Multi-scenario solid state transformer system

Abstract

The invention discloses a multi-scene solid-state transformer system which comprises a modular multilevel converter, a high-frequency transformer, a capacitor voltage balance control module, a bidirectional power flow control module and a harmonic suppression module. The modularized multi-level converter module adopts a SiC MOSFET (Metal-Oxide-Semiconductor Field Effect Transistor) sub-module cascade structure, and generates high-frequency alternating current through mixed modulation of a three-phase bridge arm and PWM / NLM (Pulse Width Modulation / Non-Local The high-frequency transformer adopts a nanocrystalline magnetic core and a litz wire winding to realize electrical isolation and voltage conversion; the capacitor voltage balance control module optimizes a sub-module switching time sequence through a distributed architecture and a dynamic weight sorting algorithm in combination with three parameters of voltage, temperature and service life. According to the system, through the modular design and the high-frequency technology, the technical problems that a traditional transformer is large in size, complex in harmonic suppression and poor in voltage adaptability are solved while the high power density is kept, and the limitation that a traditional system only supports one-way power transmission is broken through.

Description

Technical Field

[0001] The present invention relates to the field of power electronic conversion applications, and in particular to a multi-scenario solid-state transformer system. Background Art

[0002] In the field of power electronics conversion technology, traditional power conversion systems have long faced technical bottlenecks in medium-, high-voltage, and high-power applications. Existing power conversion devices generally utilize a combination of power-frequency transformers and centralized power devices, transferring energy through low-frequency switching devices and supplemented by passive filtering components to suppress harmonics. While these systems meet basic requirements in scenarios such as industrial power distribution and grid interconnection, their technical limitations are becoming increasingly prominent as power-consuming equipment continues to demand higher power density, bidirectional interaction, and adaptability to multiple scenarios.

[0003] The structural defects of common transformer systems are concentrated in three aspects: its core power conversion unit relies on a single high-power switching device, which needs to be connected in series or parallel to improve its voltage / current carrying capacity, resulting in the device switching loss increasing exponentially with the power level. At the same time, the industrial frequency transformer is large in size and heavy, which restricts the system power density; the traditional two-level or three-level topology outputs high step wave harmonic content, which requires a large passive filter to compensate, increasing the system complexity and introducing additional losses; voltage level adjustment needs to be achieved by switching transformer taps or replacing power modules, which cannot flexibly adapt to the needs of different grid levels. In particular, in scenarios such as new energy grid connection, it exposes obvious lack of adaptability and cannot meet the working requirements of power electronic conversion applications. For this reason, a multi-scenario solid-state transformer system is proposed. Summary of the Invention

[0004] The present invention provides the following technical solution: a multi-scenario solid-state transformer system, comprising: A modular multilevel converter module, a high-frequency transformer module, a capacitor voltage balancing control module, a bidirectional power flow control module, and a harmonic suppression module. The modular multilevel converter module is composed of at least three cascaded groups of identical submodules, each of which contains a SiC MOSFET power switch device, an energy storage capacitor, an anti-parallel diode, and a control circuit. The modular multilevel converter module is connected to an external circuit via a three-phase bridge arm structure, with each phase containing two bridge arms, each of which is composed of at least three groups of submodules connected in series. The bridge arms are used to control the switching timing of the submodules through PWM and the nearest level modulation to generate a high-frequency AC waveform. A high-frequency transformer module, configured to achieve voltage conversion and electrical isolation, wherein the primary side of the high-frequency transformer module is electrically connected to the output of the modular multilevel converter module, and the secondary side of the high-frequency transformer module is connected to the target load via another set of modular multilevel converter modules and a rectifier circuit, for converting high-frequency alternating current into electrical energy at a target voltage level; A capacitor voltage balancing control module, configured to dynamically adjust the order in which submodules are put into operation through a sorting algorithm to ensure that the capacitor voltages of all submodules are consistent. The capacitor voltage balancing control module is connected to the control circuit of the modular multi-level converter module via a data bus; A bidirectional power flow control module, integrated into the control circuit of the modular multilevel converter module, configured to achieve bidirectional energy flow by adjusting the switching timing of the submodules and the energy transfer direction of the high-frequency transformer module; The harmonic suppression module is used to reduce the harmonic content in the output voltage waveform through multi-level output technology and reduce the dependence on external filters. The harmonic suppression module is connected to the output end of the modular multi-level converter module through a filtering circuit.

[0005] Preferably, the SiC MOSFET power switching devices of each sub-module in the modular multi-level converter module are all configured in parallel with redundancy, and multiple tubes are connected in parallel for current sharing through a driving circuit. The energy storage capacitor adopts a mixed configuration of film capacitors and electrolytic capacitors. The film capacitors are used for high-frequency ripple absorption, and the electrolytic capacitors are used for low-frequency energy buffering. The film capacitors and electrolytic capacitors are connected in parallel through a non-inductive bus. The anti-parallel diodes are fast recovery diodes, and the anti-parallel diodes are connected in anti-parallel with the SiC MOSFET to form a bidirectional current path. The control circuit has integrated overvoltage protection, overcurrent protection and temperature monitoring functions, and communicates with the main control system through optical fiber.

[0006] Preferably, the high-frequency transformer module adopts nanocrystalline magnetic core material, the cross-section of the magnetic core material is designed to be a multi-air gap structure, the winding of the high-frequency transformer module adopts a multi-layer winding process of Litz wire, and an insulating heat sink is arranged between each layer. The primary side and secondary side windings of the high-frequency transformer module are isolated by an electrostatic shielding layer.

[0007] Preferably, the capacitor voltage balancing control module adopts a distributed architecture and sorting algorithm. Each bridge arm of the capacitor voltage balancing control module is configured with an independent control unit. The control unit communicates with the main controller through the CAN bus. The sorting algorithm is based on a dynamic weight allocation mechanism and combines the capacitor voltage, temperature and switching times of the sub-module to generate a priority queue.

[0008] Preferably, a hierarchical control strategy is provided inside the bidirectional power flow control module, wherein the upper layer of the hierarchical control strategy is a power instruction parsing layer, which is used to generate active power, reactive power and harmonic compensation reference values ​​according to external instructions; the middle layer of the hierarchical control strategy is a modulation strategy selection layer, which is used to automatically switch between PWM and NLM modulation modes according to the system operation mode, and adopt carrier phase shift modulation to reduce switching loss in forward power flow, and adopt space vector modulation to optimize harmonic performance in reverse power flow; the lower layer of the hierarchical control strategy is a drive signal generation layer, and is provided with dead time compensation and drive pulse shaping technology.

[0009] Preferably, the harmonic suppression module adopts a multi-stage filtering structure, the first stage of the multi-stage filtering structure is a passive LC filter, which attenuates the integer multiple harmonics of the switching frequency, the second stage of the multi-stage filtering structure is an active power filter, which detects the load harmonic current in real time through a current sensor, generates a reverse compensation signal and injects it into the system, and the third stage of the multi-stage filtering structure is a digital filtering algorithm, which performs software elimination of residual harmonics by embedding a moving average filter and a notch filter in the control circuit.

[0010] Preferably, the three-phase bridge arm structure of the modular multilevel converter module adopts a symmetrical layout, the number of sub-modules in the upper and lower bridge arms of each phase of the three-phase bridge arm structure is equal, and they are connected to the external circuit through a star connection. The inductance of the bridge arm adopts a mixed design of ferrite core and hollow coil. The ferrite core is used to suppress high-frequency circulating current, and the hollow coil is used to limit short-circuit current. A cross-capacitor is set between the bridge arms, and an RC buffer circuit is used to absorb voltage spikes during the switching process.

[0011] Preferably, the capacitor voltage balancing control module and the bidirectional power flow control module realize data interaction through shared memory, and the bidirectional power flow control module dynamically adjusts the voltage balancing strategy according to the bidirectional power flow demand, that is, during forward power flow, the bidirectional power flow control module prioritizes output voltage stability and realizes voltage fine-tuning by fine-tuning the number of sub-modules input, while during reverse power flow, the bidirectional power flow control module switches to current source mode and realizes output current control by adjusting the sub-module capacitor voltage.

[0012] Preferably, the modular multi-level converter module is internally configured with a dynamic expansion interface, which includes a programmable logic gate array coordination unit and a standardized power module slot. The high-frequency transformer module is built with an intelligent sensor array, which includes a distributed optical fiber temperature sensor and an ultrasonic guided wave sensor. The distributed optical fiber temperature sensor is used to monitor the temperature distribution of the winding hot spot in real time, and the ultrasonic guided wave sensor is used to detect the mechanical vibration state of the iron core.

[0013] Preferably, a loosely coupled coil is additionally provided on the secondary side of the high-frequency transformer module. The loosely coupled coil adopts a flattened spiral structure, and the surface of the loosely coupled coil is covered with a ferrite shielding layer.

[0014] In summary, compared with the prior art, the present invention provides a multi-scenario solid-state transformer system with the following beneficial effects: 1. The modular multilevel converter module of the present invention utilizes SiC MOSFET power switching devices, combined with an integrated design of a high-frequency transformer module, to improve the system's power density and energy conversion efficiency. The high-frequency switching characteristics of the SiC device reduce switching losses, while the high-frequency transformer is significantly smaller than traditional power-frequency transformers, thus resolving the bulky issue of conventional systems. Furthermore, by integrating a bidirectional power flow control module into the control circuit of the modular multilevel converter module and adjusting the submodule switching timing and the energy transfer direction of the high-frequency transformer, bidirectional energy flow is achieved. This overcomes the limitation of conventional systems that only support unidirectional power transmission and meets the bidirectional power flow requirements of scenarios such as grid interconnection and energy storage systems. 2. The harmonic suppression module added in the present invention uses the multi-level output technology of the modular multi-level converter module to make the output voltage waveform close to a sine wave, effectively reducing the harmonic content. The multi-level output characteristic generates a stepped voltage through the cascade of sub-modules, which naturally reduces the low-order harmonic components. In conjunction with the auxiliary filtering circuit, it can meet the power quality requirements without the need for traditional large filters. This not only simplifies the system structure and reduces the filter cost, but also avoids the additional losses caused by large filters, thereby improving the reliability and cost-effectiveness of the system operation. 3. By adding modular multilevel converter modules and adopting a three-phase bridge arm structure with cascaded submodules, the present invention allows the number of submodules in the bridge arm to be adjusted to flexibly expand the voltage level. When adapting to higher voltage scenarios, more submodules can be connected in series in the bridge arm, each submodule sharing the voltage stress while maintaining the output waveform quality through PWM and nearest level modulation strategies. Conversely, reducing the number of submodules can adapt to low voltage scenarios. This modular design enables the system to adaptively adjust at different voltage levels of the grid hierarchy, meeting the voltage adaptation requirements of multiple scenarios such as industrial power supply and renewable energy grid connection, significantly improving the system's application flexibility. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a schematic diagram of the system structure of the present invention. DETAILED DESCRIPTION

[0016] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0017] See also Figure 1 The present invention provides a technical solution, a multi-scenario solid-state transformer system, comprising: A modular multi-level converter module, a high-frequency transformer module, a capacitor voltage balancing control module, a bidirectional power flow control module, and a harmonic suppression module. The modular multi-level converter module is composed of at least three groups of identical sub-modules in cascade, each of which contains a SiC MOSFET power switch device, an energy storage capacitor, an anti-parallel diode, and a control circuit. The modular multi-level converter module is connected to the external circuit through a three-phase bridge arm structure, and each phase contains two bridge arms. The bridge arms are composed of at least three groups of sub-modules in series, which are used to control the switching timing of the sub-modules through PWM and the nearest level modulation to generate a high-frequency AC waveform. The SiC MOSFET power switch device of each sub-module in the modular multi-level converter module adopts a parallel redundant setting, and multiple tubes are connected in parallel for current sharing through a drive circuit. The energy storage capacitor adopts a mixed configuration of film capacitors and electrolytic capacitors. The film capacitor is used for high-frequency ripple absorption, and the electrolytic capacitor is used for low-frequency energy buffering. The film capacitor and the electrolytic capacitor are connected in parallel through a non-inductive bus. The anti-parallel diode is a fast recovery diode. The anti-parallel diode and the SiC MOSFETs are connected in reverse parallel to form a bidirectional current path. The control circuit integrates overvoltage protection, overcurrent protection, and temperature monitoring functions and communicates with the main control system via optical fiber. The three-phase bridge arm structure of the modular multilevel converter module adopts a symmetrical layout. The upper and lower bridge arms of each phase of the three-phase bridge arm structure have an equal number of sub-modules and are connected to the external circuit via a star connection. The inductance of the bridge arm adopts a hybrid design of ferrite core and air-core coil. The ferrite core is used to suppress high-frequency circulating current, and the air-core coil is used to limit short-circuit current. A cross-capacitor is provided between the bridge arms, and an RC snubber circuit is used to absorb voltage spikes during the switching process. The modular multilevel converter module is equipped with a dynamic expansion interface, which includes a programmable logic gate array (PLGAM) coordination unit and standardized power module slots. The high-frequency transformer module is equipped with a built-in intelligent sensor array, which includes distributed fiber-optic temperature sensors and ultrasonic guided wave sensors. The distributed fiber-optic temperature sensors monitor the temperature distribution of winding hotspots in real time, while the ultrasonic guided wave sensors detect the mechanical vibration of the core. The modular multilevel converter module's dynamic expansion interface achieves flexible expansion through the coordinated operation of the standardized power module slots and the PGA coordination unit. When the system needs to increase power levels, operators can directly insert prefabricated standardized power modules into the slots. Each module includes a complete SiC MOSFET switch array, a thin-film-electrolytic hybrid energy storage unit, and driver protection circuits. The PGA coordination unit automatically identifies the encoding information of the newly added module via the bus, updates the system topology in real time, and dynamically adjusts the PWM carrier phase shift angle and the number of submodules. This plug-and-play expansion method does not interrupt system operation. In industrial power grid expansion scenarios, the power level can be increased within 30 minutes, improving efficiency by 80% compared to traditional transformer retrofits. The standardized interface design ensures electrical and mechanical compatibility between modules from different batches, avoiding current sharing issues caused by device parameter differences. It also supports the intermixing of modules from different manufacturers, fostering an open power electronics ecosystem. The high-frequency transformer module's intelligent sensor array utilizes distributed fiber-optic temperature sensors and ultrasonic guided wave sensors for status awareness. The fiber-optic sensors are arranged in a spiral pattern along the winding axis, capturing the temperature distribution using the backscattering effect of laser light within the fiber. Temperature measurement points are set every 10 cm to produce a three-dimensional thermal image. When abnormally high temperatures are detected in a specific area, the system can pinpoint the specific winding section and initiate forced air cooling or reduce the current density in that area. Ultrasonic guided wave sensors, attached to the transformer core surface, transmit 50-500 kHz elastic waves, receive the reflected signals, and analyze the wave packet attenuation and spectral characteristics to detect cracks as small as 0.1 mm and deformations as small as 0.5 microns. This technology boasts two orders of magnitude higher sensitivity than traditional vibration sensors, providing 12 hours of advance warning of core loosening. The dual sensor data is integrated and processed by the edge computing chip to build a digital twin model, mapping the physical status of the transformer in real time. In key scenarios such as data center power supply, the equipment maintenance method is transformed from regular inspection to predictive maintenance. A high-frequency transformer module is used to achieve voltage conversion and electrical isolation. The primary side of the high-frequency transformer module is connected to the output end of the modular multi-level converter module through an electrical connection. The secondary side of the high-frequency transformer module is connected to the target load through another set of modular multi-level converter modules and a rectifier circuit, and is used to convert high-frequency alternating current into electrical energy of a target voltage level. The high-frequency transformer module uses nanocrystalline magnetic core material, and the cross-section of the magnetic core material is designed to have a multi-air gap structure. The winding of the high-frequency transformer module adopts a multi-layer winding process of Litz wire, and an insulating heat sink is provided between each layer. The primary and secondary windings of the high-frequency transformer module are isolated by an electrostatic shielding layer. A loosely coupled coil is added to the secondary side of the high-frequency transformer module. The loosely coupled coil adopts a flattened spiral structure, and the surface of the loosely coupled coil is covered with a ferrite shielding layer. The implementation process of the high-frequency transformer module integrates the collaborative innovation of materials science and electromagnetic technology. During the core fabrication process, nanocrystalline alloy is used as the substrate. Amorphous thin ribbons are formed through a single-roll melt-quenching process, followed by crystallization annealing. Laser cutting is used during core cross-section processing to create multiple micron-scale air gaps. The air gap spacing is optimized through electromagnetic field simulation to ensure uniform magnetic resistance distribution. This multi-air-gap structure effectively blocks high-frequency eddy current paths while maintaining high magnetic permeability. The winding is made using fully automatic Litz wire stranding equipment, which twists 7 strands of 0.1mm diameter enameled wire into a bundle to form a composite conductor that resists the skin effect. The winding process uses a segmented three-dimensional winding method: the primary winding is arranged in three layers, with ceramic silicone rubber heat sinks embedded between each layer. The heat sink surface is machined with honeycomb-shaped heat-conducting grooves and uses a nanofluid cooling medium. The secondary winding adopts a loosely coupled design, and the Litz wire is flattened into a flat spiral structure by a CNC winding machine. A high-thermal-conductivity insulating film is applied between the layers. Electromagnetic isolation is achieved through a triple protection mechanism: a copper foil electrostatic shielding layer is inserted between the primary and secondary windings, and the edges of the shielding layer are folded and overlapped to form a Faraday cage effect. The winding lead wire adopts a coaxial shielding structure, with the inner conductor transmitting electrical energy and the outer braided mesh suppressing spatial radiation. A ferrite magnetic coating is sprayed on the surface of the loosely coupled coil, and magnetic field orientation technology is used to close the leakage flux along the shielding layer, reducing axial electromagnetic interference. The capacitor voltage balancing control module is used to dynamically adjust the order in which submodules are put into operation through a sorting algorithm to ensure that the capacitor voltages of all submodules are consistent. The capacitor voltage balancing control module is connected to the control circuit of the modular multilevel converter module via a data bus. The capacitor voltage balancing control module adopts a distributed architecture and a sorting algorithm. Each bridge arm of the capacitor voltage balancing control module is equipped with an independent control unit, which communicates with the main controller via the CAN bus. The sorting algorithm is based on a dynamic weight allocation mechanism and combines the capacitor voltage, temperature, and switching times of the submodule to generate a priority queue. The capacitor voltage balancing control module achieves precise balancing of the capacitor voltages of the submodules through a distributed architecture and a dynamic weight sorting algorithm. At the hardware deployment level, each bridge arm is equipped with an independent control unit. These units adopt a modular design, with a built-in microprocessor and dual-port RAM memory, and establish a redundant communication link with the main controller via the CAN bus. When the system is powered on, each control unit first performs a self-test, reading the capacitor voltage sample values, NTC thermistor resistance values, and IGBT switching count register data from the bridge arm submodules via the SPI interface. This raw information is then packaged into a timestamped data frame. At the algorithm execution level, the dynamic weight allocation mechanism employs a three-tier decision-making model: the first tier is the voltage balancing layer, which uses the deviation of the capacitor voltage from the mean as the base weight. A weight compensation coefficient is triggered when the deviation exceeds a threshold. The second tier is the temperature regulation layer, which establishes a thermal stress model based on the submodule temperature sensor data and applies a weight attenuation factor to high-temperature modules to prevent life degradation caused by local overheating. The third tier is the life balancing layer, which constructs an aging assessment function based on the cumulative switching count and increases the weight of frequently switched submodules. The three weights are weighted and combined using a fuzzy logic controller to generate a sorted queue with 32 levels of priority. The control unit generates submodule switching instructions based on this priority queue, using an improved bubble sort algorithm that compares the states of only adjacent priority modules at a time, reducing computational resource usage. At the boundary of the PWM cycle, a drive signal is sent to the bridge arm submodule via a parallel bus to ensure that voltage balancing is strictly synchronized with the power conversion sequence. When a change in the system power flow direction is detected, the control unit automatically switches the voltage balancing target, focusing on output voltage stability during forward transmission and prioritizing current ripple suppression during reverse feedback. The capacitor voltage balancing control module and the bidirectional power flow control module implement data exchange through shared memory. The bidirectional power flow control module dynamically adjusts the voltage balancing strategy based on the bidirectional power flow demand. That is, during forward power flow, the bidirectional power flow control module prioritizes output voltage stability and achieves voltage fine-tuning by fine-tuning the number of submodules. During reverse power flow, the bidirectional power flow control module switches to current source mode and controls the output current by adjusting the submodule capacitor voltage. a bidirectional power flow control module, integrated into the control circuit of the modular multilevel converter module, configured to achieve bidirectional energy flow by adjusting the switching timing of the submodules and the energy transfer direction of the high-frequency transformer module. A hierarchical control strategy is internally provided within the bidirectional power flow control module. The upper layer of the hierarchical control strategy is a power instruction parsing layer, configured to generate active power, reactive power, and harmonic compensation reference values ​​based on external instructions. The middle layer of the hierarchical control strategy is a modulation strategy selection layer, configured to automatically switch between PWM and NLM modulation modes based on the system operating mode, and to use carrier phase shift modulation to reduce switching losses during forward power flow and space vector modulation to optimize harmonic performance during reverse power flow. The lower layer of the hierarchical control strategy is a drive signal generation layer, configured with dead time compensation and drive pulse shaping technology; The harmonic suppression module is used to reduce the harmonic content in the output voltage waveform through multi-level output technology and reduce dependence on external filters. The harmonic suppression module is connected to the output end of the modular multi-level converter module through a filtering circuit. The harmonic suppression module adopts a multi-stage filtering structure. The first stage of the multi-stage filtering structure is a passive LC filter, which attenuates harmonics that are integer multiples of the switching frequency. The second stage of the multi-stage filtering structure is an active power filter, which detects the load harmonic current in real time through a current sensor and generates a reverse compensation signal to be injected into the system. The third stage of the multi-stage filtering structure is a digital filtering algorithm, which performs software elimination of residual harmonics by embedding a moving average filter and a notch filter in the control circuit.

[0018] This solution utilizes modular multilevel converter modules and SiC MOSFET power switching devices, combined with the integrated design of high-frequency transformer modules, to improve the system's power density and energy conversion efficiency. The high-frequency switching characteristics of SiC devices also reduce switching losses, while the high-frequency transformer is significantly smaller than traditional industrial frequency transformers, thus resolving the issue of bulky traditional systems. Furthermore, by integrating a bidirectional power flow control module into the control circuit of the modular multilevel converter module and adjusting the switching timing of the submodules with the energy transfer direction of the high-frequency transformer, bidirectional energy flow is achieved. This overcomes the limitation of traditional systems that only support unidirectional power transmission and meets the requirements for bidirectional power flow in scenarios such as grid interconnection and energy storage systems.

[0019] The harmonic suppression module added to this solution uses the multi-level output technology of the modular multi-level converter module to make the output voltage waveform close to a sine wave, effectively reducing the harmonic content. The multi-level output characteristic generates a stepped voltage through the cascade of sub-modules, which naturally reduces the low-order harmonic components. Combined with the auxiliary filtering circuit, it can meet the power quality requirements without the need for traditional large filters. This not only simplifies the system structure and reduces the filter cost, but also avoids the additional loss caused by large filters, thereby improving the reliability and economy of system operation.

[0020] This solution adds modular multilevel converter modules and adopts a three-phase bridge arm structure with cascaded submodules. This allows the number of submodules in the adjustable bridge arm to flexibly expand the voltage level. When adapting to higher voltage scenarios, more submodules can be connected in series in the bridge arm, each submodule sharing the voltage stress while maintaining the output waveform quality through PWM and nearest-level modulation strategies. Conversely, reducing the number of submodules can adapt to low-voltage scenarios. This modular design enables the system to adaptively adjust within the grid hierarchy at different voltage levels, meeting the voltage adaptation requirements of multiple scenarios such as industrial power supply and renewable energy grid connection, significantly improving the system's application flexibility.

[0021] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that includes a list of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus.

[0022] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. Multi-scenario solid-state transformer system, characterized by: include: A modular multilevel converter module, a high-frequency transformer module, a capacitor voltage balancing control module, a bidirectional power flow control module, and a harmonic suppression module. The modular multilevel converter module is composed of at least three cascaded groups of identical submodules, each of which contains a SiC MOSFET power switch device, an energy storage capacitor, an anti-parallel diode, and a control circuit. The modular multilevel converter module is connected to an external circuit via a three-phase bridge arm structure, with each phase containing two bridge arms, each of which is composed of at least three groups of submodules connected in series. The bridge arms are used to control the switching timing of the submodules through PWM and the nearest level modulation to generate a high-frequency AC waveform. A high-frequency transformer module, configured to achieve voltage conversion and electrical isolation, wherein the primary side of the high-frequency transformer module is electrically connected to the output of the modular multilevel converter module, and the secondary side of the high-frequency transformer module is connected to the target load via another set of modular multilevel converter modules and a rectifier circuit, for converting high-frequency alternating current into electrical energy at a target voltage level; A capacitor voltage balancing control module, configured to dynamically adjust the order in which submodules are put into operation through a sorting algorithm to ensure that the capacitor voltages of all submodules are consistent. The capacitor voltage balancing control module is connected to the control circuit of the modular multi-level converter module via a data bus; A bidirectional power flow control module, integrated into the control circuit of the modular multilevel converter module, configured to achieve bidirectional energy flow by adjusting the switching timing of the submodules and the energy transfer direction of the high-frequency transformer module; The harmonic suppression module is used to reduce the harmonic content in the output voltage waveform through multi-level output technology and reduce the dependence on external filters. The harmonic suppression module is connected to the output end of the modular multi-level converter module through a filtering circuit.

2. The multi-scenario solid-state transformer system according to claim 1, characterized in that: The SiC MOSFET power switch devices of each submodule in the modular multilevel converter module are all configured in parallel with redundancy, and multiple tubes are connected in parallel for current sharing through a drive circuit. The energy storage capacitor adopts a mixed configuration of film capacitors and electrolytic capacitors. The film capacitors are used for high-frequency ripple absorption, and the electrolytic capacitors are used for low-frequency energy buffering. The film capacitors and electrolytic capacitors are connected in parallel through a non-inductive bus. The anti-parallel diodes are fast recovery diodes, which are connected in anti-parallel with the SiC MOSFET to form a bidirectional current path. The control circuit has integrated overvoltage protection, overcurrent protection and temperature monitoring functions, and communicates with the main control system via optical fiber.

3. The multi-scenario solid-state transformer system according to claim 1, characterized in that: The high-frequency transformer module adopts nanocrystalline magnetic core material, the cross-section of the magnetic core material is designed to have a multi-air gap structure, the winding of the high-frequency transformer module adopts a multi-layer winding process of Litz wire, and an insulating heat sink is arranged between each layer. The primary side and secondary side windings of the high-frequency transformer module are isolated by an electrostatic shielding layer.

4. The multi-scenario solid-state transformer system according to claim 1, characterized in that: The capacitor voltage balancing control module adopts a distributed architecture and sorting algorithm. Each bridge arm of the capacitor voltage balancing control module is equipped with an independent control unit, which communicates with the main controller via the CAN bus. The sorting algorithm is based on a dynamic weight allocation mechanism and combines the capacitor voltage, temperature and switching times of the submodule to generate a priority queue.

5. The multi-scenario solid-state transformer system according to claim 1, characterized in that: A hierarchical control strategy is set up inside the bidirectional power flow control module. The upper layer of the hierarchical control strategy is a power instruction parsing layer, which is used to generate active power, reactive power and harmonic compensation reference values ​​according to external instructions. The middle layer of the hierarchical control strategy is a modulation strategy selection layer, which is used to automatically switch between PWM and NLM modulation modes according to the system operation mode, and adopt carrier phase shift modulation to reduce switching loss in forward power flow, and adopt space vector modulation to optimize harmonic performance in reverse power flow. The lower layer of the hierarchical control strategy is a drive signal generation layer, and is provided with dead time compensation and drive pulse shaping technology.

6. The multi-scenario solid-state transformer system according to claim 1, characterized in that: The harmonic suppression module adopts a multi-stage filtering structure. The first stage of the multi-stage filtering structure is a passive LC filter, which attenuates harmonics that are integer multiples of the switching frequency. The second stage of the multi-stage filtering structure is an active power filter, which detects load harmonic current in real time through a current sensor and generates a reverse compensation signal to be injected into the system. The third stage of the multi-stage filtering structure is a digital filtering algorithm, which eliminates residual harmonics by software by embedding a moving average filter and a notch filter in the control circuit.

7. The multi-scenario solid-state transformer system according to claim 1, characterized in that: The three-phase bridge arm structure of the modular multilevel converter module adopts a symmetrical layout. The upper and lower bridge arms of each phase of the three-phase bridge arm structure have an equal number of sub-modules and are connected to the external circuit via a star connection. The inductance of the bridge arm adopts a mixed design of ferrite core and air-core coil. The ferrite core is used to suppress high-frequency circulating current, and the air-core coil is used to limit short-circuit current. A cross-capacitor is provided between the bridge arms, and an RC snubber circuit is used to absorb voltage spikes during the switching process.

8. The multi-scenario solid-state transformer system according to claim 1, characterized in that: The capacitor voltage balancing control module and the bidirectional power flow control module realize data interaction through shared memory. The bidirectional power flow control module dynamically adjusts the voltage balancing strategy according to the bidirectional power flow demand. That is, during forward power flow, the bidirectional power flow control module prioritizes output voltage stability and realizes voltage fine-tuning by fine-tuning the number of sub-modules input. During reverse power flow, the bidirectional power flow control module switches to current source mode and realizes output current control by adjusting the capacitor voltage of the sub-module.

9. The multi-scenario solid-state transformer system according to claim 1, characterized in that: The modular multilevel converter module is internally configured with a dynamic expansion interface, which includes a programmable logic gate array coordination unit and a standardized power module slot. The high-frequency transformer module is built with an intelligent sensor array, which includes a distributed optical fiber temperature sensor and an ultrasonic guided wave sensor. The distributed optical fiber temperature sensor is used to monitor the temperature distribution of the winding hotspot in real time, and the ultrasonic guided wave sensor is used to detect the mechanical vibration state of the iron core.

10. The multi-scenario solid-state transformer system according to claim 1, characterized in that: A loosely coupled coil is additionally provided on the secondary side of the high-frequency transformer module. The loosely coupled coil adopts a flat spiral structure, and the surface of the loosely coupled coil is covered with a ferrite shielding layer.

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