Flexible excitation system direct current short circuit fault tolerance control method, system, device and medium

Abstract

The present application belongs to the technical field of flexible excitation system control, and discloses a flexible excitation system DC short-circuit fault tolerance control method, system, device and medium, to solve the problem that the prior art cannot consider current suppression and stable operation of the unit when the DC side is short-circuited. The method comprises: identifying the no-load or load state of the generator, dynamically calculating the expected excitation current range based on the identification result; measuring the excitation current in real time, and determining that there is a fault risk when the measured value exceeds the range and exceeds the hardware limit; then switching the control mode from voltage closed-loop undisturbed to forced current limiting mode, and limiting the total excitation current within a safe range; continuously monitoring in the current limiting mode, and if the current falls back to the normal range and the voltage is stable, determining that the fault tolerance is successful and restoring the voltage closed-loop control, otherwise maintaining the current limiting mode and alarming. The present application realizes active fault tolerance control when the DC side is short-circuited, effectively suppresses the current rise while maintaining stable operation of the unit.

Description

Technical Field

[0001] This invention belongs to the field of flexible excitation system control technology, specifically relating to the method, system, equipment and medium for fault-tolerant control of DC short-circuit faults in flexible excitation systems. Background Technology

[0002] The generator excitation system is a crucial component of a synchronous generator. Its primary function is to provide excitation current to the generator rotor, establish a rotating magnetic field, and regulate the generator terminal voltage and reactive power. During generator operation, various faults can occur on the DC side of the excitation system, with DC-side short-circuit faults being among the most serious. When a fault occurs on the DC side of the excitation power cabinet, or a short-circuit fault occurs in the carbon brush slip rings, the generator excitation current will rise rapidly. If this current is not effectively suppressed, the fault point will further expand and develop into an arc short circuit, causing greater damage to the generator itself. Furthermore, the excessive fault current can damage the excitation system equipment, leading to unplanned unit shutdowns and affecting the stable operation of the power system.

[0003] For DC-side short-circuit faults, existing technologies mainly employ the following methods: One is the power cabinet pulse blocking method, which immediately blocks the pulses of all power cabinets and cuts off the excitation current when the fault current exceeds a threshold. This method responds quickly, but regardless of the severity of the fault, it directly leads to generator demagnetization and unit shutdown, lacking fault tolerance for controllable faults. Another method is the maximum excitation current limiting method, which limits the excitation current to within a set value when it exceeds the set value. This method does not affect normal regulation quality, but it can only control the total excitation current, cannot pinpoint the overcurrent situation of individual power cabinets, and has a slow response speed. It lags behind in handling short-circuit faults with rapidly rising currents and is difficult to adapt to the characteristics of IGBT devices, which have high thermal capacitance and poor short-time withstand capability. A third method is to install fast-acting fuses, which blow in the event of an overcurrent to protect the power devices. This method is widely used in traditional excitation systems, but flexible excitation systems lack fast-acting fuses that are compatible with large-capacity IGBTs, and the power cabinet cannot be restored after the fuse blows, resulting in insufficient fault tolerance.

[0004] In summary, the drawback of the existing technology is that it cannot simultaneously suppress current and maintain stable generator operation when a DC-side short-circuit fault occurs, making it difficult to avoid unit shutdown. Summary of the Invention

[0005] Based on the aforementioned shortcomings and deficiencies in the prior art, one of the objectives of this invention is to at least solve one or more of the aforementioned problems in the prior art. In other words, one of the objectives of this invention is to provide a flexible excitation system DC short-circuit fault-tolerant control method, system, device, and medium that meets one or more of the aforementioned requirements, so as to achieve the purpose of both suppressing current rise to protect the equipment and maintaining stable generator operation and avoiding unit shutdown when a DC side short-circuit fault occurs.

[0006] To achieve the above-mentioned objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a fault-tolerant control method for DC short-circuit faults in a flexible excitation system, comprising the following steps: Identify the current operating status of the generator, and based on the identification results, use the corresponding estimation model to dynamically calculate the expected excitation current range required to maintain the current terminal voltage; The excitation current is measured in real time. When the measured value of the excitation current exceeds the expected excitation current range and exceeds the preset hardware safety absolute limit, it is determined that there is a risk of DC short circuit fault. When it is determined that there is a risk of DC short circuit fault, the control mode of the excitation system is switched seamlessly from the normal voltage closed-loop control mode to the forced current limiting control mode. The total excitation current is limited within the safe setpoint range through current closed-loop control. The safe setpoint range is determined based on the theoretical excitation current estimate of the generator's current operating state at the moment before the switch. In the forced current limiting control mode, the generator operating status is continuously monitored. Based on the status changes within the preset evaluation time window, if the total excitation current falls back to the normal range and the generator terminal voltage stabilizes within the preset allowable deviation range, the fault tolerance is determined to be successful and the system returns to the normal voltage closed-loop control mode.

[0007] As a preferred approach, the current operating status of the generator is identified, specifically as follows: The stator current value of the generator is measured in real time, and the stator current value is compared with a preset stator current threshold. When the stator current value is less than the stator current threshold, the generator's current operating state is identified as no-load. When the stator current value is greater than or equal to the stator current threshold, the current operating state of the generator is identified as a load state.

[0008] As a preferred embodiment, when the generator's current operating state is identified as no-load, the expected excitation current range is dynamically calculated using a corresponding preset model, including: Based on the current terminal voltage, the theoretical value of the no-load excitation current is obtained by querying the pre-stored no-load characteristic curve. Obtain the preset margin ratio coefficient under no-load conditions; Based on the theoretical value of the no-load excitation current and the margin proportionality coefficient under no-load conditions, a no-load estimation model is constructed to determine the expected excitation current range under no-load conditions. The expression of the no-load estimation model is as follows: , In the formula, and These represent the maximum and minimum expected excitation currents under no-load conditions, respectively. This is the theoretical value of the no-load excitation current. and This is the margin ratio coefficient under no-load conditions.

[0009] As a preferred embodiment, when the generator's current operating state is identified as a load state, the expected excitation current range is dynamically calculated using a corresponding estimation model, including: The theoretical value of the load excitation current is estimated by introducing the Pt potential estimation method and the Pt reactance. Obtain the margin ratio coefficient under the preset load condition; Based on the theoretical value of the load excitation current and the margin proportionality coefficient under the load condition, a load estimation model is constructed to determine the expected range of the excitation current under the load condition. The expression of the load estimation model is as follows: , In the formula, and These represent the maximum and minimum expected excitation current under load conditions. This is the theoretical value of the load excitation current. and This is the margin ratio coefficient under load conditions.

[0010] As a preferred option: The margin ratio coefficient under no-load conditions and The values ​​are respectively less than the margin ratio coefficient under the load condition. and The value.

[0011] As a preferred embodiment, the seamless switching to the forced current limiting control mode specifically involves: At the moment of switching, the integral term of the current closed-loop controller is initialized to zero, and the initial input error of its proportional-derivative term is set to zero. The current setpoint I of the current closed-loop controller f,ref The theoretical excitation current estimate is set to the current operating state of the generator corresponding to the moment before the switch. Complete the switching from the output of the voltage closed-loop controller to the output of the current closed-loop controller.

[0012] As a preferred solution, the operation in the forced current limiting control mode includes: After entering the forced current limiting control mode, start the timer and set the evaluation time window T. assess ; In the evaluation time window T assess Internally, continuously monitor the total excitation current I. f,total and generator terminal voltage U t ; If in the evaluation time window T assess Within, the total excitation current I f,total Returning to normal range [I] f,min ,I f,max Within, and the generator terminal voltage U t If the voltage stabilizes within the preset allowable deviation range, the fault tolerance is considered successful, and the control mode is switched from the forced current limiting control mode back to the normal voltage closed-loop control mode. The voltage setpoint of the voltage closed-loop control mode is the voltage value at the moment before the switch. If in the evaluation time window T assess Within, the total excitation current I f,total The current remains above the current limit value, or the generator terminal voltage U t If a continuous drop occurs and exceeds the preset allowable range, it is determined to be an unrecoverable fault. The forced current limiting control mode is maintained, and the current setpoint I is adjusted. f,ref The generator is kept at a safe level and a serious fault alarm signal is issued until the generator's demagnetization protection device activates and cuts off the excitation main circuit.

[0013] Secondly, the present invention provides a fault-tolerant control system for DC short-circuit faults in a flexible excitation system, comprising: The status recognition module is used to identify the current operating status of the generator; The expected range calculation module is used to dynamically calculate the expected excitation current range required to maintain the current terminal voltage based on the identification result of the state identification module and the corresponding estimation model. The fault judgment module is used to measure the excitation current in real time. When the measured value of the excitation current exceeds the expected excitation current range and exceeds the preset hardware safety absolute limit, it is judged that there is a risk of DC short circuit fault. The mode switching module is used to seamlessly switch the control mode of the excitation system from the normal voltage closed-loop control mode to the forced current limiting control mode when the fault judgment module determines that there is a risk of DC short circuit fault. The current control module is used to limit the total excitation current within a safe setpoint range through current closed-loop control in the forced current limiting control mode. The safe setpoint range is determined based on the theoretical excitation current estimate of the generator's current operating state at the moment before the switch. The evaluation and decision module continuously monitors the generator's operating status under the forced current limiting control mode. Based on the status changes within the preset evaluation time window, if the total excitation current falls back to the normal range and the generator terminal voltage stabilizes within the preset allowable deviation range, the fault tolerance is deemed successful and the system returns to the normal voltage closed-loop control mode.

[0014] Thirdly, the present invention provides an electronic device, the computer device including a memory, a processor and a computer program, wherein the computer program, when executed by the processor, implements the fault-tolerant control method as described in the first aspect.

[0015] Fourthly, the present invention provides a computer-readable storage medium having a computer program stored thereon, wherein the computer program, when executed by a processor, implements the fault-tolerant control method as described in the first aspect.

[0016] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention abandons the traditional simplistic criterion relying on fixed thresholds. Based on both no-load and load operating states of the generator, it dynamically calculates the expected range of normal excitation current for maintaining voltage stability under the current operating state using the inverse function of the no-load characteristic curve and the Pté-Détente reactance model. This dynamic range is then used as the benchmark for fault judgment. This mechanism significantly improves the early warning and accuracy of fault warnings, avoids misjudgments caused by load fluctuations, and achieves sensitive and reliable early warning of potential short-circuit faults.

[0017] 2. This invention combines a dual fault judgment logic of "trend warning" and "hard limit confirmation". Only when the excitation current is detected in real time to not only exceed the aforementioned dynamic prediction range and its rate of change exceeds the preset slope (trend warning), but its absolute value also exceeds the hardware safety absolute limit set for protecting power devices (hard limit confirmation), will the system ultimately confirm the risk of a DC short-circuit fault and activate fault tolerance. This dual judgment mechanism, while ensuring high sensitivity, greatly reduces the possibility of false triggering, ensuring extremely high reliability of fault confirmation.

[0018] 3. This invention provides a "bumper-free switching" method for transitioning from a normal voltage closed loop to a fault-tolerant current closed loop. At the moment of switching, the system initializes the integral term of the current controller to zero, sets the initial input error of its proportional-derivative term to zero, and sets its current setpoint to the theoretical excitation current value corresponding to the voltage loop before switching. This avoids excitation current surges caused by controller output jumps. This mechanism ensures seamless transition of control objectives, enabling the system to proactively take over control during a fault, forcibly limiting the excitation current to a safe level and maintaining short-term stable generator operation.

[0019] 4. This invention introduces a self-diagnostic and intelligent exit strategy for fault tolerance based on time window evaluation. After entering fault-tolerant mode, the system starts timing and continuously monitors key indicators such as excitation current and terminal voltage within a preset evaluation time window. If the excitation current returns to normal and the terminal voltage stabilizes, the fault tolerance is automatically determined to be successful, and the system switches back to normal control mode. If the fault persists and cannot be suppressed, it is determined to be a permanent fault, and the system will maintain a safe current-limiting state and alarm the superior system, awaiting backup protection action. This mechanism enables the system to automatically determine the nature of the fault, automatically recover from transient faults, and orderly exit from permanent faults, achieving a leap from "passive tripping" to "active fault tolerance and intelligent decision-making."

[0020] Further or more detailed beneficial effects will be described in conjunction with specific embodiments in the detailed implementation. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present 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 only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This is a flowchart illustrating the fault-tolerant control method provided in Embodiment 1 of the present invention.

[0023] Figure 2 This is a schematic diagram of the automatic voltage control framework for a conventional generator.

[0024] Figure 3 This is a schematic diagram of the fault-tolerant control framework provided in Embodiment 1 of the present invention.

[0025] Figure 4 This is a structural diagram of the electronic device provided in Embodiment 3 of the present invention.

[0026] Figure 5 This is an experimental effect diagram as described in Embodiment 5 of the present invention.

[0027] Icon labels: 400. Electronic devices; 401. Processor; 402. Communication bus; 403. User interface; 404. Network interface; 405. Memory. Detailed Implementation

[0028] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0029] In the following description, several embodiments of the present invention are provided. Different embodiments can be substituted or combined. Therefore, the present invention can also be considered to include all possible combinations of the same and / or different embodiments described. Thus, if one embodiment includes features A, B, and C, and another embodiment includes features B and D, then the present invention should also be considered to include embodiments containing one or more other possible combinations of A, B, C, and D, even if such embodiments are not explicitly described in the following text.

[0030] The following description provides examples and does not limit the scope, applicability, or examples set forth in the claims. Changes may be made to the function and arrangement of the described elements without departing from the scope of the invention. Various processes or components may be appropriately omitted, substituted, or added to the various examples. For example, the described methods may be performed in a different order than described, and various steps may be added, omitted, or combined. Furthermore, features described with respect to some examples may be combined into other examples.

[0031] To facilitate a better understanding of the embodiments of the present invention, its application scenarios will be explained before providing a detailed explanation of the specific implementation methods.

[0032] The fault-tolerant control method described in the embodiments of this specification is applied to a flexible excitation system based on IGBT devices, specifically to DC-side short-circuit fault scenarios in synchronous generator excitation systems, including DC-side short-circuit faults in the excitation power cabinet and short-circuit faults in the carbon brush and slip ring. In these scenarios, the application of the fault-tolerant control method aims to...

[0033] The following is a brief explanation of the flexible excitation system, DC short-circuit fault, fault-tolerant control, voltage closed-loop control mode, forced current limiting control mode, no-load characteristic curve, and escalator potential estimation method involved in several embodiments of this specification: Flexible excitation systems refer to excitation control systems based on fully controllable IGBT devices. Compared with traditional thyristor-based excitation systems, they offer advantages such as faster response speed, higher control precision, and the ability to achieve higher excitation output and faster reactive power control. Flexible excitation systems can achieve more coordinated power oscillation suppression, but due to the large heat capacity and poor short-time withstand capability of IGBT devices, higher requirements are placed on protection strategies.

[0034] A DC short-circuit fault refers to a short-circuit fault occurring on the DC side of the excitation system. It mainly includes two types: DC-side short circuit in the excitation power cabinet and short circuit in the carbon brush and slip ring. When a DC short-circuit fault occurs, the excitation current will rise rapidly. If not effectively suppressed, the fault point will further expand and develop into an arc short circuit, causing damage to the generator and excitation equipment.

[0035] Fault-tolerant control refers to the system's ability to continue operating or safely shut down in the event of a fault, rather than tripping and shutting down directly. This is achieved through adjustments to control strategies, thereby preventing or delaying unplanned outages. The fault-tolerant control described in this manual includes fault prediction, seamless switching, forced current limiting, and intelligent assessment and exit mechanisms.

[0036] Voltage closed-loop control mode: The normal operating mode of the flexible excitation system, where the automatic voltage regulator (AVR) maintains voltage stability by adjusting the excitation current based on the deviation between the setpoint and actual value of the generator terminal voltage. In this mode, the control target is the generator terminal voltage, and the excitation current, as the controlled variable, adjusts naturally with changes in load.

[0037] Forced current limiting control mode: A special operating mode under fault-tolerant control. When a risk of a DC short-circuit fault is detected, the system switches to this mode. In this mode, the control target shifts to the excitation current itself. The total excitation current is precisely limited within a safe setpoint range by the current closed-loop controller, thereby suppressing further increases in the fault current.

[0038] No-load characteristic curve: This curve describes the nonlinear relationship between the generator terminal voltage and the excitation current when the generator is running at rated speed under no-load conditions. This curve can be obtained through factory testing or field testing and is used to estimate the theoretical excitation current value based on the generator terminal voltage under no-load conditions.

[0039] The Polder potential estimation method is a method for estimating theoretical excitation current under load conditions. It introduces Polder reactance to equivalently handle armature reaction, stray losses, and saturation effects. This method decomposes the total excitation current into two parts: one part is obtained by referring to the no-load characteristic curve of the Polder potential, which is used to establish the air gap flux; the other part is obtained by referring to the short-circuit characteristic curve of the stator current, which is used to counteract the demagnetizing effect of armature reaction.

[0040] Example 1: This embodiment provides a fault-tolerant control method for DC short-circuit faults in a flexible excitation system, such as... Figure 1 As shown, it includes the following steps: Step S1, Fault Prediction Preparation: Identify the current operating status of the generator, and based on the identification results, use the corresponding estimation model to dynamically calculate the expected excitation current range required to maintain the current terminal voltage.

[0041] The relationship between the excitation current and the terminal voltage of a generator differs under different operating conditions. Under no-load conditions, the stator current is approximately zero, armature reaction is negligible, and the terminal voltage is directly determined by the rotor excitation current; their relationship is described by the generator's no-load characteristic curve. Under load conditions, the armature reaction generated by the stator current affects the air gap magnetic field, causing the excitation current required to maintain the same terminal voltage to be greater than the theoretical value under no-load conditions. Therefore, it is necessary to dynamically calculate the expected excitation current range using different estimation models based on the generator's current operating state.

[0042] Specifically, the method for identifying the current operating state of the generator is as follows: the stator current value of the generator is measured in real time, and the stator current value is compared with a preset stator current threshold. When the stator current value is less than the stator current threshold, the current operating state of the generator is identified as no-load; when the stator current value is greater than or equal to the stator current threshold, the current operating state of the generator is identified as load.

[0043] When the generator is identified as being in an unloaded state, the expected excitation current range is dynamically calculated using an unloaded estimation model, which includes the following sub-steps: First, based on the current terminal voltage, the theoretical value of the no-load excitation current is obtained by querying the pre-stored no-load characteristic curve. The no-load characteristic curve describes the nonlinear relationship between the generator terminal voltage and the excitation current when the generator is running at rated speed under no-load conditions. This curve can be obtained through factory testing or field testing and is pre-stored in the excitation system.

[0044] Secondly, obtain the preset margin ratio coefficient under no-load conditions. and These two coefficients are used to construct the expected excitation current range under no-load conditions. Their values ​​can be set according to the actual characteristics and operating experience of the generator, and are usually between 0.01 and 0.1.

[0045] Finally, based on the theoretical value of the no-load excitation current Margin ratio coefficient under no-load conditions and A no-load estimation model is constructed to determine the expected excitation current range under no-load conditions. The expression for this no-load estimation model is: , In the formula, and These represent the maximum and minimum expected excitation currents under no-load conditions, respectively. This is the theoretical value of the no-load excitation current. and This is the margin ratio coefficient under no-load conditions. Since there is no load disturbance under no-load conditions, the expected excitation current range can be set relatively narrowly.

[0046] When the generator's current operating state is identified as a load state, the expected excitation current range is dynamically calculated using a load estimation model, which includes the following sub-steps: First, the theoretical value of the load excitation current is estimated based on the ballast reactance model. The Ptole reactance model uses Ptole reactance to equivalently handle armature reaction, stray losses, and saturation effects, decomposing the total excitation current into two parts: one part is used to establish the air gap flux, and the other part is used to counteract the demagnetizing effect of armature reaction. Specific estimation methods will be explained in detail in subsequent steps.

[0047] Secondly, obtain the margin ratio coefficient under the preset load conditions. and These two coefficients are used to construct the expected excitation current range under load conditions. Since there are many disturbances under load conditions, their values ​​are usually greater than the margin ratio coefficient under no-load conditions, and the value range is generally between 0.05 and 0.2.

[0048] Finally, based on the theoretical value of the load excitation current Margin ratio under load conditions and A load estimation model is constructed to determine the expected range of excitation current under load conditions. The expression for this load estimation model is: , In the formula, and These represent the maximum and minimum expected excitation current under load conditions. This is the theoretical value of the load excitation current. and This is the margin ratio coefficient under load conditions.

[0049] It should be noted that the margin ratio factor under no-load conditions and The values ​​are respectively less than the margin ratio coefficient under load conditions. and The value reflects the technical concept of a narrow expected range under no-load conditions and a wide expected range under load conditions, which is consistent with the actual operating characteristics of the generator.

[0050] Among them, the theoretical value of the load excitation current is estimated based on the ballast reactance model. The specific methods are as follows: According to the terminal voltage U t Stator current I s Power factor angle φ And the preset elevator reactance value X p Calculate the elevator potential E according to the following formula. p : , elevator reactor X p It is a preset constant, usually taken as 0.8 to 1.0 times the generator synchronous reactance, which can be obtained through theoretical calculation or experiment.

[0051] Then, the calculated latching potential E p Substituting the no-load characteristic curve, we obtain the first excitation current component I used to establish the air gap flux. f1 =F empty (E p ), F empty (˙) represents the functional relationship of the no-load characteristic curve, i.e., given the latching potential E p The corresponding excitation current value can be obtained by querying the no-load characteristic curve.

[0052] At the same time, the stator current I s Substituting into the short-circuit characteristic curve, we obtain the second excitation current component I used to counteract the armature reaction demagnetizing effect. f2 =K sc I s The short-circuit characteristic curve describes the linear relationship between the short-circuit current and the excitation current of a generator under rated speed and with a three-phase armature short circuit. Its slope K... sc This is a preset constant that can be obtained through factory testing.

[0053] Finally, the first excitation current component I f1 With the second excitation current component I f2 By combining the results, the estimated total theoretical excitation current of the load is obtained. This estimated value is the total excitation current theoretically required to maintain the current terminal voltage under the current load conditions.

[0054] Through the above step S1, the present invention realizes dynamic fault prediction based on the real-time operating status of the generator, providing an accurate benchmark range for subsequent fault risk assessment and avoiding the problem of misjudgment that is easy to occur in the traditional fixed threshold method.

[0055] Step S2, Fault Risk Assessment: Measure the excitation current in real time. When the measured value of the excitation current exceeds the expected excitation current range and exceeds the preset hardware safety absolute limit, it is determined that there is a risk of DC short circuit fault.

[0056] After calculating the expected excitation current range under the current operating state in step S1, the system measures the excitation current I in real time. f,measured This is then compared to the expected range and absolute hardware security limits. The specific judgment logic is as follows: When the measured value of the excitation current I f,measured Exceeding the expected excitation current range calculated in step S1 (i.e., I f,measured >I f,max,empty And simultaneously exceeds the preset absolute hardware security limit I. f,hardware,limit At that time, it was determined that there was a risk of DC short circuit fault.

[0057] The purpose of setting up dual criteria here is twofold: the first criterion (exceeding the expected range) ensures the sensitivity of fault identification and can detect trends in abnormal current changes; the second criterion (exceeding hardware limits) ensures the reliability of fault confirmation and avoids false tripping due to fluctuations in normal operating conditions or estimation errors. Only when both conditions are met simultaneously will the system ultimately confirm the existence of a DC short-circuit fault risk and trigger subsequent fault-tolerant control.

[0058] It should be noted that the absolute safety limit of the hardware is a fixed threshold set according to the short-time withstand capability of the power device (IGBT). It is usually taken as 1.5 to 2 times the rated current of the device, and is used to ensure that the current will not exceed the safe withstand range of the device under any circumstances.

[0059] In addition, as an optional implementation, the excitation current change rate can be introduced as an auxiliary criterion: when the excitation current change rate d(I f,measured ) / dt exceeds the preset slope threshold K slope Furthermore, if the measured excitation current exceeds the absolute safety limit of the hardware, a risk of a DC short-circuit fault is also identified. This auxiliary criterion can further improve the response speed to short-circuit faults with a sharp increase in current.

[0060] Step S3, Fault-tolerant control execution: When it is determined that there is a risk of DC short circuit fault, the control mode of the excitation system is switched seamlessly from the normal voltage closed-loop control mode to the forced current limiting control mode, and the total excitation current is limited within the safe setpoint range through current closed-loop control.

[0061] like Figure 2As shown, conventional generator automatic voltage control adopts a voltage closed-loop control mode, where the automatic voltage regulator (AVR) maintains voltage stability by adjusting the excitation current based on the deviation between the setpoint and actual terminal voltage. In this mode, the control target is the terminal voltage, and the excitation current, as the controlled variable, adjusts naturally with changes in load.

[0062] like Figure 3 As shown, in this embodiment, after determining that there is a risk of a DC short-circuit fault, the control mode is switched to a forced current-limiting control mode. In this mode, the control target is switched to the excitation current itself, and the total excitation current is precisely limited within a safe setpoint range by a current closed-loop controller, thereby suppressing further increases in the fault current.

[0063] To achieve a smooth transition from voltage closed-loop to current closed-loop and avoid excitation current jumps caused by differences in the output values ​​of the two controllers during the transition, the following specific operating method is adopted in this step: First, at the instant of switching, the integral term of the current closed-loop controller is initialized to zero, and the initial input error of its proportional-derivative term is set to zero. This operation clears the historical state of the current controller before the switch, ensuring that it starts working from a zero initial state.

[0064] Secondly, the current setpoint I of the current closed-loop controller f,ref The theoretical excitation current value is set to the generator's current operating state at the moment before the switch. This theoretical excitation current estimate is taken from the theoretical excitation current value dynamically calculated based on the current operating state in step S1 (i.e., the value under no-load conditions). or under load This operation ensures that the setpoint of the current controller at the moment of switching matches the actual excitation current value under the voltage control mode before switching, thereby avoiding control target jumps.

[0065] Finally, the switching from the output of the voltage closed-loop controller to the output of the current closed-loop controller is completed, allowing the current closed-loop controller to take over the control of the excitation current. Due to the above-mentioned initialization operation of the setpoint, the excitation current remains continuous during the switching instant, achieving a disturbance-free switching.

[0066] After entering the forced current limiting control mode, the current closed-loop controller determines the current based on the current setpoint I. f,ref The deviation from the actual measured value is precisely limited to a safe setpoint range by adjusting the output of the power cabinet. It should be noted that this safe setpoint range is not fixed, but dynamically determined based on the theoretical excitation current estimate just before the switchover. This ensures that the current is limited to a safe level in the event of a fault, without excessively reducing the excitation and causing generator instability.

[0067] Step S4, Fault Tolerance Effect Evaluation and Exit Decision: In the forced current limiting control mode, the generator operating status is continuously monitored. Based on the status changes within the preset evaluation time window, if the total excitation current falls back to the normal range and the generator terminal voltage stabilizes within the preset allowable deviation range, the fault tolerance is determined to be successful and the normal voltage closed-loop control mode is restored. Otherwise, the forced current limiting control mode is maintained and an alarm is issued.

[0068] After entering the forced current limiting control mode, the system starts a timer and sets a preset evaluation time window T. assess The length of this time window can be set according to system characteristics, typically ranging from 1 to 5 power frequency cycles (i.e., between 20 milliseconds and 100 milliseconds). Within this time window, the system continuously monitors the total excitation current I. f,total and generator terminal voltage U t The changes.

[0069] Based on the monitoring results, the system makes the following decisions: Fault-tolerant success scenario: If within the evaluation time window T assess Internally, the total excitation current I f,total Returning to normal range [I] f,min , I f,max [Within], and the generator terminal voltage U t If the system stabilizes within the preset allowable deviation range (i.e., no demagnetization characteristics are observed), the fault-tolerant control is considered successful. At this point, the system switches the control mode from the forced current-limiting control mode back to the normal voltage closed-loop control mode and returns to step S1 to continue normal monitoring. When switching back to the voltage closed-loop control mode, the voltage setpoint of the voltage closed-loop controller is set to the voltage value at the moment before the switch, thereby ensuring a smooth and disturbance-free switch between the two modes.

[0070] Fault-tolerant failure scenario: If within the evaluation time window T assess Internally, the total excitation current I f,total The current remains above the limit (i.e., cannot be effectively suppressed), or the generator terminal voltage U t If a continuous drop in current exceeds the preset allowable range (i.e., demagnetization characteristics are observed), it is determined to be an irreversible fault. In this case, the system maintains forced current limiting control mode, setting the current setpoint I... f,ref The system is kept at the lowest possible safety level to protect power devices, while immediately issuing a critical fault alarm signal to notify operators for handling. The system will remain in this state until the generator's conventional loss-of-excitation protection device activates, cutting off the main excitation circuit and enabling an orderly shutdown.

[0071] Through the intelligent assessment and exit decision in step S4, this invention can distinguish between transient and permanent faults: for transient faults, the system automatically returns to normal, minimizing the impact on unit operation; for permanent faults, the system exits in an orderly manner and issues an alarm to prevent the accident from escalating.

[0072] In summary, the flexible excitation system DC short-circuit fault-tolerant control method provided in this embodiment, through the organic coordination of steps S1 to S4, constructs a closed-loop control system covering the entire process of "intelligent early warning - active fault tolerance - safe exit", which realizes the purpose of both suppressing current rise to protect equipment when a DC side short-circuit fault occurs, and maintaining stable generator operation and avoiding unit shutdown.

[0073] Example 2: This embodiment provides a fault-tolerant control system for DC short-circuit faults in a flexible excitation system, used to implement the fault-tolerant control method described in Embodiment 1, including: The status recognition module is used to identify the current operating status of the generator; The expected range calculation module is used to dynamically calculate the expected excitation current range required to maintain the current terminal voltage based on the identification result of the state identification module and the corresponding estimation model. The fault judgment module is used to measure the excitation current in real time. When the measured value of the excitation current exceeds the expected excitation current range and exceeds the preset hardware safety absolute limit, it is judged that there is a risk of DC short circuit fault. The mode switching module is used to seamlessly switch the control mode of the excitation system from the normal voltage closed-loop control mode to the forced current limiting control mode when the fault judgment module determines that there is a risk of DC short circuit fault. The current control module is used to limit the total excitation current within a safe setpoint range through current closed-loop control in the forced current limiting control mode. The safe setpoint range is determined based on the theoretical excitation current estimate of the generator's current operating state at the moment before the switch. The evaluation and decision module continuously monitors the generator's operating status in the forced current limiting control mode. Based on the status changes within the preset evaluation time window, if the total excitation current falls back to the normal range and the generator terminal voltage stabilizes within the preset allowable deviation range, the fault tolerance is deemed successful and the system returns to the normal voltage closed-loop control mode. Otherwise, the forced current limiting control mode is maintained and an alarm is issued.

[0074] Example 3: like Figure 4 As shown, this embodiment provides an electronic device, which may include: at least one processor, at least one network interface, a user interface, a memory, and at least one communication bus.

[0075] The communication bus can be used to enable communication between the various components mentioned above.

[0076] The user interface may include buttons, and optional user interfaces may also include standard wired interfaces and wireless interfaces.

[0077] The network interface may include, but is not limited to, Bluetooth modules, NFC modules, Wi-Fi modules, etc.

[0078] The processor may include one or more processing cores. It connects various parts of the electronic device via various interfaces and lines, executing instructions, programs, code sets, or instruction sets stored in memory, and accessing data stored in memory to perform various functions and process data. Optionally, the processor can be implemented using at least one hardware form of DSP, FPGA, or PLA. The processor may integrate one or more of the following: CPU, GPU, and modem. The CPU primarily handles the operating system, user interface, and applications; the GPU is responsible for rendering and drawing the content required for display; and the modem handles wireless communication. It is understood that the modem may also be implemented as a separate chip without being integrated into the processor.

[0079] The memory may include RAM or ROM. Optionally, the memory may include a non-transitory computer-readable medium. The memory can be used to store instructions, programs, code, code sets, or instruction sets. The memory may include a program storage area and a data storage area, wherein the program storage area may store instructions for implementing an operating system, instructions for at least one function (such as touch function, sound playback function, image playback function, etc.), instructions for implementing the above-described method embodiments, etc.; the data storage area may store data involved in the above-described method embodiments, etc. Optionally, the memory may also be at least one storage device located remotely from the aforementioned processor. The memory, as a computer storage medium, may include an operating system, a network communication module, a user interface module, and a control application program. The processor can be used to call the control application program stored in the memory and execute the steps of the fault-tolerant control method mentioned in the foregoing embodiments.

[0080] Example 4: This embodiment provides a computer-readable storage medium storing instructions that, when executed on a computer or processor, cause the computer or processor to perform the above-described instructions. Figure 1 One or more steps in the illustrated embodiment. If the constituent modules of the above-described electronic device are implemented as software functional units and sold or used as independent products, they can be stored in the computer-readable storage medium.

[0081] In the above embodiments, implementation can be achieved, in whole or in part, through software, hardware, firmware, or any combination thereof. When implemented in software, it can be implemented, in whole or in part, as a computer program product. The computer program product includes one or more computer instructions. When the computer program instructions are loaded and executed on a computer, all or part of the processes or functions described in the embodiments of this specification are generated. The computer can be a general-purpose computer, a special-purpose computer, a computer network, or other programmable device. The computer instructions can be stored in or transmitted through a computer-readable storage medium. The computer instructions can be transmitted from one website, computer, server, or data center to another website, computer, server, or data center via wired (e.g., coaxial cable, fiber optic, Digital Subscriber Line (DSL)) or wireless (e.g., infrared, wireless, microwave, etc.) means. The computer-readable storage medium can be any available medium accessible to a computer or a data storage device such as a server or data center that integrates one or more available media. The available media may be magnetic media (e.g., floppy disks, hard disks, magnetic tapes), optical media (e.g., Digital Versatile Discs (DVDs)), or semiconductor media (e.g., Solid State Disks (SSDs)).

[0082] Those skilled in the art will understand that all or part of the processes in the method of Embodiment 1 described above can be implemented by a computer program instructing related hardware. This program can be stored in a computer-readable storage medium, and when executed, it can include the processes of the embodiments of the methods described above. The aforementioned storage medium includes various media capable of storing program code, such as ROM, RAM, magnetic disks, or optical disks. Unless otherwise specified, the technical features of this embodiment and the implementation scheme can be combined arbitrarily.

[0083] Example 5: To verify the effectiveness of the DC short-circuit fault-tolerant control method for a flexible excitation system described in this specification, simulation tests were conducted in this embodiment. The test object was a synchronous generator using a flexible excitation system, and the fault type was set as a rotor-side slip ring short-circuit fault to simulate the system's response characteristics when a DC-side short-circuit fault occurs.

[0084] like Figure 5As shown, without the fault-tolerant control method of this invention, when a short-circuit fault occurs in the rotor-side slip ring, the DC short-circuit current exhibits a sharp upward trend. Simulation data shows that within approximately 15 milliseconds after the fault occurs, the excitation current rapidly increases from the normal operating 1 kA to 12 kA. Such a high fault current not only causes severe damage to the generator rotor but also endangers power devices such as IGBTs in the excitation system. If not handled promptly, the fault point will expand into an arc short circuit, ultimately causing an unplanned shutdown of the unit.

[0085] After adopting the fault-tolerant control method described in this specification, the system exhibits completely different response characteristics. When steps S1 and S2 detect that the excitation current exceeds the expected range and surpasses the absolute hardware safety limit, the system immediately triggers the fault-tolerant control in step S3, seamlessly switching the control mode to the forced current-limiting control mode. Under the action of current closed-loop control, the rapidly rising DC short-circuit current is quickly pulled down to a lower level, effectively suppressing further growth of the fault current.

[0086] As the forced current limiting control mode in step S4 continues to operate, the short-circuit current is stably controlled within a safe level, the generator terminal voltage is maintained within the allowable deviation range, and the unit maintains stable operation. After a period of fault self-elimination or system adjustment, the DC short-circuit current gradually recovers to a reasonable level. The system determines that the fault tolerance is successful based on the state changes within the evaluation time window and automatically returns to the normal voltage closed-loop control mode.

[0087] Simulation results demonstrate that the fault-tolerant control method described in this specification can respond quickly to DC-side short-circuit faults, effectively suppressing the rise of fault current while maintaining stable generator operation. When the fault is transient, the system can automatically identify and restore normal operation; when the fault is permanent, the system can maintain a safe current-limiting state and issue an alarm until backup protection operates in an orderly manner. This performance verifies the effectiveness of this method in improving the reliability and fault tolerance of flexible excitation systems.

[0088] Based on the above, this embodiment verifies the effectiveness of the DC short-circuit fault-tolerant control method for a flexible excitation system described in this specification.

[0089] It should be noted that, for the sake of simplicity, the foregoing method embodiments are all described as a series of actions. However, those skilled in the art should understand that the present invention is not limited to the described order of actions, because according to the present invention, some steps can be performed in other orders or simultaneously. Furthermore, those skilled in the art should also understand that the embodiments described in the specification are preferred embodiments, and the actions and modules involved are not necessarily essential to the present invention.

[0090] In the above embodiments, the descriptions of each embodiment have different focuses. For parts not described in detail in a certain embodiment, please refer to the relevant descriptions in other embodiments.

[0091] The above description is merely an exemplary embodiment of the present invention and should not be construed as limiting the scope of the invention. Any equivalent changes and modifications made in accordance with the teachings of this invention are still within the scope of this invention. Those skilled in the art will readily conceive of embodiments of the invention upon considering the specification and practicing the disclosure herein. This invention is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not described herein. The specification and embodiments are to be considered exemplary only, and the scope and spirit of the invention are defined by the claims.

Claims

1. A fault-tolerant control method for DC short-circuit faults in a flexible excitation system, characterized in that, Including the following steps: Identify the current operating status of the generator, and based on the identification results, use the corresponding estimation model to dynamically calculate the expected excitation current range required to maintain the current terminal voltage; The excitation current is measured in real time. When the measured value of the excitation current exceeds the expected excitation current range and exceeds the preset hardware safety absolute limit, it is determined that there is a risk of DC short circuit fault. When it is determined that there is a risk of DC short circuit fault, the control mode of the excitation system is switched seamlessly from the normal voltage closed-loop control mode to the forced current limiting control mode. The total excitation current is limited within the safe setpoint range through current closed-loop control. The safe setpoint range is determined based on the theoretical excitation current estimate of the generator's current operating state at the moment before the switch. In the forced current limiting control mode, the generator operating status is continuously monitored. Based on the status changes within the preset evaluation time window, if the total excitation current falls back to the normal range and the generator terminal voltage stabilizes within the preset allowable deviation range, the fault tolerance is determined to be successful and the system returns to the normal voltage closed-loop control mode.

2. The fault-tolerant control method for DC short-circuit faults in a flexible excitation system according to claim 1, characterized in that, Identify the current operating status of the generator, specifically: The stator current value of the generator is measured in real time, and the stator current value is compared with a preset stator current threshold. When the stator current value is less than the stator current threshold, the generator's current operating state is identified as no-load. When the stator current value is greater than or equal to the stator current threshold, the current operating state of the generator is identified as a load state.

3. The fault-tolerant control method for DC short-circuit faults in a flexible excitation system according to claim 2, characterized in that, When the generator's current operating state is identified as no-load, the expected excitation current range is dynamically calculated using a corresponding preset model, including: Based on the current terminal voltage, the theoretical value of the no-load excitation current is obtained by querying the pre-stored no-load characteristic curve. Obtain the preset margin ratio coefficient under no-load conditions; Based on the theoretical value of the no-load excitation current and the margin proportionality coefficient under no-load conditions, a no-load estimation model is constructed to determine the expected excitation current range under no-load conditions. The expression of the no-load estimation model is as follows: ， In the formula, and These represent the maximum and minimum expected excitation currents under no-load conditions, respectively. This is the theoretical value of the no-load excitation current. and This is the margin ratio coefficient under no-load conditions.

4. The fault-tolerant control method for DC short-circuit faults in a flexible excitation system according to claim 3, characterized in that, When the generator's current operating state is identified as a load state, the expected excitation current range is dynamically calculated using the corresponding estimation model, including: The theoretical value of the total excitation current of the load is estimated by introducing the Ptole reactance based on the Ptole potential estimation method. Obtain the margin ratio coefficient under the preset load condition; Based on the theoretical value of the total excitation current of the load and the margin proportionality coefficient under the load condition, a load estimation model is constructed to determine the expected excitation current range under the load condition. The expression of the load estimation model is as follows: ， In the formula, and These represent the maximum and minimum expected excitation current under load conditions. This is the theoretical value of the load excitation current. and This is the margin ratio coefficient under load conditions.

5. The DC short-circuit fault-tolerant control method for a flexible excitation system according to claim 4, characterized in that: The margin ratio coefficient under no-load conditions and The values ​​are respectively less than the margin ratio coefficient under the load condition. and The value.

6. The fault-tolerant control method for DC short-circuit faults in a flexible excitation system according to claim 1, characterized in that, The seamless switching to the forced current limiting control mode specifically refers to: At the moment of switching, the integral term of the current closed-loop controller is initialized to zero, and the initial input error of its proportional-derivative term is set to zero. The current setpoint I of the current closed-loop controller f,ref The theoretical excitation current estimate is set to the current operating state of the generator corresponding to the moment before the switch. Complete the switching from the output of the voltage closed-loop controller to the output of the current closed-loop controller.

7. The fault-tolerant control method for DC short-circuit faults in a flexible excitation system according to claim 1, characterized in that, The following operations are included in the forced current limiting control mode: After entering the forced current limiting control mode, start the timer and set the evaluation time window T. assess ; In the evaluation time window T assess Internally, continuously monitor the total excitation current I. f,total and generator terminal voltage U t ; If in the evaluation time window T assess Within, the total excitation current I f,total Returning to normal range [I] f,min ,I f,max Within, and the generator terminal voltage U t If the voltage stabilizes within the preset allowable deviation range, the fault tolerance is considered successful, and the control mode is switched from the forced current limiting control mode back to the normal voltage closed-loop control mode. The voltage setpoint of the voltage closed-loop control mode is the voltage value at the moment before the switch. If in the evaluation time window T assess Within, the total excitation current I f,total The current remains above the current limit value, or the generator terminal voltage U t If a continuous drop occurs and exceeds the preset allowable range, it is determined to be an unrecoverable fault. The forced current limiting control mode is maintained, and the current setpoint I is adjusted. f,ref The generator is kept at a safe level and a serious fault alarm signal is issued until the generator's demagnetization protection device activates and cuts off the excitation main circuit.

8. A fault-tolerant control system for DC short-circuit faults in a flexible excitation system, characterized in that... include: The status recognition module is used to identify the current operating status of the generator; The expected range calculation module is used to dynamically calculate the expected excitation current range required to maintain the current terminal voltage based on the identification result of the state identification module and the corresponding estimation model. The fault judgment module is used to measure the excitation current in real time. When the measured value of the excitation current exceeds the expected excitation current range and exceeds the preset hardware safety absolute limit, it is judged that there is a risk of DC short circuit fault. The mode switching module is used to seamlessly switch the control mode of the excitation system from the normal voltage closed-loop control mode to the forced current limiting control mode when the fault judgment module determines that there is a risk of DC short circuit fault. The current control module is used to limit the total excitation current within a safe setpoint range through current closed-loop control in the forced current limiting control mode. The safe setpoint range is determined based on the theoretical excitation current estimate of the generator's current operating state at the moment before the switch. The evaluation and decision module continuously monitors the generator's operating status in the forced current limiting control mode. Based on the status changes within the preset evaluation time window, if the total excitation current falls back to the normal range and the generator terminal voltage stabilizes within the preset allowable deviation range, the fault tolerance is deemed successful and the system returns to the normal voltage closed-loop control mode. Otherwise, the forced current limiting control mode is maintained and an alarm is issued.

9. A computer device, the computer device comprising a memory, a processor, and a computer program, characterized in that, When the computer program is executed by the processor, it implements the fault-tolerant control method as described in any one of claims 1 to 7.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, it implements the fault-tolerant control method as described in any one of claims 1 to 7.

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