A compact high-temperature superconducting current-limiting and energy-storage integrated device for power distribution networks

Abstract

The application belongs to the technical field of power distribution network of power system. A compact high-temperature superconducting current limiting-energy storage integrated device for power distribution network, characterized by comprising an integrated power conversion main circuit unit, a coaxial nested superconducting integrated magnet unit, a closed-circuit integrated low-temperature refrigeration unit and a multi-working-condition coordinated comprehensive control and protection unit; the coaxial nested superconducting integrated magnet unit is electrically and structurally connected with the integrated power conversion main circuit unit and the closed-circuit integrated low-temperature refrigeration unit; the multi-working-condition coordinated comprehensive control and protection unit is signal-connected with the integrated power conversion main circuit unit, the coaxial nested superconducting integrated magnet unit and the closed-circuit integrated low-temperature refrigeration unit, realizing the coordinated control and protection of the whole system. The deep integration of current limiting and energy storage functions is realized, through the integrated topology and coordinated control strategy, the adaptive operation of power distribution network in multiple scenes and all working conditions is realized, and the power supply reliability and new energy consumption capacity of the power distribution network are improved.

Description

Technical Field

[0001] This invention belongs to the field of power system distribution network technology, and particularly relates to high temperature superconducting power equipment technology, specifically a compact high temperature superconducting current limiting-energy storage integrated device for distribution networks. Background Technology

[0002] With the large-scale integration of nonlinear loads such as distributed renewable energy and electric vehicle charging piles, my country's 10kV / 35kV distribution network faces two major challenges: First, the risk of short-circuit faults has increased significantly. Excessive short-circuit current can easily lead to circuit breaker damage, equipment burnout, and even large-scale power outages, seriously threatening the reliability of power supply. Second, the fluctuation of renewable energy output and the peak-valley difference of load have intensified, resulting in prominent problems such as voltage fluctuations, excessive power factor, and deterioration of power quality in the distribution network.

[0003] In existing technologies, the above problems are usually solved by using separate fault current limiters and energy storage devices: Among them, the high-temperature superconducting fault current limiter (SFCL) has the advantages of low impedance under normal operating conditions, microsecond-level response under fault conditions, and significant current limiting effect, making it an ideal device for short-circuit current management in distribution networks; the high-temperature superconducting energy storage system (SMES) has the advantages of millisecond-level charge and discharge response, unlimited charge and discharge times, and high efficiency, making it a high-quality technical solution for power quality management and peak shaving and valley filling in distribution networks.

[0004] However, existing technologies have the following significant drawbacks: 1. The two sets of equipment are set up separately, each equipped with an independent superconducting magnet, cryogenic refrigeration system and control and protection system. This not only occupies a large area and has high construction costs, but also cannot meet the compact installation space requirements of power distribution room and ring network cabinet. At the same time, the two cryogenic refrigeration systems operate redundantly, resulting in high cooling energy consumption and heat leakage loss, and significantly increased operation and maintenance costs.

[0005] 2. Existing integrated solutions are merely simple parallel circuits, failing to achieve deep physical integration of superconducting magnets and cryogenic systems. Superconducting materials are only reused for a single function, resulting in low material utilization and failing to fundamentally solve the issues of volume and cost. Furthermore, the lack of magnetic coupling between windings leads to poor functional synergy, making it impossible to achieve coordinated operation of fault current limiting and voltage support.

[0006] 3. Existing superconducting power devices are mostly designed for high-voltage transmission network scenarios. Their voltage levels, response characteristics, and installation methods are not compatible with the application scenarios of 10kV / 35kV distribution networks. In addition, their complex structures make on-site installation and operation and maintenance difficult, which prevents them from being promoted and applied on a large scale. Summary of the Invention

[0007] The purpose of this invention is to provide a compact high-temperature superconducting current limiting-energy storage integrated device for power distribution networks, which achieves deep integration of current limiting and energy storage functions. Through integrated topology and collaborative control strategies, it enables the power distribution network to adapt to various scenarios and operating conditions, thereby improving the power supply reliability and renewable energy absorption capacity of the power distribution network.

[0008] To achieve the above objectives, the technical solution adopted by this invention is a compact high-temperature superconducting current-limiting and energy storage integrated device for power distribution networks, characterized by comprising four main units: an integrated power conversion main circuit unit, a coaxial nested superconducting integrated magnet unit, a closed-loop integrated cryogenic refrigeration unit, and a multi-condition coordinated integrated control and protection unit; wherein, the coaxial nested superconducting integrated magnet unit is electrically and structurally connected to the integrated power conversion main circuit unit and the closed-loop integrated cryogenic refrigeration unit respectively; the multi-condition coordinated integrated control and protection unit is signal connected to the integrated power conversion main circuit unit, the coaxial nested superconducting integrated magnet unit, and the closed-loop integrated cryogenic refrigeration unit respectively, realizing coordinated control and protection of the entire system; The topology and module composition of the integrated power conversion main circuit unit are shown in Figure 1. It is used to realize bidirectional power interaction between the device and the distribution network, and to realize circuit switching between energy storage winding charging and discharging control and current limiting winding overrun protection. The integrated power conversion main circuit unit includes, in order of power flow, a grid-connected circuit breaker, a current limiting coupling branch, a three-phase LCL filter unit, a three-phase bidirectional AC / DC rectifier / inverter bridge, a DC bus, and a bidirectional DC / DC chopper unit. It is also equipped with a bypass protection branch and an energy discharge branch connected to the main circuit. Furthermore, the modules of the integrated power conversion main circuit unit are connected in series in the following order: 10kV / 35kV distribution network bus → grid-connected circuit breaker → current-limiting coupling branch → three-phase LCL filter unit → three-phase bidirectional AC / DC rectifier / inverter bridge → DC bus → bidirectional DC / DC chopper unit. The DC side of the current-limiting coupling branch is connected to the inner current-limiting winding of the coaxial nested superconducting integrated magnet unit, and the low-voltage side of the bidirectional DC / DC chopper unit is connected to the outer energy storage winding of the coaxial nested superconducting integrated magnet unit. The control signal terminals of all modules are connected to the multi-condition collaborative integrated control and protection unit.

[0009] In the integrated power conversion main circuit unit, one end of the grid-connected circuit breaker is connected to the 10kV / 35kV distribution network bus, and the other end is connected to the three-phase LCL filter unit. The three-phase LCL filter unit is connected to the AC side of the three-phase bidirectional AC / DC rectifier / inverter bridge; the DC side of the three-phase bidirectional AC / DC rectifier / inverter bridge is connected to the DC bus, realizing bidirectional power conversion between the AC grid and the DC side. The high-voltage side of the bidirectional DC / DC chopper unit is connected to the DC bus, and the low-voltage side is connected to both ends of the energy storage winding, used to realize precise bidirectional charging and discharging control of the energy storage winding under constant current / constant power. The current-limiting coupling branch is connected in series between the distribution network line and the grid-connected circuit breaker. The superconducting end of the current-limiting coupling branch is connected to both ends of the current-limiting winding. Specifically, the current-limiting coupling branch adopts a three-phase bridge rectifier structure. The AC side of the three-phase bridge rectifier is connected in series with the three-phase line of the distribution network, and the DC side is connected to both ends of the current-limiting winding. Under normal operating conditions, the current-limiting winding has zero resistance in the superconducting state. When the DC side of the bridge rectifier branch is short-circuited, the AC side presents extremely low impedance, which has no impact on the normal operation of the distribution network. During a short-circuit fault, the fault current exceeds the critical current of the current-limiting winding. The winding loses its quench and presents high impedance. The high impedance is connected in series with the fault line through the bridge rectifier structure to achieve symmetrical limitation of the three-phase short-circuit current and avoid AC loss in the current-limiting winding. The bypass protection branch adopts a combination structure of anti-parallel thyristors and freewheeling diodes, connected in parallel with the current limiting winding, for overheat protection of the winding during a fault; the energy discharge branch adopts a series structure of zinc oxide varistors and IGBTs, connected in parallel with the DC bus, for DC bus overvoltage protection and safe energy discharge of the energy storage winding.

[0010] The coaxial nested superconducting integrated magnet unit is the core component of this invention. Its complete composition, layered structure, and connection relationship are shown in Figure 2. Using an integrated cryogenic Dewar as the main sealing body, the unit is divided into two main modules: the core internal component group and the external interface group. The specific composition and connection relationships between the components are as follows: The integrated cryogenic Dewar is a horizontal, compact, high-vacuum, multi-layered, heat-insulated, and sealed cavity that encloses all internal core components. It provides a sealed, high-vacuum, heat-insulated environment and cryogenic operating cavity for the superconducting winding and is the main structural support for the entire magnet unit. The core components of the Dewar radiator employ a coaxial, nested structure from the inside out, including a nanocrystalline alloy magnetic core, an inner current-limiting winding, an epoxy insulation layer, an outer energy storage winding, distributed temperature sensors, and a chiller cold head heat exchanger. The connection relationships between the components of the core components of the Dewar radiator are as follows: The nanocrystalline alloy core is located at the innermost center of the unit and is the core of the magnetic circuit of the entire magnet. Its outer wall is tightly attached and fixed to the inner wall of the inner current limiting winding, providing a shared closed low-loss magnetic circuit for the inner current limiting winding and the outer energy storage winding, realizing deep coupling of the magnetic circuits of the two windings. The inner current-limiting winding is coaxially wound on the outer wall of the nanocrystalline alloy core. It is wound in a double-pancake style using second-generation high-temperature superconducting tape. Its outer wall is completely covered with an epoxy insulation and heat insulation layer. The leads at both ends of the winding are electrically connected to the internal conductors of the three-phase high-voltage insulating bushing of the Dewar external interface group. The epoxy insulation and heat insulation layer is a ring-shaped integrated covering structure, coaxially covering the outer wall of the inner current limiting winding. Its inner wall is tightly attached to the inner current limiting winding, and its outer wall is tightly attached to the inner wall of the outer energy storage winding, so as to achieve high-voltage electrical insulation and thermal isolation between the two sets of windings and avoid electrical breakdown and thermal conduction interference between the windings. The outer energy storage winding is coaxially wound on the outer wall of the epoxy insulation and heat insulation layer. It adopts the second-generation high-temperature superconducting tape solenoid winding and forms a completely coaxial nested structure with the inner current limiting winding. It shares the same magnetic circuit with the inner nanocrystalline alloy magnetic core. The lead wires at both ends of the winding are electrically connected to the internal conductor of the air-cooled binary current lead wire of the Dewar external interface group. Distributed temperature sensors are arranged at equal intervals along the winding axis between the inner current-limiting winding and the outer energy storage winding, and are tightly attached and fixed to the corresponding winding surface. Their signal transmission lines are connected to the internal terminals of the sensor signal interface of the Dewar external interface group. The cold head heat exchanger of the refrigeration unit is completely immersed in the liquid nitrogen cooling medium in the inner cavity of the integrated low-temperature Dewar, and is located in the same low-temperature cavity as the two sets of superconducting windings. Its cold end is fixedly connected to the refrigeration unit interface of the external interface group of the Dewar, realizing the thermal connection with the external refrigeration system.

[0011] Both the inner current-limiting winding and the outer energy storage winding are completely immersed in the liquid nitrogen cooling medium in the integrated cryogenic Dewar cavity, operating in the 77K liquid nitrogen temperature range, achieving unified immersion cooling of all superconducting components through the same Dewar.

[0012] The external interface group of the Dewar is sealed and integrated into the cavity wall of the integrated cryogenic Dewar, enabling functional communication between internal components and other units of the device. This includes a three-phase high-voltage insulating bushing, gas-cooled binary current leads, a refrigerator interface, a closed-loop liquid nitrogen circulation interface, and a sensor signal interface. The connection relationships of each interface are as follows: The three-phase high-voltage insulating bushing has its internal conductors electrically connected one-to-one with the leads of the inner current-limiting winding inside the Dewar, and its external terminals electrically connected with the current-limiting coupling branch of the integrated power conversion main circuit unit, so as to realize the electrical connection between the inner current-limiting winding and the distribution network line. The air-cooled binary current lead wire has its internal low-temperature end electrically connected to the lead wire of the outer energy storage winding inside the Dewar, and its external room temperature end electrically connected to the bidirectional DC / DC chopper unit of the integrated power conversion main circuit unit, so as to realize the electrical connection between the outer energy storage winding and the power conversion circuit. The internal interface of the refrigerator is connected to the cold end of the heat exchanger of the refrigerator cold head inside the Dewar, and the external interface is sealed and connected to the GM refrigerator cold head of the closed-loop integrated low-temperature refrigeration unit to form a complete refrigeration circuit. The closed-loop liquid nitrogen circulation interface has an internal interface that is directly connected to the liquid nitrogen chamber inside the Dewar, and an external interface that is connected to the liquid nitrogen storage tank of the closed-loop integrated cryogenic refrigeration unit through a self-circulation pipeline, forming a closed-loop liquid nitrogen self-circulation loop. The sensor signal interface has internal terminals that connect to the signal transmission line of the distributed temperature sensor inside the Dewar, and external terminals that connect to the signal of the quench protection module of the multi-condition collaborative integrated control and protection unit, so as to realize the real-time transmission and protection linkage of the winding temperature signal.

[0013] The inner current-limiting winding and the outer energy storage winding share the same magnetic circuit structure, realizing the synergistic coupling of inductance characteristics and quench current-limiting characteristics. The same magnet simultaneously realizes the dual functions of energy storage inductor and current-limiting element, maximizing the utilization rate of superconducting materials.

[0014] Furthermore, the energy storage winding and the current-limiting winding adopt a coaxial layered nested structure. The current-limiting winding is the inner winding, set close to the magnetic core, while the energy storage winding is the outer winding, coaxially nested outside the current-limiting winding. A high-strength epoxy insulation layer is set between the two windings to avoid heat conduction and electrical breakdown between the windings. The critical current parameters of the two windings are matched: the critical current of the current-limiting winding is 1.1 to 1.5 times the rated operating current of the distribution network to ensure stable superconductivity under normal operating conditions and rapid loss of superconductivity in case of fault; the critical current of the energy storage winding is 2 to 3 times the rated charge and discharge current to ensure no loss of superconductivity under charge and discharge conditions and improve operational stability.

[0015] The closed-loop integrated cryogenic refrigeration unit is a single closed-loop self-circulating refrigeration system, directly connected to the integrated cryogenic Dewar of the coaxial nested superconducting integrated magnet unit, providing a unified cryogenic operating environment for the energy storage winding and the current-limiting winding. Specifically, the closed-loop integrated cryogenic refrigeration unit includes a GM refrigerator, a cold head heat exchanger, a liquid nitrogen storage tank, self-circulating piping, a temperature and pressure monitoring module, a liquid level monitoring module, and a refrigeration control module. The cold head heat exchanger is immersed in liquid nitrogen within the integrated cryogenic Dewar. The GM refrigeration unit continuously cools and reliquefies the liquid nitrogen through the cold head heat exchanger. The liquid nitrogen storage tank is connected to the integrated cryogenic Dewar via a self-circulating pipeline, forming a closed-loop liquid nitrogen self-circulation circuit. This ensures long-term self-stable liquid nitrogen level and temperature within the Dewar, eliminating the need for frequent replenishment. Temperature and pressure monitoring modules and liquid level monitoring modules are respectively located within the integrated cryogenic Dewar and the liquid nitrogen storage tank, both connected to the refrigeration control module. The refrigeration control module communicates with the multi-condition collaborative integrated control and protection unit, enabling closed-loop control of the cryogenic system and state linkage across all operating conditions.

[0016] The multi-condition collaborative integrated control and protection unit is used to realize the operation control, fault detection, status monitoring and protection actions of the device under all operating conditions. Specifically, it includes a power grid status monitoring module, a fault rapid detection module, a charge and discharge control module, a current limiting collaborative control module, a cryogenic system control module, a quench protection module and a host computer communication module.

[0017] The power grid status monitoring module is used to collect real-time operating parameters such as distribution network bus voltage, line current, power factor, and frequency. The rapid fault detection module, based on wavelet transform and instantaneous value comparison algorithms, achieves microsecond-level identification of short-circuit faults with a response time ≤100μs, ensuring rapid triggering of current limiting function during faults. The charging and discharging control module generates charging and discharging control signals for the energy storage winding based on distribution network dispatch instructions and operating status, realizing peak shaving, power fluctuation smoothing, reactive power compensation, and voltage regulation functions. The current limiting coordination control module triggers the current limiting winding overrun protection when a fault occurs, and simultaneously coordinates with the charging and discharging control module to inject active / reactive power into the distribution network through the energy storage winding, achieving load voltage support during faults and avoiding power outages of critical loads.

[0018] The quench protection module is used to collect the voltage, current and temperature parameters of the energy storage winding and the current limiting winding in real time. Based on the voltage-temperature composite quench criterion, it realizes the rapid identification of winding quench and triggers the bypass protection branch and energy discharge branch to achieve the safety protection of the superconducting winding.

[0019] The cryogenic system control module is used to realize the closed-loop operation control and status monitoring of the integrated cryogenic refrigeration unit. It communicates bidirectionally with the refrigeration control module in real time, and collects parameters such as temperature, pressure, liquid nitrogen level, and refrigerator operating power in the integrated cryogenic Dewar and liquid nitrogen storage tank in real time. According to the operating conditions and temperature status of the superconducting winding, it dynamically adjusts the operating power of the GM refrigerator. Under normal operating conditions, it maintains the cryogenic system in a low-power steady-state operation. When the winding temperature rises after a fault current limiting, it automatically triggers the full-power refrigeration mode to accelerate the winding cooling recovery. At the same time, it has the function of cryogenic system fault early warning and protection. When abnormal vacuum, low liquid level, excessive pressure, or refrigerator failure is detected, it immediately sends an alarm signal to the host computer and links the multi-condition collaborative integrated control and protection unit to implement the safe shutdown protection to avoid damage to the superconducting components.

[0020] The host computer communication module is used to realize two-way data interaction and remote control between the device and the distribution network dispatching system and the local operation and maintenance host computer. It supports the IEC61850 power communication protocol and the Modbus industrial communication protocol, and has dual communication interfaces of wired Ethernet and fiber optic. It can upload the device's full-condition operation data in real time, including distribution network operation parameters, superconducting winding status parameters, cryogenic system operation parameters, protection action events, fault recording data, etc. At the same time, it can receive control commands such as charging and discharging plans, operation setting modification, and remote start and stop issued by the distribution network dispatching system, and forward them to the corresponding functional modules for execution. In addition, it also supports parameter configuration, setting value adjustment, historical data query, fault tracing and debugging operations of the local operation and maintenance host computer, adapting to the needs of large-scale operation and maintenance and dispatch management of the distribution network.

[0021] The beneficial effects of this invention are: 1. Deeply integrated design, significantly improving compactness: This invention achieves deep reuse of superconducting magnets for energy storage and current limiting functions through a coaxial nested winding design. At the same time, it shares a single closed-loop cryogenic refrigeration system. Compared with separate superconducting current limiting and energy storage devices, the volume is reduced by more than 60%, and the footprint is significantly reduced. This meets the limited installation space requirements of power distribution rooms and ring main units in power distribution networks, and solves the pain point that existing superconducting equipment is too large to be used on a large scale in power distribution networks.

[0022] 2. Maximizing the utilization rate of superconducting materials and significantly reducing costs: The same superconducting magnet in this invention simultaneously realizes the dual functions of energy storage inductor and current limiting element, avoiding material redundancy of two sets of superconducting windings. Compared with two sets of superconducting windings in discrete equipment, this design only requires one set of superconducting windings, increasing the material utilization rate by more than 50% and significantly reducing the construction cost of the device. At the same time, compared with two discrete systems, the single cryogenic refrigeration system reduces refrigeration energy consumption by more than 40%, significantly reducing the operation and maintenance cost of the device throughout its entire life cycle.

[0023] 3. Multi-condition collaborative operation, comprehensive functions to meet the needs of distribution network: This invention achieves peak shaving and valley filling, smoothing of renewable energy power fluctuations, reactive power compensation and voltage regulation under normal operating conditions, and microsecond-level short-circuit current limiting and dynamic voltage support under fault conditions through integrated topology and collaborative control strategy. One device solves the two core problems of distribution network short-circuit current management and power quality improvement, and greatly improves the reliability of power supply and renewable energy absorption capacity of distribution network.

[0024] 4. High reliability design, suitable for large-scale application in power distribution networks: This invention is designed with full parameter optimization for 10kV / 35kV power distribution network scenarios. It adopts a horizontal compact Dewar structure, a closed self-circulating cooling system, and a dual overrun protection mechanism, which has the ability to operate for a long time without maintenance. The modular structure design can be flexibly adapted to various power distribution network scenarios such as overhead lines, cable lines, new energy grid connection points, and important load power supply points, and has the conditions for large-scale promotion and application. Attached Figure Description

[0025] Figure 1 This is a block diagram of the overall structure of the compact high-temperature superconducting current-limiting and energy storage integrated device described in this invention.

[0026] Figure 2 This is a block diagram of the coaxial nested layered structure of the coaxial nested superconducting integrated magnet unit described in this invention.

[0027] Figure 3 This is a flowchart illustrating the full-condition operation control of the compact high-temperature superconducting current-limiting and energy storage integrated device of the present invention. Detailed Implementation

[0028] The present invention will be further described in detail below with reference to specific embodiments of a 10kV distribution network.

[0029] The compact high-temperature superconducting current-limiting and energy storage integrated device for 10kV distribution networks in this embodiment has a rated voltage of 10kV, a rated current of 630A, a current-limiting capability of limiting a 20kA expected short-circuit current to within 5kA, and an energy storage capacity of 500kJ / 250kVA, meeting the installation and operation requirements of 10kV distribution network substations.

[0030] The core structure of the device in this embodiment is as follows: 1. Coaxial nested superconducting integrated magnet unit The integrated cryogenic Dewar adopts a horizontal, compact, high-vacuum, multi-layered insulating structure made of 304 stainless steel, with an internal volume of 120L, a vacuum degree ≤1×10^-3Pa, and a heat leakage rate ≤5W. The Dewar body integrates three 10kV high-voltage insulating bushings, binary current leads, a GM refrigerator interface, a liquid nitrogen circulation interface, and a fiber optic temperature sensor interface, with overall dimensions ≤1200mm×800mm×800mm.

[0031] Both the energy storage winding and the current-limiting winding are made of second-generation YBCO high-temperature superconducting tape, with a critical current ≥200A@77K and self-field capability. The windings adopt a coaxial layered nested structure, with a nanocrystalline alloy core and a relative permeability ≥80000. The inner layer is the current-limiting winding, which is wound in a double-panel configuration, with a total of 4 double pancakes, a critical current of 700A@77K, a rated current of 630A, and a steady-state resistance ≥2Ω after quench failure. The outer layer is the energy storage winding, coaxially nested outside the current-limiting winding, and wound in a solenoid configuration, with a total of 16 layers, a critical current of 400A@77K, a rated inductance of 5H, and a maximum energy storage of 500kJ. A 2mm thick epoxy insulation layer is set between the two winding layers. Fiber Bragg grating temperature sensors are integrated between the winding layers, with one sensor every 10cm along the axial direction, enabling distributed monitoring of the winding temperature.

[0032] 2. Closed-loop integrated low-temperature refrigeration unit A single two-stage GM chiller is used, with a cooling capacity ≥10W@77K and input power ≤2.5kW. The cold head heat exchanger is made of copper and is directly immersed in liquid nitrogen inside the Dewar, allowing for thorough heat exchange with the superconducting windings. The liquid nitrogen storage tank has a volume of 50L and is connected to the integrated cryogenic Dewar via a stainless steel self-circulating pipeline, forming a closed-loop self-circulating circuit. Temperature monitoring uses a PT1000 cryogenic platinum resistance thermometer, with a measurement range of 4K~300K and an accuracy of ±0.1K; the liquid level sensor uses a capacitive cryogenic level gauge, with a measurement range of 0~100% and an accuracy of ±1%FS. The refrigeration control module uses a PLC controller to achieve closed-loop control of temperature, pressure, and liquid level, ensuring that the liquid nitrogen temperature inside the Dewar remains stable at 77K, enabling long-term self-sustaining operation without frequent liquid nitrogen replenishment.

[0033] 3. Integrated power conversion main circuit unit The grid-connected circuit breaker adopts a 10kV / 630A vacuum circuit breaker; the three-phase LCL filter unit is adapted to a 10kV / 250kVA power rating, with a filter inductance of 2mH, a filter capacitor of 50μF, and a damping resistor of 10Ω; the three-phase bidirectional AC / DC rectifier / inverter bridge adopts a three-level NPC topology, with power devices using 10kV / 50A IGBTs and a switching frequency of 5kHz; the rated voltage of the DC bus is ±5kV.

[0034] The bidirectional DC / DC chopper unit adopts a bidirectional Buck-Boost topology, using 3.3kV / 100A IGBTs as power devices to achieve bidirectional constant current charging and discharging control of the energy storage winding from 0 to 100A. The current-limiting coupling branch uses a three-phase uncontrolled rectifier bridge, with 10kV / 100A fast recovery diodes as power devices. The AC side is connected in series with the three-phase line of the 10kV distribution network, and the DC side is connected to both ends of the current-limiting winding. The bypass protection branch uses two anti-parallel 10kV / 200A thyristors connected in parallel with the current-limiting winding; the energy discharge branch uses a 10kV zinc oxide varistor connected in series with a 10kV / 50A IGBT, connected in parallel with the DC bus.

[0035] 4. Multi-condition collaborative integrated control and protection unit The hardware adopts a dual-core DSP+FPGA architecture with a sampling frequency of 100kHz, enabling high-speed acquisition and processing of grid parameters, winding parameters, and cryogenic system parameters. The fault rapid detection module uses a composite algorithm of wavelet transform and instantaneous value comparison, with a short-circuit fault identification response time ≤80μs; ​​the charge and discharge control module uses a composite algorithm of PI and repetitive control to achieve precise control of charge and discharge power, with a response time ≤1ms; the quench protection module uses a voltage-temperature composite quench criterion, with a quench identification response time ≤50μs, which can quickly trigger protection actions.

[0036] The device operation method of this embodiment includes three core modes: 1. Normal operating mode The 10kV distribution network is fault-free, with line current ≤630A. The current-limiting winding is in a superconducting state with zero resistance, and the AC side impedance of the current-limiting coupling branch is ≤1mΩ, having no impact on the normal operation of the distribution network. The multi-condition coordinated integrated control and protection unit, based on distribution network dispatch instructions, controls the energy storage winding to discharge during peak electricity demand periods, injecting active power into the distribution network to achieve peak shaving; and controls the energy storage winding to charge during off-peak electricity demand periods, storing energy to achieve valley filling. Simultaneously, to address fluctuations in distributed photovoltaic output, it controls the rapid charging and discharging of the energy storage winding to smooth power fluctuations and stabilize the bus voltage; and to address reactive power demand from the load, it achieves dynamic reactive power compensation through a three-phase bidirectional AC / DC rectifier / inverter bridge, with a power factor adjustment range of 0.8 (leading) to 0.8 (lagging). During this process, the closed-loop integrated cryogenic cooling unit continuously operates, maintaining the temperature inside the Dewar at 77K, ensuring the superconducting winding operates stably in a superconducting state.

[0037] 2. Fault-based current limiting mode When a three-phase short-circuit fault occurs in the distribution network, with an expected short-circuit current of 20kA, the fault current exceeds the critical current of the current-limiting winding (700A). The current-limiting winding loses its quench within 50μs, exhibiting a high impedance of 2Ω. This is then connected in series with the faulty line through a three-phase rectifier bridge, limiting the short-circuit current to 4.8kA, meeting the circuit breaker's breaking requirements. Simultaneously, the multi-condition coordinated integrated control and protection unit, in conjunction with the energy storage winding, injects active and reactive power into the non-faulty sections of the distribution network through a bidirectional DC / DC chopper unit and a three-phase bidirectional AC / DC rectifier / inverter bridge, maintaining the load-side bus voltage ≥0.9pu and preventing power outages of critical loads. The quench protection module monitors the current-limiting winding temperature in real time. When the winding temperature exceeds the 90K safety threshold, it triggers the bypass protection branch thyristor to conduct, short-circuiting the current-limiting winding and preventing overheating and burnout. If the fault lasts for more than 200ms, the control unit sends a trip signal, which triggers the line vacuum circuit breaker to disconnect the faulty line. At the same time, it triggers the energy discharge branch to safely discharge the stored energy of the energy storage winding, thus achieving dual protection for the device.

[0038] 3. Fault recovery and restart mode After the fault is cleared, the power distribution network returns to its normal rated voltage. The control unit sends a signal to shut off the thyristors in the bypass protection branch. The closed-loop integrated cryogenic cooling unit operates at full power to rapidly cool the current-limiting winding. When the winding temperature drops below 77K, the current-limiting winding returns to the superconducting state. Simultaneously, the control unit controls the bidirectional DC / DC chopper unit to charge the energy storage winding to its rated current, restoring it to normal standby mode. The device then re-enters normal operation mode, and the entire restart process takes ≤30 minutes.

Claims

1. A compact high-temperature superconducting current-limiting and energy storage integrated device for power distribution networks, characterized in that... It comprises four main units: an integrated power conversion main circuit unit, a coaxial nested superconducting integrated magnet unit, a closed-loop integrated cryogenic refrigeration unit, and a multi-condition collaborative integrated control and protection unit. The coaxial nested superconducting integrated magnet unit is electrically and structurally connected to the integrated power conversion main circuit unit and the closed-loop integrated cryogenic refrigeration unit, respectively. The multi-condition collaborative integrated control and protection unit is signal-connected to the integrated power conversion main circuit unit, the coaxial nested superconducting integrated magnet unit, and the closed-loop integrated cryogenic refrigeration unit, respectively, to achieve collaborative control and protection of the entire system. The integrated power conversion main circuit unit is used to realize bidirectional power interaction between the device and the distribution network, and to realize circuit switching between energy storage winding charging and discharging control and current limiting winding overrun protection. The integrated power conversion main circuit unit includes, in order of power flow, a grid-connected circuit breaker, a current limiting coupling branch, a three-phase LCL filter unit, a three-phase bidirectional AC / DC rectifier / inverter bridge, a DC bus, and a bidirectional DC / DC chopper unit. It is also equipped with a bypass protection branch and an energy discharge branch connected to the main circuit. The coaxial nested superconducting integrated magnet unit uses an integrated cryogenic Dewar as the main sealing body. It is divided into two main modules: the core component group inside the Dewar and the external interface group of the Dewar. The specific composition and the connection relationship between the components are as follows: The integrated cryogenic Dewar is a horizontal, compact, high-vacuum, multi-layered, heat-insulated, and sealed cavity that encloses all internal core components. It provides a sealed, high-vacuum, heat-insulated environment and cryogenic operating cavity for the superconducting winding and is the main structural support for the entire magnet unit. The core components of the Dewar unit adopt a coaxial layered nested structure from the inside out, including a nanocrystalline alloy magnetic core, an inner current-limiting winding, an epoxy insulation layer, an outer energy storage winding, a distributed temperature sensor, and a refrigerator cold head heat exchanger. The closed-loop integrated cryogenic refrigeration unit is a single closed-loop self-circulating refrigeration system, which is directly connected to the integrated cryogenic Dewar of the coaxial nested superconducting integrated magnet unit, providing a unified cryogenic operating environment for the energy storage winding and the current limiting winding. The multi-condition collaborative integrated control and protection unit is used to realize the operation control, fault detection, status monitoring and protection actions of the device under all operating conditions. Specifically, it includes a power grid status monitoring module, a fault rapid detection module, a charge and discharge control module, a current limiting collaborative control module, a cryogenic system control module, a quench protection module and a host computer communication module.

2. A compact high-temperature superconducting current-limiting and energy storage integrated device for power distribution networks according to claim 1, characterized in that... The modules of the integrated power conversion main circuit unit are connected in series in the order of power flow: 10kV / 35kV distribution network bus, grid-connected circuit breaker, current-limiting coupling branch, three-phase LCL filter unit, three-phase bidirectional AC / DC rectifier / inverter bridge, DC bus, and bidirectional DC / DC chopper unit. The DC side of the current-limiting coupling branch is connected to the inner current-limiting winding of the coaxial nested superconducting integrated magnet unit, and the low-voltage side of the bidirectional DC / DC chopper unit is connected to the outer energy storage winding of the coaxial nested superconducting integrated magnet unit. The control signal terminals of all modules are connected to the multi-condition collaborative integrated control and protection unit. In the integrated power conversion main circuit unit, one end of the grid-connected circuit breaker is connected to the 10kV / 35kV distribution network bus, and the other end is connected to the three-phase LCL filter unit; the three-phase LCL filter unit is connected to the AC side of the three-phase bidirectional AC / DC rectifier / inverter bridge; the DC side of the three-phase bidirectional AC / DC rectifier / inverter bridge is connected to the DC bus to realize bidirectional power conversion between the AC grid and the DC side; the high-voltage side of the bidirectional DC / DC chopper unit is connected to the DC bus, and the low-voltage side is connected to both ends of the energy storage winding to realize constant current / constant power bidirectional charging and discharging precise control of the energy storage winding; The current-limiting coupling branch is connected in series between the distribution network line and the grid-connected circuit breaker. The superconducting end of the current-limiting coupling branch is connected to both ends of the current-limiting winding. Specifically, the current-limiting coupling branch adopts a three-phase bridge rectifier structure. The AC side of the three-phase bridge rectifier is connected in series with the three-phase line of the distribution network, and the DC side is connected to both ends of the current-limiting winding. Under normal operating conditions, the current-limiting winding has zero resistance in the superconducting state. When the DC side of the bridge rectifier branch is short-circuited, the AC side presents extremely low impedance, which has no impact on the normal operation of the distribution network. During a short-circuit fault, the fault current exceeds the critical current of the current-limiting winding. The winding loses its quench and presents high impedance. The high impedance is connected in series with the fault line through the bridge rectifier structure to achieve symmetrical limitation of the three-phase short-circuit current and avoid AC loss in the current-limiting winding. The bypass protection branch adopts a combination structure of anti-parallel thyristors and freewheeling diodes, connected in parallel with the current limiting winding, for overheat protection of the winding during a fault; the energy discharge branch adopts a series structure of zinc oxide varistors and IGBTs, connected in parallel with the DC bus, for DC bus overvoltage protection and safe energy discharge of the energy storage winding.

3. A compact high-temperature superconducting current-limiting and energy storage integrated device for power distribution networks according to claim 1, characterized in that, The connection relationships of the components in the core component group inside the Dewar unit of the coaxial nested superconducting integrated magnet unit are as follows: The nanocrystalline alloy core is located at the innermost center of the unit and is the core of the magnetic circuit of the entire magnet. Its outer wall is tightly attached and fixed to the inner wall of the inner current limiting winding, providing a shared closed low-loss magnetic circuit for the inner current limiting winding and the outer energy storage winding, realizing deep coupling of the magnetic circuits of the two windings. The inner current-limiting winding is coaxially wound on the outer wall of the nanocrystalline alloy core. It is wound in a double-pancake style using second-generation high-temperature superconducting tape. Its outer wall is completely covered with an epoxy insulation and heat insulation layer. The leads at both ends of the winding are electrically connected to the internal conductors of the three-phase high-voltage insulating bushing of the Dewar external interface group. The epoxy insulation and heat insulation layer is a ring-shaped integrated covering structure, coaxially covering the outer wall of the inner current limiting winding. Its inner wall is tightly attached to the inner current limiting winding, and its outer wall is tightly attached to the inner wall of the outer energy storage winding, so as to achieve high-voltage electrical insulation and thermal isolation between the two sets of windings and avoid electrical breakdown and thermal conduction interference between the windings. The outer energy storage winding is coaxially wound on the outer wall of the epoxy insulation and heat insulation layer. It adopts the second-generation high-temperature superconducting tape solenoid winding and forms a completely coaxial nested structure with the inner current limiting winding. It shares the same magnetic circuit with the inner nanocrystalline alloy magnetic core. The lead wires at both ends of the winding are electrically connected to the internal conductor of the air-cooled binary current lead wire of the Dewar external interface group. Distributed temperature sensors are arranged at equal intervals along the winding axis between the inner current-limiting winding and the outer energy storage winding, and are tightly attached and fixed to the corresponding winding surface. Their signal transmission lines are connected to the internal terminals of the sensor signal interface of the Dewar external interface group. The cold head heat exchanger of the refrigerator is completely immersed in the liquid nitrogen cooling medium in the inner cavity of the integrated low-temperature Dewar, and is located in the same low-temperature cavity as the two sets of superconducting windings. Its cold end docking end is fixedly connected to the refrigerator interface of the external interface group of the Dewar, realizing the thermal connection with the external refrigeration system. Both the inner current-limiting winding and the outer energy storage winding are completely immersed in the liquid nitrogen cooling medium in the integrated cryogenic Dewar cavity, and operate in the 77K liquid nitrogen temperature range. The unified immersion cooling of the entire superconducting component is achieved through the same Dewar. The external interface group of the Dewar is sealed and integrated into the cavity wall of the integrated cryogenic Dewar, enabling functional communication between internal components and other units of the device. This includes a three-phase high-voltage insulating bushing, gas-cooled binary current leads, a refrigerator interface, a closed-loop liquid nitrogen circulation interface, and a sensor signal interface. The connection relationships of each interface are as follows: The three-phase high-voltage insulating bushing has its internal conductors electrically connected one-to-one with the leads of the inner current-limiting winding inside the Dewar, and its external terminals electrically connected with the current-limiting coupling branch of the integrated power conversion main circuit unit, so as to realize the electrical connection between the inner current-limiting winding and the distribution network line. The air-cooled binary current lead wire has its internal low-temperature end electrically connected to the lead wire of the outer energy storage winding inside the Dewar, and its external room temperature end electrically connected to the bidirectional DC / DC chopper unit of the integrated power conversion main circuit unit, so as to realize the electrical connection between the outer energy storage winding and the power conversion circuit. The internal interface of the refrigerator is connected to the cold end of the heat exchanger of the refrigerator cold head inside the Dewar, and the external interface is sealed and connected to the GM refrigerator cold head of the closed-loop integrated low-temperature refrigeration unit to form a complete refrigeration circuit. The closed-loop liquid nitrogen circulation interface has an internal interface that is directly connected to the liquid nitrogen chamber inside the Dewar, and an external interface that is connected to the liquid nitrogen storage tank of the closed-loop integrated cryogenic refrigeration unit through a self-circulation pipeline, forming a closed-loop liquid nitrogen self-circulation loop. The sensor signal interface has internal terminals that connect to the signal transmission line of the distributed temperature sensor inside the Dewar, and external terminals that connect to the signal of the overrun protection module of the multi-condition collaborative integrated control and protection unit, so as to realize the real-time transmission and protection linkage of the winding temperature signal. The inner current-limiting winding and the outer energy storage winding share the same magnetic circuit structure, realizing the synergistic coupling of inductance characteristics and quench current-limiting characteristics. The same magnet simultaneously realizes the dual functions of energy storage inductor and current-limiting element.

4. A compact high-temperature superconducting current-limiting and energy storage integrated device for power distribution networks according to claim 1, characterized in that... In the core component assembly of the Dewar, the energy storage winding and the current limiting winding adopt a coaxial layered nested structure. The current limiting winding is the inner winding, which is set close to the magnetic core, and the energy storage winding is the outer winding, which is coaxially nested outside the current limiting winding. A high-strength epoxy insulation and heat insulation layer is set between the two windings. The critical current parameters of the two windings are matched: the critical current of the current limiting winding is 1.1 to 1.5 times the rated operating current of the distribution network; the critical current of the energy storage winding is 2 to 3 times the rated charging and discharging current.

5. A compact high-temperature superconducting current-limiting and energy storage integrated device for power distribution networks according to claim 1, characterized in that... The closed-loop integrated cryogenic refrigeration unit specifically includes a GM refrigerator, a cold head heat exchanger, a liquid nitrogen storage tank, a self-circulating pipeline, a temperature and pressure monitoring module, a liquid level monitoring module, and a refrigeration control module. The cold head heat exchanger is immersed in liquid nitrogen within the integrated cryogenic Dewar, and the GM refrigerator continuously cools and reliquefies the liquid nitrogen through the cold head heat exchanger. The liquid nitrogen storage tank is connected to the integrated cryogenic Dewar via a self-circulating pipeline, forming a closed-loop liquid nitrogen self-circulation loop, achieving long-term self-stable liquid nitrogen level and temperature within the Dewar without frequent replenishment of liquid nitrogen. The temperature and pressure monitoring module and the liquid level monitoring module are respectively located within the integrated cryogenic Dewar and the liquid nitrogen storage tank, both connected to the refrigeration control module. The refrigeration control module is communicatively connected to the multi-condition collaborative integrated control and protection unit, realizing closed-loop control of the cryogenic system and status linkage across all operating conditions of the device.

6. A compact high-temperature superconducting current-limiting and energy storage integrated device for power distribution networks according to claim 1, characterized in that... In the multi-condition collaborative integrated control and protection unit, the power grid status monitoring module is used to collect the distribution network bus voltage, line current, power factor, and frequency operating parameters in real time; the fault fast detection module is based on wavelet transform and instantaneous value comparison algorithm to identify response time ≤100μs; the charging and discharging control module is used to generate charging and discharging control signals for the energy storage winding according to the distribution network dispatch instructions and operating status. The current limiting coordinated control module is used to trigger the current limiting winding overrun protection when a fault occurs, and at the same time, it links the charging and discharging control module to inject active / reactive power into the distribution network through the energy storage winding. The quench protection module is used to collect the voltage, current and temperature parameters of the energy storage winding and the current limiting winding in real time. Based on the voltage-temperature composite quench criterion, it realizes the rapid identification of winding quench and triggers the bypass protection branch and energy discharge branch to operate. The cryogenic system control module is used to realize the closed-loop operation control and status monitoring of the integrated cryogenic refrigeration unit. It communicates bidirectionally with the refrigeration control module in real time, and collects the temperature, pressure, liquid nitrogen level, and refrigeration unit operating power parameters in the integrated cryogenic Dewar and liquid nitrogen storage tank in real time. According to the operating conditions and temperature status of the superconducting winding, it dynamically adjusts the operating power of the GM refrigeration unit. Under normal operating conditions, it maintains the cryogenic system in a low-power steady-state operation. When the winding temperature rises after a fault current limiting, it automatically triggers the full-power refrigeration mode to accelerate the winding cooling recovery. At the same time, it has the function of cryogenic system fault early warning and protection. When abnormal vacuum, low liquid level, excessive pressure, or refrigeration unit failure is detected, it immediately sends an alarm signal to the host computer and links the multi-condition collaborative integrated control and protection unit to implement the safe shutdown protection to avoid damage to the superconducting components. The host computer communication module is used to realize two-way data interaction and remote control between the device and the distribution network dispatching system and the local operation and maintenance host computer. It supports the IEC61850 power communication protocol and the Modbus industrial communication protocol, and has dual communication interfaces of wired Ethernet and fiber optic. It can upload the device's full-condition operation data in real time, including distribution network operation parameters, superconducting winding status parameters, cryogenic system operation parameters, protection action events, and fault waveform data. At the same time, it can receive charging and discharging plans, operation setting modification, and remote start and stop control commands issued by the distribution network dispatching system and forward them to the corresponding functional modules for execution. It also supports parameter configuration, setting adjustment, historical data query, fault tracing, and debugging operations of the local operation and maintenance host computer.

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