Hybrid superconducting current limiter and method of operation thereof

Abstract

The application discloses a hybrid superconducting current limiter and a working method thereof, and belongs to the field of superconducting power equipment. The current limiter comprises a first branch and a second branch in parallel. In the first branch, a current-limiting resistor element is connected in parallel with a first controllable switch and then connected in series with a first superconducting coil. In the second branch, a second superconducting coil is connected in parallel with a variable impedance element and then connected in series with a second controllable switch. The current limiter further comprises a control system for real-time monitoring of current and temperature to cooperatively control switch timing. The working method comprises the following steps: in normal operation, the first switch is closed and the second switch is opened; when a fault occurs, the first switch is opened to trigger the first superconducting coil to lose superconductivity for current limiting; when the fault is limited, the second switch is closed and the second branch is connected in parallel for shunt; and after the fault is removed, the first switch is closed first and then the second switch is opened. The application realizes double suppression of fault current peak value and rising rate through active triggering of superconductivity loss and cooperation of the double branches, accelerates recovery of the superconducting coil, and has the characteristics of fast response, accurate current limiting and rapid recovery.

Description

Technical Field

[0001] This invention belongs to the field of superconducting power equipment technology, and specifically relates to a hybrid superconducting current limiter and its working method. Specifically, it is a hybrid superconducting current limiter and its working method that has a rapid response, fast recovery, and can suppress fault current peak and reduce fault current rise rate. Background Technology

[0002] With the continuous increase in power system capacity, the level of short-circuit fault current is rising sharply, posing a severe challenge to the withstand capabilities of core equipment such as circuit breakers and transformers. Traditional current-limiting devices (such as fuses and reactors) suffer from problems such as slow response speed, limited current-limiting effect, long recovery time, and high energy consumption, making it difficult to meet the needs of modern power grids for rapid fault isolation and system recovery. Superconducting current limiters, with their advantages of zero-resistance operation, low normal operating losses, fast automatic fault response, and significant current-limiting effect, have become a research hotspot in the field of power system protection.

[0003] However, existing superconducting current limiter technology still faces many bottlenecks: 1) The ability to suppress the rise rate of fault current is limited, and an extremely high rise rate may still cause huge electrodynamic shocks to system equipment and cause mechanical damage to the equipment; 2) The ability to suppress the peak fault current is insufficient, and the circuit breaker still needs to withstand high current breaking pressure; 3) The process of recovering the superconducting state after losing quench takes a long time, which affects the continuous power supply capability of the system; 4) Some topologies are relatively complex, and it is difficult to balance reliability and economy. Summary of the Invention

[0004] The purpose of this invention is to provide a hybrid superconducting current limiter and its operating method, which solves at least one of the above-mentioned technical problems through ingenious circuit topology design and its staged current limiting method.

[0005] To achieve the above objectives, the present invention adopts the following technical solution.

[0006] In a first aspect, the present invention provides a hybrid superconducting current limiter, comprising a first branch and a second branch connected in parallel;

[0007] The first branch includes a current-limiting resistor, a first controllable switch, and a first superconducting coil. The current-limiting resistor is connected in parallel with the first controllable switch and then in series with the first superconducting coil.

[0008] The second branch includes a variable impedance element, a second controllable switch, and a second superconducting coil. The second superconducting coil is connected in parallel with the variable impedance element and then in series with the second controllable switch.

[0009] It also includes a control system, which monitors the current and temperature of the first superconducting coil and the second superconducting coil in real time, and coordinates the operation timing of the first controllable switch and the second controllable switch according to the monitoring information and preset thresholds;

[0010] The control system is configured to: when a fault is detected, control the first controllable switch to open, so that the current flowing through the first superconducting coil changes abruptly and exceeds its critical current, thereby triggering the first superconducting coil to lose quench and transition to a high-resistance state.

[0011] In some embodiments, the first controllable switch is a first DC fast switch, the first superconducting coil is an inductive coil, and the current-limiting resistor element is a fixed resistor.

[0012] In some embodiments, the second controllable switch is a second DC fast switch, the second superconducting coil is an inductive coil, and the variable impedance element is any one of a solid-state rheostat, a segmented resistor network, or a controllable reactor.

[0013] In some embodiments, the inductive coil is made of a high-temperature superconducting material.

[0014] In some embodiments, the inductive coil is made of a high-temperature superconducting material wound in two reverse directions.

[0015] In some embodiments, the winding frame of the inductive coil is covered with a topological insulator material. Ceramic substrate for thin films; and / or,

[0016] The control system also includes an adaptive timing parameter calibration module based on random calculation. The calibration module converts the timing parameters into a probability bit stream to calibrate the timing of switching actions in real time.

[0017] In some embodiments, the inductive coil is in a superconducting state during normal operation, and when a fault occurs, the control system is configured to: at the moment when the first DC fast switch is controlled to open, denoted as t1, trigger the inductive coil to lose superconductivity and switch to a high-resistance state, so that the first branch forms a first current-limiting branch;

[0018] And at the moment when the second DC fast switch is closed, denoted as t2, and satisfying t2>t1, the variable impedance element is adjusted to a first preset value so that the second branch forms a second current-limiting branch.

[0019] In some embodiments, the control system is further configured to: at the moment when it is confirmed that the fault has been cleared and the inductive coil has returned to the superconducting state, denoted as t3, control the first DC fast switch to close to short-circuit the fixed resistor, and at the moment t4, after a preset safety threshold period Δt from the moment t3, control the second DC fast switch to open, wherein the value of Δt ranges from 0.5 seconds to 2 seconds, and t4 = t3 + Δt, t4 > t3 > t2; after the first DC fast switch closes at moment t3, the first branch resumes normal low-loss operation.

[0020] Secondly, the present invention provides a method for operating a hybrid superconducting current limiter, comprising the following steps:

[0021] When the first DC fast switch is closed, the second DC fast switch is open, the variable impedance element is adjusted to a low resistance state, the fixed resistor is short-circuited by the first DC fast switch, the inductive coil is in a superconducting state, and the normal load current of the power grid system flows through the inductive coil through the closed first DC fast switch.

[0022] The control system monitors the current and temperature in real time. When any parameter exceeds the corresponding preset threshold, it is determined to be a fault. The first DC fast switch is opened, and the fixed resistor is connected in series to the first branch, triggering the inductive coil to lose quench and switch to a high-resistance state. The inductive coil and the fixed resistor are connected in series to form the first current-limiting branch to suppress the rise rate and peak value of the fault current.

[0023] Within Δt1 time after the first DC fast switch is opened, the second DC fast switch is closed, and the variable impedance element is adjusted to a high impedance state, so that the second branch formed by the non-inductive coil and the variable impedance element in parallel forms the second current-limiting branch, and is connected in parallel with the first current-limiting branch to the main circuit.

[0024] When the control system detects that the fault current has been cleared and the inductor has returned to the superconducting state, the second DC fast switch remains closed, and the variable impedance element is adjusted to a low resistance state to accelerate the cooling of the inductor. After the inductor has fully returned to the superconducting state, the first DC fast switch is closed first, and then the second DC fast switch is opened to return the system to normal operation.

[0025] In some embodiments, when the fault occurs, the first DC fast switch opens at time t1; when the fault current is limited, the second DC fast switch closes at time t2, and t2 = t1 + Δt1, where Δt1 is 1 microsecond to 100 microseconds; when the fault is cleared, the inductive coil returns to the superconducting state at time t3, the first DC fast switch closes at time t3, the second DC fast switch opens at time t4, and t4 = t3 + Δt2, where Δt2 is 0.5 seconds to 2 seconds, where t4 > t3 > t2 > t1.

[0026] Compared to existing technologies, the beneficial effects of this invention are as follows: By cleverly combining a fixed resistor, a DC fast switch, an inductive coil, and a non-inductive coil, and introducing a parallel-series hybrid topology, and with the current limiting function being jointly undertaken by the resistive element and the switch, dual suppression of the peak fault current and its rise rate, as well as rapid quench recovery capability, can be achieved. In particular, the decoupling and coordinated control of the first and second branches ensures that the inductive coil dominates current limiting in the initial stage of current rise, followed by the non-inductive coil undertaking current limiting, current shunting, and energy dissipation; the fixed resistor accelerates the quench process of the inductive coil by increasing local power consumption, shortening the fault response time and making the current limiting effect more accurate; the shunting design and dynamically adjustable impedance design of the second branch can accelerate energy dissipation and rapid transfer, reduce the thermal load of the inductive coil, shorten the cooling recovery time of the inductive coil (from minutes to seconds), and the entire recovery process does not require external cooling equipment intervention.

[0027] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, the preferred embodiments of the present invention are described in detail below with reference to the accompanying drawings. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0029] Figure 1 This is a schematic diagram of the topology of a hybrid superconducting current limiter according to the present invention.

[0030] Explanation of reference numerals in the attached figures:

[0031] S1, First DC fast switch; S2, Second DC fast switch; L1, Inductive coil (one embodiment of the first superconducting coil); L2, Non-inductive coil (one embodiment of the second superconducting coil); R1, Fixed resistor (one embodiment of the current-limiting resistor element); R2, Adjustable rheostat (one embodiment of the variable impedance element). Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention; obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0033] Based on the technical solutions disclosed in the embodiments of this invention, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this invention. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or device that includes a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to these processes, methods, products, or devices.

[0034] Existing superconducting current limiter technology still faces many bottlenecks, such as limited ability to suppress the rise rate of fault current, insufficient ability to suppress peak fault current, long recovery time after quenching, and complex topologies in some cases. To address these issues, the hybrid superconducting current limiter provided in this invention employs a dual-branch parallel architecture. The main current-limiting branch primarily utilizes the rapid quenching characteristic of the superconducting coil to limit the fault current, while the auxiliary control branch optimizes the current-limiting effect and accelerates the recovery process through dynamic impedance adjustment. During operation, by coordinating the switching states of the first and second controllable switches and adjusting the variable impedance element, the first superconducting coil can be allowed to flow normally, or both the first and second superconducting coils can suppress the fault current.

[0035] For details, please refer to Figure 1 This invention provides a hybrid superconducting current limiter, which includes a first branch and a second branch, and the first branch and the second branch are connected in parallel and then connected in series to the main circuit of the power grid system.

[0036] Furthermore, the first branch includes a current-limiting resistor element, a first controllable switch, and a first superconducting coil, wherein the current-limiting resistor element is connected in parallel with the first controllable switch and then in series with the first superconducting coil; the second branch includes a variable impedance element, a second controllable switch, and a second superconducting coil, wherein the second superconducting coil is connected in parallel with the variable impedance element and then in series with the second controllable switch.

[0037] Furthermore, the first branch is the main current-limiting branch, which mainly uses the rapid quenching characteristic of the superconducting coil to limit the fault current. In other words, the main current-limiting branch can precisely control the timing and amplitude of current limiting by actively triggering the quenching of the superconducting coil. The second branch is the auxiliary control branch, which mainly optimizes the current limiting effect and accelerates the recovery process through dynamic impedance adjustment. In other words, the auxiliary control branch can coordinate current shunting and energy transfer, reduce the heat load of the main current-limiting branch, and shorten the recovery time of the superconducting coil in the main current-limiting branch.

[0038] In some embodiments, the first superconducting coil is an inductive coil L1, which is spirally wound using high-temperature superconducting materials such as YBCO and BSCCO. Because high-temperature superconducting materials possess high critical temperature, high critical current density, high mechanical strength, and low AC loss characteristics, the inductive coil can operate in the liquid nitrogen temperature range (77K) to reduce cooling costs, withstand large currents without losing superconductivity, withstand short-circuit electrodynamic impacts without damage, and is suitable for winding into complex structures. Simultaneously, the inductive coil is in a superconducting state during normal operation of the power grid system, exhibiting low inductance and zero resistance. By connecting the inductive coil in series in the main circuit of the power grid system, it can be used to carry normal load currents. Furthermore, to meet the rated current requirements of the power grid system, the critical current of the inductive coil can be designed to be 1.3-1.6 times the rated current of the power grid system, ensuring that the inductive coil can withstand short-circuit electrodynamic impacts.

[0039] In some embodiments, the second superconducting coil is an inductive coil L2, which is made of high-temperature superconducting material wound in reverse with two wires. The inductive coil not only possesses high critical temperature, high critical current density, high mechanical strength, and low AC loss characteristics, but also low heat capacity and low inductance. This allows the inductive coil to respond quickly to temperature changes, facilitating energy dissipation and rapid recovery. In particular, the resistance of the inductive coil increases significantly with temperature, enabling it to dynamically provide additional reactance during grid system faults, assisting in current shunting and suppressing the rate of increase of fault current, while also serving as a rapid energy transfer path. Furthermore, the resistance of the inductive coil is matched with the resistance of the inductive coil after quenching to ensure effective current shunting during faults.

[0040] During normal operation, the second DC fast switch S2 is in the open state, and the second branch is not conductive. At this time, the second superconducting coil (inductive coil L2) is in a superconducting state but no current flows through it, requiring no pre-cooling or additional maintenance. Simultaneously, the impedance of the variable impedance element (adjustable rheostat R2) can be preset to any value, as its branch is open and it does not affect the system. When a fault occurs and the second DC fast switch S2 closes, the second superconducting coil responds rapidly from the superconducting state, and its resistance increases with temperature, working in conjunction with the variable impedance element.

[0041] In some embodiments, the current-limiting resistor element is a fixed resistor R1. The resistance value of the fixed resistor and the resistance value after the inductor loses its quench are designed in conjunction with the current-limiting requirements of the power grid system. The first controllable switch is a first DC fast switch S1. When the power grid system is operating normally, the first DC fast switch closes, short-circuiting the fixed resistor so that only the inductor is connected in series with the main circuit of the power grid system in the first branch (main current-limiting branch). Almost all of the normal load current of the power grid system flows through the inductor, which is in a superconducting state and has low impedance. At this time, the first branch is equivalent to a pure inductive circuit, and the power grid system loss is extremely low. At the same time, when the power grid system fails or the current in the first branch changes abruptly (such as the current peak or rate of rise exceeding a threshold), the first DC fast switch is controlled to open rapidly, connecting the fixed resistor to the first branch so that the fixed resistor is connected in series with the inductor and connected in series with the main circuit of the power grid system. The opening of the fast DC switch actively triggers a sudden change in the current of the inductive coil, exceeding the critical current. As a result, the inductive coil loses its quench and enters a high-resistance state. This causes the first branch, in which the fixed resistor and the inductive coil are connected in series, to form the first current-limiting branch for current limiting. This effectively suppresses the rise and peak value of the fault current. Moreover, the fault response speed (microsecond level) is far superior to that of the passive quench type superconducting current limiter, and the current limiting effect is more precise. Furthermore, the first DC fast switch in the first branch is connected in parallel with the fixed resistor, which allows the voltage at the break point to be clamped by the fixed resistor when the first DC fast switch is opened. The peak voltage at the break point is smaller, which is more conducive to reducing the breaking conditions of the first DC fast switch, thereby ensuring the stability and reliability of the superconducting current limiter.

[0042] The instant the first DC fast switch S1 opens, the current flowing through S1 is forced to transfer to the parallel fixed resistor R1 branch. Since R1 has a finite positive value, the total resistance of the first branch jumps from near zero to (R1 + the quench resistance of the inductor), but the current is not interrupted. According to Kirchhoff's current law, the fault current in the power grid system is redistributed: part continues to flow through the first branch (R1 is connected in series with the quenched inductor), and the other part flows through the second branch (if the second switch is closed) or other parallel paths. Due to the sudden current change (extremely high di / dt) and the current amplitude exceeding its critical current, the inductor rapidly transitions from a superconducting state to a high-resistance state. This process ensures the continuity and reliability of the current-limiting function.

[0043] In some embodiments, the variable impedance element is any one of a solid-state rheostat, a segmented resistor network, or a controllable reactor. In this embodiment, the variable impedance element is an adjustable rheostat R2. By adjusting the impedance value of the variable impedance element in real time, the current limiting efficiency can be improved, the current shunt ratio optimized, and the recovery time of the inductive coil shortened. The adjustment mechanism of the variable impedance element is as follows: the variable impedance element uses a resistor array controlled by an IGBT or MOSFET, and the control system controls the duty cycle of the switching transistor through a PWM signal to adjust the equivalent impedance value; or a sliding contact rheostat driven by a stepper motor is used, and the control system outputs a pulse signal to drive the motor to rotate to change the connected resistance value. The response time of the adjustment mechanism is no more than 100 microseconds, which can meet the rapid response requirements of the fault current limiting stage. The second controllable switch adopts a second DC fast switch S2. When the power grid system is operating normally, the second DC fast switch is in the open state so that the second branch (auxiliary control branch) is not conducting and the power grid system loss is extremely low. When the power grid system fails and the first DC fast switch is open for a certain period of time, the second DC fast switch closes so that the second branch where the parallel structure of the non-inductive coil and the adjustable rheostat is located forms a second current-limiting branch and is connected in parallel with the first current-limiting branch to the main circuit. This is to provide an additional current-limiting path, divert part of the fault current, reduce the rise rate of the fault current, and transfer the heat load and energy of the first branch.

[0044] In some embodiments, the hybrid superconducting current limiter further includes a control system. This control system includes a current sensor and a temperature sensor, capable of real-time monitoring of the current and temperature of the inductive and non-inductive coils. It can also collaboratively control the timing of the first and second DC fast switches based on the monitoring information and preset thresholds in the control system. The preset thresholds include: a current preset threshold set to 0.8-0.9 times the critical current of the inductive coil; a current rise rate preset threshold set to 100 A / ms; and a temperature preset threshold set to a critical temperature minus a 5K safety margin, for example, when the critical temperature is 92K, the temperature preset threshold is set to 87K.

[0045] Specifically, when the power grid system is operating normally, the first DC fast switch is closed and the second DC fast switch is open. The inductive coil is connected in series to the main circuit of the power grid system and is in a superconducting state. Almost all of the normal load current of the power grid system flows through the inductive coil.

[0046] When a fault occurs in the power grid system, the fault current rises rapidly and exceeds a preset threshold, and the control system detects an abnormal current or temperature in the first branch, the control system controls the first DC fast switch to open at the moment t1. The opening of the first DC fast switch triggers a sudden change in the current of the inductive coil, which exceeds the critical current and loses quench, changing to a high-resistance state. This allows the first branch where the fixed resistor and the inductive coil are connected in series to form a first current-limiting branch to limit the current, thereby suppressing the rise of the fault current and the peak value of the fault current.

[0047] The moment when the second DC fast switch is closed is denoted as t2, and t2 > t1. The control system controls the second DC fast switch to close and simultaneously adjusts the impedance of the adjustable rheostat to a high resistance state so that the second branch containing the parallel structure of the non-inductive coil and the adjustable rheostat forms a second current-limiting branch, which is connected in parallel with the first current-limiting branch to the main circuit. This is used to provide an additional current-limiting path, divert part of the fault current, reduce the rate of rise of the fault current, and transfer the heat load and energy of the first branch.

[0048] When the fault is confirmed to have been cleared and the inductive coil has returned to the superconducting state, denoted as t3, the control system detects that the temperature of the inductive coil has returned to below the critical temperature and the current of the power grid system has dropped below the critical current. The second DC fast switch remains closed, and the impedance of the adjustable rheostat is adjusted to a low resistance state. In conjunction with the non-inductive coil, the fault current of the first branch is diverted. At the same time, the parallel structure of the first and second branches can reduce the overall thermal inertia and the rapid temperature rise of the non-inductive coil, thereby driving the local temperature field to equalize and the inductive coil to cool down. This can quickly reduce the thermal load of the inductive coil and accelerate the cooling of the inductive coil until it returns to the superconducting state.

[0049] The aforementioned Δt1 represents the time difference between t2 and t1, i.e., Δt1 = t2 - t1, and its value ranges from 1 microsecond to 100 microseconds. The lower limit of 1 microsecond for Δt1 is limited by the difference between the action time of the first DC fast switch and the response time of the second DC fast switch. If it is less than 1 microsecond, the second branch may be connected before the current-limiting impedance of the first branch is fully established, weakening the current-limiting effect. The upper limit of 100 microseconds is based on the simulation optimization results of the fault current rise rate and the heat accumulation of the superconducting coil. If it is greater than 100 microseconds, the fault current rise rate has increased significantly, and the shunting effect decreases when the second branch is connected.

[0050] The aforementioned Δt2 is the time difference between t4 and t3, i.e., Δt2 = t4 - t3, and its value ranges from 0.5 seconds to 2 seconds. The lower limit of 0.5 seconds is determined based on the shortest time required for the superconducting coil to recover from the quench state to the superconducting state, to ensure that the second branch still provides shunt protection before the recovery is complete; the upper limit of 2 seconds takes into account system efficiency while ensuring complete recovery, and avoids additional losses caused by the auxiliary branch being turned on for too long.

[0051] The detection method for the inductive coil to recover its superconducting state is as follows: A voltage detection circuit is connected in parallel across the two ends of the inductive coil. The control system calculates its dynamic resistance by monitoring the voltage across the coil and the current flowing through it. When the calculated resistance value is lower than... Furthermore, if the temperature remains below the critical temperature (e.g., 90K) for more than 10ms, the superconducting state is restored upon double confirmation.

[0052] When the control system detects that the inductive coil has returned to the superconducting state, it indicates that the power grid system has safely cleared the fault. At time t3, the control system immediately controls the first DC fast switch to close to short-circuit the fixed resistor. Then, at time t4, after a preset safety threshold period Δt from time t3, the control system controls the second DC fast switch to open. The value of Δt ranges from 0.5 seconds to 2 seconds, so that the power grid system returns to normal operation.

[0053] Furthermore, t4 = t3 + Δt, and t4 > t3 > t2 > t1. Here, t1 is the moment when the first DC fast switch is opened, t2 is the moment when the second DC fast switch is closed, and t2 = t1 + Δt1, where Δt1 is 1 microsecond to 100 microseconds; t3 is the moment when the fault is confirmed to have been cleared and the inductive coil has returned to the superconducting state, and the time difference Δt2 between t3 and t2 is related to the thermal load and heat dissipation design of the inductive coil; t4 is the moment when the second DC fast switch is opened, and t4 = t3 + Δt, where Δt is 0.5 seconds to 2 seconds to avoid secondary superconductivity failure.

[0054] Implementation Method 2 (Topological Insulator Variable Inductor Framework)

[0055] In a preferred embodiment, the inductive coil winding frame of the first superconducting coil is made of a topological insulator material. A thin-film-coated ceramic substrate. The thin film, with a thickness ranging from 5 nm to 20 nm, is grown on the surface of an alumina ceramic framework using molecular beam epitaxy. Its topological surface states maintain dissipationless conductive channels even at low temperatures. During normal operation of the superconducting coil, these topological insulator surface states provide additional dissipationless current bypass, reducing the coil's effective inductance. After a fault quench, the topological surface states are destroyed due to magnetic field penetration, restoring the coil inductance to its design value, thus achieving a reversible change in inductance value during a fault.

[0056] Furthermore, the ceramic matrix is ​​preferably made of alumina ( It has high thermal conductivity, good mechanical strength and chemical compatibility with liquid nitrogen cooling medium. Thin films can be prepared using molecular beam epitaxy (MBE) or magnetron sputtering. When using magnetron sputtering, the substrate temperature is controlled at 250℃-350℃, the sputtering power is 50W-100W, and the Ar gas flow rate is... The selection of a film thickness of 5nm-20nm is based on the following: When the thickness is less than 5nm, the topological surface states are incomplete, and the bypass effect is insignificant; when the thickness is greater than 20nm, the bulk conductive channel begins to dominate, weakening the reversible destruction and recovery characteristics of the surface states under a magnetic field. Under normal operating conditions, the dissipationless bypass provided by the topological surface states reduces the coil's equivalent inductance by approximately 15%-25%; under fault conditions, the strong magnetic field penetrates and destroys the surface states, restoring the coil inductance to its design value, thereby enhancing the current-limiting effect. After the fault is cleared, when the current drops below the critical value and the magnetic field disappears, the topological surface states can recover automatically without additional control signals. Testing has shown that... Compared to conventional ceramic bobbin coils, the inductance variation of the bobbin coil is increased by about 30% under fault conditions, and there is no additional time delay during the recovery process.

[0057] Implementation Method 3 (Adaptive Calibration of Time Series Parameters Based on Random Calculation)

[0058] Furthermore, the control system also implements an adaptive timing parameter calibration method based on random computation. This random computation module converts the values ​​of Δt1 and Δt2 into a probability bitstream. The precise value of each timing parameter is represented by the density of logic '1's in the probability bitstream. The random computation unit performs multiplication and addition operations on single-bit-width hardware to calibrate the timing parameters in real time. The random computation module uses a linear feedback shift register to generate a random number sequence as the basic random source for random computation. Its calibration accuracy is no less than 12-bit binary equivalent accuracy, while the hardware resource consumption is only one-tenth that of traditional fixed-point arithmetic. This calibration method enables Δt1 and Δt2 to adaptively adjust in real time according to power grid frequency fluctuations and ambient temperature changes, maintaining precise synchronization of the switching timing.

[0059] Specifically, the random calculation calibration method includes the following steps:

[0060] (1) A pseudo-random bit stream is generated using a 32-bit linear feedback shift register (LFSR), whose primitive polynomial is x³²+x²²+x²+x+1;

[0061] (2) Convert the basic values ​​of Δt1 and Δt2 (e.g., Δt1=50μs, Δt2=1s) into a probability bit stream of length 2¹²=4096. The density of logic '1' in the bit stream is equal to the ratio of the value to be encoded to the maximum value.

[0062] (3) Real-time acquisition of the inductive coil temperature T and the effective value of the fault current I, and conversion of them into a probability bit stream;

[0063] (4) The random computing unit performs multiplication using AND gates and addition using multiplexers to calculate the calibrated timing parameters:

[0064] Δt1_calibrated=Δt1_base×k_T×k_I

[0065] Δt2_calibrated=Δt2_base×k_T'×k_I'

[0066] Wherein, k_T' is the second correction coefficient based on temperature, and k_I' is the second correction coefficient based on current, both ranging from 0.8 to 1.2. Their values ​​can be the same as or different from k_T and k_I, and can be set independently according to the actual working conditions.

[0067] (5) Convert the calibrated probability bit stream into binary values ​​through a counter and update the switching action timing.

[0068] Tests showed that after random calculation calibration, the temperature drift error of the timing parameters was reduced from ±5% to ±0.5%, and the hardware resource consumption (number of logic gates) was only 9.6% of that of the fixed-point implementation.

[0069] This invention also provides a method for operating a hybrid superconducting current limiter, specifically including the following steps or the following operating stages:

[0070] Normal operating state: When the power grid system is operating normally, the control system controls the first DC fast switch to close and the second DC fast switch to open, and adjusts the variable impedance element to a low resistance state (this low resistance value is less than 1% of the normal resistance of the inductor). At this time, the fixed resistor is short-circuited, the inductor is connected in series to the main circuit of the power grid system and the inductor is in a superconducting state (zero resistance). The impedance of the superconducting current limiter is only the inherent inductance of the inductor. Almost all of the normal load current of the power grid system flows through the inductor in the superconducting state with low impedance. At this time, the first branch is equivalent to a pure inductor circuit, the power grid system loss is extremely low, and the influence of the variable impedance element and the second branch on the normal operation of the power grid system can be ignored.

[0071] At the moment of fault occurrence: When a fault occurs in the power grid system, the control system monitors the current and temperature in real time. When either parameter exceeds the corresponding preset threshold, it is determined to be a fault. After detecting the abnormality, the control system immediately issues a command and controls the first DC fast switch to open at the moment when it controls the first DC fast switch to open. The fixed resistor is connected in series to the first branch, triggering the inductive coil to quickly lose quench and switch to a high-resistance state. This makes the first branch where the fixed resistor and the inductive coil are connected in series form a preliminary current-limiting barrier to suppress the rise of the fault current and the peak fault current. The control system can open the first DC fast switch within microseconds, that is, before the peak current arrives, so that the fixed resistor connected in series in the circuit can work together with the inductive coil to limit the current and suppress the peak current. At the same time, the delay time of the first DC fast switch action is ≤ t1, and t1 is ≤ the time when the peak fault current arrives.

[0072] Fault current limiting phase: Within Δt1 time (Δt1 is 1 microsecond to 100 microseconds) after the first DC fast switch is opened, at the moment when the second DC fast switch is closed, denoted as t2, the control system controls the second DC fast switch to close, and simultaneously adjusts the variable impedance element to a high resistance state (this high resistance value is greater than twice the resistance after the inductive coil loses its quench), so that the second branch containing the parallel structure of the non-inductive coil and the variable impedance element forms a second current limiting branch and is connected in parallel with the first current limiting branch to the main circuit, in order to provide an additional current limiting path, divert part of the fault current, reduce the rate of rise of the fault current, and transfer the heat load and energy of the first current limiting branch; wherein, the second current limiting... During the current shunting process, the resistance of the non-inductive coil in the second current-limiting branch increases with temperature, forming a "thermal resistance gain" effect, further shunting and consuming energy to avoid voltage spikes, "absorb" the energy at the rising edge of the current, and reduce the current rise rate. The variable impedance element can dynamically adjust the impedance and shunting ratio according to the current feedback to further control the current rise rate, achieve adaptive current limiting, and reduce the thermal load of the inductive coil. At the same time, the delay time of the second DC fast switch action is ≤ t2, and t2 is slightly greater than t1 to ensure coordinated action timing and avoid conflict with the action of the first branch. t2 = t1 + Δt1, and Δt1 is usually 1 microsecond to 100 microseconds.

[0073] Fault Clearing and Recovery Phase: When the control system detects that the fault current has been cleared (i.e., the grid system current has dropped below 120% of the rated current) and the temperature of the inductive coil has dropped below the critical temperature (i.e., the resistance has dropped to near zero), the second DC fast switch remains closed. The variable impedance element is adjusted to a low-resistance state (less than 1% of the normal resistance of the inductive coil). Working in conjunction with the non-inductive coil, it diverts the fault current in the first branch. Simultaneously, the parallel structure of the first and second branches reduces overall thermal inertia and the rapid temperature rise of the non-inductive coil, leading to local temperature field equalization and cooling of the inductive coil. This rapidly reduces the thermal load on the inductive coil, accelerating its cooling until it returns to the superconducting state. The entire recovery process requires no external cooling equipment intervention. During the cooling process until the inductive coil returns to the superconducting state, the temperature or resistance value of the inductive coil can be monitored in real time. Based on the monitoring information, the impedance of the variable impedance element is dynamically adjusted to optimize the recovery speed of the inductive coil.

[0074] The control system, upon confirming that the fault has been cleared and the inductive coil has returned to the superconducting state (denoted as t3), immediately controls the first DC fast switch to close to short-circuit the fixed resistor. Then, starting from t3, after a preset safety threshold period Δt, at t4, it controls the second DC fast switch to open, with Δt ranging from 0.5 to 2 seconds, to allow the power grid system to return to normal operation. The time for the inductive coil to return to the superconducting state is t3 = t2 + Δt2, where Δt2 is related to the thermal load and heat dissipation design of the inductive coil, and is typically several seconds. The first DC fast switch closes at t3, and the second DC fast switch opens at t4 = t3 + Δt.

[0075] Simulation tests show that, using the timing control and topology of this invention, when a three-phase short-circuit fault occurs in a 10kV / 600A power distribution system, the peak fault current is limited to 32%-38% of that of an unlimited current limiter, and the fault current rise rate is reduced to 15%-20% of that of an unlimited current limiter. The time for the inductive coil to fully recover from quenching to superconductivity is approximately 1.5-1.8 seconds, which is about 90% shorter than that of a traditional resistive superconducting current limiter (which typically has a recovery time in the minutes range).

[0076] The hybrid superconducting current limiter in this invention, through innovative circuit topology design and combined with the unique properties of superconducting materials, can effectively suppress fault current in the power grid system, ensure the safe and stable operation of the power grid, and solve the bottlenecks of traditional superconducting current limiters in terms of fault current suppression efficiency, response speed, and recovery time.

[0077] Simulation verification and comparative analysis

[0078] To verify the effectiveness of the technical solution of this invention, the applicant built an electromagnetic transient simulation platform based on PSCAD / EMTDC and coupled it with a dynamic model of the electric field-temperature field of the superconducting coil. The simulation parameters are as follows: system voltage 10kV (RMS), rated current 600A, fault type three-phase metallic short circuit, and fault occurrence time 0.5ms after voltage zero crossing. The comparison objects include: no current limiter, traditional resistive superconducting current limiter (only a single branch superconducting coil connected in series with a fixed resistor), and the hybrid superconducting current limiter of this invention.

[0079] Simulation results show that:

[0080] (1) Fault current peak suppression: Without any current limiter, the first peak of the fault current is 18.7kA; the traditional resistive superconducting current limiter reduces the peak to 7.2kA (suppression ratio 61.5%); the hybrid superconducting current limiter of this invention further reduces the peak to 6.1kA (suppression ratio 67.4%).

[0081] (2) Suppression of fault current rise rate: When the current limiter is not used, the average current rise rate within 0.5ms after the fault occurs is 37.4kA / ms; the traditional resistive superconducting current limiter is 12.8kA / ms; the hybrid superconducting current limiter of this invention is 7.9kA / ms, which is 38.3% lower than the traditional solution.

[0082] (3) Superconducting coil recovery time: The inductive coil of the traditional resistive superconducting current limiter takes about 12 seconds to recover to the superconducting state under liquid nitrogen cooling; the present invention accelerates cooling by shunting the second branch, and the recovery time is shortened to 1.7 seconds, which is about 86%.

[0083] The simulation data above fully demonstrates the significant advantages of the present invention in suppressing fault current peaks, suppressing rate of rise, and enabling rapid recovery.

[0084] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the specific working processes of the devices, apparatuses, and units described above can be referred to the corresponding processes in the foregoing method embodiments, and will not be repeated here.

[0085] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in the present invention, and these modifications or substitutions should all be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A hybrid superconducting current limiter, characterized in that, Including the first and second branches connected in parallel; The first branch includes a current-limiting resistor, a first controllable switch, and a first superconducting coil. The current-limiting resistor is connected in parallel with the first controllable switch and then in series with the first superconducting coil. The second branch includes a variable impedance element, a second controllable switch, and a second superconducting coil. The second superconducting coil is connected in parallel with the variable impedance element and then in series with the second controllable switch. It also includes a control system, which monitors the current and temperature of the first superconducting coil and the second superconducting coil in real time, and coordinates the operation timing of the first controllable switch and the second controllable switch according to the monitoring information and preset thresholds; The control system is configured to: when a fault is detected, control the first controllable switch to open, so that the current flowing through the first superconducting coil changes abruptly and exceeds its critical current, thereby triggering the first superconducting coil to lose quench and transition to a high-resistance state.

2. The hybrid superconducting current limiter according to claim 1, characterized in that, The first controllable switch is a first DC fast switch, the first superconducting coil is an inductive coil, and the current-limiting resistor element is a fixed resistor.

3. The hybrid superconducting current limiter according to claim 1, characterized in that, The second controllable switch is a second DC fast switch, the second superconducting coil is an inductive coil, and the variable impedance element is any one of a solid-state rheostat, a segmented resistor network, or a controllable reactor.

4. The hybrid superconducting current limiter according to claim 2, characterized in that, The inductive coil is made of high-temperature superconducting material.

5. The hybrid superconducting current limiter according to claim 3, characterized in that, The inductive coil is made of high-temperature superconducting material wound in two reverse directions.

6. The hybrid superconducting current limiter according to claim 2, characterized in that, The winding frame of the inductive coil is covered with a topological insulator material. Ceramic substrate for thin films; And / or, the control system further includes an adaptive timing parameter calibration module based on random calculation, which converts timing parameters into a probability bit stream to calibrate the timing of switching actions in real time.

7. The hybrid superconducting current limiter according to claim 6, characterized in that, The inductive coil is in a superconducting state during normal operation. When a fault occurs, the control system is configured to: trigger the inductive coil to lose superconductivity and switch to a high-resistance state at the moment when the first DC fast switch is opened, denoted as t1, so that the first branch forms the first current-limiting branch. And at the moment when the second DC fast switch is closed, denoted as t2, and satisfying t2>t1, the variable impedance element is adjusted to a first preset value so that the second branch forms a second current-limiting branch.

8. The hybrid superconducting current limiter according to claim 7, characterized in that, The control system is further configured to: at the moment when it is confirmed that the fault has been cleared and the inductive coil has returned to the superconducting state, denoted as t3, control the first DC fast switch to close to short-circuit the fixed resistor, and at time t4, after a preset safety threshold period Δt from time t3, control the second DC fast switch to open, where Δt is 0.5 seconds to 2 seconds, and t4 > t3 > t2; after the first DC fast switch closes at time t3, the first branch resumes normal low-loss operation.

9. A method for operating a hybrid superconducting current limiter as described in any one of claims 1-8, characterized in that, Includes the following steps: When the first DC fast switch is closed, the second DC fast switch is open, the variable impedance element is adjusted to a low resistance state, the fixed resistor is short-circuited by the first DC fast switch, the inductive coil is in a superconducting state, and the normal load current of the power grid system flows through the inductive coil through the closed first DC fast switch. The control system monitors the current and temperature in real time. When any parameter exceeds the corresponding preset threshold, it is determined to be a fault. The first DC fast switch is opened, and the fixed resistor is connected in series to the first branch, triggering the inductive coil to lose quench and switch to a high-resistance state. The inductive coil and the fixed resistor are connected in series to form the first current-limiting branch to suppress the rise rate and peak value of the fault current. Within Δt1 time after the first DC fast switch is opened, the second DC fast switch is closed, and the variable impedance element is adjusted to a high impedance state, so that the second branch formed by the non-inductive coil and the variable impedance element in parallel forms the second current-limiting branch, and is connected in parallel with the first current-limiting branch to the main circuit. When the control system detects that the fault current has been cleared and the inductor has returned to the superconducting state, the second DC fast switch remains closed, and the variable impedance element is adjusted to a low resistance state to accelerate the cooling of the inductor. After the inductor has fully returned to the superconducting state, the first DC fast switch is closed first, and then the second DC fast switch is opened to return the system to normal operation.

10. The working method according to claim 9, characterized in that, When the fault occurs, the first DC fast switch opens at time t1; when the fault current is limited, the second DC fast switch closes at time t2, and t2 = t1 + Δt1, where Δt1 is 1 microsecond to 100 microseconds; when the fault is cleared, the inductive coil returns to the superconducting state at time t3, the first DC fast switch closes at time t3, the second DC fast switch opens at time t4, and t4 = t3 + Δt2, where Δt2 is 0.5 seconds to 2 seconds, where t4 > t3 > t2 > t1.

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