electronics, network PCs, minicomputers, mainframe computers, and distributed computing environments including any of the above systems or devices. This invention can be described in the general context of computer-executable instructions, such as program modules, that are executed by a computer. Generally, program modules include routines, programs, objects, components, data structures, etc., that perform specific tasks or implement specific abstract data types. This invention can also be practiced in distributed computing environments where tasks are performed by remote processing devices connected via a communication network. In distributed computing environments, program modules can reside in local and remote computer storage media, including storage devices.

[0065] Example 2 This invention provides a solid-state transformer, comprising: At least one bridge arm, comprising multiple modular multilevel sub-modules of integrated dual active bridge as described in the embodiment, cascaded on the high-voltage side; the low-voltage DC ports of all modular multilevel sub-modules of integrated dual active bridge are electrically connected in parallel to form a common low-voltage DC bus. The system-level controller is used to issue power commands to the integrated local controller of each modular multilevel submodule with integrated dual active bridges.

[0066] The MMC converter valve section is formed by directly cascading multiple (e.g., N) modular multilevel submodules with integrated dual active bridges as described in Embodiment 1 on the high-voltage side, constituting one arm or phase unit of the three-phase MMC. The modular multilevel converter functional units of all submodules work together.

[0067] The low-voltage DC ports of all submodules LV DC The ± are directly connected in parallel electrically to form a stable and unified low-voltage DC common bus LV. Common_Bus ).

[0068] The system-level controller is responsible for monitoring the operating status of the entire solid-state transformer and issuing the overall power command P to the local controllers of each submodule. total And coordinate the power balance among the three phases.

[0069] The working principle of the MMC converter valve section is as follows: When acting as a rectifier (from AC to DC), cascaded sub-modules are switched on or off according to the MMC modulation algorithm (such as Nearest Level Approximation Modulation, NLM), synthesizing a sinusoidal voltage on the high-voltage AC side and absorbing active power from the grid. The absorbed energy is stored in its respective C0. sm In the middle, and raise its voltage V sm When used as an inverter (from DC to AC), the process is reversed, and the submodule will store the data in C. sm The energy in the system is released into the high-voltage AC power grid.

[0070] The integrated submodule (core energy transfer unit) allows the integrated DAB unit within each submodule to operate independently and in parallel, regardless of whether the MMC converter valve section is operating in rectification or inversion mode.

[0071] The power transfer principle is: the system-level controller determines the total power demand P based on the total power demand P. total This is then broken down and allocated to the local controllers of each submodule (e.g., evenly distributed). Each local controller, based on the received power command P... ref By controlling the phase shift angle φ of the internal DAB, a specified share of energy is transferred from its own high-voltage side capacitor C. sm It is transmitted to the low-voltage DC common bus via a high-frequency transformer.

[0072] In some optional implementations of this embodiment, the back-end energy interface connected to the low-voltage DC common bus may further include: DC load / energy storage system: such as battery energy storage unit, can be directly connected to the DC bus to obtain or store electrical energy directly from the stable low-voltage DC bus; Inverter unit: One or more voltage source inverters convert electrical energy on the low-voltage DC bus into AC power of the required frequency and amplitude (power frequency or variable frequency) to power AC loads.

[0073] The high-voltage side port of the solid-state transformer is used to connect to the medium- and high-voltage AC power grid or the high-voltage DC power grid. The modular multilevel converter functional unit, which controls the cascaded integrated dual active bridge modular multilevel sub-module, operates in rectification or inversion mode to realize AC-DC conversion or DC voltage support.

[0074] Self-balancing refers to adjusting the zero-voltage duty cycle D through an integrated local controller. z Reused magnetized inductor L m The energy stored in the DC support capacitor Csm This is achieved through charging and discharging.

[0075] The principle of voltage self-balancing is: This is the key to this embodiment, where the local controller of each submodule continuously monitors its own capacitor voltage V. sm If the V of a certain submodule sm If the value is higher than the reference value (such as the average value), the controller will adjust the zero-voltage duty cycle D. z , so that the stored in the magnetized inductor L m The current in the medium flows back to C during periods such as zero voltage periods. sm Discharge it to reduce V sm Conversely, if V sm If it's too low, then control D. z Make L m The current in C sm Absorb energy, recharge it, and enhance V sm This process is distributed and autonomous, requiring no additional communication between submodules, and achieves fast and efficient capacitor voltage self-balancing.

[0076] The low-voltage DC common bus receives energy from all submodules, forming a voltage-stable, power-converging DC platform. Its voltage is supported by all parallel DAB secondary sides.

[0077] The working principle of the solid-state transformer in this embodiment is as follows: The electrical energy on the high-voltage side (medium-voltage AC or high-voltage DC) is first processed (rectified or inverted) by the modular multilevel converter functional units of the cascaded integrated submodules. The electrical energy is stored in the form of voltage in the capacitors C of each submodule. sm In the middle. Under the unified scheduling of the system-level controller, each submodule, through its internal integrated DAB unit, stores the data stored in C. sm The energy in the circuit is transmitted in parallel and isolated to a shared low-voltage DC bus according to a specified power share. During this process, each submodule utilizes the magnetized energy reuse mechanism proposed in this embodiment to automatically maintain the balance of its own capacitor voltage. The electrical energy on the low-voltage DC bus can be directly supplied to DC loads / energy storage, or converted into AC power by an inverter to supply AC loads, thus fully realizing the voltage transformation, isolation, and energy distribution functions of the solid-state transformer. When energy flows in the reverse direction, the process is completely reversible.

[0078] Figure 4 This is a typical application topology diagram of a solid-state transformer (SST) constructed from the modular multilevel submodule with integrated dual active bridges of this invention. For example... Figure 4 As shown, in some optional implementations of this embodiment, an example of a solid-state transformer for converting medium-voltage AC (10kV) to low-voltage DC (750V) / AC (400V) is as follows: For a three-phase system, each phase arm is composed of 50 integrated sub-modules as described in Example 1, requiring a total of 150 sub-modules.

[0079] LV of all 150 sub-modules DC + and LV DC - The ports are connected in parallel to two common copper busbars to form LV Common_Bus (750V).

[0080] The system-level central controller uses an industrial PC or a high-performance multi-core processor and communicates with the local controllers of each submodule via optical fiber to issue total power commands and receive status information.

[0081] In LV Common_Bus The system is connected to a lithium battery energy storage system (rated voltage 750V) and a three-phase full-bridge voltage source inverter. The inverter output is then filtered and connected to a 400V AC load.

[0082] The solid-state transformer in this embodiment operates as follows: When the 10kV grid supplies power to the 400V load, the MMC valve section operates in rectification mode, absorbing active power from the grid. The central controller calculates the total power P based on the load demand. total And distribute them equally among the sub-modules (P ref = P total / 150). Each submodule runs simultaneously: a) The MMC section is input / output based on the modulation wave; b) The DAB section transmits P at a phase shift angle φ. ref A portion of the power is transferred to the low-voltage bus; c) The local controller monitors its own V sm And by adjusting D z This keeps the voltage near a reference value (e.g., 1.6kV). The electrical energy on the low-voltage bus is converted by the inverter into 400V / 50Hz AC power to supply the load. Any remaining energy can be stored in the battery. The entire process is bidirectionally controllable in terms of energy and automatically balances the voltage.

[0083] The beneficial effects of implementing this embodiment are: (1) High integration and structural innovation: The MMC sub-module and DAB are deeply integrated at the level of power devices and magnetic components, and the independent DAB converter unit is completely eliminated, which is a fundamental innovation in topology.

[0084] (2) It has extremely high power density and efficiency: the number of energy conversion links and discrete components is reduced, and the utilization rate of magnetic cores and semiconductor devices is maximized. It is expected that the overall power density can be increased by more than 30%, and the peak efficiency can be increased by 1-2 percentage points.

[0085] (3) It has inherent voltage self-balancing capability: By adopting the magnetization energy reuse mechanism, the sub-module can achieve fast and efficient distributed capacitor voltage balancing without the need for externally added complex active balancing circuits, which significantly enhances the system stability and dynamic response speed.

[0086] (4) Significant cost and reliability advantages: The total number of components is greatly reduced (approximately 30%-40% reduction in switching transistors and magnetic components), lowering material costs, assembly costs, and thermal management costs. Fewer connection points and a simpler structure directly improve the inherent reliability of the system (increased MTBF).

[0087] (5) Control simplification and modularization: The complex system-level equalization control is decentralized to the local sub-module, realizing a plug-and-play modular design, which greatly simplifies the system-level control logic and facilitates capacity expansion and maintenance.

[0088] (6) High application flexibility: This integrated sub-module can be used as a general building module and can be flexibly combined to form a high-performance solid-state transformer for various application scenarios such as medium and high voltage DC grids, AC distribution networks, energy storage integration, and ship DC power systems, and has a wide range of application prospects.

[0089] Through the above description of the embodiments, those skilled in the art can clearly understand that the methods of the above embodiments can be implemented by means of software plus necessary general-purpose hardware platforms. Of course, they can also be implemented by hardware, but in many cases the former is a better implementation method. Based on this understanding, the technical solution of the present invention, or the part that contributes to the prior art, can be embodied in the form of a software product. This computer software product is stored in a storage medium (such as ROM / RAM, magnetic disk, optical disk) and includes several instructions to cause a terminal device (which may be a mobile phone, computer, server, air conditioner, or network device, etc.) to execute the methods of the various embodiments of the present invention.

[0090] Obviously, the embodiments described above are merely some embodiments of the present invention, not all embodiments. The accompanying drawings show preferred embodiments of the present invention, but do not limit the patent scope of the present invention. The present invention can be implemented in many different forms; rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing specific embodiments, or make equivalent substitutions for some of the technical features. Any equivalent structures made using the content of this specification and drawings, directly or indirectly applied to other related technical fields, are similarly within the patent protection scope of this invention.

Claims

1. A modular multilevel submodule integrating dual active bridges, characterized in that, include: The modular multilevel converter functional unit, integrated magnetic components, dual active bridge functional unit, and integrated local controller are connected sequentially via electrical connections. The modular multilevel converter functional unit includes a main power bridge arm and a DC support capacitor C. sm It is used to connect to high-voltage DC or AC busbars to achieve voltage synthesis and energy buffering; The integrated magnetic component includes a leakage inductance L. k and magnetizing inductor L m High-frequency transformers are used for electrical isolation and voltage transformation; The dual active bridge functional unit includes a primary-side high-frequency H-bridge and a secondary-side high-frequency H-bridge, with the input terminal of the primary-side high-frequency H-bridge connected to the DC support capacitor C. sm The output end is connected to the primary side of the high-frequency transformer; the input end of the secondary high-frequency H-bridge is connected to the secondary side of the high-frequency transformer, and the output end forms a low-voltage DC port. The integrated local controller connects to and controls the power switching transistors in the modular multilevel converter functional unit and the dual active bridge functional unit to achieve integrated control of power transmission and capacitor voltage self-balancing.

2. The modular multilevel submodule with integrated dual active bridges according to claim 1, characterized in that, The main power bridge arm of the modular multilevel converter functional unit is a full-bridge structure, including the first to fourth power switches S1, S2, S3, S4 and their anti-parallel diodes, and the DC support capacitor C. sm The two terminals of the full-bridge structure are connected in parallel across the DC input terminals; the two series midpoints of the full-bridge structure respectively constitute the high-voltage DC positive port (HVDC) of the submodule. P and high voltage DC negative port HVDC N .

3. The modular multilevel submodule with integrated dual active bridges according to claim 1, characterized in that, The main power bridge arm of the modular multilevel converter functional unit is a half-bridge structure, including first and second power switches S1 and S2 and their anti-parallel diodes. The DC support capacitor Csm is connected in parallel across the DC input terminals of the half-bridge structure. The series midpoint of the half-bridge structure constitutes the high-voltage output port of the submodule.

4. The modular multilevel submodule with integrated dual active bridges according to claim 1, characterized in that, The magnetizing inductor L m Connected in parallel across the primary winding of the high-frequency transformer, so that current flows through the magnetizing inductor L m The current can be controlled by the integrated local controller to supply the DC support capacitor C. sm It performs charging or discharging to achieve self-balancing of the capacitor voltage in the submodule.

5. The modular multilevel submodule with integrated dual active bridges according to claim 1, characterized in that, The integrated local controller generates drive signals through a dual phase-shift control algorithm, which includes: According to power command P ref Calculate the basic phase shift angle φ0; According to the DC support capacitor C sm voltage V sm The deviation from the reference value is used to calculate the zero-voltage duty cycle D for voltage equalization. z And the correction amount Δφ for the phase shift angle; Calculate the phase shift angle φ = φ0 + Δφ and the zero-voltage duty cycle D acting on the dual active bridge functional unit. z .

6. A solid-state transformer, characterized in that, include: At least one bridge arm, the bridge arm comprising multiple modular multilevel sub-modules of the integrated dual active bridge as described in any one of claims 1 to 5 cascaded on the high-voltage side; the low-voltage DC ports of all the modular multilevel sub-modules of the integrated dual active bridge are electrically connected in parallel to form a common low-voltage DC bus. A system-level controller is used to issue power commands to the integrated local controller of each of the modular multilevel submodules with integrated dual active bridges.

7. The solid-state transformer according to claim 6, characterized in that, It also includes DC loads or energy storage systems connected to the common low-voltage DC bus.

8. The solid-state transformer according to claim 6, characterized in that, It also includes an inverter unit connected to the common low-voltage DC bus for converting DC power into AC power to supply AC loads.

9. The solid-state transformer according to claim 6, characterized in that, The high-voltage side port of the solid-state transformer is used to connect to a medium- or high-voltage AC power grid or a high-voltage DC power grid. By controlling the modular multilevel converter functional unit of the cascaded integrated dual active bridge modular multilevel submodule to operate in rectification or inversion mode, AC-DC conversion or DC voltage support is achieved.

10. The solid-state transformer according to claim 6, characterized in that, The capacitor voltage self-balancing process of each integrated dual active bridge modular multilevel submodule is distributed and autonomous; self-balancing refers to adjusting the zero-voltage duty cycle D through an integrated local controller. z Reused magnetized inductor L m The energy stored in the DC support capacitor C sm This is achieved through charging and discharging.

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