Phase-shifting transformer adaptive fault ride-through method based on three-phase shared damping current limiting

Abstract

A phase-shifting transformer adaptive fault ride-through method based on three-phase shared damping current limiting is characterized in that each phase input connection end of a phase-shifting transformer is connected to a voltage regulating winding of a corresponding phase through a main solid-state switch, each phase output connection end is connected to a common node through a damping solid-state switch, and the common node is connected to a system reference point through a damping current limiting module; when a fault occurs, according to the operation characteristic data and a fault detection index, determining each-stage fault ride-through mode of the phase-shifting transformer, based on each-stage fault ride-through mode, controlling the main solid-state switch and the damping solid-state switch to perform switching-on and switching-off operation, and executing cooperative control of a phase-shifting angle and a voltage-regulating gear of the phase-shifting transformer and a power grid voltage; when the fault is cleared, for the phase-shifting transformer executing the first-stage or second-stage fault ride-through mode, the opening operation of the damping solid-state switch is controlled according to the operation characteristic data and the fault detection index, and then the closing operation of the main solid-state switch is controlled according to the synchronous constraint, so that the influence of the phase-shifting transformer on the line protection is eliminated, and the protection reliability is improved.

Description

Technical Field

[0001] This invention belongs to the field of phase-shifting transformer protection technology, and in particular relates to an adaptive fault ride-through method for phase-shifting transformers based on three-phase common damping current limiting. Background Technology

[0002] A phase-shifting transformer (PST) is a control device used to regulate the power flow distribution in a power system. It achieves precise regulation of active power on power lines by changing the phase of the output voltage without altering its amplitude. Its core principle is to introduce a phase shift angle between the primary and secondary windings, thereby achieving dynamic control of power distribution without changing the voltage level. This device can balance the power flow of different lines in complex power grids, optimize power transmission paths, and improve the overall economy and security of the system. Compared with traditional power flow control equipment such as series reactors and controllable capacitors, PSTs have advantages such as stable response, high control accuracy, and long-term stable operation, and are widely used in power flow regulation and inter-regional power transmission in large power grids.

[0003] With the large-scale integration of new energy sources, the randomness and volatility of power output from sources such as wind and solar power have increased significantly, making power flow distribution in the power grid more complex. Phase-shifting transformers, with their adjustable phase characteristics, can flexibly adjust the power flow direction and power sharing ratio under different operating conditions, thereby effectively improving the stability margin of the power grid and possessing significant application potential in new power systems. Especially in scenarios such as high-proportion new energy grid integration, AC / DC hybrid operation, and regional power grid interconnection, the use of phase-shifting transformers can alleviate line overload, suppress reverse power flow, and improve transmission capacity.

[0004] However, in actual operation, the phase-shifting angle and equivalent impedance of a phase-shifting transformer change with the tap position, leading to alterations in the short-circuit current, phase-to-phase voltage distribution, and protection setting characteristics of the connected line. When a line fault occurs, the original relay protection device may fail to operate, malfunction, or overstep its limit due to current amplitude and phase angle characteristic shifts, potentially threatening system stability in severe cases. This is especially true for single-core asymmetrical phase-shifting transformers, whose complex internal winding structure and magnetic coupling relationships result in inconsistent electromagnetic transient characteristics between different phases, significantly impacting protection settings. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides an adaptive fault ride-through method for phase-shifting transformers based on three-phase common damping current limiting. By using a three-phase common damping current limiting module, adaptive fault ride-through of single-core asymmetrical phase-shifting transformers is achieved. When a fault occurs, the influence of the phase-shifting transformer is quickly cut off, transient impacts are suppressed, and safe reconnection is achieved after the fault is cleared. This eliminates the impact of single-core asymmetrical phase-shifting transformers on line protection and improves the reliability of protection.

[0006] The present invention adopts the following technical solution.

[0007] This invention proposes an adaptive fault ride-through method for phase-shifting transformers based on three-phase common damping current limiting, comprising: Each phase input terminal of the phase-shifting transformer is connected to the voltage regulating tap of the corresponding phase voltage regulating winding via the main solid-state switch of each phase. Each phase output terminal is connected to the three-phase common node via the damping solid-state switch of each phase. The three-phase common node is connected to the system reference point via the three-phase common damping current limiting module. During normal operation of the system, the main solid-state switches are all kept closed and the damping solid-state switches are all kept open. Establish system fault detection indicators; acquire system operation characteristic data in real time; when a fault occurs, determine the fault ride-through modes of each stage of the phase-shifting transformer based on the operation characteristic data and fault detection indicators, including: first-stage fault ride-through mode, second-stage fault ride-through mode, and third-stage fault ride-through mode; Based on the fault ride-through modes of each stage of the phase-shifting transformer, a hierarchical control strategy is adopted to control the main solid-state switch and the damping solid-state switch to perform opening and closing operations, as well as to perform coordinated control of the phase-shifting transformer's phase angle and voltage regulation position, and the grid voltage. When clearing a fault, for a phase-shifting transformer that has executed the first-level fault ride-through mode or the second-level fault ride-through mode, the damping solid-state switch is first opened based on the operating characteristic data and fault detection indicators, and then the main solid-state switch is closed based on the synchronization constraints between the phase-shifting transformer and the system.

[0008] Preferably, the main solid-state switch and the damping solid-state switch adopt the same main body structure; The three-phase common damping current limiting module includes a damping reactor and a damping resistor connected in series.

[0009] Preferably, the system fault detection indicators include: current amplitude threshold, current change rate threshold, and current imbalance threshold; wherein,

[0010] In the formula, For the sake of separation The current amplitude threshold, For the sake of separation The current reference value, This represents the maximum allowable phase current under the current phase shift angle and voltage regulation setting. , The weighting coefficients are the current amplitude threshold values.

[0011] In the formula, For the sake of separation The threshold of the rate of change of current, For the sake of separation The historical maximum rate of change of current, The characteristic time constant of the system, , The weighting coefficients are the threshold values ​​for the rate of change of current.

[0012] In the formula, The current imbalance threshold. This is a proportional coefficient determined based on the allowable imbalance of the line. This represents the average or maximum value of the reference values ​​for each phase current.

[0013] Preferably, the system's operating characteristic data includes: the instantaneous amplitude or equivalent amplitude of the current in each phase. Current change rate of each phase negative sequence current amplitude ; A near-field fast short-circuit fault is determined when the following criteria are met: and

[0014] In the formula, The coefficient for the first action. The second action coefficient, and All are greater than 1; The logical variable FTYPE=2 represents the near-zone fast short-circuit fault, which corresponds to the first-stage fault ride-through mode of the phase-shifting transformer. The following criteria are used to determine if a mid-to-far zone asymmetric fault is present: and and

[0015] The logical variable FTYPE=1 represents an asymmetrical fault in the mid-to-far region, corresponding to the second-stage fault ride-through mode of the phase-shifting transformer.

[0016] The following criteria are used to determine whether a condition is considered slightly unbalanced or has a high resistance grounding condition: and and

[0017] The logical variable FTYPE=0 represents a mild unbalanced or high-resistance grounding condition, corresponding to the third-level fault ride-through mode of the phase-shifting transformer.

[0018] Preferably, when FTYPE=2, only the damping solid-state switch of the faulty phase is closed. If the fault is not cleared after the delay, the main solid-state switch of each phase is opened to bypass the phase-shifting transformer. When FTYPE=1, the main solid-state switch remains closed, and the phase shift angle of the phase-shifting transformer and the voltage regulation position and the grid voltage are coordinated and controlled. If the fault is not cleared after the delay, only the damping solid-state switch of the faulty phase is closed; if the fault is not cleared after the delay, the main solid-state switch of each phase is opened and the phase-shifting transformer is bypassed. When FTYPE=0, the main solid-state switches of each phase remain closed and the damping solid-state switches remain open, performing coordinated control of phase shift angle and voltage adjustment range.

[0019] Preferably, the coordinated control of the phase shift angle and voltage regulation level of the phase shift transformer and the grid voltage includes: reducing the phase shift angle adjustment rate, adjusting the number of connected turns of the voltage regulation winding to increase the leakage reactance value of the phase shift transformer, and reducing the fault phase voltage to reduce the negative sequence current.

[0020] Preferably, for a phase-shifting transformer that has implemented either the first-level fault ride-through mode or the second-level fault ride-through mode, the damping solid-state switch is tripped when the following recovery criterion conditions are met simultaneously: and and

[0021] In the formula, For the sake of separation The root mean square value of the current. , , These are the reliability coefficients for each threshold, all of which are greater than 1; When the phase angle difference between the phase-shifting transformer terminal voltage and the system voltage Less than the preset synchronization phase angle threshold And current difference All are less than the preset synchronous current threshold. At this time, the main solid-state switch performs a closing operation, and the phase-shifting transformer is reconnected to the line.

[0022] Preferably, if the monitoring quantity of any phase fails to meet the recovery criterion during operation, the re-switching operation of the corresponding phase is stopped and the operation is reverted to the state where the phase-shifting transformer is bypassed, and the monitoring quantity of each phase is re-evaluated to determine whether it meets the recovery criterion.

[0023] The present invention is also a terminal, including a processor and a storage medium; the storage medium is used to store instructions; the processor is used to perform operations according to the instructions to execute the steps of the method.

[0024] The present invention is also a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of the method.

[0025] The beneficial effects of this invention are as follows: compared with the prior art, this invention at least includes the following: by configuring a main solid-state switch and a damping solid-state switch at the input and output ends of the three-phase voltage regulating winding respectively, and converging the output ends of the three-phase damping solid-state switches to form a common node N, and then forming a three-phase shared current limiting and damping channel through damping reactors and damping resistors, the fault energy can be handled in a centralized and unified manner; this invention avoids the cumbersome design of setting up damping windings or damping reactors for each phase in the traditional scheme, greatly reducing the number of devices, reducing manufacturing costs and system size, and improving the synchronicity of fault handling between the three phases.

[0026] Because this invention uses solid-state switches as the execution unit, it has a microsecond-level operating speed compared to mechanical circuit breakers. This allows for precise control of the closing of the damping solid-state switches in the early stages of a fault, rapidly guiding the faulty phase current to the common damping path. Simultaneously, the main control module effectively distinguishes between short-circuit faults and load fluctuations based on a combined criterion of current amplitude, current change rate, and negative sequence current amplitude, improving the accuracy of fault identification and preventing false trips. Furthermore, when the fault worsens, this invention sequentially disconnects the main solid-state switches, causing the phase-shifting transformer to disconnect phase by phase, achieving multi-level protection and flexible control. During the fault recovery phase, this invention uses a soft recovery method to gradually disconnect the damping solid-state switches, close the main solid-state switches, and restore the tap angle, allowing the phase-shifting transformer to safely and smoothly reconnect to the system, avoiding secondary impacts. This invention features a simple overall structure, a comprehensive control strategy, and combines rapid current limiting, high energy efficiency, a compact topology, and good engineering feasibility, making it promising for broad applications. Attached Figure Description

[0027] Figure 1 This is a flowchart of an adaptive fault ride-through method for a phase-shifting transformer based on three-phase common damping current limiting, as proposed in this invention.

[0028] Figure 2 This is a circuit topology diagram of the single-core asymmetrical phase-shifting transformer of the three-phase common damping current limiting module in an embodiment of the present invention.

[0029] Figure 3 This is a structural diagram of the main solid-state switch and the damping solid-state switch in an embodiment of the present invention. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of this invention. The embodiments described in this application are merely some embodiments of this invention, and not all embodiments. Based on the spirit of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of this invention.

[0031] This invention proposes an adaptive fault ride-through method for phase-shifting transformers based on three-phase common damping current limiting, such as... Figure 1 As shown, it includes: Step 1: The input connection terminals of each phase are connected to the voltage regulating taps of the corresponding phase voltage regulating windings via the main solid-state switches of each phase. The output connection terminals of each phase are connected to the three-phase common node via the damping solid-state switches of each phase. The three-phase common node is connected to the system reference point via the three-phase common damping current limiting module. During normal system operation, the main solid-state switches are all kept closed and the damping solid-state switches are all kept open.

[0032] In the embodiment, the circuit topology of the single-core asymmetrical phase-shifting transformer of the three-phase shared damping current limiting module is as follows: Figure 2 As shown, the three-phase input connection terminals of a single-core asymmetrical phase-shifting transformer , , Three-phase output connection terminal , , Three-phase voltage regulating winding , Three-phase excitation winding , , ; Each phase input terminal is connected via the main solid-state switch The voltage regulating taps are connected to the corresponding phase's voltage regulating winding, and the output terminals of each phase are connected via damping solid-state switches. Access to three-phase common node The three-phase common node is connected to the system reference point via a three-phase common damping current limiting module. The three-phase common damping current limiting module includes: a damping reactor connected in series. and damping resistor ; Specifically, connect one end The other end is connected The voltage regulating tap, from Flow direction The current is ,from Flow direction The current is ; connect one end The other end is connected The voltage regulating tap, from Flow direction The current is ,from Flow direction The current is ; connect one end The other end is connected The voltage regulating tap, from Flow direction The current is ,from Flow direction The current is ; This invention proposes a circuit topology for a single-core asymmetrical phase-shifting transformer based on the circuit topology of a single-core asymmetrical phase-shifting transformer with a three-phase common damping current limiting module. This allows each phase input connection terminal to be connected to the voltage regulating tap of the corresponding phase's voltage regulating winding via a main solid-state switch, while each phase output connection terminal is connected together via a damping solid-state switch to form a three-phase common node N. The three-phase common node N is connected to the system reference point via a three-phase common damping current limiting module consisting of a damping reactor and a damping resistor connected in series. When the system is running normally, all main solid-state switches remain closed and all damping solid-state switches remain open. The current at each phase input connection terminal flows into the voltage regulating winding only through the main solid-state switch and then through the excitation winding to achieve normal phase shift regulation. At this time, the three-phase common node N and the subsequent three-phase common damping current limiting module are in an electrically isolated state and do not participate in the main current path.

[0033] Among them, the main solid-state switch and damping solid-state switches Using the same main structure, such as Figure 3 As shown, it includes: a switch module, a drive module, a cooling protection module, a main control module, a communication module, an A / D conversion module, a signal conditioning module, a power supply module, voltage and current transformers, and external modules; in this embodiment, the internal modules of the solid-state switch are arranged according to... Figure 3The arrows indicate the direction of data and control information transmission: voltage and current transformers output analog voltage and current signals from the main circuit to the signal conditioning module; the signal conditioning module filters, isolates, and amplifies the analog signals before sending the processed analog signals to the A / D conversion module; the A / D conversion module completes the digitization conversion of the analog signals and transmits the digital signals to the main control module; the main control module performs fault criterion calculations, action logic judgments, and internal state management based on the digital signals, and outputs switch on / off or soft-off commands to the drive module; the drive module drives the power devices in the switch module according to the signals and sends back information such as the on / off status and fault status of the switch module to the main control module. The system comprises several modules: a cooling protection module that monitors the temperature and operating status of the switch module in real time, feeding back temperature and protection information to the main control module, and receiving cooling or protection control commands from the main control module; a power supply module that provides power to the signal conditioning module, A / D module, main control module, drive module, and cooling protection module; a main control module that interacts bidirectionally with the communication module to upload operating status and receive external setting commands; and external modules including, but not limited to, a keyboard, LCD display, temperature detection, and real-time clock. The main control module also interacts locally with the keyboard and LCD display, and acquires operating temperature and standard time information through the temperature detection unit and real-time clock unit, respectively. Through these data interaction relationships, the solid-state switch forms a complete control link from electrical quantity acquisition, signal processing, digital analysis to switch drive execution, realizing the device's fast and reliable protection control functions.

[0034] By utilizing the natural saturation current-limiting characteristics of damping reactors, the current-limiting process possesses rapid response capabilities. In the initial stage of a short-circuit fault, the equivalent reactance increases sharply with the rise in current, effectively suppressing the steep increase in short-circuit current and enabling real-time control of the electromagnetic transients of the line fault, thereby ensuring the coordination of the setting of the next-level line protection. Subsequently, the fault current passes through the damping resistor, rapidly dissipating energy and avoiding voltage rebound problems caused by reactor demagnetization, making the current-limiting process more stable and reliable. Compared with current-limiting methods relying on pure resistance or linear reactance, this invention achieves a two-stage current-limiting mode of "nonlinear current limiting + damping energy dissipation," simultaneously optimizing the current-limiting depth and dynamic characteristics.

[0035] When a system fault occurs, the damping solid-state switch of the faulty phase is closed. Part of the faulty phase current flows into the voltage regulating winding through the main solid-state switch and then into the excitation winding. The other part of the faulty phase current flows into the three-phase common damping current limiting module from the three-phase common node.

[0036] Specifically, the fault-phase damping solid-state switch closes first, causing a portion of the current at the fault-phase input connection terminal to... The current still flows into the voltage regulating winding through the main solid-state switch and then into the excitation winding; another part... The current flows directly into the three-phase common node N via the damped solid-state switch, and then into the system reference point via the three-phase common damping current limiting module, forming a temporary fault diversion branch to achieve the first stage of current diversion and current limiting for the fault current. The method proposed in this invention closes the damped solid-state switch of the fault phase when a single-phase short-circuit fault occurs in the system. The fault phase current flows from the three-phase common node into the three-phase common damping current limiting module, realizing rapid current limiting and energy absorption. During fault recovery, each phase is sequentially disconnected to ensure the gradual reconnection of the phase-shifting transformer and stable operation. Traditional transformers or phase shifters typically aim for rapid and complete isolation when internal or external faults occur. Therefore, during a fault, the excitation winding of the faulty phase is short-circuited or disconnected, causing its magnetomotive force to rapidly collapse or become zero, resulting in severe three-phase magnetomotive force asymmetry and generating enormous zero-sequence magnetic flux and overheating in the transformer core. In contrast, the method proposed in this invention... Both the faulty and non-faulty phase currents continue to flow through the voltage regulating winding and the excitation winding to maintain the normal phase shift regulation function before the fault, thereby generating an ordered and controllable magnetomotive force in the excitation winding; based on the magnetic coupling relationship of the three-phase excitation winding, the faulty phase current... Compensating current is induced in the excitation winding of the non-faulty phase, thus forming a composite three-phase magnetomotive force during a fault. The composite three-phase magnetomotive force can offset the magnetomotive force imbalance caused by the voltage drop of the faulty phase to the greatest extent, preventing the transformer core from entering deep saturation. In the initial stage before the system fault has developed to the point where it must be completely disconnected, this composite excitation magnetomotive force can still maintain a low but relatively stable three-phase voltage in the power grid, maintain system voltage support, and buy time for the differential coordination of other protection devices in the system, preventing protection maloperation or over-level tripping. In addition, when a single-phase fault occurs in the system, the main solid-state switch remains closed. The leakage inductance of the voltage regulating winding and the excitation winding of each phase is connected in series in the faulty phase, becoming a current-limiting reactance. It works in conjunction with the damping reactance in the three-phase shared damping current-limiting module to form a controllable short-circuit impedance, thereby realizing graded and flexible short-circuit current limiting.

[0037] When the system recovers from the fault, the damping solid-state switch of the faulty phase is turned off after a set delay.

[0038] When the system fault worsens, the main solid-state switch of the faulty phase is opened and the damping solid-state switch of the faulty phase is closed. The faulty phase current flows from the three-phase common node into the three-phase common damping current limiting module. Specifically, as the system fault further deteriorates, after the main solid-state switch is opened, the current at the input connection terminal of the faulty phase no longer flows through the voltage regulating winding and the excitation winding, but instead enters the three-phase common node N through the damping solid-state switch. Furthermore, the current at the input connection terminal of the faulty phase induces a compensation current in the excitation winding of the non-faulty phase, completely isolating the phase-shifting transformer body from the main power flow path. The damping reactance and damping resistor undertake the functions of fault energy absorption and resonance suppression, ensuring that the line short-circuit current is within a controllable range. Therefore, the three-phase common damping current limiting module undertakes the functions of fault current diversion, current limiting, and energy dissipation, achieving a unified and stable fault handling effect for all three phases.

[0039] Step 2: Establish system fault detection indicators, including: current amplitude threshold, current change rate threshold, and unbalance threshold.

[0040] Collect operating data from the phase-shifting transformer, including but not limited to: the line current on the input side of each phase. , , Output current of each phase , , and the system three-phase voltage , , And calculate the positive sequence current of the system. and negative sequence current ; In this embodiment, the operating data collected by the voltage and current transformers is filtered, isolated, and gain-adjusted by the signal conditioning module before being sent to the A / D conversion module. The main control module uses a fixed sampling period. The conditioned analog signal is sampled to form an information sequence containing multi-cycle power frequency components, and samples are taken at regular time windows. Calculate the root mean square value of the current in each phase. As a reference value for the current load level It indicates the phase and also calculates the positive sequence current and negative sequence current, with the amplitude of the negative sequence current serving as an important characteristic quantity of unbalance and asymmetrical faults.

[0041] To take into account operating conditions under different phase shift angles, different voltage regulation levels and different load levels, this invention uses an adaptive current amplitude threshold instead of a fixed value, thereby constructing a fault criterion with operating condition awareness. Specifically, during N sampling periods, the main control module continuously calculates the reference values ​​of the current in each phase using the sliding window root mean square method. As shown in the following formula:

[0042] In the formula, For the root mean square function of the sliding window, For a moment The separation The current; Reference value It is relatively stable when the system is running normally or changing slowly, and can reflect the typical current level of each phase line corresponding to the operating conditions under different load levels, so as to realize adaptive adjustment based on load level; To avoid failure of a single fixed value under different phase shift angles and different voltage regulation levels, a linear fitting method is used to determine an adaptive current amplitude threshold, as shown in the following formula:

[0043] In the formula, For the sake of separation The current amplitude threshold; The maximum allowable phase current under the current phase shift angle and voltage regulation position is given by the design parameters or operating procedures; , The weighting coefficient for the current amplitude threshold is set according to the voltage level, line structure, and protection coordination requirements. When the phase shift angle or voltage regulation gear changes The system will be adjusted accordingly to maintain the consistency and sensitivity of fault criteria under different operating conditions.

[0044] For short-circuit faults, the rate of increase of line current is much higher than that of typical load surges. Therefore, the current change rate threshold is determined by combining the historical maximum change rate with the current operating conditions, as shown in the following formula:

[0045] In the formula, For the sake of separation The threshold for the rate of change of current; For the sake of separation The historical maximum rate of change of current was obtained through offline simulation or on-site recording. The characteristic time constant of the system is not specified in the embodiment, which does not include the current rise time determined by the line inductance and voltage level. , This is a weighting coefficient for the current change rate threshold, used to adjust the relative proportion of the influence of historical data and current operating conditions.

[0046] The negative sequence current amplitude is used as the main indicator to characterize the unbalance, and the current unbalance threshold is set in a form proportional to the three-phase reference current, as shown in the following formula:

[0047] In the formula, The current imbalance threshold. This is a proportional coefficient determined based on the allowable imbalance of the line. Reference values ​​for each phase current. The average or maximum value.

[0048] By constructing the above three adaptive thresholds, the present invention can maintain the rationality and stability of fault criteria even when the phase shift angle, voltage regulation level, and load change are large.

[0049] Step 3: Acquire the system's operational characteristic data in real time; when a fault occurs, determine the fault ride-through modes of each stage of the phase-shifting transformer based on the operational characteristic data and fault detection indicators, including: first-stage fault ride-through mode, second-stage fault ride-through mode, and third-stage fault ride-through mode.

[0050] After calculating each adaptive threshold, a three-dimensional feature vector is constructed within each sampling period, as shown in the following equation:

[0051] In the formula, For the sake of separation The three-dimensional feature vector of the running data; For the sake of separation The instantaneous amplitude or equivalent amplitude of the current; For the sake of separation The rate of change of current, in this embodiment, is obtained by the difference between adjacent sampling points; This represents the amplitude of the negative sequence current.

[0052] The main control module performs fault detection and classification based on the comparison results between the three-dimensional feature vector and various adaptive thresholds, as follows: 1) A near-field fast short-circuit fault is determined when the following criteria are met: and

[0053] In the formula, The coefficient for the first action. The second action coefficient, and All are greater than 1; The above criteria indicate that the difference The current amplitude is significantly greater than the current amplitude threshold, respectively A current change rate significantly greater than the current change rate threshold indicates that the current rise rate far exceeds the normal load fluctuation, and this is judged as a near-zone fast short-circuit fault. The logical variable FTYPE=2 represents a near-zone fast short-circuit fault, corresponding to the first-stage fault ride-through mode of the phase-shifting transformer.

[0054] 2) The following criteria are used to determine if a fault is asymmetrical in the mid-to-far range: and and

[0055] When a ground fault or asymmetrical short circuit occurs in the mid-to-far zone of the line, the current amplitude is slightly higher than the current amplitude threshold, but the current change rate is relatively mild. At the same time, the negative sequence current amplitude is not less than the unbalance threshold. This is judged as a mid-to-far zone asymmetrical fault. Such faults do not necessarily require the phase-shifting transformer to be shut down immediately. Instead, it is necessary to comprehensively consider the coordination with the remote protection operation. The logical variable FTYPE=1 represents an asymmetrical fault in the mid-to-far region, corresponding to the second-stage fault ride-through mode of the phase-shifting transformer.

[0056] 3) Criteria for determining a slight imbalance or high-resistance grounding condition when the following conditions are met: and and

[0057] When only the negative sequence current amplitude increases, while the current amplitude and current change rate are still within the normal range, it is judged as a mild imbalance or high resistance grounding condition. In this case, it is not advisable to frequently disconnect the phase-shifting transformer, but to improve the operating condition by adjusting the phase-shifting angle or voltage slightly. The logical variable FTYPE=0 represents a mild unbalanced or high-resistance grounding condition, corresponding to the third-level fault ride-through mode of the phase-shifting transformer.

[0058] Step 4: Based on the fault ride-through modes of each stage of the phase-shifting transformer, a hierarchical control strategy is adopted to control the main solid-state switch and the damping solid-state switch to perform opening and closing operations, as well as to perform coordinated control of the phase-shifting transformer's phase shift angle, voltage regulation level, and grid voltage.

[0059] Specifically, step 4 includes: Step 4.1, when FTYPE=2, under a near-zone fast short-circuit fault, the phase-shifting transformer is in the first-level fault ride-through mode. The main control module executes the fault ride-through and phase-shifting transformer shutdown control strategy in the order of first damping, then disconnection, and on-demand bypass. Specifically, this includes: Step 4.1.1: Close only the damped solid-state switch of the faulty phase; Specifically, after a near-zone fast short-circuit fault is identified, the main control module immediately sends a closing command to the damping solid-state switch of the faulty phase. The main solid-state switches of each phase remain closed and the damping solid-state switches of the non-faulty phases are all opened, so that the damping resistor and damping reactance are connected to the output side circuit of the phase-shifting transformer to absorb the transient energy in the early stage of the fault, limit the rate of current rise and reduce voltage transient overshoot.

[0060] Step 4.1.2: If the fault is not cleared after the delay, disconnect the main solid-state switches of each phase and bypass the phase-shifting transformer; Specifically, the damping branch is put into operation and runs for a preset time. =5ms later, the main control module issues a trip command to the main solid-state switch of each phase, cutting off the direct connection between the phase-shifting transformer and the line, thereby causing the phase-shifting transformer to exit the main power flow channel; at this time, the line is equivalent to a structure without a phase-shifting transformer, which makes it easier for the existing line protection to operate according to the original settings.

[0061] Step 4.2, when FTYPE=1, under asymmetrical faults in the mid-to-far area, the phase-shifting transformer is in the second-level fault ride-through mode. Instead of immediately disconnecting the phase-shifting transformer, a short-time fault ride-through strategy is adopted, specifically including: Step 4.2.1: Keep the main solid-state switch closed and perform coordinated control of the phase shift angle and voltage regulation level of the phase shift transformer and the grid voltage, including: reducing the phase shift angle adjustment rate, adjusting the number of connected turns of the voltage regulation winding to increase the leakage reactance value of the phase shift transformer, and reducing the fault phase voltage to reduce the negative sequence current. Specifically, the main control module imposes constraints on the adjustment rate of the phase shift angle to avoid rapid phase angle changes interfering with the remote protection criteria; it appropriately increases the equivalent series impedance as needed to reduce the impact of fault current on the protection device; and it can slightly reduce the output voltage of phases with large imbalance to lower the negative sequence current level. Step 4.2.2: If the fault is not cleared after the delay, only close the damping solid-state switch of the faulty phase; if the fault is not cleared after the delay, open the main solid-state switch of each phase and bypass the phase-shifting transformer. Specifically, when the duration of asymmetric faults in the middle and far regions exceeds a set upper limit. =15ms and the negative sequence current amplitude is not less than the unbalance threshold. If it remains at a high value for a long time, the main control module will upgrade the fault to a serious fault and then switch to the control strategy of near-zone fast short circuit fault.

[0062] Step 4.3, when FTYPE=0, under the condition of slight imbalance or high resistance grounding, the phase-shifting transformer is in the third-level fault ride-through mode, the main solid-state switches of each phase remain closed and the damping solid-state switches remain open, and the coordinated control of phase shift angle and voltage adjustment level is performed. In this situation, the fault is relatively minor and usually does not cause protection malfunctions. The phase-shifting transformer continues to operate, and the main control module adjusts the phase-shifting angle and output voltage within a small range to reduce voltage imbalance and negative sequence current. No exit or bypass operation is triggered, avoiding the impact of frequent operation on equipment life and system stability.

[0063] Through the above-mentioned hierarchical control strategy, the present invention can perform differentiated processing under different fault severity conditions, which not only ensures rapid and reliable exit under severe faults in the near area, but also takes into account the fault ride-through capability under faults in the mid-to-far area and mild imbalance conditions.

[0064] Step 5: When clearing the fault, for the phase-shifting transformer that has executed the first-level fault ride-through mode or the second-level fault ride-through mode, first control the opening operation of the damping solid-state switch according to the operating characteristic data and fault detection indicators, and then control the closing operation of the main solid-state switch according to the synchronization constraints between the phase-shifting transformer and the system.

[0065] For the first-level fault ride-through mode and the second-level fault ride-through mode, after the external line protection operates or the fault is cleared naturally, the fault current gradually decreases and the system enters the recovery phase. In order to avoid the second impact when the phase-shifting transformer is reconnected, this invention sets a self-recovery criterion and a phased soft reconnection strategy.

[0066] The main control module sets up a recovery monitoring window after a fault. The root mean square value of the current in each phase is continuously calculated within this time window. The absolute value of the rate of change of current in each phase negative sequence current amplitude When the following recovery criteria are met simultaneously, the line fault is considered to have been cleared and the system has returned to an acceptable operating state, and the soft re-connection process of the phase-shifting transformer is initiated: and and

[0067] In the formula, , , These are the reliability coefficients for each threshold, all of which are greater than 1; The main control module issues a trip command to the damped solid-state switch, removing the three-phase shared damping current limiting module and restoring the line to a state of isolation from the phase-shifting transformer; ensuring the phase angle difference between the phase-shifting transformer terminal voltage and the system voltage. Less than the preset synchronization phase angle threshold And current difference All are less than the preset synchronous current threshold. At that time, the main control module sends a closing command to the main solid-state switch, so that the single-core asymmetrical phase-shifting transformer can be reconnected to the line with a smaller impact. If the monitoring quantity of any phase fails to meet the recovery criterion during operation, the re-connection operation of the corresponding phase is stopped and the operation is reverted to the state where the phase-shifting transformer is bypassed. The monitoring quantity of each phase is then re-evaluated to determine whether it meets the recovery criterion, thereby avoiding repeated connection under unstable conditions.

[0068] This disclosure can be a system, method, and / or computer program product. A computer program product may include a computer-readable storage medium having computer-readable program instructions loaded thereon for causing a processor to implement various aspects of this disclosure.

[0069] Computer-readable storage media can be tangible devices capable of holding and storing instructions for use by an instruction execution device. Computer-readable storage media can be, for example—but not limited to—electrical storage devices, magnetic storage devices, optical storage devices, electromagnetic storage devices, semiconductor storage devices, or any suitable combination of the foregoing. More specific examples (a non-exhaustive list) of computer-readable storage media include: portable computer disks, hard disks, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), static random access memory (SRAM), portable compact disc read-only memory (CD-ROM), digital multifunction disc (DVD), memory sticks, floppy disks, mechanical encoding devices, such as punch cards or recessed protrusions storing instructions thereon, and any suitable combination of the foregoing. The computer-readable storage media used herein are not to be construed as transient signals themselves, such as radio waves or other freely propagating electromagnetic waves, electromagnetic waves propagating through waveguides or other transmission media (e.g., light pulses through fiber optic cables), or electrical signals transmitted through wires.

[0070] The computer-readable program instructions described herein can be downloaded from computer-readable storage media to various computing / processing devices, or downloaded via a network, such as the Internet, local area network, wide area network, and / or wireless network, to an external computer or external storage device. The network may include copper transmission cables, fiber optic transmission, wireless transmission, routers, firewalls, switches, gateway computers, and / or edge servers. A network adapter card or network interface in each computing / processing device receives the computer-readable program instructions from the network and forwards them to the computer-readable storage media in the respective computing / processing device.

[0071] Computer program instructions used to perform the operations of this disclosure may be assembly instructions, instruction set architecture (ISA) instructions, machine instructions, machine-dependent instructions, microcode, firmware instructions, status setting data, or source code or object code written in any combination of one or more programming languages, including object-oriented programming languages ​​such as Smalltalk, C++, etc., and conventional procedural programming languages ​​such as the "C" language or similar programming languages. The computer-readable program instructions may execute entirely on the user's computer, partially on the user's computer, as a standalone software package, partially on the user's computer and partially on a remote computer, or entirely on a remote computer or server. In cases involving a remote computer, the remote computer may be connected to the user's computer via any type of network—including a local area network (LAN) or a wide area network (WAN)—or may be connected to an external computer (e.g., via the Internet using an Internet service provider). In some embodiments, electronic circuitry, such as programmable logic circuitry, field-programmable gate arrays (FPGAs), or programmable logic arrays (PLAs), is personalized by utilizing the status information of the computer-readable program instructions to implement various aspects of this disclosure.

[0072] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the protection scope of the claims of the present invention.

Claims

1. An adaptive fault ride-through method for phase-shifting transformers based on three-phase common damping current limiting, characterized in that, include: The input terminals of each phase of the phase-shifting transformer are connected to the voltage regulating taps of the corresponding phase's voltage regulating winding via the main solid-state switch of each phase. The output terminals of each phase are connected to the common node of the three phases via the damping solid-state switch of each phase. The common node is connected to the system reference point via the damping current limiting module shared by the three phases. When a fault occurs, the fault ride-through modes of each stage of the phase-shifting transformer are determined based on the system's operating characteristic data and system fault detection indicators, including: first-stage fault ride-through mode, second-stage fault ride-through mode, and third-stage fault ride-through mode. Based on the fault ride-through modes at each level, a hierarchical control strategy is adopted to control the main solid-state switch and the damping solid-state switch to perform opening and closing operations, as well as to perform coordinated control of the phase shift angle and voltage regulation position of the phase-shifting transformer and the grid voltage. When clearing a fault, for a phase-shifting transformer that has executed the first or second level fault ride-through mode, the opening operation of the damping solid-state switch is first controlled based on the operating characteristic data and fault detection indicators, and then the closing operation of the main solid-state switch is controlled based on the synchronization constraints between the phase-shifting transformer and the system.

2. The adaptive fault ride-through method for phase-shifting transformers based on three-phase common damping current limiting as described in claim 1, characterized in that, During normal system operation, the main solid-state switches of each phase remain closed, and the damping solid-state switches of each phase remain open; the main solid-state switches and the damping solid-state switches adopt the same main structure. The three-phase shared damping current limiting module includes a damping reactor and a damping resistor connected in series.

3. The adaptive fault ride-through method for phase-shifting transformers based on three-phase common damping current limiting as described in claim 1, characterized in that, System fault detection indicators include: current amplitude threshold, current change rate threshold, and current imbalance threshold; among which, In the formula, For the sake of separation The current amplitude threshold, For the sake of separation The current reference value, This represents the maximum allowable phase current under the current phase shift angle and voltage regulation setting. , The weighting coefficients are the current amplitude threshold values. In the formula, For the sake of separation The threshold of the rate of change of current, For the sake of separation The historical maximum rate of change of current, The characteristic time constant of the system, , The weighting coefficients are the threshold values ​​for the rate of change of current. In the formula, The current imbalance threshold. This is a proportional coefficient determined based on the allowable imbalance of the line. This represents the average or maximum value of the reference values ​​for each phase current.

4. The adaptive fault ride-through method for phase-shifting transformers based on three-phase common damping current limiting as described in claim 3, characterized in that, The system's operational characteristic data includes: the instantaneous amplitude or equivalent amplitude of the current in each phase. Current change rate of each phase negative sequence current amplitude ; A near-field fast short-circuit fault is determined when the following criteria are met: and In the formula, The coefficient for the first action. The second action coefficient, and All are greater than 1; The logical variable FTYPE=2 represents the near-zone fast short-circuit fault, which corresponds to the first-stage fault ride-through mode of the phase-shifting transformer. The following criteria are used to determine if a mid-to-far zone asymmetric fault is present: and and The logical variable FTYPE=1 represents an asymmetrical fault in the mid-to-far region, corresponding to the second-stage fault ride-through mode of the phase-shifting transformer. The following criteria are used to determine whether a condition is considered slightly unbalanced or has a high resistance grounding condition: and and The logical variable FTYPE=0 represents a mild unbalanced or high-resistance grounding condition, corresponding to the third-level fault ride-through mode of the phase-shifting transformer.

5. The adaptive fault ride-through method for phase-shifting transformers based on three-phase common damping current limiting according to claim 4, characterized in that, When FTYPE=2, only the damping solid-state switch of the faulty phase is closed. If the fault is not cleared after the delay, the main solid-state switch of each phase is opened and the phase-shifting transformer is bypassed. When FTYPE=1, the main solid-state switch remains closed, and the phase shift angle of the phase-shifting transformer and the voltage regulation position and the grid voltage are coordinated and controlled. If the fault is not cleared after the delay, only the damping solid-state switch of the faulty phase is closed; if the fault is not cleared after the delay, the main solid-state switch of each phase is opened and the phase-shifting transformer is bypassed. When FTYPE=0, the main solid-state switches of each phase remain closed and the damping solid-state switches remain open, performing coordinated control of phase shift angle and voltage adjustment range.

6. The adaptive fault ride-through method for phase-shifting transformers based on three-phase common damping current limiting according to claim 5, characterized in that, The coordinated control of the phase shift angle and voltage regulation level of the phase-shifting transformer and the grid voltage includes: reducing the phase shift angle adjustment rate, adjusting the number of connected turns of the voltage regulation winding to increase the leakage reactance value of the phase-shifting transformer, and reducing the fault phase voltage to reduce the negative sequence current.

7. The adaptive fault ride-through method for phase-shifting transformers based on three-phase common damping current limiting as described in claim 4, characterized in that, For phase-shifting transformers that have implemented either the first-level or second-level fault ride-through mode, the damped solid-state switch shall be tripped when the following recovery criteria are met simultaneously: and and In the formula, For the sake of separation The root mean square value of the current. , , These are the reliability coefficients for each threshold, all of which are greater than 1; When the phase angle difference between the phase-shifting transformer terminal voltage and the system voltage Less than the preset synchronization phase angle threshold And current difference All are less than the preset synchronous current threshold. At this time, the main solid-state switch performs a closing operation, and the phase-shifting transformer is reconnected to the line.

8. The adaptive fault ride-through method for phase-shifting transformers based on three-phase common damping current limiting according to claim 7, characterized in that, If the monitoring quantity of any phase fails to meet the recovery criterion during operation, the re-switching operation of the corresponding phase is stopped and the operation is reverted to the state where the phase-shifting transformer is bypassed, and the monitoring quantity of each phase is re-evaluated to determine whether it meets the recovery criterion.

9. A terminal, comprising a processor and a storage medium; characterized in that: The storage medium is used to store instructions; The processor is configured to operate according to the instructions to perform the steps of the method according to any one of claims 1-8.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that, When executed by a processor, the program implements the steps of the method according to any one of claims 1-8.

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